Characteristics Of Track Irregularity In High-speed Railway Turnout Zone

The track irregularity in the turnout zone is more complex and serious than that in the ordinary track,and it has always been the focus and difficulty of railway maintenance.The track recording car(TRC)or comprehensive inspection train equipped with the track inspection system is an important technique to detect track defects,guide maintenance,ensure driving safety and realize the scientific management of the railway track.However,due to the uncertainty of the positioning accuracy of the TRC on the short section and the complexity of the track irregularity in the turnout zone,research on the basic characteristics of the track irregularity in high-speed turnout zone have not been widely carried out around the world.Therefore,taking the 1:18 high-speed turnout on the ballastless track at a speed of 350 km/h in China as the research object,the dynamic inspection data of the track geometry when the TRC travels straight through the turnout at a speed of 250-350 km/h is selected to focus on the dynamic detection signal characteristics of the structural irregularity of the high-speed turnout,analytical descriptions,preprocessing of data and high-precision positioning,digital characteristics of data in turnout area,and evaluation in time and frequency domains,etc.,the following main works are carried out:(1)To analyze and predict the dynamic interaction between the vehicle and the turnout,provide a benchmark model for the virtual track inspection technology,and give the analytical description of the vertical structural irregularity of the turnout in the subsequent chapters.The vehicle-turnout coupling model is divided into a vehicle sub-model and a turnout sub-model.The multi-body system dynamics(MBS)software SIMAPCK is used to establish a high-speed EMU vehicle model with a 50 degree of freedom,as well as the turnout model(rigid and flexible),and the semi-Hertz contact algorithm is used to couple the two sub-models.Finally,the models are verified by the measured wheel-rail contact force and its wheel-load transition ratio.The results show that the MBS-FE coupling model considers more structural nonlinear forces and variable rails,can show more high-frequency components,and has the highest calculation accuracy;The two rigid turnout models with higher computational efficiency can capture the global wheel-rail contact force that is more consistent with the MBS-FE coupling model.The appropriate model can be selected for analysis according to the research objectives and calculation efficiency.(2)To better understand the structural irregularity of the high-speed turnout area from the perspective of the track dynamic inspection,the inertial measuring principle of modern track inspection is integrated into the vehicle-turnout coupling dynamics model to form a virtual track inspection(VTI).The VTI method is used to analyze the dynamic inspection signal characteristics of the structural irregularity of longitudinal level and alignment when the train passes through the turnout in the facing(main and branch line)and trailing(main and branch line)directions.The results show that the two cascaded 2nd order Butterworth filters can make the filtered signal aligned with the original signal time due to the zero-phase filtering,eliminate the track design parameters,and effectively VTI signal characteristics of the structural irregularities of the switch and crossing.The amplitude of the longitudinal level of the turnout is higher than that of the alignment,and the irregularity wavelength at the switch is larger than that at the crossing.Fastener stiffness,train speed,and the addition of concrete slabs and subgrade to the rigid model have little effect on the VTI signal of the turnout.When the flexible model is used,the VTI signal will contain signal components such as non-uniform track stiffness and complex constraints.Therefore,it is recommended to use a simple single-layered rigid switch model as the basic model for analyzing the structural irregularity of the turnout.(3)To provide an analytical representation of the vertical structural irregularity of highspeed turnouts,simplify the modeling process of the turnout,and evaluate the vehicle-turnout interaction quickly and effectively,an equivalent excitation model of high-speed turnout based on dynamic response optimization is proposed using the multi-objective genetic algorithm.the equivalent excitation function is statistically analyzed and verified considering the random distribution of some dynamic parameters.The results show that even small changes in the excitation function can lead to significant wheel-rail force changes.The optimal excitation model should not only fit the input of the system but also consider the rationality of the system response.After analyzing and comparing the ensemble and single statistical results of the parameterized single harmonic excitation function response,the cusp function is not a good analytical representation of the structural irregularity of the turnout.Finally,the bump-3 function is determined as the unified excitation function at the switch and the crossing,the wheel-rail vertical force response is more consistent with the original system in the low-frequency range of about 31 Hz.(4)To obtain high-precision and reliable track irregularity in the turnout zone,the multiresolution technology based on maximal overlap discrete wavelet transform(MODWT)is used to perform decomposition of the longitudinal level.The precise positioning of the track irregularity in the turnout zone is realized using the irregular welding composition.The results show that the track irregularity in the turnout zone generally has a track irregularity rate of more than 3‰.The outlier identification method based on the time history detection data can improve the reliability of outlier identification,and avoid misjudging the local irregularity with a large value as an outlier in the turnout zone.Using the precise zero-phase characteristics of MODWT,the accuracy of locating the original irregularity through the weld composition of the turnout is guaranteed.The positioning errors are divided into sampling position error,nonlinear phase shift error of the system,and weld type error.The nonlinear phase shift error is analyzed by the VTI method.Finally,the 70 m track irregularity including the full length of the turnout is extracted,and the positioning error is controlled within 1.5 m.(5)To study the basic digital characteristics and assessment of track irregularity in the highspeed turnout zone,the stationarity and normality of track irregularity in the turnout zone were analyzed by the hypothesis testing method.Based on the dynamic irregularity management value of the Chinese high-speed railway and the power spectral density(PSD)of the high-speed railway ballastless track,the assessments of 12 high-speed turnouts are carried out in the time domain and frequency domain.The results show that the stationarity of track irregularity of the high-speed turnout is easily affected by the number of segments.When the number of segments is 14,the average value of the stationarity ratio exceeds 80%,which can be considered that most track irregularities are stationary.Strictly speaking,the vast majority of track irregularities of high-speed turnouts do not conform to the normal distribution.The track irregularity management value in the existing standards has a certain safety margin.After the sample length is shortened to the range of 70 m including the full length of the turnout,the TQI of the total 12 turnouts all meet the requirements,but individual turnouts are prone to poor state in terms of local irregularity in the lateral direction such as alignment and gauge.The 14-order autoregressive model is used to estimate the track irregularities PSD of the turnout zone.Compared with the PSD of ballastless track irregularities of high-speed railway,it is found that the longitudinal level PSD within the range of 1-9.4 m,the alignment PSD within the range of1-6.8 m,the gauge PSD within the range of 1-70 m,and the cross level PSD within the range of about 1-18 m are higher than the existing standard values.If the existing PSD standard is still used to generate random irregularity samples in the turnout zone,the amplitude in the above wavelength range will be underestimated,which will adversely affect the interaction between the vehicle and the turnout.