The Pressure Acoustics, Transient (actd) interface (), found under the Acoustics>Pressure Acoustics branch () when adding a physics interface, is used to compute the pressure variation when modeling the propagation of acoustic waves in fluids at quiescent background conditions. It is suited for time-dependent simulations with arbitrary time-dependent fields and sources.

The physics interface can be used to model linear and nonlinear acoustics that can be well described by the scalar pressure variable. Domain conditions also include background incident acoustic fields. User-defined sources can be added to, for example, include certain nonlinear effects such as a square pressure dependency of the density variations. For open problems Perfectly Matched Layers (PMLs) can be applied, also in the time domain for Pressure Acoustics, as efficient non reflecting boundary conditions.

When this physics interface is added, these default nodes are also added to the Model Builder — Transient Pressure Acoustics Model, Sound Hard Boundary (Wall), and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and source. You can also right-click Pressure Acoustics, Transient to select physics features from the context menu.

The Label is the default physics interface name.

The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.

The default Name (for the first physics interface in the model) is actd.

Select the Time stepping (method) as Manual (default and recommended) or Automatic/free and then enter the Maximum frequency to resolve in the model. The default frequency is set to 1000[Hz] but should be changed to reflect the frequency content of the sources used in the model. The generated solver will be adequate in most situations if the computational mesh also resolves the frequency content in the model. Note that any changes made to these settings (after the model is solved the first time) will only be reflected in the solver if Show Default Solver or Reset Solver to Defaults is selected in the study. The generated settings will not be adequate for highly nonlinear problems. In this case manual tuning needs to be done.