| With the rapid development of wind power industry,collapse accidents of wind turbines occur frequently,and most of the collapse accidents can be attributed to the fatigue fracture of welds.As a typical high-rise structure sensitive to wind load,the connection of the wind turbine tower between the tower and the flange,as well as the connection between the door frame and the tower are all welded.Therefore,the research on wind-induced fatigue life of tower weld caused by wind load has always been an important issue in the design of wind turbine structures.At present,most of the researches on wind-induced fatigue of the wind turbine tower are numerical simulation,and the wind load is lack of the support of measured data.In the numerical simulation of wind turbine structure response,whether the wind load is applied to the tower in the form of nodal force for structural response calculation or CFD software is used to analyze the flow field,the influence of wind direction is rarely considered.Therefore,in order to make the evaluation of wind-induced fatigue life of wind turbine tower more accurate,this paper studies the wind-induced fatigue of wind turbine tower by the main S-N curve method,based on the analysis results of measured wind speed and direction data,and considering the joint probability distribution of wind speed and direction.The contents in thesis mainly include three aspects:(1)Aiming at the structure of a 2.5MW large wind turbine,three kinds of finite element models of wind turbine tower are established(no flange and no tower door,with flange and no tower door,with flange and tower door).The influence of the construction of flange and tower door on the natural vibration characteristics of the structure is analyzed.According to the wind load simulated by Davenport spectrum and harmonic superposition method,the dynamic response of finite element model of the wind turbine tower is analyzed.To verify the mesh insensitivity of the structural stress,four kinds of finite element models with different mesh sizes are constructed to calculate the structural stress at the welding seam o f the tower flange and the tower door area.Combined with miner's linear accumulation rule and the rain flow counting method,the fatigue life of the welding seam of the tower flange and the tower door is calculated,and the wind-induced fatigue of the wind turbine tower is evaluated based on the main S-N curve method;(2)The whole finite element model of wind turbine with nacelle,hub,blades and tower is established.The change of wind direction is considered by changing the angle between the direction of wind turbine and the direction of tower door.The wind-induced vibration response analysis of the same wind speed and different wind direction,or different wind speed and the same wind direction is carried out.The structural stresses at the joint of each flange and tower as well as both sides of the tower door are calculated,and the influence of wind direction and wind speed change on the structural stresses is analyzed.The key points which are prone to fatigue damage are determined,and the fatigue l ife of each key point is calculated.The influence of wind speed and wind direction variation on the fatigue life of tower is studied;(3)Based on the 37-year measured wind speed and direction data of six wind farms in Gansu Province,the phase extremum method is used to extract extremum samples,and the distribution of wind speed and direction is analyzed in each region.The distribution functions of Gumbel,Frechet and Weibull are linearized,and then the distribution parameters of omni-directional and different wind speed and direction are fitted by the least square method.The basic wind speed of each region under 10,50 and 100 years return period is predicted.Based on the prediction results of wind speed and direction joint probability distribution,the wind-induced fatigue life of wind turbine tower is evaluated. |
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