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Prothin S.,Institute Superieure Of Laeronautique Et Of Lespace Isae Toulouse | Djeridi H.,CNRS Laboratory of Ocean Physics | Billard J.-Y.,CNRS Naval Academy Research Institute
Journal of Fluids and Structures | Year: 2014

In this paper, the influence of a single tip vortex on boundary layer detachment is studied. This study offers a preliminary approach in order to better understand the interaction between a propeller hub vortex and the rudder installed in its wake. This configuration belongs to the field of marine propulsion and encompasses such specific problem as cavitation inception, modification of propulsive performances and induced vibrations. To better understand the complex mechanisms due to propeller-rudder interactions it was decided to emphasize configurations where the hub vortex is generated by an elliptical 3-D foil and is located upstream of a 2-D NACA0015 foil at high incidences for a Reynolds number of 5×105. The physical mechanisms were studied using Time Resolved Stereoscopic Particle Image Velocimetry (TR-SPIV) techniques. Particular attention was paid to the detachment at 25° incidence and a detailed cartography of the mean and turbulent properties of the wake is presented. Proper Orthogonal Decomposition (POD) analysis was applied in order to highlight the unsteady nature of the flow using phase averaging based on the first POD coefficients to characterize the turbulent and coherent process in the near wake of the rudder. © 2013 Elsevier Ltd.

Chouippe A.,CNRS Fluid Dynamics Institute of Toulouse | Chouippe A.,Karlsruhe Institute of Technology | Climent E.,CNRS Fluid Dynamics Institute of Toulouse | Legendre D.,CNRS Fluid Dynamics Institute of Toulouse | Gabillet C.,CNRS Naval Academy Research Institute
Physics of Fluids | Year: 2014

We investigate bubble dispersion in turbulent Taylor-Couette flow. The aim of this study is to describe the main mechanisms yielding preferential bubble accumulation in near-wall structures of the flow. We first proceed to direct numerical simulation of Taylor-Couette flows for three different geometrical configurations (three radius ratios η = R1/R2: η = 0.5, η = 0.72, and η = 0.91 with the outer cylinder at rest) and Reynolds numbers corresponding to turbulent regime ranging from 3000 to 8000. The statistics of the flow are discussed using two different averaging procedures that permit to characterize the mean azimuthal velocity, the Taylor vortices contribution and the small-scale turbulent fluctuations. The simulations are compared and validated with experimental and numerical data from literature. The second part of this study is devoted to bubble dispersion. Bubble accumulation is analyzed by comparing the dispersion obtained with the full turbulent flow field to bubble dispersion occurring at lower Reynolds numbers in previous works. Several patterns of preferential accumulation of bubbles have been observed depending on bubble size and the effect of gravity. For the smaller size considered, bubbles disperse homogeneously throughout the gap, while for the larger size they accumulate along the inner wall for the large gap width (η = 0.5). Varying the intensity of buoyancy yields complex evolution of the bubble spatial distribution. For lowgravity effect, bubble entrapment is strong leading to accumulation along the inner wall in outflow regions (streaks of low wall shear stress).When buoyancy effect dominates on vortex trapping, bubbles rise through the vortices, while spiral patterns stretched along the inner cylinder are clearly identified. Force balance is analyzed to identify dominating forces leading to this accumulation and accumulation patterns are compared with previous experiments. © 2014 AIP Publishing LLC.

Komai T.,Natural History Museum and Institute | Poupin J.,CNRS Naval Academy Research Institute
Zootaxa | Year: 2012

Two new species of pagurid hermit crabs are described from shallow coral reefs of Mayotte, Comoro Islands, southwestern Indian Ocean. Cestopagurus caeruleus sp. nov., representing the fourth of the genus, is morphological similar to C. coutieri Bouvier, 1897 and C. timidus (Roux, 1830), but the new species is immediately distinguished from the latter two species by the proportionally longer antennular peduncles and the different armature of the dactylus of the right cheliped. Trichopagurus asper sp. nov., representing the third species of the genus, appears closer to T. macrochela Komai & Osawa, 2005, but the tuberculate dorsal surface of the right palm and the possession of spines on the carpus of the left cheliped readily differentiate the new species from the latter species. Copyright © 2012 Magnolia Press.

Zhou Z.,CNRS Brest Laboratory of Mechanics and Systems Laboratory | Zhou Z.,CNRS Naval Academy Research Institute | Zhou Z.,Shanghai Maritime University | Benbouzid M.,CNRS Brest Laboratory of Mechanics and Systems Laboratory | And 3 more authors.
Renewable and Sustainable Energy Reviews | Year: 2013

Increasing concerns about the depletion of fossil resources and the issue of environment lead to a global need for producing more clean energy from renewable sources. Ocean is appreciated as a vast source of renewable energies. Considering marine renewable energies, it can be noticed that significant electrical power can be extracted from marine tidal currents. However, the power harnessed from marine tidal currents is highly fluctuant due to the swell effect and the periodicity of the tidal phenomenon. To improve the power quality and make the marine generation system more reliable, energy storage systems can play a crucial role. In this paper, an overview and the state of art of energy storage technologies are presented. Characteristics of various energy storage technologies are analyzed and compared for this particular application. The comparison shows that high-energy batteries like sodium-sulphur battery and flow battery are favorable for smoothing the long-period power fluctuation due to the tide phenomenon while supercapacitor and flywheel are more suitable for eliminating short-period power disturbances due to swell or turbulence phenomena. This means that hybrid storage technologies are needed for achieving optimal results in tidal marine current energy applications. © 2012 Elsevier Ltd. All rights reserved.

Komai T.,Natural History Museum and Institute | Poupin J.,CNRS Naval Academy Research Institute
Zootaxa | Year: 2013

Three species of the pagurid hermit crab genus Pagurixus Melin, 1939, are reported from Europa Island in the Mozambique Strait, western Indian Ocean: P. haigae Komai & Osawa, 2007, P. annulus n. sp., and P. europa n. sp. Pagurixus haigae is recorded from the western Indian Ocean for the first time. Pagurixus annulus n. sp. and P. europa n. sp. are referred to the P. boninensis (Melin, 1939) species group and P. anceps (Forest, 1954) group, respectively. Diagnostic characters of these two new species are discussed. Copyright © 2013 Magnolia Press.

Scuiller F.,CNRS Naval Academy Research Institute
IECON Proceedings (Industrial Electronics Conference) | Year: 2012

On a shipboard electric power system, in steady-state operations, the electric grid disturbances due to powerfull periodic pulsed loads are estimated by the voltage and frequency modulations. Energy Storage System (ESS) with fast discharge ability allows to reduce the stress on the grid components and to meet the design standard requirements. This paper focuses on the sizing and simulation of a supercapacitor ESS (SC ESS). Regarding the chosen topology, the SC bank is directly connected to the grid converter (without DC bus stage) because reliability, efficiency and ability to ensure other functions (as voltage sag mitigations) are expected. Regarding the SC ESS management, the DC voltage is controlled at any time and SC ESS charge and discharge are ordered by stepping the reference DC voltage to minimal value or maximal value. Furthermore SC ESS charge/discharge cycle is synchronized with the pulsed load with a smooth time advance in order to compensate the lower power rise of the ESS in comparison with the one of the pulsed load. The results obtained with the shipgrid simulator are convincing: the frequency modulation is significantly reduced (by more three times) and becomes compliant with the standard requirement. Regarding the generator side, the governor torque variations are strongly mitigated. © 2012 IEEE.

Ducoin A.,University of Michigan | Andre Astolfi J.,CNRS Naval Academy Research Institute | Gobert M.-L.,University of Tours
Journal of Fluids and Structures | Year: 2012

This paper aims at characterizing experimentally laminar to turbulent transition induced vibrations. Here, the transition is known to be triggered by a Laminar Separation Bubble that results from a laminar separation of the boundary-layer flow on a hydrofoil. In this study we consider two NACA66312 (Mod) laminar hydrofoils at low angles of incidence (mostly 2° and 4°) and Reynolds numbers ranging from Re=450000 to 1200000, in order to get transitional regimes. The first hydrofoil, made of steel (E=2.1×10 11Pa), is referred to as the rigid hydrofoil, although it is seen to vibrate under the action of the LSB. To better understand the possible interaction between the flow and the foil vibrations, vibration measurements are repeated using a flexible hydrofoil (E=3×10 9Pa) of same geometry (under zero loading) and in close configurations. The experiments are carried out at the French Naval Academy Research Institute (IRENav, France). Wall pressure and flow velocity measurements enable a characterization of the laminar separation bubble and the identification of a vortex shedding at a given frequency. It is hence shown that the boundary-layer transition induces important foil vibrations, whose characteristics in terms of frequency and amplitude depend on the vortex shedding frequency, and can be coupled with natural frequencies of the hydrofoils. © 2011 Elsevier Ltd.

Benelghali S.,Aix - Marseille University | Benbouzid M.E.H.,CNRS Brest Laboratory of Mechanics and Systems Laboratory | Charpentier J.F.,CNRS Naval Academy Research Institute
IEEE Journal of Oceanic Engineering | Year: 2012

Emerging technologies for marine current turbines are mainly related to works that have been carried out on wind turbines and ship propellers. It is then obvious that many electric generator topologies could be used for marine current turbines. As in the wind turbine context, doubly-fed induction generators and permanent magnet generators seem to be attractive solutions for harnessing the tidal current energy. In this paper, a comparative study between these two generator types is presented and fully analyzed in terms of generated power, maintenance, and operation constraints. This comparison is done for the Raz de Sein site (Brittany, France) using a multiphysics modeling simulation tool. This tool integrates, in a modular environment, the resource model, the turbine hydrodynamic model, and generator models. Experiments have also been carried out to confirm the simulation results. © 2012 IEEE.

Delafin P.L.,CNRS Naval Academy Research Institute | Deniset F.,CNRS Naval Academy Research Institute | Astolfi J.A.,CNRS Naval Academy Research Institute
European Journal of Mechanics, B/Fluids | Year: 2014

The present study deals with the effect of the laminar separation bubble (LSB) induced transition on the lift, drag and moment coefficients of a hydrofoil. A 2D numerical study, based on the SST γ-Reθ transition model of ANSYS-CFX®, is conducted on a NACA66 hydrofoil. Angles of attack range from -4°to 14°and the chord-based Reynolds number is Re=7.5×105. An experimental investigation is carried out in the French naval academy research institute's hydrodynamic tunnel based on the measurements of lift, drag and moment. Experiments on a smooth, mirror finished, hydrofoil enable comparison with RANS calculations using the transition model. Experiments with a roughness added on the leading edge enable comparison with RANS calculations using the SST fully turbulent model. For angles of attack below 6°, the LSB triggered laminar to turbulent transition of the boundary layers of the suction and pressure sides is located near the trailing edge of the smooth NACA66. As the angle of attack reaches 6°, the LSB suddenly moves to the leading edge on the suction side while transition is located at the trailing edge on the pressure side. The smooth hydrofoil shows higher CL and CM and lower CD than the rough leading edge one from -4°to 6°. Both experiments lead to the same coefficients from 6°to 14°. The calculations show that both models are in good agreement with their corresponding experiments. Velocity profiles in the vicinity of the LSB at an angle of attack of 2°and pressure coefficients of the calculations using the transition model are compared with published experimental studies and show very good agreement. The SST γ-Reθ transition model proves to be a relevant, even essential, prediction tool for lifting bodies operating at a moderate Reynolds number. © 2014 Elsevier Masson SAS. All rights reserved.

Ducoin A.,University of Michigan | Andre Astolfi J.,CNRS Naval Academy Research Institute | Sigrist J.-F.,DCNS S.A.
European Journal of Mechanics, B/Fluids | Year: 2012

The structural response of a rectangular cantilevered flexible hydrofoil submitted to various flow regimes is analyzed through an original experiment carried out in a hydrodynamic tunnel at a Reynolds number of 0.75×10 6. The experiment considers static and transient regimes. The latter consists of transient pitching motions at low and fast pitching velocities. The experiments are also performed for cavitating flow. The structural response is analyzed through the measurement of the free foil tip section displacement using a high speed video camera and surface velocity vibrations using a laser doppler vibrometer. In non cavitating flows, it is shown that the structural response is linked to the hydrodynamic loading, which is governed by viscous effects such as laminar to turbulent transition induced by Laminar Separation Bubble (LSB), and stall. It is also observed that the foil elastic displacement depends strongly on the pitching velocity. Large overshoots and hysteresis effect are observed as the pitching velocity increases. Cavitation induces a large increase of the vibration level due to hydrodynamic loading unsteadiness and change of modal response for specific frequencies. The experimental results presented in this paper will help to develop high fidelity fluid-structure interaction models in naval applications. © 2012 Elsevier Masson SAS. All rights reserved.

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