The Equilibrium Discharges Interface
This physics interface requires an AC/DC Module license. For theory and physics interface feature descriptions, see the AC/DC Module User’s Guide.
The Equilibrium Discharges () interface is used to study equilibrium discharges in a magnetohydrodynamics (MHD) framework. This multiphysics interface adds three single physics interfaces: Magnetic and Electric Fields, Heat Transfer in Fluids, and Laminar Flow, together with several multiphysics coupling features. The multiphysics couplings add the MHD coupling between the Magnetic and Electric Fields and the Laminar Flow interfaces. The multiphysics couplings also add heating and cooling of the equilibrium plasma by enthalpy transport, Joule heating and radiation loss as well as special boundary conditions to model the ion and electron heating at the plasma boundaries.
When a predefined Equilibrium Discharges interface is added from the Plasma > Equilibrium Discharges branch () of the Model Wizard or Add Physics windows, Magnetic and Electric Fields, Heat Transfer in Fluids, and Laminar Flow interfaces are added to the Model Builder. In addition, the Multiphysics Couplings node is added, which automatically includes the multiphysics coupling features Equilibrium Discharge Heat Source, Magnetohydrodynamics, Nonisothermal Flow, and Equilibrium Discharge Boundary Heat Source.
On the Constituent Physics Interfaces
The Magnetic and Electric Fields interface is used to compute magnetic field and induced current distributions in and around coils, conductors, and magnets. The Magnetic and Electric Fields interface solves Maxwell’s equations formulated using the magnetic vector potential and, optionally for coils, the scalar electric potential as the dependent variables.
The Heat Transfer in Fluids interface provides features for modeling heat transfer by conduction, convection, and radiation. A Fluid model is active by default on all domains. All functionality for including other domain types, such as a solid domain, is also available. The temperature equation defined in solid domains corresponds to the differential form of the Fourier’s law that may contain additional contributions like heat sources.
The Laminar Flow interface solves for conservation of energy, mass, and momentum in fluids.
For details about predefined multiphysics couplings, see Multiphysics Modeling Workflow in the COMSOL Multiphysics Reference Manual.
Settings for Physics Interfaces and Coupling Features
When physics interfaces are added using the predefined couplings, for example Equilibrium Discharges, specific settings are included with the physics interfaces and the coupling features.
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 single Magnetic and Electric Fields, Heat Transfer in Fluids, and Laminar Flow interfaces are added, COMSOL Multiphysics adds an empty Multiphysics Couplings node. You can then choose from the available coupling features, Equilibrium Discharge Heat Source, Magnetohydrodynamics, Nonisothermal Flow, and Equilibrium Discharge Boundary Heat Source but the modified settings are not included.
Coupling features are available from the context menu (right-click the Multiphysics Couplings node) or from the Physics toolbar’s Multiphysics menu.
Table 7-1: Modified Settings for an Equilibrium Inductively Coupled Plasma Interface.
Physics Interface or Coupling Feature
Modified Settings
Magnetic and Electric Fields
The discretization of the dependent variables is set to linear.
Heat Transfer in Fluids
In the Fluid default feature, the Absolute pressure, pA (Model Input section) and the Velocity field, u (Heat Convection section) are automatically set to the variables from the Nonisothermal Flow multiphysics coupling feature.
Laminar Flow
In the Fluid Properties default feature, the Density, ρ is automatically set to the variable from the Nonisothermal Flow multiphysics coupling feature.
The Compressibility option is set to Weakly Compressible.
The Use pseudo time stepping for stationary equation form checkbox is automatically selected under the Advanced Settings section.
Equilibrium Discharge Heat Source
The Domain Selection is the same as that of the participating physics interfaces. The corresponding Magnetic Fields and Heat Transfer in Fluids interfaces are preselected in the Coupled Interfaces section.
Magnetohydrodynamics
The Domain Selection is the same as that of the participating physics interfaces. The corresponding Magnetic Fields and Laminar Flow interfaces are preselected in the Coupled Interfaces section.
Nonisothermal Flow
The Domain Selection is the same as that of the participating physics interfaces. The corresponding Laminar Flow and Heat Transfer in Fluids interfaces are preselected in the Coupled Interfaces section.
Equilibrium Discharge Boundary Heat Source
The Boundary Selection contains all boundaries of the participating physics interfaces. The corresponding Electric Currents and Heat Transfer in Fluids interfaces are preselected in the Coupled Interfaces section.
Physics Interface 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 Features
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The Equilibrium Discharge Heat Source and Equilibrium Discharge Boundary Heat Source multiphysics coupling nodes are described in this chapter.
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The Magnetohydrodynamics multiphysics coupling node is described in this chapter.
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The Nonisothermal Flow coupling node is described for The Nonisothermal Flow and Conjugate Heat Transfer Interfaces in the COMSOL Multiphysics Reference Manual.
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.
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The available physics features for The Laminar Flow Interface are listed in the section Domain, Boundary, Pair, and Point Nodes for Single-Phase Flow.
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The available physics features for the heat transfer interfaces are listed in the sections Domain Features, Boundary Features, and Edge and Point Features in the COMSOL Multiphysics Reference Manual.
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The available physics features for The Magnetic and Electric Fields Interface are listed in the section Domain, Boundary, Point, and Pair Nodes for the Magnetic Fields Interface in the AC/DC Module User’s Guide.