The Current Limits of Modeling

Discussion in 'Boat Design' started by DogCavalry, Oct 8, 2025.

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  1. DogCavalry
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    DogCavalry Senior Member

    Since I first read Marchaj back in '91, the tension between the Froude number and the Reynolds number in building physical models for tank testing has been intuitively obvious. Even back then, when I wasn't even bald yet I could see that to get a truly accurate model for towing tank work you would need a 100% scale model.

    Water and models are the same now as then, but computational modeling has improved massively. How has that affected interpreting data from scale models in the tank?
     
    DogCavalry, Oct 8, 2025
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  2. skaraborgcraft
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    skaraborgcraft Senior Member

    I have had some discussion with a designer who has modelled his own CFD programme, and he is now confidently using this analysis to refine hull shapes to suit. He admits it is not 100%, but likely just as accurate as watching a slo-mo of a model being towed in a tank. Way beyond my paygrade, but I did once make a 50% model for on water testing which gave actual data I could measure and understand. No computer i run would even run his sim-flo programme.
     
    skaraborgcraft, Oct 8, 2025
    #2
  3. DogCavalry
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    DogCavalry Senior Member

    Interesting. I wonder if it is possible to write an ap, to compensate for a small model.

    Or for that matter, what % size model to give good numbers for a planing hull.
     
    DogCavalry, Oct 8, 2025
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  4. DogCavalry
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    DogCavalry Senior Member

    I visualize using some modelling software where the user inputs how large his model in the towing tank actually is and how large the finished boat will be and the AI can extrapolate.
     
    DogCavalry, Oct 9, 2025
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  5. BlueBell
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    BlueBell . . . _ _ _ . . . _ _ _

    1/6 scale is often deemed the minimum.

    But then you wouldn't have 100% scale waves in the tank...
     
    Last edited: Oct 10, 2025
    BlueBell, Oct 9, 2025
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  6. mc_rash
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    mc_rash Senior Member

    Take a look on the ITTC recommended procedures and guidelines for towing tanks.
     
    mc_rash, Oct 9, 2025
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  7. mc_rash
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    mc_rash Senior Member

    what do you mean with 'ap' actually?
     
    mc_rash, Oct 10, 2025
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  8. DogCavalry
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    DogCavalry Senior Member

    Some software. An application
     
    DogCavalry, Oct 10, 2025
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  9. BlueBell
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    BlueBell . . . _ _ _ . . . _ _ _

    Also known as an app.
     
    BlueBell, Oct 10, 2025
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  10. DogCavalry
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    DogCavalry Senior Member

    No. I guess you'd be forced to run your 100% scale model in the ocean.
     
    DogCavalry, Oct 10, 2025
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  11. jehardiman
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    jehardiman Senior Member

    Perhaps the title could be changed to "the present..." vice "the current...". This is something I always tried to edit out any documentation that passed over my desk. Most CFD programs don't handle currents well.
     
    jehardiman, Oct 10, 2025
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  12. mc_rash
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    mc_rash Senior Member

    When you go for CFD go for full scale simulation. Keep in mind that the results are only as good as your simulation model and setup.
     
    mc_rash, Oct 11, 2025
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  13. BlueBell
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    BlueBell . . . _ _ _ . . . _ _ _

    JH,

    I had similar thoughts regarding the word "current" in the title.
     
    BlueBell, Oct 11, 2025
    #13
  14. DogCavalry
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    DogCavalry Senior Member

    @Boat Design Net Moderator can we change the title of the thread to
    "The Present Limitations of Modeling and Simulation" please?
     
    Last edited: Oct 11, 2025
    DogCavalry, Oct 11, 2025
    #14

  16. philSweet
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    philSweet Senior Member

    philSweet, Oct 11, 2025
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