The Fluid-Solid Interaction, Viscoelastic Flow Interface
Using the Fluid-Solid Interaction, Viscoelastic Flow() interface, you can model phenomena where a deformable solid and a fluid exhibiting a combination of viscous and elastic behavior 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 time-dependent study, the Fluid-Solid Interaction, Viscoelastic Flow 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.
You add a predefined Fluid-Solid Interaction, Viscoelastic Flow 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. Viscoelastic Flow and Solid Mechanics 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 feature Fluid-Structure Interaction.
At the same time, a Moving Mesh node with a Deforming Domain subnode is created under Definitions. For more information, see Deforming Fluid Domains.
The Viscoelastic Flow interface solves the continuity equation for conservation of mass and the Navier-Stokes equations for the conservation of momentum with an additional elastic stress term. To calculate the extra stress tensor, a number of constitutive relations are 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 Viscoelastic Flow interface is described in The Viscoelastic Flow Interface.
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The Deforming Domain feature is described in the Moving Mesh Features.
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 Fluid-Structure Interaction feature is 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.