摘要:

Movements of gold particles, along with gravel bed load and suspended load, were simulated in a scale model of a section of the Yangtze River in a mountainous area. The experiment showed that gold particles moved together with the gravel bed load, mainly in saltation. They consistently moved along a narrow path on the river bed. This can be called the path of gold. The path was only a fraction (1/10 to 1/2) of the width of the river bed. Almost no gold was found out side this path, although suspended load and gravel bed load were deposited there. The formation of gold placers was close to braided sections and submerged bars, with the most favorable places for gold to accumulate being in deep pools behind such bars.

ISSN:0022-1686    

DOI:10.1080/00221689409498705

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The study investigates the threshold condition for the initiation of cohesionless sediment transport on a nonhorizontal streamwise slope. Theoretical study of the stability of a sediment particle lying on a non-horizontal bed slope shows that the critical shear stress is a function of the streamwise bed slope. Experiments conducted with a closed-conduit flow show that the equation derived from force analysis adequately evaluates the critical shear stress of sediments lying on slopes ranging from steep positive to negative (adverse). Tests conducted with a closed-conduit flow avoid the problems associated with those conducted with an open channel flow. In the latter flow condition, uniform flow is often difficult to achieve in a steep channel, and impossible to achieve when the streamwise bed slope is adverse.

ISSN:0022-1686    

DOI:10.1080/00221689409498706

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The three dimensional flow field for local scour at bridge abutments was measured in the laboratory using the hydrogen bubble technique. The results show that the flow structures are dominated by a large primary vortex and its associated downflow and that they are confined predominantly within the scour hole beneath the original bed level. The value of this paper is also in the large amount of data collected, which would be useful for the future development and calibration of numerical models of flow and scour at bridge abutments.

ISSN:0022-1686    

DOI:10.1080/00221689409498707

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A mathematical model describing mean sediment concentration and turbulent boundary layer of wave-induced sheet flow is presented. The interaction of the fluid and sediment in two-phase flow is considered. The diffusion coefficient and eddy viscosity are respectively expressed as functions of gradient Richardson number, which measures the effect of suspended sediment on turbulent transfer of mass and momentum. Computational results reveal that the presence of suspended sediments retards mean velocity profile and its corresponding phase shift. The friction factor which differs from rough wall law is obtained from the integration of momentum equation. An explicit expression based on the approximation of friction factor is given to define the region where sheet flow occurs. Observations in the laboratory provide support for the validity of this criterion. The predicted mean concentration profile is compared favorably with measurements.

ISSN:0022-1686    

DOI:10.1080/00221689409498708

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Two mathematical formulations for the computation of transient flow in piping systems are compared with experimental data. The formulations are: a four-equations fluid structure interaction model (FSI) that includes Poisson coupling, and a two-equations model for the fluid. Both models are solved numericaly using the method of characteristics. A partial-closure of a valve located at an intermediate point in a pipeline is used to create transient flow. The two-equations model computed the maximum pressure peak satisfactorily but the FSI model gave an overall better simulation. An unsteady-friction model, added to the FSI model, did not influence the final results significantly. The experimental procedures followed to obtain the valve characteristics and the pressure history along the pipeline are explained in detail. Excellent numerical results at the valve are obtained when experimental data is used to simulate the time-dependent boundary condition.

ISSN:0022-1686    

DOI:10.1080/00221689409498709

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A mathematical model was developed to predict the air concentration profiles in the deaeration zone below a spillway aerator by solving the conservation equations of mass and momentum. The turbulent diffusion coefficient was calculated by ak-ε model and the air-water mixture was treated as a stratified flow. To test the mathematical model a series of experiments was conducted. Air was injected from the bed of a flow channel and air concentration profiles were measured at various downstream sections. From the comparison of the computer predictions with the experimental data it was concluded that the present analytical approach was satisfactory for practical purposes and showed promise for further development.

ISSN:0022-1686    

DOI:10.1080/00221689409498710

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An implicit time integration method for the simulation of steady and unsteady flow in pipes and channels is presented. It is based on the theory of Total Variation Diminishing (TVD) methods. A conservative linearization leads to a block tridiagonal system of equations which can be cheaply solved by means of a non-iterative matrix decomposition method. It keeps the advantages of classical implicit schemes, and properly deals with all kinds of flow. It is specially suited for steady flows including phenomena such as hydraulic jumps and also gives satisfactory results for time dependent problems. Several test cases are shown to illustrate the performance of this implicit technique in single channels and networks.

ISSN:0022-1686    

DOI:10.1080/00221689409498711

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Mean flow distributions of primary velocity and boundary shear stress were measured in a wide closed duct with a range of asymmetric compound cross-sections. The cross-sectional geometries included three different wall angles, vertical, 1:1 and 1:2 (vertical:horizontal) at the interface between the shallow and deep subsections. Results are presented for the effect of relative depth and wall angle upon primary velocity, boundary shear stress and friction factors. The particularly detailed boundary shear stress measurements indicate the presence of secondary flow on the flood plain even at the lowest relative depths, where it would not normally be identified by coarser spacing of the data.

ISSN:0022-1686    

DOI:10.1080/00221689409498712

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The risk of oil spills in rivers has increased due to oil storage facilities along rivers, inland navigation, major oil transport pipelines that cross rivers. Inland oil spills are more frequent than ocean oil spills but are usually of smaller volumes. Oil spills in inland waterways can have enormous environmental and economical impacts because of their closeness to populated areas and economic centres. Previous review studies on oil spill modelling have concentrated on ocean oil spill modelling. In this paper all existing major river oil spill models are reviewed. The specific needs of the river oil spill models that are different from the ocean oil spill models are identified. The physico chemical oil spill processes which form the model are discussed. A comparison of the different models are presented. Simulations are presented to demostrate state-of-the-art in river oil spill models.

ISSN:0022-1686    

DOI:10.1080/00221689409498713

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689409498714

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor