Consulta: subjectFacets:"Turbulence"
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Experimental study of bathymetry generated turbulence on tidal turbine behaviour
Provedor de dados: 5
Autores: Gaurier, Benoit; Ikhennicheu, Maria; Germain, Gregory; Druault, Philippe.
In high flow velocity areas like those suitable for tidal applications, turbulence intensity is high and flow variations may have a major impact on tidal turbine behaviour. A three-bladed horizontal axis turbine model (scale 1:20) is positioned in the wake of a square wall-mounted cylinder, representative of specific in situ bathymetric variation, to experimentally study these effects in a current flume tank. Local and global loads are acquired in synchronization with velocity measurements to study the turbine response to flow fluctuations. Velocity measurements need to be obtained close to the turbine, contrary to what is commonly considered, to properly correlate velocity and loads fluctuations. Results show that the loads phase average and their...
Tipo: Text
Palavras-chave: Turbulence; Experimental trials; Wall-mounted cylinder; PIV; LDV; Horizontal axis tidal turbine.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00628/73966/73325.pdf

Experimental analysis of the floor inclination effect on the turbulent wake developing behind a wall mounted cube
Provedor de dados: 5
Autores: Ikhennicheu, Maria; Gaurier, Benoit; Druault, Philippe; Germain, Gregory.
The present study aims at investigating turbulence characteristics in high flow velocity areas like those suitable for marine energy application. The Reynolds number, based on the rugosity height and mean flow velocity, is rather high: . For that purpose, experiments are carried out in a flume tank with as high as achievable in Froude similitude (in the tank: and ). Obstacles are canonical wall-mounted elements chosen to be representative of averaged bathymetric variations: a cube and a cube followed by an inclined floor. First, the wake topology past a canonical wall-mounted cube is illustrated from PIV measurements. Results show a flow behaviour already observed in the literature but for different upstream conditions ( and turbulence intensity). Second,...
Tipo: Text
Palavras-chave: Turbulence; Experimental trials; Wall-mounted obstacles; PIV; POD; Quadrant method.
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00449/56050/57570.pdf

Large-amplitude internal tides, solitary waves, and turbulence in the central Bay of Biscay
Provedor de dados: 5
Autores: Xie, X. H.; Cuypers, Y.; Bouruet-aubertot, P.; Ferron, Bruno; Pichon, Annick; Lourenco, A.; Cortes, Norbert.
Microstructure and fine-scale measurements collected in the central Bay of Biscay during the MOUTON experiment are analyzed to investigate the dynamics of internal waves and associated mixing. Large-amplitude internal tides (ITs) that excite internal solitary waves (ISWs) in the thermocline are observed. ITs are dominated by modes 3 and 4, while ISWs projected on mode 1 that is trapped in the thermocline. Therein, ITs generate a persistent narrow shear band, which is strongly correlated with the enhanced dissipation rate in the thermocline. This strong dissipation rate is further reinforced in the presence of ISWs. Dissipation rates during the period without ISWs largely agree with the MacKinnon-Gregg scaling proposed for internal wavefields dominated by a...
Tipo: Text
Palavras-chave: Internal tides; Solitary waves; Turbulence; Bay of Biscay.
Ano: 2013
URL: http://archimer.ifremer.fr/doc/00151/26232/24299.pdf

On the experimental study of the flow around a fishing net
Provedor de dados: 5
Autores: Pichot, Geraldine; Germain, Gregory; Priour, Daniel.
Selectivity of fishing gears like trawls is obviously conditioned by the fish behaviour but also by the net and the flow. As well, flow may affect fish behaviour. With the aim of a better understanding of the flow in presence of a net and a catch, we suggest, through the experimental study below, to determine and to analyze the flow over a rigid cod-end in two configurations: with a closed and an open net entrance. Trials took place in a free surface flume tank and the flow characteristics were determined from velocity measurements obtained by laser velocimetry (inside, outside and through the meshes of the stiff cod-end). The experimental device, the measures and their analyzes are given here.
Tipo: Text
Palavras-chave: Turbulence; Laser velocimetry; Fluid structure interactions; Experimental study; Hydrodynamics; Fluid mechanics.
Ano: 2009
URL: http://archimer.ifremer.fr/doc/2009/publication-4701.pdf

Planck 2018 results: XII. Galactic astrophysics using polarized dust emission
Provedor de dados: 5
Autores: Aghanim, N.; Akrami, Y.; Alves, Mir; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Ballardini, M.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Basak, S.; Benabed, K.; Bernard, J. -p.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bracco, A.; Bucher, M.; Burigana, C.; Calabrese, E.; Cardoso, J. -f.; Carron, J.; Chary, R. -r.; Chiang, H. C.; Colombo, L. P. L.; Combet, C.; Crill, B. P.; Cuttaia, F.; De Bernardis, P.; De Zotti, G.; Delabrouille, J.; Delouis, Jean Marc; Di Valentino, E.; Dickinson, C.; Diego, J. M.; Dore, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Ensslin, T. A.; Eriksen, H. K.; Falgarone, E.; Fantaye, Y.; Fernandez-cobos, R.; Ferriere, K.; Finelli, F.; Forastieri, F.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frolov, A.; Galeotta, S.; Galli, S.; Ganga, K.; Genova-santos, R. T.; Gerbino, M.; Ghosh, T.; Gonzalez-nuevo, J.; Gorski, K. M.; Gratton, S.; Green, G.; Gruppuso, A.; Gudmundsson, J. E.; Guillet, V.; Handley, W.; Hansen, F. K.; Helou, G.; Herranz, D.; Hivon, E.; Huang, Z.; Jaffe, A. H.; Jones, W. C.; Keihanen, E.; Keskitalo, R.; Kiiveri, K.; Kim, J.; Krachmalnicoff, N.; Kunz, M.; Kurki-suonio, H.; Lagache, G.; Lamarre, J. -m.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Le Jeune, M.; Levrier, F.; Liguori, M.; Lilje, P. B.; Lindholm, V.; Lopez-caniego, M.; Lubin, Pm; Ma, Y. -z.; Macias-perez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Marcos-caballero, A.; Maris, M.; Martin, Pg; Martinez-gonzalez, E.; Matarrese, S.; Mauri, N.; Mcewen, J. D.; Melchiorri, A.; Mennella, A.; Migliaccio, M.; Miville-deschenes, M. -a.; Molinari, D.; Moneti, A.; Montier, L.; Morgante, G.; Moss, A.; Natoli, P.; Pagano, L.; Paoletti, D.; Patanchon, G.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Polastri, L.; Polenta, G.; Puget, J. -l.; Rachen, J. P.; Reinecke, M.; Remazeilles, M.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rubino-martin, J. A.; Ruiz-granados, B.; Salvati, L.; Sandri, M.; Savelainen, M.; Scott, D.; Sirignano, C.; Sunyaev, R.; Suur-uski, A. -s.; Tauber, J. A.; Tavagnacco, D.; Tenti, M.; Toffolatti, L.; Tomasi, M.; Trombetti, T.; Valiviita, J.; Vansyngel, F.; Van Tent, B.; Vielva, P.; Villa, F.; Vittorio, N.; Wandelt, B. D.; Wehus, I. K.; Zacchei, A.; Zonca, A.
Observations of the submillimetre emission from Galactic dust, in both total intensity I and polarization, have received tremendous interest thanks to the Planck full-sky maps. In this paper we make use of such full-sky maps of dust polarized emission produced from the third public release of Planck data. As the basis for expanding on astrophysical studies of the polarized thermal emission from Galactic dust, we present full-sky maps of the dust polarization fraction p, polarization angle psi, and dispersion function of polarization angles ?. The joint distribution (one-point statistics) of p and N-H confirms that the mean and maximum polarization fractions decrease with increasing N-H. The uncertainty on the maximum observed polarization fraction, (max) =...
Tipo: Text
Palavras-chave: Polarization; Magnetic fields; Turbulence; Dust; Extinction; Local insterstellar matter; Submillimeter: ISM.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00654/76632/77786.pdf

The influence of environment and spawning distribution on the survival of anchovy (Engraulis encrasicolus) larvae in the Bay of Biscay (NE Atlantic) investigated by biophysical simulations
Provedor de dados: 5
Autores: Allain, Gwenhael; Petitgas, Pierre; Lazure, Pascal.
A growth and survival model of the early life stages was run along virtual drift trajectories tracked in a hydrodynamic model to simulate the annual recruitment process of anchovy (Engraulis encrasicolus) in the Bay of Biscay (NE Atlantic). These biophysical simulations concerning three different years were analysed in order to investigate the influence of environment and spawning dynamics on the survival of larvae and juveniles. The location of space-time survival windows suggested major environmental mechanisms involved in simulated recruitment variability at the different scales - retention of larvae and juveniles in favourable habitats over the shelf margins and turbulence effects. These small-scale and meso-scale mechanisms were related to the...
Tipo: Text
Palavras-chave: Turbulence; Retention; Recruitment; Physical biological interactions; Larval survival; IBM; Biscay; Anchovy.
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/publication-3423.pdf

Étude expérimentale de la turbulence dans les zones à forts courants et de son impact sur les hydroliennes
Provedor de dados: 5
Autores: Ikhennicheu, Maria.
French waters have a strong potential for tidal turbines applications. In these areas of strong currents, intense velocity fluctuations are observed in the water column. They ultimately come from variations in seabed bathymetry and can have a strong impact on tidal turbine energy production and fatigue. In order to understand the turbulent structures generation in the wake of obstacles and to build a data base for future numerical studies, the Alderney Race conditions are reproduced experimentally, in a wave and current tank, in Froude similitude and with a Reynolds number as high as possible. In this study, real bathymetric variations are represented using canonical elements : a cube, a cylinder, an inclined plane or a combination of all three. Cases with...
Tipo: Text
Palavras-chave: Turbulence; Essais expérimentaux; Hydroliennes; Obstacles; Sillage; PIV; LDV; POD; Turbulence; Experimental trials; Tidal turbines; Obstacles; Wake; PIV; LDV; POD.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00590/70177/68193.pdf

Contrasted turbulence intensities in the Indonesian Throughflow: a challenge for parameterizing energy dissipation rate
Provedor de dados: 5
Autores: Bouruet-aubertot, Pascale; Cuypers, Yannis; Ferron, Bruno; Dausse, Denis; Menage, Olivier; Atmadipoera, Agus; Jaya, Indra.
Microstructure measurements were performed along two sections through the Halmahera Sea and the Ombai Strait and at a station in the deep Banda Sea. Contrasting dissipation rates (&#x1d716;) and vertical eddy diffusivities (K z ) were obtained with depth-averaged ranges of ∼[9×10−10−10−5] W kg− 1 and of ∼[1×10−5−2×10−3] m2 s− 1, respectively. Similarly, turbulence intensity, I=ϵ/(νN2) with ν the kinematic viscosity and N the buoyancy frequency, was found to vary seven orders of magnitude with values up to 107. These large ranges of variations were correlated with the internal tide energy level, which highlights the contrast between regions close and far from internal tide generations. Finescale parameterizations of &#x1d716; induced by the breaking of...
Tipo: Text
Palavras-chave: Turbulence; Internal tides; Vertical mixing; Parameterization; Indonesian seas; Microstructure measurements.
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00441/55240/56792.pdf

Hydrodynamics and SPM transport in a man-engineered tidal estuary: The Adour river (France)
Provedor de dados: 5
Autores: Defontaine, Sophie; Sous, Damien; Morichon, Denis; Verney, Romaric; Monperrus, Mathilde.
The present paper reports on a series of field experiments aiming to characterise the functioning of a man-engineered strongly forced salt-wedge estuary: the lower estuary of the Adour river, France. Bottom-moored velocity measurements and surface boat surveys have been performed under low river discharge conditions, for both neap and spring tides, in order to provide a well-documented reference framework to understand the dynamics of water masses, turbulence and suspended particulate matter (SPM) transport in the lower estuary. An additional campaign has been carried out in high river discharge conditions. This first documented in-situ study of the Adour lower estuary demonstrates its variability in terms of hydrological regimes, from salt-wedge to...
Tipo: Text
Palavras-chave: Salt-wedge estuary; Estuarine circulation; Stratification; Turbulence; Suspended particles transport; Adour river.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00588/70049/67987.pdf

Turbulence analysis and multiscale correlations between synchronized flow velocity and marine turbine power production
Provedor de dados: 5
Autores: Medina, Olmo Duran; Schmitt, Francois G.; Calif, Rudy; Germain, Gregory; Gaurier, Benoit.
The correlation between the flow turbulence and the performances of a marine current turbine is studied. First, the incoming flow encountered in the flume tank is characterized in the framework of fully developed turbulent cascades in the inertial range. The Reynolds number, the Kolmogorov dissipation scale and the integral scale, are estimated from flow measurements. The intermittency of the turbulence is characterized in the lognormal multifractal framework, and the influence of the turbulent flow on the turbine power is assessed. The rotor speed control unit characteristics used for the turbine regulation induces non-negligible effects on the turbine behavior under fluctuations loads. Even if the power spectrum does not reveal any scale invariance, a...
Tipo: Text
Palavras-chave: Marine energy; Turbulence; Multifractal energy cascade; Intermittency; Turbine power production; High frequency data rate.
Ano: 2017
URL: http://archimer.ifremer.fr/doc/00385/49620/50134.pdf

Observations of turbulence within the surf and swash zone of a field-scale sandy laboratory beach
Provedor de dados: 5
Autores: Brinkkemper, J. A.; Lanckriet, T.; Grasso, Florent; Puleo, J. A.; Ruessink, B. G.
Current coastal-evolution models generally lack the ability to accurately predict bed level change in shallow (&lt;~2 m) water, which is, at least partly, due to the preclusion of the effect of surface-induced turbulence on sand suspension and transport. As a first step to remedy this situation, we investigated the vertical structure of turbulence in the surf and swash zone using measurements collected under random shoaling and plunging waves on a steep (initially 1:15) field-scale sandy laboratory beach. Seaward of the swash zone, turbulence was measured with a vertical array of three Acoustic Doppler Velocimeters (ADVs), while in the swash zone two vertically spaced acoustic doppler velocimeter profilers (Vectrino profilers) were applied. The vertical...
Tipo: Text
Palavras-chave: Turbulence; Plunging breakers; Swash; Laboratory experiment.
Ano: 2016
URL: http://archimer.ifremer.fr/doc/00277/38812/37538.pdf

Experimental investigation of the turbulent wake past real seabed elements for velocity variations characterization in the water column.
Provedor de dados: 5
Autores: Ikhennicheu, Maria; Germain, Gregory; Druault, Philippe; Gaurier, Benoit.
In high flow velocity areas like those suitable for marine energy application, bathymetry variations create strong velocity fluctuations in the water column. It is therefore essential to characterize the turbulence evolution in the wake of seabed elements which may impact the loads on tidal turbines. For that purpose, experiments are carried out in a flume tank with Re as high as achievable in Froude similitude, with bathymetry variations experimentally represented with various wall-mounted square elements of height H: a cylinder or a cube as unitary obstacles and combinations of these elements followed by an inclined floor to resemble smooth bathymetry changes. The onset flow is a simple boundary layer profile with height 1.3 H and a low turbulence...
Tipo: Text
Palavras-chave: Turbulence; Experimental trials; Wall-mounted obstacles; PIV; LDV; Marine energy.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00502/61356/64997.pdf

Experimental study of the turbulence intensity effects on marine current turbines behaviour. Part II: Two interacting turbines
Provedor de dados: 5
Autores: Mycek, Paul; Gaurier, Benoit; Germain, Gregory; Pinon, Gregory; Rivoalen, Elie.
The future implantation of second generation marine current turbine arrays depends on the understanding of the negative interaction effects that exist between turbines in close proximity. This is especially the case when the turbines are axially aligned one behind another in the flow.  In order to highlight these interaction effects, experiments were performed in a flume tank on 3-bladed 1/30th scale prototypes of horizontal axis turbines.  This work focuses on the interactions between two horizontal axis marine current turbines, axially aligned with the upstream flow. Thrust and power coefficients function of the rotation speed of the downstream device are presented. Besides, the wake of each turbine is characterised so as to explain their behaviour.  A...
Tipo: Text
Palavras-chave: Marine current turbine; Performance; Wake; Turbulence; Array; Tidal turbine.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00175/28644/27110.pdf

Turbulent viscosity in natural surf zones
Provedor de dados: 5
Autores: Grasso, Florent; Ruessink, B. G.
Waves breaking in the shallow surf zone near the shoreline inject turbulence into the water column that may reach the bed to suspend sediment. Breaking-wave turbulence in the surf zone is, however, poorly understood, which is one of the reasons why many process-based coastal-evolution models predict coastal change during severe storms inadequately. Here, we use data collected in two natural surf zones to derive a new parameterization for the stability function C-mu that determines the magnitude of the eddy viscosity nu(t) in two-equation turbulent-viscosity models, nu(t) = C(mu)k(2)/epsilon, where k is turbulent kinetic energy and epsilon is the turbulence dissipation rate. In both data sets, the ratio of turbulence production to dissipation is small...
Tipo: Text
Palavras-chave: Eddy viscosity; Field measurements; Parameterization; Production; Surf zone; Turbulence.
Ano: 2012
URL: https://archimer.ifremer.fr/doc/00114/22512/20204.pdf

A comprehensive assessment of turbulence at a tidal-stream energy site influenced by wind-generated ocean waves
Provedor de dados: 5
Autores: Thiébaut, Maxime; Filipot, Jean-francois; Maisondieu, Christophe; Damblans, Guillaume; Duarte, Rui; Droniou, Eloi; Chaplain, Nicolas; Guillou, Sylvain.
Velocity measurements collected by an upward-looking acoustic Doppler current profiler were used to provide the first study of ambient turbulence in Alderney Race. Turbulence metrics were estimated at mid-depth during peak flooding and ebbing tidal conditions. The dissipation rate ε and the integral lengthscale (L) were estimated using two independent methods: the spectral method and the structure function method. The spectral method provided ε and (L) estimates with standard deviations twice lower than that obtained from the structure function method. Removal of wave and Doppler noise-induced bias when estimating the dissipation rate was shown to be a crucial step in turbulence characterization. It allowed for a significant refining in (L) estimates...
Tipo: Text
Palavras-chave: Turbulence; Tidal energy; Wave; Doppler noise; ADCP; Alderney Race.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00592/70394/68478.pdf

Multidecadal variability of the overturning circulation in presence of eddy turbulence
Provedor de dados: 5
Autores: Huck, Thierry; Arzel, Olivier; Sevellec, Florian.
At low-resolution, idealized ocean circulation models forced by prescribed differential surface heat fluxes show spontaneous multidecadal variability depending critically on eddy diffusivity coefficients. The existence of this critical threshold in the range of observational estimates legitimates some doubt on the relevance of such intrinsic oscillations in the real ocean. Through a series of numerical simulations with increasing resolution up to eddy-resolving ones (10 km) and various diapycnal diffusivities, this multidecadal variability proves a generic ubiquitous feature, at least in model versions with a flat bottom. The mean circulation largely changes in the process of refining the horizontal grid (along with the associated implicit viscosity and...
Tipo: Text
Palavras-chave: Circulation/ Dynamics; Meridional overturning circulation; Rossby waves; Turbulence; Variability; Multidecadal variability.
Ano: 2015
URL: http://archimer.ifremer.fr/doc/00251/36243/34798.pdf

An Assessment of the Precision and Confidence of Aquatic Eddy Correlation Measurements
Provedor de dados: 5
Autores: Donis, Daphne; Holtappels, Moritz; Noss, Christian; Cathalot, Cecile; Hancke, Kasper; Polsenaere, Pierre; Wenzhoefer, Frank; Lorke, Andreas; Meysman, Filip J. R.; Glud, Ronnie N.; Mcginnis, Daniel F.
The quantification of benthic fluxes with the aquatic eddy correlation (EC) technique is based on simultaneous measurement of the current velocity and a targeted bottom water parameter (e.g., O2, temperature). High-frequency measurements (64 Hz) are performed at a single point above the seafloor using an acoustic Doppler velocimeter (ADV) and a fast-responding sensor. The advantages of aquatic EC technique are that 1) it is noninvasive, 2) it integrates fluxes over a large area, and 3) it accounts for in situ hydrodynamics. The aquatic EC has gained acceptance as a powerful technique; however, an accurate assessment of the errors introduced by the spatial alignment of velocity and water constituent measurements and by their different response times is...
Tipo: Text
Palavras-chave: Turbulence; Boundary layer; Fluxes; Instrumentation/sensors; Optimization; Experimental design.
Ano: 2015
URL: https://archimer.ifremer.fr/doc/00275/38577/37102.pdf

Experimental study of coherent flow structures past a wall-mounted square cylinder
Provedor de dados: 5
Autores: Ikhennicheu, Maria; Germain, Gregory; Druault, Philippe; Gaurier, Benoit.
In high flow velocity areas like those suitable for tidal applications, turbulence intensity is high and flow variations may have a major impact on tidal turbines behaviour. Large boils that can be observed at the sea surface are emitted from the sea floor and may interact with the tidal turbines. These boils have then to be characterized. The Reynolds number, based on the rugosity height and the mean flow velocity, is rather high in this context: Re ¼ 2:5 107. For that purpose, experiments are carried out in a flume tank with Re as high as achievable in Froude similitude (in the tank: Re ¼ 2:5  105 and Fr ¼ 0:23) in order to study coherent flow structures emitted behind seabed obstacles. The obstacle is here a canonical square wall-mounted cylinder chosen...
Tipo: Text
Palavras-chave: Turbulence; Experimental trials; Wall-mounted cylinder; PIV; LDV; POD; Lamb-Oseen.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00494/60527/64189.pdf

Comparison of synthetic turbulence approaches for blade element momentum theory prediction of tidal turbine performance and loads
Provedor de dados: 5
Autores: Togneri, Michael; Pinon, Grégory; Carlier, Clement; Choma Bex, Camille; Masters, Ian.
Turbulence is a crucial flow phenomenon for tidal energy converters (TECs), as it influences both the peak loads they experience and their fatigue life. To best mitigate its effects we must understand both turbulence itself and how it induces loads on TECs. To that end, this paper presents the results of blade element momentum theory (BEMT) simulations of flume-scale TEC models subjected to synthetic turbulent flows. Synthetic turbulence methods produce three-dimensional flowfields from limited data, without solving the equations governing fluid motion. These flowfields are non-physical, but match key statistical properties of real turbulence and are much quicker and computationally cheaper to produce. This study employs two synthetic turbulence generation...
Tipo: Text
Palavras-chave: BEMT; SEM; Sandia; Tidal turbines; Turbulence; Simulation.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00501/61248/64828.pdf

Assimilation de données par méthode variationnelle utilisant l’adjoint d’un code de circulation côtière tridimensionnel
Provedor de dados: 5
Autores: Devenon, Jean-luc; Dekeyser, I; Leredde, Y; Lellouche, Jm.
The optimal control technique using an adjoint method is applied to fit the parameters of a 3-D primitive equation coastal model due to a data assimilation procedure. Two of the main unknowns of coastal modelling operations - open boundary conditions and turbulent mixing processes in stratified conditions - are successively considered. The aim of the boundary control procedure is to identify boundary forcing to ensure the best fit between data and model results by minimising a function that measures model and data discrepancies. A methodology for proceeding from the continuous to the discrete formulation of a control problem is given. The robustness of the method is tested for the typical barotropic case of a semi-enclosed basin Kelvin wave. The data...
Tipo: Text
Palavras-chave: Data assimilation; 3-D coastal circulation; Boundary conditions fitting; Adjoint method; Turbulence; Data assimilation; 3-D coastal circulation; Boundary conditions fitting; Adjoint method; Turbulence.
Ano: 2001
URL: http://archimer.ifremer.fr/doc/00322/43337/42890.pdf

The importance of turbulent kinetic energy on transport of juvenile clams (Mya arenaria)
Provedor de dados: 5
Autores: Redjah, I.; Olivier, Frederic; Tremblay, R.; Myrand, B.; Pernet, Fabrice; Neumeier, U.; Chevarie, L.
Soft-shell clam, Mya arenaria, culture on the east coast of Canada is characterized by high loss following seeding. To evaluate the importance of passive transport due to currents, an experimental flume study was designed. The purpose was to measure the effects of hydrodynamic conditions, substrate, and clam size on dispersal in controlled laboratory condition and to interpret these results in relation to field measurements. Unidirectional currents with gradual increasing velocities (0 to 60 cm s(-1)) were applied to three substrates (muddy sand, medium sand, and coarse sand) in which clams from one of three size classes (10, 15, and 20 mm) had burrowed. We also examined the resulting effects of turbulent kinetic energy on the erosion of medium-grain sand...
Tipo: Text
Palavras-chave: Clam transport; Substratum erosion; Unidirectional currents; Turbulence; ADV; Flume.
Ano: 2010
URL: http://archimer.ifremer.fr/doc/00014/12507/9368.pdf

The Role of Curvature in Modifying Frontal Instabilities. Part I: Review of Theory and Presentation of a Nondimensional Instability Criterion
Provedor de dados: 5
Autores: Buckingham, Christian; Gula, Jonathan; Carton, Xavier.
In this study, we examine the role of curvature in modifying frontal stability. We first evaluate the classical criterion that the Coriolis parameter f multiplied by the Ertel potential vorticity (PV) q is positive for stable flow and that instability is possible when this quantity is negative. The first portion of this statement can be deduced from Ertel’s PV theorem, assuming an initially positive fq. Moreover, the full statement is implicit in the governing equation for the mean geostrophic flow, as the discriminant, fq, changes sign. However, for curved fronts in cyclogeostrophic or gradient wind balance (GWB), an additional term enters the discriminant owing to conservation of absolute angular momentum L. The resulting expression, (1 + Cu)fq &lt; 0 or...
Tipo: Text
Palavras-chave: Instability; Ocean dynamics; Potential vorticity; Turbulence; Frontogenesis/frontolysis; Fronts; Vortices; Angular momentum.
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00677/78920/81288.pdf

Diagnosing Surface Mixed Layer Dynamics from High-Resolution Satellite Observations: Numerical Insights
Provedor de dados: 5
Autores: Ponte, Aurelien; Klein, Patrice; Capet, Xavier; Le Traon, Pierre-yves; Chapron, Bertrand; Lherminier, Pascale.
High-resolution numerical experiments of ocean mesoscale eddy turbulence show that the wind-driven mixed layer (ML) dynamics affects mesoscale motions in the surface layers at scales lower than O(60 km). At these scales, surface horizontal currents are still coherent to, but weaker than, those derived from sea surface height using geostrophy. Vertical motions, on the other hand, are stronger than those diagnosed using the adiabatic quasigeotrophic (QG) framework. An analytical model, based on a scaling analysis and on simple dynamical arguments, provides a physical understanding and leads to a parameterization of these features in terms of vertical mixing. These results are valid when the wind-driven velocity scale is much smaller than that associated with...
Tipo: Text
Palavras-chave: Mesoscale processes; Ocean dynamics; Turbulence.
Ano: 2013
URL: http://archimer.ifremer.fr/doc/00170/28076/26291.pdf

Modélisation et analyse numérique du couplage filet-écoulement hydrodynamique dans une poche de chalut
Provedor de dados: 5
Autores: Pichot, Geraldine.
We are interested in the numerical simulation of the catch process at the end part of a trawl. The study of previous works emphasizes the lack of a convincing flow model. The need of a physical understanding of the flow leads us to perform experimental campaigns around a rigid cod-end net model, whose results are given in the manuscript. We propose a model based on the Navier-Stokes/Brinkman equations coupled to an equation for the turbulent kinetic energy by the means of an eddy viscosity, with appropriate boundary conditions. Existence of a weak solution to our coupled problem is proved in dimension 2. Then, we present the axisymmetric code we developed, called SeaNet. We set the parameters of the model and validate the code by comparison with the...
Tipo: Text
Palavras-chave: Finite Element Method; Numerical simulations; Variational formulations; Modelling; Fluid/structure interactions; Turbulence; Fluid mechanics; Selectivity of fishing gear; Méthode des éléments finis; Simulations numériques; Formulations variationnelles; Modélisation; Intéractions fluide/structure; Turbulence; Mécanique des fluides; Sélectivité des engins de pêche.
Ano: 2007
URL: http://archimer.ifremer.fr/doc/2007/these-3350.pdf

The merging of Kelvin–Helmholtz vortices into large coherent flow structures in a high Reynolds number flow past a wall-mounted square cylinder
Provedor de dados: 5
Autores: Mercier, Philippe; Ikhennicheu, Maria; Guillou, Sylvain; Germain, Gregory; Poizot, Emmanuel; Grondeau, Mikaël; Thiébot, Jérôme; Druault, Philippe.
Flows at tidal-stream energy sites are characterised by high turbulence intensities and by the occurrence of highly energetic large and coherent flow structures. The interaction of the flow with seabed roughness is suspected to play a major role in the generation of such coherent flow structures. The problem is introduced with canonical wall-mounted square obstacles representing abrupt changes of bathymetry, with high Reynolds number flow (Re = 250000). Two methods are used: a numerical model, based on the LBM (Lattice Boltzmann Method) combined with LES (Large Eddy Simulation) and an experimental set-up in a circulating tank. The numerical model is validated by comparison with experimental data. In the case of a wall-mounted square cylinder, large-scale...
Tipo: Text
Palavras-chave: Turbulence; Coherent flow structure; Numerical simulation; Lattice Boltzmann Method; Large Eddy Simulation; Wall-mounted obstacles.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00617/72940/72147.pdf

Mise en évidence de l’importance de la turbulence ambiante sur les effets d’interaction entre hydroliennes
Provedor de dados: 5
Autores: Kervella, Youen; Germain, Gregory; Gaurier, Benoit; Facq, Jean-valery; Bacchetti, Thomas.
Les futures zones d’implantation des parcs hydroliens en mer sont caractérisées par des courants de forte intensité et des taux de turbulence importants. Cette turbulence de l’écoulement est susceptible d’altérer le comportement des hydroliennes, à la fois en termes de production d’énergie mais aussi de fatigue structurelle. Afin de déterminer l’influence de la turbulence ambiante sur les effets d’interaction entre hydroliennes, des essais expérimentaux ont été effectués dans un bassin à houle et courant, sur des maquettes d’hydroliennes tri-pales à axe horizontal, régulées en vitesse de rotation. Les interactions entre trois hydroliennes placées sur deux rangées (deux hydroliennes sur la rangée amont et une sur la rangée aval, ou inversement) ont été...
Tipo: Text
Palavras-chave: Énergie marine; Hydroliennes; Turbulence; Effets d'interaction; Essais expérimentaux.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00212/32342/30782.pdf

Nutrient Patchiness, Phytoplankton Surge-Uptake, and Turbulent History: A Theoretical Approach and Its Experimental Validation
Provedor de dados: 5
Autores: Schapira, Mathilde; Seuront, Laurent.
Despite ample evidence of micro- and small-scale (i.e., millimeter- to meter-scale) phytoplankton and zooplankton patchiness in the ocean, direct observations of nutrient distributions and the ecological importance of this phenomenon are still relatively scarce. In this context, we first describe a simple procedure to continuously sample nutrients in surface waters, and subsequently provide evidence of the existence of microscale distribution of ammonium in the ocean. We further show that ammonium is never homogeneously distributed, even under very high conditions of turbulence. Instead, turbulence intensity appears to control nutrient patchiness, with a more homogeneous or a more heterogeneous distribution observed under high and low turbulence...
Tipo: Text
Palavras-chave: Nutrient patchiness; Turbulence; Phytoplankton; Surge uptake; Nutrient depletion; Turbulent history.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00643/75527/76435.pdf

Experimental study of the turbulence intensity effects on marine current turbines behaviour. Part I: One single turbine
Provedor de dados: 5
Autores: Mycek, Paul; Gaurier, Benoit; Germain, Gregory; Pinon, Gregory; Rivoalen, Elie.
The ambient turbulence intensity in the upstream flow plays a decisive role in the behaviour of horizontal axis marine current turbines.  Experimental trials, run in the IFREMER flume tank in Boulogne-Sur-Mer (France) for two different turbulence intensity rates, namely 3% and 15%, are presented. They show, for the studied turbine configuration, that while the wake of the turbine is deeply influenced by the ambient turbulence conditions, its mean performances turn out to be slightly modified.  The presented conclusions are crucial in the view of implanting second generation turbines arrays. In addition, complete and detailed data sets (wake profiles and performance graphs) are made available to the scientific community in order to encourage further...
Tipo: Text
Palavras-chave: Marine current turbine; Performance; Wake; Turbulence; Experiment; Flume tank.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00175/28647/27171.pdf

Phytoplankton Orientation in a Turbulent Ocean: A Microscale Perspective
Provedor de dados: 5
Autores: Basterretxea, G.; Font-munoz, Joan Salvador; Tuval, I.
Phytoplankton are by definition autotrophic microorganisms that passively drift with fluid motion. Accordingly, the traditional view of a turbulence-homogenized phytoplankton distribution in the ocean, where cells randomly organize and interact, is deeply rooted in biological oceanography studies. However, increasing understanding of microscopic processes in the ocean is revealing a world of microscale patterns resulting from cell behaviors and fluid-cell interactions that challenges this vision. Autotrophic cells have developed active (i.e., flagella) and passive (i.e., morphological structures and vesicles) motility mechanisms that allow them different degrees of spatial control. Their complex interaction with the ocean physicochemical landscape commonly...
Tipo: Text
Palavras-chave: Phytoplankton; Microscale; Turbulence; Orientation; Shear.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00621/73261/72476.pdf

Three tidal turbines in interaction: An experimental study of turbulence intensity effects on wakes and turbine performance
Provedor de dados: 5
Autores: Gaurier, Benoit; Carlier, Clement; Germain, Gregory; Pinon, Grégory; Rivoalen, Elie.
The development of marine current turbine arrays depends on the understanding of the interaction effects that exist between turbines in close proximity. Moreover, the ambient turbulence intensity also plays a major role in the behaviour of tidal turbines. Thus it is necessary to take ambient turbulence into account when studying interaction effects between several turbines. In order to highlight these interaction effects, experiments have been carried out in the IFREMER flume tank. These experiments focus on interactions between three horizontal axis turbines. This paper presents the experimental results obtained for three configurations with two ambient turbulence intensity rates. The results are presented in terms of turbine wakes and performance. The...
Tipo: Text
Palavras-chave: Marine current turbine; Performance; Wake; Turbulence; Array interaction; Experiment.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00588/69992/67900.pdf

Étude expérimentale des performances d’une hydrolienne, soumise aux effets de la turbulence et de l’interaction houle-courant
Provedor de dados: 5
Autores: Gaurier, Benoit.
In the context of global warming, the extraction of energy by tidal turbines from marine currents must be integrated into the future energetic mix. Being confronted with a difficult marine environment, it is required to know the turbines’ behaviour when they are submitted to realistic solicitations to guarantee an optimal use. In this work, the marine turbine performance is studied when the machine is submitted to a turbulent current or a combined wave-current effect. The physical representation of trials at reduced scale is first described focusing on the incoming flow characterisation and its effects on a turbine model at 1:20 scale. The location and measurement type of the upstream velocity are discussed to accurately define its performance and its...
Tipo: Text
Palavras-chave: Hydrolienne; Énergie marine renouvelable; Essais expérimentaux; PIV; LDV; Turbulence; Interaction houle-courant; Horizontal axis tidal turbine; Renewable energy; Experimental trials; PIV; LDV; Turbulence; Wave-current interaction.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00660/77197/78624.pdf

Influence of Reynolds number and forcing type in a turbulent von Karman flow
Provedor de dados: 5
Autores: Saint-michel, Brice; Dubrulle, B.; Marie, Louis; Ravelet, F.; Daviaud, F.
We present a detailed study of a global bifurcation occuring in a turbulent von Karman swirling flow. In this system, the statistically steady states progressively display hysteretic behaviour when the Reynolds number is increased above the transition to turbulence. We examine in detail this hysteresis using asymmetric forcing conditions-rotating the impellers at different speeds. For very high Reynolds numbers, we study the sensitivity of the hysteresis cycle-using complementary particle image velocimetry and global mechanical measurements-to the forcing nature, imposing either the torque or the speed of the impellers. New mean states, displaying multiple quasi-steady states and negative differential responses, are experimentally observed in torque...
Tipo: Text
Palavras-chave: Turbulence; Instability; Negative response; Symmetry.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00204/31503/29904.pdf

Modélisation des blooms de Gymnodinium mikimotoï le long de la façade atlantique française : répartition spatiale
Provedor de dados: 5
Autores: Loyer, Sophie; Lazure, Pascal; Gentien, Patrick; Menesguen, Alain.
In order to study the occurrence of Gymnodinium mikimotoï bloom on the French Atlantic coast, a three-dimensional model of primary production was set up. The biological model was coupled to a hydrodynamic model previously developed at Ifremer, by the intermediary of transport, diffusion and heat fluxes. The cycles of three limiting elements for the phytoplankton growth were modelised: nitrogen, phosphorus and silicon. The second phase of the study aimed at reproducing the summer dinoflagellate blooms. In this new approach a model of the species Gymnodinium mikimotoï was coupled with the previous biomass model which provides the physical and chemical environments. The study focuses on the results obtained by this specific sub-model. The parametrisation was...
Tipo: Text
Palavras-chave: Turbulence; Dinoflagellés; Gymnodinium mikimotoï; Modèle; Nutriments; Turbulence; Dinoflagellate; Gymnodinium mikimotoï; Model; Nutrients.
Ano: 2001
URL: https://archimer.ifremer.fr/doc/00479/59100/61738.pdf

The evolution of light and vertical mixing across a phytoplankton ice-edge bloom
Provedor de dados: 5
Autores: Randelhoff, Achim; Ozierm, Laurent; Massicotte, Philippe; Becu, Guislain; Gali, Marti; Lacour, Leo; Dumont, Dany; Vladoiu, Anda; Marec, Claudie; Bruyant, Flavienne; Houssais, Marie-noelle; Tremblay, Jean-eric; Deslongchamps, Gabriele; Babin, Marcel.
During summer, phytoplankton can bloom in the Arctic Ocean, both in open water and under ice, often strongly linked to the retreating ice edge. There, the surface ocean responds to steep lateral gradients in ice melt, mixing, and light input, shaping the Arctic ecosystem in unique ways not found in other regions of the world ocean. In 2016, we sampled a high-resolution grid of 135 hydrographic stations in Baffin Bay as part of the Green Edge project to study the ice-edge bloom, including turbulent vertical mixing, the under-ice light field, concentrations of inorganic nutrients, and phytoplankton biomass. We found pronounced differences between an Atlantic sector dominated by the warm West Greenland Current and an Arctic sector with surface waters...
Tipo: Text
Palavras-chave: Arctic; Phytoplankton; Ice edge; Spring bloom; Light; Turbulence.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00504/61530/65391.pdf

Modélisation biophysique pour la prévision du recrutement
Provedor de dados: 5
Autores: Allain, Gwenhael.
Exploited fish populations are dependent on recruitment (i.e. size of the new year class) to sustain their abundance. Recruitment variations are related to hydroclimatic variations and may accentuate the detrimental effects of fishing. Recruitment prediction requires accurate fisheries oceanographic tools, which are expected to be more reliable than large-scale correlation analyses between fish abundance and climate variables.  Recruitment is the result of the integration over a season and large oceanic areas of processes affecting larval survival, which are dependent on small-scale mechanisms. Hydrodynamic models are a tool to perform this integration. This thesis aims at exploring and modelling physical-biological interaction mechanisms in order to...
Tipo: Text
Palavras-chave: Anchovy; Upwelling; Turbulence; Retention; Fisheries management; Population dynamics; Stock environment interaction; Stock recruitment relation; Scale integration; Individual based models; Survival; Growth; Otolith; Physical biological interactions; Prediction; Recruitment; Turbulence; Rétention; Méso échelle; Intégration des échelles; Modèle de survie; Modèle de ponte; Modèles individu centrés; Modèles de corrélation; Modèles stochastiques; Juvéniles; Larves; Otolithe; Modèle de croissance; Interactions physique biologie; Prévision; Recrutement.
Ano: 2004
URL: http://archimer.ifremer.fr/doc/2004/these-5.pdf

A stochastic method to account for the ambient turbulence in Lagrangian Vortex computations
Provedor de dados: 5
Autores: Choma Bex, Camille; Carlier, Clement; Fur, Arnaud; Pinon, Gregory; Germain, Gregory; Rivoalen, Elie.
This paper describes a detailed implementation of the Synthetic Eddy Method (SEM) initially presented in Jarrin et al. (2006) applied to the Lagrangian Vortex simulation. While the treatment of turbulent diffusion is already extensively covered in scientific literature, this is one of the first attempts to represent ambient turbulence in a fully Lagrangian framework. This implementation is well suited to the integration of PSE (Particle Strength Exchange) or DVM (Diffusion Velocity Method), often used to account for molecular and turbulent diffusion in Lagrangian simulations. The adaptation and implementation of the SEM into a Lagrangian method using the PSE diffusion model is presented, and the turbulent velocity fields produced by this method are then...
Tipo: Text
Palavras-chave: Ambient turbulence; Synthetic Eddy Method; Lagrangian method; Turbulence; Vortex method; Wake.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00652/76458/77550.pdf

Coherent structures in wall-bounded turbulence
Provedor de dados: 42
Autores: Dennis,David J.C.
The inherent difficulty of understanding turbulence has led to researchers attacking the topic in many different ways over the years of turbulence research. Some approaches have been more successful than others, but most only deal with part of the problem. One approach that has seen reasonable success (or at least popularity) is that of attempting to deconstruct the complex and disorganised turbulent flow field into to a set of motions that are in some way organised. These motions are generally called "coherent structures". There are several strands to this approach, from identifying the coherent structures within the flow, defining their characteristics, explaining how they are created, sustained and destroyed, to utilising their features to model the...
Tipo: Info:eu-repo/semantics/article
Palavras-chave: Turbulence; Wall bounded flows; Coherent structures; Particle image velocimetry.
Ano: 2015
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652015000201161

Wall function treatment for bubbly boundary layers at low void fractions
Provedor de dados: 42
Autores: SOARES,DANIEL V.; BITENCOURT,MARCELO C; LOUREIRO,JULIANA B.R.; SILVA FREIRE,ATILA P.
Abstract The present work investigates the role of different treatments of the lower boundary condition on the numerical prediction of bubbly flows. Two different wall function formulations are tested against experimental data obtained for bubbly boundary layers: (i) a new analytical solution derived through asymptotic techniques and (ii) the previous formulation of Troshko and Hassan (IJHMT, 44, 871-875, 2001a). A modified k-e model is used to close the averaged Navier-Stokes equations together with the hypothesis that turbulence can be modelled by a linear superposition of bubble and shear induced eddy viscosities. The work shows, in particular, how four corrections must the implemented in the standard single-phase k-e model to account for the effects of...
Tipo: Info:eu-repo/semantics/article
Palavras-chave: Bubbly flow; Law of the wall; K-e; Pipe flow; Turbulence.
Ano: 2018
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652018000100573

Numerical Study of Wake Characteristics in a Horizontal-Axis Hydrokinetic Turbine
Provedor de dados: 42
Autores: SILVA,PAULO A.S.F.; OLIVEIRA,TAYGOARA F. DE; BRASIL JUNIOR,ANTONIO C.P.; VAZ,JERSON R.P.
ABSTRACT Over the years most studies on wake characteristics have been devoted to wind turbines, while few works are related to hydrokinetic turbines. Among studies applied to rivers, depth and width are important parameters for a suitable design. In this work, a numerical study of the wake in a horizontal-axis hydrokinetic turbine is performed, where the main objective is an investigation on the wake structure, which can be a constraining factor in rivers. The present paper uses the Reynolds Averaged Navier Stokes (RANS) flow simulation technique, in which the Shear-Stress Transport (SST) turbulent model is considered, in order to simulate a free hydrokinetic runner in a typical river flow. The NREL-PHASE VI wind turbine was used to validate the numerical...
Tipo: Info:eu-repo/semantics/article
Palavras-chave: Hydrokinetic turbines; Wake characteristics; CFD; Turbulence.
Ano: 2016
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652016000602441