Using smoothed particle hydrodynamics with open boundaries to model floating offshore wind turbines in realistic extreme conditions

Predicting the dynamics of floating offshore wind turbines (FOWTs) in realistic extreme conditions is important for their effective design and operation. This includes realistic extremes involving combined wave-current conditions and breaking-wave conditions, which are highly prevalent yet seldom accurately incorporated into design due to modelling challenges. Here, a smoothed particle hydrodynamics (SPH) based wave-current flume with open boundaries is employed to model the dynamics of a semi-submersible FOWT. First, FOWT motions are validated against experimental measurements in regular waves. Second, focused waves on vertically sheared currents and spilling breaking waves are replicated in the numerical flume. Following these validations, the FOWT response is examined under these conditions. For the present mooring configuration, surge and heave are primarily governed by wave excitation but are also influenced by current through the modification of wave-induced kinematics and altered mean position. Pitch exhibits a distinct two-stage response under waves on a following sheared current and under spilling breaking waves, with pitch angles reaching about 14.5° in the former, revealing potential consequences for aerodynamic and drivetrain loads and underscoring the importance of capturing these phenomena for design. Mooring design refinement shows that increasing the line length (initially 1 m) by 0.4 m reduces observed extreme pitch angle from 14.5° to 4.6°, and mooring tension from 533.7 N to 58.7 N, respectively. This study therefore develops and demonstrates a novel SPH-based framework with open boundaries to model FOWTs and other offshore renewable energy (ORE) systems in realistic extreme conditions, with the capability of refining their design. • An SPH framework with open boundaries is developed for FOWTs in realistic extremes. • Realistic extremes are generated using waves on sheared currents and breaking waves. • The FOWT dynamics in these realistic extremes exhibit a distinct two-stage response. • The ability to model any offshore system in realistic ocean extremes is demonstrated.