摘要:

A study of bedforms steepness in alluvial streams during the low flow regime is reported in this paper. By means of an empirical approach two main results were found:

ISSN:0022-1686    

DOI:10.1080/00221689209498904

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

ENERGY DISSIPATORS AND HYDRAULIC JUMPby Willy H. Hager (Laboratory of Hydraulics, Hydrology and Glaciology VAV, Swiss Federal Institute of Technology-ETH, Zurich, Switzerland). Published in 1992 by KLUWER ACADEMIC PUBLISHERS, Dordrecht/Boston/London as Water Science and Technology Library (Vol. 8), PO Box 17, 3300 AA Dordrecht, The Netherlands. ISBN 0-7923-1508-1. Price H.B. f 150, U.S. $ 89, £ 52.

ISSN:0022-1686    

DOI:10.1080/00221689209498905

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Using the results of experiments it is shown that ridges on the bed of free-surface flow are produced only when there is a stream wise variation in the mean velocity, i.e. ∂U/∂X≠ 0 whereUis the mean velocity,Xis the flow direction. Current understanding of the ridge formation mechanism suggests that ridges are formed by stationary (lee) waves. In the steady flow the effect of the lee waves is to accelerate and decelarate the boundary layer flow. When the deceleration reaches a critical value, a turbulent boundary layer is separated and an eddy is formed downstream of the wave trough. The eddy moves upward in the shear flow with captured bottom particles. As ridges grow, the amplitude and the length of the wave increase. When the steepness of the lee waves increases, three-dimensional instability of the lee waves is observed.

ISSN:0022-1686    

DOI:10.1080/00221689209498906

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper presents the results of an experimental study on intersecting circular turbulent jets of unequal momentum fluxes for an angle of intersection equal to 60 degrees. The flow has been divided into two regions, region 1 extending from the nozzle to the intersection point and region 2 covering the field downstream of the intersection point. In both these regions, the velocity and pressure fields were measured and analyzed and correlated with the ratio of the jet velocities at the two nozzles.

ISSN:0022-1686    

DOI:10.1080/00221689209498907

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Predictive mathematical models of hydraulic jump in rectangular sloping channels with a positive or negative step are presented. The models are verified with experimental data. A generalized equation for the modified Froude Number which accounts for channel slope and step height is suggested which is applicable to sloping channels with or without a step. A practical method for the determination of the sequent depth is presented and some important characteristics of the hydraulic jump in sloping channels with a step are also studied.

ISSN:0022-1686    

DOI:10.1080/00221689209498908

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A detailed analysis of energy conversions and fluxes in wind-induced countercurrent flow is provided. At the free surface mechanical energy is supplied to the waterbody by the wind. Via stages of pressure-volume work and kinetic energy (divided into a mean and a fluctuating part), the energy will ultimately leave the flow as a surface heat flux.

ISSN:0022-1686    

DOI:10.1080/00221689209498909

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Surface-active agents, present in water running at low velocities in laboratory flumes, will adsorb to the water surface and form a film on the upstream side of a surface barrier in the flow. This film has an impact on velocity measurements at the water surface. A force balance on the film indicates that the shear stress of the moving fluid below the film is equal to the negative gradient of surface tension within the film. Previous empirical measurements did not agree with laminar boundary layer theory used to predict the surface tension gradient with distance in the film. New experiments were conducted, and flow visualization showed that transition from a laminar to a turbulent boundary layer occurred. A new theory was formulated to include transition, allowing the steady-state film length to be estimated. Since the film length does not scale with Froude number, surface velocity measurements in the film region for laboratory flumes and hydraulic model studies will not scale properly. The estimate of film length from the theory formulated and tested in this paper may be used to determine if representative surface velocity measurements may be made in hydraulic model studies or experimental laboratory flumes.

ISSN:0022-1686    

DOI:10.1080/00221689209498910

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

ENVIRONMENTAL HYDRAULICS(Proceedings of the International Symposium in Environmental Hydraulics, Hong Kong, 16-18 December, 1991) edited by I. H. W. Lee and Y. K. Cheung. Balkema, Rotterdam/Brookfield, ISBN 90 54 10 03 70, price Vol. I and II H.B. £ 238,50.

ISSN:0022-1686    

DOI:10.1080/00221689209498911

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Conditions were investigated under which a given flow may exist at two sub-critical uniform depths, one with flow only in the main channel, one with flow also on the floodplains. Such stage-discharge discontinuities were found only for channels with a narrow, deep central channel and wide rough floodplains. The increase in Manning's n caused by momentum transfer to floodplains was found to be related to a factor representing the ratio of floodplain drag to the main channel driving force. A similar relationship was found for trapezoidal flume data provided the correct location of the interface between main channel and floodplain was chosen. The resulting equation enables correction of the Manning equation to allow for momentum transfer.

ISSN:0022-1686    

DOI:10.1080/00221689209498912

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The throttling orifice is introduced into air-cushion surge chambers to improve stability. The presence of the orifice adds another nonlinear term to the dynamic system, and its effect becomes predominant for oscillations with large displacements. By means of linearization, the type of singularities in the phase plane and their stability criteria in case of small oscillations are identified. The nonlinear analysis by direct numerical integration indicates that the system manifests itself as Hopf bifurcation with the surge-chamber size as its controlling factor. The bifurcation point corresponds to Svee's stability criterion. Before bifurcation, an unstable limit cycle may occur around the equilibrium state of practical interest, and it defines the domain of asymptotic stability. After bifurcation, two limit cycles may occur. Because of the existence of the stable one, the chamber size can be smaller than that specified by the Svee criterion. The orifice has stabilizing effect on surge motions.

ISSN:0022-1686    

DOI:10.1080/00221689209498913

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor