终端区域理想速度剖面的生成

本文着重探讨了飞机进入终端区域后理想速度剖面的生成问题,目的是通过执行理想剖面生成算法,达到对飞机进行精确的时间控制,消除等待时间,提高机场利用率,达到节省燃料减少延误的目的。     

静态周向总温与总压组合畸变通过轴流压气机单转子时的传递

在文献[4]的基础上,文中对静态周向总温与总压畸变的两种组合情况进行了研究:1.同相位时,总温畸变度的变化对总压畸变衰减的影响;2.总温与总压畸变之间存在不同的相位角时对总压畸变衰减的影响。数值计算结果表明,进口总温畸变度的变化以及总温与总压畸变之间相位角的变化,都将引起出口总压分布的变化;当总温畸变与总压畸变反相位时,最不利于总压畸变的衰减。本文将计算结果和文献[7]中的实验结果进行了定性比较,两者符合得较好。      

Diversity methods in phase monopulse tracking-a new approach

A novel approach relating target glint (difference between the phase-front gradient of the scattered field and the true target direction vector) to the analytic properties of the overall field is used to suggest a method by which the error in conventional (single frequency) phase monopulse trackers can be reduced. The approximate relationship between glint and amplitude is briefly developed, and an improved glint reduction scheme appropriate for single frequency data is described. The effectiveness in reducing direction angle error is demonstrated with simulated data. It is shown how techniques devised for multiple frequency data sets can be applied to multiple aspect data sets.<>     

自适应严格收敛非奇异终端滑模制导律

针对机动目标的末制导拦截问题，设计了一种带终端角度约束的有限时间收敛终端滑模制导律。首先，分析了现有非奇异终端滑模制导律存在的滑模面不能严格有限时间收敛的问题，进而构造了一种新型的非奇异终端滑模面。其次，设计了一种对目标机动上界的自适应估计，提出了一种自适应严格收敛非奇异终端滑模制导律的设计方法。最后，基于Lyapunov稳定性理论，证明了设计的制导律能够使得制导系统在有限时间内收敛到零，并且保证了滑模面在收敛过程中不存在非收敛因子，是严格有限时间收敛的。仿真实验验证了该制导律能够有效地拦截机动目标，同时和与现有的非奇异终端滑模制导律以及基于转换滑模面的非奇异制导律相比，拦截时间更短，终端攻击角度精度更高，导弹机动消耗的能量更少。     

Beamspace ML bearing estimation incorporating low-angle geometry

A problem in low-angle radar tracking, namely, bearing estimation in the presence of a strong specular multipath component that arrives within the beamwidth of the direct path signal, is studied. Three-dimensional beamspace domain maximum likelihood (3D-BDML) is a computationally simple ML bearing estimation algorithm applicable in this scenario which operates in a 3-D beamspace. A variation of 3D-BDML incorporating the multipath geometry as a priori information is presented. In symmetric 3D-BDML the pointing angle of the center beam is equal to the bisector angle between the direct path ray and the image ray, which may be estimated a priori given only the radar height and the target range. The effect of the inclusion of a priori information on the performance of 3D-BDML is analyzed in terms of the dependence on the relative phase difference between the direct and specular path signals, the sensitivity to error in the bisector angle estimate, and the results of operation when no specular multipath component is present in the data. In addition, computationally simple schemes for coherently incorporating multifrequency data into 3D-BDML are investigated     

Comparison of Two Target Classification Techniques

It has been shown that radar returns in the resonance region carry information regarding the overall dimensions and shape of targets. Two radar target classification techniques developed to utilize such returns are discussed. Both of these techniques utilize resonance region backscatter measurements of the radar cross section (RCS) and the intrinsic target backscattered phase. A target catalog used for testing the techniques was generated from measurements of the RCS of scale models of modern aircraft and naval ships using a radar range at The Ohio State University. To test the classification technique, targets had their RCS and phase taken from the data base and corrupted by errors to simulate full-scale propagation path and processing distortion. Several classification methods were then used to determine how well the corrupted measurements fit the measurement target signatures in the catalog. The first technique uses nearest neighbor (NN) algorithms on the RCS magnitude and (range corrected) phase at a number (e.g., 2, 4, or 8) of operating frequencies. The second technique uses an inverse Fourier transformation of the complex multifrequency radar returns to the time domain followed by cross correlation. Comparisons are made of the performance of the two techniques as a function of signal-to-error noise power ratio for various processing options.     

Assessment and improvement of the capabilities of a window correlator to model GPS multipath phase errors

The potential of output from a window correlator to mitigate GPS phase multipath is reviewed and assessed based on the analysis of data collected in controlled multipath environments under both static and kinematic conditions. Previous findings that the method is suboptimal for reflectors leading to additional path lengths of less than about 7m are confirmed, and methods for combining this output with two other multipath indicators: time series of signal-to-noise ratios (SNRs) and estimates of code multipath from dual frequency code and phase combinations, are investigated. A new method to combine all three indicators has been found and its application is shown to improve the quality of GPS static phase data by between 10% and 20% depending on the length of the additional path travelled by the reflected signal. The method can be applied completely automatically as it uses just the three multipath indicators; no knowledge of the surrounding environment is required. The paper concludes with some suggested practical applications.     

Multipath interferometry technique for airborne array calibration

A new technique is developed to compensate multiple-wavelength distortion in airborne antenna arrays. This approach exploits the phase information in microwave reflections from arbitrary terrain. To handle reflections incident over a broad angle, a range-Doppler preprocessor is used in each element channel to resolve wavefronts incident simultaneously from different directions. The phase information for each direction of arrival is compared between elements and processed by optimal estimators to determine the phase corrections needed to compensate the distortion. To develop the estimators, a statistical model of the complex baseband terrain reflections is developed. This is in turn used to generate conditional probability densities involving the range Doppler observations and the parameters to be estimated. These densities are subsequently used to develop minimum variance and maximum likelihood estimators. The new estimators use additional information that has not been exploited by previous techniques and therefore provide enhanced performance     

PIV测速技术实验参数分析

本文通过理论分析、计算机模拟及实验观测，对采用底片记录和杨氏条纹法判读的ＰＩＶ测速技术的动态测量范围、各种实验参数的影响及其优化取值准则进行了详细的分析讨论，并给出了一些有关的理论及经验公式。     

空域滤波器组对雷达阵列合成距离像的影响分析

为了简化雷达系统硬件设计和降低成本,可以使用多个窄带成分来合成宽带信号,从而获得满足实际需要的合成距离像。针对合成宽带信号和雷达阵列的特点,详细分析了结合合成宽带信号及传统空域滤波器组情况下所合成距离像的失真原因,指出合成距离像的失真由形状变形和位置平移两部分组成,且这两种失真分别由各个空域滤波器输出幅度和相位的波动所引起。同时,推导出计算对应相位和幅度失真度的理论公式,并由此给出了当合成距离像存在可接受失真时阵列的临界条件。计算机数值仿真结果验证了以上结论。     

Flow Diagnostics by Laser Interferometry

A survey is made of interferometric techniques receiving the optical path ? = ?nds in real time. Using differential interferometry or a new phase coupling technique, ?(t) can be obtained in a wide range of conditions. A variety of applications to gasdynamic problems is described.     

3-D Radar Based on Phase-in-Space Principle

A height-finding technique utilizing the relative phase between a series of point sources of a traveling-wave array is described. The point sources in the focal region of a torus antenna are used to control the phase of the antenna elevation pattern in space. Signals received from a given beam angle will arrive at each terminal of the traveling-wave feed with a different phase. By comparing this phase with a reference phase, the angular direction of an arriving plane wave can be measured with considerable accuracy. Thus a radar system with a single antenna and feed structure can be employed to yield instantaneous height coverage along with the usual range data.     

畸变条件下航空发动机喘振/失速适航符合性方法

为研究畸变条件下航空发动机对喘振/失速特性适航条款的符合性验证方法,将用于发动机稳定性评定的畸变试验方法应用于适航领域。以某型大涵道比涡扇发动机为研究对象,采用数值模拟方法研究了其在0°～30°迎角条件下的部件特性,并依据所得畸变图谱设计了不同结构的畸变发生器。结果表明:所设计的畸变发生器可以在一定程度上较好地模拟出不同迎角工况的畸变图谱、风扇的气动特性及流场特征,喘振裕度最大偏差4.32%。总结出发动机喘振裕度与不同迎角和畸变发生器之间的变化关系,用以确定适航条款要求的稳定工作范围。依据中国民用航空规章,发展了一种进气畸变条件下航空发动机喘振/失速特性符合性验证方法,并明确了其在型号合格审定过程的任务阶段。      

Distortion Generated in Angle-Modulation Systems by Phased Arrays

The case of linear, uniformly weighted phased arrays is examined via time and frequency domain analyses. Bounds that must be placed on array length, modulation frequency, modulation index ?, and scan angle relationships if excessive distortion is to be avoided in wideband angle-modulated communication systems are established. Distortion is shown to consist of odd harmonic terms. It is also shown that, for one class of equivalent RF signals, phased arrays produce approximately three times as much distortion in frequency-modulation (FM) systems as in phase-modulation (PM) systems. Graphs of distortion plotted as functions of signal and array parameters show that, for practical array sizes, distortion is a monotonically increasing function of the product of L and sin ? where L is the length of the array expressed in modulation wavelengths ?m and ? is the scan angle. In PM systems, distortion also increases monotonically with the modulation index ?. Plots of distortion versus L sin ? show that even relatively small arrays can produce intolerable distortion levels in wideband systems; e.g., an FM system having ? = 3,L = 0.35?m, and ? = 60 degrees exhibits approximately 20 percent distortion.     

时域内振动与噪声传递路径系统的路径传递度探索

  振动和噪声通过多重和/或多维路径传递,振源、传递路径、受体及其动态交互作用的影响至今没有很好地解决,因此对于后续采用的被动控制或者结构修改以降低振动和噪声水平的技术来说,识别出主要的传递路径是至关重要的。本文基于一般概率摄动有限元法和结构可靠性理论,解决了时域内振动与噪声传递路径系统的路径传递概率的度量问题,提出了时域内振动与噪声传递路径系统的路径传递度的新概念和方法,在考虑工程中的不确定因素以后,在时域内清晰地描述了振动与噪声传递路径系统的路径传递率。     

基于虚拟慢时间的双基地ISAR成像算法

针对双基地角时变引起的逆合孔径雷达（ISAR）图像畸变和散焦问题，提出了一种基于虚拟慢时间的成像算法。首先，分析了双基地角时变对ISAR成像的影响机理。然后，基于图像对比度最大准则估计等效旋转中心位置，完成初次相位补偿。最后，通过虚拟慢时间构建基于非均匀虚拟采样的补偿系数矩阵，并通过方位向非均匀傅里叶变换得到目标的ISAR像。算法基于图像对比度最大准则解决等效旋转中心位置估计问题，通过虚拟慢时间消除转动相位项的高次项影响，利用非均匀傅里叶变换解决随机虚拟采样的谱估计问题。理论分析和仿真结果验证了算法的有效性和鲁棒性。     

航空发动机进气旋流畸变研究综述

为完善和发展航空发动机进气旋流畸变研究体系,回顾了进气旋流畸变的产生与来源,概述了国内外模拟旋流畸变的方法。归纳总结了不同类型、不同结构的旋流畸变对压气机以及航空发动机性能和稳定性的影响。综合分析了当前旋流畸变研究存在的问题和困难,对旋流畸变的发展趋势进行了讨论,提出以下建议:发展可变式旋流畸变发生器;探究旋流畸变对发动机整机性能的影响机理,为有效扩稳打下基础;要利用多种途径开展旋流进气条件下的压气机/发动机扩稳研究;建立统一的旋流畸变评价指标,并纳入到综合畸变指数系统中;探索小畸变进气道的设计方法。     

Requirements for optimal glint reduction by diversity methods

Target “glint” (the difference between the phase-front gradient of the scattered field and the true target direction vector) is related to the analytic properties of the scattered field. The resulting model is used to reinterpret diversity methods for glint reduction and to more accurately specify system requirements. A relationship for estimating the best possible improvement in target bearing estimation is also developed     

扩压器内的冷凝对流场的影响

扩压器处于超临界工作状态时,由于喉道后面的激波与附面层的相互作用,使出口流场发生畸变.本文探讨了扩压器内发生的冷凝对畸交流场的影响.结果表明,在实验范围内,由于冷凝使畸变流场的平均紊流度增加12～25%,稳态畸变指数DC_(60)可能增加、不变或减小.可见在研究发动机与进气道的相容性时,冷凝是不可忽视的影响因素之一.     

跨声风扇周向畸变流动的谐波平衡法计算

研究了采用"相位延迟"边界条件的谐波平衡法用于周向进气畸变计算的可行性及其计算效率,考虑了进气总压畸变形式为正弦波和方波的两种情况。对于正弦波形式的进气总压畸变采用较少阶数的谐波计算就可得到和双时间推进法相近的计算结果,计算速度最大可以提高48倍。对于方波形式的进气畸变,则需要采用更多阶数的谐波计算才能还原得到较准确的非定常流场,计算速度提高了7倍。算例表明,谐波平衡法可以有效的应用于跨声风扇周向进气畸变的非定常计算中,同时大幅提高计算速度。