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排序方式: 共有168条查询结果,搜索用时 640 毫秒
31.
N.I. Ismail A.H. Zulkifli M.Z. Abdullah M. Hisyam Basri Norazharuddin Shah Abdullah 《中国航空学报》2013,26(5):1093-1105
Abstract Implementing the morphing technique on a micro air vehicle (MAV) wing is a very chal- lenging task, due to the MAWs wing size limitation and the complex morphing mechanism. As a result, understanding aerodynamic characteristics and flow configurations, subject to wing structure deformation of a morphing wing MAV has remained obstructed. Thus, this paper presents the investigation of structural deformation, aerodynamics performance and flow formation on a pro- posed twist morphing MAV wing design named perimeter reinforced (PR)-compliant wing. The numerical simulation of two-way fluid structure interaction (FSI) investigation consist of a quasi- static aeroelastic structural analysis coupled with 3D incompressible Reynolds-averaged Navier- Stokes and shear-stress-transport (RANS-SST) solver utilized throughout this study. Verification of numerical method on a rigid rectangular wing achieves a good correlation with available exper- imental results. A comparative aeroelastic study between PR-compliant to PR and rigid wing per- formance is organized to elucidate the morphing wing performances. Structural deformation results show that PR-compliant wing is able to alter the wing's geometric twist characteristic, which has directly influenced both the overall aerodynamic performance and flow structure behavior. Despite the superior lift performance result, PR-compliant wing also suffers from massive drag penalty, which has consequently affected the wing efficiency in general. Based on vortices investigation, the results reveal the connection between these aerodynamic performances with vortices formation on PR-comoliant wing. 相似文献
32.
Bagshaw EA Cockell CS Magan N Wadham JL Venugopalan T Sun T Mowlem M Croxford AJ 《Astrobiology》2011,11(7):651-664
Basaltic glasses (hyaloclastite) are a widespread habitat for life in volcanic environments, yet their interior physical conditions are poorly characterized. We investigated the characteristics of exposed weathered basaltic glass from a surface outcrop in Iceland, using microprobes capable of continuous sensing, to determine whether the physical conditions in the rock interior are hospitable to microbial life. The material provided thermal protection from freeze-thaw and rapid temperature fluctuations, similar to data reported for other rock types. Water activity experiments showed that at moisture contents less than 13% wet weight, the glass and its weathering product, palagonite, had a water activity below levels suitable for bacterial growth. In pore spaces, however, these higher moisture conditions might be maintained for many days after a precipitation event. Gas exchange between the rock interior and exterior was rapid (< 10 min) when the rocks were dry, but when saturated with water, equilibration took many hours. During this period, we demonstrated the potential for low oxygen conditions within the rock caused by respiratory stimulation of the heterotrophic community within. These conditions might exist within subglacial environments during the formation of the rocks or in micro-environments in the interior of exposed rocks. The experiments showed that microbial communities at the site studied here could potentially be active for 39% of the year, if the depth of the community within the outcrop maintains a balance between access to liquid water and adequate protection from freezing. In the absence of precipitation, the interior of weathered basaltic glass is an extreme and life-limiting environment for microorganisms on Earth and other planets. 相似文献
33.
膨胀循环具有很好的性能和很高的可靠性,这一点已由普拉特·惠特尼公司的“半人马座”上面级推进系统RL10发动机证实,但是这种循环对燃烧室压力增加和推力增加都有限制作用,因为它仅仅利用了燃料在冷却燃烧室和喷管延伸段时吸收的热能,来推进燃料和氧化剂涡轮泵.建议采用具有内部热交换器的先进方案燃烧室,这种热交换器可以收集许多燃烧热量.叙述使用内部热交换器的高压膨胀循环发动机的主要性能,并给出了这种发动机的初步试验结果.热交换器中的平均热通量是Bartz相关计算值的70%.燃烧性能不会因装了内部热交换器而受到严重影响. 相似文献
34.
Fernández-Remolar DC Gómez F Prieto-Ballesteros O Schelble RT Rodríguez N Amils R 《Astrobiology》2008,8(1):157-173
Chemolithotrophic communities that colonize subsurface habitats have great relevance for the astrobiological exploration of our Solar System. We hypothesize that the chemical and thermal stabilization of an environment through microbial activity could make a given planetary region habitable. The MARTE project ground-truth drilling campaigns that sampled cryptic subsurface microbial communities in the basement of the Río Tinto headwaters have shown that acidic surficial habitats are the result of the microbial oxidation of pyritic ores. The oxidation process is exothermic and releases heat under both aerobic and anaerobic conditions. These microbial communities can maintain the subsurface habitat temperature through storage heat if the subsurface temperature does not exceed their maximum growth temperature. In the acidic solutions of the Río Tinto, ferric iron acts as an effective buffer for controlling water pH. Under anaerobic conditions, ferric iron is the oxidant used by microbes to decompose pyrite through the production of sulfate, ferrous iron, and protons. The integration between the physical and chemical processes mediated by microorganisms with those driven by the local geology and hydrology have led us to hypothesize that thermal and chemical regulation mechanisms exist in this environment and that these homeostatic mechanisms could play an essential role in creating habitable areas for other types of microorganisms. Therefore, searching for the physicochemical expression of extinct and extant homeostatic mechanisms through physical and chemical anomalies in the Mars crust (i.e., local thermal gradient or high concentration of unusual products such as ferric sulfates precipitated out from acidic solutions produced by hypothetical microbial communities) could be a first step in the search for biological traces of a putative extant or extinct Mars biosphere. 相似文献
35.
This paper analyzes the state of the ionosphere during two geomagnetic storms of a different intensity evolving in different sectors of local time in different seasons. There were used the data from a network of ionospheric stations located in the opposite longitudinal sectors of 80°-150° E and 250°-310° E.This analysis has permitted us to conclude that the detected differences in the variations of the disturbances are likely to be determined by the local time difference of the geomagnetic storm development, its intensity and by the different illumination conditions of the ionosphere. 相似文献
36.
本文研究脉冲发动机在战术导弹,特别是空空导弹上的应用.因为其飞行任务要求对能量消耗作仔细地监控.一般的中程空空导弹使用助推-主发动机作为动力.除了接近交会之外,发射时导弹雷达导引头并不知道目标.一般的中程空空导弹使用比例导航或者在终段制导使用改进的比例导航,同时为了使导弹在较高的高度飞行以减小阻力,在中段附加了预编程的 相似文献
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39.
每个刚接触GPS的人首先了解到的是:时钟是该技术的核心。GPS卫星载有非常精确、超稳定、每个耗费数万美元的原子钟。然而,出于显而易见的原因,大多数GPS接收机中的时钟很便宜。除了跟踪卫星信号时,由于要求时钟信号中的相位噪声,对接收机时钟要求较高,其它应用对接收机时钟的要求都不是很高。这一要求通常用100美元左右或更少的温补晶振就可满足。 相似文献
40.
Guolong ZHAO Lianjia XIN Liang LI Yang ZHANG Ning HE Hans N?rgaard HANSEN 《中国航空学报》2023,36(7):114-128
High-mass fraction silicon aluminium composite(Si/Al composite) has unique properties of high specific strength, low thermal expansion coefficient, excellent wear resistance and weldability. It has attracted many applications in terms of radar communication, aerospace and automobile industry. However, rapid tool wear resulted from high cutting force and hard abrasion, and damaged machined surfaces are the main problem in machining Si/Al composite. This work aims to reveal the mechanisms of milli... 相似文献