Use the Thermoviscous Acoustics Model node to define the model inputs (the background equilibrium temperature and pressure) and the material properties of the fluid (dynamic viscosity, bulk viscosity, thermal conductivity, heat capacity at constant pressure, and equilibrium density) necessary to model the propagation of acoustic compressible waves in a thermoviscous acoustic context. Extended inputs are available for the coefficient of thermal expansion and the compressibility, which enables modeling of any constitutive relation for the fluid.

The Model Inputs, the Thermoviscous Acoustics Model, and the Thermal Expansion and Compressibility sections are the same as for the frequency domain and transient interfaces. They are described under the Thermoviscous Acoustics Model section in The Thermoviscous Acoustics, Frequency Domain Interface.

Note that for the boundary mode interface, it is equally important as for the frequency domain and transient interfaces to set the material parameters correctly. The values of the coefficient of thermal expansion and the isothermal compressibility are prone to errors, so make sure to take a thorough look at the Thermal Expansion and Compressibility section.

This section contains an input for the Propagation direction n of the modes analyzed with the interface. Typically, this direction is equal to the surface or boundary normal. The default value is (tabm.nx, tabm,ny, tabm,nz) in 3D and (tabm.nr, tabm.nz) in 2D axisymmetric. When setting up models, this vector defines the positive propagation direction for the waves and thus the sign of the wave number.