摘要:

Turbulence measurements were undertaken using a two-component laser Doppler anemometer (LDA) in a serpentine contact tank (CT) commonly used for water chlorination. A detailed examination of turbulent parameters was carried out and showed the significant effects of the baffle lee and the inlet and outlet of the tank on the CT's hydraulic efficiency. Turbulence levels were quantified along the tank and were found to be considerably high in the tank inlet, first and second compartments and to be decaying rapidly in the latter compartments. The decay rate of turbulence along the tank is similar to that of the grid generated turbulence. The turbulence generation mechanisms in the first compartment were identified using comparative studies of the turbulence characteristics in the backward-facing step flow obtained by Eaton and Johnston (1981) and in the plane wall jet flow obtained by Rajaratnam (1976). The main contribution of the high turbulence level in the compartment was found to be due to shear generated turbulence in the upper layer. Tracer measurements were also carried out and an optimum dispersion coefficient at the outlet of the tank was found to be 16.2 cm2/s. From the Marske and Boyle's equation (1973) in this tank, for b = 37, the dispersion coefficient is 2.9 cm2/s, which is one order smaller than that obtained from this study.

ISSN:0022-1686    

DOI:10.1080/00221680009498294

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper reports the numerical simulation of previously published laboratory experiments concerning deposition of a sediment mixture in a flume. The results of the simulation are analyzed and their interdependencies are discussed with reference to flume observations and previously published analyses. Cross-comparison of different parameters of the system (deposition rate, sediment transport, grain size) allows some validation of the system of equations of our modeling system. It may also give some clues and directions for further measurements and numerical experiments.

ISSN:0022-1686    

DOI:10.1080/00221680009498295

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A correction factor has been developed in this paper to account for the hiding and exposure mechanism of nonuniform sediment transport. This factor is assumed to be a function of the hidden and exposed probabilities, which are stochastically related to the size and gradation of bed materials. Based on this concept, the formulas to calculate the critical shear stress of incipient motion and the fractional bed-load and suspended load transport rates of nonuniform sediment have been established. These formulas have been tested against a wide range of laboratory and field data and compared with several other existing empirical methods. The predictions by these newly proposed formulas are very good.

ISSN:0022-1686    

DOI:10.1080/00221680009498296

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Debris flow is modelled using the equations governing the dynamics of a liquid-solid mixture. An upwind finite volume scheme is applied to solve the resulting differential equations in one dimension. These equations have a structure similar to those of the monophasic water flow, differing from them by the presence of some terms characteristic of the bifasic nature of the mixture, such as granular bed erosion velocity, sediment concentration, bed shear stress, etc. The model and the system of equations to be solved are presented with the description of the implementation of the upwind scheme for the resulting hyperbolic conservation system. The numerical method is first order in both space and time. The treatment of the source terms is specified in detail and some comparison with laboratory experiments are presented.

ISSN:0022-1686    

DOI:10.1080/00221680009498297

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Some open-channel empirical parameters lack exact values due to (a) not having definitive measurement methods and/or (b) not rendering a "properly-posed" system of equations in the formulation of their inverse problems. The values of these parameters are therefore susceptible to dataerrors, imperfections in governing equations or insufficiency of the gauged data used in inverse problems. Best values of such parameters in a mathematical sense can be identified by the implementation of inverse problems using optimisation methods but there are potential pitfalls. A comprehensive review of inverse problems is presented in this paper outlining some of the pitfalls in their implementation and illustrating the parameter quality conditions of "identifiability, uniqueness and stability". The uniqueness condition was approached by statistical methods in this paper. Other considerations of equal importance were found to include the compliance with the assumptions underlying optimisation methods and a careful selection of the objective function.

ISSN:0022-1686    

DOI:10.1080/00221680009498298

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We consider the dam break problem upon an inclined plane. The flow of a series of Newtonian fluids is generated by the collapse of a dam in a completely transparent channel with variable slope. The stage at given abscissa and the front wave evolution are accurately investigated using ultrasonic and image analysis facilities respectively. While the Navier Stokes and the continuity equations are properly rendered non dfmensional in the viscous regine and solved with the ID shallow water approximation. A successful comparison is shown between the experimental and the theoretical results.

ISSN:0022-1686    

DOI:10.1080/00221680009498299

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A large-eddy simulation of flow in an open channel has been carried out at the moderate Froude number,Fr= 0.66, and Reynolds number.Re= 20,800. A resolution has been used that allowed the simulation to be carried out on a workstation; thus enabling the results obtained to be viewed within an engineering context. The code used treats the free-surface exactly and allows it to freely deform with the underlying turbulence. The turbulent features found in this study are consistent with those found both by experimental observations and direct numerical simulations at lower Reynolds numbers where the free-surface has been treated as a stress free rigid lid.

ISSN:0022-1686    

DOI:10.1080/00221680009498300

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221680009498301

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221680009498293

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor