Rayleigh damping

[Polatoglou]

How can I find the rayleigh damping?

[vesna]

What was the question exactly?

[henycuong]

vesna wrote:
> What was the question exactly?

hi,

I have a question. Should we include the geometric stiffness matrix in stiffness matrix for calculating Rayleigh damping or not?

Yours faithfully,

Cuong

[henycuong]

vesna wrote:
> What was the question exactly?

The damping matrix D is specified as a combination of stiffness and mass-proportional damping matrices:

D = $alphaM * M + $betaK * Kcurrent +$betaKinit * Kinit + $betaKcomm * KlastCommit (1)

How to obtain alphaM, betaK ...?

We calculate alphaM and betaK (Rayleigh damping: C = anphaM*M +betaK*K) from 2 natural frequencies. (2)
Reference: Finley A. Charney, "Unintended Consequences of Modeling Damping in Structures", J. Struct. Engrg. Volume 134, Issue 4, pp. 581-592 (April 2008)

There is 3 cases for application of eq. (1):

1. D = $alphaM * M + $betaK * Kcurrent
where $alphaM = alphaM, $betaK = betaK

2. D = $alphaM * M + $betaKinit * Kinit
where $alphaM = alphaM, $betaKinit = betaK

3. D = $alphaM * M + $betaKcomm * KlastCommit
where $alphaM = alphaM, $betaKcomm = betaK

Is it right?

Thank you in advanced for your answer

[vesna]

Yes, you are right about everything.