基于SRAM型FPGA单粒子效应综合防护技术

为解决基于SRAM(Static Random Access Memory,静态随机存储器)型FPGA(Field Programmable Gate Array,现场可编程门阵列)的扩频应答机在空间环境中时常发生功能故障的难题,提出了一种低轨卫星基于SRAM型FPGA的应答机的单粒子综合防护方案。该方案在代码级、器件级、单机级、整星级综合采用器件优选、结构屏蔽设计、巡检自愈、自主复位等多种方法,有效杜绝了单粒子事件带来的种种危害,已成功应用于某在轨卫星。在轨测试结果表明:遥测、遥控、跟踪测量等功能、性能指标满足任务要求,且未发生需要地面干预的问题或现象。该技术还可推广应用于其他采用低等级器件及其他类型FPGA、DSP(Digital Signal Processing,数字信号处理)等大规模集成电路的星载单机防护。     

Effects of synthetic jet frequency on the separated flow in a diffusing S-duct

Numerical simulations were carried out to investigate the effects of synthetic jet actuation frequency on the separated flow in a diffusing S-duct. The Reynolds number based on the entrance height was 9.78×105. At first, the numerical model was validated with experimental data, and then, the interaction between the separated flow and the synthetic jets at different frequencies was discussed. The results demonstrate that the control effect is significantly dependent on the momentum mixing enhancement between inside of the separated boundary layer and the outer flow. There exists a narrow range of actuation frequency, in which effective separation control can be achieved using synthetic jets. A dimensionless frequency F+=1.0 is identified as the optimal frequency, with a momentum coefficient of 1.62×10-3, the separation area is reduced about 46%, and the aerodynamic performance of the S-duct is also greatly improved compared to uncontrolled case. Further analysis reveals that the choice of actuation frequency is mainly determined by the momentum flux produced by a single ejection and the spacing between adjacent ejections, the optimal frequency case can be understood as a balance between the two factors. In addition, it is found that the synthetic jets can also suppress the secondary flows while decreasing the separation.      

离散拓扑业务模型中多媒体LEO网络性能分析

针对快速发展的多媒体卫星网络,提出一种新的低地球轨道卫星网络性能的定量研究模型。该模型考虑了星座动态拓扑变化和全球业务需求变化的复杂特点,建立了离散时间下的业务和拓扑映射关系;依据马尔科夫过程理论和卫星链路带宽约束条件,对实时和非实时两种类型业务采用概率分析方法,推导出定量计算阻塞概率、排队时延等网络性能参数的公式。大量仿真结果表明理论分析方法的正确性和有效性。该研究方法可用于多媒体低地球轨道卫星网络QoS路由管理和资源分配设计的参考。     

深微孔内径测量技术研究

介绍了一种基于高准确度电感传感器和红宝石测头,在测长机上实现深微孔径测量的方法,解决了内径的Φ1mm～Φ5mm、深度在40mm以下的深微孔内径的测量问题。通过对深微孔径测量装置测量不确定度的分析,在95%置信概率下,装置的测量不确定度为0.6μm,满足测量要求。     

Al-Li合金搅拌摩擦焊搭接接头的疲劳性能

通过疲劳寿命试验、疲劳断口和金相组织分析,研究了Al-Li合金搅拌摩擦焊搭接接头的疲劳性能,分析了接头前进侧热机影响区(TMAZ, Thermal-Mechanically Affected Zone)出现的"钩状缺陷"对其疲劳性能的影响.结果表明,钩状缺陷容易引起裂纹萌生及扩展,减小接头的有效承载板厚,适当缩短搅拌针长度可以改善钩状缺陷,提高接头力学性能.母材与搭接接头的疲劳S-N曲线研究表明:在高疲劳应力下,接头的疲劳寿命接近母材,但随着疲劳应力水平降低,接头的疲劳寿命急剧下降,200万循环周次下的疲劳强度仅达到80 MPa,为母材的35%.     

New results and questions of lunar exploration from SELENE,Chang’E-1, Chandrayaan-1 and LRO/LCROSS

The moon has longstanding questions such as lunar environments, origin, formation and evolution, magnetization of crustal rocks, internal structure and possible life. The recent lunar missions, e.g., SELenological and ENgineering Explorer “KAGUYA” (SELENE), Chang’E-1, Chandrayaan-1, and Lunar Reconnaissance Orbiter/Lunar CRater Observation and Sensing Satellite (LRO/LCROSS), have provided new opportunities to explore and understand these issues. In this paper, we reviewed and presented the results and findings in the fields of lunar gravity, magnetic field, atmosphere, surface geomorphology and compositional variations, volcano, craters, internal structure, water and life science from new lunar exploration missions. In addition, the new objectives and scientific questions on lunar explorations in near future are presented and discussed.     

星载可展开天线热振动数值分析

根据非耦合动力学理论及有限元方法,研究分析了星载可展开天线的热振动。利用半正弦波温度冲击模拟热动力荷载,对天线典型节点的热振动位移和应力以及形面精度进行了数值分析。研究表明,急剧变化的温度荷载将导致该天线结构发生热振动,热振动响应明显大于静力学响应。     

对接口匹配的航天器双主动最优交会研究

研究了两航天器协同轨道机动（双主动）完成近距离交会任务的最优控制问题。在考虑航天器姿态变化、对接口位置及路径约束的情况下,构建了完整的6自由度、26状态的双主动最优交会数学模型。利用高斯伪谱法分别将燃料总消耗最少和交会时间最短两种最优问题离散为大型非线性规划问题,而后应用SNOPT软件包进行了求解。在此基础上通过大量数值计算分析总结了不同初始参数对最小燃料消耗和最短交会时间的影响规律,并与主被动交会形式进行了对比。结果表明,当两航天器质量接近时,双主动交会通常可明显减少燃料消耗,或缩短交会时间;而当质量差距较大时,双主动最优交会逐渐退化为主被动最优交会。     

前缘吹气控制舵面流动分离

针对各种飞行器大舵偏下出现的流动分离问题,在北航D4风洞对旨在消除舵面流动分离的舵面前缘吹气技术进行了研究,为了降低控制分离所用的吹气量,吹气点设置在舵面前缘气流分离点处.应用粒子图像测速(PIV,Particle Image Velocimetry)技术,分析了舵面绕流在吹气量由小变大过程中所经历的3个不同演化阶段;由测压得到的舵面压力分布则显示,前缘吹气造成的引射作用使前缘吸力峰随吹气量增大而增大,这是前缘吹气能够使舵面升力增大的主要机理.实验结果还表明,前缘吹气可明显提高舵面升力,同时也可以显著降低舵面阻力.     

旋翼微多普勒特性实验分析

为分析旋翼及其主要部件的微多普勒效应特点,提出了一种通过微波暗室进行旋翼微多普勒效应测试的实验方法,并通过实例验证了实验方法的可靠性;两种桨叶不同桨叶片数的系列实验结果表明,旋翼的微多普勒特性通过频率把各个散射部件的回波能量分开,旋翼的片数和转速不影响微多普勒特性的分析估算,旋翼的微多普勒特性仅与其运动特性相关;结合直升机目标识别特征,采用短时傅里叶变换方法对实验数据进行微多普勒效应提取,分析了微多普勒效应与入射波和旋翼几何属性之间的关系,得到了旋翼微多普勒效应的频率特性、极化特性和宽频带特性.