Learning Forum

[Rahat Ara Noor]

I am trying to design a sound absorber and there is no experimental data. So I need some material parameters for acoustic equivalent material model (e.g., Johnson-Champoux-Allard model). 

I would like to know if there is a library where I can find the necessary material properties. Or could you please provide me with some material example which I can use for creating absorber structure?

and if my material for the structure is acoustic equivalent then is it necessary (or possible) to use Thermo viscous boundary layer to seperate air volume and the structure? 

 

Thank you in advance. :)

[ErKo]

 

Hi

 

We do not have that (material parameters).

For more info on other questions that you might have see the help manual (search in the help manual for the below):

There are also some examples (13.5. Example: Johnson-Champoux-Allard Model of a Perforated Material)

 ANSYS Mechanical APDL Acoustic Analysis Guide

All the best

Erik

 

[Rahat Ara Noor]

Thank you! I will check that example.

But I have another confusion. Suppose, I input the material parameters for JCA (e.g., viscous and thermal characteristic length), do I need to apply Thermo visco boundary layer between my air cavity and the outer structure (which is also considered as acoustic material). In the Ansys theory guide it is said that the Thermo-Viscous BLI BC should be applied in between viscous fluid and a rigid body. And my resonator outer structure is not a rigid body (equivalent acoustic material). Can I still apply thermo-viscous BLI or is it not necessary anymore? I tried understanding from Ansys apdl theory references and acoustic analysis guide but it is not much clear for me.

[ErKo]

 

Hi

See 8.3.5.4.1. Boundary Layer Impedance (BLI) Model for more info on this model.

[411] Bossart, R., Joly, N., & Bruneau, M. (2003). Hybrid numerical and analytical systems for acoustic boundary problems in thermo-viscous fluids. Journal of Sound and Vibration. 263, 69-84.

 

As you say though it should not be applied like that – needs to go on a free face that is not attached to another part.

All the best

 

[Rahat Ara Noor]

Thank you Erik! 

Have a nice day ahead. 

[ErKo]

Many thanks - same to you.

All the best

Erik