# Discussion Forum

## Plane wave propagation inside a duct (Vibroacoustic)

 Topics: FSI, Structural Mechanics, 4.1, Solving
RSS feed   |   Turn on email notifications   |   5 Replies   Last post: August 9, 2012 12:45am UTC

Griffin Stan

May 23, 2012 1:42pm UTC

Plane wave propagation inside a duct (Vibroacoustic)

Hello everybody,

I me dealing with an interesting vibroacoustic problem and wanna model it WIth COMSOL.

The subject is : A duct (Air inside)of one meter length and cross sectional 0.2m*0.2m (width=1m)
Boundary conditions : unit velocity at one end
zero velocity Boundary condition is applied at the other end (rigid wall)
The 4 lateral sides are assigned rigid wall.

Frequency = 100hz.
Material (duct) = Any (wood, alu,etc...)

My questions are :
- COMSOL doesn't contain Velocity boundary ? (Drive me mad)
- How to handle that with COMSOL ?

Your help would be very appreciated .......

Ivar Kjelberg

May 23, 2012 2:50pm UTC in response to Griffin Stan

Re: Plane wave propagation inside a duct (Vibroacoustic)

Hi

I do not have the acoustic module, but I see you have Normal Velocity BCs from the doc and in structural prescribed velocities BC exist. what do you need more ?

--
Good luck
Ivar

Griffin Stan

May 23, 2012 3:53pm UTC in response to Ivar Kjelberg

Re: Plane wave propagation inside a duct (Vibroacoustic)

Thanks for the tip.
Great idea.

But as i m dealing with Helmholtz equation, i find aonther way, buy taking Partial diffrential equation.

My second question :

Don't know how to model interaction between A fluid AIr and solid vibrating (any) close.
I mean how to define Material in that case ?

I have tried linear elastic for the fluid and solid, but doesn't work !

What do you think ...Your tips are welcome SIr. Any !

Thanks again.

Ivar Kjelberg

May 23, 2012 5:03pm UTC in response to Griffin Stan

Re: Plane wave propagation inside a duct (Vibroacoustic)

Hi

A fluid is no linear elastic material, OK you can cheat and say Poisson =0 Young = 1/3 of absolute pressure. But i do not believe you will get very far. You can also model the air as an added mass to the solid surface (for eigenmode or frequency domain sweep), but I'm not sure how to model approximately the viscosity and damping in this way.

The Acoustic module proposes much more, but I do not have it, unfortunately, so I cannot help much here

--
Good luck
Ivar

Griffin Stan

May 23, 2012 6:54pm UTC in response to Ivar Kjelberg

Re: Plane wave propagation inside a duct (Vibroacoustic)

Sounds right.
I'm still working on it.

Thanks again.

Sankha Mukherjee

August 9, 2012 12:45am UTC in response to Griffin Stan

Re: Plane wave propagation inside a duct (Vibroacoustic)

Hi Griffin,

Have you been able to solve this issue. If yes, can you provide us with some guidelines as to how to go about solving these problems.

Thanks
Sankha

Rules and guidelines