Wind turbine tower, Spar-type platform and mooring system of the 6-MW spar-type floating offshore wind turbine (FOWT) are designed in the paper based on a given 6-MW wind turbine. And then the 6-MW FOWT model is established in the fully coupled aero-hydro-servo-elastic simulation tool of FAST. Model validation is conducted firstly. Calculation values of FOWT under combined wind- and wave-induced loads have great agreement with reference values. The factor of simulation length varied from 10min to 3 h is also studied to investigate the influence of simulation length on coupled dynamic response. And results display that the 1 h simulation length is sufficient. And then, comparison between steady wind and turbulent wind is carried out and results illustrate that the maximal response values of mean rotor thrust, mean rotor power, platform pitch motion and fairlead force under the turbulent wind conditions are larger −9.4%, −0.01%, 5.5% and 12.8% than that of the steady wind conditions, respectively. The influence of wind type on the mean rotor power is scarcely. However, the effect of wind type on the response of fairlead force cannot be ignored and should be put more attention on the phenomenon. Also, the platform pitch, surge and heave motion and fairlead force response are compared to investigate the effect of wind turbine on spar-type platform and mooring system tension. And the rotor power, out-of-plane blade tip deflection, nacelle surge acceleration and tower base fore-aft bending moment response are compared to investigate the effect of spar-type platform motion on wind turbine and tower. The results can provide a clear understanding of the wind type influence and interaction influence between the wind turbine and spar-type platform. And it is beneficial to the further study on the FOWT system.
In recent decades, with the fossil resources depletion, the wind turbine has been developed rapidly. Due to the restriction of development of the land-based wind turbine, floating offshore wind turbine (FOWT) have become the focus of research. A variety of floating offshore wind turbines concepts have been gradually focused on by industry and researchers. The deep-water spar-type FOWT concept has been researched (Duan. F. et al 2016). Spar-type platforms are favored because of their simplicity in design, suitability in modeling and propinquity to commercialization (Shin. H. 2011). The dynamic motion responses, mooring loads and instabilities of spar-type FOWT have been studied by several researchers (Jonkman J. M. 2009&2011, Karimirad M. et al 2012). However, the interactions between the rotating wind turbine and the support foundation have not yet been well understood, and the developments of theories and data validations are necessary to advance this knowledge (Koo B. et al 2014). The research with respect to FOWT is multidisciplinary, involving aerodynamics, hydrodynamics, multi-structure dynamics (elastic) and automatic control (Namik H. et al 2010, Wang L. et al 2013, Jeon M. 2014, Salehyar S. 2015, Nejad A. R. 2015), and so that it is of great importance to reveal the nature of dynamic response characteristics.
