To find Damping ratio through Harmonic dynamic analysis in ANSYS

[bkumar21]

Hello friends,
I have done modal analysis on a sandwich beam.Once I got natural frequencies I did harmonic analysis and obtained response curve (i.e amplitude vs. frequency) without initially considering any damping.Then,I used half-power method (or 3dB method)to find damping ratio.I run the Harmonic analysis once again with constant damping ratio and beta damping values to obtained the actual damping ratio.

Is this process correct? I do have experimental results and I wanted to compare those to damping ratio obtained through ANSYS.
Please,tell me the procedure to consider damping ratio or how to find damping ratio in ANSYS.Thank you !!

 

[bkumar21]

Hello everyone,

Could anyone please tell me how to find damping ratio in ANSYS(I am using ANSYS 11.0).

I am trying to obtained FRF (freq vs displacement curve )with guessing constant damping 2% and then to find damping ratio by half-power or 3 dB method.

Is it correct way ??.why we have to give damping if we have to find damping ratio?
Thank you!!!

 

[GregLocock]

If you put in a damping ratio of 2% then using the 3 dB method should give you the same answer.

You are using circular reasoning.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[spongebob007]

You can not find out what your damping is using FEA. Testing is the only way to determine damping. Damping is an input to FEA NOT and output.

In the past I have used Rayleigh damping in models where I determined the damping ratio at two frequencies by testing.