基于WPT技术的超声辅助加工系统研究进展

对超声辅助加工技术及WPT技术进行了分析归纳,总结了国内外目前有关WPT超声辅助加工系统的研究成果,提出共振式无线电能传输技术可能是超声辅助加工领域一种更为灵活、更为理想的供电模式的想法。     

单孔冲击式帽罩前缘流动换热特性数值分析

为了提高航空发动机帽罩冲击防冰结构的设计分析水平,对单孔冲击式帽罩前缘结构的流动换热特性进行数值研究,分析了不同冲击孔径与不同冲击雷诺数对帽罩前缘速度流场、换热系数与努塞尔数的分布规律。结果表明:在冲击雷诺数一定的条件下,冲击孔径越大,射流核心速度和前缘壁面附近的气流速度越小,前缘冲击区形成的涡流团越大,当孔径D=6 mm时,小孔径冲击下前缘区整体换热效果不如大孔径的,而在滞止区的换热效果则要优于大孔径的;当D>12 mm时,孔径大小对壁面换热基本没有影响;在冲击孔径相同时,增大冲击雷诺数使得冲击射流、前缘壁面附近及侧壁曲面通道内的气流流速增大,冲击区内的涡流团则逐渐减小;冲击雷诺数的增大也增强了前缘冲击区的换热特性。     

基于稀疏阵列和码分信号的机载预警雷达STAP研究

基于稀疏阵列和码分正交信号,研究了机载雷达的空时自适应处理（STAP）技术,用于空中预警背景下的地面杂波抑制和运动目标探测。提出了稀疏阵列码分多相位中心孔径综合方法,采用正交编码信号实现多发多收,使综合后不同编码信号的相位中心在数量和分布情况上和满阵天线的相同,从而避免了稀疏阵列天线旁瓣较高的问题;在孔径综合的基础上,利用空时自适应处理方法完成杂波抑制,实现运动目标检测。仿真结果表明了本文方法的有效性。     

Synthetic aperture beamformer for imaging through a dielectric wall

A coarray-based aperture synthesis scheme using subarrays and postdata acquisition beamforming is presented for through-the-wall wideband microwave imaging applications. The wall causes wave refraction and a change in the propagation speed, both effects alter the travel time between the transmitter, the target, and the receiver. Coherent combining of the pulse waveforms emitted by the different transmitters and incident at the receivers through reflections from targets and clutter requires incorporation of wall effects into the beamformer design. Simulation results verifying the proposed synthetic aperture technique for a through-the-wall imaging (TWI) system are presented. The impact of the wall ambiguities or incorrect estimates of the wall parameters, such as thickness and dielectric constant, on performance is considered.     

涡轮叶片尾缘复合通道中隔板结构对换热特性的影响

采用热色液晶测温法,测量了涡轮叶片尾缘带隔板的复合通道的温度场。主要讨论了在通道其它结构均相同的条件下分别采用4种不同结构的隔板(2种孔径的矩形隔板与2种孔径的波形隔板),研究隔板中孔径大小对通道换热和流阻的影响。结果表明:矩形隔板中将矩形隔板上的孔由原来的1.8mm放大到2.5mm(即出流孔的总面积放大一倍)后提高了通道的换热,降低了流阻;波形隔板中将隔板由波谷孔径1.5mm、波峰孔径2.1mm分别放大到波谷孔径2.1mm、波峰孔径3.0mm后对换热没有提高;矩形隔板与波形隔板比较的情况下,波形隔板的换热均高于矩形隔板,而且流阻较低。      

Iterative MMSE method and recurrent Kalman procedure for ISAR imagereconstruction

This work presents a novel approximate iterative and recurrent approach for image reconstruction from inverse synthetic aperture radar (ISAR) data. Mathematical models of the quadrature components of the ISAR signal, reflected by an object with a complex geometry, are devised. Approximation matrix functions are used to describe deterministic signals reflected by point scatterers located at nodes of the uniform grid (model) during inverse aperture synthesis. Minimum mean square error (MMSE) equations and Kalman equations are derived. To prove the validity and correctness of the developed iterative MMSE method and recurrent Kalman procedure, numerical experiments were performed. The computational results demonstrate high resolution images, unambiguous and convergent estimates of the point scatterers' intensities of a target from simulated ISAR data     

Design and implementation of near-field, wideband synthetic aperture beamformers

A coarray-based near-field, wideband synthetic aperture beamformer using stepped-frequency signal synthesis and post-data acquisition processing is presented. While coarray techniques offer significant reduction in the number of array elements for a given angular resolution, the hybrid subarray-stepped frequency realization of wideband systems simplifies implementations and offers flexibility in beamforming. Proof of concept is provided using real data collected in an anechoic chamber for several pulse shapes and array weightings.     

Aperture error mitigation via local-state estimation for frequency-based emitter location

This paper considers the problem of locating a stationary coherent emitter via a single moving platform making frequency measurements in the presence of aperture state uncertainty. It is shown that the estimated emitter location is most sensitive to the receiving aperture velocity uncertainty. The required aperture velocity accuracy is determined through a noninfinitesimal perturbation analysis. A solution to location accuracy enhancement with a minimal hardware addition is attempted. It is shown that this can be achieved by mounting a high-resolution tri-axis microelectromechanical systems (MEMS) accelerometer at the aperture to measure its velocity, which can deviate significantly from that estimated by the on-board navigation system. The Doppler shifts of the GPS signal carrier frequency, whenever it can be acquired through the aperture, are also considered as a way to aid the aperture velocity measurement. A decentralized, federated processing method for the aperture velocity estimate referenced at the aperture, integrating all measurement data, is presented. An upper bound for the error of aperture velocity estimate is derived. The potential for significant accuracy enhancement for emitter location is demonstrated.     

口径近场的特征谱

 提出口径近场特征谱的概念,以描述口径设计近场特征。特征谱包括角域谱和时域谱,分别定义为口径近场区空域场和频域场在角域和时域的变换。理论分析和计算结果表明,特征谱可以在角域和时域上分离有限大口径的直达波和绕射波,因而可以用来描述口面尺寸、形状和场分布等条件改变时绕射场的相对变化,这对紧缩场设计具有参考价值。基于口面场卷积法,计算、比较了限度为5 m×5 m圆口径和方口径近场在X波段特征谱分布。并导出：口径近场角谱为口径场角谱和网络响应函数角谱的乘积,网络响应函数等效于一个空间角谱滤波器。     

小波插值在机载超宽带合成孔径雷达成像中的应用

 通过解方程构造一组424 整数小波,利用整数小波的尺度函数作为插值基函数, 进行波数域算法的Stolt 插值,整个插值过程中只有加法和移位运算,便于硬件实现。仿真计算验证了快速算法的有效性。     

Resolution Limits with Propagation Phase Errors

Resolution limits and corresponding optimum linear apertures are determined in the presence of phase errors. Let ?(t) be the phase aberration at position t across the aperture; it is assumed that the random process ? has a power law structure function, E{[(?(t)-?(?)]2}= c|t-?|n. Beam tilting caused by the phase error is "removed" (for each sample of ?), then resolution formulas are developed. An approximate analysis is obtained in closed form and yields an optimum resolution proportional to c1/n for O < n < 2. The exact analysis is given for Gaussian ?, and again the optimum resolution is proportional to c1/n. In applications n= 5/3 is of interest, and in the Gaussian case the best obtainable equivalent rectangle resolution is ? ?)/2? (0.975)c3/5 radians with a corresponding optimum linear aperture of 14c-3/5. When long exposures are considered, imaging without removing beam tilting is of interest, and resolution is degraded by a factor of about 2.5 for a linear aperture. Alternatively, in some applications optimum focus as well as beam tilt should be considered, in this case resolution is improved by a factor of about 1.4 (again for n= 5/3). Finally, joint (tilt corrected) optimization over aperture length and taper is treated; however, as one might expect, the use of taper offers negligible resolution improvement.     

On Processing Optical Images Propagated Through the Atmosphere

The problem of how to process optical images that have propagated through a turbulent atmosphere is considered. It is assumed that either the object or its (free-space) scattered field at the receiving aperture is known, except for unknown parameters that are to be estimated. Isotropic and homogeneous turbulence as discussed by Tatarski and Chernov is assumed. It is assumed that a very short (in time) reception is made, that the turbulence-induced complex phase errors are either small or have a correlation distance short relative to the receiving aperture extent, and that the object is within an isoplanatic region. The method of maximum likelihood (ML) is used as a criterion; its applicability is discussed. The ML image-processing structure is found and is nonlinear. Asymptotic cases are examined; among other conclusions, it is shown that the ML processing of independent receptions is more complex than an ML processing of the sum of the receptions. A coherent optical system that realizes the ML image processor is described; it includes the capability to generate the scattered field. Simplifications are pointed out.     

航空复杂壳体深小孔的高效精密加工技术

针对某类复杂壳体深小孔数量多、孔径小、长径比大、精度要求高的特点,在优化设计枪钻切削刃及冷却孔结构的基础上,将枪钻、直槽内冷钻等新型孔加工刀具与加工技术应用到卧式加工中心上,研究开发孔径Φ2~Φ10、长径比20~60深小孔的高效加工方法和加工工艺,优化得到符合要求的最佳切削参数,并建立深小孔高效加工切削参数数据库。实践表明,这一技术将深小孔加工效率提高30%以上,加工质量显著改善,有效解决了深小孔的高效精密加工问题。     

某型燃气轮机燃烧室出口温度场的调试

试验研究了某型燃气轮机燃烧室掺混孔孔径比、相对孔距对出口温度场的影响.试验结果表明:随孔径比的增加,出口温度分布系数逐渐减小,但过大的孔径比易形成局部阻塞,使热点温度升高;孔径比对径向温度分布系数影响较小,仅使温度分布曲线位置移动而不会改变其形状.相对孔距与径向温度分布系数相关性较强,过大(大于0.33)、过小(小于0.29)均不利于掺混.该研究情况下,相对孔距为0.31、孔径比为0.32左右基本合理.      

Matching suitable feature construction for SAR images based on evolutionary synthesis strategy

In the paper,a set of algorithms to construct synthetic aperture radar（SAR）matching suitable features are frstly proposed based on the evolutionary synthesis strategy.During the process,on the one hand,the indexes of primary matching suitable features（PMSFs）are designed based on the characteristics of image texture,SAR imaging and SAR matching algorithm,which is a process involving expertise;on the other hand,by designing a synthesized operation expression tree based on PMSFs,a much more flexible expression form of synthesized features is built,which greatly expands the construction space.Then,the genetic algorithm-based optimized searching process is employed to search the synthesized matching suitable feature（SMSF）with the highest effciency,largely improving the optimized searching effciency.In addition,the experimental results of the airborne synthetic aperture radar ortho-images of C-band and P-band show that the SMSFs gained via the algorithms can reflect the matching suitability of SAR images accurately and the matching probabilities of selected matching suitable areas of ortho-images could reach 99±0.5%.     

口径天线绕射场的研究

介绍口径天线近场绕射计算的卷积积分法 ,该方法可用 FFT实现快速计算 ,故它是比传统的直接积分或球面波展开法更有效的一种计算模式。在此基础上 ,对圆形和矩形口径天线的近场绕射特性进行了研究。由计算结果可见 ,口径天线在观察面上的绕场分布与口径形状、口径尺寸 ( D/λ)和观察面至口径有关。还对减小口径边缘的近场绕射问题进行了分析     

Scanning Spaceborne Synthetic Aperture Radar with Integrated Radiometer

Spaceborne synthetic aperture radar systems are severely constrained to a narrow swath by ambiguity limitations. Here a vertically scanned-beam synthetic aperture system (SCANSAR) is proposed as a solution to this problem. The potential length of synthetic aperture must be shared between beam positions, so the along-track resolution is poorer; a direct tradeoff exists between resolution and swath width. The length of the real aperture is independently traded against the number of scanning positions. Design curves and equations are presented for spaceborne SCANSARs for altitudes between 400 and 1400 km and inner angles of incidence between 20° and 40°. When the real antenna is approximately square, it may also be used for a microwave radiometer. The combined radiometer and synthetic-aperture (RADISAR) should be useful for those applications where the poorer resolution of the radiometer is useful for some purposes, but the finer resolution of the radar is needed for others.     

Synthetic-aperture radar processing using fast factorized back-projection

Exact synthetic aperture radar (SAR) inversion for a linear aperture may be obtained using fast transform techniques. Alternatively, back-projection integration in time domain can also be used. This technique has the benefit of handling a general aperture geometry. In the past, however, back-projection has seldom been used due to heavy computational burden. We show that the back-projection integral can be recursively partitioned and an effective algorithm constructed based on aperture factorization. By representing images in local polar coordinates it is shown that the number of operations is drastically reduced and can be made to approach that of fast transform algorithms. The algorithm is applied to data from the airborne ultra-wideband CARABAS SAR and shown to give a reduction in processing time of two to three orders of magnitude.     

基于二维资源管理的多功能雷达任务调度算法

动态孔径分割技术为相控阵雷达针对不同任务灵活分配孔径资源提供了可能,而传统的资源调度方法仅基于单一孔径条件研究了时间资源的优化分配问题。针对雷达搜索、跟踪与成像任务的自适应调度问题,提出了一种基于时间-孔径二维资源管理的雷达资源调度算法。该算法建立了雷达孔径分割条件下的二维资源调度模型,确立了能量资源约束条件;利用基于压缩感知的稀疏孔径逆合成孔径雷达（ISAR）成像技术,使雷达在完成目标搜索和跟踪任务的同时实现对目标的成像;定义了调度算法性能的评价指标。在仿真实验中将该算法与另外2种算法进行对比,验证了所提算法在高度成功率、二维资源利用率与任务并行度这3种性能指标上具有优越性。     

Synthetic Aperture Radar

The general theory of side-looking synthetic aperture radar systems is developed. A simple circuit-theory model is developed; the geometry of the system determines the nature of the prefilter and the receiver (or processor) is the postfilter. The complex distributed reflectivity density appears as the input, and receiver noise is first considered as the interference which limits performance. Analysis and optimization are carried out for three performance criteria (resolution, signal-to-noise ratio, and least squares estimation of the target field). The optimum synthetic aperture length is derived in terms of the noise level and average transmitted power. Range-Doppler ambiguity limitations and optical processing are discussed briefly. The synthetic aperture concept for rotating target fields is described. It is observed that, for a physical aperture, a side-looking radar, and a rotating target field, the azimuth resolution is ?/? where ? is the change in aspect angle over which the target field is viewed, The effects of phase errors on azimuth resolution are derived in terms of the power density spectrum of the derivative of the phase errors and the performance in the absence of phase errors.