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Why the COMSOL results can not give infinity values at resonance?
Posted Mar 27, 2017, 9:13 a.m. EDT Acoustics & Vibrations Version 5.2 2 Replies
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Dear all,
I am now stuck in a problem about the acoustic pressure distribution inside a long duct with a monopole source in the cubic center.
Considering one-dimension wave propagation problems, when all of the surfaces were set as 'sound hard boundary', why can't the acoustic pressure reach the infinite value at resonance?
The COMSOL document gives the following discussion: when the sound waves propagate in a lossless medium, attenuation frequently occurs by interaction with the surrounding at the boundaries of the system.
There might be some assumptions in the software when dealing with the calculation, but for the influence on the maximum values at resonance, I wonder how and to what extent the boundary condition or assumption affect the final pressure results, in detail?
Thank you very much in advance.
I am now stuck in a problem about the acoustic pressure distribution inside a long duct with a monopole source in the cubic center.
Considering one-dimension wave propagation problems, when all of the surfaces were set as 'sound hard boundary', why can't the acoustic pressure reach the infinite value at resonance?
The COMSOL document gives the following discussion: when the sound waves propagate in a lossless medium, attenuation frequently occurs by interaction with the surrounding at the boundaries of the system.
There might be some assumptions in the software when dealing with the calculation, but for the influence on the maximum values at resonance, I wonder how and to what extent the boundary condition or assumption affect the final pressure results, in detail?
Thank you very much in advance.
2 Replies Last Post Mar 29, 2017, 10:44 a.m. EDT
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Posted:
7 years ago
Dear Li,
If you do a frequency domain analysis at resonance frequency with no damping at all you should get infinite deformation. The main reason this doesn’t happen in my experience is that you don’t have the resonant frequency input accurately to sufficient significant digits!
Nagi Elabbasi
Veryst Engineering
If you do a frequency domain analysis at resonance frequency with no damping at all you should get infinite deformation. The main reason this doesn’t happen in my experience is that you don’t have the resonant frequency input accurately to sufficient significant digits!
Nagi Elabbasi
Veryst Engineering
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Posted:
7 years ago
Dear Nagi Elabbasi,
Thank you so much for your answer.
I followed the suggestion you gave here and changed the frequency of the sound source, the peak pressure value gets much higher when the frequency was set as 34.3Hz, it is 1.09*10^4 Pa. but it is still not infinity.
since the default speed of sound in the air in COMSOL is 343m/s. I believe I may not really understand the ‘significant digit’ in your answer. Could you please clarify the meaning of this term? And how could I explain the not-infinite-values of the acoustic pressure under this condition? Thank you for your time.
The details of the case were in the attached file. For your information.
Regards.
LI Dongfang
Thank you so much for your answer.
I followed the suggestion you gave here and changed the frequency of the sound source, the peak pressure value gets much higher when the frequency was set as 34.3Hz, it is 1.09*10^4 Pa. but it is still not infinity.
since the default speed of sound in the air in COMSOL is 343m/s. I believe I may not really understand the ‘significant digit’ in your answer. Could you please clarify the meaning of this term? And how could I explain the not-infinite-values of the acoustic pressure under this condition? Thank you for your time.
The details of the case were in the attached file. For your information.
Regards.
LI Dongfang
Attachments: