Flapping Propulsion.

Discussion in 'Boat Design' started by kjell, Dec 29, 2005.

  1. kjell
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    kjell Senior Member

    The wave pattern for a displacement hull is well known and depending on the S/L Ratio. To explain why the wave pattern was altered is more complicated. It is necessary to make a new test boat installed with all the sensors to record boat speed, flapping frequency, power consumption etc. In this moment I can’t do this. I invite anybody to continue this investigation. From my video and my experiments I have been able to show that it is possible to alter the wave pattern with flapping propulsion.
     

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  2. Guillermo
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    Guillermo Ingeniero Naval

    From this last photo I become even more convinced that the model was moving at a very low Froude's number and so there are not appreciable bow and stern waves trains. The only waves present are the wake ones. From my point of view there doesn't exist such a thing as a bow and stern waves trains suppression fenomena. Imagine...! The whole shipping community would be crazy about this!

    On top of what I stated in my last post, it seems also possible, again from my point of view, that when altering the flapping frequencies there are times when the frecuency coincides with the natural pitching frecuency of the model so it enters in resonance and begans to rithmically picth and this creates a hull's waves train pattern. Out of this resonance zone (or zones) the model doesn't pitch and so, because of the low Froude's number, there are no bow and stern waves trains.

    But I may be wrong, because the hull induced waves in the "With Waves" photo should then probably present a bigger wave length pattern :confused: . Could you please send to me the video and info so I can have a better understanding of experiments? You may find my address at Motorsailers & Motorsailing pages. Thanks in advance.
     
  3. kjell
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    kjell Senior Member


    Hola Guillermo.
    Thanks for your interest I will send you the video and information. It is easier to see what is happening when the boat is moving.
    Saludos Kjell
     
  4. Guillermo
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    Guillermo Ingeniero Naval

    I have been carefully watching the video and photos you sent, several times, and I cannot come to a conclusion. Only more doubts and questions arise.
    Well, at least I'm almost convinced that the model seems not to pitch, so away seems to go also this possibility.
    But it is not conclusive from video that the wave trains dissapear. There are some important visual effects due to be in open air, there is not enough continuity in the film (three takes in three different spots) and we know nothing about speed at every moment. With this info, I'm not convinced at all about your statements, sorry.
    Tests should have to be done with a more scientific approach, taking carefully all relevant data, to be able to come to any kind of conclusions. Better in a professional tests tank. But, in my opinion, the results will probably not worthwhile the cost.
     
  5. icetreader
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    icetreader Senior Member

    Why not, Guillermo?

    I found this through one of the links you posted:

    'Penguin Power' Propels the Navy

    Business Week 12 May 1997 Page 107 "Developments to Watch" section
    by Paul C. Judge

    Engineers have tried for more than a century to improve on the simple but inefficient ship's propeller. The latest effort is based on penguin flippers. Massachusetts Institute of Technology researchers have built a propulsion system that utilized two oscillating blades that produce thrust by sweeping back and forth in opposite directions.
    A 12-foot scale model of the "penguin boat" has shown promise in early lab trials. The blades achieved about 87% efficiency, compared with 70% in conventional ships - which translates into lower fuel consumption. MIT researchers calculate that converting only 3% of the U.S. shipping fleet to a propulsion system that increases efficiency by just 10% would save some $15 million per year.
    Based on laboratory results, MIT's penguin boat is capable of moving as fast as conventional propeller driven craft - and it may be easier to maneuver. All this information interests the U.S. Navy, which supports the project through the Office of Naval Research.'

    Yoav

    PS--The article you found on fish propulsion is excellent -thanks.
     
  6. kjell
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    kjell Senior Member

    In August 1965, SCIENTICIC AMERICAN published. The swimming energetics of salmon, by J.R.Brett. He demonstrated that the Salmon only needed half of the energy to over come the drag of his body at cruising speed. To make this, the Salmon must be able to maintain laminar flow around his body. How is this possible?
     

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  7. icetreader
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    icetreader Senior Member

    ...and the salmon can also swim upstream in whitewater, up waterfalls, make big leaps in the air etc.
    We're just beginning to understand how fish and marine mammals can do all these things so elegantly and efficiently - It seems like these guys have many tricks 'up their sleeve' :) and we could benefit a lot from more research.


    Yoav
     
  8. Guillermo
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    Guillermo Ingeniero Naval


    Well, first because I'm not convinced at all on Kjell's satements of the waves trains dissapearing issue. Info on the experiment conditions and data is not relevant enough (As Kejll himself states), nor rigurous, as to allow us to take that conclusion.

    Secondly, because I do not know any news from this Penguin Boat since 1997 and I've not seen a single information of it being applied to commercial vessels (And I read several shipping and engineering magazines every month, on top of internet navigating). So, maybe the system is not so efficient as it seems (?)

    Probably the mechanical part of it has something to do with the apparent loss of interest. But, just in case, as I may have not enough info, I have asked the MIT. If they answer I'll let you know.
     
  9. kjell
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    kjell Senior Member


    Hola Guillermo.
    I respect your opinion and understand that there are many people that can’t understand why so much money is spending in stupid investigation. I would like to se the result from anybody that demonstrate that I am wrong.
     
  10. Stephen Ditmore
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    Stephen Ditmore Senior Member

    http://www.biology.leeds.ac.uk/staff/jmvr/BLGY3120/Loco/
    http://www.pbs.org/safarchive/4_class/45_pguides/pguide_1002/44102_swim.html#activity1
    http://www.sciamdigital.com/browse....leTypeSubInclude_BIT=0&sequencenameCHAR=itemP

    It's the last item, a Scientific American article, that provides an equation to optimize flapping. Free only at your local library, I'm afraid.... not on the internet.

    At a boat show about a decade back I saw a kayak with pedals and two flapping fins underwater. Has anyone else seen it?
     

  11. icetreader
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    icetreader Senior Member

    Yes Stephen,
    It's a kayak made by Hobie, boat manufacturers from California, and it's getting good reviews and gaining in popularity although the price is still high.

    Guillermo, I assume you know how long it takes to develop a new technology, and how long it takes to implement it in a new concept boat, especially if it's for a 'serious' application like a military or commercial one...
    Those things could take decades.
    BTW, by 'serious' I mean non-leisure and non-racing :)

    Yoav
     
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