摘要:

Solute concentrations in streams due to instantaneous slug releases are frequently influenced both by decay and by exchange with dead zones, among others. Based on the transient storage equations with first-order decay terms, explicit relationships are given for the computation of the zeroth to third temporal moments. The equations presented were applied within the framework of moment-based similarity functions which yield approximate temporal distributions of concentration. Results thus obtained were subsequently compared to finite difference solutions of the transient storage equations, in order to investigate the relationship between these approaches. Within the previously established ranges of applicability of the two similarity functions employed the comparisons indicated fairly good agreement.

ISSN:0022-1686    

DOI:10.1080/00221689509498559

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In the paper die concept of active (or mixing) layer, on which almost all the approaches of non-uniform sediment transport in rivers are based, is reviewed. Accounting for bed level fluctuations, mass balance equations are treated in the same way as Reynolds decomposition for turbulent motion: instantaneous variables are decomposed in the average, over a large number of realizations, and in the fluctuating pan. The resulting equations are correct from a theoretical point of view and have precise physical meanings. The theoretical findings are compared to some experimental data by Ribberink [1987].

ISSN:0022-1686    

DOI:10.1080/00221689509498560

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A finite element computational algorithm for the solution of one-dimensional, unsteady turbidity currents is presented. The layer-averaged governing equations form a hyperbolic system consisting of three equations, namely continuity and momentum equations for the flow, and mass conservation equation for the sediment. Tracking the front of a propagating turbidity current is akin to the problem of predicting the propagation of a dam-break wave over a dry bed. The standard Galerkin formulation does not give good results when applied to the highly nonlinear flow regime near the front, so the dissipative-Galerkin technique (Petrov-Galerkin technique) which has a selective damping property, is used. The numerical model is applied to the case of a turbidity current developing along a sloping bottom. The computed results compare favorably well against both the relationship proposed by Britter and Linden (1980) to estimate the speed of density currents fronts and the experimental observations made by Altinakar, Graf, and Hopfinger (1990) for weakly-depositional turbidity currents. Satisfactory results are also obtained in both the simulation of an internal hydraulic jump in a turbid underflow and the estimation of the amount of sediment deposited by a turbidity current event.

ISSN:0022-1686    

DOI:10.1080/00221689509498561

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Turbulent characteristics of flow velocity in a natural river were systematically analyzed in this study. Flow velocities were measured with time at six different lateral locations and at three different vertical elevations on a major navigable waterway in the United States. Analyses of the velocity data include the cross-sectional and vertical distributions of longitudinal and transverse velocity components (u,v), the fluctuating velocity components (u1,v1) and their frequency-distribution curves, turbulent intensities (σx, σy), and turbulent shear stress (-ρu1,v1). These analyses have shown that the strongest velocity fluctuation occurs near the main channel area above the river bed.

ISSN:0022-1686    

DOI:10.1080/00221689509498562

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An quasi-analytic method is presented for the calculation of free-surface flow over sills (e.g. dams under construction). Starting point is the set of shallow-water equations (SWE) valid for quasi-uniform flow. To make these equations also valid for flow over sills, adaptations to the SWE are proposed, introducing coefficients in the convection, pressure and friction terms. These terms are derived from analytical and numerical calculations with an experimental check.

ISSN:0022-1686    

DOI:10.1080/00221689509498563

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The differences between the undular jump and the undular surge are described. Further, the limit approach flow depth and the channel width are defined for undular jumps governed by the Froude similarity law. Based on previous and present observations, the main flow characteristics of undular jumps are established. These include surface characteristics along the axis and the walls of the rectangular channel. Also, generalized surface profiles are presented. Finally, the formation of shocks is physically explained as a breakdown of the supercritical approach flow.

ISSN:0022-1686    

DOI:10.1080/00221689509498564

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689509498565

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The characteristics of turbulent flow in open channels with steep slopes are studied experimentally and numerically. Velocity measurements indicate that the von Karman constantKof the log law of the wall remains constant in both the subcritical and supercritical regimes while the constantAdecreases with increasingFrnumber. A modified Preston tube method is developed for estimating the boundary shear stress in flows with unknown constant of the log law of the wall and gives satisfactory results. Two low-Returbulence models of thek-ε type are used in the computational study and are found to reproduce satisfactorily the velocity distribution except in the case of very steep slopes (highFrnumber). They also predict the reduction of the viscous sub-layer in supercritical flows but they fail to predict the reduction of the turbulence kinetic energy and turbulence intensities for such conditions due to their isotropic nature.

ISSN:0022-1686    

DOI:10.1080/00221689509498566

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689509498567

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689509498568

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor