高超声速进气道优化设计初探

以总压恢复系数为目标,利用无粘流斜激波关系式和约束最优化计算方法,在考虑混合气体比热随温度变化的条件下,对二维混压式高超声速进气道设计方法作了初步探索,利用数值模拟软件对附面层作了修正,研究了进气道的基本性能。数值模拟结果表明:该进气道在飞行马赫数Ma=4～6.5范围内能够可靠工作。     

风洞试验多通道数据采集与动态参数实时处理系统

为新型飞机发动机进气道动态畸变参数测试而研制了两代全数字化、智能化测试系统。64通道独立同时采样；高速32bit浮点运算DSP对畸变参数作实时处理；100Mbyte以上大容量在线存储器，存储全部原始数据、中间结果和处理结果；被测参数时间历程曲线、采样数据时间历程曲线及2D、3D动态图形和数表显示及输出；系统自检功能及坏点自动检测与修补功能；图形化及汉化菜单，友好的人机界面。硬件与软件的模块化与开放式结构，以便广泛应用于其他需要作多通道数据采集和动态参数实时处理的场合。     

Identification of uncatalogued LEO space objects by a ground-based EO array

A ground-based electro-optical (EO) array, deployed at the Jilin Space Tracking Base of Changchun Observatory, China, has been in operation since April 2017. The array has 8 small telescopes, each has an aperture of 15 cm and a field of view of 14° × 14°. On average, the array can collect angles data over 3–4 thousand Very Short Arcs (VSAs) of Low Earth Orbit (LEO) space objects each night. Correlation of the VSA angles data with the NORAD catalogue objects results in about 85% of all the VSAs being correlated to NORAD objects. The remaining 15% VSAs angles data could be supposed from uncatalogued objects. The Initial Orbit Determination (IOD) solutions of the VSAs with the range-search method and the association results of the IODs with the geometrical method are presented. The mean IOD success rate is about 91% and the True Positive (TP) rate is more than 86%. In addition, the classical Gauss, Laplace, Gooding and Double-r angles-only IOD methods are applied to process VSA angles data and their performance is assessed. The CBTA method is used to associate the IOD tracks and compared with the geometrical method. A set of procedures for identifying the uncatalogued objects based on the VSA angles data is designed. Processing of the VSA angles data from Aug 4 to Sep 30, 2017 reveals there are possibly 415 uncatalogued LEO objects.     

Characterizing slope correction methods applied to satellite radar altimetry data: A case study around Dome Argus in East Antarctica

Slope correction is important to improve the accuracy of satellite radar elevation measurements by mitigating the slope-induced error (SE), especially over uneven ground surfaces. Although several slope correction methods have been proposed, guidance in the form of stepwise algorithm on how to implement these methods in processing radar altimetric data at the coding level, and the differences among these methods need to be presented and discussed systematically. In this paper, three existing types of slope correction methods—the direct method (DM), intermediate method (IM), and relocation method (RM, further divided into RM1 and RM2)—are described in detail. In addition, their main differences and features for various scientific applications are analyzed. We conduct a systematic experiment with CryoSat-2 Low Resolution Mode (LRM) data in a physically stable area around Dome Argus in East Antarctica, where in-situ measurements were available for comparison. The slope correction is implemented separately using the three methods, with the latest high-accuracy Reference Elevation Model of Antarctica (REMA) as the a-priori topography model. The bias and precision of the slope-corrected CryoSat-2 data results from the RM2 is ?0.18 ± 0.86 m based on the comparison with the field Global Navigation Satellite System (GNSS) data. The results from the RM2 indicate higher precision compared to those from the RM1. According to the correlation analysis of the slope-corrected CryoSat-2 data results (RM1 and RM2), the bias enlarges and the precision becomes worse when the surface slope increases from 0 to 0.85°. After a comprehensively comparative analysis, we find that the results from the RM1 and RM2 are superior in precision (0.93 m and 0.86 m) with respect to the GNSS data. The relatively low precision (1.22 m) from the IM is due to the potential error from the a-priori digital elevation model (DEM). The DM has the lowest precision (2.66 m). Another experiment over rough topography in West Antarctica is carried out for comparison, especially between the RM1 (precision of 15.27 m) and RM2 (precision of 16.25 m). In general, the RM is recommended for the SE elimination among the three methods. Moreover, the RM2 is firstly considered over smooth topography due to the superior performance in bias and precision, while the RM1 is more suggested over the rough topography because of the slightly smaller bias and better precision. The IM relies much on the accuracy of the a-prior DEM and is not usually recommended, because of the strict requirement in the sampling time between the radar altimetry data and the a-priori DEM to avoid any surface change over time.     

经济有效的轴承修复技术

铁姆肯公司已经开展了60多年的轴承修复业务,广泛应用于航空、交通、水泥建材、冶金、电力和造纸等行业.2006年以来,铁姆肯公司在中国的修复中心也已经为水泥、钢铁和造纸等客户修复轴承达到6800余套,其中50%以上为其他进口品牌的轴承.经验表明:修复后的轴承其使用周期完全能达到新轴承的同等使用周期要求.而且轴承修复与新品轴承采购相比在交货期和降低成本上更具有突出的优势.     

Relaying Selection with Network-coded Cooperative Protocols in Aeronautical Communications

In this article, we exploit the idea of network-coded cooperative protocol in aeronautical communications which combines different source nodes'information at the relay and joint decoding at the destination. Recently, the network coding in cooperative communications has been categorized into two mainstreams, bit-level and signal-level combinations, which are both discussed in the article. And to be exclusively, multiple access relay channel(MARC) is adopted. The mutual information expressions of both above-cited network-coded protocols are deduced, which prove that without proper selected relays to perform network coding, the spatial diversity of the proposed protocol cannot be obtained. This then leads to search for the selection and grouping algorithms. An adjacency matrix is defined to describe the connectivity of the nodes in one radio contact disk, so that, the selection and grouping of algorithm is equivalent to constructing this adjacency matrix to minimize the system outage probability evaluated in term of the mutual information. Besides, a network-coded cooperative protocol requires the acyclic network, of which the construction is to avoid loop-4 in the matrix. The article ends with simulations to demonstrate the viability of the proposed algorithms.     

非稳定动态过程非定常气动力建模

现有的大迎角非定常气动力建模方法，通常是以一个或多个频率的稳定振动试验数据来预测稳定滞环。然而，飞机快速机动如过失速机动的过程，不可能是持续的稳定振动，而是一个非稳定的动态过程。因此，这个过程中的气动力不会达到稳定滞环，而是始终处于进入滞环的初始非稳定过程中。基于振动理论分析得出，非定常气动力的动态响应过程存在非稳定和稳定两个阶段，传统建模方法着眼于稳定阶段，而飞机的真实机动过程在非稳定阶段。设计了一种适于非线性系统辨识的激励输入，并以最小二乘支持向量机（LS-SVM）方法为例，实现了在大迎角区幅值和频率范围内任意运动的非定常气动力建模。模型训练完成后，用来预测某机翼在不同基准状态下大迎角范围内做俯仰运动时的升力系数、阻力系数和俯仰力矩系数。结果表明，不仅稳定滞环实现了准确预测，进入滞环的初始非稳定过程也得到了准确预测；此外，基准状态对气动力在初始非稳定过程中的特性存在明显影响。进一步的验证还表明，基于稳定滞环数据只能预测到稳定滞环，无法预测进入滞环的非稳定过程。     

MB26镁合金微弧氧化陶瓷膜层性能

文摘利用扫描电镜、表面性能测试仪和电化学测试技术等研究了在铝酸盐电解液中,不同电流密度和氧化时间对MB26镁合金微弧氧化膜的表面形貌、厚度、结合力以及耐蚀性等性能的影响。结果表明:随氧化时间和电流密度的增加,MB26镁合金微弧氧化膜层中的微孔数量减少,但孔变深。膜层厚度随氧化时间和电流密度的增加而线性增加,但与基体的结合力随之降低。氧化膜的耐蚀性随氧化时间和电流密度的增加呈先增加而后减小的趋势,该合金在铝酸盐体系中微弧氧化的最佳工艺为电流密度0.2 A/cm2,氧化时间40 m in。     

合成孔径激光雷达研究

合成孔径激光雷达是目前国内外研究的热点。文中讨论了SAL的概念和原理,建立了SAL回波信号模型,研究了RD算法的处理流程,并进行了机载SAL点目标和分布目标成像的模拟仿真。仿真结果表明,SAL具有较高的分辨能力。此外,文中还提出了在军事上利用SAL和SAR联合检测军事目标的方法。     

一种特殊的分形图像水印技术

文章介绍了一种基于分形图像的水印方法,该方法利用一种特殊的正交分形编码。分形仿射变换由值域块的均值和对比压缩系数共同决定。这种正交分形解码是一种均值常量的迭代。水印信号由m序列构成。