Nonlinear dynamic responses of a novel floating semi-submersible wind-solar-aquaculture hybrid system: An experimental study

Abstract

This paper presents a novel, maintenance-friendly, multifunctional floater that combines a 10 MW floating offshore wind turbine, a fish cage and photovoltaics (FOWT-FCP). To study its multi-body coupling dynamic characteristics under wind and waves, physical model tests of scale 1:30 are carried out in the ocean basin, providing a benchmark for establishing numerical simulations. As the coupling is associated with the nonlinear effect of fish nets, the tests are conducted in two comparative configurations, with and without nets. The dynamic responses of 6 degrees of freedom (DOFs) cage motions, the accelerations at tower top and bottom and cable tensions are collected in regular waves, white noise waves and critical wind-wave load cases. They are comprehensively analyzed in the time and frequency domains. The experimental results show that FOWT-FCP has an excellent seakeeping performance. The dynamic responses in both operational and extreme sea states are well below the code limits. The existence of nets increases not only the 6-DOF motion damping but also the fluid loads, yet from the experimental results, both increases are small. Moreover, the nets reduce the standard deviations and extreme values of responses under rated condition, while enhancing them under survival condition. Therefore, the influence of nets on dynamic responses depends on load conditions. Besides, the responses follow a heavy-tailed non-Gaussian distribution with greater extreme values, and the presence of nets increases the level of non-Gaussianity of responses under survival condition. For almost all measured dynamic responses, their low- and high-frequency components are increased by the wind loads.