Nonlinear wave-structure-mooring interactions in hurricane condition: A case study using three-dimensional time-domain simulations

Simulating the behavior of moored floating structures in real-world ocean waves presents significant challenges due to the inherent nonlinearities in both the wave environment and the dynamic response of the structure. This study introduces a novel three-dimensional (3D) time-domain solver, HOS-FNL, designed to accurately capture the complex interactions among wave components, the floating structure, and its mooring system. The High-Order Spectral (HOS) method models the energy transfer and wave profile evolution across varying frequencies and directions, while the Rankine panel method (FNL) computes the floater's hydrodynamic responses, with an embedded slender rod model coupling body motions and mooring forces. The HOS solver is validated against quartet resonance interaction benchmarks, while the full HOS-FNL system is verified through comparisons with industry-standard software under regular and irregular oblique waves. The solver is further extended to assess the hydrodynamic performance of a moored Floating Production Storage and Offloading (FPSO) under extreme hurricane conditions, using Hurricane IVAN (2004) as a case study. The buoy observed data informs the directional wave spectrum, enabling the generation of 3D nonlinear waves in the HOS domain. Visualizations of the FPSO's six degree of freedom (6-DOF) motions, load responses, mooring tensions, and velocity fields reveal significant nonlinear effects and underscore the limitations of linear wave theory.