14 Replies Latest reply on Dec 6, 2012 1:18 PM by Phil Perlich

    Curvature based mesh does not look right - picture included

    Phil Perlich

      I have a curved part that I approximated to be a portion of a sphere. I used a curvature based mesh and the nodes from one componet to the next don't seem to line up. See picture. I used the highlighter tool to show where one part stops an another begins.

      I typically use the standard mesh and this does not look right to me. Input?

       

      Capture.PNG

        • Re: Curvature based mesh does not look right - picture included
          Jared Conway

          Hi Phil, what contact conditions are set between those parts?

           

          Unless you have global > bonded > compatible set, you may be seeing that the components have been meshed with an incompatible mesh.

            • Re: Curvature based mesh does not look right - picture included
              Phil Perlich

              Thanks for the reply.

               

              Bonded contacts, but I manually defined the contact sets. I have triple checked them.

               

              I also thought it looked like an incompatible mesh. What are some things I could try?

                • Re: Curvature based mesh does not look right - picture included
                  Bill McEachern

                  the only thing that would explain that is a small gap between the surfaces - i.e. they are not coincendent. If htey are not coincendent then you can not get a compatible mesh and it would explain the need to have to set a contact set as opposed to using the default.

                    • Re: Curvature based mesh does not look right - picture included
                      Phil Perlich

                      I used the manual sets because the part in the upper right and side and the part in the lower right hand side have a no penetration set with the part you see on the left side (it continues below the other parts in the image).

                       

                      I just veried that there are no gaps in the model.

                        • Re: Curvature based mesh does not look right - picture included
                          Bill McEachern

                          what's the default contact condition? did you use a component contact for any definition on the parts under consideration? How did you conform the no gap conclusion? coincedent Interference check method?

                            • Re: Curvature based mesh does not look right - picture included
                              Phil Perlich

                              Bare with me as I'm pretty new to this.

                               

                              The default was the global component bonded contact. I suppressed that.

                               

                              Then I used contact sets (not component contacts) to define all the interactions between parts. (I selected the faces not components.)

                               

                              I do not know what the Interference check is. What I did was evaluate the radii of the faces that I am working with and verify that the concentric mate was working. Perhaps that is not a good method?

                               

                              If it makes a difference, I tried a standard mesh and it appears to have a compatible mesh across the board.

                                • Re: Curvature based mesh does not look right - picture included
                                  Bill McEachern

                                  set the default global to bonded. There is a hiearchy to the contacts - a contact set override a component contact locally and a component contact overides the global contact. so by usinghte heirarchy you can reduce the thing you need to specify to get the connectivity the way you want. Also inthe glabal you can specify compatible or incompatible as a default. Additionally in the oiptions you can specify that if the compatible fails on certain components then remesh those with incompatible. So if most of you contacts are to be bonded you set the global to bonded compatible and then when you pick specific contact sets they will override the global for those contacts selected.

                                   

                                  Under the evaluate tab use the interfernce check tool (assuming you are in an assembly and not a multibody part file) ans set the approriate option in the lower part to get coincedent to show as interference this will high light all the surfaces that are coincedent to modeller tolerance - the measure tool needs to be set at eight decimal places to tell you the same thing. You can also set options to treat subassemblies as parts and to check the individual bodies of multi body parts if they exist in your assembly document.

                                   

                                  Sometime the standard mesher is more robust than the curvature mesher and sometimes it is the other way round. It doesn't matter which one you use as long as you like the mesh it provides. if the elements sizes are similar across parts it doesn't really matter whether the mesh in compatible or incompatible. It hte coincedent surfaces are the same size it matters even less as the extents of the bonding are limited by the geometry. The advanced bonding (mortar bonding) is tolerant of much larger variation of element size on parts with imprints or where the conicedent faces are vary different in size.

                                   

                                  Sorry about the vast array of typos...

                                    • Re: Curvature based mesh does not look right - picture included
                                      Phil Perlich

                                      Thanks so much for the help. I'm doing my best to learn how to properly do simulations. I have not taken the class, but I have a couple of books I have been going through. So far this forum has been a huge help for me.

                                       

                                      Can you elaborate a little more on when an incompatible mesh is acceptable? I have been assuming that you would always want the corner nodes together.

                                        • Re: Curvature based mesh does not look right - picture included
                                          Bill McEachern

                                          run them both and see if there is any difference. In this case it probably doesn't matter. any analysis is better than no analysis but that does not mean any analysis is reflective of reality.

                                            • Re: Curvature based mesh does not look right - picture included
                                              Phil Perlich

                                              I understand that its just a simulation and not reality. I was just curious as to how solidworks handles an incompatible mesh.

                                               

                                              There must be some difference or it would even be an option. I guess now that i think about it I don't even know what an incompatible mesh is in the mathematical sense.

                                               

                                              What is really bothersome is the fact that I increased the thickness of some of the parts and now I mesh failure on the standard mesh too. I have tried all kinds of mesh controls and settings and cannot get it to mesh.

                                                • Re: Curvature based mesh does not look right - picture included
                                                  Bill McEachern

                                                  Hi Phil,

                                                  I cant spend much more time on this. With a bonded condition you need to connect the meshes whether they are identical or not. If they are idnetical you can merge the nodes to connect things. In SWX sim that doesn't exactly happen anymore but its close - the corresponding nodes are connected directly with things that allow the forces to be computed. In an incompatible mesh - ie the nodes on both parts are not in exactly the same places - you need to have some sort of connection strategy - the simple bonding connects the nearest nodes with rigid bar elements - when the elements are quite different in size the connection location at the extremties can be different than the extents of the geomertic enties because the connections have to be done at the nodes. This can lead to a different stiffness either more or less stiff depending on which nodes are connect to which conecting the two parts. The advanced bonding, also known as mortar bonding is a solver based more sophisticated connection that provide a much better approximation of the stiffness as compared to the underlying geometry.

                                                  Compatible is nice if you can get it. If not go with the advanced bonding (default I think) it just takes longer to put it togetherin the solver. If in doubt about the effects run them both and see what the difference is if any. If you have a problem size issue you can use the simplified but then you need to try and use a compatible mesh or at the very least manage the mesh sizes on the components at hand - keep them close to  the same size so any introduced stiffness errors are small. Remember everything is an approximation.

                                                  Good luck.

                                                  On your new failure to mesh it sounds like a geomery problem in your model.......figuring that out can be tricky good luck. Any lofts or spline based features in your model? If so look at those.

                              • Re: Curvature based mesh does not look right - picture included
                                Nathan Obermiller

                                Sorry to dig up a dead thread but have you tried doing a surface split.  If your geometry is coincident but the surface continues beyond the point of contact you should split the surface so you define an interfacing edge.  Use Insert>Curve>Split Line.  This will also allow you to create a better mesh control if solidworks does not automatically identify the contact edge.