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Study on the Fractal Dynamic Simulation Technology of Floc in Water

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Tutor: NanJun
School: Harbin Institute of Technology
Course: Municipal Engineering
Keywords: flocculation,simulation,fractal structure,3d-DLA,3d-DLCA
CLC: TU991.22
Type: Master's thesis
Year:  2012
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Flocculation is an important part of the water treatment process. The sizedistribution, structure and strength of the floc has a direct impact on the final effectof flocculation as well as the operation and the cost of the follow-up process. Howto observe and evaluate the change of floc in flocculation process, how to analyzethe impact of different control parameters on the flocculation, is an important issuein municipal engineering. Flocculation process has many influencing factors. Dueto the constraints of the experiments and the testing methods, we still don¡¯t have aclear acquaintance of the flocculation mechanism.A variety of floc growth models have been proposed in order to describe theflocs growth process. By comparing different models, in this article, we select theDiffusion-Limited Aggregation model (DLA) and the Diffusion-Limited ClusterAggregation model (DLCA). According to the two models, we establish a three-dimensional simulation of floc growth process in matlab platform. During thesimulation, first, we establish a virtual floc evaluation method, and using themethod we evaluate the shape of flocs, including the radius, fractal dimension,porosity, etc. Under a certain simulation condition, we can research the changes ofthe flocs during the growth process. By contacting the control parameters in themodel and influencing factors of the actual flocculation process, we can change thecontrol parameters in the model and then we can analyze the influence of differentfactors in actual flocculation process. In the three-dimensional Diffusion-LimitedAggregation model, the control variables include the number of the releasedparticles, the initial release radius and the probability of adhesion after collision. Inthe three-dimensional Diffusion-Limited Cluster Aggregation model, the controlvariables include the initial distribution of the particles, the initial number of theparticles, the movement of the particles and the clusters.By comparing the three-dimensional Diffusion-Limited Aggregation modeland the three-dimensional Diffusion-Limited Cluster Aggregation model andanalyzing the differences between them, we can see that the three-dimensionalDiffusion-Limited Cluster Aggregation model is superior to the three-dimensionalDiffusion-Limited Aggregation model. After analyzing the two-dimensionalprojection of the three-dimensional floc images formed in the three-dimensional Diffusion-Limited Cluster Aggregation model, we verify the reasonableness oftaking pictures in the actual flocculation process. Under different conditions in theactual flocculation, we can find a law of the distribution of small size floc and theparticle size fractal dimension. By comparing the law we find in actual flocculationand the conclusion we get in the three-dimensional Diffusion-Limited ClusterAggregation model, we prove that the three-dimensional Diffusion-Limited ClusterAggregation model is reasonable and improve the model based on this.
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