7 Replies Latest reply on May 26, 2014 9:28 PM by Jared Conway

    Pipeline Lift Analysis - Strange Results

    Mike Armstrong
    Mike Armstrong May 20, 2014 4:47 PM

      Hi,

       

      First post here so please bear with me.

       

      I am trying to run a pipeline spool lift analysis in Simulation and getting strange results, well strange reaction force results.

       

      It is a 4 point lift and I have assumed that the spoolpeice is supported half the pipe circumference between 3 o'clock and 9 o'clock and lifted vertically. The only applied load is gravity.

       

      The issue is that the resultant force in the Y-direction is greater than the weight of the spoolpeice c/w flanges.

       

      I am missing something?

       

      I have attached the model and simulation result files. Please let me know if these are not required in the future.

       

      Thanks,

       

      Mike

        • Re: Pipeline Lift Analysis - Strange Results
          Shaun Densberger
          Shaun Densberger May 21, 2014 2:51 PM (in response to Mike Armstrong)

          I played around with your model and with mesauring the reaction force. It seems that the coarser the mesh, the more inaccurate (and higher) the reaction loads are. The error goes from ~43% with the coarse mesh to ~0.11% with the fine mesh. It's normal to see slight changes in the calculated reaction forces with an increase in the # of DOF, but I've never seen anything like this. I'm interested in finding out how SW calculates reaction forces within the software.

           

          Reaction Force Coarse.png

           

          Reaction Force Fine.png

            • Re: Pipeline Lift Analysis - Strange Results
              Mike Armstrong
              Mike Armstrong May 21, 2014 4:49 PM (in response to Shaun Densberger)

              Thanks for the reply,

               

              Well that is strange behavior. I hope someone from Solidworks will be able to elaborate on this.

               

              What mesh size did you take it down too?

               

              Nice to see someone using Mathcad Prime. Are you using a trail version?

                • Re: Pipeline Lift Analysis - Strange Results
                  Shaun Densberger
                  Shaun Densberger May 21, 2014 5:03 PM (in response to Mike Armstrong)

                  I believe that last result ha the slider 7/8ths of the way.

                   

                  Trial period for MathCAD ended not too long ago, but when the trail period ends the license reverts to MathCAD Prime Express (which is free to use ). Express is a great program even with the reduced functionality.

                    • Re: Pipeline Lift Analysis - Strange Results
                      Mike Armstrong
                      Mike Armstrong May 21, 2014 5:07 PM (in response to Shaun Densberger)

                      I believe that last result ha the slider 7/8ths of the way

                      I am running a few checks now and will report the difference.

                      Trial period for MathCAD ended not too long ago, but when the trail period ends the license reverts to MathCAD Prime Express (which is free to use ). Express is a great program even with the reduced functionality.

                      I'm glad you feel that way. I have been an active member of the Mathcad community for years and the criticism of Mathcad Prime is extreme.

                      • Re: Pipeline Lift Analysis - Strange Results
                        Mike Armstrong
                        Mike Armstrong May 21, 2014 5:22 PM (in response to Shaun Densberger)

                        I get a similar problem to which you mentioned.

                         

                        0.2m mesh - resultant force of 2083600N ( This is the smallest mesh size I can take the spline to)

                         

                        0.15m mesh - resultant force of 227420N

                         

                        0.1m mesh - resultant force of 259340N

                         

                        The force does not increase linearly as the mesh is reduced. I cannot understand what Solidworks is doing here.

                         

                        Please note the resultant force is for the entire model.

                          • Re: Pipeline Lift Analysis - Strange Results
                            Shaun Densberger
                            Shaun Densberger May 21, 2014 5:55 PM (in response to Mike Armstrong)

                            This makes me wonder how SW is calculating reaction forces internally. If it's done using the displacement vector field and the stiffness matrix, then there shouldn't be any significant changes in the results as the mesh is modified. However, if the loads are calculated by integrating the stress over the area, then changes can arise due to stress singularities. That being said, I would think that the reaction load would increase as the mesh decreases. Very strange indeed.

                              • Re: Pipeline Lift Analysis - Strange Results
                                Jared Conway
                                Jared Conway May 26, 2014 9:28 PM (in response to Shaun Densberger)

                                Haven't had a chance to check this but is the element size reasonable where the fixed restraints are?

                                 

                                What happens when they are reduced to points instead of surface areas?

                                 

                                What does the out file report the mass to be?

                                 

                                No special options like inertial relief or anything enabled right?

                                 

                                Does the problem happen on simple models? That's is what your reseller will need for reporting the issue.