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Registros recuperados: 21
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An autoregressive model with time-varying coefficients for wind fields ArchiMer
Ailliot, Pierre; Monbet, Valérie; Prevosto, Marc.
In this article, an original Markov-switching autoregressive model is proposed to describe the space-time evolution of wind fields. At first, a non-observable process is introduced in order to model the motion of the meteorological structures. Then, conditionally to this process, the evolution of the wind fields is described using autoregressive models with time-varying coefficients. The proposed model is calibrated and validated on data ill the North Atlantic.
Tipo: Text Palavras-chave: Markov switching autoregressive model; Wind fields; Space time model.
Ano: 2006 URL: http://archimer.ifremer.fr/doc/2006/publication-1225.pdf
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Analyses of Environmental time series: Extreme Values ArchiMer
Guanche Garcia, Yanira; Prevosto, Marc; Maisondieu, Christophe; Bulteau, Thomas; Paris, François.
The knowledge of extreme events of environmental variables is an issue of increasing concern to the scientific community. Within the branch of coastal and ocean engineering there are many fields of application where an accurate estimation of long term return period events is needed, i.e. coastal defenses design, coastal flooding management, estimation of changes of the littoral morphology, offshore and onshore renewable energy devices design, etc. But not only the engineers are concerned by extreme events; biological communities in the open sea and estuarine systems are also exposed to extreme events that may affect its natural development (i.e. extreme sea levels in estuarine environments could raze fields of plants not able to deal with salt in just a...
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Ano: 2015 URL: http://archimer.ifremer.fr/doc/00378/48967/49370.pdf
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Bivariate simulation of non stationary and non Gaussian observed processes - Application to sea state parameters ArchiMer
Monbet, Valerie; Prevosto, Marc.
A method for artificially generating operational sea state histories has been developed. This is a distribution free method to simulate bivariate non stationary and non Gaussian random processes. This method is applied to the simulation of the bivariate process (H-s, T-p) of sea state parameters. The time series respects the physical constraints existing between the significant wave height and the peak period. Furthermore, we show that the persistence properties of the simulations match to those of the observations.
Tipo: Text Palavras-chave: Bivariate simulation; Non Gaussian processes; Wave data; Non parametric simulation.
Ano: 2001 URL: http://archimer.ifremer.fr/doc/2001/publication-4343.pdf
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EquiMar. Deliverable D2.2. Wave and tidal resource characterisation ArchiMer
Venugopal, Vengatesan; Davey, Thomas; Smith, Helen; Smith, George; Holmes, Brian; Barrett, Sean; Prevosto, Marc; Maisondieu, Christophe; Cavalieri, Luigi; Bertotti, Luciana; Lawrence, John; Girard, Francoise.
This report gives guidance relevant to the resource assessment of sites considered for the deployment of wave and tidal energy converters. Areas considered include: instrumentation and measurement; techniques and requirements for wave and tidal parameterisation; wave-current interaction; spatial and temporal variation. A number of case studies are also included examining several European sites.
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Ano: 2011 URL: http://archimer.ifremer.fr/doc/00250/36152/34706.pdf
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Field measurements of coastal waves and currents in Portugal and Greece ArchiMer
Paillard, Michel; Prevosto, Marc; Barstow, Sf; Soares, Cg.
The MAST II WAVEMOD Project aimed at improving stochastic modelling of ocean waves and currents in coastal waters. In order to supplement existing data, two measurement campaigns were carried our, one on the Atlantic coast of Portugal, and, secondly, on the northern coast of Crete in the Mediterranean. The Portuguese measurements covered 7 months during winter 1993-1994, while off Crete, measurements started early in February 1994 and continued for 10 months, In both sites, two directional Waveriders and one non-directional Waverider were deployed along a transect our from the coast in water depths between 10 and 100 m. In addition, the Mediterranean site also incorporated measurements of mean current velocities. Available satellite data were analysed to...
Tipo: Text Palavras-chave: Waves; Currents; Portugal; Greece.
Ano: 2000 URL: https://archimer.ifremer.fr/doc/00000/10506/66722.pdf
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HAWAI project - WP3: Hydrodynamic wave loading - Optimisation of the time-series reconstruction ArchiMer
Prevosto, Marc; Soulard, Thomas.
When Newman's approximation is used to calculate the low frequency part of the nonlinear transfer between the waves and the forces on an LNG carrier, the CPU time to make the time series reconstruction of wave loads is a small part of the total. However, using full QTF-matrices increases the required work by a factor equal to the number of wave components in the sea states and the total simulation time can be increased by 5 or 10. Moreover, if we consider the multi-directional sea, the double summation becomes a quadruple summation at second order which is extremely time-consuming. There is a way to accelerate this computation by making an algebraic or system approximation of the QTF. The aim of this report is to present the solutions, the problems and the...
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Ano: 2007 URL: http://archimer.ifremer.fr/doc/00239/34986/33520.pdf
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Infragravity waves and moored floating structures ArchiMer
Klinghammer, Christian; Prevosto, Marc; Le Boulluec, Marc; Perignon, Yves.
Up to this day, design recommendations or practices for floating structures, such as DNVs RP-C205 and F205 for example, do not account for the existence of low frequency free Infragravity (IG) waves. These are low-frequency water waves which represent an additional excitation for (moored) floating structures. In this study, the influence of free IG waves on moored floating structures response is investigated and compared to second-order low-frequency wave forces, as the standard low frequency excitation, for two selected important free IG events in 2013 and 2014 at the SEM-REV (Site d'Experimentation En Mer - Récupération de l'Energie des Vagues) test site near Le Croisic, Pays-de-la-Loire, France. The wave forces and motion response for two example...
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Ano: 2015 URL: http://archimer.ifremer.fr/doc/00384/49584/50094.pdf
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Les motivations et les moyens de quelques instrumentations " in situ " d'ouvrages en mer ArchiMer
Olagnon, Michel; Prevosto, Marc; Ozanne, Philippe.
This report gives some examples of instrumentation used or anticipated for use on some fixed platforms, aimed at obtaining answers to the questions posed by the heads of petroleum industries concerning the design techniques of these platforms : validity of calculations, guarantee of a normal behaviour of structures until the end of their anticipated serviceable lifetime, detection of serious damage, possibility of extending the serviceable lifetime of structures beyond the lifetime initially anticipated.
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Ano: 1986 URL: https://archimer.ifremer.fr/doc/00480/59128/61756.pdf
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Modeling process asymmetries with Laplace moving average ArchiMer
Raillard, Nicolas; Prevosto, Marc; Ailliot, Pierre.
Many records in environmental science exhibit asymmetries: for example in shallow water and with variable bathymetry, the sea wave time series shows front–back asymmetries and different shapes for crests and troughs. In such situation, numerical models are available but their computational cost and complexity are high. A stochastic process aimed at modeling such asymmetries has recently been proposed, the Laplace moving average process, which consists in applying a linear filter on a non-Gaussian noise built using the generalized Laplace distribution. The objective is to propose a new non-parametric estimator for the kernel involved in the definition of this process. Results based on a comprehensive numerical study will be shown in order to evaluate the...
Tipo: Text Palavras-chave: Laplace moving average; Non-linear time series; FIR estimation; Splines; High-order spectrum; Asymmetries.
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00201/31189/29588.pdf
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Probability distributions for maximum wave and crest heights ArchiMer
Prevosto, Marc; Krogstad, He; Robin, Agnes.
The paper discusses short- and long-term probability models of ocean waves. The Gaussian theory is reviewed, and nonlinear short-term probability distributions are derived from a narrow band second-order model. The nonlinearity has different impact on different measurement techniques, and this is further demonstrated for wave data from the WAVEMOD Crete measurement campaign and laser data from the North Sea. Finally, we give some examples on how the short-term statistics may be used to estimate the probability distributions for the maximum waves during individual storms as well as in a wave climate described by long-term distributions. (C) 2000 Elsevier Science B.V. All rights reserved.
Tipo: Text Palavras-chave: Maximum wave height; Maximum crest height; Non linear models; Probability distribution; Narrow band model.
Ano: 2000 URL: https://archimer.ifremer.fr/doc/00000/10507/66723.pdf
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Refinements of sea state statistics for marine renewables: A case study from simultaneous buoy measurements in Portugal ArchiMer
Saulnier, Jean Baptiste; Prevosto, Marc; Maisondieu, Christophe.
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...
Tipo: Text Palavras-chave: Sea state; Directional spectrum; Wave systems; Spectrum partitioning; Spectral bandwidth; Directional spreading.
Ano: 2011 URL: http://archimer.ifremer.fr/doc/00037/14813/12196.pdf
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Rogue Waves 2008 : Proceedings of a Workshop organized by Ifremer and held in Brest, France 13-14-15 October 2008 within the Brest Sea Tech Week 2008 ArchiMer
Olagnon, Michel; Prevosto, Marc.
Since the Rogue Waves 2000 and 2004 workshops, researchers have pursued activity in the proposition of models and descriptions that can improve our understanding of rogue waves. The Brest Rogue Waves 2008 workshop gathered again many scientists and engineers to an opportunity to confront and discuss their views on the subject. It provided an assessment of the State of the Art of research on those matters, and was one more step forward towards efficient mitigation measures.
Tipo: Text Palavras-chave: Face au risque de ces événements. Mots-clés : vagues; Extrêmes; Vagues anormales; Vagues scélérates; Ocean waves; Extremes; Rogue waves; Freak waves.
Ano: 2009 URL: http://archimer.ifremer.fr/doc/00133/24444/22459.pdf
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Statistical Analysis of Low Frequency Motions of Floating Bodies in Shallow Water ArchiMer
Prevosto, Marc; Le Louarne, Jean-franois; Guede, Zakoua.
In this study we discuss various methods to assess the statistics of extreme response of a floating structure subjected to random waves. This issue is of great importance in the case of low frequency motion of floating bodies in shallow water. Those methods are based on the evaluation of the level crossing rate, which is easily related to the extreme value statistics for stationary random processes and large levels. Four main methods are considered, namely the Rice formula with either a Gaussian assumption or an approximation of the joint distribution of the response and its first derivative by a projection method; the Breitung's formula; the Hagberg's approaches using either an asymptotic expansion or a Monte-Carlo integration and finally the time domain...
Tipo: Text Palavras-chave: Low frequency motion; Shallow water; Second order wave loading; Crossing rate; Extreme response.
Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/acte-6329.pdf
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Statistics of wave crests from second order irregular wave 3D models ArchiMer
Prevosto, Marc.
The statistics of the elevation and kinematics of waves in real seas are very rarely accessible from in-situ measurements which induced very high costs. An alternative to the actual waves observation is to derive from the spectral climatology of waves, completed with other environmental data like the wind and the current, the statistics of the individual waves. But this requires accurate models of irregular gravity waves which take into account all the main nonlinearities and interactions with the local wind, current and bathymetry. In a first step, methodologies have been based on second order irregular wave 3D models and have supplied the engineers with new better accurate models of statistics of wave crests. These models do not include yet the complex...
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Ano: 2000 URL: http://archimer.ifremer.fr/doc/00116/22715/20457.pdf
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Survey of stochastic models for wind and sea state time series ArchiMer
Monbet, Valérie; Ailliot, P; Prevosto, Marc.
The knowledge of sea state and wind conditions is of central importance for many offshore and nearshore operations. In this paper, we make a complete survey of stochastic models for sea state and wind time series. We begin with methods based on Gaussian processes, then non-parametric resampling methods for time series are introduced followed by various parametric models. We also propose an original statistical method, based on Monte Carlo goodness-of-fit tests, for model validation and comparison and this method is illustrated on an example of multivariate sea state time series. (C) 2006 Elsevier Ltd. All rights reserved.
Tipo: Text Palavras-chave: Model validation; Simulation; Nonlinear time series; Wind; Sea state.
Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/publication-2679.pdf
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Time series analysis of marine data: a key knowledge at the crossroads of marine sciences ArchiMer
Puillat, Ingrid; Prevosto, Marc; Mercier, Herle; Thomas, S..
In our time emerged the idea of a major environmental degradation, at both local and global scales, in the face of the recurrent human pollution. Consequently in the sake of a sustainable humanity development, of the ethic and of the ecology, the protection and the monitoring of our environment have become a major stake. Many scientific and technical tools contributed to improve the environmental knowledge, as helped remote and in situ observations, and forecast modeling. In situ environmental sensor systems have been designed to be increasingly sustainable even in a hostile environment such as the deep ocean. In a similar way, the infrastructures hosting those sensors are now thought and built to be permanent. In marine sciences these considerations gave...
Tipo: Text Palavras-chave: Time series; Marine data; Signal processing; Statistics.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00161/27259/25468.pdf
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WACSIS, Wave Crest Sensor Intercomparaison Study : Common Data Base, Analyses, Crest Height Models ArchiMer
Prevosto, Marc; Van Iseghem, Sylvie; Moreau, Benjamin; Forristall, George Z..
Despite its great theoretical and practical importance, the statistical distribution of crest heights has remained poorly known. The uncertainties are due to difficulties both with the theory, where nonlinear effects must be accurately modeled, and with measurements, where different sensors appear to give different results. In response to this uncertainty, the Wave Crest Sensor Intercomparison Study (WACSIS) was formed as a Joint Industry Project in order to provide data for comparing the response of wave sensors and for comparing theories of crest height distributions with the measurements. The key to the WACSIS experiment was to place all of the popular sensors on the same platform located where they were likely to experience large waves in one season....
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Ano: 2001 URL: http://archimer.ifremer.fr/doc/00117/22841/20651.pdf
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WASP - West Africa Swell Project - Final report and Appendices ArchiMer
Olagnon, Michel; Prevosto, Marc; Van Iseghem, Sylvie; Ewans, Kevin; Forristall, George Z..
The OGP Workshop on the Metocean and Engineering Aspects of Floating Systems which was held at St. Albans in April 2001 identified better discrimination of the low frequency end of the wave spectrum as one of the most pressing problems for the design and analysis of floating systems. The responses of many floating systems have proven to be very sensitive not only to the amplitude and frequency of the swell, but also to the details of the shape of the swell peak in the spectrum. There has been relatively little serious study of the low frequency end of the wave spectrum compared to the effort that has gone into the study of the high frequency tail of the spectrum. Much of the present interest in swell comes from the active deep water developments taking...
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Ano: 2004 URL: http://archimer.ifremer.fr/doc/00114/22537/20216.pdf
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Wave and turbulence measurements at a tidal energy site ArchiMer
Filipot, Jean-francois; Prevosto, Marc; Maisondieu, Christophe; Le Boulluec, Marc; Thomson, Jim.
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...
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Ano: 2015 URL: http://archimer.ifremer.fr/doc/00254/36537/35074.pdf
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Wave groupiness and spectral bandwidth as relevant parameters for the performance assessment of wave energy converters ArchiMer
Saulnier, Jean-baptiste; Clement, Alain; Falcao, Antonio F. De O.; Pontes, Teresa; Prevosto, Marc; Ricci, Pierpaolo.
To date the estimation of long-term wave energy production at a given deployment site has commonly been limited to a consideration of the significant wave height H, and mean energy period T. This paper addresses the sensitivity of power production from wave energy converters to the wave groupiness and spectral bandwidth of sea states. Linear and non-linear systems are implemented to simulate the response of converters equipped with realistic power take-off devices in real sea states. It is shown in particular that, when the converters are not much sensitive to wave directionality, the bandwidth characteristic is appropriate to complete the set of overall wave parameters describing the sea state for the purpose of estimating wave energy production. (C) 2010...
Tipo: Text Palavras-chave: Wave groupiness; Spectral bandwidth; Sea states; Wave climate; Wave energy; Wave energy converters.
Ano: 2011 URL: http://archimer.ifremer.fr/doc/00031/14178/11467.pdf
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