基于AFDX网络的飞行管理仿真系统

系统建模与数字仿真是大型客机飞行管理系统研发的重要阶段.初步建立了基于航空电子全双工交换式以太网(AFDX,Avionics Full-Duplex Switched Ethernet)的飞行管理系统分布式实时仿真系统模型.对飞行计划、飞行导引、轨迹预测、性能计算、综合导航、导航数据库、综合显示等核心功能进行了分析建模和算法开发.并在此基础上对飞行管理计算机、综合导航系统、自动飞行系统等仿真子系统进行了设计,在满足实时性要求的前提下,基于AFDX网络与分布式仿真结构实现了对以飞行管理计算机系统为核心的航空电子仿真系统的集成,给出了一种通用的、基于AFDX网络的飞行管理系统分布式仿真框架.仿真系统的运行结果证明:基于AFDX网络的分布式仿真结构能够有效满足实时性要求,提高网络通信性能.      

基于动态RCS的无人机航迹实时规划

传统的无人机航迹规划主要采用仅考虑无人机与雷达距离的简化雷达威胁模型,未充分考虑无人机雷达散射截面RCS(Radar Cross-Section)随自身姿态角改变而产生的动态变化.据此,提出了无人机周向动态RCS模型,并建立了综合考虑无人机动态RCS与雷达距离的探测概率模型,利用遗传算法进行了基于动态RCS的航迹实时规划,计算结果与传统航迹规划结果进行了对比.仿真结果表明该模型的可行性和有效性,能充分利用无人机自身的优势规避威胁,满足无人机的航迹实时规划的要求.      

基于离散事件方法的AFDX建模与仿真

采用了建模仿真的方法来分析航空电子全双工交换式以太网(AFDX,Avionics Full Duplex switched ethernet)协议.通过对AFDX协议的抽象,基于离散事件的建模方法,以基本的网络元素来抽象化网络中的端系统、交换机等设备,以离散事件来描述网络设备的行为,以此构建了AFDX网络模型,并依据模型实现了仿真.网络演算是一种理论计算AFDX最坏延迟界限的方法,将典型场景下仿真得到的结果与理论计算的结果进行比较,验证了模型.通过不同流量方案下仿真结果的对比,对AFDX进行了传输特性的分析.      

基于操纵面故障影响估计的安全飞行轨迹优化

操纵面故障将改变飞机受到的气动力和力矩,降低机动性能和控制能力,基于传统质点模型的航迹规划方法难以解决此类飞机安全飞行轨迹优化问题.因此,引入由故障引起的侧滑和侧力,估计故障后气动力系数,建立故障飞机模型;针对故障飞机控制和机动能力下降的问题,在原故障模型的基础上引入控制量变化率,构建轨迹优化对象模型,并将控制量变化率最小作为优化指标;采用高斯伪谱法优化计算安全飞行轨迹.仿真实验以副翼和方向舵故障为例进行设计,结果满足运动方程及各控制量、状态量约束,并能实现平稳飞行.     

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.     

The South Pole-Aitken basin region,Moon: GIS-based geologic investigation using Kaguya elemental information

Using Geographic Information Systems (GIS), we performed comparative analysis among stratigraphic information and the Kaguya (SELENE) GRS data of the ∼2500-km-diameter South Pole-Aitken (SPA) basin and its surroundings. Results indicate that the surface rock materials (including ancient crater materials, mare basalts, and possible SPA impact melt) are average to slightly elevated in K and Th with respect to the rest of the Moon. Also, this study demonstrates that K and Th have not significantly changed since the formation of SPA. The elemental signatures of the impact basin of Fe, Ti, Si, O through time include evidence for resurfacing by ejecta materials and late-stage volcanism. The oldest surfaces of SPA are found to be oxygen-depleted during the heavy bombardment period relative to later stages of geologic development, followed by both an increase in silicon and oxygen, possibly due to ejecta sourced from outside of SPA, and subsequent modification due to mare basaltic volcanism, which increased iron and titanium within SPA. The influence of the distinct geologic history of SPA and surroundings on the mineralogic and elemental abundances is evident as shown in our investigation.     

时域有限差分法连接边界电磁泄漏

用时域有限差分法计算目标的雷达散射截面时,一般用连接边界来引入平面入射波.理想情况下,当总场区没有散射目标时,该区域仅有入射波,散射场区电磁波为0.但在实际计算过程中,散射场区的电磁波一般不会严格等于0,这是因为在连接边界引入入射波时产生了电磁泄漏.一维情形下,用散射场区电场的平方和来衡量电磁泄漏程度.二维情形下,用等效原理将散射场区的电磁场进行远场外推,得到雷达散射截面,以此衡量电磁泄漏的大小.研究表明:时间步长、入射角度都能影响电磁泄漏大小.为使电磁泄漏较小,时间步长应接近于稳定性要求的最小步长,入射方向应避免垂直于计算区域边界.     

基于相似理论的月球车月面牵引性能预测

引入相似理论对月球车的轮土交互系统进行研究,建立了月壤-车轮交互系统的地面力学相似模型,针对原位月壤内聚力较小的特点,提出了一种无需改变车轮尺寸、以模拟月壤为土壤介质的模型试验方法,对月面重力环境下月球车轮的牵引性能进行预测.利用室内土槽试验和颗粒流仿真相结合的方法对该模型试验方法的有效性进行验证,验证结果与模型试验的理论分析结果较为接近,表明该法具有较好的可行性和有效性,可考虑用于预测月球车的月面牵引性能.     

Powered-descent trajectory optimization scheme for Mars landing

This paper presents a trajectory optimization scheme for powered-descent phase of Mars landing with considerations of disturbance. Firstly, θ–D$\theta ''–''D$ method is applied to design a suboptimal control law with descent model in the absence of disturbance. Secondly, disturbance is estimated by disturbance observer, and the disturbance estimation is as feedforward compensation. Then, semi-global stability analysis of the composite controller consisting of the nonlinear suboptimal controller and the disturbance feedforward compensation is proposed. Finally, to verify the effectiveness of proposed control scheme, an application including relevant simulations on a Mars landing mission is demonstrated.     

太阳活动与全球气候变化

太阳不断向地球辐射电磁波和粒子, 太阳辐射是地球气候系统最主要的能量来源. 地球气候系统对太阳活动的响应是一个复杂的过程, 包括辐射过程、动力学过程以及微观物理过程等. 根据太阳辐射的卫星观测结果和重建结果, 例举了古气候、温度、大气环流和云量等方面太阳影响气候的观测证据, 论述了太阳影响气候的三种可能机制, 即太阳总辐射变化可以影响地表温度, 并通过海-气耦合改变大气环流; 太阳紫外辐射通过调制平流层的温度和风场影响下面的对流层; 太阳通过行星际磁场调制银河宇宙线, 而银河宇宙线通过电离大气影响云量, 进而改变地球的能量收支.