A Two-Phase FSI Solver for Transmedia Hydrodynamics with Geometric Flux Decomposition and Consistent Mass–Momentum Transport

A two-phase fluid–structure interaction solver is developed for transmedia hydrodynamics by coupling an immersed-boundary method with the CLSVOF method on a staggered Cartesian grid. In cells containing both liquid and solid, the swept fluxes of the combined liquid–solid phase and the solid phase are evaluated separately, and their difference provides the liquid flux without explicitly reconstructing the triple-junction geometry. The resulting liquid fluxes are further decomposed to construct the mass fluxes required by the staggered momentum control volumes. The main advance is the extension of the established consistent mass–momentum transport framework to solid-intersected triple-phase cells, ensuring that the volume-fraction update and momentum convection use the same geometric liquid-flux information near moving immersed boundaries. The method is validated using representative water-entry, water-exit, and wave-breaking problems. The predicted free-surface evolution, body motion, and hydrodynamic loads agree well with available experimental and numerical results. Additional conservation and sensitivity tests further demonstrate the robustness of the proposed framework.