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Pressure acoustic boundary condition problem

Posted 5 ott 2010, 13:00 GMT-4 Acoustics & Vibrations 5 Replies

Silvina Cancelos
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Hi,

I'm having a problem with the Pressure-Acoustic module, specifically with the boundary conditions. What I'm modeling is a wave propagation in a pipe filled with water, what I'm using to model this is the pressure-acoustic transient analysis with axial symmetry and with a pulse generation at one end of the pipe as a boundary condition for a short time.

Here's the problem, when I set the sides of the pipe with hard wall condition (dp/dr=0) I get a reasonable pulse propagation but when I set the side of the pipe to soft wall (P=0), the data that I obtain of the pulse don't make any sense.

What I think that it might be the problem is due to a discontinuity between the condition in the side of the pipe with the ends of the pipe.

The pulse equation that I sent is:

P=10*sin(2*pi*t/0.00037)*sin(2*pi*t/0.0000741)*t<=0.00037/2

I attached two plots with the results. If Somebody can help me I would appreciate the help.
5 Replies Last Post 28 mar 2011, 18:36 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 6 ott 2010, 01:56 GMT-4
HI

with your oscilalting time pulse, are you using the "strict" or "intermediate" time stepping ? as the automatic one will undersample rapidly your "oscillating pulse"

--
Good luck
Ivar
HI with your oscilalting time pulse, are you using the "strict" or "intermediate" time stepping ? as the automatic one will undersample rapidly your "oscillating pulse" -- Good luck Ivar
Silvina Cancelos
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Posted: 1 decade ago 6 ott 2010, 12:02 GMT-4
I had used both of them and obtain the same result. Maybe it would be more easy to determine the problem if I upload the mph file. Thanks.
I had used both of them and obtain the same result. Maybe it would be more easy to determine the problem if I upload the mph file. Thanks.
fox mail3771
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Posted: 1 decade ago 26 mar 2011, 23:33 GMT-4

I had used both of them and obtain the same result. Maybe it would be more easy to determine the problem if I upload the mph file. Thanks.


you have input the P0 (it is the ininatial value, and can not changing with time )


have you solved this question?

[QUOTE] I had used both of them and obtain the same result. Maybe it would be more easy to determine the problem if I upload the mph file. Thanks. [/QUOTE] you have input the P0 (it is the ininatial value, and can not changing with time ) have you solved this question?
Daniel Gonzalez
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Posted: 1 decade ago 27 mar 2011, 17:06 GMT-4

HI

with your oscilalting time pulse, are you using the "strict" or "intermediate" time stepping ? as the automatic one will undersample rapidly your "oscillating pulse"

--
Good luck
Ivar


Where would you change this setting?
[QUOTE] HI with your oscilalting time pulse, are you using the "strict" or "intermediate" time stepping ? as the automatic one will undersample rapidly your "oscillating pulse" -- Good luck Ivar [/QUOTE] Where would you change this setting?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 28 mar 2011, 18:36 GMT-4
Hi

that is in the solver node/window (a few sub tabs/nodes down) v3.5 and v4

--
Good luck
Ivar
Hi that is in the solver node/window (a few sub tabs/nodes down) v3.5 and v4 -- Good luck Ivar

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