Error message “Solver pivot warning” due to element birth and death

TAGGED: degree-of-freedom, element-birth-and-death, solver-error, transient-thermal

- July 6, 2021 at 4:05 pm
  
  solani
  Subscriber
  
  Hello everybody!
  Everytime I run my simulation (transient thermal, Ansys Mechanical) I get a error message:
  A solver pivot warning or error has been detected in the TEMP degree of freedom of node 5177 located in RPCBrick-middle. 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.
- July 8, 2021 at 2:08 pm
  
  1shan
  Ansys Employee
  
  I tried using element birth death in a transient thermal and realized that it gives you pivot error if you kill elements which are scoped to a boundary condition. Try killing just half of the middle block and see if you still get the same error.
  Regards Ishan.
- July 8, 2021 at 3:17 pm
  
  solani
  Subscriber
  
  Hello @1shan, what do you mean by "killing just half of the middle block". Wouldnt that effect my simulation? Also I tried it in a bigger model and there is it not a problem. Furthermore the middle block is not scoped to any boundary condition but the radiation command.
  However thank you very much for your help.
  Ani
- July 8, 2021 at 9:00 pm
  
  solani
  Subscriber
  
  Hello again I found something interesting: The simulation works if I add convection to all outer surfaces. Why? Is this a problem for the correctness of my simulation? (Also I get (in the end) values that are lower than the ambient temperature. This is a problem that I get in every simulation I make :-(
  Best regards,
  Ani

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