水力旋流器分离过程的 Monte Carlo 模拟

根据颗粒在水力旋流器中的运动特点,提出了颗粒运动状态的交换构成三角马尔可夫链的观点,建立了水力旋流器分离过程的随机数学模型,并利用ＭｏｎｔｅＣａｒ┐ｌｏ方法进行了数值模拟,模拟程序中采用变参数设计,在输入一定的结构和工艺参数下,由计算机自动生成水力旋流器分离过程的级效率曲线,并给出总效率值;并计算了在不同容量下的模拟精度,结果表明样本容量越大,模拟精度越高     

Effect of Volume Fraction on Transient Structural Behavior of Aerosol Particles Using Off-Lattice Kinetic Monte Carlo Simulation

Fractal-like aggregates exhibit interesting properties that determine their physicochemical advantages, and thus, the control and prediction of aggregation is critical for many applications. An off-lattice kinetic Monte Carlo (KMC) simulation was performed to investigate the aggregate evolution from primary particles to three-dimensional fractal aggregates, at three different volume fractions. We have found that at low volume fraction, aggregation kinetics is slow, and aggregate morphology is widely open and stringy, with fractal dimension of (D_f) 1.8, in which the system is constantly preserved in the dilute regime. In denser volume fractions, however, the aggregation kinetics appears to be accelerated and aggregate morphology is more compact and less stringy due to the transition from dilute to dense regimes. Moreover, the volume fractions determine what kind of coagulation mechanism may occur to produce aggregates with different morphologies. At low volume fraction, coagulation is predominated by coagulation between aggregates in which the maximum probability of interpenetration event is only 18%. This suggests that aggregates at low volume fraction can maintain their self-similarity behavior. While at high volume fraction, coagulation is predominated by two subsequent coagulation mechanisms, namely, primary particle–aggregate and aggregate–aggregate interaction. The probability of interpenetration event increases up to 40%. In addition, the interpenetration process as well as the primary particle–aggregate coagulation, particularly in the dense regime, could produce superaggregates with a hybrid structure with a high fractal dimension at large size scales and a low fractal dimension at small scales. A detail mechanism for the formation of superaggregates was discussed.

Copyright © 2015 American Association for Aerosol Research     

Monte Carlo Simulation of Coalescence Processes in Oil Sands Slurries

Conditioning of an oil sand slurry is a critical step in the extraction of bitumen from oil sand ore. To model the conditioning process, a constant‐number Monte Carlo algorithm is used to simulate the mean‐field kinetics of coalescing bitumen drops and air bubbles. The coalescence rate of drops and bubbles is described by the model of Coulaloglou and Tavlarides (1977). Simulations yield results that are consistent with aerated bitumen drop sizes and conditioning times reported in the literature. The effects of turbulent energy, bitumen concentration, and initial bitumen drop size on the evolution of drop size distributions are investigated.     

含固体颗粒嵌段共聚高分子熔体微相结构的Monte Carlo模拟

采用改进的键长涨落空穴扩散算法,在立方格子上对含固体颗粒的两嵌段共聚高分子熔体的微相结构进行了Monte Carlo(MC)模拟. 重点考察了固体颗粒的大小、固体颗粒与嵌段共聚高分子的选择性作用、共聚高分子链的组成fA等因素对熔体微相结构的影响. 模拟结果表明,固体颗粒与高分子链节有选择性吸附作用时不利于形成层状相,而倾向于形成柱状或网络状结构;适当大小的惰性固体颗粒(与高分子链嵌段的长度相当)有利于系统形成层状相结构;无论系统是否含有固体颗粒,嵌段共聚高分子的对称程度增加都有利于形成层状结构.     

Kinetic Monte Carlo simulations of plasma-surface reactions on heterogeneous surfaces

Reactions of atoms and molecules on chamber walls in contact with low temperature plasmas are important in various technological applications. Plasma-surface interactions are complex and relatively poorly understood. Experiments performed over the last decade by several groups prove that interactions of reactive species with relevant plasma-facing materials are characterized by distributions of adsorption energy and reactivity. In this paper, we develop a kinetic Monte Carlo (KMC) model that can effectively handle chemical kinetics on such heterogenous surfaces. Using this model, we analyse published adsorption-desorption kinetics of chlorine molecules and recombination of oxygen atoms on rotating substrates as a test case for the KMC model.     

Atomistic Monte Carlo Simulation of Lipid Membranes

Biological membranes are complex assemblies of many different molecules of which analysis demands a variety of experimental and computational approaches. In this article, we explain challenges and advantages of atomistic Monte Carlo (MC) simulation of lipid membranes. We provide an introduction into the various move sets that are implemented in current MC methods for efficient conformational sampling of lipids and other molecules. In the second part, we demonstrate for a concrete example, how an atomistic local-move set can be implemented for MC simulations of phospholipid monomers and bilayer patches. We use our recently devised chain breakage/closure (CBC) local move set in the bond-/torsion angle space with the constant-bond-length approximation (CBLA) for the phospholipid dipalmitoylphosphatidylcholine (DPPC). We demonstrate rapid conformational equilibration for a single DPPC molecule, as assessed by calculation of molecular energies and entropies. We also show transition from a crystalline-like to a fluid DPPC bilayer by the CBC local-move MC method, as indicated by the electron density profile, head group orientation, area per lipid, and whole-lipid displacements. We discuss the potential of local-move MC methods in combination with molecular dynamics simulations, for example, for studying multi-component lipid membranes containing cholesterol.     

Reducing Statistical Noise and Extending the Size Spectrum by Applying Weighted Simulation Particles in Monte Carlo Simulation of Coagulation

The direct simulation Monte Carlo (DSMC) method is widely utilized to simulate microscopic dynamic processes in dispersed systems that give rise to the population balance equation. In conventional DSMC approaches, simulation particles are equally weighted, even for broad size distributions where number concentrations in different size intervals are significantly different. The resulting statistical noise and limited size spectrum severely restrict the application of these DSMC methods. This study proposes a new Monte Carlo (MC) method, the differentially weighted time-driven method, which captures the coagulation dynamics in dispersed systems with low noise and is simultaneously able to track the size distribution over the full size range. Key elements of this method include constructing a new jump Markov process based on a new coagulation rule for two differentially weighted simulation particles, and restricting the number of simulation particles in each size interval within prescribed bounds. The method is validated by using an ideal coagulation kernel with a known analytical solution and a real coagulation kernel for which an accurate solution can be found numerically (self-preserving particle size distribution in the continuum regime).     

Monte Carlo Simulation of the Neurofilament Brush

Grand canonical Monte Carlo (MC) simulations are performed to analyse conformations of projection domains in a neurofilament (NF) brush composed of three types of tails (L, M, and H) at different concentrations of added salt. The NF is modelled as a rigid, uniformly charged cylinder (backbone), surrounded by tethered, flexible polyampholytic chains with charge distributions and stoichiometry similar to those in natural NFs. We calculate the equilibrium trajectory for each projection; that is, the average distance of the amino acid residue from the surface of the backbone as a function of its ranking number. These trajectories demonstrate the tendency for projections to fold back and adopt loop-like conformations at moderate solution salinities. We also perform extended analysis of MC data to identify metastable states of the system, and demonstrate representative snapshots of tail conformations in major metastable states.     

钛白粉团聚体负载金属催化剂的脱硝活性

通过向工业钛白粉水相悬浮体系中添加十六烷基三甲基氯化铵作为改性助剂,制备出粒径均匀的球形二氧化钛团聚颗粒.通过傅里叶变换红外光谱、X-射线衍射、透射电子显微镜、BET比表面积测试法和扫描电子显微镜等分析手段表征了颗粒的结构形态及表面理化性质.团聚颗粒经煅烧后负载锰、钒等过渡金属氧化物制得脱硝催化剂,并对催化剂进行了脱硝活性评价.实验结果表明,与未改性的工业钛白粉相比,该颗粒物负载过渡金属氧化物时,煅烧前后均具有更大的比表面积、孔体积和孔径:与未改性钛白粉作载体相比,以该颗粒物为载体所制备的脱硝催化剂在催化剂适用温度窗口下,均表现出更好的脱硝活性.     

Sintering Behavior of Pt Metal Particles Supported on Silica-Coated Alumina Surface

The sintering behavior of Pt metal particles was studied by supporting them on silica-coated alumina. Silica coating was found to be effective for the retention of a large surface area of alumina even after calcination at elevated temperatures. Before sintering, the size of Pt metal particles on all the silica-coated aluminas, including the uncoated alumina, was identical, while the particle size was larger on silica than on alumina. After sintering the Pt catalyst at 1073 K, the particle size increased on uncoated alumina as well as on alumina coated with thicker silica layers, especially on the supports previously calcined at >1473 K. On the other hand, the size of Pt metal particles did not increase much on alumina coated with monolayer silica. The observed suppression of sintering of Pt metal particles resulted from the retention of a large surface area of alumina with a thinner silica layer. In the case of a thicker silica layer, although a large surface area was maintained after calcination at elevated temperatures, the existence of a bulk silica-like property of the support did not favor the suppression of sintering of Pt metal particles.     

基于Monte Carlo方法的聚苯硫醚聚合反应动力学建模

根据聚苯硫醚（PPS）聚合机理及过程分析并通过合理假设,提出了基于Monte Carlo方法的PPS聚合反应动力学模型。利用文献数据对模型参数进行了拟合回归,结果表明动力学模型计算值与相应的实验数据符合良好,并且模型外推预测与相同条件的实验接近,两者偏差小于2%;通过模型对反应物配比的影响进行模拟计算,结果与文献值相符合。最后,通过建立工业PPS聚合反应器模型对工业生产过程进行了模拟计算,结果表明PPS生产过程宜采用多釜串联的方式。相关研究结果可对PPS聚合反应动力学建模和工业过程的设计和优化提供理论依据。     

方阱流体汽液共存性质的Monte Carlo模拟

本文应用Ｇｉｂｂｓ系综ＭｏｎｔｅＣａｒｌｏ方法，对纯方阱流体的汽液共存性质进行了模拟计算。得到汽液两相的饱和密度，并根据模拟数据外推以估测临界点。由此得到的对比临界温度和密度分别为Ｔｃ＝ＲＴｃ／ε＝１．２７，ρｃ＝ρｃσ３＝０．３１，与Ａｌｄｅｒ等人的分子动力学模拟结果吻合。此外，还计算了六个温度下两相的构型能、压力和径向分布函数。     

基于蒙特卡洛模拟法的钻井经济评价

对石油钻井进行投资决策时,要考虑各方面的风险因素和投资成本,为了降低石油钻井中的投资风险,在钻井之前就能预测到可能的成本,可以采用蒙特卡洛模拟法对钻井投资进行风险预估。本文通过对不同的地层分别运用蒙特卡洛模拟法,在不同的地层建立蒙特卡洛模的模型,并应用matlab模拟软件处理数据解释分析结果,最终得出钻井费用的预测值和误差,为投资决策提供依据。     

水分子在高岭土中吸附特性的蒙特卡罗模拟研究(英文)

利用巨正则系综蒙特卡罗方法模拟高岭土对水分子的吸附特性。通过数值计算和实验分析,表征不同温度、压强及阳离子交换条件下高岭土的吸附机理。研究表明数值分析与实验结果吻合较好。温度和压强对高岭土的吸附性质有着明显影响。铝置换硅使得高岭土的活性有了大幅度提高。此外,不同阳离子的引入,不仅能平衡体系的电价,还能不同程度地改变高岭土的吸附特性。     

Kinetic Monte Carlo simulation of ZrO2 coating deposited by EB-PVD

Kinetic Monte Carlo (KMC) simulations have been used for electron beam physical vapor deposition (EB-PVD) of ZrO₂ coatings, with the critical potential function fitted by full first-principles calculations in the framework of density functional theory, emphasizing the effect of critical processing parameters, for example, the substrate temperature (600–1150 K), deposition rate (0.03–7.5 μm/min), and initial kinetic energy (0–0.5 eV). Here, the interaction between ZrO₂ particles is described by coarse grain (CG) model with a numerical non-bonded potential developed by multi-iterative boltzmann inversion (multi-IBI). Overall, the calculated energy barrier by the nudged elastic band (NEB) shows the internal diffusion (3.29–4.80 eV) requires more energy than the surface diffusion (2.90–3.42 eV), because of fewer surrounding particles in the latter. Moreover, the energy barrier of Line Jump is smaller than that of Schwoebel Jump, contributing to the columnar grains rather than a dense coating. Of importance, the simulated morphologies of ZrO₂ coatings are well consistent to experiments, with a weaker effect from the substrate temperature, initial kinetic energy to deposition rate. Furthermore, the porosity can be effectively reduced by increasing the temperature and initial kinetic energy, however, with a slight increase when increasing the deposition rate.     

Original Monte Carlo Methodology Devoted to the Study of Sintering Processes

A Monte Carlo methodology different from others based on the Potts model has been developed to solve capillary-driven mass transport involved in the sintering process. The addition of a cohesive energy term to the energetic model enables quantification of the stress gradients within grains, as well as the induced mass fluxes. The study of two-particle sintering involving volume diffusion has been chosen as a first example. The morphological evolution of the two-particle system to a single particle is followed. Real-time-dependent neck growth and shrinkage rates are defined. The rheological behavior of the particles induced by the Monte Carlo procedure is discussed.     

高分子蠕动Monte Carlo模拟应用研究

Monte Carlo方法与常规的数值计算相比:算法比较简单,可以模拟系统的变化过程,对于观察高分子链段的运动有独到之处。Delphi7.0具有编程语言简单,系统功能强大等特点,受到研究者的推崇。本文将二者结合开发了一种用于模拟高分子蠕动的分析软件,该软件使用旋转异构态构造的链动力学模型,通过改变体系条件参数,例如:聚合物的分子量大小、环境温度等,研究高分子链段的蠕动行为。通过与淀粉的玻璃化转变温度与其分子量关系的实验研究结果进行比较,发现二者具有同样的趋势,这表明用该软件进行模拟计算是有效的。     

蒙特卡罗仿真在安全联锁系统可靠性评估中的应用

在对比几种安全联锁系统(SIS)可靠性分析方法特点的基础上,通过算例演示,提出蒙特卡罗仿真在SIS定量评估中应用的可行性,以期能更好地解决SIS可靠性定量评估.     

Kinetic Monte Carlo Simulations of the Loading Dependence of Diffusion in Zeolites

Kinetic Monte Carlo (KMC) simulations are used to model diffusion of molecules in zeolites. A variety of loading dependences of the Maxwell‐Stefan diffusivity, ?_i, can be realized by allowing the jump frequencies, ν, of molecules to be influenced by the presence of neighboring molecules. Neighboring molecules are assumed to reduce or increase the activation energy for diffusion by δE and the jump frequencies ν are altered by a factor f = exp(δE/RT) for each neighboring molecule. By appropriate choice of ν and f the loading dependence of ?_i can be made to match those obtained from either Molecular Dynamics (MD) simulations or experiment. The major advantage of the KMC simulation strategy is that considerably less computer power is required than for the corresponding MD simulations. Furthermore, KMC simulations allow mixture diffusion to be probed without additional parameter tuning. The KMC simulations also validate the applicability of the quasi‐chemical theory of Reed and Ehrlich (Surf. Sci. 1981 , 105, 603–628) for describing the loading dependence of ?_i.     

Kinetic Monte Carlo simulation of kinetically limited copper electrocrystallization on an atomically even surface

A two-dimensional cross-sectional kinetic Monte Carlo (2DCS-KMC) model has been developed to simulate the electrodeposition of single crystal copper on an atomically even surface. The evolution of the microstructure has been visualized and is discussed here. The cluster density, average cluster size, variance of the cluster size and average aspect ratio were obtained from the simulations. The entire growth history from the deposition of the first atom until an equivalent of 100 monolayers has been deposited has been reconstructed. The model has proven capable of capturing the effects of deposition parameters including concentration of Cu²⁺, temperature and applied electrode potential on growth history. These parameters have significant effects on the microstructure in terms of variance of the cluster height, width or size. However, the peak cluster density seems independent of the deposition parameters. The concentration of Cu²⁺ and potential have significant effects, while temperature has very little effect on the rate of change of cluster density and variance of cluster size.