Reliability and Sensitivity Analysis of Transonic Flutter Using Improved Line Sampling Technique

The improved line sampling (LS) technique, an effective numerical simulation method, is employed to analyze the probabilistic characteristics and reliability sensitivity of flutter with random structural parameter in transonic flow. The improved LS technique is a novel methodology for reliability and sensitivity analysis of high dimensionality and low probability problem with implicit limit state function, and it does not require any approximating surrogate of the implicit limit state equation. The improved LS is used to estimate the flutter reliability and the sensitivity of a two-dimensional wing, in which some structural properties, such as frequency, parameters of gravity center and mass ratio, are considered as random variables. Computational fluid dynamics (CFD) based unsteady aerodynamic reduced order model (ROM) method is used to construct the aerodynamic state equations. Coupling structural state equations with aerodynamic state equations, the safety margin of flutter is founded by using the critical velocity of flutter. The results show that the improved LS technique can effectively decrease the computational cost in the random uncertainty analysis of flutter. The reliability sensitivity, defined by the partial derivative of the failure probability with respect to the distribution parameter of random variable, can help to identify the important parameters and guide the structural optimization design.     

实用化图像式油液污染实时检测系统研究

针对油液实时分析的应用需求,分析了基于显微图像的全采样式油液分析系统的各种特征参数,提出了系统改进的若干关键措施,建立了基于分流采样原理的实用化油液污染分析系统。同时根据实用化系统的特点,提出了结合图像运动特征和自动阈值选取的颗粒识别方法,分析了流场速度分布,解决了污染度计算的问题,并进行了与传统仪器的对比实验,获得较好的效果。     

固体推进剂药柱的近似不可压缩粘弹性随机有限元

采用Monte-Carlo粘弹性随机有限元法,分析了药柱的结构可靠度。针对固体火箭发动机药柱材料近似不可压缩的问题,基于Herrmann粘弹性有限元以提高计算的精度,考虑泊松比和松弛模量的随机性,采用拉丁超立方(LHS)技术计算了固体火箭发动机药柱结构的可靠度。算例表明该方法的有效性。     

线性系统采样Z变换的一个递推公式

本文给出了计算1/(s a)~n的采样z变换的递推公式,证明了其分子多项式系数的对称性质,外对α为复数的情况进行了推广。     

提高线阵采样式光学遥感器图像空间分辨率的新方法研究

介绍了提高采样式光学遥感器图像空间分辨率的国内外发展现状,以任意两维周期采样理论为基础,探索了一种通过把线阵探测器倾斜θ度而非常规线阵推扫的0°,同时把推扫方向的采样间距缩短为P/m,而非常规线阵推扫的P的新焦平面采样方法。该方法相对于常规线阵推扫采样,可以增加采样密度,提高图像空间分辨率。在原理研究的基础上,设计了一套实验验证系统,通过实验系统对该方法进行了物理及其可行性验证。试验结果表明:如果探测器阵列旋转45°并且推扫方向采样间距减半,相对常规线阵推扫采样,图像的空间分辨率可以提高1.64倍左右。相对于高模式采样技术和超模式采样技术,该方法避开了两排错位排列探测器的难题,因此工程实现上要简单。     

常增益变采样率自适应滤波

作者曾给出一种跟踪飞机机动的自适应滤波,采用直角坐标系中的9维状态量,利用最优检测统计量探测目标机动,并用估计到的机动加速度修正目标的预报值。 本文将在文献[1]的基础上,提出两种简化自适应滤波。其一,采用两套直角坐标系中的9维卡尔曼滤波,其中的一套滤波用于取代最优检测统计量,完成对目标机动的探测和估计的功能;其二,采用三通道解偶的常增益变采样率自适应滤波。     

反抽样数字滤波器设计

根据 DAC的幅频特性 ,当输入信号频率接近奈奎斯特采样率时 ,输出信号幅度衰减约 3 .9d B。文中设计了补偿此衰减的数字滤波器 ,并提出一种节省资源的高效实现方法。最后 ,给出了实验结果 ,以证明此滤波器补偿功能的可行性     

自来水管网监测调度系统设计

叙述上海闵行地区自来水管网监测调度系统的特点 ,并重点讨论了远端站数据采集器、数传电台、转发、通信规约和软件的设计     

DVB-S突发通信快速定时同步的FPGA实现

针对突发通信系统的特点,提出利用PN前导序列的良好相关特性,基于全并行流水FFT的快速同步方法。通过搜索FFT输出结果中超过自适应门限的多个峰值,找出最大峰值,实现突发数据帧头的快速捕获和最佳采样点的判决提取。该设计已经成功地在FPGA里得到实现,达到预期目标。     

Exploring Regional Variation in Spatial Language Using Spatially Stratified Web-Sampled Route Direction Documents

Spatial language, such as route directions, can be analyzed to shed light on how humans communicate and conceptualize spatial knowledge. This article details a computational linguistic approach using route directions to study regional variations in spatial language. We developed a web-sourcing approach to collect human-generated route direction documents on a geographical scale. Specifically, we built the Spatially strAtified Route Direction (SARD) Corpus through automated scraping, classifying, and georeferencing of route directions. Based on semantic categories of cardinal and relative direction terms, the analysis of the SARD Corpus reveals significant differences and patterns on both national (United States, United Kingdom, and Australia) and regional (contiguous U.S. states) levels. Combining computational linguistics and georeferencing approaches offers the potential for extending classic spatial linguistic studies.