The Fluid-Solid Interaction Interface
Using the Fluid-Solid Interaction () interface, you can model phenomena where a fluid and a deformable solid affect each other. The interface includes a predefined condition for the interaction at the fluid-solid boundaries. Arbitrary Lagrangian-Eulerian Formulation (ALE) is used for incorporating the geometrical changes of the fluid domain.
Using a stationary or a time-dependent study, the Fluid-Solid Interaction interface models two-way coupling between solids and fluids. There are, however, special study steps available in order to model one-way coupled fluid-structure interaction.
You add a predefined Fluid-Solid Interaction interface from the Fluid-Structure Interaction () group in the Fluid Flow branch () of the Model Wizard or Add Physics windows. Laminar Flow and Solid Mechanics interfaces are then added to the Model Builder.
At the same time, a Moving Mesh node with a Deforming Domain subnode is created under Definitions. For more information, see Deforming Fluid Domains.
In addition, the Multiphysics Couplings node is added, which automatically includes the multiphysics coupling feature Fluid-Structure Interaction.
On the Constituent Physics Interfaces
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The Laminar Flow interface solves the Navier-Stokes equations for the conservation of momentum and mass, to compute the fluid velocity and pressure. The interface supports incompressible flows and compressible flows at low Mach numbers (typically less than 0.3). When the CFD Module is available, turbulent flow is supported through the inclusion of a number of turbulence models.
If you also have the CFD Module, you can add a Stationary, One-Way Coupled with Initialization or Transient, One-Way Coupled with Initialization study for turbulence models requiring the wall distance. See Stationary, One-Way Coupled with Initialization and Time Dependent, One-Way Coupled with Initialization in the COMSOL Multiphysics Reference Manual for more information.
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The Solid Mechanics interface is intended for general structural analysis of 3D, 2D, or axisymmetric bodies. The Solid Mechanics interface is based on solving Navier’s equations, and results such as displacements, stresses, and strains are computed.
In 2D, plane stress or plane strain assumptions can be selected in the Solid Mechanics interface. Only the plane strain (default) should be used together with the FSI coupling.
In previous versions of COMSOL Multiphysics (up to version 5.3), a specific physics interface called Fluid-Structure Interaction was added to the Model Builder. Now, a predefined multiphysics coupling approach is used, improving the flexibility and design options for your modeling. For specific details, see The Multiphysics Branch and Multiphysics Modeling Approaches in the COMSOL Multiphysics Reference Manual.
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 Couplings node. You can choose from the available coupling features, but the modified settings are not included.
Another difference is that the Laminar Flow interface added by the predefined coupling employs pseudo-time stepping per default for stationary models, while the standalone version uses an automatic Newton damping. The latter can sometimes give shorter solution times, while the pseudo-time stepping often gives a more robust solution procedure. You can disable the pseudo-time stepping in Advanced Settings section for the fluid interface.
Coupling features are available from the context menu (right-click the Multiphysics Couplings node) or from the Physics toolbar, Multiphysics 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 Fluid-Structure Interaction coupling feature is used to couple the interfaces.
Physics Interface Features
Physics nodes are available from the Physics ribbon toolbar (Windows users), Physics context menu (Mac 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.
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The available physics features for The Single-Phase Flow, Laminar Flow Interface are listed in the section Domain, Boundary, Pair, and Point Nodes for Single-Phase Flow in the COMSOL Multiphysics Reference Manual.
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The available physics features for The Solid Mechanics Interface are listed in the Domain, Boundary, Edge, Point, and Pair Nodes for Solid Mechanics section.