19 Replies Latest reply on Sep 4, 2013 7:40 PM by Jared Conway

    Shell Global Bonding not Working

    Chris Ross
    Chris Ross Feb 13, 2013 12:57 PM

      I am modeling a section of the deck of a ship with shells.  The underside of the deck is supported by a combination of angles, flange plates, and bulkheads.  I created split lines across the entire deck surface whereever there was a member to facilitate meshing and bonding.  I then added the deck structure and a piece of equipment into an assembly file and set up the simulation.  Global contact is set to bonded.  It keeps telling me the model is unstable.  When I turn on soft springs and inertial damping to get it to run and see what is failing it shows that half of the deck plate is peeling up in several places and numerous bulkheads are just flopping around like a wet noodle.  I have confirmed in the shell model that all of the surfaces are indeed connected with no gaps.  What has me so confused is that in some areas the deck plate is staying contected and other bulkheads are also staying in place.  Anyone else encountered shells flying apart, even after you inserted a split line to facilitate the meshing?  Do I have to manually go in and apply bonding to each joint?  There is probably well over 100 seams that I would have to do this to so I really don't want to head down that path.

       

      Unfortunately I cannot share the files or screen shots due to an NDA with my client.

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        • Re: Shell Global Bonding not Working
          Bill McEachern
          Bill McEachern Feb 13, 2013 1:03 PM (in response to Chris Ross)

          What version of SWX sim are you using? If 2013 you do not need to add the split lines to get a good answer. Older versions may require split lines depending on how old it is. If the deck curvature in non simple - ie it isn't planar or circular you may have to manually bond the beams to the shells, even shells to shells. I have done a lot of shell modeling and I have come to the conclusion that is it not simulation that is the issue for most of this but rather the surface handling in SWX and how it deals with higher order geometry.

          • Re: Shell Global Bonding not Working
            Chris Fernald
            Chris Fernald Feb 13, 2013 1:17 PM (in response to Chris Ross)

            I had this exact problem a while ago and I recall that I did have to manually set bonded contact between the edges.  The selection process is less tedious if your geometry allows you to right click on the shell edge, and "Select Tangency".  Either that, set the selection filter to edge and find a way to window select the edges you want.  There might be other ways with the "Power Select" tool but I'm not sure.  You might be able to color code the surfaces based on how you want to select them, and then use power select to select those colored groups. I have no idea if this works, but something to look into...

             

            I also found the split lines helpful as you described. 

             

            Can you use model symmetry to cut down the amount of selecting you would need to do?

            • Re: Shell Global Bonding not Working
              Chris Ross
              Chris Ross Feb 13, 2013 1:25 PM (in response to Chris Ross)

              Luckily the deck is flat which helped simplify the modeling a bit.  I am using 2012 SP 5.  This geometry is about as simply as it comes.  Everything is right angles.  The loads I am applying are not symetrical so I can't get away with only modeling half of the area.  I wish I could try 2013, but my client is using 2012 so I'm stuck on that front.  Talking with Trimech, they said they found a couple of these issues reported to SW already, but they were shown as fixed and closed out in a earlier service pack of 2012.  They are going to chat with SW and see what else they can find out.  Any other ideas?

              • Re: Shell Global Bonding not Working
                Alessandro Tornincasa
                Alessandro Tornincasa Feb 13, 2013 2:08 PM (in response to Chris Ross)

                Chris, here's my tip, it will be a huge time saver.

                In 2012 you can use the automatically find contact set command to search for sheel-shell and shell-solid edge contacts, and then automatically vreate bonded contacts.

                look at this sample picture:

                 

                13-02-2013 20-05-33.jpg

                 

                In case you have any more questions don't hesitate to ask.

                Cheers,

                 

                Alex

                 

                my bi-lingual English-Italian SolidWorks Blog

                www.solidworkseducation.blogspot.com

                • Re: Shell Global Bonding not Working
                  Chris Ross
                  Chris Ross Feb 13, 2013 3:18 PM (in response to Chris Ross)

                  Just heard back from Trimech.  Apparently it is a known issue that the global bonding feature with regards to shells is unreliable and is something they are working on.  If shells are flying apart your only choices are to model it as a solid or to go in and manually create the contact sets at each of the joints. 

                   

                  So you either spend large amounts of time on the front end bonding all the shells together or you spend large amounts of processing time trying to run it as solids. 

                   

                  So far I've run 0 for 2 on my projects trying to get viable results from large shell element models.  I sure hope this doesn't affect my relationship with my customers. 

                    • Re: Shell Global Bonding not Working
                      Bill McEachern
                      Bill McEachern Feb 13, 2013 3:56 PM (in response to Chris Ross)

                      Actually in 2013 you have a new option in the automatically find the contact sets radio button and manually set them. You might want to try that. It was aimed at bonding surfaces or solid faces to circular edges. I just tried it on a pattern of shells to one at 90 deg. It worked everywhere except at the one at the edge. If the edge was inthe middle of the surface it seemed to work fine for quickly finding and setting the bonded connection condition. Give it a go and see if it works.

                    • Re: Shell Global Bonding not Working
                      A. Telet
                      A. Telet Feb 27, 2013 10:42 AM (in response to Chris Ross)

                      I'm in the same business as Chris (or at least the project he's at in this topic), and I have had the same problems many times without being able to make workaraounds. I'm not a regularily SW user (we use it mainly for simulation purposes) - so my modelling and analyses approach is quite kindergarden-style...

                      However, for my recent panel analyses, contact sets/bonding have been quite successful with respect to shell to shell bonding. I model "everything possible" as surfaces. My major problem in these panel constructions, is bonding of beams/stiffeners to shell (i.e. along direction of stiffener). No matter how I try to make contact sets, automatic/manual/component contact - the shell behave as they are not stiffened at all. Very annoying, and completely impossible for me to find out how to make this bonding (some beams ARE of course bounded - others NOT)

                      For some projects I start modelling from skretch over and over again trying variations that may provide a successful analysis. It also make it quite impossible to fine-tune the construction - all energy is focused on getting the f*** analysis done - and fingers crossed that it's enough.

                       

                      Sorry for crashing your thread, but there is just so little information and knowledge to be found on SW panel constructions and analysis (i.e. shells with beams attached)

                       

                      Anyway - all information and guidance will be appreciated.

                       

                      -a-

                      • Re: Shell Global Bonding not Working
                        Dusan Falar
                        Dusan Falar Sep 4, 2013 12:10 PM (in response to Chris Ross)

                        Hi, may be it is too late, but it may help. I have found that this problem rises when I use the loft feature from one set of edges to other set (but not always). In the loft feature there is an option "Merge tangents faces" initialy checked on. When I set off this option the global bonding started to work.