Showing papers in "Journal of Hydraulic Research in 1986"
TL;DR: In this article, the generation and decay of secondary flow in steady or quasi-steady nearly-horizontal flow models is modeled as a convection of momentum, and an approximate method is proposed which takes account of the convection.
Abstract: To implement the generation and decay of secondary flow in steady or quasi-steady nearly-horizontal flow models an approximative method is proposed which takes account of the convection of momentum...
140 citations
TL;DR: In this paper, the authors classify flow processes in terms of coherent structures, in which the vorticity of the upstream boundary layer is concentrated, and use information from flow visualization to describe these vortical structures.
Abstract: Flow processes in the mixing layer behind dunes provide the feedback between flow, sediment transport and the bed forms, which is assumed to be responsible for the development and persistence of dunes. It is attempted to classify these flow processes in terms of coherent structures, in which the vorticity of the upstream boundary layer is concentrated. Information from flow visualization is used to describe these vortical structures. The literature was reviewed to search for theoretical and experimental results of similar flow situations, which can provide the essential concepts.
114 citations
TL;DR: In this paper, a unified view of the mixing processes, quantitative laws are sought, which would be generally valid in flows with mean motion in at least one of the layers, and four such governing laws, all of a power form, applicable in different ranges of the overall Richardson number, Ri 0.
Abstract: In this paper the phenomenon of turbulent mixing at a density interface is studied. Based on a unified view of the mixing processes, quantitative laws are sought, which would be generally valid in flows with mean motion in at least one of the layers. Re-examination of available experimental data from four types of stratified flow, supplemented by theoretical considerations, leads to the identification of four such governing laws, all of a power form, applicable in different ranges of the overall Richardson number, Ri 0. Two of these laws refer to supercritical and subcritical conditions and are considered as fundamental, being related to qualitatively different mechanisms of interfacial mixing. An intermediate law applies around the critical Ri 0 value of unity, while an asymptotic law corresponds to the limit of homogeneous flow as Ri 0 tends to zero. All the above laws are given by simple expressions in terms of the mean flow characteristics, allowing their straightforward application for the quantifica...
111 citations
TL;DR: In this article, the hydraulic flow features associated with a hydraulic jump over positive and negative steps are investigated and attention is paid to the extreme positions of the phenomena, which allow the design o...
Abstract: The hydraulic flow features associated with a hydraulic jump over positive and negative steps are investigated. Attention is paid to the extreme positions of the phenomena, which allow the design o...
76 citations
TL;DR: Based on an asymptotic solution of the two-dimensional convection-diffusion equation, Galappatti as discussed by the authors developed a depth-integrated model for suspended sediment transport.
Abstract: Based on an asymptotic solution of the two-dimensional convection-diffusion equation. Galappatti [2] developed a depth-integrated model for suspended sediment transport. In the present study, a the...
69 citations
TL;DR: The formation of roll waves in laminar sheet flows in a smooth channel was examined both theoretically and experimentally in this paper, where roll waves were observed in subcritical flows at a Froude numbe...
Abstract: The formation of'a series of roll waves in laminar sheet flows in a smooth channel is examined both theoretically and experimentally. Roll waves were observed in subcritical flows at a Froude numbe...
64 citations
TL;DR: The paper describes a flood-routing scheme based upon the successive application of locally linearized parabolic equations in integral form and computation of the steady state backwater profiles (PAB) that is particularly suited to real-time forecasting and control.
Abstract: The paper describes a flood-routing scheme based upon the successive application of locally linearized parabolic equations in integral form and computation of the steady state backwater profiles (PAB). The method, which is unconditionally stable (a consequence of its integral form) is shown to be particularly suited to real-time forecasting and control. The method is generally applicable to flood routing problems in mild slope channels and rivers (apart from special cases where the inertial terms play an important role) and can also be used for routing steep front waves such as those produced by dam breaks.
62 citations
TL;DR: The main results obtained from a survey of laboratory facilities around the world on wave absorbers are presented and some future orientation regarding the research activities in this area is suggested.
Abstract: Within the context of the construction of a multi-directional seakeeping tank in the recent laboratory of the Institute for Marine Dynamics in St. John's, Newfoundland. Canada, a literature review, including a survey of laboratory facilities around the world, has been conducted on wave absorbers. The aim of the study was to help in a systematic way in developing an "optimum" wave absorber satisfying the main constraints of restricted length and variable water depths. This paper presents the main results obtained from the survey and suggests some future orientation regarding the research activities in this area.
43 citations
TL;DR: In this article, the presence of fine sediment particles in a steady horizontal vortex is examined theoretically and experimentally, starting from an homogeneous mixture, particles denser than the surrounding fluid are moved outside of the vortex core by centrifugal action.
Abstract: The presence of fine sediment particles in a steady horizontal vortex is examined theoretically and experimentally. Starting from an homogeneous mixture, particles denser than the surrounding fluid are moved outside of the vortex core by centrifugal action. As a sediment concentration gradient gradually builds up across the vortex, a diffusive flux opposite to the centrifugal flux is induced. Equilibrium is reached when the two fluxes are equal. Theoretical relationships describing the suspended sediment concentration profiles in a steady Rankine vortex are verified with experimental data.
36 citations
TL;DR: In this article, the authors deal with the dynamic forces and oscillations of vertical-lift rectangular gates submerged in freesurface flow and find that the oscillations are excited by the vortices due to the dynamic interaction between the elastic gate and the unstable shear layer underneath the gate.
Abstract: The paper deals with the dynamic forces and oscillations of vertical-lift rectangular gates submerged in freesurface flow. In the range of low reduced velocities investigated here (VT < 5) the oscillations were found to be excited by the vortices due to the dynamic interaction between the elastic gate and the unstable shear layer underneath the gate. Spectral analysis of the excitation-force and gate-response signals permitted identification of the main characteristics of the interaction process. The main similitude parameters governing this hydroelastic phenomenon are shown to be the reduced velocity and the mass-damping coefficient. The study permits a number of general conclusions to be drawn regarding model tests on vibrating structures.
33 citations
TL;DR: In this article, experiments were carried out to determine the increase in boundary shear stress associated with the zone of suction over a submerged type of river water intake, and the results were compared with predictions obtained from a mathematical model, based on a mean flow momentum equation written for successive bed elements in the suction zone.
Abstract: This paper describes experiments which were carried out to determine the increase in boundary shear stress associated with the zone of suction over a submerged type of river water intake. Conventional techniques for shear stress measurement could not be used because of the non-uniform nature of the flow. Two different experiments were devised, and the results were compared with predictions obtained from a mathematical model, based on a mean flow momentum equation written for successive bed elements in the suction zone. In one set of experiments, a grain population of known threshold shear stress, measured in uniform flow, was placed in the suction zone and the effect of suction velocity on the flow required to induce threshold conditions for these grains was determined. At threshold, shear stress was assumed to be equal in the two cases (of uniform flow, and flow with suction), the direct effect of suction on grain stability having been eliminated by suppressing suction in the immediate vicinity of the "i...
TL;DR: In this article, both breakwater distance from the shoreline and the gap between successive breakwaters are shown to be important factors in determining the amount of sand that can be entrapped by entrapping.
Abstract: Both breakwater distance from the shoreline and the gap between successive breakwaters are shown in a model study to be important factors in determining the amount of sand that can be entrapped by ...
TL;DR: In this article, self-excited vibrations of vertical lift gates were investigated and a selfexcited vibration model was proposed for the vertical lift gate's selfexciting vibrations was presented.
Abstract: (1986). Self-excited vibrations of vertical-lift gates. Journal of Hydraulic Research: Vol. 24, No. 5, pp. 391-404.
TL;DR: In this article, it was found that bubble height increases with volume for air volumes below a critical volume and above this value the height is constant, and that the abrupt decrease in bubble height at the rear of the bubble is associated with a turbulent dissipative region in the underlying flow.
Abstract: Release of a large volume of air into a rectangular duct on a slope produces a large air bubble which moves at constant velocity upward along the roof of the duct. Experiments reveal that the speed depends only on the duct slope for bubbles of large volume but it depends also on volume for bubbles below a given size. These observations agree well with a theory based on free-streamline potential flow. The measured and predicted frontal shape are also in accord. It is found that bubble height increases with volume for air volumes below a critical volume and above this value the height is constant. There is an abrupt decrease in bubble height at the rear of the bubble and this is associated with a turbulent dissipative region in the underlying flow. In large bubbles on gentle slopes where the flow beneath the bubble is uniform, the dissipative region takes the form of a hydraulic jump.
TL;DR: In this paper, a modified logarithmic law was proposed to describe the distribution of the primary velocity on the vertical and this accommodates the case when the maximum primary velocity is located below the water surface.
Abstract: In a curved channel of limited width, such as a curved channel sediment excluder, the primary velocity distribution is affected by the presence of the spiral motion and by the effect of the restricted width/depth ratio. A modified logarithmic law to describe the distribution of the primary velocity on the vertical is suggested and this accommodates the case when the maximum primary velocity is located below the water surface. Using this law and assuming non-linear distribution of the primary turbulent shear stress, the distribution of the radial velocity in the vertical is derived which takes into consideration the effect of the width-depth ratio. An expression for the deviation angle of the flow at the bed, reflecting the effects of the bed roughness as well as the width-depth ratio is also given. The result of the analysis is that the radial velocity distribution as well as the bed deviation angle are significantly affected by the width-depth ratio in addition to the bed roughness. Predicted and observe...
TL;DR: In this article, the authors presented the results of an experimental study on the behavior of plane turbulent denser Boussinesq-type wall jets and wall jumps on a smooth boundary.
Abstract: This paper presents the results of' an experimental (mainly photographic) study on the behaviour of plane turbulent denser Boussinesq-type wall jets and wall jumps on a smooth boundary. The distinction between the wall jet and wall jump has been brought out. Diagrams for predicting the growth rates of denser wall jets and wall jumps have been developed. Some interesting observations have been made regarding the temperature defect field in the denser wall jets for three values of the source Richardson number varying from 0.02 to about 0.2. A diagram has also been constructed to predict the flow regime for given source conditions and far-field stratified flow depth.
TL;DR: In this paper, a 20 mm diameter smooth sphere was held in a flow of oil by means of a device sensitive to the lift force exerted on the sphere, and lift force variations with gap ratio were reported for three approach velocity distributions, all at values of duct Reynolds number less than 1200 and at sphere Reynolds Number between 43 and 250.
Abstract: A 20 mm diameter smooth sphere was held in a flow of oil by means of a device sensitive to the lift force exerted on the sphere. Lift force variations with gap ratio are reported for three approach velocity distributions, all at values of duct Reynolds number less than 1200, and at sphere Reynolds Number between 43 and 250. At gap ratios between 2 and 4 the lift force corresponds reasonably well with the prediction of Saffman [1, 2] for much lower Reynolds number. For smaller gaps, the flow through the gap between sphere and wall is dominant and the lift force direction is reversed. Transient lift forces are found when the sphere is in mid-duct, despite the laminar character of the approach flow. They are thought to be linked to the elongation of vortex elements shed from discrete arcs of the separation line and the effect of this elongation on conditions in the wake. Limited relevance is postulated to the motion of sand grains transported by water and air, but only in the absence of spin which would prof...
TL;DR: In this article, a depth-discharge diagram for entraining flows is presented to assess these different transition paths between a supercritical discharge and an imposed subcritical downstream condition, and certain flow instabilities are predicted to occur at downstream Froude numbers of 1 or 1/2.
Abstract: On the basis of flow force conservation the two-dimensional buoyant surface discharge of a light fluid over a stagnant ambient fluid can be classified into four regimes: a fully entraining buoyant jet, a jet/jump combination, a direct jump, or a flooded jump. A depth-discharge diagram for such entraining flows is presented to assess these different transition paths between a supercritical discharge and an imposed subcritical downstream condition. Certain flow instabilities are predicted to occur at downstream Froude numbers of 1 or 1/2, respectively. Comparison with various experimental data, including additional data by the authors, confirms the flow force conservation theory. Furthermore, a more detailed analysis of the spatial development of a buoyant surface jet is made using an entrainment formulation with buoyant damping for closure of the governing equation. The predictions compare favourably with experimental data.
TL;DR: In this paper, the authors proposed a two-layer model for wall-wake flows with adverse pressure gradient (without causing separaton of the boundary layer) to obtain expressions for variations of free stream velocity and the chatacteristic length and velocity scales of the self-preserving flow.
Abstract: The flow past an obstacle attached perpendiculary to a surface (wall) is postulated to possess the characteristics of boundary layer flow in the vicinity of the wall and free-wake flow away from the wall. Analytical analyses of wall-wake flows with adverse pressure gradient (without causing separaton of the boundary layer) are made to obtain expressions for variations of free stream velocity and the chatacteristic length and velocity scales of the self preserving flow. Experiments are conducted in a wind tunnel for three arbitrary adverse pressure gradient flows. The experimental observations clearly indicate that wall-wakes in adverse pressure gradient can be adequately described by the two-layer model proposed.
TL;DR: In this article, the application of the diffusion model to bed degradation due to the sudden cessation of sediment supply to an alluvial system has been investigated and limitations of the model noted Experiments indicate that local maximum scour depths do not occur at the upstream end of an erodible reach.
Abstract: The application of the diffusion model to bed degradation due to the sudden cessation of sediment supply to an alluvial system has been investigated and limitations of the model noted Experiments indicate that local maximum scour depths do not occur at the upstream end of an erodible reach This was accounted for by modifying the diffusion model to include a mobile upstream boundary scheme The modified model was calibrated using bed load sediment transport data and diffusion coefficient values of best fit obtained Significant differences between calibrated and predicted diffusion coefficient values were obtained Measured and predicted bed profiles were also compared and conclusions about the applicability of the diffusion model to bed degradation drawn
TL;DR: In this article, a formula for estimating the longitudinal dispersion coefficients in rivers is proposed to explain the observed dispersion coefficient by reducing the value of the constant a from 0.011 to 0.0021.
Abstract: Longitudinal dispersion coefficients in ship-canals in Northern Belgium were measured by iodide tracer experiments. A formula, proposed by Fischer, for estimating the longitudinal dispersion coefficients in rivers allows to explain the observed dispersion coefficients by reducing the value of the constant a from 0.011 to 0.0021. The smaller value can be justified theoretically. This formula can also be used for canals in which an unsteady flow takes place by considering only the continuous fraction of the flow to estimate the velocity.
TL;DR: In this article, a classification method for the components of the pressure pulsations based on their statistical characteristics is presented, and a spectrum analysis for the low-frequency fluctuations is given to help explain their mechanism.
Abstract: Pressure pulsations in a cavitating venturi were measured and investigated statistically. A classification method for the components of the pressure pulsations based on their statistical characteristics is here presented. The pulsations can be classified as of three basic categories: basic flow noise, cavitation bubblecollapse pulses, and cavitation associated low-frequency pressure fluctuations. Their distinctively statistical characteristics are presented, and a spectrum analysis for the low-frequency fluctuations is given to help explain their mechanism.
TL;DR: In this article, the authors discuss some of the practical problems which have been encountered in the use of a single conductivity probe in measuring concentration in narrow layers of fluid adjacent to a solid boundary.
Abstract: Conventional two electrode conductivity probes have a relatively large sensing volume and are therefore inconvenient if measurements are to be made in narrow concentration layers of fluid A single electrode probe, first discussed by Gibson and Schwarz, has a much smaller sensing volume and the present note discusses some of the practical problems which have been encountered in its use in measuring concentration in narrow layers of fluid adjacent to a solid boundary
TL;DR: In this paper, the velocity distribution equations which have been developed recently on the basis of data of sedimentladen flow over a rigid plane bed are checked with experimental data of flow over alluvial beds of sediment mixtures.
Abstract: The velocity distribution equations which have been developed recently on the basis of data of sedimentladen flow over a rigid plane bed are checked with experimental data of flow over alluvial beds of sediment mixtures and found to be unsatisfactory for this case. Making use of the present set of data and the data collected by other investigators, a two-layer model of velocity distribution over alluvial beds has been developed. The model shows good agreement with field measurements of the Rhine and the Middle Rio Grande.
TL;DR: In this article, the concepts of onedimensional flow and quasi-uniform flow were employed to derive the fundamental differential equation of gradually varied laminar flow in open channels.
Abstract: The concepts of onedimensional flow and quasi-uniform flow are employed to derive the fundamental differential equation of gradually varied laminar flow in open channels. The equation is solved for...