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Simple supported boundary condition in Comsol

Posted Dec 10, 2012, 5:54 p.m. EST Acoustics & Vibrations, Structural Mechanics Version 4.3a 3 Replies

Marco Antonio Gaete
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Hi, guys. I'm actually studying cylindrical sound diffusers using Comsol 4.3a and I need to add simply supported boundary conditions. Is there any way to do it? I have noticed there's several conditions (displacement, acceleration, etc) and I don't know if it's possible to combine two or more to simulate a simply supported boundary condition.

Greetings from Valdivia, Chile.
3 Replies Last Post Dec 12, 2012, 1:32 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 11, 2012, 2:31 a.m. EST
Hola Marco

Good to hear that COMSOL is used in Chile too, even if the number of reps are low in south America, well the the web makes the distance shorter ;)

I'm not sure I give you the full image, particularly because ACO is on of the module I'm missing the most myself, but normally you have the prescribed displacement velocity and acceleration for "wall" which are, from my understanding, "hard walls" with or without motion, but you should also have a "spring funcdation" BC for "softer links" to ground via a spring and optionally a damper.

As ACO normally solves only for pressure and you have no gravity effects you do not necesarily need to constrain all 6 DoF as for structural

Hope this helps on the way

--
Good luck
Ivar
Hola Marco Good to hear that COMSOL is used in Chile too, even if the number of reps are low in south America, well the the web makes the distance shorter ;) I'm not sure I give you the full image, particularly because ACO is on of the module I'm missing the most myself, but normally you have the prescribed displacement velocity and acceleration for "wall" which are, from my understanding, "hard walls" with or without motion, but you should also have a "spring funcdation" BC for "softer links" to ground via a spring and optionally a damper. As ACO normally solves only for pressure and you have no gravity effects you do not necesarily need to constrain all 6 DoF as for structural Hope this helps on the way -- Good luck Ivar
Marco Antonio Gaete
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Posted: 1 decade ago Dec 11, 2012, 11:05 p.m. EST
Hi, Ivar. Thanks for your answer. I have discovered COMSOL a few weeks ago, so I'm justo a newbie.

I have forgotten to say I'm working with the Structural Mechanics Module to obtain the eigenvalues and the frequency response for the diffusers. There's some conditions in this module like displacement, acceleration, velocity, etc. Then I want to add the diffusers into a reverberant chamber to study its vibroacoustic behavior. So the question is: Can I combine two different boundary conditions using the same edges to simulate a simply supported boundary condition? Otherwise is it possible establish a custom boundary condition?

Thanks in advance for your help.

Marco.
Hi, Ivar. Thanks for your answer. I have discovered COMSOL a few weeks ago, so I'm justo a newbie. I have forgotten to say I'm working with the Structural Mechanics Module to obtain the eigenvalues and the frequency response for the diffusers. There's some conditions in this module like displacement, acceleration, velocity, etc. Then I want to add the diffusers into a reverberant chamber to study its vibroacoustic behavior. So the question is: Can I combine two different boundary conditions using the same edges to simulate a simply supported boundary condition? Otherwise is it possible establish a custom boundary condition? Thanks in advance for your help. Marco.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 12, 2012, 1:32 a.m. EST
Hi

well if you have flluid structure interaction tending to do acoustics, ideally you need the acoustic module, as there COMSOl has precooked everything. I do not have that module, unfortunately, I notice that my boss states we do not do acoustics, which is true, but the acoustic physics cover all structure fluid interactions we have also in MEMS or fine mechanics where the fluid /air pressure) has important effects on the results. And mostly you consider infinite fluid and do not want to do a full FSI model

The prescribed acceleration and velocity BC are tricky to use as in reality we apply forcesw and the model reqacts, and not true prescibed velocities. Even with acoustics, its the pressure of the fluid that applies a force onto the structure, but you need also the structure motion to apply a pressure to the fluid part

--
Good luck
Ivar
Hi well if you have flluid structure interaction tending to do acoustics, ideally you need the acoustic module, as there COMSOl has precooked everything. I do not have that module, unfortunately, I notice that my boss states we do not do acoustics, which is true, but the acoustic physics cover all structure fluid interactions we have also in MEMS or fine mechanics where the fluid /air pressure) has important effects on the results. And mostly you consider infinite fluid and do not want to do a full FSI model The prescribed acceleration and velocity BC are tricky to use as in reality we apply forcesw and the model reqacts, and not true prescibed velocities. Even with acoustics, its the pressure of the fluid that applies a force onto the structure, but you need also the structure motion to apply a pressure to the fluid part -- Good luck Ivar

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