Numerical and Experimental Analysis of the Aerodynamic Torque for Axle-Mounted Train Brake Discs

As the velocity of a train increases,the corresponding air pumping power consumption of the brake discs increases proportionally.In the present experimental study,a standard axle-mounted brake disc with circumferential pillars was analyzed using a 1:1 scale model and a test rig in a wind tunnel.In particular,three upstream velocities were selected on the basis of earlier investigations of trains operating at 160,250,and 400 km/h,respectively.Moreover,3D steady computational fluid dynamics(CFD)simulations of the flow field were conducted to compare with the wind tunnel test outcomes.The results for a 3-car train at 180 km/h demonstrated:(1)good agreement between the air resistance torques obtained from the wind tunnel tests and the related numerical results,with differences ranging from 0.95%to 5.88%;(2)discrepancies ranging from 3.2 to 3.8 N·m;(3)cooling ribs contributing more than 60%of the air resistance torque;(4)the fast rotation of brake discs causing a significantly different flow field near the bogie area,resulting in 25 times more air pumping power loss than that obtained in the stationary brake-disc case.

Antiskid Control of Railway Train Braking Based on Adhesion Creep Behavior

In modern trains wheelset skidding leads to the deterioration of braking behavior,the degradation of comfort,as well as a boost in system hazards.Because of the nonlinearity and unknown characteristics of wheelset adhesion,simplifications are widely adopted in the modeling process of conventional antiskid controllers.Therefore,conventional antiskid controllers usually cannot perform satisfactorily.In this paper,systematic computer simulation and field tests for railway antiskid control system are introduced.The operating principal of antiskid control system is explained,which is fundamental to the simulation of antiskid brakes,and the simulation model is introduced,which incorporates both the adhesion creep curve and a pneumatic submodel of antiskid control system.In addition,the characteristics of adhesion curves and the simulation target are also provided.Using DHSplus,the pneumatic submodel is created to analyze the performance of the different control strategies of antiskid valves.Then the system simulation is realized by combining the kinematical characteristics of railway trains and the pneumatic submodel.The simulation is performed iteratively to obtain the optimized design of the antiskid control system.The design result is incorporated in the hardware design of the antiskid control system and is evaluated in the field tests in Shanghai Subway Line 1.Judging by the antiskid efficiency,the antiskid braking performance observed in the field tests shows the superiority of the optimized design.Therefore,the proposed simulation method,especially in view of its ease of application,appears to be a useful one for designing railway antiskid control systems.

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.

Dynamic performance of heavy-haul combined train applying emergency braking on straight line

A heavy-haul train-track coupled model is developed. Taking the emergency braking of the 2×104 t combined train as example, the train longitudinal impulse, the coupler dynamic behaviors and wheel-rail interactions of vehicles distributing in the different positions are analyzed. The results indicate that under the coupler compressing forces, the couplers of middle locomotives may tilt to the free swing limits, which induces the unidirectional tilt of their connected wagon couplers. Consequently, the coupler longitudinal forces produce the lateral components, and then affect the wheel-rail dynamic interaction. The performance of the middle locomotive and their neighboring freight wagons deteriorate significantly, becoming the most dangerous parts in the combined train. The wagons disconnecting with the locomotives can basically keep their couplers to stabilize in the centering positions, even though the maximum coupler longitudinal force acts on it. And its corresponding running safety also has little changes.

Assessment of the curving performance of heavy haul trains under braking conditions

To study the curving performance of trains, 1D and 3D dynamic models of trains were built using nu- merical methods. The 1D model was composed of 210 simple wagons, each allowed only longitudinal motion; whereas the 3D model included three complicated wagons for which longitudinal, lateral, and vertical degrees of freedom were considered. Combined with the calculated results from the 1D model under braking conditions, the behavior of draft gears and brake shoes were added to the 3D model. The assessment of the curving performance of trains was focused on making comparisons between idling and braking conditions. The results indicated the following： when a train brakes on a curved track, the wheel-rail lateral force and derailment factor are greater than under idling conditions. Because the yawing movement of the wheelset is limited by brake shoes, the zone of wheel contact along the wheel tread is wider than under idling conditions. Furthermore, as the curvature becomes tighter, the traction ratio shows a nonlinear increasing trend, whether under idling or braking conditions. By increasing the brake shoe pressure, train steering becomes more difficult.

A simplified pneumatic model for air brake of passenger trains

Braking system performance is relevant for both railway safety and network optimization. Most trains employ air brake systems;air brake systems of freight trains mostly cannot achieve a synchronous application of brake forces, which is usually customary for passenger trains. The paper generalizes a previous air brake pneumatic model to passenger trains and describes the needed modifications. Among them, the way the pressure reduces in the brake pipe is generalized. Moreover, this paper reports an analytical bi-dimensional function for calculating the nozzle diameter equivalent to the electro-pneumatic(EP) or the electronically controlled pneumatic(ECP)brake valve as a function of the wagon length and the time to vent the brake pipe locally. The numerical results of the new model are compared against several experimental tests of high-speed passenger trains of Trenitalia, namely ETR500 and ETR1000. The model is suitable to be integrated into the UIC software TrainDy, aiming to extend its computational field to passenger trains and to simulate the safety of trains during a recovery.

HIL testing of wheel slide protection systems:criteria for continuous updating and validation

Assessment of railway wheel slide protection(WSP) systems involves the execution of complex experimental activities that are quite expensive and time-consuming, since they involve the physical reproduction of degraded adhesion conditions on a real railway line. WSP is devoted to regulating applied braking forces to avoid excessive wheel sliding in case of degraded adhesion conditions between wheel and rail. WSP must be also compliant to safety specifications related to assured braking performances and consumed air. Hardware in the loop(HIL) testing offers an affordable and sustainable way to accelerate these activities optimizing cost, duration and safety of experimental activities performed online. HIL test rigs are subjected to continuous updates, customization and natural ageing of their components. This work investigates the criteria that can be adopted to assure a continuous monitoring and validation of a real WSP test rig, the Italian test rig of Firenze Osmannoro.

Simulating train movement in an urban railway based on an improved car-following model

Based on the optimal velocity car-following model, in this paper, we propose an improved model for simulating train movement in an urban railway in which the regenerative energy of a train is considered. Here a new additional term is introduced into a traditional car-following model. Our aim is to analyze and discuss the dynamic characteristics of the train movement when the regenerative energy is utilized by the electric locomotive. The simulation results indicate that the improved car-following model is suitable for simulating the train movement. Further, some qualitative relationships between regenerative energy and dynamic characteristics of a train are investigated, such as the measurement data of regenerative energy presents a power-law distribution. Our results are useful for optimizing the design and plan of urban railway systems.

Research on the mechanics of high speed rails

In the preceding theme issue on＂Current research progress on mechanics of high speed rails＂（Acta Mechanica Sinica,30：846–909（2014））,we invited several authors in the fiel to present their research on high speed rails（HSR）,including work on dynamic derailment analysis（Ling et al.[1]）,