Rate Of Wheel Load Reduction Research Articles

A New Derailment Detection Method of Rail Vehicles

Aiming at the problem of train derailment detection, researchers at domestic and abroad mainly focus on the derailment coefficient and wheel load reduction rate, but the derailment coefficient and wheel load reduction rate can’t accurately reflect the status of rail vehicle derailment in time. In this paper, a new derailment detection method of rail vehicles is designed based on the lateral acceleration and roll angle as the key characteristic physical quantities of wheelset derailment. Firstly, the virtual simulation method is used to grasp the characteristics of the key physical quantities. Then, the appropriate scheme of derailment detection system is proposed to measure the key characteristic physical quantities and judge whether the rail vehicle is derailed. Finally, the simulation data is used to prove the effectiveness of the detection method, which can lay the foundation for the practical engineering application.

Simulation of dynamic performance and wheel-rail wear of railway wagon under deviation of cargo gravity center

A multibody dynamic model of railway wagon is established by Simpack software, and the derailment coefficient, wheel load reduction rate, impact angle and wear index of freight car are calculated under different gravity center offsets and different curve conditions. The simulation results show that the lateral and longitudinal offsets of cargo gravity center have a great influence on the derailment coefficient, wheel unloading rate, impact angle and wear index of the vehicle. The larger the offset of the cargo gravity center is, the worse the operation performance of the wagon is, the more serious the wheel-rail wear is, and the shorter the transport life of the wagon is. The smaller the radius of the curve is, the greater the impact is.

Characteristics of rail deformation caused by tunnel floor heave and corresponding running risk of high-speed train

• A four-year-long observation of uneven rail deformation is performed in two HSR tunnels. • The predominant wavelength and amplitude of rail deformation in tunnel are 3–30 m and 2–10 mm, respectively. • The heave transfer within track structure exhibits more significantly on wavelength than on amplitude. • Speed raising has strong effects on the magnitude and location of wheel-rail contact force. • The risk of derailment and passenger comfort is more sensitive to short- and long-wavelength floor heave, respectively. Floor heave is a huge threat to the safe operation of high-speed trains in tunnels. However, rare research recognizes the characteristics of the rail irregularity caused by tunnel floor heave and the corresponding running risk of high-speed trains. In this paper, uneven rail profiles observed within four years in two HSR tunnels are used to investigate the temporal variation and spatial distribution of tunnel floor heave. The predominant wavelength and amplitude of the heave profile are determined. Hypothetic floor heave profiles with a wide range of wavelength and amplitude are used as the input in the simulation of the dynamic response of a VRT (vehicle-rail-track) system. Based on the simulation, the transfer laws for the wavelength and amplitude of heave within the track structure are revealed. The wheel-rail contact force, the wheel load reduction rate, and the sperling factor under various floor heave profiles are calculated. The floor heave profile that may lead to a high risk of derailment and low passenger comfort is presented for two train speeds. The research reveals that the predominant range of the wavelength for the rail heave in the tunnel is from 3 m to 30 m, and that of the amplitude is 2 mm to 10 mm. The heave transfer law within the track structure is strongly affected by both the wavelength and amplitude of the floor heave profile. The deformation of the rail varies more significantly on wavelength than on amplitude. Speed raising strongly influences the wheel-rail contact force, the wheel load reduction rate, and the sperling factor. The passenger comfort is more sensitive to longer-wavelength floor heave, whereas the risk of the derailment is more sensitive to shorter-wavelength floor heave.

A vertical coupling dynamic analysis method and engineering application of vehicle–track–substructure based on forced vibration

PurposeThis study aims to propose a vertical coupling dynamic analysis method of vehicle–track–substructure based on forced vibration and use this method to analyze the influence on the dynamic response of track and vehicle caused by local fastener failure.Design/methodology/approachThe track and substructure are decomposed into the rail subsystem and substructure subsystem, in which the rail subsystem is composed of two layers of nodes corresponding to the upper rail and the lower fastener. The rail is treated as a continuous beam with elastic discrete point supports, and spring-damping elements are used to simulate the constraints between rail and fastener. Forced displacement and forced velocity are used to deal with the effect of the substructure on the rail system, while the external load is used to deal with the reverse effect. The fastener failure is simulated with the methods that cancel the forced vibration transmission, namely take no account of the substructure–rail interaction at that position.FindingsThe dynamic characteristics of the infrastructure with local diseases can be accurately calculated by using the proposed method. Local fastener failure will slightly affect the vibration of substructure and carbody, but it will significantly intensify the vibration response between wheel and rail. The maximum vertical displacement and the maximum vertical vibration acceleration of rail is 2.94 times and 2.97 times the normal value, respectively, under the train speed of 350 km·h−1. At the same time, the maximum wheel–rail force and wheel load reduction rate increase by 22.0 and 50.2%, respectively, from the normal value.Originality/valueThis method can better reveal the local vibration conditions of the rail and easily simulate the influence of various defects on the dynamic response of the coupling system.

Dynamic Characteristics of Metro Vehicle under Thermal Deformation of Long-Span Cable-Stayed Bridge

In order to study the influence of thermal deformation of long-span cable- stayed bridge (LSCSB) on the dynamic characteristics of metro vehicle on the bridge, based on the theory of vehicle-track coupled dynamics, the rigid-flexible coupled dynamic model of metro vehicle-track-LSCSB system is established by using finite element method and multi-rigid-body dynamics. Adopting this model, the deformation of LSCSB subject to temperature is analyzed, then the comprehensive effect of track random irregularity and rail deformation caused by temperature load is considered to study the dynamic characteristics of metro vehicle running through the bridge, and finally the influences of temperature increment and running speed on concerned dynamic indices of vehicle are studied. The results show that the LSCSB deforms obviously subject to temperature load, and the overall performance is that the cooling is arched, and the heating is bent, and the shape variable changes almost linearly with the temperature load. According to the parameters studied in this paper, the rail deformation caused by temperature load increases the wheel-rail vertical force, derailment coefficient and wheel load reduction rate by 1.5%, 3.1% and 5% respectively. The vertical acceleration of the vehicle body decreases by 2.4% under the cooling condition, while increases by 3.7% under the heating condition. The dynamic response of the bridge changes under temperature load. The maximum vertical and horizontal displacement in the middle of the main beam span are 6.24 mm and 2.19 mm respectively, and the maximum vertical and horizontal acceleration are 1.29 cm/s2 and 2.54cm/s2 respectively. The derailment coefficient and vertical acceleration of vehicle body are more affected by temperature load, and the wheel load reduction rate and wheel-rail vertical force are more affected by speed. The conclusion of this paper provides a reference for subsequent scholars to study the influence of thermal deformation on the dynamic response of vehicles on LSCSB.

Train Derailment Process Analysis on Heavy Haul Railway Bridge under Ship Impact

In order to research train derailment law under ship impact, the spatial vibration calculation model of a freight train-track-bridge (FTTB) system is used to establish the vibration model of the FTTB system under ship impact. Meanwhile, the calculation method of a train derailment process under ship impact is proposed based on the random analysis method of train derailment energy. Further, the train derailment process on a bridge under ship impact is calculated, and the variation law of the FTTB system spatial vibration response under different impact loads and speeds is analyzed. The results show that the ship impact load has a great influence on wheel lift value. When the impact load is greater than 15 MN, the wheel derails more easily. With the increase of impact load, the derailment coefficient, wheel load reduction rate, and lateral relative displacement of bogie and rail, the lateral displacement of the bridge increases significantly, but the limits of them make it difficult to determine whether the wheel has derailed. The lateral relative displacement of the bogie and rail considering the safety factor is calculated at the moment of derailment, which is taken as the early warning threshold of train derailment. The above conclusions can provide a reference for controlling train safety under ship impact.

Subway Embedded Track Geometric Irregularity Safety Limits

A coupling dynamic model of a subway train and an embedded track is established to study the safety limits of track irregularities. The simulated vehicle system was a 74-degrees of freedom multi-rigid body model, and the rail was a Timoshenko beam. The slab was a three-dimensional solid finite element model. The sensitive wavelength irregularity was first studied, and then the safety limit of the sensitive wavelength was analyzed. The wheel-rail lateral force exhibited a substantial effect on the track alignment and gauge irregularity safety limit. The wheel-rail vertical force and the rate of wheel load reduction significantly affected the height and cross-level irregularity safety limit. The results demonstrate that the safety limits of the alignment, gauge, height, and cross-level embedded track geometric irregularity are 5.3 mm, [− 10.5, 8] mm, 5.6 mm, and 6 mm, respectively.

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 crosswind 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 minimum 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 benchmark 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 coefficient 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.

Wheel Profile Optimization of Speed-up Freight Train Based on Multi-population Genetic Algorithm

The geometric shape of the wheel tread is mathematically expressed, and geometric parameters affecting the shape of the wheel were extracted as design variables. The vehicle dynamics simulation model was established based on the vehicle suspension parameters and track conditions of the actual operation, and the comprehensive dynamic parameters of the vehicle were taken as the design objectives. The matching performance of the wheel equivalent conicity with the vehicle and track parameters was discussed, and the best equivalent conicity was determined as the constraint condition of the optimization problem; a numerical calculation program is written to solve the optimization model based on a multi-population genetic algorithm. The results show that the algorithm has a fast calculation speed and good convergence. Compared with the LM profile, the two optimized profiles effectively reduce the wheelset acceleration and improve the lateral stability of the bogie and vehicle stability during straight running. Due to the optimized profile increases the equivalent conicity under larger lateral displacement of the wheelset, the lateral wheel-rail force, derailment coefficient, wheel load reduction rate, and wear index are reduced when the train passes through the curve line. This paper provides a feasible way to ensure the speed-up operation of a freight train.

Aerodynamic Response and Running Posture Analysis When the Train Passes a Crosswind Region on a Bridge

Trains running on a bridge face more significant safety risks. Based on the Unsteady Reynolds-Averaged Navier–Stokes turbulence model, a three-dimensional Computational Fluid Dynamics computational model of the train–bridge–wind barrier was proposed in this study to measure the transient aerodynamic load of the train. The transient aerodynamic load was input into the wind–train–bridge coupling dynamic system to perform dynamic analysis of running safety. Significant fluctuations in the aerodynamic coefficients were found when the train entered and exited the wind barrier due to the dramatic change in flow pattern. The maximum value of the derailment coefficient decreased with the height of wind barriers, which hardly affected the wheel load reduction rate. The 2 m high wind barrier had no evident influence on the running posture of a general high-speed train, while the 4 m high wind barrier was proven to have better protection. Over-protection was found with an even higher wind barrier.

Interaction Dynamic Response of a High-Speed Train Moving Over Curved Bridges with Deficient or Surplus Superelevation

This paper proposes a three-dimensional dynamic model for high-speed railway trains moving over curved bridges considering the transition curves, circular curves, and superelevation. Key features of this study are to consider the nonlinear geometrical relationships and creep relationships between the wheels and rail, for which the interactive iterative numerical algorithms are developed based on the equations of vertical displacement and rolling of wheelset, and the torsional resonance conditions of the vehicle–bridge system are verified. The results show that the torsional vibration will cause amplification on vertical dynamic response of the beam on the outside edge of the curve. The deficient/surplus superelevation plays an important role in the lateral and torsional angular displacements of the bridge, and the peak of the torsional resonance response can be reduced by adjusting the practical superelevation of the curve. The variations of wheel–load reduction rate and derailment coefficient in the curve section are positively correlated to the deficient/surplus superelevation. The curve radius is the key factor affecting the wear and fatigue of wheel–rail, and when the curve radius is greater than 7000 m, the wear and fatigue can be significantly reduced. Running at a deficient superelevation level can also reduce the wear and fatigue.

Sudden Variation Effect of Aerodynamic Loads and Safety Analysis of Running Trains When Entering Tunnel Under Crosswind

Sudden variation of aerodynamic loads is a potential source of safety accidents of high-speed trains (HSTs). As a follow-up investigation on the aerodynamic response of a HST that enters a tunnel under crosswind environment, this paper focuses on the transient response of a HST’s safety indices based on the train–track coupling interaction model. Firstly, a wind–train–track coupling dynamic model is proposed by introducing transient aerodynamic loads into the vehicle–track system. Secondly, the temporal evolution of safety coefficients indicates that the train’s safety risk increases during tunnel entry with crosswind. Results show that the derailment coefficients and wheel load reduction rate during tunnel entry are not only larger than those in open air, but also those inside the tunnel are due to the sudden disappearance of wind excitation at the tunnel entrance. In addition, the characteristic wind curve, which is the wind velocity against the train speed, is presented for application based on the current specification of the safety criteria threshold. The investigation will be useful in assessing the safety risk of a running train subjected to other aerodynamic attacks, such as the coupling effect of an infrastructure scenario and crosswind in a windy area.

Research on dynamic performance and influence of new mesh-hole elastic pads for railway fasteners in an extremely cold environment

In order to research the dynamic properties of elastic pads for a new pattern mesh-hole in an extremely cold environment, a three-dimensional finite element model of a mesh-hole rail pad is established. The Mooney-Rivlin constitutive model is used to simulate the mechanical properties of rubber materials at different temperatures, and the temperature-dependent characteristics of dynamic stiffness and damping coefficients of the mesh-hole rail pads are analyzed. Based on the vehicle-track coupling dynamic theory, the driving safety and stability properties of the rail pads at extremely cold climate are calculated and analyzed, and the applicability of the mesh-hole rail pads in the extremely cold environment is further evaluated. The research conclusions are as follows. The mesh-hole rail pads have significant low-temperature sensitivity. Namely, above −10°C, the dynamic stiffness and damping coefficients of rail pads are stable, while below this temperature, the dynamic stiffness and damping coefficients of elastic pads increase rapidly. The mesh-hole rail pad has an obvious influence on the dynamic performance of a vehicle-track system when the temperature changes. Namely, the wheel-rail force and wheel load reduction rate increase rapidly with the decrease in temperature, while the vertical dynamic displacement of the rail decreases. Under the extremely cold climate, the wheel load reduction rate of a high-speed passenger vehicle increases sharply, so the method for reducing train speed should be adopted to ensure the safety of train operation.

Dynamic response analysis of the wind–train–bridge coupling based on the stiffness change of the long-span track bridge

In order to analyze the influence of the stiffness change of the long-span track bridge on running safety of the train, a bridge and train analysis model, based on Chongqing Egongyan track bridge, is established to simulate and evaluate the spatial coupling dynamic response of the wind–train–bridge system through stiffness change and to propose the reasonable stiffness limit range of the long-span track suspension bridge. The results show that the dynamic characteristics of the bridge are good, and the safety of train operation and ride comfort meet the requirements when the vertical stiffness is 1/300–1/500 and the lateral stiffness is 1/600–1/1200; the dynamic response of the bridge and the running safety of the train are significantly sensitive to the stiffness change of the bridge, especially when the wind speed is 25 m/s and the vertical stiffness is 1/300, at this time, the derailment coefficient and the wheel load reduction rate reach 0.72 and 0.54, respectively, which are close to the limit standard, indicating that there are some potential safety hazards in train operation.

Research on Parameters of the Curve Negotiation Performance of High-Speed Train Composed of Multiple Vehicles

This paper calculates the wheel/rail nonlinear numerical solution that both changes in trend or in values are relatively consistent conclusion, using different methods of comparative analysis of the cycle dynamics system for studying the influence of the curve negotiating velocity and orbital parameters on the performance of high-speed train. Then based on single-section vehicle system program, a high-speed train coupling system considering vehicle terminal connection device is established. The influence of curve negotiating velocity and orbital parameters on the performance of high-speed train is analyzed. The results show that, with the curve negotiating velocity increasing, the derailment coefficient, rate of wheel load reduction, and the vertical force of wheel rail have a tendency to rise after falling first, lateral force of wheel rail monotone increasing. When the vehicle is in a superelevation state, the indicators are slightly lower than the equilibrium state. While the indicators with parameters change significantly when the vehicle is in a underelevation state. For instance, when the radius of the curve is 5000m to the radius 6700m, the derailment coefficient increases by 53.6% and rate of wheel load reduction is increased by 44.1%.

Dynamic Responses of Vehicle‐CRTS III Slab Track System and Vehicle Running Safety Subjected to Uniform Seismic Excitation

The dynamic model for the vehicle‐CRTS III slab track system is established subjected to uniform seismic excitation, and the calculation program with MATLAB is compiled and verified. The influences of track parameters, seismic intensity, and running speed of the vehicle on the dynamic responses of the system and the vehicle running safety are analyzed. The results show that (1) the track parameters have certain influence on the dynamic responses of the system, and the seismic intensity and the running speed of the vehicle have important influence on the vehicle running safety; (2) the derailment coefficient is highly sensitive to seismic intensity, and the wheel load reduction rate is also highly sensitive to the running speed of the vehicle.

Assessing the effects of subgrade frost heave on vehicle dynamic behaviors on high-speed railway

The subgrade frost heave of high-speed railways has an inevitable effect on track irregularity in severely cold regions. To research the influence of the subgrade frost heave on the dynamic behavior of high-speed railway vehicles, a multi-body dynamics rigid vehicle model and the finite element method flexible track model are coupled using the rigid-flexible coupling dynamics method. The typical frost heave deformation is used as the excitation source, and the effects on dynamic behaviors of the wheel/rail system are analyzed considering various conditions of frost heave, slab track stochastic irregularity, and train speed. The calculation results show that subgrade frost heave has a significant influence on the safety index (the vertical wheel/rail force and the wheel load reduction rate) and the stability index (the vertical acceleration of the carbody and the vertical sperling index) of the vehicle. Both the safety index and the stability index increases linearly as the frost heave amplitude grows and decreases nonlinearly as the frost heave wavelength grows. The safety index is more sensitive to the wavelength, while the stability index is more sensitive to the amplitude. The frost heave region that has an amplitude greater than 15 mm and a wavelength of less than 15 m should be focused on more. Compared to the frost heave deformation, the growth of slab track stochastic irregularity has greater influence on the vertical wheel/rail force. The influence on the other vertical indexes are relatively insignificant. Higher train speeds lead to a worse safety and stability index, and slowing down the speed is an effective way to ensure the safe and stable operation of the high-speed vehicle.

Dynamic behavior of a polyurethane foam solidified ballasted track in a heavy haul railway tunnel

Dynamic behavior of a new type of track using the polyurethane foam solidified ballast in heavy haul railway tunnels is comprehensively investigated in this study. First, a dynamic model of the vehicle–track–tunnel interaction system was developed based on the multi-body system dynamics theory and finite element method. Then, the dynamic effects of the polyurethane foam solidified ballast track on the train and the surrounding infrastructures were calculated and compared to those of the traditional ballasted track. Moreover, the effects of the elastic modulus and the solidified area size of polyurethane foam solidified ballast on the dynamic behavior were analyzed. Results show that, compared to the traditional ballast bed, polyurethane foam solidified ballast decreases the track stiffness and the vibration acceleration of the tunnel, while does not affect the vehicle safety (derailment coefficient and the rate of wheel load reduction). A larger elastic modulus of polyurethane foam solidified ballast has little effects on the wheel–rail interaction and the vibration acceleration of the tunnel, while a smaller modulus results in amplification of the displacements of rails and sleepers. Considering the vehicle–track interaction and tunnel vibration, the optimal elastic modulus of polyurethane foam solidified ballast is suggested to be 60–80 MPa. In addition, smaller solidified area of polyurethane foam solidified ballast presents lower effects on the vibration reduction and rate of wheel load reduction, while larger area leads to a higher derailment coefficient and cost. Therefore, an optimal solidified area size of polyurethane foam solidified ballast with the top width of 0.85 m is recommended.

Dynamic Responses of 87-Type Railway Steel Beam for Rush-repair under Heavy Load Trains

87-type railway steel beam for rush-repair were established by the finite element analysis software ANSYS and five different spans of beams were taken into consideration in the research of dynamic responses. DF4 locomotive hauling C70 freight heavy load marshalling trains model was established by dynamics software UM, in which specific wheel and rail relationship was used to found a combined simulation vibration system. After modeling, process of train running through the bridge was simulated to study several indexes including mid-span vertical deflection, mid-span lateral amplitude, derailment coefficient, rate of wheel load reduction and lateral force of wheel. These indexes made it possible to find out the changing pattern and the conclusion of maximum recommended speed.

Influence of slab arch imperfection of double-block ballastless track system on vibration response of high-speed train

According to the structural damage characteristics of ballastless track of high-speed railway by investigation, a novel method for evaluating the influence of ballastless track of high-speed railway is presented. The dynamic model of ballastless track with damage property is established based on train-track spatial vibration system. The calculated and in situ tested results were compared to certify the model and computation program. Taking the track slab imperfections occurred in a tunnel along the real high-speed railway as an example, the influence of vibration responses of the train-track system with slab imperfections under different conditions is calculated and analyzed in comparison with normal slab. In addition, the maintenance effect on the repaired track structure is evaluated by considering the operate safety and comfort of high-speed train. It is concluded that large amplitude of slab arch imperfection results in higher acceleration of slab and car body. Therefore, train operation speed should be controlled in accordance with the safety standard such as wheel load reduction rate and derailment coefficient. In the case of low amplitude of slab arch imperfection, train operation speed should be controlled in accordance with the comfort standard such as Sperling index. The specific operation velocities were given correspondingly. Therefore, the mechanism and conclusions above can forecast intuitively in the field of track maintenance. The paper proposes a practical and valuable method for evaluating double-block ballastless track of high-speed railway.