F-P滤波器和SOA在全光帧时钟提取中的分析和试验

F—P腔作为光滤波器用．具有稳定性高．通带窄的优点。采用低精细度的法布里-珀罗滤波器（F—P）直接提出帧时钟,保证时钟的快速建立和快速消失。利用半导体光放大器（SOA）的自增益调制效应（SGM）对F-P提取的帧时钟进行整形,降低帧时钟的幅度噪声。并推导了F—P的精细度Q和SOA的自增益调制效应对帧时钟建立时间、消失时间的影响。通过理论分析表明,利用SOA的SGM效应可以降低帧时钟的幅度噪声并加快帧时钟建立速度。实验中,用上述方案对10．075GHz的帧信号进行了全光帧时钟提取．得到了建立时间为8个信号周期．消失时间为22个信号周期抖动为2.35ps的帧时钟信号.     

120°模具室温8道次ECAP变形纯钛的组织演化

在室温下以等径弯曲通道变形(ECAP)技术制备超细晶工业纯钛,利用光学显微镜(OM)和透射电子显微镜(TEM)研究室温ECAP变形纯钛微观组织演变过程,并讨论纯钛室温ECAP变形的显微组织演化机制。结果表明:显微组织演化分为3个不同阶段,分别对应3种不同机制:第一阶段在真应变ε≤1.27时,为位错滑移和孪生交互作用细化机制,形成含有高密度位错和孪晶的板条状组织;第二阶段在真应变量1.27<ε<2.54时,为动态回复细化机制,晶粒进一步细化至~0.25μm,形成典型的变形亚晶组织;第三阶段在真应变量ε≥2.54时,为不平衡晶界的转动细化机制,形成平均晶粒尺寸约为0.2μm的等轴状大角度晶界超细晶组织。     

飞艇空气动力学及其相关问题

对低空和高空飞艇在发射、回收、驻留、巡航或系留状态下所涉及的空气动力学问题及其重要性进行分析,介绍飞艇空气动力学研究的进展和主要结论,指出需要进一步解决的问题。低空飞艇的空气动力学问题主要包括厚艇身带来的流动分离与减阻、非薄平组件的非线性干扰、柔弹性表面或系留带来的流固耦合、因低速飞行带来的环境敏感性等。大量学者进行了相应的研究。高空即平流层飞艇还涉及多种新的空气动力学问题,包括热、浮力与气动的强耦合、昼夜外形变化、发射与回收过程中的突风带影响、风切变干扰等。关于这些问题的研究处于起步阶段。另外,还针对地面及大气边界层的影响、多边形外形以及副气囊喷流与主流干扰等很少有人研究的问题对飞艇周边流场进行了初步数值模拟。     

民用飞机吊挂应急断离设计研究

应急断离设计是民用飞机吊挂设计的关键技术之一,从收集到的相关机型应急着陆事故论述吊挂应急断离设计的结构设计要求,分析波音公司和麦道公司的典型机型吊挂设计方案,提出了我国大型民用飞机吊挂应急断离设计方案的建议。     

关于特情处置训练的思考

开展特情处置训练是保证飞行安全的重要保证。由于受到体制、理论体系及技术发展的制约,特情处置训练未能有效地开展。本文分析了特情处置训练的现状,针对其不足,分别从特情处置训练的地位、理论体系、培训模式和器材开发等方面提出了改进措施。     

海上垂直回收运载火箭发展现状与关键技术分析

运载火箭的可回收重复使用不但可以降低发射成本,而且能提高发射密度,满足高密度发射需求,是人类向太空探索必须发展的技术。垂直返回海上回收方式具备高精度、高稳定落点,减小了对落区人民的安全威胁,同时也减小了火箭运载能力不足的影响。随着“猎鹰9”火箭子级成功实现了海上垂直回收并多次重复使用,引发了各国研究者对火箭子级海上垂直回收技术的重视与探索。首先,阐述了海上垂直回收运载火箭的优势与特点,其次,梳理了海上垂直回收运载火箭的发展现状,再次,根据海上回收火箭的几个阶段分析了其过程中包含的关键技术;最后,总结了海上垂直回收运载火箭的发展趋势。     

A multi-objective optimization framework of constellation design for emergency observation

To meet the urgent needs of emergency observation missions, a well-designed constellation is key to ensuring system performance. This paper presents a multi-objective optimization framework which is well suited for constellation designers to identify key trade-offs and make decisions. Firstly, this work investigates the metrics of responsiveness and coverage simultaneously to approximate to the actual conditions of emergencies, and a multi-objective mathematical model is constructed to explore solutions to enhance the overall system performance. Then, according to the characteristics of emergency missions, a hierarchical chromosome encoding method is proposed in the framework to encode a solution that explores different sized constellations without constraining its specific geometry. Finally, we propose the use of radial axes plots to help constellation designers to gain pragmatic insights for informed decision making. The simulation of disaster management verifies that the proposed chromosome encoding method effectively promotes the convergence of the algorithm, and the multi-objective optimization framework helps to generate a rapid and adequate observation satellite constellation to provide maximum coverage performance while ensuring timeliness.     

舰载无人机撞网回收自适应制导技术

针对无人机自动着舰撞网回收过程中目标舰船处于运动状态的特点,借鉴导弹导引律的比例导引法提出了基于视线角的制导律,并引入反步法的设计思想以提高制导律的自适应性。基于视线角的制导律使无人机的轨迹倾斜角变化率与视线角变化率成比例,通过控制视线角来跟踪下滑轨迹倾斜角。采用该导引律可以减小无人机运动对目标舰船参数变化的敏感性,从而获得较为稳定的下滑轨迹。仿真结果表明了该制导律的可行性,并且该制导律具有较强的鲁棒性。     

Quality assessment of sub-Nyquist recovery from future gravity satellite missions

Drawing on experience from Gravity Recovery and Climate Experiment (GRACE) data analysis, the scientific challenges were already identified in several studies. Any future mission should focus on improvement in both precision and resolution in space and time. For future gravity missions which use high quality sensors, aliasing of high frequency time-variable geophysical signals to the lower frequency signals is one of the most serious problems. The aliasing problem and the spatio-temporal resolution are mainly restricted by two sampling theorems describing the space-time sampling of satellite missions: (i) a Heisenberg-like uncertainty theorem which states that the product of spatial resolution and time resolution is constant, and (ii) the Colombo–Nyquist rule (CNR), which requires the number of satellite revolutions in a repeat period to be at least twice a given maximum spherical harmonic degree. The CNR holds under the assumption of equal ground-track spacing, and limits the spatial resolution of the gravity solution.     

基于分时融合反馈的联邦滤波算法研究

传统联邦卡尔曼滤波算法的高容错性是以牺牲精度为代价的,为此提出了改进的联邦滤波算法,采用分时融合反馈的联邦滤波信息分配方式,在提高系统容错性的同时兼顾导航精度和实时性,而且无融合反馈阶段延长了故障反应时间,提高了系统对渐变故障的检测能力,取得较为理想的结果.