A three dimensional hybrid fully nonlinear potential flow and Navier Stokes model for wave structure interactions

To minimize scale effects, many experiments involving wave-structure-interaction are carried out at large scale. To complement such experiments, numerical models capable of simulating wave-structure-interaction in large domains for long time become necessary. Potential theory is energy-preserving but cannot account for viscous effects. Navier-Stokes equations take the complete physics into consideration but are computationally expensive and numerically dissipative over the long term. Thus, it is beneficial to hybridize both models such that Navier-Stokes is applied in the vicinity of the structure with the far-field handled using potential theory. Here, we propose a new hybrid model for wave-structure-interaction through one-way coupling of two in-house codes: IITM-FNPT2D and IITM-RANS3D. Key feature of the hybrid model is the fast-fictitious-domain method to model the solid as a highly viscous fluid. Since the solid geometry is handled by a VOF model as an embedded boundary, complex interactions between waves and moving objects may be simulated without remeshing steps. The pro-posed model is applied to breaking focused waves run-up over a beach and focused waves interacting with a fixed and moving cylinder in large domains. Good agreement is reported with experiments and other conventional as well as hybrid state-of-the-art models showcasing the advantages of coupling embedded boundary-based viscous models with potential-theory-based solvers.