A question about setting up Rhino model for GHS

Discussion in 'Software' started by JOANNAZHANG, Jun 27, 2014.

  1. JOANNAZHANG
    Joined: Nov 2013
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    JOANNAZHANG Junior Member

    I made a hull model using Rhino and tried to get GHS data from it. The problem I have is that I can not join all surfaces as one, so I had to add a few components(each surface as a component) to the hull part. But it doesn't look good , since stations created for different components are not aligned. so,
    Q1: is it a must to make the hull as one piece? if not, what can I do?
    Q2: if yes, any tips on how to make surfaces in Rhino that they can be joined as one

    I am a beginner in using GHS. Your help is greatly appreciated!
     
  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    In general it is impossible to make a single surface for the whole boat, even in very simple hulls. What is important is that the hull is closed and surfaces (called patches) not intersect each other.
     
  3. JOANNAZHANG
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    JOANNAZHANG Junior Member

    Thanks for your reply. The problem is the stations created for the patch of side shell and those for the patch of bottom are not aligned. How can I fix it if I can not join these two patches. Any suggestion?
     
  4. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I'm no expert on Rhino but there may be a command that allows you to join, link, two points belonging to different surfaces. Another issue to consider is that the direction of the tangent (or normal) to the surface on their edges match
     
  5. JOANNAZHANG
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    JOANNAZHANG Junior Member

    Thanks alot. You are very helpful.
     
  6. ABoatGuy
    Joined: Aug 2004
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    ABoatGuy Member

    To rid yourself of half the problems, only model half the hull (assuming you have a boat that is symmetric about the center plane).

    Unless you have a really unusual hull, it generally is fairly easy in Rhino to join all the surfaces if you have edges that are coincident with the adjacent edges. The edges of each surface need to match the adjacent surface. Then use the "Join" command (as opposed to a boolean union). If the surfaces don't join, you have a model problem you need to sort out. You will get a much cleaner GF file with joined surfaces.

    If you can get one surface to join the next but not a third, you can cheat Rhino a bit and save yourself some work by trying to join them in a different order. Sometimes this will work if you have one bad edge and it will not affect the GF file. Of course you didn't fix the model so if you need it completely closed for another reason you will need to fix it properly.

    You are probably using curves to define the surfaces. If you have adjacent surface edges that are same length try using the same curve (or the adjoining surface edge) to define the next adjacent surface.

    Once they are joined open the "AttachGHS" command, click on "hull items"/"add part", and then choose the joined half hull model or the next part you want to add to your hull. When the dialog opens click on "centerline" box. Your hull will be mirrored and you will be good to go.

    My guess is you have a model problem that is prevent the join command from working. The surface edges need to coincide.

    One other note. If you have several parts making up a component, like the hull, the GHS sections in each part don't need to match, in fact they rarely do, particularly if you are allowing "AttachGHS" to optimize the number of sections. There will be more sections where there is a lot of curvature and very few where you have a simple shape like a cube. GHS and AutoHydro will sort out the volumes of the parts and add them together. You don't have to worry about that part.

    And one more note. Before you join the surfaces make sure all the "normals" of the surfaces face outward. There is a command to switch them if they don't. You will get funky numbers if you miss this step.

    Hope that helps without being too confusing.
     

  7. JOANNAZHANG
    Joined: Nov 2013
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    JOANNAZHANG Junior Member

    Thanks for your time and efforts to help me fix the problem.You are right that generally I can join all surfaces for half boat into one.But this time the boat was lengthened at stern based on the original Rhino model , which caused some surfaces had to be remade and some patches added to hull, and it gave me difficult time in joining them.
    Another Rhino expert helped me remake some of the surfaces, and now they can be all joined as one. The GHS data is fine too.
    Thanks again for your help!
     
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