交流阻抗谱法在热障涂层失效研究中的应用

介绍了交流阻抗谱法作为无损检测方法在热障涂层失效分析中的应用。通过对热循环、静态氧化过程中热障涂层体系的阻抗谱分析,利用交流阻抗谱对热障涂层进行拟合,得到了服役过程中D_M以及TGO电阻R拟合的结果与氧化时间呈抛物线关系;并根据阻抗的变化确定了粘结层的氧化过程中氧化物成分从Al₂O₃变化到混合氧化物的过程;对陶瓷层电阻的拟合结果表明,陶瓷层在热循环250~350次之间的电阻变化与陶瓷层内微观结构以及应力的变化有关。     

复合材料蜂窝板积水的脉冲热像检测的研究

 用数值模拟和实验研究了飞机蜂窝板积水的脉冲热像检测的规律。提出了蜂窝板积水检测的新型三维传热模型;用有限元法分析了近水检测、远水检测和立放检测3种检测模式下信息参数与积水量的关系;用脉冲热像实验验证了近水检测的基本规律。结果表明:在这3种检测模式下,最大温差和最大对比度与积水高度均呈非线性关系,随着积水高度的增加而增大。近水检测灵敏度最高,其次是蜂窝板立放检测,远水检测灵敏度最低。积水和富胶对表面温度的影响趋势一致,利用温差曲线或最大温差信息无法区分积水和富胶状态。根据可检信息参数与积水高度的关系曲线可以反向估计积水高度。这些研究结果为飞机蜂窝板积水的脉冲热像检测及评估提供了技术支持。     

Phase-Shift-Keyed Signal Detection with Noisy Reference Signals

This paper derives and graphically illustrates the performance characteristics of Phase-Shift-Keyed communication systems where the receiver's phase reference is noisy and derived from the observed waveform by means of a narrow-band tracking filter (a phase-locked loop). In particular, two phase measurement methods are considered. One method requires the transmission of an auxiliary carrier (in practice, this signal is usually referred to as the sync subcarrier). This carrier is tracked at the receiver by means of a phase-locked loop, and the output of this loop is used as a reference signal for performing a coherent detection. The second method is self-synchronizing in that the reference signal is derived from the modulated data signal by means of a squaring-loop. The statistics (and their properties) of the differenced-correlator outputs are derived and graphically illustrated as a function of the signal-to-noise ratio existing in the tracking filter's loop bandwidth and the signal-to-noise ratio in the data channel. Conclusions of these results as well as design trends are presented.     

全尺寸二元喷管红外辐射特性研究

 设计了一种全尺寸二元收敛喷管,用涡轮喷气发动机 WP-6作为燃气发生器,在发动机处于最大状态时,用红外光谱仪对二元喷管及尾喷流的红外辐射进行了测试。研究结果表明,与基准喷管相比,在发动机产生相同推力的条件下,二元喷管改善了喷口和尾焰红外辐射的光谱分布,减小了红外源的尖峰辐射,明显降低了发动机的红外辐射强度。     

Investigations of tip-jet and exhaust jet development in a ducted fan

The major aim of this work is to investigate the tip-jet and exhaust jet development in a ducted fan as well as the impact on the fan’s performance. The flow field of the ducted fans under the solidity varied from 0.2 to 0.7 are simulated by using the shear-stress transport k-ω turbulence model with a refined high-quality structured grid. The exhaust jet trajectory, expanding range and the flow intersection of the jet and mainstream in the blade passage are analyzed. As the results suggest, the flow direction of the exhaust jet is deflected by the downwash and Coanda effect. The major decay region of the exhaust jet can extend at least 2 times the blade chord downstream from the blade trailing edge. The blade circulation is impacted by the tip-jet rather than the exhaust jet from the upstream when the blade tip pitch angle is 8°, and the fan solidity is less than 0.7. The blade tip thrust is reduced by the interruption from the exhaust jet when the blade tip pitch angle is 2°, and the fan solidity is larger than 0.3.     

Measurement of Distributed Targets with the Random Signal Radar

A model of a distributed target as a collection of independent, Poisson distributed point scatterers or scattering centers in a range-velocity target space is introduced and is characterized by a deterministic function called the ?scatterer density function.? This function is the density of the point scatterers in the range-velocity space and can be estimated in a relatively straightforward manner by any radar having adequate resolution in both range and velocity and no ambiguities in the region occupied by the distributed target. The use of the random signal radar with a correlator receiver is considered here and the statistical properties of the correlator output, when the return signal is from a distributed target, are derived. It is shown that the spectral density is simply related to the scatterer density function. The technique is illustrated by an example in which the target is a tornado modeled as a cylinder with constant angular velocity. The example suggests that is a possible to remotely estimate the radar cross section per unit volume as a function of distance from the center of the tornado.     

利用卡尔曼滤波求取直升机气动导数的应用研究

本文主要介绍利用低通滤波、卡尔曼滤波及最小二乘法求取直升机气动导数的方法。本方法的特点是,通过低通滤波使旋翼高频成份的影响减至最小,同时求取试验数据的测量噪声和过程噪声,然后通过卡尔曼滤波使试验数据包含的随机噪声减至最小,最后用最小二乘法求得直升机的气动导数,为了提高卡尔曼滤波的准确度,用最小二乘法由试验数据求取直升机的气动导数作为卡尔曼滤波时的初始导数。计算结果表明,该方法可使试验数据中包含的噪声大大减小,误差带减少70％以上,而计算工作量又远远小于最大似然法。     

Optimum Position Estimation Using Multiple-Frequency Omega

The maximum-likelihood estimator of the line of position (LOP) resulting from K frequencies received from each of two Omega stations for high SNR is derived. The estimator takes advantage of interfrequency correlation of phase uncertainties by modeling them as resulting from phase velocity uncertainties which are jointly Gaussian with known covariance. The utilization of Omega for search and rescue systems is examined. For this application, the result of increasing the size of the unambiguous lanes of Omega by addition of a fourth frequency to the present three-frequency format is examined. The results of Monte Carlo simulation, performed for several easily implemented fourth frequencies, are presented. The simulation results illustrate the extent to which lane errors can be expected as a function of various fourth frequencies, phase velocity uncertainties, and SNR.     

Multipurpose visualization system

This deals with the design and architecture of the low-cost Multipurpose Flight Visualization System (MFVS). The MFVS system was originally developed as a passive IFR approach system for small general aviation planes. A relatively high adaptability is one of the main advantages. It can be easily used with many types of avionics devices. The GPSIINS system is used as the primary data source. The data from the GPSIINS system are pre-processed by proprietary neural network units that feed the 3-D visualization system. The neural network unit is responsible for adaptation of this system and can eliminate problems caused by data delays and data drop-outs. The 3D visualization unit processes data from the neural network unit and eventually from the 6DOF tracker that is placed on the pilot's Head Mounted Display (HMD). The unit then generates a 3D view of the surrounding environment that is similar to the 3D environment the pilot knows from flight simulators. The source of environment data is the terrain and object/obstacle database. The image output can be displayed on HIUD, MED, or HMD.     

A study of flight-critical computer system recovery from spaceradiation-induced error

It is well known that space radiation, containing energetic particles such as protons and ions, can cause anomalies in digital avionics onboard satellites, spacecraft, and aerial vehicles flying at high altitude. Semiconductor devices embedded in these applications become more sensitive to space radiation as the features shrink in size. One of the adverse effects of space radiation on avionics is a transient error known as single event upset (SEU). Given that it is caused by bit-flips in computer memory, SEU does not result in a damaged device. However, the SEU induced data error propagates through the run-time operational flight program, causing erroneous outputs from a flight-critical computer system. This study was motivated by a need for a cost-effective solution to keep flight-critical computers functioning after SEU occurs. The result of the study presents an approach to recover flight-critical computer systems from SEU induced error by using an identity observer array. The identity observers replicate the state data of the controller in distinct data partitions. The faulty controller can be recovered by replacing data image of the faulty data partition with that of the healthy data partition. The methodology of applying such an approach from the fault tolerant control perspective is presented. The approach is currently being tested via computer simulation     

Flowgraph Techniques for Closed Systems

A two-port with both generator and load constitutes a closed system; it can be defined as a system with only interdependent variables or as a system containing no independent variables. The flowgraph describes the relationships between variables in a closed system as determined by the topology of its components. The corresponding closed flowgraph represents a zero-port network from which N-port networks can be generated as subsets by truncation of the closed system. A constraint governing any closed system expressing the properties of its cut-sets and tie-sets is referred to as the topology equation. The topology equation can be computed from the sum of loops in the closed flowgraph, and forms the key for the derivation of properties of closed systems and derived N-port subsets. Oscillators analyzed as zero-ports are discussed in detail to illustrate the rationale for the flowgraph approach to closed systems. To exploit the closed system model conceptually and computationally for N-ports, an approach is suggested and illustrated for N = 1 by an analysis of transfer functions and for N = 2 by a sensitivity analysis of stochastic networks.     

具有不对称间隙的二元机翼自激振动的混沌分析

利用数值方法分析了无预荷载情况下具有不对称间隙的气动弹性非线性与结构非线性耦合的二元机翼颤振问题的动力学响应.通过研究速度比U*/U*L从零逐渐增大到1时系统的全局演化规律,发现在无预荷载的不对称分段线性系统中存在混沌运动形式,并对其进行具体分析,得到产生混沌的原因,为进一步控制和减小颤振提供理论帮助,对飞机的飞行结构设计及飞机结构的日常维护具有指导意义.     

The MOD:A Modular Urban Transportation System

The MOD is described as an urban transportation system which is based on a very small, two-passenger automotive rental vehicle using existing city roadways at the exclusion of the private passenger car. The proposed units of the MOD system have an empty weight of 300 pounds and have provisions for easy vertical parking. The MOD system is proposed as a self-supporting operation, run by private enterprise as a public utility. The urban transportation offered by the MOD system generates the set of institutional problems involved in proposals which exclude the private passenger car from the city.     

辅助工程师设计的知识融合设计方法:卫星舱布局设计(英文)

卫星舱布局设计属工程系统设计问题,为用传统计算方法难以解决的问题,该问题具有三重难度:工程复杂性、计算复杂性和达到工程实用难。卫星布局设计师的成功经验表明,它需要依赖设计师的经验和智慧、借鉴先验知识和辅以"计算"进行设计,并实现人机结合。本文的人机结合方法采用在线人知识、在线计算知识和先验知识(如参考布局施工图)的知识融合方法,并在卫星布局CAD、仿真与评价系统平台上实现,发挥人机各自特长。主要研究:(1)设计知识:包括在线人知识、在线计算知识和先验知识的表达;(2)上述3类知识的广义描述模型及其知识融合方法;(3)人的作用。经以简化的国际通信卫星舱布局设计为例的数值实验验证,表明了本文方法的可行性。     

High resolution miniature AMLCDs for projection and head-mountedsystems

The development of advanced active matrix liquid crystal displays is described. The displays are formed from single crystal silicon, and have integrated on-board scanner circuitry for row and column addressing. The display diagonal is 5 cm, and pixel pitch as low as 12 μm is under development. Operational 640 by 480 displays are described, and initial results with 1.250 by 1.024 displays are reported     

计算机辅助的低空风切变改出优化控制

介绍了动态系统的计算机辅助直接优化方法的原理及其在低空风切变改出飞行中的应用，利用较真实的风切变工程化模型，选择适当的控制函数模型，性能准则及其约束条件，通过计算机直接地，系统地和迭代地探寻最优条件，对飞机改出低空风切变控制进行了优化，获得了最佳改出性能飞行参数曲线，并与没有优化的改出引导策略结果作了比较，结果表明，通过优化，飞机改出低空风切变的性能获得了明显的改善。     

扭转载荷下带环状裂纹圆棒的J积分的评价

研究了扭转载荷下带环状裂纹圆棒试样的J积分的评价.首先得到了一系列带有不同深度环状切口的中碳钢圆棒试样的扭矩-扭转角关系,然后分别利用单试样的简单评价法和多试样的能量法计算J积分值.结果发现,当圆棒试样的切口深度足够深(即裂纹长度足够长)或扭转角足够小时,两种方法计算的J积分值相当一致.     

A simple smoother: closed-form solution and analytical results

A closed-form solid-state solution for a simple one-dimensional smoother is presented. The target position-velocity dynamics are modeled as a linear discrete Gauss-Markov process: the discrete position measurements are assumed to be independent and identically normally distributed. Analytical results derived from estimating optimum steady-state position and velocity are given as well as the improvement provided by smoothing relative to pure filtering estimates. Analytical results, including appropriate limiting cases, show that the ratios of the RMS smoothing to the RMS filtering error are from 1/2 to 1 in position and from 1/2 to 1/√2 in velocity. As a numerical example a highly maneuvering target characterized by an acceleration width of 30 m/s² is considered     

A method for automatic detection and characterization of plasma bubbles using GPS and BDS data

Detecting and characterizing Total Electron Content (TEC) depletion is important for studying the ionospheric threat due to the Equatorial Plasma Bubble (EPB) when applying the Ground-Based Augmentation System (GBAS) at low latitudes. This paper develops a robust method to automatically identify TEC depletion and derive its parameters. The rolling barrel algorithm is used to automatically identify the TEC depletion candidate and its parameters. Then, the depletion candidates are screened by several improved techniques to distinguish actual depletions from other phenomena such as Traveling Ionospheric Disturbance (TID) or abnormal data. Next, based on the depletion signals from three triangular receivers, the method derives EPB parameters such as velocity, width and gradient. The time lag and front velocity are calculated based on cross-correlation using TEC depletions and the geometrical distribution of three triangular receivers. The width and gradient of slope are then determined by using TEC depletion from a single receiver. By comparison, both the station-pair method and proposed method depend on the assumption that the EPB morphology is frozen during the short time when the plasma bubble moves between the receivers. However, our method relaxes the restriction that the baseline length should be shorter than the width of slope required by the station-pair. This relaxation is favorable for studying small-scale slope of depletions using stations of a longer baseline. In addition, the accuracy of the width and gradient is free of impact from hardware biases and small-scale disturbance, as it is based only on the relative TEC variation. The method is demonstrated by processing Global Positioning System (GPS) and BeiDou Navigation Satellite System (BDS) data on 15 August, 2018, in a solar minimum cycle.