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Thermal stress in resonant beams

Posted Mar 1, 2012, 11:13 a.m. EST Studies & Solvers, Structural Mechanics Version 4.2 2 Replies

Tom Larsen
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Hi All

I have tried to simulate the resonance frequency of a beam which contains some thermal stress. I do following:

1 3D -> Thermal stress (st) -> eigenfrequency

2 Make a beam and select material

3 Fix the two ends of the beam and set the strain reference temperature above the temperature of the simulated beam.

4 Compute the eigenfrequency

Then I get some resonance frequencies. However they are not different from the case where the strain reference temperature is equal to the temperature of the simulated beam.

If I then include geometric nonlinearity the resonance frequencies become dependent on the difference between strain reference temperature and the temperature of the simulated beam. The reason why I need to include geometrical nonlinerarity is not clear for me. I have been reading in the documents in the help function but I am still confused.

Can any one tell me why I need to include geometrical nonlinearity?

2 Replies Last Post Mar 6, 2012, 2:26 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 2, 2012, 1:54 a.m. EST
Hi

I would chain two solver nodes under the same study, first a sttionary to resolve your strain temperature difference into true stress levels, and then an eigenfrequency, telling COMSOL to use the results of the stored stationary case as linearisation point. (normally in v4.2a this si done by default if you shain two or mode solver sub-nodes under the same sudy, worth to check anyhow, and sometimes you need to adapt a little

This shuld work

--
Good luck
Ivar
Hi I would chain two solver nodes under the same study, first a sttionary to resolve your strain temperature difference into true stress levels, and then an eigenfrequency, telling COMSOL to use the results of the stored stationary case as linearisation point. (normally in v4.2a this si done by default if you shain two or mode solver sub-nodes under the same sudy, worth to check anyhow, and sometimes you need to adapt a little This shuld work -- Good luck Ivar
Tom Larsen
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Posted: 1 decade ago Mar 6, 2012, 2:26 p.m. EST
Hi Ivar

I have changed the model to include a stationary and an eigenfrequency solver. However I still need to include geometrical nonlinerarity. Why is it neccessary to include geometrical nonlinerarity?

Best regards
Tom
Hi Ivar I have changed the model to include a stationary and an eigenfrequency solver. However I still need to include geometrical nonlinerarity. Why is it neccessary to include geometrical nonlinerarity? Best regards Tom

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