Os principais fenômenos físicos que atuam como forçantes de movimento nos estuários são descarga fluvial, maré e vento. As diferentes intensidades com que cada um pode atuar proporcionam uma vasta gama de combinações e condições distintas, às quais estão submetidos os estuários de todo o mundo. O Complexo Estuarino do Cassurubá (CEC) está sujeito a descargas fluviais com vazões da ordem de 101 m3/s, a mesomarés variando entre 2 e 4 m, e a ventos de E/NE de ordem 101 m/s com algumas entradas de S/SO também de ordem 101 m/s. Contudo, seus canais Norte e Sul apresentam diferentes características hidrográficas e hidrodinâmicas. O objetivo deste trabalho foi confirmar e explicar esta distinção, através de dados de velocidade, temperatura, salinidade e profundidade, com suas respectivas variações temporais. Os objetivos específicos foram direcionados para se testar a hipótese de que a pequena diferença entre as vazões dos rios Caravelas e Peruípe (sendo a deste maior) pode criar configurações estruturais distintas e, consequentemente, gerar alterações no transporte de massa e volume. A análise dos dados demonstrou que ambos os canais estuarinos são influenciados principalmente por fenômenos marinhos, neste caso a maré. Os padrões estruturais e a ciclicidade das variações dos parâmetros estudados foram determinados predominantemente pela maré e a velocidade de suas correntes, com leve influência da descarga fluvial nas estruturas termohalina e hidrodinâmica. Como previsto, a pequena diferença observada a favor do rio Peruípe, associada a características geográficas e batimétricas locais, mostraram-se determinantes para os processos físicos que correm no CEC. Síntese dos resultados: Velocidades máximas de 0,5 m/s nas quadraturas e 1 a 1,5 m/s nas sizígias, em ambos os canais. Circulação estuarina clássica observada nitidamente nas quadraturas. Sizígias mostram mesmo sentido ao longo da coluna d\'água. Maior simetria entre correntes de vazante e enchente durante sizígias, menor durante quadraturas. Nova Viçosa com assimetria mais evidente devido à maior descarga fluvial. Salinidades mínimas de 32 em Caravelas e 17 em Nova Viçosa. Salinidades superiores a 36 em toda a coluna d\'água durante fases de sizígia, associadas às temperaturas de 28º, constataxv se a intrusão da Água Tropical em ambos os canais estuarinos. Temperatura passou de 25 ºC no inverno para 28 ºC no verão, em ambos. O canal de Caravelas mostrou-se importador durante três campanhas e exportador em apenas uma, porém com maior intensidade. O canal de Nova Viçosa mostrouse exportador durante as quatro campanhas. Onda de maré comportou-se como progressiva em Caravelas no inverno, e como estacionária no verão. Em Nova Viçosa foi como estacionária o tempo todo. Processos de mistura dominaram na maior parte do tempo. Estratificações formadas mais em quadratura e em torno de estofas. Classificações estação A - transição entre 1a e 2a - colunas bem misturadas, com fraca estratificação vertical; estação C - transição entre 1a, 2a, 1b e 2b - com apreciável estratificação nas quadraturas e colunas bem misturadas nas sizígias. Predomínio da difusão turbulenta no transporte de sal rio acima em A. Em C, boa participação da advecção nas quadraturas. / River discharge, tidal currents and wind stress are the main physical phenomena that drive estuarine circulation. Each of these parameters can act in different intensities, resulting in a vast diversity of estuary characteristics. Cassurubá Estuarine Complex (CEC) is influenced by river discharges on the order of 10 m3/s, mesotides ranging between 2 and 4 m, NE wind speeds of around 10 m/s, and occasionally SW winds of around 10 m/s. An interesting feature of the CEC is the distinct hydrographic and hydrodynamic characteristics between its north and south channels. In this way, the objective of this study is to corroborate and explain this dissimilarity, using data of depth, water and wind velocities, water temperature and salinity, as well as their temporal variations. Specific objectives are to test the hypothesis that small differences between Caravelas and Peruípe rivers discharges (where the latter is the largest one) can create different structural configurations of those parameters and, consequently, cause variations in mass and volume transport. Data analysis showed that both channels are mainly influenced by marine phenomenon, in this case tides. Patterns of structural and cyclical variations of studied parameters were determined mainly by tides and speed of their currents, with slight river discharge influence in thermohaline structure and hydrodynamics. As expected, the small difference observed in favor of Peruípe River, associated with local geographic and bathymetric characteristics, proved to be decisive for the physical processes that occur in CEC. Summary of results: maximum speed of 0.5 m/s in neaps and 1 to 1.5 m/s in springs, in both channels. Classical estuarine circulation observed clearly in neaps. Springs show same direction along the water column. Greater symmetry observed between ebb and flood currents during spring. Nova Viçosa showed more evident asymmetry due to higher river discharge. Minimum of salinity was 32 and 17, in Caravelas and Nova Viçosa, respectively. It reached values greater than 36 through water column during springs, associated with 28ºC temperatures, it indicates de intrusion of Tropical Water in both channels. Temperatures varied from 25 º C in winter to 28 º C in summer. Caravelas xvii channel was importer during three campaigns and exporter during one, but this one with greater intensity. Nova Viçosa channel was exporter during four campaigns. Tidal wave behaved as progressive in Caravelas estuary during winter and stationary in summer. Peruípe estuary showed stationary characteristics all campaigns. Mixing processes dominated most of time. Stratifications formed mainly in neap and around tide inversions. Classification station A - between 1a and 2a - well mixed, with weak vertical stratification; station C - between 1a, 2a, 1b, 2b - appreciable stratification in neaps and well mixed in springs. There was predominance of turbulent diffusion in upestuary transport of salt in station A. In station C, a greater role of advection appeared in neaps.

Dans certaines conditions, une baisse significative de la taille des gouttes se produit en émulsification membranaire avec vibrations transversales. Pour comprendre les mécanismes impliqués, nous avons développé deux dispositifs expérimentaux, dans lesquels une goutte unique est formée à travers un capillaire dans une phase externe, qui est soit stationnaire, soit en écoulement. Le capillaire peut être mis en vibration parallèlement à son axe.Lorsque la phase externe est stationnaire, au-delà d’une amplitude seuil de forçage, la taille des gouttes formées diminue significativement. La goutte entre en résonance quand sa fréquence propre coïncide avec la fréquence de forçage et elle se détache si elle atteint une élongation critique. La goutte est modélisée comme un oscillateur harmonique linéaire forcé. Un terme d’amortissement additionnel décrit la dissipation visqueuse entre la goutte et la surface du capillaire. Ce modèle prédit bien les amplitudes seuils et les diamètres de gouttes.Lorsque la phase externe s’écoule, nous avons étudié deux régimes de formation de gouttes, en goutte à goutte (dripping) ou à partir d’un jet (jetting). Expérimentalement, la transition du dripping au jetting se produit à un nombre de Weber interne seuil, dont la valeur dépend des nombres capillaire et d’Ohnesorge externes. Le jet se rétrécit (narrowing) ou s’élargit (widening) selon le rapport de vitesses des phases choisi. En dripping, les diamètres de gouttes sont bien prédits par un bilan des moments. En jetting, un modèle basé sur l’équation du mouvement permet d’estimer la vitesse critique permettant la transition au jetting et les diamètres de gouttes résultants. / In transversally vibrating membrane emulsification, significantly smaller drops are generated in certain conditions. We aim to explain the mechanisms involved. To do so, two experimental setups were developed. A single drop is formed from a nozzle into an outer phase, which is either stationary or cross-flowing. The nozzle can be submitted to axial vibrations.For a drop formed into a stationary phase, a transition in drop generation occurs above a critical forcing amplitude. Below the threshold, a large drop forms by dripping. Above the threshold, a drop detaches when its first eigenfrequency and the forcing frequency coincide. The drop then resonates and detaches once a critical elongation ratio is reached. We model a drop as a linearly forced harmonic oscillator and add an extra damping term to account for the viscous dissipation between the drop and nozzle surface. We well reproduce the threshold amplitudes and drop diameters.We also study drops generated into cross-flow. In dripping mode, drop diameters are described by a torque balance. At a critical inner Weber number function of the outer capillary and Ohnesorge numbers, a transition to jetting occurs. Jet widening or narrowing takes place depending on the phase velocity ratio. We propose a model to account for the transition to jetting based on the drop equation of motion. Overall, we adequately account for the jetting velocity and drop diameters, with discrepancies which were explained.

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Civil Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 269-271. / Ph.D.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Physics. / Vita. / Includes bibliographical references. / by Steven E. Koonin. / Ph.D.

Thesis. 1977. Sc.D.--Massachusetts Institute of Technology. Dept. of Civil Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Vita. / Bibliography : leaves 209-217. / Sc.D.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 148-151. / Ph.D.

Várias tentativas de correlacionar o tamanho da partícula e a resposta da flotação nas maiores usinas do Brasil (usinas de minério de ferro e fosfato) têm mostrado que partículas grossas (dp100 m) não flotam eficientemente. Uma vez que a suspensão de sólidos é uma condição necessária para a coleta de partículas, o estudo da suspensão de partículas grossas em células de flotação é totalmente justificado e constitui o objetivo desta tese. Neste trabalho, a suspensão de sólidos foi estudada em célula Denver e Wemco de laboratório (6 L) com os minerais apatita, quartzo e hematita, classificados como grossos (dp100 m). Estudo complementar foi realizado em célula piloto Metso (3000 L), no processamento de minério de Ni, no oeste australiano. A circulação de fluido nas células Denver e Wemco foi caracterizada pelo número de bombeamento do impelidor (NQ) e pela velocidade da água (vb), medida na descarga do impelidor, numa faixa de operação normalmente utilizada nos ensaios de flotação (900rpmN1300rpm). Para condições não-aeradas, NQ=0,043 e 12,7cm/s vb 18,3cm/s para célula Denver, e NQ=0,57 e 15,0cm/svb21,8cm/s, para Wemco. Em condições aeradas (0,05cm/sJG0,15cm/s para Denver e 0,52cm/sJG0,95cm/s para Wemco), assim como nas bombas centrífugas, a capacidade de bombeamento do impelidor diminui consideravelmente: 0,028NQ0,038 e 8,4cm/svb17,3cm/s para Denver e 0,42NQ0,53 e 11,6cm/svb 19,8cm/s para Wemco. Medidas obtidas com um transdutor de pressão, colocado próximo da região rotor/estator (células Denver e Wemco) ilustraram a capacidade dos impelidores de gerarem turbulência em células mecânicas de flotação. A rotação mínima do impelidor (Njs) em que nenhuma partícula permanece no fundo do tanque por mais do que 1 segundo (Critério 1-s de Zwietering) foi determinada para ambas a células (Denver e Wemco), em condições aeradas (Njsg) e não-aeradas (Njsu). Um modelo empírico foi utilizado para relacionar a rotação crítica de suspensão (Njs) com as propriedade sólido (diâmetro-dp, massa específica-s)-liquido (massa específica-L; concentração mássica de sólidos-X, viscosidade-)-gás (JG). Os resultados indicaram a influência dessas variáveis no valor de Njs, de acordo com o expoente de cada termo: (L)0,36-0,42> (dp)0,3> (X)0,2 > ()0,06-0,07. Através dos resultados de suspensão de apatita, levando em consideração seu tamanho e velocidade terminal (vt) e Njs foi possível relacionar o status da suspensão (segregação, suspensão e arraste) com a rotação do impelidor (N/Njsu) versus (vt/vb). Verificou-se que os valores de (N/Njsu) e (vt/vb) mais favoráveis para a suspensão de partículas grossas não são os mesmos para partículas finas. O perfil de distribuição axial de apatita (dp=127 m) em célula Denver, mostrou que quanto maior o valor de N, mas uniforme será a distribuição vertical de sólidos na célula, enquanto que em baixas rotações há uma segregação de sólidos no fundo do tanque. Quando a velocidade superficial de ar, em célula Metso, variou de JG=0,92 cm/s para JG=1,59 cm/s, aumentou a concentração de partículas grossas próximo ao fundo do tanque. O Modelo de Sedimentação-Dispersão possibilitou a identificação dos limites das zonas turbulenta e quiescente, nas células Denver e Metso. Em ambas as células, quanto maior a taxa de aeração, menor a espessura da zona turbulenta. / Several attempts to correlate particle size and flotation response at the biggest Brazilian plants (iron ore and phosphate) have concluded that coarse particles (dp 100m) do not float efficiently. As solids suspension is a necessary precondition for particle collection, the study of coarse particle suspension in mechanical cells is fully justified and it is the objective of this thesis. In this work, particle suspension was studied in laboratory Denver and Wemco flotation cells (6,0 dm3) with apatite, quartz and hematite coarse particles. Complementary study was carried out in pilot scale with a Metso (3,000 dm3) cell which processed Ni ore in Western Australia. Fluid circulation in Denver and Wemco laboratory cells was characterized by the impeller pumping number (NQ) and also by water velocity (vb) measured at the impellers discharge under a typical range of working rotational speed (900 rpm N 1,300 rpm). For ungassed conditions, Denver impeller showed NQ=0.043 and 12.7cm/s vb 18.3cm/s, whereas Wemco type showed NQ=0.57 and 15.0 cm/s vb 21.8 cm/s. Under gassed conditions (0.05 cm/s JG 0.15cm/s for Denver; 0.52 cm/s JG 0.95 cm/s for Wemco), like centrifugal pumps, the impeller pumping capacity decreased markedly: 0.028 NQ 0.038 and 8.4 cm/s vb 17.3 cm/s for Denver and 0.42 NQ 0.53 and 11.6 cm/s vb 19.8 cm/s for Wemco. Measures using a pressure transducer placed near the stator/impeller discharge region (Denver and Wemco) illustrated the ability of both impellers to create turbulence in the cells. The impellers rotational speed (N) at which no particle remains on the cell bottom for more than one second (Zwieterings 1-s Criterium) was determined for Denver and Wemco cells under gassed (Njsg) and ungassed (Njsu) conditions. An empirical model was used to correlate Njs to particle (diameter-dp, specific gravity-s)-liquid (specific gravity-L; solids mass concentration-X, viscosity-)-gas (JG) properties. The results of the model indicated a ranking for the influence of the variables on Njs based on its power: (L)0.36-0.42> (dp)0.3> (X)0.2 > ()0.06-0.07. Regarding apatite particles, taking into account its size, terminal settling velocity (vt) and Njsu, it was possible to address the status of particle suspension (segregation, suspension and dragging) to impeller rotation (N/Njsu) versus fluid velocity at the discharge of the impeller (vt/vb). It was verified that the values of (N/Njsu) and (vt/vb) more favorable to promote the suspension of the coarsest particles are not the same for the finest ones. Distribution of apatite particles (dp=127m) along the height of Denver cell indicated that when N increases, particles become more uniformly distributed along the impellers axis, whereas at lower values of N, a segregation occurs on the cell bottom. At Metso pilot cell, when air feed was increased from JG=0.92 cm/s to 1.59 cm/s, the concentration of coarse particles (D50 > 100 m) on the lower part of the cell increased markedly. The adoption of the Sedimentation-Dispersion Model to Denver and Metso cells allowed the identification of the limit of the turbulent zone versus quiescent zone within the cell. In both cells, the higher was the air flow-rate, the lower was the height of the turbulent zone.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Chemistry. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / Ph.D.

Extreme storms are responsible for rapid changes to coastlines worldwide. During the 2013/14 winter, the west coast of Europe experienced a sequence of large, storm-induced wave events, representing the most energetic period of waves in the last 60 years. The southwest coast of England underwent significant geomorphological change during that period, but exhibited a range of spatially variable and complex morphological responses, despite being subjected to the same storm sequence. The 2013/14 storm response along the southwest coast of England was first used as a natural field laboratory to explain the variability in storm response through the introduction and evaluation of a new classification of how sandy and gravel beaches respond to extreme storms. Cluster analysis was conducted using an unique data set of pre- and post-storm airborne Light Detection and Ranging (LiDAR) data from 157 beach sites and the calculation of volumetric beach changes and a novel parameter, the longshore variation index which quantifies the alongshore morphological variability in beach response. The method used can be applied to any sandy and gravel beaches where topographic data with sufficient spatial resolution is available. Four main beach response types were identified that ranged from large and alongshore uniform offshore sediment losses up to 170 m3 m-1 (at exposed, cross-shore dominated sites) to considerable alongshore sediment redistribution but limited net sediment change (at more sheltered sites with oblique waves). The key factors in determining the type of beach response are: exposure to the storm waves, angle of storm wave approach and the degree to which the beach is embayed. These findings provide crucial information for the development of coastal studies at regional scale, especially along coastal areas where abrupt changes in coastline orientation can be observed. A 10-year time series (2007-2017) of supra- and intertidal beach volume from exposed and cross-shore transport-dominated sites was used to examine the extent to which beach behaviour is coherent over a relatively large region (100-km stretch of coast) and predictably coupled to incident wave forcing. Over the study period, 10 beaches, exposed to similar wave/tide conditions, but having different sediment characteristics, beach lengths and degrees of embaymentisation, showed coherent and synchronous variations in sediment volumes, albeit at different magnitudes. This result is crucial for studying coastal changes in remote coastal areas or in areas where only few topographic data are available. The sequence of extreme storms of the 2013/14 winter, which represents the most erosive event over at least a decade along most of the Atlantic coast of Europe, is included in the data set, and three years after this winter, beach recovery is still on-going for some of the 10 beaches. Post-storm beach recovery was shown to be mainly controlled by post-storm winter wave conditions, while summer conditions consistently contributed to modest beach recovery. Skilful hindcasts of regional changes in beach volume were obtained using an equilibrium-type shoreline model, demonstrating that beach changes are coherently linked to changes in the offshore wave climate and are sensitive to the antecedent conditions. Furthermore, a good correlation was found between the beach volume changes and the new climate index WEPA (West Europe Pressure Anomaly), which offers new perspectives for the role and the use of climatic variations proxies to forecast coastline evolution. A process based model, XBeach, was used to model storm response at one macrotidal beach characterized by the largest sediment losses during the 2013/14 sequence of extreme storms. Beach volume changes were modelled over hypothetical scenarios with varying hydrodynamics conditions and beach states to investigate the relative roles of hydrodynamic forcing (i.e., waves and tides), beach antecedent state and beach-dune morphology in beach response to extreme storms. This modelling approach is applicable to any beach system where process based models have been implemented. Beside significant wave height and peak wave period, the beach antecedent state was shown to be the dominant factor in controlling the volumes of sediment erosion and accretion along this cross-shore dominated beach. Modelled volumes of erosion were, on average, up to three times higher along an accreted beach compared to an eroded beach for the same wave conditions. The presence of a dune, being only significantly active during spring tides and storm conditions along this macrotidal beach, was shown to reduce erosion or even cause accretion along the intertidal beach. This work provides a detailed, quantitative insight of the hydrodynamic and morphological processes involved in storm response and beach recovery on a number of spatial and temporal scales. This improved understanding of the potential impact of extreme events will hopefully aid future research efforts and ensure effective management of sedimentary coastlines.

Protoplanetary discs, composed of gas and dust, usually surround young stellar objects and serve two main purposes: they determine the accretion of matter onto the central object and also represent sites of planet formation. The accretion proceeds through the transport of angular momentum outwards allowing the disc matter to fall towards the centre. A mechanism responsible for the transport can be turbulence, waves or other coherent structures originating from various instabilities in discs that could, in addition, play a role in the planet formation process. For an understanding of these instabilities, it is necessary to study perturbation dynamics in differentially rotating, or sheared media. Thus, this thesis focuses on new aspects in the perturbation dynamics in non-magnetised protoplanetary discs that arise due to their self-gravity and velocity shear associated with the disc’s differential rotation. The analysis is carried out in the framework of the widely employed local shearing box approximation. We start with 2D discs and then move on to 3D ones. In 2D discs, there are two basic perturbation types/modes – spiral density waves and vortices – that are responsible for angular momentum transport and that can also contribute to accelerating planet formation. First, in the linear regime, we demonstrate that the vortical mode undergoes large growth due to self-gravity and in this process generates density waves via shear-induced linear mode coupling phenomenon. This is noteworthy, because commonly only density waves are considered in self-gravitating discs. Then we investigate vortex dynamics in the non-linear regime under the influence of self-gravity by means of numerical simulations. It is shown that vortices are no longer well-organised and long-lived structures, unlike those occurring in non-self-gravitating discs. They undergo recurring phases (lasting for a few disc rotation periods) of formation, growth and eventual destruction. We also discuss the dust trapping capability of such transient vortices. Perturbation dynamics in 3D vertically stratified discs is richer, as there are more mode types. We first consider non-axisymmetric modes in non-self-gravitating discs and then only axisymmetric modes in the more complicated case when self-gravity is present. Specifically, in non-self-gravitating discs with superadiabatic vertical stratification, motivated by the recent results on the transport properties of incompressible convection, we show that when compressibility is taken into account, the non-axisymmetric convective mode excites density waves via the same shear-induced linear mode coupling mechanism mentioned above. These generated density waves transport angular momentum outwards in the trailing phase, and we suggest that they may aid and enhance the transport due solely to convection in the non-linear regime, where the latter becomes outward. In the final part of the thesis, we carry out a linear analysis of axisymmetric vertical normal modes in stratified self-gravitating discs. Although axisymmetric modes do not display shear-induced couplings, their analysis provides insight into how gravitational instabilities develop in the 3D case and their onset criterion. We examine how the structure of dispersion curves and eigenfunctions of 3D modes are influenced by self-gravity, which mode first becomes gravitationally unstable and thus determines the onset criterion and nature of the gravitational instability in stratified discs. We also contrast the more exact instability criterion obtained with our 3D model with that of density waves in 2D discs. Based on these findings, we discuss the origin of 3D behaviour of perturbations involving noticeable disc surface distortions, as seen in some numerical simulations of self-gravitating discs.