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181.
介绍了一种新的刚体转动的四元数模型。这些模型可以提高再定向控制的对边界条件的适应能力,在此基础上还介绍了这些模型的一些实际应用。 相似文献
182.
星际探测器轨道的特征与探测目的密切相关,对目标天体两级地区进行探测显然采用的是极轨道(或接近极轨道)。对于这类卫星(或称轨道器),如果轨道半长径较大,则会因第三体报骚动国导致轨道偏心率增大,使其近星距减小到等于目标天体的赤道半径而落到该天体上,结束其运动寿命,即使目标天体不存在大气(如月球等)亦会如此。 相似文献
183.
184.
Mayer Humi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(5):1298-1306
In this paper we consider satellite orbits in central force field with quadratic drag using two formalisms. The first using polar coordinates in which the satellite angular momentum plays a dominant role. The second is in Levi-Civita coordinates in which the energy plays a central role. We then merge these two formalisms by introducing polar coordinates in Levi-Civita space and derive a new equation for satellite orbits which unifies these two paradigms. In this equation energy and angular momentum appear on equal footing and thus characterize the orbit by its two invariants. Using this formalism we show that equatorial orbits around oblate spheroids can be expressed analytically in terms of Elliptic functions. In the second part of the paper we derive in Levi-Civita coordinates a linearized equation for the relative motion of two spacecrafts whose trajectories are in the same plane. We carry out also a numerical verification of these equations. 相似文献
185.
T.C. Slaba G.D. Qualls M.S. Clowdsley S.R. Blattnig S.A. Walker L.C. Simonsen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
To estimate astronaut health risk due to space radiation, one must have the ability to calculate various exposure-related quantities that are averaged over specific organs and tissue types. Such calculations require computational models of the ambient space radiation environment, particle transport, nuclear and atomic physics, and the human body. While significant efforts have been made to verify, validate, and quantify the uncertainties associated with many of these models and tools, relatively little work has focused on the uncertainties associated with the representation and utilization of the human phantoms. In this study, we first examine the anatomical properties of the Computerized Anatomical Man (CAM), Computerized Anatomical Female (CAF), Male Adult voXel (MAX), and Female Adult voXel (FAX) models by comparing the masses of various model tissues used to calculate effective dose to the reference values specified by the International Commission on Radiological Protection (ICRP). The MAX and FAX tissue masses are found to be in good agreement with the reference data, while major discrepancies are found between the CAM and CAF tissue masses and the reference data for almost all of the effective dose tissues. We next examine the distribution of target points used with the deterministic transport code HZETRN (High charge (Z) and Energy TRaNsport) to compute mass averaged exposure quantities. A numerical algorithm is presented and used to generate multiple point distributions of varying fidelity for many of the effective dose tissues identified in CAM, CAF, MAX, and FAX. The point distributions are used to compute mass averaged dose equivalent values under both a galactic cosmic ray (GCR) and solar particle event (SPE) environment impinging isotropically on three spherical aluminum shells with areal densities of 0.4 g/cm2, 2.0 g/cm2, and 10.0 g/cm2. The dose equivalent values are examined to identify a recommended set of target points for each of the tissues and to further assess the differences between CAM, CAF, MAX, and FAX. It is concluded that the previously published CAM and CAF point distributions were significantly under-sampled and that the set of point distributions presented here should be adequate for future studies involving CAM, CAF, MAX, or FAX. It is also found that the errors associated with the mass and location of certain tissues in CAM and CAF have a significant impact on the mass averaged dose equivalent values, and it is concluded that MAX and FAX are more accurate than CAM and CAF for space radiation analyses. 相似文献
186.
电火花小孔加工中存在工具电极损耗严重、加工速度慢、棱角变钝出现锥度等问题。分析其存在问题的原因,提出采用铜铬复合电极进行电火花小孔加工。分析其加工机理并进行实验,实验结果表明:采用铜铬复合电极进行小孔加工比采用铜电极进行小孔加工能显著提高加工速度,减小锥度和电极相对损耗。 相似文献
187.
朱明贤 《华北航天工业学院学报》2010,(1):40-43
老子关注人的一项重要内容就是要确定身与物谁贵谁轻。他主张贵身,反对以物役身;人是目的,物为手段;人以身为贵,依道贵身;贵身有道。 相似文献
188.
牛铮铮 《华北航天工业学院学报》2005,15(4):16-19
本文针对混凝土小型空心砌块建筑极易产生的开裂渗漏问题,提出了可操作的防裂抗渗技术措施,包括建筑结构的模数协调与排块设计,芯柱、水平构件以及加强节点设计,控制缝设计,墙体抗渗措施以及设备与电气的相关设计等. 相似文献
189.
190.
航空货运网络是影响城市层级结构的重要因素之一,对其进行量化分析具有十分重要的理论和现实意义。根据2002—2008年中国航空货运数据库构建的中国航空货运网络,运用复杂网络分析的测度方法,以城市航空货运量比例为依据,将中国航空货运网络分成初始层级网络、中级层级网络和核心层级网络3个层次。基于航空货运网络视角,将中国通航城市分成核心、中级和边缘城市3类层级。通过对平均路径长度、聚类系数、度分布、密度等网络特征的分析,证明了3个层级城市所在的网络都具有小世界和无标度特性,研究表明中国城市层级结构具有金字塔特性,分布严重不均匀,值得关注。 相似文献