How fast can we swim with a dolphin like propeller?

Superfluidity

Superfluidity which normally occurs only at extremely low temperatures could possibly have a role to play in the efficiency and speed of marine animals.

When a material does become a superfluid, it displays some very strange behaviour;

• if it is placed in an open container it will rise up the sides and flow over the top
• if the fluid's container is rotated from stationary, the fluid inside will never move, the viscosity of the liquid is zero, so any part of the liquid or it's container can be moving at any speed without affecting any of the surrounding fluid
• if a light is shone into a beaker of superfluid and there is an exit at the top the fluid will form a fountain and shoot out of the top exit

So this stuff has no viscosity. Actually a superfluid has zero viscosity, zero entropy, and infinite thermal conductivity. It can form a layer, a single atom thick, up the sides of any container it is placed in.

In some superfluids Cooper pairing takes place between atoms rather than electrons, and the attractive interaction between them is mediated by spin fluctuations rather than phonons. See fermion condensate.

It may be possible that the viscosity of closely bound fluid layers is altered by the energy (capacitative) effects taking place within a few angstroms of a conductor(the animal's body) and the liquid electrolyte (water). Just speculating, though. But you could do experiments...

 

Obvious: who would be that stupid to submit themselves to a travel in a vertically oscillating submarine? And if you find a way to apply such a propulsion to a boat, that would be funny spectacle to watch from the safety of the dry land, wouldn't it?

 

Who would be that stupid to travel in a vertically oscillating submarine? And if you find a way to apply such propulsion to a boat, I'd prefer to sit on a rock watching you and laugh my head off while your tail slams the water.

 

Masrapido,

You might like it better being tied to the propellor? I would not laugh becuase you would be torn to little pieces!

Just because the propulsion device has a vertical oscilation does not mean that the passenger compartment does! Look at a manta ray.

 

Well, JonathanCole, the subject is in effect, "How fast we can SWIM with a dolfin like propellor. I did not take that literarly. I assumed that idea would refer to a vessel, rather than a propeller tied up to my feet. And when you apply vertical forces to a body, it becomes engineering drama to ballance it out to the level where forces of propulsion are small and weak enough to NOT affect travel comfort of the crew. Small forces translate in slow speed. Self-excluding. Conclusion? To make this idea work, you need a LOT of money and research. And result may be to small, in line with forces, to be worth the effort.

 

You clearly are misunderstanding the meaning of the title of this thread. VladZenin is simply pointing out the basic mathematics that allows a dolphin to swim as fast as it does and IF we could develop such a sine wave propulsion device, how we might calculate its performance. The net vertical force of the device that Vlad described is probably close to zero, any way, as one wave peak and trough would tend to cancel each other out. He is not suggesting that the whole boat go up and down like a dolphin. You should read the thread a little more carefully and also the previous thread which shows a sketch of a possible propulsion device.

 

Jonathan,
Thank you very much.

 

Many researchers supposed a dolphin know-how consist in it’s a very peculiar skin. There were suggestions to make boat/ship body coated by dolphin skin like material. They tried but nothing happened. Of course the dolphin skin evolved to provide the best way for swimming in the water. We can see all marine animals have got different skins but swim equally perfectly because of their know-how lies more in their efficient locomotion than in their special skin.

 

Vlad,

Perhaps the reason for the failure of those experiments with skin shape is that the SHAPE of the skin is not what is important, but instead the way the skin effects the Helmholz electrical double layer (do a Google search for more info) which is located in the water within a very short distance (a few angstroms) of the dolphin's skin.

This is an electronic effect that takes place at the interface of a solid conductor (dolphin skin) and a liquid water. It is especially pronounced if the liquid is an electrolyte (salt water) with positive and negative ions. A force develops between ions and the dolphin skin which is perpendicular to the dolphin's surface. This virtual spring tension is not relieved because a layer of pure water molecules coat the surface of the dolphin and act as a separator, or dielectric. In other words an electronic capacitor is formed at the surface.

However as the dolphin moves through the water, the force of the fluid flowing parallel to the surface (laminar flow) of the dolphin disrupts and feeds the ionic layer which must constantly reform under the potential difference. This dynamic is definitely effecting the the viscosity of the fluid medium adjacent to the animal. The only question in my mind is whether it is an advantage or disadvantage.

 

Jonathan,

Astrologers are fully confident stars have an influence on a human life and you can read and hear their telling fortunes. It is not true. After the Sun the Moon is the greatest power affecting life on the Earth. Women menstruations, a conception of billions new lives in the ocean and so on occur in concordance with the Moon calendar. Astrologers ignore it. The light of the nearest star goes to us for about 4 years and its gravitation influence on the Earth and people is zero. It is nothing for astrologists.

Of course all processes are more complicated than we suppose about it. I think if a natural phenomenon that you are talking about exists, it exerts weak influence on a swimming process. Dolphins have a very smooth skin, seals skin has hairiness but they swim equally perfectly.

 

When I was experimenting with flipping Tail Propulsion for boats. My model boats with different tails and tail movement’s was tested in a pool and recorded on video.
When looking to the videos, an interesting thing was possible to see. The boats normally make waves, but at one test the wave disappears. It seams that friction that produce the waver was reduced by the way the tail was moving.
http://www.dahlberg-sa.com/kd/index.html Tail Propulsion

 

Gray's paradox

That brings us back to the beginning of this thread and recalls other interesting possibilities in other similar threads. Is there something about a traveling wave in water that allows reduced friction? Maybe leading to reduced wavemaking? Perhaps only at certain resonant wavelengths? Maybe the resonant wavelength depends on temperature, turbidity, and velocity of the water stream?

Gray's paradox, brought up in a different thread (http://boatdesign.net/forums/showthread.php?t=7834&page=1) suggests that something different happens with a sinusoidal movement in water. To excerpt here: "The experimental results of tests clearly demonstrate that RoboTuna duplicates Gray's paradox (i.e. the drag of the swimming fish RoboTuna apperars to be less than the drag on the straight RoboTuna), but does so with unarguably "known" mechanical muscles. These experimental results, at least for the parameters tested, support Gray's claim that differences in marine/terrestrial muscle power are not the answer, but do not go so far as to explain what the solution to the paradox is. However, it does lend strong credence to the possiblity that some form of unconventional, highly beneficial hydrodynamic mechanism exists, which reduces drag in fish-like propulsion." This is from MIT work.

 

The wave system around the immerged portion of a moving hull is developed at the expense of energy which would otherwise produce motion.

 

I think you have to continue this experiment to give yourself and us the right answer.

I want to discuss tail propulsion. Tail and fish/dolphin propulsion are very different. In fact fishes and dolphins are the travelling wave generators. A fish swims by moving its head from side to side, which sends wave down its body. This wave increases in intensity with the help of body muscles and finally reaches the tail, which then swings from side to side and propels the fish through the water. A dolphin moves head up and down and sends waves down its body in a vertical plane. Fish and dolphin tails at the time of their swimming push creatures all the time (see Force and Reactions Diagram below). Tail itself (without flexible body) can’t do it. Flapping tail pushes water just at the time of it movement to the middle position. After crossing the middle tail push water left/right side and back. In other words after crossing the middle position it applies the brake to boat and causes turbulence.

 

Jonathan,

Here's some info on marine creatures' speed;
Emperor penguins have been observed swimmingaty 14.4 kph (8.9 mph), (Source:www.SeaWorld.org)
The Shortfin Mako shark has been reliably clocked at 31 miles (50 km) per hour, and there is a claim that one individual of this species achieved a burst speed of 46 miles (74 km) per hour. (Source: ReeefQuest Centre for Shark Research) Other sources report speeds of 88 km/h.
The fastest fish is believed to be the Cosmopolitan sailfish, which according to the Guinness World Records website was clocked at 68 mph (109 km/h)

As for who’s the fastest sea mammal, according to the Whale and Dolphin Conservation Society website a bull Orca (a dolphin species...) has been timed swimming at 34 mph (55km/h).

It looks like these guys never heard of 'hull speed' ...

In their 'Review of Fish Swimming Modes for Aquatic Locomotion' Michael Sfakiotakis, David M. Lane, and J. Bruce C. Davies say: -"Gray [34] estimated the power requirements for a cruising dolphin, assuming that its drag can be approximated by that of a rigid model and considering turbulent flow. The calculations indicated that the power required exceeded the estimates of muscle power output by a factor of seven, thus the paradox. Despite the numerous adjustments and corrections of Gray’s original estimations and the varied explanations suggested (see [11]–[13], [21]), no definite conclusions have been drawn on the matter. The new hypothesis is supported by efficiency measurements of an articulated robot swimming by body undulations (the “Robo-Tuna”— see [5] and [6]), ow visualizations of swimming fish [35], as well as experiments and simulations with oscillating foils extracting energy from incoming vortices [35]–[37]. The implication of this theory is that the apparent swimming drag is actually lower for an undulating body than that of the rigid equivalent. This is in complete contrast to the traditional assumptions that estimate the apparent swimming drag to be three to five times that of the rigid-body equivalent, due to the increased friction drag and inertial recoil energy lossesassociated with BCF undulatory motions...."
(Thanks to Guillermo for the article)

Yoav