Numerical modelling of wave interaction with offshore structures provides deep insights into the complex wave hydrodynamics and the wave-structure interaction problem. Offshore structures such as an FPSO vessel are susceptible to continuous wave loading under operational conditions and catastrophically large wave loadings under extreme conditions. It is essential to obtain accurate information on the environmental forcing due to waves on an FPSO to reliably predict the operational conditions to optimise the operational times while considering operational safety. In addition, the wave hydrodynamics involved under extreme wave conditions also have to be evaluated in order to predict the survivability of the vessel and avoid major accidents at sea.

In the current study, the open-source hydrodynamic model REEF3D is used to study the wave interaction with an FPSO structure. The numerical results are compared to available experimental data for the free surface around the structure, the pressure due to wave incidence and the motion of the structure. The wave interaction with the structure is studied for a fixed structure and considering the six degrees-of-freedom for a floating object. Different incident waves are simulated including irregular waves using the JONSWAP spectrum and phase-focussed irregular waves. The model solves the incompressible Reynolds-averaged Navier-Stokes equations with high-order discretization schemes for convection and time discretization. The local directional immersed boundary ghost cell method extended to three dimensions is used to represent the boundaries of complex objects. The level set method is used to obtain a sharp free surface. The Poisson pressure equation is solved using the multi-grid preconditioned BiCGStab algorithm provided by the Hypre high performance solver library. The numerical model is fully parallelised using the MPI library.

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