The sediment particles play a huge role in shaping the bed load transport.In this research,240 water-tunnel experiments are carried out to investigate the incipient velocity of the observation particles in two particl...The sediment particles play a huge role in shaping the bed load transport.In this research,240 water-tunnel experiments are carried out to investigate the incipient velocity of the observation particles in two particle arrangements.To accurately predict the incipient velocity of the observation particles,the equation is conceived by the rolling instability mechanism.The incipient velocity equations and experimental data are used to analyze the trend of dispersive pressure and the effect of arrangement position on velocity.We find that it is appropriate to choose the coefficient of drag as 0.261 and the coefficient of lift as 0.198 for the incipient velocity equation of spherical particles on the hemispherical bed surface.Furthermore,the dispersive pressure is closely related to the flow state,particle size,and particle arrangement,which leads to the incipient velocity of the observation particle being at a minimum when the interference particle angle is 45°.Finally,the particle spacing and the projected area changed with the arrangements,directly affecting the incipient velocity of the observed particle.The analysis of four aspects for the coefficients,dispersive pressure,different particle spacing,and projected area will facilitate the prediction of particle incipient velocity,especially on hemispherical beds.展开更多
The flow resistance in rivers is an old and partly unsolved problem. In this study, the bed surface fractal dimension(BSFD) is used to describe the bed morphology, and combined with the bed roughness, a general mode...The flow resistance in rivers is an old and partly unsolved problem. In this study, the bed surface fractal dimension(BSFD) is used to describe the bed morphology, and combined with the bed roughness, a general model experiment is developed. The results show that there is a positive relationship between the BSFD and the bed roughness, which can be further applied to estimate the roughness changes in rivers. These findings will also guide further studies of the mobile-bed flow resistance.展开更多
Aquatic vegetation plays an important role in the flow structure of open channels and thus changes the fate and the transport of sediment. This article proposes a three-dimensional turbulence model by introducing vege...Aquatic vegetation plays an important role in the flow structure of open channels and thus changes the fate and the transport of sediment. This article proposes a three-dimensional turbulence model by introducing vegetation density and drag force into the control equations of water flow in the presence of vegetation. The model was used to calculate the impacts of submerged vegetation on the vertical profiles of longitudinal flow velocities, the changes of the depth-averaged flow velocities in a compound channel with emergent vegetation in the floodplain, the removal of suspended sediment from the channels by emergent vegetation, and the bed changes around and in a vegetated island. Numerical investigations show that aquatic vegetation retards flow in the vegetation zone, reduces the sediment transport capacity, and contributes to erosion on both sides of the vegetated island. Calculated results agree well with experimental results.展开更多
基金financially supported by the National Key Research and Development Program of China(Grant No.2021YFB2601100)the National Natural Science Foundation of China(Grant No.51839002,51979014 and 52271257)+1 种基金the Natural Science Foundation of Hunan Province(Grant No.2022JJ10047)the Hunan Provincial Innovation Foundation for Postgraduate(Grant No.CX20220909).
文摘The sediment particles play a huge role in shaping the bed load transport.In this research,240 water-tunnel experiments are carried out to investigate the incipient velocity of the observation particles in two particle arrangements.To accurately predict the incipient velocity of the observation particles,the equation is conceived by the rolling instability mechanism.The incipient velocity equations and experimental data are used to analyze the trend of dispersive pressure and the effect of arrangement position on velocity.We find that it is appropriate to choose the coefficient of drag as 0.261 and the coefficient of lift as 0.198 for the incipient velocity equation of spherical particles on the hemispherical bed surface.Furthermore,the dispersive pressure is closely related to the flow state,particle size,and particle arrangement,which leads to the incipient velocity of the observation particle being at a minimum when the interference particle angle is 45°.Finally,the particle spacing and the projected area changed with the arrangements,directly affecting the incipient velocity of the observed particle.The analysis of four aspects for the coefficients,dispersive pressure,different particle spacing,and projected area will facilitate the prediction of particle incipient velocity,especially on hemispherical beds.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51579014,51339001 and 91647117)the National Key Research and Development of China(Grant No.2016YFC0402301-01)
文摘The flow resistance in rivers is an old and partly unsolved problem. In this study, the bed surface fractal dimension(BSFD) is used to describe the bed morphology, and combined with the bed roughness, a general model experiment is developed. The results show that there is a positive relationship between the BSFD and the bed roughness, which can be further applied to estimate the roughness changes in rivers. These findings will also guide further studies of the mobile-bed flow resistance.
基金the National Basic Research Program of China (973 Program, Grant No. 2006CB403302)the National Natural Science Foundation of China (GrantNo.50779006)
文摘Aquatic vegetation plays an important role in the flow structure of open channels and thus changes the fate and the transport of sediment. This article proposes a three-dimensional turbulence model by introducing vegetation density and drag force into the control equations of water flow in the presence of vegetation. The model was used to calculate the impacts of submerged vegetation on the vertical profiles of longitudinal flow velocities, the changes of the depth-averaged flow velocities in a compound channel with emergent vegetation in the floodplain, the removal of suspended sediment from the channels by emergent vegetation, and the bed changes around and in a vegetated island. Numerical investigations show that aquatic vegetation retards flow in the vegetation zone, reduces the sediment transport capacity, and contributes to erosion on both sides of the vegetated island. Calculated results agree well with experimental results.