The Fluid-Structure Interaction () multiphysics coupling provides a coupling on a boundary between a fluid domain and a solid material. The solid material can be modeled either in a neighboring domain, or on the boundary itself. In the former case, the Solid Mechanics or Multibody Dynamics interface is used; in the latter one of the Shell or Membrane interfaces is used.

The effect of the coupling depends on whether an Deforming Domain is active in the fluid domain or not. For cases when the structural deformations are so small that the change in the geometry of the fluid can be ignored, you do not have to use a deforming domain. This is called a fixed geometry. Domains with a fixed geometry have fewer degreed of freedom and are less nonlinear and are thus computationally less expensive

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 fsi1.

By default, the selection is set to All boundaries. However, only boundaries between fluid and solid domains are applicable. This is deduced automatically using the selections made on the coupled physics interfaces.

This section defines the physics interfaces involved in the Fluid-Structure Interaction coupling. The Fluid and Solid lists include all applicable physics interfaces.

You can also select None from either list to uncouple the Fluid-Structure Interaction node from a physics interface. If the physics interface is removed from the Model Builder, for example Solid Mechanics is deleted, then the Solid list defaults to None as there is nothing to couple to.

In the case when the coupling is of the fixed geometry type, you can select which aspect of the interaction you want to model. From the Fixed geometry coupling type list, select Fully coupled, Fluid loading on structure, or Velocity transmission to fluid.

In the case Fluid loading on structure, pressure and viscous forces in the fluid affect the structure, but the structure does not affect the fluid flow.

In the case Velocity transmission to fluid, the structural velocity acts as boundary condition for the fluid, but the fluid does not affect the structure.

For Fully coupled, both effects are taken into account.