Please click the following link or the above picture to redirect to our new website: Engineering A Future !
Be sure to subscribe to our new website & follow it please!
Please click the following link or the above picture to redirect to our new website: Engineering A Future !
Be sure to subscribe to our new website & follow it please!
Well, it appears that it has become time at last for Team UV to end its journey. Today marks the 345th day that TeamUV.org has been active and I can guarantee you that every one of us here at Team UV has throughly enjoyed and cherished the 29,676,840 seconds that this blog has been running (at the time of publishing this post). During this time we have had the incredible opportunity to share some of our own research and, far more importantly, help to inspire interest in the STEM fields amongst the general public with visitors from 115 countries for a total of nearly 8,300 views and well over 200 likes from 114 WordPress followers, our email followers, and many others.
This blog has far exceeded our expectations and for that we have all of our family, friends, supporters, and readers to thank. Without all of you, we would have never been able to accomplish what we have over the past year. I have been honored to lead this team and to have the chance to interact with all of you on a daily basis, all-the-while growing with my teammates and watching them progress through the challenges of the last 15+ months of our senior project. I believe that I can speak for all of us when I say that the experience of writing to all of you here at Team UV is not one that any of us will soon forget. These are the kinds of memories that stick with you.
The experience afforded to all of Team UV by sharing with you all over the past year will serve us well in the future as we push onwards and upwards in life and face new challenges, and I sincerely hope that our time here will serve all of you in the same way. From compressible flow regimes to programming Arduinos to biomedical diagnostic tests to 3D-printing makeup to insects with gear-like rear legs, we truly have covered a whole lot of incredibly diverse topics here at Team UV, but we have not even begun to scratch the surface of what the world of engineering has to offer. Part of the beauty of the world of engineering is that it truly is limitless. Boundaries to the engineering mindset do not exist and physical barriers to what engineers can do simply serve as challenges for scientists and engineers alike to accept. We hope that we have begun to shed some light on this reality and on the opportunities available within the STEM fields.
We set out hoping to reach just one person out there and help to inspire them to go on to pursue STEM-related careers or simply just to spend some time everyday thinking scientifically. I personally have heard from numerous people over the past year about how we have made a difference within their lives or the lives of their friends or families. I have also heard similar stories from my teammates, and that is the golden metric.
I am beyond proud of my team and what we have been able to accomplish and look forwards to continue to share with our readers about STEM over at our next project: EAF. For those that do not know, Engineering A Future (EAF) is a website that I originally intended to launch back in December 2012 with the goal of inspiring interest in the STEM fields amongst the general public…sound familiar? After preparing and stockpiling posts for a few short weeks, my Winter Break ended and the Winter 2012 quarter started in at Cal Poly Pomona (CPP) and my plans fell apart. I had become far too busy, did not have any help, and simply put had never done anything like EAF (or TeamUV.org) before. EAF was created with good intentions, but was not planned for properly by me, but I can assure you, that has all changed.
Flash forward three years and EngineeringAFuture.com will be relaunching on Monday (July 13th, 2015). This time the website is ready to go, as is the team. I have spent the past few months preparing EAF for its launch and am excited to cut the ribbon Monday morning. EAF will follow the same idea that TeamUV.org has, but will take it to a whole new level. EAF has been optimized with one goal in mind: to get as many people as humanly possible excited about STEM. Crazy, right? Well I believe that I have the perfect team to do it and that we are more than prepared to hit the ground running, help people to learn, learn (ourselves), and just have fun with it. Most of Team UV will be carrying over to EAF: Abraham, Ketton, and Andrew will all be bringing their massive brains, awesome outlooks, and passion for STEM-blogging and connecting with the community over to EAF. Unfortunately, Ben will not be continuing with us at EAF and so we wave a somber goodbye to a valued team member and friend. But fear not, while we may be losing a teammate, we are also introducing some awesome new features.
First is the style of posting. EAF will be posting three times a week (just like Team UV has been), but this time we will be posting on Monday, Wednesday, and Friday. Posts will go live at 0800 (purely so that our followers who check the site early will already have the content up to read, rather than having to wait around for two hours) and the social media (Facebook, Twitter, and Instagram) sharing of the posts will be sent out at 1000 hours (two hours later). Post categories have been almost completely revamped and the new categories will consist of:
On top of this, the new website is far more aesthetically pleasing, has many cool features and pages, and will hopefully mean a much more awesome experience for our readers and followers. Lastly, we have some very cool ideas in the works for some awesome new types of content that will launch later on down the road. The website is currently having its finishing touches put on with the About EAF page being finished up offline before transferring it to the site this weekend, a few member bio pages being finished up, and the graphical interface being tweaked a little bit more for Monday’s launch.
In closing, we want to thank our readers/supporters/followers for joining us along this journey and sincerely hope that all of you will continue to follow us over at EAF starting Monday! On Monday, a post redirecting our readers to EAF will be published.
Thank you for your time
Happy Independence Day from all of us here at Team UV!
As you celebrate the 239th anniversary of our the day the United States of America officially declared its independence with your friends and family today, please don’t forget the men and women who fight to protect this great country on a daily basis and remember that neither Independence Day nor the United States of America would exist had it not been for the sacrifice of the 200,000 patriots who fought for our independence and freedoms during the American Revolutionary War, more than 25,000 of whom paid the ultimate sacrifice.
So please enjoy this time with your friends and family, barbecuing, watching fireworks, just hanging out, or whatever other special plans you may have in store for today, but please also spend some time today thinking about the debt of gratitude that we owe to the brave men and women of our armed forces who have continuously fought for freedoms over the last 240 years.
Thank you for your service to all our troops, past, present, and future.
Happy Independence Day!
Today, Brian will be filling in for Ketton due to last minute scheduling issues, we apologize for the post delay.
Ferrofluids are quite complex fluids that display interesting behavior in the presence of magnetic fields. These ferromagnetic fluids are created through the colloidal suspension of ferromagnetic particles of the nano-scale. What does this all mean? In simpler terms, you essentially take tiny (nano-scale, or on the scale of a nanometer/a billionth of a meter; think the size of the base width of a single strand of DNA) magnetic particles and disperse them homogenously (or evenly) throughout a carrier fluid in a way so that the particles are fully wetted (meaning that the particles surfaces are fully coated by the liquid, without other particles in contact with them).
Once the ferrofluid has been created, the next step is as simple as subjecting the fluid to a magnetic field, at which point the ferrofluid becomes magnetized. As the ferrofluid begins to be affected by the magnetic field, it wants to follow this field and comply with its geometry; basically, the fluid wants to become shaped like the field it is being subjected to, but there is a problem: the fluid has surface tension. Because the fluid has cohesive bonding between liquid molecules, the molecules are very strongly attracted to each other on the molecular scale. This should make sense to you, as when you run your hand through water (for example), you are able to readily cause bulk disturbances (you can split up the water on the large scale), but try as you might, you will not be able to split the water apart on a molecular scale (the smallest you can get water to by hand is tiny visible droplets, which are still collections of a ridiculously large amount of water molecules (on the order of sextillions, or thousands of thousands of thousands of thousands of thousands of thousands of thousands!).
Because of the aforementioned strong attraction between the liquid molecules, fully immersed liquid molecules are pulled on by other molecules in all directions, as shown above in the picture. However, the molecules on the surface are only pulled on by molecules around and below (but not above) them, leading to a breach in the equilibrium and causing the water to be pulled in the direction of the rest of the water (hence the curved water surface exhibited in the above diagram). So, armed with this knowledge of how surface tension works, we can revisit the ferrofluids and figure out what is going on.
The magnetic field wants to push the ferrofluid outwards, but the ferrofluid itself wants to pull itself back inwards towards the liquid base due to the surface tension, all while gravity is also resisting the spike formation (this kind of interaction is explained through the normal field instability). At some point all of these forces equate and the fluid is said to be in equilibrium. The result of this? Really cool looking spikes in the ferrofluid as shown above. This gets even cooler when sculptures are created (as in the top picture) by using shaped bases and manipulating the shape of the magnetic field. It should be noted that art is most definitely not the only application for these fluids; in fact, ferrofluids also find application as: liquid seals around the shafts of spinning hard disks/drives, as a convective heat transfer fluid for wicking away heat in small scale and low gravity application, as an imaging agent in some medical imaging techniques (especially magnetic resonance imaging, MRI), as friction reducing agents, as mass dampers to cancel out vibrations, and even as miniature thrusters for small (nanoscale) sattelites!
So there you have it, another awesome engineering phenomenon! Please tune in Sunday for Ketton’s last Open Mind post and remember to continue following us at EngineeringAFuture.com when Engineering A Future (EAF) launches on Monday, July 13th! Enjoy the video below, created by altering the magnetic field in a ferrofluid sculpture!
A big thank you to Mr. Russ Neff and the rest of the team over at Bandel Manufacturing for donating the materials and lending the tools necessary for us to shape the body of our underwater vehicle! A few pictures of the process of building the body to our design are included below:
Once again, we thank Bandel Manufacturing as we could not have created the body of our vehicle without you. For more on Bandel Manufacturing, please click this link to their website or visit our Sponsors & Donations page to find the link there.
As many of you are aware, we are in the transitioning phase of this website as we close out TeamUV.org and transition to EngineeringAFuture.com over the next two months, so this will be my last Presentation post here at Team UV, but not to fear, there are still two months of posts left here and the same types of articles will be carried over onto EAF (Engineering A Future), so without further ado, please enjoy the following:
Today I’m going to be doing something a little bit different; I’m going to stick with the three-approach style of our Open Mind type posts, but rather than talking about the design/analysis/engineering/etc. behind real world science or technology, I’ll be demonstrating how engineering subject matter can be used to draw conclusions about life lessons. This is an important exercise for engineers, as many engineers and engineering students unfortunately become trapped within the framework laid out by their coursework with regards to their engineering mindset.
This is to say that many engineers only practice engineering and apply their knowledge within the confines of where/how they have been taught to apply it (i.e. in the design of a machine, or in the thermal analysis of a heat exchanger, or in the development of a control system for a robotic prosthetic arm, etc.). In reality, engineering curriculum can be applied in endless scenarios and the engineering mindset can be used in an infinite amount of situations outside of the world of engineering. Abraham demonstrated in a recent post how the engineering mindset can be used to solve everyday life problems (click here to read his post), but today we are going to talk about how the subject matter, specifically, can be used to teach life lessons by demonstrating this practice through three examples.
So without further ado, let’s get started!
Often times in life we find ourselves trying to do it all, and in doing so, stretching ourselves pretty thin. For a mechanical engineering student this might look a little bit like the following scenario: working full time, going to school for mechanical engineering, minoring in materials engineering, leading team projects for classes in materials science, heat transfer, and mechanical measurements, while on a senior project team that requires highly complex, innovative work in the subjects of materials science, mechanics of materials, fluid mechanics, heat transfer, control systems, dynamics, etc., while applying to grad school, while searching for and applying to internships, while working as a scientific/technical writer for a website, while trying to deal with car problems, issues at home, whatever it may be, things tend to stack up, and eventually it can become too much and something has to give.
Now picture if you had a circular plate-like piece of polyethylene (a polymer or “plastic”) and you attached a bunch of small clamps all the way around the circumference and started pulling with the same amount of force in all directions. Now we start increasing this force more and more…what happens? There is a phenomenon in the world of engineering called the Poisson Effect. The Poisson Effect basically tells us that as we stretch this material in this 2D plane (as shown in the picture), the material will compress in the direction orthogonal (or perpendicular to the plane)…so as we stretch the disk in all directions as shown above, the material will compress in the direction into/out of your computer screen. Now as we pull harder and harder on this disk from all of these directions, the disk will get thinner and thinner until it can no longer bear the applied loading and the material will fail. The material will likely fail near a stress riser, such as at the point where one of our clamps is pinching the material.
Flash back to the real world and we see that if we try to pull ourselves in a million directions with all of our effort, eventually something has to give. A better practice might be to prioritize our efforts and focus a little bit more in one direction than the rest. This might mean letting one of your teammates take over as team leader in one class so that you can focus more of your effort in another direction that may be more important. Perhaps the ideal situation would be to pull with all of your effort in one direction, I cannot comment on whether this is the right decision all of the time, as every situation is different. What I will say, is that you should keep in mind that from an engineering standpoint, if the plate was still to begin with and we pull equally on that plate in all directions, the plate cannot go anywhere, rather it will remain in the same position and eventually fail; however, if we focus more in one direction than the others, we can end up with a net force in one direction, and as follows from Newton’s 2nd Law, when we have a net force in one direction applied to a mass, that mass will accelerate in that direction…just something to keep in mind.
Even if we do figure out one direction to move towards, that doesn’t necessarily mean smooth sailing from there. Often times in life, we encounter distractions and obstructions to our goals. Some of these may be unavoidable, but we may be able to avoid others entirely. Perhaps when we see have a choice between being dragged down by obstacles that are avoidable and choosing the path of least resistance, we should choose the easier of the two paths. Now I am not saying that we should avoid all difficulty in life, no I’m not saying that at all, in fact, I am saying quite the opposite. It’s been said that nothing worth doing ever comes easily, and I agree with that sentiment entirely; however, there are obstacles that can be avoided so as not to distract you from focusing your effort on the unavoidable ones. These obstacles may be things like peer pressure or unhealthy habits that you know are not good for you and which will delay or maybe even prevent entirely your achieving your goals.
We can further justify this standpoint through an engineering analogy. As has been discussed many times on TeamUV.org (perhaps most recently in Andrew’s post on hydroelectric power), moving fluid can be used to generate electricity. In the picture above, we see an over-simplified diagram showing water flowing into turbines that will be used to generate electricity for power output. Now, essentially (from a very rudimentary point of view) what will happen is that the turbines will use the energy contained in the moving water to convert the water’s mechanical energy into electrical energy which can then be stored or used to power whatever we would like to power. Now let us consider the two cases shown in the picture above. In the first case, the water is flowing steadily down sloped terrain towards the turbines located downstream. This water will accelerate as it moves downstream due to the gravitational acceleration associated with change in elevation. As the water accelerates, it builds up momentum; this momentum can be seen as an increase in available energy in the fluid and once the water reaches the turbines, it will be this energy that is used to generate electricity.
Now let’s look at what happens in this second case, where the water is no longer flowing steadily in an unobstructed manner towards the turbines. The water is now running into obstacles left and right, and every time it does this, it loses a little bit of momentum. Look at it this way: the water accelerates downhill, building momentum, and then BAM!…it runs into a rock, forcing it to lose momentum and thus also lose some of that available energy. Where is that energy going? A large portion of it is being transferred to the obstacles themselves. This energy transfer may mean the rocks being pushed a little bit downstream, or perhaps even heated a small amount (although since there is water flowing over the surface of the rocks, providing efficient cooling convective heat transfer, the heating is negligible), or maybe this energy is being put towards erosion of the rocks…the point being, this energy is being transferred out of the moving fluid. By the time the fluid reaches the turbines, the available energy for doing work on the turbine blades to produce electricity has been greatly reduced. Comparing this to the first scenario, you can see how these flow obstructions can take up energy and reduce the amount of work able to be done in the end.
Moral of the story: if you are able to avoid destructive obstacles in life (as opposed to constructive ones that are necessary to get to where you want to be in life), you can avoid expending energy on trying to maneuver through these destructive obstacles, which would otherwise in the end reduce the amount and quality of the work you would have been able to produce by avoiding them altogether.
Lastly, I want to note that any obstacle, regardless of size, can be overcome if you are willing to work hard enough to do it. Take the subject of grain boundary diffusion for instance. Grain boundaries are exactly what they sound like; that is, they are boundaries between grains in a material (in this case we will think of a metal). These grain boundaries act as barriers to movement of dislocations and thus an increase in grain size results in an increase in yield strength…in simpler terms, the larger the grains in a material are, the more difficult it becomes to deform the material. What is the point of mentioning this all? The point is to underline the fact that grain boundaries serve as obstructions to movement of dislocations and atoms, just as difficulties in life lead to the impeding of forward progress. But all is not lost, atomic diffusion across grain boundaries is not impossible. With enough effort, diffusion across these grain boundaries can occur.
There is an activation energy that describes an energy threshold that must be overcome in order for diffusion across the grain boundaries to occur. This energy threshold can be breached by adding enough thermodynamic energy to start the diffusion process across the grain boundaries. In life, you may arrive at objects that seem impassible, but that is not the case. All you have to remember is that there is always a threshold, or activation energy so-to-speak, where if you can work hard enough to overcome that threshold, you can achieve your goals. It is not a matter of whether something is do-able, it is a matter of whether or not you are willing to work hard enough and put in enough energy to do it.
So there you have it, just three examples of the endless ways in which engineering subject matter can be used to each life lessons. Hopefully we all take something away from today’s post…whether its the importance of prioritizing, or the costs of letting destructive obstacles drag you down, or simply the age-old mantra of mind over matter, hopefully we all walk away a little bit more determined today, because life is what you make it and you will only get out of it what you put into it.
Enjoy the rest of your weekend and be sure to check back on Tuesday for Andrew’s last Well Read post!
As many of you are aware, we are in the transitioning phase of this website as we close out TeamUV.org and transition to EngineeringAFuture.com over the next two months, so this will be my last Presentation post here at Team UV, but not to fear, there are still two months of posts left here and the same types of articles will be carried over onto EAF (Engineering A Future), so without further ado, please enjoy the following:
Tracking tags are used to gather data that concerning the behavior of whatever they are attached to. Often times you will see these tags attached to underwater creatures in order to gather large amounts of important information regarding the migratory patterns, mating behavior, predator-prey relationships, hunting/feeding grounds, social behavior, and feeding behavior of sea (as well as other) creatures, just to name a few parameters.
As you can probably imagine, from an electro-mechanical standpoint, these devices must be very well designed and quite technologically advanced in order to be able to gather all of this information through logging positions, orientations, accelerations, temperatures, video, perhaps audio, and so on and so on. On top of this, the power supply must be capable of lasting a very long time so as to enable the data to be collected continuously without a battery change; either that or the device must be able to recharge itself (i.e. solar recharging), which would of course mean gambling on how much time the creature spends near or on the ocean’s surface where the sun can recharge the device. The device must also be attachable in a way that will keep the device in place for a long time without irritating the creature. Vibrations must be controlled so as to not irritate the creature or skew the data and interfere with the sensors, thermal management must be sufficient to not only protect the on-board electronics, but also to not provide discomfort to the animal, the device must be able to withstand impacts and the wear & tear of daily routines, and the device must not interfere with the creature’s behavior in any way. Combine all this with the fact that the device must be waterproofed, often to great depths, without interfering with the sending and receiving of signals, and you begin to see the formation of a pretty hefty problem statement. And oh yeah, we can’t forget that at some point the researcher must be able to get the data (and hopefully the device) back! And lastly, according to your boss, the design must be complete and ready for prototyping by noon Friday and you have a $30 budget!
Theses kind of issues represent the same types of issues that mechanical (and other) engineers must deal with on every project they work on; as a matter of fact, the issues above share a great deal of similarity to many of the issues we had to design for in our underwater vehicle! (except that we had much, much more to design for since we were designing an entire vehicle, so we could rather equate the amount of issues above to those we had to design for for each of our 7+ subsystems!) This provides the background for an excellent conclusion and underlying theme in the world of engineering in general (and mechanical engineering in particular): You cannot design for everything.
Uh oh, does this mean that mechanical engineers are not putting enough work into their designs? That they are being negligent? No, of course not, this is just a simple fact. As much as we might want to think it, the reality is that no design is perfect. As we have demonstrated time and time again here on TeamUV.org, mechanical engineering covers what is essentially an infinite amount of topics, and thus mechanical engineering projects require an infinite amount of considerations. It is humanly impossible to design for everything, because the engineer cannot think of everything. So what do we do instead? We pour ourselves into our work and give the project 150% of our all and do everything we can to consider as many things as we can, and then…we accept the fact that we could not have possibly considered everything, come up with a contingency plan for when (not if) an unforeseen issue arises, and we go back to work.
So what does all of this have to do with tagging marine life? Am I just getting sidetracked? Nope, the reason I am choosing to talk about these things in this context is that this is exactly what has happened with these wildlife tracking tags. The engineers who created these tags did not spend enough time on one crucial detail that may have been seen as a relatively minor issue at the time, but which may have profound consequences regarding the validity of the data gathered and the well-being of the creatures themselves. What is this parameter that was not given enough attention? Drag.
As many of you are aware, drag is essentially resistance to movement through a fluid. Underwater creatures are often streamlined very well because nature is the ultimate engineer and underwater creatures have been optimized for their lifestyle through generations of natural selection. When you attach a bulky electromechanical device to a creature that has been streamlined for the optimal results in its environment, it can have a disturbing effect on the behavior of said creature. Go figure. In fact, as researchers at the National Oceanic and Atmospheric Administration Pacific Islands Fisheries Science Center in Hawaii have found that the disturbance to the fluid flow over the creature caused by the presence of these devices is resulting in increased drag anywhere in the range from 5-100% depending on turtle size and age. This in turn translates to slower speeds for the turtles, lower accelerations, decreased maneuverability, and possibly even behavioral changes due to some unforeseen psychological or emotional effects on the turtles. As a final segue, this in turn can lead to turtles behaving radically differently with regards to patterns, travels, social behavior, etc. that could mean receiving skewed or otherwise invalidated data, as well as a possible decrease in the turtles’ psychological and even physical well-being.
As seen in the video, in this fascinating study, these researchers are studying these disturbances are using some pretty innovative means to do it. The researchers are using the bodies of turtles that deceased from natural causes to form molds to create fiberglass sea turtle bodies of various sizes, which can then be analyzed in low-speed wind tunnels to identify and quantify the flow disturbances caused by these devices. This is an excellent example of one of the major job roles for scientists and engineers: analyzing an issue that was perhaps not considered, not understood, or possibly even simply not known at all to be an issue beforehand in order to gain a better understanding of the issue and then remedy the issue by developing more polished solutions.
One would only wonder why the tail fins were not taken into account in the model, as even though the disturbance is topside and the fins are located on the bottom of the body, with that large of a disturbance upstream, the flow about the tail fins would absolutely be effected in some way by flow separation and subsequent recirculation about the aft portion of the body. Oh well, moral of the story: it is impossible to account for everything, and sometimes it may even come down to cost-savings, ease of design, manufacture, or analysis, or even just simply deadlines. So what do we do? We put our best foot forward, give it our all, be prepared for the imminent issues down range, hope for the best, and to reiterate, we never give anything less than our all to a project for reasons of pride, protecting our reputation as engineers or scientists, and ultimately to do our best in the name of science and engineering.
Please come back Sunday for my last Open Mine post on TeamUV.org! For more info on the above research, click here.
As many of you are aware, we are in the transitioning phase of this website as we close out TeamUV.org and transition to EngineeringAFuture.com over the next two months, so this will be my last Well Read post here at Team UV, but not to fear, there are still two months of posts left here and the same types of articles will be carried over onto EAF (Engineering A Future), so without further ado, please enjoy the following:
Have you ever heard the expression that someone is “as blind as a bat”? Well this expression is not entirely accurate as no species of bats are actually blind; having said this, bats do have horrible eyesight, forcing them to rely on a different way to get around and navigate obstacles. More specifically, bats use SONAR (SOund Navigation And Ranging) in order to navigate the skies. SONAR is essentially exactly what it sounds like; that is, it consists of the use of sound waves to both navigate and to determine the range (distance) to something. As we have discussed before here on Team UV, SONAR consists of both passive and active SONAR, with the former being simply listening to the sound emitted from an object in the environment and the latter being the emitting of sound and then listening for the return echos. Well, as it turns out, bats are kings of both worlds because of the intricate design of their ears and noses.
As seen in the photos above, different species of bats have different configurations of ears in order to navigate the different types of environments that they inhabit, but there are some key features of the ears that are common across almost all bats: grooves, ridges, flaps, and other kinds of ear baffles. All of these features allow the bats to effectively filter out or attenuate some signals while selecting and encoding other signals to make them more easily understandable. All of this is accomplished by the refraction of the signals on the basis of how the sound waves physically interact with the geometry of the ear or by the resonance introduced within the ear due to how the various features of the ear affect the vibrations introduced by the sound wave-ear interaction. In essence these bats are able to reject or suppress all of the irrelevant information stored in the way of sound waves, while selectively highlighting all of the relevant information that they require to be able to acrobatically maneuver through their environment with ease. But wait, there’s more! Bats can actively adjust their ear configuration by deforming their ears in order to constantly change how they filter information and what information they filter. To take this a step further, bats can do this up to ten times per second, or about three times faster than a human can blink their eyes, allowing these bats to adapt at far less than a moment’s notice!
Everything discussed so far has focused on passive SONAR abilities, but bats also excel with active SONAR. Why is this the case? Because not only can they deform their ears, they can also deform their noseleaves (leaf-like flaps on their noses) to produce a highly focused SONAR beam and to alter the properties of that beam. This translates to the bats being capable of being selective both on the emitting and receiving ends, making them extremely efficient at utilizing their SONAR (not to mention the fact that bats are capable of using far fewer SONAR pulses/beams to navigate than man-made SONAR devices due to this increased efficiency). When you combine this with the fact that they manage to pack all of these biosonar capabilities into such a small package, it is no wonder engineers are studying them to come up with smaller, less power-hungry, more cost-effective, and more efficient SONAR.
To sum up the merits of adapting this biosonar for man-made devices, I will quote Rolf Mueller, the mechanical engineer behind this research:
“The split-second decisions that bats on the wing have to make will often be based only on a very small number of echoes. Based on these few input signals, the bat’s brain is able to make the quick and reliable decisions that swift flight in confined spaces requires,”
You can find more info on this research here: Bat’s biosonar inspires sensing technology research
So there you have it, just another example of how biomimicry or biomimetics is helping to greatly advance the state of science and technology. Please come back Thursday for my last Presentation post on TeamUV.org!
Team UV was selected to represent the Mechanical Engineering department here at Cal Poly Pomona during Friday’s Engineering Project Showcase, where we presented a very brief (12 min. presentation) introductory look at some of our research to the other presenters, faculty from all of the engineering departments, and some industry representatives. We took 3rd place overall and walked away with a certificate and significant cash prize, bringing this chapter of Team UV to rest.
This was our last planned presentation, although we are considering some journal submissions, possible conferences, competitions, and the like further down the road; however, for the time being, we will be closing the book on Team UV. Over the next 2 months, we will be saying our goodbyes on TeamUV.org through some send-off posting. Not to worry, however, because the same style of posting will be carried over onto my website (EngineeringAFuture.com) with many of the same authors upon closure of TeamUV.org. I created EngineeringAFuture.com back in December 2012, but never got it off the ground…flash forward to 2 years later and TeamUV.org launched in July 2014 with the same goal of inspiring interest in the STEM (Science, Technology, Engineering, and Mathematics) fields, but with the added goal of sharing some of the progress of our project. Engineering A Future is an active domain, so you can check it out now if you would like, but everything you see on there currently will be changing as the website is retrofitted over the next 2 months in preparation for its relaunch.
In closing, while I believe that I speak for all of Team UV when I say that we will greatly miss writing for our readers here at TeamUV.org, this should not be looked at as the end, but rather simply a new chapter in our book as we transition to EAF (Engineering A Future). In the next few weeks, posts will occur as follows:
Full Week of Posts with Regular Scheduling (Well Read Tu 1000, Presentation Th 1000, Open Mind Su 1300)
Brian: June 2, 4, 7
Andrew: June 9, 11, 14
Ben: June 16, 18, 21
Abraham: June 23, 25, 28
Ketton: June 30; July 2, 5
Goodbye Posts (M, Tu, W, Th, F 1000)
Andrew: July 6
Ben: July 7
Abraham: July 8
Ketton: July 9
Brian: July 10
This means that July 10, 2015 1000 hours will mark the last post for TeamUV.org. Posting on EngineeringAFuture.com will begin the following week; I will announce the post scheduling for EAF on July 10 as a few things are still yet to be set, but it will be either 2 or 3 posts a week.
Thank you to all of our readers for all of your time and support and I look forward to continuing to write for you all over at EAF, but for now, please continue reading here at Team UV as our regular scheduling continues with my full week of posts starting on Tuesday.
Thank you for your time
Please set aside some time in your day today to remember the men and women who have given their lives so that we can continue to live free. As many have said, the greatest tragedy in war is to be forgotten, so please take this day to remember those who have fallen and paid the ultimate price for our freedom. Please show the families of the fallen that the sacrifice of their loved ones was not for nothing, that we will not simply forget their names or their actions.
Please remember the sacrifices of all of the service members who gave their lives over the history of this great country.
Remember all of those who have given their lives in service to this country, whether human or not.
And please remember that while we celebrate our freedom and remember the fallen today, men and women are stationed overseas, standing ready to protect our freedom and that of others, so please remember everyone deployed.
Show our fallen service members that their lives matter, please remember our protectors and their sacrifices. Pay tribute to the countless heroes who have kept this great country free and the many who will follow in their footsteps.
Good morning, I will be filling in for Ketton’s normal timeslot today due to a last minute complication, so this post will be pretty short.
Fluid mechanics does a lot for us as engineers and scientists with regards to everything from furthering our understanding of planetary atmospheres, to helping us to figure out how to supply an entire country with flowing water, to allowing us to analyze the aerodynamics of some of the most complex vehicles the world has ever seen, the reach of fluid mechanics extends far beyond that of the science, technology, engineering, and mathematics (STEM) fields. One are in which fluid mechanics is finding more and more application is in art.
Now, the form of fluid mechanics seen in art is a little bit different in that we are not talking about the high-order, nonlinear, partial differential equations or the highly complex scientific theory behind the flow of fluids, but rather simply the beauty associated with all that flows. The video (A Love Like Pi ‘Jack and the Giant’ by Kim Pimmel) at the top of the post is an excellent example of this and shows how fluid mechanics can be quite mesmerizing. As stated by Nicole Sharp over at FYFD (please excuse the name of this website) shares, this video essentially uses the interactions between diffusion, buoyancy, Marangoni Flow, ferrofluidics, and other fluid dynamic phenomena to create something pretty awesome. This kind of interaction between many different highly complex fluid dynamic effects within a seeming simple phenomenon is very much so characteristic of the world of fluid mechanics; and while it may take years of education and training in the field of fluid mechanics to even begin to truly understand and be able to analyze these flows on an engineering and/or scientific level, part of the beauty of fluid mechanics is that anyone, regardless of education or background, can enjoy it.
To close off this post, I have included a few more pictures of flows within the context of art with lists of some of the phenomena at play/fluids keywords in each of them. Enjoy!
Note: All images below found through FYFD.
Although ‘Dead Water’ may sound like the title of a movie that will make you steer clear from swimming in the ocean for a year, it is actually the name for an interesting fluid-dynamic phenomena experienced by nautical vessels (and, as it turns out, a detective novel by Ngaio Marsh). Right then…back on track.
Dead Water describes an effect wherein a vessel (i.e. a ship) that is moving by way of thrust produced below the water line (i.e. a propeller) begins to slow, sometimes even to a complete stall due to a mysterious force that seems to be dragging the vessel backwards. How does this happen? Well, there are things called internal waves; essentially, these are waves that appear much as the usual surface waves that you might think about when you picture ships at sea, but that exist below the surface at the interface of fluids existing at different densities. It is important to note, however, that an argument can easily be made to refer to internal waves as a type of mechanical (as opposed to electromagnetic or seismic) surface waves, as surface waves are waves that exist at an interface between differing media…just like internal waves, the usual distinction being that surface waves are generally referred to as those at an interface between a liquid and gas (i.e. the ocean’s surface and the air above the surface), while internal waves would be between a liquid and a liquid.
You may recall doing an experiment growing up where you took water (dyed blue or red, etc.) and put it in a 2L bottle with some sort of cooking oil; because the two fluids were of different densities, they did not readily mix, but rather remained stratified. If you slowly rocked the bottle side to side (to avoid mixing the fluids), you created an internal wave! This is the kind of wave we are talking about right here, but rather than being produced by your hand moving a bottle, it is being produced by a ship’s propeller beneath the water.
In essence, the ship’s propeller is inserting energy into the fluid (the ocean), and this energy is being used to create an internal wave at the internal interface. As the ship continues to input energy into the fluid, the wave grows in amplitude, until eventually (much like waves at the beach), the wave breaks. When the wave breaks, it crashes against the boat; the reason you do not see direct contact between boat and wave in the above video is that the boundary layer between the boat’s hull and the far removed water is keeping them separated, but (rest assured) the energy of the breaking wave is transmitted through the boundary layer into the boat’s hull. This wave breaking creates local turbulence around the propeller, which further draws energy from the boat’s thrust (in addition to the thrust energy still being taken up by the waves forming down the line). The next part is a simple logical progression: if a boat uses a propeller to introduce energy into a fluid to produce thrust, then if an external force (i.e. internal waves) is taking up energy from the propeller, then it is also taking up energy from the production of thrust, then this translates to the boat not producing as much thrust as before and thus slowing down, perhaps even to a standstill (if the boat no longer has enough thrust to defeat the drag forces).
With the ship slowing down and possibly even stopping, even though its propeller(s) is(are) rotating at a constant speed, it is understandable how nautical travellers might have coined the term ‘Dead Water’ for something that they likely first perceived as being due to some crazy, mysterious sea monster that wouldn’t let them go, making them dead in the water…get it?
One last word on this topic…why is there these fluid interfaces in the ocean to begin with? Well, this stratification in ocean waters is caused by many factors, but mainly the difference in temperature, salinity (salt content), and thus density. For this reason, nautical goers are more likely to encounter Dead Water in regions with large salt inlets or largely varying water temperatures, such as near sources of inland fresh-water runoff into the ocean, or near glaciers.
On Wednesday April 22nd, 2015 the Calbuco volcano in southern Chile erupted for the first time in 40 years, triggering the evacuation of 4,000 people in a 20km (~12.43mi) radius while disrupting air traffic over Chile, Argentina, and Uruguay. The eruption went on for an hour and a half and resulted in a plume of volcanic ash reaching 10km (~6.21mi) upwards.
At Team UV, our best wishes go out to those affected by this disaster and we are going to use today’s post to explore the science behind volcanic eruptions, in the hope of promoting a deeper understanding among our readers as to why and how these eruptions occur.
First off, we will be skipping over the science regarding the initial formation of volcanoes (plate tectonics, subduction, convection cells, etc.) in order to facilitate a more concise post/article; we will purely be looking at the eruption itself. So where do we begin? The answer is deep within the Earth’s mantle, far below the surface of the volcano.
The magma that exists deep in the upper mantle is under an enormous amount of pressure, and this pressure keeps the gases contained within the magma [i.e. water vapor (steam), carbon dioxide, sulfur dioxide, hydrogen sulfide, hydrogen chloride, and some additional strong acids] completely dissolved within the magma, meaning the gas molecules are distributed throughout the magma and are essentially embedded within the magma, much like the CO2 bubbles that are dissolved in your soda, that give it its carbonation, and which you do not see until after you have opened your soda, relieving the pressure within the container. Why is this the case that these gases are dissolved within the magma? Because the vapor pressure of the gases (the pressure exerted by molecules that escape from a liquid to form a separate vapor phase above the liquid surface; think of this as the pressure at which the molecules boil or evaporate out of the liquid) is lower than the surrounding confining pressure (the pressure exerted on the gases by the surrounding magma and rock, which is highly pressurized).
Okay, so we have now discussed the starting point, but what happens next? The next thing to occur will be a disruption in the balance between confining and vapor pressure. As the magma rises, it decreases in depth from the surface of the volcano, which means that it has less and less material stacked on top of it, which translates to a decrease in the confining pressure (the same way water hydrostatic pressure decreases with decreasing depth in the ocean). As the confining pressure decreases, eventually the confining pressure will drop below the vapor pressure, allowing the dissolved gases to begin to exsolve (emerge out from their dissolved state within the magma) and nucleate/form gas bubbles, or vesciles within the magma (just like when you relieve the pressure in your soda by opening the container, at which point the CO2 bubbles emerge). As this gas forms and expands, it effectively decreases the density of the gas-magma mixture, because for the same amount of weight as before, the gas-magma mixture takes up more volume than the magma-dissolved gas mixture of before, and density is defined as mass divided by volume. Since this new magma-gas mixture has a lower density than the magma-dissolved gas mixture, it floats (so to speak) to the top, allowing the bubbles to grow more and more as the magma rises further and experiences lower and lower confining pressures. In this way, the hot magma-gas mixture begins to rise faster and faster, accelerating as it moves upward.
Side Note: It is important to at least note that there are many causes for the magma to begin to rise in the first place (i.e. convection currents, insertion of new magma to pressurize the chamber further, etc.) and many considerations such as the increase in vapor pressure due to gas-content enrichment with crystallization of cooling magma, that we are not discussing here as they are not vital understanding the key fundamentals in a concise manner.
When the magma, which is moving quite quickly now, reaches the surface cap of the volcano, it can break on through if the cap is not strong enough. This cap strength is, in part, a reason why volcanoes do not erupt repeatedly day after day (in most cases), as once a volcano erupts, the magma becomes lava, which can solidify the cap once again, potentially trapping the magma and gases for another few decades until the cap has been worn away it and the volcano is ready to burst again. Having said this, a high cap strength can also produce a much more violent eruption, as the amount and pressure of the gases contained in the volcano will be much higher prior to eruption if they have been held back by a strong cap, without any side vents.
So, assuming the cap breaks, and the magma and its gases burst forth and produce lava, and ash (mostly frozen bits of gas and lava due to the transition from inner-volcano temperatures and pressures to the much lower atmospheric temperature and pressure), what decides the type of eruption? This comes down to viscosity. Now, you have probably heard the word viscosity before; this describes the resistance to shear strain/deformation in a material (usually liquid) resulting from an applied shear stress. Viscosity is often described as (although, somewhat improperly) as the molecular thickness of a fluid/plasma; so syrup is highly viscous, while water is much less viscous. The viscosity of the magma is largely determined by the percentage of silica in the mixture, and this viscosity has a direct effect on the type of eruption.
A high percentage of silica translates to a high viscosity for the magma; if the magma is very viscous, it is harder for the gases to escape out from the magma. In this case, when the volcano does erupt, the gases explode out of the magma with violent force, blowing bits of ash, rock and jets of lava into the air.
If the magma contains less silica and is more basaltic (containing more basaltic crust, which is essentially that found in the Earth’s crust beneath the ocean, which has a lower silica content), the lava will ooze out, as the gases are not strongly trapped in the magma. This is to say, the gases may freely exit from the magma, which is one reason why these eruptions tend to be much less violent, tend to ooze rather than burst, and tend to bubble more.
Side Note: In case you weren’t sure, the distinction between magma and lava is just essentially that lava is magma that is now external to the volcano.
So now that we’ve discussed volcanic eruptions, let us just take a quick second to figure out what’s going on with all the lightning shown in the first photo of this post; this lightning is termed volcanic lightning. There are multiple theories as to why this occurs, but almost all of them accept the following: as material is ejected out of the volcano, it breaks apart, either due to the explosive power of the eruption or due to collisions, as the material breaks into pieces, it is thought that differences in the aerodynamics of the positively charged vs. the negatively charged particles causes the two, differently charged particles to separate from each other. At this point, mother nature does what she usually does when there is a region of negatively charged particles separated from a region of positively charged particles: she bridges the gap by normalizing the charge imbalance with an electrostatic discharge…lightning. This seems to add another dimension of stunningly intimidating violence to the already destructive eruption.
Hopefully this post has helped to build the foundation for a deeper intellectual understanding of the process of a volcanic eruption. It is unfortunate that these eruptions tend to devastate regions all to often. The understanding of these powerful volcanoes is the domain of oceanography; and to this end, oceanologists, geologists, and volcanologists are constantly working to deepen their understandings of these acts of nature in order to improve forecasting and possibly prediction techniques.
A chordophone is defined as any musical instrument that uses vibrating strings or strings connected between two points to produce sound, so you can think of things such as harps, violins, and even guitars as falling into this category. The first chordophone that resembled the classical acoustic guitar is said to have appeared about 3,300 years ago in a Babylonian stone carving, with a stark contrast to today’s modern acoustic, electric, and acoustic electric guitars, which have become highly optimized feats of engineering. Today we are going to talk about just a few of the many, vast engineering subjects applicable to the design of the modern guitar that have helped to revolutionize the way we play music today, regardless of what genre it may fall into…Blues, Indie, Latin Funk, Country, Hair Metal, Ska, Garage Punk, even some Hip Hop, and countless other genres and subgenres!
As Keysight Technologies points out in an editorial on the guitar as an example of engineering, “The guitar touches on a rich set of engineering principles, among them: resonant frequency, period, amplitude, distortion, harmonics, wavelength, stress & strain, elastic limit, am, fm, damping coefficient, Doppler effect, step response, coupled oscillations, fft’s and signal processing”. I can assure, this is in no way a complete list as in any engineering project, an engineer generally applies every subject they’ve ever learned about in some way, shape, or form, regardless of whether they realize it or not. Today we are going to pick three of the subjects most prevalent to an understanding of the mechanics of a modern acoustic electric guitar (an acoustic guitar fitted with equipment to increase the volume, so that one can play with the volume of an electric guitar, while still maintaining the sound of an acoustic guitar), and we will utilize a logical progression to do so, meaning we will move from the user’s hand, through the strings, through the body, back out to the atmosphere.
Strings & Frets
When a guitarist plays the guitar, they use both hands actively; generally this consists of strumming or plucking the strings of the guitar with one hand and using the other hand to push the string down at the frets (those raised, generally metal, bars that are transverse to the neck of the guitar) on the fretboard/fingerboard. When the string is disturbed (plucked or strummed), it vibrates, as it is connected rigidly at two ends, or nodes, (one at the saddle of the bridge, and the other end at the nut of the head). This vibration occurs at a resonant frequency that is a function of the string material (due to differences in density), tension, length, and diameter. This is to say that if you were to strum the top string of the guitar soft, medium, hard, whatever, it will produce the same frequency every time (unless the string contacts something, or you pluck it too hard and plastically deform, or stretch in this case, the string or pull the string partially out of the bridge or tuning keys, changing the length and thus frequency). If you want to hear a different frequency, you can move to a smaller (diameter) string for a higher frequency, play a guitar with a longer neck (and thus longer strings) for a lower frequency, increase the tension in the strings for a higher frequency, or change to denser/heavier strings to reduce the frequency (& vice versa for all of these; also note that change in pitch will positively correlate with change in frequency…i.e. lower frequency will produce lower pitch sound).
Now, what happens when we start using our other hand to press down the string at frets? Rather than having the string vibrate between nodes at the saddle and nut, it will be vibrating at nodes between the saddle and fret, changing the length of the vibrating portion of the string altogether! Following from this, a fret closer to the saddle (as opposed to closer to the nut) would produce a shorter string length, and thus a higher frequency or pitch! Now, if we repeat this action, but this time we do not push the string all the way down, so as to not lock the free side of the string from vibrating, we produce a harmonic. In essence, the vibration mode is changed as we create our frequency between the fret (or our finger in this case) and the saddle, and let it propagate down the string, adding to the frequency with each harmonic. In the far right picture below, we see the original first harmonic to the right of the finger, followed by the 2nd, 3rd, and 4th harmonics down the line to the left. If the first harmonic was vibrating at a frequency of 100 Hz, then the 2nd would be at 200 Hz, the 3rd at 300 Hz, and the 4th at 400 Hz. A musician (rather than an engineer) would term the 2nd, 3rd, and 4th harmonics the 1st, 2nd, and 3rd overtones.
Now that we have produced the vibration, it must travel through the body before we can hear the sound it produces. This action begins at the bridge, where the vibration of the strings is transmitted through the saddle (and followingly, the bridge) to the soundboard (the top plate of the guitar body, to which the bridge is attached). This soundboard is lightweight and has a large amount of surface area associated with it, which is important, because now that the soundboard is vibrating, we want to be able to transmit that vibration to the air inside the body as efficiently as possible. Lightweight materials that are relatively strong, yet also are fairly springy (to use a non-technical/scientific term) are very good at transmitting these frequencies with little loss/damping through the material itself; therefore, materials such as Spruce and Cedar (both are types of wood, if that wasn’t clear here) are used. If we were talking about solid-body or semi-solid electric guitars, here would be a good place to comment on the choice of center-body material, as the vibration would have to be transmitted through significantly more material before getting to the devices that convert the vibration to sound (generally electromagnetic pickups), thus body material has an extremely significant effect on the sound of the guitar.
Back to acoustic guitars, once we have begun to vibrate the soundboard, the air inside the guitar begins to vibrate and resonate as it is pressurized by the downwards movement of the soundboard, and depressurized by the upwards movement of the soundboard. This fluctuating or resonating air now travels through the body of the guitar to the sound hole, where it exits back out to the environment as sound, largely through the phenomena associated with Helmholtz Resonance (which we discussed a while back, as it relates to automotive side-window buffeting and blowing across the top of beer, or soda, bottles).
It’s also interesting to note the how the shape of the body effects the sound. As seen above, there is a lot of structural bracing in the guitar body itself (which makes sense as the body is made from lightweight materials, but must withstand its own weight, use, and sometimes a little abuse. As you might imagine, all of this bracing will effect the vibration and sound and so it must be designed properly to have minimal effect on the sound of the guitar…with the exception of at least two vastly important features, which are not labeled above. The first is the lower bout, which is the lower part of the body that balloons out; this portion attenuates (or reduces/weakens/cuts out) lower tones. The second is the upper bout, which is the upper body portion that balloons out and attenuates higher tones, making the acoustic guitar what we term a band-pass filter, meaning it filters out lower and higher tones (frequencies), only allowing a specific bandwidth of frequencies to pass through.
So far we have seen how an acoustic guitar produces its sound, and this is fine for sitting around the campfire, but what if you want to take your acoustic guitar and play at your friend’s wedding in front of a hundred or so people? Do you expect them to all crowd around silently to hear you play? Hopefully not, and this is where the electric part of electric acoustic guitars comes in. Pickups are used to pick up the vibration of the strings/body and convert it to an output electrical signal that can be fed into an amplifier to produce a much louder sound. In electric guitars, this is generally done using magnetic pickups that utilize the effects of vibrating steel strings over the magnetic pickups mounted on the top of the guitar directly below the strings to produce a signal. In acoustic guitars this is usually not done (for a few reasons, but mainly due to the difference in sound produced, as the sound is decidedly more electric than acoustic when using magnetic pickups), instead piezoelectric pickups are used, which have an added benefit of being able to bypass the interference (that annoying buzzing/static-y sound you hear) often heard when using electromagnetic equipment. The piezo pickups (as they are often called) place a sensor on the soundboard; as the soundboard vibrates, the pressure or applied stress on the face of the sensor changes as the soundboard moves in and out. The change in stress creates a change in strain of the sensor material, leading to a really small change in size and thickness of the sensor material, which sees the change in the material’s geometry as a change in electrical resistance, and registers it a an electrical signal, which is then fed to a pre-amp which essentially just gets the signal ordered up and ready for the amplifier, where the volume is increased, just as with the electric guitar.
So there you have it, just three of the countless things an engineer must consider in the design of an acoustic electric guitar. As always, hopefully everyone learned something new today and now you can go out and rock out (or stay in and serenade) like an engineer! Lastly, take a second and apply what you just learned when you look over the infographic below!
Team UV arrived home from the National Conference on Undergraduate Research (NCUR) late last night after having traveled from California to Nevada to Idaho to Oregon to Washington, back to Oregon and finally home to Southern California yesterday, amassing over 3,000 miles between travel, the conference, food, hotels, and a bit of tourism.
The conference itself was a lot of fun and proved to be a great opportunity to share our project with students, scholars, and many others from all over the country, while also giving us the chance to check out some of the research that others have been conducting as well. Perhaps one of the coolest moments, was meeting an Eastern Washington University (site of the conference) engineering student who was familiar with our website and who told us he wished he could work on projects like ours in the future, which is a huge win in our books, as it reflects the fact that we have been at least a little bit successful in one of our primary goals here at TeamUV.org: to inspire interest in STEM (Science, Technology, Engineering, and Mathematics), especially amongst the general public. This was definitely one of the cooler moments for our team regarding the past week, as well as the duration of the project in general.
It is unfortunate that we had to run before getting the name of the person we talked to briefly regarding our website after the presentation, but to you we would like to say the following: thank you for your readership and support and please believe that none of us could have possibly imagined a scenario in which we would accomplish/learn/grow as much as we have over the past 12 months of this project when this team was first established last April. If you want to be able to do projects like this, then go for it! Don’t let anyone stand in your way, and as long as you are willing to pour yourself into it, to push yourself to your limits, to get up and fight for what you believe in, and to maintain that level of inspiration, dedication, and determination, there is not a force in this universe that can stop you from achieving your goals. Sure, there’s adversity; maybe it’s financial, maybe it’s administrative, maybe it’s the fact that there just aren’t enough hours in the day, but all of this can be overcome. We raised nearly 85% of our project costs through online crowdsourcing, filed paperwork on a daily basis for nearly three weeks to get to the national conference, put in nearly 5,000 man hours between the five of us over the first 11 months of the project (by a conservative estimate), and slept far less than we’d like to admit, but most importantly, we got to where we are today. Four conferences, representing the Mechanical Engineering department at the Engineering Showcase, a successful website, an excellent team with a great future, and an outstanding project, and we’re still kicking. Remember that seemingly-corny saying “you can do anything that you put your mind to”? Well, it’s time to start believing, because mind over matter is for real and to paraphrase Theodore Roosevelt, nothing worth doing ever comes easily.
All that’s left is to find your inspiration. For me personally, my inspiration comes from our troops. The way I see it, if someone can put their life on the line halfway around the world to protect the freedoms that I enjoy, if they can risk being shot at, blown up, captured or killed in a foreign place thousands of miles from home, possibly alone, starving, and near death (as was the case for Marcus Luttrell during Operation Red Wings), so that people they have never even met before can go on living comfortable lives, how can I possibly complain that my work is too hard, or that I am too tired or too hungry? For me, these are the considerations that make my issues pale in comparison and that push me to keep on pushing myself until there’s nothing left, and then to push further. To all of our readers, identify something worth fighting for and then go to war with your own demons over it, because you can do whatever it is that you want to do and remember, pain is temporary, pride is forever.
Until next time,
P.S. Regular post scheduling will resume Thursday.
Today Team UV will be skipping our usual Presentation post as we are out of state in Washington for the 2015 National Conference on Undergraduate Research, where we will be presenting some of our research that we have conducted thus far in the work on our project. We have traveled some 1,500 miles from California to Nevada to Idaho to Oregon to finally Washington while transporting our propulsion system demonstrator SHEILA-D (Submerged Hydrodynamically propelled Explorer, Implementation: Los Angeles – Demonstrator) and our vehicle DORY (Dynamic Observational Reconnaissance through biomimicrY), and are excited to be presenting our research later today.
More info to come later in the week. Until next time!
Today’s post will be a bit accelerated due to time constraints imposed by a long To Do List for Team UV in the coming weeks as we prepare for more testing, analysis, conference, and possible journal submissions, but I thought it would be a little fun to talk about role models in engineering today. First off, a major issue is that there really aren’t many widely publicized role models in the world of engineering, which actually stems from a fact relating to the average academic process.
Growing up, we all take classes in fields such as English (or a comparable language class if you are in a country where English is not the primary language), Mathematics, Art, History, Biology, Chemistry, Government/Politics, and (maybe) Physics, but the only people who truly take engineering classes are people who are going to become engineers. This, unfortunately, creates a huge disconnect between the engineering world and that of the general public; the public knows what a historian does, what a businessman, artist, or chemist does, or at least has a fundamental understanding of what they do, but the only ones who truly know what an engineer does, are usually the engineers themselves. This directly translates to the lack of publicity of engineering role models, in that it is not very often that a movie, or TV show, or children’s book (for example) is produced that focuses on an engineer as a role model; if there is an engineer in the story, the role of the engineer is usually vastly misunderstood and often misinterpreted. No one is truly to blame for this, it is simply a consequence of the fact that only engineers truly take engineering course work (after all, should the general public be forced to struggle through extremely difficult engineering courses if they are not interested in engineering?). So how can we remedy this?
The best way is to help form a stronger connection between the general public and the world of engineering and, generally speaking, the most effective way to do this is by trying to inform the public about engineering at a younger age. What is the perfect vehicle for this kind of education? The use of role models through TV personalities, story book heroes, and even public speakers. Below I will quickly introduce you to a few engineers who have been working very hard to introduce a younger audience to engineering in the hope of inspiring the next generation of engineers.
Bill Nye “the Science Guy” is actually a mechanical engineer; bet you didn’t know that! Nye received his B.S. in Mechanical Engineering from Cornell University in 1977 and has gone on to receive many honorary degrees including a Doctor of Science honorary degree from Rensselaer Polytechnic Institute, an honorary doctorate from Johns Hopkins University, an honorary Doctor of Science degree from Willamette University, and an honorary Doctor of Pedgogy degree from Lehigh University. Nye is of course known for his educational television program “Bill Nye, the Science Guy” which spanned 5 seasons and 100 episodes (from 1993-1998) and taught a young audience about highly complex subjects such as heat transfer (for example) in simple and fun ways, often using experiments that could be performed by kids at home with their parents. Bill Nye helped to influence an entire generation of future scientists and engineers; one can only wonder how much greater the impact could have been if the show shined the light on Nye’s role as an engineer. None-the-less, Nye’s work has had a major impact and helped to show that science can be fun. If you are unfamiliar with the show, I highly recommend you seek it out and am sure you can find old clips on YouTube. Most recently, Nye was working on an interactive video game that would utilize lightweight wings that could be strapped to the arms and moved and flapped around to teach kids about the aerodynamics of flight.
Debbie Sterling is a name you may not know, but she is an outstanding role model never-the-less. Sterling holds a degree in Mechanical Engineering/Product Design from Stanford University and upon graduating, did exactly what engineers are taught to do: she identified a problem and came up with a solution. Sterling decided to pinpoint the issue of gender under-representation in engineering, pointing out that only 14% of engineers worldwide are female. I can personally attest to the truth of this fact as, over my 5.5 year undergraduate career, I was made all too aware of the lack of gender diversity in my classes. This issue is magnified in mechanical engineering, which in my experience shows far lower numbers of females than other fields of engineering do. In my average mechanical engineering class throughout my undergraduate career, there were likely on average 1-2 females out of a class of 30-35 students on average; some classes had as many as 4 females, while many did not have any at all. In order to remedy this issue, Sterling has created a line of toys specifically targeted towards girls at younger age levels that aim to inspire interest in engineering. She essentially has made the female equivalent of the builder sets and simple machine toys that many boys enjoyed growing up, but that many girls were kept isolated from. Sterling’s company GoldieBlox is making great strides and I highly recommend that you check out their website.
Elon Musk is the last person that I will list. Some of you may not know who Musk is, while others of you might be the type to follow his every move. Musk earned two B.S. degrees, one in Physics from the University of Pennsylvania and one in Economics from the Wharton School. Following these two degrees, Musk began his Ph.D. in Applied Physics (which is often very similar regarding coursework to both electrical and mechanical engineering), but left the program two days later to start his career as an entrepreneur, going on to start some very successful companies, namely: Zip2 (a web software company that was bought up by Compaq in 1999), X.com (an online financial services company that later became PayPal after a merger with Confinity), SpaceX (short for Space eXploration), Tesla Motors (an electric car company), Solar City (which Musk came up with the concept of, with his cousins actually starting the company, which is now the 2nd largest solar power system provider in the U.S.), and is currently setting up Hyperloop (which would provide a 350 mph+ form of ground transportation between Los Angeles and San Francisco). Musk is on this list for a different reason, while he has worked as an engineer, he is on this list more for the companies that he created. All of these companies are revolutionary by nature and thus the companies inspire interest among many future engineers, while Musk helps to get the word out through public appearances and his role as the face of these companies.
There you have it, three engineering role models of today. Engineering is such an amazing field and there are many people out there who could have made limitless contributions to the STEM (Science, Technology, Engineering, and Mathematics) fields if they were only educated about engineering as a possible career option at a younger age. Having said this, it is never too late, if we continue to take positive steps today such as establishing elementary school science/engineering clubs and programs or more widely publicizing engineering role models (such as Debbie Sterling, for example), we can help to produce the finest generation of engineers the world has ever seen tomorrow. It is said that you can do anything that you put your mind to…I wholeheartedly believe this, but in order to put your mind to it in the first place, you must know that “it” exists.
Most people have probably had the experience of driving in a car on the freeway and rolling down their window only to end up with an awful buffeting sound that hurts their ears. People familiar with this phenomenon often refer to it as “side window buffeting”; but in fact, this phenomena is actually caused by something known as Helmholtz Resonance. With that, let’s jump right into it!
As air flows over your car, it decreases the pressure in the flow due to what’s known as Bernoulli’s Principle; that is, in the absence of energy input and losses (which we will assume to be zero for this simple exercise in thought), if the flow is assumed to be incompressible (valid for the relatively low car speed), inviscid (negligible friction, as follows from our assumption of no losses), and steady (not changing with time), then if we assume that the change in elevation is negligible (perfectly valid for air, which is not very dense, over the 5 feet or so from the top to the bottom of your car), we can ascertain that if the velocity of a streamline increases, the pressure decreases, and vice versa.
Now, let’s roll down a window while we are travelling on the freeway at elevated speeds. Remember, since we are moving, the pressure of the flow is lower than that of the ambient air far removed from the vehicle (outside the boundary layer); however, the air inside our car is essentially atmospheric pressure (i.e. the standard pressure of the atmosphere, no lower, no higher, just like the ambient air far removed from the vehicle), or perhaps even a little bit higher than atmospheric due to the pressurization from your air conditioning. So now we have the window open with a low pressure flow outside the car and a higher pressure inside the car.
The higher pressure air inside the car wants to go to the lower pressure region, so it is pulled out of the car. Now, we might expect that once enough air flows out to equalize the pressure, the flow will normalize and stop pulling from the car, but this is not the case; the air flowing out of the car has both mass and velocity, the two implicit components of momentum. Thus the air flowing out of the car has momentum and overshoots the equalization pressure, essentially giving away too much pressure from the inside of the car and thus leaving the car’s contents at a lower pressure now than the flow outside the car (creating an effective vacuum). Now the flow outside wants to move inside, but this flow has momentum as well and so it overshoots the equalization pressure and leaves the inside of the car over-pressured. As you might expect, this process can continue, with the flow moving back in forth across the window opening, getting larger and larger, until eventually the damping characteristics of the air itself keep the amplitude of this oscillation from increasing further, thus leading to a steady state oscillation of sorts.
This oscillation or flow buffeting is exactly what you are hearing, because as the flow buffets, it produces moving pressure waves with it, which our ears pick up as sound. Not only can this buffeting sound be very irritating, but it can also be damaging to your ear drums (which are in effect membranes that effectively convert vibration from pressure waves into sound); this can be especially true if you happen to be driving at the speed that maximizes the system resonance (which results in this Helmholtz Resonance). To better understand this, imagine pushing someone on a swing, if you push them and let go, they oscillate about the vertical swing position until the action of gravity, drag, and frictional losses brings the swing to rest. Now if you give them another push while they are moving backwards towards you, they will continue to swing, but not as fast or high as they could have because you pushed them before they got to the top of the arc. This time, you wait for them to get to the top of the arc (as far back towards you as they travel), and just as they have switch directions (and start swinging forward), you give them a big push. This time, you have added to the energy without cutting short their motion; if you continue to do this, they will swing higher and faster each time. Back to the car, if you are moving with the right speed, the air flowing into or out of the car from the next (upstream) batch of air can synchronize with the pressure osciallation already in place, leading to an increase in the oscillation amplitude (increasing the effective strength of the flow buffeting pressure); this is what happens when the buffeting gets really loud, to the point that it hurts your ears. Moreover, the pressure buffeting in and out of the window disrupts the airflow around the car, leading to vortex shedding, as can be seen in the video linked to here). So what can you do to stop this?
Well, you could slow down in order to avoid the resonance, or speed up for that matter (but not only could you reach another, higher resonant point, but you could also get a speeding ticket, which is no good). You could also roll down your window more or roll it up less (a larger opening will provide a deeper/lower pitch sound and a smaller opening will provide a higher pitch sound) or roll down other windows to relieve the pressure in the car [interestingly, rolling down the opposite, diagonal window usually provides more relief due to the direction of the airflow (rearwards due to the car’s motion and across due to the motion of the buffeting) , i.e. the back right window if the front left one is already down]. Another interesting option is that some cars (like the Chevy Volt) now come with so-called “window air deflectors” that re-route the air further from the window without messing up the car aerodynamics too much, as they deflect the air at an angle that allows it to rejoin the car immediately after the windows.
It should be noted, however, that “side window buffeting” is not the only place that you can see Helmholtz resonance; this can also be seen in the old bar trick of making noise by blowing over a bottle (as pictured at the beginning of the post), many musical instruments, in some automotive exhaust systems that aim to change the sound of the exhaust, and even in some silencing applications in which the created noise is used to cancel out unwanted noise through destructive interference (this can be seen in some aircraft engines, automotive mufflers, and even weapon suppressors/silencers, wherein chambers are used just like the cavity inside the car to produce the noise cancelling pressure waves). Lastly, it’s also worth noting that this whole Helmholtz Resonance effect is more apparent on newer cars than old ones mainly due to the fact that newer cars are more streamlined, which is great for reducing drag, but brings the airlow closer to the car, thus inspiring this phenomenon to occur more easily.
Well, I hope everyone learned something today; now you can go tell your friends about the science behind that annoying thumping! Be sure to check back for Ben’s Open Mind post on Sunday and, I almost forgot, sorry for the 1 hour post delay, I am out of town and do not have readily available Wifi.
First off, we want to apologize for missing our Thursday post, it has been a very hectic week for Team UV with almost all of the members going without sleep for 30 hours and above at some point or another; for example, I personally received about 8 hours of sleep total between Sunday morning and Thursday evening and at one point had to go about 30 hours without eating in order to get everything accomplished, but alas!, it was for a good cause and now Team UV can finally relax! (well, relax relative to other people, haha)
This past week and a half Team UV has had a week straight of building, testing, and programming for our vehicle, final exams, grad school visits, reports and projects due, graduation stuff, and of course completing our senior project! On Thursday, we delivered our final project presentation to the Mechanical Engineering board responsible for assigning our grades (we all received A’s), turned in our 140 page project report, and did a live demonstration of our vehicle Dory (Dynamic Observational Reconnaissance through biomimcrY). Dory (our Phase III vehicle) can be seen in the picture above, next to our Phase I propulsion system demonstrator Sheila-D (Submerged Hydrodynamically propelled Explorer, Implementation: Los Angeles – Deomonstrator)! (Read more about Sheila on our About page)
So this marks the “official” end of our senior project; however, this does not mark the end of the project altogether. We still have a lot of work to do regarding improving the build, adding more features, completing more advanced testing, and overall producing a more polished solution. Additionally, we will be attending the National Conference on Undergraduate Research (NCUR) at Eastern Washington University from April 16th-18th, the California State University system-wide Student Research Conference (CSU SRC) from May 1st-2nd (we are attending this because we won our session and award money at the Cal Poly Pomona Student Research Conference on March 6th), the Cal Poly Pomona (CPP) Senior Project Symposium at the end of May, and hopefully the CPP Symposium Showcase at that same time (this highlights the top project team from each engineering department).
Additionally, we will be looking to submit to some journals, quite possibly looking into at least one patent. Lastly, this website will continue publishing posts until the project ends, at which point these types of posts will continue on EngineeringAFuture.com. Anyways, thank you all for your continued support and I would like to remind everyone that we still have our fundraising campaign (GoFundMe.com/TeamUV), which will continue as long as the project is running as we still have quite a few costs ahead of us!
Please check back in tomorrow for a Well Read post from Ben!
First off, we want to apologize for missing our Thursday post, it has been a very hectic few weeks for Team UV; to make up for the missed post, we will have a post this upcoming Monday (03-23-15) at 1000 hours sharing a little bit about what Team UV has been up to recently and some major accomplishments. In the mean time, however, I’ve got an Open Mind post to share!
Today we are going to be talking about armor…the stuff that helps to protect the men and women who dedicate their lives to protecting us. More specifically, today we are going to talk about some of the most important revolutions in ground vehicle armor over the last century. Without further ado, let us begin:
Although one of the first recorded uses of sloped armor was on Confederate ironclad warships during the Civil War (it is interesting to here note that most early tanks were actually designed by naval engineers), the technology saw its first true ground vehicle implementation in French WWI era tanks. Further, the technology was brought to the spotlight through its use in the Soviet T-34 medium tank, and was made infamous by the seemingly invincible Panther (medium) and Tiger II (heavy) tanks used by Nazi Germany in WWII (that is, until the fire superiority, vast numbers, speed/agility, and overall ability of the US M4 Sherman tanks, combined with the invaluable experience of the Sherman tank crews, and the American air dominance proved overwhelming to the Axis powers). This technology, although very simple conceptually, had colossal implications.
As shown above, this sloped armor is just that…sloped. This actually has a few profound effects:
First used by the Germans in WWII, slat armor (a.k.a. cage armor) arose to greater prominence during the Vietnam War and has experienced renewed interest recently in the Middle East. The general idea behind this armor is that by simply putting a cage of slats around vital/unprotected parts of a vehicle, an incoming anti-tank weapon (say a rocket propelled grenade, or RPG) can either be forced to detonate prior to contacting the vehicle body itself (thus disrupting the path of the shape charge, which was originally intended to pierce into the vehicle) or by actually damaging the warhead beyond operational capability (effectively crushing it so it no longer works).
Slat armor is a relatively inexpensive, simple means of protecting ground vehicles; unfortunately, this armor only has about a 50% working rate and so is generally used in addition to other, more capable armor, bringing us to the next item on our list.
Easily one of the cooler revolutions in armor over the last century, reactive armor provides an opposite reaction when it experiences impact from a weapon. There are many types of reactive armor, but explosive reactive armor is the most common. This armor consists of a high explosive situated between two plates that effectively helps to offset the energy from the weapon that contacts it; when a projectile pierces the top plate, the inner explosive reacts, pushing the two plates outwards…since the outer plate is open to the atmosphere (whereas the inner one interfaces with the vehicle structure), the outer plate flies out further (taking the expended energy with it and generally destroying the projectile itself!).
This armor saw its first combat usage in the 1982 Lebanon War by the Israeli Defence Force and has found very wide usage today.
Spall liners are an interesting addition to traditional armor that came about to solve the problem of what might happen if a shape charge were to successfully penetrate a vehicle’s hull. The actual scientific explanation of spalling and the action of spall liners is truly quite complex, but from a superficial view, it can be stated as follows: spall liners essentially protect the crew inside the vehicle from fragmentation in the event of the hull being pierced. The liner is made of highly compliant material that can in effect absorb the energy and shrapnel associated with the fragmentation.
These spall liners found their first use during the Cold War.
V-Hulls are a novel idea that first arose in the 1970s as an answer to the increased use of anti-vehicle road explosives (similar to the improvised explosive devices or IEDs that have become unfortunately common in the Middle East today) during the Rhodesian Bush War in the south-eastern regions of Africa. The aptly named V-Hulls are essentially a design modification of the vehicle that alters the bottom of the vehicle from being flat to being V-shaped, which helps to redirect the shock wave from an under-vehicle blast away from the vehicle and its passengers.
This design has been vastly successful and has become a very common feature on modern infantry fighting vehicles (IFVs) and armored personnel carriers (APCs) during the conflicts in the Middle East, where the threat of IEDs has become of great concern.
The last innovation that we will cover in this post is the advent of run-flat tires, which have been used widely for military, law enforcement, government, aid groups, and protection of high-level executives since as early as the 1930s with the Michelen self-supporting run flat tires that would run on a foam lining if punctured. Today’s military vehicles use a slightly different type of run-flat tires referred to as auxiliary-supported run flat tires.
These tires essentially use a secondary support ring capable of supporting high weights at elevated speeds for long periods of time. If the tire is punctured (or perhaps shot), the vehicle can continue on its way or get out of Dodge quickly. Another big plus is the fact that these can be placed inside of standard tires and thus do not require specialty tires/wheels.
Well there you have it: some of the coolest and most useful armor technologies to emerge for ground vehicles over the last century. These technologies continue to help ensure the safety of the men and women who work to protect us (whether that be in the military, law enforcement, or even aid workers). Not only are all of these technologies vital to survivability considerations, but they also represent a fascinating field of engineering that is improved on through advance research and development on a daily basis with all kinds of crazy solutions up and coming, the likes of which most would not even dream of. Anyways, as always, thanks for the support and have a great remainder of your weekend. Until Monday!
Team UV reached the first dry powered milestone (rotating propulsor) tonight! Albeit backwards…haha
Check out the video above and we’ll be sure to post more videos as we make more progress in our testing!
Let’s start off with a scenario: You’re flying a sortie for the Navy in a reconnaissance-configured F/A-18F Super Hornet to fly in high over some mountain range in Afghanistan, take some pictures, and come home. You’re flying at 40,000 ft in order to both stay clear of the immensely tall mountain ranges and to remain undetectable and stay out of reach of small arms fire. Unfortunately, at 40,000 ft in this region, icing conditions are very common. Due to the low temperatures in this region (and especially at this elevation) combined with the all-too-often rainy or snowy conditions, you end up having to fly through falling snow or rain (which would be either already ice due to the low temperatures, or supercooled, meaning that the water drops are far below the freezing point, but have not frozen yet due to the absence of a nucleation site – which is essentially a solid surface on which the water can freeze…i.e. dust, other particulate matter, or the wing of an aircraft).
As you begin to fly into the poor weather, the water droplets begin to freeze on impact with the wing, building up a layer of ice on the wing of your aircraft. This ice quickly changes the surface roughness of your aircraft wings, changing the aerodynamics and lowering the speed or angle of attack that you can travel at without stalling (flow separation that leads to loss of lift). Furthermore, say due to the angle of incidence between your flight path and the direction the water droplets are coming from, the ice is forming more heavily on one side/wing of your aircraft than the other (and probably unevenly on each side). You start to feel the aircraft wobbling around in flight and find it much more difficult to control your roll, pitch, and yaw. You are now having issues flying the aircraft at the required speed, are having to fly at a lower angle of attack, and are having trouble controlling the aircraft. You have a decision to make: continue to put yourself, your Radar Intercept Officer (RIO), and your $60,000,000 aircraft in danger or abort the mission. Unfortunately, this situation is not too uncommon when icing presents a real problem to pilots.
With the development of unmanned drones for reconnaissance missions, we are able to push the envelope a little more, but still are wary of putting a very expensive aircraft into poor weather conditions (for both financial losses and the possibility of having a high-tech aircraft downed in enemy territory). This problem also exists for civilian air travel, and in many cases, general aviation pilots are not certified for flight into known icing conditions due to the clear and present danger. So what do we do to reduce the threat posed by icing conditions?
There are a few traditional ways of dealing with aircraft icing. One is shown above, in which a rubber “boot” is expanded in order to break up the ice on the leading edge of the aircraft; obviously, this is not an optimal solution, as it temporarily changes the profile of the wing, and also does not get rid of all of the ice. Other methods include bleeding hot engine exhaust air over the wing and using “weeping” wings that release antifreeze over the surface of the wing, to name a few. These methods are all quite complex, require a lot of power, can alter the airflow significantly, and may even present environmental dangers (as in the case of the weeping wing).
In order to fill this void of optimal solutions, a company called Batelle has employed its researchers to develop a solution that consists of a carbon nano-tube coating that can be included beneath the topcoat of the aircraft wing and then act as a resistance heater of sorts to warm the wing from inside the wing to prevent or get rid of ice on the wings. This solution employs advanced materials science concepts in order to introduce a more elegant, non-invasive means of dealing with aircraft icing. Furthermore, the coating is controlled through an “intelligent controller [that] monitors the heater performance and applies only the power levels required for the flight conditions”, making it less power-hungry and more adaptable to any given situation! These benefits are realized even further on military Unmanned Aerial Vehicles (UAVs) (their principal application), where large sensor (or other) payload power requirements and desired lightweight dictate that a smaller than ordinary amount of power can be dedicated to de-icing. This solution has the capability to revolutionize the way we go about preventing or dealing with aircraft icing; now only if they could further development this solution for use in the de-icing of pitot tubes (devices used to measure airspeed – to figure out how fast you are flying; pitot tubes are notorious for encountering problems in icing conditions, where a false airspeed reading can lead to disaster).
Read more at: Engineering.com
Stress concentrations (commonly referred to as stress risers or raisers) are areas in a material that, owing to problematic geometry, lead to…well, greater stress concentration in portions of the material/part. These concentrations can be great headaches to engineers, as the localized concentration of the stress means the part experiences much higher stresses in said specific regions than the average stress in the material as a whole (or than the material would experience without the riser), which can lead to failure at much smaller loadings than originally thought. Well what in the world does that mean?
To better explain this, we will examine a very simple case: pure tension in a rectangular sample. Imagine that you take a rectangular bar and pull on it along it’s axis, as shown below. We will make some simplifying assumptions for the purpose of ease of demonstration; assume that when you pull on the sample, you pull on the entire end face equally; that is, you distribute the loading across the entire face equally. Also assume that the material is homogenous (the same physical & mechanical properties at all points throughout the material), isotropic (the same properties in all directions), and uniform in cross-section. These assumptions will hold for demonstration and are sometimes used in applications in which strength is not of major concern, but generally speaking, it will be very difficult to apply a load evenly across a surface (picture gripping a piece of metal with a pair of pliers…the grip point is the point of load application and does not cover the entire face, but rather is localized), materials will never be homogenous (due to voids, inclusions, and other manufacturing defects), many materials will not be isotropic (a piece of un-altered steel is isotropic, but wood, for example, has directional strength in the directions of its “grains”; many other materials also express different properties in different directions), and many geometries will betray the assumption of uniform cross section (as we will see shortly).
When we pull on the material, that force is transmitted through the material with an equal and opposite reaction internal to the material, as shown in the center image of the above picture. This force may be shown as a single resultant force vector (like in the center image), but is actually distributed over the entire inside of the material (as shown in the right/3rd image). When this load/force acts over this area (and remember, we are only looking at pure tension…the load is applied perfectly perpendicular to the material cross section, as otherwise we would induce bending), it creates a normal stress that is defined as the applied load divided by the cross-sectional area. Under the assumptions we made before, this should mean that every point in the material experiences the same normal stress, meaning that in order for the material to fail, the average normal stress in the material needs to exceed the failure strength (in this case, the applicable tensile strength).
But what happens when we apply a stress concentration, by introducing a discontinuity in the geometry (i.e. a crack, sharp edge/corner, or change in cross-sectional area)? The stress distribution can no longer be uniform, as the loading has to be re-routed to avoid the discontinuity as it travels through the material (for the case of geometric stress concentration), as shown for the simple case of a circular hole in the material below.
As can be seen, the distribution tends to bunch up around the hole, creating a higher concentration of stress. From a mathematical standpoint, the local normal stress in the region of the hole has also decreased as the cross-sectional area of the sample at the hole location is now less (imagine cutting the bar in half perpendicular to the loading and looking at it from the end…instead of being the full rectangular cross-section of before, there is material missing), thus the normal stress is higher because we are applying the same load, but now are dividing it by a smaller area than before. This means that if we apply a loading to the uniform sample that created a stress under the tensile strength of the material before, that materials would not fail, but now if we apply the same exact loading to this new sample with the stress riser, the sample could very well fail due to the heightened stress at the discontinuity. This should be seen as quite alarming as this means that parts can fail at lower loadings than expected, and while our example shows a huge hole in the part, it should be noted that small cracks, or simpler sharp corners and other minimal, yet abrupt changes in the geometry can affect the state of stress in a major way.
We should also note that highly concentrated stress regions can be formed by applying loads non-uniformly, as in the example of gripping material with pliers discussed in the 2nd paragraph, where we apply a load on a very localized, concentrated region (picture taking a 10 lb weight and placing it directly on a table vs. taking the same weight, balancing it on a thumbtack, and then placing it on the table with the tack point down). Just as before, we have decreased the effective are that the load is applied over, except this time, we reduced the area of the stress region by changing how the load was applied, whereas before we did it by changing how the load was transmitted.
For this reason, engineers must be very careful when they design parts to include factors of safety to account for material imperfections, possibly use non-destructive inspection (NDI) techniques to examine critical parts for cracks in situations where a crack could prove catastrophic (for example a crack in the side wall of a submarine hull that could spread due to cyclic fatigue due to cycles of compression/de-compression when traversing great depths, surfacing, sinking again, surfacing again, etc.), and must avoid abrupt changes in geometry in the design of the part itself. Luckily, in this day and age, we understand much more about internal stresses and stress distribution thanks to new testings and stress visualization techniques, but the subject of stress concentrations is one that I cannot stress the importance of enough! (I apologize for the bad pun)
Additionally, this was purely looking at one-dimensional loading in an over-simplified material and geometry, but in the real world we can have parts of really intricate geometry, made from materials with unbelievable amounts of anisotropy (different properties in different directions), subjected to combined three-dimensional loading of tension, bending, torsion, shear, perhaps compression in a different region, with hygrothermal loading (loading due to both moisture and thermal effects), subjected to different kinds of corrosion, vibrational modes, impact loading, and the list just goes on and on! Anyways, hopefully today you learned a little bit more about one of the endless topics that engineering encompasses! I will leave you with some really cool photoelastic stress visualization pictures in which the refraction of light is a function of stress (due to birefringence), thus the material essentially shows different wavelengths (and thus different colors) due to differences in stress throughout the material, helping to visualize stress (and stress concentrations).
Here at TeamUV.org, we have often discussed some of the finer intricacies of fluid mechanics (or usually more specifically, fluid dynamics, as opposed to fluid statics). Generally speaking, however, we have looked at fluid flow and behavior from a very macroscopic view, that is we have looked at fluids as they act on the macroscopic length scale, within which objects are practically visible by the naked eye. In the various fields of engineering, most engineers would only need a macroscopic understanding of fluid mechanics in order to perform rather rudimentary calculations and analysis. For example, if an engineer was asked to determine the hydrostatic pressure exerted on a submerged pressure vessel lying on the bottom of the ocean or if they were asked to size (determine pump impeller diameter, pump speed, power input necessary, pump type, capacity/flow rate, etc. for) a pump based off of the known pressure gradient (perhaps it has to force water through a very fine filter while maintaining a certain amount of pressure), elevation change, or required change in speed, a macroscopic view of fluid mechanics would often be sufficient. But is this always the case?
Of course not! The golden rule of engineering regarding what you need to know to perform your job is that there is no golden rule of engineering regarding what you need to know to perform your job. Engineering is a highly dynamic field, with ground-breaking discoveries made continuously…right now, somewhere in the world a scientist or engineer is making a major contribution to the future of STEM. Additionally, engineers (especially mechanical engineers, who have a very large, diverse knowledge base) can be asked to do anything at any given time, and they must be able to figure it out! So to say that the macro scale is the only one an engineer needs to be aware of (especially in the field of fluid mechanics) would be a gross understatement. So where does that leave us? Well now would be a good time to explain what is meant by “length scale” and to share some of the typical ones. After that, we will very briefly roll through some of the fluid effects that exist on smaller length scales, as these highly complex phenomena are beyond the scope of this post.
A length scale is essentially a parameter for deciphering the characteristic length associated with a phenomena. For example, if we are talking about the atomic scale, we are generally talking about phenomena that occurs in the size range of atoms, on the order of magnitude of pico- to femto-meters (10^-12 or ^-15 m). If we are talking about the microscale, we are talking about things on the order of micrometers (10^-6 m) such as water droplets or the thickness of a human hair. The macroscale would be associated with cars, mountains, you and I, etc. and would be essentially anything in your field of vision, i.e. probably from millimeters on up to kilometers (although the macroscale is not precisely defined). From here, we would likely move on to the astronomic scale, which is generally used to refer to phenomena on the scale of the universe, or Megameters (10^6 or 1,000,000 m) on up. For example, if you were to move from an atomic to micro to macro to larger with regards to your hand, you could envision protons and neutrons in your skin cells and then zoom out to bacteria under a microscope and then zoom out further to your hand itself and then zoom out further to the Earth itself, further to the Milky Way Galaxy, and so on and so on. In fact, if you have a second, you should check out this zoomable tool for visualizing the scales of the universe.
So back to fluid dynamics after a very lengthy detour, why should we care about length scales smaller than the macroscale? Because turbulence (as well as all fluid motion and other physical phenomena in general), is a result of phenomena on smaller length scales. So in order to actually understand the onset of turbulence or how fluids react with each other or with structures, etc. within the framework of deeper understanding, we must understand the microscopic behavior of fluids. Much of this behavior is defined by fluid stability and instabilities, which are not only very interesting to look at, but are the building blocks for the entire field of fluid dynamics as we know it! At this point, I will quickly show some pictures of some of the more common instabilities, but will not go into descriptive detail as scientifically, mathematically, etc. they are extremely complex phenomena that many fluid dynamicists spend their entire careers studying.
Kelvin-Helmholtz Instability simulation. [Media Credit: Wikipedia.org]
First and foremost I apologize for the overall lateness of the content of this post, as I originally intended to publish this post in my previous round of posts, but due to time constraints decided to publish a post on a snake-proof full-body suit (equally interesting!) and invest a little more time into making this post a little easier to understand before publishing…hopefully it worked out, haha. So as I noted a while back (while discussing the future of undersea warfare), with growing challenges in the undersea and technological domains, innovation is becoming more and more important within the realm of defense engineering (as well as all other fields of engineering). One promising direction engineers are looking to in all fields of engineering is towards the application of advanced biomimetics (a.k.a. biomimicry) in their designs. Why might engineers and scientists want to study how we can mimic fish, or other animals or nature in general? Because nature truly is the ultimate engineer. Animals have been optimized to perform the tasks that they need to and to do so efficiently and thus have been nearly perfected for their environments and their lifestyles.
Considering the facts just presented, it becomes a little more evident why undersea warfare (as well as other undersea activities and applications) may benefit from the implementation of biomimcry. Take the Shortfin Mako Shark for example; this is the fastest species of shark in the world and it utilizes its large caudal fin (as will be defined later), slim, streamlined, torpedo-like body, and its stronger, faster-acting muscles (as enabled by its endothermic abilities, through which it generates additional heat through its unique metabolism, keeping the muscles warm and agile, thus defining the Mako as a “warm-bodied shark”) to reach cruise speeds of 25 mph and burst speeds up to 50 mph and leap 30 ft high! Another example of the awe-inspiring abilities of marine creatures and how scientists and engineers have attempted to mimic them is that of the color- and texture-changing abilities of the octopus, as Andrew talked about a while back.
To better understand more specifically how engineers can utilize biomimicry in order to advance undersea vehicle technology, we will now discuss how exactly fish swim. Fish generate forward motion, or swim, through what is termed locomotion. Locomotion is simply a fancy word for describing movement from one location to another; animal locomotion may take many forms and can be seen in all types of environments, whether terrestial (on land), aerial (through the air), or aquatic (through the water). There is a myriad of other qualifiers that can be used to further divide up the different kinds of locomotion (if you are interested, you can learn more about animal locomotion at this link), but we are going to solely focus on fish locomotion, that is, how fish get from one place to another.
Fish locomotion can be divided up into two main modes of motion: Body-Caudal Fin (BCF) and Median-Paired Fin (MPF). The BCF mode accounts for about 85% of fish families’ main mode of propulsion, whereas MPF makes up for about 15%. Now before diving into the swimming mechanisms associated with these two modes, we will make one more distinction: undulatory motion (also referred to as undulation) vs. oscillatory motion (also referred to as oscillation). Undulation is by far the most common type of motion (both within the BCF & MPF modes) and can be thought of as a lateral wavelike movement; picture a fish seemingly weaving its way through the water or a rope with waves travelling down its length…this is in essence what undulation manifests itself as: undulation in fish movement appears as lateral waves travelling down the length of the fish’s body. In short, undulation is lateral wave motion along the length of the body, relative to the body, as if the body was stationary but experiencing waves along its length. In contrast, oscillation focuses more on the body being essentially rigid and moving the tail side to side…picture your dog wagging its tail, or a pendulum oscillating about the line connecting the pivot point to the base. Now that we’ve got that covered, we can move on to quickly listing the common types of fish motion and listing a few examples!
Body-Caudal Fin (BCF)
This type of movement depends on the fish effectively wiggling its body in order to move its caudal fin sided to side, thus producing thrust which has components in the forward, backward, and transverse directions. The largest component of this thrust is that in the rearward direction, thus the movement of the caudal fin propels the fish through the water.
1. Anguilliform: With this kind of motion the undulatory waves are passed throughout the entire length of the body (except perhaps the head); because the entire body is extremely flexible, both forward and backward motion are possible. The most typical application in which you would see this kind of motion would be in eel locomotion.
2. Subcarangiform: This motion is similar to anguilliform, but the forward 1/3-1/2 of the fish does not move, while the rest of the body still generates transverse undulations. It is now significantly harder for the fish to swim backwards as it is not longer symmetric front to back and the forward portion of the fish is much more stiff than the rear. Common examples of fish with this kind of motion would be most trout and salmon.
3. Carangiform: Also similar to anguilliform, but only the last 1/3 of the body acts to produce thrust and the caudal fin itself is usually more stiff to produce greater thrust with the reduced active length of the body. Fish that swim like this are usually fairly narrow transversely, likely to increase the surface area used for thrust generation by increasing the height to width ratio; these fish also tend to be stiffer overall and faster moving.
4. Thunniform: In this group, all undulation is restricted to the caudal fin/tail and the region connecting the main body to the caudal fin (called the peduncle); these types of fish usually have very large, stiff caudal fins, have been optimized for high speeds and long distance travel, and are capable of generating hydrodynamic lift in order to compensate for the fact that many of them are not neutrally buoyant and thus need to move (and in doing so, generate lift) in order to keep from sinking. Examples are most species of tuna and sharks.
1. Ostraciiform: These types utilize slow pendulum-like movement of large caudal fins and are similar to Thunniform, but operate much more slowly. As a result, this type of swimming is usually either simply an auxiliary, low-energy style of swimming used by some MPF fish or, if used by fish as their main style of propulsion, those fish would generally have internal countermeasures such as poisons since they are incapable of fleeing predators.
Median-Paired Fin (MPF)
This type of movement depends on synchronization of various combinations of usage of the pectoral, dorsal, pelvic, and/or anal fins.
1. Rajiform: Characterized by vertical undulations along large pectoral fins…think sting rays and manta rays for example.
2. Diodontiform: Characterized by undulations that travel along large pectoral fins…like a porcupine fish!
3. Amiiform: Utilize long undulatory waves along large dorsal fins, such as a Seahorse.
4. Gymnotiform: Uses undulations of a long anal fin; much like the Amiiform, but using the anal fin on the underside of the fish rather than the dorsal fin on the top side of the fish. An example is the American Knifefish.
5. Balistiform: Anal and dorsal fins undulate; while rare, this can be seen in the Triggerfish.
1. Tetradontiform: Dorsal and anal fins oscillate either in phase (together) or opposite of each other; an example would be the Sunfish.
2. Labriform: Pectoral fins osciallate in a way in which they produce both lift and drag, which can be resolved into components, one of which would be rewards, thus producing thrust. In essence, the fish flaps and rows its pectoral fins, producing thrust. An example of a fish using this kind of motion would be the California Sheephead.
So there you have it, an organized view of the many sorts of propulsion mechanics associated with fish, each having its own advantages and disadvantages. By studying these kinds of characteristics of fish, scientists and engineers can come up with innovative solutions by looking to the sea for the answers for the one constant truth for scientists and engineers alike is that we never stop learning and so when you can’t find a sufficient answer in your textbooks and theories, you need to be able to conduct experiments and analyze the world around you in order to come up with new ideas.
This is exactly what engineers within the defense industry are doing currently as they conduct research and begin designs of new cutting-edge, innovative undersea vehicles that utilize biomimicry to provide for increased performance, better power efficiency, and increased stealth through the minimization of flow signature. While we here at Team UV are not utilizing biomimicry in the design of our propulsor (for which we use something else all together), we absolutely have biomimetic influence within our design and as can be seen in the picture at the top of this article, have looked to adapt a streamlined shape and fin-like control surfaces in addition to a number of other biomimetic schemes (i.e. stability, maneuvering, buoyancy control, drag reduction, etc.) to produce a truly innovative solution that is currently in the manufacturing/assembly stage. And so we again ask for your increased support through our fundraising campaign at GoFundMe.com/TeamUV as we near the end of our project in the coming months.
As promised, in another week or two, we will release some pictures of the current vehicle design/model.
A few days ago, Team UV was selected to present some of our research regarding our underwater vehicle and its propulsion system at the 2015 National Conference on Undergraduate Research, which will take place at the Eastern Washington University from April 16th-18th! Thank you to our readers for your support and for following our blog; we will not know what day, timeslot, or room we will be presenting on/during/in until early March.
Also, we want to thank those of you who have contributed to our fundraising campaign and mention that we have now raised $1,630 thanks to your generous donations! Thank you for your support and please continue to help spread the word as we continue in the purchasing and manufacturing stages!
We also want to note that no donation is too small and not a single penny donated will go to waste, it will all be used to increase the quality of our vehicle, to add capabilities (through additions to the sensor suite or additional drag-reducing technologies, etc.), and to enable us to conduct better testing (i.e. the construction of a flow tank for actual flow visualization). As an example of this, we are excited to inform you that through some of your donations we have been able to get our hands on a superhydrophobic substance (from Hydrobead) that will help us to decrease drag on the exterior of our vehicle significantly through the repulsion of the surrounding water. As follows from the above statements, any money that we raise above the $5,000 will be put directly into the project in one of many ways, including (but not limited to) those listed above.
In addition to this, at this point, it is unclear as to where the funding to attend our research conference will come from (whether out of pocket or at least partially funded through our school’s research office), so all donations will help us significantly!
Lastly, I want to remind our readers that we will be trying to post funding progress updates as often as possible and that you can find a full-sized PDF of our pull-tag poster on our Sponsors & Donations page if you would like to print one out and post it to help get the word out. If you would like to help out in other ways, it would mean a lot to us if you would tell your friends/family/coworkers/etc. about our fundraising campaign (and possibly ask them to share it as well), share it on Facebook, or perhaps even just spread the word about TeamUV.org in general, as our biggest goal with regards to this website is to inspire interest in the fields of Science, Technology, Engineering, and Mathematics (STEM).
Any help is greatly appreciated and please come back Sunday for Andrew’s Open Mind post!
About a week ago, NASA tested the RS-25 rocket engine on the new Space Launch System (SLS), a launch vehicle that will drive the next generation of space shuttle deeper into space than we have been able to go thus far. The video (shown below) has been made available to the public and provides an excellent excuse for the discussion of compressible flow regimes.
In the past, our readers have been exposed to the world of fluid mechanics quite often (whether through aeroacoustics, turbulent vortices, hydrodynamic drag, or various other phenomena), and have even been exposed to the subject of compressible flow briefly, so today I am going to give you a bit of an introduction to the subject of gas dynamics and then I will explain the different flow regimes associated with compressible flow.
Fluid mechanics, as discussed previously on this website, is the study of fluids (liquids, gases, plasmas), their movement, and how they interact with internal and external stimuli (loading/forces, pressure differentials, dissipative effects, heat transfer, etc.). Today, we will only be looking at gas dynamics, which differs from the study of liquids in that, for most purposes, liquids (i.e. water) are assumed to be incompressible. With gases, this is not the case. Due to the greater amount of space between free particles, gases have a much greater ability to be compressed. Owing to this compressibility, the terms “gas dynamics” and “compressible flow” are often used synonymously to refer to the same field of study, as compressibility becomes a vital factor as the speed in a gas flow is increased.
As a result of this compressibility, two important phenomena are uniquely encountered within the field of gas dynamics that play a huge role in high speed gas dynamics, as will be defined shortly. The first of these is the choked flow condition, which finds application in the usage of convergent-divergent nozzles (amongst other things), but which will not be discussed here for simplicity. The second of these is the formation of shock waves. Shock waves are essentially pressure waves that have coalesced together to form a “Mach wave”, which represents a discontinuity in the flow field….right, so what in the world does that mean? If an object were to be stationary in the air and have pressure waves emanating from it, they would propagate out in all directions at the same speed (the speed of sound) and form concentric circles about the object. However, as the object begins moving (within subsonic flow), the pressure waves become sent out at different times; in essence, the object sends out a pressure wave, then moves forward and sends out another, and so on (although, this happens basically continually).
As the object’s speeds increase, the center points of these waves get further apart, and thus the waves become compressed in the direction of motion, and expanded in the opposite direction. Eventually, if the object continues moving faster, the object will be moving at the speed of sound, meaning that the object will be travelling at the same speed as the pressure waves are being sent out…in essence, the object has matched or caught up with the pressure waves that it is sending out, and so when the object sends out more pressure waves, they can no longer propagate forward from the object, but rather travel at the same speed, while the portions of the waves traveling backwards are now being left in the dust…figuratively speaking. The waves that are being emenated from the object all at the speed of sound are now really close together and essentially stack up and coalesce into one solid pressure wave that is termed the shock wave. This shock wave can be heard as a “sonic boom” due to the discontinuity or abrupt change in pressure across the shock wave (forward of the wave, the flow is moving at the speed of sound and very low pressure, behind the wave, the flow is moving slower and at a higher pressure). As the object speeds up even further, the object is now starting to outpace the pressure waves all together in what is called supersonic flow, so that the object is leading the waves, which begin to form a mach cone around the object; inside of this mach cone is referred to as the zone of action, while outside of the cone is referred to as the zone of silence. If the object moves even faster, it will eventually get to a speed so high (that of hypersonic flow), that the shock cone will tightly hug the skin of the object so that the distance is so small between the object and the shock wave, that the air gap (the shock layer) begins to heat up due to viscous effects and the aerodynamic heating effect, leading to what we term “high-temperature chemically reacting flow”; the flow is so hot that the gas begins to dissociate or ionize!
So at what speeds does this all occur? To find this out, we define the Mach Number (a.k.a. M or Ma) as the ratio of the object’s speed to the local speed of sound; to understand this, a value of 0.5 would mean that the object is moving at half of the local speed of sound, 1.0 would mean the object is moving at the local speed of sound, and 2.0 would mean the object is moving twice as fast as the local speed of sound.
Up to a value of Ma 0.3, the flow is described as incompressible and thus is analyzed similarly to other incompressible fluid dynamics such as most liquid flow. An example of incompressible flow would be what the baseball encounters when you play catch with a friend.
Once the object hits Ma 0.3, the flow is considered compressible and subsonic in that the object is still moving slower than its pressure waves. An example of subsonic flow would be the flow around many .38 Special bullets.
Once the object reaches about Ma 0.8, transitional instabilities begin to set in and persist to about Ma 1.2; this regime is termed the transonic flow regime and can be seen in basically any application wherein an object is accelerating to supersonic speeds, as the object must pass through the transonic regime to reach the supersonic regime.
Above Ma 1.2, the shock waves have generally been established in full and the vehicle can be said to be in the supersonic flow regime. Applications include supersonic jet engines, such as those found in many military aircraft and supersonic ammunition. More photos will be included here since supersonic flow is the meat of this post.
Lastly, above Ma 5, the aerodynamic heating effect comes into play and the flow enters the hypersonic regime. Applications are hard to come by as this is a subject of a great deal of current research within the fields of mechanical and aerospace engineering (more specifically fluid dynamics); however, one instance of this kind of flow that nearly everyone is familiar with is that of the space shuttle, especially during what is termed re-entry. In fact any re-entry vehicle will experience hypersonic flow, and very likely “hyper-velocity flow” which is essentially an upper range of hypersonic flow speeds.
Prompt: Boston Dynamics is a company that specializes in producing robots that can really do the unimaginable. Take Sand Flea. Sand Flea weighs 11 lbs and can jump to heights of up to 30 ft. Such a feat represents a very attractive design goal across all industries for the coming years: the ability to store massive amounts of energy and release it very quickly. Considering that these high energy-density type systems are in fact the way of the future, using what you know about energy come up with either at least 3 ways of storing/quickly releasing a large amount of usable mechanical energy or come up with one way and describe at least 3 ways to look at your solution.
There are countless applications for these kind of high energy-density storage, quick release type systems; however, in this post, we will simply be looking at a few design considerations that a mechanical engineer would have to account for if he/she wanted to design a robot capable of jumping to great heights by taking advantage of the expansion associated with the release of compressed gases.
As shown above, Sir Isaac Newton’s 3rd Law of Motion essentially states that for every action, there is an equal and opposite reaction. This simple statement has profound complex consequences in the real world. If you have ever seen a spaceship lift off, felt the recoil from a firearm, had a hammer bounce back at you after hitting a nail, or wanted to see what would happen if you were to use a fire extinguisher as a booster while sitting in a rolling chair, you have seen the phenomena that Newton’s 3rd Law of Motion is referring to.
Now in reality, things get much more complicated as there are many inter-dependencies that affect these reactions (i.e. the reaction of air resistance on the skin of the spaceship, the rerouting of gases in automatic weapons to chamber the next round and reduce recoil, the elastic properties of the steel head of the hammer, the rolling friction of the chair wheels or that associated with the bearings of the wheels, and the list goes on…).
So getting back on topic, what would we need to consider if we wanted to design a robot that used compressed fluids to jump?
As a class of fluids, gases are much more compressible than liquids; this fact, in combination with the tendency of gases to fill the shape of their containers (or flow paths) makes them ideal for use in high-compression fluid storage to be used for imparting large amounts of kinetic energy to objects via momentum transfer from their expansion kinetics. By storing a large volume of gas under heightened pressure within a properly suited pressure vessel (PV), large volumetric expansion ratios/rates can be realized when the gas is released. This gas expansion leads to massive amounts of energy being released very quickly from these areas in which massive amounts of fluid can be stored in a very compact space (thus high energy density storage and fast release). The energy and momentum associated with this gas can be used to propel our robot up and into the air, but know what? Did we intend to design our robot to be single use or do we want it to be able to jump again? We need to find a way to refill the system.
The means by which these systems are refilled or “recharged” is most often dependent on the kind of gas being used. In order to replenish your energy stores in an air-based system, you could simply pull the air from the atmosphere using an air compressor (although this becomes significantly harder when you are for example 500m under the ocean’s surface). Another complication associated with this method is the fact that an air compressor may not be ideal for our application on the basis of size, weight, vibration, noise, power requirements (as the air compressor will up the robot’s power requirements and thus decrease its run time for the same amount of power supply or even necessitate the use of all new control circuitry), etc.
This situation is complicated even further when the gas being used is not air, as now you have to store all of your gas reserves unless you can find out some way of extracting the gas you need from the atmosphere, which is simply not feasible, especially on such a small scale. So how do we get around these limitations?
Many air-based systems use air-pistons in order to recharge their compressed gas reserves as anyone who has ever had to pump a BB gun or water gun has experienced. The mechanism for actuating this piston is not always something as obvious as the lever action on your Daisy Red Ryder BB gun (remember to always practice proper gun safety, lest you shoot your eye out…referencing the movie A Christmas Story). Some systems may have a protruding pin that (when depressed) cycles a small pump compressor or reciprocating piston to recharge thy system. In some applications, exhaust gases may be re-routed and used to actuate the compressing mechanism. Technological creativity knows no bounds and, as such, it is more realistically finding a way to recharge a system comes down to design time, costs, and other system-level tradeoffs. Would it not be easier if we simply did not allow the gas to ever leave the system in the first place?
We could create a closed-system by using a highly elastic material to cover the exit nozzles of our robot, so that when we released the gas, it would rapidly balloon out and propel our robot through the elastic collision interaction mechanics between the gas-filled elastic material and the ground (think Newton’s 3rd Law of Motion) without expelling the gases to the atmosphere. To better understand this, visualize taking one of those squeeze toys where the eyes bulge out (see below) placing the toy with the eyes against the ground and then filling the eyes with a ton of gas really rapidly and watching the thing fly up in the air! This is just one example of the open-minded nature of engineering problem solving. The only bummer would be that in reality, this feat would likely be far more difficult than stated here and would likely require the development of a custom material with the proper amount of elasticity or “stretch”, tensile strength, strain-recovery time (how fast the material returns to its original size/shape), and would likely need include stiffer/more rigid pads where contact would be made with the floor so that the material could transfer more of the gases kinetic energy to the ground (rather than simply absorbing all of the gas’s energy through the material’s ductility).
In order to bring this article to end sooner rather than later (sometimes I get carried away and don’t realize how much I’m writing, so my apologies!), I will quickly move through this subject for consideration as well as the 3rd one.
Most gases would experience significant thermal energy generation under large compression ratios and thus the surrounding system would likely require cooling to prevent damage to the electronics or to the user; this cooling could be accomplished by passive controls such as extended surfaces/fins or forced heat transfer by way of a fan – the cheapest active thermal control. You have likely seen both of these types of systems mounted to your computer’s CPU.
Mechanics of Materials
A very noteworthy consideration in this application would be the strength of the pressure vessel (PV). Depending on gas used, compression ratio, allowed temperature rise and transmittance of impulse (high energy transfer over small time period) to the PV, hoop stresses (circumferential) can become significant and therefore require thicker PV sidewalls, use of stronger material for the PV, or rib reinforcement of the PV.
So anyways, there is a long-winded look into just a few of the many, many things a mechanical engineer might consider in their design of a robot capable of jumping to great heights using compressed gas. One of the many beauties of mechanical engineering is the fact that it is such an incredibly open-minded field that requires creativity, intelligence, determination, and the realization that there is never one right answer.
Team UV would like to update our readers and supporters with regards to the progress you all have helped us to make through our fundraising campaign. As of today (January 7th, 1525 hours), we have raised $1,620 of our goal thanks to your donations!
As a way of saying thank you and hoping to share a little more about our project with you, we will be publishing some images of our project over the next few weeks. The reason we have refrained from posting any pictures from our project in the past was due to the proprietary nature of many of the systems on our vehicle (and the vehicle as a whole), but we are realizing more and more how important it is that we share a little more of what we are doing with our supporters. So without further ado, below we have posted 2 pictures of SHEILA-D (Submerged Hydrodynamically-propelled Explorer, Implementation: Los Angeles – Demonstrator).
SHEILA-D was our propulsion system demonstrator that we designed, built, and tested over a span of 36 days and 850 (by conservative estimates) man hours during Phase I of our project (which took place during our Machine Design lecture/lab combo in Spring 2014). The goal for SHEILA, was to demonstrate the ability to provide thrust with our innovative underwater propulsion system, and in this respect we succeeded. However, we were aware of many shortcomings from this initial design (i.e. poor material choice as influenced by cost/time limitations, poor tolerances, etc.) and thus revamped our efforts with regards to the propulsion system during Phase II [the senior project portion/development of the entire vehicle from late Spring 2014-mid Spring 2015 (project symposium)]. For more information on the history and plans for this project, please check out our About page.
We are currently in the purchasing portion of Phase II (to be followed by manufacturing/assembly, programming, testing, final analyses, and report/presentation preparation) and thus could use funding now more than ever. We would like to thank all of you for supporting our efforts and ask that you please continue to share our website and our fundraising campaign (GoFundMe.com/TeamUV) with as many people as possible. No donation is too small and for those who know the team personally, offline donations are welcomed as well.
This post will be reposted on our fundraising page, and 1 week from now we will post some pictures of the original Phase II full-vehicle concept, with the actual Phase II vehicle computer model pictures coming 1-2 weeks after that, so please be sure to check back often and remember, tomorrow Ben will be posting a Presentation post at 1000 hours!
First off, contrary to what I stated in my previous post, today’s post will not discuss one way in which UUV technology is being optimized for the purpose of undersea warfare through the utilization of advanced biomimetics, as I ran out of time to prepare that post and thus will publish it in my next round of posts.
Today I will be sharing something a little bit different…the design of a full body suit that was recently worn by a man who was swallowed whole by a 25 ft. anaconda…on purpose. I’ll decline to comment on the validity of this kind of feat, as that is not what I am here to write about, but will rather focus on what is effectively a pretty interesting case study in engineering design.
Anytime something must be designed to be used by humans, the level of engineering required is almost immediately stepped up [for many reasons, including (but not limited to) the increased importance of safety], and this is no exception. In all product design, engineers must begin by determining the problem statement and the constraints imposed by that statement. Dr. Cynthia Bir (a biomedical engineer), one of the project leads for the suit design, would have begun by looking at the facts: there is a man, who will be ingested by an anaconda, and that man must then come back out of the anaconda without being harmed. As ridiculous as this must sound, it is actually quite reflective of the absurd nature of the design/operational constraints that engineers must often meet. Next, Dr. Bir would have had to conduct literary (or possibly even experimental) research into the aspects of the problem statement (the snake itself, and all aspects of the human-snake interaction to take place) and then determine/look at the consequences associated with this problem statement; that is, what are the specific risks posed to the user in this scenario (in this case: constriction, snake bite, and acid attack from the gastrointestinal acids). Next, she would have started in with generating concepts, selecting a few concepts to further develop, doing some base-line evaluation and analysis of those concepts in order to cut it down to one final design, and then starting in with the actual design/calculations/analysis/testing of her chosen design. I should note that engineering design is never this simple and is actually a very complex process, that generally sees many iterations and a great deal of looping back to earlier steps of the design process.
So, as we stated before, Dr. Bir had already deciphered the situation, conducted relevant research (how a snake attacks its prey, what kind of acids are present in the snake’s stomach, etc.), resolved the situation into the key parameters/constraints associated with the situation (ability to resist snake bite, constriction, and stomach acids), and now would have come up with a few concepts. Undoubtedly, one of the decisions that would have been made early on would revolve around what kind of material system to use in the design: one material for the entire suit or multiple materials used throughout the suit. In this case, it would have been very difficult to use one material for the entire suit, as the application calls for many different material properties (hardness, strength, and fracture toughness for the snake bite, stiffness and compressive strength for the constriction, and resistance to chemical attack for the acids, etc.) and thus it would be far more economical to use multiple materials (each one targeting a few key constraints) on the suit (as opposed to having to develop a whole new material to meet all of the specific needs of the suit). In fact, this is exactly what Dr. Bir and her team did.
The innermost layer of the suit actually served a different purpose: to monitor the vital signs of the man being swallowed (his heart rate, respiration rate, core body temperature, etc.), as if something began to go wrong, they would want to stop the experiment immediately. This layer consisted of a biometric vest that was paired through Bluetooth to the project team’s computers, giving them live updates of all of his vitals (it is interesting to note that these kinds of vests are also used by special operators, astronauts, some athletes during training, and many others).
Next, came a thermal control layer in the way of a vest fitted with a pumped liquid cooling loop heat exchanger which essentially sends cold (colder than the man’s body temperature) water through small tubes that run across his body. The temperature difference between the man’s body and the water in the tubes drives heat transfer out of the man’s body into the tubes, thus cooling the man’s core temperature. This is important in order to make sure that the man does not overheat, because he will be wearing a number of thick layers of various materials and will be inside of the snake’s stomach so that he will be exposed to his own internal heat generation, the snake’s internal heat generation, and all of his insulating layers.
Next comes a chemical suit (not pictured) to provide the chemical resistance that we mentioned earlier. After this, a layer of chain mill (like that worn by Renaissance knights or people who dive with sharks) is added in order to block the snake bite.
On top of this comes a rigid carbon fiber shell that must be made custom to conform to the user’s torso and is used to resist damage to the ribs/chest cavity by constriction of the snake’s muscles. The torso shell was designed with a factor of safety of a little over 3 (meaning that the shell’s strength is over 3 times the stress that it will be subjected to during the event) and was tested by wrapping a thick rope around the shell and pulling the rope with tow trucks at either end.
On top of all of this, the user donned a thick layer of neoprene (think a wetsuit) to keep all of the other layers together and cover any otherwise unprotected parts of his body; this layer was then dusted with pig’s blood in order to attract the snake and ensure that the snake would actually want to ingest the man. Other things (a few of the many other things) that had to be considered in the design of this suit would have included the weight of each component, thickness (to ensure mobility of appendages), range of motion (note the fact that the torso shell is sleeveless), thermal conductivities of all materials (for proper heat transfer calculations), possible interference with the Bluetooth signal, ability to put on/take off the suit, and of course ability to breathe! The ability to breath is vastly secured by a combination of three things: the carbon fiber torso shell, none of the layers being too restrictive, and a sealed face mask (which also serves as eye/face protection from any objects or acids, thus the mask must also be chemical-resistant) with an external air hose (which must also be resistant to chemical infiltration) fed by an air supply from the project crew.
So there you have it, an interesting look at some of the engineering considerations behind one of the strangest things I have ever heard of anyone wanting to do. This just goes to show that the possible applications of the world of science, technology, engineering, and mathematics (STEM) are truly limitless!
Please be sure to check back Thursday for a Presentation post by Andrew and please remember to help us to share our fundraising campaign at GoFundMe.com/TeamUV
While the vast majority of the attention with regards to unmanned vehicles is generally seized by unmanned aerial vehicles (or UAVs, which have almost become a household acronym in this day and age), the aerial environment is by no means the only one within which militaries benefit through the use of unmanned vehicles. In fact the same reasons that UAVs prove so valuable in the aerial environment (information gathering, reconnaissance, surveillance, unmanned combat, logistics support, etc.) also exist for UGVs (Unmanned Ground Vehicles) and UUVs (Unmanned Underwater/Undersea Vehicles…by the way do you realize that if you shorten UUV to UV, you get half of Team UV’s name? Rest assured this is no coincidence, our senior project aims to provide a stealthy, highly maneuverable ISR UUV, but we shorten it to UV – underwater vehicle – because with our compact size it would be impossible to man the vehicle, although UV is also an acronym for Unmanned Vehicle…plus “Team UV” is catchier than “Team UUV”…).
In the design of our UV, we are essentially optimizing the vehicle for ISR (Information/Intelligence, Surveillance, and Reconnaissance) type missions; we do this by providing for higher speeds, smoother maneuvering, increased stealth (on the fronts of thermal, magnetic, and flow signature, cavitation, noise, and overall inconspicuousness), and requiring little to no human interaction. All of these mission objectives that we have for our UV increase the vehicle’s performance and stealth, making it a much more efficient solution to be used by our troops to conduct naval ISR from a distance and thus, help to save lives. While our primary application is ISR, which directly serves the military, it is important to note that UUVs are not only used by the military, but are also used by harbor security, underwater inspection contractors, marine biologists, and even recreational users in some cases. The range of applications for UUVs has no end in sight, as can be seen by the small sampling of applications for UUVs listed below.
As more conflicts arise and scientists and engineers continue to push the boundaries of technology, the role of UUVs in undersea warfare is only set to increase; this is especially true when budgetary considerations are taken into account in that the cost of a small UUV is almost negligible in comparison to a full-scale submarine. This is not to say that a UUV can replace a full-scale submarine, nor that they even share the same roles; however, as submarine fleets diminish due to the astronomical costs associated with initial acquisition and subsequent maintenance, the number of UUVs used by the military will only continue to rise. When you pair this with the fact that, as the current UUV technology becomes older and less expensive, more and more groups (whether for better or worse) will have access to UUVs, the reason that further developing UUV technology is of such great interest to the defense industry becomes more and more apparent.
Hopefully this post served as a helpful primer on unmanned drone technology and the role(s) that UUVs play in the defense (and other) industry(industries). This upcoming Tuesday (12-16), I will be continuing off this post with a Well Read post discussing one way in which UUV technology is being optimized for the purpose of undersea warfare through the utilization of advanced biomimetics (that is, by mimicking the various ways by which fish swim!). Be sure to check back Sunday for an Open Mind post form Andrew and please continue to help us to share our fundraising efforts at GoFundMe.com/TeamUV
Prompt: Entertainment engineering brings to light some of the more light-hearted aspects of engineering. Entertainment in itself is one of America’s most popular pass times and encompasses subjects such as film, television, music, games, reading, comedy, theater, circuses, magic, street performance, parades, fireworks, animal shows, and the list just goes on and on. Entertainment holds a very special place in the world and always has; whether in the form of the plays of Ancient Greece, the jesters of the medieval times, the shooting exhibitions from the days of the wild west, the black & white films that the soldiers of early wars watched to forget about their harsh reality, or the 3D special effects that seem to captivate us all on the building-sized screens of today, entertainment has always been there to help relieve the stress of those who indulge in it. Today this is especially important for the citizens of this great country as we work longer hours, spend more time stressed, and find the well-appreciated release provided through entertainment to be more and more refreshing. For all these reasons and many more, the entertainment industry is here to stay and will constantly require great engineers to keep it afloat and help it to progress. Pick 3 forms of entertainment and describe how a mechanical engineer could contribute to them, or 1 form and 3 considerations.
One interesting subset of physics and engineering that is very often modeled in movies, but is vastly overlooked, is that of fluid mechanics. Although not usually noted, fluids (liquids, gases) are not the only things that can be described by fluid mechanics; fluid mechanics is often applied to study the movement of plasmas and the flow of granulated material (i.e. sand) for example. Perhaps more significantly, fluid mechanics finds vast application in the way of FSI (Fluid-Structure Interaction), which finds usage in all kinds of fields, such as the movement of bridges in high winds, aeroacoustics (such as was seen in my earlier post on owl stealth), and the effect of water hammer on piping materials to name just a few applications. An interesting phenomena that is frequently seen in movies, and that requires a lot of work in the way of application of fluid-structure interaction theory and computational physics, is the movement of fields of tall grass in the wind. This motion is actually quite comparable to the movement marine plants in tidal currents and thus is often analyzed similarly. To learn more about the movement of grass fields in the wind, head on over to FYFD.
Additionally, if anyone has ever seen an action movie, chances are there was some shooting in it, and chances are if there was a lot of shooting in it, someone got shot. In some particularly gruesome movies, the bullet is shown to impact the skin and create the wound. The field of terminal ballistics (consisting of entry, internal, and exit ballistics) is highly complex and to model the bullet-target interaction correctly takes a vast knowledge of materials, fracture mechanics, and many other fields of physics and engineering.
Lastly, explosions have become a focal point of the majority of movies out there these days; their modeling requires a vast knowledge of combustion theory, flame-front propagation, fluid mechanics, heat transfer, and (once again) fluid-structure interaction.
So just remember, next time you see a movie and think to yourself ‘How do they make it look so real?’ or ‘These special effects are incredible!’, you have the worlds of science, technology, engineering, and mathematics to thank for helping to create a realistic experience!
Last weekend Team UV presented some of our fluids research for our underwater vehicle at the 22nd annual Southern California Conferences for Undergraduate Research (SCCUR) at the California State University, Fullerton. We enjoyed the opportunity to both get a look at some of the research students at other universities are conducting and to share some of what we have done, as well as to share the website, with students and faculty from other universities. We will also be looking into the possibility of bringing our research to more conferences in the future.
We would also like to update our readers with regards to the progress we have made in our fundraising campaign. Thus far, with your support, we have been able to raise $570! Thank you all for your donations and support, they will absolutely prove incredibly useful in the coming months as we begin to manufacture parts, have some of our more intricate components made, buy materials, equipment, and other components, and begin to design experiments and the necessary testing rigs. We would just like to remind our supporters to please continue to help spread the word about our project, share our fundraising campaign (GoFundMe.com/TeamUV), and if you feel so compelled, to donate to our senior project team to help us to reach our goals and produce our stealthy unmanned underwater ISR (Information, Surveillance, and Reconnaissance) vehicle, which we hope can one day help to save lives by taking more of our troops out of the field.
Please remember to check back tomorrow for Abraham’s Presentation post!
A while back, Team UV was selected to present some of our research regarding our underwater vehicle and, more specifically, its propulsion system at the 2014 Southern California Conferences for Undergraduate Research, which will take place at the California State University, Fullerton. So this Saturday (November 22nd), for anyone who might be in attendance, we will we will be presenting during the Oral Session III (from 1445-1545 hours) in room SGMH-2211!
Also, we want to thank those of you who have contributed to our fundraising campaign and mention that we have already raised 11% of our goal of $5,000 thanks to your generous donations! Thank you for your support and please continue to help spread the word!
We also want to note that no donation is too small and not a single penny donated will go to waste, it will all be used to increase the quality of our vehicle, to add capabilities (through additions to the sensor suite or additional drag-reducing technologies, etc.), and to enable us to conduct better testing (i.e. the construction of a flow tank for actual flow visualization). As follows from the above statement, any money that we raise above the $5,000 will be put directly into the project in one of many way, including (but not limited to) those listed above.
Lastly, I want to remind our readers that we will be posting campaign progress updates on average once a week (Wednesdays 1000 hours) and that you can find a full-sized PDF of our pull-tag poster on our Sponsors & Donations page if you would like to print one out and post it to help get the word out. If you would like to help out in other ways, it would mean a lot to us if you would tell your friends/family/coworkers/etc. about our fundraising campaign (and possibly ask them to share it as well), share it on Facebook, or perhaps even just spread the word about TeamUV.org in general, as our biggest goal with regards to this website is to inspire interest in the fields of Science, Technology, Engineering, and Mathematics (STEM).
Any help is greatly appreciated and please come back tomorrow for Ketton’s Presentation post!
A couple of days ago, Team UV launched its fundraising campaign on GoFundMe.com under the name “Experimental Marine Vehicle Project” in an effort to raise the money necessary for us to manufacture and test our college senior project – a highly maneuverable, higher speed, stealthy, unmanned underwater vehicle with Information, Surveillance, and Reconniassance (ISR) capabilities. Our project is meant to create a vehicle that can conduct naval ISR and, in doing so, take the special operators or otherwise troops who would usually conduct this ISR out of the field and thus harm’s way. More information about our senior project can be found on the About page of this website, and the fundraising campaign can be found at GoFundMe.com/TeamUV; this link is also listed in the right margin of the Home page and in the Sponsors & Donations page of this website.
We are seeking $5,000 in order to cover the manufacturing costs of our vehicle, which will feature many cutting-edge technologies and represents a stark departure from the slow, bulky, impractical, non-stealth-like designs currently in use. We also want to note that no donation is too small and not a single penny donated will go to waste, it will all be used to increase the quality of our vehicle, to add capabilities (through additions to the sensor suite or additional drag-reducing technologies, etc.), and to enable us to conduct better testing (i.e. the construction of a flow tank for actual flow visualization). As follows from the above statement, any money that we raise above the $5,000 will be put directly into the project in one of many way, including (but not limited to) those listed above.
Lastly, I will note that we will be posting campaign progress updates on average once a week (Wednesdays 1000 hours) and that you can find a full-sized PDF of our pull-tag poster on our Sponsors & Donations page if you would like to print one out and post it to help get the word out. If you would like to help out in other ways, it would mean a lot to us if you would tell your friends/family/coworkers/etc. about our fundraising campaign (and possibly ask them to share it as well), share it on Facebook, or perhaps even just spread the word about TeamUV.org in general, as our biggest goal with regards to this website is to inspire interest in the fields of Science, Technology, Engineering, and Mathematics (STEM).
Any help is greatly appreciated and please come back tomorrow for Andrew’s Presentation post!
Today is Veterans Day and represents a day when we should all take some time out of our day to some how say thank you to the brave men and women who have put their lives on the line (and, unfortunately, sometimes paid the ultimate sacrifice) in order to protect this great nation, its people, and the freedoms guaranteed us by the Constitution.
Korean war veteran Howard Osterkamp once said “We have a motto that sums it all up — ‘All gave some; some gave all.’”. I can think of no better way to encapsulate the courage and sacrifice of the men and women who have fearlessly fought to defend our country; and so in honor of our Armed Services, I would like to reflect on their mottos for those of you who are unfamiliar with them:
United States Marine Corps: Semper Fidelis (Always Faithful)
United States Army: This We’ll Defend
United States Navy: Non Sibi Sed Patriae (Not for Self, but for Country) (I’d also like to add Fair Winds and Following Seas as a thank you)
United States Coast Guard: Semper Paratus (Always Ready)
United States Air Force: Aim High…Fly-Fight-Win
Lastly, I would like to note a few upsetting statistics:
1. At any given time, there are roughly 300,000 homeless veterans; over 1.4 million veterans are at risk of becoming homeless; homeless veterans spend an average of 6 years on the streets; approximately 33% of homeless males in the US are veterans.
2. An estimated 460,000 veterans suffer from Post-Traumatic Stress Disorder (PTSD); at least 20% of Iraq and Afghanistan war veterans have PTSD, 19% of veterans have Traumatic Brain Injury (TBI), and 7% of veterans have both PTSD & TBI.
3. Nearly 5,000 veterans commit suicide every year, that’s nearly one every two hours.
The Department of Veterans Affairs only has the means to help a fraction of veterans. It is time that we begin to serve those who have served us. If you would like to get involved with or make a donation to a program that supports veterans, you can either contact the US Department of Veteran Affairs or one of the organizations listed here. I personally make a monthly donation to the Wounded Warrior Project as a way of giving back to those who have given so much for people like you and me…without even knowing or having ever met us, they are willing to put their lives on the line for us.
So please, remember what today is about, and find a way to say thank you to our veterans.
Welcome back to TeamUV.org and let me just start off by saying that we are going to have a busy next couple of days. We (of course) have this Well Read post today, will have a special Veterans day post at 1300 hours (1 p.m./in 3 hours), a post announcing the start of our fundraising campaign tomorrow (Wednesday 1000 hours/10 a.m.), and then we will be back to our regular schedule with a Presentation post by Andrew on Thursday. Whew!
Today, we are going to continue off of my last Well Read post with a discussion of the science behind fireworks. More specifically, today we are going to take a brief look at what determine the actual shape of the burst, whereas last time we took a look at the thrust created during the initial firing of the fireworks. Without getting too much into the chemistry of this subject, we can basically see the compounds within the firework’s shell as consisting of a mixture of liquids and solids (fuel, oxidizer, color-producing compounds, a binder, and possibly other additives) that are used for both the bursting charge and the aesthetic effects. When an aerial firework is initially fired, the reactants combust to produce thrust (as discussed last time), launching the actual firework shell into the air. At the same time as the shell is rocketing up into the air, a fuse (which was lit by the combustion) is burning. Eventually, that fuse will burn down to the firework’s charge, igniting the charge and thus producing the explosion, and triggering the reaction of all the other compounds within the shell. Upon explosion of the entire shell, a bunch of particulate jets are formed and are shot out in many directions. Generally speaking, these jets are what determine the form of the burst that we see when we watch fireworks. These jets are shown below; it is also interesting to note the Karman Vortex Streets visible in the turbulent wakes of the projected particulate, as caused by flow separation (and subsequent recirculation) along the blunt body of the projectiles.
So what governs the size, shape, and behavior of these jets? While a lot is unknown about the exact cause of the instabilities associated with the jets, the main factors that are commonly seen as governing the jet structure are: nature of the particles (composition; liquid, solid, etc.), geometry (shape) of the charge, and mass ratio of explosives to particles (amount of explosive vs. other compounds). These assumptions are reflected in the research video below (Video Credit: D. Frost, Y. Gregoire, S. Goroshin, F. Zhang) which shows different combinations of particle nature, charge geometry, and explosive-particle mass ratio and their effects on jet structure. A cool note is that you will be able to see the shock wave (a pressure discontinuity, or large change in pressure in a very small distance – across the shock wave) created by each blast in the video. The main conclusions of the video (and some possible reasons for these observations) are:
1. Wet mixtures produce more jets (possibly due to smaller molecule size), which disperse sooner (maybe due to liquid surface tension effects).
2. Dry mixtures produce less jets (possibly due to larger particulate), which disperse slower (possibly due to higher momentum due to larger particulate mass and more friction effects due to the generally larger particulate vs. the wetted particulate mixture).
So there you have it: a relatively brief look at what governs the shape of the burst of fireworks! Please remember to check back later today for our salute to the brave men and women who have served this great nation! I’ll leave you with another image of fireworks and the Statue of Liberty as today is a great day for patriotism!
A vastly interesting concept within mechanical engineering (as well as many other fields of engineering) is that of stability, which takes many forms, so today we are going to focus on a form of stability that would perhaps be more common within naval architecture/engineering, namely: hydrostatic stability of submarines. Hydrostatic refers to the application of water-based fluids mechanics (mechanics comprising of statics and dynamics) to situations in which there is no fluid (or in the case of hydrostatics, water) flow; this is to say that the fluid is stationary (or static, as opposed to dynamic). This truly is a topic you could spend a lifetime studying, and as such, I am only going to give a very brief primer on the category (with nearly enough pictures to rival the word count of the article!) to the end of revealing just how much consideration goes into something that most people would never stop to think about.
First off, let’s explore what we know about stability, even if we have never taken an engineering class on the subject. What do you think of when you hear the word stability? Perhaps you envision trying to balance on an exercise ball, or maybe trying to balance (hopefully successfully) your dinner plate in one hand while trying to keep the family dog at arm’s length to keep her from eating your food when you go to sit down, or maybe you think of that uncomfortable flight home for Thanksgiving with the airplane pitching, rolling, and yawing all over the place; these are all forms of stability and can each easily be complex enough of phenomena to spend an entire career studying!
Just as in an airplane, where you have to worry about controlling any inherent pitching, rolling, and yawing for stability of the aircraft, in a submarine, you have to worry about controlling rotations about these same three axis: lateral (from port to starboard side), longitudinal (from the bow to stern), and vertical (from the bottom on up). One big distinction between the stability of aerial, ground-based, and surface (ships) vehicles and that of submarines, is the fact that submarines have two very different modes of hydrostatic stability: surfaced and submerged. Surface hydrostatic stability refers to how stable the submarine is when it is sitting on the surface (important to note, that if the submarine are moving on the surface, this would be hydrodynamic stability, not static, which opens up a whole new can of worms to deal with). On the surface, submarines are inherently unstable, the main reason being the shape of the submarine. Submarines are essentially shaped like cylinders with dome-like caps; this is done for hydrodynamic reasons, including, but not limited to streamlining, or the reduction of drag by utilizing a shape that influences the external fluid flow to be smooth (this is analogous to how you have probably heard people talk about how ‘aerodynamic’ their car is/isn’t).
Now, when we take our submarine and drop it in the water, we encounter something known as Archimedes’ Principle, which states that the buoyant force (the force that the fluid/water is exerting upwards on the body) and the weight of the displaced fluid (water) are equal in magnitude and opposite in direction. When we have only a small portion of the submarine below the surface, the center of buoyancy (i.e. the center of the displaced fluid) is much lower than our center of gravity, making our submarine easy to tip over (perhaps while playing soccer or football, or some other sport, you have heard someone say that someone else who has a heavy build and is average to lower height is ‘hard to tip over on account of their low center of gravity/mass, which is not exactly the same as this situation, but ought to aid in understanding). Think about if you were to go float in the pool and take a big rock (please don’t try this at home, as it could be quite dangerous) and hold it high over your head straight up in the air. If you held it straight up, you would probably be pretty stable, but if you were to pivot your arms so that they were no longer directly above your head, the rock would carry them through further rotation and you would find a new stable position with the rock underneath you. Now, if our submarine was submerged, then we have displaced our entire volume’s worth of water, so that the center of buoyancy (CB) now lies in the center of the cylinder. Submarines are typically designed to have their center of gravity (CG) near (or a little lower than) the center of that cylinder, thus when fully submerged, their centers of buoyancy and gravity nearly coincide, leading to a very stable state (think taking the rock from earlier and hugging it against your chest while underwater, you no longer feel like you’re going to tip over!). This is a major consideration in submarine design that gets very complex, especially when you realize that you can have this CB-CG offset in all three directions (lateral, longitudinal, and vertical)! To make matters worse, every time you add anything into the submarine, its own CG affects that of the submarine, requiring the use of ballasts to relocate the CG.
Hydrostatic stability was the meat of this article; however, while hydrodynamic stability (as well as the unabridged discussion of hydrostatic stability) is beyond the scope of this article, it will be quite educational to comment on this next subject real quick. As we saw before, the big fight with regards to submarine stability involves balancing the effects of buoyancy and gravity in 3-Dimensional space. Well, what do we do when the submarine is moving and needs to remain stable? This is where control surfaces and variable ballasts come into play. Variable ballasts are essentially tanks that you can pump water into/out of to shift the position of the CG & CB on the fly. This technically could be used for controlling submarine movement, but more often than not is used to accomplish tasks such as surfacing and submerging (and can also be used to dictate the rate at which this happens).
It is interesting to note, that not even this is an easy design task, as there are a ridiculous amount of things to consider, all the way down to location of the valves/vent holes (air vents up top to make sure no air gets trapped in the tanks, changing CG/CB; water valves down low to make sure all of the water can be pumped out, once again to control effects on CG/CB). Rather than purely use the ballasts for steering/motion control, submarines use their control surfaces and a special type of variable ballast called the trim tanks.
The control surfaces point the submarine in the right direction, while the trim tanks adjust trim/attitude, or the angle at which the submarine is pointed upwards or downwards. As a last note on hydrodynamic stability, I want to relay the fact that the information above seems to neglect quite a few other effects. It seems this way because it is this way; there are endless possibilities for how the fluid flow may interact with the submarine to affect stability. The topmost (main) picture of this article, which shows a submarine surfaced during polar operations demonstrates the fact that surface stability also has to account for things such as punching through three feet of ice and then remaining seated against it or perhaps the effect of wave impact on a surfaced submarine (it should be noted that along with stealth, waves and other surface effects are among the main reasons submarines do not travel long distances on the surface, especially in rough weather!).
Well, that is more than the average person ever hoped to know about submarine stability, that much I am sure of, but I hope that you have enjoyed learning along with Team UV. Please check back for our next post on Sunday (an Open Mind post by Andrew) and our Veteran’s Day salute this upcoming Tuesday. In closing, I will leave you with a really cool info-graphic put together by BAE Systems showing some of the work that goes into actually determining the location of a newly designed submarine’s CG & CB!
Prompt: One of the most under-appreciated engineering jobs out there is that of a facility maintenance engineer. These engineers perform tasks such as making key decisions with regards to retrofitting, repairing or replacing buildings, machines, and other equipments, preparing maintenance schedules based on many machine design principles, electromechanical controls, HVAC systems, etc. (as well as supervising any onsite maintenance). One more duty they often must perform is that of assessing damage and deciding how to move forward in the event of any kind of plant/facility disaster. For example, recently a 100 year old 30 inch water main burst at [a college in California], releasing an estimated 20 million gallons of water, trapping roughly 1,000 cars in flooded parking structures, submerging athletic fields, and flooding basketball courts and other structures. If you were a facilities engineer at [the affected college], what would your top 3 priority considerations be following the incident in terms of evaluation, fixes, safeguards, etc.
1. Vital Utilities
The first priority (after having dispersed search/rescue teams to ensure no one has been trapped or injured) in an event such as this would likely be to verify that the essential facility equipment (power, sewage, phone lines, etc.) have not been damaged. You would want to visit the location of each of these main utility hubs and check for water penetration to vital systems. You would probably want to get the maintenance technicians to immediately begin evaluating and repairing any damage done to electrical circuitry, sewage and potable water systems, and the phone lines as if these systems were to be too negatively affected by the flooding, they could seriously hamper damage control efforts as well as efforts to get the school back in operation.
2. Personal Property
As soon as you have established procedures/progress for keeping (or bringing back) all vital utilities on line, you would want to immediately start taking measures to reduce damage to personal property of the students, faculty, visitors, etc. in order to reduce the amount the school might have to pay in damages. Priorities would include bringing in pumps to drain sub-level parking garages in order to get personal transport vehicles out of the water to prevent corrosion, interior staining, or electrical damage and once again making sure that no people have been trapped, injured, etc. and if they have, then to get emergency responders there ASAP. Once all vital areas and areas with personal property had been cleared, measures would need to be put in place to locate and close the property fire department connection (main shutoff), repair or replace the pipe, and drain/clean up all the water.
3. Site Damage Evaluation
Once the mishap has been cleaned up and all systems have been brought up online, you would need to immediately start in with damage assessment, most notably with respect to structural damage. You would need to tour the property and look for signs of water damage, erosion, mold, weakening of load-bearing structures, electrical switchover damage, damage to any machinery caused either by moisture or incident contact with destructive objects which may have been knocked loose or otherwise dislocated during the initial burst and subsequent period of high water flow.
As can be seen, a great deal of things must be taken into consideration when dealing with any kind of facility disaster and facility engineers are often the ones who are depended on to organize the containment/repair/re-launching efforts in these kinds of situations. These are just a few of the many, many things that a facility engineer would need to consider and it should be noted that what I have listed here is extremely superficial in that these decisions take infinitely more consideration to make.
For example, in this particular incident, one of the major concerns of the facility engineers was with regards to the draining of the parking garages. On one hand, they were worried about the water quality in the garages as the water stagnated there for longer periods of time, since the amount (and therefore concentration) of gasoline and pollutants present in the water was building, creating a possibility for the water to become flammable or explosive, not to mention the consequences of allowing the pollutant concentration in the water to build prior to entering the sewer system; for these reasons, the engineers wanted to drain the garages as quickly as possible. On the other hand, however, the faster and longer the pumps were run in the garages, the more carbon monoxide built up in the garages, creating a whole host of new problems. When you’re a facility engineer, even something as seemingly simple as draining built up water takes on whole new levels of complexity that most people would never even think to consider!
Facility engineers wear a ridiculous number of hats and really are the plant engineering equivalent to the Swiss-army knife. Hopefully after having read this article, you might find a new appreciation for what these engineers do. Thank you for the read and be sure to check back every Tuesday, Thursday, and Sunday for Team UV’s new posts!
Fireworks seemingly have the capability to fascinate people everywhere, while trouncing any language, cultural, or religious differences. But the universality associated with the magnificence of these pyrotechnic displays is not the only aspect of their prominence that makes them so vastly interesting; they are scientifically remarkable!
While one could talk for hours (if not days) on end in the aim of exposing all scientific aspects of something as seemingly ephemeral as a firework display, we are going to look at just one consideration as it relates to the world of engineering: the baseline fluid mechanics that describe the interaction of fireworks with the atmosphere around them. We will begin this by watching a quick video (below) produced by The Discovery Slowdown, as was found through an article on FYFD (you can find the original article that inspired this one through the link; pardon the blog title, the content is excellent). For the record, I have no idea what the deal is with the baby sloth in the beginning of the video, haha.
From 0:14 to 0:30 in the video, you can see the uncontrolled combustion of the reactants used in the fireworks. This gives you a basic understanding of how this combustion takes place in the absence of any kind of container or packaging. When the reactants “burn” on the table out in the open atmosphere, the gaseous exhaust products (“smoke”) billow(s) upwards in a turbulent manner, with no real direction.
From about 0:31 to 0:58 in the video, the combustion of the reactants is repeated; however, this time the reaction take place in a cylinder with the top end open. Now you have controlled combustion (with regards to direction) and the result is effectively a jet of exhaust products (and some still-combusting reactants) that fires out the end of the cylinder in a way analogous to the exhaust kicking out the back end of a rocket, providing it with its thrust.
At 0:41, the video shows a closeup of the top of the tube, where the gases leave the confines of the tube and exit out to the air. As Nicole Sharp over on FYFD notes, this provides an excellent example of what we term an “under-expanded” nozzle.
An under-expanded nozzle is simply one where the static pressure associated with the flowing fluid at the nozzle exit is greater than that associated with the atmosphere (P>Patm); in essence, the nozzle has not expanded enough to reduce the pressure in the flow to that of the atmospheric pressure, so when the exhaust gases exit the tube, they expand (or fan) outward rapidly in order to equalize their pressure to that of the atmosphere. There’s your first mini-lesson in rocket science!
It also interesting to note how (at about 0:35) the tube jumps upwards as the gases leave. This is more than likely due to the fact that as this combustion occurs and the exhaust gases blast out of the tube at high speeds, they form a near vacuum in the tube behind them (by taking the contents of the tube and forcing them upwards, thus leaving a region of relatively low pressure behind the escaping gases in the cylinder). This vacuum, however, is not representative of a natural state; in essence, the air in the cylinder wants to be at atmospheric pressure, but instead it is at a pressure far lower than the atmospheric pressure. Once the bulk of the exhaust gases have escaped, the low pressure region immediately begins to collapse upon itself (thus increasing the pressure in the tube), but since the contents of the tube are still moving upwards, the cylinder itself is tasked with collapsing the region and thus is pulled upwards to decrease the volume in the tube between the cylinder base and the escaping gases! And so the cylinder jumps upwards towards the sky before gravity goes to work pulling it back down.
So there you have it, there are some basic fundamentals of the way firework exhaust gases behave in different settings. During my next Well Read post, I will discuss how we can use science and engineering to analyze the behavior of the actual jets that shoot outwards from a firework and what charge parameters affect their behavior. Thank you for your support and please check back on Thursday for Andrew’s Presentation post!
A slipstream is essentially a region in the boundary layer along side of and a wake region behind an object moving through a fluid, in which the local velocity is very near that of the moving object. In simpler terms, the slipstream is fluid being pulled alongside of and behind an object at close to the same speed as the object is moving. These slipstreams can be found around/behind virtually any object moving through a fluid, can be a high pressure or low pressure region (depending on the Reynold’s number of the flow), can be created in both liquids and gases, and can either be a hindrance (by creating parasitic drag) or can prove advantageous (by the creation of additional thrust, lift, or by positively affecting other key parameters). We will look at slipstreams in three key applications and in each one will look at how slipstreams can be bad as well as how they can prove useful!
The first application we will look at is that of an object flying through the air. The most familiar example of these slipstreams is that which aircraft encounter; these are helical slipstreams that are produced by propellers as they rotate through the air, as seen trailing the rotors of the V-22 Osprey pictured above. This type of helical slipstream is commonly referred to as “propwash” and can commonly be made visible on a humid day as moisture may condense out of the air if the pressure and temperature within the slipstream core drop below the dew point. This propwash is usually seen as a major detriment with regards to how it may affect the ability of pilots to control smaller aircraft. As shown below, the slipstream can wrap around the plane and ultimately interfere with the vertical stabilizer (the big vertical fin at the back of the plane), causing the plane to yaw/rotate to the left, requiring the pilot to correct back to the right.
As one can imagine, this can serve as a major inconvenience and can be a bit unsettling for new pilots; in fact, in the early days of powered flight, this phenomena led to quite a few crashes, some of them fatal. So if this propwash is so bad, why did I say earlier that we would look at the usefulness of slipstreams in each of the 3 applications? While for aircraft, slipstreams are usually seen as bad, we must remember that aircraft are not the only things that fly!
Many species of birds tend to fly in a v-formation to make use of the slipstream present in the wingtip vortices of the birds in front of them. The slipstream within the wingtip vortex coming off of the lead bird’s wing creates upwash, which the next bird uses as a source of lift, and so on and so on, down the line.
The next application we will look at is that of objects moving air, while on the earth’s surface. If you have ever been too close to a train as it has passed, then you have felt the effect of this slipstream as it threatened to rip you from your feet and drag you alongside and into the train. This is not a comfortable feeling and is incredibly dangerous, so PLEASE DO NOT try this; rather, you can observe the trees and plants around the train tracks as they appear to get “sucked into” the path of the train. This slipstream can cause a high degree of drag, lead to more noise (through the turbulent vortices within the slipstream), and can be dangerous for passerby. So how is it that we may take advantage of these slipstreams on the earth’s surface?
Competition bicycle riders often take advantage of each others’ slipstreams in order to save on energy during races. Bicyclists refer to this as “drafting” and often will intentionally remain behind a competitor to save on energy and then breakout in front of their opponent at strategic locations (i.e. near the finish line). This technique is also used by speed skaters, runners, cross-country skiers, stock car racers, and many more!
The last application we will look at is that of objects moving through the water. Cavitation is a word that virtually every boat owner knows and has learned to loathe (not to worry, you are not alone, we here at Team UV have vowed to make cavitation our enemy and defeat it!). Cavitation is the rapid formation and subsequent collapse of air bubbles that accompanies a large pressure drop in a flow. When propellers move very fast, are improperly designed, or contain surface defects, the pressure of the flow along the surface of the propeller may drop below the vapor pressure (effectively boiling the water), forming air bubbles, which then collapse and in doing so effectively create implosions which cause damage to propellers through pitting, as seen below. In addition to this, these bubbles (when they form) are sucked along into the slipstream, where they create separation between the propeller blade and the working fluid (water), thus significantly reducing the efficiency of the propeller with respect to the creation of thrust. These slipstreams also threaten to expose the location of stealthy underwater craft, as the bubbles may be visible from under water (or from surface ships or anti-submarine aircraft) and may create noise as they collapse, thus diminishing acoustic stealth. With all of these bad things, how on earth could slipstreams prove useful for marine applications?!
Enter the Grim Vane Wheel (GVW), one of many devices specifically designed to take advantage of the slipstreams of marine propellers on surface vessels. The GVW is basically a freely rotating, large diameter propeller which is situated behind (aft of) the main (powered, smaller diameter) propeller. As the main propeller spins and creates its helical slipstream (hopefully without any cavitation), the slipstream continues to rotate and move on down the line. When the slipstream encounters the GVW it does two things: for the portion of the GVW that lies within the diameter of main propeller, the GVW acts as a free spinning turbine, which can be allowed to rotate freely or even be used to generate electricity for auxiliary power; for the portion of the GVW that lies outside of the diameter of the main propeller, the GVW acts as an additional propeller, creating more thrust! These devices are used in situations where rotational energy losses are high and thus the advantages of the GVW with regards to the recoverable energy in the slipstream may be justified as they compare to the added weight, complexity, and cost associated with the GVW.
So there you have it, from airplanes and geese, to trains and bicyclists, to stealthy underwater vehicles and large cargo ships, we have explored just some of the many scenarios in which slipstreams may be found as well as a few of the ways in which they may either prove harmful or, alternatively, may be taken advantage of. Hopefully those of you who have read through this entire article (yes, I know it was a little long, haha) can walk away from your computer with a little bit more of an understanding with regards to the beauty present in fluid mechanics and just one of the virtually infinite ways that this vast subject of mechanical engineering manifests itself in our world!
Wakeboarding is one of my favorite sports and provides a fascinating study in fluid mechanics and materials science (in addition to many other fields of engineering). It would be quite interesting to serve as a design engineer within the framework of a wakeboard company as I believe that there are quite a few features of today’s wakeboards that could be vastly improved; in many cases, engineers are currently making these improvements to the end of providing unheard of complexity in what many see as simply a slab of plastic/wood.
As can be seen in the above picture, many wakeboards make use of intricate channeling, “concaves”, and strategically sized, shaped, and placed fins. The use of these features create boards that are as much art pieces as they are sports equipment, but the use of these features penetrates far deeper than the superficial appearance of the board; each of these features is used to create different fluid effects in order to manipulate the board’s performance and functionality.
The fins act to provide the tracking characteristics of the board by breaking the surface tension of the water, essentially digging into the water in order to provide sufficient “traction” (think the treads on the tires of your car). If one was to remove the fin from the tail end of the wakeboard, it is immediately noticeable and acts to make the ride “squirrely”, making it difficult to keep the tail of the board seated in the water in a steady/stable fashion (think driving a car that has balding/smoothed tires). The channels act as extended fins, extending the “traction” provided at the tail in order to provide better edge tracking capabilities (for cutting on your heel-side or toe-side edge). Lastly, the concaves actually work to increase what is essentially the hydrodynamic lift of the board. In doing so, these concaves can act to elevate the tail, midsection, and/or the nose of the board, depending on the placement, sizing, shape, and orientation of the concaves, allowing the board to sit higher in the water (thus reducing drag through reduction of the waterplane area, or cross-sectional area at the waterline, as well as shifting the weight of the rider for a more comfortable ride). These concaves can even be shaped in a way so as to accelerate the flow when cutting in towards the wake, effectively giving you a speed boost right before you hit the wake.
Often times engineers will strategically combine all of these effects into one board, providing for some pretty awesome effects within the fluid flow and variety in board design that is nothing short of phenomenal. If I were to be a part of a R&D (research & development) team within the context of a wakeboard design firm, I would target the increased use of concaves in order to provide more hydrodynamic lift in strategic areas along the heel-side and toe-side edges in order to provide more wake-side pop, allowing the rider to get more air. Furthermore, it is conceivable that if designed properly, the concaves (combined with channels) could provide enough pop to, much like the hybrid rocker, mitigate the dramatic difference that currently exists between 3-stage rockers and continuous rockers as shown below (3-stage is used to get more pop out of the board, much like the lips on a skateboard, while continuous is used to provide smoother maneuvering).
Materials science plays a huge role in wakeboard design; boards have to be designed to be buoyant, smooth, stiff (yet capable of storing/releasing large amounts of energy), durable, resistant to moisture absorption, strong, lightweight, UV resistant, and much much more. In order to cater to this broad list of demands, wakeboard designers use composite materials in order to take advantage of the properties of multiple individual materials by combining them strategically. A relatively simple wakeboard construction is shown below (many boards have over twice this many layers!). A major focus for future board development with regards to composite materials would have to be the use of materials with higher specific strength (essentially strength per unit weight) to provide lighter weight boards (after all, binding/boots already weigh enough without having to worry about board weight) as well as materials with better elastic response properties for better cushioning when coming down from tricks (which would both relieve impact as well as decrease the chance of the board sinking enough to bury the nose, leading to a painful face-plant). Taking better advantage of the elastic response of the materials could also lead to a more comfortable ride in choppy water (being dragged at 20-25 knots through a wind-whipped lake doesn’t exactly feel good…each one of those little ripples feels like hitting a speed bump when you’re moving upwards of 20 mph!).
Lastly it is worth noting how it never ceases to amaze me how poorly many bindings/boots hold up in the sun. Unfortunately, in order to save money, many companies manufacture their boots/bindings with thermoplastics or thermoplastic elastomers, which readily transition to a viscous state in the sun (in essence they melt into a sticky, rubbery substance!). Many people may have also experienced this material flaw in cheap bike handlebar grips, leading to the unpleasant transfer of rubbery residue to your hands. Bindings/boots can become sticky after being used or sitting in the sun for just a few months, leading to the need to buy new boots/bindings that use leather and other expensive materials, which cause the price tag of the boots to skyrocket! All I am saying is that if I were to design wakeboard boots, I would use thermosets,or typical thermosetting elastomers, or at least make sure that the degradation temperature of the thermoplastic or thermoplastic elastomer would be high enough so that the boots function without turning into a sticky mess!
Please join Team UV today in remembering the over 3000 people who lost their lives 13 years ago on this day as well as the countless brave men and women who have unselfishly dedicated, and in some cases given, their lives to preventing it from ever happening again. Together we stand, united as one, never to forget.
O say can you see by the dawn’s early light,
What so proudly we hailed at the twilight’s last gleaming,
Whose broad stripes and bright stars through the perilous fight,
O’er the ramparts we watched, were so gallantly streaming?
And the rockets’ red glare, the bombs bursting in air,
Gave proof through the night that our flag was still there;
O say does that star-spangled banner yet wave,
O’er the land of the free and the home of the brave?
On the shore dimly seen through the mists of the deep,
Where the foe’s haughty host in dread silence reposes,
What is that which the breeze, o’er the towering steep,
As it fitfully blows, half conceals, half discloses?
Now it catches the gleam of the morning’s first beam,
In full glory reflected now shines in the stream:
‘Tis the star-spangled banner, O! long may it wave
O’er the land of the free and the home of the brave.
And where is that band who so vauntingly swore
That the havoc of war and the battle’s confusion,
A home and a country, should leave us no more?
Their blood has washed out their foul footsteps’ pollution.
No refuge could save the hireling and slave
From the terror of flight, or the gloom of the grave:
And the star-spangled banner in triumph doth wave,
O’er the land of the free and the home of the brave.
O thus be it ever, when freemen shall stand
Between their loved home and the war’s desolation.
Blest with vict’ry and peace, may the Heav’n rescued land
Praise the Power that hath made and preserved us a nation!
Then conquer we must, when our cause it is just,
And this be our motto: “In God is our trust.”
And the star-spangled banner in triumph shall wave
O’er the land of the free and the home of the brave!
Owls have the uncanny ability to sneak up on their prey while remaining almost completely silent. This is partially accomplished through their immense wingspan (Great Grey Owls such as the one shown in the picture above can have a wingspan of over 5ft); their large wings provide for large amounts of lift, which translates to them being able to glide for much longer before needing to flap their wings again. Dr. Justin Jaworski and his fellow mechanical engineering researchers at Lehigh University in Pennsylvania have been looking at how the material properties associated with various parts of owls’ wings affect their silent aerodynamic characteristics.
Dr. Jaworski’s team has highlighted three distinct features of the owl wing that help to mask its aeroacoustic characteristics in flight, as seen in the picture below. The first feature is that of the trailing edge, which is typically the dominant source of noise on airfoils of all sorts (including aircraft wings, where turbulent eddies or vortices interact with the hard trailing edge, thus creating noise). On an owl wing, the trailing edge is made up of a flexible fringe that possesses a combination of specific porous and elastic properties that attenuate or diminish the sound frequencies that would otherwise be produced off the wing’s trailing edge. In the lab, these porous and elastic characteristics could be manipulated in order to block specific sound frequency ranges and thus provide a stealth solution that could be customized for different applications. With the noise from the trailing edge silenced, the dominant source of noise becomes that associated with the other two regions of the wing.
The second wing feature/region is the mid-wing velvety down which is compliant, yet rough on the macro-scale (like a soft carpet). This section of the wing is the subject of the researchers’ current studies and thus is not very well understood yet, but they believe that somehow the “forest-like structure” of this section acts to absorb the sound that would typically be produced by the rough surface.
The last section of interest is that of the leading edge, which is made up of stiff feathers that add a serrated-like tip to the edge, producing geometry that is analogous to the tubercles that can be found on a whale’s fins. This serration divides up the flow over the wing into smaller, channeled flow streams which produce less wingtip vortex generation and thus less noise (in addition to decreasing parasitic drag).
The combined effect of all of these wing features translate to the owl’s mastery of stealth and could in the future lead to quieter airplane flight, wind turbines that produce less noise, and submarines with greater stealth characteristics. For more information click here.
“Quietness gives a submarine twin advantages: it is harder to detect, while its own sensors become more sensitive as self-induced noise diminishes.” (Submarine Technology for the 21st Century, 2e)
Submarines can be detected acoustically via 2 main mechanisms: active detection (another vessel may emit a ping into the water; the larger and closer the object to be detected, the stronger the return signal or “target strength”) and passive detection (passively listening). Just as the main acoustic detection mechanisms can be divided into passive vs. acoustic, so can the main acoustic stealth/silencing measures (however, only basic passive controls will be discussed here for simplicity).
Most passive stealth controls revolve around the use of anechoic (an-echo-ic) materials. These materials are generally elastomeric (think “rubber”) with built-in voids/air cavities and act to absorb, rather than reflect sound. By cutting down on this sound reflection, you can effectively reduce active sound ranging off an anechoically-coated hull (thus decrease the chances of being detected by sonar) and cut down on the terminal acquisition range of active sonar that may be used by torpedoes. This is all great in terms of stealth; however, there are many considerations that may go into the design of these anechoic materials. Unfortunately it is not quite as simple as just slapping rubber tires to the side of your submarine!
Elastomers are a class of polymers and thus exhibit viscoelastic characteristics, meaning their properties may be likened to both those of liquids (viscously damping, hence “visco-“) and solids (elastically responding, hence “-elastic”). Which of these effects dominates the material characteristics depends on temperature, encountered frequency (i.e. sound frequency), and many other things. Having considered this, it becomes apparent that the material must be designed properly to express the desired material properties, which can be controlled a number of ways.
The principle means of doing this would be by controlling the size and placement of the voids (which may affect material stiffness, density, porosity, relaxation modulus, sound frequency ranges attenuated/blocked, etc.). In addition to this, the variability of these properties must be considered as well. For example, you must be sure that your material properties do not change significantly with changes in operating temperatures or encountered signal frequencies, both of which may create significant changes in properties such as elastic modulus (analogous to stiffness), as shown below.
Another means by which the material properties might change is related to the chemical stability of the polymer. Water absorption may lead to polymer degradation, which may lead to acid formation, which may lead to further material degradation and thus change in material structure. These kinds of effects may be controlled through the addition of specific additives to the material.
Lastly, one must consider more practical considerations: while you could use anechoic materials to coat the exterior of your submarine as well as to provide vibration/noise absorption around internal machinery, the application of these materials can lead to cost over-runs and major weight penalties. In addition to this, often multi-layer coatings may need to be used to achieve combinations of effects or perhaps to allow sound to pass outwards (such as where sonar pings might emanate from) while still absorbing enemy sonar pings!
As you can see anechoic materials are a vastly complex subject and can be used to produce fascinating effects and thus serve as an excellent primer to a proper understanding of the complexity and importance of stealth considerations in submarine design!
Turbochargers are a class of superchargers that use a turbine and a compressor on the same shaft to increase the density of the intake air in an engine. Turbochargers come in all sizes and applications, for example: the turbocharger pictured above is for large marine vehicles, while the turbochargers that this article will be focused towards are the much smaller ones that can be found on some automotive engines. As mentioned before, the turbocharger increases the density of the air intake; this is generally accomplished by using the engine’s exhaust gases to spin a turbine which is connected by a shaft to a compressor which takes air from the environment and compresses it prior to feeding it into the engine. Why might one want to do this?
There are several reasons to want to increase the intake air density in an automotive engine. The most well known is to boost the power of the car. The maximum power an engine can deliver is limited by the amount of fuel that it can burn efficiently; the amount of fuel that can be burned efficiently is limited by the amount of air that is inducted into the engine; thus by compressing the air, more air can be introduced into the engine, meaning more fuel can be burned, meaning more power can be delivered. Other reasons for turbo/supercharging include providing more air at high elevations where the air is “thinner” (less dense) (this can be seen in the fact that most airplanes use some form of supercharging), reducing engine size/weight while maintaining the same power output, and improving fuel economy. Having said all of this, please do not go supercharge your car out of the blue, there are a ridiculous amount of potential problems (far too many to discuss here), especially if your car was not designed to be supercharged.
Now, to discuss some of the engineering analysis considerations associated with automotive turbochargers. Within the field of fluid mechanics, most of the considerations are energy related, such as: you must consider any pressure drop across the inlet (think an air filter), the pump work (power required to drive the turbocharger), obstructions to internal fluid flow (major losses associated with components in the flow path or minor losses associated with the changing geometry of the tubes – bends, curves, etc.), exit flow (does it pass through a nozzle, is it directly ducted to the engine intake, is there an expansion fitting), and any additional technologies at play such as intercooling).
From the standpoint of mechanics of materials, one interesting thing to consider would be the shaft inertial effects. What this refers to is the fact that the shaft has mass and that mass is spinning; the revolution of the shaft mass and mass of connected components puts cyclical stresses on the shaft which can lead to premature failure if the shaft is not designed properly.
Lastly, we can look at the turbocharger from the standpoint of control systems engineering: you may want to be ably to vary the compressor speed in order to provide variable exit air density to provide for different ranges of engine speeds or to account for changes in elevation/altitude (this would mostly apply to airplane turbochargers), different climates, and so on.
Ultimately, turbochargers provide an excellent example of just how complicated any given system may be from an engineering standpoint as the above text hopefully displays; however, this is not the only purpose of this post, this post also aims to show some aspects of the thought process of an engineer and how truly many ways any given problem can be looked at (and how fascinating the options are)!
New Team UV member photos have been posted on the Member Bios page! Go there now to view the pictures and read up on the individual members of Team UV!
Prompt: Highly interdisciplinary engineering teams are put to work in the design of space telescopes and many fields of engineering must be considered, including (but not limited to): classical mechanics, fluid mechanics, materials science/engineering, heat transfer, electromechanical systems, etc. If you were the head engineer for the design team of the next NASA space telescope, what would be the top 3 design areas/systems that you would choose to put the
greatest focus into developing/improving and why. Remember, there are financial, manufacturing, practical, and theoretical limits to be considered; hence you can never really design the perfect system, some sacrifices must be made, and perhaps the systems you would like to focus on might be impractical to target.
1. Vibration Control: Vibrations can cause the image to blur; however, this could be controlled through material selection and strategic placement of hardpoints along the mirror backing in order to manipulate the vibration modes, node locations, and wave interference, resulting in less vibration. Viscous dampers could also be used to damp out vibration introduced by power supply, boosters, mirror actuators, etc.
2. Thermal Control: Thermal strain within focal optics can cause significant blurring; this can be accounted for with cryocoolers tied to the optics through thermal straps. The cryocoolers use thermodynamic cycles to cool components to cryogenic temperatures, pulling heat from the optics, through the thermal straps, and eventually sinking it out to heat dissipation controls. Current cryocoolers can maintain temperatures down to about 3K which approaches a limit, thus future research could focus on more efficient cryocoolers (rather than lower temperatures) to allow more cryocoolers or other thermal controls for the same power needs.
3. Materials Science: Generally, the more mirrors, the more image blur with respect to telescopes, thus most research efforts focus on use of monocrystalline materials, which are about as optimal as they can be currently without a major revolution in materials forming/manufacturing techniques. Research could then be conducted with respect to improving control in material forming/processing to better tailor mechanical properties (i.e. rigidity) more precisely.
Welcome to the official website of Team UV!
Team UV is a senior project team made up of five Mechanical Engineering undergraduate student from Cal Poly Pomona, namely: Brian, Andrew, Ketton, Abraham, Ben. The team is incredibly passionate about all things engineering and industries covering a diverse spectrum ranging from biomedical to entertainment to defense (and many others).
Team UV’s objective is to develop an underwater vehicle (UV) which operates off of an innovative propulsion system (developed by the team in a previous class) and touts stealth, higher speeds (relative to other UVs), smooth maneuvering, and little to no human interaction. The deadline (as shown by the countdown calendar in the margin) is May 29th, 2015, giving us about 10 months from today to achieve our goal. The aim of this website is to share our passion with others, hopefully get other people interested in STEM, and to hopefully raise some money in order to help Team UV to reach their goals and achieve their dreams! For more information on the team and its goals, read the Member Bios and About pages!
We will be posting to this website at the least three times a week:
Additional posts may be made throughout the week.
Please explore our website and follow Team UV by email, WordPress, Twitter, Facebook, and Instagram (All of which can be found in the margin)!