6 Replies Latest reply on Aug 16, 2018 10:32 PM by Ben Richardson

    Simulation express - Less load, more displacement??

    Ben Richardson

      First up, I rarely use simulation so Im sure its me doing some thing wrong here.

      I need to test some drain grates im designing for a client to make sure they are going to pass load tests. I have just noticed today after changing loads for different classes that im getting the unexpected result of more displacement with a smaller load?? Ive attached the grate, when I apply a load of 80kN it gets a maximum displacement of 4.8mm, reduce that down to 10kN and it gives me 6mm?? Obviously not what I was expecting. All I have changed is the load amount, didnt remesh or anything. Visually the stresses look different, less for the smaller load but gives a higher displacement?

        • Re: Simulation express - Less load, more displacement??
          Bence Rivasz

          Hi Ben,

           

          Your data shows me that your load is 3x10000N.  Are you sure that it has the same setting with both load and not once Total and once Per item?

           

          I also cant see any mesh control or refinement. The default settings are very rough and in most case do not make an acceptable meshing.

           

          There is one more thing that i have noticed:  If you do not define any contact between the bars and the other parts the program take automatically as a bonded contact, so as one part. It can mislead the simulation (it makes a huge extra support) when they are not welded together in real life. When they are not, as a tip: Make sense to simply remove them and save time with the calculation (also take symmetry) and use them as an extra safety factor. If they are just hanging there they do not make any substantial support.

           

          Unbenannt.JPG

            • Re: Simulation express - Less load, more displacement??
              Ben Richardson

              Bence, thanks for the tips! Ive supressed the cutouts so its a solid join, how can I refine the mesh? Coarse or fine seems to be the only option? Im not sure what I would need to control anyway, I dont normally use this. Setting for the load should of been total as you picked up!

               

              Simulation is still giving me higher displacement for the lower force. Im only using simulationxpress BTW so maybe those mesh settings are not available to me?

               

              Sergio, it has been a bit glitchy for me, hiding features when I make changes to the part for some reason.

                • Re: Simulation express - Less load, more displacement??
                  Mehdi Rezaei

                  Hi Ben,

                  I second everything others mentioned. Your model shows you need some bonding or contact settings, and also it seems having many small details which need to be simplified. One method to simplify is using symmetry for model and loading. However, none of these are available for SIMxpress. If you have to use SIMxpress, then you have to do it with some engineering assumptions and bear in mind that the result will be just a estimation of what could happen in reality.

                    • Re: Simulation express - Less load, more displacement??
                      Ben Richardson

                      Mehdi, thanks, ive fixed the joints so they are simpler to mesh, but its still giving me unexpected results for displacement. I know simulationxpress is very limited but since its not something I use often I cant justify the cost, and im sure my client wont appreciate an extra 5k on their invoice. Ill just have to accept its not accurate and at best its going to give me a rough idea.

                       

                      Considering how glitchy it has been and how limited it is, its not a great demo of the paid product.

                • Re: Simulation express - Less load, more displacement??
                  Sergio Monti

                  Hi Ben,

                  I also use Simulation Express sometimes, that is a simplified version of SW Simulation - it can run on single part only, with simplified restraint-cases (fixtures).

                  This package is not very accurate. It happened once to me to run the simulation twice on the same part and got different results! It could be the mesh setting (set to auto by default) automatically changes mesh size.

                  • Re: Simulation express - Less load, more displacement??
                    Mohamed El Orche

                    Hi Ben,

                    Let me add that Simulation Xpress has only standard mesh and the mesh size is Global across the entire model.
                    Also, you can't refine the mesh in areas of interest, unfortunately.