Synthetic Performance of a Single-Point Moored Aquaculture Cage-Wave Energy Converter Hybrid System

Abstract

Integrating wave energy converters (WECs) to the outside of offshore aquaculture cages not only meets the demand for sustainable power, but also reduce destruction due to wave loads. A new concept of a single-point moored cage-WEC hybrid system is proposed. The single-point mooring device is considered as a point absorber WEC moored to the sea bottom through a linear power take-off (PTO) system. The connector between WEC and cage is a flexible rope which is simulated as a nonlinear spring without compressible property, and thus the cage is always located at the lee side of the WEC for arbitrary directional waves. A one-way coupling approach of the cage-WEC hybrid system is established to solve the rigid motions, and moreover, consider the elastic deflections of the cage including the floating collar and the curved net. This approach is based on the principle of equal buoyancy distribution and equivalent mesh group, after which is validated, a multi-parameter sensitivity is investigated to obtain wave energy conversion of WECs and hydroelastic interaction of cages. The hybrid system is found to harvest effectively wave power in a broad scope of incident wave directions. For the rigid-flexible integrated system, the in-phase and out-of-phase motion of elastic modes play constructive and destructive roles in energy extraction of short-period and long-period waves, respectively. Under the precondition of theoretical optimised PTO damper, a dumpy WEC is demonstrated to possess beneficial wave energy extraction performance, but does not contribute much to the hydroelastic response of the cage.

Keywords: Offshore aquaculture cage, wave energy converter, energy conversion efficiency, single-point mooring system, hydroelastic interaction, oblique incident waves