摘要:

Field observations provided the basis for a numerical model designed to quantify the vertical mass flux of material initially injected at the base of the water column in a small lake; a process called sub-aqueous disposal. Eddy diffusion estimation largely controlled the transport behaviour, highlighting the need for measurements of diffusion in deep strongly stratified environments. The model followed the contaminant development over 40 years and showed that (i) it is unlikely that any material can ever be completely disposed of over realistic scales and (ii) within the bounds limited by uncertainty in eddy diffusivity, turnover penetration and surface layer precipitation-driven flushing are the mechanisms most likely to have bearing on the contaminant distribution.

ISSN:0022-1686    

DOI:10.1080/00221689709498423

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The relaxation of pore pressure in the core of a rockfill dam, that is caused by a rapid discharge of the water from the reservoir, is controlled by two different time scales. The time scale due to de-consolidation is irrelevant, whereas the time scale due to the displacement rate of the phreatic surface is equal to the ratio between the conductivity and the porosity. If the core is vertical and slender, the motion of the phreatic surface is governed by an ordinary first order differential equation. If the discharge is instantaneous, the equation is separable and has been solved. Experiments with a Hele Shaw cell show that the agreement between theory and experiment is not too good. The explanation is that the discharge of liquid from the reservoir in the Hele Shaw cell is not effectively instantaneous. The practical result implies that the relaxation time is approximately 1 year for a core of a real dam composed of soil whose height and width are 50 and 4 meters, respectively.

ISSN:0022-1686    

DOI:10.1080/00221689709498424

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

It is well-known that the value of the nearbed sediment concentration peaks near the time of the passage of the wave crest, when the value of the wall stress reaches a maximum. But the presence of a second peak in sediment concentration near the time of flow reversal has also been observed in experiments. Using existing techniques for flow modelling of wave boundary layer and modelling of suspended sediment in combination with a new wall boundary condition for sediment the secondary peak has also been observed in numerical experiments. Evidence suggests that the second peak is caused by a break up in the boundary layer due to flow reversal leading to high diffusivitics near the wall.

ISSN:0022-1686    

DOI:10.1080/00221689709498425

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In compound open-channel flows, it is very important to clarify an interaction mechanism between the mainchannel and flood-plains induced by coherent vortices, so-called the“intermittent upward secondary currents”and the“large-scale horizontal vortices”, as shown in Figure 1. In the present study, time-averaged structures of secondary currents were revealed experimentally by making use of a two-component fiber-optic Laser Doppler Anemometer (LDA). Next, a new quantitative visualization technique called the “Particle-Tracking Velocimetry (PTV)” was used to investigate evolutionary patterns of horizontal large-scale vortices, which are the ultimate interest in a shallow water flood-plain. By this technique, instantaneous velocity components in arbitrary horizontal plane were obtained at all grid points of laser-light-sheet (LLS) from continuous four images of one particle, and space-time correlation structures of coherent vortices between the main-channel and flood-plain were investigated by using a conditional sampling technique.

ISSN:0022-1686    

DOI:10.1080/00221689709498426

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The three-dimensional skewed flow around circular cylinders placed on smooth, rough rigid and rough mobile (with scour hole) beds was analyzed in terms of the theories of the three-dimensional turbulent boundary layer (3DTBL). Performance of various cross-flow and near-wall similarity models was evaluated and the effects of roughness and scour hole were discerned. Perry and Joubert's model gave best results among cross-flow models. All near-wall models gave nearly identical results because of the small cross-flow but none gave good results. However, some indications of the near-wall similarity were found. The polar plots were found to be helpful in interpreting the cross-flow behavior, especially the effects of roughness and scour hole on it.

ISSN:0022-1686    

DOI:10.1080/00221689709498427

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Observation indicates that if the discharge in a conduit exceeds a certain value, the flow springs out from the whole outlet cross section, but below this discharge, the flow detaches itself from the top of the conduit before the outlet and forms a cavity whose shape and position is stable. A reduction of the discharge allows the cavity to move upstream, at first gradually, then with further discharge reductions a rapid motion can be detected, and in the end, the whole length of the conduit is seen to return to the free-surface regime, signalling the end of the cavity-flow regime. The discharges that mark the initiation and end of the cavity flow are close, so that this phase of the transitional flow is relatively abrupt.

ISSN:0022-1686    

DOI:10.1080/00221689709498428

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The supercritical flow in open-channel transitions often produces discontinuities in the flow variables. Depending on the size, shape and kind of channels, the flow can generate normal/oblique shock waves, expansion waves, hydraulic jumps and sometimes complex wave patterns due to multiple reflection of the waves at the boundary and their subsequent interactions with one another. In the numerical simulation of these flows, uniform grid distribution may introduce detrimental effects in the prediction and resolution of the How details. The use of the presently available numerical schemes to solve these problems on a uniformly spaced grid systems fail to resolve the characteristic flow features and hence do a poor job in simulating the flows. In this paper, MacCormack second-order accurate explicit predictor-corrector scheme is used to solve the two-dimensional depth averaged shallow water equations to numerically simulate the supercritical free-surface flows in open-channel transitions. However, instead of a fixed grid, an adaptive grid system which adjusts itself as the solution evolves is used for a better resolution of the flow properties. In the present approach, Rai and Anderson's method based on grid speed is used for grid adaptation. In a flow with shock, best solutions are obtained when the coordinate axes are aligned along the shock. Rai and Anderson's method to cluster the grids are found to fulfill this criteria and thus produces better quality solutions, as compared to those obtained with uniformly distributed grid with a specified number of grid points.

ISSN:0022-1686    

DOI:10.1080/00221689709498429

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The paper describes the pressure fluctuation field on a plunge pool floor subjected to jet impingement. The data for both mean and fluctuating components is presented for a range of velocities, plunge length, plunge pool depths, types of outlet devices, and jet diameters. The data for circular jets are compared in detail with other data available for wide rectangular nappes and rectangular slot jets. The effect of the degree of break-up of the jet before it enters the basin and the effect of air entrainment in the plunge pool is investigated. An example is provided to demonstrate how the findings may be used in practice.

ISSN:0022-1686    

DOI:10.1080/00221689709498430

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689709498431

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689709498432

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor