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Acoustic-Solid Interaction Coupling

Posted May 29, 2024, 3:54 p.m. EDT Structural & Acoustics, Acoustics & Vibrations, Structural Mechanics Version 6.2 5 Replies

Jeffrey Shi
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Hello,

I'm currently working with a model in the Acoustic-Solid Interaction, Frequency Domain Interface, but I'm having issues with coupling two air domains through a solid interlayer (steel). I've incorporated the acoustic-structure boundary, but it seems that the pressure acoustic domains are not talking to each other. This issue does not arise when I model the interlayer membrane using the Pressure Acoustics module, and only occurs when I have the interlayer under Solid Mechanics.

I've tried to change the thickness of the membrane (also have tried using Thin Layer and Membrane interfaces) and the material (tried using Wood) to no avail, and it just seems like I can't get the air cavities in my model to couple in the z-direction.

Any advice would be appreciated.

Best, Jeffrey

5 Replies Last Post Jun 6, 2024, 11:05 a.m. EDT
Acculution ApS Certified Consultant
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Posted: 10 months ago May 30, 2024, 2:59 a.m. EDT

There is an eigenfrequency analysis with solid mechanics disabled in the file. So you are just getting the acoustic modes for each of the two domains. Do you have a file that fits with the problem that you describe (Frequency Domain analysis)?

-------------------
René Christensen, PhD
Acculution ApS
www.acculution.com
info@acculution.com
There is an eigenfrequency analysis with solid mechanics disabled in the file. So you are just getting the acoustic modes for each of the two domains. Do you have a file that fits with the problem that you describe (Frequency Domain analysis)?
Jeffrey Shi
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Posted: 10 months ago May 30, 2024, 5:57 p.m. EDT

Hi René,

Thank you so much for the reply! I disabled the Solid Mechanics in the Eigenfrequency Study because I don't want to search for pressure modes/eigenvalues within the steel or wood. I'm only searching for the eigensolutions within the air cavities of my model. I've updated my file so that this can be illustrated more clearly.

My issue currently is that when I have the wood interlayer membrane (labeled domain 3) under Solid Mechanics, the coupling between the two layers doesn't seem to register. I've attached two screenshots, showing what I expect (and get when I select the interlayer domain under Pressure Acoustics instead) vs. what I get (interlayer under Solid Mechanics). I thought that the Acoustic-Structure boundary would properly couple the two domains, but it doesn't seem to be operating as expected. I'm wondering if there's something wrong with my modeling strategy that is resulting in this issue.

Also, would it change anything to select the interlayer domain under both Pressure Acoustics and Solid Mechanics?

Please let me know if my problem is still unclear.

Best, Jeffrey

Hi René, Thank you so much for the reply! I disabled the Solid Mechanics in the Eigenfrequency Study because I don't want to search for pressure modes/eigenvalues within the steel or wood. I'm only searching for the eigensolutions within the air cavities of my model. I've updated my file so that this can be illustrated more clearly. My issue currently is that when I have the wood interlayer membrane (labeled domain 3) under Solid Mechanics, the coupling between the two layers doesn't seem to register. I've attached two screenshots, showing what I expect (and get when I select the interlayer domain under Pressure Acoustics instead) vs. what I get (interlayer under Solid Mechanics). I thought that the Acoustic-Structure boundary would properly couple the two domains, but it doesn't seem to be operating as expected. I'm wondering if there's something wrong with my modeling strategy that is resulting in this issue. Also, would it change anything to select the interlayer domain under both Pressure Acoustics and Solid Mechanics? Please let me know if my problem is still unclear. Best, Jeffrey
Acculution ApS Certified Consultant
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Posted: 10 months ago May 31, 2024, 2:21 a.m. EDT

Again, your file is set up in a way that only includes acoustic modes, and not the actual problem that you are having. Are you interested in having the coupling present when solving an eigenmode analysis or a frequency sweep? If you enable structural mechanics and acoustics and you have a Multiphysics coupling, the coupling should be there.

-------------------
René Christensen, PhD
Acculution ApS
www.acculution.com
info@acculution.com
Again, your file is set up in a way that only includes acoustic modes, and not the actual problem that you are having. Are you interested in having the coupling present when solving an eigenmode analysis or a frequency sweep? If you enable structural mechanics and acoustics and you have a Multiphysics coupling, the coupling should be there.
Jeffrey Shi
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Posted: 10 months ago May 31, 2024, 3:08 p.m. EDT
Updated: 10 months ago May 31, 2024, 3:09 p.m. EDT

Hi René,

Thanks again for your reply. When I enable both solid mechanics and presssure acoustics in the study, it does not properly account for the coupling. I've tried this multiple times. I always have the multiphysics coupling enabled. This is why I am stuck. It should be clear if you enable it in my COMSOL file, but if not apologies for the confusion. I'm hoping to both solve an eigenmode analysis and frequency sweep, although the current file only includes the eigenfrequency study.

Please let me know if my issue is still not clear.

Jeffrey

Hi René, Thanks again for your reply. When I enable both solid mechanics and presssure acoustics in the study, it does not properly account for the coupling. I've tried this multiple times. I always have the multiphysics coupling enabled. This is why I am stuck. It should be clear if you enable it in my COMSOL file, but if not apologies for the confusion. I'm hoping to both solve an eigenmode analysis and frequency sweep, although the current file only includes the eigenfrequency study. Please let me know if my issue is still not clear. Jeffrey
Mark Cops COMSOL Employee

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Posted: 10 months ago Jun 6, 2024, 11:05 a.m. EDT
Updated: 10 months ago Jun 6, 2024, 11:06 a.m. EDT

If you solve the Eigenfrequency problem with Pressure Acoustics, Solid Mechanics, and Acoustic-Structure Boundary all enabled, you can compute the coupled natural frequencies and mode shapes. The Acoustic-Structure Boundary is showing (correctly) the boundaries for which the multiphysics is enforced.

It seems you are not getting an expected result - but this could be due to other issues instead of the multiphsyics coupling. For example, check the mesh - is this resolving the mode shape? It looks like the Young's modulus for American red oak is set to 1 Pa. Is this correct? This is very soft and will result in very slow wave speeds. Keep in mind that if you solve Domain 3 with Pressure Acoustics, along with a different physics assumption, it will utilize different material properites (speed of sound and density) compared to if the domain is solved with Solid Mechanics.

-Mark

If you solve the Eigenfrequency problem with Pressure Acoustics, Solid Mechanics, and Acoustic-Structure Boundary all enabled, you can compute the coupled natural frequencies and mode shapes. The Acoustic-Structure Boundary is showing (correctly) the boundaries for which the multiphysics is enforced. It seems you are not getting an expected result - but this could be due to other issues instead of the multiphsyics coupling. For example, check the mesh - is this resolving the mode shape? It looks like the Young's modulus for American red oak is set to 1 Pa. Is this correct? This is very soft and will result in very slow wave speeds. Keep in mind that if you solve Domain 3 with Pressure Acoustics, along with a different physics assumption, it will utilize different material properites (speed of sound and density) compared to if the domain is solved with Solid Mechanics. -Mark

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