Fishes and dolphins are powerful propellers

I was wrong putting the picture of a catamaran. Travelling wave propeller can be installed on any kind of vessels. Why do you think that the wave sheet is moved with fixed amplitude? It is well known that the amplitude of oscillation of the swimming fish and dolphin body increases from the head to the tail. It is easy to realize in a propulsion device (see picture). What do you think about efficiency this propulsion device? What a difference in exit velocity compared to the free stream velocity will be?
See also "How fast can we swim with a dolphin like propeller?"
http://boatdesign.net/forums/showthread.php?t=8257

 

I knew about it. I am a geologist by my first profession.

 

Have a look at the picture above. You can use this propulsion device in a vertical position too.

 

The most efficient way to go from A to B is of course the transporter like that used in Star Trek. You just need some dilithium crystrals and a matter/anti-matter power source.

 

Vlad,

I think to make the travelling wave propulsion device practical, it is not appropriate to utilize an expensive, complex mechanical linkage. With mechanical devices, the more moving parts, the more places for failure. Perhaps a piezoelectric device (material bends with application of voltage). Such devices are already used to make fans for electronic devices. Another approach might be the use sheets of material that expand lengthwise with the application of electricity. Two such sheets bonded together would form a curve when only one is activated. Activate the opposite side and the curve reverses.

Aloha,

Jonathan

 

My point is, you should be telling us. Nobody can just look at something and make a statement about its efficiency. At the preliminary stage, one's estimate necessarily has to be crude because you have to make a lot of assumptions to fill in for data you don't have. But I think you ought to make the effort to assess it.

To some extent, you specify what the exit velocity has to be. In order to power a given vessel at a given speed, you need a certain thrust. You can get the thrust with a high exit velocity and small exit area, or vice versa. The first step the designer has to do is chose these parameters and then see if the rest of the system is consistent with them.

 

I don’t need to do this. Mother-Nature have done this for us.

 

Storm of applause

 

It is very interesting. Do you know performance attributes of a piezoelectric effect and expanding lengthwise with the application of electricity? What size of the expanding do you expect to achieve?

 

There is a lot about this on the Internet. Here is a good departure point:
http://widget.ecn.purdue.edu/~CTRC/research/projects/Ultrasonic piezoelectric/piezofans.html
Maybe this has relevance to Kjells fish tail propulsion as well. It seems that the piezo material flexes only a tiny amount with application of voltage, but also requires very little energy. Two pieces bonded as I said earlier could possibly flex and curve quite a lot due to the constraint of one plane on the other. In any case, the traveling wave may be better if it has low amplitude and high frequency as energy is applied most advantageously at high frequencies.

 

Yes, the piezo material flexes only a tiny amount with application of voltage. But it may be good for making toys.

 

This is an electro magnetic tail drive I was testing some years ago.

 

I see my travelling wave propulsion devices do not excite curiosity. I understand they are complicated and bulky. My ultimate aim was to disclose the idea of this kind of propulsion and show some specific engineering solutions. I think there are lots of physical principles that could be used for travelling wave generation. They should be uncovered when first boat models will show high performance attributes.