Traveling wave jet propulsion.

You see the marine propulsion technology appears to be moving more quickly to offer alternatives to the venerable propeller. Undoubtedly jet propulsion is a leader in this race providing many new advantages in the marine industry. Today, water jets are the preferred propulsion choice for a wide range of pleasure and commercial craft where high efficiency, outstanding maneuverability, shallow draft capability and low maintenance are key requirements.

Why shouldn’t we take part in this fascinating race?

As we know marine jet propulsion is a function of differences in the mass-flow of water. Water enters and exits a jet drive at differing velocities, power is converted to thrust via a jet drive, and the thrust propels the boat. Steering right and left is accomplished by directing the system's exit flow in one direction or the other, much like directing the thrust of a submerged propeller-driven system. Forward and reverse motion is infinitely controllable through a reverse deflector that simply diverts the thrust fore or aft http://www.ultradynamics.com/sections/educational/why.asp.

I would like to discuss the traveling wave propulsion possibilities for jet propulsion.

We already discussed peculiarity of the sine wave or the traveling wave propulsion for boats and took a view of some devices emulating fish and dolphins locomotion in threads:
Sine wave propulsion
http://www.boatdesign.net/forums/showthread.php?t=7834
Fishes and dolphins are powerful propellers
http://boatdesign.net/forums/showthread.php?t=8191
How fast can we swim with a dolphin like propeller?
http://boatdesign.net/forums/showthread.php?t=8257
A new concept for future boats
http://www.boatdesign.net/forums/showthread.php?t=9864

A simple device for generating traveling waves includes a motor driven crankshaft assembly, beams attached to the crankshafts, and a flexible band. The beams mounted on the crankshafts are offset with respect to each other in such a way as to produce an equal phase shift between the beams the other ends of which are attached to a flexible band. The complete running wave passes in flexible material during each full rotation of the crankshaft assembly http://boatdesign.net/forums/showthread.php?t=8191&page=5 .

If we will place this flexible band M inside a square pipe as it is shown on the picture, we will get a perfect pump. The pump is exactly what we need to create a jet drive. First picture explains a principle of water transfer in the pipe. Motor driven crankshaft assembly (it is not shown on the picture) continuously generates traveling waves in the flexible band. Width and oscillating amplitude of the band M are in line with width and height of the pipe. Because of this all water located between crests and troughs of the running waves is continuously transferred by band from left to right i.e. from water intake to outlet nozzle.

It is easy to see that a pipe carrying capacity V(m3/sec) = S×l×f, where S = w×h is a pipe cross-section (m2), w and h are width and height of the pipe accordingly (m), l is a wave-length (m) and f is an oscillation frequency of the flexible band (osc/sec). It means if a cross-section S is 1 m2, l =1 m and a flexible band oscillate with a frequency f = 1 osc/sec this pipe will pump 1 cubic metre of water per second. At that the water comes out of the pipe with a velocity of 1 m/sec or 60 m/min or 3, 6 km/h. If a frequency f = 20 osc/sec the pipe carrying capacity gets 20 m3/sec, water flow velocity gets 72 km/h and so on.

 

Sorry, I do not see how this can be, as I understand from your description that those bands are in the sides of the box and you state nothing about the amplitude of the pulses. Could you clarify this to me, please?

Have you considered there is probably a limit to this, due to a possible cavitation in the flexible band surface?

 

Fantastic maths? But if Guillermo is having difficulty what chance the rest of us mere mortals? He is if nothing a mathamatician!

To me it looks as if your trying to reinvent the wheel! It has been tried (to no avail) before!

 

Actually, Vlad has specified that the amplitude is constrained by the height of the box-tube.

However the question of the attachment points (if any) of the wave generator is important. It cannot be attached to the sides of the enclosure. Is it attached to the ends? I think if it were, that the planar wave-making surface could not function properly.

Another consideration is, the parasitic losses by enclosing in a tube. The walls of that tube have to count as wetted surface area. Would this offset the advantages of enclosing the wave maker? I believe jets are less efficient for this reason, than open props.

Also it may not be straight-forward to simply increase the frequency as this may create enormous strains on the wavemaking surface. It might be better to have constant frequency and variable amplitude. Although if the amplitude is really small, then frequency thrust control might work. Nothing that says the amplitude can't be 1 cm. In electronics, frequency is where power high transferance lies.

 

I can’t rewrite for you the contents of 4 above-mentioned threads. You have to learn how travelling wave propulsion works. It doesn’t use any pulses. Picture 1 shows uninterrupted travel of the sine waves inside the pipe.

 

Could you give me some references please?

 

Certainly it is not attached to the sides of the enclosure. On the picture you can see just current position of the band. In following point of time band takes another position (see picture 1) and picture of the traveling wave's propulsion device in thread http://boatdesign.net/forums/showthr...?t=8191&page=5

 

I have been following those threads previously and even posted in one of them the recommendation to you of the reading of http://www.ece.eps.hw.ac.uk/Research/oceans/people/Michael_Sfakiotakis/IEEEJOE_99.pdf

You have to forgive me because of my ignorance. I will not disturb you again.

 

Don’t worry please. I would like to hear a criticism. I ask you to prove that my pump doesn’t work or it works badly, or something is wrong and so on.

 

Some more explanations

I want to draw your attention to formula V(cubic.m/sec) = S×l×f again. It means that a carrying capacity V of the traveling wave’s pipe is proportional to a pipe cross-section S, a wave-length l and an oscillation frequency f of the flexible band M. But a water flow velocity is proportional just to l and f. From this it follows that the bigger l is, the lesser f we can use to achieve high water flow velocity. So if l = 5 m and f = 2 osc/sec, water will come out of the jet driver with a velocity 10 m/sec or 36 km/h. The extension of l in two times increases velocity to 72 km/h. The same result comes in if cross-section of the outlet nozzle decreases in two times. Henceforth we can conclude the traveling wave jet propulsion is more suitable for big boats and ships.