8 Replies Latest reply on Jan 9, 2014 11:48 AM by Jared Conway

    Circular symmetry not working

    Ivan Collins

      I am trying to analyze a 2 degree section of a tank with a non-uniform pressure load.  I can't analyze a 90 degree section because it will be too big, its a faily complex wall section.  I have used the advanced fixture of circular symmetry and it appears to  be neglecting the hoop force to hold the wall and looks to be just pushing the wall over.  I researched this a little bit and it appears that there may be a problem with that fixture within the solidworks software, but this was dated to the 2013 Solidworks.  I have SW 2014 SP0.  Here is a shot of the wall deformed out, note the bottom is fixed.  Any thoughts?

      Wall and hook section.JPG

        • Re: Circular symmetry not working
          Mike Pogue

          Circular symmetry does not add the hoop force. It is for things like spokes that are patterned in a circle. Use regular symmetry or roller slider to add the hoop force.

           

          If you are analizing a revolved section, look at 2d axisymmetric simplification.

          • Re: Circular symmetry not working
            Ivan Collins

            I would use the regular symmetry but like I said it will be too big if I do that.  I guess I'm not seeing how the roller slider will work for this, unless there is a way to add some kind of elasticity to the perpendicular (hoop) component, please explain that one a little more. 

              • Re: Circular symmetry not working
                Jared Conway

                symmetry boundary condition = restraint normal to the direction normal to the face that is cut = roller slider

                 

                so they are all the same thing

                the only thing is that the symmetry boundary condition requires you to use quarter or half symmetry so that it can pattern the results

                when you need to use a slice, you need to manually apply the symmetry boundary condition

                 

                however as noted by Mike, the better selection is to use 2d axisymmetry. then you are solving only on a section instead of having to model a slice.

                 

                i'm not sure i fully understand your concern about the hoop direction. if there is something "circular" about your loading condition, you can't really use any symmetry other than circular symmetry. maybe a picture of your full model, your slice and your BCs (without results) would be helpful here.

                • Re: Circular symmetry not working
                  Mike Pogue

                  I apologize. I skipped over the non-uniform pressure load.  Is this a fluid tank?

                   

                  If it is vertical, then the load should vary only along the axis, not along the circumference. This means that when you apply the pressure, the tank will strain radially--the radius will grow or shrink--but not strain tangentially. If you model the entire tank, this would be enforced by the material--analogous to plane strain. But if you take a pizza slice of the tank, you can enforce this with boundary conditions.

                   

                  If the tank is horizontal, then you do not have load symmetry, and, unless I'm missing something, you will have to analize the entire tank.

                   

                  My understanding of the circular symmetry might be a little weak. It might be set up to handle this. But I'd try it with normal symmetry to see whether you get the expected results.

                    • Re: Circular symmetry not working
                      Jared Conway

                      circular symmetry should only really be used for situations where you have a "patterned" load in the tangential direction. everything else is usually regular symmetry or no symmetry. tank on its side would be no symmetry.

                        • Re: Circular symmetry not working
                          Ivan Collins

                          This is a fluid tank.  have run it before with a fake wall section to simulate the remaining 358 degrees of the tank but I was hoping to use the circular symmetry to eliminate the need for that fake wall section.  The non uniform load goes from 0 psi at the top to 3 something at the bottom.  The walls of the tank are fairly complex and require a small mesh to obtain accurate results.  The tank is very large so it takes a lot of wall sections to make up the entire assembly.  I do not have the computer power to handle that size assembly or even a 90 degree section of the assembly. 

                           

                          I have a few more ideas to try but I figured I check to see if anyone knew why I couldn't get the circular symmetry fixture to work.  Looks like that is not what it was designed for.

                            • Re: Circular symmetry not working
                              Jared Conway

                              i think the word "circular" is throwing you off

                              circular symmetry is specifically for "patterned" loads that are perpendicular to the symmetry plane (best way i can describe it)

                              your problem is standard symmetry, since you can't use a small section with standard symmetry, just apply it manually. it may be worth just proving that method out for yourself with a simpler case starting with a full model, half, quarter and then a slice. again 2d symmetry is the best if you can do it