Ensure at least six elements per wave length for the highest frequency of interest by adapting the mesh element size to the frequency range of the analysis.

Select one of the available viscothermal models: the low reduced frequency (LRF) model applies to layers and tubes below the cut-off frequency, and the boundary layer impedance (BLI) model applies to geometries that are large compared to the viscothermal boundary layer thickness.

Issue the PLAS,ALPHA command to postprocess the absorption coefficient of the system.