摘要:

This paper presents the formulation of a 3-D finite element hydrodynamic model to simulate secondary flows and their damping in channel bends and flow around obstacles. An emphasis has been focused on the formulation of viscous terms that are responsible for the secondary flow development. Basic equations and associated hypothesis are also presented in this paper.

ISSN:0022-1686    

DOI:10.1080/00221689709498414

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A numerical solution of pulsatile flow of an inelastic fluid through porous isotropic elastic pipes is presented. An implicit difference method is used to solve the equations, and to determine the pressure and the flow rate. This study is considered as a step in modelling of flow in blood vessels, but it may also contribute to other important fields such as water desalination or gel filtration.

ISSN:0022-1686    

DOI:10.1080/00221689709498415

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The present paper deals with the integral conservation of linear momentum and angular momentum in the stationary hydraulic jump in a wide rectangular channel. The flow is considered to be divided into a mainstream, that conveys the total liquid discharge, and a roller, in which no average mass transport occurs. Referring to the infinitely large case, a purely two dimensional motion is considered. The interface between the two flow regions is a streamline, corresponding to a stream function value equal to the total discharge per unit width. The present approach consists in satisfying the mechanical balances of mass, momentum and angular momentum, while no (large scale) constitutive relation is assumed for the turbulent motion of the liquid. Regarding the stress tensor, hydrostatic normal pressure distribution is assumed, while nothing is assumed regarding shear stresses, except that viscous stresses are negligible with respect to turbulent stresses. A paradox is put in evidence, that in the classical hydraulic jump (specific force conserving solution) angular momentum conservation is apparently not satisfied. Taking into account of integral balances not only in terms of linear horizontal momentum but also of linear vertical momentum and angular momentum the paradox is overcome. Under some simplified assumptions regarding uniform horizontal velocity distribution in the mainstream, and negligibility of horizontal momentum and angular momentum in the roller with respect to other terms, an analytical solution is obtained in terms of free surface profile, mainstream thickness and roller thickness. Average shear stresses acting on the mainstream by the roller and power losses for unit weight may be theoretically derived. Assuming as known the growth rate of the mainstream at the beginning of the jump, also the length of jump, here assumed identical to the length of the roller, may be determined, together with the volume of the roller, the volume of the mainstream and the volume of the whole stream between the sequent depths.

ISSN:0022-1686    

DOI:10.1080/00221689709498416

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A fully developed turbulent open channel flow with a bed consisting of a space-periodic array of triangular elements has been numerically simulated. The solution procedure is based on the pressure-correction finite volume method with a collocated variable arrangement. Decoupling of the equations, inherent to the collocated variable arrangement, is avoided by using well-known Rhie and Chow interpolation technique. Reynolds stresses are approcimated usingk-ε and a full transport Reynolds-stress models of turbulence. Wall boundary condition takes into account wall roughness while the free surface is treated as a symmetry plane for all variables apart from the dissipation of turbulence kinetic energy. Comparisons between prediction and the measurements indicate that thek-ε model of turbulence is capable of predicting the main features of the flow to the acceptable level of accuracy.

ISSN:0022-1686    

DOI:10.1080/00221689709498417

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The motion induced by particle thermals (a cloud of heavy particles released into an otherwise stagnant fluid) has been investigated by a three-dimensional numerical model. The model formulation is based on the governing equations for the conservation of mass, momentum and density excess, assuming the discrete particles can be represented by a continuous field of density difference with a specified settling velocity, and the Boussinesq approximation is valid. A mixing length model is used to represent the induced turbulence because of the existence of a well-defined length scale (the cloud size). A sensitivity analysis on the model parameters has been performed and suitable values of the parameters are identified and used in the subsequent model simulation. The model simulation results reveal an inverse relationship between the rate of spreading of the cloud and the settling velocity, and show that the frontal velocity approaches the settling velocity in the ultimate stage. These findings are supported by physical experiments.

ISSN:0022-1686    

DOI:10.1080/00221689709498418

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We investigate a procedure for carrying out experiments on the erosion of a deposited mud bed by a steady flow in a race-track recirculating flume. This is a large-scale flume 0.5 m wide consisting of two straight sections 16 m long connected by two circular bends. The currents are produced by a vertical disc pump. It is shown that experimental conditions producing uniform erosion over the whole surface of the mud bed are met when the bed is restricted in a limited straight part of the flume. Measurements of the flow kinematics by a Laser Doppler Anemometer performed in clear water confirm that the flow applies a quasi-uniform bottom shear stress over the bed. Stratification effects are suppressed in this facility due to the strong mixing of suspended sediment concentration by the disc pump. A theoretical analysis of stratification effects however indicates that they remain small as long as the depth-averaged concentration is below 13.5gl-1. A procedure to determine quasi-instantaneous erosion rates from depth-averaged suspended sediment concentration is finally presented.

ISSN:0022-1686    

DOI:10.1080/00221689709498419

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Even as hydroinformatics continues to elaborate more advanced operational tools, languages and environments for engineering and management practice, it necessarily also promotes a number of concepts and methodologies that are eminently applicable within the more traditional areas of hydraulic research. Among the many new possibilities thereby introduced, that of evolving equations from hydraulic data using evolutionary algorithms has a particularly wide range of applications. The present paper is in two parts, the first of which introduces the subject and outlines its theory, while the second is given over to four representative applications and to some of the most immediate lessons that may be drawn from these. The first of the applications is derived from a hydrologie model but provides equations with purely hydraulic interpretations. The second, taken from sediment transport studies, raises the question of ambiguity in the identification of "thresholds" in physical processes. It also provides a means for analyzing the significance of variables and indicates the need, or otherwise, for introducing further variables. A third example, based upon physical observations of salt water intrusion in estuaries, introduces the application of the present methods to accelerating prediction processes, while the fourth example extends this kind of application to cover numerically generated data, in this case appertaining to the case of flow resistance in the presence of vegetation.

ISSN:0022-1686    

DOI:10.1080/00221689709498420

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This second part of the paper is given over to describing four representative applications and to some of the most immediate lessons that may be drawn from these. The first of the applications is derived from a hydrologic model but provides equations with purely hydraulic interpretations. The second, taken from sediment transport studies, raises the question of ambiguity in the identification of "thresholds" in physical processes. It also provides a means for analyzing the significance of variables and indicates the need, or otherwise, for introducing further variables. A third example, based upon physical observations of salt water intrusion in estuaries, introduces the application of the present methods to accelerating prediction processes, while the fourth example extends this kind of application to cover numerically-generated data, in this case appertaining to the case of flow resistance in the presence of vegetation.

ISSN:0022-1686    

DOI:10.1080/00221689709498421

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

OFFSHORE BREAKWATERS AND SHORE EVOLUTION CONTROLby K. W. Pilarczyk and R.B. Ze idler A.A. Balkema, P.O. Box 1675, 3000 BR Rotterdam, The Netherlands HB560pp., ISBN 90-5410-627-1 US $140

ISSN:0022-1686    

DOI:10.1080/00221689709498422

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689709498413

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor