4 Replies Latest reply on May 30, 2014 2:43 PM by Andrew Lowe

    Simplifying Surface Geometry

    Emily Dinsdale

      Hi Everyone

       

      I am working on the model for a car which I want to analyze the flow in ANSYS 14.5. When I import the geometry into the meshing aspect of this software the program won't mesh and after technical discussions with ANSYS support they came back with the following message.

       

      "Your geometry is a very high-order NURBS surface and this is the reason that it is failing on meshing, simply because it is running out of memory due to the high complexity of the underlying topology. The geometry is not complex, but the way it has been constructed is very complex"

       

      My questions is there a way to decrease the order of the NURBS number on a surface? I am happy to split it up or whatever. I just need to decrease the complexity so that I can analyze the body work.

       

      Thank you for any help

        • Re: Simplifying Surface Geometry
          Anna Wood

          Post your SolidWorks file you are trying to bring into ANSYS for us to have a look.  Use the Advanced Editor link in the upper right of the dialog box to post your file.

           

          Cheers,

           

          Anna

            • Re: Simplifying Surface Geometry
              Emily Dinsdale

              Hi Anna

               

              I have attached the geometry file. Thank you in advance for looking at it. The biggest problem with NURBS surfaces is on the side pods as far as I can tell.

               

              Thanks again

               

              Emily

                • Re: Simplifying Surface Geometry
                  Chris Dordoni

                  I don't know ANSYS, but based on what I see in your file, I would say the issue might be that you have very few spline points in the curves. If you display the curvature combs, you can see there are very sharp transitional areas.

                   

                  You used the spline handles exclusively to shape the curves, which are causing higher "stress" areas. There is no way in SolidWorks to change the degree of curvature by entering a value for the curve, although some add-in surfacing apps might allow you to do this.

                   

                  So check with the ANSYS people first, and ask them if adding points to the spline might solve the issue. If they agree, this will take a little bit of work to preserve the overall shape you already have by adding points and moving them to maintain the shape without using the spline handles as much.

              • Re: Simplifying Surface Geometry
                Andrew Lowe

                Unfortunely, SolidWorks offers no control over the number of control points (the underlying math of the surfaces) that define NURBS geometry. SolidWorks also creates very "heavy" geometry vs other more decicated surfacing packages such as Rhino and Alias (which both offer control over the number of control points).

                 

                The only option to modify the geometry would be to re-model the body in software the offers control over the math of a surface.

                 

                The attached image of Rhino screenshots shows the problem. The top screenshot shows the controls points (white dots) of one of the car body's surfaces as generted by SolidWorks. The below screenshot show the same surface rebuilt in Rhino with a much simplier underlying structure for the same shape.

                control_points.png