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Consider damping of spring/damper in modal analysis

Pioneer
Pioneer

Hello all,

 

I have two solid parts connected by a spring/damper (each node of the spring/damper ist connected to the part by a rigid RBE3 element). I make this to explore the impact of stiffness and damping on my modal analysis results. But no matter what damping values I use in the spring/damper, it won't have an impact on the frequencies of the modal analysis.

Can anyone help me?

4 REPLIES 4

Re: Consider damping of spring/damper in modal analysis

Gears Phenom Gears Phenom
Gears Phenom
Your damping value will not change the resonant frequencies of your structure - instead they alter the peak response.

To change the frequencies the stiffness of the structure needs to change.

Re: Consider damping of spring/damper in modal analysis

Gears Phenom Gears Phenom
Gears Phenom

Svede

 

See image below regarding the effect of damping on structures. I have created a single CBUSH with a lumped mass at one end with and constrainted and loaded at the other.

 

- highest peak is zero damping

 -reduced peak is 5% damping

 

Hope this helps.

 

DAMP.JPG

Re: Consider damping of spring/damper in modal analysis

Genius
Genius

Another visual.  Damped vs Undamped.

 

Same natural frequency (distance between peaks). 

 

Recall that the natural frequency is derived from mass (m) and spring rate (k); damping doesn't play a role (which you have confirmed!) 

 

Types-of-oscillations.jpg

 

 

Re: Consider damping of spring/damper in modal analysis

Pioneer
Pioneer

Thanks guys!

It was my fault, damping has of course no impact on the frequences in modal analysis. In the frequency response analysis you can see the effect though.