Airline competition and network structure

This paper studies airline networks and their welfare implications in an unregulated environment. Competing airlines may adopt either fully-connected (FC) or hub-and-spoke (HS) network structures; and passengers exhibiting low brand loyalty to their preferred carrier choose an outside option to travel so that markets are partially served by airlines. In this context, carriers adopt hubbing strategies when costs are sufficiently low, and asymmetric equilibria where one carrier chooses a FC strategy and the other chooses a HS strategy may arise. Quite interestingly, flight frequency can become excessive under HS network configurations.     

接触网承力索相磨问题探讨

介绍防止接触网承力索相磨常用的几种方法,通过施工、大修和运营检修中对承力索相磨几种方法应用,建议优化接触网结构及采用预绞式保护条的方法,解决承力索相磨的问题。     

基于ANSYS的新型直流断路器触头应力仿真与接触电阻分析

为检验新型直流断路器接触电阻是否处于合理范围,应用有限元软件ANSYS对触头应力进行仿真。总结一些实体建模和网格划分技巧,结合接触电阻的经验估算和试验数据,验证在重点考虑接触电阻影响时触头设计的合理性。     

Effective arterial road incident detection: A Bayesian network based algorithm

Timely and accurate incident detection is an essential part of any successful advanced traffic management system. The complex nature of arterial road traffic makes automated incident detection a real challenge. Stable performance and strong transferability remain major issues concerning the existing incident detection algorithms. A new arterial road incident detection algorithm TSC_ar is presented in this paper. In this algorithm, Bayesian networks are used to quantitatively model the causal dependencies between traffic events (e.g. incident) and traffic parameters. Using real time traffic data as evidence, the Bayesian networks update the incident probability at each detection interval through two-way inference. An incident alarm is issued when the estimated incident probability exceeds the predefined decision threshold. The Bayesian networks allow us to subjectively build existing traffic knowledge into their conditional probability tables, which makes the knowledge base for incident detection robust and dynamic. Meanwhile, we incorporate intersection traffic signals into traffic data processing. A total of 40 different types of arterial road incidents are simulated to test the performance of the algorithm. The high detection rate of 88% is obtained while the false alarm rate of the algorithm is maintained as low as 0.62%. Most importantly, it is found that both the detection rate and false alarm rate are not sensitive to the incident decision thresholds. This is the unique feature of the TSC_ar algorithm, which suggests that the Bayesian network approach is advanced in enabling effective arterial road incident detection.     

高速轮轨接触几何关系的比较分析

高速轮轨接触几何关系研究涉及诸多因素。选择中国车轮踏面LMA与钢轨CHN60、日本新干线圆弧车轮踏面JP-ARC与钢轨JIS60和欧洲标准车轮踏面S1002与钢轨UIS60,比较这3种轮轨关系的几何参数差异,编制了轮轨接触几何的数值分析软件,计算不同轮对内侧距情况下的轮轨接触几何关系,比较在轮对内侧距为1353和1360mm情况下,轮对横移时的滚动圆接触半径差和接触角差的数值计算结果,探讨适应于我国高速车轮踏面形状和轮对内侧距,为高速轮轨关系的深入研究提供基础。     

斜齿轮齿面接触型故障的仿真与诊断方法研究

从齿轮的单自由度振动模型出发,运用差分算法对模型进行求解,得到斜齿轮的振动加速度响应,将齿面接触型故障等效为在局部点突加一个冲击载荷,对齿轮齿面接触型故障进行了仿真,利用小波降噪和共振解调技术分别对仿真的染噪振动加速度信号进行处理,成功地提取了轮齿接触故障的信息。     

二段生物接触氧化法处理城市污水

本文介绍了二段生物接触氧化法的构成、特点、运行情况。高明第二污水处理厂的运行实践表明,二段生物接触氧化法处理效果稳定,体积负荷高,处理时间短,占地面积小,运行操作管理简便,特别适用于厂矿企业及小城镇的生活污水处理。     

Modification of the semi-Hertz wheel–rail contact method based on recalculating the virtual penetration value

ABSTRACT

Wheel–rail contact calculation is of vital importance in vehicle system dynamics. In the existing methods of wheel–rail contact calculation, the finite element method and Kalker’s CONTACT program, which are based on the complementary energy principle, are the two methods with accuracy recognised. However, because of its very slow calculation speed, it cannot meet the requirement of online calculation, so a variety of fast non-elliptic algorithms have been proposed. The semi-Hertz method, which is recognised for its great contributions to the fast wheel–rail contact calculation, is based on the concept of virtual penetration. The calculation of virtual penetration is crucial to evaluate the shape and normal pressure distribution of the contact patch. In practice, the virtual penetration is related to the curvature of the whole contact patch; however, the range of the contact patch is determined by the value of penetration. Such an interaction leads the calculation into a dead loop. In the semi-Hertz method, the penetration is calculated by the Hertz parameters of the initial contact point. Thus, the practical range of the method is limited. In this paper, a fast-iterative method for solving virtual penetration is proposed, and a reliable value of virtual penetration can be obtained under any lateral wheel–rail relative curvature variation with good stability and speed. The normal and tangential solutions are analysed with different methods in this paper.     

Deterioration mechanisms in the wheel–rail interface with focus on wear prediction: a literature review

Wheel–rail interface management is imperative to railway operation and its maintenance represents a major share of the total maintenance cost. In general, the course of events usually called wear is a complicated process involving several modes of material deterioration and contact surface alteration. Thus material removal or relocation, plastic flow and phase transformation may take place at, just below, or in-between the contacting surfaces. A higher degree of predictability of deterioration mechanisms and a firm basis for optimisation of the wheel–rail system are anticipated to reveal a great potential for cost savings. Wear in the sense of material loss and related wheel–rail profile evolution represents one of several modes of damage. The purpose of this survey is to explore research on wear simulation, to some degree extended to neighbouring disciplines. It is believed that a cross-disciplinary approach involving, for instance, adhesive and abrasive wear, surface plasticity, and rolling contact fatigue opens new perspectives to improved damage prediction procedures.     

Black-box modelling of nonlinear railway vehicle dynamics for track geometry assessment using neural networks

ABSTRACT

The use of vehicle dynamics simulation for the track geometry assessment gives rise to new demands. In order to analyse the responses of the vehicles to the measured track geometry defects, the integration of the simulation process in the measurement chain of the track geometry recording car is envisaged. Fast and reliable simulation results are required. This work studies the use of black-box modelling approaches as an alternative to multi-body simulation. The performances of different linear and nonlinear black-box models for the simulation of the vertical and lateral bogie accelerations are compared. While linear transfer function models give good results for the simulation of the vertical responses, their use is not suitable for the highly nonlinear lateral vehicle dynamics. The lateral accelerations are best represented by recurrent neural networks. For the training and validation on high-speed lines using measured vehicle responses, the performance of the black-box simulation outperforms the multi-body simulation. Due to the larger variability of track design and track quality conditions on conventional lines, the model performance degrades and depends significantly on the analysed vehicle type and the track characteristics.