6 Replies Latest reply on Mar 26, 2018 6:32 AM by Adam Moro

    Mesh error in single part

    Adam Moro

      I'm having issues meshing a single part. Its a tube frame chassis for an FSAE car, for reference it looks like this:

      I get a warning that says the "Mesh information is not current. Model might have been updated or mesh element size/tolerance was modified". I have tried to remesh, but this dialogue box:

      that usually opens when I hit create mesh doesn't open. Instead it immediately begins to create the mesh, which looks like this:

      I have tried remaking the model from scratch, and I got the same error. I tried making a very simple part (a rectangular 1/4" plate of steel) and it meshed just fine, and the dialogue box I mentioned above opened when I hit create mesh. I have no idea what to do, do any of you?

       

      Message was edited by: Adam Moro

        • Re: Mesh error in single part
          Ryan Dark

          Hi Adam,

          The behavior of the mesher as you describe it would indicate that you have built this model with weldments (at least I hope you have) and the mesher is trying to go ahead and apply beam elements to the model you have created.  This is good, it should be doing this, however, if you have merged all the bodies together then the mesher is going to fail in this endeavor.  A beam mesh is looking for many distinct/disjoint bodies each with their own beginning/end (no branching bodies) and uniform(-ish) cross section.  When you merge all bodies into a single unit there is not a ton of branching and the beam mesher doesn't know what to do with that.

           

          So, first thing would be to make sure you have only merged bodies which will actually be one continuous bent tube in the design.  Other bodies that cope together with the greater structure will themselves be merged but you won't merge bodies at coping locations.

            • Re: Mesh error in single part
              Adam Moro

              Hi, thanks for the reply! The model was indeed built with weldments. I'm not 100% sure what you mean by merged bodies. The tubes are all separate weldments, not one continuous tube, however there is overlap between the tubes. As for cross section, the tubes are all 1" OD but have various WT ranging between 0.095" to 0.035". I tried deleting all the trim/extends, since thats worked for me before but I'm not sure if that helped or not. I added my file to my post, if that will help you understand the problem.

                • Re: Mesh error in single part
                  Ryan Dark

                  Adam,

                  From the models you attached I was able to narrow down the beginning of the mesh failure to the feature named "Round tube 1X0.049(772)".  I didn't go beyond that as your feature tree is... quite extensive.  I did look at the construction of your model up to that point to see why the mesh started failing so early in your feature tree.  The failure ended up being a combination of 3 main things:

                  1. In each of your Weldment definitions you have the "Merge arc segment bodies" option disabled.  This is causing a continuous selection of sketch lines/arcs to have a separate body made for each line and arc.  This is leading to a large number of false joints on the Simulation side as the program is interpreting your model to be 10+ separate bodies instead of one long bent Weldment member.  You will want to go top to bottom on your entire feature tree and turn this option back on in most, if not all, the structural member definitions you have made.

                    The result should look like the left body in this screen capture instead of like the right body.
                  2. The "Merge arc segment bodies" option only works if the lines and arcs are tangent.  In the second structural member feature in your feature tree some of the line/arcs are not tangent (at the top-most bend) leading to disjoint bodies and false joints in Simulation.  You will need to also modify your sketches when you find these to ensure tangency and avoid more disjoint bodies.  Below is what the model creates right now with "Merge arc segment bodies" enabled:

                    It should look more like this with joints generating just on the ends of the member.  It won't stay this way because as you generate intersecting structural members a joint will be made at the coping/trimming intersection.  But, for an isolated weldment body this is what you need going into Simulation.
                  3. This square front piece on your model was made with 4 separate Weldment definitions.  All the structural members are the same profile and they all touch each other in one continuous loop.  This should have been made with just one structural member feature.  Additionally, it looks like the top and bottom bodies were made using two separate line selections creating a false joint in the middle of each one.  You would want to make the sketch such that these two line segments were just one continuous line segment to avoid that.



                  By this point you are probably tired of reading so I'll skip ahead to where the beginning of the mesh failure was before (feature "Round tube 1X0.049(772)").  With all these changes implemented the model is now beginning to mesh where previously it was failing:

                   

                  If you continue down this path making these modifications to your model I don't doubt that you would get to the bottom of the feature tree and have a model that fully meshes in Simulation so you can start analyzing it.  That looks like a lot of work.

                   

                  A couple suggestions for when you are modeling similar things in your future that will make this a bit easier:

                  1. Build all of the sketches that control where the placement of structural members are at the top of the feature tree.
                  2. Group like profiles for structural members together.  This means making use of "groups" in the Structural Member feature definition to create multiple selections of disjoint contours.

                  Both of these things should end up making your feature tree simpler and a bit easier to manage when you have to go back and make modifications to the design.

              • Re: Mesh error in single part
                Janko Stellaard

                How did you setup the CAD model, with weldments/surfaces/solids?

                 

                If solids/surfaces: make sure you don't have interfering bodies.

                 

                I would suggest using weldment profiles and thus using beam elements in simulation.