Research On Multi-Midpoint Chord Measurement Theory And Detection Technique Of Rail Corrugation

As the foundation of train's smooth operation,the state of rail tread has long been the center of attention.Due to the extremely complicated wheel-rail relationship,rail tread's disease,such as rail corrugation,spalling,flaking occur frequently.These defects cause huge noise during train's operation.What's worse,they may even result in broken rail,loose hold-down device,faster ballast pulverization,and derailed train,which will cause a great loss of life and property.Therefore,under the present circumstances,how to measure rail tread's disease accurately,efficiently and economically,so as to deal with the disease in time and minimize the impact on the environment and the safety of train operation,becomes the hotspot of current research.This paper proceeds from the characteristics of rail tread disease in time and frequency domain and takes the rail corrugation as the main research object.It comprehensively analyzes the strengths and weaknesses of the current measurement methods,proposes a new multi-midpoint chord measurement theory and improves the data processing method.A satisfying experiment result is obtained through a real track demonstration with a self-designed trolley.It lays a firm foundation for the subsequent production and development.Details can be stated as follows:(1)The importance of rapid detection of rail tread disease is clarified based on its influence on the safety of train operation and the environment.Domestic and overseas research status of rail corrugation is analyzed.It discusses the problem that midpoint chord model makes specific wavelength amplitude gain be zero.The deficiency that asymmetrical chord model needs amplitude and phase compensation at the same time is also expounded.(2)Through theoretical analysis and calculation,a theory known as Multi-midpoint Chord Model has been proposed.It not only has the advantages of constant phases,but also prevents specific wavelength amplitude from being zero,which improves the accuracy of maximum error point.In consideration of sensor's quantity and arrangement,the structure of multi-midpoint chord model is divided into symmetrical and asymmetrical midpoint chord.What's more,the computation of the optimal combination of chords is deduced under different conditions,with examples given.(3)For the sake of improving traditional inverse filtering method,ZFFT algorithm is introduced and formulas of conjugating extension are also derived.They resolve the conflict between spatial frequency resolution and time,space consumption of algorithm.After analyzing the data of multi-midpoint chord measurement based on rail tread aperiodic damage and regional feature of corrugation,a new approach depending on wavelet coefficient sum at different locations is proposed.The data simulation and test results show that these methods can improve the accuracy of measurement value with less space and time consumption.(4)The early aperiodic damage of rail tread is too subtle to be easily identified,but it draws great attention in practical work and has a certain impact on inverse filtering result.To solve this problem,an analysis is made on the responses of midpoint chord model,and a new method is proposed on the basis of multi-midpoint chord theory.By using this method,track irregularity amplitude gain is reduced by selecting proper combinations of chords,while surface damage is enhanced.After separating test date using singular value decomposition,rail tread defects' characteristics,as well as defects' positions,can be acquired through the sliding kurtosis sequence.These provide a scientific basis for daily work.(5)A corrugation analysis trolley is made on the basis of symmetrical double-midpoint chord.The influence of chord length and mid-position deviation on final test results is analyzed.Monte Carlo method is used to evaluate the results' uncertainty.In order to compare the measured value of corrugation acquired by different equipments,a three-point subtraction method is proposed on the basis of the fundamental principle of straight ruler and corrugation analysis trolley.A site test is carried out on a part of Yin-Xia railway whose wavelength is 280 mm to 400 mm and amplitude corrugation is 1.5mm to 2mm.This test verifies the effectiveness and accuracy of corrugation analysis trolley on rail corrugation measurement and rail tread damage identification.After comparing the test results with the results obtained with the straight ruler,it is found they both are consistent with the actual value on site.In terms of amplitude,there is 95 percent probability that the error between those two results is from-0.062 mm to 0.064 mm.Thus,as a continuous and efficient method,multi-midpoint chord model can be adapted to railway corrugation check,and is suitable for engineering application.