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11.
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. 相似文献
12.
本文基于伪谱方法对浅海波导环境中的时间反演聚焦和时间反演主动声纳进行了计算,给出了声源频率为100Hz的正演和反演声场分布的演化过程。 相似文献
13.
The most frequently associated options in the physical shipping market are options to extend the charter period on time charters and additional shipment options on contracts of affreightment. The value of freight options, in practice, is estimated mostly by referring to forward curves. An option on freight has different properties from its financial counterparts, and the straightforward adoption of theoretical models does not produce promising results. In this paper, extension options, which have the property of options on futures, were transformed into regular European options before the application of the Black-Scholes model (BSM). The efficient market hypothesis, which justifies the parity of the performance of a long-term charter to that of repetitive short-term charters, worked as the basis for the transformation. The option values determined by the BSM were compared with actual realized values. Additionally, the artificial neural networks (ANN) was employed to derive the option values. This study is meaningful as the first-time application of both the closed-form solution and the ANN to the valuation of physical freight options. The research results can contribute to the quality of chartering decisions. The results could also be used in quantifying credit risk, as extension options tend to be granted to charterers with more creditability. 相似文献
14.
船舶液压起重机延迟反馈吊重消摆控制 总被引:1,自引:1,他引:0
由于操纵和工作环境的变化,起重机的吊重在工作过程中会产生摆动,这种摆动降低了起重机的工作效率和安全性能。文章以集美大学轮机工程实验中心船舶液压起重机为研究对象,采用机电液仿真建模技术及拉格朗日方程,在MATLAB Simulink仿真软件平台上,建立起重机操作液压系统及吊重摆动模型,采用与试验数据对比的方法对所建立的模型进行验证。设计基于吊重摆动位置延迟反馈的控制器,通过将延迟反馈信号叠加到操作信号上的方法实现吊重的消摆控制。结果表明,在各种操作情况下,延迟反馈控制器均能很好地抑制吊重的摆动。 相似文献
15.
Conflict detection (CD) is one of the key functions used to ensure air transport safety and efficiency. In trajectory-based operation (TBO), aircraft are provided with more flexibility in en route trajectory planning and more responsibility for self-separation. The high flexibility in trajectory planning enables random changes in pilot intent, thus increasing the uncertainty in trajectory prediction and CD. This study proposes a novel probabilistic CD approach for TBO in which the uncertainty of pilot intent is taken into account by quantifying the aircraft reachable domain constrained by the flight plan. First, a probabilistic model for aircraft trajectory prediction is developed using the truncated Brownian bridge method. Based on this model, a novel conflict probability estimation method is developed. Finally, the performance of the proposed probabilistic CD approach is demonstrated through an illustrative air traffic scenario. 相似文献
16.
文章针对重庆高家花园嘉陵江大桥实时健康监测系统的挠度长期监测数据,根据监测信息的时间序列呈季节、循环等非平稳状态特点,介绍采用ARMA时间序列预测模型,对挠度监测数据中所包含的外荷载的变化趋势及结构抗力的衰变信息进行动态预测,同时建立了结构外效应的预测函数。结果表明,采用低阶模型能对挠度监测值进行较好的动态预测。 相似文献
17.
地下工程受到周围土体的约束作用,其动力反映与地面工程有所区别,如将源于地面工程的振动法用于地下工程的动力时程计算分析,需要进行相应的改进.文章通过计算分析发现,振动法用于地下工程动力时程计算时,在计算模型边界条件和波动传播时间效应方面不能反映波动对地下工程作用的实质;通过对比分析,在这两个方面对常规振动法进行了改进;提出了适用于地下工程动力时程计算的改进振动法.该方法的计算模型采用左右两侧粘弹性底部固定的人工边界条件,波动输入采用能够反映波动传播时间效应的分层加速度动态输入法,其计算分析结果与理论解吻合较好,适用于地下工程的动力时程计算分析. 相似文献
18.
Use of the private car is often viewed as highly problematic. It is regularly associated with global physical, social and ecological harms such as climate change and the high incidence of lifestyle diseases, including heart disease. Attempts to address these problems generally include provision for day-to-day physical mobility based on alternatives to the private car. Labelled alternative transport, these modes include public transport, walking and cycling. Yet the private car continues as the preferred way to travel in many cities. A deeper understanding of this preference can reveal under explored sites of resistance to alternative transport modes.This paper contributes to these understandings by examining the role the car as a time saving device plays in sustaining automobility. Its central proposition is that individual decisions to drive are not necessarily motivated by the desire to save time. The paper draws on empirical evidence on the journey to work in Australia’s largest city, Sydney. Using a systematic process of trip substitution analysis, a group of people were identified who could use alternative transport to get to work in the same amount of time it currently takes them to drive. These people then participated in a series of in-depth interviews where deeper attachments and motivations for private car use were explored.This approach has enabled development of the multi-layered understanding that informs the central proposition that individual decisions to drive are not necessarily motivated by the desire to save time. Instead, automobility is sustained by appeals to flexibility and autonomy, as well as the interminable pull of the sensory experience provided by the cocoon of the car. This way of thinking about resistance to alternative transport exposes a series of inconsistencies between the expectations of those planning for, and those anticipated to one day use, alternative transport. 相似文献
19.
针对水平地震作用下的桩土相互作用体系,利用有限元软件ANSYS建立了单桩-地基土系统三维有限元模型。运用此模型,对系统进行考虑地基土的材料非线性和桩土界面状态非线性的单桩横向地震响应计算,并进行了自由场响应的计算。计算结果表明:土体的材料非线性与桩土界面状态的非线性特性对单桩的横向水平地震响应有着一定的影响。 相似文献
20.