大多普勒容限巴克码脉压

 本文介绍用补偿式非相干型旁瓣抑制滤波器(SSF)实现13位巴克码脉冲压缩旁瓣抑制的理论计算及实验结果。补偿式非相干型SSF采用最小二乘近似逆滤波方法设计,若子脉冲宽度为0.7μs,峰值旁瓣电平不超过-30dB,这种SSF的多普勒容限能达到-40kHz～+40kHz。理论计算及实验结果都表明,所设计的补偿式非相干型SSF的多普勒容限比具有同样长度冲激响应序列的R-G-ISSF有显著改善。     

11位巴克码的LP滤波器及其在多普勒频移下的性能

本文介绍使最大旁瓣值最小的11位巴克码滤波器（LP滤波器）的计算结果。并介绍多普勒频移对这种滤波器性能影响。LP滤波器长度为53时,旁瓣电平降到—39.5dB,比匹配滤波器改善18.7dB。对加权序列长度L为41、45、49和53的11位巴克码的LP滤波器计算结果表明,其性能受多普勒频移的影响表现为:它们的主瓣电平下降、主瓣展宽、最小旁瓣电平上升、旁瓣电平平方和上升和信噪比损失增大。在较小的多普勒频移（f_d）时,L大的LP滤波器其性能优于L小的LP滤波器,在多普勒频移交大时,这种优势逐渐消失,不同长度LP滤波器性能大体一致。     

基于常规多普勒滤波器组结构的合成宽带距离像性能分析

为了消除散布效应对宽带信号的不利影响,可以利用多个窄带信号合成宽带信号;同时,通过在子带内处理相干脉冲串,可进行杂波抑制、目标速度估计和区分不同速度的目标。然而,在子带内分别使用常规多普勒滤波器组,会引进多普勒散布效应所造成的输出失配误差,从而造成合成距离像的失真。分析了多普勒散布效应与子带常规多普勒滤波器组输出失配之间的关系,推导了运动目标通过滤波器组后所成高分辨距离像的距离走动公式,给出了适合子带常规多普勒滤波器组的目标速度临界值。仿真实验验证了以上结论。     

间歇采样转发干扰对相位编码雷达的影响分析

文章分析了间歇采样转发干扰对相位编码脉冲压缩雷达的影响。首先,推导得到了相位编码信号通过匹配滤波器的输出响应。在此基础上,推导了间歇采样转发干扰的匹配输出,研究表明,输出响应为信号编码与间歇采样编码互相关序列的线性插值函数,且只能产生一个假目标。然后,研究了旁瓣抑制网络对间歇采样转发干扰信号的影响,结果表明,旁瓣抑制网络可以有效抑制回波信号的旁瓣,但无法抑制干扰信号的旁瓣。相比输入前数值,干扰旁瓣峰值和位置均发生变化。最后,通过编程计算和仿真实验验证了本文分析的正确性。该研究为雷达对抗干扰评估试验提供重要的理论支撑。     

两种自适应方向图峰值副瓣控制方法比较

自适应阵列（或称自适应波束形成）目前已广泛应用到雷达、声纳和通信领域中用来抑制各种干扰（有意的干扰，杂波干扰和多用户干扰等）。在雷达应用中，为了减轻脉冲欺骗式干扰或旁瓣目标并利用单脉冲雷达来准确测量目标波达方向．要求自适应方向图具有低副瓣和稳定的主瓣形状。在实际应用中，各种失配误差将降低自适应阵列的性能．这些误差包括由于目标的波达方向不精确引起的信号指向误差，由通道失配和位置扰动引起的阵列校准误差和由小样本教引起的协方差矩阵估计误差。在此情况下，自适应波束形成的性能大大下降（干扰抑制性能变差。主瓣失真和高的副瓣）。已提出了一种基于二次约束的集成峰值副瓣控制（integrated peak sidelobe control，简称IPSC）方法。该方法可以精确地控制峰值副瓣电平并产生具有稳定的主瓣形状的自适应方向图。研究IPSC中目标信号的影响和信号消除方案以进一步提高IPSC的性能。并将IPSC方法和最新提出的基于二阶锥规划（second-order cone programming，简称SOCP）的分布式峰值副瓣控制（distfibuted peak sidelobe control，简称为DPSC）新方法在性能上进行了比较。仿真结果表明。在干扰抑制性能和方向图控制质量方面IPSC比DPSC性能优越。此外IPSC比DPSC计算高效。     

基于非线性自适应滤波器的海杂波抑制技术

海杂波会严重影响雷达对海洋表面目标的检测。为了提高海洋表面目标的检测性能,基于非线性自适应滤波器,提出了海杂波抑制方法,实现了海杂波抑制。介绍了非线性自适应滤波器的原理以及利用梯度下降法训练滤波器的方法。利用IPIX雷达实测海杂波数据,分别针对岸基雷达和机载雷达,进行了此方法的仿真试验,从均方预测误差(MSE)和信杂比改善因子(IF)两个方面,分析了此方法的性能。并与基于线性预测的LMS算法进行了比较,得出了此方法对慢速目标的检测性能优于线性方法。     

运动声呐空时自适应处理中的多普勒影响分析

为了将空时自适应处理(STAP)理论更好地应用于水下环境,提高运动声呐对混响的抑制性能,研究了多普勒对运动声呐STAP的影响。具体分析了由多普勒造成的回波脉宽伸缩变换以及目标空时导向向量失配带来的影响。分析结果表明,回波包络脉宽变化对于匹配滤波输出信噪比影响较小,而对空时导向向量修正可以有效提高目标方位估计精度以及混响抑制能力。     

任意采样率变换数字重构滤波器设计

针对理想重构函数在数字信号域不可实现而直接截取性能较差的情况,根据信号重构理论和FIR（Finite Impulse Response,有限脉冲响应）滤波器窗函数设计法,分析不同窗函数、不同截取长度对重构滤波器的影响,提出一种凯塞窗任意采样率变换数字重构滤波器设计方法.该方法通过选择合适的窗参数、截取长度、重构滤波器时域精度和量化位数,有效控制阻带最小衰减抑制数字重构镜像.设计的数字重构滤波器已成功应用于某卫星基带调制解调器,符合镜像抑制大于65 dB的性能要求.     

光纤数据网络线路码型分析

 运用Ｐｅｒｓｏｎｉｃｋ－ＣＣＩＴＴ法对光纤数据网络的５种线路码型分析,对比了在不同组态下的灵敏度及部分实用化特性,从而提供了在不同情况下网络线路码型选用的参考依据。     

脉冲压缩在铝薄板电磁超声导波检测中的应用

针对电磁超声换能器(EMAT)换能效率低导致超声回波信噪比(SNR)差这一问题,基于相位编码脉冲压缩技术,讨论了匹配滤波器及旁瓣抑制滤波器的设计及其在电磁超声检测中的实现.选用典型二相编码信号-巴克码作为激励信号,分析了不同码长、载波周期数的巴克码信号对电磁超声导波检测脉冲压缩效果的影响,并研究了旁瓣抑制算法的效果.以...     

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.