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41.
Cheng Hu Tao Zeng M. Cherniakov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
Bistatic SAR (BSAR) systems have recently been the subject of several studies, but little attention has been given to the potential of the location of targets. In the paper, the performance of the estimation of 3-D position of a target (TPE) in parasitic SAR is obtained analytically and illustrated by computer simulation using ambiguity function analysis, and the maximum likelihood estimate (MLE) approach. It was shown that by using a multi look parasitic BSAR all three coordinates of an isolated point target (IPT) could be evaluated. Analytical closed form equations that characterize the measurement accuracy were derived. In the final these equations will be used to demonstrate various cases of more practical, including optimal trajectories choice under any geometry configuration case, moreover, the conclusion is verified via Matlab. 相似文献
42.
弹性飞行器敏感元件位置设置与参数优化综合 总被引:1,自引:0,他引:1
本文研究了弹性飞行器敏感元件位置的设置问题,分析了敏感元件位置对弹性飞行器稳定性的影响,提出了几类飞行器自动驾驶仪敏感元件可能合适位置的选择准则。从飞行器弹性振动闭环系统方程出发研究了弹性飞行器参数优化综合的某些方法。通过算例得到控制系统返馈系数,陀螺位置,舵面位置优化综合的数值模拟结果。这些结果与该飞行器实际采用的值符合较好。 相似文献
43.
主要研究了液态单组份碳氢燃料在超燃燃烧室中的点火和稳焰性能,所用燃料为正十二烷和甲基环己烷,研究结果可以为超燃冲压发动机的燃料制备提供部分依据。试验在以蓄热式加热器为核心的直连式试验台上进行,超燃燃烧室进口总温在1040~1100K范围内,进口马赫数2.03,进口空气流量2.0kg/s左右,点火器为燃气发生器,采用串联凹腔作为火焰稳定装置,在第一个凹腔前常温燃料垂直喷射到燃烧室中。研究结果表明:与正十二烷相比,甲基环己烷在来流总温较低的超声速流中更容易被点燃和实现稳火,但总体来讲,当燃烧室进口总温低于1100K时,常温液态燃料的点火和稳焰性能较差。理论分析了两种燃料的蒸发特性,计算结果表明在来流参数相同时,甲基环己烷的蒸发特性优于正十二烷。利用一维分析方法结合试验测量的壁面静压、燃烧室入口马赫数和空气流量,得到了正十二烷和甲基环己烷不同工况时的总温分布和出口燃烧效率。 相似文献
44.
针对航空发动机燃油控制系统中二阶非定常执行机构通常出现设计困难的问题,介绍一种变结构控制方法,将二阶非定常执行机构变成确定的一阶惯性环节,该方法既充分利用其优点"不变性"又可以规避其突出缺点"抖振",特别适用于驱动脉冲比例调节阀;同时提出脉冲比例阀的变结构调节中遇到的实际问题(例如微分的精度问题)的解决办法,以及影响该方法可行性的若干必要条件。结果表明:符合条件时变结构控制在基于脉冲比例阀的燃油调节系统中是可行的。 相似文献
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高校肩负着培养和造就社会主义事业建设和接班人的要使命,思想工作在青年学生综合素质的形成和提高中着重要的地位和作用。笔者主要从学生角度谈谈提高思政治教育效果的几点思考和启示。 相似文献
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《中国航空学报》2021,34(5):523-534
Reduced order models for ignition analysis can offer insights into ignition processes and facilitate the combustor optimization. In this study, a Pairwise Mixing-Reaction (PMR) model is formulated to model the interaction between the flame particle and the surrounding cell mixture during Lagrangian flame particle tracking. Specifically, the model accounts for the two-way coupling of mass and energy between the flame particle and the surrounding shell layer by modelling the corresponding turbulent mixing, chemical reaction and evaporation process if present. The state of a flame particle, e.g., burnt, hot gas or extinguished, is determined based on particle temperature. This model can properly describe the ignition process with a spark kernel being initiated in a nonflammable region, which is of practical importance in certain turbine engines and has not been rigorously accounted for by the existing models based on the estimation of local Karlovitz number. The model is integrated into an ignition probability analysis platform and is demonstrated for a methane/air bluff-body flame with the flow and fuel/air mixing characteristics being extracted from a non-reacting simulation. The results show that for the spark location being at the extreme fuel-lean outer shear layer of the recirculation zone, PMR can yield ignition events with a significant number of active flame particles. The mechanisms for the survival of the initial flame particles and the entrainment of the survived flame particles into the recirculation zone are analyzed. The results also show that the ignition probability map from PMR agrees well with the experimental observation: a high ignition probability in the shear layer of the recirculation zone near the mean stoichiometric surface, and low ignition probabilities inside the recirculation zone and the top stagnation region of the recirculation zone. The parametric study shows that the predicted shape of the ignition progress factor and ignition probability is in general insensitive to the model parameters and the model is adequate for quantifying the regions with high ignition probabilities. 相似文献
50.
Categorical bias in location memory in geometric spaces is well established. The present study assessed the presence of the bias in locating eyes in images of human faces. Participants were presented with digital faces and indicated the position of one of the eyes in both upright and inverted orientations. Biases resulted from participants using multiple sources of accessible information. No differences were found for upright vs. inverted face images. Overall, the data were consistent with the retrieval category adjustment model. These distortions may be considered within the forensic context, when eyewitnesses work with a sketch artist or use a computer program to generate an image of the culprit. 相似文献