链路统计分析中导出参数概率计算方法研究

为了适应深空探测任务需求,有效利用测控资源,提高链路计算精度,对天地链路统计分析基本方法进行了研究,对CCSDS标准建议的3种链路参数的概率密度函数特性进行了系统分析,提出了一种当链路参数不满足李雅普诺夫（Lyapunov）条件时,利用鞍点逼近估计尾概率函数确定导出参数取值概率的方法。通过理论分析和实例计算表明,采用该方法得到的导出参数的概率分布特性与真实值基本一致,进一步完善了天地链路统计计算方法,使天地链路统计分析方法更具有普遍性。     

基于重加权低秩近似和高斯混合模型的图像块效应去除算法

针对离散余弦变换(Block-based Discrete Cosine Transform, BDCT)在图像解码器处产生的块重构伪影现象,提出了一种联合两种先验知识的图像去块效应算法,这两种先验知识分别是重加权低秩近似和高斯混合模型。该算法首先利用重加权低秩近似来增强图像块之间的局部结构和非局部的自相似性,有效地保留原始图像中更多的精细结构。其次,还利用高斯混合模型对块状伪影进行建模获得更可靠、更鲁棒的结果。通过在标准测试图像上的实验表明,提出的算法在主观视觉效果和客观评估方面均优于其他的块效应去除方法。     

阶梯函数逼近阶与若干函数类的特征

利用阶梯函数逼近给出了连续函数类的特征,并在此基础上分别导出阶梯函数逼近李普希兹函数类和狄尼-李普希兹函数类的逼近阶。     

复杂结构优化设计的二级多点逼近方法

提出了一种独特的多元逼近函数,它具有良好数值稳定性和直观意义。该逼近函数结合二级多点逼近概念形成了更完善的相应优化算法。将本文方法用于梁结构优化设计,且直接选取梁剖面细节尺寸作为设计变量而不引入特殊的中间变量。算例表明,本文方法具有令人满意的计算效率,从而也验证了方法的广泛适用性。     

使用高阶逆风通量差分裂格式的悬停旋翼流场数值模拟

为减少Jameson二阶中心差分有限体积法导致的旋翼尾迹的数值耗散,将三阶逆风格式(MUSCL)与通量差分裂方法相结合,建立了一个三维雷诺平均N-S方程数值模拟悬停状态旋翼流场的方法。为了充分考虑旋翼尾迹对流场的影响,采用周期性边界条件和由动量理论导出的远场边界条件。为进一步减少尾迹数值耗散和便于添加上述边界条件,采用了嵌套网格方法。然后,进行了算例计算,给出了桨叶表面的压强分布,与可得到的试验数据及二阶中心差分方法的计算结果进行了对比,并针对几种不同桨尖形状的旋翼悬停流场进行计算,数值结果显示:后掠桨尖可减弱超临界流动。此外,还计算和分析了旋翼下方不同位置上的涡量分布。计算结果表明,本文方法能够有效地减少旋翼尾迹的数值耗散。      

MEMS惯性器件误差建模和补偿方法研究综述

针对MEMS惯性器件的特点,结合国内外相关文献资料,讨论了MEMS陀螺、加速度计这两类惯性器件的误差建模和误差补偿方法,文中将其误差分静态、动态和随机三类,详细地分析了各自的误差模型、参数标定方法和误差补偿方法,重点讨论陀螺随机误差建模及补偿技术,供广大研究人员参考。     

涡轮叶片叶面B-spline曲面层次化拟合方法

航空发动机涡轮叶片表面形状复杂,其三维重构是叶片成型精度分析以及质量控制的重要手段。涡轮叶片叶面是一个复杂的自由曲面,其拟合是重构涡轮叶片的关键步骤之一。本文以涡轮叶片叶面拟合为研究对象,提出一种B-spline曲面层次化拟合方法,该方法首先构建网格曲面的多分辨率模型,然后完成该多分辨率三角网格模型的参数化,最后在多分辨率三角网格的基础上通过粗略拟合、精确拟合以及最终拟合3个主要步骤完成曲面拟合。该方法可以完成高阶连续自由曲面的拟合,适用于海量测量数据的快速拟合,具有较高效率并且拟合结果精度高。     

Structural optimization of elliptical-tip star propellant grain using sub-problem approximation

A method is presented here for structural optimization of elliptical-tip star grain.The grain structural integrity was improved by minimizing the most critical area of inner bore hoop strain during cool down.Optimization was done by sub-problem approximation method in conjunction with finite element analysis.Both radii of the ellipse were varied during optimization to find the optimal ellipse.The optimization resulted in grain geometry having minimum level of Inner bore hoop strain without violating the preset limits of burning perimeter.The von mises strain at grain inner bore was also reduced in resultant grain.      

大涡模拟模型燃烧室燃烧性能计算

对带双级扩压器的模型燃烧室气液两相瞬态喷雾燃烧过程,在三维贴体坐标系下采用欧拉-拉格朗日两相大涡模拟方法进行数值研究,同时采用多维经验分析法预估燃烧性能.采用 k 方程亚网格尺度模型模拟亚网格湍流黏性;亚网格EBU(eddy-break-up)燃烧模型预估化学反应速率;多维经验分析法计算燃烧性能;并在非交错网格体系下气相采用SIMPLE(semi-implicit method for pressure-linked equations)算法对控制方程进行求解,液相采用随机离散模型,两相之间的耦合采用PSIC(particle-source-in-cell)算法.通过大涡模拟瞬态及时均计算结果表明:与粒子图像测速仪(PIV)测量的瞬态速度场、出口温度分布试验数据吻合,表明在三维贴体坐标系下采用欧拉-拉格朗日两相大涡模拟方法,数值模拟模型燃烧室两相喷雾燃烧流场,所采用的亚网格模型可以用于燃烧室气液两相喷雾燃烧流场的大涡模拟;燃烧性能计算结果与试验测量结果基本一致,说明所采用多维经验分析法可以用来数值模拟航空发动机燃烧室燃烧性能的计算,特别是污染物的预估,为设计低污染高性能航空发动机燃烧室提供有用的设计依据.      

A fully automated framework for helicopter rotor blades design and analysis including aerodynamics,structure, and manufacturing

This study describes an integrated framework in which basic aerospace engineering aspects (performance, aerodynamics, and structure) and practical aspects (configuration visualiza-tion and manufacturing) are coupled and considered in one fully automated design optimization of rotor blades. A number of codes are developed to robustly perform estimation of helicopter config-uration from sizing, performance analysis, trim analysis, to rotor blades configuration representa-tion. These codes are then integrated with a two-dimensional airfoil analysis tool to fully design rotor blades configuration including rotor planform and airfoil shape for optimal aerodynamics in both hover and forward flights. A modular structure design methodology is developed for real-istic composite rotor blades with a sophisticated cross-sectional geometry. A D-spar cross-sectional structure is chosen as a baseline. The framework is able to analyze all realistic inner configurations including thicknesses of D-spar, skin, web, number and ply angles of layers of each composite part, and materials. A number of codes and commercial software (ANSYS, Gridgen, VABS, PreVABS, etc.) are implemented to automate the structural analysis from aerodynamic data processing to sec-tional properties and stress analysis. An integrated model for manufacturing cost estimation of composite rotor blades developed at the Aerodynamic Analysis and Design Laboratory (AADL), Aerospace Information Engineering Department, Konkuk University is integrated into the framework to provide a rapid and dynamic feedback to configuration design. The integration of three modules has constructed a framework where the size of a helicopter, aerodynamic performance analysis, structure analysis, and manufacturing cost estimation could be quickly investigated. All aspects of a rotor blade including planform, airfoil shape, and inner structure are considered in a multidisciplinary design optimization without an exception of critical configuration.