6 Replies Latest reply on May 20, 2016 6:06 AM by James Riddell

    Advice on setting up simulation (fixtures)

    Andy Zhou

      Hi I'm in need of some help setting up a simulation of a load test of a grate (kind of a manhole cover).

       

      The model name that needs to be tested is part named the 'heel guard'. This grate is simply supported along the 2 edges to simulate that it's sitting on a concrete surface (no clamping or sort).

       

      A load of 210kN is applied on the grate via metal and timber assembly block.

       

      To simulate the deflection of the grate resulting from the load, what type and where should the fixtures be defined to run the study?

       

      I've also tried split lines to eliminate all other components as I'm only interested in the heel guard it self.

       

      Thank you in advance.

       

        • Re: Advice on setting up simulation (fixtures)
          Keith Frankie

          Quarter the model to take advantage of symmetry.  The symmetric fixtures will partially restrain the heel guard, which is handy.

           

          Start with a bonded contact for everything to make sure you can mesh and run the model.  The mesh will have to be pretty fine to mesh that detailed geometry.

           

          I believe a virtual wall could stand in for the contacts along the edge. It should be less computationally intensive than a proper no penetration contact.

          • Re: Advice on setting up simulation (fixtures)
            James Riddell

            My personal preference is to restrain something like this as close to reality as possible.  I would use roller-slider on the underside (only where the grate is supported).  I would then restrain a couple orthogonal edges along one one side (one for X and one for Z).  I trust you have already split the surface on top and applied either a pressure or total force load.  Don't forget to add gravity.

             

            This one is pretty simple and straightforward.

            • Re: Advice on setting up simulation (fixtures)
              Andy Zhou

              Thank you for your input guys, I've got it started. However I'm getting results with excessive stress/displacements and I can't figure out why. I've played with placements of virtual walls around the restraining faces, restraining few of the edges to for x and z directions.

               

                • Re: Advice on setting up simulation (fixtures)
                  Keith Frankie

                  That result actually looks pretty cool!

                   

                  I think the model is just weak in that direction.  Those little bars are much smaller than the I-beams.

                   

                  However: this study probably just isn't realistic enough.  For one the loading condition is spreading equal loads onto each of the mid-sized beams.  In reality, with your wood pallet to spread the load, all those would move together.  Adding in the wood pallet wouldn't up the computational requirements that much.

                   

                  The biggest hindrance to realism, though, is probably the lack of membrane stresses due to the nonlinear behavior of the structure.  Try this as a nonlinear problem with no-penetration constraints in place of the virtual walls.  (Well, first try it as nonlinear with fixed boundaries, then with sliding boundaries, then with no-pen).

                   

                  Hopefully your static study is solving relatively quickly.... if not see if you can get the mesh coarser before you step up to nonlinear.

                  • Re: Advice on setting up simulation (fixtures)
                    James Riddell

                    Define 'excessive', what are you getting for values?  You may be over constraining and making the system artificially stiff.  Do your resultant values make sense?