SPH-based modeling of a direct-drive WEC in extreme waves and currents

In this work, we present a fully Lagrangian framework specifically tailored to host point absorber WECs under violent wave-current excitations. Within the open-source DualSPHysics framework, based on the Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method, a multipurpose wave tank is modeled to simulate extreme wave trains developing over uniform currents, by adopting the focusing strategy and high-order solutions. Moreover, a novel power take-off (PTO) model is implemented within the loop to unlock a swift characterization of different energetic proxy models. An Uppsala University WEC model is firstly validated under extreme sea states, and such framework is eventually tasked with the simulation of combined wave-current extreme events. The outcome we document suggests that complex buoy dynamics can develop in wave-current fields, with high sensitivity to the sea state representation: focused waves propagating over equally headed currents tend to maximize the line stretching and to develop extremely nonlinear kinematics. Floater displacement and anchoring tension patterns show no direct correlation with the wave-current layout and PTO configurations. Contrary to established knowledge, strong PTO damping does not always guarantee lower system stress. An all-around numerical strategy, leveraging high-fidelity modeling is presented, owning the necessary flexibility to anticipate both operational and ultimate limit state load combinations, accommodating increasing degrees of nonlinearity.