Ferrofluid sculpture. Photo Credit: P.Davis, et al. (FYFD)
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 ferromagneticfluids 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!).
Surface tension. Photo Credit: Wikipedia.org
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.
Ferrofluid and magnet, separated by glass. CLICK TO EXPAND TO SEE THE SPIKES BETTER! Photo Credit: Wikipedia.org
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!
Have you ever heard of Ultrasonic Melt Treatment? Me neither but I did some research and found some pretty interesting things. Ultrasonic Melt Treatment (UST) is essentially the addition of high frequency acoustic waves to a liquid melt of a metal (typically aluminum) to induce acoustic cavitation. Please note that acoustic cavitation is essential. The acoustic waves introduced into the melt have to be at a high enough amplitude and frequency to alternate pressure above the cavitation threshold to create cavities in the melt. Essentially what is happening is the rapid formation and collapse of bubbles in the melt which can have some beneficial effects before, after, and during solidification. The acoustic cavitation is said to activate the melt which means that it will accelerate diffusion, wetting, dissolution, and dispersion which will directly affect degassing, solidification, and refining of metallic alloys. Now if you’re into metallurgy this all sounds incredibly interesting, but if you’re not I will try to explain what each of these mean.
Degassing is one of the primary uses of UST in which the concentration of a certain gas will be lowered in the melt. In light aluminum alloys, acoustic cavitation will cause the growth of fine bubbles in the melt on the surface of non-wettable oxides. As a result, cavitation will cause direct diffusion of hydrogen into the bubbles from the melt. Acoustic flow will assist in floating these bubbles to the surface and out of the melt. The benefits of degassing are that lower porosities can be achieved and thus higher densities in the final material. It has also been found that lowering the concentration of hydrogen in aluminum alloys will raise the ultimate tensile strength and ductility of the material. It is noteworthy that one study concluded that UST is the best amongst other commercial degassing techniques in terms of effectiveness in degassing and in time of treatment.
Degassing of oil using UST is similar to the UST process in liquid metal melts. Photo Credit: hielscher.com
Melts are usually cleaned of inclusions before final treatment. Aluminum melts usually use mesh filters but in order to filter out very fine particulates, multiple layers of successive filters need to be used. This is often not allowed because of the restriction of capillary action of the liquid melt through the filters, however with the use of UST during filtration, a sonocapillary effect is produced. This sonocapillary effect is caused by the cavitation field that is formed which allows for the melt to freely pass through the multiple layers and disperse unwanted oxides.
Ceramic filters. Photo Credit: induceramic.com
One of the most important benefits of UST is that it produces non-dendritic structures during solidification. A dendrite is a branched tree-like structure that grows during solidification of liquid metals (fun fact: dendritic solidification is actually what is behind the unique shape of snowflakes!). As mentioned earlier, acoustic cavitation allows for the wetting of non-metallic impurities in the melt and these become sites for nucleation (aka the start of solidification). Because these nucleation sites are ahead of the solidification front, there is no growth of dendritic structures.
As non-dendritic solidification occurs, the grain becomes only a fraction of the matrix structure so there is refinement in grain size. It is important to note that grain size is only a function of cooling rate in these conditions, therefore this method of refinement is applicable to all metallic materials. One of the major benefits of materials with non-dendritic structures in Al-Si-Mg systems is that they are able to deform very easily at a semi-solid temperature ranges. Essentially what this does is allows the grains to rotate and slide relative to each other without the interference of the dendritic braches. This can dramatically improve mold filling by lowering the viscosity. The apparent viscosity of non-dendritic melts at the semi-solid temperature range is lower than that of the regular melts and is comparable to that of olive oil, at least for aluminum.
Comparison of dendritic and non-dendritic strutures. Photo Credit: scielo.org.za
Overall there are many benefits to Ultrasonic Melt Treatment in aluminum alloys such as degassing, refinement of grain size, and filtration. Although UST has only been extensively studied in non-ferrous alloys, recent research has been done on its effects in low-carbon steels and even epoxy based nanocomposites. In all cases it is the acoustic cavitation, duration of the treatment, and force of frequency that dictate the effectiveness of UST. Hopefully this taught you a little bit about UST. For more info, please refer to the paper by Eskin, G.I. “Broad prospects for commercial application of the ultrasonic (cavitation) melt treatment of light alloys”.
Ball bearings and technical drawings. Photo Credit: amanoverseas.com
Creativity is a huge part of being an innovative engineer. Thinking outside of the box it what has allowed the human race to advance their science and technology to the levels that we see today. While there are a few exceptions most of the engineering courses taken to receive the final degree focus on building a foundation of knowledge. These classes are designed to give a future engineer a solid base to develop ideas from. Creativity is a difficult thing to teach because it comes to everyone in a different way. Here are a few things that I do to help me become more creative.
The biggest thing, at least for me, is that I keep an idea notebook. It is just a small composition notebook that usually remains in my backpack, but when ever I see something that is frustrating or looks like it could be improved I jot it down. This way I have a list of problems that need solving.
Another thing for me is staying in touch with the advancements in technology by reading science blogs and sometimes the journal articles that they refer to. This keeps me learning and stretching my mind into new areas. Some of these new ideas I can tie to the list of problems that need solving and then I can start designing as system that would solve this problem.
Practicing the creative process is one of the best ways to get better at it. By seeing a problem and then attempting to design a system, either as a thought exercise or on paper, more problems come up, which in turn need solving. By going through this process, solving problems, learning new things, applying these things to existing problems, new and innovative solutions arise.
This is the method that I use to come up with new ideas and inject creativity into my work. Please feel free to comment with methods that you use. Everyone’s mind works a little differently and there are so many different ways to find inspiration.
Electric motors are used in many applications from robotics to children’s toys. Although many of these motors are DC motors, Homopolar motors are the simplest of motors and are easy to show students in a classroom setting. All it takes to build your first simple motor are three common materials you can probably find around the house: copper wire, a AA battery, and neodymium magnets.
Common heart shaped approach. Photo Credit: electronics-micros.com
Constructing the motor is simple but getting it to work can take trial and error as well as a bit of patience. Here’s how to do it:
1) Attach the magnet to the negative side of the battery. 2) Strip the copper wire completely or for safety, in the middle and at the two ends. 3) Bend the wire so that one end touches the positive terminal and the other end touches the magnet. A common approach is a heart shaped wire for better stability. 4) Watch: As the copper wire touches the magnet, the wire will begin to spin.
Current (blue) flows from the positive terminal to the magnet at the negative terminal. The current flows in the presence of a magnetic field (red). This causes a force perpendicular to those directions (in the page on the left of the battery and out of the page to the right of the battery). This force causes the wire to spin. Photo Credit: Physics Central
How does it work? Well the theory can get as detailed as you want it to be but to keeps things simple, I will explain the homopolar motor briefly. The copper wire connects the positive terminal to the magnet at the negative terminal. This completes the circuit, allowing current to flow through the circuit (and the wire). Due to the magnet, the current is flowing in the presence of a magnetic field around the battery. When current flows in a magnetic field, it will experience a force called the Lorentz force. This force acts perpendicular to the magnetic field and the flow of the current (and the wire). Consequently, the perpendicular force pushes the wire around the battery.
Once you get a working motor, you can change the shape of the wire to any shape you want! Have fun!
We’ve all been taught that water freezes at 32F (0C) but in actuality water can remain liquid below this temperature, under special conditions. Imagine you’re sitting on your couch after a long day, you’re tired and you’re starting to feel a bit hungry, but the fridge is so far away. Eventually you get hungry enough to get up, go to the fridge, and satisfy your hunger. Water can relate. When the temperature of the water drops below 32F it would prefer to be a solid, but it takes energy to change from a liquid to a solid. As the temperature gets lower the water gets “hungrier”, it wants to be a solid even more, eventually it wants to be a solid enough to overcome the energy barrier, the “walk to the fridge”.
When water wants to become a solid there are two ways it can go. It can either grow on a surface, like condensation on a cool drink or around a dust particle like rain, or, if it has enough energy, it can grow little spheres of solid within the liquid, without the help of a surface. The amount of energy required for this phase transformation is directly related to the amount of surface created. When the transformation is happening on, say the inside surface of a water bottle, the liquid only has to support the area of a dome, the bottle takes care of the rest. When there is no bottle to work with, or the liquid is far from the surface of the bottle, it has to have enough energy to support the surface area of a whole sphere.
If you’re trying to replicate the video above it’s crucial to have very clean water. This means there are no little particles that the water can use to lower the amount of energy required to freeze, it has to save up enough to grow the spheres without any help. The water also needs to be cooled slowly and handled gently because any significant energy changes, thermal or kinetic, can give the water enough energy to start freezing. This is why hitting the bottle will start the reaction. When the bottle is hit, it finally gets the “oomph” it needs to get to the fridge (freeze).
These phenomena (heterogeneous and homogenous nucleation) are also responsible for the famous Mentos and Coke experiment, why bubbles in carbonated drinks seem to come from specific points in the glass, and how engineers make aircraft aluminum strong enough to keep planes in the sky.
Of all the bird species of the world, the hummingbird has some of the most unique and impressive abilities. It has the highest metabolism of any warm blooded mammal on the planet, it is extremely light, and it flaps its wings so fast that the frequency can even be picked up by the human ear. Some of the fastest flapping hummingbirds can generate up to 200 flaps per second! And not only this but they are able to hover in place, fly backwards, and even shake off water from their bodies all in midflight! Many scientists have researched the hummingbird and have learned that it does not flap its wings in the traditional up and down movement but instead in a back and forth movement creating lift in both the up and down stroke. About 70% of the total lift is created in the down stroke and 30% in the up stroke in one cycle of flapping. Even in wind tunnels these feathered fiends are able to withstand winds of 20 mph by using their natural aerodynamic, streamlined body and tail as a rudder to maneuver through the passing air. Obviously here at Team UV we are interested in harnessing the power of nature through biomimicry and scientist and engineers are doing the same with the hummingbird. Tiny helicopters attempt to recreate the hummingbird hover but currently are not as good as the real deal. More on the mini-helicopter-drones http://www.futurity.org/hummingbirds-micro-helicopters-740052/.
Leading Edge Vortex (LEV) and Trailing Edge Vortex (TEV) shedding in hummingbird flight. Photo Credit:Nick Stockton (Wired.com)
A while back, I wrote a brief article on the pros and cons of alternative energy where I covered various forms from solar to wind. In this article, I will be covering my favorite form of power production: Hydropower! After quickly visiting the Hoover Dam in Nevada, the Washington Water Power Station in Spokane, and taking a tour of the McNary Dam in Oregon, my interest in generating electricity from moving water was rekindled. Many people flock to these large facilities for their grand views and powerful waters but may not know about the actual power production method.
Hydroelectric plants produce power in a very similar way to other common methods such as coal-fired power plants. Regardless of power source, rotation of a turbine turns a generators shaft producing electricity for us to use. Instead of using steam to turn a vapor turbine, hydroelectric plants uses the energy from flowing or falling water to turn a turbine.
Watershed. Photo Credit: wm.edu
The root idea is to find a location with a large watershed area (where a lot of rain and snow falls). This also happens to be where rivers flow. If a lot of reliable water falls in an area, a lot of reliable energy can be produced. Another consideration for finding the most ideal place for a plant is river elevation drop. This gives power designers usable “head” or pressure created by the difference in elevation. After a location is found, designers will have to match the power produced by the plant with the power consumed by the consumers (me and you). Once they have the load demand for a typical day, they can calculate the flow needed to the turbines to meet that demand. Having numbers for head and flow are the two most important factors for designing a hydropower plant.
Hoover Dam. Photo Credit: hdrinc.com
Next, a dam, or structure to hold back water, helps to create a volume of water that will be fed to the power stations turbines. The dam has to be designed to create a sufficient reservoir with low risk of emptying. Low head or an empty reservoir means no electricity to match the needs of the consumer.
Turbine/Generator setup. Photo Credit: USGS.gov
Once a dam has been built and water has filled the reservoir behind it (which can take some time), a power plant can produce electricity. An intake brings water through a penstock (a large supply pipe) to the turbines. The best part of hydropower is that it incorporates the most efficient conversion of energy: work to work. Flowing water turns a turbine which rotates a generators shaft. This produces electricity that is sent out to an electrical grid. The water’s energy has been converted and is sent away through a draft tube to continue on the rivers course.
Power Transmission. Photo Credit: 4.bp.blogspot.com
Electricity from the generator isn’t automatically ready to be used. It is often times upwards of 400V and needs to be stepped up to travel long distances. A transformer steps up the electricity to upwards of 110kV (110,000V) to limit the amount of losses incurred traveling thousands of miles to consumers. When the electricity reaches its consumers, it is then stepped down to safe usable levels such as 110V to 120V for home use.
Unpowered Dams in the U.S. Photo Credit: Forbes.com
As you can see, there is a lot of engineering behind hydropower plants and I hope I have given you all a bit of insight as to how they work. There are a ton of dams across the U.S but not many in Kansas or Florida for their relatively flat terrain. In fact, there are 80,000 unpowered dams in the United States which could provide gigawatts (billions of watts!) of electricity. There are many different forms of hydropower plants in existence with the described one above being a single style. There are run of the river dams too which don’t have any reservoir and rely on the high flow of the river more than the head of a dam.
For more information on hydropower or other forms of alternative energy, visit energy.gov
Plastic Recycling symbols; from left to right: Polyethylene Terephthelate, High-density Polyethylene, Polyvinyl Chloride (PVC), Low-density Polyethylene, Polypropylene, Polystyrene, Other/Miscellaneous. Photo Credit: cityofdavis.org
Seeing as Earth Day was yesterday it seems appropriate to learn a bit more about our favorite frenemy (friend/enemy): plastic. More and more consumer products are made of plastic and this means that more and more of our consumer waste is made of plastic. Only very special plastics biodegrade and this causes them to fill our landfills and pollute our oceans, however many of them are easily recyclable. Plastics are polymers, essentially long chain molecules, so they rarely form an ordered structure, like a crystal, they tend to be more like a lot of spaghetti. The way that these molecules, noodles, interact breaks plastics into two major categories: thermoplastics and thermosets.
Thermoplastics are the most common form of plastic. The molecules in these plastics are only weakly bonded to each other by tangling and van der Waals bonds. These can be easily broken and this makes the melting temperature of the polymer pretty low. This makes these plastics easy to recycle because they can be melted and formed into whatever shape desired, used, then melted back down and used over and over.
Thermosets are the other most common form of plastic and these are typically seen as polyurethanes, epoxies, resin and hardener combinations. The molecules in these materials are actually bonded to each other by cross-linking. This raises the melting temperature very high, for most plastics this is above the the point of decomposition so these kinds of plastics burn before they melt. This means that the materials are committed to the shape they solidified in and cannot be turned back to a liquid state and reused making them impossible to economically recycle.
Unfortunately it is usually cheaper to make new plastic than it is to use recycled plastics due to the added coloring and logos printed on bottles and packages. Plastics are also mostly produced from petroleum products, a non-renewable resource. But as technology improves new plastics are coming out that solve some of these problems, for example PLA is becoming more popular and there is a special bacteria that can decompose it. The future of plastics may lie in algae or insect exoskeletons but where ever it is, it’s looking good for the environment!
Team UV’s trip so far. Map created with: mapcustomizer.com
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.
NCUR 2015 banner. Photo Credit: EWU.edu
More info to come later in the week. Until next time!
This girl is definitely going places. Inventions to help improve the quality of life in a renewable and sustainable approach has been the main efforts of many scientists and engineers today. A participant in Google’s Science Fair, Cynthia Lam, developed a system known as H2prO that purifies water while simultaneously generating energy. In the images above; the upper portion is used for purification of water, while the bottom part is used for hydrogen generation which is connected to a fuel cell and the base unit for filtration of water.
Cynthia’s device uses titanium to separate the pollutants from the water. With the addition of oxidizing substances (methanol, glycerol, and EDTA) this mixture increases the production of hydrogen, which is used as fuel and to make the decomposition more efficient. Tests show that the H2prO has a 90% efficiency in the removal of organic pollutants, and the entire process can happen in only two hours. Unfortunately, the system is still unstable (even with such a satisfactory production of photocatalyic hydrogen) so data regarding energy production is slim to none. However, Cynthia is not giving up yet and plans to finalize her design to help many people in developing countries!
After presenting Dory (Team UV’s senior project) to our adviser and a few interested technicians, I found relaxation in the beautiful landscapes of the Central Coast. During the trip, my girlfriend and I made a visit to Monterey Bay Aquarium on Cannery Row. To our surprise, we found a lesson in science and engineering in the most unsuspecting place…the Sea Otter Exhibit!
Cute otter picture. Photo Credit: imgur.com
The incredibly cute creature above is quite the wet weasel! Belonging to the weasel family, sea otters live along the coasts of the northern Pacific Ocean. Aside from being adorable and cuddly they have a few survival traits that make them scientifically interesting. Sea otter fur is one of the most dense around with up to a million hairs per square inch. They need this much fur because they have no blubber! Living in freezing water is made doable by this dense fur which is fluffed from hours of daily cleaning. Fluffy fur traps air between the otters skin and the freezing Pacific water, where it acts as a thermal insulator.
Layers of air can act as a great insulator, reducing the amount of thermal energy lost to the environment. We see this “phenomenon” practically everywhere; birds “fluff” up their feathers and people wear layers of clothing to trap air close to their skin.
Thermal energy flows from heated region to cool region; conduction example. Photo Credit: misswise.weebly.com
Thermal energy flows in one direction: from a warmer body to a colder body. Insulation such as air is used to reduce the rate of heat transfer in that direction. Many popular building materials use trapped air pockets to slow convective heat transfer (heat transfer due to fluid motion, which is caused by density changes in the heated fluid for the case of natural convection) while also reducing conductive heat transfer (heat transfer through a body due to physical contact). These materials are placed between walls or along pipes to control thermal energy flow. Another popular application is in double pane windows where an air space acts as a thermal insulator between the inside and outside environments.
It’s cool to see the science behind nature especially when you can see its application in other forms. Who knew I would continue to learn even while on vacation!
Top: Helmholtz resonance over a bottle (Photo Credit: Youtube.com; Nick Moore/Nik282K) Bottom: Automotive airflow diagram (Photo Credit: hitechcae.com)
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.
Inverse relationship between velocity and pressure; flow acceleration and deceleration due to flow area change. Photo Credit: wwk.in
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.
Oscillation amplitude increase due to resonance. Photo Credit: AfifTabsh.com
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.
Chevy Volt window air deflector (lower right corner of the picture). Photo Credit: thecarconnection.com
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.
Constructive and destructive interference. Photo Credit: animals.howstuffworks.com
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.
Yes you read correctly, the flying boat. A hydrofoil is a term used to describe a watercraft whose hull is fitted underneath with foils (wings essentially) that produce lift to clear the hull from the water. The overall effect of this is reduction/elimination of the viscous and pressure effects on the hull which essentially means reduction in drag and allows a more efficient use of the craft’s propulsor allowing it to achieve higher speeds. So all that sounds like a bunch of mumbo jumbo, but I think this video will allow you to visualize exactly what I am talking about.
At low speeds the outside of the hull and foils sit submerged underwater but as the craft speed increases, the foils create lift. The amount of lift the foils can create depends heavily on geometry and angle of attack (as mentioned in my previous post). In simplest terms, the velocity of water over the foil is faster above it than that below and this creates a pressure distribution that is different on the top and bottom surfaces of the foil. The figure below shows the typical pressure distribution for a cambered (unsymmetrc) airfoil. The lower pressure exists above the foil then below, therefore “lifts” in the direction of the lower air pressure. A more rigorous explanation of how lift is produced might come in a later post but for right now this basic explanation will suffice.
Depending on the design of your hydrofoil, the angle of attack for the foil may be constant or variable but it will most likely be constant. With this in mind and using the basic lift equation, you can determine how much lift you can theoretically produce from your design given an operating velocity. Once this lift force is equal to the weight of the hull, crew, and cargo on your craft, voilà, the hull is lifted out of the water and you have a flying boat. Of course, there is definitely more complexity to the design but this gives you a basic idea of how a hydrofoil works. Hope this inspired some interest in a very cool, niche type of water craft.
With all the talk about drones lately, especially Amazon’s drone, I thought this would be cool to mention. Today, I want to introduce you to Gimball! The collision tolerant drone!
There is always a learning curve when first piloting a drone. You may not be as good as you think when you keep knocking into things. The last thing you really want is to watch your drone engage in a mid-air collision, but for Gimball it is it’s main selling point. Described as the first “collision tolerant drone” it won $1 million at the Drones for Good international competition held in Dubai.
It was created by Swiss company Flyability and it utilizes a rotating spherical outer cage that means it can be used safely in close proximity with people. Designed to enter hostile environments such as burning buildings and radioactive sites, Gimball maps its surroundings and can roll across ceilings and floors, navigate restricted areas, and transmit RGB and infrared images back to disaster relief services. Surrounding the multi-axis gimbal system with its built-in camera is a carbon fiber outer cage that absorbs the shock of any collisions and the gimbal system means that the cage can roll about independently of the camera.
The world we live in today is driven by how much energy we have. For example when oil prices are high, we drive less and complain about all the things wrong with oil supply. When oil prices are low, we drive more and tend to forget about the core problem. The problem is not that there isn’t enough oil in the world or where it comes from, it’s how we go about energy production. There is no doubt that energy produced from coal and oil is “dirty” but it does have it’s perks. Traditional means of energy production (petroleum and coal) have been in use for a while now so the infrastructure is already there and its technology is well known. Petroleum and coal resources are abundantly found and the power produced from these plants is highly reliable. The same can’t be said for most forms of renewable energy. Renewable energy resources like solar and wind power, although very clean for the environment, have a few major hurdles to overcome if they are ever to be mainstream. A VERY long post can be made about how energy production, both on a national scale and a global scale, can be changed to better the environment and strengthen global ties but that’s not my plan. I simply want to share the pros and cons of each renewable resource and share why they aren’t currently taking the place of traditional energy production methods.
Renewable energy is diffuse, meaning low energy content per unit area and time. This is mainly due to the resources being in variable supply. You may be thinking: How is renewable energy variable? Well, take sunlight for example. The sun rises and sets in a full day. Energy from the sun can only be used when it’s out and most efficiently, when the suns rays are collected perpendicular to the surface of the solar panel. When the sun light fades out for the day, that’s it! Makes sense since solar collectors only work when there’s sun light to collect. At night, the solar plant no longer has its resource available unlike the coal or oil plant across town which can continue to generate power long after the sun sets. Now, a solar plant can store thermal energy from the sun’s rays but it can be unpractical or too costly to do so. Let’s take a closer look at individual renewable resources and the pros and cons associated with each one.
Solar Energy
Simple Solar Grid. Photo Credit: solarpowernotes.com
Pros:
– Large resource (any incident light that passes through the Earths atmosphere can be used for energy production!) – Minimal pollution (sunlight can be used directly for electricity or as a thermal resource) -Free! (Power plants don’t have to “BUY” sunlight)
Cons:
– Diffuse – Cyclical (Can cause fluctuating thermal stresses in components) – Not dependable (Sun goes down = no more resource) – Design for high temperatures (Sun collectors need to handle the high temps of the solar irradiance) – Storage (Electricity can be stored in batteries or heat can be stored in salt thermal pools) – Concentrated Thermal Pollution (Higher temperature levels concentrated in a single area) – Land use (collectors and receiver efficiencies range from 40-70% so many are needed to make the plant worth it)
Pros:
– Long Lasting (As long as there’s rain and moving water the plant can generate power) – Low temperatures (No thermal cycles needed as it uses the energy of falling water to spin a turbine/generator) – High efficiency (Converts work (falling water) to work (rotating turbine) which is the most efficient conversion possible) – Cheap! (All it takes is a dam, a powerhouse (with a turbine and generator), and pipes!) – Reliable (Water can be stored behind a dam for long running times even through droughts)
Cons:
– Habitat loss (Animals can be forced out of their homes to build a site) – Nutrient loss (Nutrients needed downstream for plants and animals can be blocked upstream by the dam)
Wind Power
Wind Power Plant Layout. Photo Credit: yokogawa.com
Pros:
– Free! (No resource cost) – Low operating cost (No thermal cycles; similar work to work conversion found in Hydropower) – Huge resource (Wind is generated by a number of mechanisms making it abundant everywhere)
Cons:
– High capital cost (Huge Turbines = Huge Cost; machinery is large and over designed pushing cost high) – Visual pollution (Usually located by mountains and deserts, wind power plants can take away from nature’s beauty) – Noise pollution (Each passing blade produces a buffeting noise that make living near one hard) – Bird Kills (Birds often times don’t see the blades of wind turbines) – Land usage (Like solar energy, a lot of land is needed to make the plant worth it)
Biomass
Biomass Resources. Photo Credit: energy.ca.gov
Pros:
– Large Supply (literally anything can be used: plants, animals, wood, sugar cane, kelp, menure, sewage, waste, etc) – Efficient use of byproducts (Nutrient rich byproducts are left over from this process which can be re-fed to starting point) – Low pollution (low levels of carbon dioxide gas) – Cheap supply cost (example: the old grease from the fast food place down the street can be used)
Cons:
– Soil depletion and erosion (Compostables once used for fertilizing are now used for energy production) – Competes with food/feed growing (Land and resources are split between food and products used in energy production) – Bulky (Transportation of waste and resources must be considered)
There is certainly enough renewable resources out there with many of them being able to provide for the worlds energy needs on their own. The problem, as I hope I showed here, is that many design issues must be tackled before moving away from traditional fuels. There is no overnight solution and there won’t be one for little while. Some of the cleaner processes pollute less than oil but physically harm the earth they sit on. Others are just too theoretically perfect to be implemented in real life. If you want my full view on how we can tackle this energy production problem let me know…I wrote a paper!
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Stress concentration around a hole visualized using photoelastic methods, with strain gages attached to the surface to measure strain, which can be back-converted to find the state of stress. Photo Credit: alliance.seas.upenn.edu
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).
Simple case of pure tension. Photo Credit: Wikipedia.org
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.
Effect of geometric discontinuity on stress distribution. Photo Credit: Wikipedia.org
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.
Effect of geometric discontinuities on stress distribution. Photo Credit: teachengineering.org
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.
Exaggerated demonstration of effect of concentrated loading on stress distribution. Photo Credit: mace.manchester.ac.uk
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)
Effect of rounding sharp corners using “fillets” on stress concentration. Photo Credit: corrosionpedia.com
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).
Stress concentration at a sharp corner in a plastic protractor (Photoelastic visualization). Photo Credit: Wikipedia.org
Photoelastic visualization of stress distribution in plastic eating utensils. Photo Credit: flickr.com/photos/chrisar/ (Christian Rein)
Photoelastic visualization of contact stresses on a marble in a C-clamp. Photo Credit: osa-opn.org
Photoelastic visualization of rolling contact stresses due to a cylinder rolling on a flat surface; the cylinder is rolling to the left. Photo Credit: Wikipedia.org
Note: Due to miscommunication, this post was submitted late and thus scheduled late; rest assured, regular scheduling will resume on Sunday.
Back at my parent’s house in North County San Diego we have a lot of olive trees and every year they drop their fruit on the ground and make quite a mess. There is no sense in letting all of these olives go to waste so I looked into ways to turn them into a usable oil. It was surprisingly simple, just follow a few steps.
First the harvest. The olives are pretty small and there are a lot of them all over the tree making it way too labor intensive to pick by hand. The simplest way to do it is to lay a tarp on the ground, get a ladder and comb the branches with a garden fork or rake. Let the olives and leaves fall on the tarp then collect them all and pick the olives out.
Now that you’ve got a good amount of olives you’ve got to get the oil out of them. This is where industrial manufacturers use massive hammer mills and centrifuges. That’s a bit of an overkill for home production. First you need to crush the olives, to do this you can just get a strong bag, fill it with olives and go at it with a hammer. I tried a meat grinder and it worked OK but the pits jammed up the machine, a bag and hammer wont have that problem!
Once you have a pretty good pulp of olives you’ve got to mix them so that the oil can form large enough droplets to be pressed out. Don’t mix for much longer than 15 min because you’re adding oxygen to the oil and that will give it an undesirable flavor and color, but if you mix much less than that the oil won’t form large enough droplets.
Now for the pressing. It takes quite a lot of pressure to get the most out of this olive paste so I got a 20 ton bottle jack for a car, built a frame with a two plates and used the jack to press the olives. First spread the paste on burlap or cheese cloth, really any porous fabric that will allow the solids to stay in place and the liquids to flow. Then fold up the cloth, put it in the press and press. Collect all the liquid that comes out and pour it into bottles.
The liquid in the bottles will be about 90% water and 10% olive oil. Leave these bottles in a cool dark place for several weeks to give the oil plenty of time to settle out then pour off the oil on top and store for later, or enjoy now. It will taste very different from store bought oil, in a great way!
Mechanics of an airplane in flight. Photo Credit: av8n.com
Update on technical issues: issues have been fixed, regular posting will resume tomorrow (Sunday).
Turning is also tricky business. On airplanes, aerodynamic forces can be broken down into two components: drag and lift. Lift is a two dimensional vector in the plane (geometrically speaking, not to be confused with a physical airplane) perpendicular to the direction of relative wind, however in “normal flight” we can make the assumption that lift is in the direction of perpendicular to the relative wind and wing span as seen above. Basically we can assume all these forces are happening in a single plane. Weight is mass times local gravitational acceleration (which can/will change during flight). Thrust is a force produced by the engine that is in direction along the axis of the engine. This is especially important if your engine is right smack dab in the middle of your vehicle…
Only when you’re flying straight, level, at a constant speed, constant altitude, and through still air can you assume thrust+drag=0 and lift+weight=0. So pretty much in any other case there are forces going on all kinds of crazy directions in three dimensional space.
Non-intuitively, lift is less then weight in two situations: high power nose climb and low power down decent. Sounds paradoxical but in fact thrust takes up some weight in climb and drag takes up some weight in decent. Force balance, it helps.
Any who, why do we even care about these forces? Well during normal flying (sounds weird to say because I don’t consider flying normal) we don’t, except during a turn. During a banked turn the lift vector is inclined out of the plane (geometric) of the image above, so in order to pull the airplane around the turn and keep it at that altitude, the lift vector must be significantly greater than the weight. So the lift vector can be summarized into two components during a turn: a vertical component to oppose lift and a horizontal component to change direction in which the airplane is flying.
Let’s start simple. Boat turns are relatively simple because they neither have to fly or dive. A flying boat would be pretty cool though…but I digress. Say you want to make a right turn, in the figure below, turning the rudder to the right will cause the boat to yaw starboard. Relative wind will hit the port side of the boat and create tremendous drag which will incidentally turn the boat to the right. The force on the rudder by the wind is smaller than the force of the wind of the portside of the boat which means turning. Now apply all this to airplanes and you have a simple boat turn on an airplane. This sounds great and all, however, turning the airplane properly by using the wings is way more effective and efficient than boat turning. There is also a lot more going on during banked turning as well.
Boat turn. Photo Credit: av8n.com
Airplane turn. Photo Credit: av8n.com
When using your wings to turn, there is a tendency to overbank which basically means overturning. As seen in the figure below, the distance the inside wingtip has to travel is smaller than the outside wingtip and since the outside wing is traveling farther in the same amount time, it must be moving faster.
The lift generated by airfoils depends on the square of airspeed, so the outside wing will be producing more lift which leads to overbanking which leads to a spiral dive into oblivion. Luckily for us, this effect depends on the ratio of wingspan to the radius of turn. For stubby wings, high airspeed, and shallow bank angle, you’ll never notice the effect. For a glider however, you need to deflect the ailerons against the turn to create an opposing force. And to make things even more convoluted, to counteract something called long-tail slip effect, you will be holding your rudder into the turn. So your controls seem like a paradox at this point but this will mean a much better turn then a simple boat turn. Long-tail slip effect is a topic for another day, but if you’re an aspiring pilot or you just want to learn more, please visit http://www.av8n.com/how/#contents for more of your aerodynamic needs.
Swiss Federal Institute of Technology Sepios robot. Photo Credit: engadget.com
Team UV is not the only one who has an interest in underwater technology! The latest in underwater robotics has taken inspiration from the undulating motion of the cuttlefish, rather than conventional methods such as propellers and solid fins. Previous attempts at fish like robotics have produced decent mimics of fish motion, however, they have always been rather limited in terms of agility and precision. Researchers form Swiss Federal Institute of Technology (ETH) in Zurich are set to change this thought with their four finned cuttlefish inspired Sepios robot. Sepios carries a 20,000mAh battery, which is good for as much as 90 minutes of dive time with a top speed of 1.8 km per hour (~1.12 mph or 1.64 ft/s). The current version is only rated for use at depths up to 10 meters (~32.8 ft), which is plenty to explore coastal waters and film wildlife.
Sepios can see effortlessly through a forest of seagrass, even in stormy conditions. Each fin can be controlled separately allowing the robot to move in any direction with ease. The team is now working on improving the coordination of its many sensors, for example pressure and humidity detectors and an on-board camera, laser and inertial measurement unit that help it avoid collisions.
Maybe Sepios will be swimming with Team UV’s underwater vehicle in the future! 🙂
Stacked Shields on an Arduino. Photo Credit: robotshop.com
Arduino boards are very helpful and powerful tools to help connect the electronics world to the real world around us. Like I said in Part 1 of my Learning Arduino Series, they can read inputs and control outputs very quickly; faster than any human can do manually. With that said, an Arduino board, such as my handy UNO R3, can only do so much. After an “Arduinonian” has experimented with all the things in their beginners pack, they often want to venture out to more complex and demanding projects. Want to drive more than one motor? Want to drive two DC motors and 2-3 Servos? Want to connect your board to the internet or save data and images to an SD card? There’s a shield for that!
Robot Shield. Photo Credit: OpenElectronics
Shields are commonly made for microprocessors like the Arduino UNO R3 to inject it with extra functionality. They are designed to piggyback directly on top of your logic board, through the use of stacking headers, which can allow the use of pins not already in use by the shield itself. Some shields allow programmers to pull more amperage for driving bigger, hungrier motors while others add GPS or Bluetooth capabilities. There are WAY too many shields out there to describe in one post, so i will share with you some of the ones I have used and some that I plan to use in the near future.
1) Arduino Motor Shield R3
Arduino Motor Sheild. Photo Credit: Arduino.cc
The important thing about shields is that you want to make sure they are stackable with your specific board. For example this motor shield is called R3 because it fits perfectly on top of the UNO R3 but wouldn’t fit on the earlier R2. I bought this motor shield to do a few different projects that required me to use much stronger motors than the UNO R3 can handle. With the shield installed, a programmer can pull up to 4A, 2A per channel, safely with operating voltages up to 12V. It’s designed to drive relays, solenoids, DC motors, and stepper motors. In fact, it can drive two DC motors independently or one stepper motor with speed and direction control for either case. The shield can be powered by the same power supplied to the logic board (i.e UNO R3) or it can be powered by an external source through the VIN and GND terminals on the shield.
I found this shield to be very easy to use especially with everything already soldered on, even the headers. Working with the supplied library was also a breeze and allowed me to get my projects up and running in no time. I would totally recommend this shield for a beginner or even a professional looking to power up to 12V motors for its low price and easy implementation.
Power Boost 500 Shield. Photo Credit: Adafruit.com
Power Boost 500 Shield. Photo Credit: Adafruit.com
This shield is the latest shield I have worked with. I soldered up the headers and the on and off switch just yesterday! This shield by Adafruit is potentially going to be used in our Senior Project design granted it performs well in testing. The idea behind this shield is to take a single cell battery outputting 3.7V and boost the potential to 5V. This allows a single cell battery to power up your 5V Arduino project on the go! It also has a recharging circuit built in so that the LiPo battery can be charged via microUSB. All the indicators for ON, Charging, Done, and LOW are there to let you know that state of the battery. Another major plus is that depending on the size of the battery, it can fit nicely within the width and height of the stacking headers! So far testing has turned out great with 5V being supplied to my project with the use of only a single cell 3.7V 2,000mAh battery. This will save us plenty of space and take care of charging in one small stack-able package. Like most shields out there this one needed to be soldered before use and for that reason, I would recommend this shield to anyone as long as they can solder or know someone who can.
Click here for more information about this Adafruit shield.
The link above lists some cool shields to get you all started but don’t be afraid to look around for new and unique shields. Sparkfun, Adafruit, and other suppliers are constantly coming out with new stuff. To be honest, the possibilities of what you can do with an Arduino are endless especially when shields can be stacked on each other! Look out for my next Learning Arduino post about breakout boards and things I have needed to collect since starting this hobby!
As always thank you to everyone who has supported us and continue to share our posts and GoFundMe site. We really appreciate it!
The idea of 3D printing is spreading around into all kinds of different disciplines, from cooking to make up. In engineering the idea of 3D printing has been around for a while now. But more recently it has become accessible to the average consumer. Some organizations made 3D printer designs open source, meaning that they published their designs on the internet free of charge. This allowed anyone with some know how to make their own. Once the average hobbyist could invest in the technology it began to get more interest and eventually has become the thing that it is today. As an additive manufacturing method for prototypes, or single production runs, where strength isn’t a huge concern 3D printers open up a huge world of design to the interested population.
Happy New Year from Team UV! Hope you all enjoyed the past year and are looking forward to some new and beautiful things to come in 2015! Being the first post of the year, I’ve decided to start it off right with something uplifting!
Airfoils. Who needs them, right? Well actually a lot of people do, especially if you want to fly. Looking at an airfoil, you might believe that lift is created because one side is curved and the other flat. This however would suggest that lift is only possible in that particular orientation but that is simply not true! If it were, then how could airshow pilots routinely fly upside down for extended periods of time? These are the questions we should be asking people!
Airfoil pressure field distribution. Photo Credit: av8n.com
To fly, it is not necessary to change the shape of the wing when inverted. Actually, any normal shaped wing can fly fine when inverted. It may look a bit weird and the inverted-stall may not be optimized but it does create lift by the same principles as the right-side up wing. Remember, lift is more a function of angle of attack than simply shape.
Airfoil chord and camber lines. Photo Credit: av8n.com
The chord line is a straight line drawn from the leading edge to the trailing edge of the airfoil. The mean camber line is a curved line drawn from the leading edge to the trailing edge that always stays halfway between the top and bottom of the airfoil. The amount of camber an airfoil has is determined by the greatest distance between the mean cambered line and the chord line. If the mean chamber line and the chord line are the same, then you have a symmetric airfoil. A general rule of thumb is that symmetric airfoils are preferred to highly cambered airfoils in small angles of attack, and the opposite is true for higher angles of attack. This is shown in the figure below where the airfoil designated 631-012 is symmetric and 631-412 is the slightly cambered version. Besides one being slightly cambered, the airfoils are pretty much identical. Beyond 12 degrees relative angle of attack you can see that the cambered airfoil has a big advantage over its symmetric counterpart. The cambered airfoil does not stall until a higher angle of attack around 18 degrees and as a consequence its maximum coefficient of lift is much greater. An intuitive explanation would be simply that the slight camber allows for the leading edge to slice through the air easier. Taking this to another extreme, a reverse cambered airfoil would not be a good idea because it would stall even earlier than then symmetric airfoil (which is why you don’t see these). A reason for having a large camber would be in landing or lifting off situations and usually extending the flaps of the wings is sufficient in increasing the camber.
Airfoil Coefficients of Lift & Drag as a function of Angle of Attack. Photo Credit: av8n.com
Effect of wing flaps on camber. Photo Credit: boldmethod.com (modified)
Again it is important to reiterate that lift is more a function of the angle of attack rather than simply the shape of the airfoil. If the coefficient of lift was only dependent on the camber of the wing (which doesn’t change often during flight) then the plane would only be flyable at a special airspeed designed for that particular cambered wing. In reality however pilots have to constantly change the angle of attack to maintain steady lift. For more on lift, airfoils, and flight please visit: http://www.av8n.com/how/htm/airfoils.html. Have a happy new year!
While there are many stunning artificial Christmas trees on the market there is nothing that can beat a real Christmas tree. The species of tree for the festive holiday varies in different parts of the world, they all have roughly the same green foliage and smell. When it comes to getting a tree to decorate for the holidays you’re faced with one problem regardless of the species you go for in that the leaves or needles will turn brown and fall off. A group of schoolgirls in Australia have now come up with a simple solution to make the Christmas tree last longer in the home.
A year 7 class of girls from a school in Rose Bay, Sydney, Australia, looked into what made the foliage of the typical Christmas tree turn brown and shed the needles. They looked at the trees in different conditions. They placed branches into tap water, hot water, beer, energy drinks and a container that had water with the branch being sprayed with hairspray. They performed the experiment with 50 branches of Pinus Radiata, otherwise known as the Monterey Pine tree. They divided the branches into groups of 10 and checked the branches out carefully over a period of 27 days. They used an instrument to measure the leaves health by applying a pulse of light. This measured how efficiently the needles converted light energy to chemical energy.
Professor Moles said that she believed that the coating of the hairspray stopped the plant from being able to sense chemicals that came from the branches that were dying, which in turn would normally trigger more decay. This works in the same way as leaving a rotten apple in a bowl and it turning the whole bowl bad. Another theory was that the hair spray may have helped to keep moisture in. So it seems that if you want to get the best from your Christmas tree you should give the tree a spray with some hairspray. Of course, it would be advisable to do this before you decorated the tree.
This may be a tad bit late considering the timing. I know I will make sure to remember this next year!
LED Sign Example. Photo Credit: animationlibrary.com
Welcome back for another round of learning Arduino! I just want to take a moment to thank those who are continuing this journey with me. For those just joining us, please take a look at Part 1, Part 2, and Part 3 to clear up any questions! I personally have come a long way since my start in Summer and have worked on some really awesome projects this past quarter. Through the use of my personal Arduino starter kit, I have been able to build an obstacle avoiding car, a temperature controlling HVAC system, and a self-stabilizing wing. These projects were completed for a Control of Mechanical Systems class I took this past quarter and I can’t wait to share them all with you.
In Part 3, we were able to build a simple circuit and breakdown the code to control the circuit. It was a nice intro project that showed how to setup an Arduino code and upload it to the board. This time around the task will be slightly more involved but will show you important coding practices to make future projects more manageable. We will be controlling multiple LED’s and manipulating their states at any given time. Let’s get to it!
What you need:
8 x LED’s (any color)
8 x 330Ohm Resistors (if you don’t know what you have, the color code is orange-orange-brown)
Arduino board
Breadboard
Assorted Jumpers
Friendly Note: We are not responsible for any misuse or risky behavior!
Photo Credit: Vilros Starter Kit Guide by Sparkfun
Place the LED’s anywhere on the breadboard, without plugging any two legs into the same rows. This can cause a short and you will experience unwanted circuit behavior. Also, take care in knowing which leg is the longer length (positive) and the shorter length (negative). You may want to place the LED’s in an organized fashion so that the light sequencing looks nice. Remember, we want to place a resistor in series with the LED’s to protect them from excess current. Next, place jumpers from the positive LED legs to the Arduino inputs such as digital inputs 2 -9. Finally, apply a 5V potential to the positive(+) column on the breadboard and a ground jumper to the negative (-) column. Take a look above for a better view of the circuit layout!
Code
The code below is VERY good at teaching what each part does. Instead of re-analyzing each part again, I will add to it in hopes of clarifying any questions. Simply copy and paste it into your IDE and upload it to your Arduino board. I have included a video demonstration below the code to give you a better visual of what to expect once you run it.
// for tips on how to make random() even more random.
index = random(8); // pick a random number between 0 and 7
delayTime = 100;
digitalWrite(ledPins[index], HIGH); // turn LED on
delay(delayTime); // pause to slow down
digitalWrite(ledPins[index], LOW); // turn LED off
}
Video Demonstration:
Here’s what you should expect to see in your circuit! Enjoy!
In future projects you will most likely need to use For Loops and Arrays to complete tasks efficiently and to consolidate writing space. These components of code show up in all different forms of script such as VBA and Matlab so learning it now will make you better prepared. Have some fun with the code above by playing with the timing of delays and with the mixing of functions. If you’re wondering what multiple LED’s are even used for just imagine a marquee display. They are made up of a bunch of LED’s that turn on and off independently to form a desired letter, symbol, or shape.
Thanks for reading Part 4 of my Learning Arduino series and don’t forget to visit our GoFundMe site to help us reach our fundraising goal!
Photo rendering of a futuristic underwater robotic eel. Photo Credit: DefenseOne.com
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”…).
Click image for larger picture.
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.
ISR: UUVs can be used (for example) to conduct reconnaissance (R) in order to obtain the necessary intelligence (I) (strategic, operational, or tactical) for effective military action and/or to provide maritime surveillance (S) of key areas along our coastline or to protect homeland ports.
Mine detection: In areas such as the Persian Gulf, UUVs have been used to detect and (in some cases) clear sea mines.
Underwater inspection: UUVs may be used to conduct underwater inspections of outfalls, pipelines, or other underwater structures that may be too deep, dangerous, or inconvenient for humans to inspect.
Exploration: UUVs have also been used extensively by scientists, filmmakers, and even recreational users to explore the underwater habitat.
Underwater mapping: UUVs are used by the military and some other governmental agencies to map the sea floor.
Collection of weather data: The military also uses UUVs in order to collect data with regards to weather, subsea currents, faultline activity, and other related subjects. (While a little off topic, it is interesting to note that the military actually has a huge presence in the field of weather sciences and the USAF actually has a squadron – the 53rd Weather Reconnaissance Squadron – that flies directly into hurricanes and tropical storms, armed with loads of sensors for data collection!)
Object recovery: UUVs are used in recovery of sunken items from depths traditionally seen as unreachable by humans (in recent news, the US Navy’s Bluefin-21 drone has been used extensively in the search for the downed Malaysian MH370 plane; UUVs have also famously been used to recover items from historic shipwrecks).
Force/area protection: UUVs could also be used to thwart undersea attacks and help to safeguard our troops as well as key areas (i.e. harbors).
Attack missions: Lastly, UUVs could also be used in the opposite capacity by going on the offensive.
U.S. Navy Bluefin-21 drone (left) and TPL-25 (Towed Pinger Locator). Photo Credit: wsj.net; telegraph.co.uk
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
CFD study of airflow through a disc brake installed on a wheel/tire. Photo Credit: apps.exchange.autodesk.com
For much of our design we had to do some complicated analysis on the way the water acts around our vehicle. To do this we had to do some Computational Fluid Dynamics. The complex math involved in these calculations has been briefly touched on in past posts, but this post is here to tell you how we did it. Autodesk offers a massive suite of analysis software for free to students and one of them does the analysis we need: Autodesk Simulation CFD. There are many great tutorials out there on how to do this but here are the basics we used.
Create an external volume: our device interacts with the water around it so we needed to model that.
Then we assigned materials to each component. Each part has a different density and surface finish that will affect its interactions with the water so we needed to assign these values.
Then we set the boundary conditions. These are values of pressure or velocity that remain constant or change at a prescribed rate. For ours we set our pressure far away from the device to zero gauge pressure.
Next we assigned a rotational velocity to our propulsor. This sucker moves the water so we gotta have it spinning.
Then we mesh the whole thing. The automesh feature in the program does a pretty good job. The mesh connects all of the data points; the calculations will be done at each of these points so the more of them there are the longer the analysis will take.
Then click solve and take a nap, these things can take a while to solve!
All of this analysis is right at your fingertips if you know where to look (and happen to be a student!) It’s pretty cool the things you can find out!
If you were in Room 2111 in the Steven G. Mihaylo Hall at Cal State Fullerton between the hours of 2:45-3:05 PM on Saturday (11/26/14), then you probably noticed a couple things: 1) Our team looks damn good in suits. 2) Team UV considered the use of Contracted and Loaded Tip (CLT) technology in our propulsor design. Naturally you may have asked, “What in the heck is CLT?” Well do not worry, I’m here to feed you some knowledge lil guppies.
The CLT propeller spawned after claims of potential advantages of loaded tip propulsion were published for Tip Vortex Free propellers in 1976. CLT propellers became a fully realized propeller type when the contraction of the fluid vein across the blade at the tip was considered to be defining the geometry of the propeller.
So what makes a propeller a “CLT” propeller? First off, the tip chord is finite, it does not just fade away to the root of the blade. Secondly, an end plate fitted at the blade tip located on the pressure side operates as a barrier to avoid the communication of water between the pressure and suction side (this gives a finite load at the tip of the blade). Thirdly, pitch increases from the root to the tip of the blades and there is low to moderate skew on the blade itself. And fourthly, the actual tip bears a substantial load.
Fundamentally the goal of the CLT propeller is to improve open water efficiency. This means that the tip on the propeller reduces the velocities of water entering the propeller disk which, in turn, reduces the hydrodynamic pitch angle. This reduction of hydrodynamic pitch angle and induced velocities results in many advantages. To list a few, CLT propellers have higher efficiency (5-8%) resulting in fuel savings, reduced emissions, saving on maintenance, and achieving higher top speeds. CLT also inhibits cavitation and tip vortices, resulting in less noise, less vibrations, lower pressure pulses, and lower area ratios. CLT also achieves greater thrust, smaller optimum propeller diameter, and better maneuverability. And if that wasn’t enough, incorporation of CLT propellers does not require any major redesign and CLT propellers can be easily retrofitted into existing buildings and vessels.
Model tests and experimental data have shown how awesome CLT propellers can be and recent results with newly developed Computational Fluid Dynamics (CFD) codes show great promise in optimizing the design. Everyone from the US Navy to Carnival cruises is getting in on the CLT technology.
I’m sure we have all done this at some point. Whether it was your computer running especially slow or your television just wasn’t giving you that “clear” picture. It just seemed liked a quick smack was the right thing to do to fix that problem! It worked for Fonzie to fix that skipping jukebox from “Happy Days”, so why can’t it work for you? Well in the older days when devices had many more mechanical components in them, and something could get jammed, a quick hit could get it right into place or a bad solder connection would reconnect. However, these techniques would only be a temporary fix, prolonging the inevitable.
How about more modern machines where many of the components rely less on mechanical operations? Well placing a few well-placed taps could identify a weak connection on a printed circuit board giving you an indication of a weak point in the part. There are definitely items where giving them a good smack would not help but do more damage than help. For example, giving a hard drive a good whack may not be the best solution. However, this so called “percussive maintenance” is still used today to determine faults in electronics like weak solder connections. This percussive maintenance is done by professionals where knowledge and experience comes into play. They know how to perform a few well-placed taps rather than throwing a Mike Tyson punch to the side of the device.
You could compare the “smacking back to life” idea to a doctor applying a “precordial thump” to the chest of a person in cardiac arrest. However, I would not suggest you do this unless you are a certified emergency aid.
As with many things in life, you must learn to crawl before you can walk. Learning how to actually use an Arduino board is no different therefore we will continue our Arduino Journey by completing a simple project. The first thing a novice should learn is how to control an LED. Light-emitting diodes (LEDs) are small, powerful lights that are used in many different applications such as notification lights in our phones, displays, and in sensors. Designers most often times don’t want their LEDs to always be on or at their full brightness so controlling an LED’s state will be the focus of this project.
The first thing an inventor needs to do is gather all necessary components to build the project. This includes the following:
1 x LED (any color)
1 x 330 ohm resistor
Various jumper wires
Arduino Uno (or similar board)
Protoboard (to place your components)
Arduino Code (I’ll cover this after hooking everything up!)
Most beginner kits will have these basic components already but if you are missing anything your local electronics store should carry it. The setup of the circuit is very straight forward as shown below. NOTE: Be smart with your decisions! We are not responsible for misuse of electronics and injury! Before connecting anything together, it’s safe practice to disconnect the Arduino board from your computer or power source. This essentially cuts power to the board allowing the user to move things around without the risk of shock. Place a jumper wire from the 5V output on the Arduino to the red positive vertical strip on the protoboard. Do the same for ground; running a jumper from GND to the negative strip on the protoboard. The two vertical columns on the side of the protoboard are all connected to together. Anything placed on the vertical positive column will be charged to 5V. Anything placed along the negative ground column will be grounded. Conversely, the middle rows of the protoboard are connected horizontally. Anything placed along the same row will be connected together.
Courtesy of Vilros Starter Kit Guide by Sparkfun
Place a jumper wire from any pin (such as pin 13) to any location in the middle of the protoboard. Now we place our LED. The two legs of our LED are of different lengths. The longer leg should be connected to positive (+) and the shorter leg should be connected to negative (ground). LED’s are diodes which mean that the current is meant to flow from positive to negative, so knowing which leg is which is important. The positive leg of the LED is connected in the same row at the jumper from pin 13. Now that we have placed our LED we can place our resistor. Resistors are components that reduce current flow and act to lower voltage in circuits. It is used in this project to protect our LED by reducing the current flowing through it. One leg is placed in the same row as the negative LED leg and the other is connected to ground completing our circuit. You most likely have to bend the legs of your resistor by 90o to fit into the protoboard. If you are lost, just take a look above at the layout diagram to clear things up!
Now that we have hooked up all of our components, we can move onto the code. For the Arduino code to successfully operate two “functions” are necessary to define. The first is setup() which essentially sets up all the pins we need to work with. We can make our pins operate as inputs or outputs depending on what our project needs. For this specific task all we need to do is set pin 13 (or the pin you’re using) as an output. This is done by saying: pinmode(13,OUTPUT);
The next function is called loop() which runs indefinitely until we unplug our Arduino board. Here we place our desired actions, calculations, and operations. For this project we need to make the LED turn on and then turn off. This is done by saying: digitalWrite(13, HIGH) and digitalWrite(13,LOW). Setting our pin HIGH means supplying the pin with 5V, which turns our LED on. LOW supplies the pin with 0V which turns the LED off. Adding the delay, as shown in the code below, pauses the loop for a given amount of time (measured in milliseconds). Adjusting the delay value will change how long the LED stays on versus the time it stays off. You can simply copy the code below into your code window and it should work. All that’s left to do is connect your Arduino board to the computer, click verify, click upload, and your project will be up and running!
CODE
void setup() { pinMode(13,OUTPUT); }
//this is setting up pin number 13 on the arduino board as the output pin. //the first value in the parenthesis is a pin and the second value is the function.
//now we move onto the loop which will run forever until the board is unplugged or reset.
void loop() { digitalWrite(13, HIGH); // LED on.
//digitalWrite is a function used to make an ouput HIGH or LOW, 5V or 0V.
delay(1000); //this pauses the loop for a given amount of time measured in milliseconds
digitalWrite(13, LOW); //LED off.
delay(1000); }
As I said before, adjusting your delay values will result in different blinking rates so go ahead and try it out! Keep a look out for my next tutorial on controlling multiple LED’s.
We appreciate all of your support! Please check out our GoFundMe site to help us complete our senior project. Thanks!
USS Annapolis rests in the Arctic Ocean after surfacing through three feet of ice. Photo Credit: Wikipedia.org
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!
Pitching, rolling, and yawing rotations in an airplane. Photo Credit: cfi-wiki.net
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.
Centers of buoyancy and gravity for surfaced and submerged states.
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).
Ballast tank operation for surfacing/submerging. Photo Credit: Weebly.com
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.
Submarine control surfaces and trim tanks. Photo Credit: Wikipedia.org
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!).
Submarine-surface wave interaction CFD study. Media Credit: Engineering.com
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!
BAE Systems Artful submarine CG/CB testing. Photo Credit: BAESystems.com
U.S. space shuttle Atlantis. Photo Credit: Science.NationalGeographic.com
Space travel has fascinated so many of us since Kennedy promised we’d get a man on the moon. Scientists and engineers worked tirelessly to introduce humans to the rest of the universe and society has benefited greatly from their work. Space travel investment created many things from freeze dried ice cream and Tang to new, more accurate methods for heat transfer calculations. One of the huge improvements was the study of supersonic flow and the convergent-divergent nozzle. This nozzle has made space flight, supersonic jets and all kinds high speed transportation possible. It operates using some pretty interesting ideas.
Most of us are only familiar with nozzles as they apply to garden hoses or shower heads, but some of the same basic principles apply to these new supersonic devices. A converging nozzle increases the speed of the flow, like when you cover part of the head of the hose to spray the water farther. A diverging nozzle is a little less common but it reduces the speed of the flow, like when you adjust your shower head so it’s not blasting you. A convergent-divergent nozzle combines those two back to back and produces velocities greater than the speed of sound. If you’re thinking, “Wait, if a converging nozzle speeds up the flow and a diverging nozzle slows down the flow wouldn’t they just cancel each other out?” you’re pretty on top of your game. This is where compressibility effects come into play. Most of the nozzles we’re familiar with use water, an incompressible fluid, while these nozzles use gasses which are compressible. Imagine you’re coming back from a trip up in the mountains and you have a totally full water bottle and an empty one. The change in altitude will compress the air in the empty bottle, leaving it crumpled while the full water bottle will remain essentially the same.
Air can usually be assumed to act like an incompressible fluid for low speed, like figuring out how strong of winds will take down a billboard or how fast a fan can move air. When air speeds start to reach the speed of sound pretty neat things start happening but first we need to look a bit at what sound is. Sound waves are pressure waves that pass through air very fast, the important thing here is that they’re waves of high pressure. Now lets get back to the nozzle, our first section is a converging nozzle, this speeds up the flow. Lets say that the air is coming in really fast, like almost speed of sound fast, then as it passes through the nozzle it reaches the speed of sound. This means that any of those sound pressure waves trying to move back through the air will be caught in the throat of the nozzle. Kind of like when a person is walking towards the back of a subway train just as it’s leaving the station. They are moving back, but the train is moving forward, so a person standing in the station would see the person in the train as stationary. Also the air is moving so fast that not all of it can get through the throat as fast as it would like so it starts pushing and shoving like a bunch of college kids trying to get free food. This makes the throat of the nozzle a very high pressure region, so high pressure that the flow keeps accelerating through the diverging portion of the nozzle, where incompressible flows would start slowing down. The pressure of the air forces it out like gas out of a shaken soda bottle.
This simple design requires a deep understanding of the world we live in, and it provides the foundation for almost everything that moves at or faster than the speed of sound.
Submarines, UUV’s, and surface combatants all use the same or similar control surfaces like rudders, ailerons, flaps, and elevators to maneuver easily and safely underwater. (For more information on how control surfaces work here are some entertaining and educational videos). At high speeds and predictable flow areas, maneuverability using control surfaces is pretty effective, however, at low speeds this is not the case. There is a need for advanced low-speed maneuverability and the mitigation of cavitation-induced noise for all types of surface and underwater vehicles (check out WANDA). A solution to both that would avoid the use of high energy actuators would be ideal and the reduction or elimination of control surfaces in future designs would be even better. Theoretically.
Ducted propellers have been implemented in recent designs but changing the direction of flow out the trailing end through electro-mechanical actuators has been difficult to implement. Shape memory alloys (SMA) can make this deformable ‘Smart Duct’ a reality. A Smart Duct is a deformable shroud that changes the direction of flow of the propeller wash to provide a direct steering force to the vehicle. The duct itself is an electrically actuated structure that is covered by a flexible hydro-dynamically smooth sheathing whose primary movers are a set of high strength Nickel-Titanium SMA actuator cables. So basically…it’s a duct that can flex in different directions to get you moving where you want to go. A pretty basic idea but has tremendous value if it can be made and implemented correctly. SMA technology has made a series of successful demonstrations that allow for high force actuation that also greatly reduces the volume, weight, and number of moving parts as compared to competing designs. Typically made out of Nickle-Titanium, a 3% to 4% strain is possible with cyclic loads which is pretty dang impressive.
In January 2004, testing was done on the Smart Duct demonstrator at the Naval Surface Warfare Center, Carderock Division. The first tests were done with an empty duct in a water tunnel with a flow rate of 14.7 fps. The duct was able to flex and achieved a deflection of 0.7 in and resisted a peak force of 69 lb. A propeller + Smart Duct system was also tested as well and achieved similar results. Overall what these numbers mean is that effective flow turning angles of up to 15 degrees at thrust levels of operational submarines is possible with the Smart Duct. This is a pretty huge achievement. The future of this type of technology will possibly change the design of submarines and UUVs so be on the lookout for Smart Ducts. For more information please visit http://www.continuum-dynamics.com/lib-pro-duct.html.
SBI water resistant material. Photo Credit: SBIFinishing.com
Water is definitely not a friend for materials such as metals, electronics, wood, etc. For example, when metal is submerged underwater it increases the rate of corrosion of the metal (i.e steel). So we must consider how we can fight against these negative effects the water produces against devices that are made for the water like boats. There are metals out there that are able to neglect the negative attributes of water; however some of us may not have the money to spend on corrosion resistant steel. So what has been done is to create a coating that could be placed over the metal to act as a layer to protect these metals.
There are many coatings out there today however each of these coatings may serve a different purpose. When developing vehicles or devices for underwater purposes it is important to choose a coating that provides cathodic protection. Cathodic protection is used to prevent the metal from being corroded and is usually cheaper than straight out buying corrosion resistant steel. These coatings do come in different colors so you could alter the color of the metal to your choosing. If you are worried about meeting certain specifications no need to worry. There are coatings that go through testing to ensure performance. For example, a coating called Alocit made by A&E Group was tested by the navy and it is 1 of the 3 that meets the specification for the US Army Corps of Engineers! This coating provides great resistance and adhesion. The best part about this and other coatings is that the installation is simple!
It’s been some time since I posted Part 1 of this series. In my first post, I covered the idea behind Arduino and the many applications of their boards. I have taken the past month to gain experience in micro-controlling and, as promised, I will share more of my educational journey.
Photo Credit: Future Electronics
Layout
Since an Arduino board interprets inputs and controls outputs, it only makes sense that you mostly see inputs and outputs on the front face. For the sake of keeping this guide as concise as possible without technical overload, I will only highlight the most critical parts of the board. As shown in the orientation above, the UNO R3 (a popular starter Arduino board) has digital pins up top that can be used as an input and/or output. Working around the board clockwise, we have a reset button that can be used to disrupt the current task and start from the beginning again. Next, we have the ATmega328 micro-controller which acts as the brain of the board. Below the brain, we have another strip of inputs and outputs. Starting from the far left, the user has freedom to use 6 analog inputs which can be used for sensors or other components. The next 3 pins are unregulated voltage (Vin) and two ground pins. The last 3 pins are a regulated source of 5V, 3.3V, and a reset pin. Lastly, we find the external power supply and the USB plug for power and communication purposes.
Inputs and Outputs
The 14 digital pins located up top can be used as inputs or outputs to fit various needs. They operate at 5V and can stand up to 40mA of current. Some pins have special functions but I will cover that when the times comes to use them.
The 6 analog inputs on the UNO have the same 5V operations level and provide 10 bits of resolution. Working with analog and digital signals at the same time can be a bit tricky but, like stated above, I will get to that when the project calls for it.
Power
The UNO R3 can be powered via an external power supply such as a wall adapter or by USB connection. The board can be supplied with 6 to 20V but anything above 12V is NOT recommended. The board can become very hot at higher voltages! Connecting a USB cable supplies the board with 5V but more potential can be supplied using an external power supply. This is important for driving components that may need more power than the regulated 5V supplied by USB.
Software
Standing by the idea of making coding and micro-controlling easy to learn, the software supplied by Arduino allows the user to jump right in without any headaches. The IDE (Integrated Development Environment) is easy to setup and looks very clean. A sample screenshot is included below to help highlight some important areas.
Arduino IDE Screenshot. Photo Credit: Majd Srour
The 5 buttons at the top left starting from the right are: verify, upload, new, open, and save. Verify is used to compile your code and approve it for use. Upload sends your code to the Arduino board. New opens up a new “sketch”, or code. Open allows the user to open an existing sketch and Save is self-explanatory. The magnifying glass to the top right is a serial monitor that shows what the Arduino is transmitting and is useful for debugging. The large white field is open space to write your code and the black field below is a message area where the IDE tells you of any errors.
What a post! I hope Part 2 doesn’t confuse you and if you have any questions, please feel free to comment. I will get back to you as best as I can but just know that I’m learning this environment for the first time too! My next post will get into our first project dealing with LED’s and code debugging. I will also include a video to help you visualize what all is going on. Until next time!
Helical slipstream (a.k.a. prop wash) on a USMC MV-22 Osprey. Photo Credit: YoyoWall.com
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.
The effect of propwash on aircraft stability. Photo Credit: SimHQ.com
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!
Geese flying in a V-formation; Geese vortex surfing behind an ultralight aircraft. Photo Credit: Stevetabone.Files.WordPress.com; Picture-Newsletter.com
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?
CFD analysis of the turbulent vortices in the slipstream of a moving freight train. Photo Credit: Birmingham.ac.uk
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?!
Cavitation within the slipstream of a marine propeller; Pitting cavitation damage. Photo Credit: Wikipedia.org (2)
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.
Twin Grim Vane Wheels on a large ship. Photo Credit: BoatDesign.net
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!
Most modern scientists agree that the climate is changing due to the actions of humans. While that may be a controversial statement it speaks to the huge power and responsibility that we have over our planet. It’s vital that we realize that we can impact the environment negatively, be it the smog that chokes metropolitan areas, the steady acidification of the ocean, or the replacement of habitats with urban sprawl. Many articles pedal fear without solutions and leave the reader with a sense of disbelief or depression. Here I’d like to discuss some of the things that we are doing right, some of the new innovations that are making positive changes.
First off is the Sahara Forest Project. This group of people noticed that the Sahara Desert borders shrink and expand by several miles over the course of the year due to the changes in seasons. This means that the desert is not as empty as it may seem, all it needs is a chance to spring back into bloom. The Sahara Forest Project is here to give it the chance it needs. A pumping station is built near the ocean and pumps the salt water into greenhouses where the water will evaporate and water plants, leaving the salt behind. The water creates a humid breeze that causes plants to grow all around these green houses. Concentrated solar collectors are constructed to provide power to the pumps and support the local grid. While calling it the Sahara Forest Project might be a bit ambitious, this team provides power, produce, clean water, and jobs to the local area with the benefit of supporting more life in an arid climate.
Next lets take a look at middle America, a bit closer to home. Large agriculture has, for the most part abandoned crop rotation to focus on cash crops. This was all made possible by the invention of artificial fertilizers. These caused massive increases in the amount of product that farmers could produce; however these chemicals run off into the water supply and cause eutrophication,wreaking havoc in downstream ecosystem. Just across the street there are beef feedlots that eat much of the corn produced and create huge amounts of manure waste which in turn runs off into the ground water and creates similar problems. On a smaller scale there is a solution to both of these problems. A closed energy circuit can be created by combining the beef problem with the crop issue and adding some poultry into the equation. A basic circuit would look something like the following. In a field plants are cultivated and harvested, then cows are allowed to eat the stalks left behind, pooping all over the field. Bugs grow in the poop and break it down, then chickens are allowed onto the field. They eat the bugs and produce even more great fertilizer. Just like that the field is ready to be replanted. On a small scale a farmer can produce more product for less money and way less damage to the environment.
The future of the environment is in closed energy systems, where there are little to no waste products. The engineering mindset is ideal for this because of the innate understanding of energy principles drilled into every engineer’s head. While we may be hurting the environment, there are ways to help it grow back. Engineers and innovators are working to make the future a wonderful place.
Those who drive know that traveling is pretty easy on an empty freeway but maneuvering through cluttered streets where there are quick changes in the flow of traffic is rather difficult. On the streets there are many things to react to including pot holes, dips, speed bumps, changes in elevation, pedestrians, debris, and even accidents. This is a problem many vehicles run into including unmanned underwater vehicles (UUVs). In open water where flow is predictable, UUVs can travel very fast and maneuver rather easily; however, at low speeds, UUVs are not nearly as successful.
Researchers have turned to nature for inspiration trying to model a UUV that uses flapping fins to maneuver through difficult underwater environments. Many fish species use articulation of the pectorals fins to produce appropriate forces and moments propel themselves through the water and to react to dynamic changes in flow, physical obstacles, and wave forces near the shore.
A four-fin UUV named WANDA-II (Wrasse-inspired Agile Near-shore Deformable-fin Automaton) is the 2nd generation of this alternative propulsion UUV. The original prototype was 0.41 meters in length and the second has been scaled with modifications to a whopping 1.01 meters. WANDA-II has a cylinder housing for lithium batteries, control electronics, and inertial measurement sensors including three axis gyroscopes, three axis accelerometers, and compass. Other changes include increased payload space in the nose and rear and improved battery life due to better fin curvature design using less energy for more thrust and lift.
These fins are capable of producing thrust vectors in multiple directions through changes in curvature and stroke angle. All this is in the attempt to replicate the high level of controllability that fish species have near shore and in shallow water environments. The design of WANDA-II was based on computational fluid dynamics and preliminary experimental results from the first generation, so its design is not by chance or to simply look cool (even though it does).
This UUV can change heading by 180 degrees in less than 12 seconds and has a maximum forward speed of 1.2 meters per second which is a vast improvement over the first generation. Though impressive, the design of the fins was preliminary and therefore not optimized so there is definitely room for improvement for the future generations.
A four-fin UUV could be deployed in a variety of missions including harbor monitoring and protection, hull inspection, and covert shallow water operations. So basically it can be your secret spy eyes in the sea.
The bottom line is that traditional forms of propulsion are being challenged and new forms are arising. Makes you think what the future holds.
Global Ocean Currents. Photo Credit: waydownsouth.wikispaces.com
It’s a popular opinion that we have only scratched the surface of knowing everything our oceans have to offer. What we do know is how the ocean moves and why. Ocean currents are divided into 2 main categories: surface and deep.
Deep currents are ocean currents that are usually more than 100 meters deep. Deep water currents travel the globe with a force 16 times as strong as all the world’s rivers combined. Deep water current is driven by density differences in the water. These movements based on density are also known as Thermohaline Circulation because water density depends on its temperature (thermo) and salinity (haline). The density of this deep water is much greater than that on the surface so the speed of this current is slow however the amount of water being moved is more than 100 times the flow of the amazon river!
You’re likely familiar with coastal currents if you have ever gone to the beach. These are in the category of surface currents. Surface currents are ocean currents that occur at 328 feet (100 meters) deep or above. Unlike deep water currents, where differences in density causes movement, surface current movement is due to wind that flows across the top of the water’s surface.
Coriolis effect on atmospheric circulation. Photo Credit: oceanservice.noaa.gov
The picture above depicts the Coriolis Effect. Winds from the equator direct towards to the north and south poles. If there was no rotation of the earth the winds would shoot towards the equator in a straight line. However, because the Earth rotates on its axis, circulating air is deflected toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere. This deflection is called the Coriolis effect. This air drags on the oceans surface dragging it in its direction giving the current directions you see today.
After finishing that last final of the academic year, it’s all too easy to walk away from campus and fully immerse yourself into what I call “Summer Mode”. There’s no homework to worry about, no lectures to listen to, and NO DEADLINES. This is a time of pure relaxation and wearing sweatpants (unless you have to work but that’s a different story). Summer after summer, I have fallen for this paradise only wishing I had been more productive in my free time. This summer I made a commitment to better myself both personally and professionally.
Out of all the goals I had set for myself this break, I have chosen to show you one. As a mechanical engineering student, our time in the electrical and electronics field can be limited to one class and one lab. We almost have to take it upon ourselves to learn more than just the basics. After taking a few classes dealing with measurements, system response, and sensors, I realized that I have a deep fascination of electronics and computer programming. I figured the best way to continue my education in these fields was to buy an Arduino starter kit online.
You’re probably wondering…what is an Arduino? Arduino is an open-source physical computing platform first introduced in 2005. It was designed to provide students with an inexpensive and easy way to learn electronics, fast. Today, Arduino provides both microcontroller boards and a simple Integrated Development Environment (IDE) software. The uses are endless and projects can range from controlling simple robots to controlling 3D printers.
Arduino UNO board courtesy of Sparkfun. Photo Credit: Sparkfun.com
An Arduino board is a tool for gathering various inputs from sensors or switches and quickly reacting through outputs such as motors or actuators. The board controls this process by an uploaded program written in the IDE. This enables the creator to make a connection between the physical world and the electronics world.
I ordered the Ultimate Arduino Uno Starter Kit by Vilros which can be found online. It has a wide variety of basic components from simple resistors to a LCD screen module and of course the Arduino board itself. The included tutorials range from turning a LED on and off to displaying captured data on the LCD module. I plan to show you my completed projects in the next few posts of this series, as well as the code used to make them all work. Please stay tuned!
Visit Arduino.cc if you would like to explore the world of Arduino for yourself!
SONAR (SOund Navigation And Ranging). Photo Credit: WonderWhizKids.com
“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.
General amorphous polymer temperature dependence.
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!
Water is incredibly common, all of us see it on a daily basis, we know what it looks like and how it behaves. This makes life very hard for the people working in the animation business because our day to day observations alert us when the fluid isn’t acting as we would have expected. This can detract from the movie going experience. Animators have looked to engineering for the solution.
We have known for a while that the flow of fluids can be modeled using the Navier Stokes equations, a set of second order, nonlinear, partial differential equations. Unfortunately this equation is so hard to solve that it’s solution has been named one of the Millennium Problems, 7 of the hardest problems in all of mathematics. It is essentially impossible to solve, at least analytically; that is to say that the solution of the Navier Stokes equations is impossible in the traditional “solve for x” way most people are used to.
This is where numerical techniques come in; these are ways to reduce equations to the basic +,-,*,/ operations and then solve the equations a huge number of times in order to approximate (or get closer to) a real solution. This math is still quite complicated, requiring several hours to days of processing on supercomputers to solve; but, if a few assumptions are made and the initial conditions are properly set, close enough solutions can be found.
If you want to learn a bit more about the math look into the Taylor Series. It’s the little mathematical bridge that takes the calculus normally associated with solution of the Navier Stokes equations and turns it into the simpler arithmetic utilized by CFD programs.
If you’ve heard terms like “turbulent” and “laminar” flow you probably have the intuition that it’s best to have laminar flow for streamline objects because it is less chaotic than turbulent and thus haves less overall drag on the object and less uncertainty in the flow. So why on Earth would someone purposely want to trip flow from laminar to turbulent like with vortex generators?
For streamlined bodies the trend is typically that overall drag increases when the boundary layer becomes turbulent because most of the drag is due to the shear force which is greater for turbulent flow. However, for relatively blunt objects like a sphere or wing on a plane the overall drag decreases when the boundary layer becomes turbulent because turbulent flow allows the boundary layer to follow the surface closer which decreases the overall wake region. The larger this wake region is the more you see chaotic flow separation and adverse pressure gradients that can be catastrophic on aircraft because the flow separation can cause them to stall. The result of this turbulent flow on a blunt object is a thinner wake region and smaller pressure drag for turbulent boundary layer flow. The same idea applies to why a golf ball has dimples instead of being smooth. The boundary layer of a golf ball becomes turbulent much sooner and the wake region behind the sphere become smaller compared to if the flow was laminar. The result is a considerable drop in pressure drag and a slight increase in overall friction drag.
Vortex generators can be found on the wings of aircraft and even on some high performance cars. With vortex generators there is an exchange between high energy momentum and lower energy momentum by tripping laminar flow into turbulent which allows the boundary layer to remain attached over a greater length of the wing chord or car profile which results in a thinner wake region and smaller adverse pressure gradient on the rear of the object which lowers the pressure drag. This allows for many benefits like lowering the stall speed, improving stability and control during maneuvering, and decreasing the turning radius.
Altaeros Energie Buoyant Airborne Turbine (BAT). Photo Credit: EnergyMatters.com.au
Remember those huge wind turbine towers with 3 blades on them? Either standing alone or in a huge field of them? Well these stationary towers could very well get upgraded to float! A company called Altaeros Energies has revolutionized the wind turbine itself from being a structure bolted to the ground to a balloon floating in the air. The company has created a wind turbine that has a helium-filled, inflatable shell that lifts it to high altitudes where winds are stronger and more consistent than what is experienced by the traditional tower-mounted turbines you see today. The company is set to break the world record for the highest wind turbine ever deployed at 300 meters with its next-gen turbine called the BAT (Bouyant Airborne Turbine).
The BAT uses a conventional 3 blade, horizontal wind turbine that is fixed inside the shell. It is held by tethers (cables) that hold the inflatable turbine steady at high altitudes and also transmit electricity to the ground. Ground station controls tether speed and length, and aligns the shell to prevent the tethers from tangling. BAT can generate over twice the energy of similarly rated tower-mounted wind turbines reduces the second largest cost of wind energy (installation and transport) by up to 90%! The entire BAT system can be shipped in 2 containers and can be installed and generating power in under 24 hours and can be monitored remotely.
This is a prime candidate to provide power to countries that require disaster relief or countries requiring power. Who knows, maybe one of these bad boys could be connected to your house instead of solar panels in the future!
View from inside SHEILA-D (Read more in “About” page)
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:
A post in the style of what we refer to as Well Read every Tuesday at 1000 hours by one of the team members.
A post summarizing one of the team members’ Presentations every Thursday at 1000 hours by one of the team members.
A post of one of the team members’ Open Mind every Sunday at 1300 hours by one of the team members.
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)!
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