摘要:

Details are given herein of the development and application of a three-dimensional layer-integrated model to predict suspended sediment fluxes in estuarine and coastal waters. The model involves using the finite difference technique to solve the equations of mass and momentum conservation and the transport equation for suspended sediment. The operator splitting technique and a highly accurate finite difference scheme have been used to solve the suspended sediment transport equation. The model has been tested against analytical solutions and laboratory measurements for different flow types and boundary conditions, and has also been applied to predict suspended sediment fluxes in the Humber Estuary, UK.

ISSN:0022-1686    

DOI:10.1080/00221689609498470

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Suspension of sediment particles has been found to be in close association with the bursting process in a turbulent wall-layer flow. This mechanism forms the physical basis of the present heuristic turbulent diffusion model for suspended sediment in open channel flows. It is formulated using the bursting intensity and the mean duration of turbulent bursts. The bursting intensity as the fractional vertical turbulence intensity contributed by bursting is determined from its percentage, estimated using existing measured data, among the total vertical turbulence intensity calculated using an analytical solution in the literature. A skewed parabolic profile is obtained for the turbulent diffusion coefficient of suspended sediment. The unique parameter involved in the model is calibrated using measured data spanning wide ranges of suspension indices and sediment concentrations. It is found to increase with particle suspension index, indicating physically that more energetic turbulent bursts with longer durations are needed for the suspension of coarser and heavier particles. The developed model is shown to perform satisfactorily through comparison with independent laboratory data. Further refined models can be expected, given the enhanced understanding of the turbulent bursting phenomenon.

ISSN:0022-1686    

DOI:10.1080/00221689609498471

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Sediment routing in rivers can be described in terms of three one dimensional equations: the Saint Venant continuity and dynamic equations of motion, and sediment mass balance. The solution of these equations requires two supplementary relationships for friction resistance and sediment transport, which contain empirical constants in one form or the other. It is often difficult to determine these empirical constants a priori with any degree of certainty. One method of determining the constants in a particular situation is to optimise on observed river data. This paper deals with such an investigation. In this investigation a novel coupled linear implicit method is used to solve the sediment routing equations and the sediment routing parameters are identified by using the gradient techniques of optimisation. These are applied to real river data for the Missouri River.

ISSN:0022-1686    

DOI:10.1080/00221689609498472

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The Saint-Venant equations for unsteady, non uniform open-channel flow are obtained by partial integration of the Prandtl equations for newtonian or non newtonian fluids. The equations are integrated with self-similar solutions near steady, uniform flow and are extended to turbulent mean flow. For weakly unsteady, non uniform flow, a closed-form solution is given for a) the Saint-Venant kinetic energy integral with a dissipation coefficient depending only on the Reynolds number and the roughness, b) the friction coefficient varying in space and time and c) velocity and shear stress profiles varying in space and time.

ISSN:0022-1686    

DOI:10.1080/00221689609498473

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

This paper is concerned with the dual head-discharge characteristics of a modified chimney weir. It is shown by an optimization procedure that the modified chimney weir having an inward trapezoidal weir over an inverted V-notch can produce discharges proportional to both the logarithm of the head as well as the linear power of the head reckoned independently over two different reference planes, within a prefixed maximum allowable percentage error from the theoretical discharge. A new technique is adopted to optimize the weir parameters, in order to obtain the maximum ranges of measurement under logarithmic, linear as well as combined characteristics. In the case of linear weir it is shown that it is possible to enhance the linearity range of the chimney weir by more than 540% and for a weir with constant indication accuracy by more than 350%. In addition, about 86% of the overall depth of the designed linear weir and over 90% of the logarithmic weir is converted as the corresponding measurable ranges. Experiments with four typical weirs give consistent constant average coefficient of discharge for each weir confirming the theory. The practical application of the weir in minor irrigation, hydraulic and other engineering fields is highlighted.

ISSN:0022-1686    

DOI:10.1080/00221689609498474

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A general equation is proposed for the determination of water-surface slope of a steady, gradually varied openchannel flow at a critical section. Thereupon the different types of singular points and water-surface slopes are given at such a section caused by changes in (1) bed slope, (2) channel width, (3) surface roughness of the channel, and (4) discharge, or their combinations. Although these factors are very different they have similar hydraulic effects on the occurrence of a certain type of singular point and water-surface slope. It is shown that a saddle type singular point is the only one which can become a control. The water-surface slopes at a critical control are evaluated using the proposed equation and are verified by the experimental results of Wilkinson (1974) for cases (1) and (2).

ISSN:0022-1686    

DOI:10.1080/00221689609498475

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In modelling rainfall-runoff and flows in drainage systems it can be advantageous to adopt a neural network (NN). Unfortunately traditional NN learning procedures such as back-propagation can be very slow and expensive to carry out. However, if radial basis function (RBF) networks are adopted with radial centres fixed by a suitable data clustering technique then good results may be obtained very much more rapidly. RBF networks are here shown to be very effective in modelling runoff for a large rainfall database and to give broadly comparable results to those obtained by fine-tuning the much slower back-propagation procedure. The specific model is based on the assumption that runoff depends on time, rainfall intensity I, the rate of change of I and the integral of I.

ISSN:0022-1686    

DOI:10.1080/00221689609498476

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Recent studies have shown that the trajectories of drogued drifters on the ocean surface have a fractal structure which may be described by fractional Brownian motion. A method is detailed which allows the generation of fractional Brownian motions within a two dimensional particle tracking ocean surface dispersion model. This technique enables the modeller to more accurately mimic particle paths, enhancing the prediction of diffusion and dispersion.

ISSN:0022-1686    

DOI:10.1080/00221689609498477

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689609498478

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689609498479

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor