연구홍보포털

논문 초록 (Abstract)

Cohesive sediment has different characteristics compared to non-cohesive sediment. The density and size of a cohesives ediment aggregate (a so-called, floc) continuously changes through the flocculation process. The variation of floc size and densi ty can cause a change of volumetric concentration under the condition o f constant mass concentration. This study investigates how the volume tric concentration is affected by different conditions such as flow velocity,water depth, and sediment suspension. A previou sly verified, one-dimensional vertical numerical model is utilized here . The flocculation process is also considered by floc in the gr owth type flocculation model. Idealized conditions are assumed in t his study for the numerical experiments. The simulation results show th at the volumetric concentration profile ofcohesive sediment is different from the Rouse profile. The volumetric concentration decrease s near the bed showing the elevated maximum in the cases of both curren t and oscillatory flow. The density and size of floc show the minimum and the maximum values near the elevation of volumetric concent ration maximum, respectively. This study also shows that the flow veloc ity and the critical shear stress have significant effects on the e levated maximum of volumetric concentration. As mechanisms ofthe eleva ted maximum, the strong turbulence intensity and increased mass concentr ation are considered because they causethe enhanced flocculation process. This study uses numerical experiments. To the best of our kn owledge, no laboratory orfield experiments on the elevated maximum have been carried out until now. It is of great necessity to cond uct well-controlled laboratory experiments in the near futu re.