6 Replies Latest reply on Jun 27, 2014 1:32 PM by V. S

    Simulation not Observing Fixtures (Fixed Geometry/Boundary Conditions)

    V. S

      Hi all,

       

      I'm trying to conduct a frequency analysis on a larger assembly and noticed that faces I had applied fixtures to were not working. I had applied fixed geometries to these faces but the simulation results showed that they would translate and rotate. The results were the same as if I didn't have any fixtures. I had 6 rigid body modes with frequencies close to 0Hz and the rest were modes as if the model was not constrained at all.

       

      I have attached the solidworks part which seems to be the source of the problem. It is a sheet metal part. In the assembly it was in, I tried both fixed geometry and immovable fixtures but neither worked. I am a beginner so I'm wondering if there is some nuance that I am not privy to. Any help would be much appreciated. Thanks.

        • Re: Simulation not Observing Fixtures (Fixed Geometry/Boundary Conditions)
          V. S

          I suppose I should also add that in the assembly, there are no interferences and my mates and bonds are coincident. I don't think that this should have any effect as even in the part file (attached above) the simulation doesn't run as expected.

            • Re: Simulation not Observing Fixtures (Fixed Geometry/Boundary Conditions)
              Jerry Steiger

              V.S.

               

              I didn't look at your file, but from your text, I suspect that you have not applied the proper boundary conditions in the analysis. The mates in SolidWorks don't translate automatically into boundary conditions in SolidWorks Simulation. You have to set up the contacts in Simulation.

               

              Jerry S.

                • Re: Simulation not Observing Fixtures (Fixed Geometry/Boundary Conditions)
                  V. S

                  Hi Jerry,

                   

                  Thanks for the reply. I imagine that what you're saying applies to an assembly? However, while it is something I need to look into, the file I have attached above is just one part of the assembly. In my effort to track down what was wrong, I tried the simulation on just this one part and kept the fixtures in the same places I have them in the main assembly. However, when I view the results (for the part) I still get the same issues. I have rigid body modes and the other modes don't seem to follow the fixtures I have set on certain faces.

                   

                  I will attach my assembly on Monday as well but because of the failure with part simulation, it leads me to believe that it is not at the assembly level.

                   

                  V.S.

              • Re: Simulation not Observing Fixtures (Fixed Geometry/Boundary Conditions)
                V. S

                So after a little messing around, it seems like this has to do with the fact that this is a shell mesh and not a solid mesh and that it is doing a mid surface mesh. I'm still not sure what's going on with this part file in particular but this seems like a relevant point to make.

                • Re: Simulation not Observing Fixtures (Fixed Geometry/Boundary Conditions)
                  V. S

                  Just to wrap this up, using shells was very useful in terms of saving simulation time. The issue was not with the shell and solid bonding interface although being cognizent of this is useful when it is not so clear cut (can use contact sets). My main issue was with a bad mate. So as Jared has suggested, start small and then add on. Also, make sure you don't have small gaps as the countless other forum posts suggest. A good indicator to check on bonding, etc. is if during simulation run time you see, 'More accurate bonding option was chosen'. Also as I mentioned, I had 6 ~0Hz modes which you can easily determine as rigid body modes. In my case I had restraints but because of a mad mate, they were not being observed and I got these modes. Another good test!