Fluid Structure Interaction (FSI) in COMSOL Multiphysics®

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Deformed Geometry vs. Moving Mesh

Deformation of a mesh can be set up in one of two distinct ways, depending on the behaviour that is desired to be exhibited by the model: either the deformation represents a fundamental change in the shape of the geometry, or it represents the shape change that is induced by the deformation of solid materials. Both of these configurations are possible. The first feature is known as Deformed Geometry in COMSOL Multiphysics, while the second is known as Moving Mesh functionality. Deformed Geometry functionality deforms the material frame mesh relative to the geometry frame mesh, while Moving Mesh functionality deforms the spatial frame mesh relative to the material frame mesh. The distinction between the two may be explained using technical terminology. It is possible to utilise both kinds of deformation simultaneously, stacking one on top of the other.

Fixed Boundary

Use the Fixed Boundary node on boundaries of deforming domains to specify that the selected boundaries remain at their reference shape and do not move.

In fluid dynamics, laminar flow is characterized by fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing. At low velocities, the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross-currents perpendicular to the direction of flow, nor eddies or swirls of fluids. In laminar flow, the motion of the particles of the fluid is very orderly with particles close to a solid surface moving in straight lines parallel to that surface. Laminar flow is a flow regime characterized by high momentum diffusion and low momentum convection.

The Reynolds number (Re) helps predict flow patterns in different fluid flow situations. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers flows tend to be turbulent.
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
A Newtonian fluid is a fluid in which the viscous stresses arising from its flow are at every point linearly correlated to the local strain rate — the rate of change of its deformation over time.

Post processing of the results

Advanced tricks on post processing