4 Replies Latest reply on Nov 4, 2009 12:18 PM by David Anderson

    Restraining a suspended assy

    Gary Liptrot

      Im trying to run an analysis on a frame constructed of beam elements suspended from a single central point, tethered at 30 degrees to the top of four corner posts by means of pad eyes.  Probably a simple solution to this but I cant think of how to restrain it.  Suggestions?

       

      Cheers.

        • Re: Restraining a suspended assy
          Roland Schwarz

          In an assembly, you could simply model the tethers as distance mates.

           

          If you are doing a motion analysis, I would skip the distance mates and model the tethers as very stiff springs.

            • Re: Restraining a suspended assy
              Gary Liptrot

              The analysis is a linear static study with a 40kN load. I need to check stress and deflection in the frame when hoisted fully-laden.

               

              For this instance I have assumed an evenly disributed load.

               

              I have simplisticly modelled the lifting point and tethers by drawing a 3D sketch representing the lifting straps extending from the centre of the pad eye holes at 30 degrees, and placing a coordinate system at the intersection.


              I was thinking the coordinate system would be of some use in the study?

                • Re: Restraining a suspended assy
                  Roland Schwarz

                  There are different ways to get there.  I would start by using SW Motion to determine the resultant forces.  At the very least, it is a good reality check.  From there, you could use the SW Motion results to apply to your FEA.

                   

                  -OR-

                   

                  You could model the actual tethers and include them in your FEA.

                   

                  -PERHAPS-

                  You could model pins through the padeyes and constrain the pins to be a certain distance from a fixed point.  Apply gravity and see what happens.

                   

                  If I was working in NASTRAN, I would model the pins and constrain them with rigid elements to a fixed point.

              • Re: Restraining a suspended assy
                David Anderson

                alternately, you could place unit loads on the pad eyes at the resultant angles and constrain the frame appropriately at the points where it supports the load.

                 

                for a statice linear analysis, all deflections and stresses etc can them be scaled to determine maixmum load.