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Modeling an acoustic t-junction

Posted Nov 13, 2012, 11:10 a.m. EST Version 4.3a 5 Replies

Dan Fries
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Hello,

I am currently trying to model an acoustic t-junction with the frequency domain acoustic pressure module. But while the 3D simulation gives me reasonable results I only get nonsense from the 2D one. All the walls are defined as hard walls, only one side of the main duct has a plane wave radiation boundary condition with an incident pressure field.

I attached some of the results and it would be great, if anyone had an idea what I might be doing wrong or what is happening here.
The first picture is 2D at a 100 Hz.
The second one 2D at 700 Hz.

As you can see there is a singularity kind of thing in the center of the junction and the pressure distribution looks kind of strange.

Thanks for the help.
5 Replies Last Post Nov 16, 2012, 2:16 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 13, 2012, 2:56 p.m. EST
Hi

how many mesh elements do you have across your geometry ?
and could it be from some interferometric add up, reflection from the ends ?

--
Good luck
Ivar
Hi how many mesh elements do you have across your geometry ? and could it be from some interferometric add up, reflection from the ends ? -- Good luck Ivar
Dan Fries
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Posted: 1 decade ago Nov 15, 2012, 9:41 a.m. EST
Hello,

I have 16704 triangular Mesh Elements.
Looking at reference cases something like this "singularity" should not happen in the junction. Complex pressure patterns yes, but not like that. Moreover, the 3D simulation deliver a very different result which seems more viable.

I attached my COMSOL file for the 2D duct and a picture of the 3D result. So far I have done most of the simulations with 3D , but if 2D would work it would save me a lot of time. Maybe I am doing something wrong with the B.C.s?

Thanks for your help.
Hello, I have 16704 triangular Mesh Elements. Looking at reference cases something like this "singularity" should not happen in the junction. Complex pressure patterns yes, but not like that. Moreover, the 3D simulation deliver a very different result which seems more viable. I attached my COMSOL file for the 2D duct and a picture of the 3D result. So far I have done most of the simulations with 3D , but if 2D would work it would save me a lot of time. Maybe I am doing something wrong with the B.C.s? Thanks for your help.
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Nov 15, 2012, 2:45 p.m. EST
Hi Dan,

The problem with your 2D analysis is that it is 2D axisymmetric instead of 2D planar.

Nagi Elabbasi
Veryst Engineering
Hi Dan, The problem with your 2D analysis is that it is 2D axisymmetric instead of 2D planar. Nagi Elabbasi Veryst Engineering
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 15, 2012, 3:24 p.m. EST
Hi
indeed that makes a difference ;)
Hadnt noticed that one !

--
Good luck
Ivar
Hi indeed that makes a difference ;) Hadnt noticed that one ! -- Good luck Ivar
Dan Fries
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Posted: 1 decade ago Nov 16, 2012, 2:16 p.m. EST
Hello,

yes, that solved the problem, don't know why I did that.

Thank you very much for the quick help!
Hello, yes, that solved the problem, don't know why I did that. Thank you very much for the quick help!

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