6 Replies Latest reply on Aug 16, 2010 6:48 AM by Tony Gatta

    How to set boundary condition for free floating model in thermal simulation?

      Hi,

      I am doing thermal simulation. Below is the simplified model. I am checking how stress and deformation when temperature change from 180C to 0C for below assembly.

      My question is how I can set the boundary condition which enough to hold parts, and doesn't affect the simulation? I would like to solve considering the assembly in free floating like situation...

       

      Is there any option to do this, like free floating? Or ...kind of method or situation to put the assembly on top of some surface without restricting deformation?

       

      Someoen says, I can choose...boundary condition smartly....so it can hold the assembly and solve it without restricting the parts deformation. would you comment if you know or hint?

       

      Thanks,

      Cheol

      model.JPG

        • Re: How to set boundary condition for free floating model in thermal simulation?

          I have never found a free floating boundry condition. Try analyzing 1/2 or 1/4 of the model and then adding Symmetry in Advanced fixtures. Sometimes this works for me.

          • Re: How to set boundary condition for free floating model in thermal simulation?
            Tony Gatta

            Restraints in thermal models can be tricky.

            You want to be sure that they don't induce artificial stresses.

             

            Off hand you could try this a couple of ways:

            1. As Randy suggests, cut the model into 1/4ths and use 2 symmetry

            restraints.  Fix one of the vertices on the floor.  This will allow the model

            to grow in every direction and not leave the "floor" -- what it does not do

            is keep your model from rotating.

             

            You could try activating "soft spring" and see how that works in a thermal

            analysis.

             

            2. the classic way to do this is think through each and every one of your

            constraints.  Constrain vertices only.  The ones that touch the "floor" of course.

            In one corner (any corner), FIX the vertex.  This will reduce your degrees of

            freedom per above.. it can't translate anywhere, but it can rotate.

             

            to keep it from rotation add a "Reference geometry" constraint to the next

            vertex over (not the one diagonally opposite).  Make that so that you limit only

            one direction.. ie the vertex can move towards or away from the other fixed vertex

            only.  This will fully constrain your model (it can no longer spin) -- but keep in mind

            all of your deformations will be AWAY from these vertices (the model won't "grow"

            from the center when heated).

             

            Hope that helps.

            -Tony

              • Re: How to set boundary condition for free floating model in thermal simulation?

                Thanks for the good feedback...which were kind of things that I have tried. It's very good to know you are suggesting similar. I will try further as you commented.

                 

                By the way, when you say "fix one vertice on the floor"...does this mean to fix one vertice all three direction? I wonder if there is kind of "floor" in the option of restraints.

                 

                In oder to make the model grow from center of the mode, can I simply choose the one point at the center of model instead of one corner vertice?

                 

                If I fix only one vertice, as I remember, the solution becomes "error" not even go though....due to rotation issue as you mentioned. It's good to know and I am trying to fix reference plan in addition to one fixed vertice....by the way, in this case....I think that I still can not prefernt the model move up and down.....while I could prevent the rotation....

                 

                Thanks,