Models have been developed for computing the loading deformation of the Earth due to storm surges and atmospheric pressure variations. It shown that atmospheric pressure loading and storm surge loading, can cause surface deformations up to several millimeters and changes in the gravity accelerations of a few microGal. The loading effects associated with storm surge events vary faster (within hours) compared with those related with atmospheric pressure fluctuations (within 2-5 days); furthermore non-tidal ocean loading is generally larger (especially at high latitudes) but affects relatively small areas at a time (about 500 km of extension), while pressure variations generally affect very broad areas and the largest deformations are usually registered during the winter periods and mainly derive from an area within 2000 km from the observation point. The regions situated in the south east of England and along the Dutch- German-Danish coastlines exhibit the largest deformation effects associated with non-tidal ocean loading (up to -30 mm of radial displacement, 10 mm in the tangential north-west direction and gravity changes of about 8J.LGal during particularly large storm surge events). The effect decreases gradually inland with values of almost -10 mm in the vertical deformation, 1-2 mm in the horizontal and gravity variations of 2-3 pGal at distances of 150 km from the coast. Atmospheric pressure loading and storm surge loading have almost the same magnitude but opposite signs in the northern regions of the British Isles in such extreme meteorological conditions. For stations situated well inland in Europe, atmospheric pressure loading is responsible for most of the deformation induced. Storm surge and atmospheric pressure loading effects are particularly different when they are associated with winter seasons characterized by opposite NAO indices. When the NAO index is positive (negative) the vertical displacements produced by non-tidal loading are negative (positive) in sign as a consequent sinking (rising) of the areas investigated and the associated gravity variations are positive (negative). The work described in this thesis is mainly concerned with developing models for better understanding the atmospheric pressure and storm surge loading deformations in the UK and north west Europe. However, as a final part of this work, comparisons are made with available geodetic observations in this area. The comparison between the gravity measurements performed by an SG at the geophysical station of Membach (Belgium) and the predicted gravity variations induced by non-tidal ocean loading represents a useful validation of our model. On the other hand even if the signal due to the loading deformation induced by atmospheric pressure and storm surges is present in the GPS coordinates and there is some evidence that sub-daily GPS results in particular exhibit a pattern that is similar to the modelled deformation, the observed time series are too noisy at the 5-10 mm level and the comparison with modelled results are generally not conclusive.

The non-linear hyperboIic partial-differential equations governing long-wave propagation in two spatial dimensions are postulated. Through the method of characteristics, specific conditions are developed for integrating the Iong-wave equations. By introducing finite difference approximations to the characteristic conditions, an explicit numerical scheme is developed as an alternative to more standard finite differencetechniques. The modifications required at the open and closed boundary points are of particular importance and lead to a 45° characteristic numerical scheme. A practical assessment of stability and consistency criteria associated with the numerical scheme is shown to be important for the successful simulation of free and forced tidal oscillations. Tests with motion prescribed by analytical solutions verify the accuracy of the integration procedure and lead to the correct form of interpolation coefficients. A method of subdivisions is developed for improving the simulation of free wave oscillation in a closed basin of trapezoidal profile. Analytical solutions for steady and unsteady wind surges are used to examine the effect of introducing wind stress terms into the numerical scheme. A practical evaluation of the scheme is accomplished by simulating tidal propagation in the Clyae sea area. Tidal motion in this region is highlighted by the existence of an amphidromic point. Data for the model, provided by a tidal survey, confirm certain values of range and phase given in the Tide Tables (1979). Two separate surge events are simulated in the Clyde sea area. The relative size of each surge component and the interaction between tide and surge are established. The forms of the surges and the meteorological conditions required for their propagation into the Clyde sea area are also assessed. Finally, a west coast shelf model is developed to overcome the problem of specifying the external surge as a boundary condition.

Data collected in a large scale laboratory wave flume by a research team using the autonomous bottom boundary layer rig, (STABLE) was the subject of this study. The near bed suspension processes were examined relating them to the hydrodynamics. The deployment of a number of sensors allowed the assessment of their individual performance including the analysis of the pump-sampling and acoustic concentration data. Wavelet analysis was applied to identify the influence of STABLE on the vortex ripples in the vicinity of the rig. It revealed that the modification of the ripple dimensions around STABLE's feet was very localised. Sediment suspension was found to be strongly correlated to wave groups. The measured concentrations and empirical models based on convective and diffusive entrainment mechanisms were compared. A model based on the jet like ejection of particles between a vortex pair was developed and showed that lifting of sediments up to ten ripple heights above the bed was possible. A second model, capable of simulating the pumping effect, included this entrainment process to simulate the suspension under wave groups taking the suspension history into account. The behaviour of neutrally buoyant particles in a laboratory wave flume was videoed and revealed jet like ejections and horizontal movement over two or more ripple wavelengths.

The bulk of the research work in wave related areas considers sea waves as stochastic objects leading to wave forecasting techniques based on statistical approaches. Due to the complex dynamics of the sea waves’ behaviour, statistical techniques are probably the only viable approach when forecasting over substantial spatial and temporal intervals. However this view changes when limiting the forecasting time to a few seconds or when the goal is to estimate the quiescent periods that occur due to the beating interaction of the wave components, especially in narrow band seas. This work considers the multi disciplinary research field of deterministic sea wave prediction (DSWP), exploring different aspects of DSWP associated with shallow angle LIDAR systems. The main goal of this project is to study and develop techniques to reduce the prediction error. The first part deals with issues related to shallow angle LIDAR systems data problems, while the remaining part of this work concentrates on the prediction system and propagation models regardless of the source of the data. The two main LIDAR data problems addressed in this work are the non-uniform distribution and the shadow region problems. An empirical approach is used to identify the characteristics of shadow regions associated with different wave conditions and different laser position. A new reconstruction method is developed to address the non-uniformed sampling problem, it is shown that including more information about the geometry and the dynamics of the problem improves the reconstruction error considerably. The frequency domain approach to the wave propagation model is examined. The effect of energy leakage on the prediction error is illustrated. Two approaches are explored to reduce this error. First a modification of the simple dispersive phase shifting filter is tested and shown to improve the prediction. The second approach is to reduce the energy leakage with an iterative Window-Expansion method. Significant improvement of the prediction error is achieved using this method in comparison to the End-Matching method typically used in DSWP systems. The final part in examining the frequency domain approach is to define the prediction region boundaries associated with a given prediction accuracy. The second propagation model approach is the Time/Space domain approach. In this method the convolution of the measured data and the propagation filter impulse response is used in the prediction system. In this part of the research work properties of these impulse responses are identified. These are found to be quite complicated representations. The relation between the impulse response (duration and shift) with prediction time and distance are studied. Quantification of these impulse responses properties are obtained by polynomial approximation and non-symmetric filter analysis. A new method is shown to associate the impulse response properties to the prediction region of both the Fixed Time and Fixed Point mode.

Sismotectonique, paléotsunami et le tsunami scénarios sont examinés sur la côte du Nord de l'Égypte dans le cadre du tsunami européen ASTARTE projet et le projet IMHOTEP français-égyptiens. La géologie, la géomorphologie, séismicité, des mécanismes focaux, l'inversion de stress calculée et des données GPS utilisée pour identifier le régime de stress de jour présent des zones actives et les zones de tsunamigène. Tranchées et carottes ont été creusées à deux sites. Le balayage de radiographie, la sensibilité magnétique, l'analyse de taille de grain, l'échantillonnage, macrofossile détections, total des matériaux organiques et inorganiques et la datation au carbone est effectuée pour identifier les signatures tsunami. La couche sablonneuse blanche de haute énergie riche en fossiles retravaillés est corrélée avec le 21 juillet 365 dans le Kefr Saber. Les quatre couches sédimentaires de haute énergie à l'El Alamein sont corrélées les tsunamis historiques de 1600 avant J.C., le 21 juillet 365, 8 août 1303, le 24 juin 1870. / Seismotectonic, paleotsunami deposits and tsunami scenarios are investigated along the north coast of Egypt in the framework of the tsunami ASTARTE European and the French-Egyptian IMHOTEP projects. The geology, geomorphology, seismicity, focal mechanisms, calculated stress inversion, and GPS data were used to identify the present day stress regime of the main active zones and the tsunamigenic zones. Trenches and cores were dug in Kefr Saber and EL Alamein sites. X-ray scanning, magnetic susceptibility, grain size analysis, sampling, macrofossil detections, XRD analysis, total organic and inorganic matter measurements and carbon dating are carried out to identify the paleotsunami signatures. The high-energy white sandy layer rich in reworked fossils at Kefr Saber are correlated with 21 July 365, while the four characteristic high-energy sedimentary layers at the El Alamein site are correlated with the historical tsunami events of 1600 BC, 21 July 365, 8 August 1303, and 24 June 1870.

Cette thèse se focalise sur un système récupérateur de l’énergie des vagues qui est constitué d’un flotteur contenant des cuves partiellement remplis d’eau. Lorsque les vagues mettent en mouvement le flotteur, un tourbillon de type vidange apparaît dans une des cuve. Pour extraire l’énergie, une turbine, reliée à une génératrice, est plongée dans ce tourbillon. Tout d’abord, le tourbillon de vidange est étudié expérimentalement dans un contenant fixe. Les hauteurs d’eau et les vitesses du liquide sont mesurées. Ces vitesses sont estimées par vélocimétrie laser (LaserDoppler Velocimetry, LDV). Cet écoulement est modélisé numériquement en résolvant les équations de Navier-Stokes dans les deux phases (eau et air) par la méthode des volumes finis (avec le logiciel OpenFOAM). L’interface entre les deux phases est déterminée par la méthode des Volume of Fluid (VoF). Des comparaisons entre les résultats de ces deux approches sont menées. Ensuite, l’écoulement à l’intérieur du système houlomoteur est étudié en plaçant une maquette du dispositif sur un Hexapode (machine capable d’imposer des mouvements à la maquette à la manière d’un flotteur en mer). Les hauteurs d’eau et les efforts hydrodynamiques sur la maquette et, le cas échéant, la puissance électrique produite sont mesurés. Ces données sont comparées aux résultats d’un modèle numérique similaire à celui utilisé pour la première campagne expérimentale mais appliqué à ce dispositif. Enfin, l’influence de la turbine sur le reste du système est étudiée et son comportement en puissance est évalué pour différents mouvements imposés. Un premier modèle numérique de cette turbine est comparé aux données expérimentales. / This thesis focuses on the physical and numerical model of a wave energy converter (WEC). This device is made up of a buoy with compartments aboard partially filled with water. When the waves move the buoy, a bathtub vortex appears in one of these compartments. The energy is harvested with a turbine placed at the vortex’s center. First, the bathtub vortex is studied numerically and experimentally in a fixed compartment. Water levels are measured using acoustics sensors and water velocities are measured by Laser Doppler Velocimetry (LDV). This flow is modeled solving the Navier-Stokes equations in the two phases (air and water) with a finite volume method (with the software OpenFOAM). The interface is determined using the volume of fluid (VoF) method. Comparisons between experimental data and numerical data are presented. Afterwards, a second experimental campaign is conducted to study the complete flow inside the WEC. Therefore a model of the inside part of the WEC is fixed at the top of a Hexapod. This device can translate and rotate the model in the same way the waves would move a buoy. Water levels and hydrodynamic forces on the model are measured. When the turbine is there, the tension delivered by its generator is measured. This experimental device is modeled numerically. This model is closed to the first one. The results are compared with experimental data. Finally, a preliminary study of the turbine shows its influence on the general flow in the WEC and the evolution of the turbine power with the imposed motion. A first model of the turbine in a fixed compartment is presented and compared with experimental data.

En août 1883, l'éruption du Krakatau a provoqué des vagues de tsunami. Au centre et au Nord du détroit de la Sonde, peuples au moment de l’évènement de 1883 ont fourni de nombreux témoignages visuels des phénomènes volcaniques et des tsunamis. Les côtes sauvages et austères du Sud, notamment de la région de Ujung Kulon ont toujours été exemptes de populations. Il existe donc des lacunes dans les connaissances concernant le nombre et les caractéristiques des inondations de tsunamis sur ces côtes de Ujung Kulon. L’objectif de ce travail est d’explorer et de comprendre la façon dont les tsunamis générés par les différentes phases éruptives du Krakatau en1883 ont eu lieu à Ujung Kulon sur la base d’un déchiffrage aussi poussé que possible de l'enregistrement de phénomènes extrêmes dans des dépôts sédimentaire le long des littoraux sud du détroit de la Sonde. Pour atteindre cet objectif, trois méthodes d'analyse de texture et de composition sont appliquées, à savoir l'analyse de distribution granulométrique, l'identification des microfaunes et l’Anisotropie de la Susceptibilité Magnétique (ASM). Les résultats des analyses ont démontrés cependant que l'isthme en péninsule de Ujung Kulon a enregistré 4 (quatre) tsunamis liés aux éruptions et évidences que chaque vague a été enregistrée deux fois: i) par un flux direct provenant du détroit de la Sonde en ligne droite, ii) par une vague venant de l'océan Indien, retardée dans le temps après avoir été réfractée dans l’extrémité ouest de la péninsule de Ujung Kulon (près de l'île Panaitan). Cette preuve était unique et pourrait être liée au contexte géomorphologique exceptionnel de la péninsule de Ujung Kulon, y compris l'isthme et ses baies en forme de V, qui en font l'un des pièges les plus remarquables de dépôts de tsunami. / The giant tsunamis generated by the tremendous eruptions of Krakatau in 1883 were recorded along the coasts of Sunda Strait. Eyewitnesses testimony, tidal and pressure gauges recorded at Batavia (Jakarta), and tsunami signatures left by such event have been mostly used by researchers to evidencing the occurrence of the 1883-Krakatau tsunami around the Sunda Strait. Yet, there was still gap in knowledge when talking about the evidences of the 1883-Krakatau tsunami in the southern part of Sunda Strait and around Indian Ocean, due to the lack of eyewitness and a fact that some of the coasts is mostly noted as the remote areas. Laban Isthmus, one of the intriguing coastal landforms located 80 km to the south of Krakatau and connect Ujung Kulon Peninsula to Java Island, displayed the potential to record marine flooding events issuing from Sunda Strait and Indian Ocean. This study demonstrated however that the isthmus has recorded 4 (four) tsunami events related to the eruptions. Based on a new combination approach of sedimentary and micro-fossils analyses with the Anisotropy of Magnetic Susceptibility (AMS) technique, the result of the study evidenced that each wave was recorded twice: i) by a direct flow coming from the Sunda Strait in straight line, ii) by a wave coming from the Indian Ocean, delayed in time after having been refracted around the West-end of Ujung Kulon Peninsula (near Panaitan Island). Such evidence was unique and could be related to the exceptional geomorphological context of the Ujung Kulon Peninsula, including the isthmus and its V-shape bays, which made it one of the most remarkable traps of tsunami deposits.

La connaissance de la climatologie des états de mer est primordiale pour le dimensionnement de structures marines, la gestion des zones côtières ou encore la récupération de l’énergie des vagues. L'estimation de la climatologie nécessite de disposer de données d'observation sur une longue durée, ce qui n'est pas le cas de l'Afrique de l'Ouest. Pour dépasser les limites en durée imposées par les observations, nous proposons dans ces travaux une approche stochastique pour estimer une climatologie de vagues en Afrique de l’Ouest, en s’appuyant sur une représentation “par événements” des données d’états de mer. Un “événement” désigne un système de vagues (houle ou mer du vent) en évolution au cours du temps, observable pendant une durée significative et que l’on peut relier à un unique phénomène météorologique source (e.g. dépressions, tempêtes, etc.). La représentation par événements permet de reproduire la cohérence temporelle des systèmes de vagues et de structurer les données d'états de mer avec une base physique. La démarche adoptée peut se décomposer suivant trois étapes. Nous avons d'abord extrait les événements à partir d’une série temporelle de spectres directionnels d’états de mer. Nous avons ensuite développé un modèle pour représenter chacun des événements par un nombre réduit de paramètres. Enfin, nous avons construit un générateur stochastique permettant la simulation d’événements individuels et la reconstitution de climatologies sur des durées de longueurs arbitraires. Les résultats ont montré un bon accord entre la climatologie reconstituée et celle de référence, permettant de conclure que le générateur peut valablement servir à la simulation de données d’états de mer en Afrique de l’Ouest pour les applications en génie océanique. / Accurate estimation of long-term sea conditions is a major issue in design of coastal and offshore structures, coastal zone management or wave energy harvesting. An estimation of long-term sea conditions requires long duration observational data while in West Africa, only a few (3 years) years of observational data are available. To overcome the limits in duration that observations impose, a stochastic approach, event-based representation of sea state data, is proposed to model the wave climate in West Africa. An “event” refers to a wave system (swell or wind sea) evolving over time, that can be observed for a finite, yet significant duration and that can be linked to a single meteorological source phenomenon (e.g. low pressure systems, storms, etc.). Event-based approach provides structures with physical meaning and temporal consistence for the representation of sea states data. The procedure we have used is decomposed into three following steps. First, we have extracted events from a time series of directional spectra. We have then developed a model to represent each event by a reduced number of parameters. In the last step, we have constructed the stochastic events generator which allows for simulation of individual events and for reconstruction of wave climate over durations of arbitrary lengths. Results showed good agreement between reconstructed climate and that of reference and allow to conclude that the stochastic events generator can reliably be used to simulate sea state data in West Africa for a ocean engineering applications.

Les vagues courtes sont omniprésentes à la surface des océans, avec des longueurs de quelques dizaines de mètres au mètre typiquement. Connaitre leurs directions de propagation en mer est important à plusieurs titres, notamment pour la compréhension de la dynamique de l'état de mer, des échanges air-mer ou de la dérive de particules en surface. Ces distributions directionnelles sont étudiées ici au regard des progrès récents réalisés en techniques d'instrumentation. L'analyse du bruit sismo-acoustique enregistré en grandes profondeurs permet d'extraire un comportement quasi-universel qui dépend indirectement de cette distribution à travers ladite intégrale de recouvrement. Il est cohérent avec des observations directes du champ de vagues obtenues à partir de reconstructions tridimensionnelles de la surface de l'océan. Alors que la direction de propagation des vagues longues s'aligne avec celle du vent, les vagues courtes s'en détachent d'autant plus à mesure que leurs échelles diminuent (bimodalité).La comparaison de ces observations avec les prédictions d'un modèle numérique de vagues, basé sur l'environnement WAVEWATCH®III, permet de constater que ces modèles sont qualitativement valables mais encore quantitativement incorrects. Une des possibilités explorées pour corriger cet effet est la prise en compte de sources de vagues courtes à ±90° de la direction du vent, qui pourraient être associées au déferlement des vagues longues. Une telle source à elle seule n'explique pas les formes des distributions directionnelles observées. D'autres mécanismes pourraient intervenir que de futures investigations pourront tenter de clarifier. / Short surface gravity waves are ubiquitous at the ocean surface, with lengths from a few tens of meters to a meter typically.Knowing their propagation directions at sea is important in several respects, especially for the understanding of sea-state dynamics, airsea interactions and particles surface drift.Their directional distributions are here investigated in the light of the recent progress made in instrumentation techniques. The analysis of ocean bottom seismo-acoustic noise records allows for the extraction of a quasi-universal behavior which indirectly depends on this distribution through the socalled overlap integral. It is coherent with direct observations of the wave field obtained from tri-dimensional reconstructions of the ocean surface elevation field. While the propagation direction of long waves aligns with the wind direction, short waves progressively detach from it towards small scales (bimodality).Comparing those measurements with the predictions of a spectral numerical wave model, based on WAVEWATCH®III environment, allows to realize that they provide qualitatively correct but quantitatively incorrect predictions. One of the possibilities here explored to correct for it, is by accounting for the sources of energy at ±90° to the wind direction, which could be associated with the breaking of long waves. This source term on its own does not explain the shapes of the observed directional distributions. Other mechanisms could come into play that future investigations will help clarify.

This thesis describes experiments that were carried out using focused wave groups in the UK Coastal Research Facility (UKCRF). Considerable effort was put into calibrating the UKCRF to determine the relationship between the input signals sent to the paddles and the waves generated in the facility. Focused wave groups of various sizes and phases, based on NewWave theory were generated, and measurements were made of the resulting surface elevation data, water particle kinematics, wave runup and overtopping volumes. NewWave theory models the profile of extreme waves in a Gaussian (random) sea. The thesis describes the first time this model has been applied in the context of coastal wave transformation. A method for the separation of the underlying harmonic structure of a focused wave group is described and results presented. This technique has been used in relatively deep water but is shown to work successfully in the coastal zone until wave overturning. A method has been devised to provide a theoretical Stokes-like expansion of the free and bound waves to model the surface elevation and water particle kinematics of the focused wave groups. Satisfactory agreement is achieved between the theoretical predictions of UKCRF measurements. Suggestions are made for an improved model. The underlying harmonic structure of the focused wave groups is presented as stacked time histories that give insight into the wave transformation process from deep to shallow water. Particular attention is paid to the low frequency wave generated as the wave group interacts with the beach. This is compared to the low frequency wave that is generated by a solitary wave in the UKCRF. Runup and overtopping measurements are in reasonable agreement with predictions based on certain empirical formulae, but not others. These comparisons are useful in identifying those formulae able to predict runup and overtopping of extreme waves in the coastal zone.