共查询到20条相似文献，搜索用时 31 毫秒
1.
1 INTRODUCTION Increasing capital costs, emerging environmental concerns and rising maintenance expenses of conventional river training works around the world have led to the development of submerged vanes in practice. Submerged vanes are being favoured f… 相似文献
2.
《国际泥沙研究》2020,35(1):42-56
Submerged vanes are hydrofoils utilized to manage the sediment transport through the river by generating the turbulence in the flow in the form of helical currents.The vanes are placed in the flow with respect to its direction at angle of 10°to 40°.In the current study,an attempt has been made to study the effect of the introduction of vanes in form of rows on parameters like turbulence intensities,Reynolds stresses,turbulent kinetic energy,anisotropy index,and the velocity profile of the flow.It is observed that the profile of variation of turbulence intensities,turbulent kinetic energy,vertical Reynolds stress and velocity over three different marked verticals on a transect are nearly identical whereas a large scatter is observed in the variation of transverse Reynolds stress over the vertical of the aforementioned vertical locations.This observation suggests that flow turbulence is homogeneous over the vertical while scattering in the variation of the transverse Reynolds stress component may be attributed to the presence of secondary currents in the flow.After introducing rows of submerged vanes,the bed turbulence is reduced,hence,helping reduce many scour related phenomenon.It is also observed that a vortex occurred at 0.85 times the height of the vane and the variation of turbulence quantities in the presence of vanes shows the existence of a peak in these quantities.It is observed that as flow moves away from the vane rows,due to the interaction of vortices and the action of vorticity,vortices dampens down and the flow regains homogeneity.After the introduction of submerged vane rows,bed shear stress reduces as fluid from the surface replaces the slow-moving fluid near the bed due to the secondary currents generated by the vanes leading to reduction in the magnitude of turbulence intensities,Reynolds stresses,and turbulent kinetic energy near the bed.The anisotropy index is observed to increase near the bed as induced secondary currents enhanced the turbulence production in the near bed region.All the profiles of parameters obtained in the current study show the existence of a peak or inflexions at a height of 0.85 H from bed(Where,H is the height of the submerged vane).Profiles of parameters obtained in the current study suggest that as the vorticity dampens the vane-generated secondary currents,the scattering in the profiles along the vertical reduces and profiles are observed to regain the variation which they had before the introduction of vane rows,suggesting that flow turbulence has regained its homogeneity. 相似文献
3.
Most models for predicting pressure-flow scour depth are based on use of the continuity and energy equations. The current study presents a model to predict pressure-flow scour depth using the momentum equation considering the jet flow deflected by the bridge deck. When approaching the bridge deck, the upstream flow acts as a jet flow that deviates toward the bed. Below the bridge deck, a combined jet-flow is created as a result of merging the initial jet-flow and the pressure-flow. The continuit... 相似文献
4.
A rectangular flume with dimensions of length 180 cm, height 60 cm and width 20 cm was used to observe the entry angle (i.e. angle between the interface and the centerline of the slot) of a two-layer flow withdrawal by a line sink. Saline water was used to form a bottom density current and red dye was applied. Based on the experimental data, one could see that the dimensionless discharge is more influential on the entry angle than the depth-averaged concentration of the lower-layer flow. Thus, the influence of concentration on experimental conditions is negligible for evaluation of the entry angle. The absolute values of entry angles increase with the absolute values of the dimensionless discharge. Almost all absolute values of the theoretical angle are bigger than that of the measured angle with a deviation bounded within 0.15 rad. The influence on the entry angle from the dimensionless discharge is symmetrical between the drawdown curve (interface above the slot) and the suck-up curve (interface below the slot). This phenomenon can be seen from a simplified form of a theoretical formula. 相似文献
5.
A new analytical method was evaluated for predicting scour profile downstream of a submerged sluice gate with an apron. The differential equations between bed Shear stress and Scour profile Curvature(SSC model) were utilized to predict the scour profile in both temporal and equilibrium stages. A jet momentum flux was considered as an external source of erosion on a hypothetical particle ring as the boundary between the flow and sediment bed. The scour length and sediment resistance factor were t... 相似文献
6.
This study performed a bridge pier collar comparison for the purpose of reducing scour,while introducing a new collar design.The new collar,referred to as Collar Prototype Number 3,was designed based on an equilibrium scour hole and provides a method of controlling the horseshoe vortex.Numerical modelling was utilized to show the flow field and bed shear stress as a result of using Collar Prototype Number 3.A prototype model of Collar Prototype Number 3 and a flat plate collar were constructed f... 相似文献
7.
Laminar sheetflows, transporting sediment at their capacity rates, both with and without rainfall disturbance, were investigated. Values of flow depth and relative submergence were very small. In the flows without rainfall, measured velocities exceeded the predictions of the smooth-surface, clear-water laminar model by an average of 12 per cent. Reduced flow resistance due to high sediment concentrations may explain this result. Velocities in the rainfall-disturbed flows were not significantly different from the predictions of the smooth-surface, clear-water model, and the velocity reduction due to rainfall was about 12 per cent. Although the uniformity of rainfall intensity under the single-nozzle rainfall simulator is high, variation of momentum and kinetic energy fluxes along the 1-5 m long flume was significant. The rainfall angle of incidence was highly correlated with deviations from expected flow velocities in the upper and lower sections of the flume. 相似文献
8.
1 INTRODUCTION The coherent structure of turbulence is the most important discovery of turbulence studies in the last several decades. The coherent structure is a joint spatial state (Liang, 1999). In this space, there exist all kinds of motions that are organized and related. Namely, strip structures, large vortical structures, and other organizing flows are present. In 1932, researchers found that turbulence wasn抰 a fully random phenomenon and came to realize that the repeated emergen… 相似文献
9.
Various methods to control scour around bridge piers have been proposed.In the present study the application of cable or collar and a combination of cable and collar were examined experimentally,as countermeasures against local scouring at a smooth circular bridge pier,close to threshold flow conditions of initiation of uniform sediment motion.The results show that the simultaneous use of cable and collar has high efficiency in reducing the scour depth.The best configuration was found for a cable-pier diameter ratio of 0.15 and thread angle of 15°,in which the scour depth in upstream of the pier reduced to about 53%.In the case of a pier protected with cable and collar the scouring postponed more than pier protected with collar and the rate of scouring is less than in pier protected with collar.These advantages can reduce the risk of pier failure when the duration of flood is short. The results indicate that the scour reduction increases as the cable diameter increased and the thread angle decreased. 相似文献
10.
River confluences (RCs) are important features within river systems where the three dimensional (3D) flow structures and the downstream mixing of flows can cause deep scour holes. Despite this, few methods have been proposed to control scouring at RCs. In this study, application of a collar was experimentally examined for local scour control at the point where two rivers flow together. In parti-cular, experimental tests were done with and without collar application at three different locations. The results reveal that the scour depth is directly proportional to the discharge ratio, i.e. the ratio of lateral discharge to that in the channel downstream of the confluence, and the densimetric Froude number (Frg). In addition, installation of a collar at RCs can decrease the scour depth up to 100%, thus completely avoiding the scour process. The results also show that by increasing the Frg the optimal installation location for a collar changes and moves towards the river bed level. Using a collar can also reduce the height of the point bar formed downstream of the confluence. The outcomes of the study allow deri-vation of an equation for predicting scour depth when a collar is applied as a countermeasure. The analysis of this equation shows that the estimates are mostly affected by the Frg. 相似文献
11.
This paper presents an approach to modeling the depth-averaged velocity and bed shear stress in compound channels with emergent and submerged vegetation. The depth-averaged equation of vegetated compound channel flow is given by considering the drag force and the blockage effect of vegetation, based on the Shiono and Knight method (1991) [40]. The analytical solution to the transverse variation of depth-averaged velocity is presented, including the effects of bed friction, lateral momentum transfer, secondary flows and drag force due to vegetation. The model is then applied to compound channels with completely vegetated floodplains and with one-line vegetation along the floodplain edge. The modeled results agree well with the available experimental data, indicating that the proposed model is capable of accurately predicting the lateral distributions of depth-averaged velocity and bed shear stress in vegetated compound channels with secondary flows. The secondary flow parameter and dimensionless eddy viscosity are also discussed and analyzed. The study shows that the sign of the secondary flow parameter is determined by the rotational direction of secondary current cells and its value is dependent on the flow depth. In the application of the model, ignoring the secondary flow leads to a large computational error, especially in the non-vegetated main channel. 相似文献
12.
Mutsuto Kawahara 《Advances in water resources》1982,5(4):195-207
This paper presents a finite element method for the analysis of nearshore current, which is mainly induced by surface waves. The analysis is divided into two parts, i.e., the analysis of wave and the analysis of currents. The basic equations are conservation of wave number, wave energy, momentum and continuity. The first two are for wave analysis and the last two for the current analysis. The wave angle is determined from the conservation law of wave number. Using the resulting wave angle and the conservation of wave energy, the distribution of wave height is derived. The radiation stress is derived from the wave angle and height. The nearshore current flow is obtained from the conservations of momentum and continuity including the radiation stress. All the numerical procedures are based on the finite element method. For the analysis of the wave angle and wave height, the incremental iteration method and logarithmic function formulation are employed. For the analysis of the current flow, the stream function formulation is used. From the numerical computations, it is seen that the finite element method presented in this paper is very valuable in practical applications. The method is applied to the analysis of the nearshore current flow of Twan Bay in Japan. 相似文献
13.
In this experimental study,the effect of suspended sediment concentration on the characteristics of a submerged hydraulic jump in a rectangular channel has been investigated,based on the sediment conce... 相似文献
14.
Data from the SESAME storm-scale network are used in computing the momentum budget of the prestorm, storm, and poststorm environment of a severe storm complex. In the prestorm period geostrophic flow dominates the environment. With progression into the storm period all terms in the momentum equation become important, as a significant ageostrophic component in the momentum field develops. Turbulent effects are estimated as a residual, and the results indicate that they are comparable in magnitude to the other terms. Their effect is to decrease the positive momentum, particularly at levels above 500 mbar, where the vertical motion is the strongest. Vertical profiles of area means ofu andv indicate that the storm is apparently redistributing momentum downwards, thus reducing the mean shear. In the poststorm period the flow once again becomes largely geostrophic, and a maximum in wind speed reappears at upper levels. 相似文献
15.
APPLICABILITY OF SEDIMENT TRANSPORT FORMULAS 总被引：3，自引：0，他引：3
Chih Ted YANG Caian HUANG Manager Sedimentation River Hydraulics Group Technical Service Center U.S. Bureau of Reclamation Denver Colorado . Graduate student College of Harbour Waterway Coastal Engineering Hohai University Nanjin 《国际泥沙研究》2001,16(3)
1 INTRODUCTIONThe selection of aPPropriate sediment transport fOrmulas under different flow and sedfornt conditions isimPoftant tO the sedimen tusPort and river morphologic stUdies of a river. There are numrousWlas published in professional joumals and summarized in sediment transPort texthooks. Mosttextbooks shy away from direct comPallsons of the accuracies of transPort formulas. ComPllted resultsbased on differnt transport formulas may differ significanly from each other and from … 相似文献
16.
假定垂直轴为二维对称各向异性介质主轴之一，构造走向与另一主轴方向成任一夹角，用伽勒金（Ｇａｌｅｒｋｉｎ）有限元法和矩形网格，优化地合成总体刚度矩阵，使二维各向异性介质的基本方程形成有限元代数方程组，求出各节点场值，并利用ＭＯＭ法求出辅助场，进而求出张量阻抗等响应函数．同时还对有关文献的计算模型进行了数值模拟检验 相似文献
17.
SUDHIR JAIN 《Geophysical Prospecting》1966,14(2):143-148
A simple method of magnetotelluric interpretation is derived using the property that the earth currents flow in horizontal sheets. It is shown that when the depth is taken as two-thirds of the Cagniard's depth of penetration (Cagniard, 1953), the mean resistivity-over the depth is the same as the apparent resistivity of the medium. From a mean resistivity versus depth of penetration plot, resistivity can be easily computed at all depths of the sounding. This method gives satisfactory results in a short time and makes it possible to interpret the soundings over media of several layers. However, the results are inaccurate near maximum and minimum points of the plot as well as in the zone of thin layers. 相似文献
18.
Willem V. R. Malkus 《地球物理与天体物理流体动力学》2013,107(1-3):123-134
Abstract Broad band secondary instability of elliptical vortex motion has been proposed as a principal source of shear-flow turbulence. Here experiments on such instability in an elliptical flow with no shear boundary layer are described. This is made possible by the mechanical distortion in the laboratory frame of a rotating fluid-filled elastic cylinder. One percent ellipticity of a 10 cm diameter cylinder rotating once each second can give rise to an exponentially-growing mode stationary in the laboratory frame. In first order this mode is a sub-harmonic parametric Faraday instability. The finite-amplitude equations represent angular momentum transfer on an inertial time scale due to Reynolds stresses. The growth of this mode is not limited by boundary friction but by detuning and centrifugal stabilization. On average, a generalized Richardson number achieves a marginal value through much of the evolved flow. However, the characteristic flow is intermittent with the cycle: rapid growth, stabilizing momentum transfer from the mean flow, interior re-spin up, and then again. Data is presented in which, at large Reynolds numbers, seven percent ellipticity causes a fifty percent reduction in the kinetic energy of the rotating fluid. In the geophysical setting, this tidal instability in the earth's interior could be inhibited by sub-adiabatic temperature gradients. A near adiabatic region greater than 10 km in height would permit the growth of tidally destabilized modes and the release of energy to three-dimensional disturbances. Such disturbances might play a central role in the geodynamo and add significantly to overall tidal dissipation. 相似文献
19.
For the appropriate management and restoration of rivers, isolated vegetation is often a practical means for improving stream habitat and ecology. The effect of a finite vegetation patch on flow and bed morphology in an open channel was investigated using laboratory experiments. The patch containing emergent and submerged vegetation was modeled using circular cylinders and located mid‐channel along a side wall. Several configurations of the patch and submergence ratio (i.e. water depth to the height of vegetation), and two flow conditions (i.e. below and above the sediment motion threshold) were considered. For flows below the sediment motion threshold, erosion occurred primarily on the opposite side of the patch and near the leading edge of the patch. The degree of scouring depth observed in both these regions was affected by the submergence ratio and it increased with the non‐dimensional flow blockage (i.e. the product of the patch density and width). In contrast, for flows above the sediment motion threshold, sediment accumulated within and around the patch due to a reduction in bed shear stress, which was strongly influenced by the flow blockage and the obstruction ratio (i.e. the ratio of patch width to channel width). The eroded area observed within the patch was consistent with the interior adjustment region where the deceleration and diversion of flow occurred through the patch. As the flow blockage increased or as the obstruction ratio decreased, the deposition rate within and behind the patch decreased. Furthermore, the deposition rate increased with an increase in the ratio of flow rate through the patch to total flow rate regardless of the submergence ratio. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
20.
The paper addresses the problem of determination of the energy and momentum coefficients for flows through a partly vegetated channel. These coefficients are applied to express the fluid kinetic energy and momentum equations as functions of a mean velocity. The study is based on laboratory measurements of water velocity distributions in a straight rectangular flume with stiff and flexible stems and plastic imitations of the Canadian waterweed. The coefficients were established for the vegetation layer, surface layer and the whole flow area. The results indicate that the energy and momentum coefficients increase significantly with water depth and the number of stems per unit channel area. New regression relationships for both coefficients are given. 相似文献