摘要:

Based on model-technical as well as physical considerations a nodal-point relation at bifurcations is proposed for one-dimensional (ID) network morphodynamic models: the ratio between the sediment transports into the downstream branches is proportional to a power of the discharge ratio. The influence of the nodal-point relation on the behaviour of the morphodynamic model is analyzed theoretically. The exponent in the nodal-point relation appears to be crucial for the stability of the bifurcation in the model. For large values of the exponent, the bifurcation is stable, i.e. the downstream branches remain open. For small values of the exponent, the bifurcation is unstable: only one of the branches tends to remain open. The exponent also has a strong influence on the morphological time scales of the network. The conclusions from the analysis have been verified by numerical simulations using a package for one-dimensional network modelling.

ISSN:0022-1686    

DOI:10.1080/00221689509498549

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Detailed understanding of sediment particles' motion inside a tumbling mill as typical laboratory abrasion setup is needed when laboratory experiments on fluvial abrasion of river sediments with mixtures are planned. The abrasion distance for each particle may be determined through its real distance travelled on the surface of the mill charge only. This distance was found to be less than 50% of the mill circumference for one particle's revolution in this specific laboratory arrangement. The quite current approach to use the product of the number of revolutions and the mill circumference was therefore to be modified. A correction procedure is proposed, which depends on the mill rotational speed, the mill charge and the particle size, relative to the mill diameter. The recommended limits of process parameters that should be used for an abrasion experiment are given. Limitations of this sort of set-up in terms of similarity of particle movement and velocity are also discussed.

ISSN:0022-1686    

DOI:10.1080/00221689509498550

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A 3-D numerical model has been developed to investigate transport processes of solute in a compound open channel. The Navier-Stokes equations have been numerically solved in conjunction with the linear and nonlineark-ε models to predict flow fields and turbulent parameters. The predicted velocity field and eddy viscosity are then used for solving the solute transport equation to predict solute transport rates. The hydrodynamic and solute transport models have been applied to the experimental studies undertaken by Wood and Liang (1989) and the results obtained from both the linear and non-lineark-ε models are compared with their results. This comparison clearly shows the influence of the secondary currents upon the mixing processes.

ISSN:0022-1686    

DOI:10.1080/00221689509498551

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A time-dependent wave equation is developed for waves propagating over permeable rippled beds taking account of the effects of porous medium. The mean water depth and the thickness of porous layer are assumed to be slowly varying compared to the wavelength of surface waves, and the spatial scale of ripples is assumed to be the same as the wavelength of surface waves. Coupled parabolic equations are formulated from the derived wave equation, following Kirby"s (1986) method. Some numerical examples and experimental results of effects of seabed permeability on the Bragg scattering are shown in one-dimensional case and numerical examples are also shown in two-dimensional case. In the one-dimensional case, we can utilize the Bragg reflection to reduce transmitted waves behind ripples; however, in the two-dimensional case, wave heights behind ripples do not always decrease due to the diffraction effect dependent on the scale of ripple field.

ISSN:0022-1686    

DOI:10.1080/00221689509498552

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Data from turbulent flows over steep-sided trapezoidal trenches and a backward-facing step in an open channel were used to assess the performance of three alternative models of turbulence viz. the industry-standardk-ε model, a second-order closure which is linear in the Reynolds stresses and another which is quadratic in the same quantities. The computations were carried out on body-fitted coordinates and were carefully checked for numerical accuracy. It is demonstrated that the mean-flow parameters are predicted equally well by all models but that the details of the turbulence structure are best captured by the second-order closures. The significance of these results to the practical prediction of trench flows is discussed.

ISSN:0022-1686    

DOI:10.1080/00221689509498553

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper dcsribes a Large Eddy Simulation of steady uniform flow in a symmetric compound channel of trapezoidal cross-section with flood plains at a Reynolds number of 430.000. The simulation captures the complex interaction between the main channel and the flood plains and predicts the bed stress distribution, velocity distribution, and the secondary circulation across the floodplain. The results are compared with experimental data from the SERC Flood Channel Facility at Hydaulics Research Ltd, Wallingford, England.

ISSN:0022-1686    

DOI:10.1080/00221689509498554

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Experimental and numerical results concerning the flow induced by the break of a dam on a dry bed are presented. The numerical technique consists of a shock-capturing method of the Godunov type. A physical laboratory model has been employed to infer properties and validity of the numerical solution. Attention is also given to the applicability of the mathematical model, based on the shallow water equations, to this class of problems.

ISSN:0022-1686    

DOI:10.1080/00221689509498555

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Thek-ε turbulent model is used to obtain a mathematical model of a vertieal round buoyant jet in static, linearly stratified environment. The Hybrid Finite Analytic Method and a staggered grid are used to calculate the whole field of this flow pattern. The centerline velocity and temperature, the maximum height of rise, the height of neutral buoyancy, the demarcation between buoyant jet and mushroom-cloud regions, and the demarcation between mushroom-cloud and spreading layer regions are calculated.

ISSN:0022-1686    

DOI:10.1080/00221689509498556

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689509498557

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689509498548

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor