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Problem in Eigenfrequency calculus for piezoelectric model

Posted 18.12.2010, 11:30 GMT-5 Structural Mechanics Version 4.0a 3 Replies

Daniele Lupo
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Hi.

I'm trying to studi a piezoelectric model of a transducer. In my project, I create two simulation, a frequency domain simulation and an eigenfrequency.

The frequency domain simulation is right, and I've resonances that agree with experimental results, but when I calculate eigenmodes for the same model, I've got some warning, and eigenfrequency values have no-sense for me, both in values and displacement of the model.

What's the right setting for a good eigenfrequency analysis?

I'm using Comsol 4.0.0.982 on Windows 7 64bit.

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3 Replies Last Post 29.12.2010, 04:04 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 22.12.2010, 15:21 GMT-5
Hi

if your device is free hanging in space you shouldexpect at least 6 modes around 0Hz, in your sphereical symmetry wth fluid damping you could even have a few degenerated so you have pobably more than 6 modes close to "0", then you will see higher modes

then you could specify n modes around 1 higher frequency than "0Hz"


--
Good luck
Ivar
Hi if your device is free hanging in space you shouldexpect at least 6 modes around 0Hz, in your sphereical symmetry wth fluid damping you could even have a few degenerated so you have pobably more than 6 modes close to "0", then you will see higher modes then you could specify n modes around 1 higher frequency than "0Hz" -- Good luck Ivar
Daniele Lupo
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Posted: 1 decade ago 28.12.2010, 13:34 GMT-5
Hi. Thank you for your reply.

I've tried to find eigenfrequencies around a value, but I don't find anything. frequencies are always complex, and are random, both positive and negative values, and are not close to my search frequency (30kHz).

I've also noticed a warning in the solver, giving message like this one:

"The relative residual is greater than the relative tolerance.
Relative residual 4.8e+003"

Maybe it can be the problem? How can I solve it?
Hi. Thank you for your reply. I've tried to find eigenfrequencies around a value, but I don't find anything. frequencies are always complex, and are random, both positive and negative values, and are not close to my search frequency (30kHz). I've also noticed a warning in the solver, giving message like this one: "The relative residual is greater than the relative tolerance. Relative residual 4.8e+003" Maybe it can be the problem? How can I solve it?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 29.12.2010, 04:04 GMT-5
Hi

which values do you get ? for me it looks like you have not got your model "fixed" well enough or some BC are missing, but hat is just a "guess" not knowing more about your case.

The warning message could come from a too coarse mesh, it happens less often in v4.1

--
Good luck
Ivar
Hi which values do you get ? for me it looks like you have not got your model "fixed" well enough or some BC are missing, but hat is just a "guess" not knowing more about your case. The warning message could come from a too coarse mesh, it happens less often in v4.1 -- Good luck Ivar

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