On the different approaches of Rayleigh optical depth determination

Rayleigh optical depth is an integral part of many radiative transfer problems. This paper discusses different elements and approaches of its determination. Then, it presents a method, which ensures more realistic estimate of Rayleigh optical depth by using refractive index and depolarization factor (including rotational Raman lines) adjusted according to the state and composition of the atmosphere. It is based on the published experimental and theoretical results. The Rayleigh optical depth calculations are compared with the Elterman’s model calculations for trend analysis purpose. Rayleigh optical depths are found to be around 3.4% lower than previous researchers, as they ignored the constraints of conservation of angular momentum in the rotational/vibrational transitions of the molecules during scattering.     

数字调制信号误差矢量幅度校准研究

从计量领域的现状看,对于矢量信号分析仪的误差矢量幅度,分析其准确度尚没有业内统一的方法。通过对数字调制信号的调制过程和解调过程的分析,罗列出影响误差矢量幅度的各种因素。在此基础上,总结出一套对误差矢量幅度的测量结果的理论计算方法,从而提出一种EVM测量结果的不确定度评定方法。此方法能够有效地分析误差矢量幅度的数字特性。     

基于混合Beta分布的火箭弹射座椅可靠性评估

建立了一种综合利用子系统试验数据和现场整机试验数据的火箭弹射座椅Bayes可靠性评估方法。该方法通过卡方拟合优度检验确定继承因子,建立混合Beta分布后,基于后验分布评估座椅可靠性。采用该方法对某火箭弹射座椅可靠性进行了评估,在置信水平0.90情况下其可靠度达到了0.924。结果表明,在相同的现场试验情况下,评估结果比经典统计方法更合理。     

复杂结构角系数计算方法

推导了能束在辐射半球面上均匀分布的角系数计算公式.根据面元间的位置关系,把有限元和能束均匀分布法相结合计算复杂结构的角系数.采用三角形网格统一表示边界面并根据边界面网格进行角系数计算的遮挡判断.计算结果表明,方法的计算精度比有限元法和蒙特卡洛法高,计算效率比蒙特卡洛法高,遮挡判断方法准确高效.      

Research on the Plane Multiple Cracks Stress Intensity Factors Based on Stochastic Finite Element Method

Taylor stochastic finite element method (SFEM) is applied to analyze the uncertainty of plane multiple cracks stress intensity factors (SIFs) considering the uncertainties of material properties, crack length, and load. The stochastic finite element model of plane multiple cracks are presented. In this model, crack tips are meshed with six-node triangular quarter-point elements; and other area is meshed with six-node triangular elements. The partial derivatives of displacement and stiffness matrix with respect to all the random variables obtained by Taylor SFEM are derived. Meanwhile, the mean and variance expressions of SIF under uncertain factors are also derived. Parallel double-crack illustrative example of using the proposed method is given. The calculation results indicate that the uncertainty of SIF is influenced by the distance of the cracks, the smaller the distance of cracks is, the greater the SIF uncertainty is, and the uncertainties of material elastic modulus, load and crack length markedly affect the uncertainty of SIF; and the Poisson ratio of material has little influence. Among the variables, the elastic modulus has the greatest effect on SIF uncertainty. The next is external load. The crack length has lower effect on SIF uncertainty than both the elastic modulus and external load.     

菜园坝长江大桥主拱节段风洞试验及分析

中承式拱桥属于柔性空间结构,主拱上承受的脉动风荷载相互干扰。以重庆菜园坝长江大桥为研究对象,进行了湍流下的主拱单拱及双拱节段模型风洞试验。对模型表面脉动压力的功率谱、相关系数、水平和竖向相干函数进行了细致分析,讨论了双拱间距宽度比对脉动压力频域特性的影响。当间距宽度比大于5时,后拱风荷载受到前拱的干扰作用。当两拱间距宽度比小于5时,前后拱风荷载特性类似于组合截面。随间距宽度比变小,主拱涡脱落折算频率和压力功率谱逐渐增大,前后拱迎风面和背风面的相关系数及相干系数均逐步降低。     

飞机最短时间爬升轨迹的格点搜寻算法

以飞机在垂直平面的运动方程为基础,采用线性时间负荷控制的飞行模式,提出了求解飞机最短时间爬升轨迹的格点搜寻算法.该方法视飞机为一质点,以此为基础计算出每个相邻格点的时间间隔,最后用h×Ma格点数搜寻法求出飞机最短时间爬升的最优轨迹.数字仿真表明,在规定的爬升范围内用格点搜寻算法可以实现快速的时间响应,得到的最优轨迹能够准确地跟踪设定的性能指标.     

噪声干扰Link-16数据链的干扰功率分配方法

在建立对Link-16数据链的干扰模型和接收机模型的基础上,分析了噪声干扰下接收机的误码性能,研究了干扰功率分配问题,并得到了对Link-16数据链的干扰功率分配方程,最后进行了仿真分析。     

大跨悬挑屋盖风压分布风洞试验分析

通过大跨悬挑曲面屋盖刚性模型风洞试验,分析各风向角风压系数均值等值线图及跨中区域时体型系数以确定最不利风向角,研究跨中迎风边缘及顺风测点功率谱及相干特性,最后针对跨中不同位置测点风压概率分布密度特性探讨峰值因子合理取值。     

基于FPGA的高清CCD视频信号预处理电路的设计

在高清CCD图像传感器KAI-2093和视频信号处理芯片AD9847工作原理的基础上,设计了高清CCD成像系统视频信号处理电路。选用FPGA器件作为硬件设计载体,使用VHDL语言对AD9847的初始化配置和驱动时序发生器进行了硬件描述。采用ISE10．1软件对所做的设计进行了功能仿真。仿真结果表明,所研制的高清CCD视频信号处理电路不仅可以满足高清CCD成像系统视频处理的要求,而且性能可靠,使用灵活。