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Hydraulic jump is a phenomenon with destructive effects on the river bed and downstream the hydraulic structures. This study, based on experimental findings, presents a new method that can be used to prevent the detrimental impacts of the hydraulic jump downstream of hydraulic structures and to design optimal structures. In this empirical research, 135 experiments were conducted in an experimental flume where submerged vanes with angles of attack of 30 and 60°, as a novel intuitive method, were used with two different configurations and adverse slopes (0, −1.5% and −3%) to control hydraulic jump in the range of 4.58 < Fr 1 < 9.14. Based on the obtained results, the sequent depth and length of the hydraulic jump were, at most, decreased by 26.6% and 31.9%, respectively, with increasing the angle of attack of submerged vanes and the adverse slope of the bed. Also, the energy loss increased up to 7.7% in the case of φ = 60°, d = 0.2 m, and S = −3%. To calculate the sequent depth and length of the hydraulic jump, new equations were expressed through the analysis of the effects associated with the angle of attack, adverse slope, and vane configuration. All data resulting from proposed equations were then compared and validated with the experimental data. [ABSTRACT FROM AUTHOR]

The momentum-conserving staggered grid (MCS) scheme to simulate shallow water flows in channels of varying width and topography is revisited in this article. Here, we modify the MCS scheme so that it can be applied to channels of arbitrary cross-section. The scheme is validated using steady analytical solutions for channels with rectangular and trapezoidal cross sections. We found that the method was capable of solving a wide variety of test cases; including subcritical, supercritical and transcritical steady flows and flows with hydraulic jumps. This MCS scheme could handle both steady and unsteady problems. In the implementation of a channel with arbitrary cross sections, the simulation depicts the time-lapse evolution of the water level toward the steady state. These results were consistent with previous findings in the literature. All numerical experiments carried out here demonstrate the merits of the numerical MCS scheme. • Steady and unsteady flows in prismatic channels are simulated using MCS scheme. • Validation is done using MacDonald's analytical steady solutions for various flows. • The MCS scheme is extended so that it can be used to handle non-prismatic channels. [ABSTRACT FROM AUTHOR]

The current research investigates experimentally the flow passing through combined hydraulic structure consists of V-notch sharp crested weir and inverted V-shaped sharp gate installed in straight channel as a control structure. Nine structure models were used considering three different vertex angles simultaneously used for the weir and the gate (θ = 60°, 90° and 120°). Eighty-one experimental runs were executed to explore the influence of the combined structure geometry, the upstream head, and the tailwater depth on the conveyed flow, the discharge coefficient and the downstream flow pattern with special emphasize on the hydraulic jump characteristics. The outcomes were analyzed and graphically presented. The results proved that the simultaneous flow through the combined structure regardless the vertex angles conveyed more discharge with less downstream water disturbance on account the classical V-notch weir and the inverted V-shaped gate. The flow discharge increased up to 10 times, and the discharge coefficient increased by around 26% for combined structure of 120° vertex angle under similar hydraulic conditions. The conveyed discharge was influenced by the gate angle than the weir angle. The downstream flow characteristics were more sensitive to the weir angle than the gate angle under similar hydraulic conditions. The measured hydraulic jump lengths were compared to other formulas and showed good agreement. Also, the weir and gate vertex angles effectively influenced the hydraulic jump characteristics. The outcomes were used to develop empirical equations for predicting the discharge coefficient and dimensionless jump length associated to the combined structure. The results and analysis in this research are limited to tested data range. [ABSTRACT FROM AUTHOR]

The movements of fishes in natural river systems are affected by in-stream man-made structures, including dams and weirs. The effect of downstream fish passage over dam spillways has received little attention to date. In 2010, some observations of downstream fish passage were conducted at the Paradise Dam spillway, Australia during two markedly different flood events. The spillway was equipped with an un-gated crest, a steep stepped chute and a hydraulic jump energy dissipator without baffle block. The data on downstream fish passage at Paradise Dam are herein re-analysed with a focus on downstream fish passage over the spillway and associated mortality, together with some complementary information on the spillway operation. The mortality rates of fish passing on the Paradise Dam stepped spillway were very low. Under skimming flow conditions, the relative mortality rate was 0.085% of fish passing over the spillway on 3–4 March 2010. A higher mortality rate was seen under nappe flow conditions, although comparable to smooth chute fish mortality data. In average, the fish mortality data downstream of the Paradise Dam spillway was between 7 and 27 times lower than the natural fish mortality in the reservoir. Overall, the present data analyses demonstrated un-equivocally the significance of the spillway flow regime on the downstream fish passage mortality rate. It showed the adverse impact on fish during downstream passage at very-low flows, i.e. q < 0.01–0.02 m2.s−1, with both smooth-invert and stepped invert spillways. The finding highlighted a need for efficient downstream fish-friendly passage designs, adapted to the relevant spillway designs, and a number of low-flow fish-friendly channel designs are discussed. [ABSTRACT FROM AUTHOR]

High-energetic glacial lake-outburst floods are known both from ancient and current glacial environments. While a decrease in meltwater flow energy takes place, a proglacial bedform continuum is formed due to erosional and depositional processes; these have been studied in relatively little detail as compared to the sediment transport modes and deposition processes of glacial lake-outburst floods. Therefore, we consider upper-flow-regime bedforms that originate from glacial lake-outburst floods under subaerial conditions in the ice-proximal portion of floodwater spillways as the main interest of this study, and we particularly focus on a suite of features of scabland-like topography in NE Poland. A Digital Elevation Model (DEM) is used to detect the relevant landforms and to provide their morphometric parameters, and is further combined with sediment lithofacies analysis. These methods allow us to recognise a train of transverse furrows that consists of seven main and two associated depressions that altogether constitute a longitudinal cluster interpreted as cyclic steps. These bedforms developed due to (1) upstream progradation of troughs with gravelly lags, (2) scour infill with backset and foreset facies in hydraulic jump zones and (3) sedimentation on the downflow side of hydraulic jumps. The recognised cyclic steps reveal their transportational type with five scour-and-fill events under conditions of high sediment concentration and low bed resistance to floodwater erosion. Later, transverse furrows experienced aeolian accumulation and mass wasting that both made them shallower. [ABSTRACT FROM AUTHOR]

The world is increasingly shifting toward low-head hydropower as a sustainable form of renewable energy in response to the negative socioeconomic impacts of large hydroelectric plants. In this context, the article presents a novel design involving retrofitting the gates of existing dam structures with Dethridge waterwheel technology. This innovative solution installs the wheel under the gate to harvest the untapped potential energy resulting from the head difference at these already-existing facilities while simultaneously reducing the need for costly civil work and preventing new installations in freshwater systems. The El-Reah El-Tawfiqy barrage in Egypt served as the model case study for evaluating the implementation of the proposed design. According to the results, the plant's levelized cost is 29 USD/MWh, less expensive than traditional hydropower projects and achieves grid parity. With an estimated 140 MWh of electricity produced annually, the project is expected to cut around 1460 tons of CO 2 equivalent over its 25-year lifespan. This study includes several novelties, including modifying hydraulic structure gates for pico power generation. Additionally, a thorough numerical analysis was performed to estimate the output power instead of relying on theoretical approaches for the economic viability study. These results can guide policymakers and stakeholders in implementing affordable and sustainable renewable energy solutions. [Display omitted] [ABSTRACT FROM AUTHOR]

Dam-break floods, especially cascade dam-break floods, could be catastrophic and warranted further investigation to enhance understanding. This paper systematically investigated the impact of break heights of the second dam on the evolution of two-dam failure floods, comparing it with single-dam outburst floods. The experiments were carried out in an inclined rectangular flume with LiDAR technology to capture the free surface. Results indicated that a computational model for the moving hydraulic jump was developed, showing good agreement with experimental results with a relative error of about 10%. The wave height of dam-break flood increased with the increase of evolution distance. The wave front celerity (for dam spacing: L / H = 26) after the flood passed the second dam increased with the break heights. The peak discharges at the second dam site and the peak flow depth (for longitudinal coordinate: x / H = 59) both showed a linear relationship with the initial flow depth in reservoir and the break heights. An increase in the initial flow depth in reservoir or the break heights led to an increase in peak discharges and peak flow depth. This study offered constructive guidance for the risk assessment of multi-dam failure floods and disaster emergency management. [Display omitted] • Established the computational model about moving hydraulic jump. • Analyzed the impact duration of two-dam failure floods. • Wave height and wave front celerity are less affected by dam spacing. • Established equation to predict peak discharges and peak flow depth. [ABSTRACT FROM AUTHOR]

• Laboratory study of flow and sediment transport, and vortex generation under a surging wave on an equilibrium beach with rigid and sediment bed experiments. • A backwash vortex occurs at the beach step as a result of flow separation at the crest of the step. • Flow separation, accompanied by an upward-directed vertical acceleration of fluid particles during the wave breaking creates an impulsive, upward-directed pressure gradient force. • Sediment transport occurs in the sheet-flow regime in a substantial part of the equilibrium beach. Flow patterns and sediment transport induced by breaking waves on a beach profile have been studied in a laboratory wave flume. Two parallel experiments were conducted on the same profiled rigid bed and sediment (mobile) bed, each subjected to identical wave forcing. The rigid bed experiments include measurements of bed shear stress and water-surface elevation, while the sediment bed experiments involve the measurement of pore-water pressures. The beach profile features a beach step leading to the generation of a hydraulic jump at the end of the rundown phase and accordingly forms a backwash vortex. The bed shear stress measurements revealed that the maximum onshore directed mean bed shear stress occurs after the wave breaking whereas the offshore directed one occurs during rundown at the same section. The increase of the bed shear stress with respect to that in the approaching wave boundary layer during the wave breaking and hydraulic jump processes can be by as much as a factor of 13 and 4, respectively. The effect of the wave breaking on turbulence is also more pronounced by a factor of 2.2 than the hydraulic jump in terms of r.m.s values of the fluctuating component of the bed shear stress. The pore pressure measurements showed that the vortex generated during the wave breaking creates an impulsive, upward-directed pressure gradient force that can be up to 1.2 times the submerged weight of the sediment. The sediment transport occurs in the sheet flow regime in a large part of the beach profile. The turbulence generated by the backwash vortex and the hydraulic jump at the beach step directly impacts the local sediment suspension which serves as the source for the advected sediment in the swash zone. The results are compared with a previous study that used the same methodology but involved plunging waves and the initial bed profile. [ABSTRACT FROM AUTHOR]

The sedimentology of upper flow regime bedforms represents an important research topic at the present. Deposits interpreted as those of supercritical flows are widely recognized in modern fan systems, but their recovery is challenging. Most of the sedimentological information has come from channel thalwegs but supercritical bedforms are also frequently downslope from the channel mouths. Such an environment has been identified in the Paola basin, where erosive and depositional cyclic steps have been imaged and identified in a sandy submarine lobe of the Amantea Fan. High-resolution sub-bottom profiles provide insight into the bedform internal architecture and their relationships with a frontally-confining ridge. For the first time, supercritical bedforms in a submarine lobe have been interpreted in two distinct positions: in the scour of an erosional cyclic step and in the stoss side of a depositional cyclic step. Coarse to medium-grained massive sand with flame structures, indicating rapid sediment fall-out and frequently associated with the occurrence of hydraulic jumps, has been identified in the scour and at the toe of the ridge. The latter represents an example of topographically induced hydraulic jumps driven by a frontal confinement. Top-cut-out medium to fine sands with tractive structures have been interpreted as the deposits related to the stoss side of a cyclic step or small-scale antidune superimposed on the cyclic step surface. The presented data broaden the understanding of the range of processes that are driven by the interaction between turbidity currents and seafloor topography and the dip of the slope. The recognition that topography influences the density structure and the degree of criticality of the flow and, consequently, the morphodynamics and facies of the relative deposits may help to explain sediment distribution and improve depositional models of fan lobes in confined settings. • Sedimentological information about supercritical bedforms in a frontally confined submarine lobe are provided. • Observations result from the interpretation of high-resolution seismic profiles and the analysis of five gravity cores. • Sedimentary structures, generally associated with hydraulic jumps, have been identified in scour fills and at the base of a ridge. • The topography influences the distribution of supercritical bedforms and the flow criticality. [ABSTRACT FROM AUTHOR]

Submarine canyons are primary conduits for turbidity currents transporting terrestrial sediments, nutrients, pollutants and organic carbon to the deep sea. The concavity in the longitudinal profile of these canyons (i.e. the downstream flattening rate along the profiles) influences the transport processes and results in variations in turbidite thickness, impacting the transfer and burial of particles. To better understand the controlling mechanisms of canyon concavity on the distribution of turbidite deposits, here we investigate the variation in sediment accumulation as a function of canyon concavity of 20 different modern submarine canyons, distributed on global continental margins. In order to effectively assess the isolated impact of the concavity of 20 different canyons, a series of two-dimensional, depth-resolved numerical simulations are conducted. Simulation results show that the highly concave profile (e.g. Surveyor and Horizon) tends to concentrate the turbidite deposits mainly at the slope break, while nearly straight profiles (e.g. Amazon and Congo) result in deposition focused at the canyon head. Moderately concave profiles with a smoother canyon floor (e.g. Norfolk-Washington and Mukluk) effectively facilitate the downstream transport of suspended sediments in turbidity currents. Furthermore, smooth and steep upper reaches of canyons commonly contribute to sediment bypass (i.e. Mukluk and Chirikof), while low slope angles lead to deposition at upper reaches (i.e. Bounty and Valencia). At lower reaches, the distribution of turbidite deposits is consistent with the occurrence of hydraulic jumps. Under the influence of different canyon concavities, three types of deposition patterns are inferred in this study, and verified by comparison with observed turbidite deposits on the modern or paleo-canyon floor. This study demonstrates a potential difference in sediment transport efficiency of submarine canyons with different concavities, which has potential consequences for sediment and organic carbon transport through submarine canyons. • The impact of submarine canyon concavity on turbidite deposition was assessed. • Distribution of turbidite deposits varies with changes in canyon concavity. • Three distinct deposition patterns were identified. • The recognized deposition patterns align well with the observed turbidite deposits. [ABSTRACT FROM AUTHOR]

The present study aims to evaluate characteristics of the hydraulic jump formed in a circular stilling basin with baffle blocks. Baffle blocks improve performance of the hydraulic jump and stabilize its position in the basin. In addition to experimental modeling, theoretical relationships were derived to determine the sequent depth ratio and the relative energy loss in circular stilling basins with baffle blocks, deriving a relationship for estimating the force imposed by the blocks. Based on the results of the present study, baffle blocks in a stilling basin improve the characteristics of a circular hydraulic jump such as the sequent depth ratio and relative energy loss. Furthermore, increasing the obstruction ratio and the sequent radius ratio decrease the sequent depth ratio. Furthermore, an increase in the sequent radius ratio led to an increase in the relative energy loss. Also, the results show that the relative length of a circular hydraulic jump is significantly smaller than that of the classical hydraulic jump (CHJ). Error analysis on the measured data and the developed theoretical relationships indicated that the theoretically obtained results compare well with the present experimental data. • This study aims to evaluate the characteristics of the hydraulic jump in a circular stilling basin with baffle blocks. • Theoretical relationships were presented to determine the sequent depth ratio and the relative energy loss. • Increasing the obstruction ratio and the sequent radius ratio results in a decrease in the sequent depth ratio. • An increase in the sequent radius ratio led to an increase in the relative energy loss. • The relative length of a circular hydraulic jump is significantly smaller than that of the classical hydraulic jump. [ABSTRACT FROM AUTHOR]

Stepped spillways are used to improve the hydraulic performance of a water-flow structure. This research describes the study of two types of physical models to investigate the impacts of rough steps on stepped spillways in terms of energy dissipation and hydraulic jumps. To this end, six stepped spillway models, including a flat spillway with smooth steps and five models with rough steps using gravel with a given grain size (i.e., d 50 = 18.9 mm), were made with different step arrangements. The results showed that stepped spillways with rough steps and in the nappe flow regime show a better performance regarding energy dissipation of about 20.97 % compared to smooth steps. On the smooth stepped spillway, the non-dimensional residual head was 4.65, and for similar operating conditions, the average dimensionless residual head on the rough steps was 2.92. Furthermore, when rough steps are placed on all steps, the hydraulic jump characteristics, including sequent depth ratio, jump length, and roller length, decrease by 3.34, 8.61, and 8.14 %, respectively, compared to smooth steps. • Investigation of the hydraulic jump characteristics and energy dissipation using rough steps on stepped spillway. • The reduction in jump characteristics and increase in energy dissipation depends on the arrangement of the rough steps. • The reduction of the relative jump length and roller length in the rough steps was calculated as 31.13% and 35.54%. • Rough steps on stepped spillways increased the energy dissipation by 20.97 % compared to smooth steps. [ABSTRACT FROM AUTHOR]

• Shallow flow analysis predicts characteristics of laminar planar jump with much reduced computational resource. • The assumption of self-similar velocity profile is valid except at entry and the jump region. • An increase in yield stress and plastic viscosity results in a jump of higher jump strength closer to the inlet. • A higher Froude number shifts jump towards channel exit with increased strength while a higher Reynolds number forms a jump of lower strength closer to the exit. • The jump types can be presented as phase a diagram in terms of inlet Reynolds and inlet Froude number for different yield stress values. The hydrodynamics of laminar planar hydraulic jump during free surface flow of Bingham plastic liquid is investigated through numerical simulation and shallow flow analysis, both validated against experimental results. The singularity of Bingham plastic model at the yield surface is addressed by adopting the Bingham plastic Papanastasiou regularized model with the value of regularization parameter as 1000 s in order to mimic ideal BP flow. The study reveals that an increase in both yield stress and plastic viscosity creates a jump closer to the inlet with a higher film thickness and jump strength. Interestingly, a higher Froude number shifts jump towards channel exit with increased strength while a higher Reynolds number forms a jump of lower strength closer to exit. The jump types noted from simulations are presented as phase diagrams in terms of inlet Reynolds and inlet Froude number for different yield stress values. [ABSTRACT FROM AUTHOR]

• Liquid atomization on two counter-rotating wheels was studied experimentally. • Predominant atomization mechanism is by ligament breakup and head droplet pinching. • At same Weber numbers, droplet diameters are lower than for spinning discs and cups. • Liquid impingement point and wheel gap largely affect mass transfer between wheels. • Significant splashing of liquid can occur after impingement due to a hydraulic jump. This paper presents an experimental study of the liquid disintegration process on an atomizer with two counter-rotating wheels by high-speed imaging. The process was investigated for a wide range of wheel rotational speeds, liquid flow rates and impingement positions. Compared to flat disc and cup atomizers operating at similar Weber numbers, proposed atomizer design is capable of producing much finer droplets in the ligament formation mode (mean diameter under 0.15 mm when We = 106) and at a significantly larger liquid throughput. Despite the atomizer gap flow complexity, approximation of mean liquid trajectories with tangent lines proved to be fairly accurate. We were able to identify two main challenges in atomizer operation, namely the occurrence of hydraulic jump upon liquid impingement causing the formation of large droplets, and escaping of the liquid spray through the wheel gap. Nevertheless, both issues can be largely mitigated by optimization of atomizer geometry and operating parameters. [ABSTRACT FROM AUTHOR]

This study investigates the capacities of chute spillway and stilling basin under multiple flow discharge scenarios. Thirteen cases, categorised as low, medium, and high flow discharges were experimentally conducted, with a 100% increase of Probable Maximum Flood (PMF) as the modified maximum flow. An analysis is extended to flood and scour potential at the Type II and III stilling basin. Low and medium discharge scenarios have no significant impact on the spillway but posed insufficient capacity to confine efficiently the hydraulic jump within the stilling basin. Types II and III basins reduced the length of hydraulic jump up to 50% and 73%, respectively at PMF. Similarly, potential of severe scour particularly at the spillway exit increases to 5 times more than the cases for low discharge. Similarly, potential of severe scour at PMF, particularly at the spillway exit increases to 5 times more than the cases for low discharge. High discharge not only compromises the spillway integrity due to overflow but also increases flood and scour potential at the stilling basin. An up-to-date evaluation of the existing dam appurtenances capacities to withstand the future flow pattern is crucial to ensure smooth dam operations and avoiding catastrophic events such as dam breach, jeopardising the river environmental flow and water resources. [ABSTRACT FROM AUTHOR]

This study used a 3D coupled CFD-DEM model to study velocity and porosity relationships within horizontal dense phase pneumatic conveying. Inlet velocities, initial layer fractions and initial slug lengths were varied for a total of 72 single slug simulations. The linear relationship between particle velocity and slug velocity was examined and the origins and contributions of individual variables were looked at in detail. It was found that the slug velocity to particle velocity relationship can be defined using slug to bulk density ratio and propagation velocity. It was also found that within a single slug system, slugs tend to their 'preferred' steady-state length which is a function of inlet velocity and stationary layer ahead of the slug. Another finding is that hydraulic jump can be used as an analogy to the interaction between slug front and the stationary layer. This analogy can be used to define a boundary for slug flow as well as help predict slug porosity. Unlabelled Image • Slug density ratio and propagation velocity characterise velocity relationship. • Slugs tend to a steady-state length. • Hydraulic jump analogy is related to air entrainment in slugs. • Indicative boundary for slug flow can be defined using Froude number. [ABSTRACT FROM AUTHOR]

In this research, the effect of curvature radius of convex target plates on the radius of formed circular hydraulic jump is investigated using experimental investigation and numerical modeling. Ethylene glycol with constant density and viscosity is used as the working fluid. In order to simulate the hydraulic jump, the volume of fluid (VOF) method is applied using a continuous surface force model (CSF) and geometric reconstruction for determining the interface of the two fluids. The results of experimental studies and numerical simulation indicate that the hydraulic jump is a function of three important parameters, including the vertical jet radius, the curvature radius of the target plate and the volumetric flow rate. Subsequently, an empirical relation for the hydraulic jump radius formed on convex target plates is proposed. Comparing the radius of the hydraulic jump on the convex and flat target plates it is observed that the jump radius increases with increasing the volumetric flow rate and significantly decreases with increasing the curvature radius of the convex target plate and impinging jet radius. [ABSTRACT FROM AUTHOR]

We study the flow of a thin layer of fluid over a flat surface. Commonly, the 1-D Shallow-water or Saint-Venant set of equations are used to compute the solution of such flows. These simplified equations may be obtained through the integration of the Navier–Stokes equations over the depth of the fluid, but their solution requires the introduction of constitutive relations based on strict hypothesis on the flow régime. Here, we present an approach based on a kind of boundary layer system with hydrostatic pressure. This relaxes the need for closure relations which are instead obtained as solutions of the computation. It is then demonstrated that the corresponding closures are very dependent on the type of flow considered, for example laminar viscous slumps or hydraulic jumps. This has important practical consequences as far as the applicability of standard closures is concerned. [ABSTRACT FROM AUTHOR]

This experimental study investigated the air-water flow properties and bubble characteristics in hydraulic jumps with Froude numbers Fr 1 = 2.4 and 6.3, using four dual-tip phase detection probes with sensor sizes from 0.25 mm to 0.64 mm. The hydraulic jumps were characterized by a fully breaking roller with substantial air entrainment and turbulent two-phase flow patterns. The measurements encompassed distributions of void fraction, bubble count rate, interfacial velocity and bubble clustering properties and the data sets were consistent with previous studies. The comparison of the different probes showed a small impact of the tested sensor sizes on the air-water flow properties, in terms of the trends, magnitude and maximum values. Some differences were observed in terms of the bubble count rate, with the larger probes detecting a lesser number of bubbles. The trend was further confirmed through a comparison with the data set of Chanson and Brattberg (2000) [10] with a smaller probe sensor size (Ø 1 = 0.025 mm), in which the maxima of bubble count rates were almost twice that of the present dataset for identical flow conditions. The present results confirm that the traditional signal processing techniques can be used for relatively small probe sizes, although different approaches might be needed for larger probes which cannot detect sub-millimetric bubbles. Overall, the findings should facilitate the development of sturdier phase-detection needle probes and help breaching the gap between laboratory and prototype. • Experimental study of air-water flow properties in hydraulic jumps using probes with varied sensor sizes. • Small impact of sensor size on air-water properties, except for bubble count rate where larger probes detected less bubbles • Encouraging result for the development of sturdier and more robust probes for field studies and prototype measurements. [ABSTRACT FROM AUTHOR]

Hydraulic jump is used as a significant energy-dissipater downstream of hydraulic structures, spillways, gates, and chutes. The novelty of this study is the simultaneous use of divergent-convergent basins to investigate the hydraulic jump characteristics. All experiments were conducted in a channel with a length of 11 m, a depth of 0.7 m and a width of 0.48 m. The results obtained from the divergent-convergent basin models have been compared with those of the sudden divergent basin, gradual divergent basin, classical basin and also with previous research. The results indicate that the ratios of depth (y2/y1) and jump length (Lj/y1) in the divergent-convergent basin have decreased by 48.6% and 122.9%, respectively, compared to the classic basin. These values are equal to 33.8% and 46.2% for the sudden divergent basin, respectively, and 31.7% and 69.9%, respectively, for the gradual divergent basin. In comparison with the classical basins, the energy dissipation in the divergent-convergent basin has increased by 26.8%. Finally, by using dimensional analysis and regression method, several equations were developed to predict the ratio of conjugate depths, length and energy dissipation for the divergent-convergent basins. According to this research, it can be concluded that the divergent-convergent basins with smaller dimensions and more energy dissipation have a much better performance than the standard ones. • Investigation of the hydraulic jump characteristics using divergent-convergent basins. • The depth ratio (y2/y1) and jump length (Lj/y1) have decreased by 48.6% and 122.9%, respectively. • The energy dissipation in the divergent-convergent basin has increased by 26.8%. • Several equations were developed for the prediction of hydraulic jump characteristics. • Divergent-convergent basins have a much better performance than the other ones. [ABSTRACT FROM AUTHOR]

This paper addresses the challenging task of implementing dynamic jumping motions for biped wheel-legged robots, a motion mode that significantly enhances their mobility and adaptability to complex terrains. However, due to the under-actuation and dynamic instability nature of this type of robots, executing high-dynamic motions remains difficult. To tackle this issue, this paper proposes a novel Hierarchical Jumping Optimization (HJO) framework specifically designed for hydraulic biped wheel-legged robots. The framework involves an upper layer center of mass (CoM) trajectory optimization based on the dynamic properties of a dual-mass spring loaded inverted pendulum (DM-SLIP) model, along with the CoM dynamic coupling relationship introduced by the under-actuated nature of two-wheel self-balancing robots. This leads to a reduction in the dimensionality of optimization variables, facilitating effective CoM trajectory generation. Subsequently, the CoM motions of the robot in the Cartesian space are mapped into the joint space in real-time by using the middle layer hierarchical operational space control (HOSC). By incorporating centroid angular momentum as a task objective, the stability of the robot in highly dynamic motions can be enhanced. Finally, the proposed HJO framework is experimentally validated through jumping experiments on an actual robot. The experimental results demonstrate that the framework optimally utilizes the robot's under-actuated characteristics, significantly reducing computational costs associated with planning and tracking, while simultaneously preserving motion accuracy and robust. [ABSTRACT FROM AUTHOR]

• Non-circular liquid films from rectangular jet impacts were identified and characterized. • A correlation between the circumferential thickness and the shape of the spreading film is revealed. • Stagnation line in the impact zone induces inhomogeneous liquid film thickness. The vertical impact of a rectangular liquid jet was experimentally studied using a high-speed camera. Fluorescent dyes and tracer particles are used to visualize the thickness and velocity distribution of the radial liquid film. Effects of jet velocity, aspect ratio, and impact distance on the film spreading were investigated. Results show that a fusiform liquid film occurs as the rectangular jet impacts for low impact distance, and its long and short axes are opposite to the jet cross-section. When the aspect ratio is 1 and 2, the length-to-width ratio of the liquid film is equal to the nozzle aspect ratio. While for larger nozzle aspect ratios, the length-to-width ratio is lower and grows with the jet velocity. The areas of the liquid film show an approximate linear relationship with velocity. The difference in the liquid film thickness along the long and short axes is significant, and the velocities near the impact zone are close, which causes the correlation between the circumferential distribution of the thickness and the spreading of the liquid film. As the impact distance increases, the axis-switching of the rectangular jet makes the liquid film morphology more complex. [Display omitted] [ABSTRACT FROM AUTHOR]

Through installing a grid drop-type dissipator at the edge of the vertical drops with an upstream supercritical approach flow, the present study investigates hydraulic characteristics of flow up- and downstream of the drop, based on model experimentation. Experiments were conducted on three different drop heights, considering eight different grid drop-type dissipators with certain grids dimensions. Results demonstrate that assembling this type of dissipator at the edge of a vertical drop increases the rate of energy dissipation up to about 70%, compared to a plain vertical drop. Owing to the increase in flow momentum and the falling jets' collision with bottom of the downstream channel, for a given flow discharge, while the porosity of the grid drop-type dissipator is increased, the wetted length of the dissipator and the energy dissipation decrease; however, the length and depth of the pool at the drop base increase. The relative length of the pool is significantly affected by air entrainment, caused by the spaces between the separated falling jets. By increasing flow discharge, pressure fluctuations decrease and trend of the variation of average pressure becomes smoother. Although the former researchers reported a hydraulic jump downstream of the grid drop-type dissipators with an upstream subcritical approach flow, it was not the case in some tests of the present study with an upstream supercritical approach flow. Finally, based on statistical and error analyses, empirical relationships were derived to predict the flow hydraulic characteristics, to be used by design engineers in practice. • The hydraulic characteristics of flow at a grid drop-type dissipator with an upstream supercritical approach flow were investigated. • Experiments were conducted on three different drop heights, considering eight different grid drop-type dissipators. • This type of dissipator increases the rate of energy dissipation up to almost 70%, compared to a plain vertical drop. • While the porosity of the grid drop-type dissipator is increased, the wetted length of the dissipator and the energy dissipation decrease. • Finally, based on statistical and error analyses, empirical relationships were derived to predict the flow characteristics. [ABSTRACT FROM AUTHOR]

Highlights • The effect of nozzle-to-surface distance on two-phase jet impingement was investigated. • The Nusselt number attained a maximum value at the lowest nozzle-to-surface distance. • The stagnation Nusselt number is governed by the stagnation pressure. • The normalized Nusselt number is a function of the nozzle-to-surface distance only. Abstract In this study, heat transfer and hydrodynamics of air-assisted free water jet impinging a flat plate surface are experimentally investigated. The effects of the nozzle-to-surface distance (H/d = 0.02–0.51) and volumetric quality (β = 0.3–0.8) on the stagnation Nusselt number, stagnation pressure, and hydraulic jump diameter are considered. The results show that the normalized stagnation Nusselt number and hydraulic jump diameter drastically increase with decreasing the nozzle-to-surface distance, since the stagnation pressure increases due to the jet deflection effect. Based on the experimental results, new correlations for the stagnation Nusselt number and pressure are developed as a function of the nozzle-to-surface distance. [ABSTRACT FROM AUTHOR]

Abstract Kaye et al. (1995) conducted an experimental investigation of the cleaning of thin soil layers by water jets generated from stationary nozzles of diameter 0.25–2 mm and velocities ranging from 6 to 40 m s−1. The soil layers were prepared by drying a commercial cleaning suspension on polymethylmethacrylate plates. Several of their data sets have been re-analysed and are shown to fit the 'strong soil' model for cleaning by peeling reported by Bhagat et al. (2017). The model is demonstrated to be able to explain the trends in cleaning efficiency observed by Kaye et al. quantitatively, including the transition in efficiency observed at longer times. Kaye et al. also investigated the case of cleaning by a moving nozzle for one set of jet conditions, and reported an increase in cleared area with nozzle velocity. This behaviour is not predicted for the 'strong soil' and the model was modified to incorporate a contribution from the milling action of the jet in its impingent zone. This 'very strong soil' result gave good agreement with the data for the area cleared and the shape of the cleared region. Graphical abstract fx1 Highlights • Data from Kaye et al. were re-analysed using newly developed models for peeling. • 'Strong soil' model gives good description of cleaning by static nozzle. • Observed variation in cleaning efficiency is predicted by the model. • Strong soil model extended to cover cleaning by moving nozzle. • Size and shape of area cleared by moving nozzle consistent with new model. [ABSTRACT FROM AUTHOR]

Abstract Hydraulic Jump is a phenomenon that occurs in free surface flows during transition from supercritical to subcritical flow. During the impingement of a vertical fluid jet with a flat surface, a circular hydraulic jump forms, which has been studied by several researchers; but no study has been performed on the effect of convexity of the target surface on the jump radius and its form yet. Therefore, in the present study the hydraulic jump phenomenon on convex surfaces and comparison with the flat surface are presented, experimentally. The tests are performed using 3 nozzles in various volumetric flow rates. The results showed that convex surfaces significantly increased the jump radius up to about 30% compared to flat plates for about 50% increase in convex target plate radius. In addition, an experimental relation for the hydraulic jump radius in the convex target plates is proposed. Highlights • In the present study, the effect of curvature of the target surface on the radius of hydraulic jump is studied for the first time. • In addition, an experimental relation for the hydraulic jump radius in the convex plates is presented. • By using curvature in the target plate, the hydraulic jump radius is increased significantly. [ABSTRACT FROM AUTHOR]

Abstract A flume study using a surge-type flow produced by quickly lifting a gate was conducted to simulate a tsunami the height of which is larger than level 1 (prevention level) by a hybrid system comprising a forest, an embankment, and a moat while changing the layout of the components. The overflow volume, tsunami arrival time, fluid force, and moment by fluid force were measured, and the tsunami reduction effects in each model were compared. The hybrid defense system in the order of vegetation, a moat, and an embankment (Case V 40 ME) from the sea side showed the highest reduction in overflow volume, moment index, and tsunami delay effect. In terms of the fluid force index, Case V 40 ME performed best up to a certain tsunami height. For higher tsunamis, a hybrid system in the order of vegetation, an embankment, and a moat from the sea side (Case V 40 EM) performed better, although Case V 40 ME had a large advantage in total when there was a space landward of the existing forest. Suitable structures when there is space seaward and on both sides of a forest were also clarified for different wave heights through the mechanism of reflection, hydraulic jump, and vegetation resistance. Highlights • Reduction of tsunami energy by the combination of an embankment, a moat and vegetation was measured. • The effectiveness of the hybrid system was investigated in a flume using a surge-type unsteady flow. • Reflection from the components, backwater rise in front of vegetation and hydraulic jump are the key phenomena. • Delay in tsunami arrival time, reduction of fluid force and moment by fluid force are compared as the indices. • The optimum layout is discussed based on the available space of the existing forest. [ABSTRACT FROM AUTHOR]

The effect of jet length and wall curvature on the flow patterns generated by an impinging water jet were quantified and the effect on cleaning investigated in a brief study. The length of time taken to establish steady flow was characterised. Jet impingement on a flat vertical wall was investigated for jets of diameter 2-4 mm for lengths, L, up to 1 m. The amount of liquid lost to splatter was measured and found to be insensitive to L for short L (<300 mm for these nozzles) and strongly related to L for longer values. The shape of the radial flow zone on flat walls agreed with existing models once the fraction of liquid lost to splatter was accounted for. Tests on horizontal and vertical cylinders with curvatures in the range 6.9 - 20 m-1 showed that the curvature of the impinged wall did not affect the shape of the radial flow zone until higher flow rates (>1.5 dm³ min-1). The cleaning of two viscoplastic model food soils was studied briefly: a hydrophobic petroleum jelly and Carbopol®, a watersoluble gel. The splatter correction was not able to account for all the differences observed in cleaning at different jet lengths. There was no appreciable effect of curvature on cleaning behaviour. Soaking of the Carbopol® increased its cleaning rate. [ABSTRACT FROM AUTHOR]

Highlights • Novel application of four-point phase-detection measurement in highly-aerated open channel flow. • Quantitative characterisation of transverse velocity and velocity fluctuations in quasi-two-dimensional hydraulic jump. • Test of velocity measurements with phase-detection sensors in reversing flow. Abstract The measurement of turbulent velocity in highly aerated flow is difficult because of the presence of air bubbles. The characterisation of three-dimensional velocity field in highly aerated flows is even more challenging using existing phase-detection techniques. This paper presents an attempt on a quantification of transverse velocity and velocity fluctuations in quasi-two-dimensional hydraulic jumps with relatively high Froude and Reynolds numbers. A four-sensor phase-detection probe array was developed to measure the bubble convection in both streamwise and spanwise directions. A characteristic instantaneous transverse velocity component was derived together with a measure of its fluctuations. The transverse velocity component characterised the three-dimensional turbulent structures, although the time-averaged flow pattern was two-dimensional and the average transverse velocity was zero. Both the transverse velocity and velocity fluctuations were smaller than the longitudinal time-averaged velocity and velocity fluctuations in the shear flow, and were quantitatively comparable to those in the free-surface region, revealing different turbulent structures in the lower and upper roller regions. The approximate of Reynolds stresses was discussed together with the limitation of the method. The present work also provided some guidelines for the use of phase-detection probe array and correlation signal processing techniques in complex turbulent two-phase flows. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a new technique to increase the energy dissipation and reduce the floor length of the hydraulic structure, is introduced. This is done by using a pendulum sill downstream of the sluice gate of the hydraulic structure. A cylindrical steel sill with constant diameter of 3 cm was used. The location of the pendulum sill, the flow discharge and the gate opening were changed during the experimental work. The discharge capacity ranged between 2 and 4 L/s. The experimental results showed that using the pendulum sill increased the energy dissipation. It was found that the best location of the pendulum sill is in the first half of the hydraulic jump. [ABSTRACT FROM AUTHOR]

Abstract In this work, the influence of constant background vorticity on the properties of shock waves in a shallow water system are considered. It is shown that the flow-depth ratio of stationary shocks can be written as a function of two non-dimensional parameters: the Froude number, suitably defined in the presence of the shear flow, and a non-dimensional vorticity. Some properties of these hydraulic jumps are explored, and it is shown that stronger background vorticity has the effect of moderating the strength of the hydraulic jump. [ABSTRACT FROM AUTHOR]

The hydraulic jump is a phenomenon which frequently appears in nearshore, estuarine and riverine regions; it plays a major role for example in the development and migration of sand waves in mobile beds, and in controlling the propagation of infra-gravity water waves from the nearshore into the river through bar-built, shallow estuaries. Although the prediction of these natural flows becomes crucial in many circumstances, it is difficult because hydraulic jumps are complex flows, and their modeling is far from simple. The steady-state hydraulic jump may be undular or broken, and their physical properties differ significantly. Undular jump profiles are dominated by the deviation of the fluid pressure from hydrostatic conditions, with turbulence playing a secondary role. In contrast, broken hydraulic jumps are determined by the differential advection of momentum due to breaking, and turbulence stresses. Between both types, there is a complex transition involving the interaction of non-hydrostaticity and turbulence, which is difficult to mimic with depth-averaged models. Simulations of these flows are typically conducted by resorting to vertically-averaged models either using the Saint-Venant or the Serre-Green-Naghdi equations, but none of them are fully satisfactory. In this work, an alternative approach for hydraulic jumps is proposed by developing a variational Reynolds-Averaged Navier-Stokes (RANS) model which uses Kantorovich-Krylov expansions of the flow variables, and a novel depth-averaged, eddy viscosity approach suitable for non-hydrostatic flows. The model is validated through results of simulations of both undular and broken jumps compared against detailed experiments. New experiments were conducted in a simplified bar-built shallow river inlet; the variational RANS model was found to reproduce well the flow profile over the bar, the hydraulic jump position and dynamic pressures over the bar surface. • A new variational RANS model is proposed to simulate hydraulic jump flows. • A turbulence model suitable for non-hydrostatic flows is presented. • The model equations are able to simulate the transition process from undular to broken jumps. • New experiments are conducted in a simplified large-scale bar-built type estuary inlet. • The variational RANS model simulates well the flow profile, the hydraulic jump position and dynamic pressures over the bar. [ABSTRACT FROM AUTHOR]

A new method is proposed for simulating the energy dissipation resulting from depth-limited wave breaking, in combination with a universal breaking onset criterion, in two-dimensional (2D) fully nonlinear potential flow (FNPF) models, based on a non-dimensional breaking strength parameter. Two different 2D-FNPF models are used, which solve the Laplace equation based on Chebyshev polynomial expansions or a boundary element method. In these models, impending breaking waves are detected in real time using a universal breaking onset criterion proposed in earlier work, based on the ratio of the horizontal particle velocity at the crest u , relative to the crest velocity c , B = u / c > 0. 85. For these waves, wave energy is dissipated locally with an absorbing surface pressure that is calibrated using an inverted hydraulic jump analogy. This approach is first validated for periodic spilling breakers over plane beaches and bars, for which results are shown to be in good agreement with experimental data. Recasting this breaking dissipation model in terms of a non-dimensional breaking strength, the hydraulic jump analog is shown to provide results similar to those of a constant breaking strength model, and to yield good agreement for periodic plunging breakers as well. The same approach is then applied to irregular waves shoaling over a submerged bar, and is shown to agree well with experimental data for the wave height, asymmetry, skewness, and kurtosis. Future work will extend this 2D breaker model to cases of three-dimensional (3D) breaking waves, simulated in existing 3D-FNPF models, in shallow or deep water conditions. • Two fully non-linear potential flow models are used for depth-limited breaking waves. • A new method with a constant non-dimensional breaking strength is proposed. • A unified onset criterion based on crest velocity is applied to detect wave breaking. • Two-dimensional results are validated against multiple experimental cases. • Good agreement is found for spilling and plunging, regular and irregular waves. [ABSTRACT FROM AUTHOR]

For mitigating tsunamis that overtop an embankment, flume tests were conducted to clarify the energy reduction of a tsunami due to a compound defense system by a combination of a sea embankment and lined vertical piles behind the embankment. The relationship between the flow structure and energy reduction was investigated with changing pile height, spacing, and number of rows. The flow structure was classified into 10 types, and the patterns were classified into two. The energy reduction increased with smaller spacing between lined piles, and the reduction of energy and fluid force behind piles gradually decreased when the piles were submerged. In some cases, energy reduction became very low or energy was locally concentrated because standing waves were generated behind the piles. Two important parameters were proposed, ResP * , consisting of pile spacing, pile diameter, and number of lines of piles in the downstream direction, and Ps * , comprising overflowing water depth, pile height, and embankment height. Ps * discriminates whether the piles are emergent or submerged, and ResP * classifies the change in the flow structure pattern. Recommended design criteria to reduce tsunami energy and to prevent the formation of the standing waves downstream of piles were elucidated by these two parameters. [ABSTRACT FROM AUTHOR]

A disposal system for low- and medium-level nuclear waste in Hungary is being constructed inside the fractured rock body of the Lower Carboniferous Mórágy Granite. Previous studies proved that the granitoid massif is rather heterogeneous in terms of lithological composition, brittle structure and hydrodynamic behaviour. A significant part of the body consists of monzogranite, while other portions are more mafic in composition and are monzonites. As a result of at least three significant brittle deformation events, the area is at present crosscut by wide shear zones that separate intensively fractured zones and poorly deformed domains among them. Due to late mineralization processes, some of these fractured zones are totally sealed and cannot conduct fluids, while others are excellent migration pathways. The spatial distribution of these two types nevertheless does not show any systematics. Hydrodynamic behaviour clearly reflects this heterogeneous picture; in some places, hydraulic jumps as great as 25 m at compartment boundaries can be detected. In this study, the fracture network of the Mórágy Granite body is evaluated from a geometric aspect using datasets measured at a wide range of scales. 2D digitized images of a hand specimen, one large (20 × 60 m) and 12 smaller subvertical wall rocks (outcrops) and 120 images from tunnel faces representing the ground level of the underground repository site were analysed. Moreover, 1D data from 13 wells that all penetrate the granitoid massif were studied. Based on measured geometric data (spatial position, length, orientation, and aperture) fracture networks are simulated to study connectivity relations and for computing the fractured porosity and permeability at different scales. The results prove the scale-invariant geometry of the fracture system. Geostatistical calculations indicate that measurable fracture geometry parameters behave as regionalized variables and so can be extended spatially. Estimated localities of connected subsystems fit very well with fault zones mapped previously. Moreover, the spatial position of regimes of different hydrodynamic behaviours can be explained by connectivity relations both regionally and within wells. [ABSTRACT FROM AUTHOR]

A shallow water model was applied to study the hydraulic jump and Bernoulli equation across the jump. On a flat terrain, when a supercritical flow plunges into a subcritical flow, discontinuity develops on velocity and Bernoulli function across the jump. The shock generated by the obstacle may propagate downstream and upstream. The latter reflected from the inflow boundary, moves downstream and leaves the domain. Before the reflected wave reaching the obstacle, the short-term integration (i.e., quasi-steady) simulations agree with Houghton and Kasahara’s results, which may have unphysical complex solutions. The quasi-steady flow is quickly disturbed by the reflected wave, finally, flow reaches steady and becomes critical without complex solutions. The results also indicate that Bernoulli function is discontinuous but the potential of mass flux remains constant across the jump. The latter can be used to predict velocity/height in a steady flow. [ABSTRACT FROM AUTHOR]

Hydraulic jumps are a complex hydraulic phenomenon characterised by a water surface discontinuity from supercritical to subcritical flows. Along the jump roller, high turbulence, flow aeration and three-dimensional motions are key characteristics which are associated with jump toe oscillations and free-surface fluctuations. Previous studies have provided significant insights into the characterisation of the free-surface and jump toe characteristics in hydraulic jumps. However, a continuous observation of the time-varying free-surface has been so far limited to fixed data points along the hydraulic jump. Herein, novel experiments were conducted with a LIDAR measuring the continuous free-surface profiles in aerated hydraulic jumps providing detailed spatial and temporal free-surface characteristics of aerated hydraulic jumps. The free-surface observations provided basic statistics of the free-surface including mean profiles and standard deviations of the free-surface fluctuations as well as their characteristic frequencies. The effect of the jump toe oscillations on the free-surface properties was analysed for two conditions using a free moving jump toe and a fixed jump toe position. The results showed a strong effect of the jump toe oscillations on the free-surface features close to the jump toe. Based upon the characteristic frequencies, three characteristic regions in hydraulic jumps were identified. Overall the comparison with previous studies showed good agreement highlighting that a LIDAR is a suitable instrument to measure the free-surface characteristics in aerated hydraulic jumps. [ABSTRACT FROM AUTHOR]

Middle Pleistocene Gilbert-type delta in the Gulf of Corinth, Greece, has been investigated combining field methods and photo acquisition by drone to generate a high-resolution 3D model. This study case can be used to document four different dynamics in Gilbert-type bottomset deposits, each one of which is characterized by a specific range of facies, facies associations and geometries: (1) the sandy-gravelly bottomset, (2) the erosional-bypass stage, (3) the fine-grained bottomset and (4) the massive-sandy bottomset. By comparing the typologies of the bottomset, we propose a conceptual model that predicts the occurrence of these four different bottomset stage dynamics depending on the stratigraphic context. During highstand normal regression, the gravelly bottomset develops under subcritical flow. The supercritical flow undergoes a stationary hydraulic jump in the toeset due to the slope break. As a result, a low-relief channel-levees system is formed in the bottomset. The channels are filled/reworked by backstepping conglomeratic lenses interbedded with silty concave-up and concave-down levees. During normal regression, the foreset beds are steeper than during previous stage and scoured in the upper part. In the bottomset, significant erosion recording sediment bypass downstream toward the pro-delta can be observed. During lowstand normal regression, a starved fine silt to shale bottomset onlaps onto the major erosional surface. The bulk of the coarse-grained sediments is stored in the delta topset and foreset. During the transgressive to highstand stage, the former topset and foreset are eroded by high-density turbidity currents and massive-sandy turbidites are deposited in the bottomset, which onlap onto the foreset beds and form a slope apron geometry in the delta toe. The stratigraphic model improves the prediction for the sand distribution within the various parts of the bottomset. This approach is particularly relevant for clastic depositional systems with high sediment discharge and a high accommodation rate. [ABSTRACT FROM AUTHOR]

Typhoon Khanun caused over 226 mm of accumulated rainfall for 6 h (0700 to 1300 UTC), localized around the summit of Mt. Halla (height 1950 m), with a slanted rainfall pattern to the northeast. In this study, we investigated the enhancement mechanism for precipitation near the mountains as the typhoon passed over Jeju Island via dual-Doppler radar analysis and simple trajectory of passive tracers using a retrieved wind field. The analysis of vertical profiles of the mountain region show marked features matching the geophysical conditions. In the central mountain region, a strong wind (≥ 7 m s − 1 ) helps to lift low-level air up the mountain. The time taken for lifting is longer than the theoretical time required for raindrop growth via condensation. The falling particles (seeder) from the upper cloud were also one of the reasons for an increase in rainfall via the accretion process from uplifted cloud water (feeder). The lifted air and falling particles both contributed to the heavy rainfall in the central region. In contrast, on the leeward side, the seeder-feeder mechanism was important in the formation of strong radar reflectivity. The snow particles (above 5 km) were accelerated by strong downward winds (≤−6 m s − 1 ). Meanwhile, the nonlinear jumping flow (hydraulic jump) raised feeders (shifted from the windward side) to the upper level where particles fall. To support these development processes, a numerical simulation using cloud-resolving model theoretically carried out. The accreting of hydrometeors may be one of the key reasons why the lee side has strong radar reflectivity, and a lee side weighted rainfall pattern even though lee side includes no strong upward air motion. [ABSTRACT FROM AUTHOR]

Weirs may be used to control the discharge, decrease the water slope in canals and to distribute water between canals for irrigation, etc. The objective of this research was to investigate the influence of using one opening or more in weirs on discharge coefficient ( C d ), the hydraulic jump characteristics and velocity distribution downstream of these structures. This study is based on an experimental program. Three cases of openings arrangements were included, one, two and three openings. Different diameters of openings ( D ) and different heights from the bed ( Z ) were tested. The experiments showed that decreasing ( D / Z ) for weirs which have the same openings numbers and diameters decreases the discharge coefficient ( C d ) and the ratio between the length of the submerged hydraulic jump ( L j ) and the water tail depth ( y t ). Also, decreasing ( D / Z ) leads to make the maximum velocity near the bed tends to be lifted upward. Moreover, Comparing weirs with different openings numbers but have the same openings area leads to that, weirs with one opening have a bigger ( C d ) than weirs with two or three openings but the maximum velocity near the bed of the weir with three openings is less than that with one opening. Also, the hydraulic jump length downstream weir with three openings is less than that downstream weir with one opening. Finally, equations were developed to deduce the value of the coefficient of discharge for the composite structure. [ABSTRACT FROM AUTHOR]

In a natural estuary, a tidal bore may progress on a small sloping bed from the downstream to the upstream. In this study, a simple analytical solution for tidal bore formed in a small slope channel was developed using the finite control volume analysis. New unsteady experiments were conducted to verify the theoretical model. The model predictions generally agree with the observations. A general relation is obtained for the conjugate depth ratio as a function of the Froude number and the channel slope from the experimental data. The results indicate that the conjugate depth ratio increases with an increasing Froude number as well as with a decrease in channel slope. On a negative slope, the Froude number increases as the bore propagates along the channel, and decreases for a positive slope. The theoretically based model is accurate and simple to estimate the celerity of the tidal bore progressing along a small slope channel. [ABSTRACT FROM AUTHOR]

Cyclic steps are ubiquitous in modern sedimentary environments, yet their recognition remains sparse in the rock record. Here, we interpret three sets of undulating backsets (1 to 3) recognized in the late Miocene-early Pliocene Latrania Formation in the Anza-Borrego Desert, the Fish Creek-Vallecito Basin, southern California, USA as the first cm- to dm-scale outcrop record of cyclic steps, based on asymmetrical cross-sections, upstream migration, and inversely graded laminae. Upstream migration and asymmetrical cross-sections of backsets and concomitant backset laminae are attributed to supercritical-to-subcritical flow transitions through weak hydraulic jumps, which are composed of: (i) thin (tens of centimetres) and slower (reported as flow velocities ( Ū ) of 0.45 to 1.45 m s − 1 , with mean value of Ū = 0.89 m s − 1 ) subcritical (represented by internal Froude numbers ( Fr ) of 0.67 to 0.99, with mean value of Fr = 0.84) turbidity currents on the stoss sides, and (ii) thin (tens of centimetres) and faster (reported as Ū of 0.99 to 4.03 m s − 1 , with mean value of Ū = 2.24 m s − 1 ) supercritical (represented by Fr of 1.84 to 3.07, with mean value of Fr = 2.42) turbidity flows on the lee sides. The inversely graded laminae in the troughs of backsets are 2 to 5 cm thick, and consist of two discrete divisions: (i) 1 to 2 cm thick, lower finer-grained divisions made up of parallel laminated siltstones, overlain by very fine- to fine-grained sandstones, and (ii) 2 to 3 cm thick, upper divisions composed of medium- to coarse-grained sandstones, with sporadic occurrence of subrounded pebbles. These inversely graded laminae are related to stratified, collisional and/or frictional traction carpets under conditions of high fall-out rates. Due to the poor preservation potential of cyclic steps, the rock record of cyclic steps is generally considered to be rare. The present outcrop-based study presents a detailed analysis of sedimentary facies, growth patterns, and flow dynamics of marine cyclic steps, thereby contributing to better understand architectural styles and lithological properties of cyclic steps in the geological record. [ABSTRACT FROM AUTHOR]

Inferred supercritical structures and bedforms, including sediment waves and backset-bedded sets, are identified as components of coarse-grained siliciclastic and bioclastic, high-gradient clinoform wedges (Plio-Pleistocene of southern Italy) and canyon head infills (Tortonian of Venetian pre-Alps), showing evidence of having been built out in a setting influenced by shallow-marine hydrodynamics. The facies identified are dominated by a range of traction carpets, formed after segregation of coarser particles in the lower part of bipartite density underflows. The generation of backset-bedded sets is thought to imply scouring due to impact of a submerged hydraulic jump on the bed, and upstream migration of the jump, concomitant with the deposition of backset beds on the stoss side of the developing bedform. Submerged hydraulic jumps apparently formed spontaneously and in any position on the foreset and toeset, without requiring any precursor bed defect. The mostly solitary, non-cyclical character of the bedforms prevents their attribution to cyclic steps. The sets of backset beds are locally underlain by chaotic infills of deep, steep-sided scours attributed to vigorous erosion at the hydraulic jump, accompanied by instantaneous loss in transport capacity which results in rapid plugging of the scour (hydraulic jump facies of Postma et al., 2014). Gravel waves have a distinct internal stratigraphy, and their length to amplitude ratios show lower mean values and higher variability when compared to sediment waves consisting of sand. The presence of supercritical bedforms on steep foreset slopes of the studied clinoform systems, even in proximity to the topset-foreset rollover, is believed to reflect high inefficiency of mud-poor and short run-out bipartite underflows episodically transporting relatively small volumes of coarse-grained sediment. This may also account for common solitary, non-cyclical bedforms. It is proposed that during intense oceanographic events, such as coastal storms, seaward sediment entrainment, assisted by gravity, was very effective on the gently sloping subaqueous topset, and that, beyond the topset-foreset rollover, the flows evolved to high-concentration turbidity underflows with supercritical Froude numbers. The flows are inferred to have been sustained, probably lasting for the duration of the meteorological events, and to have commonly been unsteady in discharge, fluctuating in concentration and size of transported sediments, and subject to peaks in velocity. The characteristics of the structures are regarded as typical of the systems fed by oceanographic processes, and may fall into the class of coarse-grained “small sediment waves with mixed relief” of Symons et al. (2016), formed from a combination of erosion and deposition, and by the action of stratified flows depositing from denser basal layers, and typically restricted to small-scale shallow-marine slope systems. [ABSTRACT FROM AUTHOR]

Two-phase gas-liquid slug flow is the prevailing flow regime in many processes in the petroleum and chemical industries. This flow regime is the result of the growth of wavelike instabilities at the gas-liquid interface. The main characteristic of slug flow is the presence of liquid slugs that span the entire pipe diameter separated by gas bubbles. The rear end of these gas pockets can exhibit a staircase shape (also known as plug flow) or a hydraulic jump that reaches the top of the pipe when the flow rate is increased. In this paper, an experimental investigation of the statistical properties of slug flow is presented for flow initiation. A gas-liquid circuit made of acrylic tubes with a 26 mm ID was used to make these measurements. The test facility was composed of two sections: the first corresponded to a downward flow of −3 degree inclination where the prevalent flow regime was stratified flow, and the second was a horizontal section where the prevalent flow regime was slug flow. Resistive sensors located at three different positions in the horizontal section were used to acquire the liquid holdup, and the time series were processed and analyzed. Statistics for slug initiation position, slug and bubble lengths, bubble velocity, slug and unit-cell frequencies are presented. Further, the length and probability of occurrence of the bubble tail were also analyzed in the cases where the bubbles exhibited a staircase shape. Ultimately, data are provided for the validation and development of mathematical models and numerical codes for the simulation of two-phase slug flow. [ABSTRACT FROM AUTHOR]

The ocean-interior shows omnipresent internal wave motions whose importance becomes more and more acknowledged for deep mixing across the stable vertical density stratification for heat and suspended matter redistribution. To observationally study vertical propagation variations of internal tides away from a steep topographic slope, a >1-km long mooring with 760 high-resolution temperature sensors was deployed at 2380 m depth halfway Mount Josephine NE-Atlantic Ocean for 4 months. In the lower 150 m above the seafloor, internal waves slosh, become highly non-linear and break vigorously, every tidal cycle. After signal separation using semidiurnal band-pass and harmonic filters, the vertical phase propagation shows: 1. Phase differences of 90° are observed in isotherms and cross-slope currents over typically 600 m in the vertical, 2. Non-linearity is already found in harmonic records that describe 300-m large-scale internal tides, 3. Non-uniform thin-layer stratification causes about 50% of the semidiurnal variance in small-scales, 4. Upward internal tide propagation starts at the top of non-linear wave breaking, 5. Downward propagation from above leading to energy-focusing at 700 m above the ocean-floor and about 700 m below the nearest seamount-ridge generates interior hydraulic jumps during spring tide. • High-resolution observations from 760 T-sensors along a >1-km mooring. • Separation of large- and small-scale internal tides above a steep deep-ocean slope. • Internal tide generation at the top of the >100-m tall wave breaker zone. • Internal wave focusing and straining leads to hydraulic jump well above topography. • Phase differences of 90° in isotherms and cross-slope currents over vertical 600 m. [ABSTRACT FROM AUTHOR]

Floods resulting from extreme events like tsunamis may inundate widespread inland areas, but vegetation can act as a natural buffer zone to reduce the inundation area and dissipate the energy of flowing water. This paper summarizes a series of laboratory experiments in which the energy loss through emergent vegetation in a steady subcritical flow was investigated. The energy loss was determined against vegetation of variable thickness ( dn , where d = diameter of cylinder, n = number of cylinders in a stream-wise direction per unit of cross-stream width), density ( G/d , where G = spacing of each cylinder in cross-stream direction, d = diameter of cylinder), and initial Froude number. On the upstream side of vegetation, the backwater rise increased by increasing both vegetation thickness and density. Contrarily, on the downstream side a breaking undular jump with a lateral shock wave was observed for a dense vegetation arrangement ( G/d = 0.25), whereas a non-breaking undular jump with and without air bubbles was identified for intermediate ( G/d = 1.09) and sparse ( G/d = 2.13) vegetation conditions, respectively. Under these conditions, the maximum energy reduction due to a jump reached 6.4% for dense vegetation, and was reduced to 1.7% and 1.4% for intermediate and sparse vegetations, respectively. Hence, denser vegetation offers larger resistance, thus causes significant energy loss. [ABSTRACT FROM AUTHOR]

This paper investigates sloshing at shallow-liquid depths in a rectangular container by using experimental and numerical methods. A motion platform is used to perform a prescribed periodic rotational motion to excite the liquid sloshing at a range of frequencies and filling levels. Simulated free-surface elevation is compared with the experimental results for a selection of cases. The wave mechanisms at the chosen fillings are studied by combining numerical methods and the experimental results. We find that the simulated free-surface elevation is in close agreement with experimental results inside the resonance zone. But at frequencies above the bifurcation point, with several overlapping waves, the deviation is increasing. The bifurcation point is determined for a range of filling levels through observation. The numerical results provide important information about sloshing mechanisms at these depths. Complex interaction between the bottom, the lower layer and the wave influences the amount of dissipation before the wave hits the wall. The existing theory seems to be too conservative in predicting the occurrence of hydraulic jumps in the upper limit. [ABSTRACT FROM AUTHOR]

The characteristics of three-dimensional vortical flow structures in submerged hydraulic jumps (generated downstream of a sluice gate) are analyzed in this paper. Results of a careful experimental investigation of the mean flow as well as turbulence statistics obtained with the use of Acoustic Doppler Velocimetry (ADV) and Particle Tracking Velocimetry (PTV) are presented and discussed. Experiments encompass incident Froude numbers ( Fr 1 ) of 3, 4 and 5, and submergence factors ( S ) ranging from 0.18 to 1.04. First, distributions in three vertical planes of values of the stream-wise velocity component and turbulent kinetic energy ( TKE ) are shown. With this information, the influence of Fr 1 and S on turbulence statistics is assessed. For the first time to the best of our knowledge, an approximately self-similar behavior of the profiles of TKE in the fully-developed region of the submerged jump is reported herein. A “climb effect” in the TKE is identified, very much in agreement with what occurs with the velocities. Then, the analysis focuses on the zone located near the gate, aiming at explaining the physical mechanisms which are responsible for the vorticity of vertical axis in that area. A relationship between the length scale of the roller of horizontal axis ( L rsj ) and that of the vortices of vertical axis ( L v ) is introduced, revealing that the dynamics of the two vortices are strongly linked. Compelling evidence sustaining that vorticity of vertical axis appears as a consequence of boundary-layer separation associated with the lateral walls is also provided. Finally, the anisotropy of turbulence in the outskirts of the vertical vortices is addressed, finding that such anisotropy is a consequence rather a cause of the presence of the vortices. [ABSTRACT FROM AUTHOR]

The shallow-water equations for two-dimensional hydrostatic flow over a bottom bathymetry b ( x ) are h t + ( u h ) x = 0 , u t + ( g h + u 2 / 2 + g b ) x = 0 . It is shown that the combination of discontinuous free-surface solutions and bottom step transitions naturally lead to singular solutions featuring Dirac delta distributions. These singular solutions feature a Rankine–Hugoniot deficit, and can readily be understood as generalized weak solutions in the variational context, such as defined in [13,22] . Complex-valued approximations which become real-valued in the distributional limit are shown to extend the range of possible singular solutions. The method of complex-valued weak asymptotics [22,23] is used to provide a firm link between the Rankine–Hugoniot deficit and the singular parts of the weak solutions. The interaction of a surface bore (traveling hydraulic jump) with a bottom step is studied, and admissible solutions are found. [ABSTRACT FROM AUTHOR]