| With the development of high-speed railway,the seamless rail is widely used in rail industry.However,when the actual temperature is less than the locked temperature,a great tensile stress is generated inside seamless rail,which is easy to break the rail.Therefore,real-time and accurate detection of broken rail and crack on continuous welded rail(CWR)is an important technical means to ensure the safety of high-speed railway.Since ultrasonic guided waves have many advantages,such as good directivity,free from electrical and electromagnetic interference,long transmission distance,the on-line monitoring technology of broken rail for CWR based on ultrasonic guided waves is paid more and more attention.However,the present broken rail monitoring system for CWR based on ultrasonic guided waves also has some disadvantages.On the one hand,since the distance and hole have the impact on attenuation of guided waves,the installation of the system requires multiple tests to determine the detection range,and the installation process is cumbersome;on the other hand,due to the temperature,stress and other incentive effects,existing broken rail monitoring system has defects such as high false alarm rate.Based on these factors,studying the attenuation characteristics of ultrasonic guided waves in rail which helps to guide the field installation of the broken rail monitoring system and to improve its accuracy is necessary.This thesis studies the attenuation characteristics in perfect rail and defective rail by combining the ANSYS simulation and field experiments,propose the amplitude expression of ultrasonic guided waves in rail,which is of great significance for on-line monitoring technology of broken rail.Firstly,the simulation method of ultrasonic guided waves is studied,which includes establishing the finite element model of rail in ANSYS,setting the parameters in simulation process,deducing the Rayleigh damping of rail in ANSYS,and verifying the correctness of Rayleigh damping by the experimental comparison.Secondly,controlling variable method is used to change the incentive condition regularly,to study the relationship between ultrasonic guided waves and temperature,distance or stress in complete rail by ANSYS simulation and field experiments.And the quantitative relationship between ultrasonic wave attenuation and above incentives is found.Thirdly,the attenuation characteristics of ultrasonic guided waves in defective rail are studied,and the quantitative relationship between ultrasonic guided waves and rail holes is obtained.The thesis studies reflection law of ultrasonic guided waves in defective rail by doing field experiments.It is analyzed whether the received transducers can receive the reflection from each hole when the transmitted transducers are located at head,waist and bottom.After handling the received signal,this thesis calculates and compares the measuring interval and error of each hole under different conditions.Finally,the amplitude expression of ultrasonic guided waves in rail is summarized,and the installation of the broken rail monitoring system in the Beijing Circuit Railway is instructed.This thesis determines that the detection range of broken rail is 500m.In the 48 hour testing time,the false alarm rate of two signal receiving nodes was 0.21%and 0.08%respectively,and these results verify the correctness of the amplitude expression of the ultrasonic waves in the rail. |
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