卫星导航系统服务可用性分析仿真系统的设计与实现

服务可用性分析是导航工程总体仿真验证与测试评估系统的核心模块之一,用于分析卫星导航系统提供的导航服务满足用户需求的时间百分比,能够直观地反映卫星导航系统服务能力。文章介绍了卫星导航系统服务可用性的相关概念,探讨了计算服务可用性的确定性算法和随机性算法,在此基础上提出了面向卫星导航系统的服务可用性仿真模型框架,并设计和实现了一个支持服务可用性分析的仿真系统。针对中国区域格网进行了服务可用性的仿真试验分析,验证了仿真模型框架和仿真系统的有效性。     

水平管内气液两相泡状流壁面切应力的实验测量

利用TSI-1268W热膜探针测量了内径为35mm的水平管内气液两相泡状流的壁面切应力,得到了充分发展段上壁面切应力沿周向的分布数据.测量结果表明,液相中加入气泡后,在管道下部的壁面切应力增大,在含气率较高的管道上部出现了壁面切应力减小的现象.随着气相流速的增加,管道上部的壁面切应力有较小幅度的降低,管道中下部的壁面切应力有较大幅度的增加.     

大型运输机全寿命成本模型分析

大型运输机的发展,对于国民经济及国防事业发展具有重要的意义。由于研制大型运输机发展人力、财力投入大,使用周期长,因而,早期研制阶段进行全寿命成本模型分析对于研制方案的优选、提高竞争水平具有重要影响。本文从大型运输机概念设计中对经济性分析的需求出发,结合我国国情,探讨了大型运输机全寿命成本模型的建立方法。     

分离式飞机应急数据记录跟踪系统设计与试验

分离式飞机应急数据记录跟踪系统具备智能弹射与分离、拖曳式跟踪拍摄、缓降与应急漂浮和数据传输等功能,针对弹射和缓降等过程进行了系统设计和无人机试验验证。同时,针对伞-囊组合体的特点,分析了气囊尾流区中伞衣阻力系数的变化规律。结果表明:气囊半径和伞衣名义直径是影响伞衣阻力系数的主要因素;伞衣阻力系数随气囊半径增大而下降,随伞衣名义直径增大而上升;在气动力分析和数值模拟的基础上,确定了伞衣阻力系数的计算公式。无人机试验完成各项设计功能,系统整体方案合理可行,为后续工程应用提供了重要参考。      

基于实时引导修正的大口径天线对星快速校相方法

对测控站中快速校准和差通道相位的方法进行了原理分析,以18 m口径天线为例,论证了在X频段下大口径天线的空间波束相对于S频段更窄,利用X频段空间目标进行快速校相时需要天线系统提供更高的指向精度来满足校相时的角度偏置处于主瓣内.通过分析抛物面天线的指向误差源和模型,提出了基于该模型进行目标引导数据误差反向修正的工程应用方...     

高能固体推进剂燃烧转爆轰的数值模拟

利用一维两相反应流模型,建立了NEPE高能推进剂在颗粒床中燃烧转爆轰的控制方程和辅助方程,用M ac-Corm ack差分格式进行数值求解,并与实验值进行了比较。结果表明,数值预测与试验结果有较好的一致性,在DDT的各个阶段,颗粒床都存在不同程度的动态压缩,压缩波和燃烧波的相互作用是NEPE推进剂燃烧向爆轰转变的内在原因。     

Analysis of blade vibration response induced by rotating stall in axial compressor

An experimental and numerical study was conducted to investigate the forced response of blade vibration induced by rotating stall in a low speed axial compressor. Measurements have been made of the transient stalling process in a low speed axial compressor stage. The CFD study was performed using solution of 3-dimensional Navier-Stokes equations, coupled with structure finite element models for the blades to identify modal shapes and structural deformations simultaneously. Interactions between fluid and structure were managed in a coupled manner, based on the interface information exchange until convergence in each time step. Based on the rotating stall measurement data obtained from a low speed axial compressor, the blade aeroelastic response induced by the rotating stall flow field was analyzed to study the vibration characteristics and the correlation between the phenomena. With this approach,good agreement between the numerical results and the experimental data was observed. The flow phenomena were well captured, and the results indicate that the rotating field stall plays a significant role in the blade vibration and stress affected by the flow excitation.      

多舱耦合流体系统在功耗调配模式下的模拟分析

结合某种航天器,设计了一种多舱耦合的集成式热管理的流体回路系统。介绍了该系统的结构和功耗调配模式、流体回路热耦合方式,运用商业软件SINDA/FLUINT建立回路的流体和热模型,对不同功耗调配模式下流体回路不同热耦合方式进行分析。模拟结果表明,该回路最佳的工作模式为中、低温功耗调配与中温回路热耦合相结合,在这种工作模式下,调配效率可保持在η≈1,即功耗调配量与热耦合的传递热量总能近乎相等。     

High Hardware Utilization and Low Memory Block Requirement Decoding of QC-LDPC Codes

This paper presents a simple yet effective decoding for general quasi-cyclic low-density parity-check (QC-LDPC) codes, which not only achieves high hardware utility efficiency (HUE), but also brings about great memory block reduction without any performance degradation. The main idea is to split the check matrix into several row blocks, then to perform the improved message passing computations sequentially block by block. As the decoding algorithm improves, the sequential tie between the two-phase computations is broken, so that the two-phase computations can be overlapped which bring in high HUE. Two overlapping schemes are also presented, each of which suits a different situation. In addition, an efficient memory arrangement scheme is proposed to reduce the great memory block requirement of the LDPC decoder. As an example, for the 0.4 rate LDPC code selected from Chinese Digital TV Terrestrial Broadcasting (DTTB), our decoding saves over 80% memory blocks compared with the conventional decoding, and the decoder achieves 0.97 HUE. Finally, the 0.4 rate LDPC decoder is implemented on an FPGA device EP2S30 (speed grade -5). Using 8 row processing units, the decoder can achieve a maximum net throughput of 28.5 Mbps at 20 iterations.     

双组元发动机燃烧室瞬态工作过程仿真

为真实模拟双组元姿控发动机燃烧室的瞬态工作过程,耦合考虑了自燃点火与喷雾燃烧过程,提出了适合于准一维计算的求解燃烧室气体参数的新方法,发展了可反映集液腔填充和排空过程影响的喷注质量子模型,建立了分析双组元姿控发动机燃烧室瞬态工作过程的准一维模型。利用此仿真模型分析了EADS 10N姿控发动机燃烧室的单脉冲和多脉冲工作过程,得到了真空推力、液滴位置分布和总冲等结果,并与文献中的试验结果进行了比较分析。表明仿真结果与试验结果一致性较好。