导弹激光反射特性等效模拟

为了使靶标与导弹的激光反射特性相一致,研究了目标激光反射特性等效模拟理论。提出了激光反射综合因子F（A,P,Ω的概念,用其表征目标对激光反射的综合效果,如果目标的F（A,P,Ω相等,就认为其激光反射特性一致。应用三维重建理论,重建了国外某导弹的三维外形。按激光反射特性的等效模拟方法,研究了激光反射特性外场的测试方法,并进行等效模拟的测试。测试结果表明,在测试距离为800m时,在靶头上加贴半径为0．8cm玻璃微珠反射带,靶标与导弹模型回波幅度的比值Vs1／Vs2样本的平均值很接近1,认为等效模拟效果比较理想。激光反射综合因子F（A,P,Ω的提出,解决了导弹激光反射等效模拟的难题,对提高导弹试验的质量起了很大的作用。     

有限声束在固体板表面的声反射

采用将有限声束分解为一系列平面波的方法，对有限声束在液体－固体板－液体结构中的声反射问题进行了分析和计算。当有限声束以平面波反射系数相位为１８０°时的入射角入射时，在固体板表面反射的声束沿板表面存在显著的移动和展宽现象。本文的有关结果，对进一步研究有限声束在板状结构表面的声反射具有积极意义。     

反射声对室内声景主观评价的影响初探

梳理了近年来地面反射声和室内声景观的研究情况,结合实验心理学以及室内声景观主观评价等研究框架,通过三个基于反射声感知的声学可听化实验,确定了在四间房间内人耳对有无地面反射声参与的三种声音信号的绝对感觉阈。结果表明语音信号高于本底噪声10 dB(A)即可被察觉,而水流声及音乐声高于本底噪声17 dB(A)才能够被明显察觉,最后结合实验结果对地面反射声的处理给出了建议。     

音乐厅中后期反射声对空间感的影响

空间感是音乐厅音质中很重要的主观感觉。起初人们对空间感的研究主要集中在与早期侧向反射声有关的空间响应上，近年的研究结果使人们更多地了解到后期反射声也对空间感有所影响。文章将主要介绍音乐厅中后期反射声对空间感主要是听者环绕感（LEV）的影响。     

音乐厅中后期反射声对空间感的影响

空间感是音乐厅音质中很重要的主观感觉.起初人们对空间感的研究主要集中在与早期侧向反射声有关的空间响应上,近年的研究结果使人们更多地了解到后期反射声也对空间感有所影响.文章将主要介绍音乐厅中后期反射声对空间感主要是听者环绕感(LEV)的影响.     

热声热机回热器特性参数影响的模拟分析及优化

本文对回热器的长度、水力半径或板叠间隙、回热器在驻波声场中的位置等回热器特性参数对其性能的影响进行了模拟分析,并在此基础上对回热器或板叠特性参数进行了优化。     

光电经纬仪旋转靶标特性对目标跟踪的影响

旋转靶标是一种室内检测光电经纬仪跟踪性能的常用设备.本文介绍了旋转靶标的基本组成结构和影响靶标运动特性(方位俯仰角速度、角加速度)的基本参数,应用球面三角几何建立了旋转靶标的方位俯仰角坐标方程.依据方位俯仰角坐标方程分析靶标的特性参数对靶标运动特性的影响,说明旋转靶标存在运动特性与实际跟踪目标特性不一致的问题,得出应用...     

基于深海声影区海底反射损失的地声参数反演方法

海底的声速、密度、衰减系数等地声参数,在声场预报、目标定位中十分重要。因地声参数原位测量和海底采样在深海中实施困难,需要寻找新的方法来获取地声参数。在深海声影区环境下,直达波会随着距离的增加而逐渐消失,一次反射波及多次反射波是对深海声影区声场起重要作用的多途信号。文章首先对声影区多途达到结构进行分析,利用多次比较法得到随掠射角变化的反射损失,并对海底地声参数进行反演,然后将反演的地声参数代入声场模型得到海底反射损失,将其与实验测量结果进行比较,结果吻合较好。并通过对反演过程的散点图和后验概率进行分析,证明了反演结果的可靠性。该方法可用于深海声影区的海底地声参数的反演。     

影响模拟声迹质量的因素

模拟声迹在拷贝上的位置较靠近齿孔，由于电影胶片材料的敏感性使胶片齿孔周围的速度发生变化，这样模拟声迹的质量就受到一定的影响；放映机里还原声音时，会使靠近齿孔处的声迹密度发生变化；还有其它一些影响模拟声迹的质量因素。本文将对这些问题利用数据展开讨论。     

基于数值模拟的降温速率对沥青路面反射裂缝扩展研究

为了防治反射裂缝扩展对沥青路面产生的影响,该文基于数值模拟软件RFPA温度版,对预制裂缝的沥青路面模型进行了不同降温速率条件下反射裂缝扩展的数值试验研究。模拟结果显示:(1)降温速率越快,预制裂缝的AC路面结构出现贯通破坏的时间越早,且结构声发射数量也越多。(2)分析面层多单元信息得知,引起路面破坏的最主要原因是拉应力,且在2条裂缝中间位置会出现应力的最大值。最后基于模拟结果,为了防治裂缝扩展,可以设置应力吸收层或者选择传递系数较低的沥青面层材料为寒区沥青路面的施工提出了一些工程指导意见。     

水下目标壳体的镜反射亮点回波结构

文章从工程应用角度讨论水下目标壳体镜反射亮点回波结构。在声呐频率范围内把水下目标壳体作为多层平板处理。应用声线方法和递推关系导出任意多层平板的反射系数。忽略耦合水层两边的多次反射后，得到一组适合于瞬态和亮点分析的反射系数近似公式。利用这组公式依次讨论了：（1）未敷设吸声覆盖层的单层壳体；（2）未敷设吸声覆盖层的双层壳体；（3）敷设吸声覆盖层的单层壳体；（4）敷设吸声覆盖层的双层壳体等4种情况的镜反射亮点回波结构。并给出了数值计算的算例。     

回波信号限幅对声学多普勒测速偏差的影响

声学多普勒测速设备常采用复协方差算法测量多普勒频移,当回波信号出现限幅时会产生频移测量偏差,进而导致测速偏差。文章基于复协方差算法分析了回波信号限幅引起多普勒测速偏差问题的原因,得出限幅后频移测量偏差随真实频移变化而呈现正弦振荡变化的规律,分别使用窄带和宽带发射信号完成回波限幅仿真计算。基于声学多普勒测速仿真器和海上试验完成了对声学多普勒测速设备回波限幅数据的采集,仿真和试验数据结果与理论分析结果一致。     

宽带体制下混响和目标空时分布特征研究

传统的空时自适应处理(Space-Time Adaptive Processing,STAP)利用窄带混响和目标在空时平面的可分辨特征抑制窄带混响。对宽带混响和目标在空时平面分布特征进行研究,并通过理论推导,得出带宽对混响和目标空时分辨特征的影响公式。结果表明:宽带混响和目标在空时平面分布特征部分重叠,导致传统STAP效果不佳。在此基础上,借鉴STAP思想,并利用线性调频(Linear Frequency Modulation,LFM)信号在分数阶Fourier变换域上的聚焦性,分析了在空-分数阶Fourier域三维空间上抑制宽带LFM混响的可行性。     

The influence of roughness, angle, range, and transducer type on the echo signal from planar interfaces

The received electrical echo signal from a pulse-echo system insonifying a planar interface was measured for varying degrees of rms roughness [0 to 0.29 mm (0 to 1.7 λ)], angles of incidence, &thetas;, (-7° to 7°), and ranges to a planar or focused transducer. The effect of varying a is quantified in terms of the energy of the received signal, E(&thetas;), and the normalized spectrum of the received signal. E(&thetas;) is approximately Gaussian when using a planar transducer or a focused transducer with the reflecting interface located at or beyond the focal point. For focused transducers with the interface located closer than the geometrical point of focus, two maxima can sometimes be observed when varying the incident angle. As is generally known, the width of E(&thetas;) is strongly dependent on transducer type, e.g., for a smooth interface, the -3 dB width for a 25.4 mm diameter 5-MHz planar and focused transducer was approximately 0.5° and 4° (at the focal point), respectively. E(0°) as a function of surface roughness, R_q, was nearly linear on a decibel scale, with a slope of -109 dB/(R_q/λ) and -61 dB/(Rq/λ) for planar and focused transducers, respectively. The characteristic nulls present in the normalized spectra of the echo signal at non-normal incidence tend to vanish with increasing R_q when using planar transducers. For focused transducers, the normalized spectra change from relatively flat to monotonically decreasing as R_q increases, and they exhibit reduced amplitude with increased incident angle     

The influence of crystal anisotropy on mechanical behaviour

Anisotropy of crystal structure leads to complications in mechanical behaviour. Robert Cahn, 50 years ago, made valuable contributions through determination of crystallographic features of plastic deformation in large crystals in polycrystalline -uranium. This research area has become increasingly linked with the effects of internal and external stresses on many materials in polycrystalline form comprised of grains with anisotropic crystal structure. The extent of irreversibility of deformation when such materials are subjected to thermal cycles leads to the significance of crystallographic textures but major effects on mechanical behaviour are often apparent where grains are randomly aligned without preferred crystal orientation when small external stresses are imposed. The importance of these features, their main characteristics and their analysis are briefly reviewed     

The effect of a difference in the reflection coefficients of rays from symmetrical points of an object on the accuracy of a measurement of its position

A procedure for determining the particular error in measuring the position of an object using highly accurate optoelectronic instruments due to the fact that the reflection coefficients of the lens for rays from symmetrical points of the object are not identical is proposed.     

线阵声诱饵对抗具有尺度识别能力鱼雷的分析与仿真

为了研究线阵声诱饵对抗具有尺度识别能力鱼雷的性能,以分裂波束和方位走向法为例,分析了鱼雷对尺度目标回波的识别方法,以此为基础探讨了线阵声诱饵在对抗具有尺度识别能力鱼雷时的若干技术问题,通过仿真验证了线阵声诱饵对抗尺度识别能力鱼雷的有效性。本文证明了线阵式的声诱饵可以有效模拟舰船目标的尺度特征,在对抗有尺度识别能力的鱼雷时是很有意义的发展方向。本文所给出的仿真方法,除了建立线阵诱饵在诱骗有尺度识别功能鱼雷的仿真模型外,还可以作为物理模型应用在诱饵工作程序中,提供各阵元的延迟时间等声学参数。     

Effects of target shape and reflection on laser radar cross sections

Laser radar cross sections have been evaluated for a number of ideal targets such as cones, spheres, paraboloids, and cylinders by use of different reflection characteristics. The time-independent cross section is the ratio of the cross section of one of these forms to that of a plate with the same maximum radius. The time-dependent laser radar cross section involves the impulse response from the object shape multiplied by the beam's transverse profile and the surface bidirectional reflection distribution function. It can be clearly seen that knowledge of the combined effect of object shape and reflection characteristics is important for determining the shape and the magnitude of the laser radar return. The results of this study are of interest for many laser radar applications such as ranging, three-dimensional imaging-modeling, tracking, antisensor lasers, and target recognition.     

The influence of microstructure on the failure behaviour of PEEK

In this study, different molecular weight PEEK materials were used to determine the effect of spherulite size on fracture. Melt processing of the PEEK at different temperatures produced samples of different average spherulite size. A permanganic etching technique was used to reveal the spherulites. It was found that for low molecular weight 150P PEEK, the spherulite size increased with melt processing temperature; but, for the higher molecular weight 450G PEEK, the spherulite size remained approximately constant. Also, the average spherulite size was markedly lower for the material of higher molecular weight. The failure behaviour of these samples was studied using a compact tension test. It was found that the fracture toughness of PEEK varied with processing temperature. Also, the average spherulite size of this material had a profound influence on the fracture mechanism.     

The influence of microstructure on the failure behaviour of PEEK

In this study, different molecular weight PEEK materials were used to determine the effect of spherulite size on fracture. Melt processing of the PEEK at different temperatures produced samples of different average spherulite size. A permanganic etching technique was used to reveal the spherulites. It was found that for low molecular weight 150P PEEK, the spherulite size increased with melt processing temperature; but, for the higher molecular weight 450G PEEK, the spherulite size remained approximately constant. Also, the average spherulite size was markedly lower for the material of higher molecular weight. The failure behaviour of these samples was studied using a compact tension test. It was found that the fracture toughness of PEEK varied with processing temperature. Also, the average spherulite size of a PEEK material had a profound influence on the fracture mechanism.