Precise Decoupling Tracking of Airspeed and Altitude for UAV Based on Causal Solution of Stable Inversion

Use stable inversion to accomplish precise decoupling tracking of airspeed and altitude for conventional takeoff and landing of unmanned aerial vehicles (UAVs) is in essence a non-minimum phase output tracking problem. The main contribution of this article is that a new method to calculate the causal solution of stable inversion is proposed by introducing a well defined perturbed signal to the system's unstable internal dynamics. It is helpful to overcome the pitfalls resulting from non-causality in existing methods. Different from the mathematically accurate offline non-causal solution, the causal solution is an approximation with asymptotically convergent errors. The important merits are: It obviates the needs for the output trajectory to be pre-known time parameterized functions, hence broadening the application of stable inversion; The low computational workload is much more suitable for and beneficial to real-time applications than any existing method based on stable inversion. The output tracking problem is then converted into a state tracking problem based on the causal solution of stable inversion. Precise decoupling tracking of airspeed and altitude is realized by using a feedback controller. Simulations are carried out to verify the viability and low computational workload of the method.     

认知无线电网络中的喷泉编译码技术研究

针对认知无线电网络（CRN）中授权信号时间和频率的不确定性导致CR用户工作频率甚至链路质量具有严重的时变性等特点,提出利用喷泉码的编解码技术解决上述问题。阐述了喷泉码的编解码原理,对喷泉码应用于认知无线电的系统性能进行了仿真分析．仿真结果表明．由于喷泉码无需反馈以及编解码复杂度低的特性,在CRN网络的时变信道环境下能实现链路维持,提高了系统的传输性能。     

Design Principles of MIMO Radar Detectors

This paper considers the problem of multiple-input multiple-output (MIMO) radars employing space-time coding (STC) to achieve diversity. To this end, after briefly outlining the model of the received echo, a suitable detection structure is derived, and its performance is expressed in closed form as a function of the clutter statistical properties and of the space-time code matrix. Interestingly, this receiver requires prior knowledge of the clutter covariance, but the detection threshold is functionally independent thereof. At the transmitter design stage, we give two criteria for code construction: the first is based on the classical Chernoff bound, the second is an information-theoretic criterion. Interestingly, the two criteria lead to the same condition for code optimality, which in turn specializes, under the assumption of uncorrelated clutter and square code matrix, in some well-known full-rate space-time codes. A thorough performance assessment is also given, so as to establish the optimum achievable performance for MIMO radar systems.     

Analytical design of a causal multiconnected astatic observing device

A method for synthesis of a multiconnected astatic observing device that makes it possible to obtain a physically realizable (causal) solution is proposed. We determine the conditions that allow the problem solvability to be defined at the initial stage of synthesis.     

外挂物投放 发射过程数值仿真中的非均匀流场计算

本文介绍了用面元法计算外挂物投放/发射过程中的非均匀流场问题。理论分析表明三角形奇点分布形态在非均匀流场计算中具有其独特的优越性。本文还阐述了伍德沃德程序中机翼线性变化源分布中法向扰动速度公式的错误。数值结果表明,理论计算与实验值吻合较好。     

Adaptive boosting for SAR automatic target recognition

The paper proposed a novel automatic target recognition (ATR) system for classification of three types of ground vehicles in the moving and stationary target acquisition and recognition (MSTAR) public release database. First MSTAR image chips are represented as fine and raw feature vectors, where raw features compensate for the target pose estimation error that corrupts fine image features. Then, the chips are classified by using the adaptive boosting (AdaBoost) algorithm with the radial basis function (RBF) network as the base learner. Since the RBF network is a binary classifier, the multiclass problem was decomposed into a set of binary ones through the error-correcting output codes (ECOC) method, specifying a dictionary of code words for the set of three possible classes. AdaBoost combines the classification results of the RBF network for each binary problem into a code word, which is then "decoded" as one of the code words (i.e., ground-vehicle classes) in the specified dictionary. Along with classification, within the AdaBoost framework, we also conduct efficient fusion of the fine and raw image-feature vectors. The results of large-scale experiments demonstrate that our ATR scheme outperforms the state-of-the-art systems reported in the literature     

Code Division Multiplexing by Frequency Shifted Biphase Modulated M-Sequences

A new set of frequency shifted biphase modulated PN sequence signals is introduced, and it is shown that for a set of length N the cross mutual interference is bounded by (N + 1)/N2. This subject is related to the so-called near/far problem of directsequence encoded code division multiplexing networks.     

BDS接收机星间载波相位偏差

BDS(BeiDou satellite navigation System,北斗卫星导航系统)的MEO/IGSO (Medium Earth Orbit/Inclined Geosynchronous Satellite Orbit,中圆地球轨道/倾斜地球同步轨道)卫星在D1导航电文上调制了NH(Neumann-Hoffman,奈曼-霍夫曼)二次编码,而在GEO(Geostationary Earth Orbit,地球静止轨道)卫星上未使用.利用北斗MEO/IGSO和GEO卫星进行差分定位时,采用不同NH码符号映射规则的接收机之间会出现半周载波相位偏差的问题,严重影响RTK (Real-Time Kinematic,实时动态差分)应用.通过分析半周载波相位偏差的形成机理,从单差、双差、三差应用角度分别研究了半周载波相位偏差的影响.分析结果表明,接收机NH码符号映射规则与卫星不一致时,接收机直接用乘法器对NH码解调将存在反相,也即引入了半周载波相位偏差;在满足特定条件下,单差和双差应用时会存在半周载波相位偏差的问题;三差应用时不存在半周载波相位偏差的问题.最后,提出了需在北斗接口控制文件中明确卫星NH码调制或映射规则的修订建议.     

NND格式在多维理想磁流体方程组中的应用

采用修正的四步Runge-Kutta方法求解三维一般曲线坐标系下的理想磁流体方程组,为克服数值振荡,加特征型NND格式进行后处理.特征型NND格式推广到求解三维磁流体(MHD)问题需要知道雅可比通量的左右特征矩阵,在具体计算时需要克服矩阵的奇性.本文用三维程序采用推广的特征NND格式计算了一维MHD激波管和二维(MHD)喷管流动,计算结果表明,特征NND格式保持了TVD格式高精度的优点,又具有计算简单的特点,在包括强弱间断等复杂波系的定常和非定常MHD流场数值模拟中是成功的.     

An alternative to traditional software rehosting

This paper describes one alternative to rehosting TPS software to newer computer platforms. It describes the solution that Southwest Research Institute (SwRI) used to solve a problem with re-engineering legacy software into a modern object-oriented language. The advantages gained by this method are more advanced instruction to the operator (such as pictures and movies), flexible reporting scheme to diagnose system problems, and ease of software maintenance. This solution uses commercially available products including National Instruments/spl trade/ TestStand/spl trade/ and LabVIEW/spl trade/ and Microsoft/spl reg/ Visual Basic/spl reg/. The system is a four-tiered architecture to drive all test execution. The user interface is written in Visual Basic and allows the user to interact with the test execution when needed. This user interface in turn calls tests that are written in TestStand, and finally the individual tests call driver functions written in LabVIEW. A database serves as a repository for all test results, displays, and test limits. The use of this database allows for easy querying of measurement data to analyze trends in failures that help diagnose specific problems. By using this database, all test limits and test displays are contained in one central location that enables engineers to change these displays and limits on the fly without needing to change or even understand any test code. One other benefit of this data containment is that all Government classified data is separated out of the code and stored as one file, instead of in various locations as it was in the original source code.     

Multivariate interpolation for fluid-structure-interaction problems using radial basis functions

A multivariate interpolation scheme for coupling fluid (CFD) and structural models (FE) in three-dimensional space is presented using radial basis functions. For the purpose of numerical aeroelastic computations, a selection of applicable functions is chosen: a classical without compact support, and some recently presented smooth compactly supported radial basis functions. The scheme is applied to a typical static aeroelastic problem, the prediction of the equilibrium of an elastic wing model in transonic fluid flow. The resulting coupled field problem containing the fluid and the structural state equations is solved by applying a partitioned solution procedure. The structure is represented by finite elements and the related equations are solved using a commercial FE analysis code. The transonic fluid flow is described by the three-dimensional Euler equations, solved by an upwind scheme procedure.     

小型向心透平一维和三维设计分析

在分析各种因素对向心透平速比和反动度限制的基础上,给出了一种比较合理的速比和反动度的选择方法,并用C语言编写了小型燃气透平一维热力计算程序OCC(one-dimensional computer code),来进行向心透平的热力计算.通过与已发表文献中的一维热力计算程序OFC(one-dimensional computer FORTRAN code)结果进行比较,发现两者结果基本一致,且OCC设计总对静效率要高于OFC的设计效率.为了对一维程序计算结果与三维CFD(computational fluid dynamics)数值模拟进行比较,选取已发表文献中600kW燃气轮机作为分析实例,用编写的一维热力设计程序对600kW燃气轮机向心透平导叶和动叶进行了设计.一维程序计算结果与三维CFD数值模拟结果比较发现,两者的偏差小于10%.综上所述,使用的设计方法以及一维热力设计程序对于小型向心透平的初步设计是适用的.      

基于调制域增强副载波剥离的 GPS M码授权码流提取方法

针对 GPS M码授权码流获取问题,提出 1种新的基于调制域增强副载波剥离的方法。该方法利用 GPS C/A码和 M码码片起始位的相关性,在调制域上利用 BOC调制短码信息对 GPS M码信号进行累加增强,获取授权码流。首先,利用公开的 GPS C/A码辅助获取 GPS信号载波相位和 C/A码码相位;然后,分别利用获得的 GPS信号载波相位和 C/A码码相位,完成 GPS C/A码与交调量的剥离以及 M码授权码的初始相位对准;进一步,利用 BOC调制短码信息在调制域上实现累加增强,完成副载波剥离,获得 GPS M码授权码流;最后,利用实际采集信号对所提方法有效性进行了验证,并与现有方法进行了对比。结果表明,所提方法能够克服带宽内 P(Y)信号旁瓣能量对 M码授权码提 取的影响,可带来 3.5 dB左右的性能改善。     

多级轴流压气机二维性能预测方法

为了满足多级轴流压气机性能预估需求,在一个流线曲率程序基础上开展了经验、半经验关系式研究。通过对文献中的损失模型进行校验及融合,建立了相匹配的损失计算模块,并改进了端壁损失计算方法;研究了利用S₁流面计算修正S₂正问题的方法,解决了基于传统平面叶栅试验数据的攻角、落后角模型与先进技术叶型之间不匹配的问题,继而发展出了一个高精度的S₂正问题计算方法。为了验证计算方法,利用3个不同负荷水平的、经试验验证的多级压气机进行了校验计算。对比表明,发展的程序对多级压气机具有很高的计算精度和稳定性,可用于多级轴流压气机性能分析。     

Coupled thermal,structural and vibrational analysis of a hypersonic engine for flight test

This paper describes a relatively simple and quick method for implementing aerodynamic heating models into a finite element code for non-linear transient thermal-structural and thermal-structural-vibrational analyses of a Mach 10 generic HyShot scramjet engine. The thermal-structural-vibrational response of the engine was studied for the descent trajectory from 60 to 26 km. Aerodynamic heating fluxes, as a function of spatial position and time for varying trajectory points, were implemented in the transient heat analysis. Additionally, the combined effect of varying dynamic pressure and thermal loads with altitude was considered. This aero-thermal-structural analysis capability was used to assess the temperature distribution, engine geometry distortion and yielding of the structural material due to aerodynamic heating during the descent trajectory, and for optimising the wall thickness, nose radius of leading edge, etc. of the engine intake. A structural vibration analysis was also performed following the aero-thermal-structural analysis to determine the changes in natural frequencies of the structural vibration modes that occur at the various temperatures associated with the descent trajectory. This analysis provides a unique and relatively simple design strategy for predicting and mitigating the thermal-structural-vibrational response of hypersonic engines.     

局域增强系统级联双频平滑技术研究(英文)

针对电离层误差时间梯度和空间梯度对局域增强系统的不利影响,提出使用级联双频平滤波方法解决此问题。级联双频平滤波先使用一个双频平滑滤波器精确估计电离层误差,利用得到的估计值修正码伪距观测量中的电离层误差,再使用一个双频平滑滤波器削弱噪声。这样,电离层误差被完全从平滑过程中移出,由L2码观测量引入的附加的噪声也被压制。基于中国民航新航行系统实验室的局域增强系统测试平台所采集的数据对级联双频平滤波的有效性和基于级联双频平滤波的局域增强系统的精度进行了分析。结果表明级联双频平滤波技术可以同时消除电离层误差时间梯度和空间梯度导致的平滑滤波残差和差分校正残差,并具有较低的滤波噪声。     

边界层转换阶段直接数值模拟的影响矩阵法

提出一种求解时间相关、三维不可压完全Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程的影响矩阵法。考虑流动区域为上半空间的平极边界层流动,在水平方向,利用周期性条件,采用Ｆｏｕｒｉｅｒ离散,在半无穷方向,定义了一种特殊映像并利用Ｃｈｅｂｙｓｈｅｖ多项式展开。由此将Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程转化为以水平波数（ｋ１,ｋ２）为参数的一组法向Ｈｅｌｍｈｏｌｔｚ方程组,同时可更有效地求解压力。本文讨论了连续问题的影响矩阵法与原问题的等价性。影响矩阵法的离散形式,以及影响矩阵法的算法实现等。最后给出了一维Ｈｅｌｍｈｏｌｔｙ问题的数值实验结果。     

基于匹配滤波和时间恢复算法的B（AC）码数字解调技术

针对靶场时间统一系统中B（AC）码解调的现状和存在的问题,本文从匹配滤波和时间恢复两个方面入手,阐述了一种B（AC）码在噪声和波形失真条件下的数字解调技术。     

计算机辅助功能危险评估方法研究

功能和安全一直是高风险复杂系统的关键问题。传统的功能危险评估由安全工程师手工进行分析，面对高度复杂系统时，就会变得难以完成且容易出错。解决这种问题的一个途径就是利用计算机进行辅助。为此提出一种计算机辅助的功能危险评估方法，采用状态图语言搭建系统状态模型，将功能失效影响直观地从系统状态转移图上表达出来。并且在系统状态模型的基础上，采用计算机编程快速计算出导致系统故障的失效组合以及最小割集。最后以飞机为对象证明了方法的可行性。     

遗传算法在微弱GPS信号捕获方法中的应用

 研究了微弱GPS信号的捕获问题，以捕获时较低的虚警概率和较高的检测概率为目标，以累加时的粗捕获(C/A)码周期数和导航数据数，以及捕获门限等参数为决策变量，应用遗传算法(GA)来解决这一多目标优化问题。仿真结果表明，该方法能够有效地解决所提出的问题，所得解能够优化捕获时欲选取的参数，从而提高捕获性能。