Dolphin World Blog

Fluidic Peristalsis

Having recently read an interesting article in Discover magazine about the effort to understand why Dolphins are able to swim so fast, I became aware that many scientists have devoted a great deal of research effort in trying to analyze all the dynamics involved. In spite of all their efforts, it remains a mystery.

This set me to thinking; there must be a dynamic factor at work that we have overlooked. Much attention has been given to the work output of the muscles, the factors of reducing drag, streamlining design of the body and other factors that could advantage the Dolphin in any measurable way. Yet none of these investigations can account for the amazing speed these remarkable creatures can attain.

It occurred to me that so many variables are involved that we may possibly be overlooking some small dynamic effect that we had never considered. Then it hit me like a bolt, it has to be the shape! All the researchers have noted that the Dolphin’s beautifully streamlined shape conforms to our best understanding of fluid dynamics. We know much about fluid-dynamics from our years of studying aerodynamics for the development of airplanes. Elaborate studies of different shapes in wind-tunnels have made us very conscious of the importance of streamlining, drag and laminar-flow. Still, there must be a secret about the shape that has eluded us.

I thought about how all the creatures that live in the oceans have evolved separately yet all but a few special types have long-since adopted the same basic shape, unanimously. Even former land-creatures that had adapted to breathing air, then returned to the ocean, eventually re-adopted the characteristic “Fish” shape. This shape must have extraordinary advantages for aquatic denizens.

Having been a fisherman many years, I learned that trying to grasp a slippery fish by the rear half of the body is a sure way to lose the fish overboard. The harder you grasp, the more forcefully the fish will squirt out of your hand, just like a wet bar of soap. EUREKA, I found the secret. I can propel a wet bar of soap clear across the room without any effort from the bar itself.

When you analyze the” fish” shape, you see that about the first third of the body is a positive wedge-shape to separate the water for passage and the remaining two-thirds of the body is a negative taper to allow the grip of water pressure to help the tail thrust the body forward with less effort. I have coined a term for this phenomenon. I call it “fluidic peristalsis”.

Because water is a much denser medium than air, water exerts a greater pressure on the body than air would. The same phenomenon doubtless happens in air but the effect is negligible. Still it is worth noting that flying creatures have adopted a similar taper to their bodies.

The peristaltic push is not strong enough to overcome the resistance of parting the water but it is ever-present, even when standing still. It is always ready to assist the tail in forward thrust once the investment is made in parting the water for the front part of the body.

I have also noticed that ocean predators are basically round in cross-section while prey fish favor an oval shape that tends to be flatter from side to side and taller top to bottom. Still the overall taper from front to back is the same. It is obvious that the narrower shape allows prey fish greater flexibility to dart right or left to elude a pursuing predator.

If my assessment is correct, we can improve the efficiency of all our underwater vehicles by mimicking the experts who invested several million years in finding the most efficient way to travel through a dense medium. Our submarines are not very efficient because they are not shaped like fish, they are shaped like cigars.

Jack Bennett

Thanks Jack for the interesting thoughts. Does anyone out there agree or disagree with Jack? Any comments?
God Bless,
John