Discussion Forum

For modeling the acoustics of porous materials, there are a few different approaches:

• Use a Poroacoustic Material model in Pressure acoustics. This is a fluid-equivalent homogenized model, so the geometry will only be the macro scale and not include any microstructure. The material model gets assigned to the entire domain. The flow resistivity is a common input to some Poroacoustic material models. https://doc.comsol.com/6.2/docserver/#!/com.comsol.help.aco/aco_ug_pressure.05.005.html

• Use Poroelastic Waves interfaces to model the porous material based on Biot Theory

• Use Thermoviscous Acoustics to model the detailed viscous and thermal losses that occur in boundary layers surrounding the fluid-microstructure interface. In this case, the geometry includes the detailed microstructure. This is usually only feasible for a unit cell due to the scale.

The first approach is the easiest and most lightweight approach.

-Mark

Thanks Mark, my case is that I need to obtain (for scientific purposes) the acoustic parameters of the porous medium such as absorption, reflection, transmission loss, tortuosity and flow resistivity (Sigma). I studied the first three and managed to plot them in COMSOL, now the flow resistivity and tortuosity, although they are formulas, I cannot implement them analytically in COMSOL (in the variables tab!).

There should no issue in implementing a formula under variables. Which error message do you get? Also, have a look at the JCA models under Poroacoustics. You can enter user defined expressions here as desired.

You need to learn 1) AFR testing standard 2) CFD module will be needed to find the AFR