EVALUATION OF FATIGUE LIFE OF WIND TURBINE YAW BEARING BOLT CONNECTION

Due to stochastic nature of the wind, wind turbine components are subjected to varying amplitude loads. All wind turbine component should be analysed, for its proper working throughout its life time period. One of the important connections in wind turbine is yaw bearing bolt connection. The yaw bearing bolt connection is carrying total weight of the wind turbine tower top components. Beside this, different wind forces and loads raised due to gyroscopic effect also taken by this connection. If the yaw bearing connection is failed, turbine tower top component could be fall down to the ground. In this study, life of yaw bearing bolt is assessed using finite element analysis technique. In the analysis, all components in yaw bearing assembly are considered. Using finite element technique, two different approaches are followed to model yaw bearing bolt and calculating its stress level. In the first approach, beam element is used to model yaw bearing bolt and in the second approach solid bolt is used to model yaw bearing bolt. Contact non-linearity is used in between the bolt flange connections. Conservative approach is identified based on the calculated stress level. In order to carry out the fatigue analysis, detailed procedure is identified for obtaining load – time series. Using rain flow counting methodology, fatigue life of the bolt is calculated from the obtained stress values and load – time series.