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Problems with 'Impedance boundary' and 'Cylindrical Wave Radiation'?
Posted 16 mai 2016, 03:00 UTC−4 Acoustics & Vibrations, Modeling Tools & Definitions Version 4.4, Version 5.0, Version 5.1, Version 5.2 1 Reply
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Hi, when I simulate radiation of sound waves with 'Pressure Acoustics, Transient', i meet some problems with the settings of boundary.
I build a small circle as the sound source in a large circular region. The small circle isn't in the center of the large circle. The sound source generates sinusoidal waves in the total calculating time. I hope there is no reflection in the boundary of the large circle, and I used 'Impedance boundary' and the impedance value is the same as the big circular region. However, the values of tested waves in the boundary of large circle are all positive, although the wave is sinusoidal. When i used the 'Cylindrical Wave Radiation' boundary, the tested wave is right.
I thought the 'Impedance' boundary equals the effect of infinite space? Why it doesn't work?
Thanks for answering.
I build a small circle as the sound source in a large circular region. The small circle isn't in the center of the large circle. The sound source generates sinusoidal waves in the total calculating time. I hope there is no reflection in the boundary of the large circle, and I used 'Impedance boundary' and the impedance value is the same as the big circular region. However, the values of tested waves in the boundary of large circle are all positive, although the wave is sinusoidal. When i used the 'Cylindrical Wave Radiation' boundary, the tested wave is right.
I thought the 'Impedance' boundary equals the effect of infinite space? Why it doesn't work?
Thanks for answering.
1 Reply Last Post 16 mai 2016, 07:52 UTC−4
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Posted:
9 years ago
Hi Destiny
The radiation condition in the time domain is actually a simple impedance condition (a 1st order non-reflecting condition). I guess you put Z = rho*c as your impedance condition? This expression is only valid for plane waves! For for cylindrical waves it is also valid, but only at large distances from the source. The correct impedance includes a term that depends on the distance from the source (this is included in the cylindrical wave radiation). See the doc for more information.
Best regards
Mads
The radiation condition in the time domain is actually a simple impedance condition (a 1st order non-reflecting condition). I guess you put Z = rho*c as your impedance condition? This expression is only valid for plane waves! For for cylindrical waves it is also valid, but only at large distances from the source. The correct impedance includes a term that depends on the distance from the source (this is included in the cylindrical wave radiation). See the doc for more information.
Best regards
Mads