Influence Of Train Speed Research Articles

Influence of collapsible shape of Loess Foundation on high-speed railway subgrade under train vibration loading

Collapsible loess has special sensitivity to water, and its engineering mechanical properties deteriorate significantly after immersion in water, causing the foundation to sink, which seriously threatens the safety and stability of the high-speed railway subgrade under train vibration loading. Studying this effect is essential to prevent and control the disasters of high-speed railway subgrades. In this study, a model with the function of simulating foundation settlement is established to conduct disaster testing of high railway subgrade under train vibration loading. The results indicate that when different foundation shapes are settled, the surface of the subgrade under static load is gradually settled in a short time, and the settlement value of the track surface is lower than that of the corresponding subgrade surface. Under train vibration load, the maximum dynamic settlement occurs at the middle of the subgrade slope, which is smaller than the corresponding settlement under static load. The number of stabilization times required from different monitoring positions on the subgrade surface is different under different excitation forces, and the number of stabilization times required is more in the middle of the subgrade slope and the slope shoulder. The influence of train speed on subgrade has a critical respond speed that increases with increasing vibration times. There are horizontal, vertical and 45° angle cracks in the middle of subgrade slope. It is qualitatively assessed that the slope of the high-speed railway subgrade in the collapsible loess area is unstable under the effect of train load. The data and rules provided in this document provide some reference values for the construction of a high-speed railway in the collapsible loess area.

Multi-objective optimisation of wheel-rail adhesion for high-speed trains with aerodynamic lift wings

A high-speed train with aerodynamic lift wings (aero-wings) is designed to improve train speed and mitigate energy consumption. Nevertheless, the impact of aero-wings on wheel-rail adhesion and safety remains uncertain. In this examination, a multi-body dynamics (MBD) model of a high-speed train integrated with aero-wings was first created. The influences of train speed, wheel-rail contact conditions, and aerodynamic lift on the wheel-rail adhesion, wheel wear, and dynamics performance were briefly investigated, indicating that aerodynamic lift degrades wheel-rail adhesion and dynamics performance but reduced wheel wear. Then, the multi-parameters matching optimisation design for sufficient wheel-rail adhesion and minimal wheel wear was conducted. The results indicate that, under dry contact and traction conditions, the minimum wear and optimal wheel-rail adhesion can be achieved when the train speed is about 440.62 km/h, the aerodynamic lift is about 24.48% of the vehicle weight, and the wheel wear optimisation rate is 25.38%. While the train speed of 549.54 km/h and an aerodynamic lift of 12.39% corresponds to the optimal results with wear reduction of 11.62%, under wet and braking conditions. This study provides valuable insights for determining aerodynamic load limits and formulating traction/braking control strategies for high-speed trains with aero-wings.

Field measurements of aerodynamic pressures induced by suburban rail transit train passing through double-track tunnel with mid-partition wall

ABSTRACT Suburban rail lines, which provide fast connections between city centre and the surrounding suburbs, are attracting more and more attention from cities. As a train passes through the tunnel quickly, it tends to produce significant aerodynamic effects. In this study, a series of field measurement experiments were carried out in two tunnels with the mid-partition wall. The influence of train speed and tunnel length on the aerodynamic pressure was analysed. The aerodynamic pressure in adjacent tunnel was also discussed. Furthermore, the attenuation law and coefficient of aerodynamic pressure in tunnels with mid-partition walls were discussed. On this basis, a theoretical calculation model for predicting the peak positive pressure inside tunnels with different lengths and attenuation characteristics was established. The results show that the tunnel length not only affects the amplitude of the pressure, but also significantly affects the distribution trend of the pressure peak in the longitudinal direction. The propagation and reflection processes of pressure waves also exist in the adjacent tunnel on the other side of the partition, and they are synchronous. For the horse-shaped tunnel with mid-partition walls, the peak pressure inside the tunnel is directly proportional to the 2.05–2.20 power of the train speed, and the peak pressure decays exponentially with time. The pressure attenuation coefficient is greatly influenced by the placement of the measuring point, ranging from 4.957 × 10 − 5 to 8.184 × 10 − 5 depending on the position of the measurement point. This work provides important data support for studying the tunnel aerodynamic effects and verifying related numerical simulations.

Random Dynamic Analysis and Running Safety Assessment of Long-Span Cable-Stayed Bridge Under High-Speed Trains Subjected to Earthquake Excitations and Track Irregularities

Running trains on a long-span bridge under earthquake is an inevitable problem for the high-speed railway in seismic regions. This paper aims to investigate the seismically random dynamic behavior of train–cable stayed bridges interaction system using the probability density evolution method (PDEM). The system simultaneously involves the multi-effect of random multi-point earthquake excitations with traveling waves and random track irregularity. The multi-point earthquake excitations, composed of lateral and vertical positions, are generated by stochastic harmful functions (SHFs) and uniformly modulated into nonstationary random processes. The motion equation of such a system is established by coupling the 38-degree vehicles and bridges through the refined random wheel/rail contact relationship and accounting for the phase-lags of seismic travelling waves between pier excitations. PDEM is proven to be applicable to such time-dependent systems and is then used to transform the random excitations into a series of deterministic representative excitations with initial probability. By solving for the corresponding deterministic probability responses, various nonstationary random responses, including the time-dependent probability density evolution functions of random responses, mean values curves and standard deviations, can be obtained easily. A case study based on the cable-stayed bridge is then presented, and the results show the effectiveness and accuracy of the proposed method by comparison with Monte Carlo Simulation. Additionally, the influence of train speed and seismic intensity on the safety and reliability of trains is discussed.

Influence of train speed and its mitigation measures in the short- and long-term performance of a ballastless transition zone

AbstractThe ballastless track is nowadays the most popular railway system due to the required low number of maintenance operations and costs, despite the high investment. The gradual change from ballasted to ballastless tracks has been occurring in Asia, but also in Europe, increasing the number of transition zones. The transition zones are a special area of the railway networks where there is an accelerated process of track degradation, which is a major concern of the railway infrastructure managers. Thus, the accurate prediction of the short- and long-term performance of ballastless tracks in transition zones is an important topic in the current paradigm of building/rehabilitating high-speed lines. This work purposes the development of an advanced 3D model to study the global performance of a ballastless track in an embankment–tunnel transition zone considering the influence of the train speed (220, 360, 500, and 600 km/h). Moreover, a mitigation measure is also adopted to reduce the stress and displacements levels of the track in the transition. A resilient mat placed in the tunnel and embankment aims to soften the transition. The behaviour of the track with the resilient mat is evaluated considering the influence of the train speed, with special attention regarding the critical speed. The used methodology is a novel and hybrid approach that allows including short-term and long-term performance, through the development of a powerful 3D model combined with the implementation of a calibrated empirical permanent deformation model.

Dynamic response of large-section inclined shallow-buried pipe tunnel under train loads

To ensure the normal passage of an ascending road during the construction of a pipe-jacking tunnel, trains generally run at low speeds during the construction phase and adopt normal speeds later. Using Jingjiu Road, Xi’an, China, as an engineering case, this study evaluated and predicted the dynamic response of a tunnel structure and soil mass when trains run at low to normal speeds. When the train speed was controlled in the range of 30–60 km/h, the soil deformation change rate around the shallow-buried pipe-jacking tunnel was 0.41%. The maximum tensile stress growth rate of the pipe-jacking tunnel structure was 0.037%, the maximum compressive stress growth rate was 0.128%, and the maximum increase in the stress of the pipe-jacking structure was 1.82%. Thus, the soil and structure of the pipe-jacking tunnel were in a safe-stress state. The results show that the influence of train speed on soil and structural stress is small and can be ignored.

Analysis of Dynamic Characteristics of Low-Floor Train Passing Switch in Facing Direction with Bad Alignment Irregularity Ahead of the Turnout

A low-floor train–turnout coupling dynamic model considering bad alignment irregularity ahead of the turnout was established on the basis of a field test in which the dynamic performances of a low-floor train passing through a no. 6 turnout in a rail transit depot in China had been measured, as well as the line alignment and wheel and rail profiles. There are two types of wheelsets in the low-floor train: integral wheelset and independent wheelset. The model fully considers the coupling effect between the vehicle and the ballast components, and the simulated results are in consistence with measured results in the field test. Based on this, the influences of train speed, the wheel–rail friction coefficient, and the track alignment optimization of the dynamic performance of low-floor trains passing switch in facing direction are analyzed. The main results indicate that eliminating alignment irregularities before the switch can effectively improve the dynamic performance of the integrated wheelset in the switch and the lateral forces of the outer wheels of these two vehicles are reduced by about 80%, the derailment coefficients are reduced by about 70%, the vertical force is reduced by about 10–20% and wheel load is reduced by approximately 30%.

The influence of model assumptions in a hybrid prediction tool for railway induced vibration

Within the SILVARSTAR project, a user-friendly frequency-based hybrid prediction tool is developed to assess the environmental impact of railway induced vibration. This will be implemented in the existing noise mapping software IMMI. The vibration level in a building in each frequency band is expressed as the product of source, propagation and receiver terms. A hybrid approach is used that combines experimental data with numerical predictions, providing increased flexibility and applicability. The train and track properties can be selected from a database or as numerical values. The user can select soil impedance and transfer functions from a database, pre-computed for a wide range of parameters with the MOTIV and TRAFFIC models. An experimental database of force densities, transfer functions, free field vibration and input parameters is also integrated into the new tool. The building response is estimated by means of empirical correction factors. Assumptions within the modelling approach can influence the prediction accuracy and the present paper aims to quantify these. We focus on the influence of train speed and soil properties on the compliance of the track-soil system, the dynamic axle loads, and the free field response, as well as on the load transfer between track and soil.

Aerodynamic impacts of high-speed trains on city-oriented noise barriers: A moving model experiment

Two types of city-oriented noise barriers, i.e., fully-enclosed noise barrier and bilateral inverted l-shaped semi-enclosed noise barrier, have been gradually adopted in city centres along high-speed railways to reduce noise pollution. The aerodynamic impacts of high-speed trains present a threat to the long-term durability of the city-oriented noise barriers. To promote the usage and increase the sustainability of city-oriented noise barriers, a moving-model experiment system with city-oriented noise barriers and HST with a scale ratio of 1:16.8 is established. The train type is CRH380A and the train speed is up to 350 km/h. A systematic comparative study on the aerodynamic performance of the two types of city-oriented noise barriers is conducted. The similarities and differences of transient pressure time–histories, spatial distribution of pressure peaks and spectral characteristics of aerodynamic pressure acting on the two types of noise barriers are compared and discussed. Moreover, the influence of train speed on the characteristics of the train-induced aerodynamic pressure is also investigated. The results show that the pressure fluctuation of the two types of noise barriers is caused by different reasons. Compared with the fully-enclosed noise barrier, the transient pressure of the semi-enclosed noise barrier is more sensitive to train speeds. The research results may provide a reference for the engineering design of city-oriented noise barriers on high-speed railways.

Field and numerical investigations on the environmental vibration and the influence of hill on vibration propagation induced by high-speed trains

The environmental vibrations induced by high-speed trains have been taken as a real problem regarding to the safety of adjacent buildings and structures, safe operation of train, settlement and deformation of foundation and so on. It is vital to comprehensively figure out the laws of vibration propagation and the influence of the terrain conditions on vibration. To this end, an in-site vibration test was carried out to measure the vibrations of pier top, flat ground, and the hill induced by high-speed trains. The influences of train speed and the hill on vibration were studied in time- and frequency-domain in detail. And the train operation status was analyzed based on synchroextracting transform (SET). Moreover, a finite element model was established to investigate the influences of the hill location and hill shape on vibration propagation. The results indicate that the vibrations on the hill are significantly larger than those of the top of pier and the flat ground. The frequency components of the vibration are closely relative to the train speed and terrain condition. And the hill location and shape have obvious influence on vibration propagation. This research provides some practical and helpful recommendations for mitigation and control vibration.

Moving model test on the aerodynamic pressure of bilateral inverted-L-shaped noise barriers caused by high-speed trains

With the increasing speed of high-speed trains, the aerodynamic impact of trains on high-speed railway noise barriers has gradually become a focus of attention. Compared with traditional vertical noise barriers, the bilateral inverted-L-shaped noise barrier (BILSNB) has better noise insulation performance, but its aerodynamic impact may be more prominent. In this research, a moving train-BILSNB test system with a scale ratio of 1:16.8 is established, and the influence of train speed and the opening width on the aerodynamic pressure is analysed and discussed. The large eddy simulation is applied to investigate the influence mechanism of flow field on the aerodynamic performance of the BILSNB. The main conclusions are as follows. (1) The pressure amplitude caused by the passing of the train head is 36.67% greater than that generated by the passing of the train tail on average. (2) The maximum pressure of the BILSNB appears at the bottom area. When the height of the measuring point increases from 0.5H to 1.6H, the pressure coefficient of peak positive pressure, peak negative pressure and pressure amplitude decrease by 29.0%, 17.0% and 15.5%, respectively. (3) The aerodynamic pressure in the BILSNB has a longitudinal end effect: the pressure coefficient of positive peak pressure and pressure amplitude at the inlet section are 27.6% and 17.5% higher than the corresponding average value of all middle sections, respectively. (4) The pressure amplitude of the BILSNB is approximately proportional to 2.15 power of the train speed. The pressure coefficient of the BILSNB is approximately a power function of the opening width, and the value range of the index is about (−0.26, −0.30). (5) The mechanism of the longitudinal end effect is as follows: When the train arrives at the inlet section, the high-speed airflow in front of the train head cannot flow around in time resulting in the impact effect of the airflow on the inlet section becomes greater than that on the middle section. The influence mechanism of the opening width is as follows: The narrower the opening width is, the more intense the airflow inside the BILSNB is compressed, and the impact effect of the airflow on the noise barrier is more significant.

Longitudinal-vertical dynamics of a high-speed train rescued by locomotives during braking on grades

This paper describes the longitudinal-vertical coupling dynamics of a high-speed train rescued by locomotives during the braking process on grades. The coupler jackknifing behaviour under compressive forces will affect the running safety of the coupling train. In this paper, the longitudinal-vertical impacts by field testing for the locomotive to train rescue scenario are firstly introduced. The quasi-static force analyses of the train and couplers are carried out to study the coupler jackknifing mechanism on graded tracks. The three-dimensional dynamic model of the train and coupler system is then developed. In this model, the coupler rotational motions, hysteresis characteristic of draft gears, braking characteristic are taken into account. The typical responses during the braking process for the high-speed train rescued by the diesel locomotive are reproduced and verified. The running safety of the longitudinal-vertical interaction for selected scenarios is further evaluated. The Influences of train speed and track gradient on the longitudinal-vertical dynamics are also studied. Two improvement measures, including the limitation of the coupler pitch angle and coupler force, are discussed to provide possible solutions.

Air pressure and comfort study of the high-speed train passing through the subway station

• Numerical model of the train passing through tunnel and station is established. • The pressure variation of the train under different conditions is investigated. • The comfort of passengers under different air tightness is analyzed. • A series of parameters related to train safety and comfort are given. Subway is an increasingly important means of transportation, the influence of the piston effect on the train has attracted extensive attention of researchers. Nowadays, the train speed is increasingly faster, the piston effect caused by the high-speed train is increased accordingly and the pressure fluctuation in tunnel is more complex. In this study, the numerical simulation method is used to study the pressure fluctuation inside and outside the train when the train passes through the tunnel and station. The influence of train speed, mode of the train passing through the station and number of airshafts on the train pressure is analyzed. It is found that both the external and internal pressures of the train increase significantly with the increases of the train speed, and the head carriage bears the most pressure. As the mode of the train passes the station changed, there is a slight variation of train pressure. The airshafts can relieve the pressure inside the train. Finally, passenger comfort under different operating conditions is studied. Different air tightness indexes of the train are compared and analyzed. This study will contribute to the improvement of subway comfort and provide references for the design and operation of the train.

Windproof performance of wind barrier on the aerodynamic characteristics of high-speed train running on a simple supported bridge

The light-weight and high-speed of modern high-speed trains make the safety and comfort of trains running on bridges prominent in windy environments. The installation of wind barriers can significantly improve the running performance of high-speed trains by reducing the action of wind on the train body. By using the developed moving model test rig in wind tunnel, this paper analyzed the dynamic interaction of wind barrier on the aerodynamic characteristics of the moving train. The windproof performance of wind barrier with different air porosity is detailed discussed. Influences of train speed, wind velocity and lane position on train's aerodynamic coefficients are quantified according to the test results. The result reveals the difference of train's aerodynamic coefficients between static and moving model tests and found static model test may overestimate the reduction rates of wind barrier on train's aerodynamic coefficients. The decreased train speed and increased wind velocity increase the change values of side and overturning coefficients caused by the wind barrier, while decrease the change of lift coefficient. The wind barrier introduces the opposite law of changes in trains' aerodynamic coefficients with it running at the different lanes, leading to different windproof effect of wind barrier on train's aerodynamic characteristics.

Exploring pre-crash gate violations behaviors of drivers at highway-rail grade crossings using a mixed multinomial logit model

The highway-rail grade crossings (HRGCs) across the United States have been experiencing about 2500 crashes each year. Previous studies analyzed crash frequencies and fatalities; however, factors pertaining to drivers’ gate violation behaviors are little known. Also, applied methodologies for gate violation behaviors analysis did not consider their heterogeneity across regions. This study uses 20-year of crash data (1999–2018) to evaluate pre-crash drivers’ behaviors at HRGCs. A mixed multinomial logit model was developed to associate such behaviors with demographic factors, vehicle characteristics, temporal and environmental factors, as well as crossing-related factors. The study results indicated a high intra-class correlation coefficient which signifies the importance of including the random-effect parameter in the model. Further, the study found that male drivers are more likely to drive around the gate, while older drivers are more likely to stop and proceed before a train has passed. Furthermore, compared to trucks, all other vehicle types are more likely to drive around the gate. The influence of train speed, vehicle occupancy, visibility, among others, on drivers’ pre-crash behaviors, is also presented. Understanding the impact of these factors on pre-crash behaviors may assist in improving the motorist’s safety at the highway-rail grade crossings across the United States.

Resonances of railway bridges analysed in frequency domain by the modal-force-excitation, bridge-transfer and axle-sequence spectra

In this article, the passage of different trains over different bridges will be studied for resonant excitation. The intensity of the resonance will be estimated in frequency domain by using three separated spectra. At first, the excitation spectrum of the modal forces is built by the mode shape and the passage time of the train over the bridge. The second spectrum is the frequency response function of the bridge which include the modal frequency, damping and mass. The third part is the spectrum of the axle sequence of the train. The influences of train speed, bridge length, bridge support, track irregularities, and train type on the resonance amplitudes will be analysed for each of these spectra separately for getting a better insight. A variety of axle-sequence spectra and corresponding rules will be presented for different vehicles and trains. As examples, the passage of a slow freight train over a long-span bridge, a normal passenger train over a medium-span bridge, and a high-speed train over a short bridge will be analysed. Corresponding measurements show the amplification, but also the cancellation of the subsequent axle responses. Namely in one of the measurement examples, the first mode of the bridge was amplified and the second mode was cancelled at a low speed of the train and vice versa at a higher speed.

Three-dimensional finite element analyses of tyre derived aggregates in ballasted and ballastless tracks

Scrap tyres are a significant source of pollution and pose a grave threat to the environment and human health. The present study aims to examine the application of Tyre Derived Aggregate (TDA) in a concrete slab track and ballasted track and compare its performance in both track forms. In this study, long-term performance of slab track and ballasted track subjected to train induced loading is demonstrated based on the three-dimensional finite element modelling. The most suitable constitutive hyperelastic model for TDA has been identified. Subsequently, the most suitable position for the location of TDA is determined for both track types. A comparative analysis between slab track and ballasted track, with and without TDA, is presented in terms of stress transfer, vibration reduction and displacement (elastic and plastic). It is shown that TDA helps in reducing up to 50% vibration levels of both track types. The influence of train speed and axle load on the vertical and horizontal displacement and stress response of both track forms is shown for a large number of load cycles. Overall, it is observed that the long-term performance of TDA is better in slab track compared to ballasted track.

Moving model experiments on transient pressure induced by a high-speed train passing through noise barrier

The pressure variations on train surfaces and noise barriers induced by a model train passing barriers of 0.125 and 0.25 ​m are studied using a 1/20 moving model. Pressure–time history curves on train surfaces and noise barriers are presented and compared with those of BS EN 2005. The influences of train speed, noise-barrier height, and crossing speed of trains are analyzed with their respective pressure distributions. The results indicate that the pressure amplitudes on train surfaces and noise barriers increase when the train speed and the height of the noise barrier increases, and the pressure amplitudes on the same noise barriers decrease significantly when the heights of the pressure taps increase.

Influences of train speed on permanent deformation of saturated soft soil under partial drainage conditions

To better understand the cumulative settlement of railway ground under the repeated train loads, the effects of cyclic stress (σd), initial static shear stress (σs), and effective mean principal stress (p0') on the permanent deformation of saturated silty clay are examined and evaluated through a series of cyclic load triaxial tests under the partial drainage conditions. As the results, the permanent strain of soil under different test conditions increases exponentially with the increase of Cyclic Stress Ratio (CSR = σd/2p0'), which can be predicted by an empirical prediction formula, irrespective of the cyclic stress (σd) and the effective mean principal stress (p0'). Besides, the influence of different embankment stiffness and train speed on the distribution of cyclic stress (σd) railway ground is analyzed by a three-dimensional (3D) numerical simulation. For ballastless track structures, reducing stiffness of embankment slightly affect cyclic stress (σd) on the railway ground, whereas increasing train speed significantly increases cyclic stress (σd) on the railway ground. Furthermore, the cumulative settlement of soft soil ground calculated by the Chinese code method (CM) and the dynamic method (DM) considering the train speed is compared, which indicates that CM may underestimate the settlement value of railway ground when the train speed increases (i.e., v = 112 m/s).

Numerical investigation on the high‐speed wheel/rail adhesion under the starved interfacial contaminations with surface roughness

AbstractThis paper presents a new numerical model of wheel/rail in rolling contact to study the adhesion mechanism under the starved interfacial contaminations at high speed considering surface roughness. A thermal starved mixed elastohydrodynamic lubrication (EHL) theory is hired in the model. The empirical equations for analysing the contact force of rough surfaces that are based on amount of accurate finite element analysis (FEA) of an elastic‐plastic single‐asperity contact over a rigid flat are proposed. Multilevel method is used to solve the modified Reynolds equations, and sweeping column method is used to solve energy and heat conduction equations. The pressure field, the fractional film content, and the temperature field are obtained through the present model. In addition, the influences of train speed, surface roughness amplitudes, and inlet film thickness on the adhesion coefficient are investigated. The results from the present model have been compared with those from flooded analyses for water and oil‐contamination cases. The numerical results show that the inlet film thickness and the train speed had a significant effect on the wheel/rail adhesion ability.