Study On Modal Parameter Identification Method And Application Of High-speed Railway Ballastless Track

Types of ballastless tracks are used in China’s high-speed railway lines,with differences in structure,material,and size.Typical wheel-rail defects such as bogie hunting,rail corrugation,and polygonal wheels have appeared during the long-term service of the tracks.According to field investigations,the characteristics of these defects are affected by the type of ballastless track structure and are closely related to their modes.If the influence of the modes of the ballastless tracks are not considered,and only the same maintenance measures are adopted to repair the defects,their recurrences will be caused.Therefore,it is necessary to accurately identify modal parameters of various ballastless tracks and apply the identified modal parameters to theoretical models and the study of wheel-rail defect mechanisms.At present,the existing research work on modal parameter identification of ballastless track is less,and the identification accuracy is low,also there is a lack of research on the application of modal parameters of ballastless track in typical wheel-rail defects.This article was supported by the Key Program of National Natural Science Foundation of China “Research on modal parameter identification of high-speed railway ballastless track and its influence on wheel-rail relationship” and Major Instrument Development Program of National Natural Science Foundation of China “Inspection system of wheel-rail dynamic contact posture for high-speed railway based on high-precision structure-light technology”.Combined with theoretical analysis and experimental research,modal parameter identification methods of ballastless tracks based on pulse excitation and vehicle excitation were proposed,and identification of high-precision,wide frequency-band modal parameters of different ballastless tracks was realized.A method to optimize the ballastless track model based on modal parameters was proposed,which realized the fusion of the theoretical model and the field test results,and the accuracy of the track model was improved.Based on the modified dynamic model,the characteristics of typical wheel-rail defects under different ballastless tracks were analyzed,and corresponding control measures were proposed.The relevant research can provide analysis methods and references for the vibration test of high-speed railway ballastless tracks.Also,they can provide a reference for the control of wheel-rail defects.The main research work and results of the thesis are as follows:(1)The theoretical modal parameters of the ballastless track were extracted,and the modal parameter identification method of the ballastless track was optimized to realize the modal parameter identification of different ballastless tracks.Based on the dynamic theory,the natural frequency,damping ratio,and mode shape of the ballastless track model were extracted and analyzed.Combined with the established vehicle-ballastless track coupling dynamic model,the theoretical modal shape characteristics of the ballastless track were classified and determined and the comparison and analysis standards were established.Aiming at the disadvantages of the existing modal parameter identification method,an improved ballastless track modal parameter identification method was proposed,which can effectively improved the identification accuracy,the identified modal order,and the frequency range.Based on the identification method,four types of ballastless tracks used in China’s high-speed railways were identified,and the identified modal parameters and vibration transmission characteristics were compared and analyzed.(2)The modal parameter identification method of ballastless track under vehicle excitation was proposed,and its accuracy was verified by field test.In view of the limitations of the long test process and a large number of measuring points in the modal parameter identification method with impulse excitation,the adaptability of the analytical modal decomposition algorithm was improved according to the vibration response characteristics of the track structure under vehicle excitation.On this basis,a method for identifying the modal parameters of the ballastless track under vehicle excitation was proposed.This method can use the dynamic responses of the ballastless track obtained from field tests to identify its natural frequencies and damping ratios.The modal parameter identification was carried out based on the on-site ballastless track vibration acceleration test on a high-speed railway.The results showed that the method can identify the natural frequencies and damping ratios of the ballastless track with less error,and the obtained damping ratio-natural frequency relationship was accurate.(3)A method for identifying the key parameters of the ballastless track based on modal parameters and a method for updating the dynamic model of the ballastless track were proposed.Aiming at the unclear value of the damping coefficient of ballastless track in the existing theoretical research,a method for identifying the damping coefficient of ballastless track based on modal parameters was proposed.Combining with the finite element model,test results,and theoretical simulation,the accuracy of the method was verified.Aiming at the problem that the model in the existing theoretical research was mainly built by initial design parameters,and there were deviations from the actual ballastless track structure,a ballastless track model updating method based on the sensitivity of the modal parameters was proposed.Using the method,the ballastless track models with fewer errors were obtained.The updating effect was verified through the field modal parameter identification results and dynamic test results.(4)The characteristics of typical wheel-rail defects were analyzed under different ballastless tracks,and control measures were put forward.The calculation and analysis results showed that the differences in the vibration degree of the ballastless track structure in the key frequency band were the reasons for the different characteristics of the wheel-rail typical defects on different ballastless tracks.For the CRTS I double-block track,the fundamental natural frequency was higher and the stiffness was greater.Therefore,the problems of bogie hunting and wheel-rail wear that are greatly affected by low-frequency vibration were more obvious on this track.In addition,between 520 and 700 Hz,there was an isolated mode with large modal vibrations,resulting in wheel-rail coupling resonance,making rail corrugations or wheel polygons prone to occur in this frequency band.The occurrence and development of the defects could be controlled by increasing the stiffness and damping of the fasteners and reducing the design thickness of the track bed.While the modal vibration degree of the CRTS II slab ballastless track was larger in the range of950～1400Hz,which intensified the wheel-rail resonance causes corrugation to occur.The occurrence and development of defects could be controlled by increasing the stiffness of the fastener and unitizing the track slab.The fastener resonance frequency band was determined through theoretical calculations,and combined with experimental research,recommended tightening torque of WJ8 fasteners were put forward.