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331.
为进一步提升飞翼布局无人机耦合进排气系统的气动性能,针对进排气附近翼面上多鼓包开展了减阻特性与优化设计研究。基于弹性体变形思想的FFD(Free-Form Deformation,自由变形)方法,对飞翼无人机多鼓包进行有效的参数化,并构建了网格自动生成方法;结合γ-e_(θt)转捩模型进行CFD数值模拟,利用RBF代理模型及多岛遗传算法进行多鼓包优化设计。结果表明:基于FFD方法的多鼓包技术设计变量较少,优化效率高;优化后推荐鼓包构型第一个为凹鼓包,后两个为凸鼓包;多鼓包优化模型具有显著的减阻效果,迎角6°下减阻量可达6.2%,随着迎角增大,减阻效果由摩擦阻力减小为主转为压差阻力减小占据主导。 相似文献
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面向航空电子系统的新需求,对信息物理系统在机载领域的应用进行了探索。通过研究信息物理系统的基本概念和特征,提出机载信息物理系统的简化模型,分析需解决的关键技术,肯定了信息物理系统在航空领域应用的可行性。 相似文献
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Brehard T. Le Cadre J.R. 《IEEE transactions on aerospace and electronic systems》2006,42(4):1198-1223
We address the classical bearings-only tracking problem (BOT) for a single object, which belongs to the general class of nonlinear filtering problems. Recently, algorithms based on sequential Monte-Carlo methods (particle filtering) have been proposed. As far as performance analysis is concerned, the posterior Cramer-Rao bound (PCRB) provides a lower bound on the mean square error. Classically, under a technical assumption named "asymptotic unbiasedness assumption", the PCRB is given by the inverse Fisher information matrix (FIM). The latter is computed using Tichavsky's recursive formula via Monte-Carlo methods. Two major problems are studied here. First, we show that the asymptotic unbiasedness assumption can be replaced by an assumption which is more meaningful. Second, an exact algorithm to compute the PCRB is derived via Tichavsky's recursive formula without using Monte-Carlo methods. This result is based on a new coordinate system named logarithmic polar coordinate (LPC) system. Simulation results illustrate that PCRB can now be computed accurately and quickly, making it suitable for sensor management applications 相似文献
336.
为了研究环下润滑结构内部流动并优化收油叶片结构,根据环下润滑结构内部高转速、强旋流的流动特点建立了数值计算模型,分析了原始结构的油气两相流动并总结了滑油的损失机理,在此基础上提出收油叶片的优化改进结构,详细讨论了不同收油叶片结构对环下润滑内部流动和收油效率的影响规律。研究结果表明,原始结构中滑油冲击主轴产生的碰撞飞溅和在离心作用下沿收油叶片被向外甩出均是引起收油效率下降的原因;优化收油叶片结构后的气流速度在叶尖附近的最大增加幅度不超过4m/s;收油叶片叶根拐角处采用圆弧过渡且叶根延伸后的收油效率仅在低转速范围内略高于原始结构的收油效率,收油效率最大提升了1.03%;在此基础上增加阶梯结构并进一步延伸叶根后可在全部转速范围内提升收油效率,相对原始结构的收油效率最大可提升接近5.0%。 相似文献
337.
Y. Le Coq J.A. Retter S. Richard A. Aspect P. Bouyer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
We analyze the advantages of using ultra-cold coherent sources of atoms for matter-wave interferometry in space. We present a proof-of-principle experiment that is based on an analysis of the results previously published in Richard et al. (2003) from which we extract the ratio h/m for 87Rb. This measurement shows that a limitation in accuracy arises due to atomic interactions within the Bose–Einstein condensate. Finally we discuss the promising role of coherent-matter-wave sensors, in particular inertial sensors, in future fundamental physics missions in space. 相似文献
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The presence of Dirac delta function in differential equation can lead to a discontinuity,which may degrade the accuracy of related numerical methods.To improve the accuracy,a secondorder numerical method for elliptic equations with singular sources is introduced by employing a local kernel flter.In this method,the discontinuous equation is convoluted with the kernel function to obtain a more regular one.Then the original equation is replaced by this fltered equation around the singular points,to obtain discrete numerical form.The unchanged equations at the other points are discretized by using a central difference scheme.1D and 2D examples are carried out to validate the correctness and accuracy of the present method.The results show that a second-order of accuracy can be obtained in the fltering framework with an appropriate integration rule.Furthermore,the present method does not need any jump condition,and also has extremely simple form that can be easily extended to high dimensional cases and complex geometry. 相似文献