Maximal admissible mode decision delay in terminal guidance

Mode decision-maker is a critical component in the logic-based Integrated Estimation and Guidance(IEG) system. For the best possible estimation and guidance performance, the mode decision delay of the mode decision-maker should be limited to a range as small as possible. This paper presents a numerical method for computing the maximal admissible mode decision delay that varies with time-to-go. Particular attention has been paid to highly maneuvering target interception in terminal guidance. The results of this research offer useful guidelines for the design of the mode decision-maker in IEG systems.     

Event-triggered attitude control of spacecraft

The problem of spacecraft attitude stabilization control system with limited communication and external disturbances is investigated based on an event-triggered control scheme. In the proposed scheme, information of attitude and control torque only need to be transmitted at some discrete triggered times when a defined measurement error exceeds a state-dependent threshold. The proposed control scheme not only guarantees that spacecraft attitude control errors converge toward a small invariant set containing the origin, but also ensures that there is no accumulation of triggering instants. The performance of the proposed control scheme is demonstrated through numerical simulation.     

Analysis of the data processing strategies of spherical harmonic expansion model on global ionosphere mapping for moderate solar activity

Spherical harmonic (SH) expansion is widely used to model the global ionosphere map (GIM) of vertical total electron content (VTEC). According to the impact of different data processing methods of the SH expansion model on the VTEC maps, we specifically performed comprehensive analysis in terms of the data sampling rate, the time resolution, the spherical harmonic degree, and the relative constraint. One month of GPS data (January in 2016) from the International GNSS (Global Navigation Satellite System) Service (IGS) network in a moderate ionospheric activity period at the descending phase of Solar Cycle 24 was processed. To improve the computational efficiency of the daily GIM generation, the data sampling rate of 5?min was recommended allowing the GIM precision loss within 0.10 TECU (total electron content unit). The global VTEC map could be better represented in temporal and spatial domains with higher time resolution and higher spherical harmonic degree, especially at low latitude bands and in the southern hemisphere. The GIM precision improvement was about 10.91% for 1-h and about 15.15% for 0.5-h compared with the commonly used 2-h time resolution. The use of spherical harmonic degree 17 or 20 instead of 15 could improve the precision by 3.19% or 6.06%. We also found that an optimal relative constraint had to be found experimentally considering both the GIM precision and the GIM root mean square (RMS) map.     

机场终端区域电磁环境分析

主要分析了机场终端区域主要使用的无线电设备及位置分布,各种无线电设备对电磁环境的要求以及信号覆盖、信号强度,对可能存在的干扰进行简单的分析,为进一步对机场终端区电磁环境仿真奠定理论基础。最后,本文对广汉机场的电磁环境进行了具体分析。     

基于多尺度 3D-2D卷积神经网络的高光谱图像分类

设计提出了 1种针对高光谱图像分类任务的 3D-MSCNN模型。在 PCA降维的基础上,利用 3D空谱特征提 取网络和 2D多尺度特征提取网络实现高光谱图像特征提取,充分发挥高光谱图像空谱信息价值,增强对不同尺度 地表覆盖的表达能力。最后,利用 Softmax分类损失函数实现高光谱图像分类任务。实验结果表明,本文算法在 In. dian Pines和 Pavia University数据集上都取得了较好的分类效果。与 CD-CNN、3D-CNN、SS-Net和 HybirdSN等方法相 比,本文算法能够有效提升总体精度、平均精度和 Kappa系数等客观评价指标。     

延伸冲击孔冲击冷却流动与换热特性的数值研究

采用数值模拟方法研究了延伸冲击孔冲击冷却系统的冷却特性,分析了3个冲击雷诺数和5个冲击孔延伸长度对冲击腔内流动与换热特性的影响,给出了靶面努塞尔数分布、靶面压力分布、中心截面流速与综合换热性能的变化。结果表明：延伸冲击孔可以有效地防止横流对冲击射流的偏转作用,同时使射流出口更加贴近冲击靶面壁面,冲击速度更高,可以明显提高靶面的换热系数,并使整个靶面上的换热系数分布也更加均匀。冲击冷却的冷却性能随着冲击孔延伸长度的增加而增加,相较于传统冲击冷却（baseline）,在L/d=2.5时靶面平均努塞尔数提升达15%以上,但压力损失也相对较高;对比不同延伸长度冲击孔的综合换热性能,发现存在最佳的L/d取值范围使冲击冷却系统获得最佳的综合冷却性能。在本研究范围内,最佳的L/d= 2.5。     

中心锥对旋转爆轰发动机内外流场影响的三维数值模拟研究

为探究中心锥对旋转爆轰发动机(Rotating Detonation Engine,简称RDE)内外流场结构与推进性能的影响,本文设计了90°、60°、45°、30°、20°、14°锥角与无中心锥7种构型,对燃烧室内径为78mm、外径为88mm、长度为100mm的RDE进行三维数值模拟,推导了适用于带中心锥RDE的推力公式,获得了各构型下详尽的流场参数。结果表明：在本文构型下中心锥对内流场影响很小,各构型的内流场参数与结构基本一致;中心锥对外流场的爆轰产物有轴向加速与径向吸附作用,能够调控尾部区域的流场特性;中心锥对由压差项产生的推力具有显著的提升效果,最佳推力性能出现在20°中心锥构型中,RDE总推力增益达22.8%。研究结果揭示了中心锥对RDE推力影响的作用机理,阐明了锥角对推进性能的影响规律,对带锥形构型的尾喷管设计工作提供了参考。     

时间发展可压化学反应混合层直接数值模拟

基于一个简化的单步不可逆燃烧动力学模型,对时间发展二维可压化学反应平面混合流场,实现了高精度迎风紧致有限差分直接数值模拟。研究了化学反应放热与流体混合运动间的耦合作用,分析了前者对可压混合层厚度、拟序结构及产物生成率等方面的影响。     

数字散斑干涉技术在形貌测量中的应用及进展

介绍了数字散斑干涉技术用于形貌测量的基本原理及其发展,对几种主要的测量方法进行了分类与对比,分析了各种方法的特点,最后对数字散斑干涉形貌测量技术作出了展望