This paper investigates the incipient motion of sediment particles under non-uniform flow in river and laboratory. In rivers, the non-uniform flow is often observed due to the presence of various bed forms. Threshold condition has been examined by using the Shields diagram based on the uniform flow assumption, however, this approach can be led to fallacious results for non-uniform flows where the effect of pressure gradient is significant due to bed forms. This study investigates the chronological order of incipient motion of the particles, the average threshold velocity (Ucr ), and Shields parameter for non-uniform flows. River data collection with gravel is used for investigating the incipient motion of surface layer of river bed and the laboratory data collection is considered studying the incipient motion of sub-surface layer of river. Both river and laboratory data collections are conducted in the presence of bed forms. Results reveal that the Shields diagram underestimates the particle incipient motion under accelerating and decelerating flows for the both case of laboratory and river. In both weak and general motion in the laboratory, the values of the critical Shields parameter are located below the Shields diagram, showing no particle motion. Our analysis shows that the incipient motion in river is affected by the presence of bed forms, river width changes, and flow non-uniformity conditions. The results show that in the accelerating flow (the bed form exit with a negative slope), the incipient motion is greater than the decelerating flow (the bed form entrance with a positive slope).
Aquatic vegetation plays a critical role in aquatic environments and provides various valuable services. To characterize vegetation, vegetation density and flexibility are usually used as parameters, but aquatic vegetation found in nature may have a non-uniform distribution of density in the vertical direction. Studies have shown that this non-uniformity could impact the flow structure and flow resistance. With the aim of studying the effect of vertical variation of submerged vegetation density on the flow resistance and bulk flow characteristics, the hydrodynamics of three types of wooden model vegetation elements were compared in the laboratory. Vegetation models had the same density but different vertical distributions of density. All other influential parameters were kept constant so that any differences in the flow structure and the flow resistance would be attributable to the distribution of density in the vertical direction. The results show that the vertical distribution of submerged vegetation density impacts the flow field, bed shear stress, and flow resistance. There was a 41% difference in the value of the drag coefficient produced by the models. The distance between the bed and the geometrical center of vegetation elements was introduced as a parameter to quantify the effect of the vertical distribution of vegetation. There is a direct relation between this parameter with both the drag and Manning’s coefficients. The findings of this can study help researchers and practitioners use relevant vegetation parameters.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.