摘要:

Two of the most promising analytical models of unsteady friction in turbulent pipe flows are based on sharply contrasting hypotheses. One uses the history of the flow; the other uses instantaneous conditions. The purposes of this paper are to present an analysis using the former approach and to indicate how to determine which of the two methods is appropriate.

ISSN:0022-1686    

DOI:10.1080/00221689509498654

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An approximate equation is derived for wall shear stress in unsteady laminar pipe flows in terms of the instantaneous section mean velocity and acceleration. The equation, which is exact for a constantly accelerating or decelerating flow, is applied to solve for two types of pressure gradient functions, a transient start-up flow and a linearly reversing pressure gradient. Comparison with exact analytical solutions verifies that the equation is adequate for the two types of transient flows investigated, and for low frequency oscillating flows.

ISSN:0022-1686    

DOI:10.1080/00221689509498655

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Hydraulic erodibility of natural and engineered earth materials, including both soil and rock, can be evaluated in terms of a rational correlation between rate of energy dissipation of flowing water and an erodibility classification of the materials. Earth materials ranging on a continuum from cohesionless granular soil through massive hard rock can be characterized in terms of an erodibility index,Kh. The parameters of the index include key material and mass properties that can be measured in the field and at low cost. These properties include earth mass strength, block/particle size, discontinuity/inter-particle bond shear strength, shape of material units and their orientation relative to the flow. The relative magnitude of erosive power of flowing water is represented by its rate of energy dissipation for a variety of flow conditions, including head cuts, hydraulic jumps, grade changes, and open channel flow. A log-log plot of experienced rate of energy dissipation versus the erodibility index of the studied materials demonstrates a correlation from which the critical threshold to initiate erosion of a material can be predicted for any given set of hydraulic conditions. The method is based on an analysis of 137 field observations of spillway performance collected by the U.S. Department of Agriculture, observations at Bartlett Dam, Salt River Project, Arizona, at four South African dams, and published data pertaining to initiation of sediment motion.

ISSN:0022-1686    

DOI:10.1080/00221689509498656

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Laboratory experiments have been conducted to provide data for modelling the direction of sediment transport on a transverse sloping alluvial bed. Conditions with prevailing bed-load transport, and conditions in which a significant part of the bed material is transported as suspended-load are studied. The effect of a sloping bed on the direction of sediment transport is determined by conducting bed-levelling experiments. Comparison of the results with data of curved flume experiments and experience gained with numerical computation of the bed topography in natural rivers yields the conclusion that, at least for bed-load transport, a distinction should be made between laboratory conditions and natural rivers. For conditions with suspended sediment transport the transverse slope effect can not be modelled identical as for bed-load transport.

ISSN:0022-1686    

DOI:10.1080/00221689509498657

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A method has been developed for obtaining surface-velocity fields in unsteady flows which is useful for hydraulic model studies. The method is based on the established technique of Particle Tracking Velocimetry (PTV) but unlike other whole-field systems is suitable for use over relatively wide areas. Results are presented from its application to flows around conical model islands with uniform sloping sides from which strong vortex shedding occurs. To allow an assessment of accuracy, simultaneous LDA measurements were taken in the wake of an island and comparisons of velocity prediction are presented.

ISSN:0022-1686    

DOI:10.1080/00221689509498658

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The problem of computing flows in combined dendritic and looped networks of channels is shown to be closely related to the hydraulic properties of the network. This relation is expressed here in the simplest of graph-theoretical terms in such a way as to provide a completely general, unconditionally stable, accurate and fast method of solution. In particular, once any such model is instantiated, its running time increases only linearly with the number of grid points used, regardless of the complexity of the network. The algorithms, which are elaborated here for the example of sub-critical flow conditions using computer-algebraic procedures, can be easily applied to urban-drainage and irrigation networks in a physically transparent way. They thus lend themselves particularly well to mixed logical and numerical optimisation in real-time control applications.

ISSN:0022-1686    

DOI:10.1080/00221689509498659

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In a hydraulic jump, the supercritical flow suddenly changes to subcritical flow forming steep gradients of flow depth and velocity. In the numerical simulation of this flow, proper grid distribution can play a crucial role in the prediction and resolution of the solutions. In this paper, two different numerical schemes - Mac- Cormack (second-order accurate in space and time) and two-four (fourth-order accurate in space and secondorder accurate in time) -are used with grid adaptation to numerically simulate the hydraulic jump at different Froude numbers in a rectangular channel. Rai and Anderson's method is used to determine the grid speed; however, a different partial differential equation based on the conservative principle of grid arc lengths for clustering the grid points in one-dimensional flow is used along with the Boussinesq equations to simulate the flow.

ISSN:0022-1686    

DOI:10.1080/00221689509498660

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

PHYSICAL MODELS AND LABORATORY TECHNIQUES IN COASTAL ENGINEERINGby S.A. Hughes, World Scientific Publishing, HB. 568 pp., ISBN 981 02 1520 1.

ISSN:0022-1686    

DOI:10.1080/00221689509498661

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A numerical model for three-dimensional simulation of water flow in rivers with large roughness elements is developed. The bed roughness elements are large stones and rocks in the rivers. The model uses a finite volume method to solve the Navier-Stokes equations for three dimensions on a general non-orthogonal grid. The k-e turbulence model is used to solve the Reynolds-stress term. A porosity model is developed to model the bed roughness elements. The porosity model is used in combination with the solution of the Navier-Stokes equations to calculate interactions between porous and non-porous areas. To test the model, a reach of the Norwegian river Sokna is modelled. Velocity measurements from the river are taken at a number of locations and at several discharges. The measured velocities compare well with the results from the numerical model.

ISSN:0022-1686    

DOI:10.1080/00221689509498662

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689509498663

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor