Investigation on flocculation phenomenon of cohesive fine-grained sediment has been a important part of sediment dynamics. During all of three dynamical factors (i.e., Brownian motion, flow shear and differential sett...Investigation on flocculation phenomenon of cohesive fine-grained sediment has been a important part of sediment dynamics. During all of three dynamical factors (i.e., Brownian motion, flow shear and differential settling) that have been verified to play important roles in promoting flocculation of cohesive sediment, the influence of flow shear on sediment flocculation has been paid great attention by many researchers (this flocculation pattern has been termed as “orthokinetic flocculation” in most of published literatures). Among many researches regarding orthokinetic flocculation, the dynamical equation developed by Smoluchowski in 1917 (we called it as Smoluchowski equation hereafter) has been widely adopted as an origin and basement for theoretically analyzing sediment flocculation under a shear flow. Meanwhile, many researchers have also pointed out the deficiencies of Smoluchowski equation (this is because the derivation of Smoluchowski equation was based on six different assumptions), and correspondingly have amended this equation from different aspects. In this paper, we attempt to summarize these results, hopefully providing the theoretical research of sediment orthokinetic flocculation with some references.展开更多
Simultaneous orthokinetic and perikinetic coagulations（SOPCs） are studied for small and large Peclet numbers（P e） using Brownian dynamics simulation.The results demonstrate that the contributions of the Brownian m...Simultaneous orthokinetic and perikinetic coagulations（SOPCs） are studied for small and large Peclet numbers（P e） using Brownian dynamics simulation.The results demonstrate that the contributions of the Brownian motion and the shear flow to the overall coagulation rate are basically not additive.At the early stages of coagulation with small Peclet numbers,the ratio of overall coagulation rate to the rate of pure perikinetic coagulation is proportional to P 1/2 e,while with high Peclet numbers,the ratio of overall coagulation rate to the rate of pure orthokinetic coagulation is proportional to P 1/2 e.Moreover,our results show that the aggregation rate generally changes with time for the SOPC,which is different from that for pure perikinetic and pure orthokinetic coagulations.By comparing the SOPC with pure perikinetic and pure orthokinetic coagulations,we show that the redistribution of particles due to Brownian motion can play a very important role in the SOPC.In addition,the effects of redistribution in the directions perpendicular and parallel to the shear flow direction are different.This perspective explains the behavior of coagulation due to the joint effects of the Brownian motion（perikinetic） and the fluid motion（orthokinetic）.展开更多
文摘Investigation on flocculation phenomenon of cohesive fine-grained sediment has been a important part of sediment dynamics. During all of three dynamical factors (i.e., Brownian motion, flow shear and differential settling) that have been verified to play important roles in promoting flocculation of cohesive sediment, the influence of flow shear on sediment flocculation has been paid great attention by many researchers (this flocculation pattern has been termed as “orthokinetic flocculation” in most of published literatures). Among many researches regarding orthokinetic flocculation, the dynamical equation developed by Smoluchowski in 1917 (we called it as Smoluchowski equation hereafter) has been widely adopted as an origin and basement for theoretically analyzing sediment flocculation under a shear flow. Meanwhile, many researchers have also pointed out the deficiencies of Smoluchowski equation (this is because the derivation of Smoluchowski equation was based on six different assumptions), and correspondingly have amended this equation from different aspects. In this paper, we attempt to summarize these results, hopefully providing the theoretical research of sediment orthokinetic flocculation with some references.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10972217,10932012 and 11032011)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX2-YW-L08)
文摘Simultaneous orthokinetic and perikinetic coagulations（SOPCs） are studied for small and large Peclet numbers（P e） using Brownian dynamics simulation.The results demonstrate that the contributions of the Brownian motion and the shear flow to the overall coagulation rate are basically not additive.At the early stages of coagulation with small Peclet numbers,the ratio of overall coagulation rate to the rate of pure perikinetic coagulation is proportional to P 1/2 e,while with high Peclet numbers,the ratio of overall coagulation rate to the rate of pure orthokinetic coagulation is proportional to P 1/2 e.Moreover,our results show that the aggregation rate generally changes with time for the SOPC,which is different from that for pure perikinetic and pure orthokinetic coagulations.By comparing the SOPC with pure perikinetic and pure orthokinetic coagulations,we show that the redistribution of particles due to Brownian motion can play a very important role in the SOPC.In addition,the effects of redistribution in the directions perpendicular and parallel to the shear flow direction are different.This perspective explains the behavior of coagulation due to the joint effects of the Brownian motion（perikinetic） and the fluid motion（orthokinetic）.
