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Absolute Pressure Smaller Than expected

Posted 23.04.2021, 19:00 GMT-4 Acoustics & Vibrations Version 5.6 3 Replies

Ken Halverson
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The below post is related to an archived discussion

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Hello,

I have a problem with plotting absolute pressure for a single element piston ultrasound transducer. After running the pressure acoustics module, my maximum absolute pressure is ~0.47 MPa. I have defined a flat line at the bottom of a water tank as my transducer, with a dispalcement assigned. When comparing with another Matlab based simulation model (Field II), it predicts an absolute pressure value 6 times larger (~3 MPa). This 6 fold discrepency has been brought up in a past post on this forum with no answer or explanations provided. Does anyone have any ideas what is happening here?

3 Replies Last Post 28.08.2021, 20:20 GMT-4
Mark Cops Triton Systems, Inc.
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Posted: 3 years ago 01.05.2021, 06:51 GMT-4

Hi Ken, To what are you benchmarking this model against?

I simplified the attached model in the following ways: constant water material properties, no losses, and velocity boundary condition on the piston surface. This allows for direct comparison with analytical solution, for example section 7.4 in Kinsler and Frey. Here the radiation field from a circular piston is derived and an exact expression for complex acoustic pressure along the acoustic (z) axis can be determined.

When I compare the attached model to the analytical expression, the agreement is quite well (see 1D plot group "axial pressure (Pa)". The analytical expression for complex pressure is computed and stored as a variable in definitions.

Hi Ken, To what are you benchmarking this model against? I simplified the attached model in the following ways: constant water material properties, no losses, and velocity boundary condition on the piston surface. This allows for direct comparison with analytical solution, for example section 7.4 in Kinsler and Frey. Here the radiation field from a circular piston is derived and an exact expression for complex acoustic pressure along the acoustic (z) axis can be determined. When I compare the attached model to the analytical expression, the agreement is quite well (see 1D plot group "axial pressure (Pa)". The analytical expression for complex pressure is computed and stored as a variable in definitions.
Ken Halverson
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Posted: 3 years ago 03.06.2021, 20:22 GMT-4

Hey Mark,

Sorry for the late reply, I havent been checking my COMSOL account and was focuisng on some other projects. Thank you so much for your help, this is a great reference to use for validation!

I was benchmarking against a piston transducer pressure field I was simulating with Field II (a Matlab based ultrasound simulation). I was comparing absolute pressure profiles in a water tank with attenuation. In the simplified COMSOL simulation you have provided, how did you determine the value of velocity, V = 0.01 m/s, to assign to the piston transducer? Is there an advantage to using this velocity boundry condition as opposed to the normal displacement I had before?

Thank you

Hey Mark, Sorry for the late reply, I havent been checking my COMSOL account and was focuisng on some other projects. Thank you so much for your help, this is a great reference to use for validation! I was benchmarking against a piston transducer pressure field I was simulating with Field II (a Matlab based ultrasound simulation). I was comparing absolute pressure profiles in a water tank with attenuation. In the simplified COMSOL simulation you have provided, how did you determine the value of velocity, V = 0.01 m/s, to assign to the piston transducer? Is there an advantage to using this velocity boundry condition as opposed to the normal displacement I had before? Thank you
Mark Cops Triton Systems, Inc.
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Posted: 3 years ago 28.08.2021, 20:20 GMT-4

Hi Ken, I think I chose the velocity boundary condition just to match the analytical case, but I don't see a specific advantage over a normal displacement. The value used was not selected for any specific reason, just to check against the benchmark.

Hi Ken, I think I chose the velocity boundary condition just to match the analytical case, but I don't see a specific advantage over a normal displacement. The value used was not selected for any specific reason, just to check against the benchmark.

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