Digital Tank Testing Of 1924 Hull

Discussion in 'Sailboats' started by RSLOOP, Feb 3, 2007.

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    RSLOOP Junior Member

    I am the owner of a 1924 (R Class) Racing sloop.
    Recently I purchased the plans and the Lines table, spend a good number of hours in Autocad to input the data and re-create the hull. At this point the hull is in meshes.
    I am wondering if this model could be speed tested and what what form of digital data is required, in other words, meshes or solids.
  2. Eric Sponberg
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    Eric Sponberg Senior Member

    What do you hope to determine from "digital tank testing"?

    In a nutshell, with the correct data format, yes you can do what we call "computational fluid dynamics" or CFD. You need the hull in a NURBS surface model, and any of the popular modelling programs such as ProSurf, MaxSurf, Fastship, AutoShip, etc. do that. I use ProSurf. From this surface model, a CFD program might have to convert it to a mesh, and there might be certain functions and definitions that go along with that conversion. Someone who is familiar with the inner workings of CFD can chime in here and tell you more precisely what is required--I am not sure your "mesh" that you input into AutoCad will work.

    But the big question here is why do this? CFD is not really all that accurate when all is said and done, although it is getting better as time goes on. It is good for what it is at this stage of development, but it is not necessarily more accurate than model testing. And then, with model testing and for CFD, the best use of the tools is for comparative analysis, not absolute analysis. That is, you use it for comparing one feature with another within the same family of hull forms. Do variations of the hull forms to note the differences in performance. So to go through an analysis would likely be of only academic interest and may not be particularly useful for anything else. If that is all you need, that's fine. All of this does not come cheap, however, and it requires a good amount of engineering and design time to carry it out.

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    FAST FRED Senior Member

    Why not just borrow a stink pot, and large scale and do a FULL SIZED resistance test?

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    RSLOOP Junior Member

    Thank you for your input, Eric. The model is in numerous mesh pieces at this point.
    The hull has changed some what over the years. After being splined 20 years ago, she has now remained pretty much stable.
    We still race the Fantome today.
    It would be of interest to find out what speed the hull was designed for.
    My experience lies with Autocad, but I am looking to take the data into Rhino. I have little knowlage with Rhino so far.
    Hopefully I can smoothen some of the depressions and bumps.
    I am looking to finish the model to look prestine.
  5. alpamis34
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    alpamis34 Senior Member

    After you generate the surface , you can use Navier Stokes equation based programmes such as Fluent.Prior to Fluent you have to determine the conditions and domain of the problem in Gambit.Pre-processor.Then you have t orun it in FLuent.But long procedure man,cauz unless you model it with Free Surface,you will only end up with viscous drag which will not give any wave induced drag.But just to have an idea about whats goin on,you can try and see
  6. nico
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    nico Senior Member

    I think building a nurbs model, and looking at basic hydrostatics could be a good start. You'll have a general ideas of the coefficients (Cp, Lcb,..). And then you might want to predict the resistance of the yacht using the Delft series. (spreadsheet is around).
  7. patrik111
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    patrik111 Junior Member

    Try freeship + Michlet


    I would try Freeship and Michlet combination for what your after, they not to hard to use and will give you some indication. There are some threads here that you could search for more info.

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    RSLOOP Junior Member

    It is late tonight.
    thank you all for your input, I will complete the model in rhino with nurb sufaces and come back.

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    RSLOOP Junior Member

    Well the hull is finished and should be on my members site shortly, then I will take it into Rhino.
    After reworking the first data entry, the hull is pretty fair in the autocad version. The nurb surfaces in Rhino hopefully will fair the hull further.
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