The Fluid–Solid Interaction, Two-Phase Flow, Phase Field, Fixed Geometry Interface
Using the Fluid–Solid Interaction, Two-Phase Flow, Phase Field, Fixed Geometry () interface, you can model phenomena where two immiscible fluids and a deformable solid affect each other. The interface includes a predefined condition for the interaction at the Fluid–Solid boundaries. The interface between the two fluids is tracked by solving two additional transport equations, one for the phase field variable and one for the mixing energy density.
Using a time-dependent study, the Fluid–Solid Interaction, Two-Phase Flow, Phase Field, Fixed Geometry interface models bidirectional coupling between solids and the fluids. There are, however, special study steps available in order to model one-way Fluid–Structure interaction. Simulations using the interface are always time-dependent since the position of the interface between the two fluids is almost always dependent of its history.
You add a predefined Fluid–Solid Interaction, Two-Phase Flow, Phase Field, Fixed Geometry interface from the Fluid–Structure Interaction () group in either the Structural Mechanics branch () or the Fluid Flow branch () of the Model Wizard or Add Physics windows. Laminar Flow, Solid Mechanics, and Phase Field interfaces are then added to the Model Builder.
In addition, the Multiphysics node is added to the Model Builder, which automatically includes the multiphysics coupling features Fluid–Structure Interaction and Two-Phase Flow, Phase Field.
The flow regime can be laminar or turbulent (if the CFD Module is available). The solid domain has all functionality available in the Solid Mechanics interface, including contact conditions and also nonlinear materials if the Nonlinear Structural Materials Module or Geomechanics Module is available.
On the Constituent Physics Interfaces
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The Solid Mechanics interface is described in The Solid Mechanics Interface.
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The Two-Phase Flow interface is described in The Two-Phase Flow, Level Set and Phase Field Interfaces.
You can add a Stationary, One-Way FSI or Time Dependent, One-Way FSI studies. See Stationary and Time Dependent One-Way Studies for Fluid-Structure Interaction in the COMSOL Multiphysics Reference Manual for more information.
Settings for Physics Interfaces and Coupling Features
When physics interfaces are added using the predefined couplings, all 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 Laminar Flow and Solid Mechanics interfaces are added, COMSOL Multiphysics adds an empty Multiphysics node. You can choose from the available coupling features, 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 Couplings menu.
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 system.
Coupling Features
 The Two-Phase Flow, Phase Field Coupling Feature and the Fluid–Structure Interaction feature are used to couple the interfaces.
Physics Interface Features
Physics nodes are available from the Physics ribbon toolbar (Windows users), Physics context menu (macOS 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.