Mixed RP/SP models incorporating interaction effects

In order to analyse the impact of a new train service in Cagliari (Italy) a databank including information from a revealed preference (RP) and a stated preference (SP) survey was set up. The RP data concern choice between car, bus and train; the SP data consider the binary choice between a new train service (quicker, more frequent, with a lower fare and more stations than the current one) and the alternative currently chosen by car and bus users. Logit models allowing for correlation among RP alternatives were estimated for this mixed RP/SP data set using the artificial tree structure method. The analysis included level-of-service variables measured with an unusually high level of precision, latent or second order variables (such as comfort), inertia and interaction variables. Different specifications of the utility function were tested, including the expenditure rate model, and the effects of these specifications on modelling results are highlighted. Our results show that for a population mainly composed of fixed income workers, the expenditure rate model is superior to the traditional wage rate model, yielding lower and more significant subjective values of time. Moreover, we found that the non-linear specifications appear to be more suitable as not only better model results were obtained, but also the real distribution of the error terms was revealed (i.e. highlighting correlation among public transport options).     

重载电力机车钩缓系统建模研究

针对不同类型重载电力机车钩缓系统建模方法进行研究,提供了非线性迟滞特性缓冲器及两种典型重载电力机车钩缓系统的建模方法,建立了由4节机车及1节简化货车组成的列车模型。以DFC-E100及13A/QKX-100钩缓系统为例,通过列车仿真验证了建模方法的合理性与准确性。研究结果表明,文中所建立的钩缓系统模型能够较好地反映重载电力机车钩缓系统实际运行状态,仿真结果重现了两种钩缓系统在线路试验中表现出的稳定性差异现象。     

基于SD模型的城市群—交通影响机理研究

研究了城市群交通影响预景分析及城市群交通需求分析理论,对基于系统动力学(SD)的交通影响预景分析方法、城市群交通需求分析方法进行了较为深入的探讨,建立了交通影响预景分析模型和城市群交通需求分析模型体系。通过实例验证了所提方法的有效性。     

The shape of MaaS: The potential for MaaS Lite

Mobility as a Service (MaaS) is about improving mobility for people. Since Gothenburg piloted the first multi-modal Mobility as a Service (MaaS) scheme from 2012, there have been many further attempts at introducing connected and bundled services globally, invariably provided as a mobile app and a single, simple ticketing interface. As in any emerging paradigm, the varying flavour, or ‘shapes’ of MaaS that are piloted reflect the search for a sustainable business model and connectivity between transport operators at varying levels that includes risk reallocation and data sharing. The varying levels of success of MaaS and Mobility on Demand (MOD) lead the authors to propose MaaS Lite, which reflects an incremental approach to MaaS based on a simpler organisational arrangement that does not depend upon the introduction of a Mobility Operator as a new player. MaaS Lite also recognises that most trips are not complex at all, often based on one or two connected mechanised modes that meets highly local needs, including FMLM service connectivity.Overall, MaaS is not a ‘one size fits all’ solution for all regions but the benefits of the highly targeted MaaS Lite could realise early public benefits as a first step in the development of a multi-phased ‘services road map’ that evolves towards the implementation of multi-modal, region-wide operationally integrated MaaS. Case studies in Hong Kong and Brisbane demonstrate the merits of MaaS Lite in these two contrasting environments having different regulatory regimes, population densities and levels of private car ownership.     

混合交通流连续动力学建模

对现有的交通流动力学模型进行了简单的评价,在此基础上提出一种新的高阶混合交通流动力学模型,新模型重点研究了混合交通中的干扰项,用粘性项来计算交通阻力,然后对建立的交通流动力模型在特征根问题(车流应是各向异性)、负速度问题(车流倒退)和线性稳定性(主要指高密度下的车流稳定性)问题进行了理论分析。理论分析结果表明,新的高阶交通流动力学模型有效解决了困扰大多数高阶非平衡连续流模型难以处理的问题,而且新模型充分考虑了混合车流中不同车型比例车辆间的粘性阻力,相比较其他模型更能准确反映非纯小车流情况下的交通真实情况。     

Long-term wear and rolling contact fatigue behaviour of a conformal wheel profile designed for large radius curves

There are many reasons to optimise the wheel–rail interface through redesign or maintenance. Minimising wear and rolling contact fatigue (RCF) initiation on wheels and/or rails is often at the forefront of such considerations. This paper covers the design of a conformal wheel profile and its long-term wear and RCF performance to optimise the wheel–rail interface and subsequently reduce the occurrence of surface-initiated RCF on South Africa’s iron ore export line. A comparative study is performed using multibody dynamics simulation together with numerical wheel wear and RCF predictions. The advantages of a conformal wheel profile design are illustrated by evaluating the worn shape and resulting contact conditions of the conformal design. The conformal design has a steadier equivalent conicity progression and a smaller conicity range compared with the current wheel profile design over the wheel’s wear life. The combination of a conformal wheel profile design with 2?mm hollow wear and inadequate adherence to grinding tolerances often result in two-point contact, thereby increasing the probability of RCF initiation. The conformal wheel profile design proved to have wear and potential RCF benefits compared with the current wheel profile design. However, implementation of such a conformal wheel profile must be accompanied by improved rail grinding practices to ensure rail profile compliance.     

基于地质横剖面的隧道工程三维地质建模方法研究

为直观准确地表达地质与隧道工程之间的相互关系,对三维地质与隧道的建模方法进行研究。首先,提出一种基于地质横 剖面轮廓线的归一化三维地质体模型重构方法; 然后,以已建立的三维地质模型为基础,对基于隧道横断面的三维建模及隧道与 地质模型合并过程中的模型切割、分层进行研究; 最后,开发基于断面的三维隧道地质建模及可视化系统。通过建模实例显示: 采 用本文的方法能够取得良好的三维地质及隧道建模效果,直观展示隧道与地层间的相互关系,较为丰富地展现隧道的内部细节。     

Model reduction in vehicle dynamics using importance analysis

Previous work by the authors developed a novel model reduction method, namely importance analysis, that offered a unique set of properties: concurrent dynamic and kinematic reduction, applicability to nonlinear systems, preservation of realisation, and trajectory dependence. This paper investigates the utility of importance analysis as a model reduction tool within the context of vehicle dynamics. To this end, a high-fidelity model of a High Mobility Multipurpose Wheeled Vehicle (HMMWV) is considered, and this model is reduced for three different scenarios. Reduction is achieved in both dynamics and kinematics while preserving the original definition and interpretation of state variables and parameters. Furthermore, the resulting reduced models are very different in terms of complexity, containing only what is necessary for their respective scenarios, and providing important insight and computational savings. The conclusion is that importance analysis can be an invaluable reduction tool in vehicle dynamics, offering the aforementioned unique set of properties.     

250km/h客专及城际线路GSM-R系统服务质量指标的研究

根据250km/h及以下等级客专线路和城际线路的GSM-R系统的需求,分析影响GSM-R网络电路域服务质量指标的因素、单网结构对GSM-R网络服务质量指标的影响,在对已开通客专测试数据进行统计的基础上,得出原有GSM-R电路域服务质量指标仍然适用的结论,并给出单网情况下指标达标的建议。     

Real-time models for wheels and tyres in an object-oriented modelling framework

This article presents models for wheels and tyres in the application field of real-time multi-body systems. For this rather broad class of applications it is difficult to foresee the right level of model complexity that is affordable in a specific simulation. Therefore we developed a tyre model that is adjustable in its degree of complexity. It consists of a list of stepwise developed sub-models, each at a higher level of complexity. These models include semi-empirical equations. The stepwise development process is also reflected in the corresponding implementation with the modelling language Modelica. The final wheel model represents a supermodel and enables users to select the right level of complexity in an unambiguous way.