Green Turtle swimming by a reef. Photo Credit: Michael Carey (flickr.com)
As many of you are aware, we are in the transitioning phase of this website as we close out TeamUV.org and transition to EngineeringAFuture.com over the next two months, so this will be my last Presentation post here at Team UV, but not to fear, there are still two months of posts left here and the same types of articles will be carried over onto EAF (Engineering A Future), so without further ado, please enjoy the following:
Tracking tags are used to gather data that concerning the behavior of whatever they are attached to. Often times you will see these tags attached to underwater creatures in order to gather large amounts of important information regarding the migratory patterns, mating behavior, predator-prey relationships, hunting/feeding grounds, social behavior, and feeding behavior of sea (as well as other) creatures, just to name a few parameters.
As you can probably imagine, from an electro-mechanical standpoint, these devices must be very well designed and quite technologically advanced in order to be able to gather all of this information through logging positions, orientations, accelerations, temperatures, video, perhaps audio, and so on and so on. On top of this, the power supply must be capable of lasting a very long time so as to enable the data to be collected continuously without a battery change; either that or the device must be able to recharge itself (i.e. solar recharging), which would of course mean gambling on how much time the creature spends near or on the ocean’s surface where the sun can recharge the device. The device must also be attachable in a way that will keep the device in place for a long time without irritating the creature. Vibrations must be controlled so as to not irritate the creature or skew the data and interfere with the sensors, thermal management must be sufficient to not only protect the on-board electronics, but also to not provide discomfort to the animal, the device must be able to withstand impacts and the wear & tear of daily routines, and the device must not interfere with the creature’s behavior in any way. Combine all this with the fact that the device must be waterproofed, often to great depths, without interfering with the sending and receiving of signals, and you begin to see the formation of a pretty hefty problem statement. And oh yeah, we can’t forget that at some point the researcher must be able to get the data (and hopefully the device) back! And lastly, according to your boss, the design must be complete and ready for prototyping by noon Friday and you have a $30 budget!
Stress and deadlines. Photo Credit: vijesti.me
Theses kind of issues represent the same types of issues that mechanical (and other) engineers must deal with on every project they work on; as a matter of fact, the issues above share a great deal of similarity to many of the issues we had to design for in our underwater vehicle! (except that we had much, much more to design for since we were designing an entire vehicle, so we could rather equate the amount of issues above to those we had to design for for each of our 7+ subsystems!) This provides the background for an excellent conclusion and underlying theme in the world of engineering in general (and mechanical engineering in particular): You cannot design for everything.
Uh oh, does this mean that mechanical engineers are not putting enough work into their designs? That they are being negligent? No, of course not, this is just a simple fact. As much as we might want to think it, the reality is that no design is perfect. As we have demonstrated time and time again here on TeamUV.org, mechanical engineering covers what is essentially an infinite amount of topics, and thus mechanical engineering projects require an infinite amount of considerations. It is humanly impossible to design for everything, because the engineer cannot think of everything. So what do we do instead? We pour ourselves into our work and give the project 150% of our all and do everything we can to consider as many things as we can, and then…we accept the fact that we could not have possibly considered everything, come up with a contingency plan for when (not if) an unforeseen issue arises, and we go back to work.
So what does all of this have to do with tagging marine life? Am I just getting sidetracked? Nope, the reason I am choosing to talk about these things in this context is that this is exactly what has happened with these wildlife tracking tags. The engineers who created these tags did not spend enough time on one crucial detail that may have been seen as a relatively minor issue at the time, but which may have profound consequences regarding the validity of the data gathered and the well-being of the creatures themselves. What is this parameter that was not given enough attention? Drag.
Loggerhead sea turtle tracked with satellite transmitter. Photo Credit: Jim Abernethy (NMFS)
As many of you are aware, drag is essentially resistance to movement through a fluid. Underwater creatures are often streamlined very well because nature is the ultimate engineer and underwater creatures have been optimized for their lifestyle through generations of natural selection. When you attach a bulky electromechanical device to a creature that has been streamlined for the optimal results in its environment, it can have a disturbing effect on the behavior of said creature. Go figure. In fact, as researchers at the National Oceanic and Atmospheric Administration Pacific Islands Fisheries Science Center in Hawaii have found that the disturbance to the fluid flow over the creature caused by the presence of these devices is resulting in increased drag anywhere in the range from 5-100% depending on turtle size and age. This in turn translates to slower speeds for the turtles, lower accelerations, decreased maneuverability, and possibly even behavioral changes due to some unforeseen psychological or emotional effects on the turtles. As a final segue, this in turn can lead to turtles behaving radically differently with regards to patterns, travels, social behavior, etc. that could mean receiving skewed or otherwise invalidated data, as well as a possible decrease in the turtles’ psychological and even physical well-being.
As seen in the video, in this fascinating study, these researchers are studying these disturbances are using some pretty innovative means to do it. The researchers are using the bodies of turtles that deceased from natural causes to form molds to create fiberglass sea turtle bodies of various sizes, which can then be analyzed in low-speed wind tunnels to identify and quantify the flow disturbances caused by these devices. This is an excellent example of one of the major job roles for scientists and engineers: analyzing an issue that was perhaps not considered, not understood, or possibly even simply not known at all to be an issue beforehand in order to gain a better understanding of the issue and then remedy the issue by developing more polished solutions.
Large mock sea turtle set up in a low speed wind tunnel. Photo Credit: Michael Carey (flickr.com)
One would only wonder why the tail fins were not taken into account in the model, as even though the disturbance is topside and the fins are located on the bottom of the body, with that large of a disturbance upstream, the flow about the tail fins would absolutely be effected in some way by flow separation and subsequent recirculation about the aft portion of the body. Oh well, moral of the story: it is impossible to account for everything, and sometimes it may even come down to cost-savings, ease of design, manufacture, or analysis, or even just simply deadlines. So what do we do? We put our best foot forward, give it our all, be prepared for the imminent issues down range, hope for the best, and to reiterate, we never give anything less than our all to a project for reasons of pride, protecting our reputation as engineers or scientists, and ultimately to do our best in the name of science and engineering.
Please come back Sunday for my last Open Mine post on TeamUV.org! For more info on the above research, click here.
