Study On Fluid Dynamic Response Of Floating Offshore Wind Turbine

International exploitation of wind energy is growing at an accelerative speed.Compared with that of onshore wind resources,offshore wind speed is higher and more stable,which makes wind energy industry gradually moving to the ocean.Under this circumstance,offshore floating wind turbine comes into being and is developed fast.Different with inland turbine and offshore oil production platform,offshore floating wind turbine presents non-linear and unsteady characteristics in terms of its motion and loads.This thesis focuses on the prediction of overall loads and dynamic response of offshore floating wind turbine as well as the responsive characteristics of the wind rotor and the floater.As to the aerodynamics of the rotor,the following aspects have been done.First of all,the coordinated system of the turbine system is established on the basis of the inland wind turbine coordinates and the oceaneering coordinates.Secondly,with the dynamic inflow and stall correction,the aerodynamics is calculated using the yawed blade element momentum theory.Moreover,the gyroscopic torque caused by the dynamic motion of the support platform is also taken into consideration.Finally,the overall numerical model to compute the aerodynamic performance of offshore floating turbine is established,which is proved to be of high accuracy.Using the 5MW model turbine developed by the NREL,researches and analysis on respective effects of turbine gesture,speed change,motion in six DOFs and the control system on the aerodynamic performance of the turbine.The dynamic response of the overall system is solved by the time-domain non-linear coupled kinetic equation on the basis of Euler angles.The wind environment is simulated under consideration of complex offshore environment like wind shear effect,tower shadow effect and turbulent wind effect.The aerodynamic model of the offshore floating wind turbine is established on the basis of the numerical model of fixed turbine and the ocean engineering model.Taking account of the regular wave,random wave and ocean current,the water environment and the hydrodynamic model are established using the non-linear slender body theory.The mooring model is established according to the quasi-static catenary theory.Eventually,the integral model is formed and is used to analyze the hydrodynamic characteristics of an articulated platform.In reference to various types of platforms,the limitations of fixed support structure are analyzed and the articulated platform is put forward,as well as its strengths.An articulated platform is designed for the 5MW turbine.Moreover,according to the environmental conditions,how steady wind and regular wave affect articulated offshore floating wind turbine is analyzed.Under random wave condition,the overall motion response of the turbine system and the aerodynamic response of the rotor are analyzed.Furthermore,influence laws of wind and wave environment on turbine system are summarized.In terms of experiment,reduced scales about main parameters of offshore wind turbine are obtained using the Froude number as the scale criterion.According to experimental theories and practical conditions,a model for the articulated offshore floating wind turbine and the experiment scheme are designed.An experiment using the constant load to simulate the aerodynamic load of the rotor is conducted and its feasibilities and limitations are analyzed.Experiments under free attenuation condition,regular wave condition and random wave condition are also conducted to demonstrate the feasibilities of the articulated support platform and the accuracy of the numerical model.