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41.
42.
面向对象的交通网络分布式仿真并行数据结构 总被引:5,自引:0,他引:5
采用面向对象设计思想和交通并行仿真建模理论,对交通网络分布并行仿真系统数据结构进行分析。通过C++语言环境下类定义的方式建立交通网络各元素的对象,并分别对其成员变量与成员函数进行描述,准确表达交通网络节点与路段之间的关系。根据标准模板库函数建立交通网络仿真的共享并行数据结构,并利用SQL数据库技术进行并行数据结构的存取,以减少对内存资源的占用,方便各仿真单元对网络数据的同步访问。最后以24个交叉口组成的交通网络为例进行仿真,仿真结果表明,其速度提高了3.5倍。 相似文献
43.
We analyse mode choice behaviour for suburban trips in the Grand Canary island using mixed revealed preference (RP)/stated
preference (SP) information. The SP choice experiment allowed for interactions among the main policy variables: travel cost,
travel time and frequency, and also to test the influence of latent variables such as comfort. It also led to discuss additional
requirements on the size and sign of the estimated model parameters, to assess model quality when interactions are present.
The RP survey produced data on actual trip behaviour and was used to adapt the SP choice experiment. During the specification
searches we detected the presence of income effect and were able to derive willingness-to-pay measures, such as the subjective
value of time, which varied among individuals. We also studied the systematic heterogeneity in individual tastes through the
specification of models allowing for interactions between level-of-service and socio-economic variables. We concluded examining
the sensitivity of travellers’ behaviour to various policy scenarios. In particular, it seems that contrary to political opinion,
in a crowded island policies penalising the use of the private car seem to have a far greater impact in terms of bus patronage
than policies implying direct improvements to the public transport service. 相似文献
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Contemporary transport planning requires a flexible modelling approach which can be used to monitor the implementation of a long term plan checking regularly its short term performance with easily available data; the original model is periodically updated using low cost information and this allows the evaluation of the changes to the plan which may be required. Such an approach requires models suited to regular updating and to the use of data from different sources. Models to update trip matrices from traffic counts have been available for some time; however, the estimation and/or updating of other model stages with low cost data has escaped analytical treatment. The paper discusses this idea and formulates the updating problem for an example involving a joint destination/mode choice model under various assumptions about the nature of the available data. Analytical solutions are proposed as well as some general conclusions.requests for offprints 相似文献
46.
C. Vanesa Durán Grados Zigor Uriondo Manuel Clemente Francisco J. Jiménez Espadafor Juan Moreno Gutiérrez 《Transportation Research Part D: Transport and Environment》2009,14(1):61-66
Emissions from the exhausts of marine diesel engines comprises several different gases including NOX. These are currently regulated at the international level under Regulation 13 of ANNEX VI of MARPOL 73/78, but this regulation only applies to new engines and is based on bench tests, for only a single engine designated the “parent engine”. Here, the need to take measurements from across their whole range and once in operation on board a vessel is examined. This would not only improve assessment of new equipment against the current regulation, but would also detect defects in the functioning of the engine. 相似文献
47.
Juan Carlos Molinero Frdric Ibanez Sami Souissi Emmanuel Bosc Paul Nival 《Journal of Marine Systems》2008,69(3-4):271
High frequency sampling was performed in daylight hours along a 35 km transect in the Ligurian Sea to investigate the upper layer zooplankton distribution during the spring phytoplankton bloom. The results show detailed spatial structure and biomass of key zooplankton functional groups, copepods, salps and krill larvae, within the different water masses characterizing this region. Although observed values of total copepod biomass distribution were rather constant along the transect, species-specific patterns were observed in the copepod spatial distribution. The larger species Calanus helgolandicus, as well as Centropages typicus, Oithona spp., and Oncaea spp., were associated with the frontal zone. However, Acartia spp. had a scattered distribution, and Clausocalanus/Paracalanus did not have a clear pattern. In addition, krill larvae were concentrated in the frontal area and salps had a scattered pattern. The cross-shore zooplankton distribution appeared strongly influenced by both the Northern Ligurian current governing inshore waters, which acts as a major flushing forcing, and the Ligurian front, which governs offshore waters and may act as retention area for zooplankton. 相似文献
48.
Elisabetta Cherchi Juan de Dios Ortúzar 《Transportation Research Part D: Transport and Environment》2010,15(7):428-442
Recent advances in the specification of the utility function of mixed logit models allow the analyst, in principle, to consider a vast variety of individual heterogeneity. Nevertheless, when estimating the model it is common practice to experience severe difficulties in discriminating between different specifications to infer the “true” data generating process. We investigate possible sources for this difficulty focusing on the confounding effects inherent in two basic assumptions of discrete choice model utilities: linearity in the parameters and added error terms. We analyse the role of these assumptions in giving rise to confounding effects and why this increases the difficulty of discriminating among different structures. Finally, we investigate how these problems may affect benefit appraisal using these models. Empirical evidence is provided for two different environmental contexts and a more typical transport context using various kinds of data. 相似文献
49.
通过实测资料分析的方法,以宜都河道为例,研究了水库蓄水后强约束型分汉河道的冲刷调整规律.在此基础上,进而通过概化模型试验,研究强约束性分汊河道中,河床边界条件的变化对分汊河道水流运动和冲刷调整规律的影响.研究表明:1)由于水库蓄水后河床发生剧烈的冲刷调整,将导致河道河床边界条件特别是两汊高程差的变化,分流格局随之改变;2)河道边界条件发生变化,水流动力轴线可以由稳定于一汊转化为两汉交替,其冲刷调整形式也从一汉冲刷占优转化为两汊冲刷交替占优;3)分汊河道在水库蓄水初期的剧烈调整过程及其河床边界条件的变化一定程度上影响着分汊河道的发展趋势,要充分认识分汊河道在水库蓄水初期剧烈调整过程中所可能出现的问题,引导其朝好的方向发展. 相似文献
50.