Search

This study examines how the variability of the Manning coefficient (n) affects the position of hydraulic jumps downstream of hydraulic structures. Using a robust finite volume method and random field theory, the study investigates the impact of spatial variations in n on hydraulic jump characteristics. Two scenarios are considered: one with a stilling basin and one without. Both one-dimensional and two-dimensional spatial distributions of n are analyzed. The results show that without a stilling basin, there are significant variations in the location of hydraulic jumps in the riverbed. The uncertainty in the location of the hydraulic jump is much higher than the uncertainty in the values of conjugate depths. Additionally, one-dimensional spatial distribution of n leads to higher standard deviations in the estimated location compared to two-dimensional distribution. In scenarios with a stilling basin, increasing riprap length causes the hydraulic jump to move upstream, while standard deviation remains constant. [ABSTRACT FROM AUTHOR]

This study aims to develop and assess seven machine learning (ML) models, including an Artificial Neural Network (ANN), Gradient Boosting (GB), Extra Trees (ET), Lasso Regression (LASSO), Least Angle Regression (Lars), Random Forest (RF), and Adaptive Boosting (Adaboost), that are effective and simple in forecasting the roller length of a hydraulic jump in a rectangular horizontal canal. This study also proposes a novel approach for applying the Buckingham Pi theorem to ascertain four model inputs and one output, corresponding to five dimensionless Pi terms that have not previously been explored. The impact of channel surface roughness, fluid viscosity, channel geometry, and gravity on the hydraulic jump's roller length was considered to improve the model's performance. Furthermore, the importance of input features was determined, resulting in two model input scenarios. The scenario with four inputs containing the inflow Reynolds number Re1* surpasses the three-input scenario. Because of their high accuracy and efficiency, six ML models outperformed three empirical equations. The GB, ANN, and ET models showed the best performance in both validation and testing phases, whereas LASSO, Lars, RF, and Adaboost performed with lower precision, in descending order. Regarding the ANN model, the best has two hidden layers of sixteen neurons each. In the validation and testing phases, this model achieves the highest Nash–Sutcliffe efficiency of 0.992 and 0.933, respectively. As a result, this study recommends using the GB, ANN, and ET models to forecast the roller length of the hydraulic jump instead of empirical equations when the inflow Froude number, Fr1, varies between 2.4 and 15.9. [ABSTRACT FROM AUTHOR]

Hydraulic jump pressure field analysis is essential to assess slab stability in dissipation basins. This study is aimed to modelling non-dimensional extreme pressure coefficients of the minimum pressure fluctuation (CP−) and maximum pressure fluctuation (CP+) using experimental data with three deep learning (DL) techniques. Pressure coefficients were estimated using Convolutional Neural Network (CNN), Gated Recurrent Unit (GRU), and Long Short-Term Memory (LSTM) methods. For the CP− coefficient related to the tested dataset, the correlation coefficient (CC)=0.894 and Willmott’s index of agreement (WI)=0.944 are achieved using the LSTM model, compared with 0.892 and 0.936 for CNN; and 0.892 and 0.943 for GRU. For the CP+ coefficient, CC=0.910 and WI=0.950 are attained using the LSTM model, compared with 0.903 and 0.941 with CNN; and 0.905 and 0.945 with GRU. The results indicate the excellent performance of the LSTM model for estimating pressure coefficients. With laboratory conditions and the experimental data domain framework used in this study, it is shown that the DL models have been successful for modelling very complex systems. Therefore, DL techniques are recommended for estimating extreme pressure coefficients with a reduction in the need to perform expensive experiments. [ABSTRACT FROM AUTHOR]

This study employs an explicit scheme of solving the pressure Poisson equation based on the moving particle semi-implicit (MPS) method to simulate forced hydraulic jumps on different slopes. To accurately calculate velocity, a mixed source term is used in the discretized pressure Poisson equation. The mesh-free model is validated to simulate a forced hydraulic jump on a slope, and the free surface and velocity profiles are reproduced. The numerical model is then implemented to simulate the forced hydraulic jumps by varying the channel slope, inlet velocity, and height of the bottom sill. The free surface and velocity profiles in the flows are investigated and the effect on the forced hydraulic jumps by the Froude number and height of the sill are analyzed. The developing process of the hydraulic jumps including developing flow patterns and eddy formation is analyzed. It is found there are four flow stages in the developing process of the flow. [ABSTRACT FROM AUTHOR]

Dam break flows have been a focus of attention for a long in the hydraulic engineering discipline. The interest stems from their high hazard potential to human life and property. This research investigates a laboratory dam break flow using a 3D Reynolds-averaged Navier–Stokes (RANS) and a 2D shallow water Eq. (2D SWE) model. The two numerical models have been compared to measured data regarding flow depth, streamwise surface flow velocity, and point velocity. The results show that as far as a simulation of water depths at gauging stations is concerned, both models are almost at par with an error of about 20% of the mean depth value. Further, the comparison of surface velocity field reveals that though both models are capable of reproducing the salient flow features, e.g., oblique hydraulic jump, wake, etc., the 3D RANS model is more accurate in predicting the jump length and the so-called wet–dry fronts. The important contribution of this research lies in clearly enunciating the tradeoffs between a 2D SWE model and a 3D RANS model. The former model is computationally efficient and accurate as far as flow depth and velocity are concerned while the latter model provides a more complete result output, e.g., vertical flow velocity, turbulent kinetic energy and turbulent dissipation, etc. However, for obtaining significant accuracy with a 3D model a more accurate turbulence model than RANS is required which necessitate usage of very refined mesh (~ mm), thus, raising the cost of the simulation manifold. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive dataset comprising multiple data packages derived from laboratory experiments on steady and unsteady hydraulic jumps interacting with a large-scale Gaussian-shaped bed obstacle in an open-channel flume. The primary objective was to accurately measure the impact of hydraulic jump on the free surface and the bed pressure along the obstacle, ensuring the transferability of the results. A multi-process method was followed: designed experiments were recorded, images were postprocessed, and water level data were digitalized. For steady conditions, the bed pressure along the obstacle were measured by piezometers. The repository data are organized and provided in a single package, supplemented by a second package containing panoramas for each experimental time instant and graphical representations of the data, facilitating rapid evaluation of the outcomes. This study provides versatile data that can be utilized in various ways, particularly for fluvial model validation and studying turbulence-driven phenomena in open-channel flows. The detailed methodology presented herein can contribute to the advancement of enhanced laboratory techniques to study similar flow problems. [ABSTRACT FROM AUTHOR]

Sills and baffles are appurtenances used to stabilize hydraulic jump in a stilling basin. The force acting on these appurtenances are characterized by the drag coefficient (CD). This paper describes experimental methods carried out in a rectangular channel to analyze the drag characteristics of sill and baffles in free (unsubmerged) and submerged hydraulic jumps. The sills and baffles were designed as per the USBR type III stilling basin guidelines. A calibrated loadcell connected to an Arduino board was used to measure the drag force. Errors in measurements are limited to 1%. The drag co-efficient was obtained for different Froude numbers (F1=U1/√gy1) pertaining to strong jump (4.5–9) for different relative position of sills (xS/y2) and baffles (xb/y2) from the nozzle of the sluice gate. Both forced (unsubmerged) and submerged jumps were investigated. It is seen that the drag coefficient of appurtenances in submerged jumps were lower than those in free jumps. This may be attributed to the reduction in wake size in submerged jumps. Comparisons of the experimental results of the sill with the previous theoretical studies are reasonable. [ABSTRACT FROM AUTHOR]

This paper analyzes the dam-break flow propagation over a stair using a novel version of the weakly compressible moving particle semi-implicit method, which was improved with the particle shifting technique and the quintic kernel function. The proposed method was validated with the experimental data of dam-break propagation. The simulation was conducted in two scenarios, in the first of which an obstacle-shaped stair was located in the flow direction, and the collision of the water volume with the stair was modeled through the proposed approach. The results were then compared with those obtained from the finite-volume method (FVM) in STAR-CD. In the second scenario, the dam-break flow descended a stair, reaching the bed and propagating in two directions: toward the right wall and backward near the stair wall. The submerged hydraulic jump was created near the stair wall because the flow did not have enough length to make the conjugation depth. The simulation results from both scenarios were consistent with those of the FVM solver. Furthermore, a quantitative analysis was performed by calculating error norms, resulting in values within the 10–4 range. The analysis indicated a high level of accuracy and consistency between the simulated results and the reference data. In addition, the issue of particle clustering was addressed effectively using the particle shifting approach. [ABSTRACT FROM AUTHOR]

Open-channel flows over a drop structure with a trench, often seen in urban rivers, may cause an oscillating phenomenon of hydraulic jumps depending on the trench geometry and hydraulic conditions. The oscillating hydraulic jumps are accompanied by large-scale water-surface variations with wave breaking, and numerical predictions of such flows are challenging in hydraulics. Using unsteady Reynolds-averaged Navier-Stokes simulations of air-water two-phase flows, we attempted to predict an oscillating hydraulic jump at a drop structure with a trench observed in our laboratory experiment. Several high-Reynolds-number turbulence models were applied, and the effects of turbulence models and grid resolutions on predicting the oscillating hydraulic jump were investigated. Turbulence models other than the k–ω SST model resulted in a steady-state flow with no oscillations regardless of the grid resolution. The k–ω SST model succeeded in predicting the oscillating hydraulic jump using a fine grid while the flow became a quasi-steady state using a coarse grid. Moreover, the period of the oscillation and the flow fields are in good agreement with the experimental results. The k–ω SST model has the ability to predict oscillating hydraulic jumps, including wave breaking, because this model accurately simulates flows with separations or stagnations under adverse pressure gradients. [ABSTRACT FROM AUTHOR]

Twin tungsten electrode-wire electrode indirect arc welding (TTW-IAW) is a new welding method, in which the twin tungsten electrodes are connected to the power source together with the welding wire, while the base metal is not connected to the power source, so that the indirect arc is formed between the twin tungsten electrodes and the welding wire. Currently, only the arc characteristics and the droplet transition behavior have been studied, which limits the application of this process in practical welding. In this paper, the thin-plate butt welding process is applied for the first time in TTW-IAW, and the effects of process parameters on weld formation, microstructure, and its hardness are investigated. Additionally, the formation mechanisms of burn-through and hump defects are revealed by the static model and hydraulic jump model of the molten pool, respectively. The results show that TTW-IAW achieves stable weld formation at a maximum welding speed of 600 mm/min, a fourfold increase compared to conventional cold-wire single-TIG welding (conventional cold-wire STW), which reflects its advantages of large deposition rate and high welding efficiency. The degree of influence of the welding current on the penetration of base metal is greater than the welding speed, and the increase in welding current is conducive to the increase in the base metal penetration and the heat-affected zone (HAZ) width, while the increase in welding speed can reduce the convex height of the weld. However, excessive welding currents cause the downward component of arc force and droplet impact to be increased and the upward component of surface tension to be decreased, which results in destabilization of the molten pool, leading to the formation of burn-through defects. Excessive welding speed causes the flow rate of the liquid in the molten pool to be increased and the critical value for the occurrence of a hydraulic jump is exceeded, leading to the formation of a hump. [ABSTRACT FROM AUTHOR]

Free falling or controlled high velocity jets from diversion weirs or dams results in the scouring of downstream riverbeds. Monitoring and analysing scouring is a complex problem as it depends on several factors, such as the discharge characteristics from the reservoir, sediment concentration of the discharge, tail water levels, etc. Timely monitoring of dam apron scour helps in adjusting the channel capacity downstream. This paper aims to propose an experimental technique to monitor the scour at the downstream apron of free overflow spillway using piezoelectric patches. A lab-based hydraulic jump was made through an ogee spillway in the flume. A sand bed was constructed to simulate soil scour (in the actual scenario) caused due to hydraulic jumps. Piezoelectric patches were arranged in optimised distance and depth to monitor the onset and severity of scour during the jump. The experimental piezo-induced voltages were measured, which indicate the different stages of scour phenomena, and a normalised scour depth was plotted to highlight the efficiency of the proposed technique. A statistical based signal index has been proposed for better reliability of the proposed study. At last, frequency-based analysis was carried out to study piezo frequency deviations for scour phenomena. [ABSTRACT FROM AUTHOR]

Major failures of spillway occur due to the inadequate or inefficient design of the spillway. In the Khadakwasla dam spillway, Pune (Maharashtra) has erosion and scouring on the spillway bed. The roller bucket is the alternative to reduce the kinetic energy and minimize the length of the hydraulic jump. Hence, there is an urgent need to develop appropriate energy dissipators to intend for high discharges. To address these concerns, the current study concentrates on resolving them by implementing plain and slotted roller buckets for the ogee profile stepped spillway. The proposed approach involves combining roller buckets and stilling basins, integrating appropriate steps designed for the ogee profile stepped spillway. This is achieved through the creation of a physical hydraulic model in the laboratory, with a scale ratio of 1:33. A comprehensive model study was conducted and the performance was validated using the Froude model law and continuity equation for a design discharge rate of 900 m3/s. Performance evaluation of plain and slotted roller bucket for ogee and stepped spillway illustrated that 82% of specific energy is eliminated by a plain roller bucket and 78% by a slotted roller bucket. In a stepped spillway, 58% of specific energy is eliminated by a plain roller bucket and 57% by the slotted bucket. Hence, in this device, the ogee spillway with a plain bucket is more reliable than the stepped spillway and helpful in reducing the intensity of specific energy over the chute surface of the spillway at a low head of 4 m. [ABSTRACT FROM AUTHOR]

We consider fluid flow with a free boundary, which is defined as a function of height from coordinate x with two asymptotes at positive and negative infinities (hydraulic jump). The Boussinesq approximation is used to describe the phenomenon, and an additional force is introduced. The force is chosen to depend only on the height of the surface. The problem is solved analytically without using numerical schemes. This technique is used to determine the jump surface and the acting force depending on the wave propagation coordinate. [ABSTRACT FROM AUTHOR]

The results of a numerical analysis of the condensation of R113 freon vapor in a horizontal round pipe with a standard size of 38 × 3 mm in the range of mass velocities from 50 to 150 kg/(m2 s) were presented. Studies of the features of hydrodynamics and heat transfer in the stratified and stratified wave regimes of condensate flow are still relevant due to their insufficient knowledge. Thus, according to recent data, the heat-transfer intensities in the zone occupied by a stream and in the sections of the inner surface of a horizontal pipe wetted with a thin condensate film are comparable. Therefore, for an adequate assessment of the real contribution of the stream region to the average heat transfer coefficient along the pipe perimeter, the existing methods should be refined. The VOF (Volume of Fluid) method realized in in-house CFD-code ANES was used to simulate a two-phase flow. The intensity of mass transfer was calculated using a modified Lee model in which the relaxation coefficient was determined automatically based on the algorithm proposed by the authors of this work in previous publications. To describe the turbulent transport, a version of Menter's SST turbulence model was used. Models of mass transfer, turbulent flows of a liquid film and vapor phase, VOF algorithms, and software tools that implement them were verified on experimental data on R113 freon condensation in a downward flow in a vertical pipe. Numerical modeling of condensation processes has been performed and the obtained data have been compared with the results of calculations using various methods recommended in the literature. Information is presented on the distribution of local characteristics along the length and perimeter of the pipe. It is noted that at low values of mass velocity [50 kg/(m2 s)] at some distance from the pipe inlet, a hydraulic jump occurs, leading to a significant change in the distribution of the vapor void fraction along the length of the channel. [ABSTRACT FROM AUTHOR]

The three-dimensional MITgcm (MIT general circulation model) was applied to simulate wind-induced baroclinic oscillations in Cayuga Lake, to obtain an understanding of the internal seiche/surge dynamics and associated mixing in long narrow lakes. The MITgcm has not been rigorously validated for closed basins against field observations. Thus, qualitative and quantitative methods were used to validate the model and study the sensitivity to different model parameters against observed temperature data. The linear equation of state (EoS) yielded poor results, in comparison to the polynomial EoS formulations where the density gradient was large. The vertical density stratification was strongly sensitive to the background vertical viscosity and diffusivity (when > 10–5 m2s−1), because the prescribed background values control mixing in the KPP scheme, except on the surface and bottom boundary layers. After calibration, the model correctly simulated the vertical stratification, upwelling, basin-scale seiche (with a horizontal mode-one period T1 = 80 h) and surge formation with a basin-wide root-mean-square-error 1.9 °C. Flow visualization indicated that internal surges evolved due to (i) a wind-induced locally downwelled thermocline (wind duration < T1/4), (ii) a basin-scale wind-induced upwelled thermocline (wind duration > T1/4) and (iii) internal hydraulic jumps. Article Highlights: The MITgcm was extensively validated against field data in simulation of Cayuga Lake A polynomial equation-of-state and space–time variable turbulence closure scheme were applied Three distinct processes were found to generate internal surges [ABSTRACT FROM AUTHOR]

Stepped spillways are considered one of the most significant energy-dissipating structures; however, the most complicated problem that threatens the overall stability of the spillway is local scour downstream of the stepped weirs due to hydraulic jumps in the skimming flow. In this study, a series of experiments were conducted under five discharges, three tail-water depths and two sediment sizes to investigate the scour downstream of a stepped spillway to reduce scour and increase the stability of hydraulic structure. Moreover, the optimal design of parameters, including type, crest and slope of chute, step height and type of stepped spillway flow, was determined considering the economic reasons and criteria that lead to more energy dissipation. Generally, the scour dimensions decreased as the sediment size and tail-water depth increased or the particle Froude number (Frd) and critical depth reduced. With the reduction in Frd, the relative scour depth, the relative distance of maximum scour depth and the relative scour length decreased by 68.6%, 75.6% and 73.4%, respectively. Empirical equations of regression analysis were developed to estimate scour depth compared to other studies. The final equations in this study can provide good estimates of the scouring parameters downstream of the stepped weir. [ABSTRACT FROM AUTHOR]

The performance of stilling basins including a negative step was analyzed addressing its effect on the energy dissipation efficiency, dimensions and structural properties of the hydraulic jump, streambed pressures and pressure fluctuations. Six different cases were simulated, considering two possible relative heights for the step and three possible Froude numbers. The results show that the step yields to lower subcritical depths, allowing smaller basin dimensions. Nevertheless, it tends to slightly increase the roller length of the jump. Concerning the relative energy dissipation, results confirm the improvement derived from the step presence. The internal flow occurring in the jump was also analyzed, and more specifically the subzones generated upstream and downstream the impingement point. The results prove the contribution of the negative step in the stabilization of hydraulic jumps in the stilling basin. In particular, a general decrease of the streambed pressure is observed. In addition, pressure fluctuations are significantly reduced due to the negative step size influence on the hydraulic jump. Furthermore, the effectiveness of the computational fluid dynamics (CFD) techniques to simulate stilling basin flows and to adequately characterize the hydraulic jump performance was confirmed. [ABSTRACT FROM AUTHOR]

The hydraulic jump is a rapid transition state from supercritical to subcritical flow that occurs commonly in rivers, prismatic channels, and downstream of spillways. In this study, the characteristics of the hydraulic jump in a stilling basin downstream of the spillway chute channel with the slopes of α = 12° and 30° were investigated experimentally for different Froude numbers of incoming flow, Fr1 = 7, 7.5, 8, 9, 10, and 12, and relative heights of sill in the range of 4 < hs/h1 (S) < 13 (hs, the sill height, h1 the flow depth at toe of the jump, S relative height). The velocity field was measured by laser Doppler Anemometry in the experiments, it was particularly focused on the effects of both different structural configurations and flow conditions on the hydraulic jump and energy dissipation ratio. Experimental measurements showed that the length of the hydraulic jump and the roller zone increases with the decrease of the sill height for α = 12° and 30°. In addition, the length of the hydraulic jump and roller zone increased with decreasing Froude numbers. The turbulence intensity in the jump region was determined to be greater than the turbulence intensity in the region near the bottom of the stilling basin. The turbulence intensity, in general, tended to decrease with decreasing Froude number. [ABSTRACT FROM AUTHOR]

The kilometer-long sub-surface mooring 'KmT', densely instrumented with 760 high-resolution temperature 'T-'sensors, demonstrates details of turbulent mixing in the vicinity of a large seamount. Away from the internal wave breaking zone above the seafloor, turbulence is observed in two cases. It is found in thin layers along isopycnals providing non-smooth dispersal, as well as induced by internal wave breaking following strongly non-linear interaction as in a hydraulic jump more than 500 m above the local seafloor. Turbulence levels for these cases are relatively low and high, respectively, but always one to two orders of magnitude larger than in the ocean interior far from topography. Both cases imply the importance of underwater topography like a seamount for deep-sea turbulence. The seamount functions as a lens focusing internal waves into a turbulence-generator. [ABSTRACT FROM AUTHOR]

Energy dissipation structures, particularly stilling basins, are critical for defining the hydraulic jump characteristics that are suitable. Appropriate sill geometry for abruptly expanding stilling basins has been investigated and a central rectangular sill has been proposed in the literature. This study has examined the suggested central sill and alternative flip buckets for abruptly expanding stilling basins. A series of experimental and numerical studies were carried out for two different heights of the central sill and two different flip buckets. Simulations have been evaluated using experimental data of laboratory scale, which indicated that they were acceptably precise. For the simulations, the k−ε turbulence model RNG module was preferred using the volume of fluid methods. The PISO approach was chosen to resolve this equation system numerically. The results showed that the hydraulic jump characteristics are strongly influenced by sill geometry. For the Type-3 sill negative static pressures have not occurred and performs better at energy dissipation than other geometries examined in the study. Higher pressures occurred on the rectangular prism-shaped sills. Maximum static pressure happened on the Type-2 sill. The least static pressure was seen in the Type-4 sill type. [ABSTRACT FROM AUTHOR]

When a river channel is narrow, bifurcated, or intersected, or when extreme weather or geological disasters cause shed rock masses to occupy a river flood channel, local hydraulic jumps may develop in the channel. Natural disasters such as landslides, floods, and debris flows occur upstream, will result in large transport rate of large-sized gravel particles. Those particles may be blocked in hydraulic jump areas, causing river channel water depth to rise. In this study, the effect of local hydraulic jumps on the sediment deposition rate was investigated in flume experiments. The ratio of upstream and downstream Froude numbers, particle size, Sediment supply intensity, and flow discharge all affected the sediment deposition rate. With increases in the ratio of upstream and downstream Froude numbers, particle size, and sediment supply intensity, the sediment deposition rate increased. The sediment deposition rate decreased with an increase in flow discharge. Approach hydraulic conditions and particle properties jointly determined the sediment deposition rate in a hydraulic jump section, and an empirical formula was developed using those parameters to calculate the sediment deposition rate. Thus, to identify risks and prevent disasters in mountain rivers, local changes in hydraulic conditions and particle properties need to be jointly evaluated. [ABSTRACT FROM AUTHOR]

In this study, to simulate open channel flows, an explicit incompressible mesh-free method is employed in which the pressure field is obtained by explicitly solving the pressure Poisson equation. To capture the velocity information in open channel flows, the source term in the pressure Poisson equation is modified while the spatial discretization of gradient and Laplacian models is based on the moving particle semi-implicit (MPS) method. The inflow boundary condition is treated by injecting fluid particles into the domain according to the inlet discharge, and the outflow condition is handled by prescribing the pressure distribution and removing the fluid particles beyond the domain. The explicit incompressible mesh-free method is then used to simulate open channel flows, including weir flow, hydraulic jump, and flow over an obstacle. In the simulations, velocity distribution and flow pattern are examined. The simulated results are compared to available experimental measurements and other numerical results. There is a good agreement between the simulated results and the experimental measurements. It shows that the explicit incompressible mesh-free method can reproduce the flow characteristics in the open channel flows. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the physical features of hydraulic jump oscillations at an abrupt drop with high Froude numbers reaching values up to 9.92. In order to emphasize the importance of the bottom shape, different relative step heights in the range between 0.9 and 3.4 have been analysed, leading to the occurrence of different jump regimes (A-wave, A-jump, B-wave and B-jump). For the case of the B-jump type, the jump toe is drifted downstream when the Froude number increases. For the A-jump type with high Froude, the surface roller is made up of an increasing several number of vortices and thus the jump toe is drifted upstream, when the Froude number increases. In particular, for the case of the A-jump type at the highest simulated Froude number, when the toe of the jump is at its most upstream location, the maximum number of anticlockwise vortices (with decreasing sizes) is observed. At the same time, the turbulence levels decrease much faster due to the dominance of viscous forces at the small scales. Instead, when the toe of the jump is moving downstream, the neighbouring vortices tend to influence each other with their rotation and to coalesce into one larger vortex and the turbulence levels increase rapidly due to the dominance of inertial forces. A statistical analysis indicates that turbulent pressure fluctuations increase rapidly from the toe of the jump and reach a peak in the roller region, downstream of which they decrease again. The structure of the turbulent pressure fluctuations depends on the Froude number. [ABSTRACT FROM AUTHOR]

Laboratory experiments were conducted out to investigate the regimes of submerged flows over the sharp-crested weirs in sand bed Channel. These kinds of flows were classified as five states such as (I) impinging jet, (II) bed surface flow, (III) surface jump, (IV) surface wave, and (V) surface jet based on the depicted vector plots of the regimes. By increasing the submergence ratio, the impinging jet was developed as a downward jet which was impinged from the weir crest to the downstream. By continue the increasing, flow regime was developed as a bed-surface flow which is supposed that the impinging jet is turned as flow near the bed position instead of having a direct impact with the bed. Additionally, increasing constancy of the submergence ratio causes that the bed-surface regime turned to the surface jump which is accompanied by a hydraulic jump at the water surface. Subcritical condition at downstream of the weir which is provided by raising the tailwater due to constant flow discharge causes that the surface wave regime has vanished at the water surface of the downstream of the weir and some oscillating waves were transferred to downstream. Finally, by considering the maximum range of submergence ratio, the flow regime was changed to the surface jet which was accompanied by a big clockwise vortex at the lower water elevation. The present study classifies these flow regimes based on the velocity components (u, v, w). This approach was chosen by the authors to show the different classification between visual inspection and investigating the velocity direction by ADV. Then, an empirical equation was proposed to show the boundaries of the presented regimes. Also, a dynamic restriction was proposed based on experimental and literate data as a non-eroded status that is due to a submerge ratio, the scour hole is not provided at downstream of sharp-crested weir. [ABSTRACT FROM AUTHOR]

In the last two decades, the hydraulic jump has been extensively studied. In this article, attempt is made to have a comprehensive look at different characteristics of this complicated phenomenon. The aim of the present work is classification, comparison, and analysis of many research works on hydraulic jumps during the past years. It was found that there was no significant difference between jump characteristics such as the sequent depth and surface profile with developed or undeveloped approach flow, but air–water characteristics such as void fraction and bubble count rate are significantly affected. The present study also discusses the research results on pressure fluctuations, velocity field, turbulence characteristics, and air–water properties in a hydraulic jump. Investigating previous studies shows that most of the relationships presented for different characteristics of the hydraulic jump such as velocity or air concentration are dependent on other variables which are not available without measurements. The length of the stilling basin is considered equal to the length of the jump. Various definitions are given for the jump length. The results show that using the decay rate of pressure fluctuation, the stilling basin length could be calculated by less than 5% difference compared to the defined USBR I standard stilling basin length. [ABSTRACT FROM AUTHOR]

In the present study, series of laboratory experiments were conducted to investigate the effectiveness of perforated screens as energy dissipators in mixed triple wall mode in the case of small hydraulic structures. The shapes of openings for each layer of screens were either circular, square or triangular. Every layer of the screen had a porosity of 45% per unit depth of the screen. The experiments were conducted to dissipate the energy for supercritical flows of Froude number F1 ranging from 3.2 to 19.3. The screens were placed vertically with the first screen 1.5 m from the sluice gate and consecutive screen at a gap of 25 mm. The experiments showed that the energy of the supercritical flows can be dissipated effectively by using perforated screens. The difference in energy dissipation between the upstream and downstream of the screen was more significant than the energy dissipation caused by classical hydraulic jumps. Comparing the results of the present study with the previous researchers it is found that the energy loss in case of present study more than the previous researchers. The relative energy loss in the present study was found to be varying from 74 to 94%. The value of the Froude number downstream of the screen, F2, was varying from 1.1 to 1.81, with an average value of 1.35. Tailwater deficit parameter, D, if found to be varying from 0.66 to 0.90. [ABSTRACT FROM AUTHOR]

Drainage channels with step-pool configurations, one type of debris-flow drainage system used in gullies with steep gradients, have good application potential because of their high-performance control effect and engineering value. In this study, a pool depth design method is proposed based on the hydraulic jump theory. The dynamic behavior of debris flows in drainage channels with step-pool configurations is explored via a series of specially made flume experiments, where the debris-flow bulk density and the scale and depth of the step-pool configuration are the main controlling factors. The debris-flow pattern and flow depth are investigated along with the material-interchange phenomenon. There is a dramatic difference in the dynamic behaviors of different types of debris flows. Because of the associated intense turbulence and particle collision, the observed material-interchange phenomenon was greatest when the debris flow with a bulk density of 1700 kg/m3 passed through the drainage channel. The analysis indicated that, when a debris flow passes through a step-pool configuration, the flow depth increases significantly as a result of the hydraulic jump. However, a step-pool configuration with an overly large depth traps sediment, which is detrimental to transporting sediment. In addition, modified coefficients of the proposed design method were determined based on an analysis of the experimental results. The analysis further indicated that the coefficients significantly depend on the debris-flow viscosity and turbulence. Our results can be used to improve understanding of step-pool configurations and provide a reference for practical engineering design. [ABSTRACT FROM AUTHOR]

Most dams include bottom outlets consisting of tunnels or pipes to control water discharge by using valves or slide gates to regulate water level in reservoirs for service operation or during an emergency. When the gates are partially open, subatmospheric pressure can develop on the downstream side of the gates, leading to possible damage by cavitation and vibration. In order to avoid the latter, an aeration system is usually installed downstream of the gates to keep the local pressure above the vapor pressure for preventing cavitation. The present study aims to estimate the air concentration profiles for a series of hydraulic jumps that occur on the downstream side of a partially open gate of a bottom outlet using a flow visualization technique, known as Image Processing Procedure (IPP), which consists of the Image Editing and the Pixel Intensity Matrix algorithms. This technique uses a high-speed camera and is based on the hypothesis that air concentration profiles can be estimated from the pixel intensity of each photograph, and also offers the possibility to obtain such profiles in any point along the hydraulic jump without disturbing the flow. The results obtained after applying the IPP to the photographs of the experimental study have very good agreement with the profiles obtained with a conductivity probe, indicating that the IPP can be a powerful tool to complement intrusive probe measurements. In addition, to evaluate the capability of the proposed IPP the experimental data were compared with a two-dimensional diffusion equation. Comparisons between predicted and measured results show good correlation demonstrating the potential of the proposed methodology. [ABSTRACT FROM AUTHOR]

The bed elevation of the stilling basins is most often located below the river bed in order to provide the required tail water depth. Both basins located in alignment with the erodible bed or below it are studied. To this end, the scoured hole dimensions under various circumstances and the sediment transport process within the scour hole were thoroughly examined. Results revealed that the upstream slopes of the dimensionless scour profiles are approximately identical at different times. According to the results, the basin located below the erodible bed was of a greater maximum scour depth and a lower scour depth at the beginning of the erodible bed. Moreover, a simple generalized equation correlating the temporal development of the maximum scour depth and the scour depth at the beginning of the erodible bed at equilibrium time was derived for the USBR Type I basin aligned with or below the erodible bed. [ABSTRACT FROM AUTHOR]

This paper investigates hydraulic jumps in sloping pipes by means of wall-resolved large eddy simulation (LES). The purpose is to achieve an improved understanding of jump behaviours driven by pipe discharge and slope. The LES model predicts the hydraulic jump as a 3-D two-phase flow, with air as the gas phase and water as the liquid phase. The predictions yield instantaneous velocity and pressure fields as well as fluid volume fraction. The instantaneous flow variables allow ensemble averages, which quantify the internal structures and integral properties of the hydraulic jump. The predicted instantaneous velocity shows spectra in consistency with the well-known Kolmogorov −5/3 law. The ensemble averages of air and water velocities, free-surface profile, roller length and aeration length, compare well with available experimental data. The jump behaviours are complex. Some aspects such as free-surface fluctuation and jump-toe oscillation resemble the classical hydraulic jump on horizontal floors. Others like the 3-D distributions of core jet, vorticity and aeration are much more complicated. Depending on the pipe discharge and slope, the resulting jump can be a complete or an incomplete jump. The incomplete hydraulic jump causes choked flow downstream. This has severe consequences on drainage conditions in sewer pipes laid on sloping terrain. This paper proposes using the Okubo-Weiss parameter as a new way to subtly delineate the region of hydraulic jump. It is much more efficient and less ambiguous, compared with traditional visual inspections. [ABSTRACT FROM AUTHOR]

Hydraulic jump that frequently occurs downstream of hydraulic structures reduces the excess energy of the incoming flow. This study tested two different heights of discontinuous roughness elements over the horizontal bed and two adverse slopes of -1.5% and -2.5% in the stilling basin. In total, 280 data were collected in laboratory conditions to assess the impact of adverse bed slope with a variation of roughness elements height on hydraulic jump characteristics, with Froude numbers ranging from 4.9 to 12.4. The results showed that the average value of the bed shear coefficient on the adverse slope of -2.5% with relative roughness elements of h/d1 = 1.33 was 12.4 times that in a smooth bed. The observation showed that the bed shear stress caused by the bed roughness reduced the sequent depth ratio and consequently increased the energy dissipation by generating large eddies and more turbulence. The reduction was more prominent when roughness elements and adverse bed slope height increased. On the other side, a semi-theoretical solution was presented based upon momentum analysis to assess the sequent depth ratio by considering upstream Froude number, roughness element height, and bed slope. The computed values were compared with the experimental measurements. Empirical predictive relationships were proposed to estimate hydraulic jump characteristics over adverse-sloped and rough beds. [ABSTRACT FROM AUTHOR]

In this study, the FLOW 3D computational fluid dynamics (CFD) software was used to estimate the performance of the United States Bureau of Reclamation (USBR) type II and USBR type III stilling basins as energy dissipation options for the Mirani Dam spillway, Pakistan. The 3D Reynolds-averaged Navier–Stokes equations were solved, which included sub-grid models for air entrainment, density evaluation, and drift–flux, to capture free-surface flow over the spillway. Five models were considered in this research. The first model has a USBR type II stilling basin with a length of 39.5 m. The second model has a USBR type II stilling basin with a length of 44.2 m. The 3rd and 4th models have a USBR type II stilling basin with a length of 48.8 m and a 39.5 m USBR type III stilling basin, respectively. The fifth model is identical to the fourth, but the friction and chute block heights have been increased by 0.3 m. To set up the best FLOW 3D model conditions, mesh sensitivity analysis was performed, which yielded a minimum error at a mesh size of 0.9 m. Three sets of boundary conditions were tested and the set that gave the minimum error was employed. Numerical validation was done by comparing the physical model energy dissipation of USBR type II (L = 48.8 m), USBR type III (L =35.5 m), and USBR type III with 0.3-m increments in blocks (L = 35.5 m). The statistical analysis gave an average error of 2.5% and a RMSE (root mean square error) index of less than 3%. Based on hydraulics and economic analysis, the 4th model was found to be an optimized energy dissipator. The maximum difference between the physical and numerical models in terms of percentage energy absorbed was found to be less than 5%. [ABSTRACT FROM AUTHOR]

Scour downstream of smooth and rough rigid aprons under wall jets has been studied experimentally. Effect of apron roughness on scour has been investigated, and quantification of reduction in the scour depth due to rough apron has been performed. Characteristics of velocity and turbulence over smooth and rough aprons as well as within the scour hole have been analyzed to study the behavior of the jet and its interaction with the rough apron. Results show that there is a significant reduction in the equilibrium scour depth due to roughness. A maximum of 82.8% and a minimum of 31.1% reduction in the equilibrium scour depth was observed due to inducing roughness over the rigid apron. Velocity characteristics establish the cause of reduction in the equilibrium scour depth, which is due to reduction in the erosive capacity of the jet as it moves over the rough apron. The potential core of the jet gets consumed at a much lesser length due to roughness over the apron than over a smooth apron, as the boundary layer develops at a smaller distance. Further, it was observed that it takes a smaller length for the flow to get fully developed under the rough apron as compared with the smooth apron. Based on the results of the present analysis, recommendation can be made for use of roughness over the apron to restrict scour due to wall jets. [ABSTRACT FROM AUTHOR]

In order to explore the flow characteristics and working principles of oblique stilling basins, model tests were carried out on six schemes with three inlet angles in two types of stilling basin (perpendicular and oblique). The outcomes demonstrated the feasibility of oblique stilling basin. However, the oblique angle of stilling basin has an impact on the flow, and the smaller the angle, the greater the impact. The specific manifestations are: Firstly, the hydraulic jump is oblique, and when the upstream energy exceeds a certain value, a hydraulic jump occurs on the obtuse angle side formed by the starting section, while no hydraulic jump occurs on the other side. And there is a large difference in the water level between the longitudinal and cross sections in the stilling basin, and the smaller the angle, the greater the difference caused. Secondly, the water level on the obtuse angle side is higher than that on the acute angle side, and the smaller the angle, the greater the change, with the lowest water level occurring on the acute angle side; the oblique angle of the stilling basin causes uneven energy at the starting section, with greater energy on the acute angle side than that on obtuse angle side, and smaller angles have greater energy. This research showed the working principle of oblique stilling basin and can serve as a basis for subsequent research. [ABSTRACT FROM AUTHOR]

We examine theoretically the structure of the non-circular jump for an impacting circular jet, induced by azimuthally dependent edge conditions. We show that the supercritical flow remains axisymmetric for a thin film. The subcritical flow is assumed to be inertialess. The loss of axial symmetry is induced by disk non-circularity or periodic edge film thickness. The jump is treated as a shock, where the balance of mass and momentum is established in the radial and azimuthal directions, including the non-axisymmetric effect of surface tension across the jump. The geometry of a non-circular disk has little influence on the shape of the jump, except when the jump occurs close to the disk edge, but the subcritical flow field can be highly non-axisymmetric even for a circular jump. For a jet impinging on a circular disk with a variable film thickness at the edge, we find that a small azimuthal variation in the edge thickness leads to a significant loss of axial symmetry. The nonlinearities in the balance equations across the jump cause an increase in the number of peaks and valleys as the disk radius decreases. Flow reversal occurs in the polar plane at alternating valleys. It is important to mention that this is a study in (edge) controlled pattern generation and therefore not aimed at simulating or interpreting the spontaneous non-circular jumps reported in the literature. [ABSTRACT FROM AUTHOR]

The paper discloses the study of flow crisis in the Ranque—Hilsch vortex tube with a square channel. Previous studies have found the conditions for developing the hydraulic crisis for air flow in this type of tube. The crisis phenomenon is related to the event when the longitudinal velocity at the nearwall vortex-circulation zone interface approaches the value of velocity for spreading centrifugal waves along this boundary. The paper presents and discusses the new detailed results in measuring the kinematic parameters of the crisis flow, including the parameter of velocity pulsation. The evidence of a hydraulic jump near the exit of the swirl flow to the tube working channel. [ABSTRACT FROM AUTHOR]

The multiple-barrier mitigation strategy in the debris-flow source area is an effective approach to inhibit debris-flow entrainment and scale amplification along the flow path. However, less is known as debris flow overflows a filled barrier and cascades downstream. The present study investigates the physical processes and load characteristics of debris-flow overflowing a model flexible barrier, using a well-instrumented medium-scale flume. Volumetric solid concentration is varied ranging from 0.4 to 0.6 so that the control factors (e.g., state of liquefaction and turbulent drag) in the overflow process can be identified. The results demonstrate that effective stress is not observed in the incoming debris flows for solid concentration up to 0.6, denoting a contribution of turbulent drag to the overflow drag. The formed hydraulic jump substantially elevates the overflow depth above the flexible barrier, which has not been considered in the current design guideline. Decomposition of the total overflow load reveals that the increase in total load is actually dominated by the static load due to the elevated flow depth, rather than the turbulent drag. Downward momentum transfer to the lower section of barrier is observed and re-liquefaction of the deposited debris is a prerequisite for the downward momentum transfer. Different from the high solid-concentration cases, the deposit of low solid concentration (0.4) behind the barrier is partially drained with nontrivial effective stress, which further hinders the downward momentum transfer to the base of the barrier. The findings of present study indicate that the debris-flow properties are the key control factors for the complicated debris-barrier interaction. [ABSTRACT FROM AUTHOR]

The principle theme of this study is to introduce a novel countermeasure to reduce the energy of the overflowing floodwater by utilization of a water cushion. For this purpose, laboratory experiments including "LW" cases (levee with water cushion) and "OL" cases (only levee) were conducted to elucidate the role of a water cushion in the flow structure variation after a levee is overflowed and to reduce energy. A moat (a deep and wide trench) with varying non-dimensional length (Lm* = Lm/hL; Lm is the length of the moat where hL is the levee height) and depth (Dm* = Dm/hL; Dm is the moat depth) acting as a water cushion was provided at the toe of a levee with varied landward slopes (SL). The energy reductions in the LW and OL systems were found to be very close to each other at lower overflow water depths, while it was 25% greater in the LW system than in the OL system at higher overflow water depths. Changes in the landward slope (SL) of the levee, non-dimensional length (Lm*), and depth (Dm*) of moat significantly changed the flow structure and created six different flow structures. However, 1–6%, 1–3%, and 1–5% differences in energy reduction rate were observed by varying SL, Lm*, and Dm*, respectively, in LW cases. All flow structures contributed greatly to energy reduction, but the energy reduction rate was maximum in flow structure named as T-2. Flow structures named as T-2 and T-6 are preferable due to increased water depth inside the moat and presence of submerged hydraulic jump which can be achieved during landward slopes SL = 1:1, 1:2 and by decreasing Lm* Dm*, of moat during Landward slope SL = 1:3. Article Highlights: The water cushion function of moat was utilized at toe of overflowing levee. The effect of different non-dimensional overflow water depths, non-dimensional length, depth of moat and varying landward slope of levee on flow structure was investigated. Different flow structure was classified based on non-dimensional length and depth of moat. Relation between flow structure and energy reduction rate was investigated. [ABSTRACT FROM AUTHOR]

Hydraulic jumps are commonly employed as energy dissipators to guarantee long-term operation of hydraulic structures. A comprehensive and in-depth understanding of their main features is therefore fundamental. In this context, the current study focused on hydraulic jumps with low Froude numbers, i.e. Fr1 = 2.1 and 2.4, at relatively high Reynolds number: Re ~2 × 105. Experimental tests employed a combination of dual-tip phase-detection probes and ultra-high-speed video camera to provide a comprehensive characterisation of the main air-water flow properties of the hydraulic jump, including surface flow features, void fraction, bubble count rate and interfacial velocities. The current research also focused on the transverse distributions of air-water flow properties, i.e. across the channel width, with the results revealing lower values of void fraction and bubble count rate next to the sidewalls compared to the channel centreline data. Such a spatial variability in the transverse direction questions whether data near the side walls may be truly representative of the behaviour in the bulk of the flow, raising the issue of sidewall effects in image-based techniques. Overall, these findings provide new information to both researchers and practitioners for a better understanding of the physical processes inside the hydraulic jump with low Froude numbers, leading to an optimised design of hydraulic structures. Article Highlights: Experimental investigation of air-water flow properties in hydraulic jumps with low Froude numbers Detailed description of the main air-water surface features on the breaking roller Transversal distribution of the air-water flow properties across the channel width and comparison between centreline and sidewall. [ABSTRACT FROM AUTHOR]

On 19 April 2019, a mature squall-line mesoscale convective system (MCS) with the characteristics of a leading convective line and trailing stratiform landed on Taiwan, resulting in strong gust wind and heavy rainfall. This squall-line MCS became asymmetric after landfall on Taiwan. Two sets of idealized numerical simulations (mountain heights and low-level vertical wind shear) using the Weather Research and Forecasting (WRF) model were conducted to examine the impacts of realistic Taiwan topography on a squall-line MCS. Results showed numerous similarities between the idealized simulations and real-case observations. The low-level Froude number which considered the terrain height (Fmt) was calculated to examine the blocking effect of the Taiwan terrain, and the cold pool (determined by − 1.5 K isotherm) was found to be completely blocked by the 500-m height contour. The northeast-southwest orientation of the Snow Mountain Range (SMR), and the north–south orientation of the Central Mountain Range (CMR) led to the upwind side asymmetry. On the other hand, the lee-side asymmetry was associated with different intensities and occurrence locations of the hydraulic jump between the SMR and southern CMR, and the cold-pool Froude number (Fcp) indicated the flow-regime transition from subcritical to supercritical. [ABSTRACT FROM AUTHOR]

The hydraulic jump is a typical sudden change for mountain river areas. The effects of local hydraulic jumps on the particle transport capacity decrease and local flow resistance increase cannot be ignored as the sediment deposition disaster can amplify the flash flood disaster. The present research investigates the influences of a hydraulic jump on the individual particle movement and sediment deposition in a laboratory flume. The overall processes of a single particle movement are captured by a high-speed camera. The distribution of sediment deposition along the hydraulic jump is obtained statistically. The results show that both the particle size and the ratio of the upstream and downstream Froude numbers affect the particle motion process. A single particle coming from upstream gradually decelerates and finally stops at the hydraulic jump section because of hydraulic jump resistance. The particle acceleration first increases and then decreases during the time-domain process, and the attenuation trends are fast with the increase of ratio of upstream and downstream of Froude numbers. The increase of the maximum acceleration with sediment flows follows a linear trend approximately, which indicates that the kinetic features of the single sand particle are determined by the coupling effects of the hydraulic jump resistance and the sand dynamic properties. With the increase of sediment rate and sand particle size, the resistance effect of hydraulic jump on sediment deposition rate along the flow direction gets strong and the sediment deposition area is mainly located upstream of the hydraulic jump region. The present study shows that the possible sediment supply upstream must be obtained for identifying the disaster risk combined with the local hydraulic jump conditions. Further researches about the detailed critical condition deduced from the relationship between the water flow and sediment deposition are required to confirm and extrapolate present results to other applications. [ABSTRACT FROM AUTHOR]

Near-critical turbulent axisymmetric free-surface flow over a horizontal bottom is investigated. Assuming that undular hydraulic jumps occur at large radii, an asymptotic analysis of the governing equations is performed in the double limit of very large Reynolds numbers and Froude numbers close to the critical value 1. The results are kept free of turbulence modelling due to a specific coupling of the two limiting processes. The final result of the asymptotic analysis is a new steady-state version of an extended Korteweg–de Vries (KdV) equation for the free-surface elevation. The extended KdV equation is derived as a uniformly valid differential equation, describing the flow near the origin of the undular jump as well as far downstream. Numerical solutions of the extended KdV equation show that circular undular jumps can develop if the reference state is located in the region where the effect due to axisymmetry prevails over the effect of friction. In this case, the solution oscillates over a very long distance until the accumulating friction effects force a breakdown. The comparison between the theories of undular jumps in turbulent and inviscid flows shows that friction is of minor importance near the development of the undular jump. However, friction has to be taken into account to describe the flow further downstream. Remarkably, the extended KdV equation is valid and yields undular solutions for both turbulent source and sink flow. [ABSTRACT FROM AUTHOR]

The hydraulic relationships of flow through the weir of different common shapes were investigated in this study. The hydraulic performances of weirs were carried out experimentally, by using eight different types of weir models, and the effect of various shapes of the weir to specify different hydraulic parameters such as coefficient of discharge (Cd), weir geometric shape and size constants (K) and weir shape number (n), energy dissipation ratio (E %) for selecting best flow measuring weir type. The experimental work was carried out on a tilted rectangular flume with 7.5 m long, 0.30 m wide and 0.45 m deep with a discharge range 0.50–20.95 L/s. The experimental results of this study showed that the dissipation energy corresponding to triangular notches is larger than the resulted from rectangular notches. For compound notches of rectangle and triangle, turbulence inflow increases as the angle of lower notch decreases. Thus, this type with an angle of (θ = 120ο) is the most efficient between the studied models, which gives the average Cd of 0.82, the value of K is equal to 0.75 and n values of 1.96, and the dissipation of flow energy ratio of (35.86%) for strong hydraulic jump. Finally, depending on a statistical basis, this study derived empirical relationships to estimate the coefficient of discharge with acceptable values of the coefficient of determination. [ABSTRACT FROM AUTHOR]

The time-dependent plume front positioning with respect to different tidal phases and its dynamics coupled with seasonal river efflux on the shelf off Kochi, southwest coast of India, was investigated using Finite Volume Community Ocean Model (FVCOM). This region is linked with a monsoonal estuary, characterised by a mixed semidiurnal tide (1 m) and exhibited features of small and large-scale plumes. The interaction between river efflux and tidal phases modulates plume fronts on the shelf, where the density gradients are fortified or weakened by mixing dynamics. Even though the heavy river efflux in the summer monsoon imparts significant momentum on the shelf, the range of frontal fluctuation was curtailed to 2 km by strong monsoon currents. During the transient phase of the season (fall inter-monsoon), the tidal forcings on plume positioning overwhelm the shelf currents, such that the plume front fluctuates between 5 and 17 km from the inlet (range increasing to ~12 km). During low tides, the region near the inlets was almost homogenised (Rd<1), while during high tides, the region became more stratified due to the transport of high saline coastal water towards the inlet and also by the decreasing kinetic energy (Richardson number, Rd>1). The location of frontal zones suitable for the propagation of internal waves (Froude number, F≤ 1) changes as a result of the competition between river efflux and tide-topography interaction. Strong stratified plume frontal regions with high Brunt Vaisala Frequency (N) could be active zones of internal wave generation when the flow decelerates from supercritical to subcritical during the summer monsoon. The release of accumulated potential energy during the transition from high tide to low tide generates the hydraulic jump. This disturbance in the Nmax zone together with F ≤ 1 condition (supercritical flow changed to subcritical flow) favours the generation and propagation of plume-induced internal waves on the shelf. Satellite imageries demonstrate such propagation of plume-generated internal waves on the shelf off Kochi. [ABSTRACT FROM AUTHOR]

The tsunami mitigation strategies are shifting from single to multiple defense systems in recent times. In this study, the mitigation effects of continuous and discontinuous emergent coastal forest were investigated experimentally focused mainly on energy reduction of the inundating tsunami current under subcritical flow conditions. To improve the effectiveness of the coastal forest, a layer of short submerged trees with the varying condition of porosity (Pr = 98%, 95%, 91%, and 79%) was coupled/incorporated and tested with the tall emergent trees. The results revealed that the forest in discontinuous placement effectively produced resistance to the flow by notably increasing the backwater rise in the upstream and reducing the energy of the tsunami current in the downstream region, rather than a continuous forest belt. The incorporation of short submerged tree layer within an emergent tall tree forest further increased the flow resistance by causing a large water level difference between the upstream and downstream regions of the forest, which consequently resulted in a significant amount of energy loss i.e. 30–50% higher, in comparison to that of single layered emergent tree configuration. Moreover, the critical zone of high shear stress and large turbulence hydraulic jump formation zone was observed to significantly move in the further downstream region for discontinuous and layered tree forest configurations, that could possibly save the direct collision of water with the ground just behind the forest. The outcomes predicted by the statistical analysis approach also showed a strong inverse correlation between the energy dissipation of flow and forest porosity. [ABSTRACT FROM AUTHOR]

This document is a response to a previous article titled "Investigation of flow structure with moat acting as a water cushion at the toe of an overflowing levee." The response paper numerically investigates the effects of geometric parameters of the moat downstream of the overflowing levee on its hydraulic characteristics and energy reduction. The authors validate their model using the previous paper but argue that the validation is insufficient. They suggest that more information is needed to reach conclusions on the optimal geometric parameters. The publisher remains neutral on jurisdictional claims and institutional affiliations. [Extracted from the article]

Slit-check dams have a flow regulation function under normal flow conditions as well as holding large solid (debris flow control). However, the effects of such structures on flow hydraulics have not been considered much until now. In this study, the effects of slit-check dams on the flow hydraulics were investigated experimentally and numerically. First, the check-dam blocks of different sizes were placed in an open channel and their hydraulic behavior under subcritical flow conditions was experimentally investigated. Then, the blocks used in the experiments were simulated in a three-dimensional numerical environment using Computational Fluid Dynamics (CFD) under the same flow conditions. Water surface profiles, energy dissipation ratios and velocity profiles obtained from numerical and experimental models were presented and discussed. In the verification of the numerical model, it was observed that the relative error percentage found between the models for different discharges in range of 4% and 8%. The results show that a slit-check dam composed of blocks placed in a subcritical flow causes a significant hydraulic jump in the flow. For the 0.8 of the relative block thickness (t/s), the hydraulic jump was found to be the most effective. Total energy loss reached 30%, and the maximum energy loss was obtained for t/s = 1.0 of the relative block thickness. As conclusion that slit-check dams with blocks are effective in flow regulation under flood and normal flow conditions besides holding large solid materials. [ABSTRACT FROM AUTHOR]

A hydraulic jump forming in the stilling basin at the base of a high-head dam spillway is often characterized by high Froude number and inflow pre-aeration conditions. Although the air entrainment in hydraulic jump has been studied extensively, the effects of the inflow pre-air-entrainment on the downstream air–water flow properties and energy dissipation performance have not been investigated systematically, especially for high-Froude-number cases. This paper presents a comparative study of the pre-aeration effects on the air–water flow characteristics of high-Froude-number hydraulic jumps. Two pre-aeration levels were achieved using a smooth sloping chute and a ramp aerator on the chute. Apart from the change in jump length required for the same amount of energy dissipation, the major impact of the variation in pre-aeration was observed for the void fraction and air entrainment flux within the jet-shear region, whereas the bubble count rate and interfacial velocity were less affected. Differences were also observed from the prediction of previous studies under smaller Froude number and negligible pre-air-entrainment conditions. The pre-air-entrainment was found to affect the scale effects on the bubble counts and the interfacial area between air and water phases. This study may facilitate a bridging between the laboratory findings and the cases closer to the real engineering application of large-scale hydraulic jumps. [ABSTRACT FROM AUTHOR]

This paper analyzed the flow pattern around damaged and undamaged bridge piers in a channel with a mild slope. The experiments were carried out on a straight channel with a length of 12 meters and a slope of 0.008. Acoustic Doppler velocimeter (ADV) was employed to collect three-dimensional flow velocity data, and the results were analyzed and compared with particle image velocimetry (PIV) data. Sediment Simulation in Intakes with Multiblock option (SSIIM) was incorporated for the numerical simulation of the flow in this study. Generally, the results obtained from the comparisons referred to the appropriate agreement between the numerical and the experimental data. The results showed that an undular hydraulic jump occurred at a distance of two meters from the channel entrance in every case; the maximum bed shear stress in the sloped channel was 12 times that in a horizontal channel for installing two damaged and undamaged piers. With this position of the piers in the sloped channel, the upstream water level underwent a 72.5% reduction compared to similar conditions in a horizontal channel, while the amount of this water level decrease was equal to 8.3% compared to the other cases in a sloped channel. In addition, with the presence of both piers, the maximum Froude number was 5.7 times that in a horizontal channel. [ABSTRACT FROM AUTHOR]

We used waterborne Ground Penetrating Radar (GPR) for mapping stratigraphic boundaries, sedimentation environments, and specific features of lacustrine sediments of postglacial Lake Polevskoye, which is located in Eastern Fennoscandia, near Lake Onega. The purpose of our study was to examine the spatial structure of the lacustrine sediments including particular facies represented by the thin interbedding of sand and clay in order to understand the conditions for their formation. The lake bottom morphology and stratigraphic boundaries beneath were mapped with a GPR with 150 MHz antenna unit and then made drill holes to verify GPR interpretations. The GPR measurements, verified by drilling, have vertical accuracy in the range of 0.12–0.36 m. We delineation specific GPR facies in the topmost part of varved clays and classified them as lacustrine turbidites by their structure and grain size. Further studies suggested that turbidites could be deposited by hyperpycnal flows during water discharge from glacial Lake Onega in the period 11.4–10.7 cal ka BP. The architectural implications of the turbidity current in the lake include localized layered sediments 0.5 m thick overlying an erosional surface, which contain unconformable sandy layers and plant debris. A GPR-based 3D model helped us to reconstruct the turbidity current direction, establish its confinement to a lake bottom depression, and consider the associated erosion processes. The near-bottom turbidity current passed through Lake Polevskoye from north to south, along with the bottom depression, and the eastern shore was eroded with a hydraulic jump. The hyperpycnal flows in the study site are associated probably with the last phase deglaciation of the terrain and a drop of the level of Lake Onega because these processes were the most prominent in recent geological history. [ABSTRACT FROM AUTHOR]