关于船体形状对绕射增阻影响的分析

文章主要研究近两年国际海事组织（IMO）海上环境保护委员会（MEPC）所讨论的新船能效设计指数EEDI计算公式中的海洋气象因子fw,认为计算fw时计算船舶的波浪增阻是必需的。文中重点针对EEDI公式中船舶短波绕射增阻的计算方法进行研究。根据三维势流理论计算了集装箱船以及三种简化的集装箱船的波浪漂移力,以分析船体形状对短波绕射增阻的影响,并将结果与日本学者的近似方法做了比较。发现船首的形状对绕射增阻的影响相对较大,船尾次之。文中的研究成果对指导船型设计有一定的参考价值,对完善绕射增阻的计算方法有一定的帮助。     

土工格栅筋材施工机械损伤折减系数研究

土工格栅的最不利状态并不是在使用环节,而是在土工格栅铺设过程中,因此在确定土工格栅的长期强度时必须考虑的主要因素是土工格栅在铺设施工和填料碾压过程中受到的损伤。通过分析国内的一些土工格栅施工机械损伤试验数据和影响损伤的不同因素,给出了计算土工格栅机械损伤折减系数的分项系数,并提出了计算土工格栅施工机械损伤折减系数的计算公式和修正方程。研究成果对确定土工格栅的长期强度具有指导意义。     

Rail access charges in France: Beyond the opposition between competition and financing

Access charges to the railway infrastructures, and in particular of the high speed lines, poses many theoretical and practical questions. Besides the need to decide whether it is better to apply a principle of marginal cost or a full cost approach, a difficulty arises with regard to the possibilities of competition between various operators. France is especially affected by this problem since access charges are particularly high while at the same time competition is non-existent. Is this absence of competition explained by the high level of access charges? After describing the principles which underlie the pricing scheme for high speed trains in France, this paper attempts to find out if these tolls constitute a barrier to entry. After building a model that summarizes the components of supply and demand on the Paris–Lyon journey, this paper shows that the considerations relating to demand (peak hour or off-peak hour) are more fundamental than access charges, which do not in themselves constitute a barrier to entry. Barriers exist, but they involve access charges in relation to the allocation of slots which would make it possible to guarantee certain profitability to a new entrant. Break-even points are proposed which show that SNCF's potential competitors have margins for manoeuvre.     

An exploration of shoppers travel mode choice in visiting convenience stores in the UK

Using data from over 2000 convenience store customers within and outside London, this paper explores how individuals access their convenience stores and how significant the influence of their socio-demographics, shopping types and trip chaining is to their mode choice in visiting the stores. Trip chaining is found to be crucial in influencing customers' mode choice and their visit frequency. The application of logit models also shows that frequent shoppers are the ones most likely to visit the stores on foot. Interestingly, the estimation results also show that the location's density, shopping types and the day of the week are not significant in influencing travel modes. Customers who live in the most deprived areas are less likely to use a private car in visiting the stores.     

天津市校车开行的必要性分析及建议

学生通学出行是居民出行的重要构成部分.通学出行时间与工作日的早晚高峰基本重合.随着城市机动化进程的加快,利用私家车接送孩子的模式加重了城市路网的交通负荷,学校周边交通拥堵问题显著.鉴于此,在天津市第四次综合交通调查的基础上,采用人工计数法和问卷调查法选取四所小学进行交通出行调查.根据调查结果,从缓解交通堵塞、调整居民出行方式结构两方面对天津市实施校车开行的必要性进行分析.最后,从交通管理、法律保障、宣传教育等方面,提出实施校车开行的相关建议.     

The impact of outcome framing and psychological distance of air pollution consequences on transportation mode choice

Recent years, air pollution phenomenon has become one of the crucial problems of Tehran, Iran. Due to main political and economic role of Tehran, population of this metropolis is high and increasing. Urban transportation of this highly populated city contributes more than 70% of air pollution problem in this city. Although a number of urban transport developments, policy measures and regulations have been employed, Tehran’s air pollution has remained crucial thus far. Finding ways to encourage individuals to behave more sustainable can be considered as a substantial approach of tackling environmental problems such as air pollution, since it can be highly cost-effective and fast. This research attempt to evaluate the impacts of two factors of outcome framing and psychological distance of air pollution on citizen’s willingness to behave environmental friendly, particularly to change the travel mode choice. Results illustrate that communicating the consequences of air pollution can provoke individuals’ to act more environment friendly or in particular to change their intention for using more sustainable mode of transportation. Framing the positive consequences of mitigating air pollution take precedence over framing the negative consequences. Moreover the gains of mitigating air pollution have an impact on the willingness to use of bicycle and bus. Results also show that decreasing the psychological distance of air pollution in order to make manipulated frame more personally relevant has no significant impact on respondents.     

多车道交织区车辆跟驰行为风险判别与冲突预测

车路协同系统(IVICS)是保障安全高效出行的新兴技术之一,将高精度车辆轨迹数据与机器学习方法相结合,提出一种可应用于IVICS的多车道交织区的潜在风险判别与冲突预测方法.首先,基于无人机视频,从广域视角提取交织区交通矢量位置、速度等信息,并划分上下游、交织影响区等多个分区;然后,考虑决策行为(车车边缘距离、接近率)与...     

制动条件下连挂救援动车组车钩垂向偏转行为

为了研究连挂救援动车组在制动条件下产生的冲击,建立了不同编组形式下的动车组动力学模型。考虑实际的车钩运动关系和缓冲器迟滞特性,建立了钩缓装置的动力学模型。制定了连挂救援动车组的运行安全阈值,分析了紧急制动时动车和钩缓系统的动力学响应,研究了直线工况下车钩的动态偏转行为与动车编组形式、制动减速度和车钩自由转角等参数对动车组运行安全性的影响。计算结果表明:A类动车组连挂救援B类动车组,直线上制动时连挂断面的压钩力和车钩点头角分别达到799.4 kN和11.5°,钩尾框托梁垂向力和车端垂向相对位移分别达到136.2 kN和126.2 mm,明显超过允许限值,即80 kN和95 mm,车钩力垂向分量会造成车体点头和轮重减载现象,从而导致局部结构破坏和车间运动干涉。当制动档位降到7级或车钩自由点头角低至4°时,钩尾框前箱托梁垂向力低于限值,而车端垂向相对位移超过限值; 当制动档位降到6级或车钩自由点头角低至2°时,可保证车端垂向相对位移低于允许值。     

南海海区航标遥测遥控系统完善与优化

为解决航标遥测遥控系统数据准确、终端在线、监测预警、资产管理和系统平台等5个方面存在的问题,实现对南海航标的有效监测,保障船舶安全航行,对系统需求进行分析,并对其进行完善和优化。从前端通信设计的角度解决数据准确、终端在线方面的问题;利用系统后台运算解决监测预警方面的问题;通过设计实现航标、终端和卡号的自动识别与绑定,解决资产管理方面的问题;对系统结构与功能等进行设计,解决系统平台方面的问题。完善和优化后的系统可有效解决这些问题,在南海海区全面应用该系统的结果表明,该系统的使用能有效保障南海水域船舶的航行安全。     

广州地铁4号线隧道通风系统

介绍广州地铁4号线的隧道通风系统方案——采用隧道风机变频兼作车站隧道排风机,只在出站端设置活塞风道。与传统的系统方案相比,该系统方案可以大量节省初投资,并可以避免因风机全压选择偏大所带来的运行费用的增加。分析该系统方案的设计原则、设备选型原则等,可供方案推广应用所借鉴。