固体火箭发动机流体喉部推力矢量特性

针对采用水作为二次流工质的流体喉部进行了冷流实验及数值模拟研究.研究了该种固体火箭发动机流体喉部的一般规律,包括不同二次流射流方式,不同二次流流量下流体喉部的扼流性能,推力偏角及推力效率,数值模拟及实验结果吻合较好.结果表明:扼流性能与二次流的注射位置、注射角度及流量比有关,且随二次流/主流流量比的增大而增大.喉部二次流喷射能有效的调节有效喉部面积进而调节推力大小,当流量比为0.4时,最大有效喉部面积比为0.8;扩张段二次流喷射能有效调节推力方向,当流量比为0.4时,最大推力偏角为20°;喉部二次流与扩张段二次流入射位置存在相位差可有效降低喉部与扩张段二次流干扰.      

基于模型的民机液压告警系统验证方法研究

利用Simulink/Labview建立民用客机液压系统告警逻辑模型,通过注入顶层定义的根源故障获得可视化告警信息指示,符合设计分析结果,且具有故障叠加告警显示等优点,为验证复杂系统集成中面临的根源派生故障告警信息显示抑制和排序功能提供一种有意义的方法。     

基于网络编码的空间DTN中CGR改进算法

随着空间通信技术的发展,卫星节点的增多,以及容延迟容中断通信需求的不断提高,空间DTN (DelayTolerant Network,容延迟网络)环境中各通信节点间的路由技术日益重要,相继出现了多种适用于DTN的路由技术.基于空间DTN的结构与特点,对CGR(Contact Graph Routing,接触图路由)算法以及基于编码的路由算法进行了分析比较,然后针对空间DTN中CGR算法的缺点和不足,研究提出了基于NC(Network Coding,网络编码)的空间DTN中的CGR改进算法(NC-CGR),并通过仿真实验平台对算法性能进行了分析评估.仿真结果表明,相比于CGR算法,NC-CGR算法在链路传输时延、传输包裹数目、中继缓存大小、链路丢包率等不同条件下的适应性方面均表现出较大优势,更适用于具有复杂拓扑、带宽受限、高动态特性的空间DTN环境.     

基于LMI的高超声速飞行器滑模预测控制

针对高超声速飞行器非线性、多约束、快时变等特点,提出了一种基于线性矩阵不等式的滑模预测控制方法.首先设计系统的滑模面,然后对滑模面进行预测并将其作为优化性能指标,通过Schur补引理将控制律的设计转化为一个优化问题.该方法避免了常规滑模控制的高频切换,有效地克服了抖振现象.此外,相对于传统的滑模预测控制方法,该方法不需要额外计算终端约束条件和终端代价函数,只需要通过选取合适的李雅普诺夫函数即可保证系统的稳定性,且其加权矩阵和控制律是同时进行优化设计的,简化了设计过程.仿真试验表明,相比于单纯的预测控制和滑模控制,所提出的方法具有更好的跟踪性能.     

NH90航空电子系统演进

NH90是一种法、德、意、荷、葡联合研制的先进中型多用途直升机,未来将成为法、德、意等国的主力作战运输、突击、反潜、搜救机型。介绍了 NH90的航空电子系统,其中包括核心航空电子,任务航空电子及飞控系统。跟踪了 NH90航空电子软件开发团队使用软件产品线（SPL）技术对航空电子架构进一步升级的方向。     

分开排气式喷管喷流噪声预测及试验研究

为揭示涡扇发动机分开排气式喷管喷流噪声的频谱分布和指向特性,对喷管缩比模型远声场喷流噪声进行了预测及试验研究,并开展了全尺寸喷管基准型及锯齿型喷流噪声的预测工作。结果表明:采用Tam & Auriault方法可以预测出喷流噪声的声压级值和空间指向分布,喷流噪声具有明显的指向性。与基准型喷管相比,锯齿型喷管具有良好的降噪效果;内外涵锯齿型喷管在中低频段的降噪效果优于内涵锯齿型喷管,在高频段的降噪效果差于内涵锯齿型喷管;在本文研究参数范围内,指向角小于88°时内外涵锯齿型喷管总声压级(OASPL)值高于内涵锯齿型喷管。     

扩展酉矩阵束算法实现稀疏可重构天线阵的优化设计

针对方向图可重构天线阵列的稀疏布阵问题,提出一种基于扩展酉矩阵束算法的优化设计算法。首先建立以阵元位置和多组激励为变量的多方向图联合稀疏优化模型,并利用期望方向图采样数据构建Hankel块矩阵。然后通过centro-Hermitian化处理和酉变换将采样矩阵从复数域转换到实数域,舍弃实矩阵中较小的奇异值对可重构线阵进行稀疏。最后通过对等价矩阵束的广义特征值分解估计稀布阵元位置,进而得到每个方向图对应的激励。仿真验证了该方法能够以阵元非均匀稀疏分布的阵列形式有效实现多个方向图的精确重构。     

Streamwise-body-force-model for rapid simulation combining internal and external flow fields

A streamwise-body-force-model (SBFM) is developed and applied in the overall flow simulation for the distributed propulsion system, combining internal and external flow fields. In view of axial stage effects, fan or compressor effects could be simplified as body forces along the streamline. These body forces which are functions of local parameters could be added as source terms in Navier-Stokes equations to replace solid boundary conditions of blades and hubs. The val-idation of SBFM with uniform inlet and distortion inlet of compressors shows that pressure perfor-mance characteristics agree well with experimental data. A three-dimensional simulation of the integration configuration, via a blended wing body aircraft with a distributed propulsion system using the SBFM, has been completed. Lift coefficient and drag coefficient agree well with wind tun-nel test results. Results show that to reach the goal of rapid integrated simulation combining inter-nal and external flow fields, the computational fluid dynamics method based on SBFM is reasonable.     

A new steering approach for VSCMGs with high precision

A new variable speed control moment gyro (VSCMG) steering law is proposed in order to achieve higher torque precision. The dynamics of VSCMGs is established, and two work modes are then designed according to command torque:control momentum gyro (CMG)/reaction wheel (RW) hybrid mode for the large torque case and RW single mode for the small. When working in the CMG/RW hybrid mode, the steering law deals with the gimbal dead-zone nonlinearity through compensation by RW sub-mode. This is in contrast to the conventional CMG singularity avoidance and wheel speed equalization, as well as the proof of definitely hyperbolic singular property of the CMG sub-mode. When working in the RW single mode, the motion of gimbals will be locked. Both the transition from CMG/RW hybrid mode to RW single mode and the reverse are studied. During the transition, wheel speed equalization and singularity avoidance of both the CMG and RW sub-modes are considered. A steering law for the RWs with locked gimbals is presented. It is shown by simulations that the VSCMGs with this new steering law could reach a better torque precision than the normal CMGs in the case of both large and small torques.     

Day-to-day variability of equatorial anomaly in GPS-TEC during low solar activity period

The ionospheric total electron content (TEC) in the northern hemispheric equatorial ionization anomaly (EIA) crest region is investigated by using dual-frequency signals of the Global Positioning System (GPS) acquired from Rajkot (Geog. Lat. 22.29°N, Geog. Long. 70.74°E; Geom. Lat. 14.21°N, Geom. Long. 144.90°E), India. The day-to-day variability of EIA characteristics is examined during low solar activity period (F10.7∼83 sfu). It is found that the daily maximum TEC at EIA crest exhibits a day-to-day and strong semi-annual variability. The seasonal anomaly and equinoctial asymmetry in TEC at EIA is found non-existent and weaker, respectively. We found a moderate and positive correlation of daily magnitude of crest, Ic with daily F10.7 and EUV fluxes with a correlation coefficient of 0.43 and 0.33, respectively indicating an existence of a short-term relation between TEC at EIA and the solar radiation even during low solar activity period. The correlation of daily Ic with Dst index is also moderate (r = −0.35), whereas no correlation is found with the daily Kp index (r = 0.14) respectively. We found that the magnitude of EIA crest is moderately correlated with solar flux in all seasons except winter where it is weakly related (0.27). The magnitude of EIA crest is also found highly related with EEJ strength in spring (r = 0.69) and summer (r = 0.65) than autumn (0.5) and winter (r = 0.47), though EEJ is stronger in autumn than spring.