General Mechanical

General Mechanical

MPC – Problem with contact and Remote Displacements

    • Fabricio.Urquhart
      Subscriber

      Hello,


      One more time I am with this problem. The result is correct, but I recieve a message that there is a conflict with constraint.


       


      Can anybody hlp me with it?It is very simple...

    • Sandeep Medikonda
      Ansys Employee

      Fabricio, 


      Have you seen this section from the help?



      One or more MPC contact regions or remote boundary conditions may have conflicts


      ...With other applied boundary conditions or other contact or symmetry regions. This may reduce solution accuracy. Tip: You can graphically display FE Connections from the Solution Information Object. Refer to Troubleshooting in the Help System for more details.


      During solution it was found that one or more contact pairs using MPC (multi point constraint) contact formulation overlaps with another contact region or boundary condition. The same is true for remote boundary conditions overlapping with another contact region or boundary condition.


      Due to the fact that MPC formulation can cause over constraint if applied to the same nodes more than once, the program may have not been able to completely bond the desired entities together. You may check the solution output located in the Worksheet of a Solution Information object to determine which pairs and nodes are affected by this condition. Specifically this can happen when:



      • A contact pair entity (either an edge or face) also has a Dirichlet (prescribed displacement/temperature) boundary condition applied to it. In this case the MPC constraints will not be created at nodes that have prescribed conditions thus possibly causing parts to lose contact. Sometimes this warning may be disregarded in cases such as a large face with a fixed support at one edge and a contact pair on another. If it is determined that overlap does indeed exist, consider relocating the applied support or using a formulation other than MPC.

      • Two MPC contact pairs share topology (such as a face or an edge). Again it is possible for one or both of these pairs to lose contact. This message may especially occur when edge/face contact is automatically generated by the program because often 2 complementary contact pairs (that is, edge part 1/face part 2 and edge part 2/face part 1) are created. Often in this case the message can be ignored after verifying result correctness and if necessary, deleting/suppressing one of the inverse pairs. This condition may also occur when 1 part (typically a surface body), is being contacted by 2 or more parts in the same spatial region. In this case it is possible for one or more of the parts to lose contact. Consider reducing the Pinball Radius to avoid overlap or changing one or more of the regions in question to use a contact formulation other than MPC.

      • When MPC contact is used to connect rigid bodies and joints, the overconstraint situation can sometimes occur.

      • When Remote Boundary conditions overlap the Low/High Regions of the Periodic/Cyclic symmetry regions, you may experience an overconstraint situation. In a severe situation, the application may terminate.



      Regards,
      Sandeep

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