Eigenvalues in Axi Symmetric 2D

Numerical methods and mathematical models of Elmer
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AlfredBerger
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Eigenvalues in Axi Symmetric 2D

Post by AlfredBerger »

Hallo,

Is Eigenvalue calculation reasonable and doable in 2 D ?
Alfred
raback
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Re: Eigenvalues in Axi Symmetric 2D

Post by raback »

Yes. It is not question about dimension, it is more related to capabilities of specific solvers. Which solver are you considering? -Peter
AlfredBerger
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Re: Eigenvalues in Axi Symmetric 2D

Post by AlfredBerger »

Hallo Peter,

I want to analyze an ultrasonic mechanical system.
My knowledge is limited, which I can use next to StressSolver.
Problem is: I know the contour of the rotational symmetric situation which I would like to set - up with parameters.
So my sketch would be 2D. Then I would like to check the eigenmodes in the desired range to realize where longitudinal nodes in the structure are. Changing the various geometrical parameters I look for the spot for the node to fix the structure there (so far I could do it with modal anaysis).

When I have finalized the geometry I would then check the stresses of the parts over a broader frequency range (stability issue) by harmonic anaysis.

So my questions are:
Which solver would you recommend for the eigen analysis in 2 D ?
Which one for the harmonic analysis ? Checking a range of frequencies with "scanning" BC ?
Do you believe that your optimizational solver could find the optimum geometry ?

Thank you again and in advance for supporting newbies in the forum.
Alfred.
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Re: Eigenvalues in Axi Symmetric 2D

Post by raback »

Hi

StressSolver can do steady, transient, harmonic and eigenmode. So that is the solver to use.

-Peter
AlfredBerger
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Re: Eigenvalues in Axi Symmetric 2D

Post by AlfredBerger »

Hallo Peter,

from a axi symmetric 2D stress solver analysis doing looking for eigen frequencies: when I get eigenvalues I do not know, how to convert them to the frequency.
If I sqrt(Eigenvalue)/(2*Pi) this gives wrong values, but sqrt(Eigenvalue/(2*Pi)) is closer, but still not correkt.

Any issue I am missing, that need attendance for 2D Eigen value simulations ?
kevinarden
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Re: Eigenvalues in Axi Symmetric 2D

Post by kevinarden »

I believe eigenvalue = 2 * Pi * f

so

f = eigenvalue/2*Pi
mika
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Re: Eigenvalues in Axi Symmetric 2D

Post by mika »

I think the right conversion should be f = sqrt(eigenvalue)/(2 pi).

-- Mika
kevinarden
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Re: Eigenvalues in Axi Symmetric 2D

Post by kevinarden »

I agree I gave omega to frequency eigenvalue is omega squared
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