Extreme set-up and run-up on steep cliffs (Banneg Island, France)

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Semi-empirical dissipation source functions for ocean waves: Part I, definition, calibration and validation

New parameterizations for the spectra dissipation of wind-generated waves are proposed. The rates of dissipation have no predetermined spectral shapes and are functions of the wave spectrum and wind speed and direction, in a way consistent with observation of wave breaking and swell dissipation properties. Namely, the swell dissipation is nonlinear and proportional to the swell steepness, and dissipation due to wave breaking is non-zero only when a non-dimensional spectrum exceeds the threshold at which waves are observed to start breaking. An additional source of short wave dissipation due to long wave breaking is introduced to represent the dissipation of short waves due to longer breaking waves. Several degrees of freedom are introduced in the wave breaking and the wind-wave generation term of Janssen (J. Phys. Oceanogr. 1991). These parameterizations are combined and calibrated with the Discrete Interaction Approximation of Hasselmann et al. (J. Phys. Oceangr. 1985) for the nonlinear interactions. Parameters are adjusted to reproduce observed shapes of directional wave spectra, and the variability of spectral moments with wind speed and wave height. The wave energy balance is verified in a wide range of conditions and scales, from gentle swells to major hurricanes, from the global ocean to coastal settings. Wave height, peak and mean periods, and spectral data are validated using in situ and remote sensing data. Some systematic defects are still present, but the parameterizations yield the best overall results to date. Perspectives for further improvement are also given.Comment: revised version for Journal of Physical Oceanograph

Breaking waves and their applications to the offshore wind sector: Habilitation to drive research (Habilitation à Diriger des Recherches, HDR).

This document presents research efforts dedicated to improve the characterizationof breaking waves and of their multiple effects on offshore wind turbines.The manuscript focuses first on the definition of the breaking onset criterionthat is important for the design of offshore wind turbines. It further presentsrecent advances in the parameterization of the wave breaking statistics, neededto identify the design sea states, when slamming loads are considered. This isfollowed by a description of efforts to improve the spectral wave models, used toobtain the wave climatology at offshore wind farms location.Observational works to capture area of wave energy focusing (potentially featuringbreaking waves) are then introduced. The document further presents experimentalefforts to observe interactions between large amplitude breaking wavesand offshore structures.Finally, different perspectives targeting the improvement of the above-citedresearch axes are given, and extension to other applications are discussed. Theseapplications cover the effects of breaking waves on the characterization of the windproperties with spaceborne measurements and ocean-wave-atmosphere couplednumerical models

Wave breaking parameterization and spectral wave modelling

Bien que le déferlement est le plus important puits d énergie pour les vagues, il est encore assez mal compris. Le travail présenté dans cette thèse vise à unifier la dissipation d énergie associée au déferlement du large à la côte à travers le développement d un nouveau paramétrage destiné aux modèles spectraux de prévision des états de mer. Le premier résultat de cette thèse est un paramétrage de la probabilité de déferlement applicable du large à la côte et permettant de séparer les différentes échelles pouvant être présentes dans un champ de vagues. Ce paramétrage a servi de base à un nouveau terme source de dissipation d énergie liée au déferlement et destiné aux modèles spectraux de prévision des états de mer. Ce terme repose en outre sur le paramétrage de deux autres grandeurs fondamentales pour le déferlement : le taux de dissipation par unité de longueur de crête de déferlante et la densité de longueur de crête par mètre carré. Les résultats de la validation réalisée à l échelle globale ainsi qu à l échelle d une plage suggèrent qu il est possible de représenter la dissipation par déferlement par un unique paramétrage, du large à la côte. D autre part, deux études portant sur la directionalité du déferlement et sur les modulations du déferlement des vagues courtes par les vagues longues ont été abordées. Ces deux aspects peuvent aussi avoir des conséquences importantes sur la dissipation d énergie par déferlement.Although breaking is the most important energy sink term for wind-generated waves, the underlying physical processes are the least understood. The work presented in this thesis s aimed at unifying the wave breaking induced dissipation from deep to shallow water through the development of a novel parameterization designed for spectral wave models. The first result of this work is a parameterization of the breaking probability enabling to discriminate among the wave scales present within a given wave field and applicable from the deep ocean to the surf zone. This parameterization was used as the basis of a new spectral source term for the wave breaking induced-dissipation. This source function is based on the parameterization of three basics physical quantities: the breaking probability, the dissipation rate per unit crest length and the crest length density per unit area. The results of the validation performed at global scale and at beach scale suggest that it is possible to represent the wave breaking induced dissipation by a single formulation. We shall besides discuss a study of the breaking directionality and the impact of the presence of long waves on the breaking of short waves. Both effects may as well have important on the breaking dissipation parameterization.BREST-BU Droit-Sciences-Sports (290192103) / SudocPLOUZANE-Bibl.La Pérouse (290195209) / SudocSudocFranceF

Gaussian Mixture Models for the Optimal Sparse Sampling of Offshore Wind Resource

Offshore wind resource assessment is a crucial step for the development of offshore wind energy. It relies on the installation of measurement devices, which placement is an open challenge for developers. In this paper, a sparse sampling method using a Gaussian Mixture Model on Numerical Weather Prediction data is developed for the offshore wind reconstruction. It is applied on France's main offshore wind energy development areas, Normandy, Southern Brittany, and the Mediterranean Sea. The study is based on 3 years of Meteo France AROME's data, available through the MeteoNet data-set. Using a Gaussian Mixture Model for data clustering, it yields to optimal sensors' locations with regards to wind field reconstruction error. The proposed workflow is described and compared to state-of-the-art methods for sparse sampling. It constitutes a robust yet simple method for the definition of optimal sensor siting for offshore wind reconstruction. The described method yields to optimal network of 7, 4, and 4 sensors for Normandy, Southern Brittany and the Mediterranean Sea with a gain of approximately 20 % in wind field reconstruction error compared to the median Monte Carlo case, and more than 30 % compared to state-of-the-art methods

Predicting Analog Forecasting Errors using Dynamical Systems

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Wave group focusing in the ocean: estimations using crest velocities and a Gaussian linear model

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Wave runup over the steep rocky cliffs of Banneg Island, France

International audienceThe wave runup is known to depend on the offshore wave conditions and the beach slope. While most field studies on wave runup have focused on low-to-mild sloping sandy beaches, runup measurements on steep and irregular rocky beach profiles are still very sparse. Hence, little is known on the physical processes affecting the wave runup in such environments, and the range of applicability of empirical runup formula requires further investigation. This study focuses on the steep (0.1 < tan β < 0.4) rocky cliffs of Banneg Island, a small island of the Iroise Sea occasionally flooded during extreme water level events. A statistical parameter for extreme runup is derived from the measurements of pressure sensors deployed in the intertidal zone. Deep water wave parameters and highresolution topographic data are analyzed concurrently with runup time-series in order to assess the dependence of the runup on hydrodynamic conditions and foreshore slopes. The wave runup is shown to be strongly related to the surf-similarity parameter times the offshore significant wave height. Given the large topographic variability of the beach profile, the method used to compute the beach slope is shown to strongly affects the results

Numerical investigation of slamming loads on floating offshore wind turbines

International audienceThis paper presents the results of ongoing work regarding numerical simulations of breaking wave impacts on a surface-piercing cylinder. The computational fluid dynamics solver, Code Saturne, using the volume of fluid approach, is presented and utilised for offshore hydrodynamics. Phase-focused waves are employed to recreate singular breaking events under relatively controlled conditions. The fluid shape and kinematics are described during the breaking process and the load produced by a plunging breaker on a rigid cylinder is investigated