A Shock-Absorbing Nonhydrostatic Solver on σ-Grids for Wave Modeling Over Complex Bathymetry

Due to the high computational cost of computational fluid dynamics (CFD), various faster numerical wave tanks (NWTs) have been developed for large-scale wave propagation, such as high-order spectral (HOS) models and fully nonlinear potential flow (FNPF) models. These models often neglect turbulence and viscosity, which are important for coastal processes such as wave–current interactions and sediment transport. Thus, a fast wave model that can incorporate turbulence and viscosity is in demand. This research presents a three-dimensional nonhydrostatic model called REEF3D::NHFLOW, which operates on a moving σ-grid. By solving the nonhydrostatic Navier–Stokes equations, this model provides detailed results. The grid used in REEF3D::NHFLOW follows the surface and bottom topography, allowing for grid refinement near the water surface or bottom while maintaining low computational effort. Developed within the open-source hydrodynamics framework REEF3D, the new model is fully parallelized and utilizes the domain decomposition strategy and message passing interface (MPI) communication between processors. This article showcases the capabilities of this new and efficient one-phase flow model through the implementation of a free surface and bottom following the σ-grid approach. The benchmark validations on steep fifth-order Stokes waves, wave decomposition over a submerged bar, focused waves, and wave breaking over a mild slope demonstrate the model’s accuracy and stability for both deep water dispersive waves and coastal nonlinear wave transformations. The engineering relevance of the model is demonstrated through full-scale simulations of wave propagation into the Naissaar harbor and breaking wave formations over submarine canyons at Nazaré.