Water Surface Velocity Research Articles

Heat transfer analysis of multi-row helically coiled tube heat exchangers for surface water-source heat pump

An experiment system simulating the uniform flow of surface water with low velocities was established to investigate the heat transfer performance of multi-row helically coiled tube (MHCT) heat exchangers for surface water-source heat pump. Four experimental modes of variable temperatures and velocities of surface water and medium were performed on eight MHCT configurations with different geometric parameters including horizontal spacing, vertical spacing and tube length. The results demonstrate that when the surface water velocity changes and the other parameters are constant, the outside Nusselt number depends on the Reynolds number. Conversely, it depends on the Rayleigh number. Both the inside and outside Nusselt numbers increase with vertical spacing and horizontal spacing. The effect of vertical spacing is more obvious on the outside Nusselt number, but can be neglected on the inside Nusselt number. By comparison, the correlations of single-row helically coiled tubes cannot accurately calculate the inside Nusselt number of the MHCT, and the influence of surface-water velocity on the outside Nusselt number is not negligible. The correlations for the prediction of the inside and outside Nusselt numbers are developed. Additionally, the effect of tube length on the Nusselt number is small, and can be ignored for engineering applications.

Airborne Remote Sensing of Surface Velocities in a Tidal River

The global optimal solution (GOS) has proven to be very accurate for deriving water surface velocities from contemporaneous image pairs, but previous studies have used shore-based radars or satellite measurements with resolutions on the order of a kilometer or tens of meters to establish this. In contrast, the objective of this paper is to derive a GOS velocity field from infrared (IR) (3–5 $\mu \text{m}$ ) images having a 1-m pixel size. Because IR images can frequently exhibit a low signal-to-noise ratio, a newly developed GOS technique with a local similarity metric is used to retrieve velocities from such low-contrast data sets. To demonstrate the utility of this new method, we use airborne data collected in the tidal Potomac River over 11 days and spatially varying flood, ebb, and slack conditions. The resulting GOS-derived velocity estimates are compared against acoustic Doppler current profiler (ADCP) measurements taken simultaneously with the airborne collections. Velocity magnitudes and directions are found to have GOS versus ADCP correlations of 0.93 and 0.99, respectively. This high correlation suggests that the GOS technique may be applicable to a variety of lower contrast imagery that can now be collected by a low-altitude remotely controlled aircraft.

Pengaruh Organisme Perifiton dalam Memperbaiki Kualitas Air pada Lahan Basah Buatan Sistem Aliran Air Permukaan Bebas

Mekanisme utama penapisan kontaminan air pada lahan basah adalah aktivitas mikroorganisme. Salah satunya adalah perifiton yang hidup pada substrat terendam air. Oleh karena itu, diperlukan penelitian pengaruh perifiton dalam LBB, yang berperan dalam memperbaiki kualitas air. Tujuan penelitian adalah mengidentifikasi kualitas influen, komposisi alga perifiton, alga perifiton sebagai produsen primer, pengaruh faktor kecepatan aliran air permukaan, kualitas efluen, efektivitas dan efisiensi LBB. Penelitian LBB dilakukan pada bulan Januari 2017 di Bandung. Analisis kualitas air menggunakan SNI dan standar yang berlaku. Hasil penelitian menunjukkan air selokan sebagai influen LBB terkontaminasi air limbah domestik dan beberapa parameter melebihi kriteria kualitas kelas III. Ditemukan tiga kelas alga bentik perifiton (Bacillariophyta, Chlorophyta, Cyanophyta). Perifiton berperan dalam transfer oksigen kekolom air. Faktor kecepatan air permukaan berkorelasi kuat terhadap penapisan nitrat (r = 0,84) dan sangat kuat terhadap total fosfat (r = 0,90). Kualitas efluen yang memenuhi kriteria kelas III hanyaparameter total fosfat dan COD. Efektivitas pengolahan untuk BOD sebesar 6,6% ? 38,3% dan COD 6,0% ? 38%. Efisiensi pengolahan pada debit 0,01 L/s untuk amonium 3,4%; nitrat 39,2%; nitrogen organik 47,1%; fosfat total 53,6%; BOD 38,3%; COD 38%; deterjen 76,5%.

Experimental and Numerical Investigation of the Flow Hydraulic in Gradual Transition Open Channels

Channel expansions are common in both natural and artificial open channels. With increasing cross-sectional dimensions in an expansion, the flow decelerates. Due to separation of flow and subsequent eddy formation, a significant head loss is occurred along the transition. This study presents the results of experimental investigations on subcritical flow along the expansive transition of rectangular to trapezoidal channels. Also, a numerical simulation was developed using the finite volume method with Reynolds Stress turbulent model. Water surface profiles and velocity distributions of flow through the transition were measured experimentally and compared with the numerical results. Also, hydraulic efficiency of the transition and coefficient of energy head loss were calculated. The results show that with increasing the upstream Froude number, hydraulic efficiency of the transition and coefficient of energy head loss are decreased and increased, respectively. The results also showed the ability of numerical simulation for simulating the flow separation zones and bed shear stress along the transition for different inlet discharges and inflow Froude numbers.

Application of an Automated Discharge Imaging System and LSPIV during Typhoon Events in Taiwan

An automated discharge imaging system (ADIS), which is a non-intrusive and safe approach, was developed for measuring river flows during flash flood events. ADIS consists of dual cameras to capture complete surface images in the near and far fields. Surface velocities are accurately measured using the Large Scale Particle Image Velocimetry (LSPIV) technique. The stream discharges are then obtained from the depth-averaged velocity (based upon an empirical velocity-index relationship) and cross-section area. The ADIS was deployed at the Yu-Feng gauging station in Shimen Reservoir upper catchment, northern Taiwan. For a rigorous validation, surface velocity measurements were conducted using ADIS/LSPIV and other instruments. In terms of the averaged surface velocity, all of the measured results were in good agreement with small differences, i.e., 0.004 to 0.39 m/s and 0.023 to 0.345 m/s when compared to those from acoustic Doppler current profiler (ADCP) and surface velocity radar (SVR), respectively. The ADIS/LSPIV was further applied to measure surface velocities and discharges during typhoon events (i.e., Chan-Hom, Soudelor, Goni, and Dujuan) in 2015. The measured water level and surface velocity both showed rapid increases due to flash floods. The estimated discharges from ADIS/LSPIV and ADCP were compared, presenting good consistency with correlation coefficient R = 0.996 and normalized root mean square error NRMSE = 7.96%. The results of sensitivity analysis indicate that the components till (τ) and roll (θ) of the camera are most sensitive parameters to affect the surface velocity using ADIS/LSPIV. Overall, the ADIS based upon LSPIV technique effectively measures surface velocities for reliable estimations of river discharges during typhoon events.

Effect of river confinement on depth and spatial extent of bed disturbance affecting salmon redds

ABSTRACTHuman impacts on rivers threaten the natural function of riverine ecosystems. This paper assesses how channel confinement affects the scour depth and spatial extent of bed disturbance and discusses the implications of these results for salmon-redd disturbance in gravel-bedded rivers. Two-dimensional hydrodynamic models of relatively confined and unconfined reaches of the Cedar River in Washington State, USA, were constructed with surveyed bathymetry and available airborne lidar data then calibrated and verified with field observations of water-surface elevation and streamflow velocity. Simulations showed greater water depths and velocities in the confined reach and greater areas of low-velocity inundation in the unconfined reach at high flows. Data on previously published scour depth of bed disturbance during high flows were compared to simulated bed shear stress to construct a probabilistic logistic-regression model of bed disturbance, which was applied to spatial patterns of simulated bed shear stress to quantify the extent of likely bed disturbance to the burial depth of sockeye and Chinook salmon redds. The disturbance depth was not observed to differ between confined and unconfined reaches; however, results indicated the spatial extent of disturbance to a given depth in the confined reach was roughly twice as large as in the unconfined reach.

Numerical modeling of the hydraulic impact of riparian vegetation

This paper presents results of numerical modelling of riverbed segment with riparian vegetation performed with use of CCHE2 software. Vegetation zones are places where dynamic of water flow increases. Therefore, there is a need of careful examination of hydraulic impact structure of such zones. Accurate research is necessary and should be performed with use of physical or numerical models, two or three dimensional. Paper presents distribution of velocity and area of water surface for two variants of vegetation deposition acquired in CCHE2D software and modelled for riverbed with distinctive riparian vegetation. Results point to significant (30–40%) increase of maximal velocities in riverbed with riparian vegetation, while directly near the vegetation there were zones with very low velocities. Local damming occurs before vegetal zone. Maximal shear stress in zones with increased velocity is significantly augmented compared to conditions with no vegetation, which can cause more intensive erosion in those zones

Quantifying the impact of release operations and weather conditions on the flow and temperature dynamics in the cascade-reservoir system

The objective of this study was to investigate the flow dynamics and temperature characteristics under different reservoir operation scenarios and weather conditions in the river-reservoir system, which can be used to set scientific guidelines for river management and conservation planning strategies. The calibrated three-dimensional model provided simulated unsteady water surface elevation, temperature, velocity and discharge at different layers (depths) in different locations. A series of operation scenarios were modeled to understand and quantify formation, propagation, and disappearance of density currents that are resulted from combinations of daily repeated large release (DRLR) of different durations and solar heating. DRLRs (140 m3/s) with longer durations pushed the bottom cold water further downstream and maintained the bottom water temperature cooler. Variations of weather conditions (e.g., drops of air temperature and solar radiation) directly controled variations of bottom-layer water temperature. The daily drop rate of bottom temperature was related to the rate and duration of air temperature drop. Under the practice for the water turbines running at downstream, it clearly showed the shocking withdrawal and stopping effect from the downstream operation. The velocity for the whole cross-section were almost increased with same magnitude of about 0.1 m/s at GOUS and JML.

Population biology of the sea star Anasterias minuta (Forcipulatida: Asteriidae) threatened by anthropogenic activities in rocky intertidal shores of San Matías Gulf, Patagonia, Argentina

In Patagonian coastal areas, intertidal benthic communities are exposed to extreme physical conditions. The interaction between harsh environment and anthropogenic pressure can generate changes in population biology of marine invertebrates, like density and reproduction. The oral brooding sea star Anasterias minuta is a key organism in food chains of Atlantic Patagonian rocky intertidals, hence changes on its population structure can negatively affect shore communities. We studied the population biology of A. minuta and assess the effect of environmental parameters and anthropogenic activities on its population on rocky intertidal shores of San Matías Gulf, Patagonia, Argentina. Seasonal sea surface temperature, pH, salinity, water velocity, desiccation rate, boulders density, and anthropogenic influence (tourists and octopus fishermen) were recorded. In sites with less tourist influence and high refuge, an increase in density was recorded, especially during the summer. Brooding individuals were found in fall and winter, while feeding individuals were observed in all seasons (12 different prey, mainly the molluscs Tegula patagonica and Perumytilus purpuratus). Environmental variables such as boulders density and water velocity were the most important predictor of variation in population structure. Tourism and pH were the most important variables negatively correlated with density. Rev. Biol. Trop. 65(Suppl. 1): S73-S84. Epub 2017 November 01.

Estimating River Bathymetry from Surface Velocity Observations Using Variational Inverse Modeling

AbstractAccurate river bathymetry characterization is important to understanding all aspects of the riparian environment and provides crucial information for ensuring the safe passage of vessels and guiding channel maintenance operations. Verified models based on readily collected physical data facilitate accurate predictions of changes to a riverbed caused by traffic, weather, and other influences. This paper presents a methodology for estimating river bathymetry from surface velocity data by applying variational inverse modeling to the shallow-water equations. The paper describes the mathematical framework for the methodology and the algorithm, and the numerical tools developed to test the methodology. The hydrodynamic modeling uses 2D depth-averaged solvers (under the hydrostatic assumption) and applies a standard empirical correlation that relates depth-averaged velocity to surface velocity. The application of the bathymetry estimation algorithm to water-surface velocity data was tested on a 95-km reach of the Columbia River in Washington State. The root-mean-square error (RMSE) of the estimated bathymetry field relative to the ground truth data is approximately 2 m over the entire reach. The results of the test case indicate that this approach can be used to estimate river bathymetry to a close approximation based on the bank-to-bank surface velocity data on the reach of interest.

Rapidly changing subglacial hydrological pathways at a tidewater glacier revealed through simultaneous observations of water pressure, supraglacial lakes, meltwater plumes and surface velocities

Abstract. Subglacial hydrological processes at tidewater glaciers remain poorly understood due to the difficulty in obtaining direct measurements and lack of empirical verification for modelling approaches. Here, we investigate the subglacial hydrology of Kronebreen, a fast-flowing tidewater glacier in Svalbard during the 2014 melt season. We combine observations of borehole water pressure, supraglacial lake drainage, surface velocities and plume activity with modelled run-off and water routing to develop a conceptual model that thoroughly encapsulates subglacial drainage at a tidewater glacier. Simultaneous measurements suggest that an early-season episode of subglacial flushing took place during our observation period, and a stable efficient drainage system effectively transported subglacial water through the northern region of the glacier tongue. Drainage pathways through the central and southern regions of the glacier tongue were disrupted throughout the following melt season. Periodic plume activity at the terminus appears to be a signal for modulated subglacial pulsing, i.e. an internally driven storage and release of subglacial meltwater that operates independently of marine influences. This storage is a key control on ice flow in the 2014 melt season. Evidence from this work and previous studies strongly suggests that long-term changes in ice flow at Kronebreen are controlled by the location of efficient/inefficient drainage and the position of regions where water is stored and released.

Rectification of Image Velocity Results (RIVeR): A simple and user-friendly toolbox for large scale water surface Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV)

LSPIV (Large Scale Particle Image Velocimetry) and LSPTV (Large Scale Particle Tracking Velocimetry) are used as relatively low-cost and non-intrusive techniques for water-surface velocity analysis and flow discharge measurements in rivers or large-scale hydraulic models. This paper describes a methodology based on state-of-the-art tools (for example, that apply classical PIV/PTV analysis) resulting in large-scale surface-flow characterization according to the first operational version of the RIVeR (Rectification of Image Velocity Results). RIVeR is developed in Matlab and is designed to be user-friendly. RIVeR processes large-scale water-surface characterization such as velocity fields or individual trajectories of floating tracers. This work describes the wide range of application of the techniques for comparing measured surface flows in hydraulic physical models to flow discharge estimates for a wide range of flow events in rivers (for example, low and high flows).

Long-Term 3D Hydrodynamic Modeling and Water Surface Statistics in Marmara Sea

ABSTRACTMarmara Sea (MS) lies in the strategic crossroad, accommodating one of the busiest shipping routes in the world. In general, there is a two-layer current system in the MS and Turkish Straits system; the brackish waters originating in the Black Sea (BS) (18 PSU) moving southward to the Aegean Sea (AS), and a lower layer return flow of saltier Aegean waters (38.5 PSU) back to the BS. This variability poses a challenging task within the modeling perspective. In this research, 3D hydrodynamic modeling of MS is performed in order to investigate the spatial and temporal behavior of elevations between years 2000 and 2015. During the calibration process, the grid configuration, time step, and model coefficients (Manning bed roughness coefficient, a wind drag coefficient and horizontal viscosity are coefficients) are adjusted until the computed solution produced the best match to the observed data such as water surface elevations, velocities, and net discharges. To this end, a series of simulations are made. As a result, the observed and the predicted water surface elevations follow each other very closely. The developed model could accurately estimate the net discharge as well. In order to understand the behavior of MS, elevation pattern is calculated and depicted both on annual and seasonal scales. It is demonstrated that the influence of seasonally varying strong fresh water river discharges of Danube in BS have strong influence on the water mass characteristics of the MS.

Numerical simulation on tunnel spillway of Jingping-I hydropower project with four aerators

This Study presents the results of a three dimensional simulation of a tunnel spillway with four aerators of Jingping-1 hydropower project as done by using ANSYS. The study uses a combination of realizable k-ε turbulence model and volume of fluid method in order to simulate the characteristics of aeration and cavitation in aerated tunnel spillway. It is possible to yield the water surface profile, pressure distribution, velocity profile and aeration cavity length from the simulation. Results of numerical simulation were compared with experimental results showing that the realizable k-ε turbulence model and volume of fluid model can simulate the aerated tunnel spillway. The aerated cavity zone was found to be stable and within reasonable length. Results from the numerical simulation were found to resemble the experimental result to a great extent, showing the validity of the simulation.

Numerical modelling of wind effects on breaking waves in the surf zone

Wind effects on periodic breaking waves in the surf zone have been investigated in this study using a two-phase flow model. The model solves the Reynolds-averaged Navier–Stokes equations with the k − \U0001d716 turbulence model simultaneously for the flows both in the air and water. Both spilling and plunging breakers over a 1:35 sloping beach have been studied under the influence of wind, with a focus during wave breaking. Detailed information of the distribution of wave amplitudes and mean water level, wave-height-to-water-depth ratio, the water surface profiles, velocity, vorticity, and turbulence fields have been presented and discussed. The inclusion of wind alters the air flow structure above water waves, increases the generation of vorticity, and affects the wave shoaling, breaking, overturning, and splash-up processes. Wind increases the water particle velocities and causes water waves to break earlier and seaward, which agrees with the previous experiment.

Estimating discharge in gravel‐bed river using non‐contact ground‐penetrating and surface‐velocity radars

AbstractDischarge measurement is a critical task for gravel‐bed channels. Under high‐flow conditions, the elevation of the riverbed changes significantly by intensive torrential flow. The stage–discharge relations commonly used for stream discharge estimation may no longer be adequate. The contact‐type velocity measuring is also subject to measurement errors and/or instrument failures by the high‐flow velocities, driftwood, stumps, and debris. This study developed a new real‐time method to estimate river discharge in gravel‐bed channels. A systematic measuring technology combining ground‐penetrating radar and surface‐velocity radar was employed. The rating curves representing the relations of water surface velocity to the channel cross‐sectional mean velocity and flow area were established. Stream discharge was then deduced from the resulting mean velocity and flow area. The proposed method was examined in a steep gravel‐bed reach of the Cho‐Shui River in central Taiwan. The estimated stream discharge during three flood events were compared to the prediction by using the stage–discharge relation and the index‐velocity method. The proposed method of this study is capable of computing reasonable values of discharge for an entire flood hydrograph, whereas the other two methods tend to produce large extrapolation errors. Moreover, when the computed discharge is used in 2D flood flow simulation, the proposed method demonstrates better performance than the commonly used stage–discharge and index‐velocity methods.

Cultivation of Scenedesmus dimorphus using anaerobic digestate as a nutrient medium.

In this study, the microalga Scenedesmus dimorphus was cultivated phototrophically using unsterilized anaerobic digestate as a nutrient medium. A bench-scale experiment was conducted by inoculating the microalga S. dimorphus with 0.05-10% dilutions of the anaerobic digestate supernatant. It was found that 1.25-2.5% dilutions, which is equivalent to 50-100mgN/L total nitrogen concentrations and 6-12mg P/L total phosphorus concentrations, provided sufficient nutrients to maximize the growth rate along with achieving high concentrations of algal biomass. The microalgae cultivation was scaled up to 100L open raceway ponds, where the effect of paddlewheel mixing on the growth was investigated. It was concluded that 0.3m/s water surface velocity yielded the highest specific growth rate and biomass concentration compared to 0.1 and 0.2m/s. The microalga S. dimorphus was then cultivated in the raceway ponds using 2.5% diluted anaerobic digestate at 317 and 454μmol/(m2×s) average incident light intensities and 1.25% diluted anaerobic digestate at 234 and 384μmol/(m2×s) average incident light intensities. The maximum biomass concentration was 446mg/L which was achieved in the 2.5% dilution and 454μmol/(m2×s) light intensity culture. Moreover, nitrogen, phosphorus, and COD removal efficiencies from the nutrient media were 65-72, 63-100, and 78-82%, respectively, whereas ammonia was completely removed from all cultures. For a successful and effective cultivation in open raceway ponds, light intensity has to be increased considerably to overcome the attenuation caused by the algal biomass as well as the suspended solids from the digestate supernatant.

Estimating discharge in rivers through the combined use of dimensionless isovels and point velocity measurements

This paper presents a procedure for estimating discharge in a river cross-section based on the combined use of dimensionless isovels and point velocity measurements. Specifically, taking the Biot–Savart law on the magnetic field induced by an electric current in a wire as their basis as already done by other researchers, the authors propose a new formulation of the relationship characterizing the effect of the wetted perimeter on the range of velocities in a cross-section in order to take explicit account of roughness, expressed by means of Manning's coefficient. Once appropriately nondimensionalized, the isoeffect contours can be read as dimensionless isovels. Assuming in situ velocity measurements are available, discharge at a cross-section can be computed using two different methods. The proposed procedure was applied to six case studies characterized by river cross-sections which differed greatly from one another. The results show that the two methods proposed for estimating discharge lead to equivalent outcomes, and in all the cases the procedure as a whole enables a sufficiently accurate estimation of discharge, even when it is based on a limited number of velocity measurements or on the measurement of maximum surface-water velocity alone.

Lagrangian Kinematic Criterion for the Breaking of Shoaling Waves

AbstractAn experimental study was conducted with the aim of validating the Lagrangian kinematic criterion (LKC) for the case of breaking of shoaling waves. Monochromatic wave trains were generated in a large wave flume and allowed to shoal and break naturally on an artificial inclination changeable shore, thus allowing inspection of a range of slopes. Instantaneous horizontal Lagrangian water surface velocity was measured by particle tracking velocimetry and compared to the instantaneous propagation speed of the crest on a verge of breaking, the latter calculated using time series produced by resistance-type wave gauges staged along the flume. The inception of a breaker was found to occur when the monotonically increasing horizontal water velocity on the crest, during the process of steepening, approached that of the slowing steep crest, thus confirming the LKC for shoaling conditions. In addition, an objective method of breaking detection was developed utilizing the phase–time method and wavelet analysis by recognizing a specific pattern in the instantaneous local frequency fluctuations. The two main expected contributions of this study are the formation of an applicable criterion for breaking occurrences in shoaling waves and development of a wave breaking detection method independent of human decision. Incorporation of the suggested criterion into existing waves prediction models can be a significant contribution to maritime projects efficiency, whereas the breakers detection method will be useful for conducting further experimental research on waves breaking both in laboratory installations and in the highly unstable environment of an open sea.

The study of droplet‐laden turbulent airflow over waved water surface by direct numerical simulation

AbstractThe objective of the present paper is to elucidate possible effects of sea spray on the momentum transfer in marine boundary layer under strong wind forcing conditions by performing direct numerical simulation (DNS) of turbulent, droplet‐laden airflow over a waved water surface. Three‐dimensional, turbulent Couette airflow is considered in DNS as a model of a constant‐flux layer in the atmospheric surface layer. Two‐dimensional stationary waves at the water surface are prescribed and assumed to be unaffected by the airflow and/or droplets. Droplets are considered as nondeformable spheres and tracked in a Lagrangian framework, and their impact on the carrier flow is modeled with the use of a point‐force approximation. The results show that drops dynamics and their impact on the carrier airflow is controlled by the drops velocity at injection, the ratio of drops gravitational settling velocity versus the product of air friction velocity and Karman constant ( ), and the wave slope, ka. Drops injected into the flow with the surrounding airflow velocity reduce the turbulent air‐stress and increase mean air velocity as compared to the droplet‐free case. On the other hand, the opposite effect is observed for drops injected with velocity equal to the water surface velocity, which increase the turbulent air stress and reduce the mean wind velocity. This modification of the airflow by drops is most pronounced for the ratio , increases with drops mass loading, and is reduced for steeper waves and smaller settling velocity.