The Acoustic-Thermoviscous Acoustic Interaction, Frequency Domain Interface
The Acoustic-Thermoviscous Acoustic Interaction, Frequency Domain interface (), found under the Thermoviscous Acoustics branch () when adding a physics interface, combines the Thermoviscous Acoustics, Frequency Domain and Pressure Acoustics, Frequency Domain interfaces together with the Acoustic-Thermoviscous Acoustic Boundary coupling feature. To couple the two physics and use Thermoviscous Acoustics only where necessary can reduce the computational cost of a model.
The physics interface solves the equations in the frequency domain assuming all fields and sources to be harmonic. Linear acoustics is assumed.
When a predefined Acoustic-Thermoviscous Acoustic Interaction, Frequency Domain interface is added from the Acoustics>Thermoviscous Acoustics branch of the Model Wizard or the Add Physics windows, the Thermoviscous Acoustics, Frequency Domain and Pressure Acoustics, Frequency Domain interfaces are added to the Model Builder.
In addition, the Multiphysics node is added, which automatically includes the multiphysics coupling feature Acoustic-Thermoviscous Acoustic Boundary.
For details about all the multiphysics couplings in the Acoustics Module, see Multiphysics Couplings.
The use of a predefined multiphysics coupling approach helps improve the flexibility and design options for your modeling. For for details, see The Multiphysics Node and Multiphysics Modeling Approaches in the COMSOL Multiphysics Reference Manual.
On the Constituent Physics Interfaces
The Pressure Acoustics, Frequency Domain interface is used to compute the pressure variations when modeling the propagation of acoustic waves in fluids at quiescent background conditions. The physics interface solves the Helmholtz equation and is suited for all linear frequency-domain acoustic simulations with harmonic variations of the pressure field. It includes domain conditions to model losses in a homogenized way, so-called fluid models for porous materials, as well as losses in narrow regions. The domain features also include background incident acoustic fields.
The Thermoviscous Acoustics, Frequency Domain interface is used to compute the propagation of acoustic waves including thermal and viscous losses. The interface solves for the acoustic variations in pressure, velocity, and temperature. Thermoviscous acoustics is required to accurately model acoustics in geometries with small dimensions. Near walls a viscous and thermal boundary layer exists. Here viscous losses due to shear and thermal conduction become important because of large gradients. For this reason, it is necessary to include thermal conduction effects and viscous losses explicitly in the governing equations. The equations defined by the Thermoviscous Acoustics, Frequency Domain interface are the linearized Navier-Stokes equations in quiescent background conditions solving the continuity, momentum, and energy equations.
Settings for Physics Interfaces and Coupling Features
When physics are added using the predefined multiphysics interface, for example Acoustic-Thermoviscous Acoustic Interaction, Frequency Domain, the Selection on the coupling feature is automatically set to All boundaries. In this way the multiphysics coupling is automatically active on all boundaries with Thermoviscous Acoustics, Frequency Domain on one side and Pressure Acoustics, Frequency Domain on the other.
However, if physics interfaces are added one at a time, followed by the coupling features, these modified settings are not automatically included.
For example, if the single interfaces are added, COMSOL adds an empty Multiphysics node. You can choose the available coupling features, but you need manually to select on which boundaries they need to be applied, or select All boundaries to recover the predefined behavior.
Coupling features are available from the context menu (right-click the Multiphysics node) or from the Physics toolbar, Multiphysics menu.
Physics Interfaces and Coupling Features
Use the online help in COMSOL Multiphysics to locate and search all the documentation. All these links also work directly in COMSOL Multiphysics when using the Help system.
Coupling Feature
See Acoustic-Thermoviscous Acoustic Boundary in the Multiphysics Couplings chapter.
Physics Interface Features
Physics nodes are available from the Physics ribbon toolbar (Windows users), Physics context menu (Mac or Linux users), or right-click to access the context menu (all users).
In general, to add a node, go to the Physics toolbar, no matter what operating system you are using. Subnodes are available by clicking the parent node and selecting it from the Attributes menu.
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The available physics features for The Thermoviscous Acoustics, Frequency Domain Interface are listed in the section Domain, Boundary, and Pair Nodes for the Thermoviscous Acoustics, Frequency Domain Interface.
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The available physics features for The Pressure Acoustics, Frequency Domain Interface are listed in the section Domain, Boundary, Edge, Point, and Pair Nodes for the Pressure Acoustics, Frequency Domain Interface
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Theory Background for the Pressure Acoustics Branch
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Theory Background for the Thermoviscous Acoustics Branch