Fatigue Analysis Of Tripod-type Support Structure Of Offshore Wind Turbine

With the continuous development of social economy,energy demand is growing.Offshore wind power has many advantages that land wind power cannot match,so it has been paid much attention by many countries and enterprises.As the most widely used offshore wind energy development equipment,offshore wind turbines bear the major tasks of developing new energy sources and ease the conventional energy.However,with the increasing of installed capacity,environmental loads suffered by the fixed support structure of offshore wind turbine will be very complex.As the slender column structure,the support structure will be subjected to alternating random load for a long time during service period,which belongs to the typical high cycle fatigue structure,and it is very easy to produce fatigue damage,so structural fatigue failure is its main failure form.Once the fatigue damage occurs,the consequences would be disastrous.So it is very important to analyze the fatigue of offshore wind turbine support structure in the design stage.The research on support structure of domestic offshore wind turbines mostly concentrates on the single pile foundation structure,and mostly on the environmental load analysis or static and dynamic analysis,fatigue research of offshore wind turbine is relatively backward,and the calculation of fatigue life is relatively simple.It can be seen that the fatigue research structure of domestic offshore wind turbine support structure is still at the initial stage,and there are many problems need to be solved.In the light of the challenges of offshore wind turbine supporting structure,the following main research work is carried out:(1)The loads analysis of offshore wind turbine support structure is carried out.The time history curves of three typical loads are calculated,which are the wind turbine load on the top of the tower,the wind load on the column and the combined load on the wave and current on the transition section.The calculation of wind load is in accordance with the specification.The calculation of combined wave and current loads is based on Stokes finite amplitude wave theory and Morrison equation.The calculation of wind turbine load is by simulating the normal and extreme conditions respectively combined with the principle of wind turbine control principle.(2)The dynamic response analysis of offshore wind turbine support structure is conducted.The time-domain analysis is used to simulate the randomness of the marine environment as much as possible,and the combined response mode is used to combine the wind turbine working condition and the ocean condition into the combined condition.Through modal analysis and dynamic response analysis,output the representative response of the support structure.(3)Fatigue analysis offshore of offshore wind turbine support structure is realized.Firstly,the fatigue life of the wind turbine support structure under normal wind speed is calculated by the time domain method and frequency domain method respectively.Secondly,according to the standard of IEC 61400-3(2009)and ABS Guide(2010),select six limit conditions from all the basic load cases,and then analyze the effect of the failure of yaw control system and single pitch control system Under the extreme wind conditions of 50-year and 100-year regression cycles.