均方意义下三维雷达无偏转换测量误差协方差阵的推导

在以前的研究中,无偏转测量误差协方差阵是基于当前测量值得到的.为了能利用所有历史数据以得到更精确的转换测量误差协方差阵估计,文中在均方意义下,推导了三维雷达的最优无偏转换测量误差协方差阵.     

复杂曲面零件五轴加工刀轴整体优化方法

 针对复杂曲面零件五轴加工中刀轴矢量变化剧烈、严重影响工件表面加工质量的问题,提出一种基于临界约束的五轴刀轴矢量整体优化方法。首先,构造了给定切触点处所有可行摆刀平面,并在摆刀平面内根据临界约束计算出临界刀轴矢量,在获得临界刀轴矢量的基础上,对其进行平面映射,建立了刀轴摆动的初始可行域;其次,通过对初始可行域进行均匀离散,根据离散点之间相对位置关系构造邻接矩阵,并结合最短路径搜索算法获得了初始参考刀轴,从而构造了新的刀轴摆动可行域;最后,建立当前切削行内无干涉且相邻刀轴变化最小的刀轴矢量优化模型,实现自由曲面五轴加工无干涉刀轴矢量的光滑控制。两种自由曲面叶轮的加工算例分析表明,采用本文方法获得的刀轴矢量可以明显改善机床的运动性能,避免了刀具干涉的产生,可提高复杂曲面零件的加工质量与效率。     

The yaw stability analysis for stratospheric airships in float situation

When a stratospheric airship free floats at pressure altitude, the sideslip angle of the airship is neither random nor against the wind, but is stable on certain values. According to classical potential flow theory, a simplified two-dimensional ellipse and three-dimensional ellipsoid are firstly analyzed respectively, which implied that the airship could present crosswind orientation. The numerical investigations (CFD) on the yaw stability based on a bare hull and a finned airship are employed for verifying the theory conclusion. It is found that the finned airships can remain stable when its sideslip Angle is 55–70°, which is less than 90° of the stable angle of the ellipsoid and bare hull, but statically unstable at low sideslip angles, its static instability is similar to that of dynamic flight. Then the fight data of three stratospheric airships is analyzed. The yaw stability in flight data generally agrees with expectations drawn of theoretical and numerical simulation. These investigations serve to provide references for yaw control and configuration design of airships.     

非高斯杂波协方差矩阵估计新方法

针对雷达目标自适应检测中的复合高斯杂波协方差矩阵估计问题,提出了 一种基于杂波分组的约束迭代估计方法。该方法在迭代过程中有效利用所有辅助数据,并对 最终得到的估计矩阵进行关于迹的约束。在估计的杂波分组大小与实际情况匹配的条件下, 约束迭代估计方法的估计精度与杂波功率水平无关。仿真实验表明,所提出的方法对不同的 杂波分组大小失配情况具有很好的鲁棒性;与已有的两种协方差矩阵估计方法相比,约束迭 代估计方法能极大的提高估计精度,加快迭代过程的收敛速率,且计算量更小。
     

Primary Solidification Phase and Lamellar Orientation in Directionally Solidified Ti-45Al-7Nb Alloy

Primary solidification phase and lamellar orientation are investigated in Ti-45Al-7Nb alloy at very high ratio of temperature gradient to growth rate (G/v) by a liquid-metal-cooled directionally solidified method. It shows that Ti-45Al-7Nb alloy solidifies with primary α phase. Longitudinal (parallel to growth direction) microstructure shows that α dendrites in solid-liquid mushy zone are discontinuous and transverse microstructure of α dendrites is worm-like feature. Growth direction of α phase is about 80° away from〈0001〉α direction, and close to〈1120〉α direction. The corresponding lamellar orientation is aligned at the angle of about 10° to growth direction, which is consistent with α-dendrite growth direction according to Blackburn orientation relationship. Therefore, due to the altered growth direction of α phase, the lamellar orientation in Ti-45Al-7Nb alloy is controlled at the G/v ratio of 5×109 K·sm-2.     

铸造应力的特性与测算

说明铸造应力的特性,在应力分析的基础上,通过铸造应力实验,探索如何把铸造应力的定性说明发展为定量计算.     

空间谱测向超性能机理与系统评介

空间谱估计测向体制工程实现的暂时困难,影响了人们对其光明前景的认识。鉴此,文章提出了关于空间谱估计测向体制取得超过传统测向体制的精度、分辨力和对同频多信号同时测向的机理的物理解释和数学解释,以揭示这种新体制所具有的不可遏制的内在生命力。主要机理为,单点观察变为多点观察、样本域的扩张、参量估计更有效和变量方程的拓展。文章对几个实际系统进行了分析和评介。这些系统已经展示出空间谱估计测向体制所具有的超过传统体制的优异性能。     

卫星研制成本划分方法

本文提出一种卫星研制成本的划分方法。把输入的资源和输出的产品取为划分成本的基本元素。应用这些元素建立一个划分和综合成本的矩阵。提出了几种不同的成本划分,用以在预研和方案设计阶段对卫星研制成本进行估算。     

高精度星载SAR多普勒参数估算方法

提出了一种基于空间坐标转换,利用卫星位置、速度参数精确估算星载SAR(Synthetic Aperture Radar)全观测带多普勒参数的方法.利用卫星速度、位置,通过星载SAR空间几何模型和坐标转换关系,建立SAR图像中斜距同卫星下视角之间的四次方程,解出下视角并进一步计算出该斜距处的多普勒参数值.仿真结果表明,该方法在无卫星位置、速度误差情况下估算精度达到0.02Hz(多普勒中心频率)和2×10-4Hz/s(多普勒调频率);存在卫星位置测量误差(300m)以及速度测量误差(0.3m/s)的情况下,估算精度达到0.8Hz(多普勒中心频率)和0.07Hz/s(多普勒调频率).该方法适用于单星SAR以及分布式SAR高精度多普勒参数的估算.      

显式制导下定位定向误差的影响分析

建立了定位定向误差对显式制导精度影响的解析模型,提出了利用标准弹道参数估算定位定向偏差对制导精度影响的近似解析方法.结果表明,该方法计算精度高、速度快,可以满足显式制导下定位定向误差影响分析的需要.