Sine wave propulsion

[yipster]

your the same Martijn van Es right ?
welcome to these forums Martijn !
yipster

[JonathanCole]

Having read the Proceedings at the link that Martijn pointed us to, I have a few questions about how this thing works. One question relates to the float of the blades. They need an angle of attack so they must not be free floating on the pivot. Yet if they maintain a fixed angle in all portions of the orbit, then they create a lot of unnecessary drag. So the question is, how is the angle of attack controlled? Is it a complex mechanism? I can imagine that it might be advantageous to simply switch from a fixed angle of attack to a free floating pivot.

Another question is calculating the drag induced by the turbulence and wetted area of the two parallel wheels. Another issue is the duct effect if the wheels are solid surfaces. Would this propulsion device work well between the hulls of a 6 meter beam catamaran? The suggestion as to wheel diameter is for 60% of the draft. A 16 by 6 meter catamaran might only have a draft of a meter or less. Will this give enough propulsor surface area to create the desired reduction of loading? I might like to utilize this in the solar electric cat I am designing if it made enough of a difference in efficiency.

[cyclops]

Back to the original post---------Fish tail motions as a replacement for what we use now.-----------I know a fishes sinewave motion is less effecient than a screw propeller. It is constantly accelerating and decelerating and stopping at each end of the sweep, not as effecient as the constant thrust of a screw device. Next topic.------I love fish and eat them.

[yipster]

Martijn, thanks for the article and keep doing it but think i confused you with Emile vE or Martijn S, other crazy dutch guys i had contact with over torpedo propulsion. one had a couple of small submarines and build a turbine is his motorbike, the other build a human diving fishtail suit, a surfboard foilsail he could stand in and what else, does this ring your belll or do i have names and plans mixed up

[kjell]

[quote=cyclops] I know a fishes sinewave motion is less effecient than a screw propeller. It is constantly accelerating and decelerating and stopping at each end of the sweep, not as effecient as the constant thrust of a screw device. QUOTE]

The limit of propeller efficiency is when the cavitations start.

The tail propulsion don’t have problem with cavitations. In the moment cavitations start on the suction side of the tail, do to the oscillating, this side is converted to pressure side and the cavitations stops. This gives the tail the opportunity to work with more efficiency than a propeller
It is important to understand the way the tail works. You can’t compare the way a propeller accelerate the water with the way the tail accelerate the water. The amount and the speed of water is what producing the forward thrust. The propeller can’t accelerate more water than what the cavitations permits. The efficient tail is not using sinewave motion. Fishes only use sinewave motion at slow speed swimming.

[DMacPherson]

The limit of propeller efficiency is when the cavitations start.

I feel compelled to put in my two cents. I have no issue with the premise that there is merit in a sinusoidal propulsion system, but if it is based on a requirement that the above quote is true, then it will not stand up.

Efficiency really doesn't have anything to do with cavitation - efficiency is the ratio of thrust to torque (or thrust to power, if you prefer). On conventional inboard propellers, excessive cavitation can cause a reduction of both thrust (bad) and required input power (good), and in many cases it will reduce its efficiency where the "bad" loss of thrust is greater than the "good" reduction in input power. However, this is not always the case for all propellers. You just need to find the right propeller for the job.

Super-cavitating propeller designs are meant to operate in a fully-developed vapor cavity, with the majority of its thrust coming from the pressure face, which is unaffected by cavitation. High-performance outboard propellers are a good example of this type of propeller. Many super-cavitating propellers have efficiencies well above 0.60, which is certainly respectable.

So, keep plugging away on the sinusoidal propulsor, but be careful to let it stand on its own merit, not in comparison to some other propulsor type.

Regards,

Don MacPherson
Tech Dir
HydroComp

[JonathanCole]

Originally Posted by DMacPherson

So, keep plugging away on the sinusoidal propulsor, but be careful to let it stand on its own merit, not in comparison to some other propulsor type.

I hope everyone participating in this thread will take the time to carefully read the article that that Martijn has identified. According to the computer/mathematical model presented, this epicycloidal propulsion device has the potentential to be more efficient than standard props in open water use. Other benefits are also identified. Maybe the assumptions of the model are flawed, but if participants carefully look at the article, then perhaps the reasoning can be critiqued. The last page compares regular props with this whale tail propulsion unit. Actually it is not anything like a whale tail in its form. It is a rotational device with pivoting vertical wings.
http://www.nap.edu/books/0309058791/html/946.html

[cyclops]

Sinewave IS a fish tail in motion. Anything else on this post should be a seperate post. For the fish tail to be eff. it would need a ship hull like a fishbody to feed it smooth undisturbed water. The tail would be of the same proportions on both. NO ship owner would use it. Not enough cargo eff. A fish uses it's tail for getting food or fleeing. Not maximizing cargo capacity. This subject is nonesense to compare the 2 different end uses of each.

[JonathanCole]

Originally Posted by cyclops

Sinewave IS a fish tail in motion. Anything else on this post should be a seperate post. For the fish tail to be eff. it would need a ship hull like a fishbody to feed it smooth undisturbed water. The tail would be of the same proportions on both. NO ship owner would use it. Not enough cargo eff. A fish uses it's tail for getting food or fleeing. Not maximizing cargo capacity. This subject is nonesense to compare the 2 different end uses of each.

Actually, if you take any of these mechanical propulsion systems including a standard prop, they all describe a sine wave or something close to it. if you take a point on a standard prop and project it's location in time, it describes a 3 dimensional helical pattern, which looked at from the side in a 2 dimensional view, is indistinguishable from a wave.

What makes a propellor of any type more or less efficient relates to its ability to maintain laminar flow without shedding a lot of turbulent vortices. Because of the rate of flow over the surface and tortuousness of the path of flow, it would seem to make sense that there may be better solutions than the standard rotary prop. That is what this thread is about from my point of view.

It is a discussion of other approaches that incorporate the mechanisms seen in nature. If you look at the article that Martijn submitted, the device is not really trying to directly emulate nature. It is looking at the mathematics and determining that a thrust generator whose surface moves more slowly through the water, but, which has much greater surface area, may have significant efficiency advantages.

[tspeer]

There's an article in the latest Journal of Ship Research that is relevant to this thread.

Liu, Pengfei, "Propulsinve Performance of a Twin-Rectangular-Foil Propulsor in a Counterphase Oscillation," JSR, Vol 49, N0 3, Sept 2005, pp. 207-215.

Theoretical study using a panel code to compute the thrust and propulsive efficiency of two parallel foils moving toward and away from each other.

They found the two foils produced over 50% more thrust than a single foil oscillated in heave, and at a higher level of efficiency. The thrust coefficient is fairly low, and drops off rapidly when the aspect ratio of the foils drops below 12 for the twin foil. As the foils are oscillated faster, the thrust increases but the efficiency decreases. Same for increasing the amplitude of the oscillations. Placing the foils closer together increases the thrust and efficiency.

Pretty much what you might expect, but they put numbers to it.

[cyclops]

Cheese it. Everyone knows a big area, slow turning ---propellsor of whatever design--- is the most efficent. Tugboats have the highest thrust, per ton of hp. per mph.. If they thought for a split second they could increase thrust Eff. they would have done it by now. They do theory and practical to get any sales advantage.

[waveless]

High-Speed Waveless Sinusoid Propeller

I posted it at boatdesign.net in 08-07-2005, 12:22 PM, and I also post the link to china invent net(www.1st.com.cn).

here is the link:
http://boatdesign.net/forums/showthread.php?t=8340

I already made a model and tested, I do not know how to post my video here.

[JonathanCole]

Originally Posted by cyclops

If they thought for a split second they could increase thrust Eff. they would have done it by now.

Yup, and if God wanted us to fly he would have given us wings. Since he didn't we had to invent it ourselves. So I guess its OK with him if we keep on working this problem.

[kjell]

I made some experiments with horizontal tails with good result. This was a R/C rescue devise.

[kjell]

An other experiment with horizontal tail propulsion.