Fully Coupled Analysis Of Megawatt-scale Large Offshore Wind Turbines Under Highly Nonlinear Waves

According to the national development and reform commission's 13 th five-year plan for renewable energy,the proportion of non-petrochemical energy consumption in China's energy consumption structure should be raised to more than 15 percent by 2020 and 2030.Offshore wind energy as a renewable energy technology is relatively mature,and it has the scale and the commericial development of a new type of gree energy,China's offshore wind energy industry will develop rapidly.Offshore wind power system is a strong coupling system which under wind load,Hydrodynamic load,current load and sea ice load,in addition,for the specific sea area in East China sea,the waves are close breaking,so the design of offshore wind farm needs to consider the highly nonlinear waves load such as breaking wave.In this paper,the coupling dynamic response of monopile type offshore wind turbine under highly nonlinear waves action is analyzed to reveal the coupiling mechanism between highly nonlinear waves and offshore wind turbine system,as well as the dynamic response of monopile type offshore wind turbine system under the combined action of wind and wave.It is of great research significance to the design and long-term safe and stable operation of the fixed offshore wind turbine system,and has important theoretical significance and engineering application value.The main research contents of this paper include:(1)The comparison between the numerical simulation and the model test of monopile type offshore wind turbine is carried out for the regular wave and the strong nonlinear wave(breaking wave)loads.Firstly,a numerical model was built in FASTV8 to verify the dynamic characteristics of the whole structure of the monopile type offshore wind turbine through free decay vibration test,then,the Morison formula is used to calculate the hydrodynamic load,and the hydrodynamic load data obtained from the model test is imported into the fully coupled numerical model,and the numerical simulation time domain analysis of the monopile type offshore wind turbine is carried out,finally,the numerical model compares the calculated hydrodynamic load with the model test to verify the accuracy of the numerical model.(2)The dynamic response analysis of monopile type offshore wind turbine under the conbined action of wind and wave was carried out.The fully coupled numerical model of monopile type offshore wind turbine was established in FASTV8,and the time-domain and frequency domain characteristics analysis was carried out under typical load conditions.The dynamic response of the internal force at the key nodes of the monopile type offshore wind turbine was analyzed.The relationship between thrust force at the hub,blade tip displacement,blade root shear force and bending moment,tower base shear force and bending moment,shear force and overturning moment at the mudline and combined environmental load of wind and wave under normal working sea conditions and extreme survival sea conditions was emphatically studied.(3)The dynamic characteristics of monopile type offshore wind turbine under the action of breaking wave are analzed,through model test,the data of breaking wave load obtained at the breaking point are imported into Openfast for fully coupled numerical analysis.The effect of the wave stretching meghod on the calculation of the wave load of the breaking wave is considered.The interaction between the dynamic response and the breaking wave load at the tower top and at the mudline was studied,and the structural safety performance of the monopile type offshore wind turbine was evaluated.