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51.
D. Dirkx R. Noomen I. Prochazka S. Bauer L.L.A. Vermeersen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
In this paper we investigate the influence of atmospheric turbulence on the performance of the uplink of a planetary transceiver laser ranging system using a single photon detector. We numerically combine the influence of turbulence in the mean intensity profile variations, scintillation, beam-wander induced pointing errors and stochastic time-of-flight variations, using the Hufnagel–Valley turbulence profile to model the ground turbulence behavior. We map the intensity variations due to turbulence to variations in the probability distribution of the arrival time of the 1st photon in a laser pulse, which influences the range measurement error probability distribution. The turbulence models are applied to assess the influence on single-pass range accuracy and precision statistics, as well as the parameter estimation quality of a Phobos Laser Ranging (PLR) mission. 相似文献
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53.
对由导电率和硬度实验初步确定的2024铝合金新时效制度进行了拉伸试验研究,并对拉伸塑性性能试验数据进行了数理统计分析。通过实验研究和分析,证明2024铝合金采用新的时效制度,在塑性性能方面满足适航要求。 相似文献
55.
Stochastic structural optimization using particle swarm optimization, surrogate models and Bayesian statistics 总被引:4,自引:4,他引:0
This paper focuses on a method to solve structural optimization problems using particle swarm optimization (PSO), surrogate models and Bayesian statistics. PSO is a random/stochastic search algorithm designed to find the global optimum. However, PSO needs many evaluations compared to gradient-based optimization. This means PSO increases the analysis costs of structural optimization. One of the methods to reduce computing costs in stochastic optimization is to use approximation techniques. In this work, surrogate models are used, including the response surface method (RSM) and Kriging. When surrogate models are used, there are some errors between exact values and approximated values. These errors decrease the reliability of the optimum values and discard the realistic approximation of using surrogate models. In this paper, Bayesian statistics is used to obtain more reliable results. To verify and confirm the efficiency of the proposed method using surrogate models and Bayesian statistics for stochastic structural optimization, two numerical examples are optimized, and the optimization of a hub sleeve is demonstrated as a practical problem. 相似文献
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57.
汤阿妮 《北京航空航天大学学报》2011,37(6):654-657,664
受到实际条件限制,现阶段的飞机载荷谱实测均采取小子样实测方法,小子样实测数据是取自真实母体的一个简单样本,很难保证数据的充分性、完整性.传统的均值统计法无法对数据缺陷进行弥补.为了克服小子样数据不足问题,将核密度估计技术用于载荷谱统计,取得了良好效果.介绍了核密度估计的相关理论基础,并以某型机下沉速度谱的统计为例,详细介绍了将核密度估计方法用于载荷谱统计的数学过程.结果显示:核密度估计方法对还原载荷谱原貌、补充小子样数据的不足问题具有良好作用. 相似文献
58.
《中国航空学报》2021,34(2):407-419
Ionospheric variability is influenced by many factors, such as solar radiation, neutral atmosphere composition, and geomagnetic disturbances. Mainly characterized by the total electron content (TEC) and electron density, the climatology of the ionosphere features temporal and spatial changes. Establishing a multivariant regression model helps substantially in better understanding the ionosphere characteristics and their long-term variability. In this paper, an improvement of the existing ionosphere multivariate linear fitting regression model is proposed and investigated using data from both the ionosonde and the global ionosphere map (GIM) derived from ground-based Global Navigation Satellite System (GNSS) observations. The proposed method gives more consideration to the impact of the solar activity and adds modeling of the annual periodic fluctuations and half-year periodic fluctuations for the F10.7 index. The improved model is verified to have a better correlation with the real observations and can help reduce the calculation uncertainty. Moreover, the proposed model is used to evaluate the fitting accuracy of the GIMs produced by five authorized data analysis centers from the International GNSS Service (IGS). The results show that there is a fixing hole in the North America region for the GIM model where the correlation between the GIM and the proposed model always returns lower values compared to other places. 相似文献
59.
任若恩 《北京航空航天大学学报》1990,(3):72-77
研究Box-Cox转换在经济计量学中货币需求函数的函数形式设定方面的应用。并讨论与此有关的极大似然估计方法和似然比检验统计量的构造。并指出Box-Cox变换应用中的几个需要注意的问题。 相似文献
60.
针对地面结冰试验设施喷雾系统尾迹湍流模拟需求,考察了3种脱体涡模拟(DES)方法对三维亚临界圆柱绕流预测的准确性,比较和分析了瞬时流动特征和流场统计量。研究发现:1)从瞬时流动特征来看,k-ω雷诺平均NavierStokes(RANS)控制的区域对剪切应力输运k-ωDES(SSTk-ωDES)求解的准确性有显著影响;2)从流动参数统计量的误差范围来看,回流区长度和流向最小速度的预测质量能在一定程度上反应圆柱绕流数值模拟的准确性;3)综合比较,SSTk-ωDES预测值与试验值和大涡模拟(LES)数据最为吻合,具有应用于地面结冰试验设施喷雾系统尾迹湍流计算的潜力。 相似文献