基于显式有限元方法的二维楔形刚体入水砰击载荷并行计算预报

局部砰击载荷是在船舶首部结构设计时重点关注的问题。文章基于显式有限元方法,选用任意拉格朗日—欧拉算法(ALE),针对某30°二维楔形刚体入水砰击问题,开展了数值预报工作。针对模型网格密度开展了收敛性分析。数值预报的加速度、砰击压力等时域结果与已公开发表的模型实验的结果进行了比较,吻合非常好。鉴于在微机上数值计算时间比较长的问题,文中探讨了并行计算技术在模拟中的应用。     

基于轨迹数据的非机动车道内冲突事件自动识别与可视化

准确识别非机动车道内的交通冲突事件既是量化评价非机动车道安全水平的基础,也是剖析与理解非机动车道内运行风险产生与发展过程的重要前提.基于轨迹的交通冲突识别与分析技术已被运用于城市交叉口处机动车之间以及机非之间的交互安全分析,但目前鲜有聚焦非机动车道场景内交通冲突事件的分析方法.针对该问题,提出一种基于个体的(Agent...     

Cooperative GNSS positioning aided by road-features measurements

Cooperation between road users through V2X communication is a way to improve GNSS localization accuracy. When vehicles localization systems involve standalone GNSS receivers, the resulting accuracy can be affected by satellite-specific errors of several meters. This paper studies how road-features like lane marking detected by on-board cameras can be exploited to reduce absolute position errors of cooperative vehicles sharing information in real-time in a network. The algorithms considered in this work are based on a error bounded set membership strategy. In every vehicle, a set membership algorithm computes the absolute position and an estimation of the satellite-specific errors by using raw GNSS pseudoranges, lane boundary measurements and a 2D georeferenced road map which provides absolute geometric constraints. As lane-boundary measurements provide essentially cross-track corrections in the position estimation process, cooperation enables the vehicles to improve their own estimates thanks to the different orientation of the roads. Set-membership methods are very efficient to solve this problem since they do not involve any independence hypothesis of the errors and so, the same information can be used several times in the computation. Such class of algorithm provides a novel approach to improve position accuracy for connected vehicles guaranteeing the integrity of the computed solution which is pivoting for automated automotive systems requiring guaranteed safety-critical solutions. Results from simulations and real experiments show that sharing position corrections reduces significantly satellite-specific GNSS errors effects in both cross-track and along-track components. Moreover, it is shown that lane-boundary measurements help reducing estimation errors for all the networked vehicles even those which are not equipped with an embedded perception system.     

汽车轮胎与公路路面附着系数的研究

对汽车轮胎与公路路面的附着系数进行了较详细地分析与计算公式的推导。指出,附着系数是一个极值函数,在轮胎气压、车辆载荷和路面粗糙度这三项指标其中之一选择不当时,都会出现附着系数的最小值而影响行车安全。对公路施工,司机安全驾驶和交通事故的判断,提出了基本建议。     

WebQuest--探究式学习的一种形式

WebQuest是一门新兴的课程计划,在实际教学中教师为指导学生进行主动的知识构建设计Web网页,并相应设置任务和评价策略.文章着重探讨了WebQuest在实际教学中的设计方法及其一些需要注意的事项.     

SOFT COMPUTING APPROACH FOR NOISY IMAGE RESTORATION

IntroductionSoftcomputing is a consortium of different com-puting tools to deal with real world problems ef-ficiently.The aim of softcomputing is to exploitthe tolerance for imprecision and uncertainty toachieve tractability,robustness and low cost[1] .Neurocomputing is one of the major componentsof soft computing,the other two important con-stituents are fuzzy logic and probabilistic reason-ing,which subsumes belief networks,geneticalgorithms and chaotic systems.Often,to solvea fairly complex…     

Unravelling effects of cooperative adaptive cruise control deactivation on traffic flow characteristics at merging bottlenecks

Cooperative Adaptive Cruise Control (CACC) systems have the potential to increase roadway capacity and mitigate traffic congestion thanks to the short following distance enabled by inter-vehicle communication. However, due to limitations in acceleration and deceleration capabilities of CACC systems, deactivation and switch to ACC or human-driven mode will take place when conditions are outside the operational design domain. Given the lack of elaborate models on this interaction, existing CACC traffic flow models have not yet been able to reproduce realistic CACC vehicle behaviour and pay little attention to the influence of system deactivation on traffic flow at bottlenecks. This study aims to gain insights into the influence of CACC on highway operations at merging bottlenecks by using a realistic CACC model that captures driver-system interactions and string length limits. We conduct systematic traffic simulations for various CACC market penetration rates (MPR) to derive free-flow capacity and queue discharge rate of the merging section and compare these to the capacity of a homogeneous pipeline section. The results show that an increased CACC MPR can indeed increase the roadway capacity. However, the resulting capacity in the merging bottleneck is much lower than the pipeline capacity and capacity drop persists in bottleneck scenarios at all CACC MPR levels. It is also found that CACC increases flow heterogeneity due to the switch among different operation modes. A microscopic investigation of the CACC operational mode and trajectories reveals a close relation between CACC deactivation, traffic congestion and flow heterogeneity.     

Development of a simulation platform for safety impact analysis considering vehicle dynamics,sensor errors,and communication latencies: Assessing cooperative adaptive cruise control under cyber attack

While safety is one of the most critical contributions of Cooperative Adaptive Cruise Control (CACC), it is impractical to assess such impacts in a real world. Even with simulation, many factors including vehicle dynamics, sensor errors, automated vehicle control algorithms and crash severity need to be properly modeled. In this paper, a simulation platform is proposed which explicitly features: (i) vehicle dynamics; (ii) sensor errors and communication delays; (iii) compatibility with CACC controllers; (iv) state-of-the-art predecessor leader following (PLF) based cooperative adaptive cruise control (CACC) controller; and (v) ability to quantify crash severity and CACC stability. The proposed simulation platform evaluated the CACC performance under normal and cybersecurity attack scenarios using speed variation, headway ratio, and injury probability. The first two measures of effectiveness (MOEs) represent the stability of CACC platoon while the injury probability quantifies the severity of a crash. The proposed platform can evaluate the safety performance of CACC controllers of interest under various paroxysmal or extreme events. It is particularly useful when traditional empirical driver models are not applicable. Such situations include, but are not limited to, cyber-attacks, sensor failures, and heterogeneous traffic conditions. The proposed platform is validated against data collected from real field tests and tested under various cyber-attack scenarios.     

一种高可用集群的系统管理技术

在并行和分布式计算环境中,随着系统规模的增长,系统出错的概率大大增加。为提高集群系统的可靠性和可用性,采用对称式Active/Active高可用模型的原理和组通信工具,实现了一种增强头节点作业服务可用性的高可用管理方案;针对并行计算环境的特点,利用LAM/Migration检查点迁移技术,实现了集群系统中计算节点的故障自探测、任务自恢复功能。     

有限元元计算环境DPFEM的研究

利用Java语言对已有的有限元软件进行对象包装,并利用公共对象总线技术(CORBA)将它们包装成为可以远程调用的分布式计算组件,通过Java和CORBA的有机结合实现了异构网络平台上的有限元程序的互操作.在此基础上,给出了分布式有限元并行计算环境DPFEM(Distributed Parallel Finite Element Mehtod)的框架模型,实现了有限元元计算的原型.