The Fluid–Multibody Interaction, Assembly Interface
Using the Fluid–Multibody Interaction, Assembly () interface, you can model phenomena where a fluid and a rigid or deformable solid affect each other. The interface includes a predefined condition for the interaction at the fluid-solid boundaries. This interface is used when the geometry sequence is set up to form an assembly. 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, Assembly interface models bidirectional coupling between solids and fluids.
You add a predefined Fluid–Multibody Interaction, Assembly interface from the Fluid–Structure Interaction () group in the Fluid Flow branch () of the Model Wizard or Add Physics windows. Laminar Flow and Multibody Dynamics interfaces are then added to the Model Builder.
In addition, the Multiphysics Couplings node is added, which automatically includes the multiphysics coupling feature Fluid–Structure Interaction, Pair.
At the same time, a Moving Mesh node with a Deforming Domain subnode is created under Definitions. For more information, see Deforming Fluid Domains.
On the Constituent Physics Interfaces
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The Laminar Flow interface is described in The Single-Phase Flow, Laminar Flow Interface. When the CFD Module is available, turbulent flow is supported through the inclusion of a number of turbulence models.
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The Multibody Dynamics interface is described in The Multibody Dynamics 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 Multibody Dynamics 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.
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 the Advanced Settings section for the fluid interface.
Coupling features are available from the context menu (right-click the Multiphysics node) or from the Physics toolbar, Multiphysics Couplings menu.
Coupling Features
The Fluid–Structure Interaction, Pair multiphysics coupling is used to couple the interfaces.