Papers by Christophe Maisondieu
MERiFIC was selected under the European Cross-Border Cooperation Programme INTERREG IV A France (... more MERiFIC was selected under the European Cross-Border Cooperation Programme INTERREG IV A France (Channel) – England, co-funded by the ERDF. The sole responsibility for the content of this report lies with the authors. It does not represent the opinion of the European Communities. The European Commission is not
Le projet Eurêka franco-norvégien SAR-DRIFT (Search and Rescue of Drifting objects) a pour objet ... more Le projet Eurêka franco-norvégien SAR-DRIFT (Search and Rescue of Drifting objects) a pour objet la modélisation de la dérive des corps flottants dans un contexte stochastique lié aux incertitudes sur les conditions météorologiques, les conditions initiales et les chargements liés à l’environnement. A l’occasion de la préparation et de la conduite de ce projet, les auteurs ont examiné les apports potentiels des satellites dans la recherche et le sauvetage d’objets ou de personnes tombées à la mer En raison des contraintes opérationnelles liées au sauvetage, il leur est apparu difficile d’envisager dans l’immédiat une utilisation directe des satellites pour la localisation de ces objets dérivants. De même, l’amélioration par recalage en temps quasi-réel des forçages océano-météo à intégrer dans les modèles de dérive se heurte encore à des problèmes de rapidité de mise à disposition générale de données fiables et validées. Par contre, les progrès techniques offrent maintenant des mesu...
Journal of Open Source Software
The resourcecode Marine Data Toolbox is a python package developed within the Resource-CODE proje... more The resourcecode Marine Data Toolbox is a python package developed within the Resource-CODE project, to facilitate the access to a recently developed Metocean hindcast database (Accensi et al., 2021), and to a set of state-of-the-art methods for data analysis. This toolbox provides developers with a set of standard functions for resource assessment and operations planning. The advanced statistical modelling tools provided together with the embedded high resolution wave hindcast database provide the developers with a set of standard functions for resource assessment, extreme values modelling and operations and maintenance planning. Suitable for users not familiar with netCDF files handling or statistical analysis development, it is however designed to fulfil expert metocean analysis requirements. The advanced statistical modelling tools provided allow the developers of Offshore Renewable Energy (ORE) devices to conduct the necessary assessments to reduce uncertainty in expected environmental conditions, and de-risk investment in future technology design.
La base de donnees de rejeu d'etats de mer HOMERE a ete mise en place par les equipes de l... more La base de donnees de rejeu d'etats de mer HOMERE a ete mise en place par les equipes de l'Ifremer du laboratoire de Comportement des Structures en Mer (RDT/LCSM) et du Laboratoire d'Oceanographie Physique et Spatiale (LOPS). Cette base de donnees consiste en un ensemble de parametres permettant de decrire les caracteristiques principales et l'evolution des conditions d'etats de mer sur la zone de la Manche et du Golfe de Gascogne. Initialement developpee pour repondre aux besoins lies aux etudes sur la caracterisation de la ressource et du comportement des structures en mer, en particulier dans le domaine des energies marines renouvelables, son champ d’application est en fait, de par l’ensemble des parametres et l’information spectrale disponibles, mais aussi de par la haute resolution de la grille de calcul, bien plus etendu. Des applications liees a l’etude du transport sedimentaire ou des echanges ocean-atmosphere tout comme a la gestion des operations et cam...
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2020
A system of two coupled four-beam acoustic Doppler current profilers was used to collect turbulen... more A system of two coupled four-beam acoustic Doppler current profilers was used to collect turbulence measurements over a 36-h period at a highly energetic tidal energy site in Alderney Race. This system enables the evaluation of the six components of the Reynolds stress tensor throughout a large proportion of the water column. The present study provides mean vertical profiles of the velocity, the turbulence intensity and the integral lengthscale along the streamwise, spanwise and vertical direction of the tidal current. Based on our results and considering a tidal-stream energy convertor (TEC) aligned with the current main direction, the main elements of turbulence prone to affect the structure (material fatigue) and to alter power generation would likely be: (i) the streamwise turbulence intensity ( I x ), (ii) the shear stress, v ′ w ′ ¯ , (iii) the normal stress, u ′ 2 ¯ and (iv) the vertical integral lengthscale ( L z ). The streamwise turbulence intensity, ( I x ), was found to ...
Ocean Engineering, 2016
The study reviews, based on the state-of-the-art findings, some uncertainties associated with wav... more The study reviews, based on the state-of-the-art findings, some uncertainties associated with wave data and models currently used in design and operation procedures of ship and offshore structures. Although the same basic principles prevail for hydrodynamic loads on ships and offshore structures, actual problems and methods for assessing these loads in the design and operation stage are not the same. Different wave data and models are used for specifying design and operational criteria for these two types of platforms and different uncertainties are related to them. Wave data and models used to define sea state characteristics are discussed and particular attention is given to the associated sources of uncertainties. Some weaknesses of wave input used in design and operational procedures for marine structures are pointed out. Focus is also given on uncertainties related to model tests as tank testing is an important supporting tool for design and operation. Impact of some selected uncertainties on wave description and wave loads is demonstrated by examples. Highlights ► Definitions of uncertainties. ► Establishment of sea state characteristics for marine structures' analysis and model tests. ► Uncertainties associated with sea state characteristics. ► Impact of uncertainties of sea state characteristics on model tests and design and operations of marine structures.
The Wave Hub wave energy test facility is a key maritime test site in Europe. It is now operation... more The Wave Hub wave energy test facility is a key maritime test site in Europe. It is now operational for the deployment and performance assessment of wave energy converters. This paper describes some outputs from a unique wave buoy array deployed off the North Cornwall close to the Wave Hub site. The deployment of four buoys in a close array is a unique experimental facility that will contribute extensively to the understanding of oceanographic process, which includes key aspects of uncertainty and spatio-temporal variability. Four Seawatch mini II directional buoys – separated by an average distance of ~500m were deployed. This allowed an assessment of the local wave energy resource through time-domain and frequency-domain analysis. This paper presents the preliminary results obtained from the processing of such extended data including also wind and tidal information.
23rd International Conference on Offshore Mechanics and Arctic Engineering, Volume 1, Parts A and B, 2004
Flow viscous damping and energy dissipation around the keels in a wellbay are experimentally and ... more Flow viscous damping and energy dissipation around the keels in a wellbay are experimentally and numerically investigated. Experiments have been carried out using a U-shape tube. Damping coefficients are evaluated from water elevation measurements. Computations are also performed using two different numerical models under viscous fluid assumption. Comparison of results shows good agreement on both drag coefficients evaluation and velocity fields.
2015 IEEE/OES Eleveth Current, Waves and Turbulence Measurement (CWTM), 2015
This work presents the analysis of wave and turbulence measurements collected at a tidal energy s... more This work presents the analysis of wave and turbulence measurements collected at a tidal energy site. A new method is introduced to produce more consistent and rigorous estimations of the velocity fluctuations power spectral densities. An analytical function is further proposed to fit the observed spectra and could be input to the numerical models predicting power production and structural loading on tidal turbines. Another new approach is developed to correct for the effect of the Doppler noise on the high frequencies power spectral densities. The analysis of velocity time series combining wave and turbulent contributions demonstrates that the turbulent motions are coherent throughout the water column, rendering the wave coherence-based methods not applicable to our dataset. To avoid this problem, an alternative approach relying on the pressure data collected by the ADCP is introduced and shows appreciable improvement in the wave-turbulence separation.
ABSTRACT Certains navires destinés aux opérations marines sont équipés d’une baie (moonpool) perm... more ABSTRACT Certains navires destinés aux opérations marines sont équipés d’une baie (moonpool) permettant la manipulation et la mise à l’eau à l’abri de la houle de structures ou d’engins sous-marins. Un des problèmes hydrodynamiques lié à la présence d’une telle baie est l’apparition éventuelle de phénomènes de résonance. La caractérisation des écoulements dans le moonpool passe par l’identification de ces modes de résonance et des amortissements. Il convient donc en particulier de pouvoir modéliser correctement la dissipation d’énergie. Cette dissipation se fait par radiation d’un champ de vagues à l’extérieur, mais aussi et surtout par séparation de l’écoulement au niveau des bouchains vifs à la base de la baie. Ce dernier terme dissipatif étant associé à une force d’amortissement quadratique. L’étude présentée ici rassemble un certain nombre de résultats issus de développements théoriques, de simulations numériques en fluide parfait et en fluide visqueux et d’expérimentation en canal d’essais, portant sur l’identification dans une représentation bidimensionnelle des modes résonants d’une part et des phénomènes d’amortissements d’autre part
Les activités dans le domaine des Energies Marines Renouvelables sont en pleine expansion. Pour l... more Les activités dans le domaine des Energies Marines Renouvelables sont en pleine expansion. Pour l'évaluation de la ressource aussi bien que pour la caractérisation des climatologies des sites de déploiement de Convertisseurs d'Energie Marine, une description fine des conditions environnementales, notamment des états de mer, est requise à l'échelle des sites d'implantation. Afin de développer un outil adapté aux besoins de l'ingénierie et au développement des activités des Energies Marines Renouvelables, l'Ifremer construit une base de données spécifique à l'établissement de climatologies fines des états de mer. Cette base de données, réalisée à l'aide d'une configuration actualisée du modèle de vagues WaveWatch III ® sur grille déstructurée, est présentée ici. Le domaine considéré s'étend du Golf de Gascogne jusqu'au Sud de la Mer du Nord de 1996 à 2012. Le paramétrage, les données de forçage ainsi que les données de sortie du modèle et les validations sont également présentés en détail. Mots-clefs : spectre directionnel, hindcast, WAVEWATCH III ® , énergie marine renouvelable The number ofMarine Renewable Energy projects has rapidly raised over the last decades. Those require a refined description of environmental conditions, such as sea states, for resource assessments as well as for the conception of the Marine Energy Converters. Engineering studies require long-term data sets so as to assess temporal variability and extreme events of sea states at the scale of the implantation sites.,As a support to its research studies on Marine Renewable Energy, Ifremer is building a specific hindcast database, running the wave model WAVEWATCH III® on an unstructured grid. The wave model extends over the area from the South of the North Sea to the Bay of Biscay with a high spatial resolution and covers a 16 years period from 1996 to 2012. The parameterization of the model is presented in this paper, as well as the forcing, the specific output data and validation results.
IXèmes Journées, Brest, 2006
La présente étude a pour objet d'évaluer l'influence des régimes combinés de houle et de courant ... more La présente étude a pour objet d'évaluer l'influence des régimes combinés de houle et de courant cross-shore sur l'évolution à long terme du profil d'un estran vaseux. On y met en oeuvre une méthode originale de génération de données de vent et d'états de mer réalistes, appliquée à un modèle morphosédimentaire basé sur les processus d'érosion/transport en suspension/dépôt Une analyse de simulations de longue durée est proposée.
Renewable Energy, 2011
This paper presents a refined description of the wave climate observed in a Portuguese location f... more This paper presents a refined description of the wave climate observed in a Portuguese location for marine energy projects. The data used in this case study were derived from 3-month in situ measurements carried out using three directional buoys that have been deployed simultaneously-yet independently (various buoy types and water depths)-on the Atlantic coast in the neighbourhood of Figueira da Foz. Two ways of reporting the statistics were adopted. In the first one, each recorded sea state was summarized as a set of global parameters accounting for energy, mean frequency and direction, spectral bandwidth and directional spreading related to the main ongoing wave field considered as unimodal. In the second one, each sea state has been decomposed into its own wave components-swells and wind-sea-which are characterised separately and individually by the same set of parameters as previously. Besides the adopted data processing techniques and the illustration of such thorough wave climate description modes, the paper also addresses the advantages and limits of each adopted parameterization in the frame of simultaneous and independent in situ wave measurements. Highlights ► Wave statistics produced considering unimodal and multimodal sea-state descriptions. ► Spectral bandwidth and directional spreading are included in both descriptions. ► Spectral bandwidth is significantly correlated to wave energy/peak period. ► Wave directional spreading is difficult to estimate in absolute terms. ► Directional artefacts are obtained with Maximum Entropy Methods in some cases.
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Papers by Christophe Maisondieu