The main factors influencing soil erosion include the net rain excess, the water depth, the velocity, the shear stress of overland flows, and the erosion-resisting capacity of soil. The laws of these factors varying w...The main factors influencing soil erosion include the net rain excess, the water depth, the velocity, the shear stress of overland flows, and the erosion-resisting capacity of soil. The laws of these factors varying with the slope gradient were investigated by using the kinematic wave theory. Furthermore, the critical slope gradient of erosion was driven. The analysis shows that the critical slope gradient of soil erosion is dependent on grain size, soil bulk density, surface roughness, runoff length, net rain excess, and the friction coefficient of soil, etc. The critical slope gradient has been estimated theoretically with its range between 41.5 degrees similar to 50 degrees.展开更多
This paper presents an experimental investigation of the circulation of the horseshoe vortex system within the equilibrium scour hole at a circular pier, with the data measured by an acoustic Doppler velocimeter （ADV...This paper presents an experimental investigation of the circulation of the horseshoe vortex system within the equilibrium scour hole at a circular pier, with the data measured by an acoustic Doppler velocimeter （ADV）. Velocity vector plots and vorticity contours of the flow field on the upstream plane of symmetry （y = 0 cm） and on the planes ：e3 cm away from the plane of symmetry Cv = ~3 cm） are presented. The vorticity and circulation of the horseshoe vortices were determined using the forward difference technique and Stokes theorem, respectively. The results show that the magnitudes of circulations are similar on the planes y = 3 cm and y = -3 cm, which are less than those on the plane y = 0 cm. The circulation decreases with the increase of flow shallowness, and increases with the densimetric Froude number. It also increases with the pier Reynolds number at a constant densimetric Froude number, or at a constant flow shallowness. The relative vortex strength （dimensionless circulation） decreases with the increase of the pier Reynolds number. Some empirical equations are proposed based on the results. The predicted circulation values with these equations match the measured data, which indicates that these equations can be used to estimate the circulation in future studies.展开更多
The drop structure will fail as a result of local scoring downstream.This paper discusses the influence of a drop structures' upstream slope to local scour.Empirical equations of the scour hole were developed by l...The drop structure will fail as a result of local scoring downstream.This paper discusses the influence of a drop structures' upstream slope to local scour.Empirical equations of the scour hole were developed by laboratory experiment,theoretical assumptions,and regression analysis.These equations include the maximum scour depth and length during the scouring period,the maximum equilibrium scour depth and length,and the unit width scour rate.The four channel slopes(0%,2%,4%,and 6%) before the drop structure has been included in the analysis.A series of laboratory experiments were conducted to obtain 48 groups of experiments and 419 scour hole profiles during the scouring period.The material used in the scour section is uniform non-cohesive and with a median diameter of d50 = 0.5 mm.The results have been used to develop empirical equations via regression analysis to determine the coefficients of theoretical equations.The high correlation coefficient indicates that the equations developed in this study are suitable for verifying the characteristics of a scour hole at drop structure in the sloped channel.The semi-empirical equation is more accurate than the empirical equation.Compared to a horizontal channel,a sloped channel tends to cause a greater equilibriummaximum scour length,shorter equilibrium maximum scour depth,and faster unit-wide scour rate.展开更多
This paper discusses some characteristics of the phenomenon of ripping up the riverbed, which appears in the Yellow River, reviews the previous researches, and develops a formula for predicting scouring intensity.
文摘The main factors influencing soil erosion include the net rain excess, the water depth, the velocity, the shear stress of overland flows, and the erosion-resisting capacity of soil. The laws of these factors varying with the slope gradient were investigated by using the kinematic wave theory. Furthermore, the critical slope gradient of erosion was driven. The analysis shows that the critical slope gradient of soil erosion is dependent on grain size, soil bulk density, surface roughness, runoff length, net rain excess, and the friction coefficient of soil, etc. The critical slope gradient has been estimated theoretically with its range between 41.5 degrees similar to 50 degrees.
文摘This paper presents an experimental investigation of the circulation of the horseshoe vortex system within the equilibrium scour hole at a circular pier, with the data measured by an acoustic Doppler velocimeter （ADV）. Velocity vector plots and vorticity contours of the flow field on the upstream plane of symmetry （y = 0 cm） and on the planes ：e3 cm away from the plane of symmetry Cv = ~3 cm） are presented. The vorticity and circulation of the horseshoe vortices were determined using the forward difference technique and Stokes theorem, respectively. The results show that the magnitudes of circulations are similar on the planes y = 3 cm and y = -3 cm, which are less than those on the plane y = 0 cm. The circulation decreases with the increase of flow shallowness, and increases with the densimetric Froude number. It also increases with the pier Reynolds number at a constant densimetric Froude number, or at a constant flow shallowness. The relative vortex strength （dimensionless circulation） decreases with the increase of the pier Reynolds number. Some empirical equations are proposed based on the results. The predicted circulation values with these equations match the measured data, which indicates that these equations can be used to estimate the circulation in future studies.
基金the research support from Ministry of Science and Technology of Chinese Taipei,with the project no.104-2313-B-343-001
文摘The drop structure will fail as a result of local scoring downstream.This paper discusses the influence of a drop structures' upstream slope to local scour.Empirical equations of the scour hole were developed by laboratory experiment,theoretical assumptions,and regression analysis.These equations include the maximum scour depth and length during the scouring period,the maximum equilibrium scour depth and length,and the unit width scour rate.The four channel slopes(0%,2%,4%,and 6%) before the drop structure has been included in the analysis.A series of laboratory experiments were conducted to obtain 48 groups of experiments and 419 scour hole profiles during the scouring period.The material used in the scour section is uniform non-cohesive and with a median diameter of d50 = 0.5 mm.The results have been used to develop empirical equations via regression analysis to determine the coefficients of theoretical equations.The high correlation coefficient indicates that the equations developed in this study are suitable for verifying the characteristics of a scour hole at drop structure in the sloped channel.The semi-empirical equation is more accurate than the empirical equation.Compared to a horizontal channel,a sloped channel tends to cause a greater equilibriummaximum scour length,shorter equilibrium maximum scour depth,and faster unit-wide scour rate.
文摘This paper discusses some characteristics of the phenomenon of ripping up the riverbed, which appears in the Yellow River, reviews the previous researches, and develops a formula for predicting scouring intensity.
