电压骤降概率评估的建模与仿真

基于蒙特卡罗法和PSCAD/EMTDC实现对电压骤降指标进行自动随机评估仿真计算。推导了电压骤降故障信息的蒙特卡洛模型,并在PSCAD/EMTDC软件中建立和实现该模型,运用Multiple Run组件对故障信息进行多次随机抽样仿真计算,同时对仿真结果进行统计,得到各敏感负荷节点处电压骤降特征参数和电压骤降能量指标的概率分布。     

大尺寸焦平面空间相机调焦机构的精度分析

由于大尺寸焦平面空间相机调焦机构的焦平面两端存在的不可消除的同步运动误差会直接影响相机调焦精度,因此对焦平面两端同步运动精度进行了分析。首先,研究了大尺寸焦平面空间相机调焦机构的特点,提出了焦平面两端同步运动误差是影响其调焦精度的主要因素;其次,分析了影响同步运动精度的主要误差来源,建立了同步运动误差的数学模型,并采用蒙特卡罗仿真算法对数学模型进行了仿真分析;最后,通过测试焦平面两端同步运动精度对仿真结果进行了验证。仿真结果显示,同步运动精度为0.02 mm,与试验数据分析结果0.023 mm一致,说明此方法能够比较准确地确定焦平面两端同步运动精度,为后续在轨调焦策略的确定以及同类产品的研制提供技术支持。     

马斯京根模型参数抗差估计方法风险分析

针对马斯京根模型参数抗差估计方法存在将真实值作为异常值的风险,利用蒙特卡洛方法分析了不同频率、不同量级的异常值影响下马斯京根模型参数抗差估计方法风险与效果间的关系。结果表明,马斯京根模型参数抗差估计方法的风险随异常值量级和频率的减小而增大,同时还与估计方法选取的抗差权函数有关。     

太阳能热发电系统中腔式吸热器的光学性能

建立了球形、圆柱形、圆锥形和平顶圆锥形4种典型腔式吸热器与抛物面聚光器的三维模型,利用蒙特卡洛光线追踪法预测了4种典型腔式吸热器内部辐射能流的分布,其中球形吸热器内部的辐射能流分布均匀性最好,且辐射峰值最小,具有较好的光学性能。通过统计逸出腔口的反射光计算出这4种腔式吸热器的反射光损,其中球形吸热器的反射光损最小。在聚光器反射率为0.9,腔体内壁吸收率为0.9时,球形吸热器反射光损仅为0.66%,聚光器/球形吸热器的光学效率为88.9%。     

球形腔式太阳能吸热器性能的数值研究

利用蒙特卡洛光线追踪法分析了6种不同开口比(D/d)的球形腔式吸热器的光学性能,并以光学模拟所得壁面能流作为热分析的边界条件导入CFD软件中,运用CFD软件对6种不同开口比的球形腔式吸热器进行流固耦合传热计算,获得了球形腔式吸热器和内部流体的温度场分布。通过计算球形腔式吸热器的反射光损失、对流热损失和热辐射损失,得到聚光器/球形腔式吸热器系统的光热转化效率为81.9%～84.4%,球形腔式吸热器的最佳开口比1相似文献   

Defect generation during silicon oxidation: A Kinetic Monte Carlo study

We present a synthetic review of elementary chemical mechanisms source of the oxidation of pure silicon (100) surfaces. These mechanisms are then discussed from their ability to build a mesoscale model of the Kinetic Monte Carlo type dedicated to the process simulation of silicon thermal oxidation. We show that oxidation is driven by two main processes: (i) charge transfer arising from the formation of SiO bonds in contact to pure silicon at the interface, (ii) destructive oxidation in which SiO building blocks rearrange at the interface to form a hexagonal-based oxide network directly in contact to cubic Si layers. Based on these considerations, simulations at the process scale exhibit epitaxial behavior within the interfacial domain. The resulting oxide layers are analyzed in terms of local to more extended defects. We observe two types of defects: (i) “intra-domain defects” which are related to local distortion of the elementary hexagonal oxide pattern Si₆O₆ (ii) “inter-domain defects”, which are related to global oxide structural transitions from one orientation to another.     

Introducing densification mechanisms into the modelling of HfO2 atomic layer deposition

Density functional theory calculations are used to highlight some basics of the densification mechanisms arising during atomic layer deposition of HfO₂ onto silicon dioxide. The obtained results are discussed at the light of a multi-model approach that enables process simulation at the atomic scale via Kinetic Monte Carlo simulations. The impact of the proposed densification mechanisms on the growth is demonstrated. We show that a complete coverage is possible thanks to these mechanisms at a slow rate after that all surface reactive sites (OH sites) have been consumed by precursor molecules.     

A stochastic simulation method for uncertainty quantification in the linearized inverse conductivity problem

This paper considers the inverse problem in electrical impedance tomography with non‐informative prior information on the required conductivity function. The problem is approached with a Newton‐type iterative algorithm where the solution of the linearized approximation is estimated using Bayesian inference. The novelty of this work focuses on maximum a posteriori estimation assuming a model that incorporates the linearization error as a random variable. From an analytical expression of this term, we employ Monte Carlo simulation in order to characterize its probability distribution function. This simulation entails sampling an improper prior distribution for which we propose a stable scheme on the basis of QR decomposition. The simulation statistics show that the error on the linearized model is not Gaussian, however, to maintain computational tractability, we derive the posterior probability density function of the solution by imposing a Gaussian kernel approximation to the error density. Numerical results obtained through this approach indicate the superiority of the new model and its respective maximum a posteriori estimator against the conventional one that neglects the impact of the linearization error. Copyright © 2011 John Wiley & Sons, Ltd.     

中医推拿机器人末端执行器工作空间分析

 构造了一种新型中医推拿机器人末端执行器的结构形式．通过坐标变换,建立了机构的运动学模型,并进行了反解分析．针对推拿机器人的手法要求,探讨了结构参数对该并联机构工作空间的影响规律,为工作空间的综合提供了依据．基于蒙特卡罗原理,通过MATLAB编程对此并联机构的工作空间进行了数值解的描绘．并利用Pro/E建立末端执行器机构的三维模型,导入ADAMS就其运动轨迹进行模拟和分析,仿真结果表明中医推拿机器人末端执行器的设计符合推拿要求,验证了机构设计的正确性．推拿机器人末端执行器的工作空间内部工作点密集且分布均匀,满足推拿动作高效作业的要求,为中医推拿机器人的实用化提供了理论依据．