综合运输系统通道功能结构的系统分析与研究

本文分析了综合运输系统通道的构成及各系统之间的关系并运用系统科学的研究方法,对综合运输系统通道的功能结构加以深入分析.本文界定了运输通道的划分,并且阐述了综合运输系统通道与各主要外部影响因素的关系.研究了综合运输系统通道与社会经济、科技进步、供需成本之间的因果反馈环,并在此基础上,从通道内各种运输方式相互协调、竞争的角...     

Assessment of Vulnerability and Integrated Management of Coastal Dunes in Veracruz,Mexico

Dune systems are essential to the ecological balance and sediment inputs of coastal environments and they provide numerous environmental services; however, their existence is threatened by natural and human stressors that contribute to their degradation. Future impacts are expected to be greater because of global climate change in association with further rises in sea level. Beaches and dune systems occupy large areas along the coastline of the state of Veracruz on the Gulf of Mexico. The aim of this study is to establish the intrinsic vulnerability of nine dune fields in Veracruz to current and future impacts and to assess their integrated management status. These dune–beach systems are more vulnerable to the effects of economic activities and land use change than to those induced by natural forces. Results show that six of these dune systems have medium vulnerability and an ecological conservation policy should be adopted; the other three, with high or very high vulnerability, are candidates for a restoration policy.     

Real-time estimation of road–tyre adherence for motorcycles

Improving braking skills of a rider supported by a real-time training device embedded in the motorcycle represents a possible strategy to deal with safety issues associated with the use of powered two wheelers. A challenging aspect of the braking trainer system is the evaluation of the adherence between tyre and road surface on each wheel. This paper presents a possible method to evaluate the current and maximum adherence during a braking manoeuvre. The proposed approach was positively validated through multi-body simulations and experimental data acquired in naturalistic riding conditions.     

Development and validation of a wear model for the analysis of the wheel profile evolution in railway vehicles

The numerical wheel wear prediction in railway applications is of great importance for different aspects, such as the safety against vehicle instability and derailment, the planning of wheelset maintenance interventions and the design of an optimal wheel profile from the wear point of view. For these reasons, this paper presents a complete model aimed at the evaluation of the wheel wear and the wheel profile evolution by means of dynamic simulations, organised in two parts which interact with each other mutually: a vehicle's dynamic model and a model for the wear estimation. The first is a 3D multibody model of a railway vehicle implemented in SIMPACK?, a commercial software for the analysis of mechanical systems, where the wheel–rail interaction is entrusted to a C/C++user routine external to SIMPACK, in which the global contact model is implemented. In this regard, the research on the contact points between the wheel and the rail is based on an innovative algorithm developed by the authors in previous works, while normal and tangential forces in the contact patches are calculated according to Hertz's theory and Kalker's global theory, respectively. Due to the numerical efficiency of the global contact model, the multibody vehicle and the contact model interact directly online during the dynamic simulations.

The second is the wear model, written in the MATLAB® environment, mainly based on an experimental relationship between the frictional power developed at the wheel–rail interface and the amount of material removed by wear. Starting from a few outputs of the multibody simulations (position of contact points, contact forces and rigid creepages), it evaluates the local variables, such as the contact pressures and local creepages, using a local contact model (Kalker's FASTSIM algorithm). These data are then passed to another subsystem which evaluates, by means of the considered experimental relationship, both the material to be removed and its distribution along the wheel profile, obtaining the correspondent worn wheel geometry.

The wheel wear evolution is reproduced by dividing the overall chosen mileage to be simulated in discrete spatial steps: at each step, the dynamic simulations are performed by means of the 3D multibody model keeping the wheel profile constant, while the wheel geometry is updated through the wear model only at the end of the discrete step. Thus, the two parts of the whole model work alternately until the completion of the whole established mileage. Clearly, the choice of an appropriate step length is one of the most important aspects of the procedure and it directly affects the result accuracy and the required computational time to complete the analysis.

The whole model has been validated using experimental data relative to tests performed with the ALn 501 ‘Minuetto’ vehicle in service on the Aosta–Pre Saint Didier track; this work has been carried out thanks to a collaboration with Trenitalia S.p.A and Rete Ferroviaria Italiana, which have provided the necessary technical data and experimental results.     

隧道围岩稳定性改进模糊概率模型及其应用研究

为更加准确有效地判别隧道围岩稳定性,引入RandWPSO-LSSVM(随机权重粒子群算法-最小二乘支持向量机)围岩极限位 移预测模型,对传统模型的隶属函数进行优化,建立围岩稳定性改进模糊概率模型。基于改进模型方法,由围岩位移预测值u、预测 位移标准差、围岩极限位移预测值U 及预测极限位移标准差即可求解隧道围岩稳定概率,并结合8 个工程算例对模型进行验证。 结果表明,改进模型解决了传统模型隶属函数存在的极限位移取值范围不合理的问题,且有效消除了隶属函数线性简化处理导致 的偏差,由其计算的稳定概率与实际情况吻合较好,围岩稳定性评价结果的可靠性更高; 将改进模型应用于实际工程的隧道围岩 稳定性判别中,计算结果能够较好地反映实际工程情况。     

模糊评价方法在船舶动力装置安全评估中的应用

为提高船舶动力装置安全综合评价水平,依据多级模糊安全综合评价基本原理,提出了基于多级模糊安全综合评价理论的船舶动力装置的综合安全评价模型及实现方法,并以实例论证了此方法的可行性.     

基于交通约束的城市最佳用地结构模糊规划模型研究

提出了基于交通系统容量约束的城市土地使用模糊规划模型.该模型以最大开发强度为目标,以交通总生成量不超过路网交通容量为约束条件,确定土地使用优化结构.作为城市规划分析模型中的1个子模型,该模型已在城市的总体规划中得到应用.规划实践表明,模型具有重要的理论价值和较强的可操作性.     

钢筋混凝土结构可靠性模糊综合评估

根据钢筋混凝土结构的可分性，将钢筋混凝土结构分为梁、板、柱、地基基础、围护系统和结构整体性6个相对独立的部分。结合专家经验和已有研究成果，按照各自的准则和指标，构造各项目隶属函数来描述其可靠性的分级，建立各项目模糊关系矩阵。根据层次分析法原理，确定影响其可靠性的各因素权重，提出了钢筋混凝土结构可靠性模糊综合评估新方法。该评估使已有建筑物可靠性鉴定工作更加合理，并为建立相应的专家系统奠定了基础。     

Overview of public transport policy developments in South Africa

In South Africa, a restructuring of the public transport system is currently under way. In the bus industry the tender for contract system is being implemented, the commuter rail sector is being recapitalised and the minibus taxi industry recapitalization programme is in its early stages. Progress with policy implementation across the modes of transport, modal split trends and issues that hamper the full development of the public transport industry are discussed in this paper. Medium to long term policy and strategy initiatives that will further inform the development of the industry are also highlighted in this chapter.