Predict flow lines along hull

Discussion in 'Hydrodynamics and Aerodynamics' started by Janne Enlund, Mar 28, 2015.

  1. Janne Enlund
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    Janne Enlund Junior Member

    I'm trying to understand how to predict flow lines along hull when driving a boat in a straight forward motion. The boat is a traditional double ender (Saga 24) with a long keel and a hull that has almost the same look like a smaller version of a Nauticat 311. I have tried to find papers about liquid flow alog convex surfaces and such but nothing that can really explain the matter.
    I'm going to build a couple of bilge keels to prevent roll and like them to give as low resistanse as possible by making them follow natrual flow lines to prevent turbulence as much as possible.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Building a scale model might be a viable option. You could even get a sense of how much roll damping you get, as well.
     
  3. Rastapop
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    Rastapop Naval Architect

    Put a model into a CFD program.
     
  4. Janne Enlund
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    Janne Enlund Junior Member

    Both scale model and CFD is a little bit of a problem as there are no existing drawing available. I could of course measure the underwater part of the hull.
    Are there any free CDF software available?
     
  5. Leo Lazauskas
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    Leo Lazauskas Senior Member

  6. daiquiri
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    daiquiri Engineering and Design

    So you have a full-size boat, if I understood it correctly? What is the purpose of determining the flow lines?
     
  7. Janne Enlund
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    Janne Enlund Junior Member

    Just go get my bilge keels to follow water flow alog hull.
     
  8. Janne Enlund
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    Janne Enlund Junior Member

    Thanks Leo, openfoam looks promising. Luckily I'm a Linux fanatic so this will be exciting!
     
  9. Rastapop
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    Rastapop Naval Architect

  10. Leo Lazauskas
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    Leo Lazauskas Senior Member

  11. daiquiri
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    daiquiri Engineering and Design

    LOL!! :D :D
     
  12. tdem
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    tdem Senior Member

    Freeship can show flowlines, not sure how accurate. You hold alt and click somewhere under the waterline, it will trace from there.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Use bilge keels with a generous aerofoil shape rather than a thin "blade", and you have a little more room for error with your estimates of what the flow lines are. Also maybe better when the boat is pitching, in keeping turbulence down. Never had cause to worry about bilge keels, but that is what comes to my mind.
     
  14. Rastapop
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    Rastapop Naval Architect

    Well I've got to admit that whatever the joke is it went right over my head...

    But now that I've run a few test cases, and found some decent introductory tutorials on youtube, I'll say thanks again Leo.
    This was one of the better ones for anyone using OpenFoam for the first time: https://www.youtube.com/watch?v=KznljrgWSvo

    It's very handy to have a native CFD program on Linux, especially one that's (legally) free.
     

  15. Emerson White
    Joined: Aug 2012
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    Emerson White Junior Member

    Any method for computing the flow line is going to involve taking a set of lines off of the hull and doing calculations on them. There is no set of instructions for a novice that enables accurately eyeballing how the water will flow across the hull. If you don't want to take a set of lines or build a scale model, you could attach something to the hull itself, and then record how water flows along it under way, like a full scale model.
     
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