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Isolating eigenfrequency analysis for modes of interest

Posted 25 oct. 2017, 14:26 UTC−4 MEMS & Nanotechnology 2 Replies

Valerie Scott
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Is there a way to isolate for specific modes of interest in running an eigenfrequency analysis without knowing at what frequency that mode will occur? For example, if I have a resonator structure suspended by clamped arms, when you run an eigenfrequency analysis, you'll get a bunch of modes that involve those arms. Let's say I'm looking for the first bending mode of the larger structure, or a thickness mode, or a shear mode, but I don't care about the modes involving the arms except to factor in damping losses, calculating Q, etc. Is there a way to select for areas of the structure to isolate for the modes of interest?

Thanks,

2 Replies Last Post 26 oct. 2017, 04:33 UTC−4
Dave Greve
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Posted: 7 years ago 25 oct. 2017, 21:40 UTC−4

I have suggested one way to approach this, see

http://dwgreveconsulting.com/gallery/sortingmodes.pdf

What you do is come up with some quantity (that can be calculated as a Derived Value) that is large or small for the particular modes of interest. Then do an eigenfrequency analysis and plot that quantity as a function of eigenfrequency.

For a particular problem I was interested in (surface wave modes) it is easy to look for modes that have minimal energy density in the bulk and large energy density at the surface.

D.W. Greve DWGreve Consulting

I have suggested one way to approach this, see http://dwgreveconsulting.com/gallery/sortingmodes.pdf What you do is come up with some quantity (that can be calculated as a Derived Value) that is large or small for the particular modes of interest. Then do an eigenfrequency analysis and plot that quantity as a function of eigenfrequency. For a particular problem I was interested in (surface wave modes) it is easy to look for modes that have minimal energy density in the bulk and large energy density at the surface. D.W. Greve DWGreve Consulting
Henrik Sönnerlind COMSOL Employee

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Posted: 7 years ago 26 oct. 2017, 04:33 UTC−4

Hi,

For solid mechanics, the mode participation factors can be used to get some insight into the type of modes.

An example of this can be found in

https://www.comsol.com/model/truss-bridge-designer-30831

where the participation factors are scanned using a method coded in the Application Builder (mDefaultMode). The purpose is to automatically plot the most interesting mode (the first mode of the bridge deck).

Regards,

Henrik

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Henrik Sönnerlind
COMSOL
Hi, For solid mechanics, the mode participation factors can be used to get some insight into the type of modes. An example of this can be found in https://www.comsol.com/model/truss-bridge-designer-30831 where the participation factors are scanned using a method coded in the Application Builder (mDefaultMode). The purpose is to automatically plot the most interesting mode (the first mode of the bridge deck). Regards, Henrik

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