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| Registros recuperados: 91 | |
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| Mallat, Bachar; Germain, Gregory; Billard, Jean-yves; Gaurier, Benoit. |
| The bubble sweep-down phenomenon around oceanographic research vessels generates acoustic disturbances. A specific experimental protocol in a wave and current circulating tank is used to study this phenomenon around a 1/30 scale ship model in a configuration with current, waves and ship motions. 3D visualizations of the bubble clouds and Stereo-PIV (Particle Image Velocimetry) measurements results, both obtained in the bow vicinity of the ship model, are presented in this paper. The behaviour of the breaking wave with bubble generation is studied and the spatial evolution of the bubble clouds is investigated. It is demonstrated that the bubble cloud generation is mainly conditioned by the ascending vertical velocity of the flow near the bow. It is observed... |
| Tipo: Text |
Palavras-chave: Bubble sweep-down; Breaking wave; Bow wave; Fluid-structure interaction; Flume tank. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00453/56423/58534.pdf |
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| Mycek, Paul; Pinon, Gregory; Germain, Gregory; Rivoalen, Elie. |
| The modelling of diffusive terms in particle methods is a delicate matter and several models have been proposed in the literature. The Diffusion Velocity Method (DVM) consists in rewriting these terms in an advective way, thus defining a so-called diffusion velocity. In addition to the actual velocity, it is used to compute the particles displacement. On the other hand, the well-known and commonly used Particle Strength Exchange method (PSE) uses an approximation of the Laplacian operator in order to model diffusion. This approximation is based on an exchange of particles strength. Although DVM is particularly well suited to particle methods since it preserves their Lagrangian aspect, its major drawback stems in the fact that it suffers from severe... |
| Tipo: Text |
Palavras-chave: Particle method; Diffusion; DVM; PSE. |
| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00159/27006/25254.pdf |
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| Carlier, Clement; Pinon, Gregory; Gaurier, Benoit; Germain, Gregory; Rivoalen, Elie. |
| The ambient turbulence intensity is a key factor in the study of marine current turbines. Indeed recent studies have shown that ambient turbulence intensity highly modifies the behavior of horizontal axis marine current turbines. Consequently numerical simulations have to represent the ambient turbulence or at least its effects on the performance and wake of the turbines. This paper presents the latest numerical developments carried out at LOMC in collaboration with IFREMER in order to take into account the effects of ambient turbulence. |
| Tipo: Text |
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| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00252/36293/34822.pdf |
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| Pinon, Gregory; Carlier, Clement; Fur, Arnaud; Gaurier, Benoit; Germain, Gregory; Riyoalen, Elie. |
| The present paper aims at describing the use of a Synthetic-Eddy-Method (SEM), initially proposed by Jarrin et al. [12], in the 3D Lagrangian Vortex method framework. The SEM method is used here in order to generate a far-field incoming flow with a prescribed ambient turbulence intensity. However, for the account of the diffusive term in the Navier-Stokes equations, a classical Particle Strength Exchange model with a LES eddy viscosity is used. Firstly, the general characteristics of the Synthetic-Eddy-Method will be presented together with its integration in the framework of the developed 3D unsteady Lagrangian Vortex software [27]. The capability of the ambient turbulence model to reproduce a perturbed flow that verifies any turbulence intensity I∞ and... |
| Tipo: Text |
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| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00389/50002/50587.pdf |
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| Sheehan, Emma V.; Vaz, Sandrine; Pettifer, Erin; Foster, Nicola L.; Nancollas, Sarah J.; Cousens, Sophie; Holmes, Luke; Facq, Jean-valery; Germain, Gregory; Attrill, Martin J.. |
| Managing ecological systems, which operate over large spatial scales, is inherently difficult and often requires sourcing data from different countries and organizations. The assumption might be made that data collected using similar methodologies are comparable, but this is rarely tested. Here, benthic video data recorded using different towed underwater video systems (TUVSs) were experimentally compared. Three technically different TUVSs were compared on different seabed types (rocky, mixed ground and sandy) in Kingmere Marine Conservation Zone, off the south coast of England. For each TUVS, species metrics (forward facing camera), seabed impact (backward facing camera) and operational performance (strengths and limitations of equipment and video... |
| Tipo: Text |
Palavras-chave: Environmental management; Marine protected area; Meta-analyses; Sampling impact; Towed video; Underwater imagery. |
| Ano: 2016 |
URL: https://archimer.ifremer.fr/doc/00319/42984/42659.pdf |
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| Druault, Philippe; Germain, Gregory. |
| The coupled dynamics of the codend fluttering motion and its hydrodynamics behavior are investigated based on PIV measurements carried out around a 1/10 scaled model codend. The mean wake flow characteristics are firstly analyzed demonstrating the great effect of the codend motion. The differences in flow contour between fluttering motion and no-fluttering codend are highlighted by analyzing the classical mean characteristics of a body wake flow. In presence of fluttering motion, the classical results are recovered only if one considers the vertical extent of the codends oscillations as a reference length scale. Secondly, the frequency content of codend oscillations is analyzed and it is linked to the physical mechanisms. It is observed that the motion of... |
| Tipo: Text |
Palavras-chave: PIV measurements; Fishing net structure; Wake hydrodynamics; Fluttering structure. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00344/45503/45055.pdf |
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| Dussol, David; Druault, Philippe; Mallat, Bachar; Delacroix, Sylvain; Germain, Gregory. |
| When performing Particle Image Velocimetry (PIV) measurements in complex fluid flows with moving interfaces and a two-phase flow, it is necessary to develop a mask to remove non-physical measurements. This is the case when studying, for example, the complex bubble sweep-down phenomenon observed in oceanographic research vessels. Indeed, in such a configuration, the presence of an unsteady free surface, of a solid–liquid interface and of bubbles in the PIV frame, leads to generate numerous laser reflections and therefore spurious velocity vectors. In this note, an image masking process is developed to successively identify the boundaries of the ship and the free surface interface. As the presence of the solid hull surface induces laser reflections, the hull... |
| Tipo: Text |
Palavras-chave: Particle image velocimetry; Unsteady free interface; Edge detection method; Morphological analysis. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00327/43778/43335.pdf |
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| Kervella, Youen; Germain, Gregory; Gaurier, Benoit; Facq, Jean-valery; Cayocca, Florence; Lesueur, Patrick. |
| Oyster tables are artificial obstacles which are laid over muddy or sandy-muddy floors in intertidal areas. This study aims to show the current modifications related to the presence of the oyster table thanks to LDV measurement in a flume tank. Boundary layer development in different geometric configuration is underlined and suggests some important areas of velocity decrease and sediment transport modification. Shear stresses are also calculated near the bottom and around the table. The total shear stress in the water column exhibits an important increase when the flow passes through the oyster table, hence a flow energy decrease through dissipation. This study helps to understand the reasons for the increased sedimentation observed in some natural sites. |
| Tipo: Text |
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| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/00022/13359/10388.pdf |
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| Delacroix, Sylvain; Germain, Gregory; Berger, Laurent; Billard, Jean-yves. |
| Bubble sweep-down on oceanographic vessels generates acoustic perturbations. We propose in this work to characterize the sub-surface bubbles occurrence conditions from acoustic data analysis acquired during surveys in relatively shallow water with the IFREMER research vessels Thalassa and Pourquoi Pas?. The methodology of data analysis used in this work allows us to characterize the sailing conditions influence on bubble sweep-down occurrence. The correlation between sailing conditions and acoustic perturbations tends to demonstrate that the presence of bubbles under the hull is clearly related to the wind speed and natural aeration, and that surface bubbles are advected differently in the water column by the two vessels |
| Tipo: Text |
Palavras-chave: Bubble sweep-down; Acoustic perturbation; Ship motion. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00294/40557/39632.pdf |
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| Gaurier, Benoit; Germain, Gregory; Le Boulluec, Marc; Giry, Eric; Fontaine, E.. |
| The interactions between several cylinders placed in close proximity are the subject of many studies, because of the strong repeated loads that they create on these structures. For flexible or mobile structures, the wake effects can produce large amplitudes motions. These displacements can be higher than those considered during the lock-in of a single cylinder, to reach several diameters. Depending the initial spacing, they lead sometimes to clashes with potentially high intensity, between the cylinders. To better understand these phenomena, an experimental study was carried out, bearing on the interaction between two models of tensioning buoy supporting hybrid risers. After checking that the models used were able to correctly reproduce the movements... |
| Tipo: Text |
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| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/00023/13439/10447.pdf |
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| Maganga, Fabrice; Germain, Gregory; Facq, Jean-valery; Gaurier, Benoit; Rivoalen, Elie; Pinon, Grégory. |
| Le fonctionnement d’une hydrolienne est régi par les caractéristiques de l’écoulement incident. Cet article présente les résultats d’une étude expérimentale visant à déterminer les effets du taux de turbulence de l’écoulement ambiant sur le fonctionnement d’une hydrolienne et le sillage généré. Les essais expérimentaux ont été réalisés dans la veine hydrodynamique à surface libre de l’Ifremer, dont on peut faire varier le taux de turbulence de l’écoulement de 5 à 25%. Le prototype utilisé est une turbine tri-pales à axe horizontal de 0,7 m de diamètre (échelle 1/30). Des cartes de vitesses moyennes, de taux de turbulence, mais également d’énergie cinétique turbulente et de contrainte de cisaillement ont été obtenus à partir de mesures par vélocimétrie... |
| Tipo: Text |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00022/13355/10386.pdf |
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| Carlier, Clement; Pinon, Gregory; Mycek, Paul; Gaurier, Benoit; Germain, Gregory; Rivoalen, Elie. |
| The development of marine current turbines arrays still needs nowadays many studies among which we can find the study of interactions between devices. In order to highlight these interactions effects, experiments were carried out in the IFREMER’s (Boulogne-sur-Mer) flume tank. Those experiments used 3-bladed horizontal axis marine current turbines prototypes, regulated in rotation speed. To complete these experiments, a three-dimensional numerical tool is developed at the LOMC (Université du Havre) to simulate one or more turbines in a free upstream current. We present hereafter the numerical and experimental results obtained in the scope of the study of elementary interaction between two turbines axially aligned with the upstream current. |
| Tipo: Text |
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| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00247/35806/34320.pdf |
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| Magnier, Maelys; Druault, Philippe; Gaurier, Benoit; Germain, Gregory; Ifremer; Sorbonne Universités. |
| Areas with strong tidal currents that can be exploited with tidal turbines often have complex bathymetries where the turbulent intensity of these currents can reach very high values. To study the effects of bathymetric variations on the operation of a tidal turbine, an experimental device has been developed in the Ifremer circulation basin. The wake of two kinds of bathymetries, a cylinder with a square base and a cube followed by this same cylinder, are characterized and compared from PIV measurement results. The results show that the wake of the cylinder is more energetic than that of the tandem configuration. The vortex structures that it emits rise to the surface unlike those resulting from the tandem, the cube preventing their development. The effects... |
| Tipo: Text |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00660/77243/78695.pdf |
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| Germain, Gregory; Priour, Daniel; Vincent, Benoit; Billard, Jean-yves; Druault, Philippe; Bouhoubeiny, Elkhadim; Alexandrini, Bertrand; Le Touze, David; Khaled, Ramez; Mnassri, Ilyes. |
| Le comportement hydrodynamique des structures poreuses utilisées pour la pêche (chaluts, nasses, cages, seines) est aujourd’hui encore mal connu. Les chaluts étant responsables de la plus grosse part de la consommation de fuel en action de pêche, ce projet a pour objectif de développer un outil de conception de chalut permettant de réduire au maximum la traînée de l’engin.L’outil ainsi développé devrait permettre d’obtenir un gain de l’ordre de 20% sur la traînée d’un chalut, tout en conservant une efficacité en pêche comparable. Les développements réalisés pourront également être étendus pour étudier les différents types de structures poreuses utilisées pour la pêche et mieux appréhender le développement de dispositifs de sélectivité. |
| Tipo: Text |
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| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00116/22716/20683.pdf |
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| Registros recuperados: 91 | |
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