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Methods for Damping High Frequencies in FEM Thin Film Model?

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  1. Jul 15, 2017 #1
    I would like to simulate the vibrations of a thin film polymer in vacuum using nonlinear analysis. For this purpose I am using an FEM program I have written in MATLAB. I do not have any data regarding damping in the structure, so I am estimating the damping using stiffness-proportional-only Caughey damping and adjusting the damping ratio until results appear reasonable. This strategy seems to be working for finding the steady-state result, but does nothing for the high frequency oscillations induced by the discretization. This is revealed in the series of figures below:

    CD3wwn0.jpg
    The above plots appears reasonable, but upon zooming in on the lower plot:
    0Fx39fF.jpg
    a high frequency, low amplitude oscillation is revealed. Zooming in further:
    hj6wVZ9.jpg
    shows that this oscillation is not damped out, but persists at a non-relevant scale. This causes the simulation to run slow even after steady-state should have been achieved.

    I have made one attempt to work around the issue by introducing artificial static friction to cause nodes to stick when near steady-state, but this only induces the oscillations to grow (thought to be due to compounding forces from neighboring non-stuck nodes).

    Is there some other approach I could take to damp the high frequency oscillations? A non-exhaustive search of academic literature via Google only turned up results on Rayleigh damping and elementary viscoelastic models. If there is some terminology specific to this particular problem, I am not aware of it.
     
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  3. Jul 15, 2017 #2

    Nidum

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    What physical model of the film have you used ?
     
  4. Jul 15, 2017 #3
    I am currently using a hyperelastic linear stress-strain relationship with full nonlinear Eulerian strain and a modification that compressive stresses are forcibly set to zero. The FEM model regards each element as a 2D membrane.

    I realize this is not a particularly accurate model for polymers, but as I am writing my own program, I only want to increase the complexity as I can manage to have simpler models work appropriately.
     
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