I need help for creating hull surface in rhino

Discussion in 'Software' started by itugemi, May 25, 2015.

  1. itugemi
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    itugemi New Member

    How to create a fair hull surface for this boat. I created a surface using patch command but it is not usefull for engineering .
     

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  2. Dr34m3r
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    Dr34m3r Senior Member

    have u read the basic manual for rhino ? you can then easily create anything u need.
    for this one, use sweep with 2 rail.
     
  3. itugemi
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    itugemi New Member

    I think you dont understand my problem. Thank you for answer but my problem is not that simple. if you look at attached image there is a sharp corner. And this corner causes discontinuity. My question is that how can ı deal with this problem . I need a single and fair hullsurface. Is there any way to do this ?
     
  4. TANSL
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    TANSL Senior Member

    From my point of view, trying to create a single surface is a serious mistake, it can make impossible to create a good model of the hull.
    In this type of hulls can be more convenient to create the surfaces by lofting water lines, instead of using the cross sections.
     
  5. DCockey
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    DCockey Senior Member

    Do you have more information about the shape of the hull near the corner?

    The hull surface can be modeled as two or three surfaces bit either additional information or assumptions will be needed.
     
  6. TANSL
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    TANSL Senior Member

    DCockey, you have cross-sections and longitudinal profile, how much more information you need ?. Maybe you're right, but I do not see it necessary. If anything, to have everything perfect, it would take the shape of the transom.
     
  7. DCockey
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    DCockey Senior Member

    What is the shape of the transition from the section forward of the sharp corner to the section aft of the sharp corner?
     
  8. TANSL
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    TANSL Senior Member

    DCockey, that I can not know and even if I did, it is not easy to describe.
    When I have some time I will show you what you can do with the information we have.
     
  9. TANSL
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    TANSL Senior Member

    This is what you can get with what we have. It can be improved, no doubt but, have to start somewhere.
     

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  10. itugemi
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    itugemi New Member

    First of all thank you for all answer.

    I have enough information about hull. I have linesplan and offset table.I drawn sections using this information. I tried so many way but ı dont get an acceptable result yet. I am keep trying ı hope I can handle this. if I find a way to generate this challenging surface, ı will share with you.
     
  11. TANSL
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    TANSL Senior Member

    As I said in post # 4, use water lines instead of cross sections. Trace water lines by splines, not polylines. The shapes of your boat, as you can see in the file of my previous post, are quite smoothed, they require some improvements, but that's normal. Perhaps it would be enough with some changes in the forward frame. For naval architecture calculations, it is more than enough what you have at the moment.
     
  12. tspeer
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    tspeer Senior Member

    Do you use the RebuildCrvNonUniform command in Rhino to adjust the parameterization of the surfaces? I would think that having an appropriate parameterization would be essential to getting a fair surface on a shape like this. Adjusting the parameterization would also be important when joining two surfaces, especially if one surface joints to only a portion of the edge of another surface.

    As far as I can find in the Rhino documentation, there's nothing similar for surfaces. The RebuildUV command will adjust a surface to have a uniform parameterization, but that may not be a good choice when there's an abrupt change in the surface contour.

    Multisurf has a really powerful method for controlling the parameterization of curves and surface edges. You can define a graph that has any kind of nonlinear variation in the mapping of the independent parameter to the physical space.
     
  13. rwatson
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    rwatson Senior Member

    Check out this Youtube video, and follow the link to the sample files to show some useful hints



    Also, info in the attachment
     

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    Last edited: Jun 4, 2015
  14. TANSL
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    TANSL Senior Member

    The demo video is very nice and produces great results, as it could not be otherwise because hull surfaces are generated by a series of curves in space ready to achieve the desired result. The problem that exists in reality is that these curves can not be known but after creating the surface model. That is, in reality, the designer has no idea how are those curves and therefore can not use them to create the surface.
    If we want to create surfaces based on curves in space, from curves such as cross sections, longitudinal profile, the line of the deck, the knuckles on the hull, we can get several patches to simulate the hull's surface. But these curves to which I refer in this time, can be drawn by the designer quite easily. The curves used in the video are the result of an already known surface and not the reverse.
    Another difficulty is a stern as in the OP's boat, with a point of abrupt change of forms.
    It is very normal to see promotional videos that tell us how well we can do a certain thing, which suggest that other things are also possible, although it is not true at all.
     

  15. Hampus
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    Hampus Junior Member

    Hey!

    I attach a file for you where I created two surfaces. The key thing to both methods below is to first run curves along the hull as close to perpendicular to the sections as possible. using waterlines and buttocks usually doesn't work well here. While method number two benefits in accuracy from having many diagonals, method number one usually gives best results using few.

    The first hull was created using the Surface from network of curves function in Rhino. It gives you a very accurate surface but it creates quite a lot of control points so it's difficult to point edit afterwards. This command has some limitations when it comes to deeper keels, say a full keel traditional sailboat as all the vertical and horizontal curves must intersect but two vertical or two horizontal curves must not. This surface took 4 minutes to create but it would benefit from some editing at the trailing edge of the keel.

    The other surface is much less accurate but control points are few so point editing to perfection will be easy-ish. Surface number two was created using the t-splines plugin for Rhino. I simply appended faces in the areas between the curves.

    There is also a picture of a third hull. This one was created exactly in the same way as your number two hull, using t-splines. I wanted to add a bulb to a previously designed hull. The old hull was designed using just curves, no surfaces whatsoever. When I wanted to add the bulb so creating a surface from the curves and sculpt the bulb into a NACA 0025 foil shape using yet another set of curves as templates seemed the easiest way to fair the bulb into the hull. I spent maybe 4 hours point editing and refining it and it could use yet another hour.
     

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