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[comsol 3.5a] how to insert viscous damping
Posted 8 nov. 2009, 10:28 UTC−5 2 Replies
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Hello
I must do a frequency response analysis of a structure with a fixed damping of 2.75%. I note that in Structural module there is only rayleigh damping or loss factor. I watch on pdf help(smeug pag 42 chapter 4) and it says that is possible to use euivalent viscous damping with the Eq_Beta_K=loss factor/excitation frequency. I don't know the way to obtain loss factor and I also suppose that the parameter Eq_Beta_K should change in relation with the excitation frequency. So I would ask what is the way to insert a constant viscous damping of 2.75% for my analysis?
Thank you for your advices
Luca
I must do a frequency response analysis of a structure with a fixed damping of 2.75%. I note that in Structural module there is only rayleigh damping or loss factor. I watch on pdf help(smeug pag 42 chapter 4) and it says that is possible to use euivalent viscous damping with the Eq_Beta_K=loss factor/excitation frequency. I don't know the way to obtain loss factor and I also suppose that the parameter Eq_Beta_K should change in relation with the excitation frequency. So I would ask what is the way to insert a constant viscous damping of 2.75% for my analysis?
Thank you for your advices
Luca
2 Replies Last Post 10 nov. 2009, 11:32 UTC−5
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Posted:
1 decade ago
Hi
you have a couple of options, there is quite more in the 3.5a structural smeug.pdf doc about damping (i.e. pp 140++, 199, 372). Normally you can optimise the AlphadM and the BetadK such that you have +/- a constant damping between two frequencies. There is an example also somewere with a bit of matlab code to find the two values, but just now I cannot identify where that was, neither can I find back my M file, I used.
If the damping is purely viscuous, you can also add a force as F=-c*v where v=ut,vt,wt it's also described in the same doc (p146).
Do a search with "damping" "viscous damping" on the docs, see also the memsug.pdf
Good luck
Ivar
you have a couple of options, there is quite more in the 3.5a structural smeug.pdf doc about damping (i.e. pp 140++, 199, 372). Normally you can optimise the AlphadM and the BetadK such that you have +/- a constant damping between two frequencies. There is an example also somewere with a bit of matlab code to find the two values, but just now I cannot identify where that was, neither can I find back my M file, I used.
If the damping is purely viscuous, you can also add a force as F=-c*v where v=ut,vt,wt it's also described in the same doc (p146).
Do a search with "damping" "viscous damping" on the docs, see also the memsug.pdf
Good luck
Ivar
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Posted:
1 decade ago
Hello Ivar
Thank you for your advice, I already used the code but i expected to find a solution that gave to me a constant viscous damping. However you gave to me a good idea, now i will try to optimize the coefficients to find a damping near to constant value.
Thank you again
Luca
Thank you for your advice, I already used the code but i expected to find a solution that gave to me a constant viscous damping. However you gave to me a good idea, now i will try to optimize the coefficients to find a damping near to constant value.
Thank you again
Luca