Influence of Underlying Currents on the Performance of a Taut-Moored Point-Absorber WEC: an Investigation Via High-End Numerical Tools

Abstract Site-specific environmental conditions in targeted areas for offshore renewable energy deployment often feature underlying currents. The effects of the latter on wave parameters and overall hydrodynamics modifies the behavior of light offshore structures, such as wave energy converters (WEC), with unforeseen alteration of power yield and structural loads. To address such effects on a taut-moored point-absorber — potentially susceptible to wave and current motion — the high-end numerical framework of DualSPHysics is used, as it leverages the flexibility of the Lagrangian Smoothed Particle Hydrodynamics (SPH) method for simulating fluid-structure interaction and external libraries to take on multibody problem posed by power take-off (PTO) and moored connections. A dedicated numerical wave tank capable of reproducing regular waves propagating over steady uniform currents is used to numerically test the Uppsala University WEC (UUWEC), which consists of a buoy connected to a linear PTO. Clear influence of the current traits is visible in the results regarding the point-absorber motion, power output, and anchoring tension. Remarkably, the sole presence of current can hamper the harvesting capabilities of the device, up to different extents depending on its intensity and relative direction with respect to the wave propagation. Tension patterns, instead, are found to be almost linearly sensitive to current intensity and direction, with beneficial effects produced by opposing currents and vice-versa.