When the Laminar Two-Phase Flow, Moving Mesh multiphysics interface is added using the Model Wizard, a Deforming Domain node is added automatically in the Model Builder under the Definitions > Moving Mesh node. This node serves to represent domains and boundaries where the mesh can deform. By default, the selection is all domains. Under the Deforming Domain, you can also choose the Mesh smoothing type, by default set to Yeoh with a default Stiffening factor of 10. More information of the smoothing type can be found in the Deforming Domain chapter in the COMSOL Multiphysics Reference Manual.

By default, the mesh is fixed at all exterior boundaries of the geometry. Use the Symmetry/Roller node to select the exterior boundaries, where the fluid-fluid interface can slide along the boundary. You can also add other types of boundary conditions for the mesh motion, for details see Moving Mesh Features in the COMSOL Multiphysics Reference Manual.