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.     

Theoretical cross-wind speed against rail vehicle derailment considering the cross-running wind of trains and the dynamic wheel-rail effects

In this paper, a theoretical formula was proposed that predicts the derailment index due to a cross wind applied to a rail vehicle considering the cross running wind condition of two running trains as well as the dynamic wheel-rail effects. The recently developed derailment theory on a wheelset was applied to this new cross wind derailment formula. Contrary to the conventional formulas, this new derailment formula was derived considering a dynamic derailment coefficient (Q/P) under normal running, the friction coefficient between the wheel and the rail, the wheel load variation, the cross running wind effects, and the cross wind. Using this proposed formula, the derailment pattern and the critical cross wind speed of derailment could be predicted for various cross running wind conditions of two running trains. Finally, for some typical examples, the results of this proposed formula were compared and verified with those of the conventional formulas and the numerical simulation of multi-body dynamics software, Recurdyn.     

Design,development, and calibration of a force-moment measurement system for wheel–rail contact mechanics in roller rigs

A force measurement system, referred to as “dynamometer”, for accurately acquiring the contact forces and moment in a single-wheel roller rig using piezo-electric load cells is designed and developed. Accurate determination of the wheel–rail contact forces and moments is an essential requirement for studying the wheel–rail contact mechanics. The dynamometer is placed in the load-path between the wheel–rail interface and the ground, enabling it to measure the forces and moments at the interface. A series of tests are performed to determine the quasi-static and dynamic characteristics of the dynamometer. Additionally, finite element analysis and multi-body dynamic modeling are used to establish flexural modes and dynamic interface between the components. The simulation and test results indicate that the dynamometer is able to accurately and reliably measure the contact forces and moments at the wheel–rail interface.     

An easy instrument and a methodology for the monitoring and the diagnosis of a rail

Nowadays, there are no systematic methodologies for evaluating life assessment of the rail, and few systems provide the measures of vertical and lateral forces that train exchanges with the rail. These systems are quite expensive and require the substitution of a portion of the track. In the present paper is presented a simple transducer (MPQY) for measuring, at the same time, the vertical and lateral forces. The easy installation and use of this instrument are its main characteristics. It is sufficient to put it in a hole, made in the rail web in the concurrence of the drilling axis, and connect it to the transmitting station for measuring for each convoy the vertical and lateral forces induced by each wheel. It can be also used for analysing speed and mass of trains and the specific derailment ratio. In addition, by using a damage model, it is possible to estimate the residual life of a rail. In order to do this, a linear model of rolling contact fatigue damage is implemented and tested with same experimental acquisitions. Another application of this transducer can be identified in the variation of the mechanical behaviour of ballast. In fact, by using the information coming from the MPQY and comparing it with the flexural moment measurement, it is possible to evaluate the variation of ballast behaviour with respect to time and set new parameters for ballast maintenance and train safety.     

A new derailment coefficient considering dynamic and geometrical effects of a single wheelset

A new derailment coefficient of a single wheelset was theoretically developed by considering the dynamic and geometric effects from lateral acceleration and gyro factors as well as mechanical factors like flange angle, frictional coefficient, wheel-unloading, wheel radius, track gauge and position of axle bearings. This new derailment coefficient (lateral force over vertical wheel load, P/Q) can predict the commencement of various derailments, such as wheel climbing and lifting types, roll-over types and their combined types. In addition, this derailment coefficient can analyze the various dynamic and geometrical effects of a wheelset, which are not considered in the conventional derailment coefficients of Nadal’s and Weinstock’s formulas. This derailment coefficient was verified by comparing its theoretical anticipations of several examples with numerical simulation results using a commercial dynamic S/W, RecurDyn.     

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.     

Assessment of running safety of railway vehicles using multibody dynamics

An analysis model for multibody systems was developed to assess the running safety of the Saemaeul train passing through curves. Sensitivity analyses based on the variation of parameters related to derailments were conducted using this model and the ADAMS/Rail software package. These analyses showed that the derailment coefficient and the unload ratio of the right wheel were higher than that of the left wheel at low speed, but lower at high speed. The derailment coefficient and the unload ratio increased as the curve radius decreased. The derailment coefficient increased but there was no change in the unload ratio as the length of transition curves increased. The derailment coefficient and the unload rate increased in proportion to the increase in track cant.     

车轮多边形激励下的滚动接触疲劳裂纹瞬态扩展行为研究

利用ANSYS/LS-DYNA建立带车轮多边形的三维轮轨滚动接触疲劳裂纹扩展模型,将真实轮轨间瞬态滚滑和高频动力作用考虑在内,分析车轮多边形和连续钢轨裂纹造成的瞬态接触载荷对钢轨裂纹动态扩展行为的影响。速度250 km/h牵引工况的结果表明:零间隙多裂纹对法向轮轨力的影响甚微,但会造成切向轮轨力不可忽略的波动;车轮多边形会造成法向和切向轮轨力显著的周期性波动,如0. 1 mm波深23阶多边形会使得各裂纹面最大法向和切向接触力较圆顺工况分别增长19. 6%、34. 1%;任一裂纹面内法向和切向接触应力在接触斑滚过的0. 22 ms内发生了复杂的瞬态变化,进一步导致各裂纹的最大裂尖应力场强度因子的周期性波动,影响裂纹动态扩展行为;随着车轮多边形波深和阶数的增加,上述各种波动的幅度均会变大,加速裂纹扩展。     

The variation of lateral forces as a function of alignment for a cylindrical wheel rolling on a rail

Those lateral forces that arise between a steel wheel and a rail as a consequence of misalignment are analysed. The magnitude of these forces is calculated for unconed wheels as a function of the misalignment angle and the friction coefficient. The results show that by following an FEM standard (an alignment better than 1:2500) lateral forces should be less than μP/4 where μ is the interfacial friction coefficient and P is the normal load.     

车辆脱轨安全限值的调整与改进建议

针对国家标准GB5599－85评判车辆脱轨所存在的问题，提出采用车轮抬升量作为车轮脱轨的直接判据。运用车辆－轨道耦合学理论，对我国主型货车C62A分别以单轮对－轨道耦合模型和整车－轨道耦合模型为仿真计算对象，研究了脱轨系数超限时间与车轮抬升量的关系。并对国家标准GB5599－85中关于脱轨系数和轮重减载率的规定作了调整和改进，建议将脱轨系数大于目标值1．0的持续作用时间小于0．035s作为车辆脱轨的安全限值。     

激光测量大型转轴动载波动系数原理

为能够对大型复杂旋转机械转轴动态载荷特性进行在线监测,给出一个表征转轴动载特性的参量——动载波动系数KID。应用动力学理论推导出动载波动系数KID测量模型的数学表达式,该式表明测得转轴转速波动值即可求得KID值。基于激光多普勒技术,提出一种直接提取动载波动系数KID的激光测量方法。通过构造光学测试系统测量相邻时刻转轴轴段两端面的瞬态转速,得到轴段转速波动值及两端面相对转速波动值,代入KID测量模型,能够直接得到动载波动系数KID值,从而实现对转轴扭振强度的实时监测。通过试验验证了该方法的可行性,结果表明,动载波动系数KID较好地反映了转轴的动态载荷波动特性,能为工程中大型复杂旋转机械转轴动态扭振监测提供新方法。     

阵列式扰振力测量平台及其测量策略

为了测量大质量设备的多维扰振力,设计了一种基于传感器阵列式分布的多维扰振测量平台.该平台基于压电传感器采用了冗余式阵列的振动测量策略,解决了大负载及高刚度的测量要求,避免了结构耦合引入的测量精度损失.同时,为了克服阵列式测量引入的冗余测量误差,本文基于广义逆求解法进行测量精度优化,针对不同的被测振源选取不同位置的传感器...     

轮轨关系研究中的力学问题

简单论述世界铁路发展状况和铁路交通运输的优越性。详细论述轮轨关系的研究问题,其研究包含轮轨滚动接触作用和稳定性问题、轮轨粘着和强度、接触表面磨损和滚动接触疲劳破坏、轮轨噪声、轮轨蠕滑率／力理论和轮轨三维弹塑性滚动接触问题。在这些问题研究中,蕴涵十分复杂的力学和强度问题。文中就这方面的研究现状和存在问题以及问题研究的难点进行讨论,并分析今后可能的研究方向。     

Effect of Wheel Load on Wheel Vibration and Sound Radiation

The current researches of wheel vibration and sound radiation mainly focus on the low noise damped wheel. Compared with the traditional research, the relationship between the sound and wheel/rail contact is difficulty and worth studying. However, there are few studies on the effect of wheel load on wheel vibration and sound radiation. In this paper, laboratory test carried out in a semi-anechoic room investigates the effect of wheel load on wheel natural frequencies, damping ratios, wheel vibration and its sound radiation. The laboratory test results show that the vibration of the wheel and total sound radiation decrease significantly with the increase of the wheel load from 0 t to 1 t. The sound energy level of the wheel decreases by 3.7 d B. When the wheel load exceeds 1 t, the attenuation trend of the vibration and sound radiation of the wheel becomes slow. And the increase of the wheel load causes the growth of the wheel natural frequencies and the mode damping ratios. Based on the finite element method(FEM) and boundary element method(BEM), a rolling noise prediction model is developed to calculate the influence of wheel load on the wheel vibration and sound radiation. In the calculation, the used wheel/rail excitation is the measured wheel/rail roughness. The calculated results show that the sound power level of the wheel decreases by about 0.4 dB when the wheel load increases by 0.5 t. The sound radiation of the wheel decreases slowly with wheel load increase, and this conclusion is verified by the field test. This research systematically studies the effect of wheel load on wheel vibration and sound radiation, gives the relationship between the sound and wheel/rail contact and analyzes the reasons, therefore, it provides a reference for further research.     

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。     

基于ANSYS的轮轨摩擦热效应分析

随着铁路的高速化和重载化,车辆运行环境日益恶化,破坏的程度也越严重。针对机车特定轮重、相对滑动速度、摩擦系数的工况,应用有限元分析软件ANSYS对钢轨瞬态温度场作了计算研究,并利用其中的参数化设计语言(APDL)实现了移动载荷的加载。结果表明钢轨轨表面温度随摩擦系数和相对滑动速度的增加而增大,最高温升与摩擦系数和相对滑动速度呈线性关系。得出的温度场为钢轨结构优化设计提供了依据。     

Method for the reduction of measurement errors associated to the wheel rotation in railway dynamometric wheelsets

The precise experimental measurement of wheel–rail forces is vital both for railway vehicle acceptance processes and for research in vehicle–track interaction. With this aim, dynamometric wheelsets are used. These systems can be based on the installation of sensors either on the axle or on the web of the wheel. Existing measurement methods face a number of difficulties associated with wheel to rail contact, making them low accuracy solutions. One of the main difficulties encountered in methods based on wheel instrumentation is signal variation with wheel rotation. This work proposes a variety of solutions that provide an improvement over existing solutions, laying the starting basis for the development of modern dynamometric wheelsets that meet current requirements for accuracy.     

Seizure mechanisms of wheel–rail contacts under lubricated conditions using a transient ball-on-disc test method

This study focuses on the transition from mild to severe wear in the wheel and rail contact. Such a transition has been observed at increased loading (normal load, sliding velocity, or bulk temperature) which can be compared to a change from a wheel thread–rail head contact to a wheel flange–rail gauge contact. This transition was experimentally studied using a transient test method of ball-on-disc type at different sliding velocities, contact pressures, and lubricants. It can be seen in the results that different seizure mechanisms are active for different sliding velocities. Also the amount of applied lubricant clearly affects the transition to seizure.     

Optimization on the Crosswind Stability of Trains Using Neural Network Surrogate Model

Under the influence of crosswinds,the running safety of trains will decrease sharply,so it is necessary to optimize the suspension parameters of trains.This paper studies the dynamic performance of high-speed trains under cross-wind conditions,and optimizes the running safety of train.A computational fluid dynamics simulation was used to determine the aerodynamic loads and moments experienced by a train.A series of dynamic models of a train,with different dynamic parameters were constructed,and analyzed,with safety metrics for these being determined.Finally,a surrogate model was built and an optimization algorithm was used upon this surrogate model,to find the mini-mum possible values for:derailment coefficient,vertical wheel-rail contact force,wheel load reduction ratio,wheel lateral force and overturning coefficient.There were 9 design variables,all associated with the dynamic parameters of the bogie.When the train was running with the speed of 350 km/h,under a crosswind speed of 15 m/s,the bench-mark dynamic model performed poorly.The derailment coefficient was 1.31.The vertical wheel-rail contact force was 133.30 kN.The wheel load reduction rate was 0.643.The wheel lateral force was 85.67 kN,and the overturning coef-ficient was 0.425.After optimization,under the same running conditions,the metrics of the train were 0.268,100.44 kN,0.474,34.36 kN,and 0.421,respectively.This paper show that by combining train aerodynamics,vehicle system dynamics and many-objective optimization theory,a train's stability can be more comprehensively analyzed,with more safety metrics being considered.     

不同介质作用下轮轨粘着特性研究

利用MMS-2A型微机控制摩擦磨损试验机开展介质工况下的轮轨粘着特性试验,研究干态、水、油、砂、树叶等介质对轮轨粘着系数的影响。结果表明:不同介质工况下的轮轨粘着系数明显不同,干态下轮轨粘着系数最大,油水介质下粘着系数最小,加水和油将显著降低轮轨粘着系数,且油介质下的轮轨粘着系数明显小于水介质下的粘着系数;随环境湿度增加轮轨粘着系数明显降低,当湿度从20%增加到100%时,粘着系数将降低约17%;干态和油水介质下,随轴重增加轮轨粘着系数呈明显增加趋势;轮轨接触面间加入新鲜树叶后粘着系数将降低,树叶与水共同作用下的轮轨粘着系数最小;通过撒砂能提高水油介质工况下的轮轨粘着系数,但会加剧轮轨试样表面损伤,导致剥落损伤出现。