Journal of Hydraulic Engineering

Fluctuations in pressures are part of the normal behavior of water distribution systems. The common perception is that transient events dissipate quickly in a network without significant consequences; however, under certain circumstances, the superposition of waves from a transient event can magnify the pressure response, effectively accumulating head in a pipeline. This paper studies this accumulation phenomenon in a single pipeline from a theoretical point of view, with supporting numerical simulation and laboratory validation. Transient wave propagation analysis shows that after the generation of a transient event, multiple wave reflections induce an increase in the head. A cycle of accumulation is defined and the potential maximum number of cycles is studied for a pipeline connected to a long, large impedance pipe section. The analysis is then extended to a system connected to a shorter large impedance pipe section where the maximum head accumulation is not reached. Expressions to calculate the potential maximum head accumulation in pipeline systems are proposed and numerically validated. A general classification for the head accumulation is presented to specify how severe a head accumulation event may be. Experimental validation of the phenomenon has been conducted, showing that under a proposed configuration, the head in the pipeline increases significantly after the first small head rise due to a valve closure. A comparison between the maximum measured head in the laboratory and the theoretical expected maximum head has been undertaken. More realistic configurations that could result in the same phenomenon are briefly discussed.

We report findings from three-dimensional computational modeling and flume experiments on debris-flow impact force on piers with different shapes. The computational model captures the free surface with a volume-of-fluid method and the nonNewtonian fluid behavior with a calibrated Bingham model. The flume experiments were carried out within a customized system where a fixed volume of debris flow can be instantaneously released. Two debris flows (viscous and dilute) and two pier shapes (round and square) were tested in experiments, and the impact forces on piers were recorded. After extensive calibration using flume experiment results, the computational model was utilized to simulate conditions covering more parameter space where the release volume was increased, and three more common pier shapes (round-end, rectangle, and diamond) were simulated. In general, simulation results show that pier shape controls the runup, flow separation along the side, and the resulted force. The runups before piers with round, round-end, and diamond shapes are almost the same. However, they are smaller than those with square and rectangular shapes. For dilute debris flow, significant fluctuations exist in flow height, velocities, and impact forces due to the wavelike features. The influence of debris-flow types and pier shapes is quantified with drag coefficient. Simulation results also reveal a distinctive three-layer structure in the distribution of impact force in all cases.

An experimental study was conducted to better understand the settling velocity of porous spherical particles. Tests of the settlement of porous particles with porosity, $\epsilon$, ranging from 0.53 to 0.86 in glycerol–water mixtures in a range of Reynolds number from 1.9 to 24,470 were conducted. The study utilized particle tracking and image velocimetry (PTV and PIV) to digitize the settlement trajectory in order to provide additional insights on the flow field around the particle. Particle properties, namely mass, porosity, and permeability, and fluid properties, namely density and viscosity, can potentially affect the terminal settling velocity. Experimental results reveal that flow permeation through the porous particle significantly increases with increasing porosity when the latter exceeds 0.77, but the drag coefficient decreases with increasing porosity at the same Reynolds number when the latter is less than approximately 100. The terminal settling velocity of porous and solid spherical particles with equal mass in air and in liquids (settling medium) is compared independently. Concurrent permeability effects on pressure drag reduction and frictional drag increment leading to the respective increase and decrease of the terminal settling velocity of porous particles are discussed. Flow visualization around a falling particle shows that compared with solid particles, porous particles cause earlier flow separation and the formation of a wider wake at $Re<100$ but narrower wake at $Re>100$. Examination of the flow field through PIV analysis reveals that increasing porosity increases the velocity and weakens the turbulence in the recirculating (wake) region.

The surface erosion of soil samples caused by an impinging jet can be analyzed using the jet erosion test (JET), a standard experimental test to characterize the erosion resistance of soils. This paper specifically addresses the flow characteristics of a laminar impinging jet over the irregular surface of granular beds to discuss the pertinence and relevance of commonly used empirical estimations based on a self-similar model of a free jet. The JET is here investigated at the microscale with a coupled fluid-particle flow numerical model featuring the lattice Boltzmann method (LBM) for the fluid phase combined with the discrete element method (DEM) for the mechanical behavior of the solid particles. The hydrodynamics of a laminar plane free jet are confronted with the results from a parametric study of jet impingement, both on solid smooth and fixed granular surfaces, that take into account variations in particle size, distance from jet origin, and jet Reynolds number. The flow characteristics at the bed surface are here quantified, including the maximal values in tangential velocity and wall shear stress, which can be regarded as the major cause of particle detachments under hydrodynamic solicitation. It is shown that the maximal velocity at the impinged surface can be described by the free jet self-similar model, provided that a simple empirical coefficient is introduced. Further, an expression is proposed for the maximal shear stress in laminar conditions, including a Blasius-like friction coefficient that is inversely proportional to the square root of the jet Reynolds number. To conclude, finally, the JET erosion of different cohesionless granular samples is analyzed, confirming that the threshold condition at the onset of granular motion is consistent with the Shields diagram and in close agreement with previous experimental results.

Although local scour around submarine pipelines has been extensively studied in the last few decades, understanding of the mechanism of local scour around pipelines is still in its infancy stage due to the complex nature of flow–pipeline–seabed interactions, especially when the pipeline is subjected to vibrations. This experimental study aims to obtain an improved perception of the scour mechanism around a pipeline subjected to vortex-induced vibrations. The experiments were conducted in a flow recirculation flume in clear-water scour conditions in which a circular cylinder with diameter ($D$) of 35 mm was used as the pipeline model. The initial gap ($G_0$) between the underside of the pipeline and undisturbed flat-bed level was $0.45D$. The time evolution of the pipeline motion and scour profile around the pipeline was measured using a high-speed camera and laser sources. The flow fields around the vibrating pipeline were obtained using the particle image velocimetry (PIV) technique and phase-average analysis. Based on the characteristics of the development of the scour hole and pipeline motions, three scour stages are identified. The downward motion of the vibrating pipeline and interactions between the counterclockwise vortex (downstream of the pipeline) that sheds from the lower shear layer of the pipeline and sediment bed are found to be the primary mechanisms that cause the formation of the scour holes beneath the pipeline. The interactive coupling effects among the vibrating pipeline, flow field, and scour process also are discussed in this study.

In this research, physical modeling of nonhomogeneous earth dams with clay cores was performed. The effects of dam slope, dimensions, and geometrical shape of the core, as well as the materials used for the core and body, on the breaching process and corresponding output hydrographs were studied. The breaching processes of each experiment were recorded using three digital cameras, and both quantitative and qualitative results were extracted. A decrease in the dam slope decreases the peak outflow, and the corresponding output hydrograph has a lower peak discharge and longer occurrence time. In addition, results show that the cohesion of materials is a prominent factor in the breaching of the core, and with a more cohesive core, the peak outflow and occurrence time considerably increase (by approximately 40% and up to 50%, respectively). For core materials with lower cohesion, erosion of the core and body occurs simultaneously, and consequently, the breach formation process is similar to a homogeneous dam. Finally, the hydrographs of dams with various practical core shapes show that the construction of an inclined core will increase the peak outflow up to 55% and weaken the dam behavior during overtopping. In these experiments, the trapezoidal cores presented the best results.

The erodibility of mud–sand bed mixtures has been studied based on experiments in a flume and in a small, vertical tube placed on the bed (Eromes-tube of 100 mm diameter with rotating propeller). Two natural mud–sand mixtures (percentage of $\text{sand}\cong 35\%$ and 20%) were used and artificial mixtures were made by adding fine sand to the natural mud samples; the percentage of sand was varied in the range of 30%–95%. Two types of fine sand have been used: very fine sand of about 100 μm and fine sand of 180 μm. The dry density was varied in the range of $300–\mathrm{1,500}\mathrm{kg}/{\mathrm{m}}^3$ (soft to firm beds). Three types of erosion were identified (visually) during the flume experiments: particle/floc erosion, surface erosion by generation of local craters and grooves, and mass erosion (two types) by local bed collapse or by local breakout of lumps of bed material with clouds of escaping mud. Plots of the critical bed-shear stress for particle, surface, and mass erosion are given based on the data of the flume and Eromes tests. The critical bed shear for particle, surface, and mass erosion of natural mud–sand beds is found to be primarily influenced by the percentage of fines ($<63\mathrm{\mu m}$), percentage of clay-silt ($<8\mathrm{\mu m}$), and the dry bulk density of the top layer of the bed.

Two-dimensional shallow-water schemes on Cartesian grids are amendable for graphics processing units and thus a convenient choice for fast flood simulations. A comparison of recent schemes and validation of important use cases is essential for developers and practitioners working with flood simulation tools. In this paper, we discuss three state-of-the-art shallow-water schemes: a first-order upwind scheme, a second-order upwind scheme, and a second-order central-upwind scheme. We analyze the advantages and disadvantages of each scheme on historical Danube river floods at three regions in Austria. We study the Lobau region as a floodplain with several small channels, the Wachau region with the meandering Danube in a steep valley, and the Marchfeld region located at the river confluence of March and Danube. The validation case studies show that the second-order schemes provide better estimates of the water levels than the first-order scheme. Still, the first order scheme is useful because it offers fast simulations and reasonable results at higher resolutions. The best trade-off between accuracy and computational effort for simulating river floods is provided by the second-order upwind scheme.

A numerical investigation of near-field brine discharge dynamics is reported for the Gold Coast Desalination Plant offshore inclined multiport brine diffuser. Quasi-steady computational fluid dynamics simulations were performed using the Reynolds Averaged Navier Stokes equations with a $k\text{-}\omega$ Shear Stress Transport turbulence closure scheme. Simulations used an iterative mesh domain with length of 400 m, width of 200 m, and average depth of 24.2 m. Longshore crossflow conditions were examined with a current velocities range of $0.03–0.26\mathrm{m}/\mathrm{s}$. The alternating port orientation of the diffuser resulted in simultaneous co- and counterflowing discharges. Impact distance, impact dilution, and terminal rise locations were compared against the existing literature, and dimensionless empirical equations were fitted as functions of the current speed. Transverse spread and resulting salinity increases were also assessed against field measurements. For the first time, the areal extent of seafloor salinity increase is examined, with the quasi-quiescent regime holistically presenting the worst-case conditions. Plume trajectory, dilution, areal salinity intensity, and plume dispersion after impact each reflect distinct variations between jet- and crossflow-dictated regimes at a threshold value of $u_{r}F\approx 0.8$ ($u_r$ = ambient to jet velocity ratio; $F$ = jet densimetric Froude number). This behavior depends on the presence of the arrested upstream sublayer that, in turn, has consequences for the application of empirical models to multiport discharges under low-crossflow regimes. This study demonstrates significant advancements over existing empirical and integral modeling methods, with strong application potential for designers, plant operators, and regulators.

This Technical Note reports on new experiments focused on hydraulic resistance in open-channel flows over beds covered with streamwise ridges. Extensive bulk friction factor measurements, combined with particle image velocimetry (PIV) for selected cases, were carried out to investigate the effects of spanwise spacing, relative submergence, and surface roughness of the ridges. Two types of ridges were investigated, both characterized by triangular cross sections but featuring different surface roughness. Compared to friction factor estimates neglecting any changes in flow structure promoted by the ridges, the measured friction factors were found to be higher by 10% at ridge spacings of approximately $1.6H$ and lower by up to 20% at spacings smaller than $0.7H$ ($H$ is flow depth). No influence of relative submergence and ridge surface roughness on these findings was observed. The PIV data suggest that the revealed effects are likely related to secondary currents instigated and modulated by the bed ridges.