Hydrodynamic performance of a self-protected hybrid offshore wind-wave energy system

Abstract

The load-bearing capacity is a pivotal consideration in the design of offshore renewable energy structures. This paper aims to address the technical challenges associated with the additional wave loads caused by the integrated devices in a hybrid system for the multi-purpose utilization of coastal renewable energy. A self-protected hybrid wind-wave energy system is proposed, in which an oscillating water column (OWC) device is attached at a monopile foundation of an offshore wind turbine. In the meantime, the OWC is connected by a submerged horizontal perforated plate at its exterior shell, which is expected to minimize the wave loads on the system. The hydrodynamic performance of the system is investigated. A novel approach is developed to model the wave interaction with the hybrid system. This efficient approach removes the necessity of decomposing the wave-scattering field into diffraction and pressure-dependent radiation components. Detailed numerical computation is then conducted for both regular and irregular sea states. Various hydrodynamic properties related to the system, such as wave energy harvesting, wave force/moment, and free-surface elevation, have been evaluated. Numerical results manifest the feasibility of imposing a negligible effect on the high wave energy harvesting while reducing the high wave loads by manipulating the submerged horizontal perforated plate. The impact of the perforated plate on the dominant wave energy harvesting in the long-period region is found to be trivial. In contrast, it can affect the high bending moment in the short-period region, which causes a reduction of greater than 15%.