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991.
传统的在零件对缝处进行补充修切,以满足设计要求的装配安装方法,在复合材料部件的装配中已不再适用,而零件加工无佘量、装配精确定位的无余量装配方法,正逐渐得到实际应用. 相似文献
992.
Songhui Han Qingming Gui Guozhong Li Yuanlu Du 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Within the next decade, there will be a number of GNSS (Global Navigation Satellite System) available, i.e. modernized GPS, Galileo, restored GLONASS, BeiDou and many other regional GNSS augmentation systems. Thus, measurement redundancies and geometry of the satellites can be improved. GDOP (Geometric Dilution of Precision) and PDOP (Position Dilution of Precision) are associated with the constellation geometry of satellites, and they are the geometrically determined factors that describe the effect of geometry on the relationship between measurement error and position error. GDOP and PDOP are often used as standards for selecting good satellites to meet the desired positioning precision. In this paper, the related conclusions of minimum of GDOP which was discussed are given, and it is used to study the minimum of PDOP for two cases that the receiver is on the earth’s surface and the receiver is on satellite. The corresponding theorem and constructive solutions of minimum of PDOP are given. Then, the rationality of the ISL (inter-satellite link) establishment criteria in Walker-δ constellation is discussed by using the theory of minimum of PDOP. Finally, the minimum of PDOP is calculated when the number of satellites is 4–10, and these results are verified by using Monte Carlo method. 相似文献
993.
In order to improve weapon assignment(WA)accuracy in real scenario,an artificial neural network(ANN)model is built to calculate real-time weapon kill probabilities.Considering the WA characteristic,each input representing one assessment index should be normalized properly.Therefore,the modified WA model is oriented from constant value to dynamic computation.Then an improved invasive weed optimization algorithm is applied to solve the WA problem.During search process,local search is used to improve the initial population,and seed reproduction is redefined to guarantee the mutation from multipoint to single point.In addition,the idea of vaccination and immune selection in biology is added into optimization process.Finally,simulation results verify the model′s rationality and effectiveness of the proposed algorithm. 相似文献
994.
995.
Shiqiang Zheng Bangcheng Han 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
This paper presents an integrated angular velocity measurement and attitude control system of spacecraft using magnetically suspended double-gimbal control moment gyros (MSDGCMGs). The high speed rotor of MSDGCMG is alleviated by a five-degree-of-freedom permanent magnet biased AMB control system. With this special rotor supported manner, the MSDGCMG has the function of attitude rate sensing as well as attitude control. This characteristic provides a new approach to a compact light-weight spacecraft design, which can combine these two functions into a single device. This paper discusses the principles and implementations of AMB-based angular velocity measurement. Spacecraft dynamics with DGMSCMG actuators, including the dynamics of magnetically suspended high-speed rotor, the dynamics of inner gimbal and outer gimbal, as well as the determination method of spacecraft angular velocity are modeled, respectively. The effectiveness of the proposed integrated system is also validated numerically and experimentally. 相似文献
996.
997.
为了改善高压涡轮叶尖径向运行间隙(BTRRC,Blade-Tip Radial Running Clearance)设计和控制合理性,考虑典型载荷下的热载荷和机械载荷和合理选取随机变量,在确定性分析基础上对BTRRC进行了概率设计.通过确定性分析,得出涡轮盘、叶片和机匣的径向变形以及BTRRC随时间变化规律,并找出危险点(t=180 s)作为概率设计的计算点.通过概率分析,不但得到了各部件径向变形的概率分布特征及不同稳态叶尖间隙δ下的失效数、失效概率和可靠度,还找到了影响它们径向变形和BTRRC的主要因素.综合考虑航空发动机可靠性和效率,将δ设定为1.95 mm为宜,满足设计和工程要求,为BTRRC的控制和设计提供了依据. 相似文献
998.
针对高超声速飞行器执行机构饱和的控制器设计问题,提出一种多回路抗饱和鲁棒自适应切换控制方法. 首先针对高超声速飞行器的运动模态在频率上表现出显著的分离特性,将状态变量分开不同的回路设计;然后对受执行机构饱和影响明显的状态设计参考切换系统,从而降低模型和控制器参数设计的复杂性,将一系列可能导致执行机构饱和的事件视作切换信号,选定参考切换模型及鲁棒自适应控制器,保证控制输入不达到饱和状态,并通过多李亚普诺夫函数方法和线性矩阵不等式分析了控制器的稳定性. 仿真结果表明了控制方案的有效性,在存在执行机构失效故障和干扰的情况下,系统状态可良好的跟踪参考状态且控制输入小于执行机构限幅. 相似文献
999.
1000.
P.S. Marrocchesi H.S. Ahn P. Allison M.G. Bagliesi L. Barbier J.J. Beatty G. Bigongiari T.J. Brandt J.T. Childers N.B. Conklin S. Coutu M.A. DuVernois O. Ganel J.H. Han J.A. Jeon K.C. Kim M.H. Lee L. Lutz P. Maestro A. Malinine S. Minnick S.I. Mognet S.W. Nam S. Nutter I.H. Park N.H. Park E.S. Seo R. Sina P. Walpole J. Wu J. Yang Y.S. Yoon R. Zei S.Y. Zinn 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(12):2002-2009
Launched from McMurdo (Antarctica) in December 2005, the balloon experiment CREAM (cosmic ray energetics and mass) collected about 15 million triggers during its second flight of 28 days. Redundant charge identification, by two pixelated silicon arrays and a time resolved pulse shaping technique from a scintillator system, allowed a clear signature of the primary nuclei. The energy was measured with a tungsten/SciFi calorimeter preceded by a graphite target. Preliminary results from the analysis of the data of the second flight are presented. 相似文献