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Calculating Radiation Resistance of Acoustic Medium

Posted Jul 22, 2011, 8:17 a.m. EDT MEMS & Nanotechnology, Acoustics & Vibrations, MEMS & Piezoelectric Devices Version 4.2 3 Replies

Sushil Bharatan
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I am trying to determine the radiation impedance of acoustic medium (water in this case) for a clamped vibrating membrane in a waveguide. The model is 2D axisymmetric, coupling pressure acoustic (acpr) and solid mechanics (solid). Membrane motion is accomplished by applying pressure and then running a frequency domain study. I am calculating the radiation resistance as real(p/solid.u_tZ) at the solid/medium interface (where solid.u_tZ is the membrane velocity in Z direction). The radiation resistance is also normalized by dividing by the specific impedance of the medium (rho*speed of sound in medium).
The problem is that the resulting value of the normalized radiation resistance appears to be too high (>7) while I was expecting a value less than 1 since the membrane radius is smaller than the waveguide radius.
I have also run this problem assuming a piston in a waveguide and get expected value of <1.
Any insight into this would be much appreciated.
Regards,
Sushil

p.s. I do not have the acoustics module, so I am using acpr from the MEMS module.

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3 Replies Last Post Sep 23, 2011, 11:40 a.m. EDT
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Hello Sushil Bharatan

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Marc
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Posted: 1 decade ago Sep 15, 2011, 5:27 p.m. EDT
I am having the same issue with a driven baffled circular piston in a large baffle. Radiation Resistance and Reactance do not follow the expected trend with frequency and are way too small compared to an analytic solution. I used real(integral(p)/avg(u_tZ)) on piston face. Also used point(u_tZ) and avg(u_tZ) with similar results.

Has anyone successfully extracted acoustic radiation loading?
I am having the same issue with a driven baffled circular piston in a large baffle. Radiation Resistance and Reactance do not follow the expected trend with frequency and are way too small compared to an analytic solution. I used real(integral(p)/avg(u_tZ)) on piston face. Also used point(u_tZ) and avg(u_tZ) with similar results. Has anyone successfully extracted acoustic radiation loading?
Sushil Bharatan
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Posted: 1 decade ago Sep 19, 2011, 11:51 a.m. EDT
Hope this helps.
Hope this helps.
Marc
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Posted: 1 decade ago Sep 23, 2011, 11:40 a.m. EDT
Thanks for the upload- helped me debug. The problem was with my analytic solution defining critical dimension as piston radius whereas I intrepreted it as diameter in the model. COMSOL was correct all along for what I gave it.

Got this working in 2D and 3D (1/4 model symmetry for square and circular pistons...attached). Matches analytic solution quite well.
Thanks for the upload- helped me debug. The problem was with my analytic solution defining critical dimension as piston radius whereas I intrepreted it as diameter in the model. COMSOL was correct all along for what I gave it. Got this working in 2D and 3D (1/4 model symmetry for square and circular pistons...attached). Matches analytic solution quite well.

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