General Mechanical

General Mechanical

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Issues with large deformations with element birth and death

    • helen.durand


      In a coupled transient thermal - transient structural simulation, I have been having issues with large deformations leading to divergence.

      The situation is as follows:

      • The temperatures are solved for in the transient structural simulation, and the results are imported into the transient structural simulation.
      • In the transient structural simulation, some of the elements are dead (using the element birth and death) until they fall below a certain temperature. Once they are reborn, the temperature continues to decrease. The idea is that this is supposed to represent the solidification of these elements (and the temperature when the elements are reborn is the melting point).
      • I expect that the elements will have zero stress/strain when they are reborn. For this reason, I am using the MP, REFT command to set the reference temperature to the melting point.
      • However, when solving the transient structural simulation, the elements that are reborn become very deformed, leading to simulation divergence.
      • I have tried dramatically decreasing the element size and time step size, but the issue persists.
      • Right now, I am using a linear-elastic model of the stress-strain relationship. (In the future, I would like to implement a temperature dependent multilinear model.)

      Do you know why this is occurring? Does this appear to be a simulation issue, or is this perhaps related to some misunderstanding I have of the physical nature behind what I am trying to simulate?

      Thank you!

    • Ashish Khemka
      Forum Moderator

      What if you do not apply temperature when the elements are alive and keep the temperature at reference (you may keep time-integration off during this step) and then let it decrease after? See if this helps.

      Regards Ashish Khemka
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