小波变换在动力学系统识别中的应用

试图用小波变换来讨论动力学系统识别中的几个问题，并用以研究在系统分析中利用小波变换这个工具的可能性。只涉及线性时不变结构的动力学系统，它应该适用于非线性或线性时变系统的分析和识别。做为一个具体应用，给出了使用小波变换识别模态阻尼系数的模拟实侧，可用于颤振数据分析。     

水下转台系统的一种实验建模方法

针对非线性摩擦特性对伺服系统建模的影响问题,通过适当的实验设计,利用优化方法来得到系统非线性摩擦模型以及系统模型参数.实验结果表明,利用该方法可以得到与实际系统模型参数较为接近的对象模型参数.     

GNSS最优载波相位平滑伪距研究

平滑常数是影响载波相位平滑伪距精度的关键参数,实际数据处理时主要依据经验设定平滑常数。这种主观设定过程缺乏理论依据,无法达到最优平滑效果。针对此问题,以适用于实时GNSS载波相位平滑伪距的经典Hatch递推滤波算法为基础,在连续时间域上分析了载波相位平滑伪距误差的主要构成,给出了总误差估算公式,分析了平滑常数对平滑精度的影响传导机制。进一步,采用令平滑总误差最小为目标的极值法推导给出了最优载波相位平滑常数的计算公式,给出了最优载波相位平滑伪距的完整处理步骤。最优平滑常数算法在数学意义上最优,大幅压缩了伪距测量误差,又不会引入过大的电离层发散误差。通过两个实际算例,证明了算法有效性。     

Optimal control laws for heliocentric transfers with a magnetic sail

A magnetic sail is an advanced propellantless propulsion system that uses the interaction between the solar wind and an artificial magnetic field generated by the spacecraft, to produce a propulsive thrust in interplanetary space. The aim of this paper is to collect the available experimental data, and the simulation results, to develop a simplified mathematical model that describes the propulsive acceleration of a magnetic sail, in an analytical form, for mission analysis purposes. Such a mathematical model is then used for estimating the performance of a magnetic sail-based spacecraft in a two-dimensional, minimum time, deep space mission scenario. In particular, optimal and locally optimal steering laws are derived using an indirect approach. The obtained results are then applied to a mission analysis involving both an optimal Earth–Venus (circle-to-circle) interplanetary transfer, and a locally optimal Solar System escape trajectory. For example, assuming a characteristic acceleration of 1 mm/s², an optimal Earth–Venus transfer may be completed within about 380 days.     

一种缓冲装置的加工

缓冲装置的应用非常广泛。本文介绍的缓冲装置是一种多筒体结构,技术要求高,加工难度大。文章简要论述了合理工艺方案的制定和3项技术难点的攻克。     

Integrating BDS and GPS for precise relative orbit determination of LEO formation flying

Low-Earth-Orbit(LEO) formation-flying satellites have been widely applied in many kinds of space geodesy. Precise Relative Orbit Determination(PROD) is an essential prerequisite for the LEO formation-flying satellites to complete their mission in space. The contribution of the BeiDou Navigation Satellite System(BDS) to the accuracy and reliability of PROD of LEO formation-flying satellites based on a Global Positioning System(GPS) is studied using a simulation method. Firstly, when BDS is added to GPS, the mean number of visible satellites increases from9.71 to 21.58. Secondly, the results show that the 3-Dimensional(3 D) accuracy of PROD, based on BDS-only, GPS-only and BDS + GPS, is 0.74 mm, 0.66 mm and 0.52 mm, respectively. When BDS co-works with GPS, the accuracy increases by 29.73%. Geostationary-Earth-Orbit(GEO) satellites and Inclined Geosynchronous-Orbit(IGSO) satellites are only distributed over the Asia-Pacific region; however, they could provide a global improvement to PROD. The difference in PROD results between the Asia-Pacific region and the non-Asia-Pacific region is not apparent. Furthermore, the value of the Ambiguity Dilution Of Precision(ADOP), based on BDS + GPS, decreases by 7.50% and 8.26%, respectively, compared with BDS-only and GPS-only. Finally, if the relative position between satellites is only a few kilometres, the effect of ephemeris errors on PROD could be ignored. However, for a several-hundred-kilometre separation of the LEO satellites, the SingleDifference(SD) ephemeris errors of GEO satellites would be on the order of centimetres. The experimental results show that when IGSO satellites and Medium-Earth-Orbit(MEO) satellites co-work with GEO satellites, the accuracy decreases by 17.02%.     

Analysis on coverage ability of BeiDou navigation satellite system for manned spacecraft

To investigate the service ability of the BeiDou Navigation Satellite System (BDS) for manned spacecraft, both the current regional and the future-planned global constellations of BDS are introduced and simulated. The orbital parameters of the International Space Station and China׳s Tiangong-1 spacelab are used to create the simulation scenario and evaluate the performance of the BDS constellations. The number of visible satellites and the position dilution (PDOP) of precision at the spacecraft-based receiver are evaluated. Simulation and analysis show quantitative results on the coverage ability and time percentages of both the current BDS regional and future global constellations for manned-space orbits which can be a guideline to the applications and mission design of BDS receivers on manned spacecraft.     

一种适用的Multi-Agent System协同框架及其应用

概述了一种MAS协同框架通用的部分-全局规划(GPGP)和任务描述语言TAEMS.GPGP是一种不依赖于问题域的通用的MAS协同框架;它提供一个协同机制库,在不同的任务环境和协同要求下,应用不同机制集,从而动态地、柔性地描述任务环境,为GPGP应用提供根据与基础.本文在一个分布式的制造执行系统MM-MES中应用了合同网协议、TAEMS和GPGP,研究分布式的车间调度和协同.     

Presolar Grains in Meteorites and Their Compositions

Small amounts of pre-solar “stardust” grains have survived in the matrices of primitive meteorites and interplanetary dust particles. These grains—formed directly in the outflows of or from the ejecta of stars—include thermally and chemically refractory carbon materials such as diamond, graphite and silicon carbide; as well as refractory oxides and nitrides. Pre-solar silicates, which have only recently been identified, are the most abundant type except for possibly diamond. The detailed study with modern analytical tools, of isotopic signatures in particular, provides highly accurate and detailed information with regard to stellar nucleosynthesis and grain formation in stellar atmospheres. Important stellar sources are Red Giant (RG) and Asymptotic Giant Branch (AGB) stars, with supernova contributions apparently small. The survival of those grains puts constraints on conditions they were exposed to in the interstellar medium and in the early solar system.