The Unsaturated Poroelasticity multiphysics coupling node () links the Moisture Transport in Solids interfaces bidirectionally with the Solid Mechanics interface to account for poroelastic deformation.

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 unporo1.

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 unsaturated poroelasticity coupling, or select All domains as needed.

When Unsaturated Poroelasticity 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 selected.

This section defines the physics involved in the multiphysics coupling. The Solid mechanics and Moisture transport lists include all applicable physics interfaces.

You can also select None from either list to uncouple the Unsaturated Poroelasticity node from a physics interface. If the physics interface is removed from the Model Builder, for example if Moisture Transport in Solids is deleted, then the Moisture transport list defaults to None as there is nothing to couple to.

In the Reference pressure level list, choose User defined to enter a reference pressure pref (SI unit: Pa) at which the pore pressure does not affect the porous matrix deformation. The default value is mts.pf_init. If applicable, the list also contains options to inherit the value from another physics interface that announces the reference pressure level as a model input.

For the Biot-Willis coefficient list, the default is to take its value From material. Choose User defined to enter a Biot–Willis coefficient αB (dimensionless) in the text field.

The multiphysics interface Poroelasticity, Solid couples the Solid Mechanics and the Darcy’s Law interfaces, while the Unsaturated Poroelasticity interface couples the Solid Mechanics and the Moisture Transport in Solids interfaces. Although the theory for the Poroelasticity, Solid and Unsaturated Poroelasticity interfaces differs significantly as shown in Theory for the Poroelasticity Interfaces, the settings look similar. The main difference is how the pore pressure is computed.

For more information about the interface settings and the settings for the multiphysics node, see The Unsaturated Poroelasticity Interface and Unsaturated Poroelasticity (Multiphysics Coupling).