Radar Signature of a Helicopter Illuminated by a Long LFM Signal

Helicopters exhibit a very particular Doppler radar signature caused by the movement of rotor blades. This signature can easily be derived using a short-time approximation: the blades are assumed to be static during each pulse. In wideband linear frequency modulated (LFM) radars, however, this assumption cannot be made. The work presented here describes the echo of rotary blades illuminated by LFM radars without the short-time assumption and provides useful information for detection and recognition purposes.     

Shape control of spacecraft formation using a virtual spring-damper mesh

This paper derives a distance-based formation control method to maintain the desired formation shape for spacecraft in a gravitational potential field. The method is an analogy of a vir-tual spring-damper mesh. Spacecraft are connected virtually by spring-damper pairs. Convergence analysis is performed using the energy method. Approximate expressions for the distance errors and control accelerations at steady state are derived by using algebraic graph representations and results of graph rigidity. Analytical results indicate that if the underlying graph of the mesh is rigid, the convergence to a static shape is assured, and higher formation control precision can be achieved by increasing the elastic coefficient without increasing the control accelerations. A numerical exam-ple of spacecraft formation in low Earth orbit confirms the theoretical analysis and shows that the desired formation shape can be well achieved using the presented method, whereas the orientation of the formation can be kept pointing to the center of the Earth by the gravity gradient. The method is decentralized, and uses only relative measurement information. Constructing a distributed virtual structure in space can be the general application area. The proposed method can serve as an active shape control law for the spacecraft formations using propellantless internal forces.     

某型弹用发动机火药吹转模拟试验

针对某型弹用发动机火药起动试验件起动试验要求,通过静态烟火试验数据确定火药起动模拟试验设备技术指标,在试验台上进行了高压冷吹和真实火药热吹起动试验,获取了两类试验下模拟转子的起动特性.试验结果表明:通过静态烟火试验和高压冷吹测得不同压力下空气流量、转速数据可以拟合出相关关系式,通过关系式能够预估燃气发生器所用火药量在热吹试验中转子可能最大转速,最后通过0.8kg真实火药热吹试验获取的最高转速与换算压力状态下的冷吹最高转速仅相差116r/min,进一步验证了试验和预估方法的有效性和准确性,可以减少或取消不同装药量火药在模拟转子上的吹转试验,减低在发动机上的试验安全风险,为在发动机上的应用奠定基础.      

Monitoring power supply current and using a neural network routineto diagnose circuit faults

As a circuit is tested, the current drawn from a power supply can vary as different functions are invoked by the test. The current draw can be plotted against time, showing a characteristic trace for the test performed. Sensors in the ATS power supply can be used to monitor the current flow during test execution. Defective components can be classified using a Neural Network according to the pattern of variation from the “trace” of a good card. This can be performed as a background function, with the network gaining in accuracy over time. This paper discusses the Neural Network Routine for diagnosing circuit faults using monitored power supply current     

Implementation of a novel matrix converter PMSM drive

This paper proposes a neural-network current-regulated switching strategy and an intelligent controller for a matrix converter permanent magnet synchronous motor (PMSM) drive system. By using this new switching strategy, the current harmonics of the system are effectively reduced. In addition, by using the intelligent controller, position control of the drive system can be achieved and an adjustable speed range from 1 r/min to 1500 r/min can be obtained. All the current-loop, speed-loop, and position-loop control algorithms are implemented by a 32-bit TMS320C40 digital signal processor. Several experimental results are shown to validate the theoretical analysis     

Harmonic analysis of a parallel-loaded resonant converter

A method for calculating the harmonic components of the currents and voltages in a parallel-loaded resonant converter using frequency-domain techniques is presented. The converter is divided into an inverter section and a rectifier section. A harmonic model is developed for the resonant converter in which the rectifier section is treated as a voltage-dependent current sink. All voltages and currents in this model are represented by a Fourier series. The unknown coefficients in all Fourier series are calculated by using the harmonic model and Kirchhoff's laws. Because of the nonlinear nature of the rectifier section, an iterative technique must be utilized to find the unknown Fourier coefficients     

Run Diameter Statistics as a Measure of Image Texture

The new concept of "run circles" and their "run diameters," which can be used as a statistical measure of the spacing between points in a two-dimensional image, are presented. For synthetic aperture radar (SAR) images the spacing between bright spots in the image is a useful measure of image texture. The histogram of the run diameters for a set of points has been found to be useful in characterizing the spacings of the points. These histograms can be classified either using features of the histogram such as mode or median, or using classical linear classifiers. As an example, the histogram of run diameters is used to detect a set of points with approximately equal spacing interspersed with a background set of randomly located points.     

模型驱动设计方法在显控系统软件中的应用

本文介绍了应用Rhapsody支持的模型化设计方法进行显控系统的软件设计,在PC视窗环境下运用OpenGL显示图像。该技术可用于显控系统软件设计方法的提升,也可用于型号显控系统的前期论证演示。     

挠性飞行器姿态机动脉冲调宽控制系统设计

大挠性充液飞行器喷气姿态控制系统设计是一个复杂和关键的问题,为了抑制挠性振动,设计形状输入信号,选取双曲正切作为平滑函数,并和Bang-Bang控制对比研究.喷气脉冲调制采用工程上易于实现的脉冲调宽（PWM）设计方法,结合积分死区原理设计脉冲宽度,对具有挠性充液动力学特性的对象进行控制,抑制了振动模态和晃动模态,实现了平滑机动控制.通过数学仿真表明,形状输入法和合理的脉冲调宽逻辑可以有效抑制大挠性飞行器姿态机动控制过程中的挠性振动.     

Electrochemical machining of a convex strips structure on a revolving part by using site directed power interruption

Revolving parts with complex surface structures are widely used in machinery and mechanical equipment. The ECM process provides its adequacy to cut hard materials with different shapes, and its applications are widely increased, due to its outstanding advantages. In this paper, a new method for machining a convex strips structure on a cylinder by using site directed power interruption(SDPI) in the ECM process is presented. A variable correction value of the power-off time was defined and optimized to obtain the ideal interval for better machining accuracy and stability.The electric field distribution and the simulated convex profiles show that the stray current density can be reduced effectively by using the proposed method. The correction value has an important influence on the machining accuracy. A suitable correction value in the range of 0.6–1.2 s can effectively improve the machining accuracy of the convex strips structure. Experiments were also conducted to verify the proposed method. Results have confirmed that the stray corrosion on the convex strips surface is significantly reduced and the machining accuracy of convex strips structure is remarkably improved by using the proposed method with a suitable correction value in the ECM process. Finally, a convex strip with a height of 2 mm on a thin-wall revolving part was also produced successfully using a correction value of 0.9.     

Track-While-Scan Algorithm in a Clutter Environment

A track-while scan (TWS) algorithm is developed for targets in a clutter environment. The problem has been studied using only the position measurements [1, 5-8], but the simulation results have not been satisfactory. Modern processing techniques (FFT processor) ) in air traffic control and surveillance radar receivers provide both position and radial velocity. The radial velocity measurement may be conveniently used in the target-track correlation process, which will reduce the association ambiguity in the clutter environment. t. In the clear environment the algorithm using the position and radial velocity measurements has been treated in [3, 4]. A TWS algorithm, using both position and radial velocity measurements for targets in a clutter environment, is presented here. The algorithm obtained is nonlinear and adaptive. In order to evaluate the improvement due to radial velocity measurement a simulation has been performed on a digital computer. The algorithm was run with and without radial velocity measurements to compare its performances. An improvement was noted especially when the target path included an accelerated portion.     

一种基于EPLL技术的自适应正交解调技术研究

针对过零检测实现的全数字锁相环不仅锁相速度慢, 而且过零点的扰动会 直接影响锁相精度以及适合模拟电路实现的相干解调技术,在数字电路中实现则需要设 计高阶数字低通滤波器,将占用大量数字电路资源并且会显著增加系统功耗等问题,在 设计一种新型全数字锁相环(All-digital Enhanced Phase-lock Loop,EPLL)的基础上,结合自 适应正交解调技术,提出了一种基于EPLL 技术的自适应正交解调技术方案,并对该方 案进行了研究与仿真。仿真得到了满意的结果,验证了基于EPLL 技术的自适应正交解 调技术方案的可行性,并研究验证了算法的参数变化对其性能的影响,为今后算法在数 字系统中的实现以及其在各领域的应用研究奠定了坚实的基础。     

某型航空发动机整机振动分析

针对某型航空涡扇发动机整机振动过大现象进行测量并应用Matlab语言对该发动机振动信号进行了详细的时域、频域、三维谱阵分析.根据发动机转子各故障的典型特征,认为某型发动机振动异常的主要是因为高、低压转子不平衡和转动件与静止件碰摩造成的.所得出的结论对航空发动机故障诊断有一定的参考价值.     

Pulse Doppler signature of a rotary-wing aircraft

Field measurements of a modified Sikorsky S-55 helicopter target were carried out to investigate rotary-wing aircraft Doppler radar signature phenomenology. The results of the data analysis with regard to classification and identification of the aircraft based on its signature are presented. It was found that using the Doppler radar return and appropriate feature extraction techniques, the helicopter's design features can be estimated. Target backscatter from the main rotor blades, tail rotor blades, or hub can be used for target detection, acquisition, and classification as a rotary-wing aircraft. The extraction of configuration and blade count features can further define the helicopter for identification     

一类冷却导向叶片的多学科设计优化

提出含冲击、孔排及尾缘劈缝气膜、扰流柱复合冷却方式的燃气涡轮导向叶片多学科设计优化的一种方法.介绍了研究对象的结构特点、换热系数计算方法并给出了部分计算公式.建立了一种一类冷却导向叶片的多学科设计优化模型,以某燃气涡轮导向叶片为例,进行了多学科设计优化,获得了较好的效果.      

Simulation of a flexible spacecraft motion to evaluate microaccelerations

A method for simulating a flexible spacecraft motion using Lagrange’s quasivelocity formulation is considered. An algorithm of quasivelocity formation by Walsh’s means is proposed. This method can be used to evaluate a quasistatic microacceleration field component in the spacecraft internal environment.     

Crew station measurement methodology: a quantitative approach

An investigation of the difficulties associated with analyzing the geometric constraints placed upon the human operator in a work setting was conducted. Many workstations, such as a cockpit, have limited data available for creating the CAD models required for human performance analysis. To create a model, a time-consuming, labor-intensive process of collecting measurement data by hand must be performed, resulting in a CAD model of questionable accuracy. In order to conduct accurate repeatable analysis, CAD data for all workstations must be collected quickly and in a standardized format. A demonstration project assessed the feasibility of using Coordinate Measuring Machine (CMM) technology to collect workstation geometry and create a CAD Model. Baseline data for comparing hand collection methods was derived from previous aircraft cockpit CAD modeling projects. This method involved approximately two weeks for data collection alone and another week to create the CAD model. The CMM technology was determined to be a cost-effective method for creating CAD models of aircraft cockpits. This technology substantially reduced the time required to build a high fidelity CAD model while significantly improving the accuracy of the data     

Raster Scan Track of a Radar Scatterer Ensemble

A method is discussed for tracking the radar cross-section centroid of an ensemble of scatterers, using a raster scan observation technique. Estimation of the mean-squared dimensions of the ensemble is also considered. A maximum permissible beam separation is defined for the scan. Expressions for the bias and variance of the centroid estimates are given. Advantages of the approach are that individual scatterers need not be resolvable, and that the number of beams is independent of the number of scatterers.     

Error Covariance Analysis of a Karhunen-Loeve Collocation Estimator

An error covariance analysis of a two-dimensional gravity compensation technique (KLC) employing a Karhunen-Loeve gravity disturbance model and the linear least-square collocation algorithm for its estimation is presented, without actually using any data. Its performance is compared with another gravity compensation technique (KLE), whose error covariance analysis was previously presented by Gupta. From the mismodeling analysis, KLC appears to be superior to KLE.