排序方式: 共有91条查询结果,搜索用时 15 毫秒
41.
A novel method which integrates the topological flexibility of the level-set approach and the simplicity of point-sampled surfaces is proposed. The grid structure resulted from the level-set approach not only offers a wide range of powerful surface editing techniques for the point set surface editing, but also facilitates the topological change with ease. With the aid of point-based resampling, the method updates the surface shape of the point-based geometry quickly without worrying about point connectivity at all. The point set surface can also change its topology properly whenever a collision with other parts of itself is detected. The experiment demonstrates their effectiveness on several scanned objects and scan-converted models. Four examples of surface editing operations: smoothing, tapering, deforming, and Boolean operations, are presented. 相似文献
42.
43.
On the evaluation of a public transportation network quality: Criteria validation methodology 总被引:1,自引:0,他引:1
M. Carmo M. Guedes Natália Oliveira Sérgio Santiago Georgi Smirnov 《Research in Transportation Economics》2012
A public transportation network serves in adequate way a population if it evolves in time following the existent social reality. Changes made in order to improve service must be analyzed and evaluated. The introduction of modern technology to validate the fare card allowed a quick access to important, although incomplete, data. Databases with only the getting in validation information can be used to construct an origin–destination (OD) matrix, allowing a service quality analysis. Here it is presented a basic methodology to rigorously validate service quality criteria considering what might be interesting for the user. The quality analysis philosophy is the following. First, based on automatically gathered data, one reconstructs the origin–destination (OD) matrix, which contains information concerning the number of passengers traveling between zones of a certain region. The OD matrix is used to calculate some criteria characterizing the transportation network quality, such as traveling times, waiting times at a stop or transport occupation. The reconstructed OD matrix always contains errors, which cause errors in the criteria values. How significant are these errors? This question can be answered using our criteria validating methodology, which is based on statistical analysis. It has been implemented at the urban bus transport system of Porto, STCP, allowing the evaluation of the transportation network quality under a number of criteria and guaranteeing rigorous results. 相似文献
44.
Aiming to develop a theoretically consistent framework to estimate travel demand using multiple data sources, this paper first proposes a multi-layered Hierarchical Flow Network (HFN) representation to structurally model different levels of travel demand variables including trip generation, origin/destination matrices, path/link flows, and individual behavior parameters. Different data channels from household travel surveys, smartphone type devices, global position systems, and sensors can be mapped to different layers of the proposed network structure. We introduce Big data-driven Transportation Computational Graph (BTCG), alternatively Beijing Transportation Computational Graph, as the underlying mathematical modeling tool to perform automatic differentiation on layers of composition functions. A feedforward passing on the HFN sequentially implements 3 steps of the traditional 4-step process: trip generation, spatial distribution estimation, and path flow-based traffic assignment, respectively. BTCG can aggregate different layers of partial first-order gradients and use the back-propagation of “loss errors” to update estimated demand variables. A comparative analysis indicates that the proposed methods can effectively integrate different data sources and offer a consistent representation of demand. The proposed methodology is also evaluated under a demonstration network in a Beijing subnetwork. 相似文献
45.
The dispersion of traffic-related pollutants in urban street canyons is of importance for the health and quality of lives. To reveal the inherent principle, researchers have performed a lot of investigations; many dispersion phenomena have also been assessed during recent years. However, the presence of avenue trees in street canyons and their capacity for pollutant dispersion remains partly addressed. In this study, we investigated the effects of avenue trees in urban street canyons on traffic pollutant dispersion. The dispersion of CO concentration in asymmetric street canyons was simulated under varied situations. The computational results showed a good agreement with the experimental data, and the numerical model was validated to be adequate for investigating the pollutant dispersion in street canyons. Then, the numerical simulations were extended to explore the impacts of the effects of avenue trees on CO dispersion; the results indicated that avenue trees generally increase CO concentrations in asymmetric street canyons. When the wind direction is perpendicular to the street axis, a terraced building raises pollutant concentrations at the windward wall and reduces concentration at the leeward wall on the pedestrian levels. Findings of this study are expected to provide significant insight into urban road design and strategy making for avenue tree planting, particularly under the existing worldwide sustainable low-carbon urban development. 相似文献
46.
流场控制体对喷水推进器性能预报影响的研究 总被引:3,自引:0,他引:3
为准确预报喷水推进器设计工况与非设计工况的水动力性能,采用CFD方法对喷水推进器性能预报所需流场控制体进行了研究.在验证计算方法和数值模型可信的基础上,通过对比不同流场控制体的计算结果,分析了流场控制体对喷水推进器性能预报的影响.首先,确定了设计工况下流场控制体的大小;然后,对非设计工况下流场控制体的选取进行了分析讨论.结果表明,非设计工况下流场控制体的大小对喷水推进器性能预报的影响比设计工况大,而且非设计工况下所需流场控制体要大于设计工况时的情况. 相似文献
47.
针对地铁车站环境控制系统设计中常用的几种典型气流组织方案,使用计算流体力学(CFD)的方法,采用重正化群双方程紊流模型,对待建地铁车站及其隧道内的温度场和气流速度场进行三维数值模拟,得到各种方案下的温度和气流速度分布。通过分析和比较,认为屏蔽门方案能够得到最优的站台候车环境,但会使隧道内的温度有较大的升高,且投资较大;在投资较小的3种方案中,混合回/排风方案的效果最佳,对该方案造成的站台上气流速度分布不均匀的情况提出了相应的改善措施,并对数值模拟方法在地铁车站环控系统设计中的应用进行了探讨。 相似文献
48.
49.
50.