【作者】 井敏娜；

【导师】 袁宏林；

【作者基本信息】 西安建筑科技大学 ， 市政工程， 2008， 硕士

【摘要】 在水处理絮凝过程中,水中细小粒子相互碰撞、凝聚、破碎以及再凝聚过程是一个随机的过程,形成的絮凝体具有分形构造特征。研究絮凝体的成长过程以及内部构造,对提高水处理固液分离效果具有重要意义。论文借助Matlab工具,考虑了具有一定粒径分布的初始颗粒的絮凝体聚集情况,对絮凝体颗粒初始粒径呈正态分布、对数正态分布以及卡方分布的二维有限扩散凝聚(DLA)模型进行了研究,并分析计算了分形维数以及孔隙率。研究表明二维空间中的DLA模拟中,在初始粒子粒径为均一分布的情况下,模拟所得到的絮凝体具有典型的分形构造特征,分形维数随模拟絮凝体尺寸的增加其分形维数有减小的趋势,而其密度随尺寸的增加而呈幂指数减小规律,孔隙率则是呈幂指数增大规律。相比较而言,具有一定粒径分布的初始颗粒之间的聚集体,其分形维数随着粒子数目的增多也逐渐变小,与均一分布颗粒见凝聚的分形维数计算数值并无很大差异。在孔隙率分析方面,对数正态分布的孔隙率比较接近实际情况的,在0.3～0.5之间。在模拟过程中,考虑了Matlab工具使用过程出现伪随机数的情况。论文在程序中考虑了因伪随机数的产生而造成的模拟结果偏离情况,改进了以往程序的相关缺陷,提高了模拟结果的精度。更多还原

【Abstract】 Solid/liquid separation is of crucial importance in the water treatment process.As a traditional separation method,flocculation/coagulation followed by sedimentation prevails nowadays.To improve the separation efficiency,it is necessary to study the floc structure.In this paper,fractal simulation is used to investigate the floc structure and its characteristic parameters.Computer simulation is an effective method to study the floc structure.With the popular software Matlab 7.1 as the development platform,the simulation has been carried out based on DLA floc growing model,when the initial diameter of floc partical presents as a normal distribution,then analyzed the fractal dimensionality and porosity.In this paper,two-dimensional DLA model is studied on the morphological structure,the fractal dimensionality,and the porosity of the resulting flocs.Further more,the changes of the fractal dimensionality,porosity with respect to the floc characteristic length are studied.And two-dimensional image has been compared by their fractal dimensionality.Comparing to it,when the initial particle diameter presents as other distributions,the fractal dimensionality of floc diminishes obviously as the number of particles increases.It has not too much different with the initial particle diameter presents as a equal distribution.As the porosity,the value of logarithmic normal distribution is nearest the natural situation,and the value is between 0.3 to 0.5.When we simulate,we think of the influence of the pseudo-random number. Because of the pseudo-random number,the particle diameters are not stochastic,but orderliness.And then we innovate the program,improve the precision of outcome..更多还原