Local Water Velocity Research Articles

ASSESSING LOCAL PORE WATER VELOCITY ALONG PREFERENTIAL FLOW IN EARTHEN DAM USING SALT TRACER

The local pore water velocity along the preferential flow path signifies the hydraulic parameter responsible for erosion within an earthen dam. This study introduces an empirical approach to ascertain the local pore water velocity within the earth dam's leakage zones by monitoring the travel time of the salt tracer through the corresponding electric potential anomalies in the ground. The alignment of electric potential anomalies with the movement of the salt tracer plume over time was confirmed through experiments on a physical model coupled with numerical simulations. The pore water velocity, calculated based on the location of the maximum electric potential anomaly, demonstrated excellent agreement with the experimental value, with an error of under 6%. For illustrative purposes, a field-scale salt tracer test was conducted at a leaking earthen dam in Vietnam. The tracer breakthrough curve originating from the leakage point revealed that the seepage water's travel time is approximately 40 days. The results of electric potential anomalies over time indicate that the pathway of seepage flow from upstream to the leakage point forms a horizontal V-shape, with the local pore water velocity ranging from 1.7 to 9.9x10-5 m/s. These local pore water velocities are subsequently compared with the critical seepage velocity to assess in-situ information regarding the internal erosion status of the target dam.

Flash flood prediction in St. Lucia island through a surrogate hydraulic model

ABSTRACT Recent flood disasters caused by extreme meteorological events highlight the need of fast and reliable tools for flooding forecast. For our purposes, the danger associated with floods is embodied in a single risk-level flag which considers both local water depth and velocity. The methodology here derived is applied and validated for the case study of the St. Lucia island in the eastern Caribbean Sea that experiences flash flooding as a result of combined intense rainfall and steep slopes, difficult to predict with traditional early-warning systems. A multi-layer perceptron neural network is trained on a high-fidelity dataset generated through full two-dimensional shallow water simulations of real and synthetic events. The dataset is validated against social markers obtained from real events. The predictive capabilities of the neural network model are tested on the out-of-box case of the Dean and Tomas hurricanes and compared with the solutions of the shallow water solver. The surrogate solver allows a significant speed-up in the prediction time with respect to traditional CFD (seconds vs hours), showing a high precision and accuracy, with accuracy, precision and F1-score above 0.99.

Experimental and numerical investigation of flow dynamics in an upward bubbly flow in a tube undergoing oscillating rolling motion

Offshore nuclear power plants are characterized by a potential oscillatory motion depending on ocean waves. Investigating the local flow behavior in a system undergoing oscillating motion is necessary. In particular, because the local void fraction near the heating element surface significantly affects the nucleating boiling heat transfer and critical heat flux, understanding the dynamic behavior of the local void fraction is very important. Therefore, in this study, as an essential first step in predicting boiling heat transfer and departure from nucleate boiling in offshore nuclear reactors, the dynamic behavior of air–water bubbly flows has been experimentally and numerically investigated in a tube under oscillatory rolling conditions. An optical fiber Doppler probe was used to measure the local bubble parameters. The effects of the rolling period on the void fraction distributions, bubble sizes, and bubble velocities were insignificant. However, the rolling amplitude effect was significant. The void fraction was the highest at the downward-facing wall when the tube was at its maximum tilt. Moreover, the local water velocity became the highest when the tube returned to near vertical because of the combined effect of gravity and Euler force. These findings provide insights into understanding the characteristics of bubbly flow in a rolling tube.

Simulating the migration dynamics of juvenile salmonids through rivers and estuaries using a hydrodynamically driven enhanced particle tracking model

Juvenile salmonids migrate hundreds of kilometers from their natal streams to mature in the ocean. Throughout this migration, they respond to environmental cues such as local water velocities and other stimuli to direct and modulate their movements, often through heavily modified riverine and estuarine habitats. Management strategies in an uncertain future of climate change and altered land use regimes depend heavily on being able to reliably predict their ocean entry timings, route use, and survival rates through rivers and estuaries. We developed a spatially-explicit agent-based model of fish movement in response to hydrodynamic flows that uses movement dynamics gleaned from multi-dimensional tracking datasets of acoustically tagged juveniles moving through an urbanized, branched tidal estuary. We demonstrate how such models can be calibrated, and we apply it to the Sacramento-San Joaquin Delta in Central California. The quality of the out-of-sample validation of the model to predict juvenile salmon survival and route selection indicates that the model is versatile and flexible enough to be used in novel hydroclimatological conditions.

Molecular dynamics analysis of water flow through a multiply connected carbon nanotube channel

The filling process of nanoconduits is an active research topic. In this study, we use molecular dynamics simulations to identify the filling process of water molecules in a multiply connected carbon nanotube (MCCNT). For water permeation, a local change in the channel cross-section affects the water filling of MCCNTs because it may lead to irregularities in the permeation profile. A decrease in hydrogen bonds at the junctions of the structure characterizes the permeability of MCCNTs. In contrast to pristine CNTs, the complex nanochannel exhibits a different imbibition profile due to the energy changes at the junction. Next, we examine the local water density and velocity patterns in MCCNT channels to understand how junction regions affect steady-state water transport. We find that there is congestion and irregularities in steady water flow density and velocity profiles. Through this study, we expect to develop effective channels with more complex geometries for water purification and drug delivery.

An investigation into remote sensing techniques and field observations to model hydraulic roughness from riparian vegetation

AbstractRiparian vegetation provides many noteworthy functions in river and floodplain systems, including its influence on hydrodynamic processes. Traditional methods for predicting hydrodynamic characteristics in the presence of vegetation involve the application of static Manning's roughness, which does not directly account for vegetation characteristics and neglects changes in roughness due to local water depth and velocity. The objectives of this study were to (1) implement numerical routines for simulating vegetation‐induced hydraulic roughness in a two‐dimensional (2D) hydrodynamic model; (2) evaluate the performance of two vegetation roughness approaches; and (3) compare vegetation parameters and hydrodynamic model results based on field‐based and remote sensing acquisition methods. Two roughness algorithms were coupled to an existing 2D hydraulic solver, which requires vegetation parameters to calculate spatially distributed roughness coefficients. Vegetation parameters were determined by field survey and using airborne light detection and ranging (LiDAR) data for San Joaquin River, California, USA. Water surface elevations modeled using vegetation‐based roughness approaches produced an acceptable overall performance, but the results were sensitive to the vegetation parameterization method (field based vs. LiDAR). Spatial variations in roughness and hydraulic conditions (water depth and velocity) were observed based on vegetation species and discharges for vegetation‐based approaches. The proposed approach accounts for the complexities of the physical environment instead of relying on traditional roughness as model inputs. Thus, the method proposed here is beneficial for describing the hydraulic conditions for the area having spatial variation of vegetation (e.g., species and density). However, additional research is needed to quantify model performance with respect to spatially distributed water depth and velocity and parameterization of vegetation characteristics.

Flow at an Ogee Crest Axis for a Wide Range of Head Ratios: Theoretical Model

The discharge coefficient of an ogee crest is a function of the ratio of the effective head to the design head. The purpose of the present study is to derive a theoretical model of this relation, which does not depend on empirical coefficients and whose predictions over a wide range of head ratios are accurate enough for practical use. The developments consider unsubmerged ogee crests without approach flow or lateral contraction effects, heads large enough to enable surface tensions to be neglected, and heads small enough to avoid flow separation. The method is based on potential flow theory, depth integration in a curvilinear reference frame, and critical flow theory. The characteristics of the crest shape are defined by the trajectory of a free jet passing over the crest at the design head. The dimensionless equations show that the position of the critical section is not at the apex of the crest. Nevertheless, they also suggest an approximate equation at the apex of the crest from which the discharge coefficient is derived, together with the local water depth, velocity, and pressure distribution. The results compare well with experimental data for head ratios between 0 and 5, which validates the underlying assumptions of the theoretical model.

Fast imaging of the velocity profile of the conducting continuous phase in multiphase flows using an electromagnetic flowmeter

This paper describes a novel dual-frequency inductive flow tomography (IFT) system, which relies on the use of a multi-electrode electromagnetic flow meter (EMFM). This flow meter is currently capable of imaging the velocity profile of the conducting continuous phase of both single phase and highly asymmetric multiphase flows ten times every second. Uniform and anti-Helmholtz magnetic fields are simultaneously applied to the cross section of the flow tube of the EMFM. This enables flow induced potentials to be measured, at an array of electrodes, flush mounted on the inner wall of the EMFM, ten times every second using a multi-channel analogue signal conditioning system. These measured flow induced potentials are then used in an image reconstruction algorithm to reconstruct the water velocity profile in the flow cross section at 0.1 s time intervals.A series of experiments were carried out in water continuous, upward, air-water flows inclined at 15° to the vertical to measure the water velocity profile using the IFT system. The water velocity profiles were compared with air velocity profiles previously obtained for inclined air-water flows at similar flow conditions using local probing techniques. For all of the flow conditions investigated it was found that both the local axial water and air velocities were significantly greater at the upper side of the inclined pipe than at the lower side. The high local water velocities were probably due to upward momentum of the air bubbles being locally transferred to the water at the upper side of the inclined pipe. A comparison of the local axial air velocity distribution and the local axial water velocity distribution also showed that the local slip velocity between the phases varied markedly in the flow cross section – indicating that previous assumptions that the local slip velocity is constant in the flow cross section are clearly incorrect.

Imaging water velocity and volume fraction distributions in water continuous multiphase flows using inductive flow tomography and electrical resistance tomography

This paper presents the design and implementation of an inductive flow tomography (IFT) system, employing a multi-electrode electromagnetic flow meter (EMFM) and novel reconstruction techniques, for measuring the local water velocity distribution in water continuous single and multiphase flows. A series of experiments were carried out in vertical-upward and upward-inclined single phase water flows and ‘water continuous’ gas–water and oil–gas–water flows in which the velocity profiles ranged from axisymmetric (single phase and vertical-upward multiphase flows) to highly asymmetric (upward-inclined multiphase flows). Using potential difference measurements obtained from the electrode array of the EMFM, local axial velocity distributions of the continuous water phase were reconstructed using two different IFT reconstruction algorithms denoted RT#1, which assumes that the overall water velocity profile comprises the sum of a series of polynomial velocity components, and RT#2, which is similar to RT#1 but which assumes that the zero’th order velocity component may be replaced by an axisymmetric ‘power law’ velocity distribution. During each experiment, measurement of the local water volume fraction distribution was also made using the well-established technique of electrical resistance tomography (ERT). By integrating the product of the local axial water velocity and the local water volume fraction in the cross section an estimate of the water volumetric flow rate was made which was compared with a reference measurement of the water volumetric flow rate.In vertical upward flows RT#2 was found to give rise to water velocity profiles which are consistent with the previous literature although the profiles obtained in the multiphase flows had relatively higher central velocity peaks than was observed for the single phase profiles. This observation was almost certainly a result of the transfer of axial momentum from the less dense dispersed phases to the water, which occurred preferentially at the pipe centre. For upward inclined multiphase flows RT#1 was found to give rise to water velocity profiles which are more consistent with results in the previous literature than was the case for RT#2—which leads to the tentative conclusion that the upward inclined multiphase flows investigated in the present study did not contain significant axisymmetric velocity components.

CFD study on the hydrodynamics of fluidized granular activated carbon in AnFMBR applications

Abstract The anaerobic fluidized bed membrane bioreactor (AnFMBR) utilizes the fluidization of granular activated carbon (GAC) particles as an unsteady-state shear means for mitigating membrane fouling. In this study, a two-fluid model (TFM) was validated against experimental results and used to obtain a comprehensive landscape of local water and particle velocities and concentrations throughout the reactor. The results provided interesting insights. Firstly, both water and particle velocities tended to be non-uniform vertically and laterally, which indicate that the extent of fouling across the membrane would be non-uniform. Secondly, to attain the same water shear stress or particle momentum values, the power required was greater for the larger particles, which indicate that smaller particles were more energy-efficient. Thirdly, at the same power input, the water shear stress or particle momentum values for the different particle diameters overlapped, which indicates that other parameters can be manipulated to improve performance even when particle diameter has been fixed. Fourthly, generally negative correlations existed between fouling rate and the hydrodynamics of both phases, but fouling rate and power input were poorly correlated, which suggests surprisingly that increasing power would not improve the fouling mitigation.

Spillage sedimentation on large river floodplains

AbstractActive deposition across the floodplains of large rivers arises through a variety of processes; collectively these are here termed ‘spillage sedimentation’. Three groups of 11 spillage sedimentation styles are identified and their formative processes described. Form presences on large river floodplains show different combinations of active spillage styles. Only some large floodplains have prominent levees; some have coarse splays; many have accessory channel dispersion and reworking, while still‐water sedimentation in lacustrine environments dominates some lower reaches. Infills are also commonly funnelled into prior, and often linear, negative relief forms relating to former migration within the mainstream channel belt.Shuttle Radar Topography Mission (SRTM) and Landsat 8 data are used to map spillage form types and coverage along a 1700 km reach of the Amazon that has an active floodplain width of up to 110 km with a systematic character transformation down‐valley. Spillage forms associated directly with mainstream processes rarely account for more than 5% of the floodplain deposits. There is a marked decrease in floodplain point bar complexes (PBC) over 1700 km downstream (from 34% to 5%), and an increase in the prevalence of large water bodies (2% to 37%) and accompanying internal crevasses and deltas (0% to 5%). Spillage sedimentation is likely within the negative relief associated with these forms, depending on mainstream sediment‐laden floodwater inputs.Spillage style dominance depends on the balance between sediment loadings, hydrological sequencing, and morphological opportunity. Down‐river form sequences are likely to follow gradient change, prior up‐river sediment sequestration and the altered nature of spilled loads, but also crucially, local floodplain relief and incident water levels and velocities at spillage times. Considering style distribution quantitatively, as a spatially distributed set of identifiable forms, emphasizes the global variety to spillage phenomena along and between large rivers. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

A hydrologically sensitive invertebrate community index for New Zealand rivers

Identifying ecological response variables sensitive to hydrological change is a key step in determining the impacts of river flow alterations on aquatic ecosystems and in setting environmental flows that sustain certain ecological values. Building on the successful use of flow regime sensitive aquatic invertebrate indices in other countries, particularly the UK based Lotic Index for Flow Evaluation (LIFE), we provide two variants of a similar index for use in New Zealand (LIFENZ and a weighted variant: LIFENZ_W). As in the original LIFE, the New Zealand indices were based on water velocity preference categories assigned to aquatic invertebrate taxa using professional judgement. To calculate the indices a lookup table is used to assign a score to each taxon based on their velocity category and abundance. For the LIFENZ_W variant an additional step down weighted the scores if the taxon has a general compared to a more specific velocity preference. The two index variants were correlated with each other and to similar environmental parameters. Across a total of 74 sites, both indices were correlated with depth-averaged water velocity. Changes in index values, both between sites and temporally within sites, were predominantly associated with changes in hydrological parameters, such as the magnitude and length of time since a recent high flow, and to a lesser degree with other physico-chemical parameters. Commonly used indices in New Zealand designed to respond to nutrient enrichment (MCI and variants) were not correlated with local water velocity, but were correlated with antecedent flow conditions and were likely influenced by effects of flow stability on algal growth. Further testing of LIFENZ and LIFENZ_W in combination with MCI is recommended, particularly in rivers subject to more extreme hydrological and water quality stresses and with regard to other physical parameters such as hydraulic habitat. However, the LIFENZ and its weighted variant (LIFENZ_W) appear to be useful tools for understanding and managing the effects of hydrological alteration on aquatic invertebrate communities in New Zealand. As LIFENZ and LIFENZ_W were strongly correlated and only showed a relatively small deviation from a slope of 1 we recommend the use of the more straightforward LIFENZ in almost all circumstances.

Numerical simulation of the direct contact condensation phenomena for PTS-related in single and combined-effect thermal hydraulic test facilities using TransAT CMFD code

The use of CFD for the industrial studies related to PTS, including DCC is already possible; improvements of the two-phase modeling capabilities have to be undertaken to qualify the codes for the simulation of such flows. The DCC in horizontally stratified flow regime constitutes very considerable challenge exercises for a computational fluid dynamics (CFD) simulation of the thermal hydraulics PTS phenomenon because the interplay between turbulence and interfacial heat and mass transfer problem. The main purpose of our study is to investigate numerically the DCC in horizontally stratified steam water flow in a 2D and 3D channel using TransAT CMFD code. The new methodology known as Large-Eddy & Interface (LEIS) have been implemented for treatment of turbulence combined with interface tracking ITM (level set approach). Among of the so-called ‘coarse-grained’ ITM's models, the modified original surface divergence has been chosen as well as the treatment of the turbulence by URANS and VLES. This contribution addressed on the validation of interfacial phase-change heat transfer and turbulence models with special correction of the damping function at the free surface for single and combined-effect thermal hydraulic studies for LIM and KAERI & KAIST test facilities. The LIES methodology was found to apply successfully to predict the condensing steam flow rate in the all cases of the LIM test case involving a Smooth to Wavy turbulent, concurrent stratified steam-water flow in a 2D channel. The CMFD TransAT code predicting capability is analyzed, comparing the liquid temperature and to much the velocity profile of KAERI & KAIST Countercurrent Stratified Flow (CCSF) combined-effect in 2D and 3D geometry to one predicted by analytical Biberg model. The vertical profiles of CFD local water velocity calculations have been corrected using AKN free surface damping model where the agreement with KAERI & KAIST data is sufficiently good. The KAERI & KAIST test case is actually more challenging than all low subcooling cases (COSI, TOPFLOW) where the application of the ASD model (and the other interfacial DCC models) for high subcooling (ΔTsub∼70.0°K) is still questionable. A modified ASD model should be implemented, to taking into account the effect of the degree of the water subcooling through the introduction of the Jakob number.

The influence of dynamic ice formation on hydraulic heterogeneity in steep streams

AbstractDuring winter, different types of ice formation are commonly observed in northern boreal stream systems. Although largely overlooked today, river ice has profound effects on in‐stream hydraulics and therefore ice processes should be considered in freshwater stream management and assessment. In particular, limited knowledge exists about the impacts of dynamic ice formation on stream environments. Results presented from the changes of in‐stream heterogeneity in three steep stream environments caused by dynamic ice formation demonstrate that the formation of anchor ice and anchor ice dams may induce significant backwater effects by increasing wetted areas (maximum 43%) and water depths (maximum 241%) and reducing water velocities (maximum 70%); independent of minimal changes in discharge. Consequently, stream environments are transformed from fast‐flow to slow‐flow areas, even on a short temporal scale (<12 h). Furthermore, the anchor ice build‐up initiated static (surface) ice formation due to reduced local water velocities upstream ice dams. Thus, dynamic ice formation plays a key role in the balanced ice regime in steep stream environments and contributes largely to stable static ice cover in these environments. Observations from the present study suggest that the current paradigm emphasizing the role of discharge as the main controller of in‐stream heterogeneity may call for a modification in steep streams that experience seasonal ice formation. This is particularly important if future hydraulic‐/habitat models and assessment tools are to be implemented in freshwater management to realistically characterize steep stream environments in cold climate regions on a seasonal scale. Copyright © 2009 John Wiley & Sons, Ltd.

Design of a Lateral-Line Sensor for an Autonomous Underwater Vehicle

In an ongoing research project an autonomous underwater vehicle is to be built that will detect, localize, and avoid objects by means of a fully passive sensory system. Using hot-wire anemometry it measures local water velocities at the vehicle's hull and thus mimics the lateral-line system of fish and many amphibians. Fish often use the lateral-line system as their only means for navigation, especially under poor visual conditions. Simulations and theoretical calculations of the flow around an underwater vehicle show that velocity measurements with hot-wire anemometers enable an underwater vehicle to detect surfaces, so that no clear sight or active scanning is necessary for collision avoidance. A first series of experiments validates theoretical calculations and shows that a vehicle can detect parallel movement to a wall.

A modeling approach of the influence of local hydrodynamic conditions on larval dispersal at hydrothermal vents

Deep-sea hydrothermal vent animal communities along oceanic ridges are both patchy and transient. Larval dispersal is a key factor in understanding how these communities function and are maintained over generations. To date, numerical approaches simulating larval dispersal considered the effect of oceanic currents on larval transportation over hundreds of kilometers but very seldom looked at the effect of local conditions within meters around chimneys. However, small scale significant variations in the hydrodynamics may influence larval fate in its early stages after release, and hence have a knock-on effect on both dispersal and colonization processes. Here we present a new numerical approach to the study of larval dispersal, considering small scales within the range of the biological communities, called “bio-hydrodynamical” scale, and ranging from a few centimeters to a few meters around hydrothermal sources. We use a physical model for the vent based on jet theory and compute the turbulent velocity field around the smoker. Larvae are considered as passive particles whose trajectories are affected by hydrodynamics, topography of the vent chimney and larval biological properties. Our model predicts that bottom currents often dominate all other factors either by entraining all larvae away from the vent or enforcing strong colonization rates. When bottom currents are very slow ( < 1 mm s - 1 ), general larvae motion is upwards due to entrainment by the main smoker jet. In this context, smokers with vertical slopes favor retention of larvae because larval initial trajectory is nearly parallel to the smoker wall, which increases the chances to settle. This retention phenomenon is intensified with increasing velocity of the main smoker jet because entrainment in the high velocity plume is preceded by a phase when larvae are attracted towards the smoker wall, which occurs earlier with higher velocity of the main jet. Finally, the buoyancy rate of the larvae, measured to be in the range of 0.01 mm s - 1 , is generally irrelevant unless hydrodynamic conditions are balanced, i.e. if the buoyancy rate is comparable to both the bottom current speed and the local water velocity due to entrainment by close smokers. Overall, our model evidences the strong effect of the release point of larvae on their future entrainment within local fluxes. Larvae released from smoker walls might have an entirely different fate than those released further away in the water column. The latter are not, or less, affected by near-chimney hydrodynamics.

Multiple frazil ice blockages at a water intake in the St. Lawrence River

Abstract This paper presents the results of a field study of multiple frazil ice blockages of a municipal water intake located on the north shore of the St. Lawrence River at Quebec City, Canada. Instrumentation used includes a weather station, a digital camera with a telephoto lens, four water temperature probes, an Optical Backscatter System, a pressure sensor and an acoustic sensor (Ice Profiling System). Background ice data is provided by bi-weekly helicopter observations and local water velocity was obtained by analysing surface ice floes movement on digital photos and by performing 1-D and 3-D numerical modeling. Data on flow rates and head losses through the intake were provided by the City and analysed by the authors. The site is unique because the river is artificially kept open all winter by commercial shipping. It is also unique because the intake is located in a tidal reach and is therefore subject to a wide range of upstream and downstream flow velocities. Due to its location, the intake is, at times, sheltered or partially sheltered by border ice. With each change in the semi-diurnal tide, totally new water and ice reach the site. Detailed data is available for about 100 active frazil and anchor ice events leading to 35 blockage events at the intake. After presenting a global summary of the winter's environmental conditions and after presenting summary statistics on blockage events; four selected events are presented in detail. Items discussed are critical temperatures for the formation of frazil ice and the blockage of the intake as a function of time of day, tidal condition and surface ice type. Blockage events are also characterized in terms of the time required for them to develop, their severity and their duration.

Small Scale Field Study of an Ocean CO2 Plume

We have carried out a small-scale (∼20 l) CO2 sequestration experiment off northern California (684 m depth, ∼5°C, background ocean pH ∼7.7) designed as an initial investigation of the effects of physical forcing of the fluid, and the problem of sensing the formation of a low pH plume. The buoyant CO2 was contained in a square frame 1.2 m high, exposing 0.21 m2 to ocean flow. Two pH electrodes attached to the frame recorded the signal; a second frame placed 1.9 m south of the CO2 pool was also equipped with two recording pH electrodes. An additional pH electrode was held in the ROV robotic arm to probe the fluid interface. Local water velocities of up to 40 cm sec−1 were encountered, creating significant eddies within the CO2 box, and forcing wavelets at the fluid interface. This resulted in rapid CO2 dissolution, with all CO2 being depleted in a little more than 2 days. The pH record from the sensor closest (∼10 cm) to the CO2 showed many spikes of low pH water, the extreme value being ∼5.9. The sensor 1 m immediately below this showed no detectable response. The electrodes placed 1.9 m distant from the source also recorded very small perturbations. The results provide important clues for the design of future experiments for CO2 disposal and biogeochemical impact studies. These include the need for dealing with the slow CO2 hydration kinetics, better understanding of the fluid dynamics of the CO2-water interface, and non-point source release designs to provide more constant, controlled local CO2 enrichments within the experimental area.

Fish individual-based numerical simulator (FINS): a particle-based model of juvenile salmonid movement and dissolved gas exposure history in the Columbia River basin

This paper describes a numerical model of juvenile salmonid movements in the Columbia and Snake Rivers. The model, called the Fish Individual-based Numerical Simulator or FINS, employs a discrete, particle-based approach to simulate the movements and history of exposure to dissolved gases of individual fish. FINS is linked to a two-dimensional (vertically-averaged) hydrodynamic simulator that quantifies local water velocity, temperature, and dissolved gas levels as a function of river flow rates and dam operations. Simulated gas exposure histories can be input to biological mortality models to predict the effects of various river configurations on fish injury and mortality due to dissolved gas supersaturation. Therefore, FINS serves as a critical linkage between hydrodynamic models of the river system and models of biological effects. FINS model parameters were based on observations of individual fish movements collected using radiotelemetry methods during 1997 and 1998. A quasi-inverse approach was used to decouple fish swimming movements from advection with the local water velocity, allowing inference of time series of non-advective displacements of individual fish from the radiotelemetry data. Statistical analyzes of these displacements confirm that strong temporal correlation of fish swimming behavior persists in some cases over several hours. A correlated random-walk model was employed to simulate the observed behavior, and parameters of the model were estimated that lead to close correspondence between predictions and observations.

Experimental studies of the fluid dynamics in the separation zone in dissolved air flotation

Research in the field of Dissolved Air Flotation calls for studies on the fluid dynamics of the process for optimisation. This study describes a method using an Acoustic Doppler Velocimeter for measuring local water velocities in a DAF pilot plant, and presents the results from measurements done in the separation zone. A test of the ADV in bubbly water indicates a 50% reduction of the measured velocity in water containing higher concentrations of micro-bubbles. The bubble content and the hydraulic loading were shown to significantly influence the flow pattern at surface loading in the range 10–20 m/h. Micro-bubbles generated density gradients in the flotation tank and two major flow patterns were observed. Stratified flow was characterised by a horizontal flow in a bubbly upper layer and a plug-like flow in the bubble-free lower layer. The break-through flow was seen to short-circuit the water to the outlet, which most probably could be the reason for bad effluent quality at higher surface loading. Finally, three-dimensional flows were discovered, which also could have a deteriorating impact on the effluent quality.