Hi,
I am trying to validate the results of test and simulation. When I applied a constant damping ratio for every mode freqeuncies, I have similar response for some of the mode frequencies responses, but some of the responses are not really match at the mode freqeuncies. Is it possible to have different damping ratios in different mode freqeuncies for isotropic one part structure in reality?
Best Regards
It is not clear what you are really asking. But you can have different modal damping for different modes of a structure, even if the material is isotropic because the viscous damping is just a way to represent dissipation in a convenient mathematical way. Therefore, in a structure you can have experimental value of damping different for the different modes. For what concerns simulations, it is more or less the same, only few FE codes allow to insert directly modal damping, but they typically use different modelling way (material damping, rayleigh damping, etc.).
Yes, a structure could have different modal damping in different modes of vibration.
Yes damping can be different in different modes, but generally it is referred for the lowest or the fundamental mode.
Dear Anup,
Why is it reffered for the lowest or the fundemental modes? Also, what is the interval for the lowest frequency? Can't we refer the damping ratios for high frequencies?
Generally higher modes are difficult to excite since they require lot of energy to do so. Systems have lot of damping in higher modes. Mostly the lower modes have low damping and are easiest to excite, making them the the most vulnerable for external forces to make it unstable. I think it makes some sense!!
In my simulation, the response in second mode is much larger than that of the first mode, I select the same damping ratio for different modes, so I guess maybe there is sth wrong using unified damping ratio.
Mostly lower modes are critical for stability. Hence damping for these modes is very important. Damping ratios can be measured for higher modes also.
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