Abstract: To analyze flows in channel expansions and contractions, two-dimensional, depth-averaged, unsteady flow equations in a transformed coordinate system are solved numerically by using the MacCormack s...

Abstract: Considering the primary vortex in front of the pier to be the prime agent causing scour at bridge piers, a scheme has been proposed for computation of the temporal variation of scour depth during live-bed condition. An equation has also been developed for the computation of maximum scour depth around circular bridge piers in uniform sediments during live-bed condition. The equation follows logically from the scheme proposed for the computation of the temporal variation of scour. The effect of unsteadiness of flow on scour depth has been also studied.

Abstract: Experimental data obtained on a laboratory test facility for unsteady flows in straight and curved channels and on the transient reservoir depths following a simulated dam failure are presented. The water level variation was recorded at five stations in the downstream channel and at six locations in the reservoir. In addition, plan views of the wave fronts were recorded at three stations in the downstream channel. Capacitance probes were used to measure water levels in the reservoir and a procedure using video cameras was developed to record water levels in the channel. Using this procedure, the flow was not disturbed. Video images of the waves were electronically converted into digital information based on their shading density. Tests were conducted for a wide range of initial conditions by varying the upstream reservoir depth, the channel depth, and the channel roughness. Complete test data for two tests are presented.

Abstract: If stratified soil structures are not designed according to conventional filter criteria, a flow of ground water may erode and transport an underlying, finer material through the pore system of the coarser stratum above. A constitutive equation for interfacial transport rate is derived from physical principles and verified through laboratory experiments. The relationship is incorporated in a mathematical formulation for interfacial erosion processes analogous to the one commonly applied to alluvial streams. Both analysis and experiments indicate that interfacial erosion depends strongly on variation in the grain size ratio between the two strata and the porosity of the coarser stratum. A simulation example demonstrates a case in which the core in an earth-fill dam is subjected to overflow and the crest of the core is eroded.

Abstract: The paper highlights the increasing international public concern relating to hydro-environmental issues and cites examples of some of the water quality problems now being considered by hydraulic engineers on a regular basis The limitations and restrictions of both physical and numerical hydraulic models are discussed and concern is expressed with regard to the increasing use of numerical models being made by non-specialist engineers or scientists - often with little understanding of hydraulics and numerical methods - to assist in the planning and/or design of water quality related studies General details are given of numerical models used for flow and water quality concentration predictions in coastal and inland hydraulic basins and two example research projects are described In the first of these studies comparisons are made between dynamically and non-dynamically linked nested models, with the results indicating that in some circumstances nondynamically linked models can give inaccurate velocity fiel

Abstract: A simple model of two-dimensional (depth averaged) flow in topographic gyres by wind action on a shallow model lake is shown to produce chaotic particle motions in the case where the wind alternate...

Abstract: Experiments on settling of cohesive sediments were carried out in turbulent flows in an annular flume using kaolinite clay as well as a natural river sediment. Results indicate that the finer fractions were able to deposit because they were settling as floes. Data on concentration and size distribution of dispersed samples were used to calculate the effective settling velocities for the different size fractions.

Abstract: The artificial circulation and the mixing of temperature stratified water induced by an air bubble plume were studied in laboratory experiments. The time evolution of the spatial distribution of water temperatures was measured. The data were analyzed and gave information on the development of flow patterns and entrainment rates. Of particular interest were the development of the upwelling region, location of the plunge line, temperature structure in the farfield, and water entrainment by the bubble plume and by the plunging flow.

Abstract: This paper deals with the lift force on a stationary sphere close to and away from the boundary and supplements an earlier paper which dealt with the study of the drag force. The experimental setup, instrumentation, nature of boundaries, sizes of test sphere, ranges of Reynolds number and relative size of the sphere are all common to both the studies. In this study, the time-averaged lift coefficient, like the drag coefficient, is found to be a function of both the Reynolds number and the relative size. In view of the prevailing controversy concerning the direction of lift force, a criterion has been evolved for the reversal of lift force in terms of Reynolds number and relative size.

Abstract: An efficient mathematical model for calculation of the boundary shear stress field induced by raindrop impact is developed and tested using numerical and experimental data. The model comprises a series of dimensionally consistent, closed-form, algebraic equations, written in terms of physically meaningful parameters describing the fluid properties and initial conditions at the instant of drop impact. The relationships in the model are derived from the analysis of data generated by a computer code which numerically solves the Navier-Stokes equations for two-dimensional flow of a viscous, incompressible fluid with a free surface. The resulting simplified, algebraic model is validated using data from laboratory experiments which employ hot-film anemometry to measure drop induced boundary shear stresses. Substantial agreement is found between model and experimental results with regard to the boundary shear stress magnitudes and sensitivity of magnitudes to different water layer depths, drops sizes, drop veloc...

Abstract: Conditions were investigated under which a given flow may exist at two sub-critical uniform depths, one with flow only in the main channel, one with flow also on the floodplains. Such stage-dischar...

Abstract: Local scour downstream of an apron with a swept-out hydraulic jump is shown to develop very rapidly, that is in less than 1% of the time to reach the ultimate scour depth. The short-term scour although not as deep as the long-term scour, occurs much closer to the apron. The limiting short-term scour depth is found to be related to flow regime or type of hydraulic jump that dominates the flow in the scour hole. The deepest shortterm scour was associated with the plunging jump (B-jump) and the adverse jump regimes. A modification of the B-jump equation of Hager and Bretz is proposed to estimate the limiting depth of short-term local scour.

Abstract: In this work, some considerations about the problem of the unsteady flow simulation at a junction of open channels are presented. When simulating unsteady flow through junctions, the usual technique is to assume the equality of water stages. Following the theory of characteristics, we explain that this is a valid approximation for low Froude numbers but impossible to apply in other general cases. A theoretical approach of the steady state at a junction is used to state the unsteady compatibility conditions to be used. A time evolution modelling including supercritical flows, hydraulics jumps and shock propagation through the junction becomes possible and a useful tool to improve complex dam break simulations involving tributaries.

Abstract: This paper is based on further experimental investigations of bedload transport of noncohesive sediments in rough fixed bed rectangular channels with no deposition. The results have been tested with the previously published works and more reliable prediction equations have been formulated covering a much wider range of bed roughness parameter

Abstract: A numerical method which extends traditional one-dimensional characteristic methods for wave propagation to two-dimensional flow is presented for computing dam-break waves. In this method wave interactions and reflections in two dimensions are handled such that complex channel geometries can be easily analyzed. Stability requirements are less stringent than that for explicit finite difference schemes, and body-fitted coordinates are not needed to simulate flow through arbitrary geometries. The computed results compare satisfactorily with experimental data for dam-break flows in a straight channel and along the outer bank of a 180 degree bend.

Abstract: Predictive mathematical models of hydraulic jump in rectangular sloping channels with a positive or negative step are presented. The models are verified with experimental data. A generalized equation for the modified Froude Number which accounts for channel slope and step height is suggested which is applicable to sloping channels with or without a step. A practical method for the determination of the sequent depth is presented and some important characteristics of the hydraulic jump in sloping channels with a step are also studied.

Abstract: This paper presents the results of an experimental study on intersecting circular turbulent jets of equal momentum flux, with the angle of intersection increasing from 30 to 120 degrees. The resulting flow has been divided into region 1 from the nozzle to the intersection point (IP) and region 2 downstream of the IP. In both these regions, observations have been made on the axial velocity and pressure fields. Using these results and dimensional considerations, the main features of this flow configuration have been predicted.

Abstract: Field data obtained in the measurement of typhoon-generated waves in Gulf of Bei Bu, a semi-enclosed shallow water bay, is used in the validation of a 'third generation' spectral model which employs an accurate numerical solution algorithm. The linear bottom dissipation expression obtained in the JONSWAP study is adopted since it produces a more reasonable wave growth characteristics in an ideal test case as compared to the dissipation formulation based on quadratic friction law. Computational efficiency of the model is enhanced by employing digital filtering technique to suppress the numerical instability arisen from using large time step (up to about 30 minutes) and to maintain an acceptable accuracy. The performance of the model is good and provides a further support to the 'third generation' formulation of spectral models.

Abstract: The suspended sediment transport problem in open channels is studied from the conservation laws point-ofview. Beginning with equations describing the conservation of mass and momentum of both sediment and water, equations for suspended sediment concentrations in free surface flow are derived. Sediment shear and normal stresses are modeled in a manner similar to that of fluid turbulent stresses. Ordinary differential equations for concentration profiles in the viscous sublayer and in the logarithmic velocity region of a steady uniform flow are developed. Although analytical solutions of these equations were attempted, no closed form solution was found. Therefore, a numerical technique such as the fourth order Runge-Kutta method, is used to solve the concentration profile equations. For lack of data in the viscous sublayer, only the concentration profile for flow with the logarithmic velocity distribution is solved and compared to data.

Abstract: The paper describes the salient features of a three-dimensional finite difference code at present under development for Large Eddy Simulation of free-surface turbulence. It is essential in this application that the numerical approximations conserve mass, momentum, and kinetic + potential energy while allowing for large movements of the free surface and these are presented in detail for cells cut by the surface. The surface advancement is by a combined Volume-of-Fluid and height function method which conserves mass exactly over finite time steps, but does not permit breaking waves. Momentum is advanced by control volume techniques, and the potential singularity caused by very small surface cells is avoided by a new split-merge technique which is numerically stable. Results are presented for a two-dimensional inviscid large amplitude wave in a periodic box.

Abstract: The radial hydraulic jump has been simulated using a strip integral mathematical model. The model is calibrated against the writers' experimental data. The strip integral method uses velocity shape functions to permit the partial integration of the equations of motion. A Gaussian velocity distribution is used in the mixing zone and the power law is used in the inner layer. The mathematical model includes the bed shear, turbulent shear, the potential core, entrained air, centrifugal force and turbulence pressure. The strip integral method has been applied to obtain a set of first order ordinary differential equations to describe the internal velocity distribution and water surface profile for a diverging radial hydraulic jump. These differential equations are solved by a fifth order Runge-Kutta method.

Abstract: An implicit numerical method has been developed to solve the complete one dimensional shallow water equations. The principal advantage of the scheme is that for computations involving an advancing ...

Abstract: The throttling orifice is introduced into air-cushion surge chambers to improve stability. The presence of the orifice adds another nonlinear term to the dynamic system, and its effect becomes predominant for oscillations with large displacements. By means of linearization, the type of singularities in the phase plane and their stability criteria in case of small oscillations are identified. The nonlinear analysis by direct numerical integration indicates that the system manifests itself as Hopf bifurcation with the surge-chamber size as its controlling factor. The bifurcation point corresponds to Svee's stability criterion. Before bifurcation, an unstable limit cycle may occur around the equilibrium state of practical interest, and it defines the domain of asymptotic stability. After bifurcation, two limit cycles may occur. Because of the existence of the stable one, the chamber size can be smaller than that specified by the Svee criterion. The orifice has stabilizing effect on surge motions.

Abstract: Air entrainment in secondary (brook) intake shafts creates two types of problems in the waterways of hydro electric power plants; blowouts and supersaturation of dissolved air. Blowouts may damage ...

Abstract: This paper presents the results of an experimental study on intersecting circular turbulent jets of unequal momentum fluxes for an angle of intersection equal to 60 degrees The flow has been divided into two regions, region 1 extending from the nozzle to the intersection point and region 2 covering the field downstream of the intersection point In both these regions, the velocity and pressure fields were measured and analyzed and correlated with the ratio of the jet velocities at the two nozzles

Abstract: If ocean outfalls are to function effectively it is necessary that seawater be fully purged from the system. Consequently a basic design requirement of an outfall is that it has purging capability. This paper describes model studies designed to investigate the detailed nature of the purging process in outfalls with high risers. Both purging of seawater from the outfall and its subsequent intrusion into the outfall following cessation of effluent flow were investigated. The results of the study are presented in non-dimensional terms and are compared with existing theoretical models.

Abstract: The results of a preliminary experimental investigation into the merging of buoyant discharges in an ambient current are presented. Trajectory and dilution data from the merging buoyant flows are reported. The investigation shows that the conditions at the point of merging have an important effect on the behaviour of such flows. It is also shown that if there is an ambient current there may be some advantage in designing an outfall such that the buoyant flows merge.

Abstract: The governing equations for surge oscillations in a closed surge chamber yield a second-order nonlinear differential equation for constant power. The surge stability is investigated by the direct m ...

Abstract: Type III stilling basin, according to USBR classification, is conventionally designed like other basins for a single discharge which is usually the design discharge and its performance at other discharges is tested in a hydraulic model This paper presents a new method of design for a modified type 111 basin over a major range of discharges passing the spillway structure The modified basin has two rows of friction blocks in contrast to one row in the USBR basin, to improve velocity distribution of post-jump subcritical flow in the basin The design is accomplished by developing a dimensionless semi-theoretical relationship for forced jump height curves (FRJHCS) of the spillway-stilling basin combination and matching the dimensionless tailwater rating curve (TWRC) of the river site with one of the FRJHCS, translating the TWRC verticaly if necessary So as to avoid preparation of a large family of FRJHCS for the purpose of matching, an alternative method of matching has been developed based on the