Experimental Investigation on Dynamic Railway Sleeper/Ballast Interaction

In ballasted railway tracks, one of the important components that supports the rails and distributes wheel/rail loading onto the ballast supporting formation is a railway sleeper (sometimes is also called a “railway tie”). This paper presents results of an experimental modal analysis of prestressed concrete sleepers in both free-free and in-situ conditions, incorporating the dynamic influence of sleeper/ballast interaction. Dynamic interaction between concrete sleepers and ballast support is crucial for the development of a dynamic model of railway track capable of predicting its responses to impact loads due to wheel flats, wheel burns, irregularities of the rail, etc. In this study, four types of prestressed concrete sleepers were in-kind provided by the Australian manufacturers. The concrete sleepers were tested using an impact hammer excitation technique over the frequency range of interest, 0–1600 Hz. Frequency response functions (FRFs) were measured using PULSE modal testing system. The FRFs were processed using STAR modal analysis package to identify natural frequencies and the corresponding mode shapes for the sleepers. The conclusions are presented about the effect of the sleeper/ballast interaction on the dynamic properties of prestressed concrete sleepers and their use for predicting railway track dynamic responses.     

Preliminary development, simulation and validation of a weigh in motion system for railway vehicles

The development of efficient Weigh In Motion (WIM) systems with the aim of estimating the axle loads of railway vehicles in motion is quite interesting both from an industrial and an academic point of view. This kind of systems is very important for safety and maintenance purposes in order to verify the loading conditions of a wide population of vehicles using a limited number of WIM devices distributed on the railway network. The evaluation of the axle load conditions is fundamental especially for freight wagons, more subjected to the risk of unbalanced loads which may be extremely dangerous both for the vehicle safety and the infrastructure maintenance. In this work the authors present the development, the simulation and the validation of an innovative WIM algorithm with the aim of estimating the axle loads $\widehat{N}$ of railway vehicles (the axle loads include the wheelset weights). The new estimation algorithm is a general purpose one; theoretically it could be applied by considering as input different kinds of track measurements (rail shear, rail bending, sleepers with sensors, etc.) and could be easily customized for different kinds of signals. In the paper a benchmark case based on rail bending measurements is proposed in which the longitudinal deformations ε _xx measured on the rail foot through strain sensitive elements are used as input. The considered input is affected by noise and bandwidth limitations and, consequently, is a good benchmark to test the robustness of the new algorithm. To estimate the axle loads, the algorithm approximates the measured physical input through a set of elementary functions calculated by means of a single fictitious load moving on the track. Starting from the set of elementary functions, the measured signal is then reproduced through Least Square Optimization (LSO) techniques: in more detail, the measured signal is considered as a linear combination of the elementary functions, the coefficients of which are the axle loads to be estimated. Authors have also developed a physical model of the railway track. The model consists of the planar FEM (finite elements method) model of the infrastructure and of the two-dimensional (2D) multibody model of the vehicle (the effects of lateral dynamics are treated as disturbances) and takes into account both the coupling between adjacent loads moving on the track and the vehicle dynamics. The physical model of the track and the innovative WIM algorithm (both considering possible measurement errors) have been validated by means of the experimental data kindly provided by Ansaldo STS and have been implemented in the Matlab and Comsol Multiphysics environments. In particular the model of the railway track has been developed expressly to test the WIM algorithm with a suitable simulation campaign when experimental data are not available; in other words it provides simulated inputs to test the WIM algorithm when there are no experimental inputs.     

Rail wheel removal and its implication on track life: A fracture mechanics approach

Wheel/rail forces generated by wheel defects is known to be one of the contributing factors to track failure. Current strategy of removing wheels from service is dependent on the magnitude of the impact forces generated by these defects. These impact forces are estimated with wheel impact monitor established along a section of the railway track. This is also known as wayside monitoring. The impact load levels recorded by these monitors are recorded and the wheels that generate impact loads above a stated level (e.g. 400 kN) will be removed from service for maintenance. The question one poses is “What if the impact force generated by a given wheel is just below this level and stays at this level for extended period of time?” Will this, e.g. 380 kN, impact force do as much damage to the track as a 400 kN impact force if it is allowed in service? What are the implications of allowing a wheel that generate a seemingly acceptable level of 250 kN impact load to remain in service for extended period of time? In an attempt to answer these questions, a series of investigations were carried out to investigate the effect of impact loads on the propagation of a Vertical Split Head (VSH) defect found in the head of a 50 kg/m rail.     

Periodically supported beam on a visco-elastic layer as a model for dynamic analysis of a high-speed railway track

This paper presents a theoretical study of the steady state dynamic response of a railway track to a moving train. The model for the railway track consists of two beams on periodically positioned supports that are mounted on a visco-elastic 3D layer. The beams, supports, and layer are employed to model the rails, sleepers and soil, respectively. The axle loading of the train is modeled by point loads that move on the beams. A method is presented that allows to obtain an expression for the steady-state deflection of the rails in a closed form. On the basis of this expression, the vertical deflection of the rails and its dependence on the velocity of the train is analyzed. Critical velocities of the train are determined and the effect of the material damping in the sub-soil and in the pads on the track response at these critical velocities is studied. The effect of the periodic inhomogeneity of the track introduced by the sleepers is studied by comparing the dynamic response of the model at hand to that of a homogenized model, in which the supports are assumed to be not discrete but uniformly distributed along the track. It is shown that the vertical deflection of the rails predicted by these models resemble almost perfectly. The elastic drag experienced by a high-speed train due to excitation of track vibrations is studied. Considering a French TGV as an example, this drag is calculated using both the inhomogeneous and homogenized models of the track and then compared to the rolling and aerodynamic drag.     

Subsurface initiated rolling contact fatigue of railway wheels as generated by rail corrugation

A fracture mechanics based fatigue index for rolling contact fatigue (RCF) initiated at deep (10–25 mm) defects is derived and employed together with a fatigue index for more shallow (4–10 mm) subsurface RCF initiation. Integrated simulations of high-frequency dynamic train–track interaction and prediction of RCF impact are then carried out to evaluate the influence of short-pitch rail corrugation on RCF of railway wheels. Parametric studies are carried out to identify operational conditions likely to generate high RCF impact. Simulation results show how rail corrugation causes a major increase in RCF impact at high-speed operations and that corrugation magnitudes measured in-field are sufficient to generate subsurface initiated RCF. At high speeds the main cause for increased fatigue impact is the increase in dynamic load magnitudes. At lower speeds and higher axle loads also the effect of poor contact geometry will have an influence.     

车-轨-桥耦合动力系统影响参数分析

为了考虑高速列车、板式无砟轨道和桥梁相互作用的特点,需将列车模拟为质量-弹簧-阻尼多刚体相互约束的系统,通过列车车轮与钢轨的接触关系,建立车-轨-桥耦合系统的运动方程。重点分析了双线列车以不同工况通过高速铁路桥梁时,列车行驶状态(速度和加速度)、列车悬挂系数和钢轨-轨道-桥梁连接参数分别对车-轨-桥耦合系统的动力学性能影响。结果表明,(1)列车的加速度和速度的变化对耦合系统有不同程度的影响,随着列车行驶速度与加速度在一定范围内增加,车体自身结构的位移振动响应逐渐减小,而钢轨和桥梁结构的位移振动响应则不断增加;(2)列车悬挂参数的改变对列车自身结构影响较大,而对钢轨和桥梁结构影响很小;(3)车体一系刚度系数增大会引起列车系统结构振动响应变大,但车体二系刚度系数的增加却抑制了车体结构的振动响应;(4)除了钢轨的最大加速度随着连续刚度系数增加呈线性递减外,列车、钢轨和桥梁的振动响应不易受钢轨与桥梁间连接参数的影响。     

风沙影响下铁路道碴变形模量的离散元数值分析

针对风沙区有碴铁路道床的结构特性,对其在细沙贯入下的有效变形模量研究有助于理解风沙影响下的道床动力特性。采用离散单元模型对道碴碎石和细沙颗粒进行数值建模,并对不同含沙率γ下的有效变形模量进行了数值分析。结果表明,在低含沙率下(γ<30%)沙石混合体的变形模量基本保持不变,在高含沙率下(γ>30%),变形模量随含沙率的增加呈线性降低,以上变形模量随含沙量的变化规律与试验结果相一致。基于离散单元模型的数值模拟,在细观尺度上对沙石混合体的力链强度、空间分布及配位数进行了分析,揭示了沙石混合体有效变形模量随含沙量变化的内在机理。本文工作对风沙区有碴铁路道床力学行为的研究具有一定的借鉴意义,有助于促进风沙影响下有碴铁路道床的结构设计和沙害治理。     

沙丘背风侧不同铁路结构形式对风沙环境的适应性分析

当铁路穿越大风沙漠地区时,风沙灾害会对铁路工程及其正常运营产生严重威胁,而设计一种合理的铁路结构形式能够减小风沙沉积对铁路工程的危害. 在本文中,以敦煌至格尔木铁路沙山沟段落为研究对象,采用多相流的方法对越过沙丘的风沙运动过程进行数值模拟,分别讨论了风沙运动对位于沙丘背风坡的铁路路基工程和桥梁工程的影响. 主要的模拟结果显示:路基工程明显降低了风速并且将沙丘后的回流区分成了两部分,而桥梁工程的导流效应则压缩了沙丘背风坡的回流区;轨道间的道碴增大了铁路表面的粗糙度,在轨道间有少量沙粒沉积,而路基工程两侧则有大量积沙;铁路表面的积沙量与摩阻风速呈现出非线性关系,随着摩阻风速的增大,路基工程沙粒沉积的增加速度大于风蚀能力的增加速度,而桥梁工程则正好相反. 在防止风沙危害铁路方面,设置桥梁工程明显优于路基工程. 本研究为风沙运动对铁路工程的影响提供了理论支持,也为今后的铁路工程设计提供了新的思路与研究工具.      

铁路轮轨冲击振动模拟与试验

对铁路工程领域普遍存在的轮冲击振动现象进行了理论与试验研究。将车辆模拟为移动的多刚体振动系统,将轨道描述成离散点支承连续梁结构,应用快速数值 发方法编制了ＶＩＣＴ模拟软件,实现了轮轨冲击振动的快速数值模拟。     

铁路道床有砟-无砟过渡段动力特性的DEM-FEM耦合分析

针对铁路道床有砟-无砟过渡段的结构特点,采用离散元-有限元耦合模型分析散体道砟和无砟道床间过渡段的动力特性。散体道砟道床和无砟道床分别采用离散元方法 DEM和有限元方法 FEM模拟,而在过渡段将道砟颗粒嵌入无砟道床以增加道砟颗粒与无砟道床间的咬合力,并在离散元和有限元耦合区域实现了力学参数的传递。采用以上DEM-FEM耦合方法对有砟-无砟道床及其过渡段在列车荷载作用下的沉降过程进行了数值分析。计算结果表明,离散元方法中道砟颗粒间的力链呈现非对称梯形分布,其与有限元方法中的应力分布趋势一致;采用嵌入式道砟颗粒的方法可以增加有砟-无砟过渡段道砟间的咬合力,有效约束道砟颗粒的位移,减少有砟-无砟道床间的沉降差异。本文计算模型可以合理地分析有砟道床的力链分布以及无砟道床的应力分布,确定列车荷载下道床有砟-无砟过渡段的动力学行为。     

Interface damage and its effect on vibrations of slab track under temperature and vehicle dynamic loads

This paper presents a three-dimensional finite element model to investigate the interface damage occurred between prefabricated slab and CA (cement asphalt) mortar layer in the China Railway Track System (CRTS-II) slab track system. In the finite element model, a cohesive zone model with a non-linear constitutive law is introduced and utilized to model the damage, cracking and delamination at the interface. Combining with the temperature field database obtained from the three-dimensional transient heat transfer analysis, the interface damage evolution as a result of temperature change is analyzed. A three-dimensional coupled dynamic model of a vehicle and the slab track is then established to calculate the varying rail-supporting forces which are utilized as the inputs to the finite element model. The non-linearities of the wheel–rail contact geometry, the wheel–rail normal contact force and the wheel–rail tangential creep force are taken into account in the model. Setting the maximum interface damaged state calculated under temperature change as the initial condition, the interface damage evolution and its influence on the dynamic response of the slab track are investigated under the joint action of the temperature change and vehicle dynamic load. The analysis indicates that the proposed model is capable of predicting the initiation and propagation of cracks at the interface. The prefabricated slab presents lateral warping, resulting in severe interface damage on both the sides of the slab track along the longitudinal direction during temperature drop process, while the interface damage level does not change significantly under vehicle dynamic loads. The interface damage has great effects on the dynamic responses of the slab track.     

Effect of rail corrugation on vertical dynamics of railway vehicle coupled with a track

The effect of rail corrugation on the vertical dynamics of railway vehicle coupled with a curved track is investigated in detail with a numerical method when a wheelset is steadily curving. In the calculation of rail corrugation we consider the combination of Kalker‘s rolling contact theory modified, a model of material loss on rail running surface, and a dynamics model of railway vehicle coupled with a curved track. In the establishment of the dynamic model, for simplicity, one fourth of the freight car without lateral motions,namely a wheelset and the equivalent one fourth freight car body above it, is considered. The Euler beam is used to model the rails and the track structure under the rails is replaced with equivalent springs, dampers and mass bodies. The numerical results show the great influence of the rail corrugation on the vibration of the parts of the vehicle and the track, and the some characters of rail corrugation in development.     

铁路车辆/轨道耦合系统在竖向冲击载荷作用下动态响应的计算机模拟研究

车辆与轨道的动态相互作用,是铁路轮轨接触式运输系统中最基本的问题之一,它直接制约着铁路运营速度的提高和运载重量的增加,也影响着铁路安全运行。本文采用有限元方法,对我国C61型运煤货车,按照车辆/轨道系统的实际几何形状、材料性质和边界条件建立了包括车辆和轨道系统的有限元模型,应用大型非线性动力分析程序LS-DYNA3D来模拟车辆通过轨道错牙接头时的轮/轨动态响应过程。计算结果表明车轮和轨道之间的竖向动态接触力大约是静轮载的2倍,与已有的现场试验结果基本吻合。因此应用有限元方法研究车辆/轨道耦合系统是可行和可靠的。     

Effects of the dynamic wheel–rail interaction on the ground vibration generated by a moving train

Based on Biot’s fully dynamic poroelastic theory, the dynamic responses of the poroelastic half-space soil medium due to quasi-static and dynamic loads from a moving train are investigated semi-analytically. The dynamic loads are assumed to be generated from the rail surface irregularities. The vehicle dynamics model is used to simulate the axle loads (quasi-static loads) and the dynamic loads from a moving train. The compatibility of the displacements at wheel–rail contact points couple the vehicle and the track–ground subsystem, and yield equations for the dynamic wheel–rail loads. A linearized Hertzian contact spring between the wheel and rail is introduced to calculate the dynamic loads. Using the Fourier transform, the governing equations for the poroelastic half-space are then solved in the frequency–wavenumber domain. The time domain responses are evaluated by the fast inverse Fourier transform. Numerical results show that the dynamic loads can make important contribution to dynamic response of the poroelastic half-space for different train speed, and the dynamically induced responses lie in a higher frequency range. The ground vibrations caused by the moving train can be intensified as the primary suspension stiffness of the vehicle increases.     

Nonlinear dynamic responses of high-speed railway vehicles under combined self-excitation and forced excitation considering the influence of unsteady aerodynamic loads

The dynamic characteristics of a railway vehicle system under unsteady aerodynamic loads are examined in this study. A dynamic analysis model of the railway vehicle considering the influences of aerodynamic loads was established. The model not only considers the forced excitation effect of unsteady aerodynamic loads but also accounts for the effect of unsteady aerodynamic loads on the change of the wheel–rail contact normal forces as well as changes of the wheelset creep coefficients and creep forces/moments. Therefore, this model also considers the influences of unsteady aerodynamic loads on the self-excited vibration characteristics of the vehicle system. The time-history curves, phase trajectory diagrams, Poincaré sections, and Lyapunov exponents of the vehicle system running on a smooth straight track under unsteady aerodynamic loads were determined. The results show that when the critical speed is exceeded, the vehicle system usually performs quasi-periodic motion under unsteady aerodynamic loads, which is significantly different from the periodic motion under steady aerodynamic loads. In different cases, the amplitude and phase of motion are significantly different. The amplitude of the motions can be increased by more than 159%, and the difference of phase can be up to 173°. (The phase is almost reversed.) The dynamic responses of the vehicle system under unsteady aerodynamic loads contain abundant frequency components, including the frequency of the self-excited vibration, the frequency of the forced excitation, and combinations of their integer multiples. The vibration forms corresponding to the main harmonic components under unsteady and steady aerodynamic loads were compared, and the self-excited vibration component of the vehicle system under unsteady aerodynamic loads was identified. The variations in the critical speed with various parameter combinations were computed. The variation range of the critical velocity can reach 73%.

     

滚动直线导轨副摩擦系数试验研究

针对目前缺少滚动直线导轨副摩擦系数试验研究的现状,首先基于动力学分析,推导了滚动直线导轨副预加载荷与摩擦系数的关系式;然后创新性设计了一种预加载荷调节装置,构建了一种预加载荷与预紧拖动力同步在线测量系统,实现了不同载荷和速度下滚动直线导轨副动态摩擦系数的精确测量. 试验结果表明:速度一定时,摩擦系数随预加载荷增大而增大;预加载荷一定时,摩擦系数随速度增大先减小后增大;预加载荷越大,摩擦系数受速度影响程度越小.      

Interaction of railway vehicles with track in cross-winds

This paper presents a framework for simulating railway vehicle and track interaction in cross-wind. Each 4-axle vehicle in a train is modeled by a 27-degree-of-freedom dynamic system. Two parallel rails of a track are modeled as two continuous beams supported by a discrete-elastic foundation of three layers with sleepers and ballasts included. The vehicle subsystem and the track subsystem are coupled through contacts between wheels and rails based on contact theory. Vertical and lateral rail irregularities simulated using an inverse Fourier transform are also taken into consideration. The simulation of steady and unsteady aerodynamic forces on a moving railway vehicle in cross-wind is then discussed in the time domain. The Hilber–Hughes–Taylor α-method is employed to solve the nonlinear equations of motion of coupled vehicle and track systems in cross-wind. The proposed framework is finally applied to a railway vehicle running on a straight track substructure in cross-wind. The safety and comfort performance of the moving vehicle in cross-wind are discussed. The results demonstrate that the proposed framework and the associated computer program can be used to investigate interaction problems of railway vehicles with track in cross-wind.     

Dynamic model of vertical vehicle-subgrade coupled system under secondary suspension

As it is known, track transportation can be divided into track system above and track system below. While the train is moving, the parts above and below are interacted and influenced. Therefore, in fact, the problem of track transportation is the match between the vehicle and the railway line system. In this paper, on a basis of dynamic analysis of the vehicle-subgrade model of vertical coupled system under primary suspension, utilizing track maintenance standard and simulating track irregularity excitation, the dynamic interaction of vehicle-track-subgrade system is researched in theory and dynamic model of the vertical vehicle-track-subgrade coupled system under secondary suspension is established by compatibility condition of deformation. Even this model considers the actual structure of a vehicle, also considers vibration characteristic of the substructure of track including subgrade and foundation. All these work want to be benefit for understanding and design about the dynamic characters of subgrade in high speed railway.     

轨道系统高频振动分析的动态子结构法

提出了包含钢轨断面弹性变形、轨下不连续支承、横垂向交叉导的轨道高频振动分析模型。根据轮轨特点,提出适合轮轨高频振动分析的阻抗聚缩法。预测结果与试验结果吻合较好。分析表明约８００Ｈｚ以下,钢轨振动表现为整体振动,再高频率钢轨发生断面弹性变形的振动。我国轨道系统第一、第二、阶二振频率分别为１５０Ｈｚ和３２０Ｈｚ,ｐｉｎｎｅｄ－ｐｉｎｎｅｄ共振频率的１２８０Ｈｚ。