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261.
262.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(3):1397-1417
An evaluation of the hydromorphological condition of the Mahananda-Balason River system of the sub-Himalayan foothills, West Bengal, India was attempted using a multiparameter-based Hydromorphological Quality Index (HQI). After segmenting these rivers based on continuity, bed material and channel planform, a total of 18 indicators, divided into 3 subgroups Continuity (C), Planform (P), and Floodplain Morphology (FM), were quantified reach-wise and scaled upon the level of alteration (1 for highly altered and 5 for no alteration). The derived overall HQI (3.6) exhibited a moderate hydromorphological quality of the system, however, significant differences between the HQIs of confined and unconfined reaches were witnessed. Students ‘t-test and Multiple Correspondence Analysis both portrayed vast dissimilarities among the confined and unconfined reaches and the clustering was depending on their confinement. The deviations measured from the system’s mean and least altered conditions portrayed that the confined reaches with lesser human interventions were in comparatively more pristine hydromorphological conditions. Conversely, unconfined reaches showed moderate to very poor hydromorphological conditions chiefly due to intense human-induced alterations regarding urbanization, embanking and sediment extraction. Restorations on these aspects should initiate with immediate effect to avoid a shortage of riverine resources such as fluvial sediment, fish and groundwater. Overall, this methodology was found suitable for continuous monitoring of the river systems along with the precise identification of areas and aspects to be restored for upgrading the hydromorphological quality. More testing of this methodology would eventually help in validating the hydromorphological quality assessment protocol for Indian rivers. 相似文献
263.
为增强卫星的自主生存能力,研究了基于卫星轨道软件平台的自主导航计算方法。由星载导航部件获取导航参数,应用数值或解析法进行自主导航计算,以实时获得精确的轨道参数。理论分析和仿真结果表明,读方法正确可行,具有较高的工程应用价值。 相似文献
264.
为了研究不同温度下丁羟包覆层的横向弛豫时间与拉伸性能的相关性,开展了核磁共振和拉伸应力-应变性能测定试验。单因素方差分析表明温度对横向弛豫时间有显著影响;试验温度从30℃升到90℃,横向弛豫时间呈线性增大;90℃升到130℃,横向弛豫时间先减小后增大。30~90℃,升温使包覆层的拉伸强度下降,断裂伸长率升高;在100℃较90℃强度得到了提高,断裂伸长率稍有降低;在100~130℃时,受复杂化学反应和分子热运动共同影响,断裂伸长率迅速增加,强度降低。断裂伸长率、拉伸强度均与横向弛豫时间存在较好的相关性,利用该关系可以预测丁羟包覆层在不同横向弛豫时间下的拉伸性能。 相似文献
265.
《中国航空学报》2023,36(5):1-17
Serpentine nozzles are widely used in combat aircraft to realize strong stealth characteristics. Based on the layout characteristics within a confined space, a series of double serpentine nozzles with spanwise offsets are established. Using computational fluid dynamics and Taguchi method, the influence mechanisms of the Distribution of Area (DA), Distributions of Centerline for the first and second ‘S’ sections in the Vertical direction (DCV1 and DCV2), and Distribution of Centerline in the Spanwise direction (DCS) are analyzed. The impact of these factors on the total pressure recovery coefficient can be ranked as DA > DCV2 > DCS > DCV1, whereas their impacts on the discharge coefficient and axial thrust coefficient can be ranked as DCV2 > DCS > DA > DCV1. Considering the statistical significance of these factors, a nozzle in which DA changes rapidly at the exit and DCV1, DCV2, and DCS change rapidly at the entrance gives the best aerodynamic performance. Compared to the worst configuration, the total pressure recovery coefficient, discharge coefficient, and axial thrust coefficient are improved by 1.6%,3.5% and 3.6%, respectively. DA influences the gas flow acceleration in the entire serpentine channel, resulting in different wall shear stress and friction losses. The various centerline distributions influence the gas flow acceleration effects and form complex wave structures in the constant-area extension section, resulting in different local and friction losses. 相似文献
266.
267.
旋转部件转动诱导振动信号检测与分析 总被引:1,自引:0,他引:1
阐述了一个典型旋转部件振动时产生诱导振动信号的检测方法。介绍了测试系统,旋转部件振动测点布置和振动信号采集。根据两个样机的实测结果,认为旋转部件的诱导振动信号与旋转部件生产质量、安装精度密切相关,对旋转部件轴承固有特征的理论计算值和实测频谱进行了比较,进而判断轴承是否存在故障,并分析了上、下轴承间振动信号的相关性。 相似文献