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Velocity in Eigenfrequency Study

Posted Jul 11, 2014, 3:34 p.m. EDT Acoustics & Vibrations, Computational Fluid Dynamics (CFD), Studies & Solvers 3 Replies

Marta Iversen
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I trying to compute the eigenfrequecies and eigenmodes of a model (material is water) in the pressure acoustics and frequency domain. I have computed the Eigenfrequency study correctly. However, when I look at the generated values for the velocity (local RMS velocity, instantaneous, etc.) they are not what I am looking for and are all close to zero throughout the model. Is this because I am using the Sound Hard Boundary condition? Is the study even computing the velocity? Can I use another study or add another dependent variable that will actually calculate the velocity?

Thanks for any help
3 Replies Last Post Jul 11, 2014, 6:46 p.m. EDT
Edgar J. Kaiser Certified Consultant
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Posted: 10 years ago Jul 11, 2014, 4:45 p.m. EDT
Marta,

In an eigenfrequency and eigenmode study the mode amplitudes or deformations or whatever field characterizes the mode are arbitrary. If you want amplitudes or in your case velocities you have to do a frequency domain study and you have to excite the model (and the respective mode) some way.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Marta, In an eigenfrequency and eigenmode study the mode amplitudes or deformations or whatever field characterizes the mode are arbitrary. If you want amplitudes or in your case velocities you have to do a frequency domain study and you have to excite the model (and the respective mode) some way. Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com
Marta Iversen
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Posted: 10 years ago Jul 11, 2014, 5:41 p.m. EDT
Edgar,

Thanks so much for your response! I see now that there is no excitation and that is necessary for what I am looking for. Does the frequency domain study under the pressure acoustics, frequency domain physics do this? It looks like it inputs frequencies, do I use the eigenfrequencies here? I am trying to simulate sound going through my model.

Thanks for any help!!
Edgar, Thanks so much for your response! I see now that there is no excitation and that is necessary for what I am looking for. Does the frequency domain study under the pressure acoustics, frequency domain physics do this? It looks like it inputs frequencies, do I use the eigenfrequencies here? I am trying to simulate sound going through my model. Thanks for any help!!
Edgar J. Kaiser Certified Consultant
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Posted: 10 years ago Jul 11, 2014, 6:46 p.m. EDT
Marta,

I don't have the acoustics module but I am sure it can do what you need. You have to define how to excite the model by a port, source or a suitable boundary condition.
You can use the eigenfrequencies and/or do a frequency scan around the eigenfrequencies (or somewhere else) to get frequency profiles.
There should be examples in the model library.

Cheers
Edgar

--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Marta, I don't have the acoustics module but I am sure it can do what you need. You have to define how to excite the model by a port, source or a suitable boundary condition. You can use the eigenfrequencies and/or do a frequency scan around the eigenfrequencies (or somewhere else) to get frequency profiles. There should be examples in the model library. Cheers Edgar -- Edgar J. Kaiser emPhys Physical Technology http://www.emphys.com

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