Short-wave Irregularities Research Articles

Observation and Simulation of Axle Box Acceleration in the Presence of Rail Weld in High-Speed Railway

Rail welds are widely used in high-speed railways and short-wave irregularities usually appear due to limitations in welding technology. These irregularities can excite a high wheel/rail force and are regarded as the main cause of deterioration in track structures. To measure this fierce force (or deterioration of the rail weld), axle box acceleration is treated as an effective and economic measure, though an exact quantitative relation between these two quantities remains elusive. This paper aims to develop such a relation in order to provide a new theoretical basis and an analysis method for monitoring and controlling weld geometry irregularity. To better understand the characteristics of axle box acceleration, the paper consists of two parts: an observation and a numerical simulation of axle box acceleration by rail welds. Based on measured data from field tests, axle box acceleration at rail welds was found to have high-frequency vibrations in two frequency bands (i.e., 350–500 Hz and 1000–1200 Hz). Upon analyzing the vibration characteristics in time–frequency domains, the exact location of the rail weld irregularity could be identified. Subsequently, a 3D high-speed wheel/rail rolling contact finite element model was employed to investigate the effect of rail weld geometry on axle box acceleration, and led to the discovery that the weld length and depth determine the vibration frequency and amplitude of the axle box acceleration, respectively. A quantitative relation between axle box acceleration and wheel/rail force has also been determined. Finally, we propose an approach for real-time health detection of rail welds and discuss the influence of other defects and rail welds on the acceleration signal of the axle box.

Internal noise reduction in railway vehicles by means of rail grinding and rail dampers

Interior noise reduction has become an important concern in railway operating environments due to the influence of increased speeds and reduced vehicle weights on energy efficiency. Two types of measures, rail grinding and rail dampers, were proposed to reduce the internal noise within railway metro vehicles on a particular curve section of a Chinese metro line where the internal noise within metro vehicles is so excessive when the train passes that drivers and passengers complain. The dynamic property and track decay rate of the track system were carried out through mechanical shock method first. Then the measurement of rail vibration performance, external noise and internal noise were conducted when the metro train passed through this track section at the required speed. The rail corrugation with a wavelength of 0.06 m is a major cause of the excessive internal noise. After the application of rail grinding, the overall A-weighted sound pressure levels reduced from 85 to 82 dB due to the removal of the rail corrugation and other short-wave irregularities. Moreover, after the further use of rail dampers, the overall A-weighted sound pressure levels within the carriage further decreased from 82 to 74 dB, resulting from the reduction of the wheel/rail external noise transmitted into the vehicle body through leaks in the vehicle body. Therefore, the noise reduction effect of the two presented measures is significant.

Dynamic Response of Wheel-Rail Interaction at Rail Weld in High-Speed Railway

As a main part of continuously welded rail track, rail weld widely exists in high-speed railway. However, short-wave irregularities can easily initiate and develop in rail weld due to the limitation of welding technology and thus rail weld has been a main high-frequency excitation and is responsible for deterioration of track components. This work reports a 3D finite element model of wheel-rail rolling contact which can simulate dynamic wheel-rail interaction at arbitrary contact geometry up to 400 km/h. This model is employed to investigate dynamic response of wheel-rail interaction at theoretical and measured rail weld, including wheel-rail force and axle-box acceleration. These simulation results, combined with Quality Index (QI) method, are used to develop a quantitative expression, which can be easily applied for evaluating rail weld deterioration based on measured rail profiles and axle-box acceleration.

Influence of contact loss underneath concrete underlayer on dynamic performance of prefabricated concrete slab track

Contact loss between the concrete underlayer and the subgrade caused by the differential settlement or stiffness of subgrade structure is a common distress, which deteriorates the mechanical properties of the track structure and adversely affects the safety and comfort for the operation on high-speed railway. The objective of this paper is to study the damage mechanism of prefabricated slab track subjected to such contact loss and to propose a critical value for the size of contact loss that would not jeopardize the safety of rail traffic and riding comfort of passengers. Thus, a vibration calculation model for the vertically coupled vehicle-J-slab track-subgrade system is established using finite element method, both of the short-wave irregularity and the German long-wave irregularity were taken into account to calculate the dynamic response of vehicle, track structure and subgrade with different contact loss areas and speeds scenarios. Based on the numerical simulation results, a critical value of contact loss area is proposed. When the actual contact loss area is smaller than the critical value, the welded joint irregularity is the dominant factor in the vehicle dynamic response; however, when the actual contact loss area is larger than the critical value, the track irregularity induced by contact loss under the concrete underlayer becomes the dominant factor. It is suggested that the contact loss area should be controlled under the critical value in order to ease or mitigate the dynamic response of the vehicle and track structure. The numerical simulation indicates the critical contact loss area is about 10 m2 for the short-wave irregularity case and 14 m2 for the long-wave irregularity case, thus it is suggested that the contact loss area underneath the concrete underlayer should not exceed 10 m2, which is consistent with the Swedish standard and the German standard on weak areas of subgrade compaction.

A New Method for Detecting Rail Short Wave Irregularity

In order to realize continuous detection of rail short wavelength irregularity and improve its detection precision, a new four-point method based on chord reference method is derived and presented. Then a simulation waveform consisting of 10 random sine waves has been used for scientific determination of the three separation distances. The new method’s automatic recovery program is developed by MATLAB. The restored waveforms are compared with the results from RMF-2.3E devices and thus the detection precision is achieved. Results show higher detection precision and reliability by over 87% relative percentage comparing to the traditional three-point method, which shows the great applicability and superiority of the new method.

Dynamic Properties of Double-Block Ballastless Track with Unequal Sleeper Spacings

Based on the vehicle-track coupling dynamics, by means of finite element method, the vehicle-double-block ballastless track-subgrade vertically coupled model is established to research the dynamic properties of double-block ballastless track with unequal sleeper spacings under the excitation of either long wave irregularity or short wave irregularity. The results indicate that the difference between the sleeper spacing and the standard sleeper spacing of the double-block track within the range of 70mm will not effectively affect the vehicle operation. The unequal sleeper spacing has a certain influence on the vertical displacement and acceleration of vehicle, rail and wheel rail force, but its influence on the force properties of track structure and vehicle operation stability can be ignored.

Development of the Small-Sized Equipment for Detecting Short-Wave Irregularity of the Top Rail

Short-wave irregularity of top rail has great influence on status of both train operation and rail track. Based on the non-contact measurement principle and the virtual instrument development platform with powerful function, the paper designs the system for detecting short-wave irregularity of the top rail based on virtual instrument with the eddy current displacement sensor. The system can realize online real-time display, analysis, processing, storage and search of historical data and printing. With this method, we can detect the smoothness of rails and provide a better scientific basis for making a plan to guide the daily work of track maintenance.

Wheel Load Variation in Coupled Motion Between Wheel and Flexible Track with Short-Wave Irregularity

The decrease of wheel load variation is one of the most important issues which must be solved in railway dynamics. The purpose of this study is to make clear the mechanism of wheel load variation by the numerical simulation by the analytical model which is based on the concept of the multibody dynamics. In this study, we were able to figure out the in-depth mechanism of the wheel load variation, particularly, concerning the phenomenon that the wheel load variation suddenly decreases with more than wheel velocity at which the 1st natural frequency of system consists with the irregularity passing frequency.

134 車輪と短波長狂いのある柔軟軌道の連成運動を考慮した輪重変動解析

134 車輪と短波長狂いのある柔軟軌道の連成運動を考慮した輪重変動解析

A Ride Comfort Tyre Model for Vibration Analysis in full Vehicle Simulations

ABSTRACT A computer-aided simulation of the tyre, with given accuracy specifications, can be realised by accessing a family of physical and empirical tyre models. This model hierarchy offers tyre models of varying complexity to calculate the forces and moments of rolling contact. These models can be coupled adaptively to any vehicle model by way of a standardised mechanical interface, e.g. to the ADAMS MBS. The change of model on the individual wheels is initiated automatically at the time of simulation by a road surface scanner. The comparison of measurement and calculation of horizontal and vertical acceleration of two different vehicle rear axles shows that short-wave irregularity of the ground such as cleats can also be calculated with physical tyre models.

A Ride Comfort Tyre Model for Vibration Analysis in full Vehicle Simulations

ABSTRACT A computer-aided simulation of the tyre, with given accuracy specifications, can be realised by accessing a family of physical and empirical tyre models. This model hierarchy offers tyre models of varying complexity to calculate the forces and moments of rolling contact. These models can be coupled adaptively to any vehicle model by way of a standardised mechanical interface, e.g. to the ADAMS MBS. The change of model on the individual wheels is initiated automatically at the time of simulation by a road surface scanner. The comparison of measurement and calculation of horizontal and vertical acceleration of two different vehicle rear axles shows that short-wave irregularity of the ground such as cleats can also be calculated with physical tyre models.