Life Isn't Steady

Transport Student A: "So what do we do?" 

Transport Student B: "Well, at least we can assume steady-state, so let's cut that term out of the Navier-Stokes equation."

Does the above dialogue sound familiar? Those two lines are basically how most fluid mechanics or transport students begin their problem sets. Well, students from Princeton University and University of Virginia show in the video below that natural phenomena, like bugs flying and dolphins swimming really fast, cannot be explained by cutting the unsteady term out of the equation. If the unsteady term is not taken into account, the average bee would fall and the average dolphin would not be able to swim at 34 miles per hour. 

What this video is really about is explaining how animals have been able to achieve very efficient motion through fluids due to their body shape and unsteady movement of fins/wings. This unsteady movement apparently reduces the drag (viscous drag) for the animals. The perfect example of this is the Manta Ray. Apparently Manta Rays are 95% efficient in propulsion. Further, our modern day propellers, which are basically fans in water, are in fact very inefficient. Basically the video tells us that manta rays are really cool, though I am not so sure I can say the same about the corny Coldplay music they had playing in the background. Nonetheless, the researchers from the two universities wanted to imitate manta rays and possible develop a more efficient propulsion system.

What they did was pretty interesting--they scanned a manta ray fin, modeled it in CAD, made its negative, and 3-D printed it. They then used this mold and a fish pasty material to create their own artificial manta-ray fin. Additionally, they attached four rods to the mold as well, simulating the muscles. The four rods were attached to four gears and made to rotate out of phase from one another, simulating wavelike motion for the fin. The fin then actually swam at speeds in the order of magnitude of a manta ray!

To me, this shows that biological and evolutionary advancements often beat human technological advancements. Dolphins and manta rays have developed their fins over thousands of years of evolution--so do we really think that a fan in water is gonna be better than that? Imitating the rest of nature has therefore always been what scientists strive for. Finding more of these archetypes in nature can really help us advance as a society. Who knows what else we can do? Another great example of this biomimicry is water resistant clothes using the same nanoscale bumps in lotus leaves (I talk about them in one of my previous blogs!). More examples can be found in this link here.