轨枕间距对钢轨波磨的影响

主要研究轨枕间距对钢轨波磨发展的影响。研究小半径曲线内轨的小矢跨比波磨。这些出现问题的曲线段属于西班牙毕尔巴鄂区域的地铁轨道,铺设着混凝土道床和两层STEDEF型支承垫层。当初始轨枕间距为1000mm时,仅有92万组轮对通过后所测得的波磨深度峰-峰值已经达到0.42mm。随后更换产生波磨的钢轨,比较列车通过时轨枕上方和轨间中部的内轨垂向、横向加速度。当轨枕间距为1000mm时,轨间中部出现频率为204和244Hz的强烈响应,在轨枕上方却未出现。在相邻轨枕中间铺设一个轨枕,使轨枕间距变为500mm,钢轨波磨停止发展。该结论是根据2年的观测结果得到的。     

Effects of bulbous bow on cross-flow vortex structures around a streamlined submersible body at intermediate pitch maneuver: A numerical investigation

A flow field around a streamlined body at an intermediate angle of incidence is dominated by cross-flow separation and vortical flow fields. The separated flow leads to a pair of vortices on the leeside of the body; therefore, it is essential to accurately determine this pair and estimate its size and location. This study utilizes the element-based finite volume method based on RANS equations to compute a 3D axisymmetric flow around a SUBOFF bare submarined hull. Cross-flow vortex structures are then numerically simulated and compared for a submarine with SUBOFF and DRDC STR bows. Computed results of pressure and shear stress distribution on the hull surface and the strength and locations of the vortex structures are presented at an intermediate incidence angle of 20°. A wind tunnel experiment is also conducted to experimentally visualize the vortex structures and measure their core locations. These experimental results are compared with the numerical data, and a good agreement is found.     

Transit service quality analysis using cluster analysis and decision trees: a step forward to personalized marketing in public transportation

A transit service quality study based on cluster analysis was performed to extract detailed customer profiles sharing similar appraisals concerning the service. This approach made it possible to detect specific requirements and needs regarding the quality of service and to personalize the marketing strategy. Data from various customer satisfaction surveys conducted by the Transport Consortium of Granada (Spain) were analyzed to distinguish these groups; a decision tree methodology was used to identify the most important service quality attributes influencing passengers’ overall evaluations. Cluster analysis identified four groups of passengers. Comparisons using decision trees among the overall sample of all users and the different groups of passengers identified by cluster analysis led to the discovery of differences in the key attributes encompassed by perceived quality.     

The Increasing Role of Latent Variables in Modelling Bicycle Mode Choice

The growing interest in promoting non-motorised active transport has led to an increase in the number of studies to identify the key variables associated with bicycle use, and especially those related to the bicycle mode choice problem. This paper presents a comprehensive survey of the modelling literature on the choice of the bicycle for utilitarian purposes, and summarises and assesses the evolution of the explanatory variables and methodologies used. We review both the evolution of the incorporation of latent variables in bicycle mode choice models and the critical role they play. The chronological evolution of the studies is divided into three stages —initial, intermediate and late — according to the different ways of introducing attitudinal or perceptual indicators and latent variables into the models. Our review shows that the incorporation of latent variables in bicycle choice models has increased in the last decade, with a progressive use of more sophisticated methodologies until the arrival of complex models that explicitly and properly deal with psychological latent variables. In fact, with the use of hybrid choice models, latent variables have nowadays become the core of bicycle mode choice models. Based on our review, a set of questions is proposed as a uniform measurement scale to identify attitudes towards bicycling. Recommendations for future research are also presented.     

Modelling bicycle use intention: the role of perceptions

Users’ perceptions are identified as key elements to understand bicycle use, whose election cannot be explained with usual mobility variables and socio-economic characteristics. A hybrid model is proposed to model the intention of bicycle use; it combines a structural equations model that captures intentions and a choice model. The framework is applied to a case of a university campus in Madrid that is studying a new internal bike system. Results show that four latent variables (convenience, pro-bike, physical determinants and external restrictions) help explaining intention to use bike, representing a number of factors that are linked to individual perceptions.     

Forecasting vs. observed outturn: Studying choice in faster inter-island connections

Passenger demand and, in particular, mode choice between the islands of Gran Canaria and Tenerife has experienced important changes in the last decade. In 2005 the jetfoil, which had been the dominant mode for many years, was replaced by a slower but cheaper fast ferry service. This induced important changes in the market shares of all competing modes (airplane, slow ferry and another fast ferry with a shorter in-sea time, but needing a bus connection in land). We estimated several discrete choice models, with data collected two years before, with the aim to test their forecasting performance in relation with observed behaviour. Interestingly, we found that an easy to interpret multinomial logit model allowing for systematic taste variations performed best in forecasting. We also discuss some model assumptions related to forecasting that allow replicating the effects of introducing a new mode more accurately. We finally show how the model can be used to examine the social benefits of a related infrastructure improvement project in the island of Gran Canaria.     

Across the waves: a bibliometric analysis of container shipping research since the 1960s

The paper investigates collaborative and semantic patterns that emerged between 1967 and 2013 about the theme of container shipping based on a corpus of 294 articles published in scholarly journals within the fields of transportation, supply chain, economics, geography, regional planning and development, and operations research. An analysis based on the co-occurrence of title words allows identifying dominant sub-themes and their evolution. Main results point to the gradual diversification of container shipping research, from the dominance of economics towards a more trans-disciplinary set of approaches which integrate port-related activities and multimodal networks. Yet, disciplinary specialization remains strong up to nowadays so that container shipping research remains rather fragmented. While co-authorships have increased over time, they remain polarized by few, weakly connected research battalions. Our study suggests that research on container shipping would benefit from more frequent contacts between such communities to foster in-depth cross-disciplinary studies and fundamental cooperation.     

Numerical Study of the Transition Between Reentrant Jet and Twin Vortex Flow Regimes in Ventilated Cavitation

Contrary to natural cavitation, ventilated cavitation is controllable and is not harmful. It is particularly used to reduce the drag of the hydraulic vehicles. The ventilated cavitation is characterized by various gas regimes. The mechanisms of ventilated cavitation are investigated in the present work with CFD based on a 2D solver. The attention is especially focused on the transition between the reentrant jet and twin vortex regimes. The results confirm that the product of ventilated cavitation number and Froude number is lower than 1 (σ_cFr?<?1) in the twin vortex regime, while it is higher than 1 (σ_cFr?>?1) in the reentrant jet regime, as reported in the literature. Further analysis shows that ventilated cavitation is significantly influenced by the natural cavitation number.     

Multi‐criteria analysis procedure for sustainable mobility evaluation in urban areas

This paper proposes a procedure to evaluate sustainable mobility in urban areas. A set of indicators according to three dimensions of sustainability, i.e., environment, economics, and social aspects, are proposed to evaluate mobility in urban areas. The sustainable mobility evaluation is based on an Index calculated through a weighted multi‐criteria combination procedure. A group of specialists in Brazil was involved in the development of the Index by defining the weights for the criteria. An application of the methodology in the city of Belo Horizonte, capital of the State of Minas Gerais, with 2.24 million inhabitants, is presented to validate the methodology.     

The effect of financial constraints on the optimal design of public transport services

Recent experience with the design of bus services in Santiago, Chile, seems to confirm Jansson's (1980) assertion regarding observed planned bus frequency and size being too low and too large, respectively. We offer an explanation based upon the relation between cost coverage, pricing and optimal design variables. We recall that average social cost decreases with patronage, which generates an optimal monetary fare below the average operators' cost, inducing an optimal subsidy. Then we compare optimal frequency and bus size—those that minimize total social costs—with those that minimize operators' costs only. We show that an active constraint on operators' expenses is equivalent to diminish the value of users' time in the optimal design problem. Inserting this property back in the optimal pricing scheme, we conclude that a self-financial constraint, if active, always provokes an inferior solution, a smaller frequency and, under some circumstances, larger than optimal buses.