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| Registros recuperados: 91 | |
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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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| 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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| 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 |
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| Germain, Gregory; Bahaj, A.s.; Roberts, P.; Huxley-reynard, C.. |
| The utilization of marine currents for power production offers a sustainable option to augment traditional power technologies and enhance the expansion of renewables. The marine current resource is potentially large and could generate a significant part of the European Union's electricity requirements. Before the installation of marine prototypes, specific trials are necessary to evaluate the behaviour of each system and the ability to exploit tidal or marine currents. This paper presents experimental campaigns carried out on marine energy converter systems under METRI II program performed in the Ifremer free surface hydrodynamic water tunnel. Two of them concern horizontal axis marine current turbine systems: a “classical” pile-mounted tidal turbine... |
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| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/00023/13436/10444.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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| 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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| Bouhoubeiny, Elkhadim; Druault, Philippe; Germain, Gregory. |
| Time-Resolved Particle Image Velocimetry (PIV) measurements are performed to investigate the hydrodynamic flow interaction with a representative piece of fishing net structure. Using the advanced post-processing mathematical tool based on Proper Orthogonal Decomposition, the phase averaged mean properties of turbulent flows are extracted from PIV database, demonstrating the existence of a Turbulent Boundary Layer (TBL) flow developing all around the sheet of net. The results also show that the mesh opening and so the turbulent flow passing through the structure are strongly influenced by the structure oscillations. This work allows us to demonstrate that the drag computation of fishing gear, commonly based on uniform velocity, needs to consider not only... |
| Tipo: Text |
Palavras-chave: Fishing net structure; Hydrodynamics; PIV; Turbulent boundary layer flow. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00184/29552/27878.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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| Marty, Antoine; Germain, Gregory; Facq, Jean-valery; Gaurier, Benoit; Damblans, Guillaume; Germain, Nicolas; Harris, Jeffrey; Maison, Antoine; Peyrard, Christophe; Relun, Nicolas. |
| Submarine cable behaviour is experimentally studied in the frame of the France Energies Marines project STHYF. In order to evaluate on-bottom stability of cables placed on rocky seabed with high roughness and submitted to combined wave and strong current, hydrodynamic loads are measured on a fixed slender cylinder closely fixed to a horizontal plate, with or without large roughness. A specified set of load cases (forced oscillations, current, forced oscillation + current) is considered to assess the hydrodynamic loads acting on the cylinder placed near a wall for varying gap-to-diameter ratios. The roughness effects on cylinder loads and on the flow are studied in detail. The result show a significant difference between rough and smooth bottom... |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00660/77244/78696.pdf |
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| Maganga, Fabrice; Pinon, Grégory; Germain, Gregory; Rivoalen, Elie. |
| The hydrodynamics of a three bladed horizontal axis turbine is investigated. The performance of a turbine of 0.7 m of diameter and its wake were obtained from experiments and numerical simulations. A six components load cells is used for thrust and hydrodynamic power measurements, and Laser Doppler Velocimetry technics for wake characterisation. A three-dimensional software, taking into account the non stationary evolution of the wake generated by turbine blades is developed. The flow is discretised with particles carrying vorticity, which are advected in a Lagrangian frame. Both numerical and experimental power coefficient Cp and velocity maps were compared. Experiments and numerical data showed a satisfactory agreement in term of the shape of the wake... |
| Tipo: Text |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00022/13356/10387.pdf |
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| 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 in Froude similitude with a Reynolds number as high as achievable (Fr = 0.23 and Re = 2.5×10 5 ). The study focuses on large aspect ratio floor variations represented with a square wall-mounted cylinder of aspect ratio 6. The addition of a cube upstream of the cylinder is investigated. The cube impact on the wake development is larger than the side effects. Large scale turbulent events produced in... |
| Tipo: Text |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00482/59336/62114.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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| 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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| Registros recuperados: 91 | |
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