9 Replies Latest reply on Jun 16, 2015 4:15 PM by Ben D.

    rules of creating bonded contact set of beam and solid

    Ben D.

      Hello,

       

      I am about to create a contact set for a beam and four brackets:

       

      1.jpg

       

      If I create four different contact sets for each bracket, having selected the horizontal beam as a source, and all the touching surfaces of the bracket as a target, then the simulation works fine. These are the faces for selection of a bracket:

      2.jpg

       

       

      However, technically I can select the horizontal beam as a source, and ALL the appropriate faces of all four brackets as a target. This would make a selection a little faster. But in this case, I get the simulation results, that two bracket fly away (the displacement is shown to be 3*10^30 mm), meaning the software does not see this contact. If I run the simulation twice, I usually get different brackets flying away, but the other two brackets shows correct results.

       

      Is there a rule, that in the case like this, the target faces should belong to one body? I didn't find this requirement anywhere, and I think it should not be. Does anybody else have this issue? I tried it on sw2015 sp1.1 and just installed sp2.0, but it is the same.

       

      Thank you for your ideas

        • Re: rules of creating bonded contact set of beam and solid
          Ben D.

          So, after a few hours of trying, I think I found the answer. The bonding face has to be able to be projected on the beam central axes, as written in here:

          General

          So I changed the bonding faces from in the bracket. Instead of all 5 faces, I now use only one (the largest one in the middle). This way I can bond all four brackets, selecting single face from single bracket in one dialog box of contact set. And it works, so I guess this is a solution.

          Any comments anyhow would be welcome on confirming this

            • Re: rules of creating bonded contact set of beam and solid
              Jared Conway

              depending on the fidelity you're looking for, using beam elements is probably not the best fit

              they actually look like short beams which would probably be better as solids or shells

              and regarding applying the contact, selecting all the faces on multiple bodies should be ok, there may be an issue with beams

                • Re: rules of creating bonded contact set of beam and solid
                  Ben D.

                  Jared, thank you for your input. Sorry for my late response, I was trying different versions of this study to find some answers. Unfortunately, there are some things I can not clarify myself, maybe yours or somebody's else's experience will come into service.

                   

                  So, for this study, I have assembled a project BS (stands for Beam Simulation). It is a structure of some lifter, with hydraulic cylinder which can move the structure:

                  1.jpg

                  The bottom frame is fixed on 4 brackets. Then the vertical rectangular frames are able to move through the pins. Finally there is an upper part of frame, which stays parallel to the bottom frame, when the hydraulic cylinders moves.

                   

                  As usually, I started my simulation with a part of this structure, and moved forward. Firstly, I suppressed everything, except the bottom frame (assembly BS.01*). I applied some loads, and it was working fine, the stresses and displacements were reasonable.

                   

                  Then, I unsuppressed the right frame (assembly BS.02*). I applied the contact sets to it, and applied only gravity to the model:

                  2.jpg

                  I meshed and ran it. Received the error of unstable model. In order to find the problem, I turned on the soft spring. This is the result:

                  3.jpg

                  As unbelievable as it might look, now the 3 brackets fly away! As if they are not bonded. But they are bonded, and the same simulation ran well before (when the right frame was suppressed). These are the contact set faces of bonded contact between the beam and the appropriate brackets (in exploded view for easier selection):

                   

                  4.jpg

                  That being said, it looks like there is a problem with the software. I tried several times, tried creating different contact sets for each bracket, instead of bonding all brackets in one set. I also tried bonding only one horizontal face of each bracket (not bonding those two faces with radius and those two small side faces). The only difference was, that sometimes different brackets "flew" away.

                   

                  This model is created and simulation tested with SW2012, but I have tried it with 2015 - the same thing is happening. It looks like random contact set is ignored by the software.

                   

                  By the way, I purposely made this structure quite "difficult" for beam simulation: there are short beams, connected to each other at an angle, there are pins, brackets are placed pretty near to the end of the beams and so on. But I think that the software should give me an error if this would be not allowed. Now it looses the contacts, and I think it is not related to the complexity of the beam structure.

                   

                  Of course, I am almost certain that running the same simulation with all bodies as solids would run well. But now I am interested in capabilities of SW Simulation on beams, and I want to find the solution to this model, or somebody to confirm this being a software problem.

                   

                  I tried looking for the purpose of this problem in all the sources, the only short idea about the possible cause was in this thread:

                  Re: How to correct Problem define Bonded contact set between beam and solid shell?

                            "The beams can be put in contact to solids only by their ends and by the joint Group" (second post)

                   

                  But I didn't find anywhere in the official sources that this is true. Can it be true?

                   

                  I attach the model with the simulation results (the main assembly file is BS.00.00.00.000)

                   

                  I will really appreciate your experience and ideas on this issue, it's been a while since I am stuck on it ...

                    • Re: rules of creating bonded contact set of beam and solid
                      Ben D.

                      So, today I spent a few more hours on this issue. I have found this topic here:

                      Graphics Systems' SolidNotes: Bonding: Good for Families, Good for Simulation

                      "It is possible to make only one contact for both these brackets, setting the target/face set 2 to both bracket faces.... while this will work it is poor documentation and I've seen cases where the bonding still fails so I do not recommend it"

                       

                      I tried it (different contact for each face), and in this case it worked. But in this simulation with two frames (the base and the vertical one), I had to create over 90 different contact sets (and this is only a simulation out of two small assemblies!). Firstly, it makes these sets uneditable, because you would spend too much time finding them in the tree. Secondly, it is painfully time consuming. Thirdly, it is not guaranteed to work: I tried creating separate contact sets only for "problematic" brackets, leaving the merged contact sets for the working brackets. It still didn't work, I had delete them all, and recreate all the contacts with only one selection in the source (beam) and the target (face of the bracket).

                       

                      As that would not be enough, the mesher usually prompts a warning "The beam cannot be projected to the surface... Simulation might fail". So, even after going through the selection, you still can not be sure simulation will calculate successfully and how accurate the results will be.

                       

                      I think it is safe to say now that this is a software problem.

                       

                      Please notice, that the link I've mentioned above is from 2012. So, 3 years later solidworks still has the same problem bonding beam to solid. It is about time they fixed it, don't you think? I am still on SW2012, and AFAIK bug reporting requires active subscription, which I no longer have. Though it would be worth reminding DS about it, so somebody with an active subscription could do it

                        • Re: rules of creating bonded contact set of beam and solid
                          Jared Conway

                          there's a lot going on in those last couple of posts

                           

                          are you saying there is a point case where beams and solids (or shells) cannot be bonded together?

                           

                          if so, build a sample and send to your var for bug reporting

                           

                          it happens, there are a lot of combinations and not all are supported

                           

                          but if you read what i wrote previously, what you have is not likely a good fit for beams or mixed meshing because of the way the bonding would be applied. you should really be using solids or shells.

                            • Re: rules of creating bonded contact set of beam and solid
                              Ben D.

                              Jared, thank you for the input

                               

                                  are you saying there is a point case where beams and solids (or shells) cannot be bonded together?

                                  if so, build a sample and send to your var for bug reporting

                               

                              yes, it looks like that in case of this study. I will contact somebody from the var

                               

                              but if you read what i wrote previously, what you have is not likely a good fit for beams or mixed meshing because of the way the bonding would be applied. you should really be using solids or shells.

                              yes, of course I've read it, and I agree that in this particular study solids would be a better solution. But in order to get the possibilities and limitations of the beam elements simulation, I am purposely trying to make this study to run, using particularly beam elements. Lets hope in SW 2016 or 2017 it will be fixed

                                • Re: rules of creating bonded contact set of beam and solid
                                  Jared Conway

                                  the contact issue will probably be solved in a later version once reported

                                   

                                  however the use of beams for short beams won't change as it is an inherent definition of beams

                                    • Re: rules of creating bonded contact set of beam and solid
                                      Vagulus Dagg

                                      'Scuse a student getting lost in all that discussion, but, "What does this all mean?"

                                      I have a problem at the moment

                                      2015-06-16_7-18-49-Static-1-Test-Fails.png

                                      Here I have used RHS as frame members and Plate for the brackets.  I gather from your discussion that there is a problem bonding these.

                                      Is there a way to bond these so I can check what happens when a twist is applied?

                                       

                                      I see you talking about using solids instead of beams, but would that not nullify the test when I want to know what happens when I use RHS?

                                        • Re: rules of creating bonded contact set of beam and solid
                                          Ben D.

                                          It means what it says - these long beams are treated as beam elements, and little plates - as solids. Bus solidworks does not know how they are connected, therefore it can not run the study.

                                           

                                          You only have "bonded" contact, which does not necessarily define all contacts in the model. In your case, you should add more contacts describing your case. Please search the internet, youtube and webinars in the websites of VARs, like innova systems, go engineer, solidsolutions - they have hours (or event days) of useful information filmed for free in their websites