I'm using complex eigenvalue analysis for brake noise prediction, which tends to overpredict instability modes. To mitigate this, I'm employing Rayleigh damping. By setting Beta in the order of E-6, I observe a reduction in unwanted instability modes, consistent with findings from a research paper. However, my calculated Beta values are consistently coming out in the order of E-8, whereas I expect them to be in the order of E-6. I want to know whether am I missing anything in the Rayleigh damping calculation. How to cross check my calculation? I want to know whether am I missing anything in the Rayleigh damping calculation? Need suggestions regarding this
Beware that different finite element codes defines alpha and beta differently! That said, I usually get beta around 1e-6, for many problems. I can sent the equations to solve for alpha and beta later when Iam at the computer. BR Kenth
Kenth Nilsson Thanks for your reply. As you mentioned , please share the document , what you used to calculate the damping
Gurumoorthy Sp As already mentioned by Kenth Nilsson , the definition of the Rayleigh damping parameters is not uniform in the literature. In principle, any natural frequency can be used to calculate the parameters. This also shows the weakness of the approach. The main advantage is that the eigenvectors of the undamped system also diagonalize the damping matrix.
Gurumoorthy Sp, I use the formulas for calculating alpha and beta that one can find at many places, when we choose two frequencies and two damping values. I googled and the Comsol manual present this easily, see https://doc.comsol.com/5.5/doc/com.comsol.help.sme/sme_ug_modeling.05.083.html BR, Kenth
Hello, the above colleagues have answered this question nicely. The Rayleigh damping parameters are not constants over different mode shapes. Therefore, two eigenvalues should be selected within the interested frequency ranges, especially for polymers. To see the effect of this selection, I attached one of our papers for your reference.
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