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151.
A numerical optimization of high altitude testing facility for wind tunnel experiments 总被引:1,自引:0,他引:1
High altitude test facilities are required to test the high area ratio nozzles operating at the upper stages of rocket in the nozzle full flow conditions.It is typically achieved by creating the ambient pressure equal or less than the nozzle exit pressure.On average,air/GN2is used as active gas for ejector system that is stored in the high pressure cylinders.The wind tunnel facilities are used for conducting aerodynamic simulation experiments at/under various flow velocities and operating conditions.However,constructing both of these facilities require more laboratory space and expensive instruments.Because of this demerit,a novel scheme is implemented for conducting wind tunnel experiments by using the existing infrastructure available in the high altitude testing(HAT)facility.This article presents the details about the methods implemented for suitably modifying the sub-scale HAT facility to conduct wind tunnel experiments.Hence,the design of nozzle for required area ratio A/A*,realization of test section and the optimized configuration are focused in the present analysis.Specific insights into various rocket models including high thrust cryogenic engines and their holding mechanisms to conduct wind tunnel experiments in the HAT facility are analyzed.A detailed CFD analysis is done to propose this conversion without affecting the existing functional requirements of the HAT facility. 相似文献
152.
Active vibration control of piezoelectric bonded smart structures using PID algorithm 总被引:1,自引:1,他引:0
Thin-walled structures are sensitive to vibrate under even very small disturbances. In order to design a suitable controller for vibration suppression of thin-walled smart structures, an electro-mechanically coupled finite element(FE) model of smart structures is developed based on first-order shear deformation(FOSD) hypothesis. Considering the vibrations generated by various disturbances, which include free and forced vibrations, a PID control is implemented to damp both the free and forced vibrations. Additionally, an LQR optimal control is applied for comparison.The implemented control strategies are validated by a piezoelectric layered smart plate under various excitations. 相似文献
153.
Van Mulders SE Stassen C Daenen L Devreese B Siewers V van Eijsden RG Nielsen J Delvaux FR Willaert R 《Astrobiology》2011,11(1):45-55
This study investigates the effects of microgravity on colony growth and the morphological transition from single cells to short invasive filaments in the model eukaryotic organism Saccharomyces cerevisiae. Two-dimensional spreading of the yeast colonies grown on semi-solid agar medium was reduced under microgravity in the Σ1278b laboratory strain but not in the CMBSESA1 industrial strain. This was supported by the Σ1278b proteome map under microgravity conditions, which revealed upregulation of proteins linked to anaerobic conditions. The Σ1278b strain showed a reduced invasive growth in the center of the yeast colony. Bud scar distribution was slightly affected, with a switch toward more random budding. Together, microgravity conditions disturb spatially programmed budding patterns and generate strain-dependent growth differences in yeast colonies on semi-solid medium. 相似文献
154.
Greenberg R 《Astrobiology》2011,11(2):183-191
Europa has become a high-priority objective for exploration because it may harbor life. Strategic planning for its exploration has been predicated on an extreme model in which the expected oceanic biosphere lies under a thick ice crust, buried too deep to be reached in the foreseeable future, which would beg the question of whether other active satellites might be more realistic objectives. However, Europa's ice may in fact be permeable, with very different implications for the possibilities for life and for mission planning. A biosphere may extend up to near the surface, making life far more readily accessible to exploration while at the same time making it vulnerable to contamination. The chances of finding life on Europa are substantially improved while the need for planetary protection becomes essential. The new National Research Council planetary protection study will need to go beyond its current mandate if meaningful standards are to be put in place. 相似文献
155.
新一代飞机将要求航空电子设备能以更小的体积提供更为优越的系统性能。这一要求导致在各级电子包装上产生高的功率密度。由于没有新的热管理方法,元件结温将显著升高,从而导致可靠性的严重下降,在某些情况下,甚至导致元件功能的失效。为满足改进热管理的要求,已开发出一种液冷方法来代替高功率场合的常规空气冷却法。已经研制出液冷机架和液流通过模块,使结温限制到可以接受的程度。液冷也延长了冷却液损失后应急工作的时间,这对飞行关键设备而言是需要的。目前的活动着重子开发液冷机架和模块,这对综合航空电子系统联合工作组(JIAWG)管理的国防部(DOD)两级维护的创立是个有力的支持。 相似文献
156.
有时使用极坐标系对跟踪计算很有利。但因匀速目标的位置量不再象直角坐标系中一样是时间的线性函数而带来了复杂。然而这可以通过使用在预报方程中加伪加速度修正因子来近似修正系统动态的方法而解决,代价是增加了系统的噪声。对于α-β滤波器,加入这些修正因子,滤波器的稳态误差性能降低极小,同时又可大大减小偏倚误差。 相似文献
157.
本文提出了一种新的信号处理策略,它采用最佳的与信号有关的降秩来解决三维STAP(空时自适应处理)冷、热杂波抑制问题。虽然只采用空间(角度)PRI时间(多普勒)自由度,常规的二维STAP也能抑制单站(“冷”)杂波和直接路径干扰,然而,要抑制由干扰源地形散射干扰造成的所谓“热”杂波,还需要附加“快时间”自由度(在接收机带宽的倒数量级上)。引入了三维旁瓣对消器(Wiener滤波器)的多级分解,以评估降秩的理论性能限,并验证采用这种方法获得紧密干扰压缩的可能性比主分量方法获得的可能性最大。采用基于DTED测量的高保真模拟数据集合说明了3D STAP的多级Wiener滤波方法的功效。 相似文献
158.
159.
一、引言 1.背景美国航空航天局(NASA)的空间和地面应用处正在考虑一项航天飞机实验,用来验证几种比对全球高精密时钟和原始频标的技术。该实验准备在航天飞机上装一台氢脉泽时钟,利用微波和激光脉冲信号比对航天飞机上的空间时钟与地面站上的时钟。提出该项实验的目的是验证几种时间传递技术,这些技术能以1毫微秒以上的精度比对时钟时间,以10~(-14)以上的精度比对时钟频率。能以10~(-14)的精度比对频率这种能力是本项实验的独到之处。目 相似文献
160.