Computerized Simulation on the Structure of Cryolite-Alumina Melts

Monte Carlo calculations were performedon liquid ionic solution of saturated aluminain cryolite melt containing a total of 205 ions.The local structure and radial distributionfunctions of the melt were computerized by MonteCarlo method at 1283 K. It has been found thatthere exist the complex ionic clusters suchas AlOF_3~(2-), AlOF_4~(3-), AlF_4~-, AlF_5~(2-), AlOF_2~- etc.,as well as oxygen-bridge and flourine-bridgeionic clusters. In the melt studied, Al~(3+) ionstend to have preferential even coordinationnumber of 4F~- ions.     

驰豫的固体-流体界面的平衡结构:它的蒙特卡罗模拟——Ⅰ.物理模型和初步模拟结果

在考虑到固体表面原子间的键能不同于内部原子键能的基础上,建立起驰豫的固体——流体界面模型。采用该模型借助蒙特卡罗方法模拟了固体——流体界面的平衡结构。发现,与常规刚性表面相比,驰豫界面比较粗糙。其粗糙度随驰豫系数的增大而增加。这与平均场理论相一致。     

Na20-- A1203 -- SiO2微晶玻璃体系熔体结构的分子动力学模拟

采用分子动力学方法模拟了7种组分的Na20-- A1203 -- SiO2体系微晶玻璃熔体结构,分析了体系的径向分布函数、键长分布和键角分布,得出了不同含量Na＋对Na20-- A1203 -- SiO2体系玻璃网络结构的影响。     

双金属爆炸焊接窗口计算机仿真

文章根据爆炸焊接窗口理论及实验分析,开发了"爆炸焊接窗口仿真系统(EWW1.0)",通过该系统可以实现各种双金属爆炸焊接窗口曲线的计算机仿真.在双金属爆炸焊接实际工程中,应用该软件对于确定合理的工艺参数具有很好的指导意义.     

Quantitative Analysis of Dynamic Fault Trees Based on the Coupling of Structure Functions and Monte Carlo Simulation

This paper focuses on the quantitative analysis of Dynamic Fault Trees (DFTs) by means of Monte Carlo simulation. In a previous article, we defined an algebraic framework allowing to determine the structure function of DFTs. We exploit this structure function and the minimal cut sequences that it allows to determine, to know the failure mode configuration of the system, which is an input of Monte Carlo simulation. We show that the results obtained are in good accordance with theoretical results and that some results, such as importance measures and sensitivity indexes, are not provided by common quantitative analysis and yet interesting. We finally illustrate our approach on a DFT example from the literature. Copyright © 2014 John Wiley & Sons, Ltd.     

基于蒙特卡洛法溅射离子泵泵腔结构研究

采用蒙特卡洛方法对溅射离子泵腔抽气通道内的气体流动规律进行数值模拟。建立了不同溅射离子泵结构的几何模型, 计算了气体分子在不同泵腔结构中进出比例, 分析了腔结构对反流量的影响, 得到了抽气组件在不同泵腔结构中的抽气效率, 探讨各种类型腔结构的抽气特点;最后计算了舱体高度对抽气性能的影响。结果表明:在相同条件下, I型泵腔结构抽气性能最好, T型泵腔结构次之, 双侧型泵腔结构抽气性能最差。     

Surface Tension of Ni-Cu Alloys: A Molecular Simulation Approach

The Monte Carlo (MC) method and the embedded-atom method (EAM) are used to calculate the surface tension and the temperature dependence of the surface tension of nickel-copper alloys. The simulation of the surface tension is performed through the calculation of the cohesive work of the alloy. The calculated surface tensions of the alloys are 30 to 40% larger than experimental values, while the changes in surface tension as a function of Cu composition show similar behavior in both calculated and experimental results. The simulation results for the temperature dependence of the surface tension in the undercooled region appear to be identical with that above the melting point, and for the Ni-Cu alloys, the temperature coefficients decrease with an increase of copper concentration.     

正常晶粒生长形貌演化的计算机模拟研究

有关多晶材料晶体生长机理及计算机模拟方法，我们已作了详细的论述。本文以蒙特卡罗（Ｍｏｎｔｅ Ｃａｒｌｏ）方法为基础，通过对Ｑ－ｓｔｅｔｅ ｐｏｔｔｓ算法进行改进，建立快速的Ｑ－ｓｔａｔｅ ｐｏｔｔｓ算法，用Ｄｅｌｐｈｌ３．０提供的Ｏｂｊｃｅｔ Ｐａｓｃａｌ语言编写软件，在ＰＣ５８６上实现了多晶材料晶粒生长结构演化的计算机模拟及统计分析。正常晶粒演化形貌图与生产动力力学相符合，逼真度较好。生长指数的     

应用Monte Carlo算法研究大分子蠕动阻力的影响因素

采用一种基于高分子Monte Carlo模拟算法分析分子蠕动阻力的软件,借助于二维空间中的8配位点键长涨落的格子链模型,对不同温度、分子量、共混小分子时的大分子蠕动行为进行了模拟分析,考察了温度、分子长、共混小分子等因素对蠕动阻力的影响,得到了随着温度增加、分子长减小和共混浓度增加,大分子蠕动阻力减小的结果,这与传统经验理论相符合。这些结果为选择大分子量添加剂黄原胶作为抗结块剂,以及选择β-环糊抑制玻璃化转变等提供了理论依据。     

晶粒生长的蒙特卡罗模拟研究进展

概述了经典的晶粒生长蒙特卡罗(MC)模型并指出了其存在的缺陷,总结了近几年国内外研究者对经典MC模型的改进算法,综述了MC方法模拟晶粒生长的应用研究,指出了目前研究中存在的问题,并展望了今后的主要研究方向.     

Modeling of coalescence of dispersed surface cracks. Part 2. Simulation model for multiple fracture

Abstarct A simulation model for multiple fracture has been developed that reproduces random processes of initiation, growth, and coalescence of dispersed surface cracks. The model is based on the method of statistical simulation (Monte Carlo method) and on the fracture regularities determined experimentally. The main factor responsible for fracture is found to be the coalescence of dispersed cracks, especially at the final stage, which accounts for about 30% of the total life. The ultimate state of a structure is defined by the condition according to which the length of the largest of the available damages is bigger than the calculated value of the maximum crack length.Translated from Problemy Prochnosti, No. 1, pp. 108–117, January–February, 2005.     

氧化物异质外延薄膜生长的计算机模拟

利用Monte Carlo方法分别模拟了在SrTiO3基底上沉积MgO薄膜和在MgO基底上沉积SrTiO3薄膜.模拟中,选取与实验中薄膜生长相近的参数条件,引入了新的参数扩散势垒,得到了在晶格正失配(张应力)和负失配(压应力)下薄膜生长的形貌图以及薄膜粗糙度的变化曲线图,分析了张应力和压应力对薄膜生长形貌的影响.模拟结果与文献报道的外延薄膜生长模式的实验观察结果一致.     

Three Dimension Monte Carlo Simulation of Austenite Grain Growth in CGHAZ of an Ultrafine Grain Steel

In the present research Monte Carlo technique was used to simulate the grain growth in heat-affected zone(HAZ) of an ultrafine grain steel. An experimental data based (EBD) model proposed by Gao was used to establish the relation between tMCS and real time temperature kinetics in our simulation. The simulations give out the evolution of grain structure and grain size distribution in HAZ of the ultrafine grain steel. A Microsoft Window based on computer program for the simulation of grain growth in the HAZ of weldment in three dimensions has been developed using Monte Carlo technique. For the system, inputting the temperature field data and material properties, the evolution of grain structure, both image of simulated grain structure and numerical datum reflecting grain size distribution can be produced by the program. The system was applied to the ultrafine grain steel welding, and the simulated results show that the ultrafine grain steel has large tendency of grain growth.     

蒙特卡洛仿真在工程项目进度管理中的应用

对于工序时间具有随机性的复杂工程项目,在Excel中运用蒙特卡洛仿真获得项目的完成时间分布并找出关键工序。在一新产品研制项目的仿真模型中,运用Excel中的“公式”表示项目完成时间的算法,用蒙特卡洛法处理工序时间的不确定性。仿真运行后,获得了项目完成时间的频数图和相关统计量,通过灵敏度分析确定各工序对项目完成时间变动的影响程度。     

镁熔体保护用气体发生器的燃烧数值模拟及优化

将炭粉与空气按比例预混后在栽流气体发生器中燃烧生成N2+CO2混合气体是经济制备镁熔体气体保护用栽流气体的一种新方法.对发生器中连续进行的空气-炭粉两相流燃烧进行了数值仿真分析,并采用正交方法对反应器直径、反应器高度、炭粉粒度和空气过剩系数这4个主要参数进行了优化,结果表明,当炭粉粒度为100～250μm、反应器高度为1000mm、反应器直径为200mm、空气过剩系数为1.05时,燃烧反应程度最理想.     

Three-Dimensional Model of the Spectral Emissivity of Light- Scattering Exhaust Plumes

A three-dimensional model of radiation of rocket exhaust plumes is given, which is based on the Monte Carlo simulation method. Two problems associated with the determination of spectral directional radiation of rocket exhaust plumes are treated, namely, the self-radiation of multiple plumes and the scattering of solar radiation incident on a single or multiple plume at an arbitrary angle by the condensed phase of the combustion products. The suggested model enables one to calculate the spectral emissivity with averaging of the rotational structure of molecular emission spectrum by diatomic and triatomic molecules of combustion products in the spectral range from 0.1 to 10 m. The results are given of calculations of the spectral and integral emissivity of light-scattering rocket exhaust plumes of various configurations, containing Al₂O₃ particles with an average radius of 2 m, in the infrared spectral region of 2-5 m.     

Evaluation of Measurement Uncertainty Based on the Propagation of Distributions Using Monte Carlo Simulation

The uncertainty associated with a value of some quantity is widely recognized throughout scientific disciplines as a quantitative measure of the reliability of that value. In addition, measurement uncertainty is increasingly seen as essential in quality assurance for industry. The Guide to the Expression of Uncertainty in Measurement (GUM) provides internationally agreed recommendations for the evaluation of uncertainties. This paper outlines the current situation of uncertainty evaluation in the context of international norms and arrangements. It describes the basic ideas and concepts that underlie the GUM and serves as a brief tutorial on methods for evaluating measurement uncertainty in a manner consistent with the GUM. It recommends an approach to evaluating measurement uncertainty based on the propagation of distributions using Monte Carlo simulation. An example is presented to illustrate Monte Carlo simulation.     

Monte-Carlo program MODEX: Simulation of point defect clustering during irradiation and subsequent annealing

A Monte Carlo program MODEX is presented, capable of simulating the defect clustering process during ion implantation and subsequent annealing. The program considers four different types of point defects, e.g. implanted ions, vacancies, self-interstitials and impurities, as mobile. Depending on the mobility of the point defect the diffusion equations are solved in the stationary or non-stationary form. The clustering process of point defects is described by a set of rate equations and is simulated through a number of elementary trapping and dissociation events. The use of the program is demonstrated in examples of helium implantation in molybdenum, vanadium and silicon and the simulation results are discussed in relation to the results of helium desorption experiments.     

Importance Sampling for Reliability Evaluation With Stochastic Simulation Models

Importance sampling has been used to improve the efficiency of simulations where the simulation output is uniquely determined, given a fixed input. We extend the theory of importance sampling to estimate a system’s reliability with stochastic simulations. Thanks to the advance of computing power, stochastic simulation models are employed in many applications to represent a complex system behavior. A stochastic simulation model generates stochastic outputs at the same input. Given a budget constraint on total simulation replications, we develop a new approach, which we call stochastic importance sampling, which efficiently uses stochastic simulations with unknown output distribution. Specifically, we derive the optimal importance sampling density and allocation procedure that minimize the variance of an estimator. Application to a computationally intensive aeroelastic wind turbine simulation demonstrates the benefits of the proposed approach. Supplementary materials for this article are available online.     

Solution of the First-Passage Problem by Advanced Monte Carlo Simulation Technique

A selective Monte Carlo simulation procedure for the evaluation of the reliability of nonlinear structures subjected to dynamic loading is presented. The proposed Russian Roulette and Splitting procedure allows generation of important low-probability samples in nonlinear dynamics. This procedure is quite efficient in comparison to the straightforward Monte Carlo simulation method and allows evaluation of the nonlinear stochastic response in a very low probability domain.