摘要:

The practice of numerical simulation of flows and other processes occurring in water has now matured into an established and efficient part of hydraulics. At the same time, however, the models themselves often become very extended. In many situations, given the divergence between the response-time requirements and the computational- time requirements of numerical models, the need arises to reduce the time needed to simulate the impact of given input events on hydraulics systems. In this study the possibility of using systems composed of agents consisting only of artificial neural networks (ANNs) as modelling tools for the simulation of tidal flow in a two-dimensional flow field is investigated. In particular this involves the modelling of a process that evolves in time and the ANNs themselves function as non-linear dynamic systems that effectively reproduce the behaviour of the fluid at any one place and any one time from the behavior at other places at earlier times. Different types of ANN-agent architectures are investigated in order to asses their ability and relative performance in encapsulating the sitespecific knowledge and data necessary to reproduce the temporal sequence of states observed in a modelled area.

ISSN:0022-1686    

DOI:10.1080/00221686.1999.9628261

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221686.1999.9628262

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Using the principle of maximum entropy and field data, this paper derives the mechanism and conditions for change in the channel pattern of alluvial rivers. Theoretical analyses indicate (i) the mechanism of formation of different channel patterns in a river system is one of maximizing entropy of the system under different local flow and boundary conditions, and (ii) the river pattern with sinuosity S = π/2 ≈ 1.57 conforms to the principle of maximum entropy. The equations governing the change in a channel pattern are derived and thresholds, as the conditions of channel pattern changes, determined, using theory and field data from 70 alluvial rivers having different channel patterns. The result of this study suggests that river management and training works should help rivers achieve and maintain a sinuosity S close to 1.57 and the stability criterion Scr> 0.2.

ISSN:0022-1686    

DOI:10.1080/00221686.1999.9628263

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Using a two-phase formulation, the vertical and horizontal momentum equations for sediment are used to obtain the concentration and velocity profiles of a dilute suspension of particles in a 2D uniform flow. Assuming the form of the vertical turbulent intensities and dilute concentrations of sediment, one can solve the equations analytically and compare them with experimental data. No empirical coefficients in the model are tuned to match individual experiments, for which the experimental data cover a large range of particle sizes and densities. The models are shown to accurately predict two experimentally observed but theoretically unexplained phenomena: the increased diffusive flux of large particles, and the measurable velocity lag of particles. The increased diffusion of large particles is shown to originate from the added diffusive nature of the sediment's Reynolds stresses. The horizontal velocity lag of particles is due to an induced velocity, termed the drift velocity, resulting from the correlation of particle concentration with areas of low horizontal velocity fluid.

ISSN:0022-1686    

DOI:10.1080/00221686.1999.9628264

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper describes an experimental programme carried out in a laboratory channel, to investigate the velocity distributions over a rippled bed in combined wave-current flows. In this study, waves propagate against a turbulent current. Velocity measurements were made with a laser-Doppler anemometer. The Nikuradse roughness lengthks, of the bed has been estimated from the traditional logarithmic velocity profile for current alone. The most significant effect of the superposition of waves on a current is the increase of the apparent roughness of the bed with increasing wave height. This effect is well described by Sleath's [49] model. As for rough flat beds, the turbulence intensity over ripples varies inversely with height at sufficiently large distance from the bed for wave-dominated flows.

ISSN:0022-1686    

DOI:10.1080/00221686.1999.9628265

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The results of an experimental investigation into the behaviour of advected plumes are presented. Measurements of tracer concentration are made using laser-induced fluorescence and image processing techniques. These measurements provide the basis for studying the bulk properties and fluctuation statistics of the flows. The experimental results show that the appropriate characteristic velocity for predicting the centreline location of an advected plume is the cross-sectional average velocity and not the centerline velocity (which has been utilised for this purpose in the past). The reason for this is discussed in the context of the large scale turbulent structures evident in the flow. In addition, it is shown that reasonably accurate predictions of the bulk properties of advected plumes can be made by assuming the behaviour of an advected plume is similar to that of a plume discharged in a still ambient fluid (a still plume), which is simply advected by the ambient current. Notable differences can be found in the fluctuation statistics of still and advected plumes. Detachment of tracer from the plume is observed, but it does not have any significant impact on the bulk properties of the flow. In the context of the advected plume experimental results the behaviour of an advected thermal is discussed, with particular reference to the appropriate characteristic velocity for defining its path. The data set also enables us to locate the transition from an advected plume to an advected thermal with some confidence.

ISSN:0022-1686    

DOI:10.1080/00221686.1999.9628266

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper investigates oscillating characteristics and cyclic mechanisms in several hydraulic jumps, with experimental study made of the hydraulic jumps under two periodically repeated flow conditions. The analysis shows that the vortex roll-up process is linked to fluctuations of the longitudinal location of the jump toe. The paper includes comments on those few works in literature which deal with the subject. Measurements were made of the time interval during which each type of hydraulic jump was present along with the surface profile elevations downstream of the roller. Results, oscillating characteristics and cyclic mechanisms are in agreement with the new concept of turbulence. Indeed, it has become increasingly evident that the organized periodic motion is superimposed on a background of random turbulence, with many flows containing eddies, vortices whose description is more influential than previously thought.

ISSN:0022-1686    

DOI:10.1080/00221686.1999.9628267

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The influence of turbulence on the entrainment of sediment particles from a plane mobile bed was investigated using image processing techniques to record sediment particle motion in an experimental flume while simultaneously monitoring the turbulence characteristics of the flow. The importance of the image processing techniques applied arise from the use of the collected images for determination of the area of sediment entrained and the instantaneous particle velocity.

ISSN:0022-1686    

DOI:10.1080/00221686.1999.9628268

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221686.1999.9628260

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor