摘要:

An attempt is made to structure and unify a sizable amount of valuable but dispersed information in the relatively new field of forced aeration. This concept materialized as a measure to prevent cavitation in hydraulic structures with high velocity flows.

ISSN:0022-1686    

DOI:10.1080/00221688709499284

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Local scour around cylindrical bridge piers in uniform, cohesionless sediment was investigated experimentally. Three empirical functions which relate equilibrium scour depth with approach velocity, sediment size and How depth were obtained. The variations of equilibrium scour depth with approach velocity show that the depth of scour decreases at velocities just above the threshold until it reaches a minimum at about twice the threshold velocity. Thereafter, it increases again until a maximum is reached at the transition flat bed condition. At still higher velocity, the equilibrium scour depth decreases due to the formation of antidunes. Both the effects of sediment size and flow depth were found to be independent of the stage of bed particle motion and the approach velocity. Adjustment factors, for the effects of sediment size and flow depth were defined and evaluated.

ISSN:0022-1686    

DOI:10.1080/00221688709499285

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The recent boom in micro-computer hardware giving computing power unexpected some fifteen years ago, permits nowadays all engineering firms, if not individuals, to solve large scale problems. As a result, methods disregarded in the early seventy's now become attractive. One of those is the element method for pipe network analysis which is appealing when one considers not only network flow balancing but shock waves propagation analysis and storing of the network in a data base for quick references or modification of the system layout. The proposed modified method addresses the convergence behaviour by using a Newton- Raphson procedure on the residue of a partionned matrix system. Reordering of the elements gives a submatrix topology of particular types that can be inverted with efficient algorithms. It results in a matrix, the order of which corresponds to the number of loops in the system, to be inverted during the iterative process. Two examples, taken from previous papers, are analysed and discussed.

ISSN:0022-1686    

DOI:10.1080/00221688709499286

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Two new finite-difference schemes - Gabutti, and Beam and Warming - are introduced and compared for the analysis of unsteady free-surface flows resulting from the breaking of a dam. These schemes split the fluxvector into positive and negative parts, each of which corresponds to the direction of a characteristic, thereby allowing use of proper finite differences for the space derivatives. Central finite differences are used for subcritical flow and upwind differences are used for supercritical flow. The details of these schemes are presented and the computed results are compared with the analytical solution to demonstrate their validity. Because of their simplicity, these schemes are attractive for solving the dam-break problem, especially when supercritical flow is present.

ISSN:0022-1686    

DOI:10.1080/00221688709499287

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The development of a wind-induced boundary layer at the free surface downwind from a shore is studied analytically and experimentally in the case of a water body of limited depth. The analytical approach is based on the integral boundary layer equations assuming similarity, and velocity measurements in a wind flume. The experimentally observed transition to fully developed flow at a larger distance from the shore is also discussed in some detail.

ISSN:0022-1686    

DOI:10.1080/00221688709499288

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Turbulence measurements of the backward-facing step flow, including the reverse flow region, in an open channel were conducted using a two-component Laser Doppler anemometer. The mean velocity distribution and turbulence characteristics were revealed in and around the separated shear layer and recirculation region (separation bubble). Reattachment properties and the dynamic pressure distribution were analyzed varying the Reynolds and Froude numbers. The structure of the shear stress was also analyzed on the basis of the momentum equation. The separated step flow and its recirculation in an open channel are similar to that in boundary layer and duct flows. But, the former is more complicated than the latter, because the pressure is relaxed by the existence of the free surface.

ISSN:0022-1686    

DOI:10.1080/00221688709499289

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The flow in a suddenly expanding rectangular channel with movable bed comprised of 0.28 mm diameter material is studied using expansion ratios up to 4.5. The longitudinal velocity distribution is found to follow cosine law for small expansion ratios, which gradually changes to Gaussian distribution for expansion ratio of 4.5. The scour depth profiles are found to follow cosine law. The other characteristics studied include shape of separating stream lines and average height of longitudinal deposition bar.

ISSN:0022-1686    

DOI:10.1080/00221688709499290

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The eigenfunction solution to the problem of dispersion of neutrally buoyant material presented in Nokes et al. (1984) is extended to encompass the dispersion of particles with a rise or fall velocity in two dimensional open channel flow. Steady state conditions are modelled as this allows the turbulent diffusion equation to be separated and hence reduces it to a Sturm-Liouville eigenvalue problem. A general solution in the form of an eigenfunction expansion can be found for arbitrary velocity and diffusivity distributions but attention in this paper is centred on a comparison between a uniform velocity and diffusivity and the more realistic power law velocity and parabolic diffusivity. The power series technique of solution to ordinary differential equations is used to generate the eigenfunctions and eigenvalues for these two cases.

ISSN:0022-1686    

DOI:10.1080/00221688709499291

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Experiments were conducted to determine the behaviour of turbidity currents laden with non-cohesive silt (silica flour) moving down a slope the bed of which is covered with similar silt. Each current was sustained with constant inlet conditions for six to eight minutes. The motion of the head was not studied; measurements were concentrated on the continuous part of the current that was essentially constant in time but developing in space. Only supercritical currents were studied. The currents were free to erode sediment from, and deposit sediment on, the bed.

ISSN:0022-1686    

DOI:10.1080/00221688709499292

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221688709499294

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor