Adaptive Fault Estimation for Dynamics of High Speed Train Based on Robust UKF Algorithm

This paper proposes an adaptive unscented Kalman filter algorithm(ARUKF)to implement fault estimation for the dynamics of high⁃speed train(HST)with measurement uncertainty and time⁃varying noise with unknown statistics.Firstly,regarding the actuator and sensor fault as the auxiliary variables of the dynamics of HST,an augmented system is established,and the fault estimation problem for dynamics of HST is formulated as the state estimation of the augmented system.Then,considering the measurement uncertainties,a robust lower bound is proposed to modify the update of the UKF to decrease the influence of measurement uncertainty on the filtering accuracy.Further,considering the unknown time⁃varying noise of the dynamics of HST,an adaptive UKF algorithm based on moving window is proposed to estimate the time⁃varying noise so that accurate concurrent actuator and sensor fault estimations of dynamics of HST is implemented.Finally,a five-car model of HST is given to show the effectiveness of this method.

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

The ballastless track is nowadays the most popular railway system due to the required low number of maintenance opera-tions 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 embank-ment 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.

Study on dynamic response of high speed train window glass under tunnel aerodynamic effects

Purpose-This paper aims to analyze the bearing characteristics of the high speed train window glass under aerodynamic load effects.Design/methodology/approach-In order to obtain the dynamic strain response of passenger compartment window glass during high-speed train crossing the tunnel,taking the passenger compartment window glass of the CRH3 high speed train onWuhan-Guangzhou High Speed Railway as the research object,this study tests the strain dynamic response and maximum principal stress of the high speed train passing through the tunnel entrance and exit,the tunnel and tunnel groups as well as trains meeting in the tunnel at an average speed of 300 km$h-1.Findings-The results show that while crossing the tunnel,the passenger compartment window glass of high speed train is subjected to the alternating action of positive and negative air pressures,which shows the typical mechanic characteristics of the alternating fatigue stress of positive-negative transient strain.The maximum principal stress of passenger compartment window glass for high speed train caused by tunnel aerodynamic effects does not exceed 5 MPa,and the maximum value occurs at the corresponding time of crossing the tunnel groups.The high speed train window glass bears medium and low strain rates under the action of tunnel aerodynamic effects,while the maximum strain rate occurs at the meeting moment when the window glass meets the train head approaching from the opposite side in the tunnel.The shear modulus of laminated glass PVB film that makes up high speed train window glass is sensitive to the temperature and action time.The dynamically equivalent thickness and stiffness of the laminated glass and the dynamic bearing capacity of the window glass decrease with the increase of the action time under tunnel aerodynamic pressure.Thus,the influence of the loading action time and fatigue under tunnel aerodynamic effects on the glass strength should be considered in the design for the bearing performance of high speed train window glass.Originality/value-The research results provide data support for the analysis of mechanical characteristics,damage mechanism,strength design and structural optimization of high speed train glass.

Formation mechanism of aerodynamic drag of high-speed train and some reduction measures

Aerodynamic drag is proportional to the square of speed. With the increase of the speed of train, aerodynamic drag plays an important role for high-speed train. Thus, the reduction of aerodynamic drag and energy consumption of high-speed train is one of the essential issues for the development of the desirable train system. Aerodynamic drag on the traveling train is divided into pressure drag and friction one. Pressure drag of train is the force caused by the pressure distribution on the train along the reverse running direction. Friction drag of train is the sum of shear stress, which is the reverse direction of train running direction. In order to reduce the aerodynamic drag, adopting streamline shape of train is the most effective measure. The velocity of the train is related to its length and shape. The outer wind shields can reduce train's air drag by about 15%. At the same time, the train with bottom cover can reduce the air drag by about 50%, compared with the train without bottom plate or skirt structure.

Numerical study on wake characteristics of high-speed trains

Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of un- steady Reynold-averaged Navier-Stokes （URANS） and de- tached eddy simulation （DES） are utilized, respectively. Re- suits reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.

Numerical simulation and control of welding distortion for double floor structure of high speed train

The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elastic-plastic FEM analysis based on SYSWELD code.Then,the welding distortion of floor structure was predicted using a linear elastic FEM and shrinkage method based on Weld Planner software.The effects of welding sequence,clamping configuration and reverse deformation on welding distortion of floor structure were examined numerically.The results indicate that the established elastic FEM model for floor structure is reliable for predicting the distribution of welding distortion in view of the good agreement between the calculated results and the measured distortion for real double floor structure.Compared with the welding sequence,the clamping configuration and the reverse deformation have a significant influence on the welding distortion of floor structure.In the case of30 mm reverse deformation,the maximum deformation can be reduced about 70%in comparison to an actual welding process.

Detached-eddy simulation of flow around high-speed train on a bridge under cross winds

In order to describe an investigation of the flow around high-speed train on a bridge under cross winds using detached-eddy simulation(DES), a 1/8th scale model of a three-car high-speed train and a typical bridge model are employed, Numerical wind tunnel technology based on computational fluid dynamics(CFD) is used, and the CFD models are set as stationary models. The Reynolds number of the flow, based on the inflow velocity and the height of the vehicle, is 1.9×10~6. The computations are conducted under three cases, train on the windward track on the bridge(WWC), train on the leeward track on the bridge(LWC) and train on the flat ground(FGC). Commercial software FLUENT is used and the mesh sensitivity research is carried out by three different grids: coarse, medium and fine. Results show that compared with FGC case, the side force coefficients of the head cars for the WWC and LWC cases increases by 14% and 29%, respectively; the coefficients of middle cars for the WWC and LWC increase by 32% and 10%, respectively; and that of the tail car increases by 45% for the WWC whereas decreases by 2% for the LWC case. The most notable thing is that the side force and the rolling moment of the head car are greater for the LWC, while the side force and the rolling moment of the middle car and the tail car are greater for the WWC. Comparing the velocity profiles at different locations, the flow is significantly influenced by the bridge-train system when the air is close to it. For the three cases(WWC, LWC and FGC), the pressure on the windward side of train is mostly positive while that of the leeward side is negative. The discrepancy of train's aerodynamic force is due to the different surface area of positive pressure and negative pressure zone. Many vortices are born on the leeward edge of the roofs. Theses vortices develop downstream, detach and dissipate into the wake region. The eddies develop irregularly, leading to a noticeably turbulent flow at leeward side of train.

Simulation Analysis and Verifcation of Temperature and Stress of Wheel-Mounted Brake Disc of a High-Speed Train

During the braking process,a large amount of heat energy is generated at the friction surfaces between the brake disc and pads and rapidly dissipates into the disc volume.In this paper,a three-dimensional thermo-mechanical coupling model of high-speed wheel-mounted brake discs containing bolted joints and contact relationships is established.The direct coupling method is used to analyze the temperature and stress of the brake discs during an emergency braking event with an initial speed of 300 km/h.A full-scale bench test is also conducted to monitor the temperatures of the friction ring and bolted joints.The simulation result shows that the surface temperature of the friction ring reaches its peak value of 414°C after 102 s of braking,which agrees well with the bench test result.The maximum alternating thermal stress occurs in the bolt hole where the maximum circumferential compressive stress is−658 MPa and the maximum circumferential tensile stress is 134 MPa.During the braking process,the out-of-plane deformation of the middle part of the friction ring is larger than that of the edge,which increases the axial tensile load of the connecting bolt.This work provides support for the design of brake discs and connecting bolts.

Shear Flows in the Near-Turbulent Wake Region of High Speed Trains

Two flow cases for scaled high speed train models with different length are numerically analyzed in the framework of the improved delayed detachededdy simulation model.Specific attention is paid to the shear flows and related mechanisms in the near turbulent wake created by these moving models.In particular,a comparative analysis is made on the distributions of turbulent kinetic energy(TKE)and turbulence production(TP)in planes perpendicular to the streamwise direction.The numerical results suggest that,in the wake region very close to the tail,significant TKE and TP can be ascribed to the dynamic interaction between powerful eddies and strong shear,which explain why these quantities are sensitive to the shear strength.The shear flows are essentially governed by the boundary layers developing along the streamwise direction on the train surfaces,especially from the under-body region and the side walls.For other positions located in the downstream direction away from the tail,the interaction of vortices with the non-slip ground serves as a mechanism to promote transfer of energy from weak eddies to turbulence through the shear present in planes parallel to the ground.

Experimental study on dynamic load magnification factor for ballastless track-subgrade of high-speed railway

The magnitude of dynamic load produced by high-speed trains depends on many factors,of which train speed is the most critical one.However,it is quite difficult to determine the effect of train speed on dynamic load using the theoretical methods due to the complexity of the interaction between vehicle and track-subgrade.Thus large-scale model test has gradually become an important approach for studying dynamic responses of ballastless track-subgrade of high-speed railway.In this study,a full-scale model of ballastless track-subgrade was constructed in accordance with the design and construction standards for Shanghai-Nanjing intercity high-speed railway line firstly.Then,the dynamic strain of slab and the dynamic earth pressure of subgrade were measured by conducting single wheel axle excitation test.In addition,the relationship between the dynamic load magnification factor（DLF） and the train speed was obtained.Finally,the DLF of track-subgrade under different train speeds was proposed,similar to that given by German Railway Standard.

Information fusion of train speed and distance measurements based on fuzzy adaptive Kalman filter algorithm

The measurement accuracy of speed and distance in high speed train directly affects the control precision and driving efficiency of train control system. To improve the capability of train self control, a combined speed measurement and positioning method based on speed sensor and radar which is assisted by global positioning system（GPS） is proposed to improve the accuracy of measurement and reduce the dependence on the ground equipment. In consideration of the fact that the filtering precision of Kalman filter will decrease when the statistical characteristics are changing, this paper uses fuzzy comprehensive evaluation method to evaluate the sub filter, and information distribution coefficients are dynamically adjusted according to filtering reliability, which can improve the fusion accuracy and fault tolerance of the system. The sub filter is required to carry on the covariance shaping adaptive filtering when it is in the suboptimal state. The adjustment factor of error covariance is obtained according to the minimized cost function, which can improve the matching degree between the measured residual variance and the system recursive residual. The simulation results show that the improved filter algorithm can track the changes of the system effectively, enhance the filtering accuracy significantly, and improve the measurement accuracies of train speed and distance.

Analysis of torque transmitting behavior and wheel slip prevention control during regenerative braking for high speed EMU trains

The wheel-rail adhesion control for regenerative braking systems of high speed electric multiple unit trains is crucial to maintaining the stability,improving the adhesion utilization,and achieving deep energy recovery.There remain technical challenges mainly because of the nonlinear,uncertain,and varying features of wheel-rail contact conditions.This research analyzes the torque transmitting behavior during regenerative braking,and proposes a novel methodology to detect the wheel-rail adhesion stability.Then,applications to the wheel slip prevention during braking are investigated,and the optimal slip ratio control scheme is proposed,which is based on a novel optimal reference generation of the slip ratio and a robust sliding mode control.The proposed methodology achieves the optimal braking performancewithoutthewheel-railcontactinformation.Numerical simulation results for uncertain slippery rails verify the effectiveness of the proposed methodology.

Impact of train speed on the mechanical behaviours of track-bed materials

For the 30,000 km long French conventional railway lines(94% of the whole network),the train speed is currently limited to 220 km/h,whilst the speed is 320 km/h for the 1800 km long high-speed lines.Nowadays,there is a growing need to improve the services by increasing the speed limit for the conventional lines.This paper aims at studying the influence of train speed on the mechanical behaviours of track-bed materials based on field monitoring data.Emphasis is put on the behaviours of interlayer and subgrade soils.The selected experimental site is located in Vierzon,France.Several sensors including accelerometers and soil pressure gauges were installed at different depths.The vertical strains of different layers can be obtained by integrating the records of accelerometers installed at different trackbed depths.The experimentation was carried out using an intercity test train running at different speeds from 60 km/h to 200 km/h.This test train was composed of a locomotive(22.5 Mg/axle) and 7 'Corail'coaches(10.5 Mg/axle).It was observed that when the train speed was raised,the loadings transmitted to the track-bed increased.Moreover,the response of the track-bed materials was amplified by the speed rise at different depths:the vertical dynamic stress was increased by about 10% when the train speed was raised from 60 km/h to 200 km/h for the locomotive loading,and the vertical strains doubled their quasistatic values in the shallow layers.Moreover,the stressestrain paths were estimated using the vertical stress and strain for each train speed.These loading paths allowed the resilient modulus Mrto be determined.It was found that the resilient modulus(M_r) was decreased by about 10% when the train speed was increased from 100 km/h to 200 km/h.However,the damping ratio(D_r) kept stable in the range of speeds explored.

A Study on the Structure of Linear Synchronous Motor for 600 km/h Very High Speed Train

Recently, an interest in a hybrid system combining only the merits of the conventional wheel-rail system and Maglev propulsion system is growing as an alternative to high-speed maglev train. This hybrid-type system is based on wheel-rail method, but it enables to overcome the speed limitation by adhesion because it is operated through a non-contact method using a linear motor as a propulsion system and reduce the overall construction costs by its compatibility with the conventional railway systems. Therefore, a comparative analysis on electromagnetic characteristics according to the structural combinations on the stator-mover of LSM （linear synchronous motor） for VHST （very high speed train） maintaining the conventional wheel-rail method is conducted, and the structure of coreless superconducting LSM suitable for 600 km/h VHST is finally proposed in this paper.

Guest editorial: special issue on high mobility wireless communications

The high-speed railway and high-way networks are now expanding at a phenomenal speed in Chinaand in many other parts of the world. The related broadband wireless communication over high-speed trains and highway vehicles is a very challenging task due to hostile transmission channel conditions. The demand for such services is growing rapidly, following the proliferation of laptop/tablet computers and smart phones. This motivates the research on wireless communications in the high mobility environments.

A Non-homentropic Numerical Method for Calculating Pressure Transient in Tunnels with Airshafts

A one dimensional unsteady compressible non homentropic flow prediction method for calculating the pressure transient generated by a high speed train passing through a tunnel with airshafts is presented. Boundary conditions for airshafts are proposed. The calculated results coincide with experiments well. The computational results of a high speed train passing through a tunnel with two airshafts indicate that airshafts can be used to reduce the magnitude of the pressure generated by the train in tunnel effectively.

Energy Saving for Automatic Train Control in Moving Block Signaling System

With rapid development of the railway traffic, the moving block signaling system （MBS） method has become more and more important for increasing the track capacity by allowing trains to run in a shorter time-headway while maintaining the required safety margins. In this framework, the tracking target point of the following train is moving forward with its leading train. This paper focuses on the energy saving tracking control of two successive trains in MBS. Nonlinear programming method is used to optimize the energy-saving speed trajectory of the following train. The real-time location of the leading train could be integrated into the optimization process. Due to simplicity, it can be used for online implementation. The feasibility and effectiveness are verified through simulation. The results show that the new method is efficient on energy saving even when disturbances present.

The Hubei Provincial Building Technology Project in 2021(No.43)

This study aims to optimize energy consumption by modifying the train’s maximal speed and coasting velocity.The methods used in the simulation are brute force and genetic algorithm(GA).The introduction briefly introduces the aim and objectives of the study,as well as the scope and the methodology.The following section gives an overview of the current rail transit development and the existing issues.Despite the rapid development of rail transit and its successful operation,energy consumption is a major issue.The methodology of brute force and genetic algorithm is then introduced.The exact algorithm of the two methods in MATLAB is explained so as to make preparations for the latter simulation optimization.The results from the brute force and genetic algorithm methods are obtained and compared for data analysis.The driving strategy for using STS(Single Train Simulator)is then optimized for an advanced modification.By inserting more values in the code,an optimal speed profile is obtained,and the energy saving target is achieved.Overall,the energy consumption of the studied line could be decreased by optimizing the maximal speed of different sections between the stations and the coasting velocity.However,influencing factors such as service and infrastructure,application of acceleration,and braking power should also be considered as improvements in future studies.

Comparative analysis between single-train passing and double-train intersection in a tunnel

Aerodynamic pressure significantly impacts the scientific evaluation of tunnel service performance.The aerodynamic pressure of two trains running in a double-track tunnel is considerably more complicated than that of a single train.We used the numerical method to investigate the difference in aerodynamic pressure between a single train and two trains running in a double-track tunnel.First,the numerical method was verified by comparing the results of numerical simulation and on-site monitoring.Then,the characteristics of aerodynamic pressure were studied.Finally,the influence of various train-tunnel factors on the characteristics of aerodynamic pressure was investigated.The results show that the aerodynamic pressure variation can be divided into stage I:irregular pressure fluctuations before the train tail leaves the tunnel exit,and stage II:periodic pressure declines after the train tail leaves the tunnel exit.In addition,the aerodynamic pressure simultaneously jumps positively or drops negatively for a single train or two trains running in double-track tunnel scenarios.The pressure amplitude in the two-train case is higher than that for a single train.The maximum positive peak pressure difference(P_(STP))and maximum negative peak pressure difference(P_(STN))increase as train speed rises to the power from 2.256 to 2.930 in stage I.The P_(STP) and P_(STN) first increase and then decrease with the increase of tunnel length in stage I.The P_(STP) and P_(STN) increase as the blockage ratio rises to the power from 2.032 to 2.798 in stages I and II.

Experimental research on reasonable lubricant quantity for transmission gears used in high-speed train

The transmission efficiency, bulk temperature, integrate temperature, and scuffing load of test gears were investigated by a modified FZG rig. These values were measured in four different oil immersion depths with one kind of potential oil that may be used to replace the current synthetic oil in order to find the reasonable lubricant quantity that meets not only the need of transmission performance but also the need of scuffing resistance for high-speed train gears. For the purpose of evaluating the efficiency of the test gears, there were two sensors added to measure the output torque of testing gears and the compensation torque of motor. The minimum lubrication film thickness at the pitch point was gained through an EHL model. The ratio of the film thickness A was used to identify the friction status when scuffing occurred at different oil levels. The results demonstrated that no matter what kind of the immersion depth was, the minimum film thickness on the pitch point was about 0.1 ~m and the ratio of film thickness was about 1.5 when scuffing occurred. According to the relationship of contact pressure and ratio of film thickness at the pitch point, it was found that the immersion depth of pinion should not be less than one module of the gear when the contact pressure of high-speed train gear at pitch point was about 580 MPa, which was the actual pressure at start-up stage.