Investigation of cavitation inception characteristics of hydrofoil sections via a viscous approach

Unlike traditional approaches based on potential theory, this work investigated the cavitation inception characteristics of hydrofoil sections by solving Reynolds-averaged Navier–Stokes (RANS) equations. The viscous effects at high Reynolds numbers were taken into account through calculation of the eddy viscosity using a k- model. This viscous approach delivers the lift and drag forces in a more self-contained way, which cannot be obtained directly from the potential theory. A comparison with smooth surface measurements validates the proposed numerical method. Two approaches to include the roughness effects are also described. The predictions of cavitation bucket characteristics based on potential theory are more conservative than those reached by the proposed viscous computations. Hydrofoil sections with different camber ratios, foil thicknesses, and Reynolds numbers were studied numerically. A decrease in the Reynolds number tends to increase the cavitation-free region without changing the shape of the steep region. An increase in foil thickness gives a range increase in the angle of attack where no cavitation is expected. An increase in the camber ratio moves the cavitation-free location of the angle of attack, and slightly increases its range.     

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.     

A cost performance analysis of transport infrastructure construction in Slovenia

Due to limited data availability only a few studies have been able to provide statistically significant evidence on cost overruns in transport infrastructure investments and their systematic nature, and fewer still for road infrastructure investments. The body of available evidence refers to the most economically developed countries, while very little evidence was found regarding other countries. In this article the authors focus on cost performance of road infrastructure constructed through the National Motorway Construction Programme in Slovenia. Methodologically the study departs from other studies in this field by building on detailed expenditure data and not aggregate reports from the relevant institution. This enabled the analysis of four individual project cost categories (construction cost, land acquisition damages and others) and comparably more accurate results. A representative sample of randomly selected completed projects in the period 1995–2007 revealed that the cost overruns (19%; SD = 46.10%) in the entire period studied do not appear to be higher than in other comparable studies. At the same time the study results showed that cost overruns were unstable, i.e. much higher for older projects.     

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.     

Analysis of personal action space using a model system with multiple choice structures

The concept of heterogeneity in choice structure is applied in this study to examine individuals’ action space, which is defined in terms of the reported frequencies of visits. A disaggregate model system that predicts the frequency of visits is condensed using a nested logit model with multiple choice structures.     

青岛董家口港城公共交通安全规划探索与实践

城市交通运行安全关乎千家万户,现已成为人们越来越关注的热点,2019年,我国发生的道路交通事故共导致14527人死亡[1],交通事故产生的损失越来越大.公共交通是城市交通的重中之重,其交通安全的社会影响极大.交通事故产生原因受到人、车、道路以及周围环境等多维度因素影响,交通安全规划研究需要围绕以上因素展开.本文以董家口...     

An improved cyclostationary feature detection based on the selection of optimal parameter in cognitive radios

Spectrum sensing is an important part of cognitive radio systems to find spectrum hole for transmission which enables cognitive radio systems coexist with the authorized radio systems without harmful interference. In this paper, an improved cyclostationary feature detection method is proposed to reduce computational complexity without loss of good performance based on the optimal parameter selection strategy for choosing detection parameters of cyclic frequency and lag. Taking binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) signals as examples, the theoretical analyses are presented for choosing the optimal parameters. Simulation results are given to certify the correctness of the proposed parameter selection strategy and show the performance of the proposed method.     

检测故障管道 英国科学家找到了更好的办法，使危险的管道在爆裂前就能被检测出来

锅炉壁中的高压管或高温工艺管道（比如在石化工业中）会变得越来越薄，这在正常使用中会产生灾难性故障的风险。因此必须定期检查锅炉或管壁的厚度，以对任何管壁厘度夏薄的状况进行监控。目前Warwick大学开发出一种新技术，使锅炉及管道的厚度变化更容易被检测，从而更容易防止出现故障。     

Application of Ant System to network design problem

Network design problem (NDP) is the problem of choosing from among a set of alternative projects which optimizes an objective (e.g., minimizes total travel time), while keeping consumption of resources (e.g., budget) within their limits. This problem is difficult to solve, because of its combinatorial nature and nonconvexity of the objective function. Many algorithms are presented to solve the problem more efficiently, while trading-off accuracy with computational speed. This increase in speed stems from certain approximations in the formulation of the problem, decomposition, or heuristics. This study adapts a meta – heuristic approach to solve NDP, namely Ant System (AS). The algorithm is first designed, and then calibrated to solve NDP for the Sioux Falls test network. The behavior of the algorithm is then investigated. The result seems encouraging.     

Modelling route choice behaviour in multi-modal transport networks

The paper presents new findings on the influence of multi-modal trip attributes on the quality and competitiveness of inter-urban multi-modal train alternatives. The analysis covers the entire trip from origin to destination, including access and egress legs to and from the train network. The focus is on preferences for different feeder modes, railway station types and train service types as well as on the relative influence of time elements and transfer penalties. Data from dedicated surveys are used including individual objective choice sets of 235 multi-modal homebound trips in which train is the main transport mode. The observed trips have origins and destinations within the Rotterdam–Dordrecht region in The Netherlands with an average total trip time of 50 minutes. Hierarchical Nested Logit models are estimated to take account of unobserved similarities between alternatives at the home-end and the activity-end of the trip respectively, resulting in two-level nesting structures which differentiate between intercity (IC) and non-intercity railway station types at the upper level and between transit and private access modes at the lower level. In order to reflect the multi-dimensional structure of the data a more advanced so-called Multi-Nested GEV model according to the Principles of Differentiation has been estimated which significantly improves the explanatory power and stresses the importance of the home-end of the multi-modal trip.