The Pair Thermoviscous Acoustic–Structure Boundary coupling () is used to couple the Thermoviscous Acoustics, Frequency Domain or the Thermoviscous Acoustics, Transient interface to the Solid Mechanics interface in an assembly geometry where identity pairs have been created. This allows the use of a nonconforming mesh at the acoustic-structure boundary. As the wave speeds differ in solids and fluids, the computational mesh can take advantage of this when resolving the waves. In this way saving degrees of freedom when solving.

This section defines the physics involved in the multiphysics coupling. The Acoustics and Structure lists include all applicable physics interfaces.

Select a condition for the temperature variations either Isothermal (the default) or Adiabatic.

These settings are shown when the Advanced Physics Options is selected. It controls how the constraints (continuity in displacement and the thermal condition) are handled. For the Mechanical constraints type, select either Study controlled (the default), Weak constraints, or Pointwise constraints. For the Thermal constraint type, select either Pointwise constraint (the default) or Weak constraints. Finally, select the Constraint method to apply to the pointwise constraints, either Elemental or Nodal (the default).

When the Mechanical constraints type is set to Study controlled, the weak constraints are automatically selected when an eigenfrequencies study is performed. This type of coupling is necessary as the eigenvalue (the angular frequency ω) enters the coupling expression. This will create extra variables at the boundary (so-called Lagrange multipliers), ensuring the correct behavior and solution. For a normal frequency domain study, the pointwise constraint is automatically selected. In the time domain a penalty/Nitsche formulation is always used automatically.