Strength analysis of the pitchbox in MW wind turbine
                                YANG Yang, HE Hai jian, MENG Ling rui, DONG Shu yan, CHAO Guan liang, SU Feng yu
                                             (XJ Group Wind Power Technology Company, Xuchang 461000, China)

Abstract: Aiming at the problem of the weld cracking of the pitchbox in MW wind turbine, the multi body dynamics analysis and the finite element analysis technologies were applied to the strength analysis of the pitchbox, and then the structure optimization and strength assessment of the pitchbox were carried out. Firstly, the dynamics modeling and simulation analysis of the assembly of the pitchbox were made by the dynamics analysis software Simpack to determine the critical localtions where the variation of the stress amplitude of the pitchbox weld was biggest. Then these locations were used as the calculation conditions of the finite element analysis; Secondly, the FE model including the pitchbox and support was built and the static strength analysis was carried out by the finite element analysis software ANSYS. And then the extrapolation stresses of the pitchbox welds were calculated by the weld hot spot stress method according to the GL and the IIW specifications, which could use to assess the ultimate strength of the pitchbox welds. Finally, the fatigue strength assessments of the pitchbox welds were studied by the fatigue analysis software Fesafe combining the fatigue load spectrum of the pitbox and S/N curve of the weld. The results indicate that the safety factors of the welds of the pitchbox are above 1 and have sufficient strength to fulfill the design requirement and the method in this study is feasible.

Key words: wind turbine; pitchbox welds; dynamic analysis; finite element analysis; strength assessment; hot spot stress method