Typical fluid-structure interation (FSI) simulations attempt to couple the full structural analysis FEA code with the CFD solver and compute the structural stresses and deformations after each iteration. The approach taken in the EZ_FSI product takes advantage of a lumped-mass model of the solid part to simplify the analysis.

First, the solid part is meshed and the fluid-structure interaction points (the "wetted" points) are identified. The solid part is then analyzed to determine lumped mass, damping, and stiffness values for the wetted points. The lumped system will behave exactly as the full system for linear systems with small deformations.

Next, the fluid portion of the domain is meshed and the fluid structure interaction points are identified as a special moving boundary. As the transient, CFD solution progresses, the pressure on the wetted points is used as a forcing function on the lumped mass system to determine the new location at the current time. The boundary is moved to the new location, the CFD mesh is updated, and the process repeats. This is all done within the CFD solver -- eliminating the need to communicate with an external structural analysis package every iteration.

Finally, after completing the CFD analysis, the transient pressure data can be imported into the structural analysis package to determine dynamic stresses within the solid.