Water Velocity Fields Research Articles

Swimming in an Unsteady World.

When animals swim in aquatic habitats, the water through which they move is usually flowing. Therefore, an important part of understanding the physics of how animals swim in nature is determining how they interact with the fluctuating turbulent water currents in their environment. We addressed this issue using microscopic larvae of invertebrates in "fouling communities" growing on docks and ships to ask how swimming affects the transport of larvae between moving water and surfaces from which they disperse and onto which they recruit. Field measurements of the motion of water over fouling communities were used to design realistic turbulent wavy flow in a laboratory wave-flume over early-stage fouling communities. Fine-scale measurements of rapidly-varying water-velocity fields were made using particle-image velocimetry, and of dye-concentration fields (analog for chemical cues from the substratum) were made using planar laser-induced fluorescence. We used individual-based models of larvae that were swimming, passively sinking, passively rising, or were passive and neutrally buoyant to determine how their trajectories were affected by their motion through the water, rotation by local shear, and transport by ambient flow. Swimmers moved up and down in the turbulent flow more than did neutrally buoyant larvae. Although more of the passive sinkers landed on substrata below them, and more passive risers on surfaces above, swimming was the best strategy for landing on surfaces if their location was not predictable (as is true for fouling communities). When larvae moved within 5 mm of surfaces below them, passive sinkers and neutrally-buoyant larvae landed on the substratum, whereas many of the swimmers were carried away, suggesting that settling larvae should stop swimming as they near a surface. Swimming and passively-rising larvae were best at escaping from a surface below them, as precompetent larvae must do to disperse away. Velocities, vorticities, and odor-concentrations encountered by larvae fluctuated rapidly, with peaks much higher than mean values. Encounters with concentrations of odor or with vorticities above threshold increased as larvae neared the substratum. Although microscopic organisms swim slowly, their locomotory behavior can affect where they are transported by the movement of ambient water as well as the signals they encounter when they move within a few centimeters of surfaces.

Visualisation and measurement of high-speed pulsating and continuous water jets

The results of an experiment focused on the visualisation of pulsating and continuous water jets are presented in this paper. Water jet technology is widely used for surface cleaning, removal of damaged material layers, preparation of surfaces, and in many other applications. The aim of the experiment was to test the applicability of the shadowgraph technique combined with PIV processing algorithms to visualise water jet structure and analyse flow velocity field. Knowledge of the geometry and velocity fields of pulsating water jets generated by a high-pressure system is necessary for the optimal tuning of the system in respect of the maximum disintegration effect on treated material. Visualisation methods also significantly contribute to the development of new pulsating systems at the design stage. The presented procedures and experimental results demonstrate the above mentioned method as an effective analytical tool for the study of water jet geometry and velocity fields. Problems related to the application of this method are also described in the paper, together with a concept of how the problems could be solved.

Physical modeling of a stepped spillway without sidewalls

The interest of a consulting company in designing stepped spillways in roller compacted concrete (RCC) dams led us to propose the possibility of building this type of spillway without sidewalls. Previous research on stepped spillways has focused on characterizing the complex hydraulic behavior of flow on these structures, as well as design criteria. Such studies have usually been conducted on stepped spillways with a constant width along the spillway, that is, with sidewalls. In the present work, we report the results of the physical modeling of a generic stepped spillway without sidewalls (slope 1v:0.8h). In general terms, the lack of sidewalls produces a lateral expansion of water and therefore a non-uniform longitudinal and transversal discharge distribution. Consequently, the flow type, characteristic water depth, velocity, air concentration, and pressure fields change along and across the spillway. The resulting data demonstrate that the distribution of the different variables studied depend on the s...

GPU implementation of the 2D shallow water equations for the simulation of rainfall/runoff events

Hydrological processes that occur in catchments usually require large space resolution over long periods of time. The advance on numerical methods as well as the increasing power of computation are making possible the physically based simulation of these phenomena. In particular, the 2D shallow water equations can be used to provide distributions of water depth and velocity fields. The necessity of spatial resolution involves the use of a large number of elements hence increasing the computational time when simulating realistic scenarios for a long time period. This work deals with an efficient GPU implementation of the 2D shallow water equations on unstructured meshes analysing the influence of the mesh resolution both on the computational performance and the quality of the results to simulate a rainfall/runoff event. The numerical method to solve them has been developed and compared following three programming approaches: the sequential implementation and its adaptation to the multi-thread and many-core architectures. The particular detail of the influence of the mesh ordering when using unstructured triangular meshes is paid attention in this work to find the best strategy to further reduce the computational time in the context of GPU simulation. The resulting approach is efficient and can become very useful in environmental simulation of hydrological processes.

IDENTIFICATION OF SHIP PROPELLER TORSIONAL VIBRATIONS

The article presents identification methods of ship propeller torsional vibrations in dimensional space and ways for their dumping. Propeller torsional vibrations are caused by static, dynamic and hydrodynamic unbalance of propeller itself and its operation in non-uniform velocity field of ship hull. The propeller working in uneven velocity field of the hull creates cyclic thrust forces, peripheral vibrations of shaft as well as flexural and torsional load of propeller shaft. Vibrations cause additional thrust load on shaft bearings and shaft bending moment. Vibrations of ship hull, particularly its stern section cause variation of pressure field created by propeller. Amplitude of particular parts of the hull comes from the action of cyclic forces created by working ship propeller. They can be very large. Therefore, the ways to reduce vibrations caused by running propeller are very important. Given in the article methods of vibration dumping calculations conduct to determination of vibration dumping coefficients. Calculation results are comparable to measuring results in spite of fact they were determined under assumption of different velocity fields of water flowing through propeller circle. Amplitudes of vibrations depend on number of propeller blades and pulsate with the basic frequency equal to product of the rotational speed and number of blades. Causes of such vibrations and additional load of vessel stern are described in the article. An attention was paid to assure the greatest possible uniformity of velocity field by adequate design of stern shape and accessories. The ways to reduce torsional vibrations of propeller by the appropriate selection of blades number and their accurately machining are also given in the article.

Wave reflection and vortex evolution in Bragg scattering in real fluids

The vortex generation and dissipation accompanying Bragg scattering of water waves propagating over a series of submerged rectangular breakwaters are investigated both numerically and experimentally. The present model, which takes effects of non-linearity, viscosity and turbulence into consideration, is applied to simulate the entire vortex evolution process as water waves pass over a series of artificial rectangular bars. Particle image velocimetry is used to measure the velocity field in the vicinity of the bars. The numerical model is validated via a comparison with measured water surface elevations and velocity fields; the results show good agreement. The mechanism of vortex evolution and its influence on the interaction of water waves with submerged structures for cases with and without resonance are studied. The corresponding wave reflection coefficients for both cases are calculated and compared with experimental data and solutions based on linear wave theory. Examination of the turbulence properties shows that the turbulent intensity decreases on the weather side but increases on the lee side under the Bragg scattering conditions.

Hydrographic situation during cruise M84/3 and P414 (spring 2011) in the Mediterranean Sea

Abstract. Aspects of hydrography and large-scale circulation observed in the Mediterranean Sea during the M84/3 and P414 cruises (April and June 2011, respectively) are presented. In contrast to most of the recent expeditions, which were limited to special areas of the basin, these two cruises, especially the M84/3, offered the opportunity of delineating a quasi-synoptic picture of the distribution of the relevant physical parameters along a section extending through the whole Mediterranean, from the Lebanese coast up to the Strait of Gibraltar. The foci of our analysis are the observed water mass properties and velocity fields. The first are investigated through T–S diagrams and an optimum multiparameter (OMP) analysis and the results are discussed also in the context of recently identified modes of variability; the second are studied by comparing the velocity fields observed using a vessel-mounted Acoustic Doppler Current Profiler and those calculated from the observed density fields. Overall, a distribution of temperature, salinity and geostrophic velocities emerges, which is far from that observed before the beginning of the so-called "Eastern Mediterranean Transient", a major climatic shift in the hydrography and circulation of the Mediterranean Sea which began at the end of the 1980s. The picture which emerges helps to further address the complexity of long-term evolution of hydrography and large-scale circulation of the Mediterranean Sea.

Quantifying lateral and intratidal variability in water level and velocity in a tide‐dominated river using combined RTK GPS and ADCP measurements

Cross‐sectional gradients in water levels and velocities play a determining role in the circulation dynamics of tidal rivers and estuaries. Documenting and analyzing their variability throughout a tidal cycle require observations with high spatial and temporal resolution. A survey strategy and a data analysis procedure have been designed to obtain continuous and synoptic water level and velocity fields over a tidal cycle, along 13 cross‐sections of the St. Lawrence fluvial estuary dominated by large tidal ranges. The method combines both RTK GPS and ADCP technologies for the simultaneous measurement of water levels and velocities along repeated boat transects, allowing fast data acquisition over wide river sections and under rapidly changing conditions. The reconstruction of continuous and synoptic fields is made by interpolation. Simplifying assumptions about data stationarity and/or homogeneity are avoided by adapting the interpolation procedures to the shape and distribution of the underlying data in a space‐time reference frame, thus minimizing distortion in the reconstructed quantities. The capabilities and limitations of the method are assessed through error computations and comparisons with alternate data analysis methods and complementary data sets from tide gauges. With these latest observations, new insights into the tidal hydrodynamics of the St. Lawrence fluvial estuary are gained in regions of contrasting tidal and fluvial properties, specifically related to the effects of channel curvature and bathymetry on tidal propagation and cross‐channel flow properties at the intratidal scale.

River ice flux and water velocities along a 600 km-long reach of Lena River, Siberia, from satellite stereo

Abstract. Knowledge of water-surface velocities in rivers is useful for understanding a range of river processes. In cold regions, river-ice break up and the related downstream transport of ice debris is often the most important hydrological event of the year, leading to flood levels that typically exceed those for the open-water period and to strong consequences for river infrastructure and ecology. Accurate and complete surface-velocity fields on rivers have rarely been produced. Here, we track river ice debris over a time period of about one minute, which is the typical time lag between the two or more images that form a stereo data set in spaceborne, along-track optical stereo mapping. Using a series of nine stereo scenes from the US/Japanese Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard the NASA Terra spacecraft with 15 m image resolution, we measure the ice and water velocity field over a 620 km-long reach of the lower Lena River, Siberia, just above its entry into the Lena delta. Careful analysis and correction of higher-order image and sensor errors enables an accuracy of ice-debris velocities of up to 0.04 m s−1 from the ASTER data. Maximum ice or water speeds, respectively, reach up to 2.5 m s−1 at the time of data acquisition, 27 May 2011 (03:30 UTC). Speeds show clear along-stream undulations with a wavelength of about 21 km that agree well with variations in channel width and with the location of sand bars along the river reach studied. The methodology and results of this study could be valuable to a number of disciplines requiring detailed information about river flow, such as hydraulics, hydrology, river ecology and natural-hazard management.

CANDU-6 감속재 탱크 모형의 유동장 전산해석 및 예비측정

We are planning to construct a scaled-down moderator facility to simulate the CANDU-6 moderator circulation phenomena during steady state operating and accident conditions. In the present work a preliminary experiment using a 1/40 scaled-down moderator tank has been performed to investigate the anticipated problems of the flow visualization and measurement in the planning scaled-down moderator facility. We shortly describe CFD analysis result for the 1/40 scaled-down test model and the flow measurement techniques used for this test facility under isothermal flow conditions. The Particle Image Velocimetry (PIV) method is used to visualize and measure the velocity field of water in a transparent Plexiglas tank. Planar Laser Induced Fluorescence (PLIF) technique is used to evaluate the feasibility of temperature field measurement in the range of of water temperature using an one-color method.

Two-phase flow modelling of spilling and plunging breaking waves

A two-phase flow model, which solves the flow in the air and water simultaneously, has been employed to investigate both spilling and plunging breakers in the surf zone with a focus during wave breaking. The model is based on the Reynolds-averaged Navier–Stokes equations with the k–ϵ turbulence model. The governing equations are solved using the finite volume method, with the partial cell treatment being implemented in a staggered Cartesian grid to deal with complex geometries. The PISO algorithm is utilised for the pressure–velocity coupling and the air–water interface is modelled by the interface capturing method via a high-resolution volume of fluid scheme. Numerical results are compared with experimental measurements and other numerical studies in terms of water surface elevations, mean flow and turbulence intensity, in which satisfactory agreement is obtained. In addition, water surface profiles, velocity and vorticity fields during wave breaking are also presented and discussed. It is shown that the present model is capable of simulating the wave overturning, air entrainment and splash-up processes.

Unstructured finite volume discretisation of bed friction and convective flux in solute transport models linked to the shallow water equations

The finite volume discretisation of the shallow water equations has been the subject of many previous studies, most of which deal with a well-balanced conservative discretisation of the convective flux and bathymetry. However, the bed friction discretisation has not been so profusely analysed in previous works, while it may play a leading role in certain applications of shallow water models. In this paper we analyse the numerical discretisation of the bed friction term in the two-dimensional shallow water equations, and we propose a new unstructured upwind finite volume discretisation for this term. The new discretisation proposed improves the accuracy of the model in problems in which the bed friction is a relevant force in the momentum equation, and it guarantees a perfect balance between gravity and bed friction under uniform flow conditions. The relation between the numerical scheme used to solve the hydrodynamic equations and the scheme used to solve a scalar transport model linked to the shallow water equations, is also analysed in the paper. It is shown that the scheme used in the scalar transport model must take into consideration the scheme used to solve the hydrodynamic equations. The most important implication is that a well-balanced and conservative scheme for the scalar transport equation cannot be formulated just from the water depth and velocity fields, but has to consider also the way in which the hydrodynamic equations have been solved.

AMass Conservation AlgorithmFor Adaptive Unrefinement Meshes Used By Finite Element Methods

The AdaptiveHydraulics (ADH) model is an adaptivefinite element method to simulate three-dimensional Navier-Stokes flow, unsaturated and saturated groundwater flow, overland flow, and two-or three-dimensional shallow-water flow and transport. In the shallow-water flow and transport, especially involving multispecies transport, the water depth (h), the product of water depth and velocities (uh and vh), as well as water depth and chemical concentration (hc) are dependent variables of fluid-motion simulations and are often solved at various times. It is important for the numerical model to predict accurate water depth, velocity fields, and chemical distribution, as well as conserve mass, especially forwater quality applications. Solution accuracydepends highly on mesh resolution. Adaptive mesh refinement (AMR), particularly the h-refinement, is often used to add new nodes in the region where they are needed and to remove others where they are no longer required during the simulation. The AMR is proven to optimize the performance of a computed solution. However, mass withgain or loss can occur when elements are merged due to removing a node at mesh coarsening. Therefore, we develop and implement the mass-conservative unrefinement algorithm to ensure the mass conserved in a merged element in which a node has been removed. This study describes the use of the Galerkin finite element method to redistribute mass to nodes comprising a merged element. The algorithmwas incorporated into the ADH code. This algorithm minimizes mass error during the unrefinement process to conserve mass during the simulation for two-dimensional shallow-water flow and transport. The implementation neither significantly increases the computational time nor memory usage. The simulation was runwithvarious numbersof processors.The resultsshowedgoodscalingof solutiontimeasthenumberof processors increases.

Turbulent velocity measurements in open channel bores

In an open channel, a sudden rise in free-surface elevation is associated with the development of a bore. The bore front is a hydrodynamic shock with a sharp discontinuity in terms of water depth and velocity field. In this study, some turbulent velocity measurements were conducted in breaking bores. The unsteady turbulent properties were analysed using three methods: an ensemble average (EA) technique based upon 20 repeated experiments, a variable interval time average (VITA) method based upon a single experiment, and the variable interval time average (VITA) method averaged over 20 experimental runs. The instantaneous free-surface and velocity measurements showed a marked effect of the bore front passage. The longitudinal velocity components were always characterised by a rapid flow deceleration at all vertical elevations, and some large fluctuations of all velocity components were recorded beneath the surge. The EA and VITA methods showed some comparable long-term trends superposed to some rapid turbulent fluctuations, as well as close results in terms of the turbulent Reynolds stress components. The VITA data based upon a single run presented some differences with the EA median results, but all methods exhibited comparable long-term trends superposed to rapid turbulent fluctuations.

Feature‐based vector simulation of water waves

AbstractWe present a method for simulating local water waves caused by obstacles in water streams for real‐time graphics applications. Given a low‐resolution water surface and velocity field, our method is able to decorate the input water surface with high resolution detail for the animated waves around obstacles. We construct and animate a vector representation of the waves. It is then converted to feature‐aligned meshes for capturing the surfaces of the waves. Results demonstrate that our method has the benefits of real‐time performance and easy controllability. The method also fits well into a state‐of‐the‐art river animation system. Copyright © 2011 John Wiley & Sons, Ltd.

EXPERIMENTAL STUDY ON BOTTOM TOPOGRAPHY CHANGE IN HARBOR DUE TO TSUNAMI

Bottom topography change due to tsunami was experimentally investigated using a rectangular harbor model in a 2-D wave flume. Water surface level and velocity field were obtained as well to discuss the external forces. Accumulation region was observed in the middle of the harbor inside. Formed was conical bed topography. Erosion was around the accumulated region and at the breakwater head as local scour. These topography changes were caused by the tsunami-induced vortices inside the harbor and at the breakwater head.

REFINED HYDRODYNAMIC MODELLING OF THE GIRONDE ESTUARY, FRANCE

In the centre of the Gironde estuary, EDF exploits a power plant. A hydrodynamic model is required to prevent different risks. Indeed, accurate water levels and velocity field are needed for flood control, sediment transport and associated deposition and transport of algae or pollutant. In order to enhance the accuracy of the hydrodynamic results and to tend to a fully predictive model, two attempts have been envisaged. The first one focuses on the tide imposed at the border by a combination of different harmonic waves whose constant harmonics are extracted from a tide model. Harmonic constants from different tide models have been compared and the influence of the harmonics number have been studied. The second attempt focuses on the friction coefficient. The values of the friction coefficient have been calibrated and compared to values predicted by the equation of van Rijn 2007.
 With the calibrated values, the differences between the measured and computed water levels are less than 10 cm.
 With the predictive friction formula, limited accuracy losses have been observed, which demonstrates the feasibility of using van Rijn formula for a configuration such as the Gironde.

Numerical simulation of sediment erosion by submerged jets using an Eulerian model

The erosion of loose beds by submerged circular impinging vertical turbulent jets is simulated using an Eulerian two-phase model which implements Euler-Euler coupled governing equations for fluid and solid phases, and a modified k-ɛ turbulence closure for the fluid phase. Both flow-particle and particle-particle interactions are considered in this model. The predictions of eroded bed profiles agree well with previous laboratory measurements and self-designed experiments. Analysis of the simulated results reveals that the velocity field of the jet water varies with various scouring intensities, that the scour depth and shape are mainly influenced by the driving force of the water when the density, diameter and porosity of the sand are the same, and that the porosity is an important contributor to sediment erosion. In this study, the scour depth, the height of dune and the velocity of the pore water increase with increasing porosity.

Overland flow computations in urban and industrial catchments from direct precipitation data using a two-dimensional shallow water model

This paper presents the experimental validation and the application to a real industrial catchment of a two-dimensional depth-averaged shallow water model used for the computation of rainfall-runoff transformation from direct precipitation data. Instead of using the common approach in flood inundation modelling, which consists in computing the water depth and velocity fields given the water discharge, in this study the rainfall intensity is imposed directly in the model, the surface runoff being generated automatically. The model considers infiltration losses simultaneously with flow simulation. Gullies are also included in the model, although the coupling between the surface runoff and the sewer network is not considered. Experimental validation of the model is presented in several simplified laboratory configurations of urban catchments, in which the surface runoff has been measured for different hyetographs. The application to a real industrial catchment includes a sewer network flow component, which is solved with the SWMM model. The numerical predictions of the discharge hydrograph generated by a 12 hours storm event are compared with field measurements, providing encouraging results.

Three-dimensional numerical study of flow structure in channel confluences

Channel confluence is one of the important features of each river system and some hydraulic structures. The features that can dominantly control flow characteristics in a confluence are confluence angle, discharge, width ratios, and Froude number of flow. Several research studies have been conducted however a comprehensive three-dimensional (3-D) numerical study of flow characteristics in a confluence has not yet been reported. In the present study, SSIIM2.0, a 3-D numerical model, is validated and applied to investigate secondary currents, velocity distribution, flow separation, and water surface elevation in different conditions. The results of the present study illustrate that flow structure and water surface variations in a confluence are highly influenced by confluence angle, discharge, and width ratios as well as Froude number because of their effect on flow deflection, separation, and secondary currents. The graphs from the present study can be used to analyze water surface variation, velocity field, and flow separation dimensions in difference conditions for engineering designs.