The value of travel time savings in freight transport: a meta-analysis

Transportation - The value of freight travel time savings (VFTTS) is a monetary value that is considered an important input into cost–benefit analysis and traffic forecasting. The VFTTS is...     

Do frequent satisfying trips by public transport impact its intended use in later life?

Transportation - Previous studies have indicated that factors such as the built environment, attitudes and past behaviour can influence travel behaviour. However, the possible effect of travel...     

预应力锚索地梁的内力计算

讨论了高边坡工程中预应力锚索地梁的内力按Winkler假定和弹性半无限地基梁计算等方法,通过工程实例对比了这些计算方法,并根据对计算结果的分析讨论了各自的适用条件.分析了锚索张拉阶段和工作阶段地梁的受力机理,提出应对这两个阶段分别计算地梁的内力,并建议了合理的验算方法.     

Factors contributing to bicycle–motorised vehicle collisions: a systematic literature review

Bicycle–motorised vehicle (BMV) collisions account for the majority of the recorded bicyclists’ fatalities and serious injuries. This systematic review intends to examine the main factors contributing to BMV collisions. We performed a comprehensive literature review on Scopus, TRID, ProQuest, and Web of Science databases. Fifty-nine English-language peer-reviewed articles met the eligibility criteria and were included in the final analysis. The main factors contributing to BMV collisions identified were classified in accordance with a recently published conceptual framework for road safety. The majority of studies have identified factors related to road users’ behaviour (59.3%) and infrastructure characteristics (57.6%). A minority of studies identified variables related to exposure (40.7%) and vehicles (15.3%) as contributor factors to BMV collisions. A small but significant proportion of studies (20.3%) provided evidence that environmental factors may also play a role, although to a lesser extent, in determining BMV collisions. In addition to the three factors comprised in the applied conceptual framework for road safety, we identified environmental conditions as a category of factors contributing to BMV collisions.     

Port competition in Latin America and the Caribbean: the role of concessions and competition policy

Appropriate port regulation and competitive forces tend to be related to higher levels of operational and economic performance of ports. From a policy-making perspective, pursuing efficiency and securing competition in ports to reach a level playing field is a two-step process requiring (1) ex-ante regulations to set the rules that maximize the competition for the market, especially when the policy objective is to attract private operations to ports on competitive concession processes and (2) ex-post competition policy to monitor and preserve competition in the market. This paper studies port regulation in Latin America and the Caribbean (LAC) from a competition perspective, analyzing both ex-ante and ex-post policies implemented in the region. The analysis reveals that the competitive environment in LAC is low, giving room for possible anticompetitive practices in the LAC port sector. Since the end of the 1990s, approximately 80% of container terminals in the region were granted to only five companies. Chile and Mexico have been found to be the best practices in the region, with better conditions assuring robust competition in the market. The main policy implication from this analysis is the need for a stronger involvement of antitrust agencies throughout the port concession processes.     

船舶概念设计阶段多学科和多目标优化研究

船型设计之初,设计者往往会通过船舶多个学科的分析,并从很多船型方案中进行选择比较.该文基于多学科设计优化(MDO)的框架,采用多目标进化算法和决策技术的运用,讨论了船舶概念设计阶段的综合性能优化问题.将船舶总体概念设计按MDO的要求分解为系统控制层和5个子系统,考虑了排水量、综合效率、相对回转直径和造价等多目标函数,采用改进的非支配解排序的多目标进化优化算法(NSGA Ⅱ)和多学科可行解方法(MDF)求出Pareto最优解.然后用逼近理想解的排序方法(TOPSIS)对这些Pareto解进行选优.应用文中的方法,对35 000吨载重量的油船进行了概念设计分析.数值算例表明,综合多学科设计和多目标优化以及决策,能够有效、客观选择合理的船型和主尺度参数.     

船体纵骨典型节点疲劳裂纹扩展寿命评估

基于有限元软件ABAQUS,结合虚拟裂纹闭合法、裂纹扩展判据及子结构技术,应用脚本语言Python开发出模拟疲劳裂纹扩展的程序(FCG-System)。对含初始裂纹的油船纵骨典型节点在侧面压力作用下进行疲劳裂纹扩展数值模拟,并探讨了软趾、背肘板及防倾肘板对疲劳裂纹扩展路径和寿命的影响。结果表明,增设软趾、背肘板或防倾肘板都会使裂纹扩展路径曲率增大,且软趾、防倾肘板可使裂纹扩展寿命增大,背肘板可使裂纹扩展寿命减小。     

Predicting auto-ignition characteristics of RCCI combustion using a multi-zone model

The objective of new combustion concepts is to meet emission standards by improving fuel air mixing prior to ignition. Since there is no overlap between injection and ignition, combustion is governed mainly by chemical kinetics and it is challenging to control the phasing of ignition. Reactivity Controlled Compression Ignition (RCCI) combustion aims to control combustion phasing by altering the fuel ratios of the high- and low octane fuel and injection timings. In this study the dual fuel blend is prepared with gasoline and diesel fuels. The applied injection timings of the diesel are very early (90 to 60° CA bTDC). In the detailed reaction mechanism, n-heptane and iso-octane represent diesel and gasoline fuel, respectively. A multi-zone model approach is implemented to perform RCCI combustion simulation. Ignition characteristics are analyzed by using CA50 as the main parameter. In the experiments for the early direct injection (DI) timing advancing the injection time results in a later ignition. Qualitatively, the trend effect of the diesel injection timing and the effect of the ratio gasoline/diesel are captured accurately by the multi-zone model.     

极限工况下湿式制动器摩擦特性模拟仿真研究

文中在充分考虑全封闭湿式制动器多构层、有间隙结构特点的基础上,建立了全封闭湿式多盘制动器摩擦元件的有限元分析模型。分别从制动强度和制动时间两方面定义极限工况,进而来研究湿式制动器热源、温度场、应力场的特性及变化规律。建立了温度、应力与制动时间、摩擦盘半径的关系曲线,掌握湿式制动器温度场—热变形—热应力三者之间的影响规律并建立相关模型,对改进湿式制动器结构,为制动器冷却系统的设计及冷却时间的循环周期选取提供依据,对提高使用寿命有非常重要的指导意义。     

Activities,resources and inter-organizational relationships: key factors in port competitiveness

In the last decade, the port economics literature has given great emphasis to the Supply Chain Management approach as the new paradigm for the definition of port competitiveness. SCM supports the development of partnerships between the actors of the supply chain and considers the integration of activities and resources along business processes as source of competitive advantage. Nevertheless, the application of SCM approach to the port is particularly compiex given the traditional hostile relationships between port actors. In the effort to overcome such complexity, some authors have considered ports as Logistics Service Providers and interpreted their role within supply chains through the integrative practices undertaken by Global Players–mainly Shipping Companies and Terminal Operators–in the supply of integrated logistics services. Even tough these actors are crucial for the port competitiveness, they determine a passive role of port in the new competitive scenario. The definition of a potential and pro-active role of port in the supply chains is the objective of this paper that presents, through a literature review on SCM and port competitiveness, a new framework for port competitiveness. According to this framework, that is based on the value constellation concept value is generated by joint effort of port actors in the satisfaction of clients' needs, through the exploitation of different I mterdependencies (serial, pooled and reciprocal) between supply chains. In this context, Port Authority has a I fundamental role in identifying those resources–the so called critical assets–that encourage the development of inter-organisational relationships between port actors in the value generation process.