Rayleigh damping causing problem

suktansuktan
The attached model works fine without the Rayleigh damping activated. Z displacement is within 1 mm. When Rayleigh damping enabled, Z displacement is unreasonably large.

Is it related to the element type?

Comments

  • VictorVictor
    It works OK for me. Can you attach the broken model to reproduce the problem?
  • suktansuktan
    Sorry, I did not attach the right file. The file is attached now. It works fine with Rayleigh disabled.
  • disladisla
    edited January 2018
    Load your file, change to ccx solver and go back to internal. Suddenly I get an error on the menu for the Rayleight BC (Red). When asking what's wrong I get the attached picture.BC must be applied to whole model and it is not.

    Once applied to the whole model solver starts but fails :

    00:00 Start 01:01:04
    00:06 Assembling matrices .
    00:14 Solving matrices
    00:15 .
    00:16 Error: Rayleigh damping coefficients are too large. Damping ratio for mode 4 = 1.666903
    00:16 Failed

    Reducing beta one order of magnitude solution converge.
    I have to apply BC to whole model each time I try to run the solver because BC on Rayleight turns red again.

  • suktansuktan
    Rayleigh is applied to the rubber surround. It is supported by the internal dynamic solver.
  • suktansuktan
    Are you using Mecway 8?
  • VictorVictor
    disla: It looks like you have Mode superposition method turned on in Analysis settings. Without that, it doesn't have those errors.

    suktan: I haven't worked out what's wrong yet. If I reduce beta, the problem gets pushed back to later time steps but damping also disappears with it. It only happens when the damping is applied to just the rubber surround. If you set it to Whole model, it seems to be fine.
  • suktansuktan
    Victor: Thanks for looking.
  • VictorVictor
    I think the problem is caused by an interaction between the extremely high stiffness elastic supports and the Rayleigh damping on the same elements. I solved it by reducing the elastic support stiffness on the surround to 10^12 Pa/m. I didn't notice this before, but the value you had (10^21 Pa/m) is higher than I'd be comfortable with because it's so much bigger than the other stiffnesses. It might be safer to reduce all of the elastic supports by 5-10 orders of magnitude in case they cause other numerical errors.
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