Journal of Hydraulic Engineering

Hydraulic transients with the movement of an interface between pressurized flow and free surface flow can be observed in rapid water emptying in the pipes. This study focuses on air cavity intrusion into horizontal and inclined circular pipes. Laboratory experiments were carried out to observe the negative surge during depressurization in a circular pipe. In order to generate the undular bore in a circular pipe, in some cases a sharp-crested weir at the open end of the horizontal pipe was used. Various behaviors of air cavity were observed for a series of weir heights. A numerical model is proposed and applied to the cavity flow in a circular pipe. To reproduce the undular bore in circular pipes (when water depth is greater than pipe radius), this study derived the depth-averaged shallow water equations with the effects of vertical acceleration using the Boussinesq equation. In this study, the continuity and the momentum equations of free surface and pressurized flows with the hydrostatic and the Boussinesq pressure assumptions have been used. The results from the model showed good agreement with the experimental results.

With the advent of acoustic Doppler current profiler (ADCP), the velocity profile method or index velocity method based on a single profile or a fixed-depth cell has been recommended for estimating discharge in tidal reaches. However, in large tidal reaches with a width of nearly 6 km and cross-sectional variability of flow, such as Yangtze Estuary, these methods are not accurate enough for the discharge estimation. Therefore, an improved method named the multiprofile method, is proposed in this paper. The method includes four main steps: (1) calculating the cross-sectional area $A$ with stage data by considering the transverse slope; (2) calculating the depth-mean velocity $u$ at each fixed ADCP; (3) establishing the $u-U$ model with the multiprofile $us$ and estimating the cross-sectional mean velocity $U$; (4) estimating the final discharge through $U$ multiplied by $A$. The proposed method was tested at the Xuliujing section of the Yangtze Estuary. The result shows that the multiprofile method averagely improves the accuracy by approximately 5.8% relative to the single-profile method in the discharge estimation, which proves the proposed method to be valid in the discharge estimation of large tidal reach.

Sediment-pickup rate is useful for deriving bedload function and specifying boundary conditions for numerical modeling of sediment transport. Previous pickup functions were developed based only on data measured under the plane bed condition, and they may not be applicable for dune-covered beds. The present study compares pickup rates for three bed conditions, i.e., plane bed, fixed dunes, and mobile dunes. All pickup functions are formulated by involving the densimetric Froude number instead of the Shields number. The results show that the sediment-pickup rates measured over fixed dunes can be described using the pickup function developed for the plane bed. However, the presence of mobile dunes causes a considerable reduction in the pickup rate when the densimetric Froude number is greater than 5, which is largely due to flow–particle and particle–particle interaction. This study also shows that under mobile dune conditions, the particle step length for dune bed conditions scales with the dune length rather than the particle diameter.

Flood disasters such as dam breaks and surges from extreme hurricanes or tsunamis entrain and transport substantial amounts of submerged or floating debris. Understanding of motion and spatiotemporal distribution of debris entrained by a flood is thus of great importance to hydraulic, coastal, and structural engineers; the displacement of debris to a location where it may eventually impact critical infrastructure requires scientific attention at the laboratory scale first. In this context, the design and application of a novel smart debris system utilizing off-the-shelf components is presented and discussed. The system tracks the spatial location and orientation of a multitude of debris specimens and it proposes an accurate tool to assess their individual trajectory, velocity, and momentum in a laboratory environment. Contrary to the traditional camera-based approach of video tracking, which often fails once objects are submerged, the proposed smart debris system delivers six-degree-of-freedom (6DOF) data in a reliable, timely manner. Miniaturized inertial measurement units (IMU), commonly called motion sensors, which are used for attitude heading reference systems are deployed to output time series of spatial orientation along with filtered 3D acceleration readings. A Bluetooth low-energy (BLE) tracking system is applied along with the motion sensor to track the 3D debris positions. A detailed investigation in controlled laboratory conditions reveals the detailed individual performance of the tested spatial orientations and positions. As an application, debris transport tests were conducted in a newly built tsunami wave basin at Waseda University in Tokyo, Japan. For this test series, a typical harbor layout with a vertical quay wall adjacent to a horizontal container-stacking platform was constructed. The advection by a broken tsunamilike bore of multiple down-scaled shipping containers in basic arrangements was then tracked from their initial position. The performance of the innovative smart debris system is qualitatively tested in order to provide guidance for their future application in hydraulic and coastal engineering as well as to provide a solid basis for its application in field studies.

A two-dimensional coupled solid-fluid numerical model was modified and applied to simulate the dam-overtopping event of landslide-generated waves in an idealized reservoir. The model employed was based on the two-dimensional Reynolds-Averaged Navier-Stokes (RANS) in a vertical plane with the $k-\epsilon$ equations for turbulence closure. The motion of the solid landslide was modeled using the equation of motion for rigid body, and the free surface was tracked using volume of fluid (VOF) method. For model validation, experiments were conducted for the case of dam overtopping in an open channel. Particle image velocimetry (PIV) was used to measure velocity variations of the first wave during dam overtopping in one field of view (FOV), and wave gauges were used to record variations of the free-surface elevation at three selected locations in the open channel. The calculated and measured data comparisons were performed for time histories of surface elevation, surface profile, and vertical velocity distribution, and showed reasonable agreement. Following model validation, the numerical model was also used to illustrate the velocity and turbulence kinetic energy features during wave-generation and overtopping processes.

This study integrates a large eddy simulation model to investigate the effect of a submerged rectangular cylinder on the hydrodynamics of free surface flows. The simulation results are validated by the results of flume experiments. Then the numerical model is utilized to examine the influences of Reynolds number, Froude number, and blockage ratio on the flow field and the force coefficients of the deck. The simulation results reveal that the drag coefficient is dependent on the deck’s Froude number and blockage ratio of the bridge deck, rather than the Reynolds number. For both subcritical and transcritical flows, the drag coefficient increases as the blockage ratio increases. However, due to the wave-induced drag, the drag coefficient of the cylinder in transcritical flows is greater than that in subcritical flows with the same blockage ratio. On the other hand, the lift coefficient is a function of the submergence ratio and the deck’s Froude number. The separation shear flow on the upper side of the cylinder is constrained by the water surface when the submergence ratio $h^{*}<2.0$, and resulting in an asymmetric pressure distribution on the upper and lower sides of the deck, which subsequently generates a downward force on the bridge deck.

A stability parameter for rock in bed protections under nonuniform stationary flow is derived. The influence of the mean flow velocity, turbulence, and mean acceleration of the flow are included explicitly in the parameter. The relatively new notion of explicitly incorporating the mean acceleration of the flow significantly improves the description of stone stability. The new stability parameter can be used in the design of granular bed protections using a numerical model for a large variety of flows. The coefficients in the stability parameter are determined by regarding the measured low-mobility entrainment rate of rock as a function of the stability parameter. Measurements of flow characteristics and stone entrainment of four different previous studies and many configurations (uniform flow, expansion, contraction, and sill) are used. These configurations have different relative contributions of mean flow, turbulence, and stationary acceleration. The coefficients in the parameter are fit to all data to obtain a formulation that is applicable to many configurations with nonuniform flow.

This study developed a methodology by which to determine the optimal spatial distribution of submerged vanes positioned across a river channel to protect the stream bank from erosion. The methodology is based on an improved model for estimating the interaction between a row of vanes and the banks of the channel. The results show that the optimal spatial distribution of vanes is related primarily to the radius of the channel curve and the width of the channel. The sediment Froude number and angle of flow to the vanes were shown to have far less effect. The best results were obtained when the spacing between vanes in a row increased gradually outward from the target bank at an average ratio of approximately 1.2. This provides a handy guideline for the preliminary layout of vane arrays.

This paper presents the results of the calibration by means of a microgenetic algorithm, using Kelvin-Voigt viscoelastic parameters, to reproduce experimental unsteady flow tests in a polymeric pipe. During the tests, different pipe lengths—which give rise to different periods of the pressure oscillations—and initial discharges have been considered. The mechanical parameters of the viscoelastic models are estimated using both one-dimensional (1D) and quasi two-dimensional (2D) models. The calibration of Kelvin-Voigt models with 2, 3, 5, and 7 parameters, respectively, proves the substantial independence of the elastic modulus and the dependence of the retardation time on the pipe period (i.e., the pipe length). Moreover, in most cases, the increase in the number of mechanical parameters allows a better simulation of a single transient. However, the larger the number of parameters, the greater the risk of overfitting, and the more difficult the search for general laws of dependence of the parameters on the characteristics of the pipe—primarily of the retardation time on the period of the pressure oscillations.

One of the main causes of lining damage in stilling basins and at the toe of chute spillways is the global instantaneous uplift forces due to the difference in pressure acting on the upper and the lower surface of protection slabs or rock elements. Spillway stilling basin linings can be built according to two different techniques: using sealed joints or unsealed joints. In the case of sealed joints, the pressure underneath the slab is constant and the uplift force results from the pressure fluctuations acting on the slab. In the case of unsealed joints, the pressure propagation at the lower surface of the slab, being transferred through the joints, should also be considered. The aim of the paper is to study, define, and compare the design criteria in these two cases. In the present study, the pressure field on the slab is evaluated according to a recent method based on the Taylor hypothesis, whereas the pressure propagation under the slab is computed by a new 3D model based on unsteady flow analysis of seepage through porous media. By this approach, it is possible to consider the effect of finite thickness foundation layers, typical in the case of weirs for run-of-river power plants, earth dams, and rock-fill dams. Furthermore, to complete the presented design criteria, the dynamic behavior of anchored slabs is experimentally investigated with reference to the sealed joint case due to a lack of studies in the literature.

Integral models of single-phase plumes are often closed using the entrainment hypothesis, which assumes the entrainment velocity is proportional to a characteristic plume velocity, but the corresponding theoretical development for modeling particle plumes has received less attention. In this paper an integral model is developed by proposing a new spreading hypothesis for particle plumes, in which the fluid phase spreading rate is taken as that of a single-phase plume, whereas the particle phase spreading rate is a function of the particle phase and fluid phase average vertical velocity. The change in momentum flux of the particle and fluid phases are calculated by considering the cross-sectional integrated buoyant and drag forces acting on the particles, and their reaction force acting on the fluid. Mixing characteristics of the particle plume can then be determined. The model was validated by laboratory particle plume experiments conducted for various particle sizes and initial plume-to-particle-settling velocity ratios, as well as experiments in the literature. Centerline particle and fluid velocities, as well as particle concentrations were generally well predicted. The inferred entrainment coefficient for a particle plume and the importance of lift force are also discussed.

A detailed computational parametric study of a perforated pipe underdrain surrounded by loose aggregate has been conducted. Several controlling geometric parameters (i.e., trench width, head, aggregate depth over the pipe, pipe wall perforation area per unit length of pipe, and the area of individual perforations) were considered and the variation of pipe discharge characteristics as a function of these parameters has been quantified. Results indicate that, for each combination of these parameters, there is a finite pipe length after which discharge does not increase with increasing pipe length. This pipe length depends on the pipe wall perforation area per unit length of pipe, pipe cross-sectional area, and losses associated with them. It was found that the effective pipe system discharge coefficient is independent of the channel width, aggregate depth, and head over the pipe for the range of parameters tested. The computational fluid dynamics (CFD) results were used to develop an equation for the system discharge coefficient as a function of the pipe geometry. This equation can be used for sizing underdrains in low-impact development (LID) best management practice (BMP) stormwater systems. These results have practical applications in many stormwater LID/BMPs of similar setup to that used in this study (e.g., porous pavements and infiltration trenches) for sizing and analyzing the hydraulic behavior of the underdrains. This allows design engineers to quantify the peak outflow from the underdrain when the systems are flooded.

The comparison between spatial and temporal growth of perturbations in a shear layer is revisited for the case of a viscous open-channel flow with velocity inflection. Turbulence is characterized by two distinct scales: a subdepth turbulence associated with the bed shear stress and a large-scale turbulence associated with the large horizontal eddies that develop in the shear layer. Temporal and spatial linear stability analyses are performed. The base flow is assumed to be affected only by the subdepth scale turbulence. Therefore, the base flow represents not the average flow but the flow completely free of the effect of the instability of the shear layer. Temporal and spatial approaches present less discrepancy in the viscous than in the previously analyzed in-viscous case. In particular, the phase velocity was found to be strongly correlated to the frequency in both the temporal and spatial approaches.

Modeling of dam break flows is frequently required in civil and environmental engineering because of the risk associated with this catastrophic flow. Typically, model predictions are conducted using the Saint-Venant hydrostatic theory, which can lead to unrealistic predictions. The prediction of the amplitude of nonhydrostatic waves generated during dam break flows is an important engineering problem given the risk of overtopping of flow in manmade canals or the increasing of flooding areas in natural watercourses. The weakly nondispersive and fully nonlinear Serre equations are a suitable choice for modeling these flows, but there is a lack of a systematic assessment of this system of equations for dam break flow modeling reported in the literature. In this paper, the Serre equations are applied to dam break flows over horizontal rigid bottoms, whereas in the second part of this research, the nonhydrostatic dam break waves over erodible beds are considered. Here, a high resolution finite volume model is developed where a suitable time stepping scheme is systematically investigated. The impact of the vertical pressure distribution shape, nonlinear terms in the equations, and the enhancement of the linear frequency dispersion are examined in detail. The model is successfully tested against the experimental data, a solitary wave propagation test, and the three-dimensional (3D) simulations. The results obtained from finite volume method are further compared with those obtained from finite element and finite difference methods available in the literature.

The dam break flow over a movable bed is an important problem in fluvial flow processes. These flows are usually predicted by a one-dimensional (1D) approach based on a hydrostatic pressure distribution. Recent three-dimensional (3D) nonhydrostatic simulations of dam break waves over movable beds based on the Reynolds-averaged Navier-Stokes (RANS) equations revealed that the Saint Venant theory is not accurate in predicting the flow dynamics within the scour hole developed. In this work, a generalized 1D nonhydrostatic model for flow over movable beds is proposed assuming a linear, nonhydrostatic, pressure distribution. The new set of 1D equations accounts for the vertical acceleration, which is important in dam break waves over movable beds given the instantaneous curved beds generated over the erodible terrain. These equations account for both the bed and suspended-load transport modes. A high-resolution finite volume numerical scheme with a semi-implicit treatment of nonhydrostatic terms is developed to solve the governing equations, producing solutions that are in good agreement with 3D computational results and experimental data. The free surface profiles predicted by the new model show a significant improvement as compared to those obtained from the existing hydrostatic simulations. The unsteady nonhydrostatic simulations are shown to be convergent to steady flow solutions with nonhydrostatic pressure.

Bendway weirs are submerged, in-stream rock structures that redirect impinging flow away from outer-banks toward the center of a channel. Riprap weirs are composed of stone and sized using the average channel velocity in conjunction with existing design guidance. A physical model study and field study were conducted to determine the magnitude of the convective velocity that accelerates around the tip or toe of the weir. The ratio of the maximum tip velocity to the average channel velocity (prior to weir installation) was determined to be approximately 1.70. Stone sizing criteria that significantly increase the riprap median size over traditional approaches were presented for consideration.

This note proposes a new quasi-two-dimensional (quasi-2D) numerical scheme for simulating a water hammer that significantly reduces the computational burden compared to two existing quasi-2D schemes, as numerically demonstrated in this note by application to a reservoir-pipe-valve system. Computational cost is decreased through using one-dimensional (1D), rather than two-dimensional equations for pressure head and discharge and using a staggered grid with half of the computational nodes compared to a rectangular grid. It is valid to use the proposed 1D characteristic equations for the pressure head and discharge, as it is proved that these yield identical results to explicit quasi-2D solution procedures previously introduced in the literature.

The suspension flow of quartz silt (geometric mean grain size of 4.15 μm), in unfavorable conditions for deposition, is the motivation for the development of different bed morphologies. Particles deposit over a plane nonerodible surface and develop well-defined barchan ripples, barchanoids, and plane beds in flume experiments. Bedload transport of quartz silt by bedform migration is several orders of magnitude smaller than the suspended transport. The final bed morphology is controlled by the suspended sediment concentration and running time of the experiment. The average dimensions of the bedforms after 1-day experiments are 4.93 cm wide, 10.33 cm long, and 0.45 cm high. Cohesive plane beds appear after 2-day and 3-day experiments with very high sediment concentrations ($\ge 22.5\mathrm{kg}/{\mathrm{m}}^3$). Viscous effects are deemed relevant for the formation of the beds.