PLC实现机床主轴自动换挡

以一台数控五坐标机床技术改造为实例，采用 Ｐ Ｌ Ｃ 实现主轴的自动换挡。通过状态及数据接口分析，提出主轴换挡的控制流程，总结出在机床控制中主轴换挡控制的一般原理与方法。     

关于氩等离子体热导率的测量

本文对《空气动力学学报》１９９７年第４期上发表的氩等离子体的热导率的实验研究结果的可靠性做了讨论。提出了一些提高实验数据可靠性的建议。     

基于DTC的开关磁阻电机转矩脉动抑制方法研究

开关磁阻电机(SRM)具有诸多性能优势,发展前景广阔,然而严重的转矩脉动极大地限制了其应用范围.对SRM直接转矩控制方法(DTC)进行了研究,对DTC的核心思想进行了介绍,给出了空间电压矢量的选取原则.采用有限元法(FEM)和神经网络(NN)相结合的方法,在Matlab中搭建了一个四相8/6极SRM的动态仿真模型.在不同的工况下,对DTC的控制性能进行了仿真分析,结果表明,DTC的引入可以有效地抑制SRM的转矩脉动,同时保证系统具有良好的调速和带载能力.     

采用机头边条改善飞机大迎角横侧气动特性的风洞试验研究

飞机大迎角横侧气动特性是决定其机动性及敏捷性的主要因素之一。本文就采用机头边条改善飞机大迎角横侧气动特性进行了讨论。着重对机头边条的大小、安装位置等对飞机稳定性的影响进行讨论。试验是在气动中心低速所４ｍ×３ｍ和３．２ｍ风洞中进行的。     

Plasma and electromagnetic wave simulations of meteors

Every day billions of meteoroids impact and disintegrate in the Earth’s atmosphere. Current estimates for this global meteor flux vary from 2000 to 200,000 tons per year, and estimates for the average velocity range between 10 km/s and 70 km/s. The basic properties of this global meteor flux, such as the average mass, velocity, and chemical composition remain poorly constrained. We believe much of the mystery surrounding the basic parameters of the interplanetary meteor flux exists for the following reason, the unknown sampling characteristics of different radar meteor observation techniques, which are used to derive or constrain most models. We believe this arises due to poorly understood radio scattering characteristics of the meteor plasma, especially in light of recent work showing that plasma turbulence and instability greatly influences meteor trail properties at every stage of evolution. We present our results on meteor plasmas simulations of head echoes using particle in cell (PIC) ions, which show that electric fields strongly influence early stage meteor plasma evolution, by accelerating ions away from the meteoroid body. We also present the results of finite difference time domain electromagnetic simulations (FDTD), which can calculate the radar cross section of the simulated meteor plasmas. These simulations have shown that the radar cross section depends in a complex manner on a number of parameters. These include the angle between radar and meteor entry, a large dependence on radar frequency, which shows that for a given meteor plasma size and density, the reflectivity as a function of probing radar frequency varies, but typically peaks below 100 MHz.     

Synthetic Environments for Simulated Missions

Synthetic environments offer Space Flight projects an opportunity to perform rapid, comprehensive, and rigorous modeling of the critical elements of a mission in order to compute quantitative measures of design performance, associated risk, and actual mission utility value. Significantly, these studies can be performed early in the mission cycle. These synthetic terrains are generated on parallel, high-performance computers and served to remote simulations at near-interactive speeds. The terrain creation uses a realistic sequence of physical phenomena such as cratering and dusting with parametric control of features such as surface roughness and rock density. Terrain resolution may be arbitrary but typically ranges from 0.01 to 10 meters. The terrain server has been used for two rover simulations, one using the actual Sojourner autonomy flight code, and the other a more general algorithm. Monte Carlo studies of rover designs interacting with synthetic environments were executed in parallel to quickly compute performance statistics and risk estimates.     

基于云计算的舰艇编队协同防空作战体系研究

为推进云计算在军事领域中的应用,对基于云计算的舰艇编队协同防空作战体系进行研究。介绍了云计算的定义和特点,设计了基于云计算技术的协同防空作战体系架构,实现了编队协同防空反导,最大限度地发挥了舰艇编队的整体防空作战能力。     

WIOBSS: The Chinese low-power digital ionosonde for ionospheric backscattering detection

The ionospheric laboratory of Wuhan University has developed an ionosonde over about seven years. The prototype is designed as a portable, low-power digital MF (medium frequency) and HF (high frequency) radio system with high range and Doppler resolution. The first system is used for ionospheric oblique backscattering detection and called WIOBSS (Wuhan Ionospheric Oblique Backscattering Sounding System). WIOBSS is a portable monostatic ionosonde for both ionospheric research and HF channel management, adopting alternate transmitting and receiving patterns to transmit long coded pulse trains for high pulse compression gain. The almost perfect sequences are applied to modulate the pulse train for sounding without range sidelobes and the echo phase is used to estimate the Doppler velocity and velocity fluctuation. This paper introduces the new techniques adopted by WIOBSS and presents some observations.     

提高执行力——雷达管制现场运行管理初探

随着改革开放的进一步深入,我国的民航运输事业也步入了发展的快车道,航空运输总周转量、飞行架次等各项运行指标年均以两位数的幅度攀升。近年来,为了应对和适应日益增长的空中交通流量,提升空管保障水平,部分管制中心开始实施雷达管制,在缩小了安全间隔的同时增强了安全余度,