Three dimensional numerical simulations of long-span bridge aerodynamics, using block-iterative coupling and DES

The design of long-span bridges often depends on wind tunnel testing of sectional or full aeroelastic models. Some progress has been made to find a computational alternative to replace these physical tests. In this paper, an innovative computational fluid dynamics (CFD) method is presented, where the fluid-structure interaction (FSI) is solved through a self-developed code combined with an ANSYS-CFX solver. Then an improved CFD method based on block-iterative coupling is also proposed. This method can be readily used for two dimensional (2D) and three dimensional (3D) structure modelling. Detached-Eddy simulation for 3D viscous turbulent incompressible flow is applied to the 3D numerical analysis of bridge deck sections. Firstly, 2D numerical simulations of a thin airfoil demonstrate the accuracy of the present CFD method. Secondly, numerical simulations of a U-shape beam with both 2D and 3D modelling are conducted. The comparisons of aerodynamic force coefficients thus obtained with wind tunnel test results well meet the prediction that 3D CFD simulations are more accurate than 2D CFD simulations. Thirdly, 2D and 3D CFD simulations are performed for two generic bridge deck sections to produce their aerodynamic force coefficients and flutter derivatives. The computed values agree well with the available computational and wind tunnel test results. Once again, this demonstrates the accuracy of the proposed 3D CFD simulations. Finally, the 3D based wake flow vision is captured, which shows another advantage of 3D CFD simulations. All the simulation results demonstrate that the proposed 3D CFD method has good accuracy and significant benefits for aerodynamic analysis and computational FSI studies of long-span bridges and other slender structures.     

802.11g保护机制对网络性能影响的仿真与分析

在探讨IEEE802.11g保护机制工作模式的基础上,构建OPNET仿真网络以测试保护机制对WEAN网络性能的影响.实验结果表明,保护机制的引入可显著地降低WLAN网络吞吐率.纯802.11g模式下,网络平均吞吐率最大可达23.95 Mb/s;启用CTS-to-self保护机制的802.11b/g混合模式下,网络平均吞吐率仅为11.45 Mb/s,约为前者的50%;启用RTS/CTS保护机制时,网络平均吞吐率只有7 Mb/s,减少到前者的30%,且此时单个802.11g站点仅获得约7.5 Mb/s的TCP传输速率.为更好地规划和部署802.11无线网络提供了较准确的数据分析依据.     

Multiple Condensation filters for road detection and tracking

In this paper, we present a novel and robust road tracking system for vision-based personal navigation. Novelty of the work includes the use of multiple Condensation filters to track the road of arbitrary shape and automatic switching between trackers according to road conditions. The approach allows the road to be represented as a simple hyperbola. It also supports the representation of the road as a sequence of connected arcs/segments so that information from a digital map can be integrated into tracking. The parameters of the hyperbola road model are estimated using multiple vanishing points located in image strips. The road tracking method is robust in dealing with complex road shapes, background clutters, shadows, and road markings. Experiments using real videos demonstrate the robustness of our approach.     

卫星天线自动对星控制系统研究与设计

卫星天线手动对星方式存在精度不高、速度慢、操作复杂等缺点,针对这一现状,文章提出了一种二维卫星天线自动对星控制系统方案;系统以ATMega1280为控制核心,通过GSP、电子罗盘和绝对式编码器获取天线姿态信息,从而控制伺服电机来调整天线姿态,达到对星的目的;另外还实现了多组卫星数据存储、手动调节、误差补偿和参数实时显示等功能;实验表明,该系统工作稳定、精度高、响应速度快、操作方便,在军事和民用卫星通讯中均有较高的实用价值.     

基于主题图的文献资源组织模型及应用研究

文章分析了主题图的相关理论和传统文献组织方法优劣,论证了主题图在文献资源组织中的可行性,提出了基于主题图的文献资源组织模型及构建方法,引申了基于该模型的文献检索、主题导学、个性化资源推荐等应用研究。     

研讨支持系统中基于主题聚类的热点提取

研讨支持系统是一种旨在通过计算机技术代替传统面对面的研讨方式,并利用信息处理、数据挖掘等方法自动形成决策的网络研讨平台。研讨过程中会产生海量发言,如何自动挖掘和提取发言中的热点是本文研究重点。文章采用文本聚类的方法从发言中得到主题簇,并结合提出的热度值计算公式找出热门主题和热门观点。最后引用一个实例分析和验证了热点提取过程。     

Fuzzy sets and similarity relations for semantic web service matching

Semantic Web Services (SWS) were introduced to facilitate the publication, discovery, and execution of web services. A semantic matchmaker enhances the capability of UDDI service registries in the SWS architecture and it is able to recognize various degrees of matching for web services. On the basis of SWS and fuzzy-set theory, a fuzzy matching approach for semantic web services is proposed, to support a more automated and veracious service discovery process.     

Synthesis of quantum size ZnO crystals and their gas sensing properties for NO2

Quantum size ZnO crystals have been synthesized successfully by a room temperature sol-gel process. Oleic acid (OA) has been used as capping agent to control the particle size of ZnO. The crystal structure and size of the ZnO are characterized by the X-ray diffraction (XRD) and transmission electron microscope (TEM). The XRD results show the as-synthesized ZnO has hexagonal wurtzite structure and the average crystallite size is 5.7 nm which is little less than TEM result. It is testified by photoluminescence (PL) and Raman spectra that the quantum size ZnO keeps the crystal structure of the bulk ZnO and possesses more surface defects. The quantum size ZnO has the highest response of 280 to NO₂ and the highest selectivity of 31 and 49 corresponding to CO and CH₄ at operating temperature of 290 °C. The effect of calcination temperatures on sensing property and transient response of the ZnO sensor are also investigated.     

DCS电源供电系统的可靠性定量分析

根据DCS电源系统的现状,对目前几种不同的电源设计方案进行可靠性定量分析.通过建立不同DCS电源系统可靠性框图并估算相关的可靠性指标,比较了不同方案下的平均无故障工作时间 (MTBF),给出了系统可靠性的分析结果和改进措施,定量分析了改进后的方案.结果表明电源系统的MTBF有了明显的改善.     

基于WinCE的电梯监控系统多串口通信实现

提出了一种基于WinCE的多串口电梯远程监控系统的实现方法.该方法以S3C2440微处理器为核心构建硬件平台,实现了与其他设备的串口通信;同时以WinCE5.0为软件平台,完成多串口分层流驱动的设计.通过文件映射,解决了访问多串口设备时产生的竞态问题.测试结果表明,该系统通信正常、数据稳定,能充分满足电梯监控对串行通信的要求.