Polar auroras

Conclusion We have reviewed the somewhat conflicting data which have accumulated on such a vast scale in recent years. It is now becoming clearer which studies are likely to produce significant results, and this in itself may be a very important consequence of the assimilation of accumulated data. We must however ask in conclusion: does the outer radiation belt exist during the polar aurora? If the interplanetary media or the solar wind, carry magnetic fields, then these fields can be of two kinds. Firstly, they may be magnetic lines of force dragged by the plasma from the Sun. Secondly, the interplanetary medium or the solar wind are capable of carrying closed magnetic lines of force which are not related to the Sun. When such fields approach the Earth, the high-latitude geomagnetic lines of force which previously passed through the equatorial plane on the boundary of the magnetosphere, may deform in such a way as to pass out of one geomagnetic poles, miss the equatorial plane, enter the interplanetary plasma, and after passing through a very considerable volume of this plasma reach the other geomagnetic pole. This will in effect amount to an attachment through the medium of magnetic lines of force of enormous regions of ionised interplanetary matter or of solar wind to the Earth's magnetosphere. As these extraneous magnetic fields depart from the Earth's neighbourhood, the original dipole field will be reestablished. Rapid variations in the configuration of the geomagnetic field will occur during the interaction. It is possible that energetic particles appear with a very high degree of probability on the boundary of the geomagnetic field during such deformations. If this is so, then the outer radiation belt is merely a temporary formation appearing during the quiet intervals between geomagnetic disturbances, and containing a small residue of energetic charged particles, which exist during the polar auroras but do not succeed in entering the lower atmosphere during this time. In this process the particles giving rise to the polar auroras originate in the plasma of the solar corpuscular streams flowing past the Earth.Under the action of a solar wind the geomagnetic field is compressed at the front and elongated at the rear. This resembles the original Chapman theory of geomagnetic storms more closely than any other theory. Since the elongated geomagnetic field on the night side of the Earth is of a lower intensity, it may be associated with the magnetic fields brought in by the incident medium right down to very great depths. This may be responsible for the observed displacement at the zone of the polar auroras towards lower geomagnetic latitudes at night.Translated by the Express Translation Servies, Wimbledon, London.     

Electron precipitations and polar auroras

In the first part (Sections I–III) a brief historical review of the progress of our knowledge of the precipitation of auroral electrons is given. Observations by different techniques, in terms of detectors aboard balloons, sounding rockets, and polar-orbiting satellites, are reviewed (Sections I). The precipitation morphology is examined in terms of synoptic statistical results (Section II) and of latitudinal survey along individual satellite passes (Section III). In the second part (Section IV), a large number of simultaneous observations of auroras and precipitating auroral electrons by DMSP satellites are examined in detail, and it is shown that precipitation characteristics of auroral electrons are distinctly different for the discrete aurora and the diffuse aurora. In the third part (Section V), the source region of auroral electrons is discussed by comparing the auroral electron precipitation at low altitudes observed by DMSP satellites with the simultaneous ATS-6 observations near the magnetospheric equatorial plane approximately along the same geomagnetic field line. It is shown that the diffuse aurora is caused by direct dumping of the plasma sheet electrons from the equatorial region, whereas discrete auroras require acceleration of electrons between the plasma sheet and the polar atmosphere. The parallel electric field along the geomagnetic field line above the ionosphere is a likely candidate for the acceleration mechanism.Applied Physics Laboratory, The Johns Hopkins University, Laurel, Maryland 20810, U.S.A.     

转子动力特性及动平衡研究综述

对转子动力特性及动平衡研究进行了综述.主要内容包括:转子动力特性研究,转子产生不平衡的原因及不平衡所引起的振动特点,柔性转子的平衡条件、平衡特点、评价标准、平衡目的和要求,柔性转子高速动平衡的一般方法,转子新型动平衡方法,转子自动平衡技术.     

动力伞的飞机原理与控制

本文对动力伞的原理及飞行要领做了概况性的介绍。     

基于动态空域配置的航路调整问题研究

动态空域配置旨在通过对各类型空域功能块的设计、构架、配置和使用,实现空域的动态配置功能,使管制空域灵活地匹配空中交通实际变化的需求。在此概念下建立了以最小运营成本为目标的航路调整规划模型,在模型中考虑某些航路段可以动态地开关-闭合,引入动态航路的开放成本和使用成本,以最短开放时间、最大管制负荷和航路复杂度、安全性为约束条件,采取改进的遗传算法进行求解,验证了模型的正确性和可行性。计算结果表明:用模型制定的优化策略,充分利用了空域资源,减少了延误损失,总的航班运营成本减少了15%。     

Wide Dynamic Range Preselectors

Crowding of the Military communication spectrum has aggravated the need for preselectors capable of receiving a low-level desired signal in the presence of a high-level adjacent channel signal. Described herein are two novel HF preselection approaches which appear eminently suitable to cope with this problem. Applicable to the frequency range of 2 to 30 Mc/s, one preselector employs parametric mixing and the other exploits the low loss properties of superconductivity. In addition to other advantageous features, both preselectors have demonstrated an outstanding dynamic range capability in the order of 140 dB. Each of the preselectors is evaluated as a conventiona1 filter. In addition, performance data of a high quality military receiver is compared with that obtained when the receiver is preceded by each of two preselectors. Considerable stress is placed on the use of crossmodulation characteristics as a more meaningful and precise measure of preselector performance.     

一种先进的直升机动部件综合系统动力特性综合试验技术

由旋翼/传动/发动机/操纵组成的动部件综合系统的动力特性,直接关系到直升机的飞行安全、整机的振动水平、乘员的舒适性、各部件仪表的工作环境和使用寿命,是决定当代直升机先进程度最主要的因素之一。如何获得该综合系统的真实动力特性,是型号研制过程中非常关键的问题。本文将简单介绍一种先进可靠的、能获得该综合系统真实动力特性的综合试验技术。     

Dynamic Modelling of the Hipparcos Attitude

We present a new method for a high-accuracy reconstruction of the attitude for a slowly spinning satellite. This method, referred to as the fully-dynamic approach, explores the possibility to describe the satellite's attitude as that of a rigid body subject to continuous external torques. The method is tried out on the Hipparcos data and is shown to reduce the noise for the along-scan attitude reconstruction for that mission by about a factor two to three. The dynamic modelling is expected to give a more accurate representation of the satellite's attitude than was obtained with a pure mathematical modelling. As such, it decreases the degrees of freedom in the a posteriori reconstruction. Some of the decrease is obtained through accumulating and subsequently implementing information on high frequency components in the solar radiation torques, which show to be systematic and predictable. This could be expected, as they are primarily linked to the external geometry and optical properties of the satellite. In the context of an astrometric mission, the methods presented here can only be applied as a final iteration step: the star positions that are used to reconstruct the attitude are also part of the scientific objectives of the mission. An estimate for the potential of a re-reduction of the Hipparcos data using the fully-dynamic model for the attitude reconstruction was obtained from test reductions of the first 24 months of mission data. Improvement of the accuracies of the astrometric parameters for all stars brighter than Hp=9.0 appears possible. The noise on the astrometric parameters for these stars was affected significantly by the along-scan attitude noise, which dominated for stars brighter than Hp=4.5. The possible improvement for stars brighter than about Hp=4.5 may, after iterations, be as much as a factor three. The reduced noise levels also allow a more accurate calibration and monitoring of instrument parameters, leading potentially to a better understanding of the instrument and the scientific data obtained with it. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dynamic modeling of flexible multibody structures

This work is primarily concerned with the development of a mathematical formulation capable of treating the problems of maneuvering and control of flexible multibody structures. The analytical formulation is based upon equations of motion in terms of quasi-coordinates derived for each substructure independently. The individual substructures are made to act as a single structure by means of a consistent kinematical synthesis. In recognition of smaller elastic motions, a perturbation approach is developed whereby the rigid-body maneuvering of the system defines the zero-order kinematical dynamics, while the elastic motions and perturbations from the rigid-body maneuvering define the first-order kinematical synthesis. As a numerical example, the Planar Articulating Controls Experimental (PACE) test article is maneuvered according to a bang-bang control law by means of torque applied to the shoulder and the elbow. The numerical simulation shows a close match with the detailed modal survey     

DS—1型动力升降伞的研制

本文介绍的动力长降伞的研制是在充分的气动、飞行、强度试验基础上，进行精心的总体设计和另构件及系统设计。以满足和达到人机飞行器的设计性能指标。     

考虑缓冲器非线性的桨毂中心动特性仿真分析

通过试验数据拟合建立缓冲器非线性动力学模型,采用仿真分析方法,仿真考虑缓冲器非线性动力学特性的桨毂中心动特性试验.仿真结果与试验结果进行比较表明,采用缓冲器非线性动力学模型能较准确地预计桨毂中心非线性动力学特性.分析了缓冲器非线性动力学特性对桨毂中心动特性的影响.     

遥测参数动态分发技术

针对某卫星地面运控系统按需分发遥测参数的要求,提出了一套低成本解决方案.该方案引入遥测参数分发软件,从而化解遥测处理设备和业务系统之间的多对多关系;并基于以配置方式实现对遥测参数的订阅,以模板填写方式实现对输出数据的动态封装,设计出保证数据包可靠传输的机制.在此基础上,对遥测参数分发软件进行了总体设计,给出了主要功能的实现逻辑.软件的运行效果表明,该方案有效实现了多星多方遥测参数的动态分发,降低了系统复杂度.     

航空铆钉的动态力学性能测试

在飞机鸟撞的课题研究中,数值模拟占据着日益重要的地位,而数值模拟的精度在很大程度上依赖于铆钉力学参数的准确性,但是目前航空铆钉的动态力学性能参数还很匮乏。本文测定了航空铝合金铆钉在不同加载速度下的剪切和拉伸力学性能。设计了基于分离式Hopkinson拉杆系统的铆钉动态性能测试装置,并利用此装置对7种不同型号的航空铆钉进行了动态剪切和拉伸试验,得到了每种型号铆钉的动态力学性能。利用电子万能试验机对7种铆钉进行了两种应变率下的准静态剪切和拉伸试验,并且和动态试验结果进行对比。讨论了加载速度、加载形式、铆钉直径以及铆钉形式对铆钉力学性能的影响,并利用扫描电子显微镜(SEM)观察了铆钉剪切破坏以及拉伸破坏的断口形貌,分析了其破坏形式。本文的研究结果对于航空铝合金铆钉在工程中的应用、尤其是在抗冲击领域的应用具有指导意义。     

系统动态安全评价与预测的灰色方法

本文提出定量安全评价与预测的动态安全指标，灰色逻辑代数，然后使用ＧＭ（１，１）给出了系统动态安全评价与预测的新方法。     

面向敏捷制造的动态工艺规划技术

基于敏捷制造模式下企业必须能够快速响应客户的需求为背景,提出了基于加工特征的零件通用工艺模型.在此基础上,利用遗传算法,根据车间实时资源状况,以产品的加工时间最短作为优化目标,实现整个产品工艺方案的动态规划,以适应现代柔性生产的要求.     

涡轮增压器转子动力分析

H1C型涡轮增压器存在着严重的转子碰磨故障。本课题对该增压器转子结构进行了强度动力分析,找出了产生故障的主要原因,为产品的排故、结构改进提供了理论依据。     

超机动飞机动态逆-PID控制器设计

对超机动飞机在大迎角机动下的控制律进行设计,并完成相关仿真验证.通过引入推力矢量技术,建立带推力矢量的飞机非线性数学模型;采用奇异摄动理论,将飞机状态划分为快慢变换不同的同路,分别应用动态逆设计飞行控制律;并采用PID控制补偿由于未精确建模带来的系统逆误差;最后对所设计的控制律进行了机动指令飞行仿真.仿真结果表明,设计的控制律能在大迎角机动条件下控制飞机跟踪指令飞行,并保证闭环系统的稳定性.     

关于涡量的动力学边界条件

本文讨论了以涡量为变量的流体动力学描述方法中涡量的边界条件问题，并且用有关的数值计算结果对应用各种边界条件的结果进行了验证。     

齿轮箱系统动态特性分析及优化

为了进一步提高航空发动机传动系统的可靠性,本文采用MASTA和ANSYS软件,通过分析齿轮传递误差,分析机匣箱体振动特性,实现在设计阶段对机匣箱体振动的预测,并进行了箱体结构的优化与分析。结果表明,该优化方法对机械系统箱体结构设计和改进具有一定的指导意义。     

小型无人机纵向动态特性试验验证

应用气动力估算方法得到某小型无人机的纵向气动力数据;通过风洞试验和飞行试验对估算结果进行动态特性验证,并重点讨论了小型无人机的脉冲激励飞行试验验证。研究发现,选择飞行试验激励信号既要考虑小型无人机的特殊性,又要考虑信号的频谱特性;激励信号的选择为同类飞行测试提供了参考。