10 Replies Latest reply on Nov 9, 2018 7:51 AM by Roger Toogood

    Unable to create boundary condition

    Peter Zwart



      I'm struggling to create a boundary condition into a part I have created. I keep getting the message: Face<1> is not laying on the boundary between solid and fluid region.




      I have tried many things, but I cant make it work. Can someone help me? I have attached the file.


      Kind regards,



        • Re: Unable to create boundary condition
          Chris Michalski

          run check geometry.  I'm assuming based on the image that you need lids on the ends to create a fluid volume.  It is complaining that you do not have a close fluid volume, there is a gap somewhere.

          • Re: Unable to create boundary condition
            Wei Siong Low

            Greetings All,


            I'm not sure whether this could be a coincidence or not, but I seem to be having a similar problem to yours.


            Even though my Lid is laying within the Computational Domain that i have specified, it still give me the error "Face<1>@LID5-1 is not laying on the boundary between solid and fluid region.”




            You can clearly see that the LID is inside the Domain yet it says that the LID is not lying within the boundary.


            However, this is not the case for my 2nd configuration.


            IMG 2.JPG


            Not sure why this is happening. Any advice or comments would be appreciated.







              • Re: Unable to create boundary condition
                Chris Michalski

                Have you used Check Geometry to make sure there are no invalid contacts?  Are there any hidden solid bodies? 


                Can you post a section view to clarify?

                  • Re: Unable to create boundary condition
                    Wei Siong Low



                    Thank you for your quick response.


                    Yes, one thing to note here is that I ran a "Check Geometry" but it has failed saying that there are "Cavities without Flow Conditions". Could this be a reason for this error?


                    And also, I still cannot figure out where are my cavities. I have simplified the design of the inner piston and it no longer has an cavities or grooves for that matter. Am still trying to work that out with my SW Support team to be honest. But if you can provide assistance, i would be more than happy.


                    IMG 4.JPG


                    Sorry for hijacking your thread Peter.


                    Thanks in advance Chris.

                      • Re: Unable to create boundary condition
                        Chris Michalski

                        No, the cavities without flow conditions: in the general settings, there is a box for "ignore fluid volumes without flow conditions".  This is simply to speed calculations if there are fluid volumes you do not need to simulate.


                        Try increasing your mesh or adding a local initial mesh near your lid.  This error also means that when it determines the mesh and attemps to place boundary conditions that the location of your BC has not been meshed fine enough for the software to realize it is a boundary between solid and fluid.

                          • Re: Unable to create boundary condition
                            Wei Siong Low

                            Very weird phenomena, if it could create a boundary condition on the "Valve Fully Opened" configuration why can't it do the same on the 2nd Configuration?


                            2ndly i wont be able to create a mesh in the first place because when i "Run" simulation this error prevents me to create any mesh what so ever.


                            Nevertheless, i appreciate all your feedback Chris. Lets see if there will be more input from other forumers.





                              • Re: Unable to create boundary condition
                                Chris Michalski

                                Wei -

                                from your pictures, you can see that the computational domain is different when the valve moves.  This means that the mesh will be reconfigured.

                                Try making your lids thicker.  As long as the inside surface remains the same, you can make it thicker in the other direction without changing your model.  But the extra solid mesh cells may help it locate your boundary.

                      • Re: Unable to create boundary condition
                        Wei Siong Low

                        As for your case Peter, i think you are meant to select the inner surface of that "LID" not the outer surface. Does this solve your problem?


                        IMG 3.JPG

                        • Re: Unable to create boundary condition
                          Jared Conway

                          Peter's issue, based on the normal direction, Wei is bang-on. The boundary condition needs to be applied on the inside of the computational domain. Chris' suggestion is a good one though. We should always check that there is a closed fluid geometry. In this case before adding features, I would have made sure that import diagnostics returned no errors and would have eliminated the interferences and checked that all faces touched using interference detection. (For multibody parts, drop them in an assembly and turn on the multibody part option)



                          Wei, can you post your model? Without the shaded edges and different colors for the parts, it is hard for me to tell where one part starts and the other ends.


                          Chris is going down the right path, this is most likely related to the geometry. Flow Simulation can't figure out what the computational domain should be. (it can't find the fluid volume)


                          First thing to do is check if you have any imported bodies. if you do, delete all features other than the imported body and use import diagnostics.

                          If you have any fancy parts, use CTRL-Q with verifciation on rebuild enabled to make sure none of them have issues.

                          Remove any interferences between components. Make sure to use the multi-body part option.

                          Check that all components (including lids) are touching face to face. You can do this with the interference detection tool, just enable the option "treat coincidence as interference".

                          Reset the computational domain and leave automatic rebuild enabled. If you have heat conduction in the solids enabled, your comp domain is not working at all.

                          Use tools > check in solidworks and flow simulation to make sure there is nothing else bad happening with the model.


                          If you're still having trouble, isolate which part is causing the problem by suppressing all components except for a housing and the lids.

                          If you want to do another check, draw a large solid block over top of your model and use the cavity feature to remove all the components from your assembly from the block. If it can't do it, Flow Sim won't be able to find the fluid volume either. That means you have a leak somewhere or some bad geometry.

                          • Re: Unable to create boundary condition
                            Roger Toogood

                            " ~~~~ not laying on the boundary between solid and fluid region."

                            I have this error message when I insert Boundary Condisiton.

                            at that time my boundary parts have many holes and covered it with lid tool.

                            but after so many times failure..

                            at last I thought there is a problem at lid tool. so I erased all holes in the part ... so no hole..

                            and I made a body on inlet and outlet of the part, by using no merge.

                            I used the nomerged body as the inlet and outlet boundary.

                            problem solved !!!