## 6 Conclusions and Discussion  
In this study, a new concept of floating offshore wind turbine that is integrated with a steel fish-farming cage (FOWT-SFFC) is exposed. Firstly, the configuration and dimensions of this concept are presented. The FOWT-SFFC possesses the essential feature of a spar buoy type offshore wind turbine with excellent hydrostatic stability, as the center of gravity of the whole system is below the center of buoyancy in its equilibrium position. Then, the hydrodynamic properties of FOWT-SFFC are investigated by the hydrodynamic program WAMIT and compared with the existing and well known OC3 Hywind and OC4 DeepCwind concepts. The motion RAOs reveal the superiority of seakeeping performance of FOWT-SFFC. Lastly, a coupled aero-hydro-servo-elastic model is developed in FAST, in which both potential-flow theory and Morison's equation are taken into account to calculate the fluid forces. The comprehensive performance of FOWT-SFFC under three load cases is examined. Through comparative study, it has been shown that the anti-overturning ability, surge, heave and pitch motions of FOWT-SFFC outperform those of OC3 Hywind and OC4 DeepCwind. For instance, in load case #2 the maximum heave of FOWT-SFFC is only 37% and 17% of its counterparts, and in load case #3 the maximum pitch of FOWT-SFFC is less than 4.5 degrees, while OC3 Hywind and OC4 DeepCwind have pitch angles exceeding 8 degrees and 6 degrees respectively. Load case #3 corresponds to a 50-year harsh sea state, in which the parked wind turbine is assumed to experience most unfavorable wind load. The spectra of responses like surge, pitch and tower base stress, contain appreciable densities at low frequencies since these responses are heavily subjected to the effects of wind. In terms of the statistics of short-term stochastic response with Gaussian waves and wind as input, it is also shown that the level of non-Gaussianity in FOWT-SFFC's responses is weak, though superharmonic response does exist in structural response. In addition to abovementioned hydrostatic, hydrodynamic and structural dynamic advantages in engineering technology, the FOWT-SFFC system also carries economic merits. Protected by the cage foundation, the fish farming can be executed safely in open sea with harsh environments. Also, healthier fish in water can be expected as the FOWT-SFFC system can be deployed in distant ocean. Therefore, considerable profits from fish farming help to rapidly shorten the payback period of heavy investment in wind turbine. The technological and economic benefits of FOWT-SFFC manifest a great potential in offshore industry for both power exploitation and aquaculture in deep waters. In this paper although the NREL 5-MW wind turbine has been used as a prototype in feasibility analyses of the FOWT-SFFC concept, an upscale wind turbine larger than 10 MW can be employed, with adjustments on the fishing cage foundation. In case that the fish farming has difficulties, an upscale wind turbine to some extent will also shorten the payback period of investment. In addition, it must be noted that the performance comparisons of FOWT-SFFC with OC3 Hywind and OC4 DeepCwindmay be not ideally fair due to their different operating depths, but the outstanding performance of FOWT-SFFC can be validated still. Future works can be extended to investigate the nonlinear viscous damping of copper alloy nets which has been simplified as a linear damping matrix, and to identify the drag coefficients of wave forces on copper alloy nets and rectangular pontoons using model tests in ocean basin and computational fluid dynamics (CFD) simulations. In addition, as motions of FOWT-SFFC are of low frequencies; in-depth study of the effect of second-order random waves and frequency-difference wave loads is required. Furthermore, FOWT-SFFC with an upscale wind turbine (possibly larger than 10 MW) and larger steel fish-farming cage (with contained water volume greater than 250,000 m\({}^{3}\)) should be studied to probe the scalability of this integrated concept.