If you’ve never had an experience involving a dolphin, it should, in my humble opinion be right up there on your bucket list!
Dolphins are a unique group of mammals; in fact their ability in the water is so astounding that it gave rise to ‘Grays Paradox’; where-by in 1936, British zoologist Sir James Gray hypothesised that “the high speeds and accelerations dolphins produce with their [relatively] small muscle mass, is insufficient to overcome the drag forces of water”! Basically he thought they defied the laws of physics!
As a direct result, what followed has been nearly 80 years of research into these fascinating animals that has not only advanced our understanding of the species, but of fluid dynamics itself!
The dolphin’s characteristic body, with its rounded front, crescent moon shape fins and fluke and slowly tapering tail, is nearly perfect at displacing water and minimising the effects of ‘form drag’ (caused by the friction of fluid on their skin). Like that of an elongated teardrop this ‘fusiform shape’ has a maximum thickness 34-45% the length of their body; which is so efficient it actually modifies the water as it swims, a by-product of which is something called ‘drafting’.
Drafting is defined as “the transfer of forces between individuals without actual physical contact between them”, and dolphins have figured out how to take advantage of this between mum and calf…
As the mother moves through the water at high speed, the pressure of water around her drops, this results in an attractive force called ‘Bernoulli suction’ that pulls mother and calf together!
It also creates the ‘displacement effect’; as the mother swims it causes the water in front of her to move forwards and out and the water behind her to move in and replace it. So by swimming next to her midsection in the forward-moving water young dolphins can gain a ‘free ride’ and save up to 60% of the energy they would need to keep up with mum!
Dolphin body shape is inspiring a redesign in both the aeronautical and naval industries as wing, hull and fuselage designs are taking into consideration ways to minimise drag, increase lift and save fuel, just like a dolphin. In fact the Civil Aviation Authority in the UK (along with major aviation manufacturers) is investigating flying passenger jets in formation to take advantage of drafting in the same way as a dolphin mother and calf.
But dolphin-inspired research hasn’t stopped there; magnifying the lens even further dolphin skin has even captivated scientists and biomimics alike, for 3 main reasons:
Dolphin skin cell production occurs at a rate 250–290 times that of humans! In fact some species shed their skin every 2 hours, up to 9 times quicker than we can! Early research theorised that the flaking skin broke down the turbulence around their bodies further minimising drag, but it is actually more likely it prevents build up of parasites and algae that would otherwise increase the effects of drag on their bodies by 4-times!
Most people would imagine their skin to be smooth, but researchers have found it’s not so; tiny ridge-like rings around their body (0.5-2mm apart) cover their body from head to tail. Initially it was thought the ridges might help channel the water, but they are so tightly packed with blood vessels and bundles of nerves they actually match the sensitivity of a human fingertip, eyelid or lip. It is more likely the ridges give the dolphin an ability to constantly sense each current, eddy and vortex in their watery world. But also create a surface that is difficult for parasites to attach to; reinforces the anti-fouling effect of shedding their skin.
And, as water rushes over them, their skin acts like elastic: rippling and undulating over the hard rubber-like blubber bellow. This may help cushion and absorb the effects of turbulent water; reducing drag by up to 7%!
As a result of these adaptive features, dolphin skin is inspiring biomimetic solutions to; reduce drag-inducing parasites/ algae on ships and submarines and ways to break up the effects of drag in water and air using microstructures to channelize flow and elastic layers to dampen turbulence on planes, boats and high performance vehicles.
The ultra-sonic clicks made famous by the series Flipper cant be ignored either! Dolphins can recognize a call of specific individuals up to 25 km’s away! By using several frequencies in each short burst of ultrasound, dolphins have found a way to cope with the challenges of passing sound long distances through water, and still get their message reliably heard. As a result a company called EvoLogics has developed a high-performance underwater modem that emulates dolphins’ unique acoustics! These devises are currently used in the tsunami early warning system throughout the Indian Ocean.
Lastly, the main time we see dolphins is when they surface to breath, leaping from the water and seemingly playing as they go. But there is much more to it than having a good time:
Just half a body length under water drag created by waves is 5-times the drag from friction deeper down! So, while maintaining high speeds, a dolphin leaps to the surface: “porpoising”. Models of porpoising show that at high speeds the energy needed to leap a given distance is lower than the energy needed to swim the same underwater; so ironically they leap to save energy and move quicker!
Also while underwater, during deep dives (more than 20m), dolphins can reduce energy costs by 20% by collapsing their lungs! Once collapsed their buoyancy reduces causing them to sink and glide rather than actively swim. When going back up the reverse happens and the dolphin actively swims up until its lungs re-inflate sufficiently to provide positive buoyancy to glide the rest of the way. How these might inspire biomimics in the future is yet to be seen…
And the list goes on…!
In fact, the inventory of adaptive features that dolphins have in order to manage their environment is almost endless; it’s easy to see how Gray and his paradox believed dolphins somehow challenged the very foundations of scientific thinking.
But each adaption, moulded over millions of years, are a sure sign we have a lot to learn from dolphins alone as each inspires new and exciting ways to adapt to the challenges fluids present to us.
Conserving and respecting these extraordinary creatures should be a priority for their success and, in fact for our own!
If you want to look further into Biomimicry you will find some great links here;