Study On Seismic Fragility Of Typical Onshore Wind Turbine Tower Structures

With the increasing depletion of fossil energy sources worldwide,new clean energy sources,mainly wind power,are gaining rapid development.China’s installed wind power capacity has ranked first in the world for 13 consecutive years,and with the further growth of installed wind power capacity in the future,more and more wind farms will be laid out in high-intensity seismic-prone areas,and the seismic risk of wind power structures increases greatly.Seismic fragility analysis is an effective method to evaluate the seismic performance of structures in the form of damage probability.In this paper,by means of numerical analysis,the probability of onshore wind turbine towers in various levels of damage under the action of ground shaking at different sites is studied,and the seismic fragility curves of wind turbine towers are drawn to make a preliminary assessment of the seismic performance of wind turbine towers.The main research-contents of this paper are as follows:(1)An elasto-plastic analysis model of the onshore wind turbine tower is established using the finite element software ABAQUS.The principles of elasto-plastic analysis and the basic modeling process as well as the settings of damping and boundary conditions are introduced.The correctness of the model is further verified by modal analysis and analysis of environmental pulsation test data.Due to the importance of meshing,the meshing method of the finite element model is investigated,and a more accurate calculation model is adopted through the validation trial calculation.(2)The classification of the damage level and the definition of the limit state of the wind turbine tower were carried out.According to the actual operation function of the wind turbine tower and the performance under the earthquake,the damage level of the wind turbine tower is divided into four levels:Ⅰ:basically intact,Ⅱ:stop operation,Ⅲ:long-term stop operation,Ⅳ:collapse.The relative displacement of the tower top is selected as the damage index of the wind turbine tower to measure the performance of the wind turbine tower under ground motion.The limit states and judgment criteria for different damage levels of wind turbine towers are defined,and the stop operation state of wind turbine towers is defined by reference to the code.Using the pushover analysis method of multi-modal superposition,considering the effect of higher-order vibration modes,the pushover load is applied to the wind turbine tower with the combination of third-order vibration modes,and the limit values of the wind turbine tower in the limit states of long-term stop operation and collapse are obtained.(3)Twenty-five ground shaking records were selected from the PEER website for each category Ⅰ,Ⅱ and Ⅲ site,and the PGA was used as the ground motion intensity parameter to perform incremental dynamic time analysis of the wind turbine towers,and the structural response of the wind turbine tower under different ground shaking effects was obtained.The seismic fragility curves of the wind turbine tower under various sites are fitted using a log-normal distribution function,and the goodness of fit of the curves is verified.The calculation results show that the wind turbine towers is basically intact at 0.1 g and below;when PGA=1.0g,the exceedance probability of the three categories of sites reaching the stop operation state is between 40%and 70%;When PGA=2.0g,the probability of wind turbine towers reaching a long-term stopping state at Class Ⅲ sites is more than 50%,but it is very difficult for wind turbine towers to collapse because the probability of ground shaking above 2.0g is very small.The probability of wind turbine tower reaching each limit state under ground motions is relatively the largest for category Ⅲ sites,followed by category Ⅱ sites and the smallest for category Ⅰ sites.(4)The probability of occurrence of each damage level of the wind turbine tower was calculated.A seismic hazard analysis was conducted for wind turbine towers,and a probabilistic seismic damage analysis was performed for wind turbine towers based on the results of seismic fragility and site hazard analysis,and an outlook was given for the application of the analysis results in the wind power seismic insurance industry.(5)Considering the importance of wind loads,a preliminary estimation of the fragility of wind turbine towers under the coupled action of wind and earthquake is made,and the fragility curve of wind turbine towers under the coupled action of wind and earthquake is obtained.