Water Surface Profiles Research Articles

Numerical study on hydraulic characteristics of improved X-shaped FGP

The three dimensional numerical simulation was carried out for flood discharge and energy dissipation process of five improved X-shaped FGPs in hydropower project by using coupled Level set and VOF model and RNG k-ε turbulent model. The change laws of flow pattern, water surface profile and velocity distribution of X-shaped FGP and lock chamber were gained. The results of numerical simulation were compared with the model test data and good agreement was found. It validated the numerical simulation method is reliable, It can provide strong references for the design of energy dissipation and shape optimization of practical project, the results from computation can be supplement for experiment.

Numerical Study of Discharge-Head Relationship of Piano Key Weirs for Low Heads

Piano Key Weirs (PKW) is a free-flowing weir, and an improvement over the labyrinth weir family. PKW has higher discharge for the same head as compared to other types of weirs. They tend to reduce the upstream submergence in reservoirs or other flow systems and can be effectively used for flood risk mitigation. CFD studies have been carried out earlier but mostly for H/P (Total head to height ratio) greater than 0.1. The present paper investigates the use and validation of Computational Fluid Dynamics (CFD) for modeling Open Channel flows over common hydraulic structures such as PKW for small discharges with the entire range of head to height ratio h/P from 0.035 to 0.1, where h is not the total head upstream of PKW but the head measured at the crest of PKW. The numerical results have been validated with experimental results. Since the discharge is minimal surface tension force has been incorporated in the numerical model. The numerical model is a half PKW unit model with the same geometrical parameters as the experimental setup from Literature. The results show that CFD simulations can reproduce flow depths near PKW with reasonably good accuracy. The present paper compares the head obtained from CFD with that of empirical formula in the Literature but with head measured at the crest of PKW. Investigation of water surface profile and velocity profile near the upstream of PKW has also been carried out.

A Methodical Assessment of Floodplains in Mixed Land Covers Encompassing Bridges in Alabama State: Implications of Spatial Land Cover Characteristics on Flood Vulnerability

The mixed land covers encompassing bridges (MLB) are integral indicator of the socio-economic hydrological system, and their progressions are vital for flood risk assessment. However, most of the previous studies have neglected a thorough evaluation of MLBs (e.g., types, areas, and depths) on impacting flood vulnerability. This paper addresses this research gap by methodically assessing the spatial characteristics of MLBs in floodplains and their divergent impacts on flood vulnerability using four case studies of Alabama State in the USA. The hydrological and bridge data were synthesized from United States Geological Survey and National Bridge Inventory, respectively. A union of Hydrologic Engineering Center's-River Analysis System (HEC-RAS), Geographic Information System, and Surface Difference Model were employed to retrieve water surface profiles and floodplain assessments in MLBs. The results highlighted that the occurrence of floodplains was more correlated to flood depths compared to flood areas in the MLBs of Alabama. The spatial contribution of the diverse MLBs in producing deep (19%) and shallow (30%) flood depths in the bridges of Alabama were 49%, while medium flood depths were impacted only on 4% of the MLBs. The highest and lowest flood areas were noticed in the MLBs of pastures and mixed forests, respectively. Overall, the findings implied that the contribution of the individual MLBs in floodplains is multifaceted in the bridges of Alabama with spatially varying land cover distribution. Further, it is recommended that for assessing flood vulnerability, the stakeholders should focus not only on the MLBs but also on its spatially dynamic characteristics.

A Study on the accuracy of finite volume numerical models with non-rectangular mesh

During numerical simulation of complex geometries and flow depth variations, non-rectangular computational cells are to be generated. However, application of this kind of mesh cause numerical errors. A 3-D model, which was verified and validated before, was used to illustrate the problem in a simple open channel flow. A zigzag computational mesh was used to study the effect of non-rectangular cells on the accuracy of the model. Results showed that water surface and velocity profiles oscillated around the correct answer. Investigating the reason for this oscillation showed that assuming constant velocity at non-rectangular computational cell surfaces, which is a usual practice in all numerical schemes, cause this error. Variation of velocity at mesh surfaces was then added to the computation model and as a result, the oscillations in velocity profiles and water surface were eliminated. Further analysis showed that this is a general problem in any finite volume model with non-rectangular mesh.

Numerical Modeling of Venturi Flume

In order to measure flow rate in open channels, including irrigation channels, hydraulic structures are used with a relatively high degree of reliance. Venturi flumes are among the most common and efficient type, and they can measure discharge using only the water level at a specific point within the converging section and an empirical discharge relationship. There have been a limited number of attempts to simulate a venturi flume using computational fluid dynamics (CFD) tools to improve the accuracy of the readings and empirical formula. In this study, simulations on different flumes were carried out using a total of seven different models, including the standard k–ε, RNG k–ε, realizable k–ε, k–ω, and k–ω SST models. Furthermore, large-eddy simulation (LES) and detached eddy simulation (DES) were performed. Comparison of the simulated results with physical test data shows that among the turbulence models, the k–ε model provides the most accurate results, followed by the dynamic k LES model when compared to the physical experimental data. The overall margin of error was around 2–3%, meaning that the simulation model can be reliably used to estimate the discharge in the channel. In different cross-sections within the flume, the k–ε model provides the lowest percentage of error, i.e., 1.93%. This shows that the water surface data are well calculated by the model, as the water surface profiles also follow the same vertical curvilinear path as the experimental data.

Analysis of the water surface profiles of spatially varied flow with increasing discharge using the method of singular points

Spatially varied flows with increasing discharge can be encountered in several hydraulic systems. The analysis of water surface profiles in such flow conditions is useful for the verification and design of these systems. In this paper, a comprehensive analysis of the possible flow profiles in non-prismatic trapezoidal channels is performed using the method of singular points, by taking into account bed slope and friction. Different cases are identified depending on whether singular points occur or not along the collecting channel. It is verified that a singular point can be of the saddle, nodal, or spiral type, and that two singular points may occur in special circumstances. Furthermore, water depth profiles may be non-monotonic, showing a minimum or a maximum. The method is applied to both a theoretical example and three experimental tests taken from the literature, and to a real-field case concerning the side spillway channel of a dam.

Infrastructure Study for Solving Connectivity Problems Through the Nile River

Fiber optics cables present various benefits over regular cables when used as a data transportation medium in today’s communication networks. It is noted that there are significant challenges in the connectivity of inner cities that are located far inland away from the coastal areas. Most of the networks developed in Africa, especially in Egypt, are connected via submarine cables flowing across coastal areas. Very few connections are constructed to connect inner cities by crossing the Nile. The Nile River is characterized by a wide area, offering a natural path for underwater cables’ laying areas. In this study, the analysis and evaluation of the laying of these cables along the bed of the Nile River in Egypt, rather than crossing it, is investigated. There are many issues with laying fiber optic cables across the Nile River. Some of these are the requirement of using more than one node over fiber optic cable for each. When the number of nodes increases, the cost of installation and drilling effort increases with each node. The fiber optic cable path along the Nile River is simulated with a numerical model (Delft-3D). Two different scenarios for laying cables were applied and analyzed to evaluate the effect of the predicted water surface and sediment profiles on the fiber optic cable path. Based on the results obtained, the fiber-optic network infrastructure is proposed to solve connectivity problems by laying fiber optic cables along the Nile River.

Sensitivity Analysis of Rock-Fill Dam Break Flood on Different Dam Break Durations

The dam break pattern of rock-fill dams is normally gradual failure. This kind of dam failure is caused by seepage piping or overtopping, in which dam crest overflow is more common. The dam breach expansion process shall depend comprehensively on the structure pattern, material property of dam, and damsite cross sectional topography. And the break duration has a significant impact on the magnitude of break flood and the counter-measures for excess-standard flood. Take the Karot Hydropower Project constructed on the Jhelum River in Pakistan as an example, the dam break mathematical model is set up to analyze the sensitivity of damsite discharge process, downstream highest flood water surface profile and flood peak appearance time to dam break duration. The results show that: with the increase of dam break duration, damsite peak discharge is decreased sharply, flood peak appearance time extends, on-way highest water levels below Karot dam are lowered significantly, and some settlement places below Karot dam can avoid being inundated until the break duration reaches a critical value. If encountering probable maximum flood, the dam break occurs when the reservoir water level reaches dam top EL, some measures can be taken to extend the break duration, so as to effectively reduce the loss of downstream flood. The research results will help to understand the relationship mechanism between rock-fill dam break flood and break duration and provide a scientific basis or some solutions for optimization design of dam and counter-measures of dam break flood.

The Effect of Geometric Parameters of the Antivortex on a Triangular Labyrinth Side Weir

Side weirs are important structural measures extensively used, for instance, for regulating water levels in rivers and canals. If the length of the opening is limited, the amount of water diverted out of the channel and the effective length can be increased by applying a labyrinth side weir. The present study deals with numerical simulations regarding the hydraulic performance of a labyrinth side weir with a triangular plan in single-cycle mode. Specifically, six different types of antivortexes embedded inside it and in various hydraulic conditions at different Froude numbers are analyzed. The antivortexes are studied using two groups, permeable and impermeable, with three different heights: 0.5 P, 0.75 P, and 1 P (P: Weir height). The comparison of the simulated water surface profiles with laboratory results shows that the numerical model is able to capture the flow characteristics on the labyrinth side weir. The use of an antivortex in a triangular labyrinth side weir reduces the secondary flows due to the interaction with the transverse vortexes of the vertical axis and increases the discharge capacity by 11%. Antivortexes in a permeable state outperform those in an impermeable state; the discharge coefficient in the permeable state increases up to 3% with respect to the impermeable state. Finally, based on an examination of the best type of antivortex, taking into account shape, permeability, and height, the discharge coefficient increases to 13.4% compared to a conventional labyrinth side weir.

FLOOD INUNDATION MODELLING FOR TUNGABHADRA BASIN USING HEC-RAS: A CASE STUDY OF HARALAHALLI DISCHARGE SITE

The Hydrologic Engineering Center’s River Analysis System (HEC-RAS) can model flood events and produce water surface profiles over the length of the modeled stream. Flood Inundation Modelling is important for engineers, planners, and government agencies used for municipal and urban growth planning, emergency action plans, flood insurance rates, and ecological studies. This paper describes the application of the HEC-RAS model for the development of floodplain maps for the part of Tungabhadra River, Haralahalli discharge site that lies in Haveri district of Karnataka. Since most of the flood plain area/area vulnerable to flooding is currently used for agriculture. By understanding the extent of flooding and floodwater inundation, we can decide how to best allocate resources to prepare for emergencies. Keywords: Flood; Inundation; HEC-RAS Modelling

Application of the sampling moiré method to shallow open-channel flows with circular roughness elements

This research presents an application of the sampling moiré method, a novel technique originally developed for measuring slight deformation of a static object such as a plate, to fluctuating free water surface in rough open channel flows. The method was used to capture the two-dimensional water surface deformation at a high sampling rate by dyeing the color of water white. The target flow was a very shallow subcritical flow with a depth of 1.5 times the height of the roughness. As a result, a series of instantaneous water surface profiles with non-uniform rough planes were successfully measured at a sampling rate of 100 Hz.It has become clear that the effect of dispersive gravity waves traveling on the water surface is greater than that of non-dispersive waves driven by the turbulence, and that this feature becomes more pronounced as the Froude number increases in such shallow flow conditions. Furthermore, it was experimentally and theoretically verified that the intensity of water surface fluctuation increases with the square of the Froude number. The decomposition of surface fluctuations due to gravity waves and subsurface turbulence using the wavenumber frequency spectrum revealed that the effects of subsurface turbulence are about 20%. This is much less than the contribution from gravity waves in very shallow flows as in this experiment.

Comparison and verification of turbulence Reynolds-averaged Navier\u2013Stokes closures to model spatially varied flows

The robustness and accuracy of Reynolds-averaged Navier–Stokes (RANS) models was investigated for complex turbulent flow in an open channel receiving lateral inflow, also known as spatially varied flow with increasing discharge (SVF). The three RANS turbulence models tested include realizable k–ε, shear stress transport k–ω and Reynolds stress model based on their prominence to model jets in crossflows. Results were compared to experimental laser Doppler velocimetry measurements from a previous study. RANS results in the uniform flow region and farther from the jet centreline were more accurate than within the lateral inflow region. On the leeward side of the jet, RANS models failed to capture the downward velocity vectors resulting in major deviations in vertical velocity. Among RANS models minor variations were noted at impingement and near the water surface. Regardless of inadequately predicting complex characteristics of SVF, RANS models matched experimental water surface profiles and proved more superior to the theoretical approach currently used for design purposes.

Numerical Simulation of Flow over Stepped Spillways with varying Step-Angle

In the present study, the flow over the stepped spillway was ‎ numerically investigated by using Flow3D model. The effect of step angle on different properties of Nappe flow regime such as the water surface profile, location of free-surface‎ aeration inception, Froude number at the ‎spillway’s toe, and pressure, flow velocity, air concentration and cavitation index were evaluated. The realizable k–ε was applied as the turbulence ‎model, and Volume of Fluid (VOF) model was used to determine the free surface flow profiles of the spillway. ‎The model was verified using experimental data. In order to investigate the different ‎characteristics of Nappe flow regime, 17 numerical runs was designed, in which, ‎four step angles, four flow discharge were considered to investigate the flow characteristics over the stepped spillway. The results indicated that the numerical model is well suited with the experimental data over the stepped spillway (RMSE = 0.147 and ARE = 6.9%). In addition, with increasing the step angles, the aeration inception point is generally moved ‎downstream. By increasing the step angles from zero to 10 degrees, the Froude number does not change ‎significantly, however, at the angle of 15 degrees, the Froude number decreases by about 42 ‎percent.

A Cartesian cut-cell based multiphase flow model for large-eddy simulation of three-dimensional wave-structure interaction

A multiphase flow numerical approach for performing large-eddy simulations of three-dimensional (3D) wave-structure interaction is presented in this study. The approach combines a volume-of-fluid method to capture the air-water interface and a Cartesian cut-cell method to deal with complex geometries. The filtered Navier–Stokes equations are discretised by the finite volume method with the PISO algorithm for velocity-pressure coupling and the dynamic Smagorinsky subgrid-scale model is used to compute the unresolved (subgrid) scales of turbulence. The versatility and robustness of the presented numerical approach are illustrated by applying it to solve various three-dimensional wave-structure interaction problems featuring complex geometries, such as a 3D travelling wave in a closed channel, a 3D solitary wave interacting with a vertical circular cylinder, a 3D solitary wave interacting with a horizontal thin plate, and a 3D focusing wave impacting on an FPSO-like structure. For all cases, convincing agreement between the numerical predictions and the corresponding experimental data and/or analytical or numerical solutions is obtained. In addition, for all cases, water surface profiles and turbulent vortical structures are presented and discussed.

Experimental and Numerical Investigation of Flow Over Ogee Spillway

Ogee type spillway is one of the most preferred sluice types due to its functional suitability and high safety factor. It is used for controlling the flow rates and water levels in reservoirs, such as lowering the water level in emergency situations, maintaining normal river functions and discharging excess water. The main aim of this study is to investigate the flow over ogee type spillway by performing experiments in an open channel flume in the laboratory and simulating with numerical model. The numerical model having the same dimensions with the physical model is modeled with two different programs of ANSYS-Fluent and OpenFOAM. The flow depths of the models were measured at four points, H1, H2, H3, H4. In the numerical analysis, two different turbulence models, K-e and K-ω SST turbulence model were used in order to investigate the accuracy of the turbulence models in the open channel. According to the results, R2 values, obtained from ANSYS- Fluent for the each measurement points where H1, H2, H3, H4, are 0.9776, 0.9859, 0.9701, 0.9916 and obtained from OpenFOAM for the each measurement points 0.9920, 0.9687, 0.9855, 0.9926 respectively. The findings show that the numerical tools have been sufficiently developed to simulate flow depths and water surface profiles.

Analysis of water surface profile and flood discharge of Cijangkelok river

The downstream of Cisanggarung River Basin is often affected by floods with an increasing degree of intensity every year. For instance, the 2017 severe floods caused economic losses and fatalities, especially along the border of Cirebon and Brebes Regency. The flood was attributed to high rainfall intensity and the meeting point between Cisanggarung River and the Cijangkelok River. Therefore, a study on the flood in this area is highly vital to reduce the affected area in the future. This study aims to analyze the maximum flood discharge capacity in the Cijangkelok River and analyze cross-sectional river capacity using numerical model simulations. Based on the hydrological calculations and analysis, it is known that the planned flood discharge in the Cijangkelok River in the 5-year return period is 256,25 m3/s, the 10-year return period is 310,35 m3/s, the 25-year return period is 392,91 m3/s, and the 50-year return period is 465,93 m3/s. The analysis of the water surface profile of each flood discharge return period shows that overflow occurs in the cross-section 4090, 8254, 9166, 9753, and 11970. It is also revealed that the existing cross-section of the Cijangkelok River is unable to accommodate hydrological discharge. Field visit results show that the river has siltation or sedimentation, the river embankments are irregular, and land-use changes around the Cijangkelok River that affects the river.

Hydraulics of sharp-crested weir culverts with downstream ramps in free-flow, partially, and fully submerged-flow conditions

Laboratory experiments were conducted to investigate the hydraulics and discharge characteristics of sharp-crested weir culverts with downstream ramps for hydraulically smooth wall boundary and for free, partially submerged, and fully submerged-flow conditions. Four weir-culvert models were tested with different weir heights, ramp lengths, and culvert heights. The partially submerged-flow conditions were created when a slight increase in tailwater caused the headwater to rise due to partial submergence of the culvert. In this flow regime, supercritical flow over the ramp interacted with culvert outflow and this flow regime was classified as Supercritical Jet Interaction Regime or SJIR. Once tailwater reached the weir crest, the weir flow regime became submerged indicating fully submerged-flow condition. Based on the variations of water surface profiles, submerged flows were further classified into Surface Jump Regime (SJR), Surface Wave Regime (SWR), and Deeply Submerged Regime (DSR) and the boundaries between each flow regime were defined by regime plots. To predict discharge of weir culverts with downstream ramps, variations of discharge coefficient with weir geometry and flow regimes were studied and empirical formulations were developed. In addition, free and partially submerged flow discharges were predicted by implementing the interaction factor. It was found that the interaction factor was independent of the Froude number in SJR, while it correlated with the Froude number in SJIR. Under submerged-flow conditions, evaluation of the discharge characteristics of the proposed weir-culvert model showed correlations with water surface flow regimes and a three-stage prediction formula was proposed for estimation of submerged flow. The energy losses over weir-culvert models were also calculated and it decreased with submergence.

Laboratory investigation of coastal beach erosion processes under storm waves of slowly varying height

Storm-induced large coastal waves are a predominant driver for coastal erosion problems, but the physical processes of storm erosion have not been fully understood due to some technical difficulty in simulating storm waves with timely varying heights in the laboratory and collecting storm beach profiles in the field. In this study, novel series of experiments are proposed to study sandy beach processes under coastal storm conditions in a laboratory wave flume of 60 m long, 3 m wide and 1.5 m high. Two water depths of h = 0.5 m and h = 0.7 m were used to investigate beach response under low and high tidal levels. Two initially uniform plane beach slopes of tanβ=1/15 for dissipation beach and tanβ=1/5 for reflection beach were used to study beach profile changes. Additionally, intermediate beach tanβ=1/10 was also experimentally investigated under regular waves in another wave flume of 30 m long, 0.6 m wide and 1 m high. Non-intrusive instrumentation of high-resolution cameras was used to record time-series photo images on beach profile evolution in spatial resolution of 0.2 cm and a temporal resolution of 0.1 s. Image analyzing techniques were also developed to transform the recorded photo images to digital data on both beach and water-surface profiles. In analyzing the collected data, it is found that the variation of storm wave height results in changes of wave breaking point and also sediment transport direction before and after the wave breaking point. Sediment transport direction was found to move onshore initially under small storm waves, and then a sand-bar was generated and a certain portion of sediment also moved offshore under large waves, but such monotonic relationship between sediment transport and wave forcing could transform as morphology feedback and phase lags between wave orbital fluid velocity and sediment concentration. The wave energy flux at the breaking point is shown to be suitable parameter in predicting beach mass change or storm erosion rate, while the dimensionless sediment settling velocity parameter Ω′ may not be a suitable criterion for predicting beach erosion or accretion under storm waves.

Experimental Study on Dam-Break-Like Tsunami Surge Impacts on Small Balls Climbing on Different Slopes

An experimental study was carried out to investigate the tsunami surge impacts on small balls climbing on different slopes. Dam-break flows were generated in a flume to simulate tsunami surge. The water surface profiles at the sluice gate were observed, the tsunami inundation height and the surge velocity in the flume were measured, and the maximum climbing heights of small balls on different slopes were recorded. Results show that the dam-break speed and the tsunami surge strength increase with increasing reservoir water level. The increasing tsunami inundation height, the decreasing ball density, and the decreasing ball diameter have positive effects on the maximum ball climbing height. Based on the normalized experimental data, equations for estimating the maximum ball climbing heights on different slopes were proposed as functions of the inundation height, the ball diameter, and the ball density. The calculated values from the equation are generally within [Formula: see text]% of the measured values in the experimental ranges.

A new one-dimensional numerical model for unsteady hydraulics of sediments in rivers

This paper presents the model UMHYSER-1D (Unsteady Model for the HYdraulics of SEdiments in Rivers 1-D), a one-dimensional hydromorphodynamic model capable of representing water surface profiles in a single river or a multiriver network, with different flow regimes considering cohesive or non-cohesive sediment transport. It has both steady and unsteady flow and sediment modules. For steady gradually varied flows, UMHYSER-1D uses the standard step method to solve the energy equation and the “NewC” scheme for the de St Venant equations. For sediment transport, UMHYSER-1D uses two methods: for long-term simulation, the unsteady terms of the sediment transport continuity equation are ignored, and a non-equilibrium sediment transport method is used. For short-term simulation, the convection–diffusion equation, with a source term arising from sediment erosion/deposition is solved using the fractional step method. The equation without the source term is solved with an implicit finite-volume method, then the equation with source term is solved. Internal boundary conditions, such as time-stage tables, rating curves, weirs, bridges, and gates are simulated. Incorporated is the active layer concept, which allows selective erosion, enabling the simulation of bed armoring. Non-cohesive sediment transport equations and cohesive sediment physical processes are applied to calculate the sediment deposition and erosion. Finally, UMHYSER-1D empirically accounts for bed geometry adjustments by using a relationship between erosion width and flow rate, an angle of repose condition for bank stability and three minimization theories. The presented validation and application cases show UMHYSER-1D’s capabilities and predicts its promising role in solving complex, real engineering cases.