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101.
M. K. Rahman
J. B. Caldwell
《Marine Structures》1992,5(6):467-490A rule-based overall design methodology for midship structures of small inland waterways vessels is presented. It is shown how the designer, under conflicting requirements, can select the optimum design by using a combined objective function with priority factors assigned to individual design criteria. The concept of optimization, in large-scale structural design problems, is extended to the local members (the stiffening elements) of the ship structure, so that the stiffeners can be specified by their actual dimensions instead of section moduli. The effects of price-structure (labour rate to material price ratio) and the choice of type of stiffener on design are investigated. Standard sections and optimized fabricated sections are taken as the alternative options for selecting the stiffeners. Conversion of exact mathematical optimum solutions into production-oriented designs is also demonstrated in a series of practical applications of the proposed method. 相似文献
102.
David Kahn André De Palma Jean Louis Deneubourg 《Transportation Research Part B: Methodological》1985,19(2):143-153
Mode choice under stochastically varying demand is studied via a dynamic mathematical model which describes the behavioural interactions between population groups. The model is developed by assuming competing attractivity functions for automobile and public transit which motivate their use subject to an overall demand for transportation. When this demand is allowed to vary stochastically, a set of stochastic differential equations describing the model are obtained. These are solved for their steady-state values. It is found that noisy demand can structure the system qualitatively differently than when the demand is fixed. The noise is found to generally reduce the level of public transit ridership, but it also changes the values of the threshold at which new regimes occur and, most interestingly, it induces new steady-state solutions for ridership at critical values of the variance of demand. In the latter case, noise becomes a source of new possibilities in the system by triggering a steady-state solution not present in the noise-free environment. 相似文献
103.
ABSTRACTThis paper focuses on understanding to what extent the components of LUTI models and their mutual interactions are conceptually represented by eight operational LUTI models. This is important for the understanding of LUTI models’ mechanisms, firstly because it may reduce communication barriers between planning communities, secondly because it may help us understand the models’ applicability, and thirdly it may highlight the models’ shortcomings and point for future research. We present a discussion about what subsystems should be considered for LUTI modelling, from which we derived an “a priori” conceptual ALUTI model (incorporating Activities, besides Land Use and Transport). By comparing the rationale behind each model with this conceptual model, we establish the basis for our review, focussing on whether these models incorporate the ALUTI components, its inner workings and the relationships between these components. Results indicate three main limitations of the reviewed models. First, models not always adequately include all the components of the a priori ALUTI model. Second, the ALUTI subsystems’ internal functions are not explicitly modelled in several of the models reviewed, making it difficult to evaluate how planning decisions affect the subsystem. Third, only few models recognise all mutual interactions, especially in respect to the Activity subsystem. 相似文献
104.
The aim of the present study is twofold. First, to provide new information concerning the technical characteristics of urban bus companies on the basis of a sample of medium and large-size cities in Spain. Second, to analyze the degree of efficiency of those companies and to quantify the reasons for this efficiency. The results should be useful in evaluating possible changes in public policies relating to urban transport, specifically changes in the way the market is organized and in pricing.The analysis is carried out by estimating a cost function. The sample is made up of a panel data set consisting of observations of nine Spanish companies that operated during the period 1983–1995. The specified functional form is translogarithmic. The output unit of measure adopted is bus*kms run. The cost function includes the network length for each company, thus permitting evidence concerning economies of density and economies of scale.The use of panel data allows us to estimate the cost function, taking into account that each company is affected by the specific characteristics of each individual city, the different features of the network in question and by different levels of efficiency. The economies of scale have been calculated, taking into account that the features of the network and of the city – represented by their specific individual effect – will vary with the company's level of output.Finally, an analysis is made of the relative productive efficiency of the companies, as well as of the variables likely to influence that efficiency. 相似文献
105.
Of the many public initiatives used to promote the use of bicycles in the urban environment, the one that has achieved the most spectacular results in a short period of time is the public bicycle hire system. The experience of Seville is one of the most successful internationally, where 6.6 % of mechanised trips were being made by bicycle within 30 months. This paper analyses this experience in the university community, which represents one-third of system users. We conclude that the people who are most satisfied with the system are those who use it for leisure and recreation activities, non-residents of the city, more environmentally aware people and those who have no alternative mode of transportation. Their satisfaction is also closely linked to their appreciation of the bicycles’ level of comfort, the ease with which users can hire bicycles and return them and the small amount of paperwork involved required to sign up for the system. However, user appreciation has fallen over time because the system’s rapid success has caused it to become overloaded. This experience therefore provides one main lesson: the system’s success can result in eventual difficulties. 相似文献