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Modal assurance criterion (MAC) calculation

Posted Mar 21, 2019, 1:08 a.m. EDT Structural & Acoustics, Acoustics & Vibrations Version 5.4 3 Replies

Panson Poon
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Does COMSOL calculate MAC of mode shapes obtained by FEA and mode shapes derived from experimental modal analysis (EMA)?

Is there a command for MAC?

Thank you!

3 Replies Last Post Mar 21, 2019, 6:13 a.m. EDT
Henrik Sönnerlind COMSOL Employee

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Posted: 6 years ago Mar 21, 2019, 3:46 a.m. EDT

Hi Panson,

There is no built-in MAC functionality. You can however compute an index by using the built-in integration operators and integrate a normalized inner product between two modes. For two modes computed inside COMSOL Multiphysics, you can use expressions like this:

intop1(withsol('sol3',u,setind(lambda,1))*withsol('sol4',u,setval(lambda,2))+ withsol('sol3',v,setind(lambda,1))*withsol('sol4',v,setval(lambda,2))+ withsol('sol3',w,setind(lambda,1))*withsol('sol4',w,setval(lambda,2)))

This expression computes the inner product between the first mode in solution 'sol3' and the second mode in the solution 'sol4', assuming that 'intop1' integrates over the whole domain and that mass matrix normalization has been used.

The crucial point if you have measured data is how to import it, so that the experimental mode shape is attached to the computational domain so that a similar integral can be computed.

Regards,
Henrik

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Henrik Sönnerlind
COMSOL
Hi Panson, There is no built-in MAC functionality. You can however compute an index by using the built-in integration operators and integrate a normalized inner product between two modes. For two modes computed inside COMSOL Multiphysics, you can use expressions like this: intop1(withsol('sol3',u,setind(lambda,1))\*withsol('sol4',u,setval(lambda,2))+ withsol('sol3',v,setind(lambda,1))\*withsol('sol4',v,setval(lambda,2))+ withsol('sol3',w,setind(lambda,1))\*withsol('sol4',w,setval(lambda,2))) This expression computes the inner product between the first mode in solution 'sol3' and the second mode in the solution 'sol4', assuming that 'intop1' integrates over the whole domain and that mass matrix normalization has been used. The crucial point if you have measured data is how to import it, so that the experimental mode shape is attached to the computational domain so that a similar integral can be computed. Regards, Henrik
Panson Poon
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Posted: 6 years ago Mar 21, 2019, 3:52 a.m. EDT

Hi Henrik,

Thank you for your response!

Would LiveLink for MATLAB make thing easier? Mode shapes in COMSOL experted to Matlab where processes experimental data.

Cheers, Panson

Hi Henrik, Thank you for your response! Would LiveLink for MATLAB make thing easier? Mode shapes in COMSOL experted to Matlab where processes experimental data. Cheers, Panson
Henrik Sönnerlind COMSOL Employee

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Posted: 6 years ago Mar 21, 2019, 6:13 a.m. EDT

Hi Panson,

Yes, LiveLink for MATLAB can be useful here.

Using a Model Method could be another alternative.

Regards,
Henrik

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Henrik Sönnerlind
COMSOL
Hi Panson, Yes, LiveLink for MATLAB can be useful here. Using a Model Method could be another alternative. Regards, Henrik

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