Dynamic Performance Comparisons Of Floating Wind Turbines Using Experimental And Numerical Methods

With the traditional energy gradually depleting and the awareness of environmental protection increasingly enhancing,clean and environmentally friendly renewable energy has attracted more attentions than ever before all over the world.Wind energy is the most commercial resource form of renewable energy.Due to advantages of high wind speed,stable wind field,wide development space,less visual pollution and far away from coastal densely populated areas,wind turbines are gradually developed from land and offshore areas to the ocean.With the increase of water depth,the costs of fixed-bottom wind turbines increase rapidly,floating ones will inevitably become the direction of wind power development in the future.However,with the influence of combined windwave-current loads,the dynamic responses of the floating wind turbines are much more complicated than those of fixed-bottom ones.Therefore,it has significance to choose appropriate methods to analyze the dynamic responses of floating wind turbines.In this paper,fully coupled time domain numerical calculation codes and model test are both applied to investigate two types of 5 MW floating wind turbine for a water depth of 200 m.By the comparison and validation between numerical calculation and model test,the dynamic response characteristics of floating wind turbine under different sea conditions are concluded and the discrepancies between numerical calculation and model test are discussed.The main contents of this paper are as follows:1.The hydrodynamic properties of OC3 spar-type floating platform and OC4 semi-type floating platform are calculated respectively.2.Taking the OC3 spar-type floating system and OC4 semi-type floating system as supporting structures of the 5 MW wind turbine respectively,dynamic models of the floating wind turbine are established.3.The dynamic responses of the spar-type floating wind turbine under wind only,wind-wave and wind-wave-current conditions are calculated by FAST V8 and DARwind numerical calculation code.Compared with 1:50 model test,the influences of wind,wave and current on dynamic responses are investigated,and the characteristics of key loads on floating wind turbine are discussed.It is found that the average values of motion responses are mainly determined by wind load,and will be enhanced by current load.The amplitude of motion responses are mainly determined by wave load,but will be weakened by current load.4.The dynamic responses of the semi-type floating wind turbine under wind-wave condition are calculated by FAST V8 and DARwind and validated by 1:50 model test.It is found that surge,pitch,heave and yaw are relatively independent without coupling.5.Comparing the results of numerical calculation and model test,the accuracy and limitation of these two methods in predicting motion responses of spar-type and semi-type floating wind turbines can be proved.The research of this paper has well reference significance to the floating wind turbine engineering application.