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DSPN的SCI建模与性能分析

在新一代综合航电系统中,由于传统总线传输上的"瓶颈"问题,使得1553B总线远远满足不了系统信息传输的要求,可变规模相干接口(SCI)的出现,弥补了传统总线技术的不足,大大提高了信息交互的效率和带宽,满足了系统中和系统间的互连要求,成为先进互连技术的代表,其低延迟高带宽的特点完全可胜任各种关键应用领域.给出了一套完整的基于确定与随机Perei网的可变规模相干接口建模和性能分析算法.通过解决SCI性能评估建模的问题,进而得到系统吞吐量与延迟时间之间的关系.     

基于网络编码的空间DTN LTP协议改进

随着空间通信技术与应用的不断发展,空间DTN (Delay Tolerant Network,容延迟网络)中节点之间数据传输的重要性日益明显。针对空间DTN的可靠信息传输需求,首先介绍了空间DTN的特点及信息传输协议体系,并对LTP (Licklider Transmission Protocol,立克里德传输协议) 进行了重点分析。然后针对空间DTN中LTP协议的缺点和不足,研究提出了基于网络编码的空间DTNLTP传输协议改进策略——NC-LTP协议,并通过数学仿真对算法性能进行了分析评估。仿真结果表明,相比于LTP协议,NC-LTP协议在不同信道传输时延、不同丢包率等条件下的适应性方面表现出较大的优势,因此NC-LTP协议更适用于具有高动态特性、高信道误码率、带宽受限的空间DTN环境。     

基于非合作LEO卫星辅助GNSS联合定位技术CSCD

针对全球导航卫星系统(GNSS)在受挑战的环境中,出现导航卫星信号被干扰或遮挡,导致可见卫星数目无法满足定位最低要求的情况。利用低轨(LEO)卫星具有信号到达地面功率高、抗干扰能力强,以及在未来将进行大量部署的特点,可为GNSS的导航服务提供备份与补充。提出了基于非合作LEO卫星辅助GNSS联合定位算法,不同于现有的LEO/GNSS联合定位算法将低轨卫星简单地视为轨道降低的导航卫星,该算法以LEO为通信卫星,从非合作、非导航特性的实际情况出发,将LEO的多普勒与GNSS的伪距、多普勒相结合求解用户位置信息,并以ORBCOMM低轨通信卫星联合GPS为例进行了仿真实验,实验结果验证了算法的可行性与性能。     

深空通信中CFDP协议应用优化分析

在对CCSDS(空间数据系统咨询委员会)的CFDP(CCSDS文件传输协议)工作过程和延时性能进行分析的基础上,提出深空通信环境下,适用于工程实际的协议传输效率优化目标。针对提高传输性能进行参数优化分析,并给出了获取最优化的PDU(协议数据单元)长度的方法。仿真分析了传输文件数据量、距离、误码率、带宽等任务和环境因素对CFDP协议实际使用效果和最优PDU长度选取的影响。仿真结果表明,根据具体的任务和环境条件使用分析优化后的PDU长度参数,可以使CFDP协议达到更高的实际传输效率。     

VxWorks6.8操作系统下NVMe驱动设计

非易失存储器(NVMe)协议是寄存器级的传输协议,用于实现主控软件与非易失存储设备间的数据传输,其在设计时针对固态硬盘(SSD)特性优化了命令发送和完成路径,通过PCIe链路传输数据,利用PCIe高带宽实现高速数据传输。阐述了VxWorks 6.8实时操作系统下NVMe驱动设计流程,实现了NVMe协议的基本功能,并测试验证其功能和效率;测试结果表明,该系统下NVMe驱动发挥了较高的性能,单向数据传输速率约为700 MB/s(PCIe1.0×4),相较于SATA接口SSD有极大的性能提升,具有广泛的应用价值。     

消息队列在智能优化算法中的应用

针对启发式智能优化算法的特点,为提高算法的优化效率,以消息队列机制为基础提出了一种多线程并行计算技术。讨论了多线程并行计算的模型及原理,介绍了多线程之间通过消息队列相互通信的同步控制技术。通过气动优化问题在不同线程数目下并行计算的比较,表明消息队列可以简化线程间的通信过程,显著提高计算效率,具有一定的实用价值。     

空间通信中的一种滑动窗口BATS码传输方案研究

针对空间通信中链路传播时延大、丢包率高、中继节点多的问题,在具有良好多级中继传输性能的BATS码基础上,提出一种滑动窗口传输方案,以提高空间传输的可靠性和时效性。利用小度值Batch对滑动窗口的非重叠区域进行编码传输,并采用不等滑动步长,实现了对滑动窗口的重叠部分和非重叠部分的均衡保护,使传输既具有较高可靠性,又具有较高的传输效率。仿真结果表明,在维持与传统的连续重叠滑窗相近可靠性的同时,传输效率提高约20%。     

台速度估计(英文)

针对惯性稳定平台中高精度和高带宽的速度信号需求,提出了基于低成本MEMS传感器的最优速度估计算法。采用一种新颖的传感器组合形式,包括一个低带宽的MEMS陀螺和两个低性能的MEMS加速度计。陀螺由于自身动态特性的影响,主要提供速度的低频信息,加速度计组合则由于自身偏置的影响,主要提供速度的高频信息,而估计器将两者信号进行融合。实验表明:最优状态估计器能够在时频域上,提供无偏的、高性能的速度信号。同时,在单自由度微型惯性稳定平台的应用过程中,其控制性能得到了相应的提高。该算法也适用于机器人控制、姿态估计和摩擦补偿等领域。     

基于FC 桘AE桘ASM的可靠传输协议

光纤通道匿名用户消息协议（ FC-AE-ASM ）被设计应用于航空电子环境中各子系统的互联通信,但其并未提供数据端到端的可靠性保证,因此不能被直接应用于大规模数据传输及文件下载等应用。在FC-AE-ASM协议上层,针对ASM消息采用滑动窗口机制保证数据无重复、无丢包地按序递交,实现数据的高速可靠传输。在PC机上采用2．125 GB／s的FC仿真卡进行测试,结果表明,提出的可靠传输协议能在保证数据可靠传输的同时有效提高带宽利用率。实际测试带宽可达到34．9MB／s,相比停止等待协议提高了50％,满足实际应用需求。     

The effect of inlet conditions on the flow and heat transfer in multiple rotating cavity with axial throughflow

This paper discusses experimental results from two different build configurations of a heated multiple rotating cavity test rig.Measurements of heat transfer from the discs and tangential velocities are presented.The test rig is a 70% full scale version of a high pressure compressor stack of an axial gas turbine engine.Of particular interest are the internal cylindrical cavities formed by adjacent discs and the interaction of these with a central axial throughflow of cooling air.Tests were carried out for a range of non-dimensional parameters representative of high pressure compressor internal air system flows(Re up to 5×106 and Rez up to 2×105).Two different builds have been tested.The most significant difference between these two build configurations is the size of the annular gap between the(non-rotating) drive shaft and the bores of the discs.The heat transfer data were obtained from thermocouple measurements of surface temperature and a conduction solution method.The velocity measurements were made using a two component,LDA system.The heat transfer results from the discs show differences between the two builds.This is attributed to the wider annular gap allowing more of the throughflow to penetrate into the cavity.There are also significant differences between the radial distributions of tangential velocity in the two builds of the test rig.For the narrow annular gap,there is an increase of non-dimensional tangential velocity V/Ωr with radial location to solid body rotation V/Ωr=1.For the wider annular gap,the non-dimensional velocities show a decrease with radial location to solid body rotation.      

Research on Auto-detection for Remainder Particles of Aerospace Relay Based on Wavelet Analysis

Aerospace relay is one kind of electronic components which is used widely in national defense system and aerospace system. The existence of remainder particles induces the reliability declining, which has become a severe problem in the development of aerospace relay. Traditional particle impact noise detection (PIND) method for remainder detection is ineffective for small particles, due to its low precision and involvement of subjective factors. An auto-detection method for PIND output signals is proposed in this paper, which is based on direct wavelet de-noising (DWD), cross-correlation analysis (CCA) and homo-filtering (HF), the method enhances the affectiv-ity of PIND test about the small particles. In the end, some practical PIND output signals are analysed, and the validity of this new method is proved.     

Preparation of Highly Dispersed Antimony-doped Tin Oxide Nano-powder via Ion-exchange Hydrolysis of SnCl4 and SbCl3 and Azeotropic Drying

Antimony-doped tin hydroxide colloid precipitates have been synthesized by hydrolysis of SnCl4 and SbCl3 using: (1) an ion-exchange hydrolysis to remove chlorine ions, and (2) isoamyl acetate as an azeotropic solvent to obviate water. The obtained dried powder is of high dispersivity without any need for further grinding. The size and dispersivity of the final particles are investigated with the aid of TG-DTA, BET, XRD and TEM. After having calcined, the antimony-doped tin oxide nanopowder possesses a tetragonal rutile structure with high dispersivity, uniform particles and low hard agglomeration.     

Effects of Mo on the Microstructure and Hydrogen Sorption Properties of Ti-Mo Getters

The effects of Mo on the microstructure evolution, porosity and hydrogen sorption properties of Ti-Mo getters are investigated in this work. The results show that the addition of Mo prolongs the densification process of Ti-Mo getters and results in a significant amount of sintered pores. With the Mo content increasing, the porosity of getters firstly increases reaching the maximum value as it at- tains about 7.5wt.%, and then drops. At the room temperature, the hydrogen sorption property of getters increases progressively with the Mo content increasing, but the tendency is not very clear before its content lies below 2.5wt.%. When the Mo content achieves about 7.5wt.%, the hydrogen sorption property proves to be the best. The discussion is made about the above mentioned phenomena inclusive of hydrogen sorption properties of getters under different activation conditions (from 500-750 ℃).     

超声速燃烧数值模拟中的湍流与化学反应相互作用模型

高精度数值模拟有助于理解超声速湍流燃烧中湍流与化学反应的相互作用,可为发动机燃烧室等工程应用设计提供可靠的预测模型。除直接数值模拟外,目前在湍流燃烧应用中使用的大涡模拟和雷诺平均Navier-Stokes模拟均需要借助模型模化发生在湍流小尺度上的流动与化学反应过程对湍流大尺度运动的影响。现有的湍流与化学反应相互作用模型大致可分为:火焰面类模型和概率密度函数类模型,2类模型在不同的应用中各自具有优势和局限性。此外,现有模型大都基于低马赫数燃烧,而超声速燃烧中通常会伴随快速混合、局部熄火和再着火以及激波等复杂过程,这为发展其中的湍流与化学反应相互作用模型提出了更多的挑战。     

适于低轨卫星IP网络的单核共享树组播算法(英文)

为了解决低轨卫星IP网络中现有典型源组播算法的信道资源浪费问题,本文提出了一套单核共享树组播算法,即核心群合并共享树(CCST)和加权核心群合并共享树(w-CCST)算法。CCST 算法包括动态近似中心(DAC)选核方法和核心群合并组播路径构建方法。DAC方法专为周期、规律运动的低轨卫星网络提出,不需要复杂的星上计算。在核心群合并方法中,以核节点作为初始核心群,通过核心群和剩余组成员的最短路径方法逐步扩展直至整棵组播树构建完成,从而使得组播树的树代价最小,大大提高了网络的带宽利用率和组播传输效率。w-CCST 算法中所提出的加权因子可以调整树代价和端到端传播时延之间的折衷程度,因此,可以通过调整加权因子来适度增大树代价、降低端到端传播时延以支持某些端到端时延要求苛刻的实时组播业务。最后,与低轨卫星 IP 网络中典型算法进行了性能比较,仿真结果说明,CCST 算法的平均树代价比其它算法显著降低,w-CCST 算法的平均端到端传播时延小于 CCST 算法。     

Jet Vectoring Control Using a Novel Synthetic Jet Actuator

A primary air jet vectoring control system with a novel synthetic jet actuator (SJA) is presented and simulated numerically. The results show that, in comparison with an existing traditional synthetic jet actuator, which is able to perform the duty of either “push” or “pull”, one novel synthetic jet actuator can fulfill both “push” and “pull” functions to vector the primary jet by shifting a slide block inside it. Therefore, because the new actuator possesses greater efficiency, it has potentiality to replace the existing one in various appli- cations, such as thrust vectoring and the reduction of thermal signature. Moreover, as the novel actuator can fulfill those functions that the existing one can not, it may well be expected to popularize it into more flow control systems.     

Nonlinear Adaptive Slewing Motion Control of Spacecraft Truss Driven by Synchronous V-gimbaled CMG Precession

The slewing motion control of a truss arm driven by a V-gimbaled control-moment-gyro (CMG) is a nonlinear control problem. The V-gimbaled CMG consists of a pair of gyros that must precess synchronously. The moment of inertia of the system, the angular momentum of the gyros and the external disturbances are not exactly known. With the help of feedback linearization and recursive Lyapunov design method, an adaptive nonlinear controller is designed to deal with the unknown items. Performance of the proposed controller is verified by simulation.     

An SOR Implicit Time-accurate Scheme in Calculating Unsteady Flows

A new time-accurate marching scheme for unsteady flow calculations is proposed in the present work. This method is the combination of classical Successive Over-Relaxation (SOR) iteration method and Jacobian matrix diagonally dominant splitting method of LUSGS. One advantage of this algorithm is the second-order accuracy because of no factorization error. Another advantage is the low computational cost because the Jacobian matrices and fluxes are only calculated once in each physical time step. And, the SOR algorithm has better convergence property than Gauss-Seidel. To investigate its accuracy and convergency, several unsteady flow computa- tional tests are carried out by using the proposed SOR algorithm. Roe’s FDS scheme is used to discritize the inviscid flux terms. Un- steady computational results of SOR are compared with the experiment results and those of Gauss-Seidel. Results reveal that the numerical results agree well with the experimental data and the second-order accuracy can be obtained as the Gauss-Seidel for unsteady flow computations. The impact of SOR factor is investigated for unsteady computations by using different SOR factors in this algorithm to simulate each computational test. Different numbers of inner iterations are needed to converge to the same criterion for different SOR factors and optimal choice of SOR factor can improve the computational efficiency greatly.