7 Replies Latest reply on Sep 1, 2009 9:27 AM by Rich Bayless

    Zero Fluid Volume error

    Chris Michalski

      I have an assembly of parts built up to run a simulation.  I perform a geometry check -> boolean error, check geometry

       

      so, I create a part to encompass the entire computational domain

       

      systematically create a cavity from each component

       

      find several failures (i.e. tube tangent to a plate -> line contact, etc)

       

      remove all failures - generate 1 solid part with 18 cavities to comprise all 188 parts - this is essentially how Flow generates the fluid volume from everyone I've talked to

       

      Problem: I can generate the equivalent of the fluid volume, but geometry check says "Boolean operation failed.  Check model geometry"

       

      Any Suggestions?!?!?  

       

      This is all in SW2009 x64 SP3 in XP x64

        • Re: Zero Fluid Volume error
          Rich Bayless

          Hi Chris,

           

          When you tell FS to 'create solid body assembly' and 'create fluid body assembly' under Check Geometry, the bodies are solid or empty, and fluid volume is zero, yes?

           

          I had one case where this happened, and I found the problem area in the original solidworks assembly by using 'Create Lids'.  Go around your assembly and keep trying to create lids.  At some point, it will find an opening where it can make a lid, except it's not a valid lid type of spot.

           

          In our case, it looked like a perfectly valid assembly in Solidworks, except Flow Sim couldn't figure it out, so we changed our assembly approach.

           

          Cheers,  Rich.

            • Re: Zero Fluid Volume error
              Chris Michalski

              Rich -

                   since I mostly work in 07 still I'm not very versed in using the "make lids" function - 09 won't let you create lids in places that aren't realistic? I had a cap on a part and it let me make a lid on the cap before so I just kept using the old way of defining my own lids.  It's a pretty complicated system I'm looking to simulate (essentially part of a CVD coating system) so there are numerous convoluted flow paths and I don't want to accidentally block passages by putting in extra lids.  I have the VAR working on finding the problem but it seems one of them has a similar issue but the other is making progress (how that is I don't know)

               

              I haven't been using the create solid body or create fluid body.  Is there a good justification for having it do this?  How can you use the result to eliminate problems like this?  I've just been trying to get it to calculate a non-zero fluid volume.

               

              One interesting thing this morning, I opened the original version in 2007 (with some of the extra fasteners and such still in place that I had removed in 2009 to simplify the simulation) and tried to setup the simulation there and it must have found a fluid volume because it has let me add boundary flow conditions.

               

              Why does it always seem I manage to find the bugs?  Why didn't anyone tell me 2009 x64 SP3 was a still BETA release? that's what it feels like somedays.

               

               

              Thanks for the advice, any input on how to utilize the make solid or fluid bodies to locate problems would be appreciated.

                • Re: Zero Fluid Volume error
                  Rich Bayless

                  Hi Chris,

                   

                  Your comment "09 won't let you create lids in places that aren't realistic?" hits the nail on the head.  If there is a spot in your assembly that 'isn't realistic' (at least flow sim doesn't think it's realistic), then the create lid tool may try to make a lid there.  In other words, it will highlight an issue with your model.  It could be a perfectly realistic spot in terms of a 3d body, but there may be something that flow sim can't figure out.  the create lids option can be a useful tool in finding issues.

                   

                  the create fluid body is an option under check geometry and it will create a new part that is just the flow area of your model.  If it can create a body, you can inspect it to look for funny areas.  it could also be used to export the fluid side of a model to say STL format.

                   

                  Cheers,  Rich.

                    • Re: Zero Fluid Volume error
                      Chris Michalski

                      Rich -

                           but when 2009 generates a solid block for the solid model assembly and nothing for the fluid body it means there's an issue somewhere in there.  All I know to do is start at the inlet and try to make a lid a slight distance down the flow path, then continue adding lids to increase the fluid volume (by adding separate distinct volumes) until it won't let me add the next stage because there is an unexpected leak somewhere between the last good lid and the one I can't make.

                           2007 only ran into a problem when I told it to generate the fluid body assembly and it got somewhere near 130 bodies and then crashed.  I'm not sure if that means there were 130 separate fluid bodies or it had added the 130th of the total 188 parts to the assembly it was using to define the fluid body.

                       

                      I guess I'll just have a LID party this afternoon and see what I can find.  Thanks again.

                       

                      Chris

                        • Re: Zero Fluid Volume error
                          Rich Bayless

                          Hello Chris,

                           

                          how did your lid party go?

                           

                          Cheers,  Rich.

                            • Re: Zero Fluid Volume error
                              Chris Michalski
                              Actually I didn't need a lid party, I got to thinking about things and tried it in 2007 with all of the geometry instead of simplifying anything.  2007 gave a slightly different wording in the error message and how it denoted the "tool bodies".  I had several parts that were generated by "cavity" to mimic insulation for the simulation.  I edited those parts to add a gap between the complex 3d faces (make a 3d sketch and sweep cut a slightly larger diameter path) and that eliminated the problem.  I think there were just a whole bunch of coincident faces/lines/points that it didn't like.  It only took 3 hours to mesh and 31hrs to run then.
                                • Re: Zero Fluid Volume error
                                  Rich Bayless

                                  Hello Chris,

                                   

                                  Glad to hear you found the geometry problem.  That makes two of us that had the same kind of problem.

                                   

                                  I went back to the solidworks sales literature and it says:

                                   

                                  "SolidWorks Flow Simulation eliminates the need to modify your design for a different computational fluid dynamics (CFD) application saving considerable time and cost."  Here's the link:  http://www.solidworks.com/sw/products/cfd-flow-analysis-software.htm

                                   

                                  I think it should say 'almost eliminates', considering how many hours were wasted trying to find the problem geometry, which then 'needed modification of the design'.

                                   

                                  Any one else out there with similar experience?

                                   

                                  On a more positive note, here's my suggestion: add something to 'Check Geometry' that would highlight problem areas.  Flow Sim 2009 immediately shows the fluid volume once you add the final lid.  It doesn't seem to take time to compute, so it's not meshing, it is searching for internal surfaces.  The 'Create Lid' tool searches for openings in the internal surface, allowing addition of a lid to close the internal surface.  Perhaps a 'Highlight Openings' button inside of 'Check Geometry', would be more informative and would lead one to the problem area faster than just saying 'Zero Volume'.

                                   

                                  Cheers,  Rich.