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Eigenfrequency Analysis
Posted 25.07.2023, 06:46 GMT-4 MEMS & Piezoelectric Devices Version 5.6 3 Replies
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Hello, i want to model a cantilever beam piezoelectric bimorph with 2 blocks of PZT-5A and a middle block of stainless steel.When i compute the analysis the 6 eigenfrequencies are correct but the expression of the displacement is displacement magnitude and not total displacement like other studies i have seen and the values are way wrong. Any suggestions?
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Hi George,
An eigenfrequency analysis solves for the natural frequencies and mode shapes. The mode shape is a vibration pattern (it can be scaled or normalized and still the same mode shape is maintained). The mode shapes are not meant to be interpreted as physical displacement amplitudes.
To determine physical displacement amplitudes, you need to solve a frequency domain study with an actual load condition applied.
Best, -Mark
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Thank you Mark for your response. My problem is at the default plote of Mode Shape the eigenfrequencies are correct and the mode shapes are correct but it shows at displacement magnitude and not at total displacement and they are completely wrong .I ran some models from the Comsol Video Gallery and the results are way off(my model 1.02 x 10^-4 mm and the correct was 3214 mm). My thoughts are than some options are wrong.
Thank you again.
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Hello George,
To rephrase what Mark said earlier, the magnitude of an eigenmode is arbitrary - it has no meaning. You can multiply an eigenmode by any number and it's still the same eigenmode for the same eigenfrequency.
Best,
Jeff
-------------------Jeff Hiller