16 Replies Latest reply on Dec 22, 2011 2:27 PM by Tyler Kemp

    New to simulation- gravity related setup question

    Tyler Kemp

      Hi guys, gals

       

      I have a question related to setting up a study for a gravity related simulation. I have just began recently trying to kind of navigate the simulation bundle of the software and I think i have come to a place in one of my designs that i feel could be analyzed through a gravity study. Problem is because i really havent had any training and cant really find answers through the tutorials and such , i was hoping I could lean on the forum here to maybe get me pointed in the correct direction. Im certainly not looking for anyone to do my work for me, but i would like to learn none-the-less. So heres my question.

       

      I have designed a simple hopper that will rest between two structural beams. The hopper will utilize some formed brackets that will rest on the top of these beams. What i would like to "Study" is the amount of stress or fatigue the brackets will experience with just its own gravitational mass pulling it down. Ive tried a few things but have not had any success in getting a result.

      hopper.jpg

      Thus far i have made my "fixture" the two bottom faces that will rest on the beams and made my gravity the top plane of the model. I get a good mesh , but when i try to run the analysis i either get an error about inadequate relations (ive tried the soft spring and inertial releif ) or it just simply wont solve.

       

      hopper sim.jpg

      Any suggestions ?

       

      Thanks in advance

       

      Tyler

        • Re: New to simulation- gravity related setup question
          David Maxham

          Tyler,

           

          I don't know if this will help, but did you check for correct bonding between the surfaces?  That is, if you have more than one part in your image above, check to see that the "mating" surfaces are bonded correctly.  Probably a wild guess on my part, but it couldn't hurt to check.

           

          Dave

            • Re: New to simulation- gravity related setup question
              Tyler Kemp

              well, im not sure i guess. Based on your suggestion would i be wrong to assume that because the peices are mated to one another  that they arent bonded by default? I see an option for bonding in the connections menu, so ill give it a try regardless and see what happens.

                • Re: New to simulation- gravity related setup question
                  Tyler Kemp

                  well.. i bonded the model globally and re-meshed it and ran the study again but i still have a failure. Good guess though, i know thats certainly part of the puzzle now, so thanks Dave

                    • Re: New to simulation- gravity related setup question
                      David Maxham

                      "Based on your suggestion would i be wrong to assume that because the peices are mated to one another  that they arent bonded by default?"

                       

                      If the pieces are mated to one another they are usually bonded by default but..... I think the exception to that rule is sheet metal parts.  You may want to look at the contact sets and manually make contact sets between the sheet metal faces that should be bonded.  I may be way off here, so hopefully someone can correct me where I'm steering you wrong. 

                       

                      Also, maybe try running the model with just the big piece alone?  Divide and conquer?

                       

                      Dave

                        • Re: New to simulation- gravity related setup question
                          Tyler Kemp

                          well... the 2nd picture i posted is the sub -assembly which is seperate from the main assembly in the first pic. So i feel like its about as divided up as i can get it for now. So.. i dunno... ill keep tinkering in my spare time and see if i get anywhere.

                            • Re: New to simulation- gravity related setup question
                              Brian Zias

                              Tyler, can you kindly post your sub-assembly as a ZIP so we can take a look?  It's most likely a contact issue, meaning wherever there is a gap between parts the software will not automatically bond.  Additionally, if this is a SolidWorks sheet metal part, or parts, then you may have to manually bond the edges depending how they come into contact.

                               

                              Do you have SolidWorks Simulation Professional?  One cool trick when you have issues with contacts is to run a Frequency study.  The first several modes will be the rigid body modes and you'll see the "loose" edges as the modeshapes.

                               

                              Brian

                                • Re: New to simulation- gravity related setup question
                                  Tyler Kemp

                                  Brian

                                   

                                  I am using solidworks professional. I attached the file. It you have any questions about why something is the way it is feel free to ask.


                                  Thanks
                                  Tyler

                                    • Re: New to simulation- gravity related setup question
                                      Brian Zias

                                      Tyler, please use a Pack and Go (from the file menu) to send over all the referenced parts along with the assembly?

                                          • Re: New to simulation- gravity related setup question
                                            Brian Zias

                                            Tyler, no worries, we've all sent just the assembly before

                                             

                                            Here are a few suggestions:

                                            1.  In the study properties, uncheck the "Large Displacement" option.  Why is this checked and what does it do?  See #2.

                                            2.  When the study tries to solve, it sees there are 'large displacements' and throws the prompt "Excessive displacements detected... would you like to re-run with Large Displacement enable?"  It's tempting to say "Yes" but always say "No" to this prompt.  If you say yes, the solver will re-start with the "Large Displacement" option enabled.  This should be off in this study.  If you say No, the solver will continue to solve using small displacement assumption.  There's a lot of explanation behind it, but suffice to say that "Large displacement" option invokes an iterative solution that takes a lot longer and is a lot more likely to fail when you have a rigid body mode.  So just turn off this option and also turn on Soft Springs.

                                            3.  See picture below.  This is what your results look like after answering "No" to the "Excessive displacement..." prompt.  YOu can see the issue right away, the far panel is loose.  There is nothing bonding it to the other bodies, so it just flies away in space.

                                             

                                            no contact.png

                                             

                                            4.  You have Global and Component Contact both defined and set to Bonded, however both Global and Component will only apply to components that have initially touching faces.  In your case, you have a lot of edge to edge contact between panels.

                                            5.  To account for these edge-edge contacts, you have a few options:  create local bonded contact sets, use rigid connectors, model in the weld as a solid, use Edge Welds.  Each have their benefits and drawbacks.  The quickest option is the first one but the results in the weld gaps won't be truly accurate.  Sometimes it's an iterative approach - add a few contact sets, re-run, check results and see where it's coming un-glued, repeat - just make sure and say "no" to the large displacement prompt each time so the option doesn't get checked.

                                             

                                            local contact.PNG

                                             

                                            I had to add 9 contact sets but then the model was bonded properly:

                                            results.PNG


                                            This is actually a great model to learn on since it doens't have the usual ideal face-face contact.  There are other lessons on this model you could practice too, such as using shell elements to represent the panels.  That will come in handy when you start to run bigger assemblies.  The best thing you could do is invest in the Simulation training class with your local VAR.  You'll cover the different contact types, how to use them, different elements, checking for convergence... so much value and it's worth the time if you're going to be using this tool as part of your process.