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521.
基于飞行状态造成的疲劳损伤,引入“影响因子”的概念,建立飞行状态时间比例改变对动部件使用费用影响的数学模型,分析各种飞行状态时间比例改变对动部件使用费用的影响程度。采用此模型对某型直升机的研究表明,计算得到的只有一个飞行状态时间比例主动改变和只有一个飞行状态时间比例未主动改变的影响因子可以定性和定量地分析飞行状态对使用费用的影响,在此型直升机所有的飞行状态巾只有两种飞行状态造成的使用费用在飞行状态时间比例变化0.1时变化超过0.01。 相似文献
522.
为了探索纳米银浆在大功率器件组装中的应用可靠性,亟待获得纳米银浆的烧结特性和热力学性能。本文对不同烧结温度、烧结时间、升温速率、烧结方式的纳米银浆样件烧结强度,结合烧结形貌进行了系统研究,并与航天电子产品中常规的互连材料Au80Sn20焊料、Sn90.5Ag3Cu0.5焊料以及H20E导电胶的散热性进行了对比分析。研究结果表明:采用可控升温速率空气氛围的烧结方式,在200 ℃下保温90 min,银浆样件的剪切强度最高可达40 MPa。纳米银浆导热性能与Au80Sn20相当,明显高于H20E和SAC305。在经历严酷的热应力和机械应力试验后,其剪切强度保持稳定,因此纳米银浆作为高导热连接材料在宇航大功率器件组装中具有良好的应用前景。 相似文献
523.
抽油机示功图直观显示了抽油机工作情况,但实际工况情况呈现典型的长尾分布特性,类别严重不平衡。传统方法无法准确识别小类别工况,也无法获得井下工作状态准确识别。针对这一问题,提出一种基于分布驱动的多类别长尾数据代价敏感主动学习算法(Cost-sensitive active learning algorithm based on distribution -driven multi-class long-tailed data, CALA)。首先,考虑数据分布特性,以最小化代价为优化目标确定数据的最佳聚类簇数;其次,通过加入预分类误差代价来更新之前得到的最佳聚类簇数;然后,构建集成分类模型作为分类器;最后,通过迭代来平衡数据分布。采用某油田真实的示功图数据进行测试,显著性实验分析证明CALA在小类别工况诊断上具有更好的性能。 相似文献
524.
Titanium alloy plays a crucial role in the electrochemical field due to its excellent corrosion resistance. The passivation and dissolution behaviors of Ti-6.5Al-2Zr-1Mo-1V(TA15) alloy in Na Cl solution were studied by simulating the electrochemical machining process in a rotating condition, which made the anode in a state with alternating high and low current density. Electron probe micro analysis, ultra-depth microscope, scanning electron microscope, and X-ray photoelectron spectrometer were u... 相似文献
525.
针对涡桨发动机复杂、非线性的工作环境,利用层次分析(AHP)法提取发动机工作状态特征参数,考虑各特征参数对工作状态识别的影响,以特征参数加权的改进蚁群算法为基础,进行发动机同一工作状态识别、聚类,并采用Mann-Kendall法开展发动机性能预测分析。利用多台涡桨发动机性能参数飞参数据进行验证,结果表明:该方法能准确识别发动机起飞、额定工作状态,巡航以下工作状态识别准确率达84%以上;此外,发动机性能预测效率提升了近50%,而预测错误率小于10%,可以满足航空兵部队维修保障工作的实际需要。 相似文献
526.
《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
527.
为深入了解真实航空发动机燃烧室极端条件下点火性能,在自有CFD平台上对不同高空来流条件下典型航空发动机双旋流燃烧室点火过程进行了数值模拟。为保证模拟精度,对模型包括全部气膜冷却小孔在内的所有精细结构均进行了完全仿真,并完整再现了燃烧室内从燃油雾化到点火燃烧全过程。结果表明3种高空来流条件下单次点火均失败。点火过程显示高温燃气越过旋流杯中心向上回流区扩张是点火的关键时空区域,在此时补充点火可推动火焰顺利传播到整个主燃区。对8km和6km两种状态分别增加点火次数到3次和5次后最终点火成功,结果表明前者着火极限油气比约为0.057,后者为0.038~0.042。 相似文献
528.
529.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(3):1486-1509
Sea-surface solar radiation (abbreviated as photosynthetically available radiation, PAR) in the visible wavelength (400–700 nm) is an essential parameter to estimate marine primary productivity and understanding phytoplankton dynamics, upper ocean physics and biogeochemical processes. Although many remote-sensing models were developed to estimate daily PAR (DPAR) from ocean colour data, these models often produce biases in the DPAR products under cloudy-sky and complex atmospheric conditions due to the lack of parameterization to deal with the cloud cover conditions and insufficient in-situ DPAR data. This study presents an Extended Sea-surface Solar Irradiance Model (ESSIM) for estimating DPAR over the global ocean. The ESSIM uses the direct and diffuse components from the Simple sea-surface Solar Irradiance Model (SSIM) along with a new parameter to handle cloudy conditions. The ESSIM produced DPAR products with greater accuracy under both clear and cloudy conditions. Its performance was tested on the time-series MODIS-Aqua images and compared with the concurrent in-situ data and the results from two global models. Results showed that the DPAR values produced by ESSIM agree with in-situ data better than the global models for all-sky conditions (with a mean relative error of 11.267 %; a root mean square error of 5.563 Em?2day?1; and a mean net bias of 2.917 Em?2day?1). The ESSIM performed slightly better than the SSIM for clear conditions and the Frouin's Operational Algorithm (FOA) for all-sky conditions. As the new parameterization accounts for cloudy conditions, the ESSIM produced more accurate results for cloud cover conditions across latitudes (up to 60°). The time-series Level-3 binned MODIS-Aqua data (global gridded) also demonstrated that the ESSIM improved the accuracy of DPAR products and produced spatially and temporally consistent DPAR products over the global ocean regardless of the seasons and sky conditions. 相似文献
530.