Two Methods of Ambiguity Resolution in Pulse Doppler Weather Radars

A comparison is made of the performance of a weather Doppler radar with a staggered pulse repetition time and a radar with a random (but known) phase. As a standard for this comparison, the specifications of the forthcoming next generation weather radar (NEXRAD) are used. A statistical analysis of the spectral moment estimates for the staggered scheme is developed, and a theoretical expression for the signal-to-noise ratio due to recohering-filtering-recohering for the random phase radar is obtained. Algorithms for assignment of correct ranges to pertinent spectral moments for both techniques are presented.     

Pseudorandom Frequency Modulation in Range-Doppler Radar

In many radar systems, efficient use of transmitter power requires the transmission of a constant-amplitude signal for a substantial fraction of time; for a monotonic transmission, however, the range resolution is restricted by the length of the transmitted pulse. Linear frequency modulation removes this constraint for targets with negligible, or known, radial velocities; it is not suitable, however, for simultaneous observations of range and radial velocity (Doppler shift). This paper describes a class of waveforms suitable for simultaneous measurement of range and Doppler shift. These waveforms are characterized by a uniform distribution in frequency and by pseudorandom frequency changes. Uniform frequency distribution is attained by a uniform spacing of frequencies with each frequency present for an identical length of time. Frequency changes are effected by sequencing the frequencies with a pseudorandom number generator. Ambiguity functions are computed for pseudorandom frequencymodulated waveforms designed for ionospheric backscatter studies. By suitable choice of parameters, the ambiguity function becomes a narrow central peak surrounded by a plateau whose height varies randomly between zero and approximately twice its average. Waveform generation by means of a digital frequency synthesizer and data reconstruction considerations are described.     

直升机外挂吊运技术研究

直升机外部吊挂运送物资在国防和国民经济建设中有极为广泛的用途。本文以直8A型机和米171直升机为例，对直升机外挂吊运的飞行性能计算、全机稳定性、吊具系统的设计、飞行员和指挥员、信号员和索具员如何协调等问题进行了研究分析，为今后执行外挂吊运任务的设计和实施，提供了有价值的建议。     

Intelligent control of a planning system for astronaut training

This work intends to design, analyze and solve, from the systems control perspective, a complex, dynamic, and multiconstrained planning system for generating training plans for crew members of the NASA-led International Space Station. Various intelligent planning systems have been developed within the framework of artificial intelligence. These planning systems generally lack a rigorous mathematical formalism to allow a reliable and flexible methodology for their design, modeling, and performance analysis in a dynamical, time-critical, and multiconstrained environment. Formulating the planning problem in the domain of discrete-event systems under a unified framework such that it can be modeled, designed, and analyzed as a control system will provide a self-contained theory for such planning systems. This will also provide a means to certify various planning systems for operations in the dynamical and complex environments in space. The work presented here completes the design, development, and analysis of an intricate, large-scale, and representative mathematical formulation for intelligent control of a real planning system for Space Station crew training. This planning system has been tested and used at NASA-Johnson Space Center     

Algorithms of constructing a neural network model for a dynamic object of control and adjustment of PID controller parameters

The paper presents an algorithm for constructing a neural network model for a dynamic object of control based on the data sample obtained as a result of the object operation. The algorithm being considered applies a neural network approach and a genetic algorithm. An algorithm is presented for determining a domain of possible values for a proportional-integral-derivative controller (PID controller) based on application created neural network model of the controlled object.     

飞机噪声环境对结构影响的研究

本文介绍测量飞机噪声环境,获得的结构噪声载荷分布与频谱的结果,并分析了影响其量值的因素与结构声振响应特性;归纳了结构噪声载荷谱及其编制方法;简述了进行结构声疲劳试验的方法与参数选择原则和实例;列举了分析与排除声疲劳故障的方法和效益     

并联TBCC可调进气道并联方案

对并联涡轮基组合循环(TBCC)可调进气道并联方案进行了归纳分析,提出了一种分类方法和两种并联方案。对4种典型并联方案在马赫数为2.5的模态转换工况进行了稳态仿真分析。结果表明:后开纯内并联方案在模态转换过程中总流量变化很小,其余3种的总流量系数随着涡轮通道的关闭都是逐渐减小的,涡轮通道流量系数逐渐降低,冲压通道升高。4种方案冲压通道流量系数在模态转换过程中均是逐渐升高的,后开纯内并联方案具有最低的冲压通道平均流量系数,变化幅度最大,其余3种方案变化幅度均较小。前开纯外并联和混合式内并联两种方案的涡轮通道出口总压恢复在模态转换过程中呈减小趋势,另外两种方案的总压恢复呈略微增大趋势,其中前开纯外并联平均总压恢复最低,而混合式内并联方案的平均总压恢复最高。      

Subsonic impulsively starting flow at a high angle of attack with shock wave and vortex interaction

Impulsively starting flow, by a sudden attainment of a large angle of attack, has been well studied for incompressible and supersonic flows, but less studied for subsonic flow. Recently, a preliminary numerical study for subsonic starting flow at a high angle of attack displays an advance of stall around a Mach number of 0.5, when compared to other Mach numbers. To see what happens in this special case, we conduct here in this paper a further study for this case, to display and analyze the full flow structures. We find that for a Mach number around 0.5, a local supersonic flow region repeatedly splits and merges, and a pair of left-going and right-going unsteady shock waves are embedded inside the leading edge vortex once it is sufficiently grown up and detached from the leading edge. The flow evolution during the formation of shock waves is displayed in detail. The reason for the formation of these shock waves is explained here using the Laval nozzle flow theory. The existence of this shock pair inside the vortex, for a Mach number only close to 0.5, may help the growing of the trailing edge vortex responsible for the advance of stall observed previously.     

Effect of a Few Dominant Specular Reflectors Target Model Upon Target Detection

Some data indicate that aircraft targets viewed from certain aspects are well modeled as consisting of a few specular reflectors. The effect of a simplified form of this target model upon radar detection performance for two different waveforms has been analyzed. The signal-to-noise ratio (SNR) required for detection as a function of waveform bandwidth for a conventional-single-channel waveform and for a four-channel frequency diversity waveform is evaluated. It is shown that for either waveform there is an optimum bandwidth to minimize the SNR required for detection. In addition, the single-channel minimum is less than the four-channel minimum. The best performance occurs for the single-channel waveform when the waveform bandwidth just resolves the individual reflectors. For typical targets, this bandwidth is of the order of 35 to 75 MHz. It is also shown that only a 0.8-dB loss relative to this minimum is incurred when using a four-channel narrow bandwidth waveform.     

Space Applications of a Minimization Algorithm

A detailed account is given of the application of a minimizationprogram to several design problems. Specifically these applications areconcerned with the design of a curve function generator for a massspectrometer for a proposed Mars probe and the design of autonomousshift registers with linear and nonlinear feedback, used for classificationion of binary sequences and counting tasks for spacecraft scientificdata processing.     

Optimum FFT-based frequency acquisition with application toCOSPAS-SARSAT

In the case of a single sinusoid or multiple well-separated sinusoids, a coarse estimator consisting of a windowed Fourier transform followed by a fine estimator which is an interpolator is a good approximation to an optimal frequency acquisition and measurement algorithm. The design tradeoffs are described. It is shown that for the fine-frequency estimator a good method is to fit a Gaussian function to the fast-Fourier-transform (FFT) peak and its two neighbors. This method achieves a frequency standard deviation and a bias in the order of only a few percent of a bin. In the case of short-time stationarity, for a moderate number of averages and for an adaptive threshold detector, only between 0.5 and 1 dB is lost when averaging is traded off for FFT length, in contrast to the asymptotic result of 1.5 dB. The COSPAS-SARSAT satellite system for emergency detection and localization is used to illustrate the concepts. The algorithm is analyzed theoretically, and good agreement is found with test results     

一个面向可变形模型实时有效的接触反馈框架

由于力反馈需要很高的计算速度及变形反馈需要详细的图形信息 ,本文提供一个实时有效的接触反馈框架 ,通过在粗糙三角形网格上进行局部细分来实现。当检测到接触后 ,将发生碰撞的表面细分以产生一个粒子系统。利用此粒子系统 ,用近似速度锥理论对形变进行模拟。同时 ,采用弹簧 -阻尼模型计算形变力。最后 ,对此框架进行了测试并实际应用于一个医疗规化仿真系统。     

某系列飞机蓄电池组新型自动加温装置的技术研究

航空蓄电池组是我军航空兵部队某系列飞机的地面起动、机载备份应急化学电源。本文分析了我军现役某系列飞机的航空蓄电池组使用状况和温度性能后,揭示了研制稳定高效的蓄电池组自动加温装置的必要性并给出了初步的设计方案。     

Modeling the Superconducting Alternator with Thyristor Bridge

Steady state equations are derived for the superconducting alternator with a thyristor bridge (dc) output. This is accomplished by modification of a previous analysis for a machine with a diode bridge. The approach used avoids the need to numerically solve the differential equations for the system, and it is quite efficient in terms of computation time. Numerical simulations for both the diode and thyristor bridge circuits are included for comparison.     

Analytic example of a Schweppe likelihood-ratio detector

A low-dimensional test problem with a known solution is used to verify various computer implementations of F.C. Schweppe's likelihood detector (1965). In this case a closed-form solution is provided for a Schweppe likelihood detector in terms of an intermediate Kalman filter, as utilized in its implementation, for detecting the presence of a two-state signal model in Gaussian white noise. The associated error probabilities are also evaluated following a procedure that utilizes optimized Chernoff-like bounds for a tight approximation. A methodology is demonstrated for appropriately setting the decision threshold for this example as a tradeoff against allowable observation time. By using this or similar examples, certain qualitative and quantitative aspects of the software implementation can be checked for conformance to anticipated behavior as an intermediate benchmark, prior to modular replacement of the various high-order matrices appropriate to the particular application     

A safety kernel for traffic light control

The success of kernels for enforcing security in software systems has led to proposals to use kernels for enforcing safety. This paper presents a feasibility demonstration of one particular proposal for a safety kernel via the application of traffic light control. The paper begins with the safety properties for traffic light control and specifies a kernel that maintains the safety properties. An implementation sketch of the kernel in Ada is given and use of the kernel is discussed. The contribution of the paper is a demonstration that a kernel is a feasible and desirable technique for software in a realistic, safety-critical application. The paper also illustrates how formal methods aid the software engineer in constructing and reasoning about such software     

超机动飞机的非线性动态逆控制

讨论了应用非线性动态逆进行超机动飞机飞行控制系统的设计。对快变量角速率进行非线性逆控制器的设计,由此来稳定纵向短周期运动,并通过气动舵面与推力矢量的融合,来改善大迎角范围的侧向响应,对慢变量姿态角进行非线性逆控制器的设计可使飞行员控制飞机慢运动。     

Achieving higher levels of electronic integration throughsystem-on-chip

All aerospace vehicles have the common constraint of limited space for the electronic systems. The challenge has always been how to pack effective electronic systems into the space available. Higher levels of electronic integration can give a competitive advantage; for example, by providing extra channels in a communications satellite thereby increasing revenue to the operator. Today's deep sub-micron manufacturing processes for integrated electronics offer an opportunity for a step change for electronic functionality that can be packaged in a given space. This technology makes possible, for the first time, a true system-on-chip approach to electronic systems, which is already being exploited by the commercial sector in products such as the mobile telephone     

AI techniques in uninhabited aerial vehicle flight

This describes the development of an application of artificial intelligence (AI) for unmanned aerial vehicle (UAV) control. The project was part of the requirements for a class in AI at NOVA Southeastern University and a beginning project at NASA Wallops Flight Facility for a resilient, robust, and intelligent UAV flight control system. A method is outlined which allows a base level application for applying an artificial intelligence method, fuzzy logic, to aspects of control logic for UAV flight. One element of UAV flight, automated altitude hold, has been implemented and preliminary results displayed.     

超音通流风扇发动机循环分析

超音通流风扇发动机概念新、优点突出.本文发展的计算机程序能对不同类型发动机进行循环分析和某些参数的优化计算,对一架Ma=2.7的超音巡航运输机进行了算例分析.计算结果表明,超音通流风扇发动机耗油率大大低于常规涡扇和涡喷发动机,重量轻,推重比高,亦有明显优势.有效解决飞行剖面上进气道与发动机相容性问题,对提高推进系统性能关系很大.