Literatura científica selecionada sobre o tema "Ocean ventilation"
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Artigos de revistas sobre o assunto "Ocean ventilation"
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Primeau, François W., e Mark Holzer. "The Ocean’s Memory of the Atmosphere: Residence-Time and Ventilation-Rate Distributions of Water Masses". Journal of Physical Oceanography 36, n.º 7 (1 de julho de 2006): 1439–56. http://dx.doi.org/10.1175/jpo2919.1.
Texto completo da fonteResumo:
Abstract A conceptually new approach to diagnosing tracer-independent ventilation rates is developed. Tracer Green functions are exploited to partition ventilation rates according to the ventilated fluid’s residence time in the ocean interior and according to where this fluid enters and exits the interior. In the presence of mixing by mesoscale eddies, which are reasonably represented by diffusion, ventilation rates for overlapping entry and exit regions cannot meaningfully be characterized by a single rate. It is a physical consequence of diffusive transport that fluid elements that spend an infinitesimally short time in the interior cause singularly large ventilation rates for overlapping entry and exit regions. Therefore, ventilation must generally be characterized by a ventilation-rate distribution, ϕ, partitioned according to the time that the ventilated fluid spends in the interior between successive surface contacts. An offline forward and adjoint time-averaged OGCM is used to illustrate the rich detail that ϕ and the closely related probability density function of residence times ℛ provide on the way the ocean communicates with the surface. These diagnostics quantify the relative importance of various surface regions for ventilating the interior ocean by either exposing old water masses to the atmosphere or by forming newly ventilated ones. The model results suggest that the Southern Ocean plays a dominant role in ventilating the ocean, both as a region where new waters are ventilated into the interior and where old waters are first reexposed to the atmosphere.
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Bopp, L., L. Resplandy, A. Untersee, P. Le Mezo e M. Kageyama. "Ocean (de)oxygenation from the Last Glacial Maximum to the twenty-first century: insights from Earth System models". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, n.º 2102 (7 de agosto de 2017): 20160323. http://dx.doi.org/10.1098/rsta.2016.0323.
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All Earth System models project a consistent decrease in the oxygen content of oceans for the coming decades because of ocean warming, reduced ventilation and increased stratification. But large uncertainties for these future projections of ocean deoxygenation remain for the subsurface tropical oceans where the major oxygen minimum zones are located. Here, we combine global warming projections, model-based estimates of natural short-term variability, as well as data and model estimates of the Last Glacial Maximum (LGM) ocean oxygenation to gain some insights into the major mechanisms of oxygenation changes across these different time scales. We show that the primary uncertainty on future ocean deoxygenation in the subsurface tropical oceans is in fact controlled by a robust compensation between decreasing oxygen saturation (O 2sat ) due to warming and decreasing apparent oxygen utilization (AOU) due to increased ventilation of the corresponding water masses. Modelled short-term natural variability in subsurface oxygen levels also reveals a compensation between O 2sat and AOU, controlled by the latter. Finally, using a model simulation of the LGM, reproducing data-based reconstructions of past ocean (de)oxygenation, we show that the deoxygenation trend of the subsurface ocean during deglaciation was controlled by a combination of warming-induced decreasing O 2sat and increasing AOU driven by a reduced ventilation of tropical subsurface waters. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.
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Naveira Garabato, Alberto C., Graeme A. MacGilchrist, Peter J. Brown, D. Gwyn Evans, Andrew J. S. Meijers e Jan D. Zika. "High-latitude ocean ventilation and its role in Earth's climate transitions". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, n.º 2102 (7 de agosto de 2017): 20160324. http://dx.doi.org/10.1098/rsta.2016.0324.
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The processes regulating ocean ventilation at high latitudes are re-examined based on a range of observations spanning all scales of ocean circulation, from the centimetre scales of turbulence to the basin scales of gyres. It is argued that high-latitude ocean ventilation is controlled by mechanisms that differ in fundamental ways from those that set the overturning circulation. This is contrary to the assumption of broad equivalence between the two that is commonly adopted in interpreting the role of the high-latitude oceans in Earth's climate transitions. Illustrations of how recognizing this distinction may change our view of the ocean's role in the climate system are offered. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.
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Katavouta, Anna, e Richard G. Williams. "Ocean carbon cycle feedbacks in CMIP6 models: contributions from different basins". Biogeosciences 18, n.º 10 (27 de maio de 2021): 3189–218. http://dx.doi.org/10.5194/bg-18-3189-2021.
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Abstract. The ocean response to carbon emissions involves the combined effect of an increase in atmospheric CO2, acting to enhance the ocean carbon storage, and climate change, acting to decrease the ocean carbon storage. This ocean response can be characterised in terms of a carbon–concentration feedback and a carbon–climate feedback. The contribution from different ocean basins to these feedbacks on centennial timescales is explored using diagnostics of ocean carbonate chemistry, physical ventilation and biological processes in 11 CMIP6 Earth system models. To gain mechanistic insight, the dependence of these feedbacks on the Atlantic Meridional Overturning Circulation (AMOC) is also investigated in an idealised climate model and the CMIP6 models. For the carbon–concentration feedback, the Atlantic, Pacific and Southern oceans provide comparable contributions when estimated in terms of the volume-integrated carbon storage. This large contribution from the Atlantic Ocean relative to its size is due to strong local physical ventilation and an influx of carbon transported from the Southern Ocean. The Southern Ocean has large anthropogenic carbon uptake from the atmosphere, but its contribution to the carbon storage is relatively small due to large carbon transport to the other basins. For the carbon–climate feedback estimated in terms of carbon storage, the Atlantic and Arctic oceans provide the largest contributions relative to their size. In the Atlantic, this large contribution is primarily due to climate change acting to reduce the physical ventilation. In the Arctic, this large contribution is associated with a large warming per unit volume. The Southern Ocean provides a relatively small contribution to the carbon–climate feedback, due to competition between the climate effects of a decrease in solubility and physical ventilation and an increase in accumulation of regenerated carbon. The more poorly ventilated Indo-Pacific Ocean provides a small contribution to the carbon cycle feedbacks relative to its size. In the Atlantic Ocean, the carbon cycle feedbacks strongly depend on the AMOC strength and its weakening with warming. In the Arctic, there is a moderate correlation between the AMOC weakening and the carbon–climate feedback that is related to changes in carbonate chemistry. In the Pacific, Indian and Southern oceans, there is no clear correlation between the AMOC and the carbon cycle feedbacks, suggesting that other processes control the ocean ventilation and carbon storage there.
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Sallée, Jean-Baptiste, Kevin Speer, Steve Rintoul e S. Wijffels. "Southern Ocean Thermocline Ventilation". Journal of Physical Oceanography 40, n.º 3 (1 de março de 2010): 509–29. http://dx.doi.org/10.1175/2009jpo4291.1.
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Abstract An approximate mass (volume) budget in the surface layer of the Southern Ocean is used to investigate the intensity and regional variability of the ventilation process, discussed here in terms of subduction and upwelling. Ventilation resulting from Ekman pumping is estimated from satellite winds, the geostrophic mean component is assessed from a climatology strengthened with Argo data, and the eddy-induced advection is included via the parameterization of Gent and McWilliams, together with eddy mixing estimates. All three components contribute significantly to ventilation. Finally, the seasonal cycle of the upper ocean is resolved using Argo data. The circumpolar-averaged circulation shows an upwelling in the Antarctic Intermediate Water (AAIW) density classes, which is carried north into a zone of dense Subantarctic Mode Water (SAMW) subduction. Although no consistent net production is found in the light SAMW density classes, a large subduction of Subtropical Mode Water (STMW) is observed. The STMW area is fed by convergence of a southward and a northward residual meridional circulation. The eddy-induced contribution is important for the water mass transport in the vicinity of the Antartic Circumpolar Current. It balances the horizontal northward Ekman transport as well as the vertical Ekman pumping. While the circumpolar-averaged upper cell structure is consistent with the average surface fluxes, it hides strong longitudinal regional variations and does not represent any local regime. Subduction shows strong regional variability with bathymetrically constrained hotspots of large subduction. These hotspots are consistent with the interior potential vorticity structure and circulation in the thermocline. Pools of SAMW and AAIW of different densities are found along the circumpolar belt in association with the regional pattern of subduction and interior circulation.
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Thiele, G., e J. L. Sarmiento. "Tracer dating and ocean ventilation". Journal of Geophysical Research 95, n.º C6 (1990): 9377. http://dx.doi.org/10.1029/jc095ic06p09377.
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Shepherd, John G., Peter G. Brewer, Andreas Oschlies e Andrew J. Watson. "Ocean ventilation and deoxygenation in a warming world: introduction and overview". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, n.º 2102 (7 de agosto de 2017): 20170240. http://dx.doi.org/10.1098/rsta.2017.0240.
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Changes of ocean ventilation rates and deoxygenation are two of the less obvious but important indirect impacts expected as a result of climate change on the oceans. They are expected to occur because of (i) the effects of increased stratification on ocean circulation and hence its ventilation, due to reduced upwelling, deep-water formation and turbulent mixing, (ii) reduced oxygenation through decreased oxygen solubility at higher surface temperature, and (iii) the effects of warming on biological production, respiration and remineralization. The potential socio-economic consequences of reduced oxygen levels on fisheries and ecosystems may be far-reaching and significant. At a Royal Society Discussion Meeting convened to discuss these matters, 12 oral presentations and 23 posters were presented, covering a wide range of the physical, chemical and biological aspects of the issue. Overall, it appears that there are still considerable discrepancies between the observations and model simulations of the relevant processes. Our current understanding of both the causes and consequences of reduced oxygen in the ocean, and our ability to represent them in models are therefore inadequate, and the reasons for this remain unclear. It is too early to say whether or not the socio-economic consequences are likely to be serious. However, the consequences are ecologically, biogeochemically and climatically potentially very significant, and further research on these indirect impacts of climate change via reduced ventilation and oxygenation of the oceans should be accorded a high priority. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.
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Mecking, Sabine, e Kyla Drushka. "Linking northeastern North Pacific oxygen changes to upstream surface outcrop variations". Biogeosciences 21, n.º 5 (7 de março de 2024): 1117–33. http://dx.doi.org/10.5194/bg-21-1117-2024.
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Abstract. Understanding the response of the ocean to global warming, including the renewal of ocean waters from the surface (ventilation), is important for future climate predictions. Oxygen distributions in the ocean thermocline have proven an effective way to infer changes in ventilation because physical processes (ventilation and circulation) that supply oxygen are thought to be primarily responsible for changes in interior oxygen concentrations. Here, the focus is on the North Pacific thermocline, where some of the world's oceans' largest oxygen variations have been observed. These variations, described as bi-decadal cycles on top of a small declining trend, are strongest on subsurface isopycnals that outcrop into the mixed layer of the northwestern North Pacific in late winter. In this study, surface density time series are reconstructed in this area using observational data only and focusing on the time period from 1982, the first full year of the satellite sea surface temperature record, to 2020. It is found that changes in the annual maximum outcrop area of the densest isopycnals outcropping in the northwestern North Pacific are correlated with interannual oxygen variability observed at Ocean Station P (OSP) downstream at about a 10-year lag. The hypothesis is that ocean ventilation and uptake of oxygen is greatly reduced when the outcrop areas are small and that this signal travels within the North Pacific Current to OSP, with 10 years being at the higher end of transit times reported in other studies. It is also found that sea surface salinity (SSS) dominates over sea surface temperature (SST) in driving interannual fluctuations in annual maximum surface density in the northwestern North Pacific, highlighting the role that salinity may play in altering ocean ventilation. In contrast, SSS and SST contribute about equally to the long-term declining surface density trends that are superimposed on the interannual cycles.
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Jones, C. S., e Ryan P. Abernathey. "Isopycnal Mixing Controls Deep Ocean Ventilation". Geophysical Research Letters 46, n.º 22 (16 de novembro de 2019): 13144–51. http://dx.doi.org/10.1029/2019gl085208.
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Schiffbauer, James D., e Natalia Bykova. "Paleontology: Ediacaran ecology drove ocean ventilation". Current Biology 34, n.º 15 (agosto de 2024): R734—R736. http://dx.doi.org/10.1016/j.cub.2024.06.043.
Texto completo da fonteTeses / dissertações sobre o assunto "Ocean ventilation"
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MacGilchrist, Graeme. "Lagrangian perspectives on ocean ventilation". Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:de6c14b7-a55c-44e7-8c2b-2f94a601ab8e.
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Within the global climate system, the ocean operates as a vast store of important components such as heat and carbon dioxide that it exchanges with the atmosphere on timescales from days to millennia. Its facility to do so is in large part due to the process of ocean ventilation by which water is moved from the surface mixed layer, where it is in contact with the atmosphere, and transported through the subsurface. An understanding of ocean ventilation, therefore, is crucial in establishing the magnitudes and timescales of ocean-atmosphere exchange. In this thesis, a predominantly Lagrangian approach is adopted, evaluating trajectories in an eddy-permitting numerical ocean circulation model to explore different aspects of the ventilation process. Following critical assessment of the fidelity of the trajectory analysis, a dynamical systems approach is applied to assess the role of ocean turbulence in the transport of ventilated water in the subsurface, with application to the subtropical gyre of the North Atlantic. The pathways of ventilation, represented by Lagrangian maps, are found to be highly chaotic and characterised by a non-dimensional filamentation number that compares the ventilation and filamentation timescales of the flow. Subsequently, the mechanisms and variability of ventilation of dense water masses in the high-latitude North Atlantic are considered, a crucial component in present-day oceanic uptake of heat and carbon dioxide. A Lagrangian approach allows us to link surface processes to their subsurface signature, and reveals that variations in annual re-entrainment establish substantial inter-annual variability in the water that enters the deep ocean. Furthermore, the results reveal that mechanisms of ventilation in the numerical simulation differ substantially from observations, with possible implications for the fidelity of future climate projections. Finally, the translation into the ocean interior of a biologically and chemically active tracer, such as carbon dioxide, is considered, and how this is dependent on the interaction between ventilation, circulation and biogeochemical processes. From observations in the Weddell Gyre, it is shown that biological export and the horizontal circulation are critical in sustaining regional uptake of carbon dioxide from the atmosphere. Broadly, these various results serve to emphasise the complexity of the ventilation process and its associated role in the oceanic storage of climate-relevant components, from the chaotic nature of pathways, short timescales of variability, its difficulty of representation in numerical models, and its interaction with the biogeochemical system.
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Millet, Bruno. "Tracer and model constraints on the ventilation of the deep Pacific Ocean". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASJ019.
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L'océan Pacifique représente environ 50% du volume global des océans, ce qui en fait un acteur essentiel des cycles biogéochimiques globaux et de leur réponse aux perturbations. En particulier, l'océan Pacifique profond abrite des réservoirs majeurs de carbone et de nutriments, dont la taille et les variations sont largement contrôlées par les transports physiques de traceurs. Dans cette thèse, nous visons à mieux comprendre et contraindre le transport de traceurs dans l'océan Pacifique profond à travers les états climatiques. Pour cela, nous générons de nouvelles et utilisons d'anciennes observations de traceurs conservatifs, notamment les isotopes de l'oxygène, ainsi que des modèles numériques de circulation océanique. Nous montrons que le mélange isopycnale a un contrôle essentiel sur la ventilation des profondeurs moyennes du Pacifique. Un retour des eaux abyssales vers la surface est identifié dans le Pacifique subarctique moderne. Cette voie de remontée semble avoir diminué pendant le dernier maximum glaciaire, il y a environ 20 000 ans, et le Pacifique Nord profond pourrait avoir été plus fortement stratifié. Cependant, les preuves de changements nécessaires dans le sud du bassin pour expliquer cette stratification profonde restent rares. Les modèles de pointe de circulation océanique peinent à représenter les trajectoires des traceurs et les vitesses de ventilation dans le Pacifique Nord moderne, déduites des observations. Cependant, ces trajets de traceurs restent insuffisamment contraints et la dynamique sous-jacente est mal comprise. L'analyse des mesures in situ du rapport isotopique de l'oxygène 18 (18O) de l'eau de mer constitue un moyen efficace pour mieux contraindre les origines et les itinéraires des traceurs dans l'océan profond : les observations actuelles de 18O dans les océans Austral, Indien et Pacifique permettent de mieux comprendre ces itinéraires. Nous suggérons que des mesures supplémentaires de 18O à partir d'échantillons d'eau de mer modernes et de coquilles de calcite dans les carottes de sédiments fourniraient des contraintes précieuses sur les réservoirs et les flux de traceurs actuels et passés dans l'océan profondThe Pacific Ocean represents about 50% of the global ocean volume, making it an essential player in global biogeochemical cycles and their response to external perturbations. In particular, the deep Pacific Ocean hosts major reservoirs of carbon and nutrients, whose size and variations are largely controlled by physical tracer transports. In this thesis, we aim to better understand and constrain the transport of tracers in the deep Pacific Ocean across climate states. We use historical and new observations of conservative tracers, notably oxygen isotopes, combined with numerical models of ocean circulation. We show that isopycnal mixing is an essential control of the ventilation of Pacific mid-depths. A return of abyssal waters to the surface is identified in the modern subarctic Pacific. This upwelling pathway may have been weaker during the Last Glacial Maximum about 20,000 years ago, and the deep North Pacific may have been more strongly layered; however, evidence for the required end member changes in the south of the basin to explain this deep layering remains sparse. State-of-the-art prognostic models of global ocean circulation struggle to represent observationally inferred tracer pathways and turn-over times in the modern North Pacific. However, these tracer pathways remain insufficiently constrained and the underlying dynamics are poorly understood. Analysis of in-situ measurements of the oxygen-18 (18O) isotopic ratio of seawater provides an efficient means to better constrain the origins and routes of tracers in the deep ocean: insights on these routes are derived from existing 18O observations in the Southern, Indian, and Pacific Oceans. We suggest that additional measurements of 18O from modern ocean water samples, and from calcite shells in sediment cores, would provide valuable constraints on present-day and past tracer reservoirs and fluxes in the deep ocean
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Zhao, Ning Ph D. Massachusetts Institute of Technology. "Reconstructing deglacial ocean ventilation using radiocarbon : data and inverse modeling". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108960.
Texto completo da fonteResumo:
Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 137-149).
Significant changes occurred during the last deglaciation (roughly 10-20 thousand years (ka) before present) throughout the climate system. The ocean is a large reservoir of carbon and heat, however, its role during the deglaciation is still not well understood. In this thesis, I rely on radiocarbon measurements on fossil biogenic carbonates sampled from the seafloor to constrain deglacial ocean ventilation rates, using new data, an extensive data compilation, and inverse modeling. First, based on a sediment core that is absolutely dated from wooden remains, I argue that the deglacial ¹⁴C reservoir age of the upper East Equatorial Pacific was not very different from today. Combined with stable carbon isotope data, the results suggest that the deglacial atmospheric CO₂ rise was probably due to CO₂ released directly from the ocean (e.g., in the Southern Ocean) to the atmosphere rather than first mixed through the upper ocean. Then using a high-deposition-rate sediment core located close to deep water formation regions in the western North Atlantic, I show that compared to today, the mid-depth water production in the North Atlantic was probably stronger during the Younger Dryas cold episode, and weaker during other intervals of the late deglaciation. However, the change was not as large as suggested by previous studies. Finally, I compile published and unpublished deep ocean ¹⁴C data, and find that the ¹⁴C activity of the deep ocean mirrors that of the atmosphere during the past 25 ka. A box model of modern ocean circulation is fit to the compiled data using an inverse method. I find that the residuals of the fit can generally be explained by the data uncertainties, implying that the compiled data jointly do not provide strong evidence for basin-scale ventilation changes. Overall, this thesis suggests that, although deep ocean ventilation may have varied at some locations during the last deglaciation, the occurrence of basin-scale ventilation changes are much more difficult to be put on a firm footing. An imbalance between cosmogenic production and radioactive decay appears as the most natural explanation for the deglacial ¹⁴C activity decline observed in both the atmosphere and the deep ocean.
by Ning Zhao.
Ph. D.
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Stöven, Tim [Verfasser]. "Ocean ventilation and anthropogenic carbon based on evaluated transient tracer applications / Tim Stöven". Kiel : Universitätsbibliothek Kiel, 2015. http://d-nb.info/107440470X/34.
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Chandana, K. R., Ravi Bhushan e A. J. T. Jull. "Evidence of Poor Bottom Water Ventilation during LGM in the Equatorial Indian Ocean". FRONTIERS MEDIA SA, 2017. http://hdl.handle.net/10150/626606.
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Multi-proxy approach for the reconstruction of paleo-redox conditions is attempted on a radiocarbon (C-14) dated sediment core near the equatorial Indian Ocean. Based on the behavior and distribution of redox sensitive and productivity proxies, study demonstrates prevalence of anoxic bottom water conditions during LGM due to poorly ventilated bottom waters augmented by high surface productivity resulting in better preservation of organic carbon (OC). During early Holocene, the equatorial Indian Ocean witnessed high sedimentation rates resulting in high organic carbon (OC) with depleted redox sensitive elements thereby causing better preservation of OC. The study underscores poor bottom water ventilation during LGM and preservation of OC as a result of high sedimentation rate in early Holocene.
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Radwan, Jean. "Contribution à la mise au point d'une technique de mesure du Kr85 dans l'océan : étude et réalisation d'un système d'extraction, de séparation et de mesure du Krypton total dissous". Paris 6, 1986. http://www.theses.fr/1986PA066529.
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Le Kr85 est un isotope radioactif produit par l'industrie nucléaire. Sa qualité de gaz rare, sa période de 10. 76 ans, son histoire atmosphérique bien documentée et sa fonction d'entrée dans l'océan raisonnablement connue en font un traceur océanographique intéressant pour l'étude de la dynamique océanique à des échelles de temps de quelques années à quelques décennies (formation des eaux profondes, ventilation de la thermocline). Du fait de la faible activité spécifique du Kr85 (quelques dpm/m3 d'eau) la mesure de cet isotope exige des moyens de prélèvement lourds (200 l d'eau par échantillon) et une procédure analytique en plusieurs étapes : le dégazage "in situ" de grandes quantités d'eau de mer. De 3 à 4 l d'air dissous, dont 15 mu de Kr, sont récupérables à partir d'échantillons de 200 l d'eau de mer; la séparation quantitative du krypton total (15 mu l pour 4 l d'air) de l'échantillon gazeux conditionné en mer; le comptage du programme indigo (indian gas ocean) (1983) avec 3 campagnes dans l'océan indien de 1985 à 1987, notre laboratoire s'est doté de moyens de prélèvements lourds et a décidé de développer sa propre technologie de mesure du Kr85 océanique. Le travail que nous présentons concerne les deux premières étapes, désormais acquises de l'analyse du Kr85 océanique : nous avons étudié et réalisé une installation embarquable et fiable de dégazage sous vide capable d'extraire, sous un débit de 8 l/mn, les gaz dissous dans des échantillons de 200 l d'eau de mer. Cette unité d'extraction a permis le dégazage de 160 échantillons d'eau de mer (campagne indigo 1 et 2), avec un rendement > 91% (comparable aux résultats de Smethie, et un taux de contamination par du Kr atmosphérique de l'ordre de 0,05%. Parallèlement à la préparation logistique de ces campagnes, nous avons conçu et réalisé une installation de séparation qui permet de récupérer quantitativement le Kr total de l'échantillon océanique par une série d'élutions fractionnées sur charbon actif, suivie de la purification définitive et de la mesure du Kr par chromatographie en phase gazeuse. Seuls 4% des 15 mu l de Kr attendus (pour 4 l d'air) sont perdus.
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Neale, James Richard Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Experimental and numerical investigation of noise generation from the expansion of high velocity HVAC flows on board ocean going fast ferries". Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2006. http://handle.unsw.edu.au/1959.4/28371.
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This thesis details a study of strategies used to limit the flow generated noise encountered in the outlet diffusers of high velocity heating, ventilation and air conditioning (HVAC) duct systems. The underlying noise rating criterion is drawn from the specifications covering ocean going aluminium fast ferries. Although directed primarily towards the fast ferry industry the results presented herein are applicable to other niche high velocity HVAC applications. Experimental tests have been conducted to prove the viability of a high velocity HVAC duct system in meeting airflow requirements whilst maintaining acceptable passenger cabin noise levels. A 50 mm diameter circular jet of air was expanded using a primary conical diffuser with a variety of secondary outlet configurations. Noise measurements were taken across a velocity range of 15 to 60 m/s. An optimum outlet design has been experimentally identified by varying the diffuser angle, outlet duct length and the termination grill. A 4 to 5 fold reduction in required duct area was achieved with the use of a distribution velocity of 20 to 30 ms-1, without exceeding the prescribed passenger cabin noise criteria. The geometric configuration of the diffuser outlet assembly was found to have a pronounced effect on the noise spectrum radiating from the duct outlet. The development of a numerical model capable of predicting the flow induced noise generated by airflow exiting a ventilation duct is also documented. The model employs a Large Eddy Simulation (LES) CFD model to calculate the turbulent flow field through the duct diffuser section and outlet. The flow-generated noise is then calculated using a far field acoustic postprocessor based on the Ffowcs-Williams and Hawkings integral based formulation of Lighthill???s acoustic analogy. Time varying flow field variables are used to calculate the fluctuating noise sources located at the duct outlet and the resulting far field sound pressure levels. This result is then used to calculate the corresponding far field sound intensity and sound power levels. The numerical acoustic model has been verified and validated against the measured experimental results for multiple outlet diffuser configurations.
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Vergara, Oscar. "Ventilation de la circulation océanique dans le Pacifique sud-est par les ondes de Rossby et l'activité méso-échelle : téléconnexions d'ENSO". Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30356/document.
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L'objectif principal de cette thèse est l'étude de la connexion entre la variabilité dans l'océan Pacifique équatorial et la circulation de subsurface le long des côtes du Pérou et du Chili, à des échelles de temps interannuelles à décennales. Les diagnostiques menés dans ce travail se basent sur un modèle régional océanique. L'accent est mis sur l'interprétation de la propagation verticale de la variabilité dans les couches intermédiaires de l'océan, où l'on trouve une intense zone de minimum d'oxygène (OMZ ; de l'anglais Oxygen Minimum Zone), et la relation de cette propagation verticale avec les processus advectifs et diffusifs. La propagation verticale est diagnostiquée à travers le flux vertical d'énergie associé à la propagation verticale de l'onde de Rossby extratropicale (ETRW; de l'anglais Extra-Tropical Rossby Wave). Aux échelles de temps interannuelles, les résultats montrent que 80% du flux vertical d'énergie dans l'océan Pacifique Sud-Est (SEP ; de l'anglais South-Eastern Pacific) est associé aux événements El Niño extraordinaires. Ce flux d'énergie s'étend vers l'Ouest en suivant les rayons théoriques WKB, avec une pente plus prononcée au fur et à mesure que la latitude augmente. Les analyses du flux d'énergie mettent aussi en évidence l'existence d'une modulation du flux d'énergie interannuel à l'échelle décennale, qui serait liée aux fluctuations décennales et inter-décennales dans le Pacifique équatorial. Une décomposition de la stratification en modes verticaux montre que le flux d'énergie associé à El Niño et aux fluctuations décennales se projette sur les trois premiers modes baroclines, ce qui confirme l'interprétation du flux d'énergie comme la propagation de l'onde de Rossby. Des tests de sensibilité menés avec un modèle linéaire ajusté aux conditions de la simulation montrent que la propagation d'énergie verticale pendant les événements El Niño est aussi impactée par la contribution des modes baroclines supérieurs. La variabilité méridienne/verticale du flux d'énergie vertical met en évidence une atténuation de l'amplitude le long de la trajectoire de l'onde, ce qui est interprété comme un flux diffusif de chaleur induit par la dissipation de l'onde. La variabilité de subsurface de la circulation à l'échelle saisonnière est aussi étudiée dans cette région à travers la ventilation de l'OMZ. Les résultats montrent que la variabilité saisonnière de l'OMZ en dessous de 400 m de profondeur possède des caractéristiques de propagation similaires à celles du flux d'énergie associé à l'ETRW annuelle, ce qui indique que l'ETRWpourrait influencer la variabilité de l'OMZ profonde, du moins à l'échelle saisonnière. Au-dessus de 400 m de profondeur, le processus dominant qui influence la ventilation de l'OMZ à l'échelle saisonnière est le transport d'oxygène par les tourbillons de méso-échelle. Dans ce travail, nous mettons en évidence la nature complexe de la variabilité de la circulation de subsurface dans le SEP. Nous montrons en particulier la connexion entre la circulation sous la thermocline extratropicale et les modes climatiques de variabilité du Pacifique équatorialThe oceanic circulation in the subthermocline of the South Eastern Pacific remains poorly documented although this region is thought to play a key role in the climate variability owed to, in particular, the presence of an extended oxygen minimum zone (OMZ) that intervenes in the carbon and nitrogen cycle. The subthermocline in this region is also largely unmonitored and historical estimates of ocean heat content are mostly limited to the upper 500 m. In this thesis we document various oceanic processes at work in the subthermocline based on a regional modeling approach that is designed to take in account the efficient oceanic teleconnection from the equatorial region to the mid-latitudes, in particular at ENSO (El Niño Southern Oscillation) timescales. The focus is on two aspects: (1) the seasonality of the turbulent flow and its role in modulating the OMZ volume off Peru, and (2) the planetary wave fluxes associated with interannual to decadal timescales. It is first shown that the vertical energy flux at interannual timescales can be interpreted as resulting from the vertical propagation of extra-tropical Rossby waves remotely forced from the equatorial region. This flux primarily results from extreme Eastern Pacific El Niño events, despite that a significant fraction of interannual Sea Surface Temperature (SST) variability in the tropical Pacific is also associated with Central Pacific El Niño events and La Niña events. Vertically propagating energy flux at decadal timescales is also evidenced in the model, which, like for the interannual flux, is marginally impacted by mesoscale activity. On the other hand, the wave energy beams experience a marked dissipation in the deep-ocean ( 2000 m) which is interpreted as resulting from vertical diffusivity. While the oxygen field within the OMZ appears to be influenced by the vertical propagation of isopycnals height anomalies, induced by the seasonal Rossby waves, the seasonality of the OMZ is shown to be dominantly associated with the seasonal change in the eddy flux at its boundaries. Implications of the results for the study of both the low-frequency variability of the OMZ and the Earth's energy budget are discussed
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Akhoudas, Camille. "Un nouveau regard sur la dynamique de l’océan Austral et ses interactions avec la cryosphère révélé par une approche isotopique". Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS464.
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L’océan Austral est un acteur central de la circulation océanique mondiale et du système climatique terrestre. Malgré l’essor des observations in situ dans cette région reculée du globe depuis les années 1990 (avec notamment le début de « l’ère satellitaire » et des grands programmes internationaux d’observations tel que WOCE, CLIVAR, GO-SHIP, ou ARGO), ce vaste océan reste encore aujourd’hui largement méconnu. Il est pourtant nécessaire de parvenir à mieux observer et comprendre les mécanismes de sa dynamique océanique ainsi que sa variabilité afin de prédire au mieux l’évolution future du système climatique. Notamment, une des particularités qui rend l’océan Austral essentiel dans le système climatique est qu’il est l’un des principaux lieux de ventilation de l’océan profond, qui permet une redistribution et un stockage de chaleur, d’eau douce, de carbone, d’oxygène, et de nutriments, entre autres. Cette ventilation est en partie dirigée par une circulation verticale unique connectant la surface aux abysses océaniques, mise en mouvement par les intenses interactions et échanges de flux d’énergie et de flottabilité entre atmosphère, océan et cryosphère. Je me penche dans cette thèse sur certains aspects de la dynamique australe en m’efforçant d’apporter une vue mécanistique de la circulation grande échelle et des changements en cours. Un fil rouge méthodologique que j’emploie sur l’ensemble de cette thèse est l’utilisation d’observations des isotopes stables de l’eau, traceur passif utilisé couramment dans un grand nombre de disciplines des sciences de la terre, mais jusque récemment assez peu en océanographie physique. La mesure des isotopes de l’eau constitue un outil, qui en tant que traceurs de l’origine de l’eau, permet de mieux caractériser les différentes composantes du cycle hydrologique ainsi que son évolution. En particulier, la composition isotopique de l’eau de mer représente une empreinte importante des masses d’eau, contenant des informations sur les conditions de leur formation et leur évolution. Dans cette thèse, au-delà du travail méthodologique important sur le terrain et en laboratoire pour l’échantillonnage, l’analyse et la calibration des mesures isotopiques, j’utilise les isotopes de l’eau en combinaison avec d’autres traceurs plus conventionnels pour aborder avec un nouveau regard, les questions du rôle des interactions entre océan et calotte polaire à la circulation grande échelle, de la signature des eaux de surface dans les abysses, ou encore de l’impact des changements de régimes atmosphériques ou de fonte de la cryosphère sur l’océan de surface. Au-delà de la seule utilisation des isotopes stables de l’eau, les approches que j’ai mises en place m’ont permis de documenter la quantité de fonte et de regel d’une des plus grandes cavités glaciaires au monde, qui influence les caractéristiques des masses d’eau denses, précurseurs des eaux abyssales se formant en mer de Weddell. Mes résultats mettent également à jour la proportion que représente, in fine, ces eaux denses dans la production des eaux abyssales dans le secteur Atlantique de l’océan Austral. Je détaille les processus qui mènent à la formation des eaux abyssales et avec cette nouvelle force, je montre que des estimations passées de la production d’eaux abyssales en apparente contradiction, s’attaquaient en réalité à différents processus. Finalement, je quantifie les changements des apports en eau douce lors des trois dernières décennies sur les tendances des propriétés de surface dans le secteur Indien de l’océan Austral. Mes résultats démontrent que des changements dans le régime des précipitations expliquent les changements des caractéristiques de l’océan surface affectant la stratification avec des conséquences sur la formation des masses d’eau et la circulation de retournement de l’océan Austral à grande échelleThe Southern Ocean is a key component in global ocean circulation and the Earth's climate system. Despite the increase of in situ observations in this remote region since the 1990s (notably with the « satellite era » and major international observation programs such as WOCE, CLIVAR, GO-SHIP, or ARGO), this immense ocean remains largely unknown. However, it is essential to observe and understand the mechanisms of its dynamics as well as its variability with the aim to predict the future evolution of the climate system. In particular, one important characteristic of the Southern Ocean is that it is one of the main sites of deep ocean ventilation, which allows redistribution and sequestration of heat, freshwater, carbon, oxygen, and nutrients. This ventilation process is mainly associated with a vertical circulation connecting the ocean surface to the abyss, fueled by intense interactions and exchanges of energy and buoyancy fluxes between atmosphere, ocean and cryosphere. In this thesis, I apprehend some aspects of the Southern Ocean dynamics by providing a mechanistic view of large-scale circulation and its ongoing changes. The approach I use throughout this thesis is based on observations of stable water isotopes, a passive tracer commonly used in a large number of earth science disciplines, but until recently only sparsely used in physical oceanography. Stable water isotopes constitute a robust tool which, as a tracer of the origin of water, help to better characterize the different components of the hydrological cycle as well as its evolution. In particular, the isotopic composition of seawater represents an important imprint of water masses, containing information on the conditions of their formation and their evolution. In this thesis, beyond the important methodological work at sea and in the laboratory for the sampling, analysis and calibration of isotopic measurements, I use the stable water isotopes in combination with other more conventional tracers to apprehend, with a new perspective, the questions of the role of interactions between the Southern Ocean and the Antarctic Ice Sheet in large-scale circulation, the signature of surface waters in the abyss, or even the impact of changes in atmospheric or cryosphere regimes on the surface ocean. Beyond the only use of stable water isotopes, original approaches have allowed me to document melting and refreezing of one of the largest ice shelves in the world, which influences the characteristics of the dense waters, precursors of abyssal waters produced in the Weddell Sea. My results also reveal the proportion of these dense waters in bottom water formation in the Atlantic sector of the Southern Ocean. We detail the processes that lead to the formation of bottom waters and with this new insight, we demonstrate that past estimates of bottom water production, in apparent contradiction, were actually focusing on different processes. Finally, I propose to quantify the changes in freshwater inputs over the past three decades that influence the trends in surface properties in the Indian sector of the Southern Ocean. The results demonstrate that changes in the precipitation regime explain changes in the surface ocean characteristics impacting stratification with consequences for large-scale water mass formation and overturning circulation in the Southern Ocean
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Andrié, Chantal. "Utilisation des traceurs helium-3 et tritium en oceanographie". Paris 6, 1987. http://www.theses.fr/1987PA066241.
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Le traceur transitoire que constitue le tritium est devenu l'un des outils les plus prometteurs dens l'etude de la circulation oceanique generale et de la capacite de l'ocean a absorber le gaz carbonique anthropogene. L'utilisation simultanee du tritium et de son descendant par voie radioactive l'helium-3 ajoute une information supplementaire: la paire de traceurs tritium et helium-3 constitue une horloge dans l'etude des masses d'eau. En plus de son origine "tritiumgenique", l'helium-3 est emis au niveau des dorsales oceaniques et il constitue un traceur de choix dans l'etude de la circulation oceanique profonde. Toutes les mesures d'helium-3 et de tritium ont ete faites par spectrometrie de masse. Protocole analytique, limite de detection et reproductibilite de la methode sont reportes dans ce travail. Sont abordes au niveau de l'interpretation des resultats: -1) les donnees d'helium-3 a la campagne merou a (ete 1982) ont permis de localiser une source active et de mettre en evidence un courant de retour intermediaire (centre vers 1000 m de profondeur), prolongement du courant profond upwelle dans la partie meridionale du bassin. -2) l'utilisation des donnees de tritium concernant la mission phycemed 1 (avril 1981) a permis de decrire la grande variabilite spatio-temporelle des processus de convection ayant lieu dans le bassin nord; le temps de renouvellement des eaux profonbdes du golfe du lion est evalue a 11 +ou- 2 ans. Les circulations profondes et de subsurface au niveau des detroits de sardaigne et de gibraltar sont precisees. -3) l'etude simultanee, suivant des niveaux isopycnaux, des donnees tritium et helium-3 de la mission topogulf (ete 1983) a permis de localiser les zones ou les processus de convection sont actifs. Une approche theorique relative a l'utilisation simultanee du tritium et de l'helium-3 est abordee. Elle utilise un modele de melange distinguant, pour une masse d'eau consideree, le temps de transit du temps de ventilation. La validite de "age tritium-helium" est testee par comparaison avec les temps de transit et de ventilation determines par le modele
Livros sobre o assunto "Ocean ventilation"
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Ronski, Stephanie. Ventilation der Grönlandsee: Variabilität und ihre Ursachen 1994-2001 = Ventilation of the Greenland Sea : variability and its causes in 1994-2001. Bremerhaven: Alfred-Wegener-Institut für Polar- und Meeresforschung, 2003.
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Doney, Scott Christopher. A study of North Atlantic ventilation using transient tracers. Woods Hole, Mass: Woods Hole Oceanographic Institution, 1991.
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Madeja-Strumińska, Barbara. Ocena przewietrzania kopalń głębinowych. Wrocław: Oficyna Wydawnicza Politechniki Wrocławskiej, 2000.
Encontre o texto completo da fonteCapítulos de livros sobre o assunto "Ocean ventilation"
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Wang, Pao K. "Ventilation Effect of Falling Ice Hydrometeors". In Atmosphere, Earth, Ocean & Space, 149–76. Singapore: Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-33-4431-0_5.
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Olsen, Alexander, e Pamela Rossi Ciampolini. "Ventilation System Related and Installation Criteria Requirements". In Synthesis Lectures on Ocean Systems Engineering, 33–36. Cham: Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-56245-7_4.
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Banse, Karl, e James R. Postel. "Wintertime convection and ventilation of the upper pycnocline in the northernmost Arabian Sea". In Indian Ocean Biogeochemical Processes and Ecological Variability, 87–117. Washington, D. C.: American Geophysical Union, 2009. http://dx.doi.org/10.1029/2008gm000704.
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Woods, J. D. "Chapter 34 The physics of Thermocline Ventilation". In Coupled Ocean-Atmosphere Models, 543–90. Elsevier, 1985. http://dx.doi.org/10.1016/s0422-9894(08)70730-x.
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Paull, C. K., P. D. Fullagar, T. J. Bralower e U. Rohl. "Seawater Ventilation of Mid-Pacific Guyots Drilled during Leg 143". In Proceedings of the Ocean Drilling Program, 143 Scientific Results. Ocean Drilling Program, 1995. http://dx.doi.org/10.2973/odp.proc.sr.143.222.1995.
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Ergin, S. "Flow Characteristics of air-caps for tank ventilation in ships". In Maritime Transportation and Exploitation of Ocean and Coastal Resources, 643–50. Taylor & Francis, 2006. http://dx.doi.org/10.1201/9781439833728.ch75.
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Rohling, Eelco, e Ramadan Abu-Zied. "The Marine Environment: Present and Past". In The Physical Geography of the Mediterranean. Oxford University Press, 2009. http://dx.doi.org/10.1093/oso/9780199268030.003.0012.
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The Mediterranean is a landlocked, semi-enclosed marginal sea that spans a maximum of 3,860 km in the west–east direction, and a maximum of ∼1, 600km in the north–south direction. Along its roughly 46,000 km of coastline, the basin is enclosed by mountainous terrain, except for a part of the North African margin to the east of Tunisia. The Mediterranean Sea contains very deep basins, more than 4 km, and has an average depth of approximately 1,500 m. Its only natural connection with the open (Atlantic) ocean is through the narrow Strait of Gibraltar, which contains a 284-m deep sill (at a width of ∼30 km), and reaches a minimum width of only 14 km (at a depth of 880 m) (Bryden and Kinder 1991). The Strait of Sicily subdivides the Mediterranean Sea into a western and an eastern basin. This strait is relatively wide (about 130 km) and contains a topographically complex sill-structure with an estimated average depth of 330 m (Wust 1961), reaching 365 and 430 m in the two major channels (Garzoli and Maillard 1979). The eastern Mediterranean contains two smaller marginal basins, namely the Adriatic Sea and the Aegean Sea. Watermasses are exchanged through both the Strait of Gibraltar and the Strait of Sicily by eastward surface and westward subsurface flows. This pattern of exchange results from a net buoyancy loss in the basins on the easterly side of the sills, primarily due to strong net evaporative loss from the Mediterranean, and secondarily to some net cooling. Deep water ventilation in the Mediterranean is primarily salt-driven, and secondarily temperature-driven. This is similar to the mode observed in the present-day Red Sea, but contrasts with the temperature-dominated mode in the modern world ocean. As such, the Mediterranean deep ventilation might be more appropriately described as halo-thermal rather than with the common term thermo-haline. This offers a useful analogue for world ocean circulation modes in past times with very warm and relatively equable global climates, such as the Mesozoic. Interestingly, the Mediterranean is characterized by periodic, widespread deposition of organic-rich sediments or ‘sapropels’ over periods of several thousands of years, similar (in miniature) to the deposition of ‘black shales’ in the Mesozoic oceans.
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Lauga, Eric. "8. Researching fluids and flows". In Fluid Mechanics: A Very Short Introduction, 129–34. Oxford University Press, 2022. http://dx.doi.org/10.1093/actrade/9780198831006.003.0008.
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‘Researching fluids and flows’ summarizes current research in fluid mechanics by starting with environmental flows, motivated by climate change, and the active fluid dynamics of our changing environment. Examples include atmospheric flows, ocean transport, ice dynamics, flow of rivers and lakes, and the role of stratification. The fluid mechanics of energy is motivated by the desire to build a greener world. Examples include wind farms, natural ventilation, biofuels, pollution transport, and remediation. Complex fluids and materials, including non-Newtonian fluids, can behave as a combination of both fluids and solids. Examples include cosmetic products, granular materials, suspensions, and liquid crystals. It is worth looking at flows on small scales, where a new fundamental understanding of flows at the limit of the continuum scale is now possible. Flows are relevant to the biological world. Examples include locomotion, vascular plants, blood flow, and the fluid dynamics of disease transmission. there are two fundamental mysteries at the heart of fluid mechanics: the nature of turbulence and the mathematical structure of the equations for fluid flows (Navier–Stokes equations).
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Waite, Lowell E., Richard B. Koepnick e James R. Markello. "The Miocene World: A Brief Summary". In Cenozoic Isolated Carbonate Platforms—Focus Southeast Asia, 32–48. SEPM (Society for Sedimentary Geology), 2023. http://dx.doi.org/10.2110/sepmsp.114.03.
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This paper presents a brief synopsis of the Miocene Epoch, an important transitory chapter in the history of the Earth. It was during the Miocene that the major continents and oceans attained a “modern” configuration in terms of paleogeography and tectonics, oceanic ventilation and circulation, ocean chemistry, and faunal and floral assemblages. It also was during the Miocene that global climate fully transitioned into its current icehouse state, including marked growth of the Antarctic ice sheet and initiation of the Arctic ice cap. Long-term global cooling was controlled by a number of factors including tectonics, the large-scale changes in the distribution of flora, particularly the expansion of grasslands, and by fluctuating orbital parameters of the Earth. This global cooling trend was briefly interrupted by a short period of warming in the middle Miocene. Miocene sea-level changes consisted of a number of glacio-eustatic third-order (1–5 million year [m.y.] duration) cycles superposed upon three longer-term, second-order (5–20 m.y. duration) supercycles. Development of large-scale tropical carbonate systems in the Miocene was relegated to three main geographic regions: the circum-Caribbean, Mediterranean, and Indo-Pacific. In addition, a pronounced cool-water platform system developed along the southern margin of Australia. Miocene reefal buildups were dominated by tropical to subtropical framework assemblages consisting primarily of large scleractinian corals, encrusting red algae, and rhodoliths (free-living coralline red algae) that grew on platform margins and interiors or on isolated atolls. Miocene carbonates were deposited in a variety of oceanic and structural settings and constitute important petroleum reservoirs, particularly in Southeast Asia. Deep-water terrigenous clastic sediments of Miocene age are also important petroleum reservoirs in some regions. In addition, the Miocene interval contains numerous prolific petroleum source rocks, most composed of Type III (gas-prone) kerogen.
Trabalhos de conferências sobre o assunto "Ocean ventilation"
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Talley, Lynne D., Rana Fine, Rick Lumpkin, Nikolai Maximenko e Rosemary Morrow. "Surface Ventilation and Circulation". In OceanObs'09: Sustained Ocean Observations and Information for Society. European Space Agency, 2010. http://dx.doi.org/10.5270/oceanobs09.pp.38.
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Hagesteijn, G., e J. Brouwer. "Experimental Investigation of the Effect of Waves, Ventilation and Cavitation in Bollard Pull Conditions". In ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/omae2013-10814.
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Ventilation is a feared working condition of ship propulsors, especially in Dynamic Positioning operation, since it leads to the lost of thrust of the propeller resulting into an uncontrollable ship. Experience showed that the risk of ventilating propellers was negligently underestimated in traditional towing tank experiments but better predicted in depressurised towing tanks, where the ambient pressure is scaled down according to Froude similarity. In 2012 MARIN’s Depressurized Wave Basin (DWB) has taken into service. This unique facility is the only one in the world that is able to generate waves in a large depressurized towing tank. This ensures correct representation of the pressure inside the enclosed ventilation bubbles and vortices, resulting into a correct physic behaviour. The EU-funded Streamline project was the first project for which ventilation inception measurements were carried out in the DWB. Tests were carried out with a fully instrumented podded ship model, sailing and in bollard pull condition, in waves and depressurised conditions. In order to acquire detailed load measurements, MARIN used their in house developed 6 component and 5 component transducers. The 6 component transducer was used for measuring the omnidirectional propeller loads, while the 5 component transducer was used for measuring 2 blade forces and 3 blade moments. At the same time synchronised high speed video recordings were made to acquire insight in the occurring phenomena. In the present paper a description of the test set up will be presented briefly, followed by a discussion of the recordings and the observations that were made for bollard pull condition in waves.
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Mak, Lawrence, Andrew Kuczora, Brian Farnworth, Rob Brown e Michel B. DuCharme. "Thermal Protection and Microclimate of SOLAS Approved Lifeboats". In ASME 2010 29th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2010. http://dx.doi.org/10.1115/omae2010-20500.
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Lifeboats are used as an evacuation system on a wide variety of offshore structures and marine vehicles. Currently, International Maritime Organization (IMO) Lifesaving Appliances (LSA) Code does not specify thermal protection and ventilation criteria for lifeboats. A test program was conducted to assess the system thermal protection and microclimate of SOLAS approved lifeboats for the Arctic environment. Some of the research findings of the first phase experiments are reported in this paper. In conducting experiments with a 72-person SOLAS approved lifeboat, the study found that the lifeboat only had a ventilation rate of 2 litres per second with vents open only, which may not be adequate. Inadequate ventilation will result in high concentration of carbon dioxide, causing headache, dizziness, restlessness, breathing difficulty, sweating, and increased heat rate, cardiac output and blood pressure. All of these may adversely affect lifeboat occupants in performing survival tasks. Using a thermal manikin, only slight decrease in thermal resistance (less than 10%) was observed in many test cases, when active ventilation was implemented (ventilation rate of 31 and 42 litres per second) and when side hatches were opened (ventilation rate of 95 litres per second). This suggests that reasonable increase in ventilation rate may be implemented without trading off much in thermal protection. However, a more noticeable decreases in thermal resistance (15% to over 30%) were observed when clothing was wet. This suggests it is critical to stay dry. A mathematical model was also developed to assess heat and cold stress of lifeboat occupants under different environment, lifeboat, occupant and ventilation conditions.
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Gray-Stephens, Angus, Tahsin Tezdogan e Sandy Day. "Strategies to Minimise Numerical Ventilation in CFD Simulations of High-Speed Planing Hulls". In ASME 2019 38th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/omae2019-95784.
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Abstract Numerical Ventilation (NV) is a well-known problem that occurs when the Volume of Fluid method is used to model vessels with a bow that creates a small, acute entrance angle with the free surface. These are typical of both planing hulls and yachts. There is a general lack of discussion focusing upon Numerical Ventilation available within the public domain, which is attributable to the fact that it only affects such a niche area of naval architecture. The information available is difficult to find, often fleetingly mentioned in papers with a different focus. Numerical Ventilation may be considered one of the main sources of error in numerical simulations of planing hulls and as such warrants an in-depth analysis. This paper sets out to bring together the available work, as well as performing its own investigation into the problem to develop a better understanding of Numerical Ventilation and present alternate solutions. Additionally, the success and impact of different approaches is presented in an attempt to help other researchers avoid and correct for Numerical Ventilation. Interface smearing caused by the simulations inability to track the free surface is identified as the main source of Numerical Ventilation. This originates from the interface between the volume mesh and the prism layer mesh. This study looks into the interface to identify strategies that minimise Numerical Ventilation, presenting a novel solution to prism layer meshing that was found to have a positive impact. Through the implementation of a modified High Resolution Interface Capture (HRIC) scheme and the correct mesh refinements, it is possible to minimise the impact of Numerical Ventilation to a level that will not affect the results of a simulation and is acceptable for engineering applications.
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Li, Z. P., L. Q. Sun, X. L. Yao e Y. Piao. "Three-Dimensional Numerical Analysis of Horizontal and Vertical Coalescence of Bubbles at Two Submerged Horizontal Orifices on the Wall". In ASME 2019 38th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/omae2019-95850.
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Abstract In the process of bubbling from two submerged adjacent orifices, bubbles coalescence becomes inevitable. But the study of the evolution and interaction of bubbles from submerged orifices is little, especially numerical simulation. In this paper, combined with mesh smoothing technique, mesh subdivision technique and the technique of axisymmetric coalescence and 3D coalescence, a three-dimensional model of bubbles coalescence at two submerged adjacent orifices on the wall is established by the boundary element method. Then, numerical simulations were carried out for horizontal and vertical coalescence before detachment. Finally, by changing the ventilation rate and the Froude number, the effects of different ventilation rates and buoyancy on the process of bubbles coalescence at two adjacent orifices were investigated. The results show that for horizontal coalescence, the effect of ventilation rate is more pronounced than buoyancy. As the ventilation rate increases or the influence of buoyancy is decreased, the amplitude of internal pressure fluctuation of the bubble decreases and the coalescence time decreases. For vertical coalescence, the effect of buoyancy is more pronounced than ventilation rate. With the influence of buoyancy is decreased, the vertical coalescence time is increased, the internal pressure of the bubble is decreased. The influence of ventilation rate is similar to that of horizontal coalescence.
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Hagesteijn, Gerco, Karola van der Meij e Cornel Thill. "Distributed Propulsion: A Novel Concept for Inland Vessels". In ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/omae2015-41845.
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In the drive to reduce the fuel consumption of inland vessels, one of the main limitations, the risk of propeller ventilation was investigated. The aim was to reduce the resistance of the vessel, while at the same time an acceptable margin against propeller ventilation had to be assured. A typical inland vessel has up to two high loaded relative large propellers, with tip regions in the lighter loading condition above the water line. To eliminate the risk of propeller ventilation, these ships often have inbuilt shape features such as tunnels and skirts, only having the intention to avoid air being drawn by the rotating propeller. These devices however have a noticeable own resistance, imposing a mortgage to the ship’s total resistance. Current design practice for these devices is that as long as you cannot quantify a risk, take care of a sufficient safety margin. With the research done within the EU-funded STREAMLINE project new insights were gained into the prediction of air suction. As a result, the margin against ventilation could be reduced which resulted into a large reduction of the resistance of the vessel. Reducing the high loading of propellers means to gain efficiency with at the same time reducing the risk of propeller ventilation as the suction by the propeller(s) can be decreased as well. This leads to the idea of a “distributed thrust” concept (DTC). Within STREAMLINE DST developed a sample case for such a novel design with six thrusters, with the aim to reduce ventilation against zero and to achieve maximal performance improvements. The measurements were carried out in MARIN’s Depressurized Wave Basin (DWB). These tests were carried out with a 1:10 scale ship model, in sailing condition, and depressurized conditions. In this way, the correct representation of cavitation and possible ventilation bubbles and vortices is ensured, resulting in a correct physical behavior. At the same time synchronized high speed video recordings were made to acquire insight in the occurring phenomena. Within the project CFD calculations were carried out, aimed at characterizing the performance, loads, cavitation nuisance and ventilation risk in full-scale operating conditions. Validation of these calculations was done using the towing tank results.
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Kim, Jeong Hwan, Soung Woo Park e Jung Kwan Seo. "An Experimental Study on the Diffusion Characteristics of Hydrogen by Ventilation System". In ASME 2024 43rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2024. http://dx.doi.org/10.1115/omae2024-123243.
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Abstract Hydrogen gas exhibits a broader flammable limit concentration range in comparison to hydrocarbon gas, possesses lower ignition energy and ignition temperature, and manifests a heightened propagation speed of explosive flames. In the eventuality of a hydrogen gas leak, it is noteworthy that the density of hydrogen is lower than that of air, leading to its dispersion into the surrounding atmosphere within an open space. Nevertheless, within a confined environment, the hydrogen gas cloud has the potential to stagnate and accumulate. The presence of an accumulated hydrogen gas cloud elevates the risk substantially, rendering it susceptible to ignition or explosion, even in the presence of a minor ignition source. The purpose of this study is to experimentally investigate diffusion characteristics in response to diverse ventilation methods in the event of hydrogen leaks within the Fuel Gas Supply System (FGSS) room. A FGSS room, representative of the dimensions of an operational hydrogen fuel propulsion ship, was fabricated for the purpose of this investigation. Ventilation capacity was systematically compared and analyzed, taking into consideration variables such as ceiling type, ventilation method, and the length of the ventilation duct. Moreover, the FLACS program was employed for numerical analysis, and a modeling technique for simulating hydrogen leakage diffusion in enclosed spaces was developed through a comprehensive comparison and verification with the experimental findings. The amalgamation of experimental results and the refined numerical approach holds potential utility in informing adjustments to existing International Maritime Organization (IMO) guidelines and the International Code of Safety for Ships using Gases or other Low-flashpoint Fuels (IGF Code).
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Huang, Huai-Hsuan, Curtis Deutsch e Thomas Cronin. "OSTRACOD BODY SIZE VARIABILITY LINKED TO ARCTIC OCEAN VENTILATION DURING QUATERNARY CLIMATE CHANGES". In GSA Connects 2023 Meeting in Pittsburgh, Pennsylvania. Geological Society of America, 2023. http://dx.doi.org/10.1130/abs/2023am-395056.
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Lu, Ping, e Sue Wang. "Investigation of Ventilation and Current Effect of Tunnel Thruster for DP Applications". In ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/omae2015-42127.
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This paper presents a CFD simulation to study the ventilation phenomenon of tunnel thrusters in dynamic positioning (DP) mode of a typical North Sea shuttle tanker consisting of two main propellers, two rudders, and two bow tunnel thrusters. Measurements of blade thrust and moment for the propeller shaft (corresponding to propeller torque) with ventilated propellers at different submersion positions are presented and discussed. Additionally, in order to obtain insight into the effect of waves on ventilation which further affects propeller loading and dynamic fluctuations, simulations of a tunnel thruster are performed at different immersion ratios. This paper also presents and discusses the factors in the evaluation of thruster performance, such as, the extent of present knowledge for tunnel thrusters as related to ahead ship speed, and interaction between thruster jet flow and the mainstream with various drift angles. Moreover, thrust degradation of tunnel thrusters is considered in the thrust allocation algorithms for the DP capability calculation. The objective of this study is to understand the dynamics of thruster forces. In addition, results of the study provide knowledge for a robust thrust allocation algorithm for dynamic positioning capability assessment.
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Tregde, Vidar. "Compressible Air Effects in CFD Simulations of Free Fall Lifeboat Drop". In ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/omae2015-41049.
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A free fall lifeboat is typically dropped from heights between 30 and 40m, but during full scale testing, drop heights have been exceeding 60 m. During a drop, the free fall lifeboat is going through several phases; sliding on the skid, rotation on skid, free fall, water entry, ventilation, maximum submergence, resurfacing and the sailing phase. During impact and submergence the lifeboat will go through a ventilation phase. In this phase the lifeboat creates an air cavity behind the pilot house and a larger one behind the stern. The air cavity formed on top of canopy, aft of the pilot house is compressed and then starts to oscillate in time giving rise to large oscillating pressures. Computational Fluid Dynamics (CFD) simulations with compressible air flow model are compared with full scale experimental results. The results compare very well, both in oscillating frequency and amplitude. Later in the ventilation phase, an air bubble aft of the vessel will be drawn down several meters below the water surface. This bubble collapses in an imploding manner and slams with large pressures on the aft bulkhead of the lifeboat. This is simulated in CFD with compressible air model and compares very well to the full scale experimental results. Using incompressible air flow will not capture these effects, and the calculated pressures on the aft bulkhead are a fraction of the real pressures. The water surface in the cavity eventually hits the aft bulkhead with a high slamming velocity. The structure of the air pocket does not have any symmetry, and seem to be chaotic in nature. The local pressures can be very high and distributed over a small area. The effects of the air cavity also influence the motion and acceleration of the lifeboat in the ventilation phase; this is shown and compared to full scale experimental results.
Relatórios de organizações sobre o assunto "Ocean ventilation"
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Nadiga, Balasubramanya T., e Nathan Mark Urban. A simple model of the effect of ocean ventilation on ocean heat uptake. Office of Scientific and Technical Information (OSTI), janeiro de 2018. http://dx.doi.org/10.2172/1418778.
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