Nonlinear stochastic responses of a newly developed floating wind-solar-aquaculture system

Abstract

Offshore wind and solar energy are more abundant and stable than the land. Like modern offshore wind industry, the traditional marine aquaculture is moving rapidly into deep waters. To more comprehensively exploit the deepwater resources, recently authors have conceived of a novel floating wind-solar-aquaculture (WSA) concept (Zheng et al., 2020) that combines multi vertical-axis wind turbines (VAWTs) and solar panels with a steel fishing cage as the supporting substructure. The present study focuses on the nonlinear stochastic responses of this state-of-the-art floater when subjected to wind-wave combined actions. The fully coupled analysis involves VAWTs' aerodynamics, control system, structural dynamics and hydrodynamics of the whole system. In-house computer codes are developed in Python and then coupled with software (WAMIT and Orcaflex) for constructing a fully coupled simulation package. The accuracy of codes is validated against ANSYS and experiments first. Then using the simulation package, stochastic responses of WSA driven by wind and waves in a number of operating environmental conditions are investigated from the aspects of hydrodynamics, aerodynamics, structural dynamics and their coupling. Particularly, the 2nd-order hydrodynamic load is included and the corresponding responses are compared to that caused by a similar slowly varying aerodynamic load. The numerical results show that aerodynamic loads have greater influences on platform surge and pitch motions, tower bending moments and mooring tensions. By contrast, the effects of 2nd-order hydrodynamics on tower bending moments and mooring tensions are negligible. Heave motions of WSA are mainly controlled by 1st-order hydrodynamics rather than aerodynamics and 2nd-order hydrodynamics. Besides, the 3Ω effects, due to wind action on rotating rotors, are insignificant to platform motions but pronounced in tower bending moments.