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271.
耦合求解流场、组分浓度场、基于SNBCK模型的气体辐射传输/能量方程以求准确模拟飞行器排气系统气动热力及红外特性.窄带模型参数由HITEMP逐线计算数据库计算得到.通过CO24.3μm波段吸收率计算,圆柱炉膛辐射换热特性计算两个算例验证了所采用程序求解辐射传输/能量方程的准确性.最后计算了两种二元喷管的红外特性,结果表明大宽高比二元喷管地面和空中状态红外辐射特性差异巨大. 相似文献
272.
给出了利用能量守恒方法求定CHAMP卫星加速度计标校参数的基本原理和算法.对2001年8月-2003年12月共约两年半的CHAMP卫星加速度计数据进行了标校,导出了尺度、偏差和偏差漂移参数的时间序列,分别采用最小二乘谱分析和抗差谱分析对这些时间序列进行了分析.结果表明,尺度、偏差和偏差漂移参数都有明显的周期变化,但各主周期项略有差异.尺度的主周期是441d、220d、126d和13.4d的周期变化,其中220d和441d的周期变化的贡献相对较大.偏差中有明显的220d、126d和13.4d周期变化,各周期变化的贡献几乎相当;偏差漂移的主周期是220d、13.4d和9d的周期变化,其中13.4d的周期变化最为显著,几乎比其他周期项变化高出一个数量级.另外尺度和偏差参数还有明显的长期变化,而偏差漂移参数的长期变化不明显. 相似文献
273.
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275.
ARINC 653分区实时系统的可调度分析 总被引:1,自引:0,他引:1
ARINC 653规范定义了综合模块化航空电子(IMA)实时操作系统的行为逻辑以及向应用程序提供的接口规范。该规范规定了系统采用分区内调度和分区间调度的两级调度方案,如何分析系统的可调度性以保证实时任务能够在截止时间内完成计算是需要研究的新问题。基于负载请求与平台资源提供能力的供需约束关系导出了系统可调度的判定依据。证明了判据的约束是系统可调度的充分必要条件。实际应用表明,提出的可调度判定定理能够应用于判定ARINC 653分区实时系统的可调度性,辅助提升系统的安全属性。 相似文献
针对一类具有不确定性的多输入多输出(MIMO)非线性系统控制问题,提出了基于模糊神经网络的自适应解耦控制方法.根据分散控制理论和反馈线性化方法设计了MIMO非线性系统的分通道解耦控制律,然后把通道耦合项和不确定性项归结为总的系统扰动项,利用模糊神经网络观测器得到其估计值,并作为补偿信号加入到解耦控制律中.证明了所设计的解耦控制律、模糊神经网络观测器以及模糊神经网络权值向量自适应律可以保证控制误差、扰动估计误差和权值向量误差一致最终收敛.仿真中将本文的方法与传统的输出反馈控制律进行了对比,结果表明加入的补偿控制信号消除了通道耦合和不确定性带来的不利影响,验证了该方法的有效性和稳定性. 相似文献
277.
To develop an understanding of near-Earth space's response to solar activities and the coupling among different layers in geospace, China has initiated a ground base program to monitor China's geospace environment called the Meridian Space Weather Monitoring Project (Chinese Meridian Project). The effort consists of a chain of 15 ground-based observatories located roughly along 120°E longitude and 30°N latitude. Each observatory is equipped with multiple instruments to measure key parameters such as the baseline and time-varying geomagnetic field, as well as the middle and upper atmosphere and ionosphere from about 20 to 1000 kilometers. This project started collecting data in 2012. We will give a brief introduction to the Chinese Meridian Project, and present recent scientific results mainly in ionospheric and atmospheric studies. 相似文献
278.
Recent studies on human missions to Mars suggest revisiting the parameters that have the most important impact on the complexity, the initial mass in low Earth orbit, the risks and the development costs for the first journey to the red planet. In the last NASA reference mission, a trade tree is proposed. 相似文献
279.
Optimization of geosynchronous satellite constellation for independent regional navigation and positioning in Middle East region 总被引:1,自引:0,他引:1
Regional Navigation and positioning systems using geosynchronous satellites are emerging for different parts of the world. Optimal constellation geometry achievement for a set of geosynchronous satellites is a key sector in designing of such systems. Genetic algorithm is applied for optimization of constellations with 6 and 7 satellites which is to be used in Middle East region where these systems have been deprived of. Based on the fact that the coverage criterion is not sufficient enough to guarantee a good navigation service, positioning process by the satellite systems is discussed and the performance of the system on the basis of position dilution of precision is collected as the fitness criterion. Placing the satellites in groups to pass over the same ground track is applied as a constraint to the genetic algorithm. By simulation, performance of the best obtained results and GPS are compared in terms of position dilution of precision, visibility and the required epochs (time span) to resolve the ambiguities with a 99% success rate, in this region. Also, capability of the GA for such problems is demonstrated. 相似文献
280.
V.V. Kalegaev I.I. Alexeev I.S. Nazarkov V. Angelopoulos A. Runov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The magnetic field structure and the spatial characteristics of the large-scale currents in the magnetospheric tail were studied during quiet and moderately disturbed geomagnetic conditions in 2009. The magnetic field of the currents other than the tail current was calculated in terms of a paraboloid model of the Earth’s magnetosphere, A2000, and was subtracted from measurements. It was found on the base of obtained tail current magnetic field radial distribution that the inner edge of the tail current sheet is located in the night side magnetosphere, at distances of about 10 RE and of about 7 RE during quiet and disturbed periods respectively. During the disturbance of February 14, 2009 (Dstmin ∼ −35 nT), the Bx and the Bz component of the tail current magnetic field near its inner edge were about 60 nT, and −60 nT that means that strong cross-tail current have been developed. The tail current parameters at different time moments during February 14, 2009 have been estimated. Solar wind conditions during this event were consistent with those during moderate magnetic storms with minimum Dst of about −100 nT. However, the magnetospheric current systems (magnetopause and cross-tail currents) were located at larger geocentric distances than typical during the 2009 extremely quiet epoch and did not provide the expected Dst magnitude. Very small disturbance on the Earth’s surface was detected consistent with an “inflated” magnetosphere. 相似文献