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.

Influence of Posture Change on Train Running Safety under Crosswind

High-speed trains serving in a crosswind region are bearing more significant safety risks. Based on the three-dimensional (3D) Unsteady Reynolds-Averaged Navier–Stokes (URANS) turbulence model, a Computational Fluid Dynamics (CFD) computational work was conducted in the present study to predict the transient aerodynamic load of the train. The transient aerodynamic load was then employed as the input of the dynamic system to perform a dynamic analysis of running safety. Noticeable changes in the aerodynamic coefficients were found when the train entered and left the crosswind region due to the dramatic change in flow patterns. The original posture also provided significant changes to the train’s aerodynamic responses. A slightly larger maximum derailment coefficient was found on the first bogie of the leading car with a preset posture. There were obvious differences in the displacement characteristics of the three cars in the lateral direction and the rolling rotation, and the magnitude of the posture changes decreased from the leading car to the trailing car. The train with the consideration of posture was proven to withstand weaker crosswinds.

Assessment of derailment risk in railway turnouts through quasi-static analysis and dynamic simulation

Train derailments in railway switches are becoming more and more common, which have caused serious casualties and economic losses. Most previous studies ignored the derailment mechanism when vehicles pass through the turnout. With this consideration, this work aims to research the 3D derailment coefficient limit and passing performance in turnouts through the quasi-static analysis and multi-body dynamic simulation. The proposed derailment criteria have considered the influence of creep force and wheelset yaw angle. Results show that there are two derailing stages in switch panel, which are climbing the switch rail and stock rail, respectively. The 3D derailment coefficient limit at the region of top width 5 mm to 20 mm is much lower than the main track rail, which shows that wheels are more likely to derail in this area. The curve radius before the switch rail is suggested to be set as 350 m. When the curve radius before turnout is 65 m, the length of the straight line between the curve and turnout needs to be larger than 3 m. This work can provide a good understanding of the derailment limit and give guidance to set safety criteria when vehicles pass through the turnout.

Influence of Wheel Profile Wear Coupled with Wheel Diameter Difference on the Dynamic Performance of Subway Vehicles

In view of the coexistence of wheel profile wear (WPW) and wheel diameter difference (WDD) on an actual subway line, a dynamic analysis method based on coupling between WPW and equivalent in-phase WDD was proposed. Based on the measurements from a subway vehicle in operation on this line, dynamics modeling and calculations were performed for a single carriage of this vehicle. Later, the interaction between the effects of WPW and equivalent in-phase WDD on the vehicle dynamic performance was analyzed, and the dynamic response in the presence of coupled damage was compared between the outer and inner wheels. Furthermore, the difference in the dynamic response caused by different positions of the larger-diameter wheels (i.e., on the inner track or outer track) was analyzed for the case where equivalent in-phase WDD occurred between the front and rear bogies. The results show that when the vehicle ran on a straight line, the coupling between WPW and WDD reduced the vehicle’s stability but improved its ride comfort. When the vehicle traveled on a curved line, it showed reductions in the lateral wheel/rail contact force, derailment coefficient, axle lateral force, and wear index if the outer wheels had a larger diameter. As a result, the deterioration of the vehicle’s dynamic performance due to the increasing degree of WPW slowed down, and its curve negotiation performance improved. Meanwhile, the outer wheels had significantly greater lateral wheel/rail contact force, derailment coefficient, and wear index compared to the inner wheels. When a −1 mm WDD was coupled with the worn wheel profile for 14 × 104 kilometers traveled, the dynamic performance indexes of the vehicle were close to or even exceeded the corresponding safety limits. The findings can provide technical support for subway vehicle maintenance.

Study on the Influence of the Marshalling Position of Vehicles Without Braking Function on the Safety of Empty Freight Trains Under Braking Condition

In order to study the influence of the position of without braking function on the safety of empty freight trains, a dynamic model of the locomotive and vehicle-track coupling system was established based on the theory of vehicle system dynamics and the theory of train-track coupling dynamics. And the safety indicators of the empty freight train’s lateral wheelset force, derailment coefficient, and wheel unloading rate were analyzed and compared with the dynamic safety indicators of the empty freight trains with normal braking function, while the vehicles without braking function located in the front, middle and rear parts of the freight train. The results show that during the service brake conditions, whether there are vehicles without braking function or not, the safety performance of the empty freight train is not much different, and all meet the requirements of the GB5599-2019 standard, the safety performance of the vehicles without braking function is not significantly different from that of the normal vehicles, the lateral wheelset force and the derailment coefficient are slightly greater than those in other parts while the vehicles without braking function located at the front part of the train, and the dynamic performance is not much different when the vehicles without braking function located in the middle and rear of the train.

Influence of asymmetric out-of-roundness coupled with wear of subway wheels on vehicle dynamics

Out-of-roundness and tread wear are common types of damage to subway wheels, which greatly affect the dynamic performance of subway vehicles. In light of the coupling and asymmetry of out-of-roundness and tread wear found in real-world subway wheels, an analysis method that considers asymmetric out-of-roundness coupled with tread wear was proposed for vehicle dynamics. A vehicle dynamics model featuring asymmetric out-of-roundness coupled with tread wear was used to investigate the influences of asymmetric wheel damage and coupled damage on the dynamic performance of the vehicle system. The vehicle’s dynamic performance was simulated under different conditions, including asymmetric out-of-roundness and symmetric out-of-roundness, uncoupled damage and coupled damage, asymmetric coupled damage and symmetric coupled damage. Then the estimated data was compared against the measured data. The study finds that the vertical wheel/rail contact force, lateral wheel/rail contact force, derailment coefficient and wheel unloading rate increased in the case of asymmetric out-of-roundness. In the presence of coupled damage, the degree of tread wear had a relatively great influence on the lateral wheel/rail contact force, axle lateral force, and derailment coefficient, but had little influence on the vertical contact force. Compared to symmetric coupled damage, asymmetric coupled damage had a greater influence on peak vertical vibration acceleration and stability index, and their values are closer to the measured values in the case of asymmetric coupled damage. This suggests that the dynamics model that considers asymmetric out-of-roundness coupled with tread wear can provide more accurate results as guidance on the maintenance and overhaul of subway wheels.

Dynamic response of a high-speed train under a type of gust with different durations

In order to study the effect of different gust durations on the safety of a high-speed train passing by a wind-break breach at a speed of 120 km/h, the root locus method is used to analyze the suspension modes of the train under different speeds. The original gust is obtained based on the Unsteady Reynolds-averaged Navier-Stokes (URANS) model when the train passes by a 12 m breach between two windbreaks with a normal crosswind speed of 32 m/s. A group of scaling factors for stretching and compressing the time windows is applied to change the gust duration without changing the amplitude. The results show that when the gust duration is close to the natural period of the suspension system, the train responses and derailment coefficient of the train can be amplified. As the attack angles of the first and second wheelset are still in the clockwise direction when overlooking the wheelset, the first wheelset is more vulnerable than the second wheelset. When the gust duration is longer than the natural period of lower sway, the initial fluctuation of the train response can be relieved.

Analysis on Steering Performance of Active Steering Bogie According to Steering Angle Control on Curved Section

In this paper, prior to the commercialization of a developed active steering bogie, we want to analyze steering performance experimentally according to steering angle level with the aim of obtaining steering performance data to derive practical design specifications for a steering system. In other words, the maximum steering performance can be obtained by controlling the steering angle at the 100% level of the target steering angle, but it is necessary to establish the practical control range in consideration of the steering system cost increase, size increase, and consumer steering performance requirements and commercialize. The steering control test using the active steering bogie was conducted in the section of the steep curve with a radius of curvature of R300, and steering performance such as bogie angle, wheel lateral force, and derailment coefficient were analyzed according to the steering angle level. As the steering angle level increased, the bogie indicated that it was aligned with the radial steering position, and steering performance such as wheel lateral force and derailment coefficient was improved. The steering control at 100% level of the target steering angle can achieve the highest performance of 83.6% reduction in wheel lateral force, but it can be reduced to about one-half of the conventional bogie at 25% level control and about one-third at 50% level. Considering cost rise by adopting the active steering system, this result can be used as a very important design indicator to compromise steering performance and cost rise issues in the design stage of the steering system from a viewpoint of commercialization. Therefore, it is expected that the results of the steering performance experiment according to the steering angle level in this paper will be used as very useful data for commercialization.

Statistical Method for Investigating Transient Enhancements of Dynamical Responses due to Random Disturbances: Application to Railway Vehicle Motion

The paper presents a statistical method for determining a specific variation of random excitations that leads to large transient enhancements (peaks) of a particular dynamical response in a stochastic mechanical system. Such a variation is found by calculating the weighted mean of the excitation variations close to a small number of largest peaks of the response obtained for a single long realization of the system motion. This statistical formula is derived by using the conditional expectation with respect to the rare event of unusually large response values and the ergodic theorem; optionally, a minimal interpeak distance is introduced. A similar formula gives the specific variations of other system variables around the peaks, and it can also be generalized to investigate any multivariable stochastic dynamical system or any set of correlated random signals. This method is applied to transient enhancements of quantities related to running safety and ride comfort of a railway vehicle: the derailment coefficient and the vertical acceleration of the vehicle body, respectively, obtained in simulations of the vehicle motion along a track with random irregularities. The averaged variations of the lateral irregularities and track superelevation close to the track locations of largest peaks of the derailment coefficient show characteristic oscillations leading to enhanced wheelset hunting in a short track section before the peak occurrence. A different pattern is found for the average variation of vertical track irregularities in the vicinity of the track points where largest maxima (or minima) of the vertical body acceleration occur.