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291.
The capturability of the Three-Dimensional(3D) Realistic True Proportional Navigation(RTPN) guidance law is thoroughly analyzed. The true-arbitrarily maneuvering target is considered, which maneuvers along an arbitrary direction in 3D space with an arbitrary but upperbounded acceleration. The whole nonlinear relative kinematics between the interceptor and target is taken into account. First, the upper-bound of commanded acceleration of 3D RTPN is deduced,using a novel Lyapunov-like approach. Sec... 相似文献
292.
P.A. Higgins P.T. GallagherR.T.J. McAteer D.S. Bloomfield 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We present an automated system for detecting, tracking, and cataloging emerging active regions throughout their evolution and decay using SOHO Michelson Doppler Interferometer (MDI) magnetograms. The SolarMonitor Active Region Tracking (SMART) algorithm relies on consecutive image differencing to remove both quiet-Sun and transient magnetic features, and region-growing techniques to group flux concentrations into classifiable features. We determine magnetic properties such as region size, total flux, flux imbalance, flux emergence rate, Schrijver’s R-value, R∗ (a modified version of R), and Falconer’s measurement of non-potentiality. A persistence algorithm is used to associate developed active regions with emerging flux regions in previous measurements, and to track regions beyond the limb through multiple solar rotations. We find that the total number and area of magnetic regions on disk vary with the sunspot cycle. While sunspot numbers are a proxy to the solar magnetic field, SMART offers a direct diagnostic of the surface magnetic field and its variation over timescale of hours to years. SMART will form the basis of the active region extraction and tracking algorithm for the Heliophysics Integrated Observatory (HELIO). 相似文献
293.
为了研究上下游叶片的相位对低压涡轮流动的影响机理,使用商用 CFX 软件进行数值模拟,并辅以试验校核。选取了
0°和180°2个流动相差较大的相位,分析边界层分离与转捩、边界层积分参数,对吸力面的载荷系数、壁面剪力、附面层形状因子及
动量厚度等进行对比,并从边界层的瞬态流动分析着手,在1个尾迹扫掠周期内对Klebanoff条纹、K-H涡等结构进行分析。结果
表明:不同相位的流动特性差异主要取决于势流的压力扰动与速度扰动的相位,这将决定尾迹诱导转捩与寂静区之间的主导关
系。当压力扰动与速度扰动同相时,寂静区处于逆压梯度逐渐增强的阶段,保持层流的能力被削弱;反之当二者异相时寂静区强
度较大,尾迹诱导转捩带来的湍流损失可以被寂静区平衡。通过瞬态分析可知,0°相位尾迹诱导全展向K-H涡的卷起,全展向涡
的破碎会带来较大的能量耗散,且其诱导的Klebanoff条纹强度较大,二者共同作用使得尾缘动量损失较大。 相似文献
294.
L. Hoffmann K. WeigelR. Spang S. SchroederK. Arndt C. LehmannM. Kaufmann M. ErnP. Preusse F. StrohM. Riese 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The new remote sensing experiment CRISTA-NF (Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere – New Frontiers) successfully participated in the SCOUT-O3 Tropical Aircraft Campaign in November and December 2005. CRISTA-NF operated aboard the high-altitude research aircraft M-55 Geophysica. Mid-infrared spectra (4–15 μm) were measured in the limb sounding geometry with high spatial resolution (250 m vertical sampling, 5–15 km along track sampling). Measurements were carried out during transfer flights between Oberpfaffenhofen, Germany, and Darwin, Australia, as well as during several local flights near Darwin. Water vapor volume mixing ratios in the upper troposphere and lower stratosphere were derived from the CRISTA-NF radiance measurements by utilizing a rapid radiative transfer forward model and the optimal estimation retrieval approach. CRISTA-NF water vapor measurements below the hygropause have a total retrieval error of 15–40% (i.e. root mean square of accuracy and precision). The systematic terms are dominating in the retrieval error budget. The contributions of a priori information to the retrieval results are less than 5–10%. The vertical resolution of the observations is about 250–500 m when permitted by instrument sampling. In this paper we present first results for three transfer flights of the campaign. Being generally in good agreement with corresponding ECMWF operational analyzes, the CRISTA-NF measurements show significantly higher variability and local structures in the upper tropospheric water vapor distributions. 相似文献
295.
续航性能是飞机的主要战术技术指标之一。从飞机巡航段航程的基本公式出发,利用导数求极值的性质,推导出确定飞机巡航爬升和平流层内最佳巡航条件的方程,证明了最优巡航马赫数出现在飞机阻力增加区段,最优巡航高度存在于飞机阻力最小处。最后以某型飞机的巡航爬升条件和平流层平飞最优马赫数和高度的确定作为算例,说明用此方法确定飞机巡航条件,将使飞机获得最大航程。 相似文献
296.
297.
J.S. Pickett L.-J. Chen R.L. Mutel I.W. Christopher O. Santolı´k G.S. Lakhina S.V. Singh R.V. Reddy D.A. Gurnett B.T. Tsurutani E. Lucek B. Lavraud 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(10):1666-1676
Nonlinear isolated electrostatic solitary waves (ESWs) are observed routinely at many of Earth’s major boundaries by the Wideband Data (WBD) plasma wave receivers that are mounted on the four Cluster satellites. The current study discusses two aspects of ESWs: their characteristics in the magnetosheath, and their propagation in the magnetosheath and in the auroral acceleration (upward current) region. The characteristics (amplitude and time duration) of ESWs detected in the magnetosheath are presented for one case in which special mutual impedance tests were conducted allowing for the determination of the density and temperature of the hot and cold electrons. These electron parameters, together with those from the ion experiment, were used as inputs to an electron acoustic soliton model as a consideration for the generation of the observed ESWs. The results from this model showed that negative potential ESWs of a few Debye lengths (10–50 m) could be generated in this plasma. Other models of ESW generation are discussed, including beam instabilities and spontaneous generation out of turbulence. The results of two types of ESW propagation (in situ and remote sensing) studies are also presented. The first involves the propagation of bipolar type ESWs from one Cluster spacecraft to another in the magnetosheath, thus obtaining the velocity and size of the solitary structures. The structures were found to be very flat, with large scale perpendicular to the magnetic field (>40 km) and small scale parallel to the field (<1 km). These results were then discussed in terms of various models which predict such flat structures to be generated. The second type of propagation study uses striated Auroral Kilometric Radiation (SAKR) bursts, observed on multiple Cluster satellites, as tracers of ion solitary waves in the upward current region. The results of all studies discussed here (pulse characteristics and ESW velocity, lifetime, and size) are compared to in situ measurements previously made on one spacecraft and to theoretical predictions for these quantities, where available. The primary conclusion drawn from the propagation studies is that the multiple spacecraft technique allows us to better assess the stability (lifetime) of ESWs, which can be as large as a few seconds, than can be achieved with single satellites. 相似文献
298.
299.
远距离支援干扰下的目标跟踪技术 总被引:1,自引:0,他引:1
针对远距离支援干扰下雷达较难检测到干扰机掩护区域内的目标,其他区域内目标航迹不稳定的问题,提出了噪声干扰下的PF-TBD(Particle Filter based Track Before Detect)算法和门限自适应的MHT(Multiple Hypothesis Tracking)算法,并将这两种算法进行整合,使其能够根据雷达探测区域受干扰的程度选取相应的算法.研究了不同雷达探测区域内目标的航迹管理.仿真表明,此方法充分整合了两种算法的优点,提高了20%以上的雷达探测区域范围,兼顾了算法的时效性,同时该方法对干扰是否存在具有较强的适应性,对远距离支援干扰或其他压制干扰下目标跟踪具有一定的理论参考意义和实际应用价值. 相似文献
300.