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1.
A new formula for the concentration profile of nonuniform sediment is derived using the diffusion differential equation with equilibrium bed concentration.The interaction coefficient for nonuniform sediment particles as a function of both relative diameter and geometric standard deviation of nonuniform sediment is taken into account in the settling velocity.The diffusion coefficient is obtained from the logarithmic velocity profile.This new formula possesses several advantages as follows:(1)avoids theoretical defect of the Rouse formula,which states that the sediment concentration is infinite at the bottom and zero at the water surface.(2)suitable for an arbitrary fraction of nonuniform sediment,and(3)easy to apply with a simple form.The formula yields less difference among concentration profiles for various particles than that for uniform sediment and reveals the lawfor fractional concentration distribution of nonuniform sediment.The calculated concentration agrees well with the measured data from the Yangtze River. 相似文献
2.
This numerical investigation was carried out to advance mechanistic understanding of sediment transport under sheet flow conditions. An Euler–Euler coupled two-phase flow model was developed to simulate fluid–sediment oscillatory sheet flow. Since the concentration of sediment particles is high in such flows, the kinematics of the fluid and sediment phases are strongly coupled. This model includes interaction forces, intergranular stresses and turbulent stress closure. Each phase was modeled via the Reynolds-Averaged Navier–Stokes equations, with interphase momentum conservation accounting for the interaction between the phases. The generation and transformation of turbulence was modeled using the two-equation k–ε turbulence model. Concentration and sediment flux profiles were compared with experimental data for sheet flow conditions considering both symmetric and asymmetric oscillatory flows. Sediment and fluid velocity variations, concentration profiles, sediment flux and turbulence parameters of wave-generated sheet flow were studied numerically with a focus on sediment transport characteristics. In all applications, the model predictions compared well with the experimental data. Unlike previous investigations in which the flow is driven by a horizontal pressure gradient, the present model solves the Navier–Stokes equations under propagating waves. The model’s ability to predict sediment transport under oscillatory sheet flow conditions underscores its potential for understanding the evolution of beach morphology. 相似文献
3.
Hongguang Sun Shiqian Nie Aaron I.Packman Yong Zhang Dong Chen Chengpeng Lu Chunmiao Zheng 《国际泥沙研究》2023,38(1):12-23
The Rouse formula and its variants have been widely used to calculate the steady-state vertical concentration distribution for suspended sediment in steady sediment-laden flows, where the diffusive flux is assumed to be Fickian. Turbulent flow, however, exhibits fractal properties, leading to non-Fickian diffusive flux for sediment particles. To characterize non-Fickian dynamics of suspended sediment, the current study proposes a Hausdorff fractal derivative based advection-dispersion equation(H... 相似文献
4.
The particle size distribution of bed materials in the sandy river bed of alluvial rivers is important in the study of topics such as friction, river bed evolution, erosion, and siltation. It also can reflect the dependency relation between river bed sediment and flow intensity. In this paper, the critical pattern of sediment movement in the near-wall region of a sandy river bed was analyzed. According to the principle of momentum balance, the critical settling-rising condition of bed material in a sandy river bed was found to be instantaneous turbulent velocity equal to 2.7 times the sediment settling velocity in quiescent water. Based on a vertical instantaneous turbulent velocity with a Gaussian distribution, a theoretical relation for calculating the particle size distribution of bed materials in a sandy river bed without pre-known characteristic grain sizes was developed by solving a stochastic equation. The for-mula is verified using measured data, and the results show that the proposed formula was in accordance with the measured data. This study has theoretical significance and practical value for determining the bed material particle size distribution of the sandy bed of alluvial rivers. 相似文献
5.
J. Bouchez F. Métivier M. Lupker L. Maurice M. Perez J. Gaillardet C. France‐Lanord 《水文研究》2011,25(5):778-794
Large rivers have been previously shown to be vertically heterogeneous in terms of suspended particulate matter (SPM) concentration, as a result of sorting of suspended solids. Therefore, the spatial distribution of suspended sediments within the river section has to be known to assess the riverine sedimentary flux. Numerous studies have focused on the vertical distribution of SPM in a river channel from a theoretical or experimental perspective, but only a few were conducted so far on very large rivers. Moreover, a technique for the prediction of depth‐integrated suspended sediment fluxes in very large rivers based on sediment transport dynamics has not yet been proposed. We sampled river water along depth following several vertical profiles, at four locations on the Amazon River and its main tributaries and at two distinct water stages. Depending on the vertical profile, a one‐ to fivefold increase in SPM concentration is observed from river channel surface to bottom, which has a significant impact on the ‘depth‐averaged’ SPM concentration. For each cross section, a so‐called Rouse profile quantitatively accounts for the trend of SPM concentration increase with depth, and a representative Rouse number can be measured for each cross section. However, the prediction of this Rouse number would require the knowledge of the settling velocity of particles, which is dependent on the state of aggregation affecting particles within the river. We demonstrate that in the Amazon River, particle aggregation significantly influences the Rouse number and renders its determination impossible from grain‐size distribution data obtained in the lab. However, in each cross section, the Rouse profile obtained from the fit of the data can serve as a basis to model, at first order, the SPM concentration at any position in the river cross section. This approach, combined with acoustic Doppler current profiler (ADCP) water velocity transects, allows us to accurately estimate the depth‐integrated instantaneous sediment flux. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
6.
磁尾电流片在磁尾动力学过程中起着重要作用.卫星观测表明磁尾电流片经常处于拍动状态.但磁尾电流片拍动的特性和产生机制至今仍然没有被完全弄清楚.本文主要利用欧洲空间局Cluster卫星数据,研究一个伴随高速离子流的电流片拍动事件.该电流片拍动事件具有很强的周期性.拍动的周期约是2min,磁场振荡幅度约为20nT.能量电子和离子的通量具有周期性增强和减弱的特征.电流密度X和Y分量也具有周期性的振荡,并且振荡周期与磁场振荡周期一致.通过对粒子流速矢量与电流矢量的分析,发现粒子运动具有涡旋的特征.因此可以推断,该磁尾电流片的拍动不是由磁尾等离子体片高速流产生的,而是与局地等离子体不稳定性有关. 相似文献
7.
Parameterized expressions for an improved Rouse equation 总被引：1，自引：0，他引：1
The equilibrium profile of suspended sediment concentration （SSC） in steady, uniform turbulent flow has been extensively studied since the proposition of Rouse equation （Rouse, 1937）. Many researchers keep studying and attempting to improve the Rouse equation by modifying the mixing length concept. Bose and Dey （2009） improved Rouse equation based on the modified sediment diffusivity, however, their proposed sediment diffusivity has two parameters, the depth modification factor α and the reciprocal of the sediment Schmidt number β = 1/S, and the corresponding expressions were not given properly in their paper. This paper aims to parameterize the relevant coefficients, the results shows： （1） α is parameterized from a reasonable approximation by the analysis of surface boundary condition of SSC; （2） considering some effect factors on the settling velocity, β can be expressed by an extended and modified Montes-Ippen formula, and its related parameters are calibrated by substantial data about the relationship between the primary Rouse parameter Z. = ω/ku and its counterpart Z＇ = ω/βku.. Through verification with some experimental and field datasets, and comparison with related formula, the results show that the sediment diffusivity and SSC profiles have a good agreement with measured data used the present parameterized expressions of a and,8, so the present improved Rouse equation is reasonable, and can be applied in practical applications. Finally, an approximation and simplified expression of the improved Rouse equation is deduced by using the approach of perturbation, which can be applied easily for the estimation of suspended sediment transport rate. 相似文献
8.
Limo TANG Shanghong ZHANG Mingzhong YU Xingkui WANG 《国际泥沙研究》2006,21(4):272-280
1 INTRODUCTION The mechanism of particle movement in the flow is one of basic problems of sediment transport research. The conventional measurement approaches usually disturb the structure of the flow, consequently inducing errors. With the development of… 相似文献
9.
地铁隧道爆破施工时严重威胁邻近居民楼的结构安全,因此研究邻近居民楼爆破峰值振速是非常必要的。文章基于群孔荷载简化模型、柱面波理论及传统的应力波衰减理论,在考虑高程效应影响下推导质点峰值振速公式。依托乌鲁木齐地铁一号线工程,对一邻近六层居民楼的爆破施工响应进行监测,并将实测质点峰值振速、提出的修正公式预测振速和传统萨道夫公式预测的振速进行对比分析。研究结果表明:采用修正公式预测的质点峰值振速与现场实测值的分布规律一致,呈现出随着高程增大而逐渐增大的趋势;而且现场实测值与修正公式预测值相对误差较小,表明考虑高程因子的修正公式是可行的。 相似文献
10.
Philippe Frey 《地球表面变化过程与地形》2014,39(5):646-655
Depth profiles of particle streamwise velocity, concentration and bedload sediment transport rate were measured in a turbulent and supercritical water flow. One‐size 6 mm diameter spherical glass beads were transported at equilibrium in a two‐dimensional 10% steep channel with a mobile bed. Flows were filmed from the side by a high‐speed camera. Particle tracking algorithms made it possible to determine the position, velocity and trajectory of a very large number of particles. Approximately half of the sediment transport rate was composed by rolling grains, and the other half by saltation. This revealed a complex structure, with several concentration and flux peaks due to rolling, and one peak due to saltation. With an increase of the sediment transport rate, the depth structure remained the same at the water/granular interface, with peak value increases but with no shift in elevations. The saltation region expanded towards higher elevations with an increase of the particle velocity commensurate to the water velocity. The proportion of the sediment transport rate in saltation did not vary significantly. The particle streamwise velocity profiles exhibited three segments: an exponential decay in the bed, a linear increase where rolling and saltation co‐existed, and above this, a logarithmic‐like shape due to saltating particles. These results are comparable to profiles measured and modelled in dry granular free surface flows and in more intense bedload such as sheet flows. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
11.
A Reynolds stress model for the numerical simulation of compound open-channel flows with vegetation on the floodplain is described. The Reynolds stress model consists of various sub-models such as Speziale et al.’s model, Mellor and Herring’s model, and Rotta’s model for the pressure–strain correlation term, the turbulent diffusion term, and the dissipation term, respectively. For validation of the model, plain compound open-channel flows are simulated. The computed results were compared with measured data by [Tominaga A, Nezu I. Turbulent structure in compound open-channel flows. J Hydraul Eng, ASCE 1991;117(1):21–41] and the results show that the Reynolds stress model successfully simulates the mean flow and turbulence structure of plain compound channel flows. The model was then applied to compound open-channel flows with vegetated floodplains. Good agreement between the simulated results and data from an algebraic stress model by [Naot D, Nezu I, Nakagawa H. Hydrodynamic behavior of partly vegetated open channels. J Hydraul Eng, ASCE 1996;122(11):625–33] was found. However, it was shown that the RSM is capable of predicting the velocity dip and lateral shift in the maximum streamwise velocity, which were not observed in the data from algebraic stress modeling. Finally, a depth-averaged analysis of the streamwise momentum equation was performed to investigate the lateral momentum transfer in compound channel flows with vegetated floodplains. Compared with components by the secondary currents and Reynolds stress, the drag force due to the presence of vegetation appears to be a factor in reducing the bottom shear stress in both main channel and floodplain. 相似文献
12.
T.SONG Post-Doctoral Fellow School of Civil Structural Engineering Nanyang Technological University Nanyang Avenue Singapore . Presently Civil Engineer Engineering Depatment Technology Division Maritime Port Authority of Singapore. 《国际泥沙研究》1997,(3)
I.INTRODUCTIONBedloadtransportinsteadyuniformopenchannelflowhasbeenextensiVelystudied.Manyoftheformulasdevelopedforthepredictionofbedloadtransportinuniformopen-channelflowcanbebroughtinthefollowingform(ChienandWan,1983);ac=f(O)(l)xvhereacisthedimensionlessparameterofbedloadtranSPortandOisthedimensionlessparameterofflowintensity.TheseparametersaredefinedasfwheregsisthebedloadtranspoftratePerunitwidthindryweight;disthesedimentdiameter,Sisthebedslopeofthechannel;Rbisthehydraulicradiusdue… 相似文献
13.
稀性泥石流的平均运动速度研究 总被引：1，自引：0，他引：1
泥石流的运动速度是泥石流动力学研究中最重要的参数。稀性泥石流是常见也是危害较大的泥石流类型,准确而简洁地计算稀性泥石流的运动速度非常重要。现有的稀性泥石流平均速度经验公式,在使用上和适用地区上还存在一些问题。本文通过分析一系列稀性泥石流观测资料中的体积浓度与稀性泥石流的运动速度和阻力特征的关系,得出了一个新的计算稀性泥石流平均运动速度的经验公式,该公式能适应各种类型的泥石流沟,适用于一般急流的稀性泥石流;对于缓流稀性泥石流,计算值与观测值相比偏大,但很接近;不适用于缓慢稀性泥石流。本文提出的经验公式,使用简洁,计算稳定,与其他方法计算的稀性泥石流平均运动速度很接近。该速度计算经验公式也适用于稀性泥石流堆积扇上游沟道,但对于堆积扇上的速度,计算值偏大,且越往堆积扇的下游,偏差越大。 相似文献
14.
《Journal of Atmospheric and Solar》2000,62(6):505-512
A test particle study of the ionospheric source of plasma in the Earth’s plasma sheet has been performed, in an effort to understand an apparent inconsistency between the results of forward and backward (in time) test particle calculations. Most, if not all, forward calculations of polar wind ion outflows result in energetic plasma sheet ion populations; yet most, if not all, backward trajectory calculations from typical plasma sheet ion populations lead elsewhere than to low energy polar cap outflows. Using a trajectory discovered through forward calculation to connect these two regions, we found that the trajectory was only accurately reversible within an extremely narrow range of energy, pitch angle and gyrophase angle in the plasma sheet, referred to herein as ‘the source groove’. This implies that ionospheric plasma tends to appear in the plasma sheet within narrow regions of velocity space, but is effectively diffused by fluctuations to form the observed more isotropic plasma sheet populations. The implications for backtracking test particle studies are discussed, and it is concluded that test particle backtracking from highly chaotic regions is impractical and should be supported by forward modeling of plasma flows up to the boundaries of such regions. 相似文献
15.
Vertical profiles of fluid velocity and suspended sediment concentration in nearshore 总被引：2，自引：0，他引：2
Based on the power function of velocity and the friction velocity,a velocity profile is obtained.By solving the Schmidt’s diffusion equation,an equilibrium suspended sediment concentration profile is further deduced.The profiles of velocity and suspended sediment concentration agree well with the field data,and the profile of suspended sediment concentration avoids the unreasonableness of the classical Rouse profile such as a zero value at the water surface.According to these profiles,an expression which is easy to use for calculating the suspended sediment transport rate is derived. 相似文献
16.
Grain-size distributions of suspended load over a sand-gravel bed at two different flow velocities were studied in a laboratory flume.The experiments had been performed to study the influence of flow velocity and suspension height on grain-size distribution in suspension over a sand-gravel bed.The experimental findings show that with an increase of flow velocity,the grain-size distribution of suspended load changed from a skewed form to a bimodal one at higher suspension heights.This study focuses on the determination of the parameter β_n which is the ratio of the sediment diffusion coefficient to the momentum diffusion coefficient of n th grain-size.A new relationship has been proposed involving β_n,the normalizing settling velocity of sediment particles and suspension height,which is applicable for widest range of normalizing settling velocity available in literature so far.A similar parameter β for calculating total suspension concentration is also developed.The classical Rouse equation is modified with β_n and β and used to compute grain-size distribution and total concentration in suspension,respectively.The computed values have shown good agreement with the measured values of experimental data. 相似文献
17.
Analytic stage–discharge formulae are derived for flow in straight trapezoidal channels, based on the 2D analytic velocity distribution in open channels given by Shiono and Knight [Shiono K, Knight DW, Turbulent open-channel flows with variable depth across the channel. J Fluid Mech 1991;222:617–46]. A simple hand-calculation method is provided. Legendre incomplete elliptic integrals of the first and second kinds and a binomial series expansion are used in the derivation of these analytic formulae, together with physically based hydraulic parameters, such as local friction factor (f), dimensionless eddy viscosity (λ) and secondary flow (Γ). The stage–discharge results obtained from the formulae are shown to be in good agreement with experimental data, as are the corresponding analytic velocity and boundary shear stress distributions. The influences of f, λ and Γ on the stage–discharge relationship are also discussed. 相似文献
18.
The Poisson distribution is required for the evaluation of counting results. Its availability can be checked with the dispersion index and graphically with a probability sheet. It is shown by an example that with increasing particle density the deviation from the Poisson distribution increases and how these anomalies become visible in the dispersion index and the per-cent error of the count. For the calculation of confidence intervals, a simple approximation formula and the asymptotic behaviour with growing random sample size are represented. The phenomena of over- and under-distribution as well as of “contagion” (Neyman distribution) are mentioned, and the high-speed method of counting according to Tippett and the variance-analytical evaluation methods are referred to. 相似文献
19.
VELOCITY PROFILES OF TURBULENT OPEN CHANNEL FLOWS 总被引：1，自引：0，他引：1
WANG Dianchang WANG Xingkui YU Mingzhong LI Danxun Doctor Prof Dept. of Hydraulic Engineering Tsinghua University Beijing China 《国际泥沙研究》2001,16(1)
1 INTRODUCTIONThe vertical velocity profile of open channel flows is the most basic infOrmation for the stUdy of flowresistance, channel bed stability, river nuvial process and sediment transport. Although it has been asubject of great interest for many years, there does not exist a consensus on some perPlexing questions,such as the position of the theoretical bed level. In order to investigate the properties of velocity profile,data measured in open channel nows from eight sources were … 相似文献
20.
This study is aimed at investigating the vertical velocity profile of flow passing over a vegetal area by an analytical approach. The soil ground is considered as pervious and thus non-zero velocity at the ground surface can be estimated. The soil and vegetation layers are regarded as homogeneous and isotropic porous media. Therefore the solution of the flow can be obtained by applying the theory of turbulent flow and Biot’s theory of poroelasticity after dividing the flow field into three layers: homogenous water, vegetation and pervious soil. The velocity distribution is compared with the experimental data of [Rowiński PM, Kubrak J. A mixing-length model for predicting vertical velocity distribution on flows through emergent vegetation. J Hydrol Sci 2002;47(6):893–904] to show its validity. In addition, five dimensionless parameters denoting the variation of slope, permeability of soil, Reynolds stress, density of vegetation, and relative height of vegetation are proposed to reveal their effects on the surface water flow. The analytical solutions of flow velocity can also be simplified into simpler expressions to describe the flow passing over a non-vegetated area. 相似文献