In an FSI context, the flow applies forces on the interface boundary with the solid, which will deform; the resulting displacements of the solid domain will in turn lead to a deformation of the fluid domain. The communication between the fluid and the solid occurs in terms of forces from the fluid to the solid and in terms of displacements from the solid to the fluid. When the displacements undergone by the solid domain are small, feedback from the solid deformation to the fluid domain can be neglected: this is referred to as one-way FSI simulation. When the displacements undergone by the solid domain are no longer negligible, feedback of the solid deformation onto the fluid domain is necessary: this is referred to as two-way FSI simulation.