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Acoustic Analysis 6dB drop not observed

Posted 16 mar 2010, 14:44 GMT-4 2 Replies

Mihir Shetye
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Hi all,

I am modeling a simple membrane in free space using the Acoustic-Structure interaction. The membrane is fixed at the edge and driven on the bottom surface. The membrane is 40 mm diameter and 19 um thick. I have modeled a 3d symmetry model and have also tried the 2d axi-symmetry model. There are two models, one with the membrane by itself and the other the membrane sitting on a baffle. The outermost boundary is modeled as infinite using radiation condition. I am looking at the SPL at certain distances from the membrane as a result of a harmonic analysis.
For the model with the membrane on the baffle, I am observing an expected 6 dB drop in the SPL with doubling of distance. When I remove the baffle, the SPL drops 12 dB, which I cannot explain. Can anyone point out the error in the model or the modeling scheme?

Thanks,
Mihir
2 Replies Last Post 3 mag 2011, 12:41 GMT-4
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Hello Mihir Shetye

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Mustafa Kavasoglu
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Posted: 1 decade ago 3 mag 2011, 05:03 GMT-4
Hello

I also have a similiar problem only difference is I have a plate instead of a membrane.

For me there is also a exactly 6 dB difference between teory and simulation in all points did you solve the problem ?

Best Regards

Mustafa
Hello I also have a similiar problem only difference is I have a plate instead of a membrane. For me there is also a exactly 6 dB difference between teory and simulation in all points did you solve the problem ? Best Regards Mustafa
Mihir Shetye
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Posted: 1 decade ago 3 mag 2011, 12:41 GMT-4
Hi Mustafa,

I think the problem is with the domain not being perfectly infinite. One of the things that I did was to completely separate the front and the back domains i.e. create the model of the membrane with the baffle. Then create the air domains on the front and back separately starting from the end of the baffle. This way the only interaction between front and back is through the membrane. This seemed to help my model and now I see a 6 dB drop as expected.

Try it and let me know if it works.

Mihir
Hi Mustafa, I think the problem is with the domain not being perfectly infinite. One of the things that I did was to completely separate the front and the back domains i.e. create the model of the membrane with the baffle. Then create the air domains on the front and back separately starting from the end of the baffle. This way the only interaction between front and back is through the membrane. This seemed to help my model and now I see a 6 dB drop as expected. Try it and let me know if it works. Mihir

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