8 Replies Latest reply on Sep 15, 2014 2:59 PM by Shaun Densberger

    Solid Body VS. Shells showing different results?

    Patrick McMahon

      Hello,

       

      I have set up two simulation static studies. I've keep the mesh, forces, and fixtures the same. After running both studies they are giving me significantly different results. From what I understand this should be a good assembly to use shells on since it has large parts with comparatively thin sections/walls. I don't know which results I should trust and If I have set them both us correctly. Anyone feel like reviewing my work?

       

      Thanks

      Pat

       

      Edit: It won't allow me to attach the model and results. File is too large. I have attached pictures of the mesh and results. May make it difficult to check things so this is more of a theoretical discussion at this point.

        • Re: Solid Body VS. Shells showing different results?
          Jerry Steiger

          Pat,

           

          I would wait until you hear from some of the guys who are much more familiar with this type of structure and SolidWorks Simulation, but I would put more faith in the shell model. With the same size mesh for solids, you only have one element through the thickness of your parts. That isn't enough to get a realistic result. You need at least two, preferably three or more.

           

          Jerry S.

          • Re: Solid Body VS. Shells showing different results?
            Shaun Densberger

            Couple questions, Patrick:

            1. Did both shell and solid element models active converged stress results?
            2. Can you post the displacement plots for both shell and solid?
            3. Can you post the strain energy plots for both?
            4. Can you post a plot of the jacobian for each mesh type?
            • Re: Solid Body VS. Shells showing different results?
              Jared Conway

              this comes up once every 6 months or so, you may want to check the forum for previous discussions

               

              you've posted stress and FOS results, have you looked at displacements?

               

              before you go trying to troubleshoot a software bug or your model, i'd suggest building some really simple beam models with solids and shells to give yourself the warm and fuzzy about shells vs solids being equivalent when setup the same. from there you can start addressing some of the questions that shaun suggested.

               

              i would guess the setups aren't the same or your evaluation method is not valid, ie use displacement to compare, not stress

              • Re: Solid Body VS. Shells showing different results?
                Patrick McMahon

                Hey Guys,

                 

                Thanks for all the responses.

                 

                Jerry - I had originally created the shell study because I had heard the rule that you need minimum of 2 elements across the thickness to get accurate results. I feel like shells is the right way to handle this study but looking at the results it seems like the shells study isn't producing meaningful data that I would expect. Hopefully I can get it fixed up because I really need to learn more about dealing with shells.

                 

                Shaun - I'm sorry but I don't understand your first questions. I can do some basics in simulation but unfortunately I don't work with FEA often enough to progress out of the rookie status. Please see the attached pictures you requested. I did not even know you could do mesh quality plots. Do you know of a good resource that would give me more information on using and interpreting them?

                 

                Jared - I will go back and do a more careful search to see if I can find any of the older relevant discussions. I have confidence that shells and solids will produce the same results if I can set them up with in the parameters of their capability. It's more a lack of confidence in my portion of setting them up correctly. We don't have anyone I would consider an expert in simulation in my office so I'm hoping to get more insight from the folks here.

                 

                Appreciate all the help guys. See my notes on the screen shots below.

                Pat

                 

                 

                I had a follow up question. I did my contact sets for the shells in groups. There are three tubes with a bonded contact to the shell surface above it. Is this an acceptable method?

                Shell - Contact Sets.jpg

                Shells - Displacement

                Shell - Displacement.jpg

                Shells - Jacobian

                Shell - Jacobian.jpg

                Shells - Strain

                Shell - Strain.jpg

                Solid - Displacement

                Solid - Displacement.jpg

                Solid - Jacobian

                Solid - Jacobian.jpg

                Solid - Strain

                Solid - Strain.jpg