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排序方式: 共有463条查询结果,搜索用时 687 毫秒
361.
讨论高斯白噪声背景下基于周期图法的残留载波BPSK(RC-BPSK)信号的检测问题。标准周期图法在正弦信号检测中的性能最优,但是在RC-BPSK信号检测中的性能却不佳;能量检测法只在信噪比很低的情况下性能较好;在信噪比较高时,虽然Bartlett法有较好的性能,但需要分段多次计算周期图,不利于与其他检测方法配合使用。文中在频谱匹配法的基础上发展了一种频谱相关检测方法,仿真结果表明该方法可以获得和Bartlett法相似的性能,同时只需要计算一次周期图。 相似文献
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双燃烧室冲压发动机亚燃模块进气道非设计点工作特性 总被引:1,自引:0,他引:1
对适用于轴对称双燃烧室冲压发动机的亚燃模块进气道非设计点工作特性进行了风洞实验和数值计算研究,获得了该进气道的非设计点性能,并分析了其流态特征和再起动特性。实验数据显示,该进气道的马赫数4临界状态性能为:总压恢复系数0.425,出口截面平均马赫数0.519,可承受反压为自由流静压的56.52倍,而马赫数5的相应临界性能参数则分别为0.240,0.486和125.94。非设计状态下,该进气道的流量系数下降显著,马赫数5时的流量系数为0.813,马赫数4时则进一步下降至0.593,为此对高超声速进气道非设点综合性能的改善迫在眉睫。另外,该进气道在马赫数4时具有再起动能力。 相似文献
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Minghu Tan Colin McInnes Matteo Ceriotti 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(8):2099-2115
Since the Sun-Earth libration points L1 and L2 are regarded as ideal locations for space science missions and candidate gateways for future crewed interplanetary missions, capturing near-Earth asteroids (NEAs) around the Sun-Earth L1/L2 points has generated significant interest. Therefore, this paper proposes the concept of coupling together a flyby of the Earth and then capturing small NEAs onto Sun–Earth L1/L2 periodic orbits. In this capture strategy, the Sun-Earth circular restricted three-body problem (CRTBP) is used to calculate target Lypaunov orbits and their invariant manifolds. A periapsis map is then employed to determine the required perigee of the Earth flyby. Moreover, depending on the perigee distance of the flyby, Earth flybys with and without aerobraking are investigated to design a transfer trajectory capturing a small NEA from its initial orbit to the stable manifolds associated with Sun-Earth L1/L2 periodic orbits. Finally, a global optimization is carried out, based on a detailed design procedure for NEA capture using an Earth flyby. Results show that the NEA capture strategies using an Earth flyby with and without aerobraking both have the potential to be of lower cost in terms of energy requirements than a direct NEA capture strategy without the Earth flyby. Moreover, NEA capture with an Earth flyby also has the potential for a shorter flight time compared to the NEA capture strategy without the Earth flyby. 相似文献
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Paul R. Mahaffy Mehdi Benna Todd King Daniel N. Harpold Robert Arvey Michael Barciniak Mirl Bendt Daniel Carrigan Therese Errigo Vincent Holmes Christopher S. Johnson James Kellogg Patrick Kimvilakani Matthew Lefavor Jerome Hengemihle Ferzan Jaeger Eric Lyness John Maurer Anthony Melak Felix Noreiga Marvin Noriega Kiran Patel Benito Prats Eric Raaen Florence Tan Edwin Weidner Cynthia Gundersen Steven Battel Bruce P. Block Ken Arnett Ryan Miller Curt Cooper Charles Edmonson J. Thomas Nolan 《Space Science Reviews》2015,196(1-4):49-77
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Experimental and Numerical Investigation of the Effects of Passive Vortex Generators on Aludra UAV Performance 总被引:3,自引:3,他引:0
A study of the effects of passive vortex generators (VGs) on Aludra unmanned aerial vehicle (UAV) aerodynamic characteristics is presented. Both experimental and numerical works are carried out where an array of VGs is attached on Aludra UAV’s wing. The flow measurements are made at various angles of attack by using 3-axis component balance system. In the numerical investigation, the Reynolds-averaged Navier-Stokes (RANS) code FLUENT 6.3TM is used in the simulations with fully structured mesh with Spalart-Allmaras (S-A) turbulence model and standard wall function. The comparison between the experimental and numerical results reveals a satisfactory agreement. The parametric study shows that higher maximum lift coefficient is achieved when the VGs are placed nearer to the separation point. In addition to this, shorter spanwise distance between the VGs also increases the maximum lift coefficient, rectangular and curve-edge VG performs better than triangular VG. 相似文献