A New Approach for Wave-Structure Interaction Modeling Using the Shock Absorbing Non-Hydrostatic Solver REEF3D::NHFLOW

Abstract Previously, the non-hydrostatic wave model REEF3D::NHFLOW has been introduced with the ability to model phase-resolved wave propagation over large ocean and coastal domains. The model possesses shock-capturing capabilities due to the Godunov-type scheme which contributes to excellent numerical stability for steep and breaking wave modeling. The HLL approximate Riemann solver with 5th-order WENO flux reconstruction assures high numerical accuracy. An efficient pressure-correction algorithm based on the projection method delivers very good dispersion properties. The model is integrated in the open-source hydrodynamic framework REEF3D and uses the domain decomposition strategy with MPI communication for parallelization. As either the Euler or Navier-Stokes equations are solved, it is straightforward to add source and forcing terms directly to the governing momentum equations, which can be challenging for fully non-linear potential flow solvers. This opens the intriguing possibility to implement a direct forcing immersed boundary method to consider non-grid conforming solid structures in the flow domain. In NHFLOW, the immersed boundary is represented geometrically through a signed-distance function. With the σ-grid approach, the mesh is moving with the free surface and changes the mesh dynamically over time. Accordingly, the solid signed distance function is updated every time step with an optimized ray-casting algorithm. A Heaviside function is connected to the signed distance function and controls the activation of the direct forcing terms inside the governing equations. The new method is tested and validated against experimental measurements for wave-structure interaction cases. NHFLOW reproduces the hydrodynamic forces accurately at a fraction of the cost of typical two-phase flow CFD-based numerical wave tanks.