深空测控系统中的射电星校相方法

深空测控系统要求具有角度自跟踪功能,而和差双通道跟踪体制下测控设备在任务前需要进行校相。传统校相依赖标校塔,深空测控系统天线口径大,无法建造满足远场条件的标校塔,从而只能采用其他校相方案。本文通过分析校相过程的机理,并结合射电星具有全天候、分布广、星历精确已知的特点,得到了利用射电星校相的方法。通过前期大量试验证明了该方法的可行性,并已确定应用于深空测控系统的研制。     

吸气式高超声速飞行器气动热试验研究

为获得吸气式高超声速飞行器气动热环境的数据,开展了气动热试验研究。在激波风洞中,来流马赫数Ma=6.12,来流单位雷诺数Re/L=1.37×107(1/m)试验条件下,对吸气式高超声速飞行器1/4缩比模型进行了表面气动热的测量。试验获得了小攻角变化范围内的飞行器头部前缘、头部上下交线、机身上下表面中心线、机身横截面周向、平尾垂尾前缘、发动机唇口等位置的热流率分布。研究结果表明,吸气式高超声速飞行器头部前缘、前体进气道壁面、发动机唇口、平尾垂尾前缘气动加热最为严重,另外乘波体外形的设计与布局影响热流的分布。     

Conjecture on superrotation in planetary atmospheres: A diffusion model with mixing length theory

Superrotation on Venus is discussed in the context of comparative planetary atmospheres. In our planetary system, the rigid shell component (global average) of superrotation is ubiquitous (Jupiter, Saturn, Earth, Venus, Mars, Titan). The largest equatorial values of the component are between 25 and 150 m/sec. We present a simplified, heuristic analysis, utilizing mixing length theory to describe the small scale non-linear advections of energy and angular momentum, thereby providing a closure of the dynamic system. This leads to the conjecture that the zonal velocity may be crudely estimated by

, approximating the observed planetary trends; with c the speed of sound, the parameter a being 1 or 2 for geostrophic or cyclostrophic conditions respectively, P_α an effective Prandtl number which becomes less than one when radiative cooling is important, S_o the average stability, Γ the adiabatic lapse rate and γ the ratio of specific heats.     

Dust in and Around the Heliosphere and Astrospheres

Space Science Reviews - The ESA Swarm mission, launched on 22 November 2013, consists of three spacecraft each equipped with a Micro Advanced Stellar Compass ( $\mu $ ASC) from the Technical...     

Coordinated Frequency and Voltage Control of Synchronous Generators

Three different types of controllers, i.e., the conventional controller, the linear optimal controller (LOC), and the variablestructure controller (VSC) are proposed for the coordinatedfrequency and voltage control of synchronous generators. Theinteraction between the frequency and voltage control loops is takeninto account by incorporating both the speed-governing system andthe excitation system into the mathematical model of thesynchronous generator. Results obtained from computer simulationindicate that the variable structure controller can yield the bestdynamic responses following a step load change.     

Excitation control of a synchronous generator using a lookup table

A scheme involving the use of a lookup table is developed for the excitation control of a synchronous generator. The proposed control scheme, generator speed deviation, and acceleration deviation are taken as the input signals. These input signals are sampled and converted to linguistic terms before they are fed into the controller. The controller generates the desired output (control) signal by using a set of production rules (if-then rules) that are based on previous experience to relate the input signals to the output. The output signal is converted from linguistic terms to a numerical value before it is sent to the excitation system of the synchronous machine. To demonstrate the effectiveness of the proposed control scheme, digital simulations of a synchronous generator subject to a three-phase fault under different operating conditions were performed. It was found that the controller can improve the dynamic performance of a synchronous generator over a wide range of operating conditions. Since the controller does not require model identification, it is computationally efficient and is suitable for online excitation control, using a microcomputer     

Self-organizing fuzzy learning CLOS guidance law design

A new self-organizing fuzzy logic control (SOFLC) design method is proposed. The proposed method is applied to the command line-of-sight (CLOS) guidance law design. The SOFLC contains two sets of fuzzy inference logic. One is the fuzzy logic controller and the other is the rule modifier. The new learning method of the rule modifier is developed based on a fuzzy learning algorithm. The modification value of each rule is based on the fuzzy firing weight, so that learning of the rule bases is reasonable. Finally, two engagement scenarios are examined, and a comparison between a fuzzy logic control (FLC), an optimal learning FLC, and the proposed SOFLC CLOS guidance laws is made. Simulation results show that the proposed SOFLC guidance law can achieve better guidance performance than the other guidance laws.     

Damping of Generator Oscillations Using Static VAR Compensators

The design of a novel static VAR compensator for the damping of electromechanical oscillation in a synchronous generator is presented. The proposed compensator, which is made up of a fixed capacitor and a thyristor-controlled inductor, is installed at the generator terminal to provide the required damping without deteriorating the voltage profile under disturbance conditions. In order to have better dynamic performance, a supplementary proportional-integral-derivative (PID) controller of which the parameters are determined by eigenvalue assignment is incorporated in the static VAR compensators. The dynamic responses of the synchronous machine subjected to a three-phase fault are given to demonstrate the effectiveness of the static VAR compensators. A comparison study of the proposed controller and a PID excitation controller is made with respect to damping enhancement and terminal voltage deviation.     

水面波作用下平面射流振翅运动的频率锁定现象

通过激光流动显示 (LIF)和测量方法 ,就表面水波对垂直平面射流的振翅运动的影响进行了实验和理论研究。研究表明 ,在表面波的影响下 ,振翅运动依然存在。同时 ,波高计和多谱勒激光测速仪的测量结果显示 ,当表面波的频率接近但低于射流振翅运动的自然频率时 ,射流振翅运动的实际振动频率将被锁定在表面波的频率上。而当表面波的频率大于射流振翅摆动的自然频率时 ,频率锁定现象将不存在。     

Adaptive Two-Stage Extended Kalman Filter for a Fault-Tolerant INS-GPS Loosely Coupled System

The well-known conventional Kalman filter requires an accurate system model and exact stochastic information. But in a number of situations, the system model has an unknown bias, which may degrade the performance of the Kalman filter or may cause the filter to diverge. The effect of the unknown bias may be more pronounced on the extended Kalman filter (EKF), which is a nonlinear filter. The two-stage extended Kalman filter (TEKF) with respect to this problem has been receiving considerable attention for a long time. Recently, the optimal two-stage Kalman filter (TKF) for linear stochastic systems with a constant bias or a random bias has been proposed by several researchers. A TEKF can also be similarly derived as the optimal TKF. In the case of a random bias, the TEKF assumes that the information of a random bi?s is known. But the information of a random bias is unknown or partially known in general. To solve this problem, this paper proposes an adaptive two-stage extended Kalman filter (ATEKF) using an adaptive fading EKF. To verify the performance of the proposed ATEKF, the ATEKF is applied to the INS-GPS (inertial navigation system-Global Positioning System) loosely coupled system with an unknown fault bias. The proposed ATEKF tracked/estimated the unknown bias effectively although the information about the random bias was unknown.