ISSN:0022-1686    

DOI:10.1080/00221680009498352

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Two-dimensional mesoscale experiments and a theoretical analysis show that the formation of clusters in a geotechnical filter is associated with fine particles that form arches between the grains of the matrix. The analysis of the stability of such arches indicates two critical parameters. The characteristic size of a cluster is obtained as a function of the uniformity of the matrix. If the matrix is uniformly spaced, the clusters occupy large domains, whereas if the matrix is non-uniform the clusters form in small pores.

ISSN:0022-1686    

DOI:10.1080/00221680009498353

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A tributary flowing into a reservoir or lake is nearly always at a density different from the receiving surface water. The difference is due to temperature, dissolved and suspended materials. An understanding of density current phenomena is therefore essential to lake or reservoir water quality modeling. In this study the dependence of plunging characteristics (dilution, depth and location at plunging) on inflow conditions (densimetric Froude number and channel aspect ratio) and bottom friction is quantified by an integral jet model. The jet-like flow from a shallow channel over a sloping bottom into standing water was studied as an approximation of the flow of a tributary into a lake or reservoir. The integral jet flow analysis used similarity hypotheses for transverse (Gaussian) and vertical (power law) velocity profiles. The model especially includes momentum reductions by bottom and side wall friction and a flow development region, which were not addressed in other previous studies, and were found to have a significant effect on dilution characteristics. Depth and volumetric flow rate of the inflow were determined at the “plunge” point of negatively buoyant (sinking) inflows which in turn is characterized by a critical densimetric Froude number. These characteristics can serve as inflow boundary conditions for lake water quality or sediment transport models in reservoirs including density currents. The model predictions were validated against laboratory data and one set of field data. For slopes steeper than 0.5°, dilution at plunging (QP/Q0) was found to increase linearly with inflow densimetric Froude number F0. Dilution is sensitive to the bed friction coefficient ct and the channel aspect ratio AR0, but insensitive to the bottom slope. Maximum dilution at plunging is given as a function of F0and (AR0cf).

ISSN:0022-1686    

DOI:10.1080/00221680009498354

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Laboratory and river data has been analyzed in terms of applied power principles to determine the relationships between absolute roughness and bed deformation under steady state sediment transport conditions. It has been found that the full spectrum of bed conditions can be represented by simple relationships within a single system.

ISSN:0022-1686    

DOI:10.1080/00221680009498355

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Grain shear stress has been used in many earlier studies to estimate the sediment transport capacity of interrill overland flow. However, this procedure may be flawed because turbulent eddies generated by large-scale roughness elements contribute to sediment transport in this type of flow, whereas they do not in deeper (river) flow. In this study a procedure is developed for estimating the proportion of total shear stress contributing to sediment transport in overland flow. Application of this procedure to 1506 flume experiments representing a wide range of discharge, slope and surface roughness conditions reveals that the proportion of total shear stress contributing to sediment transport decreases from 1.0 to 0.83 as roughness concentration increases from 0 to 0.37. Concomitantly, the grain shear stress expressed as a proportion of total shear stress decreases from 1.0 to 0.14. Clearly, the proportion of total shear stress involved in sediment transport is higher than is indicated by grain shear stress. Consequently, use of grain shear stress to predict the sediment transport capacity of overland flow on rough surfaces will result in significant underestimation of the transport capacity.

ISSN:0022-1686    

DOI:10.1080/00221680009498356

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This study addresses the longitudinal dispersive effect due to mass transport induced by progressive surface waves. Lagrangian drift is investigated to be the mechanism creating cross-sectional mean velocity variation, an essential component for Taylor dispersion. The dispersive effect is found to be more significant if the wave height is much larger thanwhereDis the diffusivity andTthe wave period. The longitudinal dispersion coefficient with a Stoke drift profile is first established. Subsequently drift profiles with viscous effect are considered and the dispersive effect increases substantially. The coupling of the oscillatory orbital motion of the pollutant particles under linear waves with background diffusion is further examined through a random walk numerical approach. Results show that, despite the possible modulation of the probability density with the wavy surface, the magnitude of the dispersion is not affected by the inclusion of the orbital motion.

ISSN:0022-1686    

DOI:10.1080/00221680009498357

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221680009498358

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The present paper concerns the computation of regime channel characteristics in cohesionless alluvium. The computational method proposed rests on the channel formation criterion derived from the thermodynamic principles, and on the expression of the aspect ratio determined in the earlier works of the authors on the basis of zero cross-transport rate at the regime stage. The thermodynamic considerations are based on the first and second laws, and the Gibbs' TdS equation: the alluvial stream is treated as an isolated, uniform system. The regime channel formation process is determined by the flow rate and the physical nature of the materials involved (alluvium and water): the sediment transport rate is viewed as an outcome of the phenomenon rather than as one of its characteristic parameters. The regime channel characteristics computed from the suggested method are compared with field and laboratory data of various sources.

ISSN:0022-1686    

DOI:10.1080/00221680009498359

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Details of recently undertaken numerical study to analyze the physics of the flow past a submerged vane is presented. The numerical model solves the fully three-dimensional Reynolds-averaged Navier-Stokes equations in conjunction with the standard two-equation k-t turbulence closure. The governing equations are formulated in generalized boundary-fitted coordinates to accurately resolve the bed topography and the shape of the vane. The bed roughness effects are introduced by means of a two-point wall functions approach. The predictions from the numerical model are compared against measurements from an experimental study performed in a deformable-bed straight rectangular channel. Detailed experimental measurements of all three components of velocity, both in the neighborhood as well as in the far field of the vane are compared to judge the performance of the numerical mod

ISSN:0022-1686    

DOI:10.1080/00221680009498360

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Numerical flow analysis in turbomachinery is an indispensable tool for water turbines design. Following the design of axial runner, the energetic and cavitation characteristics can be predicted using the numerical method. In this paper it is described how the multiobjective genetic algorithm aids the human decision of the best design solution, based on objective functions obtained by numerical flow analysis. Theoretical and empirical knowledge of the design procedure enables to start the optimization procedure with good initial geometry. A very effective procedure for developing water turbines has been provided merging design procedure, numerical flow analysis and multiobjective genetic algorithm.

ISSN:0022-1686    

DOI:10.1080/00221680009498361

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor