Numerical study on moving train parameter identification system through a simply supported bridge

This paper presents a new experimental system for moving train parameter identification on bridge. The numerical method is adopted to simulate the experimental system and to investigate the effect of the system on identification of the moving train parameters. Displacement responses are obtained by solving the equation of motion of a simply supported bridge model. Basic parameters of the train (i.e., moving speed, wheel axle numbers, and axle spacing) are recognized with a self-designed parameter recognition system. Axle load values on bridge are identified with a load identification system based on simulated annealing genetic algorithm and by minimizing the errors between measured and reconstructed displacements from the moving train loads at each time step. Measured data are simulated by adding artificial noise to the calculated data. A series of numerical simulations is performed to analyze the effect of the system under various train situations. The results show that the experimental system is feasible and valid for identification of moving train parameters, thereby providing effective preparation for practice.     

Extracting modal parameters of high-speed railway bridge using the TDD technique

In case the excitation frequency induced by a high-speed train passage coincides with the natural frequency of a railway bridge, a resonance of the bridge occurs. In addition, if the train is passing through the bridge very quickly, measurable time samples can be of limited numbers and thus modal parameters of the bridge can hardly be obtained. To get over this, effective technique for the extraction of modal parameters is proposed in the present study. With the cross correlations among free vibration responses immediately after the train passes, mode shapes are obtained by TDD (time domain decomposition) technique while temporal modal parameters are extracted by the proposed sensitivity-updating system identification technique. A two-span steel composite girder bridge, which is of typical Korean high-speed railway bridge system, is employed to verify the proposed approach. Comparative studies reveal that the predictions of the proposed approach agree well with those by the well-known existing methods. It is thus postulated that the present approach is promising in terms of both accuracy and applicability.     

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.     

列车提速后的铁路桥梁横向振动控制

列车提速后,列车轮轴横向荷载击打轮轨-桥梁的频率提高,列车横向蛇形运动加剧.跨距大于等于32 m的桥梁可能出现拍击振动.在建立桥梁横向振动方程的基础上,分析了列车时速与列车轮轴激振荷载频率的关系.依据所建立的列车轮轴荷载作用的横向振动模型,提出了在两桥(或两梁)间增设弹性连接和加装调谐质量阻尼器的减振方案.     

桥梁行车激励辨识的实验模态方法

摘要提出了在运行状态下桥梁行车激励辨识的实验模态方法.在运行模态识别的基础上,建立结构动刚度模型,通过对运行状态下结构振动加速度时程的滤波分解,求得各阶模态的瞬时振幅,从而反演结构所受的各阶模态力时程.运用随机振动基础理论,计算桥梁各阶活跃振型所对应的等效静荷载大小,并统计由于结构振动引起的荷载放大系数.结合某120 m跨径钢管混凝土系杆拱桥的原型实验说明该方法的有效性.结果表明,所提方法能够克服荷载辨识过程中由于反分析奇异性所带来的不确定性问题,使用简便,适合应用于桥梁结构健康监测系统.     

Theoretical research and experimental validation of elastic dynamic load spectra on bogie frame of high-speed train

When a train runs at high speeds, the external exciting frequencies approach the natural frequencies of bogie critical components, thereby inducing strong elastic vibrations. The present international reliability test evaluation standard and design criteria of bogie frames are all based on the quasi-static deformation hypothesis. Structural fatigue damage generated by structural elastic vibrations has not yet been included. In this paper, theoretical research and experimental validation are done on elastic dynamic load spectra on bogie frame of high-speed train. The construction of the load series that correspond to elastic dynamic deformation modes is studied. The simplified form of the load series is obtained. A theory of simplified dynamic load–time histories is then deduced. Measured data from the Beijing–Shanghai Dedicated Passenger Line are introduced to derive the simplified dynamic load–time histories. The simplified dynamic discrete load spectra of bogie frame are established. Based on the damage consistency criterion and a genetic algorithm, damage consistency calibration of the simplified dynamic load spectra is finally performed. The computed result proves that the simplified load series is reasonable. The calibrated damage that corresponds to the elastic dynamic discrete load spectra can cover the actual damage at the operating conditions. The calibrated damage satisfies the safety requirement of damage consistency criterion for bogie frame. This research is helpful for investigating the standardized load spectra of bogie frame of high-speed train.     

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.     

Dynamic interaction analysis of a LIM train and elevated bridge system

A three-dimensional dynamic interaction model is developed for a LIM (linear induction motor) train and elevated bridge system, which is composed of a LIM-driven vehicle submodel and a finite element bridge submodel. Each LIM vehicle is modeled by a 27 degrees-of-freedom dynamic system. The expressions for the electromagnetic force between the linear motor and the reaction plate are derived, and the force model is established. By applying a modal superposition technique to the bridge submodel and using the measured track irregularities as the self-excitations of the train-bridge system, the equations of motion are established for analyzing the dynamic responses of the LIM vehicle and the elevated bridge. The proposed framework is applied to a 3-span elevated bridge with 29.9 m simply-supported girders. The full histories of the LIM train traversing the bridge are simulated, from which the dynamic responses of the LIM vehicle and elevated bridge system are obtained. The proposed method may help to find a way to assess the dynamic properties of elevated bridges and the running safety of a LIM train with reasonable computational effort.     

Measurements of dynamic properties of a medium span suspension bridge by using the wavelet transforms

The aim of this paper is to show the capabilities of the real-time kinematic (RTK) global positioning network system (GPS) to measure the low-frequency vibration of a medium span suspension bridge. In particular, this paper presents the results of studies conducted on the identification of modal parameters including natural frequencies, damping coefficients and mode shapes of a suspension bridge using ambient excitation loads. A real-time kinematic (RTK) global positioning system (GPS) was designed and installed on the Nottingham Wilford Bridge to provide long-term and real-time measurement of bridge deck movement. An approach to estimate modal parameters, from only output data in the time domain using the wavelet transform, is presented. Displacements responses of the bridge are used in the wavelet transform to identify its dynamic characteristics. The modal properties were extracted using a two-step methodology. In the first step, the random decrement method was used to transform random signals in free vibration responses. Secondly, a wavelets-based technique was used to extract natural frequencies and to determine the mode shapes of the structure. This method was compared with the well-established techniques eigensystem realisation algorithm showing a difference of 1% in the estimated first natural frequency.The efficiency of RTK–GPS was demonstrated in the full-scale measurement. In particular, the results showed that the RTK–GPS data can be used for extracting modal properties from in-service-loads induced low-frequency vibration (<5 Hz) by processing the signal with the wavelets transform.     

交通荷载作用下桥梁结构参数识别方法

应用动力节点加载法,将作用在桥梁上的交通荷载转化为等效节点荷载,再用两步构造法识别结构物理参数.第1步,用Newmark-β方法变换结构运动方程,并用结构的加速度响应求得变换空间内的位移、速度和加速度响应;第2步,基于最小二乘原理,构造出变换空间内求解结构参数的递推式,进行结构物理参数识别.数值模拟结果表明,在交通荷载作用下,该方法能够快速、准确地进行桥梁结构参数识别.     

钢筋混凝土简支梁超载后动力特性试验研究

基于采用动态法评估桥梁结构构件超载后损伤的目的,设计和开展了试验研究和相应理论分析。通过对钢筋混凝土简支梁进行反复超载试验,测出构件从完整到破损,以及不同超载幅值和次数对应损伤状态下的频率和阻尼比等模态参数,考查了其与构件承载力的关系,为采用结构动力参数评估结构损伤分析了频率和阻尼比随损伤状态不同的变化规律,根据试验结果得到频率和荷载等级关系的经验公式,为采用动态法评估既有桥梁提供了理论依据     

Short-pitch rail corrugation: A possible resonance-free regime as a step forward to explain the “enigma”?

Rail corrugation has been noticed at least for 100 years, but (particularly short pitch one in the range 20–80 mm) has been considered an enigma because measured corrugation wavelength did not relate well with wear-instability models. The apparently large number of governing parameters has resulted in many independent efforts to generate models, which do not entirely correspond to the collected experimental evidence, and therefore there is still some uncertainty over the possible critical factors dominating the phenomenon.We show in the paper that there is a simple possible mechanism of corrugation in longitudinal direction, apparently not noticed before in the literature by other authors, which does not necessarily correspond to a resonance in the system, not even the pinned–pinned resonance associated with the effect of discrete supports, but may depend on geometrical and loading conditions (normal load, creepage ratio, shape of the contact area, etc.), in general overall agreement with experiments.Additionally, some approximate calculations including discrete supports, using a typical concrete sleepers vertical receptance of BR use, show no evidence of corrugation mechanism at the pinned–pinned resonance, at least in the longitudinal direction. A full comparison between lateral and longitudinal mechanisms would depend on the particular value of the lateral creepage vs. longitudinal creepage, system-specific. The present “resonance-free” mechanism is a possible alternative for the data which fall outside the pinned–pinned resonance range.     

A semi-analytical/FEM model for predicting ground vibrations induced by high-speed train through continuous girder bridge

This paper develops a method based on a semi-analytical/FEM model to predict the ground vibrations induced by high-speed train running through continuous girder bridge. The prediction method has two steps: the solution of reaction on top of pier and the solution of ground vibrations. The reaction on pier top is solved by the semi-analytical dynamic interaction model for train-track-continuous girder bridge system, taking the dynamic characteristics of train, track, and bridge into account. The solution of ground vibrations is accomplished by establishing the 3-dimensional pile foundation-soil finite element model and then applying the negative reaction force got from pier top to the pile foundation-soil model. The effectiveness of the presented model is verified by comparing with other existed results.     

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.     

列车模拟运行系统的运行控制

构建了能够实时模拟列车在不同轴重、不同线路下运行的列车模拟运行系统,利用列车实时仿真的结果对系统进行有效地控制,从而实现了不同运行工况下的模拟,而为电力牵引系统的开发提供了与实际列车运行工况基本吻合的模拟负载。     

时变位姿下行星齿轮传动系统动应力计算模型及其参数影响研究

考虑行星轮系内部非惯性和机体时变位姿外部非惯性的综合影响,推导了任意时变位姿下带有机匣的行星轮系构件运动方程,计入时变啮合刚度、啮合误差、侧隙和啮入冲击,建立了时变位姿下行星齿轮传动系统级动力学模型,并采用精细积分时程法（Precision integration method,PIM）求解得到了动态啮合力序列。根据齿间载荷分配关系进一步得到单齿啮合力序列。最后结合修正Heywood公式与Hertz公式构建了时变位姿下行星齿轮传动系统齿根弯曲动应力和接触动应力计算模型,并研究了机体平飞、滚转和筋斗位姿参数对接触动应力、弯曲动应力的影响规律。结果表明：不同时变位姿参数对弯曲、接触动应力影响显著,且对不同齿轮副影响不同,即加剧了齿轮副间承载不均;筋斗运动角速度对动应力影响比平飞加速度、滚转角速度以及筋斗回转半径对其影响复杂;机匣对动应力影响随加速度增大而增加。研究成果为时变位姿下行星齿轮传动动应力计算与高可靠性设计提供了理论依据。     

基于ANN和动应变的梁桥移动荷载识别及试验

为了实现桥梁上车载参数的快速识别,基于欧拉梁动力解析解分析桥梁挠度和应变对移动荷载的敏感性,选择敏感性更强的应变作为输入参数,研究将人工神经网络(artificial neural networks,简称ANN)用于识别梁桥移动车载的理论和方法。对简支梁桥在移动车载作用下的动应变响应进行理论分析及数值模拟,选取不同工况下的模拟数据对网络进行训练,分析激活函数组合和训练方法对网络精度的影响及噪声水平对动荷载工况下正确识别率的影响。通过车-桥模型动力试验验证该方法的合理性和可用性。结果表明,不同激活函数组合对识别结果影响较小,而不同的训练算法对识别结果影响较大,在应用神经网络识别桥梁移动荷载时,可以通过桥梁的动应变,对车辆的位置、速度和动荷载进行识别。     

直升机动力—传动—旋翼扭振系统的模态参数计算与识别

应用动力学基本原理建立直升机的动力－传动－旋翼系统的动力学扭振方程,以此获得系统的理论动态特性能数。根据该参数确定试验方案,对系统进行静,转动态试验,获得试验响应数据。     

机器人负载惯性参数的快速辨识

机器人的惯性参数辨识是基于动力学模型控制器设计的基础,除了需要辨识机器人自身的惯性参数外,还需要快速准确地辨识负载的惯性参数。针对需要更换负载的工作场景,提出了一种快速辨识负载的激励轨迹,该轨迹不需要经过优化,即可在短时间内覆盖更多的机器人运动状态,从而获得更为全面的采样参数集,提高了辨识效率的同时增强了辨识模型的泛化能力。实验表明,辨识的结果与负载模型的CAD参数符合,机器人关节理论力矩能较好地拟合实际驱动力矩,验证了负载参数的正确性。