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1.
Numerical modeling of local scour of non-uniform graded sediment for two arrangements of pile groups
A three-dimensional(3D) non-hydrostatic numerical model is established to investigate local scour around four aligned circular piles in uniform and non-uniform sediment mixtures and to provide information for improving scour countermeasures design. In the current study, unsteady Reynolds averaged Navier-Stokes(URANS) equations along with a Re-normalization Group(RNG) k-ε model were applied to simulate the flow field. A non-uniform sediment transport model was applied to estimate the bedload tran... 相似文献
2.
Spur dikes are river training structures that have been extensively used worldwide for towards enhancing flood control and the stability of embankments and riverbanks.However,scour around spur dikes can be a major problem affecting their stability and hydraulic performance.The precise computation of temporal scour depth at spur dikes is very important for the design of economical and safe spur dikes.This study focuses on experimentally assessing the temporal variation of scour depth around a vertical wall spur dike and identifying the parameters,which mostly influence spur dike performance for a channel bed surface comprised of sand-gravel mixtures.In the current study,the authors did physical experiments in a flume based study to obtain new data,aimed at deriving a new predictive model for spur dike scour and comparing its performance to others found in the literature.It was found that the dimensionless temporal scour depth variation increases with an increase in(i)the threshold velocity ratio,(ii)the densimetric Froude number of the bed surface sediment mixture,(iii)the flow shallowness(defined as the ratio of the approach flow depth,y,to the spur dike’s transverse length,l),and(iv)the flow depth-particle size ratio.It is also concluded that the temporal scour depth variation in the sediment mixture is influenced by the non-uniformity of sediment and decreases with an increase in the non-uniformity of the sediment mixture.A new mathematical model is derived for the estimation of temporal scour depths in sand-gravel sediment mixtures.The proposed equation has been calibrated and validated with the experimental data,demonstrating a good predictive capacity for the estimation of temporal scour depth evolution. 相似文献
3.
《国际泥沙研究》2022,37(5):662-674
Bridge abutment-induced sediment scour in compound river channels is time-sensitive during floods, and, thus, estimating the scour rate has significance in design. In the current study, large-scale laboratory experiments were done to examine the influence of multiple factors on scour evolution, including channel geometry, bed mobility (clear-water or live-bed), and lateral (embankment intrusion) and vertical (deck submergence) flow contractions. A new method is applied for scour measurement and determination of characteristic scour trends. Results show that the non-dimensional time scale is related to flow intensity and may peak before reaching the clear-water scour threshold; the corresponding equations also are derived. It is found that the use of scour countermeasures has a significant impact on the scour rate, and the existing equations for unprotected abutments have limitations. Under clear-water conditions, the scour rate is closely related to the overall flow contraction, which can be better reflected by the ratio of the approaching unit discharge to that at the bridge section. Specifically, the effect of vertical flow contraction on scour rate is more dominant than other factors. Two scour rate curves are derived to suit different structural and flow contraction types for clear-water scour. In contrast, the live-bed scour rate data are generally consistent and fall in a narrow band, showing less dependence on other factors. Finally, a new design approach is established to estimate the time scale and scour rate using the new equations proposed in this paper. 相似文献
4.
Large woody debris(LWD) reduces the flow area,deviate the flow and increases the velocity in correspondence of the bridge pier,therefore increases the maximum scour hole depth and accelerates sediment removal.Logs and drifts accumulated on bridge piers are of different dimensions.According to logs characteristics and river morphology,drift accumulations can either extend downstream the bridge pier or they can accumulate totally upstream.This paper aims to analyze the effect of drift accumulation planimetry on bridge pier scour.The experimental investigation has been carried out at the PITLAB hydraulic centre of Civil Engineering Department,University of Pisa,Italy.Drift accumulation was characterized by different relative longitudinal lengths,flow area occlusions,length of longitudinal drift and downstream planimetrical positions relative to the pier center.The experimental investigation has been carried out in clear-water conditions.Several pier sizes,channel widths and sediment materials have been tested.Maximum scour hole in presence of drift accumulation have been compared to the maximum scour hole for an isolated pier.Finally,data were compared with previous literature findings,which highlight the effect of the downstream extension of drift accumulation on bridge pier scour.New relationships have been proposed to predict the effect of drift accumulation on bridge pier scour,both in terms of relative maximum scour and temporal scour evolution. 相似文献
5.
6.
In the current study, 108 flume experiments with non-uniform, cohesionless sediments have been done to investigate the local scour process around four pairs of side-by-side bridge piers under both open channel and ice-covered flow conditions. Similar to local scour around bridge piers under open channel conditions and a single bridge pier, it was observed in the experiments that the maximum scour depth always occurred at the upstream face of the pier under ice-covered conditions. Further, the smaller the pier size and the greater the spacing distance between the bridge piers, the weaker the horseshoe vortices around the bridge piers, and, thus, the shallower the scour holes around them. Finally, empirical equations were developed to estimate the maximum scour depth around two side-by-side bridge piers under both open channel and ice-covered flow conditions. 相似文献
7.
Evolution of scouring process downstream of grade‐control structures under steady and unsteady flows
For many incised channels, one of the most common strategies is to install some hard structures, such as grade‐control structures (GCSs), in the riverbed to resist further incision. In this study, a series of experiments, including both steady and unsteady flow conditions, were conducted to investigate the scouring process downstream of a GCS. Three distinct phases, including the initial, developing and equilibrium phases, during the evolution of scour holes were identified. In addition, a semi‐empirical method was proposed to predict the equilibrium scour‐hole profile for the scour countermeasure design. In general, the comparisons between the experimental and simulated results are reasonably consistent. As the studies on temporal variation of the scour depth at GCSs caused by floods are limited, the effect of flood hydrograph shapes on the scour downstream of GCSs without upstream sediment supply was also investigated experimentally in this study. Based on the dimensional analysis and the concept of superposition, a methodology is proposed to simulate the time evolution of the maximum scour depth downstream of a GCS for steady flows. Moreover, the proposed scheme predicts reasonably well the temporal variations of the maximum scour depth for unsteady flows with both single and multiple peak. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
8.
Yong-Nian XU Zhi-Yong LIANG Thao-Yin WANG China Institute of Water Resources Hydropower Research Beijing China. International Research Training Center on Erosion Sedimentation Beijing China. 《国际泥沙研究》2001,16(2)
1 wrsoooCTIoxThe Yeuow mver crtes a huge amoun of sedimcht and the noods often cause raPid and severeerosinn and dePOsihon. The channl bed of the YelOw mver often exPeriences degIadation in the mainchannel during fioods. In some cases vigorous erosion uP to l0 meters takes place in a shOrt Period oftiIn. Such phenomenon usually occurs in the ndddie reaChs of the Yelow mver and its tributaries suchas the Wdse mVer the Beiluohe mver etc. For examPle, th6 hyPenconcentraed nood in July l… 相似文献
9.
Estimating the time evolution of a local scour hole downstream of submerged weirs can help determine the maximum scour depth and length and is essential to designing submerged weir foundations.In the current study, artificial neural networks with a backpropagation learning algorithm were used to estimate the temporal variation of scour profiles downstream of submerged weirs under clear water conditions. Physical factors, such as the flow condition, weir size, and sediment characteristics, are ge... 相似文献
10.
The local scour around bridge abutments has been an active research topic for many decades. But very few studies have been conducted regarding the impacts of ice cover on the local scour phenomenon aro... 相似文献
11.
Watercourse morphology is affected by local scouring when the flow interferes with anthropic structures. Controlling the scour hole size is of predominant importance to guarantee bridge safety as well as to limit the variations of river morphology. A combined countermeasure against bridge pier scour is proposed and tested in order to reduce the maximum scour depth and deviate it away from the bridge foundation. In the first part of the laboratory campaign, combination of two countermeasures (bed-sill and collar) was evaluated for a circular pier under clear-water and live-bed steady flow conditions. The proposed combined countermeasure exhibited an efficiency of about 64% in terms of scour depth reduction. Afterwards, it was tested in unsteady flow conditions, first for a circular pier, then in the case of a rectangular pier with round nose and tail, two circular in-line piers and two rectangular in-line piers, under a hydrograph with a peak flow velocity slightly above the threshold condition of sediment motion. Results showed that the combined countermeasure had an efficiency of about 63% for a single circular pier; however, higher efficiency (about 75%) was obtained in applications to rectangular pier and two in-line circular or rectangular piers. 相似文献
12.
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
13.
N. P. Wallerstein 《地球表面变化过程与地形》2003,28(1):49-68
Large woody debris (LWD) can have a significant impact upon local channel morphology by creating scour pools and zones of reduced shear stress in which sediment is deposited. It is important to predict scour depths associated with LWD, as it is becoming increasingly common for debris to be added into river channels to improve sediment retention and create pools for aquatic habitat. Engineered log‐jams should therefore be designed using factor of safety engineering analysis, which includes estimates of associated scour and deposition rates. However, the rate and total depth of scour associated with LWD have not been modelled comprehensively, with authors resorting to the use of generic local and constriction scour models to predict scour depths. Also, constriction scour models presented, to date, do not calculate the rate of scour development. In this paper a model is presented for predicting the rate and total depth of scour associated with a channel constriction. The model is one‐dimensional and is based upon the sediment continuity equation, the calculation of specific head changes through the constricted reach and also allows for a variable free surface elevation above the bed at the constriction. This model could be applied to any channel constriction problem but here is used to determine scour rates and depths associated with deflector‐type LWD jams. Deflector jams are one category of jam type presented in a debris jam classification scheme, in which jam type is a function of the ratio of average riparian tree height to average channel width. Deflector jams, as the name implies, partially block the flow and therefore act as a channel constriction, which results in constriction scour. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
14.
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. 相似文献
15.
One-dimensional numerical simulation of non-uniform sediment transport under unsteady flows 总被引：16，自引：9，他引：7
One-dimensional numerical models are popularly used in sediment transport research because they can be easily programmed and cost less time compared with two- and three-dimensional numerical models. In particular, they possess greater capacity to be applied in large river basins with many tributaries. This paper presents a one-dimensional numerical model capable of calculating total-load sediment transport. The cross-section-averaged sediment transport capacity and recovery coefficient are addressed in the suspended load model. This one-dimensional model, therefore, can be applied to fine suspended loads and to hyperconcentrated flows in the Yellow River. Moreover, a new discretization scheme for the equation of unsteady non-uniform suspended sediment transport is proposed. The model is calibrated using data measured from the Yantan Reservoir on the Hongshui River and the Sanmenxia Reservoir on the Yellow River. A comparison of the calculated water level and river bed deformation with field measurements Shows that the improved numerical model is capable of predicting flow, sediment transport, bed changes, and bed-material sorting in various situations, with reasonable accuracy and reliability. 相似文献
16.
The mechanism of bridge pier scour becomes more complex in the presence of debris accumulation upstream of the pier. While using countermeasures may be effective in reducing scour, their efficacy could be undermined in such a situation. The current study investigates the effectiveness of using a collar in the presence of different types of floating debris accumulation in reducing scour around a cylindrical bridge pier with non-cohesive bed sediment. The experimental results reveal that using a c... 相似文献
17.
Zhaoyin WANGProf Dr. International Research Training Center on Erosion Sedimentation. P.O.Box Beijing China Jinchi HUANG Dr. Senior Engineer China Institute of Water Resources Hydro-Power Research P.O.Box Beijing . Chi 《国际泥沙研究》1997,(3)
I.INTRODUCTIONhiverchannelsaresubjecttocontinuouschangeingeometryduetoillteraCtionbetWeentheflowanderodibleboundaries.Ofconcerntothedesignersofoilpipelinesacrossariver,bridgesandhydraulicworksistheproblemofscourwhichcanunderminetheStructures.Scouratsiteofbridgesandhydraulicworksoccursduetoconstrictedflowandexistenceofbridgepiers.SuchatabOfscouroccursonlyinashortsection,usuallyillthesameorderofthelengthofthehydraulicworksorbridges.Therefore,thispatternofscouriscalledlocalscour.Man}rresea… 相似文献
18.
To explore the seismic performance of a high-rise pile cap foundation with riverbed scour, a finite element model for foundations
is introduced in the OpenSees finite element framework. In the model, a fiber element is used to simulate the pile shaft,
a nonlinear p-y element is used to simulate the soil-pile interaction, and the p-factor method is used to reflect the group effects. A global and local scour model is proposed, in which two parameters,
the scour depth of the same row of piles and the difference in the scour depth of the upstream pile and the downstream pile,
are included to study the influence of scour on the foundation. Several elasto-plastic static pushover analyses are performed
on this finite element model. The analysis results indicate that the seismic capacity (or supply) of the foundation is in
the worst condition when the predicted deepest global scout depth is reached, and the capacity becomes larger when the local
scour depth is below the predicted deepest global scout depth. Therefore, to evaluate the seismic capacity of a foundation,
only the predicted deepest global scout depth should be considered. The method used in this paper can be also applied to foundations
with other soil types. 相似文献
19.
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
20.
Numerical modeling of local scour at a submerged weir with a downstream slope using a coupled moving-mesh and maskedelement approach 总被引：2，自引：2，他引：0
This paper presents a model for local scour at submerged weirs with downstream slopes that uses a coupled moving-mesh and masked-element approach.In the developed model,the fluid-sediment interface is tracked using a moving-mesh technique,and the effects of the structure on the hydrodynamics and bed morphology are resolved using a masked-element technique.Compared to traditional sediment scour models,based on the moving-mesh technique,the present model has the advantage of allowing for a simpler setup of the computational grids and a larger-amplitude deformation.Laboratory experiments on local scour at a submerged weir with a downstream slope were conducted,which provided bed profiles at different time instants.The results obtained by the present model are compared to the experimental data.The comparisons demonstrate the performance of the model in satisfactorily predicting local scour at a submerged weir with a downstream slope.The model was further modified and employed to carry out additional computations to investigate the influence of various parameters and sub-models. 相似文献