Multiphysics Couplings

The coupling is similar to the Thermal Expansion (for Materials) node (

) that can be added under, for example, the or 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.

The is the multiphysics coupling feature name. The default (for the first multiphysics coupling feature in the model) is Thermal Expansion 1.

The 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 field. The first character must be a letter.

The default (for the first multiphysics coupling feature in the model) is te1.

When nodes are added from the context menu, you can select (the default) from the list to choose specific domains to define the coefficient of thermal expansion and the different temperatures that cause thermal stress, or select as needed.

When is added, 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 choosen.

This section defines the physics involved in the multiphysics coupling. The and 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 ribbon (Windows users), contextual toolbar (macOS 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 or window, then the two participating physics interfaces are selected.

You can also select from either list to uncouple the node from a physics interface. If the physics interface is removed from the , for example is deleted, then the list defaults to as there is nothing to couple to.

	If a physics interface is deleted and then added to the model again, then in order to reestablish 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 Workflow in the COMSOL Multiphysics Reference Manual.

The Tref is the temperature at which there are no thermal strains. As a default, the value is obtained from a . You can also select to enter a value or expression for the temperature locally.

Select an to select how the thermal strain is specified. The default is , in which case the thermal strain is given by

where α is the secant coefficient of thermal expansion. α can be temperature dependent.

When is , the thermal strain is given by

where αt is the tangential coefficient of thermal expansion.

When is , enter the thermal strain dL as function of temperature explicitly.

In all three cases, the default is to take values . When entering data as , select , or to enter one or more components for a general coefficient of the thermal expansion tensor or the thermal strain tensor. When a nonisotropic input is used, the axis orientations are given by the coordinate system selection in the parent node.

Select to include the reverse coupling where the changes in stress act as a heat source in the heat transfer analysis. Thermoelastic damping is only used when Structural Transient Behavior is set to .

Select to make any energy dissipation computed in the structural interface act as a heat source in the heat transfer interfaces. Examples of such contributions are work done by plastic deformation, and viscous damping.