A series of experiments was carried out in a large symmetric compound channel composed of a rough main channel and rough floodplains to investigate the resistance characteristics of inbank and overbank flows. The effe...A series of experiments was carried out in a large symmetric compound channel composed of a rough main channel and rough floodplains to investigate the resistance characteristics of inbank and overbank flows. The effective Manning, Darcy-Weisbach, Chezy coefficients and the relative Nikuradse roughness height were analyzed. Many different representative methods for predicting the composite roughness were systematically summarized. Besides the measured data, a vast number of laboratory data and field data for compound channels were collected and used to check the validity of these methods for different subsection divisions including the vertical, horizontal, diagonal and bisectional divisions. The computation showed that these methods resulted in big errors in assessing the composite roughness in compound channels, and the reasons were analyzed in detail. The error magnitude is related to the subsection divisions.展开更多
This paper presents a further study of the Manning and Darcy-Weisbach resistance coefficients, as they play a significant role in assessing the cross-sectional mean velocity, conveyance capacity and determining the la...This paper presents a further study of the Manning and Darcy-Weisbach resistance coefficients, as they play a significant role in assessing the cross-sectional mean velocity, conveyance capacity and determining the lateral distribution of depth mean velocity and local boundary shear stress in compound channels. The relationships between the local, zonal and overall resistance coefficients, and a wide range of geometries and different roughness between the main channel and the flood plain are established by analyzing a vast amount of experimental data from a British Science and Engineering Research Council Flood Channel Facility （SERC-FCF）. And the experimental results also show that the overall Darcy-Weisbach resistance coefficient for a compound channel is the function of Reynolds number, but the function relationship is different from that for a single channel. By comparing and analyzing the conventional methods with the experimental data to predict composite roughness in compound channels, it is found that these methods are not suitable for compound channels. Moreover, the reason why the conventional methods cannot assess correctly the conveyance capacity of compound channels is also analyzed in this paper.展开更多
The governing equation of the discharge per unit width, derived from the flow continuity equation and the momentum equation in the vegetated compound chan- nel, is established. The analytical solution to the discharge...The governing equation of the discharge per unit width, derived from the flow continuity equation and the momentum equation in the vegetated compound chan- nel, is established. The analytical solution to the discharge per unit width is presented, including the effects of bed friction, lateral momentum transfer, drag force, and secondary flows. A simple＇ but available numerical integral method, i.e., the compound trapezoidM formula, is used to calculate the approximate solutions of the sub-area discharge and the total discharge. A comparison with the published experimental data from the U. K. Flood Channel Facility （UK-FCF） demonstrates that this model is capable of predicting not only the stage-discharge curve but also the sub-area discharge in the vegetated com- pound channel. The effects of the two crucial parameters, i.e., the divided number of the integral interval and the secondary flow coefficient, on the total discharge are discussed and analyzed.展开更多
A simple but applicable analytical model is presented to predict the lat- eral distribution of the depth-averaged velocity in meandering compound channels. The governing equation with curvilinear coordinates is derive...A simple but applicable analytical model is presented to predict the lat- eral distribution of the depth-averaged velocity in meandering compound channels. The governing equation with curvilinear coordinates is derived from the momentum equation and the flow continuity equation under the condition of quasi-uniform flow. A series of experiments are conducted in a large-scale meandering compound channel. Based on the experimental data, a magnitude analysis is carried out for the governing equation, and two lower-order shear stress terms are ignored. Four groups of experimental data from different sources are used to verify the predictive capability of this model, and good predictions are obtained. Finally, the determination of the velocity parameter and the limitation of this model are discussed.展开更多
The lateral distributions of depth-averaged velocity in open compound channels with emerged and submerged vegetated floodplains were analyzed based on the analytical solution of the depth-integrated Reynolds-Averaged ...The lateral distributions of depth-averaged velocity in open compound channels with emerged and submerged vegetated floodplains were analyzed based on the analytical solution of the depth-integrated Reynolds-Averaged Navier-Stokes equation with a term to account for the effects of vegetation.The three cases considered for open channels were two-stage rectangular channel with emerged vegetated floodplain,rectangular channel with submerged vegetated corner,and two-stage rectangular channel with submerged vegetated floodplain,respectively.To predict the depth-averaged velocity with submerged vegetated floodplains,we proposed a new method based on a two-layer approach where flow above and through the vegetation layer was described separately.Moreover,further experiments in the two-stage rectangular channel with submerged vegetated floodplain were carried out to verify the results.The analytical solutions of the cases indicated that the corresponding analytical depth-averaged velocity distributions agree well with the simulated and experimental prediction.The analytical solutions of the cases with theoretical foundation and without programming calculation were reasonable and applicable,which were more convenient than numerical simulations.The analytical solutions provided a way for future researches to solve the problems of submerged vegetation and discontinuous phenomenon of depth-averaged velocity at the stage point for compound channels.Understanding the hydraulics of flow in compound channels with vegetated floodplains is very important for supporting the management of fluvial processes.展开更多
The experiments were conducted in compound channels with vegetated floodplains for investigating the influence of vegetation types on the characteristics of secondary flows. In terms of the streamwise and transverse v...The experiments were conducted in compound channels with vegetated floodplains for investigating the influence of vegetation types on the characteristics of secondary flows. In terms of the streamwise and transverse velocities and the depth-averaged velocity, the secondary flow coefficient, M, is proposed, with good physical meanings, and it may characterize the rotational direction and the intensity of the secondary currents. The experimental results show that, for the cases without vegetation and with grass, the rotational directions of the secondary flows are all antielockwise while for the cases with shrubs, they are all changed to the clockwise direction in the whole cross-section. However, when trees are planted, the secondary flows rotate in the anticlockwise direction in the main channel and in the clockwise direction on the floodplain. In addition, for all cases, the intensities of the secondary currents on the floodplain are stronger than those in the main channel.展开更多
Results of research into a compound channel having width ratio （a） in excess of 11 are presented in the form of boun-dary shear distributions across the compound cross section. New relationship is derived between th...Results of research into a compound channel having width ratio （a） in excess of 11 are presented in the form of boun-dary shear distributions across the compound cross section. New relationship is derived between the percentage of shear carried by the flood plains （%S fp ） and the percentage of area occupied by the flood plains （%Afp ） . The equation so derived is taken as the basis to develop a new methodology to predict the stage discharge relationship specifically for wide compound channels using Darcy＇s friction factor （ f ） for the main channel and flood plain regions. The methodology also is used for compound channels with smaller width ratios by applying the appropriate relation for %S fp derived earlier by different researchers and seems to work well. Next, as a corollary to the methodology, separate formulae are proposed to estimate flow distribution in main channel and flood plain regions. The proposed method and its corollary are tested for their validity against well-published small-scale data series of pre-vious researchers along with some large-scale data series from EPSRC-FCF （A-Series） compound channel experiments and very good agreement is observed between the measured values and predicted values for total flow as well as zonal distribution of flow. The methodology is also applied to some compound river section data published in literature and is found to serve well the purpose of predicting flow in real world application. This new method gives the least RMS value of error for discharge prediction compared with some other well-known methods used for estimating stage-discharge relation in compound channels by considering all data sets.展开更多
Stage-discharge curves are particularly important in river basin management. For a compound channel, the stage-discharge curve is often difficult to be extrapolated to yield estimates of level for a given frequency of...Stage-discharge curves are particularly important in river basin management. For a compound channel, the stage-discharge curve is often difficult to be extrapolated to yield estimates of level for a given frequency of flow. By analyzing a large number of experimental data from Science and Engineering Research Council Flood Channel Facility (SERC-FCF) and applying system dynamics method, the authors established system dynamics model of conveyance capacity when rivers flow in an overbank mode, spilling onto the adjoining flood plain. The model was applied to a compound channel. And the corresponding simulated results are shown to attain high accurcy.展开更多
The momentum transfer coefficient is an important parameter for determining the apparent shear stress at the vertical interface between the main channel and its associated flood plains,the cross-sectional mean velocit...The momentum transfer coefficient is an important parameter for determining the apparent shear stress at the vertical interface between the main channel and its associated flood plains,the cross-sectional mean velocity and the discharge capacity in compound channels. In this article,under the Boussinesq assumption and through analyzing the characteristics of velocity distribution in the interacting region between the main channel and its associated flood plain,the expression of momentum transfer coefficient was theoretically derived. On the basis of force balance,the expression of vertical apparent shear stress was obtained. By applying the experimental data from the British Engineering Research Council Flood Channel Facility (SERC-FCF),the relationship between the momentum transfer coefficient with the relative depth and the ratio of the flood plain width to the main channel width,was established,And hence the conveyance capacity in compound channels was calculated with Liu and Dong’s method. The computed results show that the momentum transfer coefficient relationship obtained is viable.展开更多
Experimental results were compared with the computed results obtained from the nine most well-known methods for computation of discharge in a compound channel. The results demonstrate a high accuracy of the divided ch...Experimental results were compared with the computed results obtained from the nine most well-known methods for computation of discharge in a compound channel. The results demonstrate a high accuracy of the divided channel method with the horizontal division lines, while the length of division line is included within the calculation of the wetted perimeter. In addition, as relative depth increases, the results of the all methods converge to each other and also in case of steeper slopes in lower relative depths, more agreements between different calculated methods and experimental results were observed. Furthermore, the results show the effects of the maximum momentum transfer on the horizontal interface between the main channel and flood plains, while further angular distance from the horizontal interface toward the vertical interface between main channel and flood plains causes gradual decrease of momentum transfer effects.展开更多
Shear stress distribution prediction in open channels is of utmost importance in hydraulic structural engineering as it directly affects the design of stable channels.In this study,at first,a series of experimental te...Shear stress distribution prediction in open channels is of utmost importance in hydraulic structural engineering as it directly affects the design of stable channels.In this study,at first,a series of experimental tests were conducted to assess the shear stress distribution in prismatic compound channels.The shear stress values around the whole wetted perimeter were measured in the compound channel with different floodplain widths also in different flow depths in subcritical and supercritical conditions.A set of,data mining and machine learning algorithms including Random Forest(RF),M5P,Random Committee,KStar and Additive Regression implemented on attained data to predict the shear stress distribution in the compound channel.Results indicated among these five models;RF method indicated the most precise results with the highest R2 value of 0.9.Finally,the most powerful data mining method which studied in this research compared with two well-known analytical models of Shiono and Knight method(SKM)and Shannon method to acquire the proposed model functioning in predicting the shear stress distribution.The results showed that the RF model has the best prediction performance compared to SKM and Shannon models.展开更多
Hydraulic calculation of steady uniform flows in trapezoidal compound open channels is studied. Based on the force balance of water in each sub-section, the average velocities of the main channel, side slope, and floo...Hydraulic calculation of steady uniform flows in trapezoidal compound open channels is studied. Based on the force balance of water in each sub-section, the average velocities of the main channel, side slope, and floodplain are derived. The lateral momentum exchanges between the sub-sections are expressed by using the apparent shear stress. To verify the model, seven groups of UK Flood Channel Facility （UK-FCF） measured data with a relative water depth between the floodplain and the main channel varying from 0.057 to 0.4 are used for comparison. The result shows that the calculated velocity is larger than the measured data when the relative water depth is small, while it is less than or close to the measured value in the case of a larger relative water depth. The influence of the apparent shear stress on the calculation of velocity on the floodplain is not obvious, while it is much greater on the main channel. The three-stage model is compared with Liu’s two-stage model, showing that the former can give a better prediction for a three-stage trapezoidal compound channel. Finally, the apparent shear stress is calculated and compared with the measured data. The result shows that the chosen values of the momentum transfer coefficients are appropriate.展开更多
Instead of a large number of measurements of the streamwise velocity, a simple method is proposed to estimate the bed shear stress in smooth and vegetated compound channels, based on the Darcy-Weisbach equation. This ...Instead of a large number of measurements of the streamwise velocity, a simple method is proposed to estimate the bed shear stress in smooth and vegetated compound channels, based on the Darcy-Weisbach equation. This method contains a dimension- less parameter Ai, to represent the relationship between the bed shear stress and the velocity close to the channel bed （Ub）, which is determined in each divided domain. This method is verified in two smooth compound channels with different geometries, and in one compound channel with emergent floodplain vegetation. The comparison of predicted and measured bed shear stresses indicates the good predictive capability of this method, particularly in the mixing region. This method is further discussed for a channel with submerged vegetation. Once the values of Ai in the main channel and the floodplain are determined, this method is a practical tool展开更多
The distribution of velocity is one of the basic issues in river dynamics.Based on the experimental data measured by ADV in the flume of State Key Hydraulics Laboratory (SKHL),this paper analyzed the ver- tical distri...The distribution of velocity is one of the basic issues in river dynamics.Based on the experimental data measured by ADV in the flume of State Key Hydraulics Laboratory (SKHL),this paper analyzed the ver- tical distribution of point velocity and the varying law of turbulence intensity in straight mobile compound chan- nel with an asymmetric floodplain.Above certain relative height,the streamwise point velocity follows the loga- rithmic distribution.Below the location,the velocity varies linearly approxim...展开更多
This paper presents a two-dimensional analytical solution for compound channel flows with vegetated floodplains. The depth-integrated N-S equation is used for analyzing the steady uniform flow. The effects of the vege...This paper presents a two-dimensional analytical solution for compound channel flows with vegetated floodplains. The depth-integrated N-S equation is used for analyzing the steady uniform flow. The effects of the vegetation are considered as the drag force item. The secondary currents are also taken into account in the governing equations, and the preliminary estimation of the secondary current intensity coefficient K is discussed. The predicted results for the straight channels and the apex cross-section of meandering channels agree well with experimental data, which shows that the analytical model presented here can be applied to predict the flow in compound channels with vegetated floodplains.展开更多
The theory of an eddy viscosity model is applied to the study of the flow in a compound channel which is partially vegetated. The governing equation is constituted by analyzing the longitudinal forces acting on the un...The theory of an eddy viscosity model is applied to the study of the flow in a compound channel which is partially vegetated. The governing equation is constituted by analyzing the longitudinal forces acting on the unit volume where the effect of the vegetation on the flow is considered as a drag force item, The compound channel is divided into 3 sub-regions in the transverse direction, and the coefficients in every region＇s differential equations were solved simultaneously. Thus, the analytical solution of the transverse distribution of the depth-averaged velocity for uniform flow in a partially vegetated compound channel was obtained. The results can be used to predict the transverse distribution of bed shear stress, which has an important effect on the transportation of sediment. By comparing the analytical results with the measured data, the analytical solution in this paper is shown to be sufficiently accurate to predict most hydraulic features for engineering design purposes.展开更多
The RNG κ-ε model considering the buoyancy effect, which is solved by the hybrid finite analytic method, is used to simulate the mixture of the horizontal round thermal buoyant jet in compound open channel flow. The...The RNG κ-ε model considering the buoyancy effect, which is solved by the hybrid finite analytic method, is used to simulate the mixture of the horizontal round thermal buoyant jet in compound open channel flow. The mixing features near the spout and flowing characteristic of the secondary currents are studied by numerical simulation. Meanwhile, （1） the distribution of the measured isovels for stream-wise velocity, （2） secondary currents, （3） the distribution of the measured isovels for temperature of typical cross-section near the spout, were obtained by the three-dimensional Micro ADV and the temperature measuring device. Compared with experimental data, the RNG κ-ε model based on buoyancy effect can preferably simulate the jet which performs the bifurcation phenomenon, jet reattachment （Conada effect） and beach secondary currents phenomenon with the effect of ambient flow, buoyancy, and secondary currents of compound section and so on.展开更多
This paper presents the results of an experimental study on the influences of floodplain impermeable groynes on flow structure, velocity, and water depth around the groyne（s）. A wooden symmetrical compound channel w...This paper presents the results of an experimental study on the influences of floodplain impermeable groynes on flow structure, velocity, and water depth around the groyne（s）. A wooden symmetrical compound channel was used. Groyne models with three different groyne relative lengths, 0.5, 0.75, and 1.0, were used on one floodplain with single and series arrangements. Analysis of the experimental results using the measured flow velocity and water depth values showed that flow structure, velocity, and water depth mainly depend on groyne relative length and the relative distance between series groynes. The flow velocity at the main channel centerline increased by about 40%, 60%, and 85%, and in other parts on the horizontal plane at the floodplain mid-water, depth by about 75%, 125%, and 175% of its original value in eases of one-side floodplain groyne（s） with relative lengths of 0.5, 0.75, and 1.0, respectively. The effective distance between two groynes in series arrangement ranges from 3 to 4 times the groyne length. Using an impermeable groyne with a large relative length in river floodplains increases the generation of eddy and roller zones downstream of the groyne, leading to more scouring and deposition. To avoid that, the groyne relative length must be kept below half the floodplain width,展开更多
Compound section is referred to a section the surface of which is made of several sub-sections with different flow characteristics. The difference in the hydraulic and geometry characteristics causes a complexity in f...Compound section is referred to a section the surface of which is made of several sub-sections with different flow characteristics. The difference in the hydraulic and geometry characteristics causes a complexity in flow hydraulic and creates an interaction between the main channel and floodplains, resulting in an apparent shear stress and a transverse momentum transfer. The amount of such a stress plays an important role in many river engineering measures [1]. Due to the flow complexity, the common approximate analytical methods are not enough to identify the flow profile. The FLOW3D Software with its great features in three-dimensional analysis of flow field is used as a tool to investigate the shear stress in a direct symmetrical compound rectangular channel. After the simulation of models, it is found that an increase in the relative width and relative depth parameters decreases the percentage of apparent shear stress and an increase in the relative roughness causes it to be increased [2].展开更多
Compound open channel flows appear in most natural rivers are of great importance in river management and flood control.In this study,large eddy simulations were carried out to simulate the compound open channel flows...Compound open channel flows appear in most natural rivers are of great importance in river management and flood control.In this study,large eddy simulations were carried out to simulate the compound open channel flows with four different depth ratios(hr=0.10,0.25,0.50,and 0.75).The main flow velocity,secondary flow,Reynolds stress,and bed shear stress were obtained from numerical simulations.The depth-averaged stream wise momentum equation was used to quantify the lateral momentum exchange between the main channel and floodplain.The instantaneous coherent structures were presented by the Q criterion method.The impact of hr on flow structure and turbulence charac-teristics was analyzed.The results showed that with the increase of hr,the high velocity area in the main channel shifted to the floodplain,and the dip phenomenon became more obvious;the Reynolds stress largely contributed to the lateral momentum exchange within the flows near the side walls of floodplain;and the vortex structures were found to significantly increase in the floodplain region.展开更多
基金The project supported by the Major State Basic ResearchDevelopment Program of China(973 Program)(2003CB415202)+1 种基金the National Natural Science Foundation of China(50579040,50579041)The English text was polished by Yunming Chen.
文摘A series of experiments was carried out in a large symmetric compound channel composed of a rough main channel and rough floodplains to investigate the resistance characteristics of inbank and overbank flows. The effective Manning, Darcy-Weisbach, Chezy coefficients and the relative Nikuradse roughness height were analyzed. Many different representative methods for predicting the composite roughness were systematically summarized. Besides the measured data, a vast number of laboratory data and field data for compound channels were collected and used to check the validity of these methods for different subsection divisions including the vertical, horizontal, diagonal and bisectional divisions. The computation showed that these methods resulted in big errors in assessing the composite roughness in compound channels, and the reasons were analyzed in detail. The error magnitude is related to the subsection divisions.
基金The project supported by the National Natural Science Foundation of China(50279024)the National Key Basic Research and Development Program of China(973 Program)(2003CB415202)the Specialized Research Fund for the Doctoral Program of Higher Education(2
文摘This paper presents a further study of the Manning and Darcy-Weisbach resistance coefficients, as they play a significant role in assessing the cross-sectional mean velocity, conveyance capacity and determining the lateral distribution of depth mean velocity and local boundary shear stress in compound channels. The relationships between the local, zonal and overall resistance coefficients, and a wide range of geometries and different roughness between the main channel and the flood plain are established by analyzing a vast amount of experimental data from a British Science and Engineering Research Council Flood Channel Facility （SERC-FCF）. And the experimental results also show that the overall Darcy-Weisbach resistance coefficient for a compound channel is the function of Reynolds number, but the function relationship is different from that for a single channel. By comparing and analyzing the conventional methods with the experimental data to predict composite roughness in compound channels, it is found that these methods are not suitable for compound channels. Moreover, the reason why the conventional methods cannot assess correctly the conveyance capacity of compound channels is also analyzed in this paper.
基金Project supported by the National Natural Science Foundation of China(Nos.51279117 and 11072161)the Program for New Century Excellent Talents in University of China(No.NCET-130393)the National Science and Technology Ministry of China(No.2012BAB05B02)
文摘The governing equation of the discharge per unit width, derived from the flow continuity equation and the momentum equation in the vegetated compound chan- nel, is established. The analytical solution to the discharge per unit width is presented, including the effects of bed friction, lateral momentum transfer, drag force, and secondary flows. A simple＇ but available numerical integral method, i.e., the compound trapezoidM formula, is used to calculate the approximate solutions of the sub-area discharge and the total discharge. A comparison with the published experimental data from the U. K. Flood Channel Facility （UK-FCF） demonstrates that this model is capable of predicting not only the stage-discharge curve but also the sub-area discharge in the vegetated com- pound channel. The effects of the two crucial parameters, i.e., the divided number of the integral interval and the secondary flow coefficient, on the total discharge are discussed and analyzed.
基金Project supported by the National Natural Science Foundation of China(Nos.11171238,51279117,and 11072161)the Program for New Century Excellent Talents in University of China(No.NCET-13-0393)the National Science and Technology Ministry of China(No.2012BAB05B02)
文摘A simple but applicable analytical model is presented to predict the lat- eral distribution of the depth-averaged velocity in meandering compound channels. The governing equation with curvilinear coordinates is derived from the momentum equation and the flow continuity equation under the condition of quasi-uniform flow. A series of experiments are conducted in a large-scale meandering compound channel. Based on the experimental data, a magnitude analysis is carried out for the governing equation, and two lower-order shear stress terms are ignored. Four groups of experimental data from different sources are used to verify the predictive capability of this model, and good predictions are obtained. Finally, the determination of the velocity parameter and the limitation of this model are discussed.
基金Under the auspices of National Basic Research Program of China(No.2011CB403303)National Key Research and Development Program of China(No.2016YFC0402408-5)National Natural Science Foundation of China(No.51179181,40788001)
文摘The lateral distributions of depth-averaged velocity in open compound channels with emerged and submerged vegetated floodplains were analyzed based on the analytical solution of the depth-integrated Reynolds-Averaged Navier-Stokes equation with a term to account for the effects of vegetation.The three cases considered for open channels were two-stage rectangular channel with emerged vegetated floodplain,rectangular channel with submerged vegetated corner,and two-stage rectangular channel with submerged vegetated floodplain,respectively.To predict the depth-averaged velocity with submerged vegetated floodplains,we proposed a new method based on a two-layer approach where flow above and through the vegetation layer was described separately.Moreover,further experiments in the two-stage rectangular channel with submerged vegetated floodplain were carried out to verify the results.The analytical solutions of the cases indicated that the corresponding analytical depth-averaged velocity distributions agree well with the simulated and experimental prediction.The analytical solutions of the cases with theoretical foundation and without programming calculation were reasonable and applicable,which were more convenient than numerical simulations.The analytical solutions provided a way for future researches to solve the problems of submerged vegetation and discontinuous phenomenon of depth-averaged velocity at the stage point for compound channels.Understanding the hydraulics of flow in compound channels with vegetated floodplains is very important for supporting the management of fluvial processes.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11072161, 50709021)the National Science and Technology Ministry (Grant No.2012BAB05B02)the National Excellent Doctoral Dissertation of China (Grant No. 201051)
文摘The experiments were conducted in compound channels with vegetated floodplains for investigating the influence of vegetation types on the characteristics of secondary flows. In terms of the streamwise and transverse velocities and the depth-averaged velocity, the secondary flow coefficient, M, is proposed, with good physical meanings, and it may characterize the rotational direction and the intensity of the secondary currents. The experimental results show that, for the cases without vegetation and with grass, the rotational directions of the secondary flows are all antielockwise while for the cases with shrubs, they are all changed to the clockwise direction in the whole cross-section. However, when trees are planted, the secondary flows rotate in the anticlockwise direction in the main channel and in the clockwise direction on the floodplain. In addition, for all cases, the intensities of the secondary currents on the floodplain are stronger than those in the main channel.
基金support received by the second author from DST India(Grant No.SR/S3/MERC/066/2008)
文摘Results of research into a compound channel having width ratio （a） in excess of 11 are presented in the form of boun-dary shear distributions across the compound cross section. New relationship is derived between the percentage of shear carried by the flood plains （%S fp ） and the percentage of area occupied by the flood plains （%Afp ） . The equation so derived is taken as the basis to develop a new methodology to predict the stage discharge relationship specifically for wide compound channels using Darcy＇s friction factor （ f ） for the main channel and flood plain regions. The methodology also is used for compound channels with smaller width ratios by applying the appropriate relation for %S fp derived earlier by different researchers and seems to work well. Next, as a corollary to the methodology, separate formulae are proposed to estimate flow distribution in main channel and flood plain regions. The proposed method and its corollary are tested for their validity against well-published small-scale data series of pre-vious researchers along with some large-scale data series from EPSRC-FCF （A-Series） compound channel experiments and very good agreement is observed between the measured values and predicted values for total flow as well as zonal distribution of flow. The methodology is also applied to some compound river section data published in literature and is found to serve well the purpose of predicting flow in real world application. This new method gives the least RMS value of error for discharge prediction compared with some other well-known methods used for estimating stage-discharge relation in compound channels by considering all data sets.
文摘Stage-discharge curves are particularly important in river basin management. For a compound channel, the stage-discharge curve is often difficult to be extrapolated to yield estimates of level for a given frequency of flow. By analyzing a large number of experimental data from Science and Engineering Research Council Flood Channel Facility (SERC-FCF) and applying system dynamics method, the authors established system dynamics model of conveyance capacity when rivers flow in an overbank mode, spilling onto the adjoining flood plain. The model was applied to a compound channel. And the corresponding simulated results are shown to attain high accurcy.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 50579040, 50579041).
文摘The momentum transfer coefficient is an important parameter for determining the apparent shear stress at the vertical interface between the main channel and its associated flood plains,the cross-sectional mean velocity and the discharge capacity in compound channels. In this article,under the Boussinesq assumption and through analyzing the characteristics of velocity distribution in the interacting region between the main channel and its associated flood plain,the expression of momentum transfer coefficient was theoretically derived. On the basis of force balance,the expression of vertical apparent shear stress was obtained. By applying the experimental data from the British Engineering Research Council Flood Channel Facility (SERC-FCF),the relationship between the momentum transfer coefficient with the relative depth and the ratio of the flood plain width to the main channel width,was established,And hence the conveyance capacity in compound channels was calculated with Liu and Dong’s method. The computed results show that the momentum transfer coefficient relationship obtained is viable.
文摘Experimental results were compared with the computed results obtained from the nine most well-known methods for computation of discharge in a compound channel. The results demonstrate a high accuracy of the divided channel method with the horizontal division lines, while the length of division line is included within the calculation of the wetted perimeter. In addition, as relative depth increases, the results of the all methods converge to each other and also in case of steeper slopes in lower relative depths, more agreements between different calculated methods and experimental results were observed. Furthermore, the results show the effects of the maximum momentum transfer on the horizontal interface between the main channel and flood plains, while further angular distance from the horizontal interface toward the vertical interface between main channel and flood plains causes gradual decrease of momentum transfer effects.
文摘Shear stress distribution prediction in open channels is of utmost importance in hydraulic structural engineering as it directly affects the design of stable channels.In this study,at first,a series of experimental tests were conducted to assess the shear stress distribution in prismatic compound channels.The shear stress values around the whole wetted perimeter were measured in the compound channel with different floodplain widths also in different flow depths in subcritical and supercritical conditions.A set of,data mining and machine learning algorithms including Random Forest(RF),M5P,Random Committee,KStar and Additive Regression implemented on attained data to predict the shear stress distribution in the compound channel.Results indicated among these five models;RF method indicated the most precise results with the highest R2 value of 0.9.Finally,the most powerful data mining method which studied in this research compared with two well-known analytical models of Shiono and Knight method(SKM)and Shannon method to acquire the proposed model functioning in predicting the shear stress distribution.The results showed that the RF model has the best prediction performance compared to SKM and Shannon models.
基金Project supported by the National Natural Science Foundation of China (Nos. 50709025 and50979078)the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry
文摘Hydraulic calculation of steady uniform flows in trapezoidal compound open channels is studied. Based on the force balance of water in each sub-section, the average velocities of the main channel, side slope, and floodplain are derived. The lateral momentum exchanges between the sub-sections are expressed by using the apparent shear stress. To verify the model, seven groups of UK Flood Channel Facility （UK-FCF） measured data with a relative water depth between the floodplain and the main channel varying from 0.057 to 0.4 are used for comparison. The result shows that the calculated velocity is larger than the measured data when the relative water depth is small, while it is less than or close to the measured value in the case of a larger relative water depth. The influence of the apparent shear stress on the calculation of velocity on the floodplain is not obvious, while it is much greater on the main channel. The three-stage model is compared with Liu’s two-stage model, showing that the former can give a better prediction for a three-stage trapezoidal compound channel. Finally, the apparent shear stress is calculated and compared with the measured data. The result shows that the chosen values of the momentum transfer coefficients are appropriate.
基金Project supported by the National Natural Science Foun-dation of China(Grant Nos.11171238,51539007 and 51479128)
文摘Instead of a large number of measurements of the streamwise velocity, a simple method is proposed to estimate the bed shear stress in smooth and vegetated compound channels, based on the Darcy-Weisbach equation. This method contains a dimension- less parameter Ai, to represent the relationship between the bed shear stress and the velocity close to the channel bed （Ub）, which is determined in each divided domain. This method is verified in two smooth compound channels with different geometries, and in one compound channel with emergent floodplain vegetation. The comparison of predicted and measured bed shear stresses indicates the good predictive capability of this method, particularly in the mixing region. This method is further discussed for a channel with submerged vegetation. Once the values of Ai in the main channel and the floodplain are determined, this method is a practical tool
基金Supported by Key Project of Chinese.Ministry of Education (03134)
文摘The distribution of velocity is one of the basic issues in river dynamics.Based on the experimental data measured by ADV in the flume of State Key Hydraulics Laboratory (SKHL),this paper analyzed the ver- tical distribution of point velocity and the varying law of turbulence intensity in straight mobile compound chan- nel with an asymmetric floodplain.Above certain relative height,the streamwise point velocity follows the loga- rithmic distribution.Below the location,the velocity varies linearly approxim...
基金supported by the National Natural Science Foundation of China (Nos. 50679061, 50709025,and 50749031)
文摘This paper presents a two-dimensional analytical solution for compound channel flows with vegetated floodplains. The depth-integrated N-S equation is used for analyzing the steady uniform flow. The effects of the vegetation are considered as the drag force item. The secondary currents are also taken into account in the governing equations, and the preliminary estimation of the secondary current intensity coefficient K is discussed. The predicted results for the straight channels and the apex cross-section of meandering channels agree well with experimental data, which shows that the analytical model presented here can be applied to predict the flow in compound channels with vegetated floodplains.
基金the National Natural Science Foundation of China(Nos.50679061,50709025and50749031)
文摘The theory of an eddy viscosity model is applied to the study of the flow in a compound channel which is partially vegetated. The governing equation is constituted by analyzing the longitudinal forces acting on the unit volume where the effect of the vegetation on the flow is considered as a drag force item, The compound channel is divided into 3 sub-regions in the transverse direction, and the coefficients in every region＇s differential equations were solved simultaneously. Thus, the analytical solution of the transverse distribution of the depth-averaged velocity for uniform flow in a partially vegetated compound channel was obtained. The results can be used to predict the transverse distribution of bed shear stress, which has an important effect on the transportation of sediment. By comparing the analytical results with the measured data, the analytical solution in this paper is shown to be sufficiently accurate to predict most hydraulic features for engineering design purposes.
基金Project supported by the National Natural Science Foundation of China (Nos.50479038 and 50679061)the Open Foundation of State Key Laboratory of Coastal and Offshore Engineering,Dalian University of Technology (No.LP0601)
文摘The RNG κ-ε model considering the buoyancy effect, which is solved by the hybrid finite analytic method, is used to simulate the mixture of the horizontal round thermal buoyant jet in compound open channel flow. The mixing features near the spout and flowing characteristic of the secondary currents are studied by numerical simulation. Meanwhile, （1） the distribution of the measured isovels for stream-wise velocity, （2） secondary currents, （3） the distribution of the measured isovels for temperature of typical cross-section near the spout, were obtained by the three-dimensional Micro ADV and the temperature measuring device. Compared with experimental data, the RNG κ-ε model based on buoyancy effect can preferably simulate the jet which performs the bifurcation phenomenon, jet reattachment （Conada effect） and beach secondary currents phenomenon with the effect of ambient flow, buoyancy, and secondary currents of compound section and so on.
文摘This paper presents the results of an experimental study on the influences of floodplain impermeable groynes on flow structure, velocity, and water depth around the groyne（s）. A wooden symmetrical compound channel was used. Groyne models with three different groyne relative lengths, 0.5, 0.75, and 1.0, were used on one floodplain with single and series arrangements. Analysis of the experimental results using the measured flow velocity and water depth values showed that flow structure, velocity, and water depth mainly depend on groyne relative length and the relative distance between series groynes. The flow velocity at the main channel centerline increased by about 40%, 60%, and 85%, and in other parts on the horizontal plane at the floodplain mid-water, depth by about 75%, 125%, and 175% of its original value in eases of one-side floodplain groyne（s） with relative lengths of 0.5, 0.75, and 1.0, respectively. The effective distance between two groynes in series arrangement ranges from 3 to 4 times the groyne length. Using an impermeable groyne with a large relative length in river floodplains increases the generation of eddy and roller zones downstream of the groyne, leading to more scouring and deposition. To avoid that, the groyne relative length must be kept below half the floodplain width,
文摘Compound section is referred to a section the surface of which is made of several sub-sections with different flow characteristics. The difference in the hydraulic and geometry characteristics causes a complexity in flow hydraulic and creates an interaction between the main channel and floodplains, resulting in an apparent shear stress and a transverse momentum transfer. The amount of such a stress plays an important role in many river engineering measures [1]. Due to the flow complexity, the common approximate analytical methods are not enough to identify the flow profile. The FLOW3D Software with its great features in three-dimensional analysis of flow field is used as a tool to investigate the shear stress in a direct symmetrical compound rectangular channel. After the simulation of models, it is found that an increase in the relative width and relative depth parameters decreases the percentage of apparent shear stress and an increase in the relative roughness causes it to be increased [2].
基金supported by the Fundamental Research Funds for the Central Universities(Grants No.B200202116 and B200204044)the National Natural Science Foundation of China(Grant No.51879086)the 111 Project from the Minstry of Education and State Administration of Foreign Expert Affairs of China(Grant No.B17015).
文摘Compound open channel flows appear in most natural rivers are of great importance in river management and flood control.In this study,large eddy simulations were carried out to simulate the compound open channel flows with four different depth ratios(hr=0.10,0.25,0.50,and 0.75).The main flow velocity,secondary flow,Reynolds stress,and bed shear stress were obtained from numerical simulations.The depth-averaged stream wise momentum equation was used to quantify the lateral momentum exchange between the main channel and floodplain.The instantaneous coherent structures were presented by the Q criterion method.The impact of hr on flow structure and turbulence charac-teristics was analyzed.The results showed that with the increase of hr,the high velocity area in the main channel shifted to the floodplain,and the dip phenomenon became more obvious;the Reynolds stress largely contributed to the lateral momentum exchange within the flows near the side walls of floodplain;and the vortex structures were found to significantly increase in the floodplain region.
