Trimming Surfaces in Maxsurf

Discussion in 'Software' started by Dick Sarre, Mar 25, 2021.

  1. Dick Sarre
    Joined: Mar 2021
    Posts: 3
    Likes: 0, Points: 1
    Location: France

    Dick Sarre New Member

    Hello
    When trimming surfaces in Maxsurf Modeler (for example a skeg keel to a hull) two intersection edge lines are created, one for the hull and one for the skeg keel. The section lines of the hull/skeg keel at the intersection either overlap or are discontinuous. This is only visible when zooming right in to the trimmed intersection and the overlaps or 'open' sections are only in the order of a few mm. When looking at the sectional area curve, all is OK with no discontinuities. Is this normal? If not, what might be causing the problem? All surface penetrations are good and surfaces trim correctly, with the exception of the very small overlaps/discontinuities.
    I need to use the model in Hydromax for stability calculations, so want to be sure that the model will be analysed correctly.
    Thanks in advance for any assistance/clarification that anybody can offer.
     
  2. jehardiman
    Joined: Aug 2004
    Posts: 2,981
    Likes: 504, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    It has to do with the way that the surfaces are trimmed. Maxsurf inserts a new boundary edge for each surface based upon the numerical model of the respective surface. Therefore the two boundary edges are not the same. What works is to choose/insert a boundary edge that is the same for both surfaces. Also important is to make sure that the direction of the new trimmed surface is the proper orientation.

    Read here about Maxsurf NURBS and trimming.
    Why We Use NURBS for Surface Modeling http://www.kastenmarine.com/why_NURBS.htm#:~:text=Maxsurf%20is%20a%20Direct%20(free,envelope%20for%20fairing%20and%20analysis.&text=Working%20with%20a%203D%20NURBS,a%202D%20or%203D%20spline.
     
  3. DCockey
    Joined: Oct 2009
    Posts: 4,933
    Likes: 457, Points: 83, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Comment based on experience in Rhino. I have no experience with Maxsurf.

    In Rhino if you zoom for high magnification of a surface edge, partcularly a trimmed edge, in a shaded or "rendered" view there can be apparent gaps of the shaded surface along the edge of the surface. This is due to the coarseness of the display mesh. Wireframe display and will be accurate The underlying geometry used for calculations will be more accurate. In Rhino the user can adjust settings to refine the display mesh. I do not know if anything similar occurs in Maxsurf.
     
  4. Dick Sarre
    Joined: Mar 2021
    Posts: 3
    Likes: 0, Points: 1
    Location: France

    Dick Sarre New Member

    Thanks for your reply. How would you go about choosing or inserting a boundary edge and deleting the existing two boundary edges? I suppose, I just need to be sure that Maxsurf Stability will produce the correct results in spite of this anomaly.
     
  5. jehardiman
    Joined: Aug 2004
    Posts: 2,981
    Likes: 504, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    That can also be a rendering issue from the mathematical surface to the displayed mesh. However, when actually generating the physical mesh polygons from NURBS surfaces, it is important to make sure all the edge nodes are co-incident.
    Polygonal and NURBS Modeling: What’s The Difference? https://conceptartempire.com/polygonal-vs-nurbs/
     
  6. jehardiman
    Joined: Aug 2004
    Posts: 2,981
    Likes: 504, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    I believe that Maxsurf has a tolerance setting that will gather in "close" nodes and make them coincident. But it is up to you to assure that you set up the surface to generate the proper number of mesh nodes along the surface intersection to get them within this set tolerance.
     
  7. TANSL
    Joined: Sep 2011
    Posts: 6,562
    Likes: 412, Points: 93, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Maxsurf automatically fills the gaps between surfaces. If you want, we can verify your results with an application of mine that also makes those calculations. Send me the model of your boat and we will compare the results.
     
    jehardiman likes this.
  8. jehardiman
    Joined: Aug 2004
    Posts: 2,981
    Likes: 504, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Since we used Maxsurf to generate meshes to feed other programs <WAMIT and custom codes>, I am unsure how good the handoff to Hydromax is. Making sure the polygons stitched correctly the first time was a huge time saver.
     

  9. Alexanov
    Joined: Feb 2003
    Posts: 222
    Likes: 28, Points: 38, Legacy Rep: 10
    Location: Norway Sola

    Alexanov Senior Member

    Intersections line of two surfaces presented by lines on each surface. Intersection lines can’t be exactly same. It depends from intersection precision.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.