7 Replies Latest reply on Jul 10, 2014 3:53 PM by Jared Conway

    Displacement Control Question

    Peter MacDonald

      I suspect the answer to this is in the knowledge base which I don't yet have access to.

       

      For nonlinear displacement control studies, I do not understand the relation to the specified force (If any).

       

      1) Does it, in fact, never use the specified value of force? And therefore it only takes information from the force such as how it's applied and to what faces, and then uses that to acheive the displacement?

       

      2) If so, I don't suppose there's a way of finding what force it used to acheive the full displacement?

       

      Sorry for such questions, I just recently started learning about nonlinear studies.

       

      Many thanks as always

        • Re: Displacement Control Question
          Shaun Densberger

          For nonlinear displacement control studies, I do not understand the relation to the specified force (If any).

           

          I'm not sure what you mean by this; can you clarify? A displacement control study means that the "loads" on the structure are enforced displacements, i.e. you've specified additional values for the displacement vector (beyond those needed to prevent rigid body motion for a static analysis) and the force vector is all unknowns in the equation:

          {F} = [K]{d}

           

          Does it, in fact, never use the specified value of force? And therefore it only takes information from the force such as how it's applied and to what faces, and then uses that to acheive the displacement?

           

          Additional clarification is needed here as well. What are you referring to when you say, "the specified value of force"? Again, in a displacement control analysis, there are no defined terms in the force vector {F}; there are only unknowns.

           

          If so, I don't suppose there's a way of finding what force it used to acheive the full displacement?

           

          Are you asking if there is a way to determine the force at the enforced displacement control? If so, then yes you can measure it by looking at the reaction force.

          • Re: Displacement Control Question
            Jared Conway

            is there a specific reason you want to go to displacement control?

            • Re: Displacement Control Question
              Peter MacDonald

              One reason for trying displacement control was because I was having problems getting a force control study to converge. I now realise that this could be because the part is buckling, so I have tried a buckling study to check. However, I don't think this study is accurate. Too many simplifications were required in order to run it. The BLF is less than half that suggested by the the force control study (if the force control study was stopping due to buckling, which seems very likely given that there are areas reaching yeild).

               

              I also now realise that a displacement control study would not be able to compute the contacts in this model.

               

              I was confused as to how the specified displacement is applied in a displacement control study, but now I'm considering that my confusion is due to the nature of this particular model. I didn't think it was simply taking the specified point and displacing it, it looked as though it was actually applying a load in the same way as I had specified for the force control study. I wasn't expecting the result I got based on the displacement I specified, but it's most likely my interpretation that was wrong.

               

              This is a good example of what happens when you don't start off with small simple models!

              The world of nonlinear analysis is a steep learning curve.