The Thermoviscous Acoustics, Transient (tatd) interface (
), found under the
Thermoviscous Acoustics branch (
) when adding a physics interface, is used to compute the transient evolution of the acoustic variations in pressure, velocity, and temperature. The interface is the time domain equivalent of
The Thermoviscous Acoustics, Frequency Domain Interface. This physics interface is required to accurately model acoustics in geometries of small dimensions. Near walls, viscous losses and thermal conduction become important because boundary layers exists. The thicknesses of these boundary layers are known as the viscous and thermal penetration depth. For this reason, it is necessary to include thermal conduction effects and viscous losses explicitly in the governing equations. It is, for example, used when modeling the response of transducers like microphones, miniature loudspeakers and receivers. Other applications include analyzing feedback in hearing aids, smart phones and in mobile devices, or studying the damped vibrations of MEMS structures.
When no Background Acoustic Fields feature is present (the background field values are zero per default) the total field is simply the field solved for,
pt =
p,
ut =
u, and
Tt =
T. All governing equations and boundary conditions are formulated in the total field variables.
When this physics interface is added, these default nodes are also added to the Model Builder —
Thermoviscous Acoustics Model,
Wall, and
Initial Values. Then, from the
Physics toolbar, add other nodes that implement, for example, boundary conditions and sources. You can also right-click
Thermoviscous Acoustics 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
tatd.
Expand the Equation section to see the equations solved for with the
Equation form specified. The default selection for
Equation form is set to
Study controlled. The available studies are selected under
Show equations assuming.
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. Select the
Time stepping (method) as
Fixed (preferred) the default and recommended or
Free. The
Free option is in general not recommended for wave problems. 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.
From the list select the element order and type (Lagrange or serendipity) for the Pressure, the
Velocity field, and the
Temperature variation, respectively. The default is
Linear for the pressure and
Quadratic Lagrange for the velocity and the temperature.
This physics interface defines these dependent variables (fields), the Pressure p, the
Velocity field u and its components, and the
Temperature variation T. The names can be changed but the names of fields and dependent variables must be unique within a model.
