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Halifax Harbour is one of the world's largest natural harbours and has significant environmental and economic value. A good understanding of oceanographic processes is required for pollution control and sustainable development of the Harbour. A five-level nested-grid coastal ocean circulation model known as the Nested-grid Coastal Ocean Prediction System for Halifax Harbour (NCOPS-HFX) is used to reconstruct the three-dimensional circulation and hydrography and associated temporal and spatial variability of the Harbour. The NCOPS-HFX is driven by tides, meteorological forcing, and buoyancy forcing associated with river and sewage discharges. Model performances are assessed by comparing model results with available observations including sea level from tide gauges, CTD observations, current meter records and monthly mean climatology of temperature and salinity. Model results are also used to examine the main physical processes affecting circulation and hydrography in the Harbour. It is found that the near-surface currents in the Harbour are significantly affected by tides and wind forcing with an intense tidal jet in the Narrows and a salinity front in the upper layer of Bedford Basin. The time-mean circulation produced by the model is characterized by a typical two-layer estuarine circulation with seaward flow in the upper layer and landward flow in the lower layer. The model also reproduces reasonably well the seasonal changes of temperature and salinity in the Harbour. Dispersion and retention in the Harbour are studied based on numerical passive tracer and particle tracking experiments. The e-folding flushing time is about 40 and 90 days in the upper and entire Bedford Basin respectively, 2-5 days over the Inner and Outer Harbour, and about 1 day in the Narrows.

Variações temporais na tensão de cisalhamento do vento, na Plataforma Continental Sudeste do Brasil (PCSE), perturbam o equilíbrio geostrófico gerando movimentos com frequências próximas à inercial local. Estas perturbações se propagam horizontalmente e verticalmente, interagindo com o fluxo médio e alterando as características hidrográficas e hidrodinâmicas. Foram analisados dados observacionais de corrente, registrados por correntógrafos fundeados às isóbatas de 50 m e 100 m, ao largo de Arraial do Cabo (RJ) e Ubatuba (SP), de vento registrados por bóias meteorológicas e de salinidade e temperatura perfilados em função da profundidade em estações hidrográficas, obtidos no âmbito do Projeto DEPROAS (Dinâmica do Ecossistema de Plataforma da Região Oeste do Atlântico Sul), entre 2001 e 2002. Os resultados das análises indicaram que a média de duração dos eventos de oscilações inerciais é 7,5 dias com desvio padrão de 3,8 dias, sendo 6,8 o número médio de oscilações em cada evento (desvio padrão de 3,3 oscilações). O período inercial efetivo médio foi calculado em 26,5 h com deslocamento médio da frequência inercial em 12,2%, devido ao desvio Doppler causado pelas interações com a vorticidade relativa do fluxo básico. As correntes inerciais horizontais, filtradas a partir das séries correntográficas, apresentaram valores entre 3 e 10 cm/s. Foi observada propagação vertical das oscilações inerciais e calculado o valor da velocidade de grupo vertical em -2,59 .10-2 cm.s-1. A partir desse resultado, foi obtido o valor de 28,3 m de profundidade para o valor máximo de velocidade vertical das partículas de água na onda interna inercial forçada pela oscilação das isotermas, em acordo com resultados observados de máxima corrente inercial logo abaixo da camada de mistura. O valor calculado para a amplitude da oscilação vertical das isotermas foi 17,2 m, próximo aos 19 m registrado com os resultados observacionais em períodos de mudança do campo de ventos. O modelo numérico hidrodinâmico ROMS (Regional Ocean Modelling System) comprovou resultados observacionais em relação à capacidade de mudanças na tensão de cisalhamento do vento, em períodos menores que o inercial local, gerarem oscilações inerciais. Os resultados numéricos com o ROMS permitiram analisar a interação das oscilações inerciais com o fluxo médio em diferentes regiões da PCSE, através de diferentes condições de estratificação da coluna de água e, a partir da trajetória de pseudoderivadores, estimar os raios das trajetórias com ordem 10 km. / Temporal variations in the wind stress, on the South Brazil Bight, disturb the geostrophic equilibrium and generate motion with near inertial frequencies. The disturbances propagate horizontally and vertically, interacting with the basic motions and altering the hydrodynamics and hydrographic characteristics. Observational data of currents, collected by currentmeters deployed in the 50 m and 100 m isobaths, offshore Arraial do Cabo (RJ) and Ubatuba (SP), of winds collected in meteorological buoys and of salinity and temperature vertically profiled in hydrographic stations, during the project DEPROAS (Dinâmica do Ecossistema de Plataforma da Região Oeste do Atlântico Sul), in the years of 2001 and 2002, have been analyzed. Results showed that the mean duration of the inertial oscillations events is 7.5 days, with standard deviation of 3.8 days, being 6.8 the mean number of oscillations in each event (standard deviation of 3.3 oscillations). The calculated mean effective inertial period is 26.5 h, with a mean difference of the local inertial frequency of 12.2% due to the Doppler shift caused by interactions with the relative vorticity of the basic flow. The horizontal inertial currents, filtered from the current time series, presented values between 3 and 10 cm/s. Vertical propagation of the inertial oscillations were observed and the calculated value for the vertical group velocity was -2.59 . 10-2 cm/s. From these results, the calculated value for the depth of maximum water vertical velocity was 28.3 m for the internal inertial wave forced by the isotherms oscillations, in accordance with results observed of maximum vertical velocities occurring below the mixing layer. The calculated value for the amplitude of vertical oscillations of isotherms was 17.2 m, approximately equal to the 19 m observed in the data set during periods of wind shift. The numerical hydrodynamical model ROMS (Regional Ocean Modeling System) confirmed the observational results that changes in the wind field with periods smaller than the local inertial period generate inertial oscillations. The numerical results with ROMS allowed to analyze the interaction between the inertial oscillations and the basic flow in different regions of the South Brazil Bight, due to vertical different stratification characteristics of the sea water, and from the trajectories of pseudo-drifters it was possible to estimate the radius of the trajectories as having order of magnitude of 10 km.

Variações temporais na tensão de cisalhamento do vento, na Plataforma Continental Sudeste do Brasil (PCSE), perturbam o equilíbrio geostrófico gerando movimentos com frequências próximas à inercial local. Estas perturbações se propagam horizontalmente e verticalmente, interagindo com o fluxo médio e alterando as características hidrográficas e hidrodinâmicas. Foram analisados dados observacionais de corrente, registrados por correntógrafos fundeados às isóbatas de 50 m e 100 m, ao largo de Arraial do Cabo (RJ) e Ubatuba (SP), de vento registrados por bóias meteorológicas e de salinidade e temperatura perfilados em função da profundidade em estações hidrográficas, obtidos no âmbito do Projeto DEPROAS (Dinâmica do Ecossistema de Plataforma da Região Oeste do Atlântico Sul), entre 2001 e 2002. Os resultados das análises indicaram que a média de duração dos eventos de oscilações inerciais é 7,5 dias com desvio padrão de 3,8 dias, sendo 6,8 o número médio de oscilações em cada evento (desvio padrão de 3,3 oscilações). O período inercial efetivo médio foi calculado em 26,5 h com deslocamento médio da frequência inercial em 12,2%, devido ao desvio Doppler causado pelas interações com a vorticidade relativa do fluxo básico. As correntes inerciais horizontais, filtradas a partir das séries correntográficas, apresentaram valores entre 3 e 10 cm/s. Foi observada propagação vertical das oscilações inerciais e calculado o valor da velocidade de grupo vertical em -2,59 .10-2 cm.s-1. A partir desse resultado, foi obtido o valor de 28,3 m de profundidade para o valor máximo de velocidade vertical das partículas de água na onda interna inercial forçada pela oscilação das isotermas, em acordo com resultados observados de máxima corrente inercial logo abaixo da camada de mistura. O valor calculado para a amplitude da oscilação vertical das isotermas foi 17,2 m, próximo aos 19 m registrado com os resultados observacionais em períodos de mudança do campo de ventos. O modelo numérico hidrodinâmico ROMS (Regional Ocean Modelling System) comprovou resultados observacionais em relação à capacidade de mudanças na tensão de cisalhamento do vento, em períodos menores que o inercial local, gerarem oscilações inerciais. Os resultados numéricos com o ROMS permitiram analisar a interação das oscilações inerciais com o fluxo médio em diferentes regiões da PCSE, através de diferentes condições de estratificação da coluna de água e, a partir da trajetória de pseudoderivadores, estimar os raios das trajetórias com ordem 10 km. / Temporal variations in the wind stress, on the South Brazil Bight, disturb the geostrophic equilibrium and generate motion with near inertial frequencies. The disturbances propagate horizontally and vertically, interacting with the basic motions and altering the hydrodynamics and hydrographic characteristics. Observational data of currents, collected by currentmeters deployed in the 50 m and 100 m isobaths, offshore Arraial do Cabo (RJ) and Ubatuba (SP), of winds collected in meteorological buoys and of salinity and temperature vertically profiled in hydrographic stations, during the project DEPROAS (Dinâmica do Ecossistema de Plataforma da Região Oeste do Atlântico Sul), in the years of 2001 and 2002, have been analyzed. Results showed that the mean duration of the inertial oscillations events is 7.5 days, with standard deviation of 3.8 days, being 6.8 the mean number of oscillations in each event (standard deviation of 3.3 oscillations). The calculated mean effective inertial period is 26.5 h, with a mean difference of the local inertial frequency of 12.2% due to the Doppler shift caused by interactions with the relative vorticity of the basic flow. The horizontal inertial currents, filtered from the current time series, presented values between 3 and 10 cm/s. Vertical propagation of the inertial oscillations were observed and the calculated value for the vertical group velocity was -2.59 . 10-2 cm/s. From these results, the calculated value for the depth of maximum water vertical velocity was 28.3 m for the internal inertial wave forced by the isotherms oscillations, in accordance with results observed of maximum vertical velocities occurring below the mixing layer. The calculated value for the amplitude of vertical oscillations of isotherms was 17.2 m, approximately equal to the 19 m observed in the data set during periods of wind shift. The numerical hydrodynamical model ROMS (Regional Ocean Modeling System) confirmed the observational results that changes in the wind field with periods smaller than the local inertial period generate inertial oscillations. The numerical results with ROMS allowed to analyze the interaction between the inertial oscillations and the basic flow in different regions of the South Brazil Bight, due to vertical different stratification characteristics of the sea water, and from the trajectories of pseudo-drifters it was possible to estimate the radius of the trajectories as having order of magnitude of 10 km.

Caractériser la circulation et l'évolution de la qualité des eaux côtières en Manche orientale est un enjeu majeur pour de multiples applications dans une région riche en bio-diversité et en ressources halieutiques. L'hydrodynamisme, dominé par un régime megatidal, joue un rôle essentiel dans les processus de dispersion et de mélange le long du littoral du Nord-Pas-de-Calais. La physionomie en "entonnoir" de la Manche orientale donne lieu à une dyssimétrie de l'onde de marée qui induit un flot plus intense et plus bref que le jusant, engendrant une dérive résiduelle vers la mer du Nord accentuée par les vents dominants de sud-ouest. Ce contexte atypique confère une structure complexe à l'écoulement côtier, dans une région dite "à influence d'eau douce". L'utilisation du modèle hydrodynamique MARS3D a permis de mettre en évidence certains phénomènes complexes à l'échelle régionale et comprendre la gense et la dynamique du fleuve côtier. Grâce à la modélisation haute résolution, à l'échelle dite locale, la circulation dans l'enceinte du port de Boulogne-sur-Mer a pu être caractérisée. Il a été démontré qu'un tourbillon anti-cyclonique, caractéristique du régime de flot, permet une évacuation rapide des traceurs passifs transitant par le port. Lors du jusant, une dérive intense vers le sud piège les traceurs dans le port. Ce piégeage peut être accentué ou atténué selon le sens du vent ou le débit fluvial. Une étude de modifications morphologiques de la rade a été réalisée afin de montrer l'utilité de la modélisation pour proposer des solutions innovantes pouvant améliorer la qualité de l'eau. Un travail similaire a été mené en baie de Somme pour comprendre les problèmes relatifs à la qualité de l'eau. Certaines activités sont soupçonnées d'être à l'origine de contamination microbienne et en particulier les moutons de pré-salés, accusés de contribuer majoritairement à l'apport en E. Coli. En assimilant les traceurs passifs au matériel bactérien, nous avons pu appréhender la problématique de la qualité de l'eau. Notre étude a permis de mettre en exergue les conditions environnementales propices à la rétention ou à l'évacuation de matières contaminantes émises par de nombreuses sources alimentant la baie. La convergence des courants, et l'accumulation du matériel contaminant, ont été révélées au voisinage du Crotoyce qui peut expliquer en partie, la qualité médiocre de ces eaux. Ces schémas de circulation interne à la baie de Sommesuivant les conditions environnementales contribue à améliorer les études sur la qualité de l'eau et les futurs aménagements côtiers durables. / Characterizing the circulation and the coastal water quality evolution in the EEC is a major stake in many applications, particularly in a such bio-diversified region. The hydrodynamism plays an essential role in dispersal and mixing processes along the Nord-Pas-de-Calais shores. The EEC funnel physiology gives place to a tidal asymmetry which induces flood conditions stronger but shorter then ebb conditions, involving a residual northern drift, strengthened by the dominant south-west winds. This atypical context confers a complex structure of the coastal flow in a ROFI (Region Of Freshwater Influence). Using the hydrodynamical model MARS3D permitted to underline complexes phenomenon at regional scale and understand the genesis and dynamic of the so called, "coastal river". Thanks to high resolution modelling, circulation pattern inside Boulogne-sur-Mer harbor has been characterized. We identified an anti-cyclonic eddy, characteristic of the flood conditions and responsible of a rapid evacuation of tracers passing through the harbor. In opposition, during ebb, a southward drift traps passive tracers inside the port. This trapping effect can be limited or emphasized depending on wind directions and freshwater inputs. Besides, harbor morphological changes have been assessed in order to propose innovative solution to improve water quality inside the harbor. A similar work was developed in the "baie de Somme" (France) to understand water quality existing issues. Many activities are suspected to supply microbial contamination within the bay, especially the marshes sheep accused to be the major contributor in E. Coli. Assuming passive tracers as bacterial material we have studied dispersion and transport processes within the bay. This study permit to underline environmental conditions favorable to evacuate or maintain pollution emitted from several water sources supplying the bay. A current converging zone has been shownsurrounding the Crotoy area (were the water quality is bad), and simulations reveal an accumulation place for most of the different water bodies relative to the fresh water inputs. This work on circulation pattern in the Bay of Somme regarding environmental conditions, contribute to improve water quality studies and further sustainable coastal managements.

Cette thèse pose les fondations du modèle « the Second-generation Louvain-la-Neuve Ice-ocean Model » (SLIM) qui est basé sur la méthode des éléments finis et les maillages non-structurés. Ce modèle fait partie d'une seconde génération de modèles numériques de circulation marine ou océanique. Notre travail a principalement porté sur les aspects géométriques liés à l'utilisation des maillages non-structurés. Nous avons implémenté un algorithme de triangulation qui génère automatiquement des maillages anisotropes non-structurés sur le plan et la sphère et nous avons défini des stratégies de raffinement de maillage adaptées aux applications marines. Ces stratégies orchestrent la distribution de la taille et de la forme des éléments du maillage afin d'optimiser la précision et le coût en temps de calcul du nouveau modèle. Nous avons aussi abordé l'interpolation contrainte de champs scalaires et vectoriels d'un premier maillage vers un second. L'utilisation conjointe de ces trois outils combinée avec un estimateur d'erreur a posteriori permettra l'adaptation dynamique de maillages au cours de simulations transitoires. Finalement, nous avons bâti les outils géométriques nécessaires à l'écriture d'une formulation discrète des équations de la dynamique des fluides géophysiques sur la sphère. Basée sur un système de coordonnées curvilignes propre à chaque élément du maillage, cette approche originale ne possède aucune des difficultés mathématiques et numériques liées aux singularités des pôles et auxquelles les modèles de la première génération n'ont pu apporter de solution entièrement satisfaisante.

Cette thèse pose les fondations du modèle « the Second-generation Louvain-la-Neuve Ice-ocean Model » (SLIM) qui est basé sur la méthode des éléments finis et les maillages non-structurés. Ce modèle fait partie d'une seconde génération de modèles numériques de circulation marine ou océanique. Notre travail a principalement porté sur les aspects géométriques liés à l'utilisation des maillages non-structurés. Nous avons implémenté un algorithme de triangulation qui génère automatiquement des maillages anisotropes non-structurés sur le plan et la sphère et nous avons défini des stratégies de raffinement de maillage adaptées aux applications marines. Ces stratégies orchestrent la distribution de la taille et de la forme des éléments du maillage afin d'optimiser la précision et le coût en temps de calcul du nouveau modèle. Nous avons aussi abordé l'interpolation contrainte de champs scalaires et vectoriels d'un premier maillage vers un second. L'utilisation conjointe de ces trois outils combinée avec un estimateur d'erreur a posteriori permettra l'adaptation dynamique de maillages au cours de simulations transitoires. Finalement, nous avons bâti les outils géométriques nécessaires à l'écriture d'une formulation discrète des équations de la dynamique des fluides géophysiques sur la sphère. Basée sur un système de coordonnées curvilignes propre à chaque élément du maillage, cette approche originale ne possède aucune des difficultés mathématiques et numériques liées aux singularités des pôles et auxquelles les modèles de la première génération n'ont pu apporter de solution entièrement satisfaisante.

Title: Modelling of global ocean circulation and ocean-induced magnetic field Author: Libor Šachl Department: Department of geophysics Supervisor: prof. RNDr. Zdeněk Martinec, DrSc., Department of geophysics Abstract: The ocean modelling community commonly use several renown ocean general circulation models (OGCMs) such as NEMO, MOM and FESOM. These models have been developed by research groups for many years, which resulted in complex mathematical and numerical algorithms. There are geophysically rele- vant problems, such as the glacial isostatic adjustment, in which the global ocean plays an important role. Ocean circulation does not need to be modeled extremely complex, but other phenomena such as time changing geometry of ocean domain needs to be considered. Geophysical applications motivated us to develop a new OGCM called LSOMG. The LSOMG model is not meant to substitute the ex- isting OGCMs but to provide a modelling framework for geophysical rather than purely oceanographic applications. LSOMG is a 3-D baroclinic ocean model fully parallelized using the MPI standard. It is forced by atmospheric fluxes (wind stresses, heat fluxes, etc.) but also by tides. The model can be run in a simplified 2-D barotropic version if 3-D effects can be neglected. LSOMG was tested in a series of simplified...

Cette thèse s’intéresse au courant profond de bord ouest dans l’Atlantique Nord, le Deep Western Boundary Current (DWBC). Ce courant transporte des eaux denses, formées dans la gyre subpolaire, vers l’équateur et constitue une des composantes majeures de la circulation méridienne Atlantique, l’AMOC (pour Atlantic Meridional Overturning Circulation). Cette circulation contribue au transport de chaleur vers les hautes latitudes et stabilise le climat actuel. L’AMOC calculée dans différents modèles de circulation générale de l’océan présente une diversité dans son intensité, sa structure spatiale et sa variabilité temporelle. De nombreux facteurs peuvent expliquer cette hétérogénéité de réponses, dont les incertitudes qui subsistent sur le lien entre la formation d’eau dense par convection dans la gyre subpolaire, qui contribue à connecter les branches supérieure et inférieure de l’AMOC, et l’intensité de l’AMOC aux moyennes latitudes. Ces incertitudes proviennent en grande partie d’une méconnaissance de la circulation profonde dans l’Atlantique Nord, car difficile à observer et souvent incorrecte dans les modèles d’océan de faible résolution spatiale.L’objectif de cette thèse est donc d’étudier la dynamique du DWBC et son influence sur l’AMOC, à l’aide de simulations numériques réalistes d’un modèle de circulation générale de l’océan (NEMO). Dans cette optique, trois configurations de résolution horizontale croissante ont été mises en place en utilisant l’outil de raffinement de grille AGRIF : une grille globale de référencer à 1/2◦ de résolution (configuration ORCA), à laquelle a été ajouté une première grille raffinée à 1/8◦ couvrant l’Atlantique nord (configuration ERNA) incluant elle-même une seconde grille à 1/32◦ centrée sur la gyre subpolaire (configuration FER). ERNA et FER sont deux configurations originales, par la prise en compte du modèle de glace de mer dans l’emboîtement des grilles, et par la résolution horizontale de FER dans la gyre subpolaire.Dans un premier temps, nous étudions l’influence de la résolution horizontale sur la circulation moyenne en Atlantique Nord avec un intérêt particulier pour l’AMOC en contrastant les simulations issues des configurations ORCA et ERNA. L’augmentation de la résolution se traduit par l’amélioration de la dynamique des courants de bord ouest, en surface et également en profondeur. En effet, le transport du DWBC s’intensifie de l’ordre de 8Sv dans la gyre subpolaire, ce qui est en partie lié à une meilleure représentation de l’écoulement des eaux denses en provenance des Mers Nordiques. En outre, alors que dans ORCA le DWBC s’écoule vers le sud principalement le long de la ride médio-Atlantique, dans ERNA la route le long du bord ouest est privilégiée avec une circulation secondaire à l’intérieur de l’inetrgyre, ce qui est en meilleur accord avec les observations. Le chemin suivi par le DWBC le long du talus continental permet une intensification de l’AMOC et de la localisation de son maximum vers 35 ̊N. Ce résultat tend à réduire l’influence de la convection aux hautes latitudes sur l’intensité de l4AMOC par l’intermédiaire de l’interaction des courants de surface et de fond.Nous nous sommes intéressés par la suite à la structure dynamique et thermohaline du DWBC, en lien avec la représentation de la méso-échelle, dans la mer du Labrador, en utilisant la configuration FER. Dans cette configuration qui résout explicitement les processus de méso-échelle dans la gyre subpolaire, la dérive en température et salinité est nettement moins importante que dans ERNA. De plus, la structure verticale du courant de bord, notamment sa barotropisation entre l’est et l’ouest sde la section AR7W dans la mer du Labrador, est en très bon accord avec les observations. A partir d’une équation simplifiée de la vorticité relative, nous avons cherché à identifier les processus principaux qui contrôlent la dynamique du DWBC. Il ressort de cette analyse que le stretching associé aux vitesses […] / The present study tackles the Deep Western Boundary Current (DWBC) dynamics in the North Atlantic basin as its impact on the AMOC. The DWBC advects dense water masses equatorward, produced in the subpolar gyre, and is one of the major component of the Atlantic Meridional Overturning Circulation (AMOC). This circulation contributes to the northward heat transport to high latitudes and allows to stabilise climate. When computing the AMOC in different ocean general circulation models (OGCM), results cover a wide range of intensity, spatial shape and temporal variability. Such response diversity is due to several factors. One of them is the remaining uncertainty on the link between dense water formation due to convection in the subpolar gyre, which contributes to connect the AMOC upper and lower branches, and the AMOC intensity at mid-latitudes. Those uncertainties are largely due to the knowledge gap of the deep circulation in North Atlantic because its direct observation is difficult and incorrectly reproduced in ocean models with a low spatial resolution. The methodology used rely on realistic numerical simulations based on the NEMO ocean general circulation model. Three configurations with an increasing spatial resolution have been developped using the grid refinement tool AGRIF : a global grid at 1/2◦ resolution (ORCA configuration), within which a first refined grid at 1/8◦ covering the whole North Atlantic (ERNA configuration) in which a second grid at 1/32◦ over the subpolar gyre (FER configuration). Both ERNA and FER are advanced and original by two aspects; they include a Sea-Ice model within embedded grids and FER reaches a high horizontal resolution over the subpolar gyre. We study the spatial horizontal resolution impact on the mean circulation in the North Atlantic with a focus on the AMOC contrasting simulations obtained with ORCA and ERNA solutions. Increasing the resolution improves the western boundary current dynamics at surface and depth. Indeed, the DWBC transport is intensified by 8Sv in the subpolar gyre partly due to a better representation of overflows coming from Nordic Seas through the Denmark Strait. Furthermore in ORCA the DWBC flows to the south along the Mid-Atlantic ridge ; in ERNA the flow along western continental shelf is dominant while a secondary circulation within the subpolar gyre arises being in better agreement with observations. The path followed by the DWBC along the continental shelf allows an interaction between surface and deep currents which seems to result both in an AMOC intensification and a maxima located close to 35 ̊N. This result tends to limit the influence of the convection, occuring at high latitudes, on the AMOC intensity at mid latitudes, often raised, and shed light on a modulation process of the AMOC intensity through the surface and deep currents interaction. We then addressed the thermohaline and the dynamical structure of the DWBC, asssocia- ted with the mesoscale representation, within the Labrador Sea using the FER configuration. With this configuration, which solved explicitly mesoscale eddies in the subpolar gyre, tempera- ture and salinity drift are clearly reduced compare to ERNA. Furthermore the vertical DWBC structure, especially its barotropisation from the eatstern to western side of the AR7W section within the Labrador Sea, is in very good agrement with observations. Using a simplified equation for relative vorticity, we try to identify the main processes handling the DWBC dynamics. The analysis reveals that the stretching associated with vertical velocities above topography and exchanges between isopycnal layers within boundary current dominate the vorticity balance. We also identify two areas within the DWBC where diapynal flux occur : along the Labrador Current on the western side of the Labrador Sea and seaward of Cape Desolation where eddy activity is marked. These results are close to two previous studies based on conceptual model and […]

Placing wave energy devices within close proximity to each other can be beneficial as the costs of deployment, maintenance and infrastructure are reduced significantly compared to if the devices are deployed in isolation. A mathematical model is presented in this thesis which combines linear wave theory with a series of linear driven harmonic oscillators to model an array (group) of floating wave energy devices which move predominantly in heave (vertically) in a train of incident regular waves. Whilst similar mathematical models have been used previously to investigate interactions between fluids and groups of structures, much of the published work does not address array configurations or device constraints that are relevant to designers of structure-supported array devices. The suitability of linear theory for application to closely spaced arrays is assessed in this thesis through comparison to small-scale experimental data and by evaluation of the magnitude of second-order hydrodynamic forces. Values of mechanical damping and mass are determined for each element of an array in order to achieve the maximum power from an array of floats without requiring the knowledge of the motion of every float within the array in order to apply the forces to any one float. Further to this, the analysis of floats of varying geometry is performed in order to assess the possibility of array optimisation through the variation of float geometries within a closely spaced array.It is shown in this thesis that linear theory provides a reasonable prediction of the response of floats that are sufficiently close together to interact for most wave frequencies to which the arrays are likely to be subjected. Under the assumption of easily implementable mechanical damping, it is determined that the power output from an array of floats of equal geometry can be increased by specifying different magnitudes of mechanical damping on each float independently of the radiation damping. Variations in submerged float geometries for the purpose of manipulating array characteristics according to the incident wave frequency are best applied through the variation in draft of a single geometry. Variations in submerged float geometry which occur close to the free surface are found to be of the greatest significance. Where the float is uniform in cross-section, the most appropriate method to select float drafts within an array is found to be based on the evaluation of the total damping on each float.