Poroelasticity (Multiphysics Coupling)
The Poroelasticity multiphysics coupling node () links the Solid Mechanics and Darcy’s Law interfaces bidirectionally to account for poroelastic deformation.
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 poro1.
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 poroelasticity coupling, or select All domains as needed.
When Poroelasticity is added as an effect of adding a Poroelasticity 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.
The Poroelasticity coupling handles geometric nonlinearity automatically in order to apply a strain formulation that is consistent with the geometric nonlinearity settings in the solid material model for each domain selected, see Geometric Nonlinearity for the Solid Mechanics Interface in the Structural Mechanics Modeling chapter for details.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling. The Solid mechanics and Flow in porous media 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 (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 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 Poroelasticity node from a physics interface. If the physics interface is removed from the Model Builder, for example if Darcy’s Law is deleted, then the Flow in porous media 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 reestablish the coupling, you need to choose the physics interface again from the Solid mechanics or Flow in porous media 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.
Poroelastic Coupling Properties
In the Poroelasticity model list, choose between Biot and Biphasic. The Biot poroelasticity model (default) is commonly used in geotechnical applications where the compressibility of the solid and/or fluid phase is important. In contrast, the biphasic model assumes that both the solid and the fluid phases are incompressible, which is valid for soft materials like biological tissues and hydrogels. Note that even if both constituents are modeled as incompressible, the porous medium can still undergo large volume changes as a result of fluid inflow or outflow.
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 1 atm. 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 example, the reference pressure level can often be inherited from the corresponding input in the Darcy’s Law interface that is part of the Poroelasticity coupling.
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 user input is only required if the Poroelasticity model is set to Biot.