Simulation of wave-induced heave motion of a buoy using solvers based on the Navier–Stokes equations and spectral wave explicit Navier–Stokes equations

Based on the NS (Navier–Stokes) equations and the SWENSE (Spectral Wave Explicit Navier–Stokes Equations), a domain decomposition potential–viscous-flow coupling solver and a functional decomposition potential–viscous-flow coupling solver using the overset mesh method are established in this paper. In the NS solver, the potential-flow wave field is prescribed using the stream function wave theory, and the viscous-flow wave field is resolved by the NS equations. In the SWENSE solver, the total wave field is decomposed into incident and complementary components. The incident field is obtained from the stream function wave theory, whereas the complementary field is governed by the SWENSE, which are derived by subtracting the Euler equations from the NS equations. A numerical study is conducted to compare the performance of the developed solvers. One regular-wave condition is used for wave-only and buoy-response validation, while additional wave conditions with different wave steepnesses are considered for wave-load assessment. The vertical displacement and wetted height predicted by both solvers agree well with the experimental results. The SWENSE solver reduces the number of mesh cells and computational cost by using a reduced cylindrical domain while maintaining satisfactory accuracy. Under different wave-steepness conditions, the NS- and SWENSE-based simulations provide consistent wave-load predictions, and the horizontal load is more sensitive to wave steepness than the vertical load.