基于星载毫米波顺轨-交轨InISAR的空间运动目标三维成像技术研究

研究了低信噪比情况下的星载毫米波顺轨/交轨In\|ISAR空间目标三维成像问题。由于传统的RD成像算法在目标尺寸较大和分辨率要求较高时不能取得较好的成像效果,故将波数域成像算法引入运动目标成像处理以获得高分辨率的二维图像,继而将顺轨/交轨三天线ISAR图像分别进行干涉处理,获得了目标上各散射点的三维位置。作为二维成像、图像配准等重要环节的基础参数,对低信噪比下的目标检测和三维运动参数估计进行了研究,分析了速度估计精度要求。最后,仿真结果表明了顺轨/交轨In-ISAR系统的有效性。     

一种正向乘波前体设计方法初步研究

以定楔角乘波体设计方法为基础,研究了影响高超/超声速乘波体"乘波"的主要因素,给出了前体前缘实际气流压缩角的确定方法及影响因素,可知在相同的来流马赫数和压缩角δ下,随着前缘角θ和气流与前缘夹角α的增加,实际气流偏转角γ减小。据此,基于幂函数进气道前体构形,给出了前缘激波不脱体的限制条件及具体的判定方法,分析了乘波体典型几何特征参数对前缘激波不脱体的影响规律,结果显示在相同的来流马赫数和压缩角度下,增大前缘形状因子n,减小前体的长宽比L/W及增大前缘角均有利于激波不脱体。根据给出的前体几何参数对前缘激波脱体的影响规律曲线,对一种"前体几何外形构造+前缘激波附体条件限制"的正向前体乘波器工程设计方法进行了研究,给出了具体设计流程,并进行了初步的数值仿真验证,表明通过该方法设计的乘波前体流动特征与预期的结果吻合,说明文中所给出的激波附体条件及影响规律是可信的,乘波前体设计方法是可行的。     

Sound insulation performance of plates with interconnected distributed piezoelectric patches

This paper deals with the sound insulation performance of a thin plate with intercon-nected distributed piezoelectric patches. Piezoelectric patches are periodically bonded on the sur-faces of the plate in a collocated fashion, and are interconnected via an inductive circuit network. This piezoelectric system is termed as piezo-electromechanical (PEM) plate in the paper. Homogenization methods are involved under a sub-wavelength assumption to analytically develop the dynamical equations for the PEM plate. The dispersion relationships and energy densities of the wave modes propagating in the PEM plate are studied;the sub-wavelength assumption is verified for the simulations in this paper. The coincidence frequency of the PEM plate is researched, and results show that the coincidence frequency of the PEM plate will disappear at certain circum-stances;mathematical and physical explanations are made for this phenomenon. The disappearance of the coincidence frequency is used to optimize the value of inductance, for the purpose of improv-ing the sound transmission loss of the PEM plate.     

Investigation of dynamics of discrete framed structures by a numerical wave-based method and an analytical homogenization approach

In this article, the analytical homogenization method of periodic discrete media (HPDM) and the numerical condensed wave finite element method (CWFEM) are employed to study the lon-gitudinal and transverse vibrations of framed structures. The valid frequency range of the HPDM is re-evaluated using the wave propagation feature identified by the CWFEM. The relative error of the wavenumber by the HPDM compared to that by the CWFEM is illustrated in functions of fre-quency and scale ratio. A parametric study on the thickness of the structure is carried out where the dispersion relation and the relative error are given for three different thicknesses. The dynamics of a finite structure such as natural frequency and forced response are also investigated using the HPDM and the CWFEM.     

A novel approach for predicting inlet pressure of aircraft hydraulic pumps under transient conditions

Cavitation caused by insufficient suction is a major factor that influences the life of aircraft pumps. Currently, pressurizing the tank can solve the cavitation problem under steady large-flow conditions. However, this method is not always effective under transient conditions (from zero flow to full flow in a very short time). Moreover, to apply and design other measures, such as a boost impeller, the suction dynamics during the transient period must be investigated. In this paper, a novel approach based on the pressure wave propagation theory is proposed for predicting the inlet pressure of an aircraft pump under transient conditions. First, a dynamic model of a typical aircraft pump is established in the form of differential equations. Then, the transient flow model of the inlet line is described using momentum and continuity equations, and the governing equations are discretized by the method of characteristics and the finite difference method. The simulated results are in good agreement with the results from verification tests. Further simulation analysis indicates that the wave velocity and transient time may influence the inlet and reservoir pressure as well as the size of the inlet line. Finally, solutions for upgrading the inlet pressure are discussed. These solutions provide guidelines for designing inlet installations.     

多功能信号发生器的设计与制作

仪器由AT89C55单片机进行控制,通过键盘、LCD显示模块进行人机对话,完成波形选择、频段选择,频率、幅度输出控制。由MAX038产生正弦波、方波、三角波,其波形选择由单片机进行控制;频段选择由五档组成,可通过旋扭开关完成;频率由单片机输出数据经D/A转换后控制MAX038;幅度由单片机输出数据经D/A转换后改变放大器负反馈深度来实现输出信号幅度的变化。     

LSDW速度随激光参数和环境气体压强变化规律的实验研究

对LSDW速度随入射激光能量、激光聚焦角度和环境气体压强变化的规律进行了实验研究。研究发现,入射单脉冲激光能量越大,聚焦角度越小,环境气体压强越小,LSDW的传播速度越大。实验测量得到的LS-DW速度随入射激光能量、聚焦角度和环境气体压强的变化规律与一维理论公式中体现的规律完全一致。将相同条件下的实验数据与理论结果进行比较后发现,二者在定性上取得了很好的一致性,但在定量上有所差别,因此需要对现有一维理论公式进行修正,以便更深入地研究LSDW的传播演化规律和特性。     

引导场对无碰撞电流片低频电磁不稳定性的影响

通过数值求解无碰撞电流片中可压缩磁流体力学模型下得到的一般形式的色散关系,讨论了无碰撞电流片中引导场对低频电磁波不稳定性的影响.结果表明,平衡态磁场中的引导场,对于三维扰动传播的波不稳定性有很强的影响.(1)在电流片中间平面上(z=0),无引导场时,没有不稳定性发生,但若存在引导场,不稳定性便发生,并随着引导场的增强,不稳定性明显增强,不稳定的波模可能是低混杂模.(2)在中间平面附近(z=0.2),电流片是不稳定的.随着引导场的增强,不稳定性增长率明显地增强,不稳定的波模从平行和反平行两个方向传播变为反平行方向一个方向传播,并且是斜传播的,具有低频哨声模或低混杂模的特征.(3)在电流片边缘附近(z=0.8),引导场对不稳定的波模和增长率没有明显影响,不稳定的波模都是准平行的哨声波.      

基于波形综合的雷达目标识别的自相关法

讨论雷达反隐身技术中的目标识别方法。重点介绍基于自然频率的波形综合雷达目标识别方法。针对实际雷达目标均被噪声污染 ,提出一种抗干扰能力强的自相关函数算法 ,给出该算法的实现步骤 ,进行计算机仿真试验 ,仿真结果表明 ,所提出的雷达目标识别方法有效。     

旋转飞行器应答式速度测量研究

由于受单天线的方向性限制,采用传统的天线模式不能实现对旋转飞行器连续跟踪测量。通过多天线分集和合成2种模式,可以实现信号的全向接收和转发,但同时带来接收信号阶跃以及信号干涉区等新问题,这些问题会导致信号变化剧烈,能否正确描述信号动态下的特征,并分析其对设备多普勒回路的影响是实现连续高精度跟踪的关键。本文推导了多天线动态下的双程应答多普勒测速方程,详细分析了分集、合成2种天线模式下信号的特征及信号对多普勒回路的影响,并根据分析结果对多普勒回路提出改进建议。