Dissertations / Theses: 'Destratification'

1

Littlejohn, Carla Louise, and n/a. "Influence of Artificial Destratification on Limnological Processes in Lake Samsonvale (North Pine Dam), Queensland, Australia." Griffith University. Australian School of Environmental Studies, 2004. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20050211.133123.

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Artificial destratification equipment was installed in Lake Samsonvale in October 1995 to reduce the biomass of potentially toxic cyanobacteria in the reservoir. This study was undertaken to investigate the effects of the destratifier on the limnological processes occurring in the lake and to determine if operation of the destratifier has been effective at reducing the summer populations of Cylindrospermopsis raciborskii and Microcystis aeruginosa. The study showed that artificial destratification of Lake Samsonvale has been successful at reducing the surface to bottom thermal gradient and increasing dissolved oxygen concentrations at depth. While the destratifier has not resulted in the lake becoming completely 'mixed' during summer, it has weakened resistance to mixing from meteorological events, which has led to a reduction in mean concentrations of total and dissolved phosphorus during summer. Although not conclusive, it is likely that the influence of the destratifier is restricted to a narrow radial distance around the bubbleplumes during periods of strong stability, so internal loading may continue to provide a substantial source of nutrients for cyanobacterial growth, particularly in regions of the lake less influenced by the destratifier. The results for cyanobacteria are less encouraging. Despite the reduction in concentrations of dissolved phosphorus, the destratifier has not been effective at reducing summer populations of C. raciborskii and M. aeruginosa. On the contrary, there is evidence to suggest that populations have actually increased which could have serious operational consequences for the lake by mixing the previously buoyant cyanobacteria to the level of the water off-take. The growth season for C. raciborskii has been extended by up to 3 months and population onset now occurs during spring. This increase in spring populations could be a result of significantly greater baseline populations during winter, or the earlier germination of akinetes as a result of increased sediment temperatures. The seasonal successional relationship between C. raciborskii and M. aeruginosa appears to have shifted from one of alternating dominance between the two species to one of co-existence under conditions of intermediate disturbance. It was concluded that although the continued operation of the destratifier may prove useful to minimise water treatment costs through reducing internal loading of dissolved constituents, it has not been successful in achieving its original objective of controlling cyanobacterial populations in the lake.

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2

Littlejohn, Carla Louise. "Influence of Artificial Destratification on Limnological Processes in Lake Samsonvale (North Pine Dam), Queensland, Australia." Thesis, Griffith University, 2004. http://hdl.handle.net/10072/365764.

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Abstract:

Artificial destratification equipment was installed in Lake Samsonvale in October 1995 to reduce the biomass of potentially toxic cyanobacteria in the reservoir. This study was undertaken to investigate the effects of the destratifier on the limnological processes occurring in the lake and to determine if operation of the destratifier has been effective at reducing the summer populations of Cylindrospermopsis raciborskii and Microcystis aeruginosa. The study showed that artificial destratification of Lake Samsonvale has been successful at reducing the surface to bottom thermal gradient and increasing dissolved oxygen concentrations at depth. While the destratifier has not resulted in the lake becoming completely 'mixed' during summer, it has weakened resistance to mixing from meteorological events, which has led to a reduction in mean concentrations of total and dissolved phosphorus during summer. Although not conclusive, it is likely that the influence of the destratifier is restricted to a narrow radial distance around the bubbleplumes during periods of strong stability, so internal loading may continue to provide a substantial source of nutrients for cyanobacterial growth, particularly in regions of the lake less influenced by the destratifier. The results for cyanobacteria are less encouraging. Despite the reduction in concentrations of dissolved phosphorus, the destratifier has not been effective at reducing summer populations of C. raciborskii and M. aeruginosa. On the contrary, there is evidence to suggest that populations have actually increased which could have serious operational consequences for the lake by mixing the previously buoyant cyanobacteria to the level of the water off-take. The growth season for C. raciborskii has been extended by up to 3 months and population onset now occurs during spring. This increase in spring populations could be a result of significantly greater baseline populations during winter, or the earlier germination of akinetes as a result of increased sediment temperatures. The seasonal successional relationship between C. raciborskii and M. aeruginosa appears to have shifted from one of alternating dominance between the two species to one of co-existence under conditions of intermediate disturbance. It was concluded that although the continued operation of the destratifier may prove useful to minimise water treatment costs through reducing internal loading of dissolved constituents, it has not been successful in achieving its original objective of controlling cyanobacterial populations in the lake.
Thesis (Masters)
Master of Philosophy (MPhil)
Australian School of Environmental Studies
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3

Hayward, Donald Max. "Contribution to the hydrobiology of the York River: predicting surface mixed layer depth (destratification, tidal, semilunar, Virginia)." W&M ScholarWorks, 1986. https://scholarworks.wm.edu/etd/1539616690.

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Destratification in the York River, USA, during high spring tides is the result of the interruption of normal two-layer estuarine flow by advection of relatively fresh water in to the River mouth from the Chesapeake Bay. This is due to the presence of a longitudinal salinity gradient in the Bay and a difference of tidal current phase between the River and the Bay. Similar behavior is seen in other subestuaries of the Chesapeake Bay and may be common in subestuary-estuary interactions. Correlation and regression analysis are used to examine relationships between stratification variation in the lower York River and a variety of tidal and environmental parameters. A gross measure of stratification was derived from near surface and deep salinity samples. One hundred fifty six observations were made over a 434 day period from February 1982 to April 1983. The environmental and tidal factors evaluated were assessed on a daily basis and incorporated a variety of transformations. The factors included wind speed and direction, fresh water river flow from both the York and Rappahanock Rivers, water temperature, mean sea level and the following tidal parameters: observed and predicted daily mean and maximum high and low tide height, flood, ebb, and combined flood and ebb tidal ranges for Gloucester Point and for Hampton Roads. The results indicate that: (1) almost all of the tidal range or high tide height factors tested are equally strongly correlated with salinity difference, being associated with as much as 48% of the variation in that value; (2) that a combination of functions of tidal range and mean sea level at Gloucester Point are associated with more than 70% of the variation; and (3) that with the addition of wind stress terms as much as 80% of the variation can be included in the model. Over a range of observed salinity differences from 0.01 to 11.06 per mille the 25 term model predicts a range of -1.01 to 11.09 per mile with a root mean squared error of 0.99 per mile. A model predicting variation in surface mixed layer depth from salinity difference is also presented.

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4

Hein, Birte [Verfasser], and Thomas [Akademischer Betreuer] Pohlmann. "Processes of stratification and destratification in the Mekong ROFI - seasonal and intraseasonal variability / Birte Hein. Betreuer: Thomas Pohlmann." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2013. http://d-nb.info/1041716753/34.

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5

Gorieu, Olivier. "Étude de la destratification d'une interface épaisse en convection naturelle double-diffusive : application aux cuves de stockage de GNL." Nantes, 1999. http://www.theses.fr/1999NANT2105.

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Lorsque le reservoir de stockage est complete par du gaz naturel liquefie provenant d'un methanier, la difference de masse volumique avec le gnl initialement stocke peut creer une stratification verticale stable. Plusieurs auteurs ont montre que son evolution est lie aux transferts de masse et de chaleur a travers la zone interfaciale situee entre les deux couches. Dans la premiere partie, la convection double-diffusive explique le comportement d'un milieu stratifie chauffe lateralement et le comportement d'une interface diffusive. Les phenomenes de penetration a la paroi et d'entrainement sont introduits afin d'estimer l'influence de la convection naturelle sur le comportement du milieu stratifie. Dans la deuxieme partie, l'etude des stockages de gnl a mis en evidence un manque de comprehension sur le comportement des interfaces epaisses pendant la destratification. Dans la troisieme partie, le dispositif experimental, utilisant du freon et comprenant une cuve cylindrique transparente, a ete developpe pour etudier des interfaces epaisses. Dans la quatrieme partie, la synthese des 22 stratifications permet de caracteriser les mecanismes qui font evoluer l'interface epaisse vers une interface fine avant le melange. Dans la cinquieme partie, des simulations numeriques avec le code estet, en 2d-3 plans laminaire, ont mis en evidence la difficulte de reproduire quantitativement les resultats experimentaux. Dans la sixieme partie, des modeles de comportement sont proposes pour modeliser les phenomenes physiques tels que le developpement d'intrusions convectives, le phenomene de penetration a la paroi ou encore l'entrainement de part et d'autre de l'interface epaisse. Enfin, dans la septieme partie, la synthese compare les resultats experimentaux a des etudes anterieures et les perspectives de ce travail sont presentees.

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6

Marek, Tomáš. "Průběh destratifikace na vodní nádrži Brno." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2013. http://www.nusl.cz/ntk/nusl-216964.

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This thesis deals with the process of destratification at the Brno dam reservoir within the activities of a larger project "Clean Svratka", aimed to improvement of water quality in the catchment area upstream the Brno dam. At the Brno dam the project "Implementation of measures at the Brno Reservoir" has been in progress for the third year. Its aim is the proposal and implementation of measures to suppress the cyanobacteria mass development in the dam lake. One of the key measures is aeration and mixing of dam water through a 20 aeration tower. The theoretical part of this thesis focuses on seasonal conditions in the dam lake, the technology suitable for destratification and aeration and possibilities of their use. In the practical part of the thesis the seasonal destratification and the impact of meteorological conditions are monitored.

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7

Sluše, Jan. "Destratifikace vodních nádrží." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-446791.

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This doctoral thesis is focused on design of new equipment for aeration of water surface with low depth of water column. Aeration is one of ecological preventive methods to prevent growth of cyanobacteria. Increase of dissolved oxygen content in water mass leads to support of the growth of organisms which are disadvantaged by impossibility of movement in water mass and thus also to support biodiversity. Given biodiversity has a positive effect on water quality because it avoids the outbreak of one species of aquatic organism, in particular of cyanobacteria. Designed aeration equipment uses membrane formed by hollow fibre to transport oxygen into the water. When aeration dissolution of oxygen occurs directly on the membrane surface which prevents air leak in the form of bubbles. This type of aeration has low operating costs and high efficiency of input of the oxygen into the water. Distribution in the aquatic environment is ensured by special boat. This boat is moving on the water surface and the technology is installed on the upper deck. The aeration is carried out by an aeration module situated in the water. The movement of the boat is partially ensured by autonomous control.

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8

Oucherfi, Myriam. "Contribution à l'étude de la ventilation transversale lors d'un incendie en tunnel routier." Phd thesis, Université Claude Bernard - Lyon I, 2009. http://tel.archives-ouvertes.fr/tel-00652385.

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L'objectif de cette thèse est de présenter des critères simples pour l'évaluation des performances d'une ventilation transversale. On définit l'efficacité et le rendement, calculés à partir du flux de déficit de densité créé par l'incendie. Après une étude préliminaire permettant de caler les modèles numériques, l'influence de différents paramètres sur ces valeurs a été évaluée. Dans un premier temps, l'étude a porté sur une seule trappe et a montré que le courant d'air dans le tunnel est le paramètre le plus important. A l'inverse, la forme de la trappe pour une surface donnée n'a que très peu d'importance, sauf dans des cas limites (fente sur toute la largeur du tunnel). L'étude d'un canton à huit trappes confirme l'importance du contrôle du courant d'air. Lorsqu'on diminue le nombre de trappes en conservant la même surface totale d'aspiration, cette sensibilité tend à disparaître, mais l'efficacité diminue. Enfin, l'étude de l'influence de l'encombrement montre une légère amélioration de l'efficacité, due à l'obstruction d'une partie de la section par des camions, qui bloquent les fumées au droit des trappes.

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9

Oucherfi, Myriam. "Contribution à l'étude de la ventilation transversale lors d'un incendie en tunnel routier." Phd thesis, Lyon 1, 2009. http://n2t.net/ark:/47881/m6cc0z3v.

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L’objectif de cette thèse est de présenter des critères simples pour l’évaluation des performances d’une ventilation transversale. On définit l’efficacité et le rendement, calculés à partir du flux de déficit de densité créé par l’incendie. Après une étude préliminaire permettant de caler les modèles numériques, l’influence de différents paramètres sur ces valeurs a été évaluée. Dans un premier temps, l’étude a porté sur une seule trappe et a montré que le courant d’air dans le tunnel est le paramètre le plus important. A l’inverse, la forme de la trappe pour une surface donnée n’a que très peu d’importance, sauf dans des cas limites (fente sur toute la largeur du tunnel). L’étude d’un canton à huit trappes confirme l’importance du contrôle du courant d’air. Lorsqu’on diminue le nombre de trappes en conservant la même surface totale d’aspiration, cette sensibilité tend à disparaître, mais l’efficacité diminue. Enfin, l’étude de l’influence de l’encombrement montre une légère amélioration de l’efficacité, due à l’obstruction d’une partie de la section par des camions, qui bloquent les fumées au droit des trappes
The aim of this study is to present simple criteria to evaluate the performances of a transverse ventilation system. Efficiency and yield have been defined, based on the flux of density deficit createdby the fire. After a preliminary study of numerical models, the influence of different parameters on those criteria has been investigated. First, the study focused on the simplified case of a single damper. We showed that the air flow speed in the tunnel is the more important parameter. On the contrary, the shape of the damper has little influence on the efficency, except in unusual cases (slit on the whole width of the tunnel). Then, the study of a longer portion of the tunnel confirmed the prominence of the limitation of air flow speed. Comparison with a case with fewer dampers but the same total extraction section showed that this sensibility to air flow speed tends to disappear for larger dampers, but that the efficiency is lowered. Finally the study of the influence of heavy-goods-vehicules obstructing the tunnel reports better results, due to the fact that big objects tend to confine smokes

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10

Merrick, Chester John. "Phytoplankton-zooplankton interactions in Mt. Bold Reservoir, South Australia /." Title page, contents and summary only, 1990. http://web4.library.adelaide.edu.au/theses/09PH/09phm568.pdf.

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11

Linden, Leon Gareth. "Impact of destratification on the treat-ability of natural organic matter in drinking water reservoirs." Thesis, 2008. http://hdl.handle.net/2440/56819.

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Full text not available, contact Library_theses@adelaide.edu.au
The aim of this study was to describe the potential impact of stratification, and therefore destratification, and inflow hydrodynamics on the raw water quality in drinking water reservoirs, from the perspective of NOM. Investigations of the changes in the concentration, character and removal of NOM by conventional treatment processes during inflow hydrodynamics and thermal stratification were performed using observational and manipulative experiments and empirical and process based modelling. Further conceptual models were developed in place NOM within the existing frameworks of reservoir management from the perspective of other water quality hazards.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2008

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12

Linden, Leon Gareth. "Impact of destratification on the treat-ability of natural organic matter in drinking water reservoirs." 2008. http://hdl.handle.net/2440/56819.

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Title page, contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library.
The aim of this study was to describe the potential impact of stratification, and therefore destratification, and inflow hydrodynamics on the raw water quality in drinking water reservoirs, from the perspective of NOM. Investigations of the changes in the concentration, character and removal of NOM by conventional treatment processes during inflow hydrodynamics and thermal stratification were performed using observational and manipulative experiments and empirical and process based modelling. Further conceptual models were developed in place NOM within the existing frameworks of reservoir management from the perspective of other water quality hazards.
http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1321572
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2008

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13

Lewis, David M. "Surface mixers for destratification and management of Anabaena circinalis / by David Milton Lewis." 2004. http://hdl.handle.net/2440/22047.

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"March 2004"
Bibliography: leaves 221-234.
xxiv, 249 leaves : ill. (some col.), maps, photos (col.) ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
This research is part of the SA Water and Cooperative Centre for Water Quality and Treatment project entitled Destratification for control of phyloplankton. The major objective of this project was to assess a novel method of destratification and control of cyanobacteria, in particular Anabaena circinalis Rabenh. ex Born. et Flah, with the use of raft-mounted mechanical surface mixers with draft-tubes.
Thesis (Ph.D.)--University of Adelaide, School of Civil and Environmental Engineering, 2004

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14

Lewis, David Milton. "Surface mixers for destratification and management of Anabaena circinalis / by David Milton Lewis." Thesis, 2004. http://hdl.handle.net/2440/22047.

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Abstract:

"March 2004"
Bibliography: leaves 221-234.
xxiv, 249 leaves : ill. (some col.), maps, photos (col.) ; 30 cm.
This research is part of the SA Water and Cooperative Centre for Water Quality and Treatment project entitled Destratification for control of phyloplankton. The major objective of this project was to assess a novel method of destratification and control of cyanobacteria, in particular Anabaena circinalis Rabenh. ex Born. et Flah, with the use of raft-mounted mechanical surface mixers with draft-tubes.
Thesis (Ph.D.)--University of Adelaide, School of Civil and Environmental Engineering, 2004

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15

Oucherfi, Myriam. "Contribution à l’étude de la ventilation transversale lors d’un incendie en tunnel routier." Thesis, 2009. http://www.theses.fr/2009LYO10037/document.

Full text

Abstract:

L’objectif de cette thèse est de présenter des critères simples pour l’évaluation des performances d’une ventilation transversale. On définit l’efficacité et le rendement, calculés à partir du flux de déficit de densité créé par l’incendie. Après une étude préliminaire permettant de caler les modèles numériques, l’influence de différents paramètres sur ces valeurs a été évaluée. Dans un premier temps, l’étude a porté sur une seule trappe et a montré que le courant d’air dans le tunnel est le paramètre le plus important. A l’inverse, la forme de la trappe pour une surface donnée n’a que très peu d’importance, sauf dans des cas limites (fente sur toute la largeur du tunnel). L’étude d’un canton à huit trappes confirme l’importance du contrôle du courant d’air. Lorsqu’on diminue le nombre de trappes en conservant la même surface totale d’aspiration, cette sensibilité tend à disparaître, mais l’efficacité diminue. Enfin, l’étude de l’influence de l’encombrement montre une légère amélioration de l’efficacité, due à l’obstruction d’une partie de la section par des camions, qui bloquent les fumées au droit des trappes
The aim of this study is to present simple criteria to evaluate the performances of a transverse ventilation system. Efficiency and yield have been defined, based on the flux of density deficit createdby the fire. After a preliminary study of numerical models, the influence of different parameters on those criteria has been investigated. First, the study focused on the simplified case of a single damper. We showed that the air flow speed in the tunnel is the more important parameter. On the contrary, the shape of the damper has little influence on the efficency, except in unusual cases (slit on the whole width of the tunnel). Then, the study of a longer portion of the tunnel confirmed the prominence of the limitation of air flow speed. Comparison with a case with fewer dampers but the same total extraction section showed that this sensibility to air flow speed tends to disappear for larger dampers, but that the efficiency is lowered. Finally the study of the influence of heavy-goods-vehicules obstructing the tunnel reports better results, due to the fact that big objects tend to confine smokes

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Dissertations / Theses on the topic 'Destratification'

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