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直升机雷达回波的分析与检测 总被引:5,自引:0,他引:5
直升机在军事上的广泛应用对现有雷达系统提出了挑战.低空慢速、悬停式武装直升机的探测是一个迫切需要解决的课题.利用专门的电磁仿真软件,通过以美制直升机“阿帕奇”为例的飞行和转台等多种试验,分析了直升机回波的时域、频域和时频分布的特性,并根据这些特点提出了雷达探测武装悬停直升机的初步方案. 相似文献
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Bo Cheng Jesse Roll Yun Liu Daniel R. Troolin Xinyan Deng 《Journal of the Royal Society Interface》2014,11(91)
Flapping wings continuously create and send vortices into their wake, while imparting downward momentum into the surrounding fluid. However, experimental studies concerning the details of the three-dimensional vorticity distribution and evolution in the far wake are limited. In this study, the three-dimensional vortex wake structure in both the near and far field of a dynamically scaled flapping wing was investigated experimentally, using volumetric three-component velocimetry. A single wing, with shape and kinematics similar to those of a fruitfly, was examined. The overall result of the wing action is to create an integrated vortex structure consisting of a tip vortex (TV), trailing-edge shear layer (TESL) and leading-edge vortex. The TESL rolls up into a root vortex (RV) as it is shed from the wing, and together with the TV, contracts radially and stretches tangentially in the downstream wake. The downwash is distributed in an arc-shaped region enclosed by the stretched tangential vorticity of the TVs and the RVs. A closed vortex ring structure is not observed in the current study owing to the lack of well-established starting and stopping vortex structures that smoothly connect the TV and RV. An evaluation of the vorticity transport equation shows that both the TV and the RV undergo vortex stretching while convecting downwards: a three-dimensional phenomenon in rotating flows. It also confirms that convection and secondary tilting and stretching effects dominate the evolution of vorticity. 相似文献
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低空目标的中、近程探测是当前紧迫的研究课题之一。文中主要对低空、超低空的悬停直升机和巡航导弹的理论模型进行信号仿真 ,同时提出相应的检测方法 ,并在不同信杂比条件下用MATLAB对检测方法进行了仿真验证 ,结果表明该方法是可行的 相似文献
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研究了近地小行星433 Eros本体悬停轨道的稳定控制问题.用三轴椭球体模型近似Eros引力场分布,建立了航天器在其引力场内的动力学模型,并且应用等加速度变截距时变滑模控制设计了悬停控制器.该方法的滑模面选取与常规滑模控制不同,且不存在到达阶段.仿真分析从不同的初始条件和悬停条件入手,验证控制器的有效性,并讨论了航天器的速度与控制加速度的幅值随滑模面切换时间的变化情况. 相似文献
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《Architectural Design》2007,77(6):92-97
The work of Mathew & Ghosh Architects (Nisha Mathew-Ghosh and Soumitro Ghosh) boldly extends an abstract Modernist language and at the same time draws from the vitality of places. While the firm's early works were small in scale, mostly residential in nature and based on a reappraisal of the early Corbusian idiom, recent projects include large-scale urban and landscape interventions with diverse conceptual and metaphorical imperatives. They have moved from a more reticent stance to the urban exuberance of their more recent projects (for example, their own office building), something akin to a ‘savage architecture’ as posited by Kazuo Shinohara in the context of the unsynchronised nature of the modern city. The architects' object of contemplation is the urban ‘box’, whether a private residence, office or part of a church. The box is first fractured and reconstructed as a bricolage of tectonic fragments, memories and events, all tenuously related as if unity in a contemporary culture is for ever denied. Like the Japanese notion of ‘ma’, the moment between fragments - a slit or an emptiness between two hovering planes - is telling. Mathew & Ghosh participate in the continuity of a historical narrative yet mark out the fissures and disjunctions; sometimes negotiations with the continuity emerge from unintended interstices. While these configurations of the contemporary urban ‘box’ are both contextual and abstract, they are also phenomenologically rich. There is a sustained dialect to the architecture of Mathew & Ghosh that includes consummate materiality and fine crafting, light as a medium, and always, as Nisha Mathew-Ghosh states, ‘good spatial possibilities’. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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