Estimation of wheel–rail friction for vehicle certification

In certification of new rail vehicles with respect to running characteristics, a wide variety of operating conditions needs to be considered. However, in associated test runs the wheel–rail friction condition is difficult to handle because the friction coefficient needs to be fairly high and the friction is also generally hard to assess. This is an issue that has been studied in the European project DynoTRAIN and part of the results is presented in this paper. More specifically, an algorithm for estimating the wheel–rail friction coefficient at vehicle certification tests is proposed. Owing to lack of some measurement results, the algorithm here is evaluated in a simulation environment which is also an important step towards practical implementation. A quality measure of the friction estimate is suggested in terms of estimated wheel–rail spin and total creep. It is concluded that, tentatively, the total creep should exceed 0.006 and the spin should be less than 1.0 m^?1 for the algorithm to give a good friction estimate. Sensitivity analysis is carried out to imitate measurement errors, but should be expanded in further work.     

A three-stage evacuation decision-making and behavior model for the onset of an attack

Pedestrian behavior models have successfully reproduced human movement in many situations. However, few studies focus on modeling human behavior in the context of terrorist attacks. Terrorist attacks commonly occur in crowded public areas and result in a large number of casualties. This paper proposes a three-stage model to reproduce a series of complex behaviors and decision-making processes at the onset of an attack, when pedestrians generally do not have clear targets and have to deal with fuzzy information from the attack. The first stage of the model builds a Bayesian belief network to represent the pedestrians’ initial judgment of the threat and their evacuation decisions. The second stage focuses on pedestrians’ global assessment of the situation through an analogy with diffusion processes. The third stage uses a cost function to reproduce the trade-offs of distance, safety, and emotional impact when considering a path to take. The model is validated using a video from the November 2015 Paris attack. The behavioral characteristics and trajectories of three pedestrians extracted from the video are reproduced by the simulation results based on the model. The research can be used to set rules when performing risk analysis and strategic defensive resource allocation of terrorist attacks using agent-based simulation methods.     

交通恐怖袭击特点及反恐措施研究

统计分析了2003年至2009年全球针对交通的恐怖袭击事件,表明交通恐怖袭击主要目标由传统的航空交通转向地面交通、袭击手段以爆炸为主,重大交通恐怖袭击的时间选择意图明显.概述了国外交通反恐的主要措施,建议我国加强交通反恐立法、交通反恐技术及交通设施防恐怖爆炸研究.     

无线网络可靠性分析与计算方法研究

网络可靠性是网络安全性能的重要方面,通过对无线网络可靠性的分析和计算,可以有效地反映网络攻击对其造成的影响。这里提出了节点毁坏度、关键链路毁坏度、网络恢复时间和网络公平性四个指标来衡量网络的可靠性,并提出利用节点和链路重要度来计算节点和关键链路的毁坏度,结合不同网络拓扑结构给出了具体的计算方法。     

桥梁断面静三分力系数的CFD计算分析

利用流体分析软件Fluent计算了不同桥梁断面型式在中等雷诺数时和不同攻角下的阻力系数和升力系数。文中选用6类不同桥梁断面型式进行了计算分析。通过计算得出的阻力、升力系数随攻角的变化对比以及风场压力云图直观反映,初步分析了各类断面在静风作用下三分力系数值的特性。计算结果表明,钝体断面其阻力系数的变化形式相似,而上下不对称开口会造成其升力系数的变化;而流线型断面,其阻力系数与钝体断面截然不同,与攻角有直接的关系,实际应用需要多注意。     

高速铁路连续梁桥三分力系数的数值模拟分析

连续梁桥是高速铁路上的一种典型桥梁,利用计算流体力学软件对其不同截面在不同工况下的静气动性能进行了数值模拟,研究了平均风速、风攻角、宽高比以及桥上列车分布状况分别对桥梁截面三分力系数的影响.研究结果表明:风速和风攻角对桥梁的静气动性能影响显著；梁高的增大使桥梁处于不利的风荷载作用下；在桥上有列车状态下桥梁的静气动性能不如无车时稳定.     

舰艇作战系统网络的鲁棒性分析

鲁棒性是现代军事网络的一个重要性能指标。采用复杂网络理论,对现代舰艇作战系统网络的鲁棒性进行研究,建立了一般舰艇作战系统网络拓扑图,在此基础上,探讨了舰艇作战系统网络在“随机失败”和“选择性攻击”两种网络损毁方式下的的鲁棒性,提出了一种改善舰艇作战系统网络受到“选择性攻击”时的鲁棒性的方法——“接种”法。     

武广客运专线边坡支护结构中锚固体抗腐蚀性的技术措施

针对边坡支护结构中锚固体腐蚀是引起结构破坏失效的重要因素,其主要表现为锚固用水泥砂浆灌浆不足、浆体自干燥收缩裂缝大、抗环境水侵蚀能力差等方面。以武广客运专线为研究背景,针对锚固体易出现的腐蚀情况和特点设计试验,考察锚固用水泥砂浆的流动性、匀质性、自收缩性能及抗硫酸盐侵蚀性能等因素,提出改善锚固体抗腐蚀性能的技术措施。结果表明:粉煤灰、矿渣等矿物掺合料和新型外加剂KS-Ⅰ能够有效提高水泥砂浆的工作性能和抗侵蚀能力,满足工程应用的需要。试验结果为武广客运专线锚固结构防腐设计提供了依据,并可为类似设计提供技术储备。     

不同纵摇轴位置下的二维柔性鳍推进性能与流场特性研究

利用FLUENT软件数值计算了二维柔性鳍作升沉纵摇运动时的推力系数及推进效率,探讨了修正Bose变形方程、均匀载荷和非均匀载荷悬臂梁变形方程等三种柔性模式下纵摇轴位置对摆动鳍推进性能的影响,其中纵摇轴在尾缘处能够获得更大的推力,而最高的推进效率分别对应修正Bose模式下纵摇轴距首缘1／3弦长处和悬臂梁柔性变形模型下纵摇轴距首缘2／3弦长处．同时计算分析了斯特劳哈尔数、最大攻角等参数对柔性鳍水动力性能的影响,建立了最大推力系数和最高推进效率所对应的参数区间,其中低St数的最高推进效率发生在低αmax,高St数的最高推进效率发生在高αmax．     

潜射直航鱼雷协同作战研究

研究了多潜艇协同使用直航鱼雷作战问题。首先对潜艇的协同打击系统做了分析,然后对鱼雷协同作战必须解决的目标位置修正、发射阵位选择及鱼雷避碰等问题进行研究,最后给出了协同作战的流程及鱼雷协同形成交叉火力对目标同时打击的方法,并对鱼雷协同打击的命中概率做了计算。研究表明,该作战方法可将火力集中于目标位置概率最大处,并保证散布区域的可靠打击,提高了鱼雷打击的力度和精度。