Simulation research on monomer agglomeration of nonmetallic inclusions in steel with a diffusion limited aggregation model

The monomer agglomeration of nonmetallic inclusions was simulated with a diffusion limited aggregation （DLA） model of the fractal theory. The simulation study with a random two-dimensional diffusion was carried out. The results indicate that the DLA model can be used for the simulation of agglomeration behavior of the cluster-type inclusions. The morphology of clusters was observed with SEM and compared with the simulated agglomerates. The modelling procedure of the DLA model is applicable for the agglomeration process. The uncertainty of agglomeration process and the persuasive average agglomerative ratio was analyzed. The factors about the agglomerative ratio with the collision path distance and the size of particles or seed were discussed. The adherence of the nonmetallic inclusions on the dam, the weir and the walls of a tundish, and the absorption of inclusions by stopper or nozzle were also discussed.

Investigation into mechanisms and kinetics of asphaltene aggregation in toluene/n-hexane mixtures

Determining the rate of asphaltene particle growth is one of the main problems in modeling of asphaltene precipitation and deposition.In this paper,the kinetics of asphaltene aggregation under different precipitant concentrations have been studied.The image processing method was performed on the digital photographs that were taken by a microscope as a function of time to determine the asphaltene aggregation growth mechanisms.The results of image processing by MATLAB software revealed that the growth of asphaltene aggregates is strongly a function of time.Different regions could be recognized during asphaltene particle growth including reaction-and diffusion-limited aggregation followed by reaching the maximum asphaltene aggregate size and start of asphaltene settling and the final equilibrium.Modeling has been carried out to predict the growth of asphaltene particle size based on the fractal theory.General equations have been developed for kinetics of asphaltene aggregation for reaction-limited aggregation and diffusion-limited aggregation.The maximum size of asphaltene aggregates and settling time were modeled by using force balance,acting on asphaltene particles.Results of modeling show a good agreement between laboratory measurements and model calculations.

分形生长DLA模型在粘性指进模拟中的应用探讨

粘性指进现象,普遍存在于油气开采的众多驱替过程中,是多相渗流的重要特征之一。以扩散限制凝聚模型(简称DLA模型)为代表的分形生长模型的出现,为研究粘性指进现象带来了新的生机。文章介绍了DLA模型的模拟的基本思路、数学背景和粘性指进实验模拟装置,讨论了DLA模型在粘性指进模拟中应用的依据和主要方法,指出了粘性指进的实验与计算机模拟研究中存在的问题及其发展方向,对DLA模型在粘性指进中的进一步应用具有较强的参考意义。

荷电粒子对分形结构的影响

在有限扩散凝聚（ＤＬＡ）模型基础上，讨论了部分粒子荷电对分形结构的影响。在一定荷电几率范围内（荷电几率Ｐ≤３０％），分形结构的维数随着粒子荷电几率的增加而增大，且分形结构的形状亦同时发生变化。给出了粒子荷电使分维增大的初步解释。

分形聚集生长性质研究

本文在分形生长DLA模型和有限步扩散反应置限聚集模型的基础上 ,考虑粒子扩散置限和粒子 扩散有限步数的影响的同时 ,引入扩散粒子与种子或聚集集团粒子相遇时的聚集反应概率 p ,种子或聚集粒子对 次近邻位置扩散粒子的吸引作用引起扩散粒子向各方向的行走概率变化 (行走偏向概率 )wp ,研究粒子随机行走 的分形聚集生长性质 .通过计算机模拟得到一系列的分形聚集生长图形 ,计算其相应的分形维数 .结果表明 :在粒 子浓度较小时 ,分形生长为DLA生长 ,随粒子向外扩散置限范围dr ,反应概率 p和行走偏向概率wp的增大 ,聚 集体的分形维数df也随之增大 ;在粒子浓度较大时 ,一般聚集体呈密集结构 。

疏水冷面霜晶生长的有限扩散凝聚模型

为了深入了解霜晶的动态生长过程,以有限扩散凝聚模型为基础建立了疏水冷面霜晶二维生长模型.通过在表面上设置不同冰珠数量来模拟冷面不同疏水性能,无涂层金属表面则布满冰珠;采用粒子在网格节点上随机移动来描述水蒸气分子的运动,粒子沿各方向移动的概率相同.数值结果表明,霜晶动态生长的可视化结果与实验图像在形态上保持一致;树枝状霜晶具有分形特征,相应的分形维数为1.44～1.78,与实验值相近.疏水冷面霜晶生长缓慢且分布稀疏;采用疏水效果不好的冷面的结霜情况与金属表面相似.

RDX的分形生长探索

采用溶剂挥发法,在玻璃基底上制备出具有分形结构特征的RDX晶体,利用扫描电子显微镜(SEM)表征样品的形貌,初步研究了RDX溶液浓度及表面活性剂十六烷基三甲基氯化铵对RDX分形结构的影响,并对RDX分形结构的形成机理进行初步分析。结果表明,借助玻璃基底上的非平衡结晶过程,可实现RDX的多种分形生长;当RDX浓度较低时形成具有明显主干与分枝的分形结构,浓度较高时形成无规分杈的分形结构;表面活性剂对RDX分形结构影响较大。

气溶胶凝聚粒子的分形模拟

分析了大气气溶胶特性的研究意义及气溶胶粒子的分形特征。基于DLA模型模拟了不同原始微粒数目凝聚生长的分形气溶胶凝聚粒子,并将模拟结果与实验观察结果相比较,验证了模拟结果的可靠性。给出了凝聚粒子分形维数随原始微粒数目的变化曲线,结果显示,原始微粒数目直接影响凝聚粒子的分形维数。

Numerical Modeling of Dendrite Growth in Al Alloys

Dendritic grains are the most often observed microstructure in metals and alloys. In the past decade, more and more attention has been paid to the modeling and simulation of dendritic microstructures. This paper describes a modified diffusion-limited aggregation model to simulate the complex shape of the dendrite grains during metal solidification. The fractal model was used to simulate equiaxed dendrite growth. The fractal dimensions of simulated Al alloy structures range from 1.63-1.88 which compares well with the experimentally-measured fractal dimension of 1.85; therefore, the model accurately predicts not only the dendritic structure morphology, but also the fractal dimension of the dendrite structure formed during solidification.

模拟区域土地利用变化的多主体模型及其在鄱阳湖区的应用(英文)

在较大区域内,城市用地扩张和农村土地利用发展一般同步进行。为了能够正确理解这类区域内土地利用/土地覆被变化的动力机制,本研究开发了一个基于多主体系统的土地利用模型。模型将鄱阳湖区视为一个典型区域,利用有限扩散聚合算法模拟城市主体的行为,采用基于涌现理论的主体模型模拟农村土地利用。农村子模型包括多种类型的主体和环境影响层,其中最重要的是农户主体,农户主体可以根据自身条件和周围的环境影响参数确定下一步土地利用的决策,政府主体则通过实施不同的政策对土地利用进行宏观控制。我们根据农户总收入和外出务工人员比例将农户主体分为6类,每种类型的农户主体遵循不同的决策规则。结果表明,本模型的模拟结果与鄱阳湖区1985 – 2005年的土地利用/土地覆被变化趋势高度相符。尤其重要的是,模拟结果充分表明农户主体的土地利用决策与国家政策紧密相关。这表明本研究建立的基于多主体的土地利用模型是一种评估政府土地管理政策效果的有效手段。