深水SPAR风机系统全耦合动力响应分析研究

文章采用联合开发的计算程序对深水SPAR风机的浮体、锚泊和风机各子系统进行了水—气动力的全耦合数值分析,研究了深水浮式风机系统的动力响应特点。浮体水动力计算采用基于二阶精度的混合波浪模型(Hybrid Wave Model)的MORISON公式,锚泊系统采用细长杆理论通过非线性有限元方法实现,风机系统的空气动力分析采用基于多体气动弹性理论的FAST模块。以浮体控制方程为主体,通过模块间的载荷与位移传递在每个时间步上迭代求解,形成完全耦合的时域分析方法。通过对NREL的5MW SPAR风机系统在随机海况下的水动力响应分析,验证了该方法的有效性,并分析了浮式风机子系统间的混合动力作用。     

考虑残余应力效应的深潜器耐压壳体疲劳研究

本文考虑焊接残余应力的影响,给出包含裂纹萌生和裂纹扩展全过程的载人深潜器耐压球壳疲劳寿命预报方法,分别基于局部应力-应变法和能计及负应力比效应的裂纹扩展单一曲线模型预报了耐压球壳的工艺疲劳寿命和使用疲劳寿命,研究焊接残余应力大小对球壳疲劳寿命的影响。结果表明,忽略拉伸残余应力的影响将导致疲劳寿命预测结果偏于危险;耐压球壳整体受压时,拉伸残余应力使得球壳局部区域承受拉-压循环载荷,计算使用疲劳寿命过程中须考虑其影响;降低拉伸残余应力可有效提高耐压球壳的疲劳寿命。     

基于船模水池试验的船舶顺浪纯稳性损失计算扩展模式

船舶顺浪航行的纯稳性损失研究,已成为国际航海界和国际海事组织(IMO)关注的课题之一.在Ю.И.涅查耶夫根据28艘渔船和运输船船模水池试验的船舶顺浪纯稳性损失计算方法的基础上,提出了扩展模式,扩大了其适用范围,并给出了大长宽比(船长/船宽)舰艇纯稳性损失的算例,同时实现了该扩展模式的程序化,生成了实用化的软件.最后通过与CFD试验方法和一般理论计算法所得结果的对比,验证了该扩展模式计算结果的可信度.     

基于相关性模型的舰船系统测试性建模与分析

本文提出一种基于相关性模型的舰船系统级产品的测试性建模与分析方法.该方法通过建立产品任务模型、相关性图示模型等,利用一阶相关性列矢量法求解产品的相关性数学模型,进而建立产品诊断树和进行测试性预计,并为优化产品诊断策略提供建议.同时,根据舰用燃气轮机滑油系统组成和任务特征,建立其典型任务模型并进行精简,并在此基础上进行测试性建模、诊断树建立、测试性预计以及诊断策略优化等工作,为舰船系统级产品的测试性建模、分析和诊断策略研究提供新思路和手段.     

Assessing the impact of reduced visibility on traffic crash risk using microscopic data and surrogate safety measures

Due to the difficulty of obtaining accurate real-time visibility and vehicle based traffic data at the same time, there are only few research studies that addressed the impact of reduced visibility on traffic crash risk. This research was conducted based on a new visibility detection system by mounting visibility sensor arrays combined with adaptive learning modules to provide more accurate visibility detections. The vehicle-based detector, Wavetronix SmartSensor HD, was installed at the same place to collect traffic data. Reduced visibility due to fog were selected and analyzed by comparing them with clear cases to identify the differences based on several surrogate measures of safety under different visibility classes. Moreover, vehicles were divided into different types and the vehicles in different lanes were compared in order to identify whether the impact of reduced visibility due to fog on traffic crash risk varies depending on vehicle types and lanes. Log-Inverse Gaussian regression modeling was then applied to explore the relationship between time to collision and visibility together with other traffic parameters. Based on the accurate visibility and traffic data collected by the new visibility and traffic detection system, it was concluded that reduced visibility would significantly increase the traffic crash risk especially rear-end crashes and the impact on crash risk was different for different vehicle types and for different lanes. The results would be helpful to understand the change in traffic crash risk and crash contributing factors under fog conditions. We suggest implementing the algorithms in real-time and augmenting it with ITS measures such as VSL and DMS to reduce crash risk.     

Intermodal transport in freight distribution: a literature review

There has been significant growth in research on intermodal transport in freight distribution since the 1990s. Differentiating itself from previously published literature reviews, this paper evaluates the current state of this research using Systematic Literature Review methodology. The complementary aims are: (a) to identify the research lines developed and to propose a criterion for classifying the literature, and (b) to discuss the empirical evidence that identifies existing interrelationships. The analysis has enabled three main lines of research to be identified. The first research line, basic principles of intermodal transport, groups together works related to the definition of intermodal transport and the results obtained using this transportation system. The second, improvements to the way that intermodal transport systems work, frames elements and variables that impact intermodal transport systems’ logistics efficiency, such as quality of service, information and communication systems, and freight planning and linkages among system operators to provide an adequate service. Finally, the third line, intermodal transport system modelling, identifies the main variables used to optimise these transport systems, the different focuses and approaches used in modelling, and the advantages and disadvantages of each focus. These research lines take in more specific sublines that incorporate articles that develop related research questions. Lastly, the discussion of the content of each of these research sublines enables us to identify gaps in the literature and comment on directions for future research.     

Long-term impact of the Shinkansen on rail and air demand: analysis with data from Northeast Japan

This paper analyses how the high-speed rail construction in Northeast Japan (Tohoku) has affected total demand and interregional travel patterns. We use annual interregional passenger data from 1989 to 2012 and apply regression analysis with the demand between Tokyo and the Tohoku prefectures as the dependent variable. We distinguish particularly between the ‘Full-’ and the ‘Mini-’ Shinkansen, where the latter are branch services running with reduced speed. We find that the ‘Full-Shinkansen’ quickly increases rail and total public transport trips and generates additional rail demand year on year. The ‘Mini-Shinkansen’ impacts are less pronounced. Furthermore, our analysis shows that the Shinkansen has shifted some demand from air to rail once it started operation and increased rail share gradually. We therefore suggest that predictions of demand impacts should carefully distinguish immediate from gradual impacts. We also discuss differences in regional demand in that not all prefectures have gained equally from Shinkansen construction.     

Genetics of traffic assignment models for strategic transport planning

This paper presents a review and classification of traffic assignment models for strategic transport planning purposes by using concepts analogous to genetics in biology. Traffic assignment models share the same theoretical framework (DNA), but differ in capability (genes). We argue that all traffic assignment models can be described by three genes. The first gene determines the spatial capability (unrestricted, capacity restrained, capacity constrained, and capacity and storage constrained) described by four spatial assumptions (shape of the fundamental diagram, capacity constraints, storage constraints, and turn flow restrictions). The second gene determines the temporal capability (static, semi-dynamic, and dynamic) described by three temporal assumptions (wave speeds, vehicle propagation speeds, and residual traffic transfer). The third gene determines the behavioural capability (all-or-nothing, one shot, and equilibrium) described by two behavioural assumptions (decision-making and travel time consideration). This classification provides a deeper understanding of the often implicit assumptions made in traffic assignment models described in the literature. It further allows for comparing different models in terms of functionality, and paves the way for developing novel traffic assignment models.     

A logit-based model for measuring the effects of transportation infrastructure on land value

Mutual interactions between transportation and land use have long been debated. Despite progress made in computational technology, the study of these interactions is not adequately developed. The most important aspect of such interactions is given by the changes in land values due to changes in transportation infrastructures. We consider the behavioural features of these interactions along with the constraints on the land and/or zoning restrictions and propose a reliable model for the first time to predict land value changes with respect to changes in transportation facilities and accessibility. The proposed model is a logit-based mathematical programming methodology where the relative price of land is predicted with respect to transportation accessibility, neighbourhood amenities, location premium, availability of land, and zoning regulations. A real-world case study is used to exhibit the applicability of the proposed methodology and demonstrate the efficacy of the algorithms and procedures.     

Drivers of transit service loyalty considering heterogeneity between user segments

Users’ loyalty to public transit service is fundamental to promote its popularity in the transportation market. A four-step analytical framework is advanced to investigate the importance of service attributes that heterogeneous transit user segments place on their public transit service loyalty, measured in terms of overall satisfaction and re-use intention. Critical service attributes perceived by transit users that are relevant for loyalty enhancement are explicitly determined, which vary between user segments. It is suggested that the design of strategies aimed to promote the use of public transit by increasing user loyalty towards transit service be targeted at specific attributes that contribute most to loyalty and specific user segments whose original loyalty level is significantly different to others.