In order to shorten the payback period of the investment of floating offshore wind farms, an innovative structure integrating a floating offshore wind turbine with a steel fish farming cage (FOWT-SFFC) has recently been developed by authors. In this study, a brief description of this concept is given first and then the stability behavior and hydrodynamic behavior are studied. The dynamic performance of FOWT-SFFC subjected to wind and wave actions is investigated. The effects of fish nets on the dynamic responses of FOWT-SFFC are also discussed.
Since year 2000, the offshore wind technology has been developing rapidly due to rich resources of wind power in oceans. Because the traditional bottom-fixed foundations are uneconomical for harvesting wind energy in waters deeper than 50m, floating offshore wind turbine (FOWT) concepts appear more suitable for deeper waters. Over the most recent decade, dozens of FOWT concepts have been proposed and studied worldwide.
However, there is still a long way to reach a wide commercial application of FOWT due to the weak economic competitiveness. In order to increase the economic feasibility, a number of different FOWT concepts have been developed, such as the hybrid spar type FOWT whose foundation was made of prestressed concrete and steel (Utsunomiya et al., 2015), the W2Power concept which is a hybrid wind & wave energy platform (Legaz et al., 2018) and the Hexicon concept which is a multi-turbine platform (Hexicon AB, 2020). The engineering success achieved by projects Hywind (Equinor, 2017) and Windfloat (EDP Renewables, 2019) has greatly boosted the confidence in offshore wind industry and the academia society. Recently, Zheng and Lei (Zheng and Lei, 2018) developed an innovative structure integrating a floating offshore wind turbine with a steel fish farming cage (FOWT-SFFC). In this concept, considerable profits from fish farming help to significantly shorten the payback period of heavy investment in wind turbine. The relevant patent was granted in China. The dynamic responses of FOWT-SFFC under various environmental conditions have been studied by FAST. Nevertheless, some simplifications were made in previous study, i.e., the rectangular pontoons were modeled by equivalent circular cylinders with the same drag coefficients in transverse directions, the drag force on the nets was ignored. These simplifications might lead to inaccurate description of the dynamic and stochastic characteristics of responses.