Wayside system for wheel–rail contact forces measurements

The system for assessment of the wheel–rail contact forces can be used for multiple purposes, among them for estimation of the train running safety, for train axle load measuring or wheel flats detection, as well as for the other research analyses. As the wheel–rail rolling contact moves along the track during train motion, it is very difficult to establish a reliable and accurate system for measuring of contact forces. Measurement principle of the wayside system, presented in this paper, is based on rail strains measurements using strain gauges, connected into the Wheatstone bridges in a smart way, in order to achieve signal proportional to applied load. This principle uses independent component analysis (ICA) model in combination with system calibration for successful separation of vertical and lateral contact forces from recorded strain signals. In addition, the system provides identification of the contact point position on the rail during train passing over it, which further expands the possibilities of its application to wheel–rail wear analysis, contact geometry optimization etc.     

Analysis of new method for vertical load measurement in the barycenter of the rail web by using FEM

Continuous method for measuring the forces between the wheel and rail is very important to monitor track loads. One of the usual methods is installing a strain gauge on the rail surface. Thus, strain gauge exposed to aggressive environment that makes it difficult for system to measure exclusively vertical force component and has complex installation operation. In this paper, strain measurement to assess the vertical load on cross section barycentric of rail and the lateral surface of rail web are studied. For this purpose, finite-element analysis was performed and the forces that exchange between wheel and rail in contact location were replaced with the moving loads that were applied to the railhead directly. Size of the effective contact patch was obtained from Hertz contact theory and patch switching time was considered short enough to reach an approximate continuous moving load. The results demonstrate the magnitude of strain in vertical direction is approximately same for the cross section barycentric and lateral surface of the rail web. However, the great advantage of measurement in the cross section barycentric of rail better distinguishes longitudinal and lateral strains from the vertical and also lateral load on a rail has less effect on vertical load measurement.     

A tribological characterization of the “damage mechanism” of low rail corrugation on sharp curved track

This paper focuses on the “damage mechanism” of short pitch corrugation on low rail on sharp curved track. This remains a major problem for European mass transit authorities. Several tribological and metallurgical investigations are performed on samples of corrugated low rail taken from a sharp curved track at site 1. A similar corrugated track from site 2 is instrumented to observe the vertical and transversal forces and the displacements of the rail. A parallel is then drawn between the measurements and real corrugation geometry. As both sites are affected by corrugation with the same morphological characteristics, a parallel is also drawn between tribological and metallurgical investigations and on-site measurements. The results highlight the existence of a rapid inversion in the lateral displacement of the railhead. This inversion only occurs with the leading wheelset and is localized at the beginning of the trough, where lateral third body flow fronts and lateral particle detachments on the rail surface are observed. The results of these investigations into the “damage mechanism” of corrugation on low rail at sharp curved track are discussed.     

Sensitivity analysis of track parameters on train-track dynamic interaction

Dynamic behavior of railway tracks when trains are running is influenced by several factors, i.e. rolling stock, the components of superstructure and their specifications. Usually, features like the sleeper spacing, rail pad stiffness, ballast damping and stiffness have an effect on the dynamic response of the track. The best method to study the dynamic behavior of the track is to model the track assembly and the train as a whole and carry out an analysis of dynamic interaction. Such analysis makes the identification of the track’s dynamic behavior easer and helps to anticipate the deterioration of the track elements, and determines the effects of increase or decrease of mentioned parameters. This paper presents track-train dynamic interaction without considering irregularity of the rail face. A sensitivity analysis was carried out on the selected model. The analysis was undertaken with the view of varying one of the mentioned parameters and the results were presented to further identify the deterioration of the track elements. The results indicate that reducing sleeper spacing, rail pad stiffness, ballast stiffness, and increasing ballast damping reduces wheel-rail, rail-sleeper, and sleeper - ballast contact forces.     

Analysis of the wheel/rail rolling contact fatigue of a high-speed train under the transient mechanism

The Rolling contact fatigue (RCF) damage of high-speed wheels is a main factor that affects railway safety. This paper presents a Finite element model (FEM) of high-speed transient rolling contact that considers kinetic parameters as initial conditions. This model is used to calculate wheel/rail RCF. With a CRH2 high-speed train as the research object, a head car model is established with the multibody dynamics software UM. The train is driven on a straight track at a speed of 300 km/h. Different contact geometric parameters, such as lateral displacement and attack angle, are obtained. A 3D high-speed transient elastic-plastic FEM of wheel/rail rolling contact is then developed by using ABAQUS with the initial dynamic contact geometric parameters. The actual geometries of the wheel tread and rail head as well as the elastic-plastic properties are considered in this model. This consideration makes the model highly suitable for solving 3D transient rolling contact behavior. The normal force, creep force, and contact area in the contact patch are solved and used in the fatigue model. Owing to the hunting movement of wheels, the wheel/rail force and lateral displacement change significantly at 0.2 and 0.5 s. The longitudinal and lateral creep force increase sharply with the increase in shear stress. The work states of the wheel/rail at 0.2 and 0.5 s easily reach the ratchet effect zone, and the fatigue index is large. The fatigue damage of the wheels is generally near the nominal rolling circle.     

Dynamic analysis of train-bridge system and riding comfort of trains with rail irregularities

In this study, a modal superposition approach was adopted to derive the dynamic response of coupled vehicle and bridge systems. The train comprises a number of railway cars, each of which is modelled with ten degrees of freedom. The railway bridge was represented by a simply supported beam modelled as Euler-Bernoulli beam. In the numerical simulations, dynamic responses at the mid-span of the bridge and dynamic responses of the train under different train speeds are computed with random and non random rail irregularities. Effect of parameters like the depth and the position of the imperfection on the rail are taken into account. The coupled system of equations is integrated numerically by the newmark’s β method. The results obtained show that the rail irregularities affect the vertical acceleration of the train, which serves as a measure of the riding comfort of the trains moving over a bridge.     

高速铁路钢轨预打磨型面优化分析

高速铁路的发展使钢轨磨损和滚动接触疲劳损伤日益受到重视。研究表明,预打磨后钢轨可有效延长服役寿命。为实现预打磨最佳廓形的选择,基于蒙特卡洛方法建立假设轮对横移量服从高斯分布的轮轨接触概率分析模型。据此,确定出列车运行时考虑轮对横移量的轮轨接触位置,并采用轮轨三维有限元模型计算得到相应接触应力的概率分布。结果表明,轮对横移量对最大接触应力值具有显著影响,横移量为10 mm、0 mm、8 mm时其值分别为1 712.6 MPa、1 362.1 MPa、448.7 MPa。亦发现虽然累积接触应力和平均接触应力均可作为衡量不同钢轨廓形力学性能优劣的指标,但二者的预测结果并不一致,如60 kg/m(CHN60)钢轨的平均接触应力,在轨距角附近(距钢轨中心线30 mm处内侧)的值4倍于踏面中心区域,相应的累积接触应力,在踏面的中心区域的值则接近10倍于轨距角附近。为综合考虑钢轨累积接触应力和平均接触应力对预打磨型面的影响,提出加权累积和平均接触应力,并以此作为钢轨预打磨廓形优化的评价指标。依据该指标对按照打磨工程经验设计的四条钢轨预打磨廓形进行评价分析,得到较优的钢轨打磨廓形。对制定钢轨廓形优化和打磨方法具有一定的工程参考价值。     

Dynamic analysis of a train-bridge system under multi-support seismic excitations

A numerical solution for the dynamic responses of a train-bridge interaction system subjected to multi-support seismic loads was studied. The train vehicle was modeled by the rigid-body dynamics method, and the bridge was modeled by the finite element method. The vertical and lateral wheel-rail interaction forces were defined according to the wheel-rail corresponding assumption and the simplified Kalker creep theory. Three-dimensional seismic accelerations were incorporated using the large mass method. In a case study, the dynamic responses were simulated for a high-speed train traversing a steel truss cable-stayed bridge with different seismic intensities and different train speeds, and train safety was evaluated.     

变轨距高速列车的动力学

高速列车通过改变轮对的内侧距实现在不同轨距线路上联运,而轮轴装配间隙及轨距、轨底坡、钢轨廓形等参数变化将引起轮轨接触关系改变,进而引起车辆动力学性能变化。分析我国两种高速踏面在准轨和宽轨线路上的轮轨接触关系发现,轨底坡由1/40变为1/20时,LMA踏面等效锥度降低约30%,LMB10踏面可兼容两种轨底坡,磨耗后的踏面对轨底坡变化更敏感。理论公式推导表明准轨和宽轨线路上自由轮对、刚性和柔性定位转向架的蛇行频率相同,但含轮轴间隙的变轨距高速列车动力学模型仿真表明,间隙导致宽轨线路上的车辆稳定性略差,间隙达到0.6mm时发生低速小幅蛇行;间隙对车辆运行安全性和平稳性影响仅9%。因宽轨线路的欠超高量大和车辆稳定性差,其运行安全性和横向平稳性比准轨差15%和38%。间隙横向力与轮轨横向力幅值相同但反向,造成轮对内侧距动态变化;左右侧旋转间隙扭矩的幅值相同但反向,在纵向蠕滑力作用下间隙压死-分离状态反复。研究成果有助于掌握变轨距转向架的轮对内侧距动态变化、间隙载荷和车辆动力学性能。     

城轨列车悬挂系统显遗传自适应模糊控制

为有效抑制城轨车辆行驶时悬挂系统出现的横向振动,提升车辆平稳性与舒适度,引入调控效果优于传统模糊控制的显遗传自适应模糊控制方法,扩展其收敛条件并证明其适用于城轨列车悬挂系统,扩大了该方法的使用范围。在Matlab/Simulation中根据时速为80km/h的某型城轨列车参数搭建车辆悬挂系统模型,并设计了显遗传自适应模糊控制器。仿真实验结果表明,显遗传自适应模糊控制对城轨列车悬挂系统横向振动抑制效果良好,在其控制下列车横向合成加速度、横移振动加速度、侧滚振动加速度以及摇头振动加速度的最大值、均方根值以及功率谱密度值均有所降低。与普通模糊控制相比,显遗传自适应模糊控制能够有效抑制城轨列车横向振动,大幅度提高乘客舒适度。     

Field investigation of variation of loading pattern of concrete sleeper due to ballast sandy contamination in sandy desert areas

Sleeper is one of the most important components in a railway track system. Thus, for accurate analysis and design of concrete sleepers, knowledge of imposed loading pattern is necessary. Sandy desert areas are critical regions where loading status of concrete sleeper is different from other areas. In these areas, the influence of flowing sand grains between the ballast aggregates increase the stiffness of ballast layer; consequently, rail support modulus increases, so the received share of total axle load subsequently increases on the sleeper which is placed under the wheel load. On the other hand, the pressure distribution underneath the sleeper changes considerably. In this paper, the results of a field investigation about the variation of rail support modulus and also variation of loading pattern of concrete sleeper followed by the variation of bending moment of sleepers in sandy desert regions were presented.     

Continuous measurement of interaction forces between wheel and rail

Oscillatory wheel load fluctuation of considerable amplitude is always observed in railway cars traveling at high speed. This paper describes a continuous method for measuring the derailment coefficient and the forces between the wheel and rail. The acceleration measured on the axle box indicates that the frequency of this fluctuation can be as high as 70 Hz. Continuous measurement of wheel load using conventional methods is not possible due to this high frequency phenomenon. We have developed a new method for continuous measurement of these forces and the derailment coefficient using two pairs of strain gauge bridges with output phases shifted by 90°, and summing their outputs with a weighting function. This method works for measuring the forces between wheel and rail at high frequencies.     

接触刚度对高速列车轮轨接触动力学时变特性的影响及其机制

以CRH3型高速列车头车与标准CHN60型轨道为研究对象,利用动力学软件RecurDyn建立车辆-轨道耦合动力学模型;采用弹簧阻尼模型定义轮轨接触关系,跟踪检测服役列车不同运行里程下的车轮粗糙度,根据相关文献的轮轨接触刚度计算结果,对高速轮轨滚动接触动力学性能进行研究,并取该头车的后转向架二位轮对处结果进行数据分析。计算结果表明:随着高速列车运行里程的增加,车轮表面粗糙度减小,使得轮轨接触刚度增大;轮轨横向力随着运行里程的增加先减小后增大,其频率主要分布在10 Hz以下的低频段;轮轨垂向力随着运行里程的增加而增加,并在5、10、28 Hz附近有比较明显的主频率段;轮轨纵向力主要由切向蠕滑力的纵向分量构成,与轮轨垂向力在时域分布和频域分布上均非常相似。     

高速动车组减振器载荷特征研究

减振器的主要功能是提供阻尼力以衰减和抑制车辆系统振动,对高速动车组动力性能有十分重要的影响。既有研究主要将减振器处理为阻尼力以研究车辆系统动力性能,极少从动力学和结构可靠性角度关注减振器自身承受的载荷。制作某型高速动车组转向架抗蛇行减振器、轴箱减振器、二系横向和垂向减振器测力元件,在大同-西安高速线路上测试并获得该型动车组运行过程中四种减振器载荷引起的应变信号。对测试数据进行处理和分析,获得高速动车组运行工况下四种减振器载荷的时间历程,分析减振器载荷的时域和频域特征。采用雨流计数法统计减振器载荷峰谷值和频次,获得不同速度等级下载荷分布。结果表明,高速动车组抗蛇行减振器载荷最大、二系横向减振器载荷最小。轴箱减振器相对速度最大、二系横向减振器相对速度最小。减振器载荷总体上呈正态分布,而且一般有列车运行速度越高减振器载荷越大。列车正线行驶时曲线半径对轴箱减振器、二系垂向减振器以及二系横向减振器载荷影响不明显,列车速度和线路小半径曲线对抗蛇行减振器载荷影响明显。     

Analysis of the particle stability in a new designed ultrasonic levitation device

The use of acoustic levitation in the fields of analytical chemistry and in the containerless processing of materials requires a good stability of the levitated particle. However, spontaneous oscillations and rotation of the levitated particle have been reported in literature, which can reduce the applicability of the acoustic levitation technique. Aiming to reduce the particle oscillations, this paper presents the analysis of the particle stability in a new acoustic levitator device. The new acoustic levitator consists of a piezoelectric transducer with a concave radiating surface and a concave reflector. The analysis is conducted by determining numerically the axial and lateral forces that act on the levitated object and by measuring the oscillations of a sphere particle by a laser Doppler vibrometer. It is shown that the new levitator design allows to increase the lateral forces and reduce significantly the lateral oscillations of the levitated object.     

Fatigue life estimation of MD36 and MD523 bogies based on damage accumulation and random fatigue theory

Bogies are one of the multifunctional parts of trains which are extremely subjected to random loads. This type of oscillating and random excitation arises from irregularities of the track including rail surface vertical roughness, rail joints, variance in super-elevation, and also wheel imperfections like wheel flats and unbalancy. Since most of the prementioned sources have random nature, a random based theory should be applied for fatigue life estimation of the bogie frame. Two methods of fatigue life estimation are investigated in this paper. The first approach which is being implemented in time domain is based on the damage accumulation (DA) approach. Using Monte-Carlo simulation algorithm, the rail surface roughness is generated. Finite element (FE) model of the bogie is subjected to the generated random excitation in the first approach and the stress time histories are obtained, and consequently the fatigue life is estimated by using the rain-flow algorithm. In the second approach, the fatigue life is estimated in frequency domain. Power spectral density (PSD) of the stress is obtained by using the FE model of the bogie frame and the fatigue life is estimated using Rayleigh technique in random fatigue theory. A comprehensive parametric study is carried out and effects of different parameters like the train speeds and level of the rail surface vertical roughness on the estimated fatigue life are investigated. This paper was recommended for publication in revised form by Associate Editor Hong Hee Yoo Davood Younesian received his MSc and PhD in Mechanical Engineering, both from Sharif University of Technology, Iran. He joined the Iran University of Science and Technology in 2005 as an Assistant Professor in the School of Railway Engineering. Dr Younesian’s research area is mainly focused on non-linear and random vibrations, optimal control of vibrations, dynamics and vibration of structures and railway vehicle systems. He has published more than 75 papers in international journals and conference proceedings in the areas of his research. Ali Solhmirzaei received his BSc in Railway Engineering (Rolling Stock) from Iran University of Science and Technology and his MSc in Mechanical Engineering from K.N.T University of Technology, Iran. His research is mainly focused on finite elements, railway vehicle dynamics and fatigue analysis of railway structures. Alireza Gachloo received his BSc in Railway Engineering (Rolling Stock) from Iran University of Science and Technology, Iran. His research is mainly focused on random vibration, railway vehicle dynamics and random fatigue.     

基于离线监督性学习的高铁轮轨关系在线检测技术

为维持高铁稳定运行,提升资源运输安全,在离线监督性学习算法的基础上,提出了一种轮轨关系在线检测技术。通过高速摄像机获取待检测图像,并进行拼接处理;计算加速度、轮轨力和轮轨间关系,依据关键部分的振动值得到列车的加速度值,以此判断列车是否处于平稳运行状态;通过间接测量法计算列车的横向力平衡方程和侧滚力矩平衡方程,得到轮轨力具体值;通过 k 均值算法聚类处理以明确各个样本的类中心,找出样本数量最少的类,设为异常类,完成高铁轮轨关系的在线检测。仿真实验结果表明,在稳定性、数据可靠性和实际应用方面,各项参数曲线变化幅度极为相同,曲线走向几乎一致,且使用后的轮轨接触状态较好,满足高铁轮轨关系在线检测技术的实际应用需求。     

地铁列车-嵌入式轨道系统动力学性能研究I：理论建模、试验分析及验证

嵌入式轨道作为一种减振降噪轨道结构型式,通常是基于城市街道路面的低地板有轨电车系统设计的,而嵌入式轨道的连续支承特性及其减振降噪优点使其在地铁中具有较好的应用前景。嵌入式轨道在地铁中应用,将面临更高运行速度、更大轴重、更复杂线路条件等挑战,地铁列车-嵌入式轨道系统的动力学行为有待研究。建立地铁列车-嵌入式轨道系统的动力学模型,模型包括轨道系统模型、列车系统模型以及轮轨相互作用模型。其中,轨道子系统为嵌入式轨道系统,是建模和研究的重点。模型考虑了TIMOSHENKO钢轨模型、等效弹簧-阻尼单元支承的柔性轨道板模型、以及钢轨周围的填充材料模型,填充材料模型采用考虑质量的黏弹性弹簧-阻尼单元来模拟以考虑填充材料的惯性、弹性和阻尼特性。在我国首例运用于地铁的嵌入式轨道试验线开展了动力学性能试验研究,基于试验分析了动力学性能并通过试验验证了动力学模型的有效性,建立的分析模型和相关结论为嵌入式轨道结构在我国地铁的应用提供了理论基础和参考。     

汽车ABS侧向稳定性能道路试验评价系统研究

汽车ABS侧向稳定性是主动安全性的重要方面，目前研究的主要方法是基于虚拟现实和硬件在环（HiL）技术。提出了主要基于多维轮力测量并辅以车身轨迹姿态测量的汽车ABS侧向稳定性能道路试验评价系统。基于该系统直接建立车轮六维力与车轮、车身运动参数间的关系，为研究和评价汽车制动稳定性和操纵性提供了试验依据。介绍了多维轮力传感器、测试系统的架构以及车身轨迹姿态测量原理，探讨了汽车ABS侧向稳定性能试验方法，给出了基于某轿车弯道制动试验分析实例。     

Effect of liquid high positive friction (HPF) modifier on wheel-rail contact and rail corrugation

This paper presents an experimental study on the influence of HPF friction modifier on rail corrugation. The tests were carried out on a curve section of a commuter line, where corrugation appeared in the inner rail of the curves. The influence of HPF on wheel-rail contact forces has been studied based on acceleration measurements on the rail. These measurements were carried out with and without corrugation on the rail.Also, in order to compare the corrugation levels developed with and without the HPF, the evolution of corrugation was analyzed for this particular curve. The corrugation amplitudes and wavelengths were studied. It was found that the application of HPF substantially reduces the acceleration levels on the rail in vertical and lateral directions and delays the corrugation growth.