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| Registros recuperados: 91 | |
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| Gaurier, Benoit; Germain, Gregory; Cebron, David. |
| A model using wake oscillators is developed to predict the 2D motion in a transverse plan of two rigid cylinders in tandem arrangement. This model of the wake dynamics is validated with experimental data from previous trials which took place at the Ifremer flume tank in Boulogne-sur-Mer, France. The agreement between the model and the experimental results allows using this model as a simple computational tool in the prediction of 2D Vortex-Induced Vibrations (VIV) and, after some futher developments, Wake-Induced Oscillations (WIO) effects. |
| Tipo: Text |
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| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/00022/13368/10392.pdf |
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| Gaurier, Benoit; Ordonez-sanchez, Stephanie; Facq, Jean-valery; Germain, Gregory; Johnstone, Cameron; Martinez, Rodrigo; Salvatore, Francesco; Santic, Ivan; Davey, Thomas; Old, Chris; Sellar, Brian. |
| This Round Robin Test program aims to establish the influence of the combined wave and current effect on the power capture and performance of a generic tidal turbine prototype. Three facilities offering similar range of experimental conditions have been selected on the basis that their dimensions along with the rotor diameter of the turbine translate into low blockage ratio conditions. The performance of the turbine shows differences between the facilities up to 25% in terms of average power coefficient, depending on the wave and current cases. To prevent the flow velocity increasing these differences, the turbine performance coefficients have been systematically normalized using a time-average disc-integrated velocity, accounting for vertical gradients... |
| Tipo: Text |
Palavras-chave: Marine energy; Wave and current interactions; Round Robin Tests; Flow measurements; Horizontal axis tidal turbine. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00635/74735/74725.pdf |
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| Bouhoubeiny, Elkhadim; Germain, Gregory; Druault, Philippe. |
| Flow field measurements behind a rigid cod-end and a moving bottom trawl are conducted using Time Resolved PIV method. This method is based on an image acquisition rate allowing the time resolved sampling of the vortex shedding phenomenon. Based on such measurements, the main flow characteristics around fishing net structure are investigated. Moreover, the vortex shedding frequency phenomenon associated with both the rigid cod-end and the moving bottom trawl is analyzed. We then present the analysis of the instability of the shear layer separating a moving trawl having 3 degrees of freedom. Using also the Proper Orthogonal Decomposition (POD) for such investigation, it is demonstrated the effectiveness of this procedure to extract not only the large scale... |
| Tipo: Text |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00022/13280/10324.pdf |
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| Knoery, Joel; Cossa, Daniel; Thomas, Bastien; Germain, Gregory; Rigaud, Sylvain. |
| In aquatic environments, the benthic water column exhibits strong concentration gradients of various substances. They result from transfers and chemical reactions that may occur both within this layer, and at the sediment–water interface (SWI). Characterization of these gradients yields important information for the quantification of such processes and transfers. However, it is difficult to actually sample these gradients in the field, since turbulence decreases their vertical scale. This article describes a sampler designed to collect simultaneously 16 discrete water column samples at a centimeter‐scale vertical resolution. This small device (40 × 40 × 60 cm) is reliable, safe to handle, and easily deployed from a small boat using a cable or a Scuba... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00495/60665/64203.pdf |
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| Gaurier, Benoit; Germain, Gregory; Le Boulluec, Marc; Giry, Eric; Fontaine, Emmanuel. |
| Vortex-Induced Vibrations (VIV) are well-known and related to the majority of cylindrical structures subjected to strong winds or currents. The VIV limit the lifetime of the structure because they increase the forces and so the fatigue. When several structures of this kind are put together in close interaction, the wake effects (Wake Induced Oscillations - WIO) sometimes involve strong instabilities. If these structures are flexible or mobile, oscillations of several diameters can be observed and collisions can occur ([4] & [6]). Such structures are widespread in the oil industry where the extraction of oil in deep water can be done by means of risers. In some cases, risers are connected to a floating support called FPSO (Floating Production Storage... |
| Tipo: Text |
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| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/2008/publication-6584.pdf |
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| Delacroix, Sylvain; Germain, Gregory; Gaurier, Benoit; Billard, Jean-yves. |
| Bubble sweep-down is a significant issue for the oceanographic vessels, which affect the acoustic surveys. Experimental trials, carried out in the Ifremer wave and current circulating tank on a 1/30 model of the Pourquoi pas?, are presented. The results demonstrate that this kind of experimental facility is well suited to study the phenomenon of bubble sweep-down encountered around the bow of a ship under specific conditions. From these results, two kinds of bubble clouds formation have been observed and analysed: bubble clouds generated by vortex shedding and breaking waves. The vortex shedding bubble clouds appear randomly in all the configurations tested, even without waves or motions. This phenomenon is due to the interaction between the turbulent flow... |
| Tipo: Text |
Palavras-chave: Bubble sweep-down; Experimental trials; Ship motions; Bow waves. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00335/44578/44315.pdf |
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| Gaurier, Benoit; Druault, Ph.; Ikhennicheu, Maria; Germain, Gregory. |
| In the main tidal energy sites like Alderney Race, turbulence intensity is high and velocity fluctuations may have a significant impact on marine turbines. To understand such phenomena better, a three-bladed turbine model is positioned in the wake of a generic wall-mounted obstacle, representative of in situ bathymetric variation. From two-dimensional Particle Image Velocimetry planes, the time-averaged velocity in the wake of the obstacle is reconstructed in the three-dimensional space. The reconstruction method is based on Proper Orthogonal Decomposition and enables access to a representation of the mean flow field and the associated shear. Then, the effect of the velocity gradient is observed on the turbine blade root force, for four turbine locations... |
| Tipo: Text |
Palavras-chave: Tidal turbine; Blade force; Turbulent wake; Experimental trials; PIV; POD. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00643/75535/76540.pdf |
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| Druault, Philippe; Germain, Gregory; Facq, Jean-valery. |
| To gain a better understanding of the fluid–structure interaction and especially when dealing with a flow around an arbitrarily moving body, it is essential to develop measurement tools enabling the instantaneous detection of moving deformable interface during the flow measurements. A particularly useful application is the determination of unsteady turbulent flow velocity field around a moving porous fishing net structure which is of great interest for selectivity and also for the numerical code validation which needs a realistic database. To do this, a representative piece of fishing net structure is used to investigate both the Turbulent Boundary Layer (TBL) developing over the horizontal porous moving fishing net structure and the turbulent flow passing... |
| Tipo: Text |
Palavras-chave: Unsteady turbulent flow; Particle Image Velocimetry; Oscillating structure; Fishing structure. |
| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00271/38216/36479.pdf |
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| Kervella, Youen; Germain, Gregory; Gaurier, Benoit; Facq, Jean-valery; Cayocca, Florence; Lesueur, Patrick. |
| Oyster farming structures are artificial obstacles which disturb tidal flow and wave propagation. These effects can induce modifications of erosion and sedimentation patterns, turbidity changes, local silting up and can be threatening for the shellfish farming itself. The understanding of the impact of these structures in terms of hydrodynamics and sediment dynamics in the far-field, i.e. at the scale of a bay, is a very challenging task. In order to investigate the far-field impact, it is very important to understand in the first place all the changes which occur at a smaller scale, i.e. at the scale of a single table for a farm consisting of oyster tables made of metallic wire structures on which porous bags of oysters are laid. This work is carried out... |
| Tipo: Text |
Palavras-chave: Sediment dynamics; Roughness length; Boundary layer; Particle Image Velocimetry; Laser Doppler Velocimetry; Flume; Oyster table. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/2010/publication-7389.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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| Maganga, Fabrice; Pinon, Grégory; Germain, Gregory; Rivoalen, Elie. |
| This paper presents numerical results for the wake behind a three bladed horizontal axis turbine in a uniform free upstream current. A three-dimensional software, initially issuing from Pinon et al. [6], taking into account the non stationary evolution of the wake emitted by turbine blades is developed in order to assess the disturbances generated on the sea-bed and on the free surface. So an unsteady Lagrangian method is considered for these simulations using Vortex Method. The vortex flow is discretised with particles carrying vorticity, which are advected in a Lagrangian frame. |
| Tipo: Text |
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| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/00023/13429/10436.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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| Maganga, Fabrice; Germain, Gregory; King, J.; Pinon, G.; Rivoalen, E.. |
| Experimental results of tests carried out to investigate the hydrodynamics of marine current turbines are presented The objective is to build an experimental database in order to validate the numerical developments conducted to characterise the flow perturbations induced by marine current turbines For that purpose, we used a tri-bladed horizontal axis turbine The work is dedicated to measuring the behaviour of the system and to characterising the wake generated by the turbine The efficiency of the device is quantified by the measurement of the thrust and the amount of power generated by the rotor for various inflow conditions, whereas the wake is characterised by Laser Doppler Velocimetry Particular attention is paid to the flow characteristic effects on... |
| Tipo: Text |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00019/13033/10194.pdf |
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| Maganga, Fabrice; Germain, Gregory; Pinon, Grégory; Rivoalen, Elie. |
| Numerical results for the wake of a three bladed horizontal axis turbine in a uniform free upstream current are presented. A three-dimensional software, taking into account the non stationary evolution of the wake emitted by turbine blades is developed in order to assess the disturbances generated on the sea-bed and on the free surface. An unsteady Lagrangian method is considered for these simulations using Vortex Method. The vortex ow is discretised with particles carrying vorticity, which are advected in a Lagrangian frame. |
| Tipo: Text |
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| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/00022/13367/10391.pdf |
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| Registros recuperados: 91 | |
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