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151.
提出了双层板防护结构的超高速碰撞数值模拟的工程算法模型,采取理论分析、经验公式和数值模拟相结合的研究方法来模拟碎片云的产生,以及碎片云对结构的破毁过程。本模型中,碎片云的产生采用理论分析和经验公式得到,结构响应采用有限元动力学软件Dyna3D进行计算。数值模拟结果与文献中给出的破坏效果基本一致,说明提出的工程算法是可行的,模拟得到的结果能定性的描述相应的超高速碰撞的现象,得到基本正确的结果。 相似文献
152.
提出一种改进的差分进化算法,采用一种“位变”方法计算收缩因子,该方法首先根 据适应值对种群排序,然后根据各个体的排列位置确定收缩因子;采用正态分布函数对算法 参数进行随机扰动来维持种群的多样性;该算法还提出一种新的变异算子,并将其与基本的 差分变异算子结合使用以提高算法的寻优精度。经过对多个Benchmark函数的测试、分析和 比较,结果表明该算法具有较高的收敛精度和较快的收敛速度。最后将该算法用于火箭发动 机涡轮气动优化,以较小的计算成本将涡轮气动效率提高了2.5%。应用结果表明该算法 适用于快速仿真优化问题,能有效地节约计算成本。
相似文献
相似文献
153.
Mai-Julie Nguyen François Raulin Patrice Coll Sylvie Derenne Cyril Szopa Guy Cernogora Guy Israël Jean-Michel Bernard 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
In the present work, we focused on the possible isotopic fractionation of carbon during the processes involved in the formation of Titan’s tholins. We present the first results obtained on the 12C/13C isotopic ratios measured on Titan’s tholins synthesized in laboratory with cold plasma discharges. Measurements of isotopic ratio 12C/13C, done both on tholins and on the initial gas mixture (N2:CH4 (98:2)) used to produce them, do not show any evident deficit or enrichment in 13C relatively to 12C in the synthesized tholins, compared to the initial gas mixture. This observation allows to go further in the analyses of the ACP experiment data, including part of the Cassini–Huygens mission. 相似文献
154.
R. G. Gratton 《Space Science Reviews》2007,130(1-4):43-52
This paper briefly reviews a few relevant features about the abundances of light elements (D, 4He, 6Li, 7Li, 9Be) in the Milky Way. It places special emphasis on metal-poor stars. Observational concerns are discussed. The use of 7Li and 6Li as cosmological probes and of 9Be as a chronometer for the early evolution of our Galaxy are discussed. 相似文献
155.
基于单一产品数据源的BOM管理 总被引:18,自引:2,他引:16
如何管理产品生命周期中的各种物料项清单BOM(Bill of Material)是产 品数据管理的关键,其核心是产品生命周期中BOM的全局数据模型,即BOM之间关系的建立和 维护.借鉴波音公司提出的单一产品数据源SSPD(Single Source of Product Data)思 想,从分析产品生命周期中BOM的演化过程出发,提出了BOM演变原理,并在此基础上,提出 了一种基于SSPD统一管理BOM的框架模型. 相似文献
156.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(11):2692-2710
The space environment around the Earth is populated by more than 130 million objects of 1 mm in size and larger, and future predictions shows that this amount is destined to increase, even if mitigation measures are implemented at a far better rate than today. These objects can hit and damage a spacecraft or its components. It is thus necessary to assess the risk level for a satellite during its mission lifetime. Few software packages perform this analysis, and most of them employ time-consuming ray-tracing methodology, where particles are randomly sampled from relevant distributions. In addition, they tend not to consider the risk associated with the secondary debris clouds. The paper presents the development of a vulnerability assessment model, which relies on a fully statistical procedure: the debris fluxes are directly used combining them with the concept of vulnerable zone, avoiding the random sampling the debris fluxes. A novel methodology is presented to predict damage on internal components. It models the interaction between the components and the secondary debris cloud through basic geometrical operations, considering mutual shielding and shadowing between internal components. The methodologies are tested against state-of-the-art software for relevant test cases, comparing results on external structures and internal components. 相似文献
157.
D. J. Lennon 《Space Science Reviews》1993,66(1-4):127-135
We present new estimates of He/H and CNO abundance ratios in the atmospheres of a selection of B2 supergiants which imply that the C/N ratio in the most luminous Ia stars is close to its equilibrium value. The is also some evidence for more moderate CN abundance anomalies in the B2Ib and B2II supergiants. These results, together with other recent work, imply that the effects of the CNO bi-cycle on the composition of B-supergiant atmospheres are most severe for the more luminous and massive stars. Furthermore, studies of LMC B-supergiants indicate that a small fraction of these very luminous stars are nitrogen weak. This picture is qualitatively consistent with theoretical predictions whenever massive stars perform blue loops in the HR diagram, returning from a red supergiant phase to become core helium burning blue supergiants with atmospheres contaminated by nuclear processed material. 相似文献
158.
159.
Requirements are rarely static, and are ever more likely to evolve as the development time of a system stretches out and its service life increases. In this paper, we discuss the evolution of requirements for the US spacesuit, the extravehicular mobility unit (EMU), as a case study to highlight the need for flexibility in system design. We explore one fundamental environmental change, using the Space Shuttle EMU aboard the International Space Station, and the resulting EMU requirement and design changes. The EMU, like other complex systems, faces considerable uncertainty during its service life. Changes in the technical, political, or economic environment cause changes in requirements, which in turn necessitate design modifications or upgrades. We make the case that flexibility is a key attribute that needs to be embedded in the design of long-lived, complex systems to enable them to efficiently meet the inevitability of changing requirements after they have been fielded. 相似文献
160.
针对高分四号(GF-4)卫星影像波段较少导致传统云检测算法难以区分云与冰雪像元的问题,提出一种多时相多通道云检测算法。该算法首先对GF-4卫星影像进行辐射定标和配准,然后利用云与典型地表的光谱差异得到潜在云像元,之后利用序列GF-4卫星影像之间的差异识别出移动的云像元,最后利用中红外波段反演地表亮度温度来去除冰雪像元。该算法在海南、辽宁和安徽3个研究区域进行验证,并将检测结果与传统单时相云检测算法、支持向量机(SVM)云检测算法和实时差分(RTD)云检测算法的检测结果进行对比。结果表明,该算法优于其他3种云检测算法,准确识别率均达到90%以上,误检率均低于5%,有利于GF-4卫星影像的进一步利用。 相似文献