Evaluation of vertical impact factor coefficients for continuous and integral railway bridges under high-speed moving loads

In the railway bridge analysis and design method,dynamic train loads are regarded as static loads enhanced by an impact factor(IF).The IF coefficients for various railway bridges have been reported as a function of span length or frequency of the bridges in Eurocode(2003).However,these IF coefficient values neglect the effects of very high speeds(>200 km/h)and soil-structure interaction(SSI).In this work,a comprehensive study to assess the impact factor coefficients of mid-span vertical displacements for continuous and integral railway bridges subjected to high-speed moving loads is reported.Three different configurations,each for the three-dimensional(3D)continuous and integral bridge,are considered.Also,single-track(1-T)and two-track(2-T)“real train”loading cases for both these bridge types are considered.Subsequently,finite element analysis of the full-scale 3D bridge models,to identify their IF values,considering the effects of SSI for three different soil conditions,is conducted.The IF values obtained from the study for both bridge types are comparable and are greater than the values recommended by Eurocode(2003).The results reveal that with a loss of soil stiffness,the IF value reduces;thus,it confirms the importance of SSI analysis.

Numerical modelling of vibration response in loess hills due to a high-speed train on railway viaduct

In order to accurately analyze vibration characteristics and site effects of loess hills under moving load of a highspeed train,four types of loess hill models under railway viaduct was established by ABAQUS of finite element analysis software by field test.The dynamic response and stability of loess hills under two different vibration sources under high-speed train load were studied by using two-dimensional equivalent linear response timehistory analysis,and the influence of the mechanical parameters of loess on the vibration of different types of loess hill was analyzed.Results show that there are obvious differences between peak displacement cloud maps of loess hills under the railway viaduct under gravity and train load action.We analyzed the influence of the change of elastic modulus on vibration propagation of soil of foundation and loess knoll,and found that the change of elastic modulus of soil in different position of foundation has more effect on vibration propagation than that of loess knoll soil.At the same time,the vertical acceleration cloud maps of the four types of loess hills are obviously different.

Computation of Impact Factor of High-Speed Railway Bridge by KTX Train Riding Test

The design live load of railway is divided into common railway and high-speed railway separately inKorea. Accordingly, the Korean design specification of railway specifies the impact factor for common railway and high-speed railway respectively. The impact factor for high-speed railway is based on Eurocode. Since the impact factor criteria inKoreawere established by adopting those of the Eurocode and without dedicated investigation relying on research results reflecting the domestic circumstances, thorough examination should be implemented on these criteria. Therefore the evaluation of impact factor based on field tests is required. Both dynamic and static vertical displacements are necessary to compute the impact factor. The dynamic response can be obtained from the measurement of deflection of the bridge slab crossed by the firstKoreahigh-speed train (KTX, Korea Train eXpress) running at high-speed. The main difficulties encountered are in obtaining static response because static response corresponds to the response of the bridge when the train remains immobile on the bridge or crosses the bridge at speed slower than5 km/hr. This study introduces the static response derived by applying the moving average method on the dynamic response signal. To that goal, field measurements was conducted under train speeds of5 km/hr and ranging from100 km/hr to300 km/hr on Yeonjae Bridge located in the trial section of the Gyeonbu High-Speed Railway Line before its opening. The validity of the application of the moving average method is verified from comparison of measured static response and derived static response by moving average method. Moreover, evaluation is conducted on the impact factor computed for a bridge crossed by the KTX train running at operational speed.

Influence of ground effect on flow field structure and aerodynamic noise of high-speed trains

The simulation of the ground effect has always been a technical difficulty in wind tunnel tests of high-speed trains.In this paper,large eddy simulation and the curl acoustic integral equation were used to simulate the flow-acoustic field results of high-speed trains under four ground simulation systems(GSSs):“moving ground+rotating wheel”,“stationary ground+rotating wheel”,“moving ground+stationary wheel”,and“stationary ground+stationary wheel”.By comparing the fluid-acoustic field results of the four GSSs,the influence laws of different GSSs on the flow field structure,aero-acoustic source,and far-field radiation noise characteristics were investigated,providing guidance for the acoustic wind tunnel testing of high-speed trains.The calculation results of the aerodynamic noise of a 350 km/h high-speed train show that the moving ground and rotating wheel affect mainly the aero-acoustic performance under the train bottom.The influence of the rotating wheel on the equivalent sound source power of the whole vehicle was not more than 5%,but that of the moving ground slip was more than 15%.The average influence of the rotating wheel on the sound pressure level radiated by the whole vehicle was 0.3 dBA,while that of the moving ground was 1.8 dBA.

Moving Mechanism of a High-speed Insect-scale Microrobot via Electro-magnetically Induced Vibration

This paper presents the moving mechanism of a high-speed insect-scale microrobot via electromagnetically induced vibration of two simply supported beams.The microrobot,which has a body length of 12.3 mm and a total mass of 137 mg,can achieve reciprocating lift motion of forelegs without any intermediate linkage mechanisms due to the design of an obliquely upward body tilt angle.The gait study shows that the body tilt angle prevents the forelegs from swinging backward when the feet contact the ground,which results in a forward friction force applied on the feet.During forward movement,the microrobot utilizes the elastic deformation of the simply supported beams as driving force to slide forward and its forelegs and rear legs work as pivots alternatively in a way similar to the movement of soft worms.The gait analysis also indicates that the moving direction of the microrobot is determined by whether its body tilt angle is obliquely upward or downward,and its moving speed is also related to the body tilt angle and as well as the body height.Under an applied AC voltage of 4 V,the microrobot can achieve a moving speed at 23.2 cm s1(18.9 body lengths per second),which is comparable to the fastest speed(20 cm s-1 or 20 body lengths per second)among the published insect-scale microrobots.The high-speed locomotion performance of the microrobot validates the feasibility of the presented actuation scheme and moving mechanism.

Discussion on Development Mode of Large Railway Hubs in High-speed Rail Era:From Transportation Complex to Urban Complex

At present, most of China's railway hubs are developed to be transportation complexes, with some problems like unsmooth traffic circulation, mixed but disordered functions, separated spaces, etc. In high-speed rail era, high-speed railway hubs should be regarded as the catalyst to promoted urban development. The mode of urban complex should be developed, to closely connect the railway hub and the surrounding area within walking distance, so as people could get to their destinations in the most convenient way. Furthermore, it would strengthen people's aggregation, thus to bring about larger scale urban development by the successful development of urban complex.

Spatial differentiation and influence mechanism of the connection-distribution performance of urban high-speed railway hub in the Yangtze River Economic Belt

A transportation hub is the key link in the construction of the comprehensive three-dimensional transportation corridor of the Yangtze River Economic Belt,and is the basic factor responsible for the promotion of this belt.A high-speed railway hub has the“last kilometer of time-space compression”effect and is the key to building an efficient,convenient,modern,and comprehensive transportation system.This study constructed a model for measuring the connection-distribution performance of the high-speed railway hub,determined the connection-distribution performance of the urban high-speed railway hub in the Yangtze River Economic Belt,and analyzed its spatial differentiation characteristics,further revealed the influencing mechanism of the connection-distribution performance of the high-speed railway hub.The main results are as follows:(1)The connection-distribution performance of the high-speed railway hub in the Yangtze River Economic Belt presented an“olive-shaped pattern”grade structure with two small ends and a large middle section,that is,the number of high-speed railway stations with high performance and average performance was small,and the number of high-speed railway stations with good performance and medium performance was large.(2)The connection-distribution performance of the high-speed railway hub in the Yangtze River Economic Belt showed a regional differentiation pattern of“high in the east and low in the west”and“high in the north and low in the south”,and showed an urban agglomeration differentiation pattern of“high in the core areas but low in the marginal areas”;moreover,spatial differences were prominent in the distribution of nine evaluation indexes of the connection-distribution performance of the high-speed railway hub.(3)GDP,urbanization rate,city level,station passenger flow and frequency of shuttle bus were key driving factors affecting the connection-distribution performance of the high-speed railway hub.At the same time,there were significant differences in the key driving factors for the connection-distribution performance grades of high-quality,good,medium and average.

Comparison and Selection of Arch-Rib Construction Schemes for Continuous Beam arch Composite Bridge of High Speed Railway

The paper summarizes the four different construction schemes based on engineering cases for the arch rib construction of continuous beam-arch composite bridges for high-speed railways.These methods include in-situ assembly,segmental lifting,incremental launching and longitudinal moving,and vertical rotation.The temporary structural designs,process methods,and technological equipment for each construction scheme are described in detail.The advantages and disadvantages of each scheme and its application scope under various conditions are analyzed,and opinions and suggestions for guiding the application of each scheme are proposed.The comparison and selection analyses show that the four arch rib construction schemes have certain applicability under different conditions such as bridge site status,bridge span,and construction environment.With the continuous increase of bridge span and progress of construction technological equipment,the arch rib construction technology is developing towards the overall erection direction.This leads to more obvious technical advantages of the segmental lifting method,incremental launching and longitudinal moving method,and vertical rotation method.Therefore,it is necessary to select the best construction scheme according to the construction status and technical conditions during application.

Effects of Comprehensive High-speed Transportation Hubs on Spatial Structure of Urban Development:A Case Study on Changsha-Zhuzhou-Xiangtan Area

This paper, by studying the mechanism of the spatial restructuring of urban development and the effects of comprehensive high-speed transportation hubs on it, analyzes the development trends of comprehensive high-speed transportation in Changsha-Zhuzhou-Xiangtan Area and the impacts of the growing urban area centered on comprehensive high-speed transportation hubs, like airport and high-speed railway station, on the urban development of this area. It also proposes some strategies for the spatial restructuring of Changsha-Zhuzhou-Xiangtan Area in view of the development of the comprehensive high-speed transportation hubs, like Huanghua Airport and Wuhan-Guangzhou High-speed Railway Station.

金城津、关的设置及其交通路线

北周、隋代是中原王朝经由分裂到统一的重要时期,然而此时西北方向的吐谷浑与突厥对边境侵寇不止,为了加强河陇地区的防御体系,北周设置金城津,隋代又改津为关。北周时期金城郡治东迁至汉金城县,即今甘肃省兰州市城关区,金城关就位于其西北二里的黄河沿岸。随着金城郡治的迁移,政治军事中心也随之东迁,金城关成为金城河上通往凉州、临州、河州、鄯州路线中最重要的交通枢纽。

Numerical simulation of high-speed train induced ground vibrations using 2.5D finite element approach

An efficient 2.5D finite element numerical modeling approach was developed to simulate wave motions generated in ground by high-speed train passages. Fourier transform with respect to the coordinate in the track direction was applied to re-ducing the three-dimensional dynamic problem to a plane strain problem which has been solved in a section perpendicular to the track direction. In this study, the track structure and supporting ballast layer were simplified as a composite Euler beam resting on the ground surface, while the ground with complicated geometry and physical properties was modeled by 2.5D quadrilateral elements. Wave dissipation into the far field was dealt with the transmitting boundary constructed with fre-quency-dependent dashpots. Three-dimensional responses of track structure and ground were obtained from the wavenumber expansion in the track direction. The simulated wave motions in ground were interpreted for train moving loads traveling at speeds below or above the critical velocity of a specific track-ground system. It is found that, in the soft ground area, the high-speed train operations can enter the transonic range, which can lead to resonances of the track structure and the sup-porting ground. The strong vibration will endanger the safe operations of high-speed train and accelerate the deterioration of railway structure.

Optimal deployment schedule of an active twist rotor for performance enhancement and vibration reduction in high-speed flights

The best active twist schedules exploiting various waveform types are sought taking advantage of the global search algorithm for the reduction of hub vibration and/or power required of a rotor in high-speed conditions. The active twist schedules include two non-harmonic inputs formed based on segmented step functions as well as the simple harmonic waveform input. An advanced Particle Swarm assisted Genetic Algorithm（PSGA） is employed for the optimizer. A rotorcraft Computational Structural Dynamics（CSD） code CAMRAD II is used to perform the rotor aeromechanics analysis. A Computation Fluid Dynamics（CFD） code is coupled with CSD for verification and some physical insights. The PSGA optimization results are verified against the parameter sweep study performed using the harmonic actuation. The optimum twist schedules according to the performance and/or vibration reduction strategy are obtained and their optimization gains are compared between the actuation cases. A two-phase non-harmonic actuation schedule demonstrates the best outcome in decreasing the power required while a four-phase non-harmonic schedule results in the best vibration reduction as well as the simultaneous reductions in the power required and vibration. The mechanism of reduction to the performance gains is identified illustrating the section airloads, angle-of-attack distribution, and elastic twist deformation predicted by the present approaches.

Investigations on lubrication characteristics of high-speed electric multiple unit gearbox by oil volume adjusting device

In this paper,a numerical simulation model of the flow field in a gearbox with an oil volume adjusting device is established for the first time to study its influence on the lubrication characteristics of a high-speed electric multiple unit(EMU)gearbox.The moving particle semi-implicit(MPS)method is used to numerically simulate the internal flow field of the gearbox of the high-speed EMU under working conditions.The effects of the velocity of the high-speed EMU,the immersion depth,and the oil sump temperature on the power loss of the gears and the lubricant quantity of each bearing are studied and provide an effective tool for the quantitative evaluation of the lubrication characteristics of the gearbox.The lubrication characteristics of the gearbox under different working conditions are studied when the oil volume adjusting device is closed and opened.The results show that the oil volume adjusting device mainly changes the amount of lubricant stirred by the output gear by changing the flow rate of lubricant from the cavity pinion(Cavity P)to the cavity gear(Cavity G),and thus affects the power loss of gears and the lubricant quantity of each bearing.

城市双修背景下的新型人非共板道路设计

在城市双修提出修补城市功能的背景下,分析了道路空间应承担的功能,认为道路应重点解决机非冲突交通安全、公交慢行优先出行、多功能设施集约化占地布置等问题。提出了以综合绿化设施带整合公交站点、机非停车、市政交通杆件等需求并集约化布置的新型人非共板道路设计方法。给出了标准横断面布置、综合绿化设施带宽度取值、功能整合的平面布置、交叉口基于人非过街优先的平面设计、交叉口与地块进出口处提高非机动车舒适度的平纵大样图设计、无缝衔接换乘的路边微枢纽布置、以及道路与建筑空间一体化空间组织等设计要点。解决了快慢交通分离、慢行与生活空间融合要求下的人非共板道路设计问题。

Effect of Moving Endwall on Hub Leakage Flow of Cantilevered Stator in a Linear Compressor Cascade

The cantilevered stator has the advantages of reducing mass and axial length of highly loaded com-pressor.The details of the hub leakage flow resulting from the clearance between the high-speed moving hub and the cantilevered stator hub are unclear.In this paper,the effect of a moving endwall on the hub leakage flow of a cantilevered stator in a linear compressor cascade was studied.After the simulation method was verified with the experimental results,the time-averaged results of unsteady Reynolds averaged Navier-Stokes(URANS)were selected to study a case with a hub clearance of 2 mm.The results show that the effect of the moving endwall of the cantilevered cascade on the general characteristics with below 30%span increases the leakage mass flow rate and reduces the static pressure coefficient at three conditions of 0°,6°,and-7°incidences,and the change is most significant at-7°incidence.The effect of the moving endwall on the total pressure loss coefficient varies with different operating conditions,which decreases by 15.94%at 0°incidence,and increases by 4.77%and 18.51%at 6°incidence and-7°incidence,respectively.The influence of the moving endwall is below 14%span at-7°incidence,below 23%span at 0°incidence,and below 30%span at 6°incidence.These effects correspond to the static pressure coefficient and the difference of static pressure coefficient representing the blade loading.In designing the cantilevered stator and matching between the stages of a multistage compressor,the quantitative research results of this paper have certain guiding significance.

动叶可调轴流通风机叶片安装及调整工艺研究

本文详细研究了动叶可调轴流通风机叶片安装及调整施工工艺,在保证叶片安装精度的要求下适度简化了动叶可调轴流通风机的叶片安装调整工艺,并以小结的方式归纳了动叶可调轴流通风机叶片安装及调整施工过程中切实符合安装现场的施工要点。

悬臂静子叶栅与高速运动轮毂间隙流研究

悬臂静叶结构可以减轻压气机的重量并降低轴向长度,但在高速运动轮毂作用下其叶根泄漏流细节尚不明确。本文采用经过实验数据校准的数值模拟方法探究了高速运动轮毂情况下不同间隙对于悬臂静叶性能和泄漏流场细节的影响。结果表明,当间隙增大时,悬臂静叶总压损失呈非线性增大,近轮毂处叶片载荷峰值先增大后减小且其位置向尾缘方向移动。泄漏流轨迹呈现三区分布,间隙增大使得通道70%轴向弦长后的高湍动能区在周向和径向范围更大。

双筒提升机液压调绳离合器的改进

由于液压调绳离合器中拨动环与移动毂之间的转动配合及润滑方式不合理,常引起油液泄漏,影响制动效果;环境恶劣或润滑不充分时,局部易干枯发生胶合事故。针对以上问题,将拨动环与移动毂之间的滑动面摩擦转动配合方式改为双滚珠滚动摩擦,减少了接触摩擦面积,增加了润滑空间;增设专用润滑脂储存及输送通道,改善其工作条件。经模拟分析及实践应用表明,液压调绳离合器的改进效果良好。