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Artykuły w czasopismach na temat "Near-surface stratification"
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Reverdin, G., S. Morisset, H. Bellenger, J. Boutin, N. Martin, P. Blouch, J. Rolland, F. Gaillard, P. Bouruet-Aubertot i B. Ward. "Near–Sea Surface Temperature Stratification from SVP Drifters". Journal of Atmospheric and Oceanic Technology 30, nr 8 (1.08.2013): 1867–83. http://dx.doi.org/10.1175/jtech-d-12-00182.1.
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Abstract This study describes how the hull temperature (Ttop) measurements from multisensor surface velocity program (SVP) drifters can be combined with other measurements to provide quantitative information on near-surface vertical temperature stratification during large daily cycles. First, Ttop is compared to the temperature measured at 17 -cm depth from a float tethered to the SVP drifter. These 2007–12 SVP drifters present a larger daily cycle by 1%–3% for 1°–2°C daily cycle amplitudes, with a maximum difference close to the local noon. The difference could result from flow around the SVP drifter in the presence of temperature stratification in the top 20 cm of the water column but also from a small influence of internal drifter temperature on Ttop. The largest differences were found for small drifters (Technocean) for very large daily cycles, as expected from their shallower measurements. The vertical stratification is estimated by comparing these hull data with the deeper T or conductivity C measurements from Sea-Bird sensors 25 (Pacific Gyre) to 45 cm (MetOcean) below the top temperature sensor. The largest stratification is usually found near local noon and early afternoon. For a daily cycle amplitude of 1°C, these differences with the upper level are in the range of 3%–5% of the daily cycle for the Pacific Gyre drifters and 6%–10% for MetOcean drifters with the largest values occurring when the midday sun elevation is lowest. The relative differences increase for larger daily cycles, and the vertical profiles become less linear. These estimated stratifications are well above the uncertainty on Ttop.
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Santos-Garcia, Andrea, Maria Marta Jacob i W. Linwood Jones. "SMOS Near-Surface Salinity Stratification Under Rainy Conditions". IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 9, nr 6 (czerwiec 2016): 2493–99. http://dx.doi.org/10.1109/jstars.2016.2527038.
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Fischer, Tim, Annette Kock, Damian L. Arévalo-Martínez, Marcus Dengler, Peter Brandt i Hermann W. Bange. "Gas exchange estimates in the Peruvian upwelling regime biased by multi-day near-surface stratification". Biogeosciences 16, nr 11 (5.06.2019): 2307–28. http://dx.doi.org/10.5194/bg-16-2307-2019.
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Abstract. The coastal upwelling regime off Peru in December 2012 showed considerable vertical concentration gradients of dissolved nitrous oxide (N2O) across the top few meters of the ocean. The gradients were predominantly downward, i.e., concentrations decreased toward the surface. Ignoring these gradients causes a systematic error in regionally integrated gas exchange estimates, when using observed concentrations at several meters below the surface as input for bulk flux parameterizations – as is routinely practiced. Here we propose that multi-day near-surface stratification events are responsible for the observed near-surface N2O gradients, and that the gradients induce the strongest bias in gas exchange estimates at winds of about 3 to 6 m s−1. Glider hydrographic time series reveal that events of multi-day near-surface stratification are a common feature in the study region. In the same way as shorter events of near-surface stratification (e.g., the diurnal warm layer cycle), they preferentially exist under calm to moderate wind conditions, suppress turbulent mixing, and thus lead to isolation of the top layer from the waters below (surface trapping). Our observational data in combination with a simple gas-transfer model of the surface trapping mechanism show that multi-day near-surface stratification can produce near-surface N2O gradients comparable to observations. They further indicate that N2O gradients created by diurnal or shorter stratification cycles are weaker and do not substantially impact bulk emission estimates. Quantitatively, we estimate that the integrated bias for the entire Peruvian upwelling region in December 2012 represents an overestimation of the total N2O emission by about a third, if concentrations at 5 or 10 m depth are used as surrogate for bulk water N2O concentration. Locally, gradients exist which would lead to emission rates overestimated by a factor of two or more. As the Peruvian upwelling region is an N2O source of global importance, and other strong N2O source regions could tend to develop multi-day near-surface stratification as well, the bias resulting from multi-day near-surface stratification may also impact global oceanic N2O emission estimates.
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Iyer, Suneil, i Kyla Drushka. "Turbulence within Rain-Formed Fresh Lenses during the SPURS-2 Experiment". Journal of Physical Oceanography 51, nr 5 (maj 2021): 1705–21. http://dx.doi.org/10.1175/jpo-d-20-0303.1.
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AbstractObservations of salinity, temperature, and turbulent dissipation rate were made in the top meter of the ocean using the ship-towed Surface Salinity Profiler as part of the second Salinity Processes in the Upper Ocean Regional Study (SPURS-2) to assess the relationships between wind, rain, near-surface stratification, and turbulence. A wide range of wind and rain conditions were observed in the eastern tropical Pacific Ocean near 10°N, 125°W in summer–autumn 2016 and 2017. Wind was the primary driver of near-surface turbulence and the mixing of rain-formed fresh lenses, with lenses generally persisting for hours when wind speeds were under 5 m s−1 and mixing away immediately at higher wind speeds. Rain influenced near-surface turbulence primarily through stratification. Near-surface stratification caused by rainfall or diurnal warming suppressed deeper turbulent dissipation rates when wind speeds were under 3 m s−1. In one case with 4–5 m s−1 winds, rain-induced stratification enhanced dissipation rates within the stratified layer. At wind speeds above 7–8 m s−1, strong stratification was not observed in the upper meter during rain, indicating that rain lenses do not form at wind speeds above 8 m s−1. Raindrop impacts enhanced turbulent dissipation rates at these high wind speeds in the absence of near-surface stratification. Measurements of air–sea buoyancy flux, wind speed, and near-surface turbulence can be used to predict the presence of stratified layers. These findings could be used to improve model parameterizations of air–sea interactions and, ultimately, our understanding of the global water cycle.
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Pernica, Patricia, i Mathew Wells. "Frequency of episodic stratification in the near surface of Lake Opeongo and other small lakes". Water Quality Research Journal 47, nr 3-4 (1.08.2012): 227–37. http://dx.doi.org/10.2166/wqrjc.2012.001.
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Wind-driven mixing in the epilimnion of a deep lake can be suppressed when there is a weak near surface stratification, which occurs frequently during periods of strong solar heating and weak winds. Using data from a vertical chain of fast response thermistors, we analyze the frequency of near surface stratification in the top 2 meters of the epilimnion in Lake Opeongo, Ontario for the periods between May and August in 2009 and 2010. Near surface thermoclines (as defined by dT/dz > 0.2 °C m−1 between 1 and 2 m) occur for 24% of the sampling period in 2009, 37% of the sampling period in 2010 and correspond to periods of high values of gradient Richardson number. During daytime the epilimnion is stratified up to 45% of the time. At night, cooling generally leads to a more isothermal profile, but near surface thermoclines still form at least 20% of the time. Extended periods of near surface stratification (>1 h), account for more than 80% of the stratified period. We compare these findings with previous observations from the Experimental Lakes Area in Northern Ontario, and discuss the biological implications of episodic stratification.
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Li, Yifan, Matthew Marander, Rebecca Mort, Fei Liu, Xin Yong i Shan Jiang. "Who wins the race near the interface? Stratification of colloids, nano-surfactants, and others". Journal of Applied Physics 132, nr 11 (21.09.2022): 110901. http://dx.doi.org/10.1063/5.0098710.
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The diffusion of colloids, nanoparticles, and small molecules near the gas–liquid interface presents interesting multiphase transport phenomena and unique opportunities for understanding interactions near the surface and interface. Stratification happens when different species preside over the interfaces in the final dried coating structure. Understanding the principles of stratification can lead to emerging technologies for materials’ fabrication and has the potential to unlock innovative industrial solutions, such as smart coatings and drug formulations for controlled release. However, stratification can be perplexing and unpredictable. It may involve a complicated interplay between particles and interfaces. The surface chemistry and solution conditions are critical in determining the race of particles near the interface. Current theory and simulation cannot fully explain the observations in some experiments, especially the newly developed stratification of nano-surfactants. Here, we summarize the efforts in the experimental work, theory, and simulation of stratification, with an emphasis on bridging the knowledge gap between our understanding of surface adsorption and bulk diffusion. We will also propose new mechanisms of stratification based on recent observations of nano-surfactant stratification. More importantly, the discussions here will lay the groundwork for future studies beyond stratification and nano-surfactants. The results will lead to the fundamental understanding of nanoparticle interactions and transport near interfaces, which can profoundly impact many other research fields, including nanocomposites, self-assembly, colloidal stability, and nanomedicine.
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Mellado, Juan Pedro, Chiel C. van Heerwaarden i Jade Rachele Garcia. "Near-Surface Effects of Free Atmosphere Stratification in Free Convection". Boundary-Layer Meteorology 159, nr 1 (17.11.2015): 69–95. http://dx.doi.org/10.1007/s10546-015-0105-x.
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Sutherland, Graig, Louis Marié, Gilles Reverdin, Kai H. Christensen, Göran Broström i Brian Ward. "Enhanced Turbulence Associated with the Diurnal Jet in the Ocean Surface Boundary Layer". Journal of Physical Oceanography 46, nr 10 (październik 2016): 3051–67. http://dx.doi.org/10.1175/jpo-d-15-0172.1.
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AbstractDetailed observations of the diurnal jet, a surface intensification of the wind-driven current associated with the diurnal cycle of sea surface temperature (SST), were obtained during August and September 2012 in the subtropical Atlantic. A diurnal increase in SST of 0.2° to 0.5°C was observed, which corresponded to a diurnal jet of 0.15 m s−1. The increase in near-surface stratification limits the vertical diffusion of the wind stress, which in turn increases the near-surface shear. While the stratification decreased the turbulent dissipation rate ε below the depth of the diurnal jet, there was an observed increase in ε within the diurnal jet. The diurnal jet was observed to increase the near-surface shear by a factor of 5, which coincided with enhanced values of ε. The diurnal evolution of the Richardson number, which is an indicator of shear instability, is less than 1, suggesting that shear instability may contribute to near-surface turbulence. While the increased stratification due to the diurnal heating limits the depth of the momentum flux due to the wind, shear instability provides an additional source of turbulence that interacts with the enhanced shear of the diurnal jet to increase ε within this shallow layer.
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LaCasce, J. H. "Surface Quasigeostrophic Solutions and Baroclinic Modes with Exponential Stratification". Journal of Physical Oceanography 42, nr 4 (1.04.2012): 569–80. http://dx.doi.org/10.1175/jpo-d-11-0111.1.
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Abstract The author derives baroclinic modes and surface quasigeostrophic (SQG) solutions with exponential stratification and compares the results to those obtained with constant stratification. The SQG solutions with exponential stratification decay more rapidly in the vertical and have weaker near-surface velocities. This then compounds the previously noted problem that SQG underpredicts the velocities associated with a given surface density anomaly. The author also examines how the SQG solutions project onto the baroclinic modes. With constant stratification, SQG waves larger than deformation scale project primarily onto the barotropic mode and to a lesser degree onto the first baroclinic mode. However, with exponential stratification, the largest projection is on the first baroclinic mode. The effect is even more pronounced over rough bottom topography. Therefore, large-scale SQG waves will look like the first baroclinic mode and vice versa, with realistic stratification.
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LAMB, KEVIN G. "A numerical investigation of solitary internal waves with trapped cores formed via shoaling". Journal of Fluid Mechanics 451 (25.01.2002): 109–44. http://dx.doi.org/10.1017/s002211200100636x.
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The formation of solitary internal waves with trapped cores via shoaling is investigated numerically. For density fields for which the buoyancy frequency increases monotonically towards the surface, sufficiently large solitary waves break as they shoal and form solitary-like waves with trapped fluid cores. Properties of large-amplitude waves are shown to be sensitive to the near-surface stratification. For the monotonic stratifications considered, waves with open streamlines are limited in amplitude by the breaking limit (maximum horizontal velocity equals wave propagation speed). When an exponential density stratification is modified to include a thin surface mixed layer, wave amplitudes are limited by the conjugate flow limit, in which case waves become long and horizontally uniform in the centre. The maximum horizontal velocity in the limiting wave is much less than the wave's propagation speed and as a consequence, waves with trapped cores are not formed in the presence of the surface mixed layer.
Rozprawy doktorskie na temat "Near-surface stratification"
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Sree, Lekha J. "Space-time variability of near-surface salinity in the Bay of Bengal". Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4649.
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Freshwater from monsoon rain and rivers leads to a 5-10 m deep low-salinity layer in the north Bay of Bengal from August to February. The thin fresh layer, with strong stratification at its base, is highly responsive to air-sea momentum and heat flux. Moored observations at 18N, about 500 km away from major river mouths, show a 3-8 psu drop in surface salinity within a week as water from the Ganga-Brahmaputra-Meghna (GBM) river arrives at the mooring in late August-early September each year, and from the Irrawady river in November-December. In conjunction with satellite sea surface salinity (SSS) and surface currents, the moored observations indicate that dispersal of river water in the open ocean is mainly driven by the flow in mesoscale (order 100 km) eddies during calm phases of the summer monsoon, and by a swift, shallow wind-driven Ekman flow as monsoon winds strengthen.
Six years of moored observations at 18N 89.5E show that surface salinity has a distinct quasi-biweekly (10-25 day) variability, which is not due to changes in freshwater input. Rather, changes in salinity are related to variations in surface winds associated with the quasi-biweekly mode of the Asian summer monsoon. During the active phase of the monsoon, a shallow wind-driven Ekman flow disperses river water to the north and east, leading to increased salinity at the moorings, and a rise of coastal sea level by 0.3-0.6 m within days along the eastern boundary. In situ and satellite observations show that the response of sea surface temperature (SST) to quasi-biweekly variations of surface heat flux is enhanced by a factor of two because the mixed layer is very shallow within the pool of river water, thus revealing a direct link between SST and surface salinity.
During research cruises of ORV Sagar Nidhi in August-September 2014 and 2015, upper ocean temperature (T), salinity (S) and ocean currents (V) in the Bay of Bengal were measured with 0.5-1.5 km horizontal resolution and 1-2 m vertical resolution in order to study sub-mesoscale (1-10 km) variability. Underway CTD data show numerous sub-mesoscale salinity-dominated surface density fronts. The spatial scale of 30 major fronts lies in the range 3-25 km, and net density change across the fronts exceeds 0.3 kg/m3. An east-west asymmetry in isopycnal slope is due to Ekman flow, which drives relatively saltier, denser water over lighter water on the western side. Ship-borne ADCP measurements show that flow at sub-mesoscale fronts has Rossby number of order one. Of the 30 fronts, two are associated with swift 5-10 km wide jets in the upper 20 m. Mixed layer depth is shallower at the fronts than on either side, and is less than 10 m if lateral density gradient exceeds 0.1-0.2 kg/m3 per km. The observations indicate that slumping of sub-mesoscale salinity-dominated fronts is an important mechanism sustaining near-surface stratification in the north Bay of Bengal.
Finally, basin-scale diapycnal diffusivity is estimated from freshwater balance within a control volume bounded by the 1018 kg/m3 isopycnal - T, S and V are from an eddy-permitting daily ocean analysis, and rainfall, evaporation and runoff from a continental runoff dataset and satellite observations. The amount of pure freshwater in the control volume increases from June to November each year due to net input from rain and runoff, and decreases from December to May. Water lighter than 1018 kg/m3 is not transported across the southern boundary of the Bay of Bengal, implying that the freshwater lost from the control volume is mixed to deeper layers within the basin. The freshwater balance indicates that average diapycnal diffusivity across the 1018 kg/m3 isopycnal surface in winter is nearly 5x10-5 m2/s, 3-5 times higher than in spring or summer. Winter mixing in the upper ocean is highest during episodes of cool, dry surface air, leading to enhanced evaporation and surface buoyancy loss.
Części książek na temat "Near-surface stratification"
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Vishnu, S. B., i Biju T. Kuzhiveli. "Effect of Roughness Elements on the Evolution of Thermal Stratification in a Cryogenic Propellant Tank". W Low-Temperature Technologies [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.98404.
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The cryogenic propulsion era started with the use of liquid rockets. These rocket engines use propellants in liquid form with reasonably high density, allowing reduced tank size with a high mass ratio. Cryogenic engines are designed for liquid fuels that have to be held in liquid form at cryogenic temperature and gas at normal temperatures. Since propellants are stored at their boiling temperature or subcooled condition, minimal heat infiltration itself causes thermal stratification and self-pressurization. Due to stratification, the state of propellant inside the tank varies, and it is essential to keep the propellant properties in a predefined state for restarting the cryogenic engine after the coast phase. The propellant’s condition at the inlet of the propellant feed system or turbo pump must fall within a narrow range. If the inlet temperature is above the cavitation value, cavitation will likely to happen to result in the probable destruction of the flight vehicle. The present work aims to find an effective method to reduce the stratification phenomenon in a cryogenic storage tank. From previous studies, it is observed that the shape of the inner wall surface of the storage tank plays an essential role in the development of the stratified layer. A CFD model is established to predict the rate of self-pressurization in a liquid hydrogen container. The Volume of Fluid (VOF) method is used to predict the liquid–vapor interface movement, and the Lee phase change model is adopted for evaporation and condensation calculations. A detailed study has been conducted on a cylindrical storage tank with an iso grid and rib structure. The development of the stratified layer in the presence of iso grid and ribs are entirely different. The buoyancy-driven free convection flow over iso grid structure result in velocity and temperature profile that differs significantly from a smooth wall case. The thermal boundary layer was always more significant for iso grid type obstruction, and these obstructions induces streamline deflection and recirculation zones, which enhances heat transfer to bulk liquid. A larger self-pressurization rate is observed for tanks with an iso grid structure. The presence of ribs results in the reduction of upward buoyancy flow near the tank surface, whereas streamline deflection and recirculation zones were also perceptible. As the number of ribs increases, it nullifies the effect of the formation of recirculation zones. Finally, a maximum reduction of 32.89% in the self-pressurization rate is achieved with the incorporation of the rib structure in the tank wall.
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"Biology and Management of Inland Striped Bass and Hybrid Striped Bass". W Biology and Management of Inland Striped Bass and Hybrid Striped Bass, redaktorzy James A. Rice, Jessica S. Thompson, Jamie A. Sykes i Christian T. Waters. American Fisheries Society, 2013. http://dx.doi.org/10.47886/9781934874363.ch6.
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<em>Abstract</em>.—Historically, striped bass <em>Morone saxatilis</em> summer kills have been attributed to two mechanisms: stressors associated with crowding when striped bass are confined in isolated, cool refuges; and thermal stress or energetic deficit when hypolimnetic hypoxia (dissolved oxygen less than 2 mg/L) forces them into high-temperature surface waters. Here, we present observations suggesting that a third mechanism may account for some of these striped bass mortality events. During summer stratification, many relatively deep southeastern reservoirs develop hypoxia in the metalimnion, as well as near the bottom, isolating a layer of oxygenated hypolimnetic water between them. As these hypoxic zones expand in thickness and severity of oxygen depletion, the oxygenated layer between them shrinks both horizontally and vertically, and its oxygen content declines. Evidence suggests that striped bass summer kills can occur when fish are trapped in this isolated layer and its oxygen concentration declines below 2 mg/L or disappears altogether. The presence of coolwater forage fish such as alewife <em>Alosa pseudoharengus </em>or blueback herring <em>A. aestivalis </em>may increase the risk of striped bass kills by attracting them into the hypolimnetic oxygenated layer where they may become trapped. We draw upon examples from two southeastern reservoirs to illustrate this phenomenon, and discuss its implications for reservoir fisheries management, as well as possible approaches to minimize or avoid impacts.
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Kraus, Eric B., i Joost A. Businger. "Turbulent Transfer Near the Interface". W Atmosphere-Ocean Interaction. Oxford University Press, 1995. http://dx.doi.org/10.1093/oso/9780195066180.003.0009.
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The atmosphere and the ocean are in intimate contact at their interface, where momentum, water substance, heat, and trace constituents are exchanged. This exchange is often modest when a light breeze strokes the surface; sometimes the processes are violent, when gale force winds sweep up ocean spray into the atmosphere and when braking waves engulf air into the ocean. It may even appear that the transition between ocean and atmosphere becomes gradual and indistinct. The transition from ocean to atmosphere is usually an abrupt transition of one fluid to another. The interface may then be considered a continuous material surface. On both sides of the interface the fluids are usually in turbulent motion and properties are transported readily, but upon approaching the interface turbulence is largely suppressed so that on both sides of the interface a very thin layer exists where the molecular diffusion coefficients play a major role in the transport. The interface is consequently a significant barrier to the transport from ocean to atmosphere and vice versa, with little or no turbulent transport of scalar quantities across it. The quantitative determination of the thickness of the molecular sublayers and the strength of the gradients and shear layers within them are discussed in Section 5.1. We also examine the transition from the molecular sublayers to the well-mixed turbulent layers that exist beyond them, and the structure of these turbulent layers on either side of the interface. In Section 5.2 we discuss the effect of stratification on the structure of these surface layers. Some of the nonstationary interactions between the wind and the sea surface are described in Section 5.3. Sections 5.4 and 5.5 deal with practical applications: a formulation of gas transfer across the interface and of the sea surface temperature. Several observational techniques are discussed in Section 5.6.
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Schoepfer, Shane D., i Charles M. Henderson. "Paleogeographic Implications of Open-Marine Anoxia in the Permian–Triassic Slide Mountain Ocean". W Late Paleozoic and Early Mesozoic Tectonostratigraphy and Biostratigraphy of Western Pangea, 205–25. SEPM (Society for Sedimentary Geology), 2022. http://dx.doi.org/10.2110/sepmsp.113.10.
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The end-Permian mass extinction was associated with the onset of anoxia in widespread marine environments; however, the extent of this anoxia remains controversial. Proposed models range from near-universal “superanoxia” in the Panthalassic Basin to a more limited expansion of anoxia in the upper water column in response to enhanced primary productivity. The Peck Creek and Ursula Creek sections of northern British Columbia were deposited at ~200 m water depth in the Ishbel Trough, on the margin of cratonic North America. This trough was generally contiguous with the Slide Mountain Ocean, and thus with the broader Panthalassic Ocean, though it may have been partially separated by structural highs at various times during the Permian. Both sections include continuous Wordian to Changhsingian sedimentary successions, which span the end-Permian mass extinction boundary and continue into the earliest Triassic. The extinction is recognizable as the disappearance of biogenic silica from the environment, which defines the contact between the Fantasque Formation and overlying Grayling Formation. This surface also corresponds with the onset of anoxia, and the accumulation of redox-sensitive trace metals. The covariation trends in these metals, and in other isotopic proxies, can be used as tools to trace the degree of communication between the Ishbel Trough–Slide Mountain Ocean and the broader Panthalassic Basin. Molybdenum-uranium covariation trends indicate that the northern Slide Mountain Ocean and Ishbel Trough remained in communication with the larger global ocean throughout this interval, suggesting inversion of the Wordian structural high to form a depositional subbasin by the Changhsingian. This is in contrast to the Opal Creek section of southern Alberta, which shows evidence for some degree of restriction, suggesting that the Slide Mountain Ocean may have maintained a north–south gradient in water chemistry. Several lines of evidence suggest that this onset of anoxia was not related to expansion of an upwelling-driven oxygen minimum zone. No clear changes in primary productivity, as recorded by organic carbon or authigenic phosphorus and barium, are observed across the extinction horizon. Changhsingian nitrogen isotope values are generally in the 2 to 3‰ range, suggesting minimal denitrification at thermocline water depths, and these values decreased in the earliest Triassic, likely in response to enhanced nitrogen fixation. This suggests that anoxia was driven by shoaling of a chemocline that developed due to stratification of the Slide Mountain Ocean, rather than western-boundary upwelling effects.
Streszczenia konferencji na temat "Near-surface stratification"
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Santos-Garcia, Andrea, Maria Marta Jacob i W. Linwood Jones. "Near-surface salinity stratification observed by SMOS under rainy conditions". W IGARSS 2015 - 2015 IEEE International Geoscience and Remote Sensing Symposium. IEEE, 2015. http://dx.doi.org/10.1109/igarss.2015.7325712.
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Giese, Graham S., i David C. Chapman. "Evidence of Near-Surface Density Stratification as a Factor in Extreme Seiche Events at Ciutadella Harbor, Menorca Island". W Fourth International Symposium on Ocean Wave Measurement and Analysis. Reston, VA: American Society of Civil Engineers, 2002. http://dx.doi.org/10.1061/40604(273)163.
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Howard, Alicia H., i Issam Mudawar. "Pool Boiling Critical Heat Flux on a Downward-Facing Convex Surface". W ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1503.
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Abstract Heat transfer measurements and photographic studies were performed to capture the detailed evolution of liquid-vapor interfacial behavior near critical heat flux (CHF) for a 90-degree downward-facing convex surface. The test surface, with a width of 3.2 mm and a 102.6-mm radius, consisted of a series of nine heaters which dissipated equal power. Instrumentation within each heater facilitated localized heat flux and temperature measurements along the convex surface, and transparent front and back windows enabled optical access to a fairly two-dimensional liquid-vapor interface. Near CHF, vapor behavior along the convex surface was cyclical in nature and somewhat similar to that observed in pool boiling on horizontal downward-facing flat surfaces. The vapor repeatedly formed a stratified layer at the bottom of the convex surface, which stretched as more vapor was generated, and then departed from the surface. Subsequently, the bottom (downward-facing) heaters, followed by the other heaters, were wetted with liquid before the nucleation/coalescence/stratification/release process repeated itself. Prior to CHF, the surface was adequately cooled by the liquid wetting. At CHF, the surface was still wetted for a brief period, but the wetting time was too short to allow adequate cooling of the downward-facing heaters, and the temperature of these heaters began to rise. This study proves that despite the pronounced thickening of the vapor layer as it propagates upwards along the convex surface, CHF always commences on the downward-facing heaters.
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Emery, A. F., D. R. Heerwagen, C. J. Kippenhan i D. E. Steele. "Thermal Performance of a Residential Basement". W ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1427.
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Abstract This paper describes the measurement of ground and internal wall temperatures, local surface heat fluxes on the basement walls and floor, and overall heat losses for a concrete wall basement. The heat fluxes were measured with heat flux meters and mimic boxes. Daily and seasonal measured performances are displayed. A portion of the walls was covered with additional insulation. This allowed comparison of insulated and non-insulated basements and showed that a modest amount of insulation could reduce the annual heat loss by approximately 50%. The local fluxes are shown to vary significantly with depth and the insulation was most effective when applied to the upper wall surface which communicated with the ambient air through a relatively short path through the earth near grade level. Temperature stratification effects are shown to be important, especially with respect to floor heat fluxes.
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Turner, Trevor B., Ryan F. Schkoda, John R. Wagner i Robert T. Leitner. "Wind Shear Modeling for Wind Turbine Siting Studies". W ASME 2009 Dynamic Systems and Control Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/dscc2009-2696.
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A wind turbine generator offers a green renewable alternative to the traditional fossil and nuclear fuel processes to generate electrical power. Both wind energy technology and wind turbine farm designs remain in demand given the current growth in energy requirements and the public’s preference for clean sources. Simply put, wind energy offers a safe, relatively cost effective solution for global energy production. For example, the energy demand for populated coastal cities encourages offshore farms to fulfill future electrical needs. Similarly, wind turbines may be placed in land-locked regions and power transmitted through electric grids to population centers. Most wind models available to engineers offer superb capabilities for predicting wind velocities on land and far offshore (5 km and greater). However, near shore winds have proven difficult to determine due to surface roughness, thermal stratification, and abrupt displacement height variances. This paper discusses the model comparison of two foremost wind speed prediction tools, AWS Truewinds’ MASS and WindPro’s WAsP. The model comparison is related to measured South Carolina coastal data and suggests AWS Truewind’s MASS wind shear model is the more effective near-shore wind speed prediction tool. In arriving at these results, several areas of future work are discussed.
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Chen, Meilan, i Zeming Zheng. "Validation of a CFD Code for the Analysis of Hydrogen Behaviors and Thermal Hydraulics in Containments". W 2018 26th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icone26-82192.
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During the process of core melt-down accident in light water reactors, large quantities of hydrogen generated by drastic water-metal reaction are released to the containment. Subsequently, hydrogen-rich layer may be formed under the dome of the containment, threatening the integrity of nuclear Power Plants (NPPs). In the framework of a China national R&D project, China Nuclear Power Research Institute (CNPRI) has developed a three dimensional CFD Code for the assessment of hydrogen behaviors and relative thermal hydraulics in containment. The code solves the time-dependent Navier-Stokes Equations with multi-gas species. Validation with International Standard Problems (ISP) and other test data based on a Phenomena Identification and Ranking Table (PIRT) has been undergoing together with the development of this code. In this paper, the test cases of HYJET, COPAIN and TOSQAN 101 Test are validated. Stratification, buoyancy induced mixing in gases, convection heat transfer and condensation on surface are evaluated in the former two cases, while gas entrainment and mixing by spray droplets in the later one. Excellent agreements between experimental data and model predictions are obtained. In order to meet the requirements for application of the code in practical NPP design and safety analysis, further validations of other phenomena in PIRT should be performed in the near future.
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Kurup, Nishu V., Shan Shi, Zhongmin Shi, Wenju Miao i Lei Jiang. "Study of Nonlinear Internal Waves and Impact on Offshore Drilling Units". W ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2011. http://dx.doi.org/10.1115/omae2011-50304.
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Internal waves near the ocean surface have been observed in many parts of the world including the Andaman Sea, Sulu Sea and South China Sea among others. The factors that cause and propagate these large amplitude waves include bathymetry, density stratification and ocean currents. Although their effects on floating drilling platforms and its riser systems have not been extensively studied, these waves have in the past seriously disrupted offshore exploration and drilling operations. In particular a drill pipe was ripped from the BOP and lost during drilling operations in the Andaman sea. Drilling riser damages were also reported from the south China Sea among other places. The purpose of this paper is to present a valid numerical model conforming to the physics of weakly nonlinear internal waves and to study the effects on offshore drilling semisubmersibles and riser systems. The pertinent differential equation that captures the physics is the Korteweg-de Vries (KdV) equation which has a general solution involving Jacobian elliptical functions. The solution of the Taylor Goldstein equation captures the effects of the pycnocline. Internal wave packets with decayed oscillations as observed from satellite pictures are specifically modeled. The nonlinear internal waves are characterized by wave amplitudes that can exceed 50 ms and the present of shearing currents near the layer of pycnocline. The offshore drilling system is exposed to these current shears and the associated movements of large volumes of water. The effect of internal waves on drilling systems is studied through nonlinear fully coupled time domain analysis. The numerical model is implemented in a coupled analysis program where the hull, moorings and riser are considered as an integrated system. The program is then utilized to study the effects of the internal wave on the platform global motions and drilling system integrity. The study could be useful for future guidance on offshore exploration and drilling operations in areas where the internal wave phenomenon is prominent.
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Wang, Di, i Xuewu Cao. "Preliminary Analysis of Hydrogen Distribution During Severe Accident Induced by Loss of Coolant Accident". W 2017 25th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/icone25-66497.
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During hypothetical severe accidents in nuclear power plants, a large amount of hydrogen is generated rapidly as a result of Zirconium-Steam reaction and released into the containment. Hydrogen mixes with air and may come into combustion or detonation under proper conditions, which threatens the integrity of containment. Therefore, getting detailed hydrogen flow and distribution in various physical mechanisms is a key issue to resolve the hydrogen risk in containment and compartments. To study local hydrogen distribution in the containment of advanced passive PWR, an analysis model is built by 3-dimensional CFD code. Computational domain is divided by structured grid which contains over 100,000 cells. the shape and surface area of walls and obstacles of steel shell and internal structure, which have great impact on gas flow and heat transfer, are included. Hydrogen distribution in containment simulating with different turbulence models is studied, the result shows that during large amount of hydrogen release stage. In hydrogen distribution result simulating with algebraic model, hydrogen is all gathered in the dome and the peak concentration reaches 17%. When k-ε model is adopted, the peak concentration in the dome is 8%, hydrogen stratification is established in whole large space. Besides, hydrogen distribution near source also shows algebraic model cannot simulate turbulence diffusion in local compartment. It is more reasonable choosing k-ε model to study hydrogen behavior in containment. Based on adopted k-ε model, the effect of steam on hydrogen distribution is investigated. With steam injection, the hydrogen distribution is more homogeneous in upper space and average concentration is lower. In local compartment, due to diffusion enhanced by steam, the hydrogen concentration is higher in the bottom.
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Pitz, Diogo B., i William R. Wolf. "Direct Numerical Simulation of Radial Convection in a Cylindrical Annulus With and Without Rotation". W ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-5025.
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Abstract In rotating systems with temperature gradients, convection may occur due to gravitational or centrifugal effects. In cases where rotation is strong enough so that the centrifugal acceleration is higher than gravity, the flow is induced by centrifugal buoyancy and gravitational effects can be neglected. The problem of flow induced by centrifugal buoyancy in a cylindrical annulus has been used as a canonical setup to investigate industrial configurations, such as buoyancy-driven flows occurring in gas turbine secondary air systems, as well as geophysical flows, such as convection in the core of planets and the global circulation of the atmosphere. Due to the constraints imposed by the Taylor-Proudman theorem, such flows are quasi-homogeneous along the axial direction, and heat transfer as well as turbulent fluctuations tend to be suppressed by the action of the Coriolis force. Previous work has demonstrated that when the annulus is bounded by parallel disks, boundary layers scaling consistently with laminar Ekman layers are formed near each of the disks, even though the flow is purely buoyancy-induced. Also, the Nusselt number measured on the outer cylindrical surface has been shown to scale with the Rayleigh number as in natural convection between horizontal plates. In the present work we use direct numerical simulation (DNS) to investigate buoyancy-induced flow in an air-filled cylindrical annulus bounded by two adiabatic parallel disks, with and without rotation around the axis. In both cases the outer cylindrical surface is at a higher temperature than the inner one, so that a radial acceleration directed outwards induces an unstable stratification. In the case with rotation, the flow is induced by the centrifugal acceleration in the radial direction, and Coriolis forces are considered. For the case without rotation, the Coriolis terms are suppressed in the calculations, whereas the radial acceleration is the same as in the rotating case. Statistics are obtained and compared in the two cases, including the time-averaged Nusselt number, mean temperature profiles, velocity and temperature fluctuations, as well as terms of the turbulent kinetic energy equation. By analysing such statistics, the extent to which rotation suppresses heat transfer and turbulent fluctuations, as well as the contribution of each term to the turbulent kinetic energy budget, can be assessed.
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Ohno, Shuji, Takashi Takata i Yuji Tajima. "Evaluation of Sodium Pool Fire and Thermal Consequence in Two-Cell Configuration". W 2016 24th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/icone24-61095.
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Evaluation of accidental sodium leak, combustion, and its thermal consequence is one of the important issues to be assessed in the field of sodium-cooled fast reactor (SFR) since the liquid sodium is chemically active and might give thermal load to plant building structure due to its exothermic reaction with oxygen in air atmosphere. Therefore, many experimental investigations and numerical simulation tools development have been and still now are being carried out to understand the details of sodium fire behaviors and to contribute to the investigation and preparation of appropriate mitigation measures in the plant design. From various kinds of sodium fire situations, the present paper treats the sodium pool fire and subsequent heat transfer behavior in air atmosphere two-cell geometry both experimentally and analytically because such two-cell configuration is considered as the typical one to possess important characteristic of multi-compartment system seen in an actual plant. Main description of this paper consists of a sodium pool fire experiment that was performed in a rectangular-shaped two-cell system with an opening between the cells, and the discussion of the experimental results. Inner volume of the experimental cells is about 70 m3. The amount of used sodium and the prepared pool surface area in the experiment are about 55 kg and 2.25 m2, respectively. The experiment has provided the temperature data measured in more than 100 positions for atmospheric gas and structures other than the data of oxygen concentration and suspended sodium aerosols concentration in the cells. The analyses of the measured data clarify the basic characteristics of sodium pool combustion and consequential heat and mass transfer in the cells, for instance, suggesting several features of multidimensional thermal-hydraulic behaviors such as thermal stratification near the opening between the two cells. In the discussion, numerical analysis using a lumped-parameter based zonal model safety analysis code ‘SPHINCS’ and the comparison of its results with the experimental data are also carried out to investigate the validity and applicability of the code to this type of sodium fire situation.