Changes In Water Velocity Research Articles

Mass-loss effects on the non-Darcy seepage characteristics of broken rock mass with different clay contents

A seepage testing system was designed and a series of seepage experiments on broken rock was conducted using different original porosity conditions and clay contents. The mass-loss process of the broken rock and the change in water flow velocity were investigated. After the mass-loss test, the non-Darcy seepage characteristics of the broken rock were tested through a step-by-step pressure-reduced seepage test. The experimental results show that the mass-loss and water velocity evolution during the water inrush could be divided into four stages: acceleration, stable with slight fluctuations, reacceleration, and stable. The lost-mass and change in water velocity were positively correlated with the clay contents and negatively correlated with the original porosity. By introducing the evolution equation of the Kozeny-Carman equation and the liquid limit index which characterises the effective particle size, the prediction model of the permeability coefficient was built. Six prediction models of the non-Darcy coefficient were verified against the testing results. The prediction model of the critical flow velocity from a Darcy flow to a non-Darcy flow using the Forchheimer number was also established. The results could provide an important reference for understanding water inrush mechanisms, adopting effective control measures for water inrush events, and calculating the water influx of tunnels.

Analysis of water velocity changes in time-lapse ocean bottom acquisitions - A synthetic 2D study in Santos Basin, offshore Brazil

Time-lapse seismic is an important tool for reservoir management. As seismic data quality improves, there is a drive for moving towards quantitative interpretation, which demands data of higher repeatability. In deep water time-lapse projects, the changes in the speed of sound of the water layer between baseline and monitor acquisitions play a significant role in the data processing. In this work, we study the effects of these water velocity changes, in a scenario of ocean bottom nodes (OBN) acquisition. We perform 2D elastic seismic modeling with high-resolution property models for two distinct survey dates. In each date, different water velocity profiles, measured in field experiments in a Brazilian Pre-salt area, are considered. To incorporate source and receiver non-repeatability, some differences in the acquisition geometries are also tested for each vintage. The synthetic data are compared in terms of time-lapse amplitudes, and repeatability is quantified via the normalized root mean squared attribute (NRMS). For the parameters considered in our study, the deterioration of NRMS seems to be dominated by the non-repeatability of the receivers and by water velocity variations, with source non-repeatability having a lower contribution. We believe the results presented in this work are a first step towards a more robust methodology for time-lapse feasibility studies, which incorporates imaging uncertainties and allows us to understand the contribution of each element that could affect the 4D seismic image quality.

Assessment of Steady and Unsteady Friction Models in the Draining Processes of Hydraulic Installations

The study of draining processes without admitting air has been conducted using only steady friction formulations in the implementation of governing equations. However, this hydraulic event involves transitions from laminar to turbulent flow, and vice versa, because of the changes in water velocity. In this sense, this research improves the current mathematical model considering unsteady friction models. An experimental facility composed by a 4.36 m long methacrylate pipe was configured, and measurements of air pocket pressure oscillations were recorded. The mathematical model was performed using steady and unsteady friction models. Comparisons between measured and computed air pocket pressure patterns indicated that unsteady friction models slightly improve the results compared to steady friction models.

Numerical investigation of water and temperature distributions in a proton exchange membrane electrolysis cell

A three-dimensional, non-isothermal, two-phase model for a PEM water electrolysis cell (PEMEC) is established in this study. An effective connection between two-phase transport and performance in the PEMECs is built through coupling the liquid water saturation and temperature in the charge conservation equation. The distributions of liquid water and temperature with different operating (voltage, temperature, inlet velocity) and physical (contact angle, and porosity of anode gas diffusion layer) parameters are examined and discussed in detail. The results show that the water and temperature distributions, which are affected by the operating and physical parameters, have a combined effect on the cell performance The effects of various parameters on the PEMEC are of interaction and restricted mutually. As the voltage increases, the priority factor caused by the change of inlet water velocity changes from the liquid water saturation increase to the temperature drop in the anode catalyst layer. While the priority influence factor caused by the contact angle and porosity of anode gas diffusion layer is the liquid water saturation. Decreasing the contact angle or/and increasing the porosity can improve the PEMEC performance especially at the high voltage. The results can provide a better understanding of the effect of heat and mass transfer and the foundation for optimization design.

The Effect of Heat Transfer Fluid Velocity on Heat Exchange Efficiency in Cold Energy Storage Tank: A Numerical Simulation Study

Developing a cold thermal energy storage (CTES) technology is one of the most effective methods to solve energy shortage and environmental pollution all over the world. The current study deals with the modelling and simulation of a cold thermal energy storage tank consisting of an polyvinyl chloride pipe (PVC) heat exchanger partially filled with a phase change material (PCM). Water, as the heat transfer fluid (HTF), flows through the inner tubes and the outer one while propylene glycol as the phase change material fills. This paper focuses on studying the effect of the velocity characteristics on the heat transfer efficiency of polyvinyl chloride pipe (PVC) heat exchanger in cold thermal energy storage system by the numerical simulation. In this paper, the detail of heat transfer performance within the heat exchanger is numerically solved using computational fluid dynamics (CFD), for various velocity as well as different heat transfer for optimal design. Several results of changes in the temperature field at the outlet of the cold thermal energy storage tank are presented when the inlet water velocity changes from 1 m/s to 1.4 m/s. The results indicate that low input water velocity will provide better heat exchange efficiency. However, it is required to make sure that the flow inside the heat exchanger is the turbulent flow because the study uses turbulent flow modules.

Swimming performance in early life stages of three threatened Iberian Leuciscidae

Rivers are dynamic systems where flow is constantly changing, making early fish life stages with lower swimming abilities potentially vulnerable to rapid changes in water velocity. In this study, we evaluated the response of critical young life stages of three Iberian leuciscids – Achondrostoma occidentale, Iberochondrostoma lusitanicum, and Iberochondrostoma almacai – to increasing water velocities, by determining their critical swimming speed (Ucrit) and its relation with morphometric traits potentially associated with better swimmers. Results suggest a positive relation between both fish length and body depth with Ucrit and species-specific differences in swimming performance. Moreover, most fish could not withstand the maximum velocity tested (20 cm s−1), which can be surpassed in the rivers they occur. This study highlights the importance of considering individual traits for future management of fish stocks in rivers.

A Classification Method for Fish Swimming Behaviors under Incremental Water Velocity for Fishway Hydraulic Design

In fishway design, the combination of fish swimming behaviors and suitable fishway hydraulic characteristics increases the fish passage efficiency. In this study, the most representative grass carp among the “four major Chinese carps” was selected. Under conditions similar to the time period for feeding migration, juvenile grass carps were targeted to study the swimming characteristic indicators (i.e., critical and burst swimming speeds) and swimming behaviors that were closely associated with fishway hydraulic design using the incremental water velocity method in a homemade test water tank. (1) The study results reveal that both the absolute critical (Ucrit) and burst (Uburst) swimming speeds increased linearly with increasing body length and both the relative critical (U’crit) and burst (U’burst) swimming speeds decreased linearly with increasing body length. There existed a quantitative relationship between Uburst and Ucrit, which could facilitate the fishway hydraulic design. (2) This study analyzed the effects of water velocity changes on fish swimming behaviors and proposed a classification method for four fish swimming behaviors—swimming freely, staying, dashing at a long distance, and dashing at a short distance—of tested fish during the process of adapting to water velocity changes interspersed with one another. The entire swimming process under the incremental water velocity was divided into four stages. (3) This study suggests that the maximum water velocity of the mainstream in a fishway using grass carp as the major passage fish should not exceed 52–60% Uburst at stage 1. For the high-water velocity areas of a fishway, such as vertical slots and orifices, the optimal water velocity should not be higher than 76–79% Uburst at stage 2 and should absolutely not exceed 90–96% Uburst at stage 3.

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.

Tailrace surge shaft optimization procedure for minimum downsurge

Tailrace surge shafts are required in hydropower projects where the spent water is conveyed through a long tailrace tunnel under pressure to the recipient. Startup and shutdown of the turbine can cause sudden changes in water velocity and can develop dangerously high and low pressures. Surge shafts are provided in water conductor systems to significantly reduce these pressure surges. Based on numerous transient analyses carried out, it was observed that the cross-sectional area of the tailrace surge shaft can be optimized based on the relationship between the differences in the tailwater level and the minimum downsurge level at the tailrace surge shaft obtained with respect to the different lengths of the tailrace tunnel and different cross-sectional areas of the tailrace surge shaft. In this study, a procedure was proposed by which the tailrace surge shafts can be optimized and, hence, the cost of the hydropower projects with tailrace surge shafts can be minimized.

Transient Thermal Stress Analysis of BOF Hood Failure

The failure of BOF hood tube is a common industrial problem that has received little attention in literature. The major mode of failure as observed by most of the industries is thermal fatigue failure. Earlier people have studied the thermal stress profile in hood system considering constant water temperature. However, in reality there are fluctuations in water temperature due to cyclic thermal load caused by BOF gas. Present study reveals that the water temperature fluctuation is having significant impact in causing thermal fatigue failure. The change in water velocity and tube thickness has negligible effect in thermal fatigue failure compared to that observed for water temperature fluctuation. However, tube material of construction is also having significant impact on its failure.

Water velocity limits the temporal extent of herbivore effects on aquatic plants in a lowland river

The role of herbivores in regulating aquatic plant dynamics has received growing recognition from researchers and managers. However, the evidence for herbivore impacts on aquatic plants is largely based on short-term exclosure studies conducted within a single plant growing season. Thus, it is unclear how long herbivore impacts on aquatic plant abundance can persist for. We addressed this knowledge gap by testing whether mute swan (Cygnus olor) grazing on lowland river macrophytes could be detected in the following growing season. Furthermore, we investigated the role of seasonal changes in water current speed in limiting the temporal extent of grazing. We found no relationship between swan biomass density in 1 year and aquatic plant cover or biomass in the following spring. No such carry-over effects were detected despite observing high swan biomass densities in the previous year from which we inferred grazing impacts on macrophytes. Seasonal increases in water velocity were associated with reduced grazing pressure as swans abandoned river habitat. Furthermore, our study highlights the role of seasonal changes in water velocity in determining the length of the mute swan grazing season in shallow lowland rivers and thus in limiting the temporal extent of herbivore impacts on aquatic plant abundance.

Are vibrissae viable sensory structures for prey capture in northern elephant seals, Mirounga angustirostris?

Little is known about the tactics northern elephant seals (NES) use to capture prey due to the difficulties in observing these animals underwater. NES forage on vertically migrating prey at depths >500 m during day and at night where light levels are negligible. Although NES have increased visual sensitivity in deep water, vision is likely a limited sensory modality. Still images of NES foraging show that the mystacial vibrissae are protracted before prey capture. As a representative phocid, harbor seals can follow hydrodynamic trails using their vibrissae, and are highly sensitive to water velocity changes. In lieu of performance data, vibrissal innervation can be used as a proxy for sensitivity. Although comparative data are few, seals average 1,000 to 1,600 axons per vibrissa (five to eight times more than terrestrial mammals). To test the hypothesis that NES have increased innervation as other pinnipeds, vibrissae from the ventral-caudal mystacial field from nine individuals were sectioned and stained for microstructure (trichrome) and innervation (Bodian silver stain). Follicles were tripartite and consisted of lower and upper cavernous sinuses separated by a ring sinus containing an asymmetrical ringwulst. The deep vibrissal nerve penetrated the follicular capsule at the base, branched into several bundles, and coursed through the lower cavernous sinus to the ring sinus. Axons in the ring sinus terminated in the ringwulst and along the inner conical body. NES averaged 1,584 axons per vibrissa. The results add to the growing body of evidence that phocids, and perhaps all pinnipeds, possess highly sensitive mystacial vibrissae that detect prey.

Juvenile and adult hardhead Mylopharodon conocephalus oxygen consumption rates: effects of temperature and swimming velocity

California’s populations of hardhead Mylopharodon conocephalus, a species of special concern, have declined, possibly due to dam construction with consequent temperature and water-velocity changes, and the introduction of non-native species. Environmental temperature effects on this large (to 60 cm SL) cyprinid, and its swimming abilities, are not well known. To address these deficiencies and to assist conservation efforts, we measured resting and swimming metabolic rates of adult and juvenile hardhead acclimated to four temperatures (11, 16, 21, or 25 °C). Resting metabolic rates (RMR, mg O2 kg−0.79 h−1) generally increased with acclimation temperature, in adults and juveniles, with low to moderate thermal sensitivity (Q10 range: 1.33–2.04). Swimming metabolic rates, in Brett-style respirometers, of adults ranged from 209 to 1342 mg O2 kg−1 h−1 at velocities from 30 to 90 cm s−1, and juveniles ranged from 393 to 769 mg O2 kg−1 h−1 from 10 to 50 cm s−1. Adults were lethargic at 11 °C and juveniles frequently refused to swim at 11 and 16 °C, but all fish swam well at 21 and 25 °C. These results suggest that hardhead are well-suited for sustained aerobic activity over a range of flow velocities, at moderate temperatures (ca. 16 to 21 °C). However, juveniles, emerging in spring, may not be able to perform in cold water and/or high flow velocities, providing a caution to dam managers and regulators to avoid spring and summer operations whereby juveniles experience conditions outside of those occurring in unregulated rivers.

Avian community responses to variability in river hydrology.

River flow is a major driver of morphological structure and community dynamics in riverine-floodplain ecosystems. Flow influences in-stream communities through changes in water velocity, depth, temperature, turbidity and nutrient fluxes, and perturbations in the organisation of lower trophic levels are cascaded through the food web, resulting in shifts in food availability for consumer species. River birds are sensitive to spatial and phenological mismatches with aquatic prey following flow disturbances; however, the role of flow as a determinant of riparian ecological structure remains poorly known. This knowledge is crucial to help to predict if, and how, riparian communities will be influenced by climate-induced changes in river flow characterised by more extreme high (i.e. flood) and/or low (i.e. drought) flow events. Here, we combine national-scale datasets of river bird surveys and river flow archives to understand how hydrological disturbance has affected the distribution of riparian species at higher trophic levels. Data were analysed for 71 river locations using a Generalized Additive Model framework and a model averaging procedure. Species had complex but biologically interpretable associations with hydrological indices, with species’ responses consistent with their ecology, indicating that hydrological-disturbance has implications for higher trophic levels in riparian food webs. Our quantitative analysis of river flow-bird relationships demonstrates the potential vulnerability of riparian species to the impacts of changing flow variability and represents an important contribution in helping to understand how bird communities might respond to a climate change-induced increase in the intensity of floods and droughts. Moreover, the success in relating parameters of river flow variability to species’ distributions highlights the need to include river flow data in climate change impact models of species’ distributions.

The impact of vegetation on the bank erosion (Case study: The Haraz River)

Vegetation establishment is a suitable biological method of erosion control. Bank erosion is one form of water erosion and its adverse effects include an increase in turbidity, degradation of riverbank lands, difficulties caused by sediments depositing in the downstream. The rate of riverbank erosion can be decreased by application of biological methods in sensitive reaches identified. In this study, a 3250 m section of the Haraz River was studied to evaluate the effects of vegetation establishment on shear stress, water velocity and finally on the bank erosion. In this research, Geographical Information System (HEC-GeoRAS extension), HEC-RAS software, and topographic maps of riverbed at the scale of 1:500 were used to simulate hydraulic behaviour of the Haraz River. In order to evaluate the effect of vegetation cover on the bank erosion, roughness coefficient of Manning was determined with the Cowan method for two seasons (winter and summer) separately, due to changes in vegetation in the considered sections during different seasons of the year. The results showed that vegetation establishment on riverbanks caused changes in water velocity, water depth, power of shear stress and this all should finally be reflected in the rate of bank erosion.

Go with the flow: water velocity regulates herbivore foraging decisions in river catchments

Foragers typically attempt to consume food resources that offer the greatest energy gain for the least cost, switching between habitats as the most profitable food resource changes over time. Optimal foraging models require accurate data on the gains and costs associated with each food resource to successfully predict temporal shifts. Whilst previous studies have shown that seasonal changes in food quantity and quality can drive habitat shifts, few studies have shown the effects on habitat choice of seasonal changes in metabolic foraging costs. In this study we combined field and literature data to construct an optimal foraging model to examine the effect of seasonal changes in food quantity, food quality and foraging costs on the timing of a switch from terrestrial to aquatic habitat by non‐breeding mute swans Cygnus olor in a shallow river catchment. Feeding experiments were used to quantify the functional response of swans to changes in aquatic plant biomasses. By sequentially testing alternative models with fixed or variable values for food quantity, food quality and foraging cost, we found that we needed to include seasonal variance in foraging costs in the model to accurately predict the observed habitat switch date. However, we did not need to include seasonal variance in food quantity and food quality, as accurate predictions could be obtained with fixed values for these two parameters. Therefore, the seasonal changes in foraging costs were the key factor influencing the behavioural decision to switch feeding habitats. These seasonal changes in foraging costs were driven by changes in water velocity; the profitability of aquatic foraging was negatively related to water velocity, as faster water required more energy to be expended in swimming. Our results demonstrate the importance of incorporating seasonal variation in foraging costs into our understanding of the foraging decisions of animals.

Effects of Decelerating and Accelerating Flows on Juvenile Salmonid Behavior

AbstractMigratory and resident fish species have evolved inherent flight responses to avoid potentially harmful situations. At many dams, fish screens or other structures have been installed to guide fish away from turbines or attract them to routes that will result in higher survival. Avoidance responses of fish to rapidly decelerating and accelerating flows at these structures have been repeatedly observed and can result in ineffective fish guidance. By using controlled flume experiments, we analyzed the avoidance behavior of actively migrating spring Chinook salmon Oncorhynchus tshawytscha smolts in relation to flow decelerations and accelerations. As smolts drifted into areas with decreasing velocities, they actively swam into the current; the larger was the change in water velocity with distance (spatial velocity gradient [SVG]), the faster was the swimming speed exhibited by smolts. Under accelerating flows, the response velocity varied significantly with flow conditions, but the median SVG at which smolts displayed an avoidance response was similar over all flows tested. For both decelerating and accelerating flows, the avoidance response occurred at an SVG of approximately 1 cm·s−1·cm−1. We suggest that this threshold is in part fixed by the energetically optimum swimming speed of the fish (∼1 body length/s).

Estimation of changes in water column velocities and thicknesses from time lapse seismic data

Sea-bed diffractions are frequently observed for several of the fields in the Norwegian Sea and the Barents Sea. This is a challenge in time lapse seismic analysis, since diffracted multiples are difficult to remove by processing and therefore is a major source of poor time lapse data quality. In this work we test if the diffractions can be used for enhanced 4D interpretation. By analysing the time-shift of the sea-bed diffraction hyperbola between the base and monitor it is tested if changes in water velocity and tides can be estimated. Two models using time lapse diffraction analysis are tested: the first one simply adds time-shifts for the two branches of the diffraction hyperbola and this average time-shift is then used to estimate the water velocity change. The other method uses an inversion method based on the diffraction equation for a point diffractor to estimate the velocity change. In-line common-midpoint shifts are estimated by subtracting the time-shifts of both hyperbola branches followed by direct inversion. The diffraction based time-shifts are compared to time-shifts estimated by standard cross-correlation of the sea-bed reflection. The averaging method gives slightly higher uncertainties, while the inversion using an exact traveltime equation gives similar uncertainties compared to the sea-bed reflection method.

Water Velocity, Turbulence, and Migration Rate of Subyearling Fall Chinook Salmon in the Free‐Flowing and Impounded Snake River

AbstractWe studied the migratory behavior of subyearling fall Chinook salmon Oncorhynchus tshawytscha in free‐flowing and impounded reaches of the Snake River to evaluate the hypothesis that velocity and turbulence are the primary causal mechanisms of downstream migration. The hypothesis states that impoundment reduces velocity and turbulence and alters the migratory behavior of juvenile Chinook salmon as a result of their reduced perception of these cues. At a constant flow (m3/s), both velocity (km/d) and turbulence (the SD of velocity) decreased from riverine to impounded habitat as cross‐sectional areas increased. We found evidence for the hypothesis that subyearling Chinook salmon perceive velocity and turbulence cues and respond to these cues by varying their behavior. The percentage of the subyearlings that moved faster than the average current speed decreased as fish made the transition from riverine reaches with high velocities and turbulence to upper reservoir reaches with low velocities and turbulence but increased to riverine levels again as the fish moved further down in the reservoir, where velocity and turbulence remained low. The migration rate (km/d) decreased in accordance with longitudinal reductions in velocity and turbulence, as predicted by the hypothesis. The variation in migration rate was better explained by a repeated‐measures regression model containing velocity (Akaike's information criterion = 1,769.0) than a model containing flow (2,232.6). We conclude that subyearling fall Chinook salmon respond to changes in water velocity and turbulence, which work together to affect the migration rate.

Flow-dependent growth in the zooxanthellate soft coral Sinularia flexibilis

Growth characteristics of colonies of the branching zooxanthellate octocoral Sinularia flexibilis, with potential pharmaceutical importance, were measured over a range of water velocities. The highest mean specific growth rate (μ d − 1 ) was found at a flow velocity of 11 cm s − 1 . An optimal range of water turbulence was found at a Reynold's number of ≈ 10,000, with a minimum thickness of boundary layer for rapid mass transfer. There was a similar dependency on water velocity for the contents of zooxanthellae, chlorophyll a, and protein, indicating that photosynthesis also runs at an optimum rate at 11 cm s − 1 , thus maximizing coral growth. Moreover, the corals showed morphological responses to the changes in water velocity: increase in the number of protruding branches (buds) in proportion to increased flow and then decrease at higher flows, as well as reduced sizes of the colonies at high velocities.