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General Mechanical

General Mechanical

Topics related to Mechanical Enterprise, Motion, Additive Print and more.

Im running into pivot warnings when trying to solve my simulation

    • Inan
      Subscriber

      Hi there, I'm trying to do some finite element modelling of a suspension bridge for my final year project. I have designed the bridge using DesignModeler and I'm trying to get some results on Mechanical. I keep running into pivot warnings and cant seem to find the problem. I have been at this for a week now and all my designs have the same problem. The error message I get when trying to solve my model is:

      A solver pivot warning or error has been detected in the UY degree of freedom of node 21548 located in Deck. This is usually a result of an ill conditioned matrix possibly due to unreasonable material properties, an under constrained model, or contact related issues. Check results carefully. You may select the offending object and/or geometry via RMB on this warning in the Messages window.

    • peteroznewman
      Subscriber
      nDrag and drop a Modal analysis on the Model cell.nOpen the model and drag and drop the two Fixed Supports from Static Structural onto Modal. Then Solve.nThe Modal will show you if anything is unconnected. In this example, one of the Line Bodies is floating away, unconnected at both ends.nThe problem is the elements in the top thick cable have no connection to the vertical thin cables. DM failed to create any Shared Topology. Neither are the thin cables connected at the bottom to the deck. This is the cause of your Pivot Errors in Static Structural. nThe geometry doesn't touch.nThere are 412 thin cables. In DM, you could delete the long thick cables and draw 412 short pieces of thick cable. This is the safe but tedious approach.nAnother approach is to use a very fine mesh on the thick cable and do a mesh merge and hope to get a node close enough to the node on the end of the thin cable to merge and thereby connect the thin cable to the thick cable. This is less work but has the danger of collapsing elements which will cause the solver to fail.nHere is a first attempt, it looks like the Mesh Connection group merged nodes between the thin cable and the deck, but not between the thin cable and the thick cable.nn
    • Inan
      Subscriber
      Hi there Array nThank you very much for the reply! I decided to take the more tedious approach and draw the short thick cables individually. Like you mentioned I do think this is the safer option. I am now able to extract the results I wanted from my model.n
    • peteroznewman
      Subscriber
      nI suggest you follow the directions, and filter the tree with the Scoping option set to Partial and find out which objects have lost scoping. Repair any objects and then you can have a clean model.n
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