The Pressure Acoustics, Time Explicit (pate) 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. The interface is used to solve large transient linear acoustic problems containing many wavelengths. It is suited for time-dependent simulations with arbitrary time-dependent sources and fields. The interface includes a Background Acoustic Field option for modeling of scattering problems. Absorbing layers are used to set up effective nonreflecting-like boundary conditions. The exterior field can be calculated by combining the Exterior Field Calculation feature with a Time to Frequency FFT study step. The interface exists in 2D, 2D axisymmetry, and 3D. Losses at boundaries can be modeled with the Impedance condition. The interface has built-in options that allow setting up frequency dependent impedance conditions in the time domain, by using the very general and flexible General local reacting (rational approximation) impedance option. Losses in porous domains materials can be modeled with the Poroacoustics feature.

If the acoustic waves propagate in a background flow, for example, inside a flowmeter, then use The Convected Wave Equation, Time Explicit Interface.

For modeling vibroacoustic problems that involve acoustic structure interaction (ASI) the Pressure Acoustics, Time Explicit interface can be combined with The Elastic Waves, Time Explicit Interface using the Acoustic–Structure Boundary, Time Explicit multiphysics coupling.

When this physics interface is added, these default nodes are also added to the Model Builder — Pressure Acoustics Time Explicit 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, Time Explicit 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 pate.

To display this section, click the Show More Options button () and select Advanced Physics Options. In the Filter Parameters for Absorbing Layers section you can change and control the values set for the filter used in the Absorbing Layers. The values of the filter parameters defined here are used in all absorbing layers added to the model and they override the value of filter parameters enabled in the material model (Pressure Acoustics, Time Explicit Model). The default values of the filter parameters α, ηc, and s are set to 0.1, 0.01, and 2, respectively. Inside the absorbing layer it is important to use a filter that is not too aggressive since this will result in spurious reflections.

The settings selected here are only used if the transient solution solved is transformed into the frequency domain using the Time to Frequency FFT study. The zero level on the dB scale varies with the type of fluid. That value is a reference pressure that corresponds to 0 dB. This variable occurs in calculations of the sound pressure level Lp based on the root mean square (rms) pressure prms, such that

where pref is the reference pressure and the star (*) represents the complex conjugate. This is an expression valid for the case of harmonically time-varying acoustic pressure p.

Select a Reference pressure for the sound pressure level based on the fluid type:

Enter a value for the Maximum frequency to resolve fmax (the default is 1000[Hz]). This value is used to set up the physics-controlled mesh for the Pressure Acoustics, Time Explicit interface.

Select the Use accelerated solver formulation for an option where the system data is extracted and cashed for efficient evaluation on either on GPU or CPU. With this option selected, the number of available boundary conditions and features is limited.

Select Compute residual on GPU (the default) so that the accelerated solver runs on GPU. When selected, the option Use single precision on GPU is active and selected per default. Single precision is then used on the GPU. If the Use single precision on GPU is not selected, double precision is used. Single precision is often adequate for wave propagation problems and gives the best speedup and performance.

If the Compute residual on GPU is not selected, the residuals are computed on CPU, but still extracted and cashed, which will result in solver speedup, compared to the default formulation. If the solved problem can fit in the memory of the GPU, this results in the most significant speedup.

If changes are made to the settings in this section, make sure to Reset Solver to Default on the study level.

The available features, when Use accelerated solver formulation is selected, are:

The Use accelerated solver formulation is also supported in Absorbing Layer domains, for modeling open problems. When enabled the source definition in Pressure and Normal Velocity also needs to redefined. See the features for details.

In this section you can select the discretization for the Acoustic pressure and Acoustic velocity. Per default both are set to Quartic (4th order). Using quartic elements together with a mesh size equal to approximately half the wavelength to be resolved, leads to the best performance when using the DG method. For further details see the Meshing, Discretization, and Solvers section.

The dependent variables are the Acoustic pressure, and the Acoustic velocity. The names can be changed, but the names of fields and dependent variables must be unique within a model. The name for the Acoustic velocity, components can also be selected individually.