The Galileo Dust Detector

The Galileo Dust Detector is intended to provide direct observations of dust grains with masses between 10^-19 and 10^-9 kg in interplanetary space and in the Jovian system, to investigate their physical and dynamical properties as functions of the distances to the Sun, to Jupiter and to its satellites, to study its interaction with the Galilean satellites and the Jovian magnetosphere. Surface phenomena of the satellites (like albedo variations), which might be effects of meteoroid impacts will be compared with the dust environment. Electric charges of particulate matter in the magnetosphere and its consequences will be studied; e.g., the effects of the magnetic field on the trajectories of dust particles and fragmentation of particles due to electrostatic disruption. The investigation is performed with an instrument that measures the mass, speed, flight direction and electric charge of individual dust particles. It is a multicoincidence detector with a mass sensitivity 10⁶ times higher than that of previous in-situ experiments which measured dust in the outer solar system. The instrument weighs 4.2 kg, consumes 2.4 W, and has a normal data transmission rate of 24 bits s^-1 in nominal spacecraft tracking mode. On December 29, 1989 the instrument was switched-on. After the instrument had been configured to flight conditions cruise science data collection started immediately. In the period to May 18, 1990 at least 168 dust impacts have been recorded. For 81 of these dust grains masses and impact speeds have been determined. First flux values are given.     

离散事件系统的Petri网图仿真

1.前言 离散事件动态系统DEDS(Discrete Event Dynamic System)的传统分析方法——应用排队论和随机过程理论为离散事件动态系统建立排队网络模型,在很多情况下已不适用。新的理论和研究方法相继提出。其中之一是“皮特里网”(Petri Nets)理论。另一种比较成熟的方法是仿真法,但是,仿真法要以高昂的计算机设备的大量计算时间为代     

硅基内衬喷管扩张段烧蚀和温度场的耦合计算方法

本文叙述固体火箭喷管扩张段硅基内衬烧蚀和温度场的耦合计算方法.烧蚀采用非定常的液体层烧蚀模型;温度场计算采用圆柱坐标系下的一维径向瞬态导热模型,考虑材料在高温下形成的炭化层和热解层,而由烧蚀产生的边界移动问题用坐标变换的方法处理.利用烧蚀和导热计算方程组中二者的结合部,通过充分耦合,获得了更准确的预示计算结果.     

Electromechanical Actuation Technology for the All-Electric Aircraft

Electromechanical actuation is a critical element that must be developed and verified to make the all-electric aircraft a viable concept. For several years the Flight Control Division of the Air Force Wright Aeronautical Laboratories has sponsored activities to demonstrate the credibility of electromechanical actuation systems (EMAS) for primary flight control actuation functions. The foundation for these EMAS activities and several electromechanical actuation development programs are described here. One involves the design, fabrication, and laboratory test of a rotary, hingeline electromechanical actuator. Another involves the development and flight test demonstration of a linear electromechanical actuator for controlling an aileron of a C-141 aircraft. A third involves the design and development of a linear electromechanical actuator for missiles having severe performance, temperature, and volumetric requirements. In addition, a brief summary of the results from two aircraft actuation trade studies compare the baseline (conventional) hydraulic flight control system with an all-electric airplane concept including quantitative comparisons of weight, reliability and maintainability, and life cycle costs.     

State Estimation and Divergence Analysis

A growing memory discrete dynamic model for performing temporal extrapolations along a predetermined path in a random field is presented. This dynamic model is used to drive a linear system that is itself driven by discrete white noise. The coupled system is used to derive a state estimation scheme that recursively processes noisy measurements of the system. In addition, using the aforementioned dynamic model as a reference (truth) model, the authors develop a covariance analysis to measure the estimation errors that occur when the dynamics along the path through the field are modeled as a Markov linear model and state estimation is performed using discrete Kalman filtering. The performance evaluation of an inertial navigation system influenced by the Earth's gravity field aboard a maneuvering ship is provided as a specific illustrative example.     

Weak Signal Detection in Non-Gaussian Noise of Unknown Level

An adaptive threshold detector to test for the presence of a weak signal in additive non-Gaussian noise of unknown level is discussed. The detector consists of a locally optimum detector, a noise level estimator, and a decision device. The detection threshold is made adaptive according to the information provided by the noise level estimator in order to keep a fixed false-alarm probability. Asymptotic performance characteristics are obtained indicating relationships among the basic system parameters such as the reference noise sample size and the underlying noise statistics. It is shown that, as the reference noise sample size is made sufficiently large, the adaptive threshold detector attains the performance of a corresponding locally optimum detector for detecting the weak signal were the noise level known.     

高负荷跨音速复合气冷涡轮叶片的试验研究

在燃气涡轮研究所 ( GTE)的涡轮叶片综合冷却效果试验器上对四套大载荷跨音速复合式气冷涡轮叶片 (多种气膜孔方案 ) ,成功地进行了 2 90小时试验。试验结果表明 ,导叶在 2 - 8% ,动叶在 1- 6%宽广的冷气流量比范围内 ,具有良好的冷却特性。此外还分析了叶片参数对冷却效果的影响     

Parallel resonant converter with LLC-type commutation

It is shown that by using a proper transformation of state variables, the third-order system of the parallel resonant converter (PRC) with LLC-type commutation can be analyzed by means of a two-dimensional state-plane diagram. A set of characteristic curves which can be used for the converter design is derived from the analysis. It is shown from these curves that the converter possesses more desirable features than the conventional PRC     

Investigations of Stability & Dynamic Performances of a Current-Injected Regulator

The stability and dynamic performances of a buck/boost regulator employing a current-injected control are examined. Small-signal models for the power state, the multiloop error processor, and the duty-cycle pulse modulator are developed. The error-processor model which incorporates the current-injected loop, the dc loop, and the compensation network permits evaluation of the effects of each individual control loop and their combined efforts toward shaping the performance characteristics of the closed-loop system. Comparisons are made between this modeling approach and earlier approaches. Some important yet subtle dissimilarities are discussed. This model predicts the constant-frequency 50-percent duty-cycle instability which is inherent to the current-injected control.     

The Measurement of Echo Direction in a Phased-Array Radar

For a planar-array antenna with a monopulse feed horn, this study describes a simple algorithm for the determination of the direction of target echoes. Antenna pattern measurements of the array indicate that the direction sines of a received wavefront can be independently obtained with one simple relation between a normalized difference channel output and a direction sine. This paper determines the accuracy of the algorithm.