Rayleigh damping coefficients
Rayleigh damping coefficients
(OP)
Dear members,
In our present task, we have to evaluate Rayleigh damping coefficients.
--> Could anyone suggest how they can be evaluated?
--> Do Rayleigh damping co-efficients vary with modes?
Suggestions are most welcome.
Regards
In our present task, we have to evaluate Rayleigh damping coefficients.
--> Could anyone suggest how they can be evaluated?
--> Do Rayleigh damping co-efficients vary with modes?
Suggestions are most welcome.
Regards





RE: Rayleigh damping coefficients
2)No, they are a bodge.
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Rayleigh damping coefficients
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Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Rayleigh damping coefficients
Thanks for the reply. I couldn't understand the answer for my 2nd query.
As per the calculations which I peformed, I am with varying coefficients (varying with the modes). Which means,
mode1 has one set of coefficients and likewise for other modes.
Regards
RE: Rayleigh damping coefficients
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Rayleigh damping coefficients
D=1/2*(alpha*omega+beta/omega)
alpha and beta are the stifness and mass proportional damping constants. In order to determine these constants you need to solve two simultaneous equations. From experimental data you should have the damping ratio for two frequencies. The right way to do it is to use the lowest natural frequency and the highest frequency of interest and the correspinding damping ratios.
Then solve the following:
alpha=2*(D2*omega2-D1*omega1)/(omega2^2-omega1^2)
beta=2*omega1*omega2*(D1*omega2-D2*omega1)/(omega2^2-omega1^2)
RE: Rayleigh damping coefficients
I thank you once again for your response. In my task, I have to evaluate damping co-efficients. For this purpose, I did an experiment with the aim of extracting first 6modes and resp modal parameters.
All this is done to evaluate damping coefficients.
So, now I am with 6 equations, 2 constant unknowns ( alpha and beta). These 2 constants have to satisfy all the 6 equations. But in my case, I am with different values of alpha and beta. Can anyone suggest??
RE: Rayleigh damping coefficients