Study On Motion Responses Reliability Of Semi-submersible Offshore Wind Turbine Platform

With the increasing awareness of global environmental protection and the rapid development of clean energy,offshore wind power has also ushered in new opportunities and challenges.Compared with onshore wind power and offshore fixed wind turbines,the motion performance of semi-submersible wind turbine platform is very important for the function and structural safety of the wind turbine platform,and it is subject to wind,waves and currents and other complex marine environmental conditions,and the wind,waves and currents have strong randomness,which makes the safety of the wind turbine platform more complex,and it is important to study the safety of semi-submersible wind turbine platform under the action of random wind,waves and currents.It is important to study the safety of semi-submersible wind turbine platform under random wind,wave and current.In order to fully consider the impact of wind,wave and current randomness on the safety of the semi-submersible wind turbine platform,this paper adopts the research methods of equivalent static reliability and dynamic reliability to study the reliability of the motion response of the semi-submersible wind turbine platform,and the main research contents and conclusions are as follows.(1)Analysis of the motion characteristics of the semi-submersible wind turbine platform.In this paper,with reference to the conceptual design of Braceless semi-submersible wind turbine platform,ANSYS-AQWA is used to establish a numerical model of the platform base hydrodynamics and verify the grid quality of the computational model,while a complete stability analysis of the semi-submersible wind turbine platform is carried out,and the computational results meet the engineering requirements specified for the floating wind turbine platform.The additional mass,radiation damping,amplitude response operator and inherent period of the semi-submersible wind turbine platform are calculated to provide an important basis for the motion response calculation of the semi-submersible wind turbine platform.(2)Equivalent static reliability analysis of the kinematic response of the semi-submersible wind turbine platform based on the response surface method.Considering the maximum value of the response of the engineering structure,the maximum value of the time range of the motion response of the semi-submersible wind turbine platform under the action of wind,wave and current characteristic parameters is equivalent to the static response value of the platform motion under the action of wind,wave and current,so as to establish the equivalent static reliability calculation method of the motion response of the semi-submersible wind turbine platform based on the response surface method.Based on the statistical data and extreme value theory to determine the load probability model for the 25-year design base period of wind,wave and current related elements,the equivalent static reliability of the extreme values of surge,heave and pitch motion response for normal operating conditions are 0.9980,0.9921 and 0.9526,respectively;the equivalent static reliability of the extreme values of surge,heave and pitch motion response for extreme self-storage conditions are 0.9410,0.9288 and 0.9929,respectively.(3)Dynamic reliability analysis of the motion response of the semi-submersible wind turbine platform based on the probability density evolution theory.The kinematic response of the semi-submersible wind turbine platform with different wave heights,wind speeds and flow velocities at 149 discrete representative points is calculated by AQWA,and the extreme value probability density method is used to establish the probability density evolution equation to solve the extreme value distribution of the kinematic response of the semi-submersible wind turbine platform.By integration in the specified limit domain,the kinematic reliability of the surge,heave and pitch kinematic response of the normal operating conditions are 0.9969,0.9881 and 0.9929,respectively;the dynamic reliability of surge,heave and pitch motion response for extreme self-storage conditions are 0.9399,0.9261 and 0.9925,respectively.The results are similar to the equivalent static reliability of the response surface method,and they all obey similar laws.For such a towering offshore structure as a semi-submersible wind turbine platform,extra attention should be paid to the safety of the rotational motion response in the normal operating conditions and the translational motion response in the extreme self-storage conditions.