This type of FSI component can be used to model a check valve. The pressure load is integrated over the selected boundary to provide a force acting on the body. An additional resistive force is applied proportional to the velocity of the body, with a user-supplied proportionality constant.

Which gives the body's acceleration:

The body's new position is then marched in time explicitly.

A displacement threshold may be specified to control when the FSI part would start to move. The FSI part would not move geometrically until the tracked displacement would exceed the displacement threshold. A maximum displacement may also be specified, and an option may be set to limit the spring motion to travel in only the positive direction.

From the physical properties of the spring mechanism controlling the valve, the spring constant, mass of the body, damping coefficient, and direction must be provided.