Thermal Expansion (Multiphysics Coupling)
The Thermal Expansion coupling is similar to the Thermal Expansion (for materials) node () that can be added under, for example, the Linear Elastic Material or Hyperelastic Material for the Solid Mechanics interface. The purpose is the same, and if both nodes are used for the same selection, the settings in the coupling node takes precedence.
Settings
The Label is the default multiphysics coupling feature name.
The Name is used primarily as a scope prefix for variables defined by the coupling node. Refer to such variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different coupling nodes or 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 multiphysics coupling feature in the model) is te1.
Domain Selection
When nodes are added from the context menu, you can select Manual (the default) from the Selection list to choose specific domains to define the coefficient of thermal expansion and the different temperatures that cause thermal stress, or select All domains as needed.
When Thermal Expansion is added as an effect of adding a Thermal Stress interface, the selection is the same as for the participating physics interfaces.
Only domains that are active in the physics interfaces selected in the Coupled Interfaces section can be selected.
Thermal Expansion Properties
Select an Input type to select how the thermal strain is specified. The default is Secant coefficient of thermal expansion, in which case the thermal strain is given by
where α is the secant coefficient of thermal expansion. α can be temperature dependent.
When Input type is Tangent coefficient of thermal expansion, the thermal strain is given by
where αt is the tangential coefficient of thermal expansion.
When Input type is Thermal strain, enter the thermal strain dL as function of temperature explicitly.
In all three cases, the default is to take values From material. When entering data as User defined, select Isotropic, Diagonal or Symmetric to enter one or more components for a general coefficient of the thermal expansion tensor or the thermal strain tensor. When a non-isotropic input is used, the axis orientations are given by the coordinate system selection in the parent node.
Enter a value or expression for the Strain reference temperature Tref which is the reference temperature that defines the change in temperature together with the actual temperature.
Select Thermoelastic damping to include the reverse coupling where the changes in stress act as a heat source in the heat transfer analysis. Thermoelastic damping is only active when Structural Transient Behavior is set to Include inertial terms.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling. The Heat transfer and Solid mechanics lists include all applicable physics interfaces.
The default values depend on how the coupling node is created.
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If it is added from the Physics ribbon (Windows users), Physics contextual toolbar (Mac and Linux users), or context menu (all users), then the first physics interface of each type in the component is selected as the default.
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If it is added automatically when a multiphysics interface is selected in the Model Wizard or Add Physics window, then the two participating physics interfaces are selected.
You can also select None from either list to uncouple the Thermal Expansion node from a physics interface. If the physics interface is removed from the Model Builder, for example Heat Transfer in Solids is deleted, then the Heat transfer list defaults to None as there is nothing to couple to.
If a physics interface is deleted and then added to the model again, then in order to re-establish the coupling, you need to choose the physics interface again from the Heat transfer or Solid mechanics lists. This is applicable to all multiphysics coupling nodes that would normally default to the once present interface. See Multiphysics Modeling Approaches in the COMSOL Multiphysics Reference Manual.
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Thermoelastic Damping
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Entropy and Thermoelasticity