Durant cette thèse, nous avons exploré l'impact qu'engendre une modification de la gravitation sur les courants de marée. Nous avons effectuer les premières simulations N-corps de la formation d'un courant de marée galactique dans le paradigme MOND. Nous avons comparer les résultats ainsi obtenus aux prédictions du modèle standard de la cosmologie, ΛCMD, dans le but de trouver des différences entres-elles qui pourraient être observables. Nous avons remarqué que la brisure du principe d'équivalence fort engendrée une telle modification de la gravitation conduisait les amas globulaires à avoir une morphologie ovoïdale, contrairement à la dynamique Newtonienne où ceux-ci sont elliptiques. Cette morphologie des amas génère également une asymétrie de longueur et de nombre entre les deux bras d'un courant de marée similaire à celle observée récemment dans le courant de Palomar 5. / During this thesis, we explored the impact of a modification of the gravitation on the tidal streams. We made the first N-body simulations of the formation of a galactic tidal stream in the MOND paradigm. We compared the results obtained with the predictions of the standard model of the cosmology, ΛCMD, with the aim of finding differences between them that can be observed. We have noticed that the break of the strong equivalence principle generated by a such modification of the gravitation led to a lopsided morphology of the globular clusters, contrary to their elliptical shape in Newtonian dynamics. This morphology of the cluster also generates an asymmetry of length and of number between the two arms of a tidal stream similar to that observed recently in the Palomar 5 stream.

O objetivo do presente estudo é caracterizar a hidrodinâmica e o transporte de material particulado em suspensão (MPS) no estuário de Caravelas sob diferentes condições de maré e vazão fluvial. Foram realizadas quatro campanhas hidrográficas durante ciclos completos de maré, sendo em condições de maré de sizígia e quadratura, e durante os períodos seco e chuvoso. Dados de nível de água, velocidade e direção de correntes, salinidade, temperatura e turbidez foram obtidos em uma estação fixa próxima da desembocadura do estuário. A partir destes dados foram obtidos os transportes residuais de MPS e calculado os mecanismos de transporte. As maiores concentrações médias de material particulado em suspensão ocorreram em condições de sizígia. Em condições de maré de quadratura o transporte resultante de MPS foi com sentido estuário acima, porém de pequena intensidade. Em condições de sizígia o estuário é caracterizado por correntes mais intensas e assimétricas, com dominância de vazante. Durante a condição de sizígia o estuário pode atuar como importador ou exportador de MPS. O estuário do rio Caravelas foi classificado como bem misturado e fracamente estratificado. A hidrografia e o balanço sedimentar são principalmente modulados pela altura da maré e o aporte de água doce é irrelevante. / The objective of the present study is to characterize the hydrodynamics and the suspended particulate matter (SPM) in the Caravelas Estuary under different tidal and river regimes. Four hydrographic campaigns were carried out comprising a complete semi-diurnal tidal cycle, comprising neap and spring tidal phases, and during dry and wet seasons. Water level, current speed and direction, salinity, temperature and turbidity were recorded in an anchored station near to the estuarine mouth. The residual SPM flux and the mechanisms of transport were calculated. The higher SPM concentrations were recorded during the spring tidal phase. During neap tides, the net SPM flux 1 was up-estuary, although with low scale. During spring tides the tidal currents are strongly ebb dominant, and the net flux can be either up- or down-estuary. The estuary was classified as well mixed or weakly stratified. The hydrography and the sediment balance are firstly modulated by the tidal range, and the fresh water inflow is negligible.

Este estudo visa à descrição pontual do comportamento hidrodinâmico do estuário do Rio Mearim, analisando os padrões de corrente de maré, do registro de marés e das possíveis relações entre eles. Durante novembro e dezembro de 2012 um ADCP foi fundeado no canal do estuário, onde coletou dados por 31 dias. Os dados foram qualificados e processados para futura análise e inter-relações. Foi observado que a coluna de água estuarina no ponto de medição move-se como uma coluna de água homogênea com fluxo bidirecional no eixo NE-SW. As medições ocorreram no período de baixo índice de pluviosidade. O espectro de energia de velocidade de correntes indicou contribuições parciais dos harmônicos M2, M4, M6 e M8 no padrão de correntes encontrados. Defasagens no tempo entre os picos de máxima velocidade de corrente durante enchente e vazante mostraram a dominância do processo de maré vazante sobre a enchente no estuário. A análise integrada apresentada permitiu uma melhor compreensão no entendimento do comportamento das correntes forçadas pela maré, as chamadas correntes de maré, no estuário do Rio Mearim. / This study aim to describe the punctual hydrodynamic behavior of Mearim River estuary, analyzing the pattern of the tidal current, the tidal data and possible relationship between them. During 2012 november and december an ADCP was deployed in the estuary channel, where it collected data for 31 days. The data were qualified and processed for further analysis and inter-comparisons. It was observed the estuarine water column in the point of deployment moved as a homogeneous water column with bidirectional flux in axis NE-SW. The deployment was made in a period of low pluviosity index. The energy spectrum of current velocity indicated partial contribution of harmonics M2, M4, M6 e M8 in the current pattern found. Delays between the maximum velocity during flood and ebb conditions, showed the dominance of the edd process over the flood in the estuary. An analysis integrated presented on this paper allowed a better understanding of the behavior of the current forced by tides, called the tidal current in the Mearim River estuary.

O objetivo do presente estudo é caracterizar a hidrodinâmica e o transporte de material particulado em suspensão (MPS) no estuário de Caravelas sob diferentes condições de maré e vazão fluvial. Foram realizadas quatro campanhas hidrográficas durante ciclos completos de maré, sendo em condições de maré de sizígia e quadratura, e durante os períodos seco e chuvoso. Dados de nível de água, velocidade e direção de correntes, salinidade, temperatura e turbidez foram obtidos em uma estação fixa próxima da desembocadura do estuário. A partir destes dados foram obtidos os transportes residuais de MPS e calculado os mecanismos de transporte. As maiores concentrações médias de material particulado em suspensão ocorreram em condições de sizígia. Em condições de maré de quadratura o transporte resultante de MPS foi com sentido estuário acima, porém de pequena intensidade. Em condições de sizígia o estuário é caracterizado por correntes mais intensas e assimétricas, com dominância de vazante. Durante a condição de sizígia o estuário pode atuar como importador ou exportador de MPS. O estuário do rio Caravelas foi classificado como bem misturado e fracamente estratificado. A hidrografia e o balanço sedimentar são principalmente modulados pela altura da maré e o aporte de água doce é irrelevante. / The objective of the present study is to characterize the hydrodynamics and the suspended particulate matter (SPM) in the Caravelas Estuary under different tidal and river regimes. Four hydrographic campaigns were carried out comprising a complete semi-diurnal tidal cycle, comprising neap and spring tidal phases, and during dry and wet seasons. Water level, current speed and direction, salinity, temperature and turbidity were recorded in an anchored station near to the estuarine mouth. The residual SPM flux and the mechanisms of transport were calculated. The higher SPM concentrations were recorded during the spring tidal phase. During neap tides, the net SPM flux 1 was up-estuary, although with low scale. During spring tides the tidal currents are strongly ebb dominant, and the net flux can be either up- or down-estuary. The estuary was classified as well mixed or weakly stratified. The hydrography and the sediment balance are firstly modulated by the tidal range, and the fresh water inflow is negligible.

Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós-Graduação em Engenharia Oceânica, Escola de Engenharia, 2008. / Submitted by Lilian M. Silva (lilianmadeirasilva@hotmail.com) on 2013-04-23T20:01:48Z No. of bitstreams: 1 Processos de Alterações Da Maré Astronômica Na Desembocadura da Lagoa Dos Patos.pdf: 5559394 bytes, checksum: d5348a72601c4539f3d215ebe5cbad74 (MD5) / Approved for entry into archive by Bruna Vieira(bruninha_vieira@ibest.com.br) on 2013-06-13T17:34:41Z (GMT) No. of bitstreams: 1 Processos de Alterações Da Maré Astronômica Na Desembocadura da Lagoa Dos Patos.pdf: 5559394 bytes, checksum: d5348a72601c4539f3d215ebe5cbad74 (MD5) / Made available in DSpace on 2013-06-13T17:34:41Z (GMT). No. of bitstreams: 1 Processos de Alterações Da Maré Astronômica Na Desembocadura da Lagoa Dos Patos.pdf: 5559394 bytes, checksum: d5348a72601c4539f3d215ebe5cbad74 (MD5) Previous issue date: 2008 / Diversos estudos têm sido realizados sobre a circulação estuarina da Lagoa dos Patos. Devido a menor importância das marés, a maioria dos trabalhos têm se concentrado nos efeitos que o vento e a descarga fluvial exercem sobre a hidrodinâmica da lagoa e, embora o efeito da maré seja secundário na circulação estuarina, existe uma complexa interação entre as marés, a descarga fluvial e os ventos. A Lagoa dos Patos está localizada na planície costeira do Estado do Rio Grande do Sul, entre as latitudes de 30° S e 32° S. Este estudo está baseado na análise estatística dos dados, principalmente de séries temporais de nível das águas registradas na desembocadura da Lagoa dos Patos e na aplicação de técnicas de modelagem numérica. Para se verificar os efeitos do vento e da descarga fluvial na variabilidade das constantes harmônicas da região, são usados como referência, séries de velocidade e direção do vento e dados de descarga fluvial dos principais afluentes da Lagoa dos Patos. Os componentes harmônicos caracterizam a maré de um determinado local e, por isso, é necessário o estudo dos constituintes a fim de analisar as oscilações existentes. A previsão das séries está diretamente relacionada a esta variabilidade e, devido a este motivo, são testadas diferentes séries para se obter uma previsão mais eficaz. O modelo TELEMAC é utilizado para simular os componentes harmônicos O1, K1, M2 e S2. As análises mostraram que os ventos e a descarga fluvial, influenciam nas variações que ocorrem nas amplitudes dos componentes harmônicos estudados (O1, K1, M2 e S2). / Several studies have been conducted on the movement of estuarine of Patos Lagoon. Due to the minor importance of the tides, most of the previous studies carried out in the area focused on the effect of wind and river discharge carry on the hydrodynamics of the lagoon, and although the effect of the tide is secondary in estuarine hydrodynamics, there is a complex interaction between the tides, river discharge and the winds. The Patos Lagoon is located in the coastal plain of the State of the Rio Grande do Sul, between latitudes 30 ° S and 32 ° S. This study is based on analysis of data, particularly of time series of water levels recorded in the entrance of Patos Lagoon and the analysis of the results of a numerical model adapted to the conditions of the lagoon. To ascertain the effects of wind and river discharge in the variability of harmonics in the region, are used as reference, data sets of speed and direction of wind and river discharge data of the main tributaries of Patos Lagoon. The harmonic components characterize the tide of a particular place and therefore it is necessary to study their constituents to analyze existing fluctuations. The forecast of the series is directly related to this variability, and because of this reason, are tested different series for a more effective forecasting. Model TELEMAC is used to simulate the behavior of the harmonic components O1, K1, M2 and S2 under different wind and river discharge regimes. The analyses had shown that to the winds and the river discharge, influence in the variations that occur in the amplitude of the studied harmonic components (O1, K1, M2 e S2).

O presente trabalho dedica-se a uma modelagem da interação entre corpos celestes, em regime Newtoniano, levando-se em consideração as influências que suas deformações e viscosidades internas exercem sobre seus movimentos orbitais e suas velocidades angulares. A abordagem adotada é uma variação do conhecido problema do corpo pseudo-rígido, a qual simplifica drasticamente a determinação dos equilíbrios relativos e torna a questão da dinâmica matematicamente acessível. Com este tratamento, podemos relacionar ou comparar os resultados com aqueles estabelecidos na literatura, dentre eles: formato de equilíbrio de um fluido isolado em rotação, deformação de maré causada pela interação gravitacional e o torque de maré induzido no mesmo. Pela simplicidade do modelo pode-se ainda fazer uma análise qualitativa da dinâmica do sistema e obter estimativas sobre a velocidade com que se aproxima dos equilíbrios. / The present work is devoted to model the interaction among celestial bodies, in a Newtonian regime, but considering the role played by the internal deformation and viscosity on the orbital motion and angular velocities of the components of the system. The work is mainly developed with an alternative approach to the pseudo-rigid body model, which simplifies the determination of the relative equilibria and allows precise conclusions about the dynamics. So, we are able to compare the results of this theory with those established in the literature, namely: the equilibrium shape of an isolated fluid in rotation, the tidal elongation induced by gravitational interaction and the tidal torque. Due to its simplicity, we can further perform a qualitative analysis of the dynamics of the system and estimate the velocity of attraction of the equilibrium states.

The aim of this research was to quantify the influence of waves on arrays of tidal turbines. Experiments measured the wake of a turbine operating in combined wave-current flows, these were found to reduce velocity deficit as opposed to current only flow. The vertical region of the wake affected was dependant on the wave depth parameter, kd.RANS-BEM and Actuator Line methods were implemented within a commercial CFD code to provide computationally efficient methodologies for the simulation of both large turbine arrays and a turbine subjected to unsteady flow. For scaled experiments thrust coefficient was within 7% and 1% of the flume experiments for the RANS-BEM and Actuator Line methods respectively. The methods were found to give good prediction of a single turbine wake at distances greater than four diameters downstream, provided values of inlet turbulence intensity and length scale were equal to those measured experimentally.An unsteady Actuator Line method was used to quantify rotor loads and wake generation for a turbine operating within combined wave-current flow. The use of a streamwise pulsatile flow was found to give similar rotor and blade loads to simulations using a wave in a two phase volume of fluid simulation. The control strategy adopted by the turbine was found to greatly influence the computed rotor loads and blade bending moments. The wake generated by an Actuator Line method showed a reduction in velocity, however this was smaller than that measured experimentally for equivalent wave conditions.The accuracy with which the RANS-BEM method computed turbine loads and wakes was quantified for a number of one, two and three row arrays. The square of the disk averaged velocity encountered by turbines downstream of a single row of five turbines was found to be predicted to within 5% and 28% for an aligned and staggered arrangement respectively. For the two row arrays, the thrust of individual turbines was within 31% of the experimental measurements. The merged wake downstream of the multiple turbines was well predicted.Measurements of the wake of five porous disks showed combined wave-current flow did not alter the wake in the same manner as a single isolated disk. Measurement of wave energy over the wake showed the downstream current field altered wave propagation, causing a reduction in wave energy over the wake but an increase over the bypass flow. The accuracy of the wave model SWAN was assessed for the calculation of this change in wave characteristics. The model gave good prediction of the lateral variation of wave height over the far wake, however discrepancies in the near wake and upstream of the disk occurred.

Simultaneous in-situ measurements of waves, currents, water depth, suspended sediment concentrations and bed profiles were made in a rip channel on Perranporth Beach, Cornwall, UK. Perranporth is a high energy beach (annual offshore Hs = 1.6 m) which is macro-tidal (mean spring range = 6.3 m) and the grain size is medium sand (D50 = 0.28 – 0.34 mm). It can be classified as a low tide bar – rip beach and exhibits a relatively flat inter-tidal zone with pronounced rhythmic low tide bar - rip morphology. Data were collected over two field campaigns, totalling 14 tidal cycles and including 27 occurrences of rip currents, in a range of offshore wave heights (Hs = 0.5 – 3 m). The in-situ measurements were supplemented with morphological beach surveys. Sediment samples were taken for grain size analysis. The rip current was found to be tidally modulated. The strongest rip flow (0.7 m/s) occurred at mid to low tide, when waves were breaking on the adjacent bar. Rip flow persisted when the bar had dried out at the lowest tidal elevations. The rip was observed to pulse at a very low frequency (VLF) with a period of 15 - 20 minutes, which was shown to be influenced by wave breaking on the adjacent bar. The rip was completely in-active at high tide. Bedforms were ubiquitous in the rip channel and occurred at all stages of the tide. Visual observations found bedforms to be orientated shore parallel. When the rip was active, mean bedform length and height was 1.45 m and 0.06 m respectively. The size and position of the bedforms in the nearshore suggested that they were best classified as megaripples. When the rip was not active, the mean bedform length and height was 1.09 m and 0.06 m respectively. In rip conditions, with typical mean offshore flow rates of > 0.3 m/s, the bedforms migrated in an offshore direction at a mean rate of 0.16 cm/min and a maximum rate of 4.6 cm/min. The associated mean bedform sediment transport rate was 0.0020 kg/m/s, with a maximum rate of 0.054 kg/m/s. In the rip, migration rates were correlated with offshore directed mean flow strength. In non-rip conditions, bedform migration was onshore directed with a mean rate of 0.09 cm/min and a maximum rate of = 2.2 cm/min. The associated mean bedform transport rate was 0.0015 kg/m/s, with a maximum rate of = 0.041 kg/m/s. The onshore bedform transport was correlated with incident wave skewness, and was weakly correlated with orbital velocity. Over a tidal cycle, the offshore directed bedform transport was only marginally larger in rip currents than when it was when onshore directed in non-rip conditions. Sediment suspension in the rip current was shown to be dependent on the presence of waves. Suspended sediment transport was dominated by the mean flux. The mean flux contributed > 70% of total suspended transport on 19 out of the 27 observed rip current occurrences. The net contribution of the oscillatory flux was small compared to the mean flux. Within the oscillatory component, a frequency domain partitioning routine showed that the VLF motion was an important mechanism for driving offshore directed sediment transport. This was balanced by onshore directed sediment transport at incident wave frequency of a similar magnitude. Depth integration showed that the mean total suspended sediment transport was in the range of 0.03 kg/m/s to 0.08 kg/m/s. At high tide, when the rip was inactive suspended sediment transport rates were minimal compared to when the rip was active. Bedform transport was (on average) 6% of the total suspended sediment transport in a rip current. The new results presented here show that rip currents make an important contribution to offshore directed sediment transport. The magnitudes of transport indicate that future improvements to morphology change models should include rip driven offshore sediment transport.

There is a growing interest in tidal energy, owing to its predictable nature in comparison to other renewable sources. In the case of the UK, its importance also lies on the availability of exploitable areas as well as their total capacity, which is estimated to cover more than 20% of the country demand. However, the level of development of this kind of technology is still far behind other types of renewable energy. However, several studies focused on a variety of individual devices, followed by more recent research on the deployment of large arrays or tidal farms. Potential sites for energy extraction can be found in narrows between islands and the coast or estuaries. The latter present some advantages for the installation and the connection to the grid but estuaries are often prone to flood risk from tides and surges. Therefore, the objective of this thesis is to evaluate the effect that very large groups of turbines could have on peak water levels during flooding events in the case of being deployed in estuarine areas. For that purpose, a new methodology has been developed, which implies the use of a numerical model (MIKE 21 by DHI), and it has been demonstrated against a real case study in the UK: the Solway Firth estuary. Another objective has consisted of integrating in this thesis the results from detailed CFD modelling and optimisation techniques involved in the project. A literature review has been carried out in order to identify the current state of the art for the different subjects considered in the thesis. Different aspects of the numerical model used for this study (MIKE 21) have been presented and the modelling of the turbines within the code has been validated against experimental and CFD data. The procedure to include large numbers of turbines in the code is also developed. An analysis has been done of the different estuaries existing in the UK suitable for tidal energy extraction, identifying their main geometrical features. Based on this, idealised models of estuaries have been used to assess the influence that the channel geometry could have on the impact of tidal farms under extreme water levels. The effect has been measured by comparing the results of the numerical model between the case with and without turbines under different flooding scenarios. Finally, the same methodology has been applied to a real case study selected from the previous group of estuaries namely the Solway Firth. An initial model has been created, according to the available data at the start of the research, which contained some errors related to the water depth at the intertidal areas in the upper estuary. Therefore, when a more realistic dataset became available, an improved model was created. The improved model has been used to assess the effects of tidal farms in the estuary under a coastal flooding event. It is concluded that there is significant influence of the channel geometry over the locations where the maximum changes in water levels due to the tidal farms will happen. Nevertheless, the effects seem to be more relevant in terms of the decrease rather than the increase of peak water levels for all geometries and the maximum changes seem to be in the order of dm. This is in agreement with the results of the Solway Firth models and can be summarised as a positive net effect over flood risk. On the other hand, a concern has been raised about the impact on intertidal areas, which could be the subject of future research.

Avec le développement de la technologie, les mesures des champs de vitesse instationnaire sont disponibles maintenant. Il s'en suit une augmentation de l'intérêt de l'analyse lagrangienne des données. Un outil central pour analyser les écoulements est l'exposant de Lyapunov à temps fini (FTLE). Il permet d’identifier les structures cohérentes lagrangiennes LCS qui apparaissent comme des crêtes du champ de FTLE. Les LCS sont des quasi barrières de transport et séparent le domaine fluide en régions aux propriétés dynamiques différentes. Cependant, la méthodologie de calcul actuelle des FTLE exige l'évaluation numérique d'un grand nombre de trajectoires de particules fluides sur un maillage cartésien ou adaptatif qui est superposé aux champs de vitesses simulées ou mesurées.Dans ce travail de thèse, nous proposons une nouvelle méthode de calcul du champ de l'exposant de Lyapunov à temps fini FTLE. Pour cela, nous utilisons la méthode des moments d'ordre 2 qui permet d'évaluer au cours du temps la dispersion des particules distribuées uniformément dans un domaine circulaire ou elliptique. Nous appelons ce nouveau champ scalaire, champ de M-FTLE. Nous validons cette approche, théoriquement en tout point du domaine fluide en comparant M-FTLE et FTLE et aussi en faisant la comparaison sur des exemples classiques (champ de vitesse linéaire, circulaire ou hyperbolique) et sur un exemple numérique (champ de vitesse du double gyre). Cette méthode est alors appliquée sur des données expérimentales du champ de vitesse du mascaret, obtenues au sein l'institut 'Pprime' par vélocimétrie par image de particules PIV. / With the development of technology, instantaneous flow fields coming from experiments or numerical simulation are available now. It has been followed by a rise of interest for the Lagrangian analysis of such data. One central tool to analyze the flow fields is the Finite Time Lyapunov Exponent (FTLE). It allows to the identify of the Lagrangian Coherent Structures (LCS) which appear as ridges in the FTLE fields. The LCS are quasi transport bareers and separatte the fluid domain into regions which have different dynamic properties. However, the computation methodology currently used in order to obtain the FTLE requires numerical evalution of a large number of fluid particle trajectories on cartesian or adaptive meshes that are superimposed on the original data grid.In this thesis, we propose a new method for calculating the Finite Time Lyapunov Exponent FTLE fields. For this, we use the method of second-order moments which allows to evaluate over time the dispersion of particles uniformly distributed in a circular or elliptical domain. We call this new scalar field, the M-FTLE field. We validate this approach theoretically, at every point of the fluid domain by comparing FTLE and M-FTLE and also by the comparison of the classic examples (linear velocity field, circular and hyperbolic) and a numerical example (velocity field of double gyre). This method is then applied on experimental measurements of tidal bore velocity fields, obtained within the institute 'Pprime' by using a measurement technique called particle image velocimetry (PIV).