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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.

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.

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.

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.

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