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991.
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D. Sudheer Reddy N. Gopal Reddy A.K. Anilkumar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The events that occurred after 2007 such as Chinese anti-satellite test, explosion of Briz-M upper stage, break up of cosmos-2421 and collision of cosmos-2251 with Iridium-33 satellites have completely changed the spatial density patterns in low earth orbits. This has increased the risk of collision between active satellites and debris created by them. Aftermath, the risk assessment of possible collisions called as conjunction analysis of working satellites from day to day has become more crucial. Spatial density models are useful in understanding the long-term likelihood of a collision in a particular region of space and helpful in pre-launch orbit planning. In this paper we present an algorithmic procedure for automatically estimating exact model parameters corresponding to the peak location and number of peaks using wavelets that will speed up the parameter estimation process for the models with peaks. 相似文献
994.
目前无线传感器网络对时间空间连续分布的物理量进行监测时存在着节点分布不合理,覆盖效率低,网络计算量大等问题。采用流体力学中数值分析的动态嵌套网格技术,设计了一种新的基于动态嵌套网格技术的无线传感器网络覆盖算法。最后对该算法进行仿真实验,结果表明该算法在相同监测精度时所得到的覆盖效率、覆盖均匀性、能效指标等比传统的覆盖算法有所优化。 相似文献
995.
《中国航空学报》2020,33(9):2281-2294
This paper presents an analytical, numerical, and experimental study on atomization characteristics and droplet distribution of a twin-fluid two-phase internal mixing atomizer to develop a Maximum Entropy Method (MEM). A two-phase Eulerian-Lagrangian method is utilized for atomization modeling of the inside and outside atomizer. In order to modify energy and momentum sources in the MEM, parametric studies are performed, and experimental tests are carried out to verify the results by applying the shadowgraph method. An advanced test stand is developed to prepare a wide range of changes in atomization characteristics and mixing ratios. A high degree of consistency is found between numerical results from the developed MEM and experimental tests with different gas-phase pressures and liquid flow rates. The droplet diameter and velocity distribution are reviewed based on various Weber numbers, sources of energy, and momentum. Turbulence modeling assists to estimate the breakup length and time scale precisely in the developed MEM, and distribution ranges with mean values are achieved. With reference to a strong correlation between upstream turbulence flow and the developed MEM verified by experimental tests, an ideal droplet size and velocity distribution prediction is observed. 相似文献
996.
997.
Acceptance sampling plan of accelerated life testing for lognormal distribution under time-censoring
Lognormal distribution is commonly used in engineering.It is also a life distribution of important research values.For long-life products follow this distribution,it is necessary to apply accelerated testing techniques to product demonstration.This paper describes the development of accelerated life testing sampling plans(ALSPs)for lognormal distribution under time-censoring conditions.ALSPs take both producer and consumer risks into account,and they can be designed to work whether acceleration factor(AF)is known or unknown.When AF is known,life testing is assumed to be conducted under accelerated conditions with time-censoring.The producer and consumer risks are satisfied,and the size of test sample and the size of acceptance number are optimized.Then sensitivity analyses are conducted.When AF is unknown,two or more predetermined levels of accelerated stress are used.The sample sizes and sample proportion allocated to each stress level are optimized.The acceptance constant that satisfies producer and consumer risk is obtained by minimizing the generalized asymptotic variance of the test statistics.Finally,the properties of the two ALSPs(one for known-AF conditions and one for unknownAF conditions)are investigated to show that the proposed method is correct and usable through numerical examples. 相似文献
998.
A.H. Maghrabi H.M. Al Dajani 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Water vapor is the most important greenhouse gas. It plays a major role in the dynamics of atmospheric circulation, radiation exchange within the atmosphere, and climate variability. Knowledge of the distribution of water vapor is important for understanding climate change and global warming. 相似文献
999.
Traditional Global Sensitivity Analysis (GSA) focuses on ranking inputs according to their contributions to the output uncertainty.However,information about how the specific regions inside an input affect the output is beyond the traditional GSA techniques.To fully address this issue,in this work,two regional moment-independent importance measures,Regional Importance Measure based on Probability Density Function (RIMPDF) and Regional Importance Measure based on Cumula tive Distribution Function (RIMCDF),are introduced to find out the contributions of specific regions of an input to the whole output distribution.The two regional importance measures prove to be reasonable supplements of the traditional GSA techniques.The ideas of RIMPDF and RIMCDF are applied in two engineering examples to demonstrate that the regional moment-independent importance analysis can add more information concerning the contributions of model inputs. 相似文献
1000.
基于退化量分布的可靠性建模方法为长寿命、高可靠性产品的可靠性评估提供了一种有效手段,尤其适用于产品个体间的退化轨迹相差较大的情况。为了提高关于退化量分布族和分布族参数假定的可信度,提出了通过拟合优度检验选择退化量分布族以及通过数据拟合确定分布族参数的方法。以某金属产品的裂纹退化数据为例,详细阐述了所提出方法的具体应用步骤,研究结果证明这种处理方法具有较高的准确度和可信度。 相似文献