Introduction of dispersive effects and treatment of horizontally moving pressurized regions in a semi-implicit fluid–structure interaction model

In geophysical fluid structure interaction problems with moving free surface, large relative motions between the fluid and solid domains generate not only physical waves on the free surface, but may also trigger numerical instabilities. This is also the case in models for moving floating structures above water. Since the governing equations change type from hyperbolic below the free surface to elliptic below the moving floating object within the cells of the computational domain, the horizontal motion may exhibit a numerical instability that is not observed solely with the vertical heave motion. When a ship enters a new cell, the pressure at the bow increases and decreases sharply, leading to oscillations that can create an unphysical void below the vessel. After examining the origin of the problem, several measures were taken at the discrete level to reduce these spurious oscillations. All of these modifications were effective in controlling the oscillations, making numerical simulations with horizontal motion of moving floating objects more robust, stable and accurate.

To enhance the range of application of the model, we also include some additional weakly dispersive terms. The same study is then performed in presence of these non-hydrostatic effects, showing a reliable and robust prediction of the interaction of moving bodies interacting with hydrostatic and non-hydrostatic waves.