Water Surface Velocity Research Articles

Simulation research on hydraulic characteristics of conical X-shaped flaring gate piers in lock chamber based on CLSVOF method

3-D numerical simulation was carried out for flood discharge and energy dissipation process of conical X-shaped flaring gate piers in a hydropower project by using coupled Level Set and VOF method and RNG k-ε turbulent model. The change laws of flow pattern, water surface profile, velocities and pressures distributions in lock chamber of conical X-shaped flaring gate piers were gained. The results of numerical simulation were compared with the model test data and good agreement was found. The numerical results show that, there are differences on both of water surface profiles in lock chamber. With the increase of discharge, water surface profiles falls at the longitudinal axis and vertical diffusion of ski-jump flows are large on the downstream of flaring gate piers.

Physical modeling of vanishing bores in open-channel flows

When an undular bore propagates upstream against a subcritical flow in a flat channel, its leading front may weaken and vanish. The present study physically investigated the entire decaying process of vanishing bores in a relatively large facility. The invert was made of mobile or fixed natural river gravel. Detailed sampling of water surface elevations and velocities was performed in combination with high-resolution photos and video recordings. Despite some increased turbulence characteristics linked to the bore front arrival, no sediment motion was observed underneath the vanishing bores. The quantitative results provide a unique benchmark dataset for further study of later-stage bore propagations.

Simulation of flow around a permeable dike using physical and 3D-CFD models

ABSTRACT In this research, complementary numerical and experimental physical models were conducted to investigate flow parameters around an isolated permeable spur dike using ANSYS FLUENT ver. 16.1 software. The volume of fluid method VOF with the help of CFD technique and the turbulence model was used to simulate the complex free-surface flow by applying a geometric reconstruction scheme. Two different mediums with different porosities were used, namely, gravel and glass beads. It was found that, for low flow rate values, there are no significant changes in the water profiles in both longitudinal and lateral directions for both media. Although for high flow rate values, the differences tend to be clearer. Results showed that there is a slight effect of the medium's properties if the dike width is less than 1/3 of width of the channel, in particular with low flow rate values. Good agreement was observed between the computational and the measured results for the water surface profiles. Also, there is an exact match between the lateral velocity distribution of gravels and glass beads. Downstream the dike, the lateral velocity profiles exhibit an S shape curve due to high velocity in the free flow and small flow velocity behind the porous dike. The results show good agreement between the CFD results and the experimental observations of the water surface profiles and velocity distribution according to the statistical analysis using some standard indexes error.

A well-balanced and positivity-preserving SPH method for shallow water flows in open channels

A well-balanced and positivity-preserving meshless method based on smoothed particle hydrodynamics (SPH) is developed to simulate one-dimensional (1D) and two-dimensional (2D) shallow water (SW) flows in open channels with irregular geometries. A new form of the characteristic equations that govern the water-surface level and water velocity is introduced to specify the numerical inflow/outflow boundary conditions. An additional condition, derived from temporal discretization to determine the time-step size, forces the water depth to be positive. A 1D finite volume shallow water (FVSW) model based on the first-order Godunov upwind method is built to conduct a comparison of the 1D meshless-based and mesh-based SW models. Six benchmark cases – still water, single trapezoidal and rectangular and prismatic and non-prismatic channels, and a dendritic channel network – are employed to validate the proposed models and compared with the exact and mesh-based numerical solutions. A real-world case of the Chicago Area Waterways System (CAWS) is investigated to highlight the performance of the proposed 1D model for a practical hydraulic system.

EDNA is a useful tool to evaluate the success of the eradication program of Xenopus laevis in Portugal

Biological invasions are widely recognized as a major driver of global biodiversity loss. The most cost-effective answer is often population eradication, while the number of individuals is still limited. The detection of the invasive species at low densities is essential for eradication success, which can be difficult using traditional methods. Environmental DNA (eDNA) can facilitate the detection and monitoring of invasive aquatic species at low densities and can be more sensitive than traditional sampling. The African clawed frog (Xenopus laevis) is a highly invasive species and has been recorded in several European countries. In Portugal, the species was discovered in 2006 and since 2010, streams of the Lisbon area, suspected or at risk of invasion, are being monitored every year and removal is ongoing. The main method of detection is electrofishing but methods like draining artificial ponds have also been used. This program so far succeeded in containing the spread and reduced frog abundance, although total eradication has not yet been accomplished. To evaluate the success of this program, we collected water samples from fifteen sites. In each site we sampled both pools and riifles to test if lotic microhabitat influences X. laevis eDNA detection and concentration. Surface water velocity in each sampling point was also measured. We filtered the samples, extracted DNA from filters, and assayed the extracted DNA for X. laevis DNA using quantitative polymerase chain reaction (qPCR). From the fifteen sites sampled, five were positive for X. laevis eDNA: four lotic sites and one lentic site. Local eradication success was evident mainly in lentic habitats, and three potential failures were also identified. Finding X. laevis at one of these sites only after X. laevis eDNA detection was an important contribution of this technique for the success of the control and eradication program. No significative differences were found between lotic microhabitat (riffles and pools) regarding X. laevis eDNA concentration and detection but velocity affected the concentration of X. laevis eDNA captured. Our results corroborate other studies that recommend eDNA as a complementary sampling approach to other traditional methods and suggests its suitability as a tool for the detection of invasive amphibians. To be presented as a flash oral presentation at the DNAQUA International Conference - First international conference on the use of DNA for water biomonitoring.

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.

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 on thermal performance of multirow helically coiled tube heat exchanger for surface water heat pump system

Owing to their good heat transfer advantage, multirow helically coiled tubes (MHCTs) have been widely used in industrial engineering, including surface water heat pump systems. To investigate the thermal performance of MHCTs at low surface-water velocities, a detailed numerical simulation is conducted based on a previous experimental system. The SST k–ω turbulence model and temperature dependent properties are used. The special feature in this study is that the heat convection inside and outside the tube is concerned instead of using constant heat flux or wall temperature. The results show that the variation characteristics of the Nusselt number and the outer wall temperature of the MHCT are consistent with the experimental results. Owing to the velocity attenuation of surface water flowing through the MHCT, the convective intensity in the negative area is lower than that in the positive area by more than 50%. When the natural convection is enhanced and the forced convection is weakened on the surface-water side, the outside Nusselt number decreases with the rows. Therefore, if the temperature of the surface water is not ideal or the velocity is small, the row number should not be extremely high. Moreover, the average inside Nusselt numbers corresponding to the average coil diameter are similar to the results of the MHCT. The effect of the flow direction of the medium on the thermal performance is insignificant and hence negligible.

Two-Dimensional Numerical Modeling of Flow in Physical Models of Rock Vane and Bendway Weir Configurations

While there are a wide range of design recommendations for using rock vanes and bendway weirs as streambank protection measures, no comprehensive, standard approach is currently available for design engineers to evaluate their hydraulic performance before construction. This study investigates using 2D numerical modeling as an option for predicting the hydraulic performance of rock vane and bendway weir structure designs for streambank protection. We used the Sedimentation and River Hydraulics (SRH)-2D depth-averaged numerical model to simulate flows around rock vane and bendway weir installations that were previously examined as part of a physical model study and that had water surface elevation and velocity observations. Overall, SRH-2D predicted the same general flow patterns as the physical model, but over- and underpredicted the flow velocity in some areas. These over- and underpredictions could be primarily attributed to the assumption of negligible vertical velocities. Nonetheless, the point differences between the predicted and observed velocities generally ranged from 15 to 25%, with some exceptions. The results showed that 2D numerical models could provide adequate insight into the hydraulic performance of rock vanes and bendway weirs. Accordingly, design guidance and implications of the study results are presented for design engineers.

A Drone‐Borne Method to Jointly Estimate Discharge and Manning's Roughness of Natural Streams

AbstractImage cross‐correlation techniques, such as particle image velocimetry (PIV), can estimate water surface velocity (v surf) of streams. However, discharge estimation requires water depth and the depth‐averaged vertical velocity (U m ). The variability of the ratio U m /v surf introduces large errors in discharge estimates. We demonstrate a method to estimate v surf from Unmanned Aerial Systems (UASs) with PIV technique. This method does not require any ground control point (GCP): the conversion of velocities from pixels per frame into length per time is performed by informing a camera pinhole model; the range from the pinhole to the water surface is measured by the drone‐borne radar. For approximately uniform flow, U m is a function of the Gauckler‐Manning‐Strickler coefficient (K s ) and v surf. We implement an approach that can be used to jointly estimate K s and discharge by informing a system of two unknowns (K s and discharge) and two nonlinear equations: i) Manning's equation and ii) mean‐section method for computing discharge from U m . This approach relies on bathymetry, acquired in situ a priori, and on UAS‐borne v surf and water surface slope measurements. Our joint (discharge and K s ) estimation approach is an alternative to the widely used approach that relies on estimating U m as 0.85·v surf. It was extensively investigated in 27 case studies, in different streams with different hydraulic conditions. Discharge estimated with the joint estimation approach showed a mean absolute error of 19.1% compared to in situ discharge measurements. K s estimates showed a mean absolute error of 3 m1/3/s compared to in situ measurements.

PHYSICAL MODEL INVESTIGATION OF PARCEL SCALE MANGROVE EFFECTS ON FLOW HYDRODYNAMICS AND PRESSURES AND LOADS IN THE BUILT ENVIRONMENT

Rising seas, tropical cyclones, and tsunamis threaten increasingly populated coastal areas, leaving coastal communities searching for sustainable, resilient adaptation solutions to mitigate the impacts of chronic and acute coastal flood hazards. This work specifically investigates parcel-scale effects of the Rhizophora mangle (red mangrove) species during extreme wave and/or storm surge conditions. We constructed 100 physical models of the Rhizophora species' trunk-prop root system on a 1:16 scale, and conducted tests in Oregon State University's Directional Wave Basin to measure the effects of mangroves of varying cross-shore thickness on water surface elevation, water velocities, and load reduction on idealized inland structural elements. The presence of mangroves affected hydrodynamic conditions near the mangroves and reduced pressures and forces on inland structures.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/XjtCmHYvgVQ

Flow characteristics in open channels with aquatic rigid vegetation

In order to study the flow characteristics in water bodies with rigid aquatic vegetation, series of laboratory experiments are carried out in an open channel, in which glass rods are used as plants with diameters of 6mm, 8mm and 10mm, respectively. For each diameter of glass rods, four typical cases are considered with various densities and arrangements of glass rods. The flow velocities in the four cases are measured by the 3-D laser Doppler velocimeter (LDV). The water surface slope, the flow velocity, the water head loss, the vegetation drag force and the hydraulic slope are calculated, analyzed and discussed. The horizontal, vertical and total vegetation densities in the vegetation area are defined and the relationship between these physical parameters and the water surface slope are studied. The head loss and the hydraulic slope in the vegetation area are also calculated, compared and analyzed. It is indicated that the water surface slope and velocity, the head loss and the hydraulic slope in the vegetation area have a close relationship with the arrangement, the density, and the plant diameter of the vegetation.

Real-Time, Inexpensive, and Portable Measurement of Water Surface Velocity through Smartphone

The purpose of this research is to propose a real-time, inexpensive, and portable method for measuring water surface velocities, in which a particle tracking velocimetry (PTV) system is developed by using a smartphone device. The system uses the mobile camera to capture the tracer floating on the river surface, whose movement is expected to represent the velocity of the water surface. The recorded tracer images are identified from the background by using the normalized RGB color model. The magnification ratio, which transforms the distance in pixel to the real distance, is estimated by using the pre-specified mobile height from the water surface, or the characteristic length of the tracer. The proposed system is built based on the iPhone 6s device. The system is tested in two cases. One case is the artificially generated images recording the movement of table tennis, and the relative error does not exceed 3%. The other is the comparison to the velocity measured by acoustic doppler current profilers (ADCP) in the river, and the relative error is not more than 15%. Finally, the limitation of the proposed method is discussed.

Physical model investigation of mid-scale mangrove effects on flow hydrodynamics and pressures and loads in the built environment

Large (km-scale) mangrove forests can provide protection to shorelines and near-coast structures during extreme coastal flood events, including tsunamis and tropical cyclones. However, little is known about the effects of mangroves with a modest cross-shore thickness (~10–50 m), on flow hydrodynamics and resulting inland pressures and forces on near-coast structures. We constructed a 1:16 geometric-scale physical model of a Rhizophora mangle (red mangrove) fringe with modest cross-shore thickness to measure the effects of a mangrove forest's cross-shore thickness on wave attenuation and subsequent load reduction on near-coast structures, idealized during experiments with an array of cubes. Three configurations, one baseline with zero mangroves and two with mangrove cross-shore thicknesses corresponding to prototype-scale forest widths of 8.2 m and 19.0 m, were considered in front of an array of idealized slab-on-grade residential buildings. Transient wave conditions with varying incident parameters (wave amplitude, wave representative time scale, water level/mangrove emergence, and presence of a background current) were considered. Water surface elevations, water velocities, cross-shore forces, and pressures measured near and against the building array indicate that mangroves affected inland flow hydrodynamics and forces. The presence of mangroves was associated with elevated water levels and reduced peak velocities between the mangroves and inland structures. Increasing the mangrove cross-shore thickness reduced the cross-shore force on a structure by 11%–65% compared to the baseline case without mangroves. The force reduction by the mangrove configurations varied with incident wave representative time scale; waves with longer representative time scales required larger cross-shore thicknesses to provide similar force reductions to those observed for shorter waves. Further investigation into a wider range of mangrove cross-shore thicknesses, trunk densities, and wave conditions is needed to inform engineering performance of natural and nature-based features for resilient coastal design.

Scale issues and the effects of heterogeneity on the dune-induced hyporheic mixing

Hyporheic mixing plays a vital role in physical, biogeochemical, and thermal processes in river networks. While many studies have emphasized the role of streambed heterogeneity in hyporheic mixing processes, this study articulates the scale issues inherent in concentration, mixing, heterogeneity, and modeling approaches. It subsequently conducted simulations of hyporheic mixing in synthetic, heterogeneous, 2-D cross-sectional river beds based on prescribed hydraulic conductivity defined at the local-scale. It then investigated the flux variation distribution and the mixing zone under different degrees of heterogeneity and flow scenarios. Since the characterization of the heterogeneities in detail at the local scale is practically impossible, Monte Carlo simulation based on stochastic theory was used to demonstrate the hyporheic mixing under the large-scale control volume (macromixing). Afterward, a first-order stochastic analysis was undertaken to explore the relationship between local-scale flux variance distribution and the mixing zone under different heterogeneity and flow scenarios. The results of this study show that the flux variance in the streambed is an appropriate metric for assessing the magnitude of hyporheic mixing at all scales. Further, surface water velocity and upwelling groundwater are found to be the dominant controlling factors of the flux variance and in turn, the mixing process, followed by the streambed heterogeneity. In addition, it demonstrates that the hyporheic mixing process is significantly affected by the complex surface and groundwater circulation regimes and the stagnation zone under steady-state flow conditions.

MAPPING OF WATER SURFACE LEVELS AND SLOPES WITH SINGLE PHOTON LIDAR – A CASE STUDY AT THE RIVER RHINE

Abstract. Precise knowledge of water surface level heights is crucial for safe ship navigation and as basis for calibration of hydrodynamic-numerical models. While Airborne Laser Scanning (ALS) is a well established technique for topographic mapping, ALS-based water surface mapping using conventional infrared lasers suffers from the high degree of specular reflection which leads to data voids for off-nadir angles beyond 5–7 degrees. The advent of single photon sensitive ALS systems using green laser sources presents the prospect of large-area, high-resolution water surface mapping due to the high receiver sensitivity and measurement rate of such systems. Building on previous studies on subject matters, we present the results of a pilot project initiated and conducted by the German Federal Institute of Hydrology (BfG, Koblenz) at the Rhine River. Three specific test sites with varying water surface and flow velocity properties were captured on October 30th and 31th, 2019 with the Leica SPL100 from flying altitudes of 3000 m, 2500 m, 1600 m, and 800 m, respectively. As anticipated, the water surface laser pulse density was high and exhibited 20–145 points/m2 depending on flying altitude. After quality control, strip adjustment, and point cloud analysis, three water surface classification methods were implemented based on: (i) height quantiles, (ii) point cloud segmentation, and (iii) inverse DTM filtering. All approaches featured relative and absolute water level height accuracies better than 10 cm. We conclude that Single Photon LiDAR based high resolution mapping of water surface levels and tilts is feasible when employing application specific data acquisition parameters, i.e., off-nadir angle ≤10° and flying altitude ≤3000 m.

Estimation of Water Surface Flow Velocity in Coastal Video Imagery by Visual Tracking with Deep Learning

Kim, J. and Kim, J., 2020. Estimation of water surface flow velocity using coastal video imagery by visual tracking with deep learning. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 522-526. Coconut Creek (Florida), ISSN 0749-0208.This paper describes the method of flow velocity estimation of water surface in video imagery by tracking waves using deep neural network for visual object tracking with unsupervised learning. The model of deep neural network consists of two stages for scene separation and image registration to extract waves only and track the propagated waves, respectively. The dataset of video imagery acquired at Anmok beach of south Korea has been used to training the model and it learns the behavior of propagated waves. The performance of model is evaluated by measuring image similarity using test dataset. And the estimated flow velocity of water surface in propagated waves is compared with the flow from conventional image processing method of particle image velocity. The results show that our proposed approach with deep learning method is very promising to measure and predict coastal waves especially in the surf zone.

Flood mapping using hydraulic modeling and Sentinel-1 image: Case study of Medjerda Basin, northern Tunisia

In northwestern Tunisia, floods are the most widespread natural hazard. Indeed, this problem is posed seriously in the Medjerda basin. In fact, the plain of Jendouba - Bou Salem is the most affected area by this plague. It has the form of a shallows that collects runoff water and promotes flood extent and duration. So the main objective of this study is to determine the extent of the hydraulic hazard through the flood mapping of February 2015 event which has seriously affected the urban and peri-urban landscape of the plain. The hydraulic hazard extent mapping was determined through the HEC-RAS model. It's one of the most popular free hydraulic models developed by the Hydrological Engineers Center of the U.S. Army Corps. The new version (HEC-RAS v-5) is a two dimensional (2D) model based on the resolution of hydraulic Saint Venant which can simulate floodplain inundation, determine the water surface elevation and velocity distribution of floods. It allows modeling flow with permanent and non-permanent free surface by evaluating water flows and heights over the all sections of a river so it allows to integrate hydraulic works (bridge, dam …).The result showed that this flood reached heights of more than six (6) meters in flooded areas. The result from the HEC-RAS model was validated using the Sentinel-1 radar image acquired on February 28th, 2015.The study shows the applicability and the capabilities of the 2D HEC-RAS version for flood studies.

Transport of citrate and polymer coated gold nanoparticles (AuNPs) in porous media: Effect of surface property and Darcy velocity

With the release of nanoparticles (NPs) into the subsurface, it is imperative to better understand the fate and transport of NPs in porous media. Three types of stable AuNPs were used as model NPs to investigate the impact of surface coatings (type and coverage) and water velocity on the NP transport in a porous media (column studies). The NPs were electrostatic stabilized citrate AuNPs and sterically stabilized AuNPs with amphiphilic block co-polymer (PVA-COOH) in two particle/polymer ratios (weak vs. strong stabilization). The citrate AuNPs transport was sensitive to ionic changes in the mixing front of the plume, where destabilization occurred, and will therefore depend on the size/type of release. Blocking of deposition sites by aggregates was seen to facilitate transport, whereby a higher flow velocity (larger shadow zone) also resulted in better transport. The polymeric surface coating had great impact with steric repulsion as a main force contributing to the transport of NPs in the porous media. Sufficient polymer coating was crucial to obtain highly unfavorable attachment conditions (very low α) where the enhanced NP mobility was independent of the water velocity (comparable to solute tracer). Without sufficient steric stabilization, the transport and recovery was significantly reduced compared to the solute tracer, but increased with increasing water velocity. This highlights the importance of sufficient surface coating to achieve enhanced mobility, but also the increased risk of spreading to down-gradient receptors. For the (weakly) sterically stabilized NPs, the loss of polymer through ligand exchange with the porous media negates transport.

Real-Time and Automatic River Discharge Measurement With UHF Radar

River discharge measurement is of great significance, and as such, many methods and measuring instruments have been developed by many hydrologic researchers. However, most commonly used measuring instruments must be in contact with the water and are difficult to place and maintain. In this letter, a noncontact measurement method is proposed using ultrahigh- frequency (UHF) radar. The index-velocity method is employed to calculate the mean cross-sectional velocity, and the water-surface velocities on the cross section detected by the UHF radar are used to select the optimum index velocity. A field experiment was conducted in the Hanjiang River at Xiantao, Hubei, China, from March to July 2018. Data from March to June were processed for selecting the optimum index velocity, and the maximum water-surface velocity of the cross section was proven to be optimal. The fit relationship between the mean cross-sectional velocity and the index velocity was used to estimate the mean cross-sectional velocities and river discharges for June to July. The results were compared with those provided by the Hubei Xiantao hydrologic station, and the errors were mostly within ±5%. This confirms that the UHF radar can be used to accurately, automatically, and continuously measure river discharge.