Wave resistance of rudder, using Michlet

Discussion in 'Hydrodynamics and Aerodynamics' started by Remmlinger, Sep 1, 2012.

  1. Remmlinger
    Joined: Jan 2011
    Posts: 242
    Likes: 20, Points: 18, Legacy Rep: 172
    Location: Germany

    Remmlinger engineer

    I use the VPP for different purposes:

    1.) The simulation of a towing tank. The purpose is to test the physical models in the VPP. If the modeling is valid, the measured data from the tank should be met. In this case a short executable like you described it would be helpful.

    2.) My main interest, as described on my website, is optimization. The VPP is practically the merit function. Since the optimization runs almost a week, computing time is absolutely crucial. For resistance calculations anything else than a look-up table (Delft method) or a closed mathematical formula is just too costly in time.

    Michlet is already a great tool as it is.
    Appreciate you interest in my search for a straw to hang on to.

    Uli
     
  2. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 148, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    Too late!!!!!
    ULIMICH has been released. LOL WTF.
     
  3. Remmlinger
    Joined: Jan 2011
    Posts: 242
    Likes: 20, Points: 18, Legacy Rep: 172
    Location: Germany

    Remmlinger engineer

    Update

    Attached are the equations that include the influence of submergence.
    The diagram compares the approximation for the aspect ratio 2.0
    To be honest, I have not yet checked other AR.
    To produce a foil with a flat top beneath the surface in Michlet is tricky!
    Uli
     

    Attached Files:

  4. DCockey
    Joined: Oct 2009
    Posts: 4,703
    Likes: 315, Points: 83, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Uli, thanks for sharing the results. Is "h" the depth of the top below the surface?

    I'm skeptical of the validity of modeling a flat top over foil in Michlet (or any other "thin ship" code).

    Leo, any suggestions on how to estimate the wave drag of an isolated, vertical lifting foil in a computationally efficient manner similar to thin ship theory for symmetric foils? Vortex lattice method or the equivalent constant strength doublet panels? Possibly determine the approximate vortex/doublet strength using a conventional aerodynamics code, and then apply that strength to a vortex/doublet distribution using singularities which satisfy the linear free-surface conditions. Doublets would be attractive since a doublet can be obtained by differentiating a source.
     

  5. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 148, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    1.For a non-lifting surface, I can't see that a keel could have
    very large wave resistance. Deep submergence will damp out the
    diverging waves; the short chord implies a high Froude number and,
    therefore, small transverse waves.

    2. I have not thought about how to solve the full lifting surface
    equation in the presence of a free-surface. It's just too tough
    and there are difficulties with hydraulic jumps behind the trailing-
    edge of surface-piercing bodies.

    Any of the methods you proposed would be a reasonable 1st attempt
    for straight-edged surfaces. Curved planforms might be awkward for
    some VLM codes.

    You could try using Havelock sources and vortices (or dipoles)
    but they can be tough to calculate.

    3. I cheat by prescribing a vortex distribution, as did Tuck in
    "Can lateral asymmetry of the hulls reduce catamaran wave resistance"
    http://www.maths.adelaide.edu.au/ernie.tuck/pdfiles/vortex04.pdf

    The great advantages of the "trick" are that you don't have to solve
    a very nasty integral equation, and the same numerical methods I
    use for Michell's Integral can be used for distributions of Havelock
    vortices.
    I have been extending that Tuck paper to far-field wave patterns
    with viscous damping but, you know, time and all that.
     
Loading...
Similar Threads
  1. anuprdk
    Replies:
    3
    Views:
    561
  2. AAbercrombie
    Replies:
    6
    Views:
    2,182
  3. dpaws
    Replies:
    21
    Views:
    4,111
  4. quequen
    Replies:
    5
    Views:
    4,017
  5. PHQ
    Replies:
    11
    Views:
    2,280
  6. Erwan
    Replies:
    16
    Views:
    3,608
  7. Greg Woulfe
    Replies:
    7
    Views:
    372
  8. myszek
    Replies:
    5
    Views:
    418
  9. PieroF
    Replies:
    1
    Views:
    464
  10. misanthropicexplore
    Replies:
    6
    Views:
    1,770
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.