Modeling Tuned Mass damper in NX Nastran

[caemagic]

any body has an idea on how to a viscoelastic tuned mass damper on Nastran

Thank you

cae magic

 

[rob768]

To my understanding, a tuned mass damper should have as little damping as possible in order to be most functional. It should be a separate mass/spring system with the same natural frequency as the system it is applied to. The result is two natural frequencies, one above and one below the original resonance, with lower "peaks" as the orignal resonance. Any dampign lowers the effect of the added mass.
This is easily modelled using mass and spring elements.
I have not heard of a visco elastic tuned mass damper, but off course that doesn't mean i can't be wrong here.

 

[caemagic]

Dear rob

Thank you so much for your reply , I have a visco-elastic tuned mass damper in a structure which I would like to model , since the mass added is rubber , hence there's some damping , if an equivalent in terms of springs, dampers and mass to be made , how do we model it ?

 

[electricpete]

rob - an undamped TMD does well at reducing response at a single tuned frequency of interest, at the expense of introducing two new resonances nearby on either side of that single tuned frequency. A damped TMD does not do quite as well at the single frequency, but the two new resonances nearby are much "smaller" (damped). So for single-frequency excitation, an undamped TMD would often be chosen, while for variable frequency excitation a damped TMD would often be chosen.

caemagic - it should be representable as combination of ideal mass, spring, damper elements. Exactly how to arrange them and what values to use... maybe start with whoever sold/built the damper?


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(2B)+(2B)' ?

 

[rob768]

Thx for correcting me Pete. We usually see only such dampers aimed at detuning a single frequency. I didn't know the principle was applicable to more than one frequency. Should it still be called a "tuned" mass damper?
I suppose a viscous or rubber engine damper is something like this?

regards
rob

 

[caemagic]

Dear Guys

Thank you so much for your reply , it is so exciting for to share knowledge. Please refer to the attachment for further detail of the problem , I have a machine which has a vibration problem , i add these visco-elastic materials, rubber. by trial and error , I reduce the response. Now that I would to model the material in SOL 103 , I thought that a combination of springs and dampers should do , however , I dunno how to test it. I am not sure whether it's a correct practice to just model the damper into a spring and mass only. Please refer to attachement for further detail