SEM-Based Method for Performance Evaluation of Wired LANs

For wired local area networks(LANs),their effectiveness and invulnerability are very critical.It is extraordinarily significant to evaluate the network performance effectively in the design of a reasonable network topology and the performance improvement of the networks.However,there are many factors affecting the performance of the networks,and the relation among them is also complicated.How to evaluate the performance of the wired LANs more accurately has been a heavy challenge in the network research.In order to solve the problem,this paper presents a performance evaluation method that evaluates the effectiveness and invulnerability of the wired LANs.Compared to traditional statistical methods,it has the distinct advantage of being able to handle several dependent variables simultaneously and tolerates the measurement errors among these independent variables and dependent variables.Finally,the rationality and validity of this method are verified by the extensive experimental simulation.     

微重力环境下大叶片板式贮箱内流体行为的数值仿真与试验验证

大叶片板式贮箱是当前最为先进的一种新型贮箱,大叶片板式结构是该贮箱推进剂管理的核心部件.对微重力条件下大叶片板式贮箱内流体行为进行了数值仿真和微重力试验验证.采用液体体积分数法(VOF,volume of fluid)两相流动模型数值模拟板式贮箱内流体流动特性,得到了流体分布规律.搭建了大叶片板式贮箱缩比模型试验系统,对板式贮箱内流体行为进行微重力落塔试验,得到微重力环境下流体特性.数值仿真和试验结果表明,大叶片板式贮箱在微重力环境下管理流体性能良好,大叶片板式结构为空间流体(包括低温流体)管理提供一种良好的途径.同时本文仿真和试验为国内板式贮箱设计提供了必要的支撑数据.     

RANS/LES在超声速突起物绕流中的应用研究

安装在超声速/高超声速飞行器表面的突起物如机翼、控制舵等通常会导致复杂的激波/边界层干扰,对突起物的局部气动特性甚至飞行器整体的气动特性产生较大的扰动.在采用计算流体力学(CFD)数值模拟此类问题时,传统的求解雷诺平均Navier-Stokes(RANS)方程方法由于不能准确预测湍流脉动流场并且精度有限,在应用上受到一定的限制.本文在研究B-L (Baldwin-Lomax)内层模型和Smagorinsky亚格子模型优缺点的基础上,提出了一种新型的RANS/LES(Large Eddy Simulation)混合模型,并进行了算例验证,证实了该方法的可行性.在此基础上,对火箭表面突起物的干扰流场进行了数值模拟研究,细致地刻画了突起物附近的激波/边界层干扰、剪切层失稳和底部分离涡形成的非定常过程,获得了突起物及火箭表面上的压力脉动历程并进行了频谱分析.研究发现,相对于突起物底部的非定常分离流动,突起物前缘的激波和边界层相互干扰的非定常过程是突起物周围压力脉动的主导因素,这种高频的压力脉动可能对火箭内设备的正常工作产生不利的影响.     

Use of land＇s cooperative object to estimate UAV＇s pose for autonomous landing

The research of unmanned aerial vehicles＇（UAVs＇）autonomy navigation and landing guidance with computer vision has important signifcance.However,because of the image blurring,the position of the cooperative points cannot be obtained accurately,and the pose estimation algorithms based on the feature points have low precision.In this research,the pose estimation algorithm of UAV is proposed based on feature lines of the cooperative object for autonomous landing.This method uses the actual shape of the cooperative-target on ground and the principle of vanishing line.Roll angle is calculated from the vanishing line.Yaw angle is calculated from the location of the target in the image.Finally,the remaining extrinsic parameters are calculated by the coordinates transformation.Experimental results show that the pose estimation algorithm based on line feature has a higher precision and is more reliable than the pose estimation algorithm based on points feature.Moreover,the error of the algorithm we proposed is small enough when the UAV is near to the landing strip,and it can meet the basic requirements of UAV＇s autonomous landing.     

高功率微波导弹发展现状分析研究

简要介绍了高功率微波武器的概念、毁伤机理、基本特点,对高功率微波武器的发展脉络进行了梳理.重点介绍了美国CHAMP高功率微波导弹的发展情况,对其可能的应用情况进行了探讨.     

一种在轨改善偏置动量卫星控制精度的方法

对多个偏置动量卫星在轨飞行的遥测数据观察后发现．其中一些卫星的X轴和Z轴控制误差较大，且有明显的常值偏差存在．对这一现象进行分析，从偏置动量卫星的控制原理上找到了姿态偏差较大的原因，进而提出修正方法．在轨飞行测试表明：原姿态超差的偏置动量卫星采用本方法后，姿态控制精度得到明显改善，证明了本方法行之有效．     

航天器姿态控制的区间参数化方法

考虑一类航天器姿态最优控制问题，通过控制参数化的方法和约束转录的方法，将航天器姿态最优控制问题转化为最优参数选择问题.提出一种新的区间时间变换方法用于解决最优参数选择问题的切换时间点的计算问题.将时间切换点按顺序分为一系列子集，将每个集合的所在的时域宽度作为决策变量进行优化，每个子集内的切换时间点将会随着此决策变量线性变化.由此，控制值将分布在数个稠密或稀疏的区间内，而不是由均分的分段常值函数表示.相比于全时间节点优化技术，此方法有效的降低了需要计算的决策变量的数量，增加了算法的执行效率.     

基于微格教学法的管制教员培训模式研究

为解决一线空中交通管制教员培训存在的诸多问题,提高管制教员培训效率,将目前教育界流行的微格教学法引入到管制教员的培训中,打破了传统培训"黑板+粉笔"的单一做法。首先对管制教员培训模式进行创新,重新设计后的培训模式分为理论环节和实践环节两部分,在理论环节中加入了微格教学法相关理论知识;在实践环节中融入了微格教学法的先进方法和手段。然后组织3名院校教师和15名一线程序管制教员进行了验证,验证结果表明,与传统培训模式相比,该培训模式更具针对性、规范性和高效性。     

CAS在DVB系统中的软件实现方式

CAS(条件接收系统)是DVB(数字视频广播)重要的组成部分。研究一种基于ALI工作平台的CAS系统。给出了CAS的组成结构和系统设计方案,重点论证其加解扰和加解密部分,应用C语言分析CAS的工作原理和实现过程,分析并解决实现过程中出现的问题。     

Effect of turbulence on NO formation in swirling combustion

Turbulence affects both combustion and NO formation. Fluctuation correlations are ideally used for quantitative analysis. From the instantaneous chemical reaction rate expression,ignoring the third-order correlation terms, the averaged reaction rate will have four terms, including the term of averaged-variable product, a concentration fluctuation correlation term, and temperature-concentration fluctuation correlation term. If the reaction-rate coefficient is denoted as K, the temperature fluctuation would be included in the K fluctuation. In order to quantitatively study the effect of turbulence on NO formation in methane-air swirling combustion, various turbulencechemistry models are tested. The magnitudes of various correlations and their effects on the time-averaged reaction rate are calculated and analyzed, and the simulation results are compared with the experimental measurement data. The results show that among various correlation moments, the correlation between the reaction-rate coefficient K fluctuation with the concentration fluctuation is most important and is a strong nonlinear term.