Hello.
I am trying to use Rayleigh damping in “DYNA_LINE”.
When I enter the desired values for “AMOR_ALPHA” and “AMOR_BETA” in “DEFI_MATERIAU”, the output result is clearly too damped.
When I multiply the desired values by 1/100, the result seems to be correct.
Is it possible that “AMOR_ALPHA” and “AMOR_BETA” are being multiplied by 100?
Thank you in advance.
hello tinoue
Rayleigh damping works fine and correctly.
Consider: alpha is stiffness proportional, beta is mass-proportional (opposite as named in some dynamics text books). Could this be the reason or your incorrect results?
If not: how do you judge that the damping is false? You must have a reference case which must be correct! But the most reliable check is to make a complex eigenvalue analysis which will list you the modal damping values, so easy to check.
complex eigenvalue analysis is done with
ceig=CALC_MODES(OPTION=‘CENTRE’, # centre works best
MATR_RIGI=Stiffn,
MATR_MASS=Mass,
MATR_AMOR=Damping,
CALC_FREQ=_F(FREQ=centralFrequency, NMAX_FREQ=3,),)
centralFrequency any freq near to your interested range
best regards
Johannes_ACKVA
CODE-ASTER-courses at Ingenieurbüro für Mechanik
online or in-class
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Hello Dr. Johannes ACKVA
Thank you very much for your kind reply. It was really helpful.
As you pointed out, I had switched alpha and beta. It was a basic mistake, and I apologize.
Also, I would like to thank you for your advice on how to check the results and perform complex eigenvalue analysis.
Thank you
Takafumi Inoue