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31.
采用随机响应量的前四阶统计矩来度量目标函数和概率约束条件的稳健性, 通过引入“权重因子”来确定新构造的目标函数中原 函数和敏感系数的比重, 利用加权组合法将稳健优化设计这一多目标优化问题转化为单目标问题, 从而建立新的基于高阶矩的稳健优化设计数学模型. 矩估计方法可高效地评估目标函数和概率约束条件的统计矩, 且不需要搜索技术, 因此不构成嵌套循环(即稳健优化过程是单循环的), 从而可以大大降低优化的计算工作量. 对多个桁架结构进行了确定性优化设计、可靠性优化设计、传统的和该文所提的稳健优化设计, 验证了所建立的基于高阶矩的稳健优化设计数学模型的合理性和正确性, 比较并解释了计算所得的优化结果. 相似文献
32.
Zhenzhou Cheng Feng Song Changguang Zou Ruiyuan Su Xiaochen Yu Weiping Zang Jianguo Tian Shibin Jiang 《Optical and Quantum Electronics》2008,40(13):1021-1031
In this work, a model for analyzing the gain characteristics of heavily Er3+/Yb3+ co-doped compact fiber amplifier is presented. Four-level rate equations and finite-difference beam propagation method are
applied to simulate the optical field evolution along the active fiber. Based on this model, the influences of ion concentration,
fiber length and pump power on the gain characteristics of Er3+/Yb3+ co-doped phosphate glass fiber amplifiers are theoretically investigated. Numerical results show that for a fiber length
of 3.6 cm the internal gain can reach 27.2 dB with N
Er = 2.6 × 1026 ions/m3 and N
Yb = 1.2 × 1027 ions/m3 when pumped with 224 mW at 980 nm. The gain per centimeter is 7.56 dB/cm. The results can provide useful information to optimize
the gain performance of these compact fiber amplifiers. 相似文献
33.
For models with dependent input variables, sensitivity analysis is often a troublesome work and only a few methods are available. Mara and Tarantola in their paper (“Variance-based sensitivity indices for models with dependent inputs”) defined a set of variance-based sensitivity indices for models with dependent inputs. We in this paper propose a method based on moving least squares approximation to calculate these sensitivity indices. The new proposed method is adaptable to both linear and nonlinear models since the moving least squares approximation can capture severe change in scattered data. Both linear and nonlinear numerical examples are employed in this paper to demonstrate the ability of the proposed method. Then the new sensitivity analysis method is applied to a cantilever beam structure and from the results the most efficient method that can decrease the variance of model output can be determined, and the efficiency is demonstrated by exploring the dependence of output variance on the variation coefficients of input variables. At last, we apply the new method to a headless rivet model and the sensitivity indices of all inputs are calculated, and some significant conclusions are obtained from the results. 相似文献
34.
We investigate the resonant transmission of Dirac electrons through inhomogeneous band gap graphene with square superlattice potentials by transfer matrix method. The effects of the incident angle of the electrons, Fermi energy and substrate-induced Dirac gaps on the transmission are considered. It is found that the Dirac gap of graphene adds another degree of freedom with respect to the incident angle, the Fermi energy and the parameters of periodic superlattice potentials (i.e., the number, width and height of the barriers) for the transmission. In particular, the inhomogeneous Dirac gap induced by staggered substrates can be used to manipulate the transmission. The properties of the conductance and Fano factor at the resonant peaks are found to be affected by the gaps significantly. The results may be helpful for the practical application of graphene-based electronic devices. 相似文献
35.
为了根据不同需求找到输入变量相关情况下最优重要性测度分析方法,非常有必要对现有重要性测度方法之间的关系进行探究比较. 分别以不含交叉项和包含交叉项的二次多项式输出模型为例,解析推导了相关正态输入变量情况下基于协方差分解的重要性测度指标,包括总贡献、结构贡献和相关贡献. 进一步以所推导的解析结论为基础,理论推导了传统基于方差的重要性测度指标与基于协方差分解的重要性测度指标之间的关系.并从特殊二次多项式模型的研究结果对一般模型做出推断,然后从高维模型分解的角度验证所推断的结论,并详细阐述了不同重要性测度指标的优缺点. 最后结合具体算例深入地分析了各指标之间的关系,为输入变量相关情况下结构性能对输入特性的重要性分析与工程设计提供指导. 相似文献
36.
多项式输出中相关变量的重要性测度分析 总被引:2,自引:0,他引:2
为了解决一般工程问题中输出量为多项式情况下相关正态输入变量的贡献识别问题, 以二次不含交叉项的多项输出量为例, 利用多维相关正态分布及其条件分布的性质, 解析地推导了相关正态输入变量对输出量总方差的独立贡献及相关贡献, 采用算例验证了所推导的解析表达式的正确性. 文中所推导的相关正态变量独立贡献和相关贡献的表达式可直接用于输出量为二次不含交叉项多项式或一次多项式情况下的输入变量贡献的识别,并且为其他新的算法提供了对照解, 另外此方法亦可以推广至含交叉项的高阶多项式, 解决更为复杂输出量情况下输入量的贡献识别问题. 相似文献
37.
38.
39.
Xiaochen Yu Wentao Wang Lanjun Luo Chengguo Ming Zhenzhou Cheng Lin Han Tongqing Sun Hua Yu Jianguo Tian 《Optics Communications》2009,282(10):2045-123
We have prepared Er3+/Yb3+ co-doped transparent phosphate glass ceramics by the high-temperature melting technique, and demonstrated the influence of energy acceptors Ce3+ ions on the up-conversion and 1.54 μm emission properties of Er3+. The energy transfer mechanism is discussed based on the energy matching and the energy level structure. The phonon-assisted energy transfer between Er3+ and Ce3+ favors population feeding from the 4I11/2 to the 4I13/2 level, and therefore drastically decreases the up-conversion emission intensity of Er3+. Meanwhile, 1.54 μm fluorescence enhances greatly with the introduction of Ce3+ ions at the proper concentration. 相似文献
40.
结构可靠度计算中的描述性抽样法 总被引:2,自引:0,他引:2
本文提出描述性抽样方法的实质,即利用更少的时间抽取更多的服从要求概率分布的样本点,讨论了该方法的计算步骤和适用范围,并将描述性抽样方法与重要抽样方法结合起来计算多变量多模式的结构失效概率,比较了描述性抽样方法与一般抽样法的方差,算例结果表明描述性抽样方法具有较好的收敛性. 相似文献