Qualification des données acquises par la station de mesure MOLIT en baie de Vilaine entre mars et octobre 2015

Ce rapport présente les éléments qui ont conduit à la qualification des données acquises en 2015 par la station de mesure haute fréquence MOLIT (Mer Ouverte Littoral). La bouée MOLIT est déployée depuis 2008 en baie de Vilaine, une des zones de la côte atlantique les plus menacées par l’eutrophisation. Cette bouée instrumentée constitue un des systèmes de mesure du réseau de mesure haute fréquence Ifremer HOSEA (High frequency Observation network for the environment in coastal SEAs). Cette station est équipée d’une sonde multiparamètre qui mesure les paramètres température, salinité, oxygène dissous, turbidité et fluorescence. Les mesures sont effectuées à deux niveaux (surface et fond) avec une fréquence d’une mesure horaire. Ce rapport synthétise les informations qui ont permis de qualifier les données sur le site des réseaux eulériens d’Ifremer (Coriolis) : contrôles in-situ, historique des opérations de maintenance, constats de vérification des sondes avant et après campagne. Les données ont été qualifiées en quatre états : 1-BON, 2-MOYEN, 3-DOUTEUX, 4-MAUVAIS.

Caractérisation du fonctionnement d'une hydrolienne à membrane ondulante pour la récupération de l'énergie des courants marins

This manuscript presents three approaches : analytical, experimental and numerical, to study the behaviour of a flexible membrane tidal energy converter. This technology, developed by the EEL Energy company, is based on periodic deformations of a pre-stressed flexible structure. Energy converters, located on each side of the device, are set into motion by the wave-like motion. In the analytical model, the membrane is represented by a linear beam model at one dimension and the flow by a 3 dimensions potential fluid. The fluid forces are evaluated by the elongated body theory. Energy is dissipated all over the length of the membrane. A 20th scale experimental prototype has been designed with micro-dampers to simulate the power take-off. Trials have allowed to validate the undulating membrane energy converter concept. A numerical model has been developed. Each element of the device is represented and the energy dissipation is done by dampers element with a damping law linear to damper velocity. Comparison of the three approaches validates their ability to represent the membrane behaviour without damping. The energy dissipation applied with the analytical model is clearly different from the two other models because of the location (where the energy is dissipated) and damping law. The two others show a similar behaviour and the same order of power take off repartition but value of power take off are underestimated by the numerical model. This three approaches have allowed to put forward key-parameters on which depend the behaviour of the membrane and the parametric study highlights the complementarity and the advantage of developing three approaches in parallel to answer industrial optimization problems. To make the link between trials in flume tank and sea trials, a 1/6th prototype has been built. To do so, the change of scale was studied. The behaviour of both prototypes is compared and differences could be explained by differences of boundary conditions and confinement effects. To evaluated membrane long-term behaviour at sea, a method of ageing accelerated by temperature and fatigue tests have been carried out on prototype materials samples submerged in sea water.

Géodiversité sous-marine de Nouvelle-Calédonie. 1ère partie

The object of this article is to offer a synthesis of the knowledge clarifying the originality and the diversity of the submarine geological formations of the New Caledonian EEZ. A reminder is given onto the geologic history of the region, based upon the dislocation of the Gondwana Continent, the opening of the Tasman Sea, the presence of submarine volcanism, the setting up of heavy peridotitic rocks, the building up of the Fairway and Lord Howe Ridges and of sedimentary basins, the formation of volcanic domes and sea-mounts or guyots, the subduction along the Vanuatu Trench, the uplift of the Loyalty Islands, the development of carbonated ptatforms around the islands etc.... Of this complex history ensues an exceptional submarine geo-diversity. After this presentation the article clarifies the methods and the tools used in marine geosciences to map, explore, observe, analyze, sample, that they are embarked or are autonomous, teleoperated or inhabited systems. A chapter describes the programs which were set up since about forty years and the results obtained as well as the scientific teams concerned with. In conclusion, based on the unpublished character of this geo-diversity, the article introduces the second text to come in a next issue of theTai Kona magazine, text which will focus on the scientific, economic (mineral resources), environmental (deep biodiversity) and risks (seismicity) challenges that are worn by one of the most original submarine geologic context in the world.

Sémaphore, suivi de services opérationnels

L’unité IDM fournit des services opérationnels utilisés par différents utilisateurs des scientifiques, des partenaires mais également le grand public. L’unité IDM souhaite mieux connaitre ses utilisateurs et évaluer la performance de ses services, afin : . D’améliorer le service rendu . D’effectuer du reporting mensuel/annuel . De répondre aux engagements de service (SLA) Pour cela, il faut utiliser différentes sources d’informations : Monitoring : permet de surveiller les services opérationnels et de connaitre l’état actuel et déterminer le taux de disponibilité . Logs d’activité o Logs serveurs (http, ftp, … ) : permet de connaître l’activité réelle des utilisateurs o Logs applicatifs : permet de récupérer des informations plus précise sur les différentes briques logicielles des services opérationnels L’objectif IDM, à travers cette alternance est de mettre en place une infrastructure commune à l’ensemble des systèmes d’informations.