对称面圆周角对轴对称降落伞流场特性的影响

根据降落伞的特点,通过3点假设(伞衣薄膜、伞的轴对称和流场定常),将三维复杂流动问题转化成二维轴对称问题,以节约计算时间.定义对称面圆周角,保持伞衣幅底部直径和顶孔直径不变,选取对称面圆周角在80°~140°范围内变化,建立一系列轴对称降落伞的计算模型.利用数值模拟手段,求解RNG (Renormalization Group)k-epsilon湍流模型下的N-S方程组,获得与有关单位试验相吻合的计算结果.分析发现对称面圆周角和伞衣幅高度对降落伞阻力影响很小.算例中阻力随对称面圆周角的变化在±0.28%以内.对称面圆周角的变化对轴对称降落伞尾流区流场的拓扑结构没有影响.对称轴上存在2个鞍点,随着对称面圆周角的增大,第1个鞍点的位置几乎不变,第2个鞍点的位置向尾流方向推移.      

太阳X-EUV成像望远镜波长选择装置

太阳X射线-极紫外射线(X-EUV,X rays-Extreme Ultraviolet)成像望远镜是我国专门服务于空间天气预报研究的太阳短波成像监测仪器,望远镜工作在0.4~10 nm的X射线波段和19.5 nm的极紫外谱段,能够提供全日面、高分辨率的成像观测.波长选择装置是该望远镜的一个重要子系统,可以增强望远镜动态响应范围,有助于获取更多的反演日冕等离子体参数,这些参数可用来诊断日冕活动.该装置的运动控制具有低功耗的特点,能够满足空间应用环境的特殊要求.其中,步进电机精位置控制是设计的重点,有2种光电编码矩阵可以用于位置检测,从工程可实现角度优选出其中一种,并且从工程可靠性角度分析了该光电编码矩阵的故障模式,提出了在轨故障处理的预案.      

MC-CDMA中的RLS-DRMTA算法

多载波码分多址(MC-CDMA)系统是将OFDM技术与CDMA技术结合起来的一种综合技术.MC-CDMA系统中同信道干扰仍然是影响系统性能的主要因素,这就需要使用智能天线来提高系统的性能.介绍一种适用于MC-CDMA系统的自适应阵的盲算法递推最小二乘解扩重扩多目标阵列(RLS-DRMTA)算法,利用扩频码的信息进行波束形成,不需要训练序列,节约了频谱资源;与LS-DRMTA算法相比,RLS-DRMTA算法节省了运算时间;另外仿真表明在正交频分复用(OFDM)解调后进行波束形成,提高了系统的性能;为了降低系统的复杂度,还用到了载波分组技术,但分组技术又会降低系统的性能,所以分组时考虑了系统性能和运算速度的折衷.仿真结果表明RLS-DRMTA算法能使方向图的主波束对准信号方向,而在干扰方向形成零陷,从而达到抑制干扰的目的.      

一种基于共轭的发射码字的多普勒补偿方法

在相位编码信号脉冲压缩技术中,存在着多普勒频率敏感性问题,需要对多普勒频率进行补偿。在分析多普勒敏感性原因的基础上,提出了一种基于共轭的发射码字的补偿算法,可以从根本上解决相位编码信号对多普勒频率的敏感性问题,MATLAB仿真证明了该算法的正确性与可行性。     

基于贝叶斯网络分析空间态势

战场态势分析是指挥决策的基础,作为一种知识推理和进行概率推理的框架,贝叶斯网络在具有内在不确定性的决策问题中得到了广泛的应用。因果推理是态势评估中的一个重要环节,用叶斯网可以找出态势假设和事件之间的潜在关系,切合了态势评估所需完成的功能。     

Towards an effective and adequately verifiable PPWT

The 2008 Russia–China proposal to the Conference on Disarmament on preventing space weapons has attracted wide attention. Lengthy debates have been made on the need for such a treaty and for two of its most disputed elements, namely prohibition of ground-based anti-satellite weapons and verification. This article argues that, regardless of verifiability, such a treaty is urgently needed for the benefit of international peace and security, and for the security interests of spacefaring countries. But in order to serve these purposes effectively, the treaty should at least explicitly prohibit testing, deployment and use of space-based weapons and ground-based anti-satellite weapons. Given the necessary political will, it is feasible to “adequately verify” these constraints. The verification regime should permit the incorporation of new measures in the future, combine international technical means and national technical means, combine remote-sensing technologies and on-site inspections, and be complemented by transparency and confidence-building measures.     

CFZ0.4D型家用除湿机毛细管结构参数的确定

小型制冷系统的节流装置通常采用毛细管。它具有平衡较快、结构简单、成本低、质量稳定等特点。论文对CFZ0.4D型家用除湿机制冷系统中的节流装置——毛细管进行了实验研究,得出了符合设备性能要求的毛细管最佳参数值。     

我心目中的空管人

空管,我并不陌生,甚至曾经走得很近。空管,也曾是我为之努力的理想。本科四年,在飞行学院学的正是空中交通管制,而且还是该校的第一届“。右转30度”“爬升至9000米报告”,面对模拟机上密密麻麻的飞机,一条条指令由我们口中发出,那是一种自豪,那更是一种责任。模拟机训练构建了     

漂亮的军火出口成绩单 2004年俄罗斯军火销售的绩效评析

在政府的积极推动下．俄罗斯2004年的军火销售再度取得55亿美元的亮丽成绩，销售的种类和层次不仅已有所提升，在北非和阿拉伯半岛的军火市场亦有所突破。不过俄国军火企业的基本问题倘无法获得解决，对其未来发展恐怕会有相当影响，非常值得注意。     

AE9, AP9 and SPM: New Models for Specifying the Trapped Energetic Particle and Space Plasma Environment

The radiation belts and plasma in the Earth’s magnetosphere pose hazards to satellite systems which restrict design and orbit options with a resultant impact on mission performance and cost. For decades the standard space environment specification used for spacecraft design has been provided by the NASA AE8 and AP8 trapped radiation belt models. There are well-known limitations on their performance, however, and the need for a new trapped radiation and plasma model has been recognized by the engineering community for some time. To address this challenge a new set of models, denoted AE9/AP9/SPM, for energetic electrons, energetic protons and space plasma has been developed. The new models offer significant improvements including more detailed spatial resolution and the quantification of uncertainty due to both space weather and instrument errors. Fundamental to the model design, construction and operation are a number of new data sets and a novel statistical approach which captures first order temporal and spatial correlations allowing for the Monte-Carlo estimation of flux thresholds for user-specified percentile levels (e.g., 50th and 95th) over the course of the mission. An overview of the model architecture, data reduction methods, statistics algorithms, user application and initial validation is presented in this paper.