| Bolted connection is an important assembly method in wind turbine,which involves almost all parts such as tower drum,blade,engine room and variable propeller bearing.Once the bolt is broken or loosened suddenly in operation,it will cause serious safety accident.Therefore,combined with the working conditions of wind power bolts,this thesis mainly studies the ultrasonic guided wave detection technology of bolts,and analyzes the transmission characteristics of guided wave in bolts.Firstly,based on the basic theory of ultrasonic guided wave detection,the dispersion equation of guided waves in the rod is solved,and the numerical solution of the dispersion equation is carried out to analyze the variation trend of guided wave group velocity in the rod,which provides a theoretical basis for the subsequent analysis of the propagation characteristics of guided waves in bolts and the selection of appropriate frequency and mode.Then,the propagation characteristics of the guided wave in the bolt are simulated,and the feasibility of the two-dimensional axisymmetric model instead of the three-dimensional model is verified by comparative analysis and verification.By analyzing the propagation characteristics of the guided wave in the bolt and rod,the optimal excitation frequency of the guided wave in the bolt is obtained,and the feasibility of using the rod with the same nominal diameter as the bolt to replace the bolt for the guided wave detection is verified.By optimizing the structural parameters of the electromagnetic ultrasonic transducer,such as the AC coil and permanent magnet,the energy transfer efficiency of the ultrasonic guided wave transducer is improvedFinally,by solving the dispersion equations of high and low frequency guided waves,the propagation characteristics and influencing factors of guided waves in bolts covered with concrete are analyzed.The results show that under the action of concrete coating,the attenuation of the high frequency guided wave in the bolt is small,and it is suitable for long distance detection.Compared with the center excitation and the ring excitation,it is found that the ring excitation is more suitable for the guided wave detection of bolts.The ultrasonic guided wave probe excited by the ring is used to test the bolt.It is found that the larger the defect is,the smaller the required gain is.The farther the defect location is from the excitation end,the greater the required gain is. |
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