wave lenght by Michlet

Discussion in 'Software' started by pavel915, Dec 26, 2009.

  1. pavel915
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    pavel915 Senior Member

    is it possible to find the wave length of transverse wave system so that i can see whether my ship is operating in displacement or planning region for a particular speed?
    If yes, then how?
     
  2. Leo Lazauskas
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    Leo Lazauskas Senior Member

    The wavelength of "pure" transverse waves is

    Lambda = (2 * pi * U^2)/g

    where

    U = ship speed
    g = gravity

    This wavelength, however, does not tell you anything about whether a hull is, or is not, in "planing" mode. You have to find some other method.

    All the best,
    Leo.
     
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  3. pavel915
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    pavel915 Senior Member

    Thanks Leo for your reply,
    Actually i knew the equation you have written,
    But i am confused that, does not the wave length depend on the hull form at all? For any kind of hull the wave lengh will be equal to ships lenght at Froude number 1/Square-root(2Xpi) ?
     
  4. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Yes, the wavelength very close to the hull is affected by the shape of the hull. But you asked about the wavelength in Michlet.

    Michlet results are only valid behind the hull, i.e. it only calculates far-field waves using linear wave theory. In that case, the wavelength of pure transverse waves in deep water is given by the equation I gave previously.

    To see the separate near-field and far-field components see, for example, the SWPE report at:
    http://www.cyberiad.net/library/pdf/tsl00a.pdf

    Leo.


    Leo.
     
    Last edited: Dec 26, 2009
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  5. pavel915
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    pavel915 Senior Member

    Thanks Leo,
    I get it now,
     
  6. gonzo
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    gonzo Senior Member

    You are overthinking the problem. A planing hull is running over the bow wave. The wave has the lenght of the boat's waterline.
     
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  7. Leo Lazauskas
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    Leo Lazauskas Senior Member

    And you have grossly under-thought the problem :)

    Displacement boats can operate at a Froude number where the wavelength is exactly same as the boat length. And planing hulls at exactly the same Froude number may not actually be planing.

    Cheers,
    Leo.
     
  8. pavel915
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    pavel915 Senior Member

    Actually i was trying to talk about the highest speed upto which a displacement boat should operate,(may be called transition between displacement and semi-displacement) i.e. where the wave length is equal to the boats lenght. But i was confused about whether this wavelength depends on the hull form or not,
    Leo has made this clear to me,
     
  9. gonzo
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    gonzo Senior Member

    The wave length depends on the waterline length. However, the hull shape can have different waterline lenghts at different speeds. This is used to advantage on sailboats.
     
  10. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Not in Michlet.

    The wavelength of the transverse wave system is given by the equation I gave earlier. Hull length does not appear in that equation.

    Leo.
     

  11. terhohalme
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    terhohalme BEng Boat Technology

    Gonzo, no

    I ask you to repeat your tank tests.
     

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