Sine wave propulsion

Living in Hawaii I do a lot of diving. Quite sometime ago I started swimming underwater in an undulating, sine wave motion and noticed a dramatic increase in the speed I could swim versus simply kicking my fin-shoed legs and flapping my hands.

So I started to think about one of the sea creatures that uses such a mode of propulsion - the manta ray - and realized that it was possible to create such an underwater motion by encasing springy skeletal pieces made from carbon fiber (like fishing rods) in an undulating, flexible propulsion mechanism cast from silicone. Has anyone heard of any work like this being done for marine propulsion? Being flexible it may be more durable as well, in addition to being less injurious to sea life and swimmers.

Here's a sketch of an underwater craft that might use such a propulsion system. However, if I am correct about my sense of the efficiency of this general means of applying thrust to water, it could be also advantageously used for regular boats and ships. Any ideas?

 

I thought all fish swim that way. Except most fish's bodies form one cycle only (or less), and their motion is horizontal rather than vertical.

Here's one project: RoboTuna

 

Most engineering schools have yearly contests in which the submarines are all propelled that way. VERY efficient mode. Mother Nature wins another one.

 

Thanks Skippy. Check out these excerpts from the M.I.T. Robo Tuna that are at that link. (color highlights added by me)

"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.

Based on this background, consider the fundamental questions raised, by the biological data, and how the Tuna's experimental results address them:

1) Can the flow past an undulating body propelled by an oscillating foil be "tuned" such that the body's drag is reduced and its thrust is enhanced in a beneficial way?

Yes, clearly it can be, as both Gray's paradox suggests and the results of RoboTuna's experiments conclusively show, this flow can be altered by the correct body-wave/tail-foil motion to use the hydrodynamics in a benificial way.

2) What are the parameters which control this tuning?

In the case of the RoboTuna the parameters which control this tuning are the set of traveling body-wave/tail-foil control parameters given by: *the forward speed *the tail fin's maximum angle of attack *the wavelength of the travelling body wave *linear amplitude of the body wave *a set of fluid dynamics parameters. These may not be the only or the optimal set of such parameters. As with coordinate or modal systems, there is probably an infinite variety of ways to express the same charateristics, but this particular set is eplicitly tied to body dynamics, in such a way as to be easy to observe, to measure, and to comprehend.

3) What is the maximum benifit that can be achieved?

Gray's paradox implies that a seven-fold reduction in drag be acheived. The RoboTuna only experimentally reduced its drag by about half. Obviously Mother Nature is the better engineer. For the sake of argument, assuming the RoboTuna has a purely internal mechanical efficiency in the range of 90%, by extension, it can be claimed that its apparent reduction in drag is in fact probably in the range of 60%, but obviously, there may still be a way to go.

4) Can a man-made (non-biological) system successfully exploit this phenomenon?

Yes, as the RoboTuna clearly demonstrates, it can. But a more appropriate question based on the Tuna's results is now; What level of performance can be acheived by a man-made system, redesigned based on the information collected during this phase of the program? These results also raise a host of intriguing new questions such as; What happens at higher speed?, What is actually going on in the flow about and behind the body?, and Can this be replicated in a free swimming fish?" So if there is a potential 7 fold reduction of drag, how come nobody is working on it for the real world? The price of "unlimited petroleum? Or is the problem to complex?

How about a vessel with three hulls. The two outer hulls are standard catamaran hulls (but super fine, thin, deep) and the center "hull" is an undulating propulsion mechanism. Perhaps it is operated by motor(s) or perhaps by a wind power device. With super low drag, in a SWATH design the sine wave hull might leave other designs in the mist. Any thoughts?

 

Lets not ask more of Nature than she wants to give. Maximum speed about 60 mph with tunas and Makos as large and eff.

 

60 MPH is not too shabby a goal.

Imagine a wind collector on a boat that would be a row of masts (shorter than the usual length). They would be set up to pivot on a ball socket that would only allow side to side motion. They would also be attached together by some elastic medium (Like a bungee cord) which could be adjustable in terms of the height above the pivot point. The masts would have a wind collecting surface of some desirable shape and square footage that would collect the wind and cause/allow the masts to wave side to side, constrained by the elastic interconnects. The masts would continue past their pivot points into a flexible hull (this hull might even be a 2 dimensional flat sheet) where the mast ends would be firmly attached. Being constrained by the elastic interconnects and ball joints, allowing movement only on the plane perpendicular to the axis of the hull, a sine wave motion would ensue in the collectors and thus in the flexible hull.

By moving the elastic interconnects higher or lower you change the wave amplitude which determines power. By changing mast spacings you change wavelengths. Longer wavelengths for higher speeds, shorter wavelengths for lower speeds.

If there is no wind, a simple crank (not me, I'm a complicated crank) interconnect from a motor, or even hand driven could set the craft in motion. I have seen art mobiles that create sine wave motions like this atop the entrance to the subway in Porter Square in Cambridge, Massachusetts. So it definititely can work.

 

And I thought I am a design thinking "out in orbit somewhere" person. I am a child.

 

Jonathan,
I can suggest a simple propulsion device for Manta ray submarine. Do you know people that will be very interested in such a project?

 

But in the Kingdom of the Blind, you are King!

 

Jonathan Cole,

If you read my posts, you'll see that I did not say it is impossible. I said that it is not practical idea. First you suggested that I want it strapped to my feet, what is exactly what VladZenin was suggesting, read his original post; and then you claim that I did not understand the thread. Well, imagineer, you better wake up and read better yourself. Because, as I said then, this idea IS unpractical. It has been tested in late 80', admittedly the movement of the "propeller" was horisontal (from left to the right and back).

But, as they (some team somewhere in US, at some university - come on, it was long time ago. Can't remember everything.) said then: the movement IS efficient. But unpractical because propulsion IS strapped to the rest of the vessel and, as basic law of conservation of mass says, if you push something with a force, something will push you with the same opposing force.

Which part of the law you do not understand?

Now, the future is probably in a screw type of a propeller because rotary movement can achieve speeds and reduce vibrations a lot better than just a vertical movement. Rotations tend to create less vibrations to start with and when a certain speed is achieved (y'know, resonance and frequency thing) vibrations disappear.

No amount of linear movement can beat rotational movement.So, for the comfort sake I will look for propulsion other than you discuss here because, while commendable, it is simply not practical for human transport.

But, you feel free to keep imagineering. Galilleo dreamed about parachute and helicopters long before they became functional.

 

I think you are leaving a lot of things out of your analysis, but I don't want to rehash all that has been said in these various speculative and imaginative conversations concerning unconventional propulsion. You have a right to your opinion, all though your attitude is not one that lends itself to constructive brainstorming. Maybe you should avoid these types of speculative threads. In any case, the guy in the picture below doesn't see it your way!

 

If you don’t like a vertical movement change it on horizontal. Black Tuna has length up to 3 m and swims with the highest speed about 80 km/h; Swordfish is up to 4.0 m length and swims under water with maximum speed about 96 km/h. Could you tell us please what kind of propeller do you need to push these fishes through the water with such high speeds? How much energy/fuel do you need for a circumnavigation with these propellers? Could you tell us please what will happen in marine environment if all creatures will have propellers? Why a human being does dominate over marine environment and does not reckon with marine creatures? In that way we do harm ourselves. We kill creatures and destroy marine environment. If a man made sine wave propulsion devices are still not practical for human transport, you can create the better one and I am sure you will be rewarded for this generously.

 

JonathanCole.

What, just because I offeer a different view and one that clearly shoots your fantasy down I have an attitude? What cind of discussion is that?

You came up with an old idea that was proven in 1980' as doable but unusable and unpractical for application in human transport and I draw you attention to its' defficiency. If you are unable to discuss negative aspects of your idea like a reasonable person, maybe you have attitude problem and should not be participating in forums like this.

Be nice and ask an engineer about some basics in physics and then feel free to apologise. There's a reason why airplanes do not flap their wings; it's the same reason why boats will not "swim" like fish do.

Instead of availing to offensive remarks and inappropriate comments, try to learn how to accept limits of your knowledge and try to learn from others. That is what these forums are for, not for people like you to abuse other people just because your lack of knowledge means nothing to you.

Now, if you have something technical to discus, and counter my suggestion, offer a technical solution for problems or offer solutions that make this type of propulsion useable for human transport, I am more than willing to listen. But if you don't, at least please respect this forum and abide by the rules about the language you use towards others.

 

JonathanCole.

What, just because I offeer a different view and one that clearly shoots your fantasy down I have an attitude? What cind of discussion is that?

You came up with an old idea that was proven in 1980' as doable but unusable and unpractical for application in human transport and I draw you attention to its' defficiency. If you are unable to discuss negative aspects of your idea like a reasonable person, maybe you have attitude problem and should not be participating in forums like this.

Be nice and ask an engineer about some basics in physics and then feel free to apologise. There's a reason why airplanes do not flap their wings; it's the same reason why boats will not "swim" like fish do.

Instead of availing to offensive remarks and inappropriate comments, try to learn how to accept limits of your knowledge and try to learn from others. That is what these forums are for, not for people like you to abuse other people just because your lack of knowledge means nothing to you.

Now, if you have something technical to discus, and counter my suggestion, offer a technical solution for problems or offer solutions that make this type of propulsion useable for human transport, I am more than willing to listen. But if you don't, at least please respect this forum and abide by the rules about the language you use towards others.

 

It works

Sculling is an ancient and well known, simple human powered method of propulsion that uses sine wave propulsion, usually at the stern.
The Chinese Yuloh, Japanese Ro, Venetian Gondola and other examples from around the world are highly efficient and enable a single person to propel and steer fairly large and heavily loaded boats across long distances.

Yoav