The Joule Heating and Thermal Expansion Interface
The Joule Heating and Thermal Expansion () interface combines thermal, electric, and structural multiphysics effects. The predefined interaction adds the electromagnetic losses from the electric field as a heat source. In addition, the temperature from the Heat Transfer in Solids interface acts as a thermal load for the Solid Mechanics interface, causing thermal expansion.
You can use this multiphysics coupling for coupled thermal, electrical, and structural analysis of, for example, the movement of some actuator, where an electric current causes a temperature increase, which in turn leads to a displacement through thermal expansion.
When a predefined Joule Heating and Thermal Expansion interface is added from the Structural Mechanics branch () of the Model Wizard or Add Physics windows, Solid Mechanics, Electric Currents, and Heat Transfer in Solids interfaces are added to the Model Builder.
In addition, the Multiphysics node is added, which automatically includes the multiphysics coupling features Thermal, Expansion Electromagnetic Heat Source, Boundary Electromagnetic Heat Source, and two Temperature Coupling nodes.
On the Constituent Physics Interfaces
The Electric Currents interface computes electric field, current and potential distributions in conducting media under conditions where inductive effects are negligible; that is, when the skin depth is much larger than the studied device. Depending on the licensed products, time and frequency domain formulations that account for capacitive effects are also provided. The Electric Currents interface solves a current conservation equation based on Ohm's law using the scalar electric potential as the dependent variable.
The Solid Mechanics interface is intended for general structural analysis of 3D, 2D, or axisymmetric bodies. In 2D, plane stress or plane strain assumptions can be used. The Solid Mechanics interface is based on solving Navier's equations, and results such as displacements, stresses, and strains are computed.
The Heat Transfer in Solids interface provides features for modeling heat transfer by conduction, convection, and radiation. A Heat Transfer in Solids model is active by default on all domains. All functionality for including other domain types, such as a fluid 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.
In previous versions of COMSOL Multiphysics, a specific physics interface called Joule Heating and Thermal Expansion was added to the Model Builder. Now, a predefined multiphysics coupling approach is used, improving the flexibility and design options for your modeling. For specific details, see The Multiphysics Node and Multiphysics Modeling Approaches in the COMSOL Multiphysics Reference Manual.
Settings for Physics Interfaces and Coupling Features
When physics interfaces are added using the predefined couplings, for example Joule Heating and Thermal Expansion, 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 Solid Mechanics, Electric Currents, and Heat Transfer in Solids interfaces are added, COMSOL adds an empty Multiphysics node. You can then choose from the available coupling features, Thermal Expansion, Electromagnetic Heat Source, Boundary Electromagnetic Heat Source, and Temperature Coupling, but the modified settings are not included.
Coupling features are available from the context menu (right-click the Multiphysics node) or from the Physics toolbar, Multiphysics menu.
Table 10-2: Modified Settings for a Joule Heating and Thermal Expansion Interface
Physics Interface or Coupling Feature
Modified Settings
Solid Mechanics
For the Solid Mechanics interface, under Structural Transient Behavior, the Structural transient behavior is set to Quasi-static.
Electric Currents
No changes.
Heat Transfer in Solids
For the Heat Transfer in Solids interface, under Discretization, the shape function order for the temperature is set to Linear.
Thermal Expansion
The Domain Selection is the same as that of the participating physics interfaces.
The corresponding Solid Mechanics and Heat Transfer in Solids interfaces are preselected in the Thermal Expansion section.
Electromagnetic Heat Source
The Domain Selection is the same as that of the participating physics interfaces.
The corresponding Electric Currents and Heat Transfer in Solids interfaces are preselected in the Electromagnetic Heat Source section.
Boundary Electromagnetic Heat Source
The Boundary Selection contains all the boundaries of the participating physics interfaces.
The corresponding Electric Currents and Heat Transfer in Solids interfaces are preselected in the Boundary Electromagnetic Heat Source section.
Temperature Coupling
Two Temperature Coupling nodes (described in the COMSOL Multiphysics Reference Manual) are generated, one for the transfer of temperatures to the Solid Mechanics interface and one for the transfer of temperatures to the Electric Currents interface.
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.
Coupling Features
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The Thermal Expansion (Multiphysics Coupling) coupling feature node is described for The Thermal Stress Interface.
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The Electromagnetic Heat Source, Boundary Electromagnetic Heat Source, and Temperature Coupling coupling feature nodes are described for The Joule Heating Interface 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. 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 Solid Mechanics Interfaceare listed in the section Domain, Boundary, Edge, Point, and Pair Nodes for Solid Mechanics.
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The available physics features for The Heat Transfer in Solids Interface are listed in the section Feature Nodes for the Heat Transfer in Solids Interface.
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The available physics features for The Electric Currents Interface are listed in the section Domain, Boundary, Edge, Point, and Pair Nodes for the Electric Currents Interface in the COMSOL Multiphysics Reference Manual.
If you have an add-on module, such as the Heat Transfer Module or AC/DC Module, there are additional specialized physics nodes available and described in the individual module documentation.