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521.
D. Altadill S. Magdaleno J.M. Torta E. Blanch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Monthly average electron density profiles have been calculated from hourly electron density N(h) recorded in 26 digisonde stations distributed worldwide encompassing the time interval 1998–2006. The ionospheric electron density peak height of the F2 region, hmF2, and the effective scale height at the hmF2, Hm, deduced from average profiles have been analyzed to obtain the quiet-time behavior and have been analytically modeled by the spherical harmonic analysis (SH) technique using the modip latitude as the coordinate of the reference system. The coefficients of the SH models of hmF2 and Hm are bounded to the solar activity, and the temporal and seasonal variations are considered by Fourier expansion of the coefficients. The SH models provide a tool to predict hmF2 and Hm located anywhere in the range of latitudes between of 70°N and 70°S and at any time. The SH analytical model for hmF2 improves the fit to the observations by 10% in average compared to the IRI prediction, and it might improve the IRI prediction of hmF2 by more than 30% at high and low latitudes. The analytical model for Hm predicts the quiet behavior of the effective scale height with accuracy better than 15% in average which enables to obtain a good estimation of vertical profiles. These results could be useful to estimate information for the topside profile formulation. 相似文献
522.
针对实际工程项目需求,分析了消失模铸造的特点,运用IDEF0方法建立了消失模设计活动模型,在此基础上,遵循面向对象方法,利用EXPRESS信息建模语言建立了基于特征的消失模参数化设计系统的信息模型,并阐述了其系统框架及关键技术。 相似文献
523.
P.H. Krisko M. Horstman M.L. Fudge 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(7):1138-1146
In this paper we revisit the 1995 Kaman database of the SOCIT4 fragment characteristics with added analysis of a subset of the cataloged fragments from the test. This database was compiled from the last of a series of four hypervelocity impact tests conducted under a U.S. Department of Defense program in 1991–1992. This test targeted a flight-ready, U.S. Transit navigation satellite, yielding collision fragments in the size regime of sub-millimeter through tens of centimeters. Results in this database were used in the 1998 NASA Standard Breakup Model to represent characteristic length (size) and area-to-mass distributions of fragments smaller than 10 cm. 相似文献
524.
Michael W. Liemohn Yingjuan Ma Rudy A. Frahm Xiaohua Fang Janet U. Kozyra Andrew F. Nagy J. David Winningham James R. Sharber Stas Barabash Rickard Lundin 《Space Science Reviews》2006,126(1-4):63-76
Atmospheric photoelectrons have been observed well above the ionosphere of Mars by the ASPERA-3 ELS instrument on Mars Express.
To systematically interpret these observations, field lines from two global MHD simulations were analyzed for connectivity
to the dayside ionosphere (allowing photoelectron escape). It is found that there is a hollow cylinder behind the planet from
1–2 R
M away from the Mars-Sun line that has a high probability of containing magnetic field lines with connectivity to the dayside
ionosphere. These results are in complete agreement with the ELS statistics. It is concluded that the high-altitude photoelectrons
are the result of direct magnetic connectivity to the dayside at the moment of the measurement, and no extra trapping or bouncing
mechanisms are needed to explain the data. 相似文献
525.
526.
527.
排球球缝随机气动力辨识建模 总被引:5,自引:0,他引:5
本文应用H(Householder)变换求解病态法方程之最小二乘法及三次样条函数最小二乘法,对不同球缝随机性气动力模型进行辨识,提高了参数估计精度。讨论了不同球缝和各种发政治协商会议方式气动力的建模方法,给出了数学模型,并进行了验证,所得结果与实践经验一致。表明气动力模型较符合实际,建模方法可行,模型简单实用,为研究运用球缝发飘球技术,提供了重要的模型依据。 相似文献
528.
From computers to aeronautics, many industries have achieved great cost savings through the use of modular engineering approaches. In standardizing interfaces between elements and by reusing functional units, projects can achieve direct reductions in required development labor and secondary savings from enhanced reliability via improved process control from manufacturing identical units. Issues involved in the extension of modular design to the space industry are discussed. A cost model is developed to resolve some of the conflicting advantages and disadvantages between modular and customized designs. Key regimes are identified that represent the best opportunities for applying modular concepts. 相似文献
529.
提出了一种用于失谐叶盘动力学特性分析的减缩计算方法.该方法采用基于周期对称的谐波平衡法,建立非线性的迭代方程,能够基于单扇区的矩阵求解整个失谐叶盘的强迫响应,且不存在任何截断误差,因而效率高于部件模态综合法但精度并不降低.从周期对称结构理论出发给出了方法原理的数学推导,在此基础上通过一个失谐叶盘有限元模型算例对该方法的效率与精度进行了讨论.结果表明:相较部件模态综合法,周期对称谐波平衡法矩阵维度减小59.5%,计算复杂度减少93.4%,计算时间节省57.4%. 相似文献
530.
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%。 相似文献