Impact of parabolic breakwater on the safety characteristics of shared mooring floating oscillating water column devices array under freak waves

The energy capture efficiency of oscillating water column (OWC) device can be enhanced through the focusing effect of waves by a parabolic breakwater (PB). However, the focusing effect may also increase the survival threat to devices under extreme sea conditions. This paper conducted a fully coupled high-fidelity numerical simulation study to investigate the interaction process between freak waves and the combined PB-OWC array system. A numerical coupling model using discrete element method (DEM) and computational fluid dynamics (CFD) was established to realize the coupling between PB-OWC array, shared moorings, and freak waves. The combined wave focusing model and the push plate wave-making theory were used to simulate the freak waves. Hydrodynamic motion response, wave pressure, mooring tension and captured power of a 5-OWCs array under shared mooring with and without the PB were analyzed. Results show that the PB diminishes extreme wave forces on OWCs during the theoretical freak wave period, enhancing survivability while increasing higher-order wave forces. The extreme mooing tension on the seaward side is reduced by 26.2%. The PB leads to more stable pressure and flow velocity in device at the central of the array, resulting in a significantly higher energy capture compared to outer devices. However, the PB increases wave slamming pressure on the leeward side of central OWC and causes negative pressure at higher elevations. For the 5-OWCs array without PB, the seaward slamming pressures of OWCs exhibit strong nonlinearity and a double-peak phenomenon, with the second slamming occurring after the freak wave period.