6 Replies Latest reply on Jul 27, 2012 5:36 AM by Kevin De Smet

    Flow simulations with surfaces

    Carlos Garcia

      Hello,

      I would like to do a simulation with flow simulation in a model made with surfaces, but the software says that there has to be at least one component for the analysis.

      Is it not possible to do an analysis with a surfaces model, just with a solid model?

       

      Specifically I have a car modeled with surfaces and i want to do an aerodynamic analysis, drag, down force etc...

      How could i do this?

       

      Thanks in advance!

      I am just learning flow simulation.

        • Re: Flow simulations with surfaces
          Chris Michalski

          Add thickness to your surfaces.  As long as you don't need flow on both sides of the surfaces, if you give them thickness it can solve the flow conditions.

            • Re: Flow simulations with surfaces
              Carlos Garcia

              Thanks, I tried it but i cant give thickness, i get an error... Maybe giving thinckness at the beggining, so surface by surface while you are building them.... but once all them are made i cant..

              Anyway it should be easier and faster to solve a problem with surfaces instead of solids, due that the mesh would be shells and not solid elements.

                • Re: Flow simulations with surfaces
                  Chris Michalski

                  The problem is that flow requires thickness to separate gases.  If you try to make 2 blocks touch only along an edge >< it sees zero thickness at the interface and gas passes right through.  With a surface of zero thickness the gas passes right through also.

                   

                  How to get your surfaces to function right with thickness.... someone else would have to pop in, I don't work in surfaces, everything we do is machined from billet. 

                   

                  First thing, if possible, post your models here (reply and click advanced editor in the upper right) would make it easier for others to attempt to help. 

                  • Re: Flow simulations with surfaces
                    Bill McEachern

                    You don't understand how the program works. Chris is essentially right but it would be more informative to say, since the program computes the flow volume, it can't do a bolean operation on something with zero thickness to establish the solid/fluid interface. The program doesn't care how thick it is but it has to have a thickness. If your set of surfaces are constructed with rigor then they should sew up into a solid body and enclose a volume - I get why that wouldn't be the case but at some point in your design process you will have to deal with it one way or the other. Use the roll back bar and put the thicken surfaces commands as you go before you stitch them up. If they will not thicken you have other issues. You could also try extruding a block and then cut the block with the surfaces - might require quite a number of trim and extend's to make it work - that may be even more work to deal with the "holes" but I would contend it can be done one way or the other. If you know ahead of time it should be pretty easy to avoid this issue.

                      • Re: Flow simulations with surfaces
                        Carlos Garcia

                        Thank you to both Chris and Bill, I understand now why flow simulation does not work with surfaces. I tried to give thickness using the back bar, in some i got succes but then in others I got issues in the next surfaces since they are conected and use their edges. So I have to correct every surface what is really a pain... I will try to extrude a block and cut it with my surfaces but suspect that it will be also a pain. Maybe it's even easier to remake my surfaces from the beggining given thickness surface by surface. I will try it too if I fail with the block...

                        Im not an expert in surfaces netiher but this is being a good exerciese to learn, and thanks to you both too!

                          • Re: Flow simulations with surfaces
                            Kevin De Smet

                            If I understand you correctly, you don't want to do that. Instead of giving a thickness surface by surface, you'll want to make a quilt of surfaces that simply join up together (using Surface > Knit feature) think of this step of the process like the outside skin of your model. Then at the end you can thicken it using Surface > Thicken.