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Dissertations / Theses on the topic 'Boundary currents'
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Cuny, Jerome. "Labrador Sea boundary currents /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/10959.
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Kuehl, Joseph J. "On the dynamics of oceanic gap-traversing boundary currents /." View online ; access limited to URI, 2009. http://digitalcommons.uri.edu/dissertations/AAI3401123.
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Chadwick, David Bartholomew. "Tidal exchange at the bay-ocean boundary /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9823709.
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Chang, Kyung-Il. "The shelfward penetration of western boundary currents." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239963.
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Le, Bras Isabela Astiz. "Dynamics of North Atlantic western boundary currents." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/109056.
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Thesis: Ph. D., Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 163-174).<br>The Gulf Stream and Deep Western Boundary Current (DWBC) shape the distribution of heat and carbon in the North Atlantic, with consequences for global climate. This thesis employs a combination of theory, observations and models to probe the dynamics of these two western boundary currents. First, to diagnose the dynamical balance of the Gulf Stream, a depth-averaged vorticity budget framework is developed. This framework is applied to observations and a state estimate in the subtropical North Atlantic. Budget terms indicate a primary balance of vorticity between wind stress forcing and dissipation, and that the Gulf Stream has a significant inertial component. The next chapter weighs in on an ongoing debate over how the deep ocean is filled with water from high latitude sources. Measurements of the DWBC at Line W, on the continental slope southeast of New England, reveal water mass changes that are consistent with changes in the Labrador Sea, one of the sources of deep water thousands of kilometers upstream. Coherent patterns of change are also found along the path of the DWBC. These changes are consistent with an advective-diffusive model, which is used to quantify transit time distributions between the Labrador Sea and Line W. Advection and stirring are both found to play leading order roles in the propagation of water mass anomalies in the DWBC. The final study brings the two currents together in a quasi-geostrophic process model, focusing on the interaction between the Gulf Stream's northern recirculation gyre and the continental slope along which the DWBC travels. We demonstrate that the continental slope restricts the extent of the recirculation gyre and alters its forcing mechanisms. The recirculation gyre can also merge with the DWBC at depth, and its adjustment is associated with eddy fluxes that stir the DWBC with the interior. This thesis provides a quantitative description of the structure of the overturning circulation in the western North Atlantic, which is an important step towards understanding its role in the climate system.<br>by Isabela Astiz Le Bras.<br>Ph. D.
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Munday, David R. "On the flow separation of western boundary currents." Thesis, University of Reading, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415521.
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Stahr, Frederick R. "Transport and bottom boundary layer observations of the North Atlantic deep western boundary current at the Blake Outer Ridge /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/10998.
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Parsadous, Ali. "Vertical sidewall boundary layers in combined waves and currents." Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339101.
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Edberg, Richard. "Vortex Currents near the Boundary of a Two-Component Superconductor." Thesis, KTH, Fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209923.
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Ceballos, Lina Isabel. "North pacific gyre oscillation synchronizes climate fluctuations in the eastern and western boundary systems." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26552.
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Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2009.<br>Committee Chair: Di Lorenzo, Emanuele; Committee Member: Bracco, Annalisa; Committee Member: Webster, Peter J.. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Springer, Scott R. "Dynamics of western boundary currents in simple models of low-latitude circulations /." Thesis, Connect to this title online; UW restricted, 1994. http://hdl.handle.net/1773/11010.
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Elge, Murat. "Langmuir circulations in a coastal environment during CBLAST." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Sept%5FElge.pdf.
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Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, Sept. 2004.<br>Thesis advisor(s): Timothy P. Stanton. Includes bibliographical references (p. 95-99). Also available online.
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Johnstone, Henry Webb 1956. "CONFINED JET-INDUCED MIXING AT A DENSITY INTERFACE (TURBULENT, SHEAR FLOW)." Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/292003.
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Combes, Vincent. "Upwelling and cross-shelf transport dynamics along the Pacific Eastern Boundary." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34814.
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The upwelling and cross-shelf transport dynamics along the Pacific Eastern Boundary is explored using a high resolution ocean model for the last 60 years. Three ocean circulations have been modeled. From North to South, we investigate the dynamics of the Gulf of Alaska (GOA), the California Current System (CCS) and the Humboldt Current System (HCS, also known as the Peru-Chile Current System). The statistics of coastal waters transport are computed using a model passive tracer, which is continuously released at the coast. By looking at the passive tracer concentration distribution, we find that the Pacific Decadal Oscillation modulates the coastal variability of the GOA, the North Pacific Gyre Oscillation controls the upwelling of the CCS, while the El-Niño Southern Oscillation affects the upwelling of Peru and Chile mainly through coastally trapped Kelvin waves. Results also emphasize the key role of the mesoscale eddies in the offshore transport of coastal waters masses. The passive tracer experiments, performed in this study in the GOA, CCS, and HCS, therefore could provide a dynamical framework to understand the dynamics of the upwelling/downwelling and offshore transport of nutrient rich coastal water and to interpret how it responds to atmospheric forcing. This also could reinforce our interpretation (and therefore predictions) in the changes in vertical and offshore advection of other important biogeochemical quantities, essential in understanding ecosystem variability.
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Deese, Heather E. "Chaotic advection and mixing in a western boundary current-recirculation system : laboratory experiments /." Online version, 2000. http://hdl.handle.net/1912/3036.
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Thesis (S.M.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), February 2001.<br>Includes bibliographical references (p. 116-118).
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Palau, Masoliver Anna. "Critical currents and dissipation of grain boundary networks in coated conductors." Doctoral thesis, Universitat Autònoma de Barcelona, 2005. http://hdl.handle.net/10803/3367.
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Les cintes superconductores d'alta temperatura han sorgit com un material molt prometedor per aplicacions de potència en alts camps magnètics ja que s'ha demostrat la possible utilització del material YBaCuO-123 (YBCO) per produir cintes superconductores amb prestacions de densitat de corrent crítica de l'ordre de 1MA/cm2 a 77K sota camps magnètics elevats (1-5T). Les cintes superconductores de YBCO estan formades per una estructura bi-dimensional de fronteres de gra de baix angle (FGBA) (~4º-8º) induïdes per la textura del substrat metàl·lic flexible sobre el qual estan dipositades amb previ condicionament mitjançant el dipòsit de capes tampó.<br/> La granularitat present en aquests materials representa la limitació més important al pas de corrent elèctrica i estableix la presencia de dos mecanismes de dissipació interactuants associats per una banda al pas de corrent percolativa a través de les FGBA (limitada per la densitat de corrent crítica associada a les fronteres de gra JcFG) i per altra banda a la corrent que flueix al interior dels grans superconductors (limitada per la densitat de corrent crítica associada als grans, JcG). Si be JcG esta clarament determinada per l'ancoratge dels vòrtex Abrikosov en els grans superconductors, la dissipació associada a JcFG es encara un interrogant. Estudis teòrics han predit l'existència d'una nova classe de vòrtex superconductors associats a les fronteres de gra que han estat anomenats vòrtex Abrikosov-Josephson.<br/>En aquesta tesi doctoral hem analitzat la resposta electromagnètica de les cintes superconductores de YBCO mitjançant mesures magnètiques de cicles de histèresi menors. A partir de la forma característica dels cicles de histèresi s'ha desenvolupat un formalisme que ens ha permès determinar de manera independent i simultània les densitats de corrent crítica JcG i JcFG a baix camp magnètic, en el marc del model d'estat crític. La metodologia desenvolupada ens ha permès estudiar la relació existent entre els efectes de granularitat, l'ancoratge de vòrtex Abrikosov als grans i la dissipació associada al moviment de vòrtex Abrikosov-Josephson a les FGBA i per tant ens ha permès inferir en els mecanismes físics que regeixen el transport elèctric d'aquests materials. Hem realitzat un estudi complert de la relació entre aquests mecanismes variant diferents paràmetres característics de les cintes superconductores tal com l'angle mig entre fronteres de gra, el tamany de gra, el gruix de la capa superconductora o el procés de creixement. <br/>Addicionalment, mitjançant mesures de susceptibilitat ac, hem identificat i caracteritzat diferents dominis de percolació de corrent en diverses cintes superconductores de YBCO associats a diferents valors de JcFG. Aquest estudi ens ha permès complementar l'anàlisi magnètic de la granularitat inherent a aquests materials i caracteritzar la dissipació associada. A partir de l'estudi de les corbes de susceptibilitat ac mesurades a diferent freqüència hem determinat l'energia d'activació tèrmica a diferents camps magnètics i diferents densitats de corrent. Comparant els valors obtinguts amb els valors de Jc mesurats mitjançant magnetització dc hem pogut determinar un diagrama de fases magnètic (camp magnètic/temperatura) per a les cintes superconductores de YBCO on es poden distingir diferents règims de moviment de vòrtex.<br>High temperature coated conductors has emerged as a very promising material for power applications at high magnetic fields since it has been demonstrated the possible utilization of YBaCuO-123 (YBCO) for performing coated conductors able to support current densities higher than 1MA/cm2 at 77K and high magnetic fields (1-5T). YBCO coated conductors consist on a bi-dimensional structure of low angle grain boundaries (LAGB) (~4º-8º) induced by the texture of the metallic tape used as a substrate, which is usually covered with several buffer layers.<br/>The granularity present in this materials represent the major limitation for the electrical current to flow and establish the presence of two different interactive dissipation mechanisms associated on one hand to the percolative current flowing through the LAGB (limited by the grain boundary critical current density, JcGB) and on the other hand to the current flowing inside the superconducting grains (limited by the grain critical current density, JcG). While JcG is clearly limited by the Abrikosov vortex pinning inside the superconducting grains, the dissipation associated to JcGB is still an open issue. Theoretical studies has predicted the existence of a new kind of vortex located at the grain boundaries called Abrikosov-Josephson vortices.<br/>In this Thesis we have analyzed the electromagnetic response of YBCO coated conductors by means of magnetic measurements of minor hysteresis loops. From the characteristic feature of the hysteresis loops we have developed a new formalism which has allowed us to determine independently and simultaneously both critical current densities, JcG i JcGB, at low applied magnetic field, in the framework of the Critical state Model. The methodology devolved has allowed us to study the relationship between granularity effects, Abrikosov vortex pinning inside the grains and the dissipation associated to the motion of Abrikosov-Josephson vortices at the LAGB and thus, it has allowed us to infer in the physical mechanisms which governing the electric transport in these materials. We have performed a complete study of the relationship between these mechanisms by changing different characteristic parameters of the YBCO coated conductors such as the average misorientation angle in the grain boundaries, the grain size, the thickness of the YBCO layer or the growing process.<br/>Additionally, by means of ac susceptibility measurements, we have identified and characterized different current percolative domains in several YBCO coated conductors associated to different values of JcGB. This study has allowed us to complement the analysis of magnetic granularity inherent at these materials and characterize the associated dissipation. By means of the study of ac susceptibility curves measured at different frequency we have determined the thermal activation energy of YBCO coated conductors at several magnetic fields and current densities. By comparing the resultant values with the values of Jc measured by means of dc magnetization we have determined a general magnetic phase diagram (magnetic field/temperature) for YBCO coated conductors where we have distinguished different vortex motion regimes.
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Guthrie, Vanessa M. "Dynamics of eastern boundary currents and their effects on sound speed structure." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Jun%5FGuthrie.pdf.
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Thesis (M.S. in Physcial Oceanography)--Naval Postgraduate School, June 2006.<br>Thesis Advisor(s): Mary L. Batteen, John A. Colosi. "June 2006." Includes bibliographical references (p. 69-73). Also available in print.
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Akuetevi, Cataria Quam Cyrille. "Dynamics of turbulent western boundary currents at low latitudes, a numerical study." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU002/document.
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Les courants turbulents de bord ouest sont l'un des phénomènes les plus dominants des océans, il en existe aux faibles latitudes aussi. Ils sont caractérisés par une dynamique très turbulente avec une forte production d'énergie cinétique, et une forte variabilité interne. Plusieurs régions existent où les courants de bord ouest se rétrofléchissent (décollage de la côte) pour former des structures cohérentes: des anticyclones, des bursts (arrachements) et des dipoles. Circulant le long de la côte, les courants de bord ouest interagissent très fortement avec le bord ouest et la bathymétrie et sont donc un problème de couche limite. Cependant aucune étude du point de vue de la théorie de couche limite n'a été jamais été faite. Cette thèse aborde le problème d'un point de vue de couche limite par l'utilisation d'un modèle idéalisé "shallow water" à très haute résolution (2.5km) afin d'isoler et de comprendre les processus. Les résultats sont ensuite appliqués à des sorties de modèle réaliste Drakkar (~10km) basé sur le code NEMO. Le courant de Somali est ensuite pris pour cette application<br>Strong western boundary currents are one of dominant features of the world oceans, also at low latitudes. They exhibit a turbulent dynamics and their region is a source of strong kinetic energy production and internal variability of the worlds oceans. Several places exists where the western boundary currents retrofect (i.e separation from the coast) and generate coherent structures as anticyclonic eddies, bursts and dipoles. The dynamics of turbulent western boundary currents has so far not been extensively studied in the viewpoint of turbulent boundary-layer theory. The approach followed in this thesis is to use a fine resolution (2.5km) reduced-gravity shallow water model to understand the turbulent boundary-layer processes and then apply these findings to the Ocean General Circulation Model NEMO in the Drakkar configuration (~10km). The case of the Somali Currentis considered for this application
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Sheldon, Luke. "The role of deep moist convective processes in western boundary currents-troposphere coupling." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/25755.
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Previous studies have suggested that atmospheric deep convection is occurring above the oceans western boundary currents. To investigate the occurrence of deep (ocean surface to troposphere) convection in mid-latitudes, diagnostics of upright and slantwise convective instability are created and used in the ERA-interim re-analysis dataset. These diagnostics find that deep convection is restricted to the western boundary currents in winter. However, over the ocean currents deep convection can occur up to 50% of the winter. As these ocean currents, including the Gulf Stream and Kuroshio, are warm and carry large quantities of heat polewards they could influence the frequency of deep convection. A simple calculation demonstrates that decadal ocean variability can change the atmospheric stability by 80% in the core of the Kuroshio and Gulf Stream. The deep convective instability occurs in synoptic systems that pass over the ocean currents. Specifically, instability occurs on the atmospheric fronts in the extra-tropical cyclones. To investigate the convective instability and related circulation at atmospheric fronts a composite of all atmospheric fronts in the Gulf Stream region is produced. The front composites show that where slantwise instability occurred at a front an associated increase in frontal ascent throughout the troposphere and precipitation is also found. An investigation into the possible mechanisms that produced the increased ascent at slantwise unstable fronts concludes that a possible cause is a coarse resolution of slantwise circulations in the ERA-interim dataset. This increase in deep ascent associated with slantwise instability could explain, at least partially, the deep ascent found by previous studies over the Gulf Stream. This is consistent with the finding that the deep ascent in the Gulf Stream annual mean is a product of extreme events. The occurrence of deep slantwise instability and the associated circulations are also resolution dependent. A comparison between 25 km, 60 km and 135 km grid-spacing atmospheric model runs are made using the UPSCALE project dataset. The 25 km model runs indicate greater deep slantwise and upright convective instability. The 25-km set-up is also the only one where increased deep ascent at slantwise unstable fronts is observed.
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Culp, Jeffrey Parker. "Do Muds Sort? Experimental Test of a Hypothesis Key to Understanding Marine Bottom Currents." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/101548.
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Accumulations of fine sediments in deep-ocean contourites form a sedimentary record that has been hypothesized to be directly related to bottom-current behavior. This is known as the 'sortable silt' hypothesis and states that the non-cohesive, coarse silt in the 10 to 63 µm size range within a deposit can be used as a proxy for paleocurrent velocity. Slow deposition rates on contourites (2−10 cm/kyr) make it difficult to test this hypothesis in the field and few laboratory studies have been conducted. To test the 'sortable silt' hypothesis in the laboratory, a non-recirculating flume was constructed in which silt and clay could be deposited under a variety of velocities, sediment concentrations, and silt to clay ratios. Samples of the deposited material from each experiment were analyzed to determine the grain-size distribution using a Micromeritics Sedigraph 5120 particle size analyzer. The results of these experiments were used to evaluate the following two hypotheses: 1. The proportion of sortable silt (SS%) compared to the proportion of clay is a better indicator of current velocity than the mean size of the sortable silt (SS). 2. The presence of clay will impact the movement and sorting of silt in the bed. Results show that increased velocity correlates with increased (SS), and that (SS) generally decreases downstream of the sediment source. (SS) was found to be more representative of velocity than (SS%) and, counter to the original hypothesis, clay did not have a significant effect on silt deposition.<br>Master of Science
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Bourg, Natacha. "Interactions between boundary currents, fronts and eddies in the Northern Current and the East Australian Current. : Transport dynamics and application to the journey of Physalia spp." Electronic Thesis or Diss., Toulon, 2024. http://www.theses.fr/2024TOUL0001.
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Les courants de bords, caractérisés par de fortes vitesses et de nombreuses interactions dynamiques avec les marges continentales, sont les principaux moteurs de la variabilité océanique dans les régions côtières qu’ils traversent. La première partie de cette thèse se concentre sur les observations Radar Haute-Fréquence du Courant Nord dans la Méditerranée Nord-Occidentale et du courant est-australien dans l’océan Pacifique Sud. Nous étudions la variabilité saisonnière et interannuelle du courant et le développement de tourbillons de (sous) méso-échelle dans le système du Courant Nord. Concernant le courant est-Australien, nous examinons plus particulièrement sa dynamique de séparation, ses caractéristiques frontales et son impact sur la concentration de chlorophylle-a en surface.Les courants de bord, de par leur grande étendue et leur position le long du plateau continental,sont importants car ils agissent à la fois comme des barrières et des courroies de transport de matière passive. La deuxième partie se concentre sur Physalia spp., un organisme urticant pseudo-passif flottant à la surface de l’océan qui atteint régulièrement les côtes australiennes. Nous avons pu estimer l’impact relatif des variables météo-marines sur leur échouage. A partir d’expériences en laboratoire, nous établissons une paramétrisation de la dérive de maquettes 3D de Physalia spp. induite par le vent. Ce résultat,intégré dans une modélisation de suivi lagrangien selon des scénarios typiques du courant est-Australien nous permet de déterminer l’influence cumulée du vent et du courant sur les trajectoires des Physalia spp. Les résultats présentés dans cette thèse contribuent à la connaissance de deux courants de bord, caractérisés par des échelles et des modes de variabilité différents, et illustrent leur rôle dans le transport de matière passive à travers l’étude de la dérive de Physalia spp<br>Boundary currents, characterized by strong velocities and dynamic interactions with continental margins are the main drivers of ocean variability in the adjacent coastal regions. The first part of the thesis focuses on High-Frequency RADAR observations of the Northern Current in the North Western Mediterranean Sea and of the East Australian Current in the South Pacific Ocean. In the Northern Current system, we investigate the seasonal and inter-annual variability of the current and the occurrence of (sub) mesoscale eddies, while we focus on the study of the separation dynamics of the East Australian Current, its frontal characteristics and overall impact on surface chlorophyll-a concentration. Boundary currents, by their spatial extent and position along the continental shelf, are important in acting both as barriers and conveyers of transport of passive matter. The second part of the thesis focuses on Physalia spp., a pseudo-passive stinging organism floating at the ocean surface which regularly reaches Australian shores. We are able to estimate the relative impact of atmospheric and oceanic variables on Physalia spp. beaching. From laboratory experiments, we establish a parametrization of the wind-induced drift of 3D-printed replicas of Physalia spp. This result is then incorporated into a Lagrangian tracking model based on the most recurrent East Australian Current separation scenarios to assess the combined effects of winds and currents on the pathways of Physalia spp. The results presented in this thesis contribute to the knowledge of two boundary currrents characterized by different scales and modes of variability, giving insights in their role in transport of passive material through the study of Physalia spp journey
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Taljaard, Carolina Augusta. "Urban Currents: urban regeneration + boundary of isolated natural sites in the context of Wonderboom Nature Reserve." Diss., University of Pretoria, 2020. http://hdl.handle.net/2263/78569.
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Situated within the Wonderboom Poort on the banks of the Apies River, this architectural manifestation is a culmination of the exploration of how the forgotten or left over urban spaces can be revived to contribute to the creation of sustainable facilities and infrastructures accommodating ‘Third space’ within the South African urban context. These forgotten spaces include isolated and underutilised natural spaces, such as Wonderboom Nature Reserve. This dissertation briefly explores the shortfalls of traditional urban planning, while addressing how architectural interventions can contribute not only to urban fabric, but also how they create a platform for positive change through combining socio-economic programme and natural processes. The designer utilises Landscape Urbanism and similar theories as lens to explore appropriate interventions at various scales. This is not only an interrogation of site and context to identify the most appropriate site for intervention, but also an interrogation of form, function and the larger role architecture plays in the social and environmental context of the city. In conclusion it is evident that fragmented (lost/forgotten) urban spaces possess the latent potential to positively alter the status quo of South African cities, generating network continuity (whether natural, infrastructural or social) through the implementation of appropriate architectural intervention when rooted in sustainability theory. In this case the intervention will primarily be focussing on the continuity of public space, serving as a catalyst for future growth and improvement in the area and significantly encouraging the inclusion of the ‘human focus’ – setting a precedent for future development or intervention.<br>Mini Dissertation (MArch(Prof))--University of Pretoria, 2020.<br>Architecture<br>MArch (Prof)<br>Unrestricted
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Deese, Heather E. (Heather Elizabeth) 1975. "Chaotic advection and mixing in a western boundary current-recirculation system : laboratory experiments." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/53538.
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Thesis (S.M.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2001.<br>Includes bibliographical references (p. 116-118).<br>I study the exchange between a boundary current and flanking horizontal recirculations in a 'sliced-cylinder' rotating tank laboratory experiment. Two flow configurations are investigated: a single recirculation and a double, figure-8, recirculation. The latter case involves a hyperbolic point, while the former does not. I investigate the stirring and mixing under both steady and unsteady forcing. I quantify the mixing in each case using effective diffusivity, Keff, and a corollary effective length, Leff, as derived by Nakamura (1995, 1996). This approach involves diagnosing the geometric complexity of a tracer field. Geometric complexity is indicative of advective stirring. Because stirring creates high gradients, flows with high advective stirring also have high diffusion, and stronger overall mixing. I calculate effective length from images of dye in the tank and find much higher values of Leff in the unsteady hyperbolic cases than in the other cases. Slight unsteadiness in flows involving hyperbolic points gives rise to a chaotic advection mechanism known as 'lobe dynamics'. These lobes carry fluid in and out of the recirculations, acting as extremely effective stirring mechanisms. I demonstrate the existence of these exchange lobes in the unsteady hyperbolic (figure-8) flow. The velocity field in the tank is calculated utilizing particle image velocimetry (PIV) techniques and a time series U(t) demonstrates the (forced) unsteadiness in the flow. Images of dye in the tank show exchange lobes forming at this same forcing period, and carrying fluid in and out of the recirculation. Based on the results of these experiments, I am able to confirm that, at least in this controlled environment, basic geometry has a profound effect on the mixing effectiveness of a recirculation. I demonstrate radically increased stirring and mixing in the unsteady hyperbolic flow as compared to steady flows and flows without hyperbolic points. Recirculations are ubiquitous in the world ocean; they occur on a variety of scales, in many different configurations, and at all depths. Some of these configurations involve hyperbolic points, while others do not. Chaotic advection via lobe exchange may be an important component of the mixing at multiple locations in the ocean where hyperbolic recirculation geometries exist.<br>by Heather E. Deese.<br>S.M.
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Calado, Leandro. "Dinâmica da interação da atividade de meso-escala da Corrente do Brasil com o fenômeno da ressurgência costeira ao largo de Cabo Frio e Cabo de São Tomé, RJ." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-24092009-140739/.
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Os meandros da Corrente do Brasil ao largo do sudeste brasileiro s~ao singulares em termos de sua composic¸ ~ao termohalina. Estes v´ ortices, principalmente na regi~ao de Cabo Frio e Cabo de S~ao Tom´e, constituem um sistema integrado a ressurg^encia costeira e a pr´opria Corrente do Brasil, caracterizando um sistema din^amico que propomos denominar Corrente do Brasil-v ´ ortice-ressurg^encia. Apresentamos uma metodologia de construc¸ ~ao de modelos param´etricos das feic¸ ~oes oceanogr´aficas (ou Modelos de Feic¸ ~ao) que comp~oem o sistema. Estes modelos s~ao capazes de construir tridimensionalmente feic¸ ~oes oceanogr´aficas individuais a partir de dados sin´oticos de superf´?cie e fundo para elaborac¸ ~ao de campos iniciais de modelos num´ericos, com o objetivo de compreender a interac¸ ~ao do sistema din^amico Corrente do Brasil-v´ ortice-ressurg^encia. Atrav´es da simulac¸ ~ao num´erica dos campos iniciais baseados nos Modelos de Feic¸ ~ao investigamos o processo que conduz `a assimetria termohalina dos v´ ortices da Corrente do Brasil, acima descrita. Esta foi devida a aproximac¸ ~ao desses v´ ortices junto ao talude continental e ao ajustamento barocl´?nico das correntes `as menores profundidades. Verificamos, ainda, que a penetrac¸a~o da A´ gua Central do Atla^ntico Sul pela camada de Ekman de fundo n~ao tem efeito significativo na estrutura dos v´ ortices. Realizamos experimentosnum´ericos adicionais com o objetivo de investigar quais os tipos de instabilidade geof´?sica estariam envolvidas no fen^omeno do crescimento dos meandros e v´ ortices da Corrente do Brasil. Analisando os resultados atrav´es de c´alculos de convers~ao de energia pudemos concluir que o sistema Corrente do Brasil-v´ ortice-ressurg^encia apresenta instabilidade mista ( barotr ´opica e barocl´?nica). Contudo, verificamos quantitativamente que a instabilidade barocl´?nica foi dominante. O sistema, no entanto, mostrou-se sens´?vel `a ac¸ ~ao da tens~ao de cisalhamento do vento de nordeste na regi~ao e consequentemente `a ressurg^encia costeira. Interpretamos tal sensibilidade como fator respons´avel pela relev^ancia da instabilidade barotr ´opica no processo de crescimento dos meandros da Corrente do Brasil. Por fim, verificamos que um meandro cicl ^onico frontal, quase-estacion´ario, em condic¸ ~oes especiais de crescimento por mecanismo de instabilidade, pode auxiliar no estabelecimento da ressurg^encia costeira. O v´ ortice do Cabo de S~ao Tom´e simulado apresenta velocidade de fase muito baixa e cresce em direc¸ ~ao a oceano aberto, de forma praticamente perpendicular `a quebra de plataforma. Logo, o crescimento do vo´ rtice de Cabo de Sa~o Tome´ faz com que o mesmo advecte A´ gua Costeira para seu interior provocando, por continuidade, afloramento da A´ gua central do Atla^ntico Sul junto `a costa. Assim, podemos dizer que h´a, de fato, uma interac¸ ~ao entre o sistema costeiro e a atividade de meso-escala da Corrente do Brasil.<br>The Brazil Current meanders off the Brazilian southeast coast are unique in terms of their thermohaline structure. These eddies, especially off the Cape Frio and S~ao Tom´e region constitute an integrated system with the Brazil Current and the coastal upwelling, characterizing a dynamic system which we propose to nominate as Brazil Current-eddy-upwelling system. We present a methodology of parametric model construction of the oceanographic features (or Feature Models) which compose the inferred system . These models are capable of three-dimensionally building independent the relevant features from synoptic surface and bottom data in order to compose the initial fields for numerical models with the objective of understanding the dynamics of the interaction of Brazil Current-eddy-upwelling system. By means of numerical simulation usingthe initial fields based on the Feature Models, we investigated the process which conducts to the thermohaline asymmetry of the eddies in the Brazil Current as mentioned above. This is due to the baroclinic approximation of the currents to shallower depths. The penetration of the Central Water in the South Atlantic by the bottom Ekman layer does not have a significant effect on the eddy structure. Additional numerical experiments were carried out with the objective of unders tanding which of the geophysical instabilities were involved in the growth of the Brazil Current meanders and eddies. The results analyzed through calculation of energy conversion allowed us to conclude that the Brazil Current-eddie-upwelling system presents mixed instability (barotropic and baroclinic). However, the baroclinic instability is dominant and is mostly associated to the vertical shear of the oceanic currents. The system, however,was sensitive to the action of the northeast wind shear and consequently to the coastal upwelling. Such sensibility was interpreted as the main responsible for the relevance of barotropic instability in the growth process of meanders in the Brazil Current. Lastly, we verified that a quasi-stationary frontal cyclonic meander, in special growth conditions by instability mechanisms, mayhelp in establishing coastal upwelling. The simulated S~ao Tom´e Cape Eddy presented a very low phase velocity and grew towards the open sea, almost perpendicularly to the continental shelf break. Therefore, the growth of the S~ao Tom´e Cape Eddy advects Coastal Water into its center and, therefore, lead to upwelling of South Atlantic Central Water near the coast. We can therefore say that there are in fact interaction mechanisms between the coastal system and the meso-scale activity of the Brazil Current.
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Yang, Hu [Verfasser], Gerrit [Akademischer Betreuer] [Gutachter] Lohmann, and Rüdiger [Gutachter] Gerdes. "Dynamic changes of subtropical western boundary currents under global warming / Hu Yang ; Gutachter: Gerrit Lohmann, Rüdiger Gerdes ; Betreuer: Gerrit Lohmann." Bremen : Staats- und Universitätsbibliothek Bremen, 2016. http://d-nb.info/1127701398/34.
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Douillet, Guilhem Amin [Verfasser], and Donald Bruce [Akademischer Betreuer] Dingwell. "Flow and sedimentation of pyroclastic density currents : from large scale to boundary layer processes / Guilhem Amin Douillet. Betreuer: Donald Bruce Dingwell." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2015. http://d-nb.info/1072038501/34.
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Yokoyama, Yoshihiro. "Characteristics of the mesoscale field-aligned currents in the dusk sector of the auroral oval based on data from the Swarm satellites." Kyoto University, 2021. http://hdl.handle.net/2433/261602.
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Costa, Andrea. "Marine connectivity : exploring the role of currents and turbulent processes in driving it." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0091/document.
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La connectivité marine est le transfert de larves et/ou d'individus entre des habitats marins éloignés. Grâce à la connectivité, les populations marines éloignées peuvent faire face à la pression de l'habitat en s'appuyant sur le transfert qui vient des populations éloignées de la même espèce. Le transfert entre les populations éloignées dans l'océan est possible par le transport dû aux courants. Cependant, il est pas encore clair si le champ des courants détermine totalement la persistance des espèces marines ou si la démographie locale joue un rôle. Les mesures in situ de la connectivité sont extrêmement difficiles. Par conséquence, notre connaissance de la connectivité est déduite des simulations numériques de dispersion. Le but de cette thèse est de préciser si la persistance de la connaissance du champ des courants et d’étudier l'effet des paramétrisations numériques dans l'estimation de la connectivité. Premièrement, je compare la théorie des graphes et le modèle de métapopulation pour déterminer si les courants ont un rôle prédominant. Cela permet d'identifier quelles mesures de la théories des graphes identifient de manière fiable les sites reproductifs importants pour la persistance en s'appuyant sur la connaissance des seuls courants. Deuxièmement, j’étudie les avantages et les lacunes de différents schémas de fermeture de turbulence. Ceci permet de préciser quel schéma reproduit mieux l'activité de turbulence dans des modèles numériques. Troisièmement, j'étudie les mécanismes générateurs de turbulence aux limites du fond. Ceci permet de connaître le coefficient de traînée effectif dû aux flux sur la topographie brute et de mieux estimer les flux turbulents<br>Marine connectivity is the transfer of larvae and/or individuals between distant marine habitats. Thanks to connectivity, distant marine population can face habitat pressure by relying on the transfer from distant populations of the same species. The transfer between distant populations in the ocean is made possible by the transport due to the currents. However, it is still not clear if the current field totally determines the persistence of the marine species or if the local demography plays a role. Crucially, in situ measurements of connectivity are extremely difficult. Therefore, our knowledge about connectivity is inferred from numerical dispersal simulations. The aim of this thesis is to clarify if we can deduce the persistence from the knowledge of the current field and to investigate the effect of numerical turbulence parameterizations in estimating connectivity. Firstly, I compare graph theory and metapopulation model to determine if currents have a predominant role. This allows to identify which graph theory measures reliably identifies reproductive sites important for persistence by relying on the knowledge of currents only. Secondly, I investigate the advantages and shortcomings of different turbulence closure models. This allows to clarify which TCS better reproduces turbulence activity in numerical models. Thirdly, I investigate generating mechanisms of bottom boundary turbulence. This allows to know the effective drag coefficient due to flow over rough topography and better estimate turbulent fluxes
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Costa, Andrea. "Marine connectivity : exploring the role of currents and turbulent processes in driving it." Electronic Thesis or Diss., Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0091.
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La connectivité marine est le transfert de larves et/ou d'individus entre des habitats marins éloignés. Grâce à la connectivité, les populations marines éloignées peuvent faire face à la pression de l'habitat en s'appuyant sur le transfert qui vient des populations éloignées de la même espèce. Le transfert entre les populations éloignées dans l'océan est possible par le transport dû aux courants. Cependant, il est pas encore clair si le champ des courants détermine totalement la persistance des espèces marines ou si la démographie locale joue un rôle. Les mesures in situ de la connectivité sont extrêmement difficiles. Par conséquence, notre connaissance de la connectivité est déduite des simulations numériques de dispersion. Le but de cette thèse est de préciser si la persistance de la connaissance du champ des courants et d’étudier l'effet des paramétrisations numériques dans l'estimation de la connectivité. Premièrement, je compare la théorie des graphes et le modèle de métapopulation pour déterminer si les courants ont un rôle prédominant. Cela permet d'identifier quelles mesures de la théories des graphes identifient de manière fiable les sites reproductifs importants pour la persistance en s'appuyant sur la connaissance des seuls courants. Deuxièmement, j’étudie les avantages et les lacunes de différents schémas de fermeture de turbulence. Ceci permet de préciser quel schéma reproduit mieux l'activité de turbulence dans des modèles numériques. Troisièmement, j'étudie les mécanismes générateurs de turbulence aux limites du fond. Ceci permet de connaître le coefficient de traînée effectif dû aux flux sur la topographie brute et de mieux estimer les flux turbulents<br>Marine connectivity is the transfer of larvae and/or individuals between distant marine habitats. Thanks to connectivity, distant marine population can face habitat pressure by relying on the transfer from distant populations of the same species. The transfer between distant populations in the ocean is made possible by the transport due to the currents. However, it is still not clear if the current field totally determines the persistence of the marine species or if the local demography plays a role. Crucially, in situ measurements of connectivity are extremely difficult. Therefore, our knowledge about connectivity is inferred from numerical dispersal simulations. The aim of this thesis is to clarify if we can deduce the persistence from the knowledge of the current field and to investigate the effect of numerical turbulence parameterizations in estimating connectivity. Firstly, I compare graph theory and metapopulation model to determine if currents have a predominant role. This allows to identify which graph theory measures reliably identifies reproductive sites important for persistence by relying on the knowledge of currents only. Secondly, I investigate the advantages and shortcomings of different turbulence closure models. This allows to clarify which TCS better reproduces turbulence activity in numerical models. Thirdly, I investigate generating mechanisms of bottom boundary turbulence. This allows to know the effective drag coefficient due to flow over rough topography and better estimate turbulent fluxes
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Amorim, Fabiola Negreiros de. "A Dinâmica Sazonal da Plataforma Continental Leste Brasileira entre 10ºS e 16ºS." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-19042012-111805/.
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A circulação sazonal da Plataforma Continental Leste Brasileira (PCLB) entre 10oS e 16oS é investigada com base em um inédito conjunto de dados in situ e em modelagem hidrodinâmica. Os dados observados possibilitaram a compreensão da dinâmica da circulação em partes específicas da região de estudo e a sua interação com os diversos mecanismos forçantes, ilustrando a forte influência da circulação atmosférica e oceânica de meso/larga escalas, de processos transientes e da topografia local, na circulação regional, apresentando cenários distintos entre as estações do ano. Os resultados da modelagem hidrodinâmica não só complementaram os estudos observacionais, como também permitiram uma maior compreensão da variabilidade sazonal e espaço-temporal da circulação na PCLB, assim como a sua interação com os diversos mecanismos forçantes, para uma região mais ampla (10oS-16oS). A PCLB é fortemente afetada pela sazonalidade de larga escala do regime dos ventos alísios e da latitude da Zona de Convergência Intertropical (ZCIT). Seguindo esta dinâmica, durante as estações de primavera/verão, as correntes na Plataforma Continental (PC) ao sul de 12oS ficam sujeitas a ventos preferenciais de E-NE e, no oceano, a bifurcação da Corrente Sul Equatorial (bSEC) atinge a sua posição mais ao norte (~13oS em novembro). Nas regiões da quebra da PC e do talude continental, as correntes são também influenciadas pelas Correntes de Contorno Oeste (CCO). No domínio norte (10oS), a circulação na PC interna é para sul, seguindo o campo de ventos preferencial, enquanto a circulação na PC média e na quebra da PC é mais influenciada pelas correntes na região do talude continental, que são claramente dominadas pela dinâmica da Corrente Norte do Brasil/Sub-Corrente Norte do Brasil (CNB/SCNB). No domínio central (14oS), embora a circulação seja de certa forma similar à observada para o domínio norte, a circulação no talude continental apresenta uma maior variabilidade como resposta à presença dos fluxos contrários da Corrente do Brasil (CB) e da SCNB. A circulação no domínio sul (16oS) possui uma clara divisão ao longo da PC/talude continental, apresentando um intenso e organizado fluxo direcionado para sul na PC interna e média, como resposta à forçante remota do vento, e uma circulação polarizada na direção perpendicular à costa nas regiões da quebra da PC/talude continental, sugerindo uma associação com a CCO e com a topografia local do Banco Royal Charlotte. Durante as estações de outono/inverno, seguindo o regime sazonal dos ventos alísios e da latitude da ZCIT, a PC ao norte de ~20oS fica sujeita a ventos preferenciais de E-SE e as correntes sofrem uma reversão do fluxo médio, e a bCSE atinge seu limite sul (~17oS em julho). A circulação na PC interna e média no domínio norte durante estas estações, apresenta um fraco fluxo para norte com uma alta variabilidade. Enquanto na PC interna esta variabilidade está relacionada à entrada mais frequente de frentes frias, na PC média está relacionada com a circulação na região do talude continental. A circulação nesta região possui uma alta correlação com aquela na região da quebra da PC e ambas apresentam um fluxo médio para norte mais intenso e menos variável, que pode estar relacionado com o fluxo da CNB/SCNB, que ocupa toda a região do talude continental durante estas estações do ano. O fluxo médio para norte no domínio central, apresenta uma fraca intensidade e alta variabilidade nas regiões da PC interna e média e na quebra da PC, que pode estar relacionada com o aumento da frequência de sistemas frontais, ao fato desta região ser influenciada pela bifurcação do fluxo médio em superfície e, para a região da quebra da PC, à variabilidade da SCNB, que apresenta maiores episódios em que ocupa esta região. A CNB/SCNB exerce uma clara influência na circulação da região do talude continental. A circulação no domínio sul é principalmente gerada pelo vento remoto nas regiões da PC interna e média, enquanto nas regiões da quebra da PC e talude continental apresenta uma significativa influência da CCO.<br>The seasonal circulation of the Eastern Brazilian Shelf (EBS) between 10oS and 16oS is investigated based on original in situ data sets and hydrodynamic modeling. The observational data provided an understanding of the circulation dynamics within specific parts of the the study region and its interaction with the various forcing mechanisms, illustrating the strong influence of the large/meso scales atmospheric and oceanic circulation, transient processes and local topography on the regional circulation, presenting very distinct scenarios between seasons. The hydrodynamic modeling results not only complemented the observational studies but also allowed for a broader understanding of the seasonality and time-space variability of the EBS circulation, as well as its interaction with the various forcing mechanisms, in a wider region (10oS-16oS). The EBS is highly affected by large-scale seasonality in the trade wind regime and the latitude of the Intertropical Convergence Zone (ITCZ). Following this dynamics, during the spring/summer seasons, the currents within the continental shelf south of 12oS are influenced by preferential E-NE winds and, in the ocean, the bifurcation of the South Equatorial Current (bSEC) reaches its northernmost position (~13oS in November). At the shelf break and slope region, the currents are also influenced by the Western Boundary Currents (WBC). At the northern domain (10oS) the inner shelf circulation is to the south following the preferential winds, while the circulation at the mid shelf and shelf break is more influence by the currents at the slope, which are clearly dominated by the North Brazil Current/North Brazil Undercurrent (NBC/NBUC) dynamics. At the central region (14oS), although the circulation is somehow similar to that observed for the northern domain, the slope circulation presents a greater variability in response to the presence of the opposing Brazil Current (BC) and NBUC flow. At the southern domain (16oS) the circulation has a clear division along the continental shelf/slope regions, presenting an intense and organized southward flow at the inner and mid shelves, as a response to the remote wind forcing, and a polarized cross-shelf circulation at the shelf break/slope region, suggesting an association with the WBC and the local topography of the Royal Charlotte Bank. During the autumn/winter seasons, following the seasonal regime of the trade winds and the latitude of the ITCZ, the continental shelf north of ~20oS are influenced by preferential E-SE winds and the currents experience a reversal of the mean flow, and the bSEC reaches its southernmost position (~17oS in July). The circulation during these seasons at the northern domain inner and mid shelves presents a weak northward flow with a strong variability. While at the inner shelf this variability is related to the more frequent cold front passages at the mid shelf it is related to the slope region circulation. The circulation at this region has a high correlation with the circulation at the shelf break and both present a less variable and more intense northward net flow which could be related to the NBC/NBUC flow, that occupies the entire slope region during these seasons. The northward net flow at the central domain presents a weak intensity and high variability at the inner/mid shelves and shelf break regions, which could be related to the increase in the cold fronts frequency, to the fact that this region is under the influence of the bifurcation of the surface net flow and, for the shelf break region, to the NBUC variability which presents more episodes that occupies this region. At the slope region the NBC/NBUC exerts a clear influence in the circulation. The circulation at the southern domain is mainly driven by the remote wind forcing at the inner and mid shelves, while at the shelf break/slope regions presents a significant WBC influence.
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Peña-Molino, Beatriz. "Variability in the North Atlantic Deep Western Boundary Current : upstream causes and downstream effects as observed at Line W." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62495.
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Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 165-174).<br>The variability in the DWBC, its connection to the forcing in the northern North Atlantic and interaction with the Gulf Stream were explored from a combination of remote sensing and in-situ measurements in the western North Atlantic. Using satellite altimetry and Sea Surface Temperature (SST) we found evidence of the relation between changes in the Gulf Stream path and the variability in the temperature and velocity fields in the Slope Water. This relation was such that southward shifts of the main axis of the Gulf Stream were preceded by cold temperature anomalies and intensification of the southwestward flow. The analysis of 5.5 years of moored CTD and horizontal velocity data in the DWBC at 69 0W recorded during the period 2002-2008, showed that the variability along the DWBC is linked to changes in the dense water formation regions. The evolution of potential vorticity (PV) at the mooring site, characterized by a transition from deep to upper Labrador Sea Water (LSW), was similar to that observed in the Labrador Sea 6 to 9 years earlier, and imply spreading rates for the LSW that varied over time from 1.5 to 2.5cm/s. The time dependence of the spreading rates was in good agreement with changes in the strength of the DWBC at the mooring site. The evolution of the DWBC transport was explored in more detail from a 5- element moored array, also at 69'W. The results, for the period of 2004-2008, were consistent with the single mooring analysis. The variability measured from the array showed that upper, intermediate and deep water mass layers expand and contract at each other's expense, leading to alternating positive and negative PV anomalies at the upper-LSW, deep-LSW and Overflow Water (OW). Larger DWBC transports were associated with enhanced presence of recently ventilated upper-LSW and OW, rather than deep-LSW. The relative contribution of the different water masses to the observed circulation was investigated by inverting individual PV anomalies isolated from the observations. We found that changes in the depth-integrated circulation were mostly driven by changes in the OW.<br>by Beatriz Peña-Molino.<br>Ph.D.
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Werner, Sandra R. (Sandra Regina). "Surface and bottom boundary layer dynamics on a shallow submarine bank : southern flank of Georges Bank." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/58515.
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Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1999.<br>Includes bibliographical references.<br>The thesis investigates the circulation at a 76-m deep study site on the southern flank of Georges Bank, a shallow submarine bank located between the deeper Gulf of Maine and the continental slope. Emphasis is placed on the vertical structure of the bottom boundary layer driven by the semidiurnal tides and the flow field's response to wind forcing. The observational analysis presented here is based on a combination of moored array and bottom tripod-mounted current, temperature, conductivity, and meteorological data taken between February and August 1995. Results from the bottom boundary layer analysis are compared to numerical model predictions for tidal flow over rough bottom topography. The flow response to wind forcing is examined and brought into context with the existing understanding of the wind-induced circulation in the Georges Bank region. Particular attention is given to the vertical distribution of the wind-driven currents, whose variation with background stratification is discussed and compared to observations from open ocean studies.<br>by Sandra Regina Warner.<br>Ph.D.
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Soares, Saulo Muller. "Ondas instáveis no sistema de correntes de contorno oeste ao largo de Abrolhos." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-19072007-145643/.
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O sistema de correntes de contorno oeste que flui ao largo da costa leste brasileira entre 15°S e 22°S, é composto pela Corrente do Brasil (CB) fluindo para sul, a Sub-Corrente Norte do Brasil (SNB) fluindo para norte e a Corrente de Contorno Oeste Profunda (CCP) também fluindo para sul. Vigorosos meandros e vórtices são observados à jusante dos Bancos de Abrolhos (BA) e Royal Charlotte (BRC) e da Cadeia Vitória-Trindade. O objetivo central desta dissertação é o estudo da estabilidade deste sistema de correntes, aqui denomidado Sistema CB-SNB-CCP, utilizando o modelo oceânico da Universidade de Princeton (POM) em um cenário idealizado. Buscamos responder o quão instável é este sistema e quais seriam as características das ondas instáveis geradas a fim de contribuir para o conhecimento acerca da rica dinâmica de meso-escala observada nesta região. Objetivamos também, elucidar o papel dos BA e BRC nesta dinâmica. Embasados na alta baroclinicidade do sistema de correntes de contorno ao largo do sudeste brasileiro, optamos por representar o escoamento CB-SNB-CCP através de um modelo paramétrico do campo de massa, calibrado com os dados hidrográficos oriundos dos Cruzeiros Abrolhos [Silveira et al., 2006]. Mantendo o caráter idealizado do estudo, também empregamos topografia de fundo analítica, onde representamos o talude da região por uma função tangente hiporbólica. O BA e o BRC foram aproximados através de funções gaussianas devidademente ajustadas aos contornos da isóbata de 80 m extraídas do conjunto ETOPO 2. Para identificar os mecanismos de crescimento das possíveis ondas instáveis, calculou-se o balanço de energia das simulações realizadas de acordo com o método de [Xue & Bane, 1997]. Os resultados de três experimentos numéricos realizados sugerem que o sistema CB-SNB-CCP é instável. Ciclones quase-estacionários do lado costeiro da CB surgem como o principal modo de variabilidade desta corrente. De acordo com a análise do balanço energético, o crescimento dessas feições resulta primariamente de instabilidade baroclínica do escoamento. A escala horizontal típica das ondas e vórtices instáveis modelados é dada pelo raio de deformação interno, como esperado pela teoria de instabilidade baroclínica de escoamentos realisticamente estratificados. Em particular, os resultados do experimento com o BA e o BRC idealizados comprovam que estes funcionam como gatilhos para o desenvolvimento de ondas instáveis, favorecendo amplamente o crescimento das estruturas verticais. Os trens de onda instáveis quase-estacionários aqui obtidos sugerem que provavelmente o meandramento da CB observado em latitudes que se estendem até 28°S pode ser parte de um único sistema que se origina na região dos BA e BRC.<br>The western boundary currents system that flows off the eastern brazilian coast between 15°S e 22°S is composed by the southward-flowing Brazil Current (BC), the northward-flowing North Brazil Under Current (NBUC) and the Deep Western Boundary Current (DWBC) that flows south. Vigorous meanders and eddies are observed downstream of the Abrolhos (AB) and Royal Charlotte Banks (RCB) and the Vitória-Trindade Ridge. The main goal of this dissertation is to study the stability of this currents system, hereby named BC-NBUC-DWBC system, using the Princeton University Ocean Model (POM) in an idealized scenerio. We seek to answer how unstable is this system and what are the characteristics of the unstable waves in order to contribute to the understanding of the rich mesoescale dynamics observed in this region. We also aim to elucidate the role of the AB and of the RCB on this dynamics. Based on the high degree of baroclinicity of the western boundary currents system off the southeastern brazilian coast, we opted to represent the BC-NBUC-DWBC system through a parametric model of the mass field, calibrated with hydrographic data from the Abrolhos Cruises [Silveira et al., 2006]. Maintaining the idealized character of the study, we have also employed an analytical bottom topography, in which the region\'s continental slope is approximated by hyperbolic tangent function. The AB and RCB were approximated by gaussian functions properly adjusted to the 80 m isobath extracted from the ETOPO 2 database. To identify the growth mecanism of the unstable waves, the energy budget of the simulations was calculated according to [Xue & Bane, 1997]. The results from the three experiments conducted here suggest that the BC-NBUC-DWBC system is indeed unstable. Quasi-stationary cyclones in the coastal side of BC arise as the main mode of variability of this current. According to the energy budget analisys, the growth of these features results primarily from baroclinic instability of BC-NBUC-DWBC flow. The typical horizontal scale of the modeled unstable waves and eddies is given by the internal radius of deformation, as expected by baroclinic instability theory of realistically stratified flows. The quasi-stationary unstable wave trains modeled in the present study also suggest that the meandering of the BC observed down to 28°S are probably part of a single system that originates at the AB and RCB region.
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Germineaud, Cyril. "Circulation océanique et variabilité en mer des Salomon." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30348/document.
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Dans le Pacifique sud-ouest, le cheminement des eaux depuis la gyre subtropicale vers l'équateur est réalisé via les courants de bord ouest (WBCs), associés à des changements de température ou de quantité d'eau à di?érentes échelles de temps. La mer des Salomon située au sud de la Pa- pouasie Nouvelle-Guinée est considérée comme une région clé pour étudier les WBCs juste avant qu'ils rejoignent l'équateur. Dans le cadre d'une collaboration internationale, deux campagnes en mer ont été réalisées en mer des Salomon pendant deux périodes contrastées de la saison des alizés (Juillet-Août 2012 et Mars 2014). En Juillet-Août 2012, pendant la saison de forts alizés, les WBCs transportent 36 ± 3 Sv à travers l'entrée sud de la mer des Salomon depuis la surface jusqu'à 1000 m de profondeur, mais seulement 11 ± 3 Sv en Mars 2014 (réduction de 70%) quand les alizés faiblissent. Les WBCs sont associés à des propriétés de masses d'eau distinctes qui subissent d'importantes modifications au cours de leur passage en mer des Salomon. En dessous de 2000 m de profondeur, l'Upper Circumpolar Deep Water (UCDW) est tracée depuis le bassin de Fidji et la fosse de la Nouvelle-Calédonie avant d'entrer en mer des Salomon, asso- ciée à un transport de masse de 2 à 3 ± 2 Sv. L'étude préliminaire des mouillages au niveau des détroits de sortie a permis d'identifier une modulation de l'intensité et de la structure ver- ticale des WBCs en relation avec la variabilité saisonnière des alizés. Les eaux de thermocline entre les différents mouillages varient généralement de manière cohérente et en phase à l'échelle intra-saisonnière et saisonnière<br>The Low Latitude Western Boundary Currents (LLWBCs) of the Southwest Pacific establish a major connection between the subtropics and the equator. They are believed to play a key role in heat and mass budgets of the equatorial Pacific and cross, as a final passage, the Solomon Sea southeast of Papua New Guinea. As part of a France-U.S. collaboration, two oceanographic multidisciplinary cruises were conducted in the Solomon Sea during contrasting trade wind sea- sons, in July-August 2012 and March 2014 to characterize currents, water properties and their modifications. During July-August 2012, the season of strong southeasterly trade winds, an in- tense flow of 36 ± 3 Sv from the surface down to 1000 m is entering the Solomon Sea, that falls by 70% to 11 ± 3 Sv in March 2014 when the winds over the sea are weaker. The LLWBCs are associated with distinct water mass properties across the Solomon Sea that can be tracked along their pathways, and undergo significant modifications between the southern entrance and the northern exits of the sea. Below 2000 m, the Upper Circumpolar Deep Water (UCDW) has been traced from the New Caledonia Trench and the South Fiji Basin into the Solomon Sea, associ- ated with a volume transport of 2-3 ± 2 Sv. Preliminary analyses of the mooring array in each major exit channel indicate large time variability of the LLWBCs in both =intensity and vertical extent, where thermocline pathways vary in most cases, coherently and in phase at intraseasonal to seasonal time scales
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Barreto-Acobe, Clary Denisse 1976. "Turbulent wave-current boundary layers revisited." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/84239.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001.<br>Includes bibliographical references (leaves 91-94).<br>by Clary Denisse Barreto-Acobe.<br>S.M.
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Frank, Donya P. "Wave-Current Bottom Boundary Layer Interactions." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1229087949.
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Phan, Quang Anh. "Contribution à la modélisation des courants de Foucault par la méthode des équations intégrales de frontière." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAT080.
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Au cours des dernières décennies, la modélisation numérique des dispositifs électromagnétiques en présence de courants de Foucault a été l'objet d'un nombre important de développements reposant sur différentes formulations et méthodes numériques.La méthode des éléments de frontière ou méthode intégrale de frontière est une méthode numérique très compétitive puisque, par opposition aux approches volumiques, elle ne nécessite que la discrétisation de la frontière du domaine. Elle est toutefois limitée aux matériaux isotropes, homogènes et linéaires, ce qui est une limitation importante. Elle peut tout de même s’avérer être attractive pour certaines applications où une telle hypothèse peut être formulée.Dans le cadre de cette thèse, nous allons nous concentrer sur la modélisation du problème courants de Foucault par la méthode des équations intégrales de frontière soumis à des excitations harmoniques. Ce rapport propose une synthèse sur ces formulations notamment avec une comparaison fine des formulations présentes dans la littérature. Plusieurs nouvelles formulations sont ensuite proposées et développées, dans l’objectif de comparer la méthode des équations intégrales de frontière à d’autres méthodes numériques (méthode couplée éléments finis / équations intégrales de frontières, méthode intégrale de volume avec une condition impédance de surface)<br>In recent decades, the numerical modelling of electromagnetic devices in the presence of eddy currents has been the subject of a significant number of developments based on different formulations and numerical methods.Among these, integral methods are methods based on the evaluation of remote interactions of active parts via Green's kernels. They thus have the particularity of not requiring the discretization of the air region. In addition to the fact that the number of degrees of freedom to be handled only concerns active regions, these methods show good behaviour in terms of accuracy.The boundary element method is a very competitive numerical method because, unlike volume approaches, it only requires the discretization of the boundary of the domain. However, it is limited to isotropic, homogeneous and linear materials, which is an important limitation. It may still be attractive for some applications where such a hypothesis can be formulated.In this thesis, we will focus on the modeling of the eddy current problem by the method of integral boundary equations subjected to harmonic excitation. This report provides a synthesis of these formulations, including a detailed comparison of the formulations in the literature. Several new formulations are then proposed and developed, with the objective of comparing the integral boundary equations method with other numerical methods (coupled finite element - integral boundary equations method, volume integral method with a surface impedance boundary conditions)
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Wikramanayake, Palitha Nalin. "Turbulent wave-current bottom boundary layer flows." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14353.
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Becker, Thijs, Katherine Nelissen, and Bart Cleuren. "Current fluctuations in boundary driven diffusive systems." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198029.
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Becker, Thijs, Katherine Nelissen, and Bart Cleuren. "Current fluctuations in boundary driven diffusive systems." Diffusion fundamentals 24 (2015) 5, S. 1-2, 2015. https://ul.qucosa.de/id/qucosa%3A14519.
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Johnson, Catherine Lynn. "Dormancy in an eastern boundary current copepod /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3091321.
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Nichols, Claire S. "Evaluation of wave-current bottom boundary layer modelstitle." Connect to this title online, 2005. http://hdl.handle.net/1811/318.
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Thesis (Honors)--Ohio State University, 2005.<br>Title from first page of PDF file. Document formattted into pages: contains x, 62 p.; also includes graphics. Includes bibliographical references (p. 62). Available online via Ohio State University's Knowledge Bank.
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Lee-Thorp, Andrew Michael. "The atmospheric boundary layer above the Agulhas current." Master's thesis, University of Cape Town, 1996. http://hdl.handle.net/11427/19455.
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This thesis describes the atmospheric boundary layer above the Agulhas Current using shipboard meteorological measurements and rawinsonde ascents. The juxtaposition of the warm Agulhas Current and cool shelf waters is shown to have far-reaching effects on the overlying atmosphere. Air-sea fluxes of momentum, sensible and latent heat and resultant boundary layer characteristics demonstrate high horizontal inhomogeneity. The results suggest that this inhomogeneity is permanent. The spatial heat flux gradient is reflected in the overlying atmosphere by a transition in stability of the boundary layer and potential cumulus formation from the cool shelf to the warm current. For airflow perpendicular to the Agulhas Current an internal boundary layer was observed to develop at the inshore sea surface temperature front. Onshore-moving air accumulated a significant quantity of moisture during its trajectory over the current. When airflow is parallel to the current an atmospheric moisture front exists along the axis of the inshore sea surface temperature front. The mean thermodynamic structure of the atmosphere was investigated. An inversion capped the boundary layer whilst a second, higher-level subsidence inversion was found which acts to limit the vertical development of cumulus clouds and therefore the redistribution of heat and moisture above the boundary layer. The results presented in this thesis are useful in two ways. The Agulhas Current has frequently been linked to South African climate. This is the first dedicated study which quantifies and characterizes the atmospheric boundary layer in this region. Secondly, maritime airmasses are dramatically modified above the Agulhas Current. The resultant large horizontal inhomogeneity, its vertical extent and permanence suggest that its inclusion is vital to any successful climate model. Atmospheric general circulation models have been criticized for not taking into account regions of strong horizontal inhomogeneity. The results of this thesis support this argument and highlight the need for similar studies. Bibliography: pages 116-123.
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Waterman, Stephanie N. "Eddy-mean flow interactions in western boundary current jets." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/55330.
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Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2009.<br>Includes bibliographical references (p. 257-264).<br>This thesis examines the nature of eddy-mean flow interactions in western boundary current jets and recirculation gyre dynamics from both theoretical and observational perspectives. It includes theoretical studies of eddy-mean flow interactions in idealized configurations relevant to western boundary current jet systems, namely (i) a study of the mechanism by which eddies generated from a localized forcing drive mean recirculation gyres through the process of nonlinear rectification; and (ii) a study of the role of eddies in the downstream evolution of a baroclinic jet subject to mixed instabilities. It also includes an observational analysis to characterize eddy-mean flow interactions in the Kuroshio Extension using data from the downstream location of maximum eddy kinetic energy in the jet. New insights are presented into a rectification mechanism by which eddies drive the recirculation gyres observed in western boundary current systems. Via this mechanism, eddies drive the recirculations by an up-gradient eddy potential vorticity flux inside a localized region of eddy activity. The effectiveness of the process depends on the properties of the energy radiation from the region, which in turn depends on the population of waves excited. In the zonally-evolving western boundary current jet, eddies also act to stabilize the unstable jet through down-gradient potential vorticity fluxes. In this configuration, the role of eddies depends critically on their downstream location relative to where the unstable time-mean jet first becomes stabilized by the eddy activity. The zonal advection of eddy activity from upstream of this location is fundamental to the mechanism permitting the eddies to drive the mean flows.<br>(cont.) Observational results are presented that provide the first clear evidence of a northern recirculation gyre in the Kuroshio Extension, as well as support for the hypothesis that the recirculations are, at least partially, eddy-driven. Support for the idealized studies' relevance to the oceanic regime is provided both by indications that various model simplifications are appropriate to the observed system, as well as by demonstrated consistencies between model predictions and observational results in the downstream development of time-mean and eddy properties.<br>by Stephanie N. Waterman.<br>Ph.D.
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Zhang, Xuan. "Structure of turbulence in combined wave-current boundary layers." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10057048/.
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This thesis is based on an experimental programme conducted in two laboratory flumes with different scales, to examine the near bed boundary layer under combined surface waves and a turbulent current. Flow conditions have covered a range of wave frequencies and amplitudes, and current conditions. The results give an enhanced understanding of turbulence structures close to the bed in a combined wave-current flow, in terms of coherent vortices and eddy viscosities. A two-dimensional Particle Image Velocimetry system was used to measure the velocity field. Average properties of turbulence characteristics were determined. Hydrogen bubble techniques were employed to provide flow visualisation of the near-wall flow patterns. Results for the unidirectional current are consistent with many previous studies on the existence of coherent vortices. In particular, the measured flow velocity vectors and contours of magnitude demonstrate the presence of low-speed and high-speed streaks in the wall region and bursts in the outer flow. Further quantitative analysis also shows that the characteristic length scales agree well with previous research. For tests with combined wave-current flow, results demonstrate that streamwise vortices are also present. However, the spacing between adjacent low-speed streaks changes periodically within one wave cycle. In addition, measurements also reveal that the maximum Reynolds shear stress induced by ejections is increased when waves are superimposed on the turbulent current. The increase is observed to be more significant for waves with higher frequencies and amplitudes. In order to relate turbulent behaviour with time-averaged velocities in a combined wave-current boundary layer, an eddy viscosity distribution was computed based on experimental results from the flumes and a large oscillating water tunnel from previous tests. These results show a different distribution from those in existing models of wave-current interaction. These results are expected to improve the accuracy on prediction of the hydrodynamics and sediment transport in combined wave-current flows.
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Paolucci, Jonathan David. "NOVEL CURRENT-FED BOUNDARY-MODE PARALLEL-RESONANT PUSH-PULL CONVERTER." DigitalCommons@CalPoly, 2009. https://digitalcommons.calpoly.edu/theses/112.
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The inherent difficulty in designing high voltage power supplies is often compounded by demands of high reliability, high performance, and safe functionality. A proposed high step-up ratio DC-DC converter meets the exacting requirements of applications such as uninterruptible power systems, radar, and pulsed power systems. The proposed DC-DC converter topology combines a multi-phase buck input stage with a novel self-tracking zero-voltage-switching (ZVS) resonant output stage. Traditionally, the inclusion of multiple power processing stages within a power supply topology severely degrades the overall converter efficiency. Due to the inherent high efficiency per stage, however, this effect is minimized. The self-tracking switching scheme ensures that ZVS occurs across the full range of load variation. Furthermore, the switching scheme allows significantly increased flexibility in component tolerances compared to traditional resonant converter designs. The converter also demonstrates indefinite short-circuit protection and true ZVS during transient processes. Computer simulation and hardware analysis verify the efficacy of the topology as a rugged and efficient converter.
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White, Martin George. "The temperature and current structure on the sloping benthic boundary layer." Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315088.
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Santos, Simão Pedro Silva. "Calculus of variations of Herglotz type." Doctoral thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/22503.
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Doutoramento em Matemática<br>We consider several problems based on Herglotz’s generalized variational problem. We dedicate two chapters to extensions on Herglotz’s generalized variational problem to higher-order and first-order problems with time delay, using a variational approach. In the last four chapters, we rewrite Herglotz's type problems in the optimal control form and use an optimal control approach. We prove generalized higher- order Euler-Lagrange equations, first without and then with time delay; higher-order natural boundary conditions; Noether's first theorem for the first-order problem of Herglotz with time delay; Noether's first theorem for higher-order problems of Herglotz without and with time delay; and existence of Noether currents as a version of Noether's second theorem of optimal control.<br>Consideramos vários problemas com base no problema variacional generalizado de Herglotz. Dois capítulos são dedicados à extensão do problema variacional generalizado
de Herglotz para ordem superior e para problemas de primeira ordem com atraso no tempo, utilizando uma abordagem variacional. Nos últimos quatro capítulos, reescrevemos os problemas de Herglotz na forma do controlo ótimo e usamos essa abordagem. Demonstramos equações generalizadas de Euler-Lagrange de ordem superior, inicialmente sem e depois
com atraso no tempo; condições de fronteira de ordem superior; o primeiro teorema de Noether para o problema de Herglotz de primeira ordem com atraso no tempo; o primeiro teorema de Noether para problemas de ordem superior de Herglotz sem e com atraso no tempo; e a existência de leis de conservação de Noether numa versão do segundo teorema de Noether do controlo ótimo.
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Brugler, Eric T. "Interannual variability of the Pacific water boundary current in the Beaufort Sea." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/85389.
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Thesis: S.M., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2013.<br>Includes bibliographical references (pages 133-141).<br>Between 2002 and 2011 a single mooring was maintained in the core of the Pacific Water boundary current in the Alaskan Beaufort Sea near 152° W. Using velocity and hydrographic data from six year-long deployments during this time period, we examine the interannual variability of the current. It is found that the volume, heat, and freshwater transport have all decreased drastically over the decade, by more than 80%. The most striking changes have occurred during the summer months. Using a combination of weather station data, atmospheric reanalysis fields, and concurrent shipboard and mooring data from the Chukchi Sea, we investigate the physical drivers responsible for these changes. It is demonstrated that an increase in summertime easterly winds along the Beaufort slope is the primary reason for the drop in transport. The intensification of the local winds has in turn been driven by a strengthening of the summer Beaufort High in conjunction with a deepening of the summer Aleutian Low. Since the fluxes of mass, heat, and freshwater through Bering Strait have increased over the same time period, this raises the question as to the fate of the Pacific water during recent years and its impacts. We present evidence that more heat has been fluxed directly into the interior basin from Barrow Canyon rather than entering the Beaufort shelfbreak jet, and this is responsible for a significant portion of the increased ice melt in the Pacific sector of the Arctic Ocean.<br>by Eric T. Brugler.<br>S.M.
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Humbyrd, Chelsea Joy. "Turbulent combined wave-current boundary layer model for application in coastal waters." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78234.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 149-153).<br>Accurately predicting transport processes, including sediment transport, in the coastal environment is impossible without correct current velocity and shear stress information. A combined wave-current boundary layer theory is necessary to predict these quantities, and while the previous Grant-Madsen type boundary layer models are effective, they inconsistently apply a discontinuous two layer eddy viscosity structure to the wave and current problems. We have therefore developed a new continuous three layer model which consistently applies all three layers and leads to a strong coupling between the wave and current solutions. Boundary layer models require an estimate of the movable bed roughness, and while this roughness is scaled by the sand grain diameter for flat beds, in the coastal environment it is often the case that either wave-generated ripples cover the bed or the near-bed sediment is transported as sheet flow, in which case the roughness is much larger and less straightforward to characterize. The common method of predicting roughness in the ripple regime, while effective, unnecessarily predicts ripple geometry and requires a model-dependent factor, which varies widely, relating ripple geometry and bottom roughness. We have therefore developed an alternative, more direct method of predicting bed roughness: the wave energy dissipation factor is predicted from flow and sediment information and then any desired theoretical friction factor model is used to back-calculate the roughness. This proposed method can also be used in the sheet flow regime, allowing a continuous transition between the two regimes, not possible with the common method. This thesis derives the new three layer combined wave-current boundary layer theory, develops the common and proposed methods of predicting roughness in the ripple and sheet flow regimes, and presents results of evaluating the theory and methods with field data. The new theory combined with either roughness method successfully predicts current shear velocities in wave-current field flows over beds in the lower flat-bed, ripple, and sheet flow regimes, with the proposed method yielding the smaller bias. Remaining questions concerning the appropriate near-bottom orbital velocity required to describe field conditions must be resolved when additional field data becomes available.<br>by Chelsea Joy Humbyrd.<br>S.M.