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Showing papers in "Journal of Hydraulic Research in 1991"


Journal ArticleDOI
TL;DR: In this article, a quasi-two-dimensional model of transient flows in pipes of circular cross-section is developed, using the one dimensional method of characteristics in concentric cylindrical annuli.
Abstract: A quasi two-dimensional model of transient flows in pipes of circular cross-section is developed, using the one dimensional method of characteristics in concentric cylindrical annuli. Lateral velocity components are permitted between adjacent cylinders. The model can nominally incorporate any desired relationship between shear stresses and local velocities. In this paper, it is applied to laminar flows and to a five-region model of turbulent flows. The accuracy of Zielke's (1969) one-dimensional expression for transient wall-shear stresses in laminar flows is verified, and it is shown that his expression is also a reasonable approximation for smooth-wall, turbulent flows, at least at low Reynolds numbers. Quasi-steady relationships are shown to be highly inaccurate in transient laminar or turbulent flows.

196 citations


Journal ArticleDOI
TL;DR: In this article, the role of mathematical models in the analysis of large-scale coastal behavior (LSCB) is discussed, where the constituent processes (waves, currents, sediment transport) and their interaction with the bottom topography changes (morphodynamics) are considered at various space and time scales.
Abstract: The paper addresses the possible role of mathematical models in the analysis of large-scale coastal behaviour (LSCB). The constituent processes (waves, currents, sediment transport) and their interaction with the bottom topography changes (morphodynamics) are considered at various space and time scales. The overall conclusion is, that mathematical modelling has much to add to the analysis and interpretation of large-scale coastal dynamics, especially if it can be integrated with laboratory and field measurements.

130 citations


Journal ArticleDOI
TL;DR: In this paper, a high-speed photographic study was made of the hydraulic jump and it was found that the surface roller was made up of several vortices, which are generated in the early part of the jump and travel downstream.
Abstract: A high-speed photographic study was made of the hydraulic jump. It was found that the surface roller was made up of several vortices. These vortices are generated in the early part of the jump and travel downstream. As they move downstream, they grow by pairing. At the same time, water spills down the steepened surface to replenish the toe and subsequently is rolled up into new vortices. A Fourier analysis of the time series of the toe position indicates a cyclic mechanism, the frequencies of which appear to scale with the upstream velocity and downstream depth.

125 citations


Journal ArticleDOI
TL;DR: In this paper, a systematic investigation on the transition from supercritical to subcritical flow at an abrupt drop is presented, and the hydraulic conditions required to form various types of flow and their length characteristics have been clarified.
Abstract: This paper presents a systematic investigation on the transition from supercritical to subcritical flow at an abrupt drop. Over a wide range of experimental conditions various types of flow have been classified and the concept of low and high drops defined. When the flow on the step is supercritical, the direction of the main flow passing over the step can be decided from the momentum equation. The reason why various flow conditions are formed has been explained. The hydraulic conditions required to form various types of flow and their length characteristics have been clarified.

74 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the influence of skin friction on spreading and entrainment of plane jets in shallow water and showed that depending on the distance from the origin scaled by depth, the jets can be divided into three fields with distinct behavior.
Abstract: Plane jets in shallow water are often encountered in geophysical flows and engineering applications. The present investigation shows that depending on the distance from the origin scaled by depth, the jets can be divided into three fields with distinct behaviour. A model is then presented allowing discussion of the conditions related to the observed increase or decrease of momentum flux in the vicinity of the orifice. The influence of skin-friction on spreading and entrainment is studied on the basis of existing experimental evidence including the one in the present work.

73 citations


Journal ArticleDOI
TL;DR: This paper relies almost exclusively upon modelling approaches in use at Laboratoire National d'Hydraulique, Chatou, France, which are well experienced today in numerical simulation of cohesive sediment transport.
Abstract: The state of the art in numerical simulation of cohesive sediment transport has advanced considerably in the past ten years. Nevertheless, for engineering applications, reliable predictive results are not yet within our reach and model use is often restricted to sensitivity analysis purposes, already very useful. Reasons of relative failure in gaining quantitative results do not come from the numerical techniques, which are well experienced today, but from the incomplete knowledge of basic processes such as deposition, erosion and consolidation of cohesive sediment. The still unsatisfactory predictions of numerical models may also originate from a possible discrepancy between specifications of physical laws, derived from laboratory experiments, and prototype behaviour. This paper relies almost exclusively upon modelling approaches in use at Laboratoire National d'Hydraulique, Chatou, France.

70 citations


Journal ArticleDOI
TL;DR: In this article, the modification of the velocity profile in an open channel caused by a region of rapid infiltration through the bed, such as that associated with a bed-type river intake, has been made.
Abstract: Laboratory measurements have been made of the modification of the velocity profile in an open channel caused by a region of rapid infiltration through the bed, such as that associated with a bed-type river intake. The results have been analysed to provide an estimate of bed shear stress in the suction zone. The measurements were obtained using Laser-Doppler anemometry, and are compared with hot-wire measurements over a similar zone of suction in a wind tunnel.

61 citations


Journal ArticleDOI
TL;DR: In this article, a standard two-dimensional k-e turbulence model is used to predict the mean flow and turbulence characteristics of submerged hydraulic jumps and an offset control volume method is developed to facilitate computation of the variable free surface.
Abstract: A standard two-dimensional k-e turbulence model is used to predict the mean flow and turbulence characteristics of submerged hydraulic jumps An offset control volume method is developed to facilitate computation of the variable free surface The numerical predictions are compared with experimental measurements under three conditions with supercritical Froude numbers ranging from 32 to 82 and submergence factors ranging from 024 to 085 Finally the numerical performance is evaluated and discussed in detail It is concluded that the model is adequate for predicting the surface profile, mean velocity field and to some extent, the turbulence structure of submerged hydraulic jumps

61 citations


Journal ArticleDOI
TL;DR: In this article, extensive new experimental investigations of bedload transport of noncohesive sediments in fixed bed conveyances with no deposition were made to resolve some differences in previously published work and to advance the understanding of the processes involved.
Abstract: This paper is based on extensive new experimental investigations of bedload transport of noncohesive sediments in fixed bed conveyances with no deposition. Using these new as well as previously available data an attempt has been made to resolve some differences in previously published work and to advance the understanding of the processes involved. The paper summarises the proposed methodologies and provides a thorough comparison with the alternative ones that exist in loose and fixed boundary conveyances.

55 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the influence of acceleration on the velocity profiles of spatially accelerating flows in a smooth open channel and found that the velocity distributions cannot be represented entirely by the universal log-law, however, this law seems to follow the data very close to the wall up to about y/d = 0.02 ∼ 0.05.
Abstract: Laboratory experiments on the structure of spatially accelerating flows in a smooth open channel are reported. The influences of acceleration (i) on the velocity profiles; (ii) on the turbulence intensity profiles; and (iii) on the longitudinal evolution of the bottom shear stress are investigated. The most important conclusions of the study can be summarized as follows: a. The velocity distributions cannot be represented entirely by the universal log-law. However, this law seems to follow the data very close to the wall, up to about y/d = 0.02 ∼ 0.05. Higher in the flow, the data increasingly deviate from this law. In the external layer, the equilibrium state of the flow was tested: some near-equilibrium flow situations exist, but mostly the flow was out of equilibrium; b. The generalization of Coles' model was tried, resulting in correlation of the wake parameter, Π, and the dimensionless pressure gradient parameter, β, for β<–0.5; c. The acceleration of the mean velocity field leads to reduction of the...

54 citations


Journal ArticleDOI
TL;DR: In this article, the distribution of turbulence in the wave boundary layer is investigated using standard one-and two-equation models, and it is shown that the distribution is similar to the one in this paper.
Abstract: The distribution of turbulence in the wave boundary layer is investigated. Turbulent kinetic energy, eddy viscosity, and other quantities predicted by use of standard one-equation and two-equation ...

Journal ArticleDOI
TL;DR: The authors concerne le role potentiel des modeles mathematiques dans la prediction de l'evolution des cotes a grande echelle (ECGE) and conclude that modelisation mathematique offre de bonnes perspectives on the prediction quantitative de la dynamique cotiere a great echelon, specialement si elle peut etre soutenue par des experiences de laboratoire and des mesures in-situ.
Abstract: L'article concerne le role potentiel des modeles mathematiques dans la prediction de l'evolution des cotes a grande echelle (ECGE). Plusieurs concepts de modelisation sont proposes et la recherche necessaire pour leur developpement ulterieur est identifiee. La conclusion generale est que la modelisation mathematique offre de bonnes perspectives sur la prediction quantitative de la dynamique cotiere a grande echelle, specialement si elle peut etre soutenue par des experiences de laboratoire et des mesures in-situ.

Journal ArticleDOI
TL;DR: In this article, a forced-hydraulic jump-type stilling basin was designed and an experimental formula for the drag force acting on the sill has been proposed considering the characteristics of the flow condition over the sill.
Abstract: As a basis for designing a forced-hydraulic-jump-type stilling basin, the pressure magnitude on the upstream and downstream faces of a continuous-vertical sill has been investigated experimentally, and the nature of the pressure distribution on the faces of the sill has been discussed. Furthermore, an experimental formula for the drag force acting on the sill has been proposed considering the characteristics of the flow condition over the sill.

Journal ArticleDOI
TL;DR: In this paper, a systematic review of the effects of benthic settlement on the action of flow and on sediment stability is presented, where the qualitative description centered on the physical mechanisms is supplemented by a tabulated summary of numerical results available from the literature.
Abstract: Apart from the physical and chemical properties of the bed of a watercourse, its biological settlement can also have a major influence on bed erosion. The present paper contains a systematic review of the effects of benthic settlement on the action of flow and on sediment stability. The qualitative description centered on the physical mechanisms is supplemented by a tabulated summary of the numerical results available from the literature.

Journal ArticleDOI
TL;DR: The behavior of a submerged vertical round buoyant jet as it interacts with a free surface in an unstratified, stagnant receiving fluid is considered in this paper, where the entrainment within a region that typically extends a few flow depths away from the source is analyzed as a radial internal hydraulic jump and computational results indicate dilution increases even greater than within the submerged jet.
Abstract: The behavior of a submerged vertical round buoyant jet as it interacts with a free surface in an unstratified, stagnant receiving fluid is considered. Conventional analyses for estimating dilution within such a jet consider only the mixing due to the rising jet and neglect further dilution in the region where the jet is deflected and begins to spread radially along the surface. The present study explicitly accounts for the entrainment within a region that typically extends a few flow depths away from the source. This region is analyzed as a radial internal hydraulic jump and computational results indicate dilution increases even greater than within the submerged jet.Two experimental studies were performed to measure dilution within the radially spreading flow region and supplement data previously collected in other studies. The data indicate that the surface dilution directly above the jet can be predicted on the basis of allowing for a thin blocking layer at the surface. The data also indicate a three to...

Journal ArticleDOI
TL;DR: In this paper, the results of many years of laboratory, field and theoretical investigations of scour processes have been generalized and analytical expressions of permissible (nonscouring) velocities are given for cohesive and noncohesive soils.
Abstract: Scouring processes of beds in cohesive and noncohesive soils are discussed. Results of many years of laboratory, field and theoretical investigations of scour processes have been generalized. Critical velocities of erosion and governing factors are considered. Analytical expressions of permissible (nonscouring) velocities are given for cohesive and noncohesive soils.

Journal ArticleDOI
TL;DR: The fourth generation of modelling is built on earlier development, but in such a way as to provide modelling systems that can be used by professional engineers who are not computational-hydraulics experts.
Abstract: First-generation modelling was concerned only with computer adaptations of established, human-friendly methods. In second-generation modelling, on the other hand, methods were used that were more specifically “computer friendly”, even if “human-unfriendly” (e.g., finite-difference and finite-element methods). In third-generation modelling, these methods were incorporated into modelling systems, or “shells”, with which a model of any area could be constructed and run automatically by the system when provided with a suitably-formatted description of the area and its ancillary conditions. During the course of the second- and third-generation developments, however, modelling became an increasingly specialised and hermetic activity, confined for most practical purposes to computational-hydraulics experts. The fourth generation then builds on this earlier development, but in such a way as to provide modelling systems that can be used by professional engineers who are not computational-hydraulics experts. The pa...

Journal ArticleDOI
TL;DR: In this article, the phase difference optical method was used for simultaneous measurements of particle velocity and size and the calculation of time average concentration in a rectangular channel with a glass sphere movable bed.
Abstract: Velocity and concentration profiles of solids in a rectangular channel with glass sphere movable bed for given hydraulic conditions are reported. The measurements are carried out using the phase difference optical method which allows simultaneous measurements of particle velocity and size and the calculation of time average concentration. A comparison with some theoretical formulae is reported too.

Journal ArticleDOI
TL;DR: In this article, a study of air entrainment above an spillway aerator is presented and discussed with a dimensional analysis, and it is concluded that similitude of the air entraining processes for spillway Aerator is not possible between model and prototype.
Abstract: A study of air entrainment above an spillway aerator is presented and discussed with a dimensional analysis. We conclude that similitude of air entrainment processes for spillway aerator is not possible between model and prototype. New informations on the aeration region are presented and an analytical solution of the upper nappe entrainment is developed.

Journal ArticleDOI
TL;DR: In this paper, the motion of the front of plane gravity currents spreading on a horizontal floor can be analyzed by neglecting any energy dissipation in the intruding fluid, but the corresponding results for the maximum intrusion depth and the front velocity are not in good agreement with measurements.
Abstract: The motion of the front of plane gravity currents spreading on a horizontal floor can be analyzed by neglecting any energy dissipation in the intruding fluid. The corresponding results for the maximum intrusion depth and the front velocity are, however, not in good agreement with measurements. The differences are found to be partly due to a visual determination of the depth of the intruding layer by previous investigators; an attempt is also made to relate the remaining differences to the discharge in the intruding and in the continuous layers.

Journal ArticleDOI
TL;DR: In this article, the boundary element method (BEM) is applied to study the waves generated by a plunger-type wavemaker, where the computational domain is truncated by introducing two auxiliary boundaries at three times wave length distance away from the wavemaker.
Abstract: Based on a two dimensional linear water wave theory, the boundary element method (BEM) is developed and applied to study the waves generated by a plunger-type wavemaker. The computational domain is truncated by introducing two auxiliary boundaries at three times wave length distance away from the wavemaker. Radiation condition is used along the auxiliary boundaries. The accuracy of the numerical technique is demonstrated by comparing numerical results with previously published results, experimental and other techniques. However the actual wave height is smaller in the experiments than predicted by numerical models. The discrepancy between predicted and observed wave height can be attributed to the effects of leakage of wave energy under the plunger-type wavemaker. In order to predict waves generated by plungertype wavemaker accurately, the influence of leakage, under the plunger-type wavemaker, is included in the present study. The ratios between wave amplitude and stroke are established for two different...

Journal ArticleDOI
TL;DR: There are three schools of thought in the study of sediment transport based on the concept that rate of energy dissipation of flowing water should be related to the sediment transport or concentration as discussed by the authors.
Abstract: There are three schools of thought in the study of sediment transport based on the concept that rate of energy dissipation of flowing water should be related to the rate of sediment transport or concentration They are the unit stream power by Yang, the stream power by Bagnold, and the gravitational theory by Velikanov Theoretical analyses are made to compare the validity of these theories Laboratory and river data are used to test the assumptions used in the derivation of sediment transport equations based on these theories

Journal ArticleDOI
TL;DR: An integral model of the behavior of a single horizontally discharged buoyant flow in a co-flowing ambient fluid is presented in this article, where the model differs from those presented previously by using the spread assumption rather than the more usual entrainment assumption and explicitly forcing the initially gaussian velocity distribution to become a thermal distribution.
Abstract: An integral model of the behaviour of a single horizontally discharged buoyant flow in a coflowing ambient fluid is presented. The usual integral equations for the conservation of mass, momentum and buoyancy flux are used. However, the model differs from those presented previously by using the spread assumption rather than the more usual entrainment assumption and by explicitly forcing the initially gaussian velocity distribution to become a thermal distribution. The position and the form of this transition is determined from laboratory data (Brown [1984], Knudsen [1988]) and field data (Lee and Neville-Jones [1987]). The performance of the model is compared with both laboratory and field data and it reproduces the data for a wide range of cases. A model of this type is essential in gaining an understanding of the range of behaviour of merging plumes (Cheng, Davidson and Wood) and is a preliminary to the understanding of the more general case where the buoyant discharge is ejected at an angle to the flow.

Journal ArticleDOI
TL;DR: In this paper, the results of an experimental program concerning the movement of particulates in a porous medium under conditions of non-linear flow are presented. But the results are compared with the limited existing data and a model developed by Sakthivadivel [8] for linear flow conditions.
Abstract: Results of an experimental program concerning the movement of particulates in a porous medium under conditions of non-linear flow are presented. The results are compared with the limited existing data and a model developed by Sakthivadivel [8] for linear flow conditions. Modifications were required to this model to allow it to be used under the present conditions. Examination of the results suggested an alternative transport model using suitable dimensionless parameters. This model is shown to be superior to the existing model.

Journal ArticleDOI
TL;DR: In this paper, a finite thickness porous wavemaker located in an infinite one dimensional channel is studied and small amplitude waves are generated in the channel, while the equations derived from the simplified Biot's theory of poroelasticity are used within the porous wavemakers.
Abstract: A finite thickness porous wavemaker located in an infinite one dimensional channel is studied Small amplitude waves are generated in the channel, while the equations derived from the simplified Biot's theory of poroelasticity are used within the porous wavemaker Regular perturbation expansions, with a small parameter R, are applied The flow-efficiency parameter, R, represents the easiness of water flow relative to the skeleton inside the porous wavemaker The larger R is, the greater inertial reaction and the less viscous damping will be For R much less than 1, the increase of inertial reaction is greater than the decrease of viscous damping as R increases It is also found that the thickness of the porous wavemaker is a significant factor to the hydrodynamic pressure on the porous wavemaker when the thickness is small, but it is not a significant factor to wave profile

Journal ArticleDOI
TL;DR: In this article, the effect of benthic organisms (Oligochaeta and Chironomidae) on the erosion of cohesive sediments was studied in a laboratory flume.
Abstract: The effect of benthic organisms (Oligochaeta and Chironomidae) on the erosion of cohesive sediments was studied in a laboratory flume. The critical erosive velocities were shown to be 2-3 times smaller than that of the control sediments. The effect depends strongly on the population density of benthos and temperature of sediments. It was also shown that micro-organisms (bacteria and protozoa), attached to small particles have a great impact on the transportation of suspended sediments due to the decrease in the settling velocity and the critical tractive force.

Journal ArticleDOI
TL;DR: In this paper, the water kinematics induced by air bubble barriers were studied to evaluate their effectiveness in protecting water intakes from jellyfish attack, and the experiments were carried out in a laboratory environment.
Abstract: Laboratory experiments were carried out to study water kinematics induced by air bubble barriers, to evaluate their effectiveness in protecting water intakes from jellyfish attack. The experiments ...

Journal ArticleDOI
TL;DR: In this article, the dependence of the drifting behavior in NaCl-sensors in turbulent flows has been investigated using conductivity probes, which are suitable for local concentration measurements in electrolyte turbulent flows.
Abstract: Conductivity probes, as they are proposed by Gibson and Schwarz, are suitable for local concentration measurements in electrolyte turbulent flows. The dependence of the drifting behaviour in NaCl-s...

Journal ArticleDOI
TL;DR: In this paper, a study of plane thermal-buoyant jets is presented, and the results are compared with two integral models, namely a buoyant jet model and a thermal jet model.
Abstract: A study of plane thermal-buoyant jets is presented. Experiments were conducted in water, and the results are compared with two integral models, namely a buoyant jet model and a thermal jet model. In the buoyant jet model the equation of state is linear, while in the thermal jet model the equation of state is nonlinear. It is concluded that the buoyant jet model does not adequately predict the behaviour of thermal buoyant jets in a cold water environment. For such flows it is necessary to use the actual equation of state for water.

Journal ArticleDOI
TL;DR: In this article, the authors describe the design and operation of a traverse gear for the automatic measurement of boundary shear stress and velocity distributions in a fully developed turbulent flow, and investigate the mean flow structure in a duct of compound cross-section, and the data collected will be used in the development of mathematical models for application in river hydraulics.
Abstract: This paper describes the design and operation of a traverse gear for the automatic measurement of boundary shear stress and velocity distributions in a fully developed turbulent flow. The purpose of the equipment was to investigate the mean flow structure in a duct of compound cross-section, and the data collected will be used in the development of mathematical models for application in river hydraulics.