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| 1 | Influence of bank vegetation and gravel bed on velocity and Reynolds stress distributions显示文摘This paper presents the results of a laboratory flume experimental study on the interaction of bank vegetation and gravel bed on the flow velocity(primarily on the location of the maximum velocity,Umax) and the Reynolds stress distributions. The results reveal that the dip of the maximum velocity below the water surface is up to 35% of flow depth and the difference between Umax and the velocity at the water surface is considerable in the presence of vegetation on the walls. The zone of the log-law varies from y/h=2 up to 15 percent of flow depth and it does not depend on distance from the wall. Deviation of the velocity profile in the outer layer over a gravel bed with vegetation cover on the walls is much larger than the case of flow over a gravel bed without vegetation cover on the walls. The presence of vegetation on the walls changes uniform flow to non-uniform flow. This fact can be explained by considering the nonlinear Reynolds stress distribution and location of maximum velocity in each profile at different distances across the flume. The Reynolds stress distributions at the distance 0.02 m from the wall have negative values and away from the wall,they change the sign taking positive values with specific convex form with apex in higher location. Average of von Karman constant κ for this study is equal to 0.16. Based on κ=0.16,the methods of Clauser and the Reynolds stress are compatible for determination of shear velocity. | Hossein AFZALIMEHR Subhasish DEY | 2009 | International Journal of Sediment Research2009，24，2： | 14 |
| 2 | Reduction of local scour around bridge pier groups using collars显示文摘In this paper reduction of scour around group of two and three piers using circular collar has been carried out for the case of clear-water flow over uniform sediment. The efficiency of collars, with different sizes and spaces between piers is studied through experiments in group of two and three piers. The result reveals that collar has more influence in reduction of scour depth in rear piers than the first pier. Also, when the spacing between the piers increases the area without protection between the piers is washed away resulting deeper scour holes at the rear piers. | Manouchehr HEIDARPOUR Hossein AFZALIMEHR Elham IZADINIA | 2010 | International Journal of Sediment Research2010，25，4： | 8 |
| 3 | Effects of vegetation channel banks and gravel size on flow structure显示文摘Vegetation on river banks and bed roughness are important factors affecting flow structure, sediment transport, erosion and geomorphology in rivers. In this experimental study, the impacts of vegetation on flume walls, grain size of bed gravels and aspect ratio on characteristics of shear stress distribution, Coles' wake parameter, the kinematic energy correction factor (α) and the momentum correction factor (β) have been assessed. Reynolds stress distribution illustrates a three-layer pattern when the aspect ratio is smaller than 2. In addition, the aspect ratio and changes of vegetation affect α, β as well as the Coles' wake parameter Π. | NASIRI DEHSORKHI AFZALIMEHR Jueyi SUI | 2010 | International Journal of Sediment Research2010，25，2： | 4 |
| 4 | Investigation of turbulence characteristics in channel with dense vegetation显示文摘In this experimental study,the turbulent flow in a channel with vegetation by using sprouts of wheat on channel bed was investigated.Two different aspect ratios of channel were used.An Acoustic Doppler Velocimetry was used to measure parameters of turbulent flow over submerged sprouts of wheat,such as velocity profiles.The log law and the Reynolds shear stress distribution were applied. Results indicate that the position of the maximum turbulence intensity superposes on the inflection point situated over the top of submerged vegetation cover.Quadrant analysis shows that near the vegetation bed,the sweeps and ejections appear to be the most dominant phenomenon,while far from the vegetated bed,the outward is dominant event.Results also show that the aspect ratio plays an important role on the contribution of the different bursting events for Reynolds stress determination. | Hossein AFZALIMEHR Razieh MOGHBEL Jacques GALLICHAND Jueyi SUI | 2011 | International Journal of Sediment Research2011，26，3： | 3 |
| 5 | Flow structure over a wavy bed with vegetation cover显示文摘On the basis of experiments carried out in flume with a wavy bed with vegetation cover,flow velocity,turbulence intensities and Reynolds stress distributions are investigated.The wavy bed was similar to dune in this study.The fixed artificial dunes were constructed over the bed and artificial vegetation put over them in a laboratory flume.An Acoustic Doppler Velocimeter and spatially-averaged method were applied to determine turbulent flow components and shear velocity.Results were compared with a gravel bedform.It was observed that vegetation cover influences considerably the flow structure and displays clearly the flow separation and reattachment point.The law of the wall was not valid within the vegetation cover,but it was fitted well to the zone above the vegetation cover within the inner layer.For a wavy bed having the same dimensions,shear velocity and friction factor over vegetation cover are 1.7 and 2.6 times of those for the gravel bedform,respectively.The results of laboratory study were compared with those of river study. | Fazeleh Kabiri Hossein Afzalimehr Jueyi Sui | 2017 | International Journal of Sediment Research2017，32，2： | 3 |
| 6 | Clear-water scour around semi-elliptical abutments with armored beds显示文摘Experimental study has been carried out under a clear-water scour condition to explore the local scour around semi-elliptical model bridge abutments with armor-layer bed, compared with the local scour process around semi-circular abutment. Two types of model bridge abutments, namely semi- elliptical and semi-circular abutments have been used in this experimental study. The model abutments had a ratio of streamwise length of abutment to the length of abutment transverse to the flow of 2 for semi-circular abutments and 3 for semi-elliptical abutments. In total, 50 Experiments have been designed and conducted under different flow conditions such as bed shear velocities, flow depth, and dimensions of bridge abutment model, as well as grain size of the bed material. Based on these experiments, the scour process around bridge abutments has been assessed. The dependence of the equilibrium scour depth of the scour hole on hydraulic variables has been studied. Empirical equation describing the equilibrium scour depth of the scour hole around bridge abutments has been developed. | Jueyi SUI Hossein AFZALIMEHR Abdolreza Kabiri SAMANI Mehmoosh MAHERANI | 2010 | International Journal of Sediment Research2010，25，3： | 2 |
| 7 | Estimation of Gravel- Bed River flow resistance显示文摘 | AFZALIMEHR H ANCTIL F | 1998 | Journal of Hydraulic Engineering1998，124，10： | 1 |
| 8 | Effect of accelerating and decelerating flows on incipient motion in sand bed streams显示文摘 | Adel Emadzadeh Yee Meng Chiew Hossein Afzalimehr | 2010 | Advances in Water Resources2010，，9： | 1 |
| 9 | Estimation of gravel-bed river flow resistance显示文摘 | AFZALIMEHR H ANCTIL F | | 0，，10： | 1 |
| 10 | Hydraulic parameters in channels with wall vegetation and gravel bed显示文摘In this experimental study,field observations and laboratory experiments have been carried out to assess the impacts of the vegetated channel walls and aspect ratio on flow velocity profiles,shear stress distribution and roughness coefficient of channel.Results show that the presence of vegetation cover on channel wall causes deviation of the Reynolds stress distribution from the linear one under uniform flow condition.It is also noticed that the Reynolds stress distribution is influenced by the aspect ratio(W/h).The vegetation cover planted on the flume wall considerably influences the location of the umax.With the changes of the position of umax,the zero Reynolds stress position also changes.The Manning coefficient n of channel with gravel bed and vegetated walls have been assessed and calculated by using the boundary layer characteristics method. | Hossein AFZALIMEHR Jueyi SUI Razieh MOGHBEL | 2010 | International Journal of Sediment Research2010，25，1： | 1 |
| 11 | Velocity Distribution and Shear Velocity Behavior of Decelerating Flows over a Gravel Bed 显示文摘 | AFZALIMEHR H ANCTIL F | 1999 | Canadian Journal of Civil Engineering1999，26，4： | 1 |
| 12 | Effect of non-uniformity of flow on velocity and turbulence intensities over a cobble-bed显示文摘 | AFZALIMEHR H | 2010 | Hydrological Pprocesses2010，24，3： | 1 |
| 13 | Effects of accelerating and decelerating flows in a channel with vegetated banks and gravel bed显示文摘实验在 8 m 被进行有生长银行和石子床的长、 40 厘米宽、 60 厘米深的 re-circulating 斜槽流动学习加速并且速度的效果在流动结构上。重要剧降现象在速度下面在速度侧面被观察流动和速度缺点法律不由于生长银行的效果是合适的。在生长银行附近,骚乱紧张说明了凸的分发因为加速并且速度流动。象限分析的申请表明生长银行的效果在流动结构和雷纳兹压力分发上是重要的。加速并且速度的流动没在冲破周期的在内的每种狂暴的事件占据的时间的百分比上显示出重要差别,但是在水平、垂直的方向影响狂暴的紧张的联合概率分布的形状。 | Hossein AFZALIMEHR Elham Fazel NAJAFABADI Jacques GALLICHAND | 2012 | International Journal of Sediment Research2012，27，2： | 1 |
| 14 | Effect of accelerating and decelerating flows on incipient motion in sand bed streams 显示文摘 | Emadzadeh A Chiew Y M Afzalimehr H | 2010 | Advances in Water Resources2010，33，9： | 1 |
| 15 | Effect of vegetated-banks on local scour around a wing-wall abutment with circular edges显示文摘Failure of bridges due to local scour in the vicinity of bridge abutments is a common occurrence. In this study, experiments under two different channel conditions were conducted to assess the impacts of vegetation on channel banks on local scour around a wing-wall abutment with circular edges. Some experiments were conducted in channel with vegetation on channel banks, and other experiments in channel without vegetation on channel bank. The flow velocity and Reynolds stress distributions in scour holes around a wing-wall abutment with circular edges were compared under these 2 different channel conditions. Results reveal that the vegetated-banks can reduce the time for achieving the equilibrium condition from 17 h to 9 h. Also, vegetated-bank channels can result in a significant decrease in the maximum scour depth from 0.084 m(for bare channel bank) to 0.00032 m. Additionally, around the abutment, vegetated-banks play a significant role in diminishing the Reynolds stress(RS) near the bed and removing negative values in RS distribution by weakening unfavorable pressure gradient and down-flow in the upstream of abutment. | AFZALIMEHR Hossein BAKHSHI Somayeh GALLICHAND Jacques SUI Jueyi | 2014 | Journal of Hydrodynamics2014，26，3： | 1 |
| 16 | Turbulence measurements above sharp-crested gravel bedforms 显示文摘 | NASIRI E AFZALIMEHR H GALLICHAND J | 2013 | International Journal of Hydraulic Engineering2013，2，5： | 1 |
| 17 | Effect of flow non-uniformity on velocity and turbulence intensities in flow over a cob- ble-bed显示文摘 | AFZALIMEHR H | 2010 | Journal of Hydrological Processes2010，24，3： | 1 |
| 18 | Effects of non-submerged boulder on flow characteristics——A field investigation显示文摘The effect of fully submerged boulders on the flow structure in channels has been studied by some researchers. However, many natural streams have bed material with boulders that are not fully submerged under water. In many natural streams, boulders cover between 1% and 10% of the area of the stream reach. The effect of non-submerged boulders on the velocity profile and flow characteristics is very important for assessing riverbed deformation. The objectives of this paper are to find the pattern of velocity distribution around a non-submerged boulder and to compare it with the classical studies on flow resistance and Reynolds stress distribution in open channels. Also, by considering the variation in the Reynolds stress distribution at different locations around a non-submerged boulder, the effect of a non-submerged boulder on the estimation of shear velocity and resistance to flow has been investigated. Results indicates that inside the scour hole caused by a non-submerged boulder in a river velocity distributions are irregular. However, velocity distributions are regular outside the scour hole. The presence of the boulder causes a considerable deviation of the Reynolds shear stress from the classic distribution, showing a non-specific distribution with negative values. The classical methods for calculating shear velocity are not suitable because these methods do not give detailed velocity and Reynolds stress distributions in natural rivers with a lot of boulders. Thus, the effect of a non-submerged boulder on the estimation of the resistance to flow by considering the variations in velocity and Reynolds stress distributions at different locations around a non-submerged boulder is important and needs to be studied in a natural river instead of just in laboratory flumes. The negative values in Reynolds stress distribution around a boulder indicate that the classical methods are unable to predict resistance to flow, and also show strong turbulence inside the scour hole where the complex flow conditions present ambiguous Reynolds stress distributions. In the current study, to obtain a reasonable estimation of parameters in natural rivers, the classical method has been modified by considering velocity and Reynolds stress distributions through the boundary layer method. | Hossein Afzalimehr Mohammad Reza Maddahi Danial Naziri Jueyi Sui | 2019 | International Journal of Sediment Research2019，34，2： | 0 |
| 19 | Impacts of vegetation over bedforms on flow characteristics in gravel-bed rivers显示文摘In the present study,among six gravel-bed river reaches,two natural gravel-bed river reaches with approximately similar bedforms and flow conditions have been found,one river reach with vegetation on bedforms and the other without vegetation on bedforms.Based on field measurements,the impacts of vegetation over bedforms on flow characteristics have been investigated.Flow velocity,Reynolds stress and turbulence intensity distributions over bedforms with vegetation have been compared with those over gravel bedforms without vegetation.By using the quadrant analysis,the dominant events of turbulent flow structures have been assessed for flows over gravel bedforms with vegetation and without vegetation.Results show that the effect of vegetation enhances the anisotropy in turbulence and generates strong secondary currents,which lead to the occurrence of dip phenomenon at the stoss section and the crest of vegetated bedforms.The change of bed roughness from gravel bed to vegetated bed causes a development of a new boundary layer.This resulted in the different shape of velocity distributions over bedforms with vegetation from those over bedforms without vegetation,which can affect the lives of aquatic animals.Reynolds shear stress at downstream section of gravel bedform without vegetation is much higher than that of vegetated bedform,which shows that the erosion takes place from downstream of vegetated bedforms,while in the bare beds;the deposition is at downstream of bedforms.It is found that the presence of vegetation causes a chaotic distribution pattern of Reynolds shear stress,while it has more orderly pattern at the downstream section of gravel bedform without vegetation.Besides,the distribution of turbulence intensity in the lee side of vegetated bedform has a concave shape and in the stoss section,turbulence is generated in ejections and sweeps near the vegetation cover.These findings are significant to the practice of river ecological restoration. | Hossein Afzalimehr Mohammad Reza Maddahi Jueyi Sui Majid Rahimpour | 2019 | Journal of Hydrodynamics2019，31，5： | 0 |
| 20 | Effect of slope angle of an artificial pool on distributions of turbulence显示文摘Experiments were carried out over a 2-dimentional pool with a constant length of 1.5 m and four different slopes.The distributions of velocity,Reynolds stress and turbulence intensities have been studied in this paper.Results show that as flow continues up the exit slope,the flow velocity increases near the channel bed and decreases near the water surface.The flow separation was not observed by ADV at the crest of the bed-form.In addition,the length of the separation zone increases with the increasing of entrance and exit slopes.The largest slope angle causes the maximum normalized shear stress.Based on the experiments,it is concluded that the shape of Reynolds stress distribution is generally dependent on the entrance and exit slopes of the pool.Also,the shape of Reynolds stress distribution is affected by both decelerating and accelerating flows.Additionally,with the increase in the slope angle,secondary currents are developed and become more stable.Results of the quadrant analysis show that the momentum between flow and bed-form is mostly transferred by sweep and ejection events. | Atefeh Fazlollahi Hossein Afzalimehr Jueyi Sui | 2015 | International Journal of Sediment Research2015，30，2： | 0 |
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