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How reflection is modeled in acoustic module?

Posted Feb 8, 2019, 4:50 a.m. EST Acoustics & Vibrations Version 5.4 1 Reply

Ze Zhang
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Hi,

Recently I am modeling a transmission and reflection problem using background pressure field+PMLs. I found that the scattered field (acpr.p_s) can only be visualized in background field. The value of acpr.p_s is the same as the total pressure filed (acpr.p_t) on all the other domains. My questions are:

  1. Is there a prefered practice on where to assign the background pressure field?
  2. Is the acpr.p_s still accouted during the calculation but not stored in all the other domains?
  3. Can pressure acoutics module capture multiple reflections in the domain? A simple case is a point source in the room, instead of being only one time reflection, in deed there will be multiple times of reflection.
  4. If it's capable of capturing this, is there a limit on how many times the software can capture?

BR, Zhang Ze

1 Reply Last Post Feb 11, 2019, 9:46 a.m. EST
Kirill Shaposhnikov COMSOL Employee

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Posted: 6 years ago Feb 11, 2019, 9:46 a.m. EST
Updated: 6 years ago Feb 12, 2019, 3:31 a.m. EST

Hi Zhang Ze,

The Pressure Acoustics interface solves for the total field, acpr.p_t, which is the sum of the background, acpr.p_b, and the scattered, acpr.p_s, fields. That is to say, acpr.p_t = acpr.p_s in the domains without a background field. All three exist over the whole computational domain and can be visualized there. One thing is that the amplitude of scattered field can differ significantly in the domains with and without a background field.

Regarding your questions:

  1. This is prescribed by the formulation of your certain problem: where the background field is defined and what it looks like.
  2. It is stored. Try to add the Selection node to your plots and choose different subdomains (see my screenshots of the acpr.p_s for the whole domain and a selection provided that a background field is only defined in the lower subdomain and mind my comment about its amplitude).
  3. If your model is in the frequency domain, everything is captured, for it corresponds to the sinusoidal steady-state mode. If your model is in the time domain, fx. the source is a pulse that lives for a certain time interval, the simulation must be run until the steady-state is reached, so that all reflections are captured.
  4. This is only for the time domain problems. The question here should be not how many times, but rather how long the time interval should be to reach the steady-state. It depends on the geometry, the fluid material, the signal and its frequency content - on the problem you are solving, in other words.

Best regards,
Kirill

Hi Zhang Ze, The Pressure Acoustics interface solves for the total field, *acpr.p_t*, which is the sum of the background, *acpr.p_b*, and the scattered, *acpr.p_s*, fields. That is to say, *acpr.p_t = acpr.p_s* in the domains without a background field. All three exist over the whole computational domain and can be visualized there. One thing is that the amplitude of scattered field can differ significantly in the domains with and without a background field. Regarding your questions: 1. This is prescribed by the formulation of your certain problem: where the background field is defined and what it looks like. 2. It is stored. Try to add the Selection node to your plots and choose different subdomains (see my screenshots of the *acpr.p_s* for the whole domain and a selection provided that a background field is only defined in the lower subdomain and mind my comment about its amplitude). 3. If your model is in the frequency domain, everything is captured, for it corresponds to the sinusoidal steady-state mode. If your model is in the time domain, fx. the source is a pulse that lives for a certain time interval, the simulation must be run until the steady-state is reached, so that all reflections are captured. 4. This is only for the time domain problems. The question here should be not how many times, but rather how long the time interval should be to reach the steady-state. It depends on the geometry, the fluid material, the signal and its frequency content - on the problem you are solving, in other words. Best regards, Kirill

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