盾构管片接头破坏类型及 参数敏感性分析

盾构管片接头是整环管片力学性能的薄弱部位,容易发生破坏。通过分析盾构管片接头的受力特性、管片接头的破坏类型以及管片内力和其影响因素之间的关系,再进行人工神经网络敏感性分析,计算得到不同影响因素的相对重要性指数大小。研究结果表明:盾构管片接头的破坏类型为受拉破坏;管片外径(RI=54.4%)对管片最大拉应力影响最大,其次是围岩等级(RI=35.3%),隧道埋深和混凝土强度对管片最大拉应力影响较小,相对重要性指数RI小于6%。     

Simulation assessment of incident detection by cellular phone call-in programs

This research study was designed to assess by simulation the efficacy of incident detection by cellular phone call-in programs. The assessment was conducted by varying the proportion of drivers with cellular phones on the highway so as to mirror the cellular industry statistics that show a continued growth of ownership of cellular phones in the United States. An analytical model, which combined simulation and the limited field data available in the literature, was used to determine measures of effectiveness of the cellular phone-based detection system. The results showed that a cellular phone detection system offers fast incident detection times and higher detection rates for both shoulder and lane blocking incidents. For example, in moderate traffic flow (i.e. 1,550 vehicles per hour per lane), 90 percent of incidents blocking two lanes were detected in 1.5 minutes when the proportion of drivers with cellular phones was one out of 10 drivers, even with only 20 percent of them willing to report incidents. When the current proportion of cellular ownership, i.e. 1 out of 3, was used in the simulation, the detection time improved to 0.8 minutes. The simulation analysis of incident detection by cellular phones also showed that there is a direct relationship between the probability of detection and the detection time; that is, the specification of a higher detection rate resulted in slower detection times. This is in sharp contrast with the results of field study of automatic incident detection (AID) systems which demonstrated an inverse relationship between probability of detection and detection time. This revised version was published online in June 2006 with corrections to the Cover Date.     

A multioutput cost function for the services of Spanish ports' infrastructure

A long run multioutput cost function for the infrastructure services of Spanish ports is estimated using 286 observations on 26 ports during 11 years. Cargo specific marginal costs and the degree of economies of scale and scope are calculated up to a port level. Results show that liquid bulk and non-containerised general cargo present the lowest and largest marginal cost, respectively. Increasing returns to scale are present in general and for each and every port. A scope analysis indicates that port specialisation is not appropriate from the viewpoint of infrastructure.     

Fatigue life reliability prediction of a stub axle using Monte Carlo simulation

A stub axle is a part of a vehicle constant-velocity system that transfers engine power from the transaxle to the wheels. The stub axle is subjected to fatigue failures due to cyclic loads arising from various driving conditions. The aim of this paper was to introduce a probabilistic framework for fatigue life reliability analysis that addresses uncertainties that appear in the mechanical properties. Service loads in terms of response-time history signal of a Belgian pave were replicated on a multi-axial spindle-coupled road simulator. The stress-life method was used to estimate the fatigue life of the component. A fatigue life probabilistic model of a stub axle was developed using Monte Carlo simulation where the stress range intercept and slope of the fatigue life curve were selected as random variables. Applying the goodness-of-fit analysis, lognormal was found to be the most suitable distribution for the fatigue life estimates. The fatigue life of the stub axle was found to have the highest reliability between 8000–9000 cycles. Because of uncertainties associated with the size effect and machining and manufacturing conditions, the method described in this paper can be effectively applied to determine the probability of failure for mass-produced parts.     

Editorial: Young maritime researchers—a note of respect

Globalization, liberalization, competition and spatial interaction are significant factors affecting the transformation of manufacturing industries worldwide. In the transportation and logistics industry, however, cooperation is becoming even more critical than competition in determining firms' efficiency. Cooperation has always characterized the liner sector in which strategic alliances, mergers and acquisitions have generated twin effects: notable increases in ship size and falls in freight rates. Meanwhile, the stevedoring industry is undergoing privatization-driven consolidation and the emergence of global pure terminal operators. This article focuses on vertical integration between global carriers and terminal operators. We address the following key current issues: 1. dedicated terminals as a strategy for cutting costs and controlling integrated transport chains;

2. the struggle for supply chain control, involving global carriers versus global terminal operators, driven by financial power and technical and managerial capability.

We close analysing one of the core problems of the market, namely the evolving role of the dedicated terminals. For the pure stevedores they represent an opportunity to secure a cargo, while in the hands of the liners they enable cost stability and the possibility to put pressure on pure terminal operators.     

Book review

Coastal Resource Use: Decisions on Puget Sound by Robert L. Bish, Robert Warren, Louis F. Weschler, James A. Crutchfield, and Peter Harrison.

Published by University of Washington Press in cooperation with Washington Sea Grant Program, 1975. 206 pp., 15 figs.     

Inclusionary housing in the California coastal zone

Abstract

This article evaluates the performance of the California Coastal Commission's inclusionary housing program by examining: (1) the scope of the housing regulations, (2) initial permit decisions on residential projects, (3) the disposition of these permits overtime, and (4) the composition of completed projects and a best‐case projection of possible project completions. Using a case study of Southern California, factors affecting program success are discussed, including the effects of the various regulations, the availability of project subsidies, local government permit policies, and housing market fluctuations. The authors conclude that such state regulatory programs cannot be expected to succeed in urbanized coastal areas without incentives for developers and augmented state agency authority, superseding local land use controls.     

Fuel burn and environmental implications of airline hub networks

Hubs act as switching points for interactions and so are places through which flows are concentrated. This research uses the interactions between a system of cities as an experimental context for understanding selected environmental costs and benefits of concentrated flow. Whether hub based networks create additional environmental costs has been debated in the literature. In this paper, fuel burn is used as an indicator of environmental cost. The essential ideas are: (1) to examine fuel costs associated with larger aircraft; (2) to determine implications of higher loads on dense routes; and (3) to model the resulting implications for hub and gateway location. Variants of these questions apply to passenger and freight flows, and the paper will initially concentrate on passenger models.The paper shows that by modeling fuel burn and introducing a fixed charge (like a set up cost), a multiple allocation hub and spoke model can be adjusted to direct more or less flow onto the inter-facility connector. In other words, usage of multiple connections and direct links can be controlled and modeled as a function of the fixed charge. The resulting networks are characterized by quite different levels of passenger miles, aggregate fuel burn and fixed charges. The preferred network in terms of minimal fuel burn is found by subtracting the fixed set up charge, thereby focusing attention on the modeled fuel burn. The lowest cost set up is a network with a high degree of connectivity, and a pure single assignment hub network has the highest fuel cost (as a result of larger passenger miles needed by connecting paths). The data also allow a tabulation of total passenger miles, which, not surprisingly, track very closely with the fuel burn. In an interesting application of the ideas, it is shown that a fuel efficient network may require a large number of smaller regional jets, and in the interests of avoiding noise and congestion from so many extra airport operations, the carriers may choose to substitute a smaller number of larger planes, thereby slightly increasing fuel needs. This paper also provides a key ingredient for models of an international network where it is impossible to serve many long distance market pairs without consolidation.     

Bonnet weight reduction and VRU protection: Design proposals implementing non-conventional materials

The use of non-conventional and innovative materials is increasingly important in automotive design. They allow reductions in the weights of structures with consequent reductions in fuel consumption and carbon dioxide emissions. At the same time, they ensure excellent safety levels. Once excellent results in terms of active and passive safety have been obtained, the attention of car manufacturers, and of the public opinion, is focused on the safety of vulnerable road users (VRU), pedestrians and cyclists. Some examples concerning the redesign of a bonnet with the double targets of weight reduction and pedestrian safety are illustrated. Hybrid metal/plastic and more conventional metal sheet solutions are compared. The static performance (stiffness and denting resistance), as well as the impact against a pedestrian head, are evaluated by means of FEM models along with actual regulations.     

Changements institutionnels et efficience de l’affrètement au voyage dans le transport fluvial de marchandises

VNF’s statistical data shows a remarkable resilience of inland navigation in France during the recession. Yet at least part of the profession is in crisis: the independent barge operators are now likely to be close to bankruptcy. The small independent barge owners who are the key players in the fully liberalized spot market since 2000 bear the brunt of low prices resulting from a destructive competition which is exacerbated in recession. Transaction costs associated with this new institutional environment exacerbate this procyclical behaviour detrimental to the entire profession. Based on insights from transaction costs economics, the article assesses the conditions of efficiency of voyage charter in the spot market. It analyses these costs through a transactional review of the history of the voyage charter modalities and thereby leading to recommendations to improve organization and efficiency of this market segment.