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1
Reid, Kevin John. "Effect of leakage flows on turbine performance." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613838.
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Kang, Eugene K. (Eugene Kim) 1976. "Control of tip-leakage flows using periodic excitation." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/80620.
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Popović, Ivan. "Aerothermal investigation of hub leakage flows in high-pressure turbines." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608563.
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Sivo, Joseph Michael Acosta Allan J. "Rotordynamic forces due to annular leakage flows in shrouded centrifugal pumps /." Diss., Pasadena, Calif. : California Institute of Technology, 1997. http://resolver.caltech.edu/CaltechETD:etd-03262007-103727.
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Saleh, Zainab Jabbar. "An investigation into turbine blade tip leakage flows at high speeds." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/33937.
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This investigation studies the leakage flows over the high pressure turbine blade tip at high speed flow conditions. There is an unavoidable gap between the un-shrouded blade tip and the engine casing in a turbine stage, where the pressure difference between the pressure and the suction surfaces of the blade gives rise to the development of leakage flows through this gap. These flows contribute to about one third of the aerodynamic losses in a turbine stage. In addition they expose the blade tip to a very high temperature and result in thermal damages which reduce the blade‟s operational life. Therefore any improvement on the tip design to reduce these flows has a significant impact on the engine‟s efficiency and turbine blade‟s operational life. At the engine operational condition, the leakage flows over the high pressure turbine blade tip are mostly transonic. On the other hand literature survey has shown that most of the studies on the tip leakage flows have been performed at low speed conditions and there are only a few experimental works on the transonic tip flows. This project aims to explore the tip leakage flows at high speed condition which is the real engine condition, both experimentally and computationally and establish a comprehensive understanding of these flows on different tip geometries. The effect of tip geometry was studied using the flat tip and the cavity tip models and the effect of in-service burnout on these two tip models was established using the radius-edge flat tip and the radius-edge cavity tip models. The experimental work was carried out in the transonic wind tunnel of Queen Mary University of London and the computational simulations were performed using RANS and URANS. As the flow approached each tip model it turned and accelerated around its leading edge in the same way as the flow turns around the leading edge of an aerofoil. In the case of the tip models with sharp edges the tip flow separated at the inlet to the tip gap. For the flat tip model the flow reattachment occurred further downstream whereas in the case of the cavity tip model the length of the pressure side rim was not sufficient for the reattachment to occur and the separated flow left the rim as a free shear layer. The cavity tip model was found to have a smaller effective tip gap and hence smaller discharge coefficient in comparison to the flat tip model. For the radius-edge tip models, no separation occurred at the inlet to the tip gap and the effective tip gap was found to be the same as the geometrical tip gap. Therefore it was concluded that the tip model with radius-edges had a larger effective tip gap and hence a greater discharge coefficient than the tip geometry with sharp edges. It was observed that in the case of the supersonic tip leakage flows, decreasing the pressure ratio PR (i.e. the ratio of the static pressure at the tip gap exit to the stagnation pressure at the inlet to the tip gap) increased the discharge coefficient Cd for the tip models with sharp edges but it decreased the Cd value in the case of the tip models with radius edges. The cavity tip model with sharp edges was found to have the smallest discharge coefficient and thus the best performance in reducing the tip leakage flows as compared to all the other tip models studied in this investigation.
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Knost, Daniel G. "Parametric Investigation of the Combustor-Turbine Interface Leakage Geometry." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/29145.
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Engine development has been in the direction of increased turbine inlet
temperatures to improve efficiency and power output. Secondary flows develop
as a result of a near-wall pressure gradient in the stagnating flow approaching
the inlet nozzle guide vane as well as a strong cross-passage gradient within the
passage. These flow structures enhance heat transfer and convect hot core flow
gases onto component surfaces. In modern engines it has become critical to cool
component surfaces to extend part life.
Bypass leakage flow emerging from the slot between the combustor and
turbine endwalls can be utilized for cooling purposes if properly designed. This
study examines a three-dimensional slot geometry, scalloped to manipulated
leakage flow distribution. Statistical techniques are used to decouple the effects
of four geometric parameters and quantify the relative influence of each on
endwall cooling levels and near-wall total pressure losses. The slot geometry is
also optimized for robustness across a range of inlet conditions.
Average upstream distance to the slot is shown to dominate overall cooling
levels with nominal slot width gaining influence at higher leakage flow rates.
Scalloping amplitude is most influential to near-wall total pressure loss as formation
of the horseshoe vortex and cross flow within the passage are affected.
Scalloping phase alters local cooling levels as leakage injection is shifted laterally
across the endwall.Ph. D.
7
Wallis, Anne Marjorie. "The control of secondary and leakage flows in a shrouded multistage turbine." Thesis, University of Cambridge, 1997. https://www.repository.cam.ac.uk/handle/1810/272686.
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Rosic, Budimir. "The control of shroud leakage flows in low aspect ratio multistage turbines." Thesis, University of Cambridge, 2006. https://www.repository.cam.ac.uk/handle/1810/251997.
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Chan, John Ka Ki Carleton University Dissertation Engineering Mechanical. "Measurement of the interaction between tip leakage and secondary flows in a turbine cascade." Ottawa, 1993.
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Lehmann, Knut. "Heat transfer and aerodynamics of over-shroud leakage flows in a high pressure turbine." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608775.
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Ranson, William Wayne. "Adiabatic Effectiveness Measurements of Leakage Flows along the Hub Region of Gas Turbine Engines." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/77017.
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To prevent melting of turbine blades, numerous cooling schemes have been developed to cool the blades using cooler air from the compressor. Unfortunately, the clearance gap between adjacent hub sections allows coolant to leak into the hub region. Coolant flow also leaks into the hub region through gaps between individual stages. The results of a combined experimental and computational study of cooling along the hub of a first stage turbine blade caused by leakage flows are discussed in detail. Additionally, this study examines a novel cooling feature, called a microcircuit, which combines internal convective cooling with external film cooling.
For the experimental investigation, scaled up blades were tested in a low speed wind tunnel. Adiabatic effectiveness measurements were made with infrared thermography of the entire hub region for a range of leakage flow conditions. For the computations, a commercially available computational fluid dynamics (CFD) code, FLUENT 6.0, was used to simulate the various flows.
Results show that featherseal leakage flows provide small cooling benefits to the hub. Increases in featherseal flow provide no additional cooling to the hub region. Unlike the featherseal, leakage flows from the front rim provide ample cooling to the hub region, especially the leading edge of the blade passage. None of the leakage flows provide significant cooling to the pressure side region of the hub or trailing edge suction side. With the addition of the hub microcircuits, there is improved hub cooling of the suction side of the blades. Though the coolant exit uniformity was low and affected by the featherseal flow, the microcircuits were shown to provide more cooling along the hub region. Good agreements were observed between the computational and experimental results, though computations over-predicted front rim cooling and microcircuit uniformity.Master of Science
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Fournis, Camille. "Study of tip clearance flows." Thesis, KTH, Flygdynamik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-244423.
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The tip leakage vortex is responsible for the generation of stagnation pressure losses inside the compressor along with the outbreak of rotating stall and surge. The current paper analytically proved that a part of the losses is proportional to the vortex circulation squared. The evolution of this circulation has been investigated as part of a parametric study which tested several clearance heights. The work consists in adopting a simplified single blade configuration to study the physics of the flow by means of wind tunnel experiments and numerical calculations. Upon visualising the main features of the flow, a model based on the study of jet in crossflows was implemented to describe the tip clearance flow for small gap sizes. For big gaps, the flow is assumed to behave as an isolated wing tip vortex which circulation is easily computed by the so called lifting line theory. The main vortical structures highlighted by the topology of the flow justified the use of the model of a jet in crossflow for small gap sizes. This model was challenged by experimental and numerical data and proved to well predict the evolution of the clearance vortex circulation for an increasing clearance height although some numerical results remain further away from the model.Gapvirveln är ansvarig för lufttryckförluster i motorn av ett flygplan och kan orsaka utbrottet av kompressorstall och pumpning. Artikeln bevisade matematiskt att en del av de här förlusterna är proportionell mot gapvirvelncirkulationen upphöjd. Utvecklingen av den där cirkulationen undersöktes med hjälp av en parametrisk studie som provkörde flera gapstorlekar. Arbetet bestå av att adoptera en förenklad enda blad konfiguration för att studera flödes fysik med vindtunnel experiment och flödesberäkningar. Efter att man analyserar flödes viktigaste egenskaper genomfördes en modell baserad på studien av en jet i ett korsflöde. Den här modellen används för att beskriva flödet för små gapstorlekar. För stora gap antar man att flödet beter sig som en vingspetsvirvel som cirkulationen kan beräknas utan svårighet med hjälp av lyftledningsteorin. Flödes topologi visualiserades tack vare numeriska beräkningar och legitimerade användningen av modellen av en jet i ett korsflöde för små gapstorlekar. Teoretiska, experimentella och numeriska resultat jämfördes och bevisade att modellen väl förutsäger utvecklingen av gapvirvelncirkulationen mot gapstorlek även om några numeriska resultat är långt från modellen.
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Anker, Jan Eric [Verfasser], and Michael V. [Akademischer Betreuer] Casey. "The simulation of turbomachinery flows at arbitrary Mach numbers and the analysis of leakage flows in shrouded axial turbines / Jan Eric Anker. Betreuer: Michael V. Casey." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2013. http://d-nb.info/1043688803/34.
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Khan, Mohammed Ajaz. "Leakage flow in labyrinth seals." Thesis, University of Bradford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.482781.
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Hansen, Douglas Dale. "Analytic modeling of leakage in confined aquifer systems /." Diss., ON-CAMPUS Access For University of Minnesota, Twin Cities Click on "Connect to Digital Dissertations", 2002. http://www.lib.umn.edu/articles/proquest.phtml.
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Palafox, Pepe. "Gas turbine tip leakage flow and heat transfer." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427699.
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Tilton, James S. "Tip leakage flow in a linear turbine cascade." Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/101324.
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An experimental investigation was performed to study the details of flow in the tip clearance gap of a linear turbine blade cascade. The cascade was designed and built to be geometrically similar to the earlier VPI&SU cascade; however, the new cascade also had a tip gap (2.1 percent of blade height) and two endwall boundary layer bleeds upstream of the blade row. The boundary layer bleeds were designed to reduce secondary flow other than the tip gap leakage flow in the cascade, and they performed well. The cascade flow had an exit Reynolds number based on the axial chord of 4.5 x 10⁵.
Static pressure measurements were made on the blades and on the endwall with particular attention given to the tip gap. Also, flow visualizations on the endwall and on the suction surface of the middle blade were performed.
From the pressure measurements, a minimum static pressure coefficient of -6.85 (based on the freestream velocity head) was obtained along the bottom of the blade, near the tip gap inlet. Avena contracta was evident, also in the tip gap entrance region, and a contraction coefficient of 0.61 was calculated from measured data. Mixing occurred after the vena contracta with the static pressure across the tip gap exit being fairly uniform. The flow visualizations showed a separation and reattachment on the endwall under the blade and a tip gap leakage vortex in the passage.
Models of the tip gap flow, based on potential flow theory and potential flow theory with mixing were discussed and developed. Potential flow theory accurately models the unloading along the pressure surface of the blade, and the endwall static pressure distribution of the tip gap, up to the vena contracta. It also predicts a contraction coefficient of 0.61.
The combined potential flow and mixing model accounts for the pressure rise in the tip gap due to mixing. It predicts a minimum static pressure coefficient under the blade of -6.81, which agrees well with measured data.M.S.
18
Adefila, Kehinde. "Flow measurement and leakage detection of gaseous CO2." Thesis, University of Kent, 2015. https://kar.kent.ac.uk/49162/.
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In order to combat the climate change caused by increasing emissions of CO2 from industrial processes, Carbon Capture and Storage (CCS) technologies have been accepted worldwide to address these pressing global warming concerns. So as to efficiently manage material and financial losses across the entire stream, accurate accounting and monitoring through fiscal metering of CO2 in CCS transportation pipelines are core and required features for the deployment of CCS technologies. Moreover, these technical requirements are part of the legal compliance schemes and guidelines from various regulatory bodies. This thesis reports experimental studies of two different metering technologies, an Averaging Pitot Tube (APT) and a Coriolis mass flowmeter (CMF), for CO2 flow measurement, together with the design and implementation of a CO2 flow calibration facility. A prototype system for the leak detection of the gas phase of CO2 is also developed. A review of the methodologies and technologies for the flow measurement and leak detection of CO2 gas is firstly given, followed by the discussion of the main challenges and technical requirements in their applications. Based on this review, two flow metering technologies, APT and CMF, are selected for experimental studies and a calibration platform using both volumetric and direct mass measurement methods for the gas phase of CO2 is also developed. The APT and CMF were calibrated and evaluated in the test facility. Experimental results obtained in this test facility demonstrate that the instruments are capable of accurately metering gaseous CO2 within a measurement uncertainty of ±1.5%. Flow characterization of the fluid under wet and mixed components conditions were further assessed with both meters. Under wet CO2 flow, results obtained show that both flow instruments are subject to significant measurement errors. The APT gave an error of up to ±25%, for a liquid fraction of 20%, while the error of the CMF was up ±6%, for a liquid fraction of 10%. Further investigations show that these errors can, however, be corrected through simple and straightforward algorithms that can be easily incorporated into computing processes in the flowmeters. In binary gaseous mixture tests, the CMF proved to be very reliable in the gas combination processes and likewise in the metering of the CO2 mixture (≤ ±1%), while a higher degree of uncertainty was registered for the APT (≤ ±4%). Overall analyses from investigations confirmed the APT and CMF instruments as promising technologies for CO2 flow measurement and can be further improved for application in actual CCS conditions. In addition, this thesis describes experimental investigations of the leak detection of CO2 gas from a pipeline, with emphasis on full controllability and flexibility of the operational process. An imaging system using passive temperature change detection techniques is designed, implemented and evaluated. The effectiveness of the developed technique is examined on a laboratory-scale flow rig system. Results obtained from tests confirmed the operability of the system configuration and validation of the thermal imaging approach. Suggestions for future development and enhancement of the proposed techniques are finally given.
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Sirakov, Borislav Todorov 1975. "Effects of upstream unsteady flow conditions on rotor tip leakage flow." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/82235.
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Henry, Gregory S. "A study of tip-leakage flow through orifice investigations." Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45779.
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"Compressible fluid dynamics of flow through plain-faced long orifices was investigated with the hope of gaining insight into the fluid dynamics of tip leakage flow. The Reynolds number range investigated was greater than 10*. Measurements were made of the discharge coefficient as a function of back pressure ratio for a sharp-edged orifice and long orifices with an l/d from 1/2 to 8. The discharge coefficient measurements indicate the mass flow rate in an orifice with an l/d of approximately 2 is the largest and the flow rate in a sharp-edged orifice is the smallest for pressure ratios greater than 0.27. The mass flow rate in a sharp-edged orifice is largest for pressure ratios below 0.27. To visualize the flow in a long orifice and model centerline pressure variation, a water table study was performed. The results demonstrate that the flow separates from the sharp corner at the orifice entrance, it accelerates to a maximum Mach number, and then the pressure increases. For back pressures above 0.50, a pressure decrease follows the initial pressure increase. If the maximum Mach number is supersonic, oblique shocks will exist. At the higher back pressures that produce supersonic maximum Mach numbers (0.50 PB/P0 < 0.70), the oblique shocks reflect from the centerline as ""Mach reflections"" and the flow is subsonic after the pressure increase. The maximum Mach number for a back pressure ratio of 0.50 is approximately 1.5. At lower back pressure ratios (PB/P0 <0.70), the oblique shocks reflect from the centerline in a ""regular"" manner and the flow remains supersonic on the centerline once supersonic speeds are reached. The flow in a long orifice is relatively constant for all back pressure ratios below approximately 0.30. The maximum Mach number for pressure ratios below 0.30 is approximately 1.8.
One-dimensional analyses were used to model the flow in long orifices with maximum Mach numbers less than 1.3. Higher discharge coefficients of long orifices compared to sharp-edged orifices are due to pressure rises in the orifices caused by mixing and shock waves. These increases in the discharge coefficients are partly offset by friction and boundary layer blockage. For maximum Mach numbers greater than 1.3, the flow in long orifices is believed to become significantly two-dimensional because of supersonic effects."Master of Science
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Joubert, Stephanus Lourens. "Mathematical modeling of leakage flow through labyrinth seals / Lourens Joubert." Thesis, North-West University, 2003. http://hdl.handle.net/10394/389.
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Optimization of gas turbine systems has identified the need for simplified mathematical
models to calculate the losses experienced within turbo machines. One such loss is that of
the flow through labyrinth seals. As part of a larger study, this study concentrates on the
development of such loss models to aid in the performance prediction of turbo machines.
The aim of this study was therefore firstly to understand the nature of labyrinth leakage
flows and secondly to investigate mathematical models to calculate or predict such
leakages through most common geometries. Finally the ability of these models was
evaluated by implementing the models into an "engineering tool" in Engineering
Equation Solver (EES).
From a detailed literature survey, a few models for calculating and describing labyrinth
seal leakages were identified. An "engineering tool" was subsequently developed by
combining these models and the governing coefficients in the EES software. Although
experimental validation would have been the optimum, a lack of such facilities together
with a limited budget required alternative methods to be investigated. It was therefore
decided to use Computational Fluid Dynamics (CFD) software such as Star-CD and
Fluent. These software packages are accepted by the industry as a design standard and
visualizing tool for validation. The results obtained compared favourably with that of the
"engineering tool". It therefore proved that the suggested models offer good potential to
be used for performance prediction of labyrinth seals.Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2004.
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Kondo, Daishi. "Preventing information leakage in NDN with name and flow filters." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0233/document.
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Au cours des dernières années, les réseaux de type (NDN) sont devenus une des architectures réseau les plus prometteuses. Pour être adopté à l'échelle d'Internet, NDN doit résoudre les problèmes inhérents à l'Internet actuel. La fuite d’informations fait partie de ces problèmes, et il est très important d’évaluer ce risque pour les réseaux de type NDN. La thèse se propose d'évaluer ce risque. En supposant (i) qu'un ordinateur appartient au réseau d'une entreprise basée sur une architecture NDN, (ii) que l'ordinateur a déjà été compromis par un support malveillant, et (iii) que la société installe un pare-feu, la thèse évalue la situation dans laquelle l’ordinateur infecté tente de divulguer des données à un attaquant externe à l'entreprise. Les contributions de cette thèse sont au nombre de cinq. Tout d'abord, cette thèse propose une attaque par fuite d'informations via un paquet donné et un paquet intérêt propres à NDN. Deuxièmement, afin de remédier à l'attaque fuite d'informations, cette thèse propose un pare-feu basé sur l'utilisation d'une liste blanche et d'une liste noire afin de surveiller et traiter le trafic NDN provenant des consommateurs. Troisièmement, cette thèse propose un filtre de noms NDN pour classifier un nom dans un paquet d'intérêt comme étant légitime ou non. Le filtre de noms peut ainsi réduire le débit par paquet d'intérêt. Cependant, pour adapter la vitesse de l'attaque, les logiciels malveillants peuvent envoyer de nombreux intérêts en très peu de temps. De même, le logiciel malveillant peut exploiter un intérêt avec une information explicite dans le nom (comme peut le faire un message véhiculé par un POST sur HTTP). Cela dépasse alors la portée du filtre de nom proposé et rend le filtre inefficace. Pour prendre en compte le flux de trafic analysé par le pare-feu NDN, cette thèse propose comme quatrième contribution la surveillance du flux NDN à travers le pare-feu. Enfin, afin de traiter les inconvénients du filtre de noms NDN, cette thèse propose un filtre de flux NDN permettant de classer un flux comme légitime ou non. L'évaluation des performances montre que le filtre de flux complète de manière tout à fait performante le filtre de nom et réduit considérablement le débit de fuite d'informationsIn recent years, Named Data Networking (NDN) has emerged as one of the most promising future networking architectures. To be adopted at Internet scale, NDN needs to resolve the inherent issues of the current Internet. Since information leakage from an enterprise is one of the big issues even in the Internet and it is very crucial to assess the risk before replacing the Internet with NDN completely, this thesis investigates whether a new security threat causing the information leakage can happen in NDN. Assuming that (i) a computer is located in the enterprise network that is based on an NDN architecture, (ii) the computer has already been compromised by suspicious media such as a malicious email, and (iii) the company installs a firewall connected to the NDN-based future Internet, this thesis focuses on a situation that the compromised computer (i.e., malware) attempts to send leaked data to the outside attacker. The contributions of this thesis are fivefold. Firstly, this thesis proposes an information leakage attack through a Data and through an Interest in NDN. Secondly, in order to address the information leakage attack, this thesis proposes an NDN firewall which monitors and processes the NDN traffic coming from the consumers with the whitelist and blacklist. Thirdly, this thesis proposes an NDN name filter to classify a name in the Interest as legitimate or not. The name filter can, indeed, reduce the throughput per Interest, but to ameliorate the speed of this attack, malware can send numerous Interests within a short period of time. Moreover, the malware can even exploit an Interest with an explicit payload in the name (like an HTTP POST message in the Internet), which is out of scope in the proposed name filter and can increase the information leakage throughput by adopting a longer payload. To take traffic flow to the NDN firewall from the consumer into account, fourthly, this thesis proposes an NDN flow monitored at an NDN firewall. Fifthly, in order to deal with the drawbacks of the NDN name filter, this thesis proposes an NDN flow filter to classify a flow as legitimate or not. The performance evaluation shows that the flow filter complements the name filter and greatly chokes the information leakage throughput
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Stathis, Jonathan Alexander. "A Model for Determining Leakage in Water Distribution Systems." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/46422.
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Leaks in pipe networks cause significant problems for utilities and water users in terms of lost revenue and interrupted service. In many cities the leakage is as high as forty percent. A water audit is carried out to assess system-wide leakage. However, to detect leakage at the level of a pipeline, a physical measurement technique is generally employed. For large cities the distribution piping length amounts to a few thousand miles. Therefore, the physical measurements can become tedious and expensive. In this thesis it is assumed that a spatial distribution of leakage can be estimated at nodes based on a water audit bookkeeping scheme. A mathematical formulation consisting of continuity, energy (headloss), pressure-dependent demands and/or leakage, and flow direction preservation equations are utilized to distribute demand flows and leakage among pipes. The leakage is attributed to the formation of corrosion holes. Based upon the extent of corrosion, the leakage flow arriving at a particular node is apportioned among all pipes that are converging at that node. Therefore, the formulation presented in this thesis captures the two essential elements behind leakage, namely, pressure driven flow distribution and the vulnerability of pipes to corrosion.
The proposed formulation allows utilities to be more proactive in identifying leakage prone districts within the water distribution system. An understanding of the pressure-dependent leakage in the system is helpful when performing a water audit and in developing strategies for leak repair programs. Restoring the full capacity of the water distribution system will greatly increase the reliability of the system, thereby benefiting local utilities and water users.Master of Science
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Anderson, C. Scott. "Analysis of the tip leakage flow field in an axial turbine." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA371278.
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Thesis (Degree of Aeronautical Engineer) Naval Postgraduate School, June 1999."June 1999". Thesis advisor(s): Garth V. Hobson. Includes bibliographical references (p. 161-163). Also Available online.
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Chen, Han. "Quantitative information flow, maximum leakage and its applications to anonymity protocols." Thesis, Queen Mary, University of London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509676.
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Newton, Paul John. "Aerodynamic and heat transfer measurements in turbine tip leakage flow models." Thesis, University of Bath, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421250.
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This thesis describes experiments performed to investigate the heat transfer and aerodynamic aspects of tip leakage flow in an unshrouded axial turbine. Experiments were performed in a transonic 2-D tunnel and in a low speed 3-D cascade. The influence of varying a number of parameters influencing the tip flow has been studied and analysed both using standard aerodynamic measurement techniques and full surface heat transfer measurements employing thermochromic liquid crystal. The heat transfer study utilised a mesh heater to generate the transient required for solution of Fouriers' 1-0 conduction equation. To the authors' knowledge this is the first such study to employ this method for tip leakage flow investigations, and the strategies used in successfully implementing it have been detailed. An improved technique for transient heat transfer analysis has been developed and extensively investigated with regards to uncertainties and the controls that can be put in place to minimise them in the design phase of the experiment. Experiments were performed on a number of cooled and uncooled geometries. Measurements in both transonic 2-D and low speed 3-D environments displayed similar salient features. For a plain tip the leakage flow is dominated by a venacontracta which is formed when the leakage flow separates off the pressure side corner into the tip gap. The separation reduces the leakage flow through the gap but upon reattachment to the tip surface generates the highest levels of heat transfer encountered on the blade. Squealer and cavity geometries were designed and investigated and, for the profiles studied, there was found to be a trade off between the reduction of discharge through the tip gap and the reduction of heat transfer to the tip surface. Where as the suction side squealer profiles displayed the lowest heat transfer in both 2-D and 3-D experiments the cavity profiles yielded the lowest discharge coefficient. Coolant configurations were designed to optimise delivery of the coolant to the regions which had indicated highest heat transfer based on the results of the uncooled tests. As such coolant holes were located so as to infiltrate the reattachment region. Coolant performance relative to that of the profiled squealer tip geometries was quantified by means of the Net Heat Flux Reduction (NHFR), a technique that compiles the heat transfer and film cooling effectiveness data and transposes the experimental measurements to engine conditions. Locating coolant holes inside the separation bubble with a sub unity blowing rate was found to reduce the heat flux to the tip by up to 37%
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Schabowski, Zbigniew. "Aero-thermal investigation of tip leakage flow in unshrouded axial turbines." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608523.
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Wang, Yu. "Tip Leakage Flow Downstream a Compressor Cascade with Moving End Wall." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/31628.
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A large-scale moving end-wall system has been designed and built at the Aerospace and Ocean Engineering Department of Virginia Tech. This system forms part of a low-speed linear compressor cascade wind tunnel, where it is used to simulate the effects of the relative motion between the blade tips and casing upon the flow. Detailed 4-sensor hot wire measurements were made at various locations downstream the cascade. The results are presented in term of mean flow field and turbulence flow field. In order to reveal the effects of moving end wall, the results also compared with the results obtained with stationary end wall.Master of Science
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Krishnababu, Senthil Kumar. "A computational investigation of tip leakage flow and heat transfer in unshrouded axial flow turbines." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614265.
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Zhou, Chao. "Aero-thermal performance of tip leakage flow in high pressure turbine cascades." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609146.
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Wang, Haotian. "Influence on tip leakage flow in a compressor cascade with plasma actuation." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-264269.
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As one of the key components of aero engines, compressor is required to endure higher pressure, possess higher efficiency and wider operating range. Intensive studies have been made on tip leakage flow and researchers find that by reasonably organizing tip leakage flow, aero engines are more likely to achieve better performance and reliability. Conventional flow controlling methods like casing treatment and micro jet could substantially modify tip leakage flow, unfortunately with a price of additional loss, not to mention the difficulty in manufacturing such structure. Whereas plasma actuation flow control method uses plasma actuators, such equipment is easy to build, responses fast and has a wide excitation bandwidth. This method has become a new trend in internal flow active control field. In this research, a phenomenological model is adopted to simulate DBD plasma actuation in the flow field inside a compressor cascade. The aim is to find out how plasma actuation will influence tip leakage flow. Meanwhile possible means to improve plasma actuation performance are discussed. First of all, numerical simulation of flow inside a compressor cascade without plasma actuation is conducted to validate accuracy of the numerical methodology adopted and then determine one numerical approach that satisfies specific needs sufficiently. Meanwhile, influence of casing movement on tip leakage flow as well as possible mechanism of tip leakage vortex core generation is investigated in detail. The results indicate: 1. Generating position of tip leakage vortex moves towards leading edge with increasing moving speed of shroud. 2. As shroud moving speed increases, trajectory of tip leakage vortex moves away from suction side of blade and closely towards shroud. 3. Casing movement tends to transform tip leakage vortex from circular to oval shape due to circumferential shearing. 4. Casing movement has little influence on total pressure field concerning absolute pressure value. While total pressure loss does reduce slightly with increasing moving speed of shroud. 5.Vorticity transport from tip clearance into passage may be contributing significantly to generation of tip leakage vortex inner core. Secondly, a simplified model of DBD plasma actuation based on literature [1] is derived and applied through UDF function of commercial software Fluent into the flow field. Different actuation positions, voltages and frequencies are applied in simulation and compared. After that casing movement is included. Main conclusions are as follow: 6. Plasma actuation shows significant suppressing effect on tip leakage vortex on both size, trajectory and strength. 7. The suppressing effect on tip leakage vortex grows stronger as actuator moves towards leading edge. 8. Increasing actuation voltage results in stronger suppressing effect on tip leakage vortex. 9. Plasma actuation can effectively improve total pressure loss situation near shroud region with increasing actuation power. 10. Increasing actuation frequency results in stronger suppressing effect on tip leakage vortex as well. Additionally, frequency performs slightly better than voltage. 11. Casing movement tends to weaken suppressing effect of tip leakage vortex by plasma actuation. More actuation power is needed to achieve sufficient suppressing effect in real compressors.Som en av de viktigaste komponenterna i flygmotorer krävs det att kompressorn utsätts för högre tryck, har högre effektivitet och större driftsintervall. Intensiva studier har gjorts om skovlarnas toppspel läckageflöde och man anser att det är mer sannolikt att flygmotorer uppnår bättre prestanda och tillförlitlighet genom att på ett rimligt sätt reglera läckageflödet i toppspelet. Konventionella metoder för reglering av flödet, som behandling av “casing” och mikrojet, skulle kunna ändra läckageflödet avsevärt, men medför tyvärr ytterligare förlust, för att inte tala om svårigheten att tillverka en sådan struktur. Samtidig flödeskontroll med hjälp av plasma aktuatorer som är relativt lätta att bygga, reagerar snabbt och har en bred excitationsbandvid. Denna metod har blivit en ny trend inom det interna flödesaktiva kontrollområdet. I denna forskning antas en modell för att simulera plasmaaktivering av DBD i flödesfältet i en kompressorskaskad. Man försöker ta reda på hur plasmaaktivering påverkar läckageflödet. Möjliga sätt att förbättra effekten av plasmaaktivering diskuteras. För det första genomförs numerisk simulering av flödet i en kompressorskaskad utan plasmaaktivering för att validera noggrannheten i den numeriska metoden. Därefter undersöks i detalj vilken inverkan den relativa rörelsen av ”casing” har på läckageflödet genom toppspelet och mekanismen för toppspelsvirvel analyseras. Resultaten visar: 1. Startposition för läckagevirveln rör sig mot skovelns framkant när man introducerar och ökar den relativa hastigheten för ”casing”. 2. I takt med att den relativa hastigheten ökar, kretsbanan för läckage virveln rör sig bort från skovelns sugsida och närmare mot ”casing”. 3. Den relativa rörelsen tenderar att omvandla virveln från cirkulär till oval form på grund av skjuvkrafter. 4. Den relativa rörelsen av ”casing” påverkar inte det totala tryckfältet när det gäller det absoluta tryckvärdet. Samtidigt som den totala tryckförlusten minskar något med ökad hastighet. 5. Virveltransport från toppspelet till huvudkanalen kan på ett betydande sätt bidra till att skapa virvelns inre kärna. I senare delen av arbetet utvecklas och tillämpas en förenklad modell för plasmaaktivering av DBD baserad på litteratur [1], genom att använda UDF‐funktionen i kommersiell CFD programvara Fluent. Olika aktuatorläge, spänningar och frekvenser prövas i simuleringen och jämförs. De viktigaste slutsatserna är följande: 6. Aktuering av plasma visar en betydande dämpningseffekt på läckagevirveln i toppspelet både va det gäller dess storlek, bana och styrka. 7. Den dämpande effekten på läckagevirveln blir starkare när aktuator monteras närmare skovelns framkant. 8. Ökad aktuatorspänning leder till en starkare dämpande effekt på läckagevirveln. 9. Ökad aktuatorfrekvens leder till starkare dämpningseffekt på läckagevortex också.mDessutom fungerar frekvensen något bättre än spänningen. 10. Den relativa rörelsen av ”casing” försvagar effekten av plasmaaktuering. För att uppnå tillräcklig dämpningseffekt i riktiga kompressorer krävs mer effekt till aktuatorn.
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Murphy, David Wayne. "The application of passive flow control to bileaflet mechanical heart valve leakage jets." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31700.
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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Co-Chair: Ajit Yoganathan; Committee Co-Chair: Ari Glezer; Committee Member: Rudy Gleason. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Brewer, Wesley Huntington. "On simulating tip-leakage vortex flow to study the nature of cavitation inception." Diss., Mississippi State : Mississippi State University, 2002. http://library.msstate.edu/etd/show.asp?etd=etd-04102002-134949.
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Li, Bo. "Aerodynamic and acoustic analysis of the tip-leakage flow past a single ailfoil." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEC042/document.
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L'écoulement de jeu est un phénomène très important dans les turbomachines. Il provient du mouvement relatif entre la pale et la paroi d'extrémité, et la différence de pression à travers la pale. L'écoulement de jeu est extrêmement complexe pour sa nature tridimensionnelle et instable, et son existence conduit à de nombreux effets défavorables, par exemple, les pertes de performance aérodynamique et les émissions de bruit. C'est pourquoi l'écoulement de jeu a motivé de nombreuses recherches expérimentales et numériques. Afin d'améliorer la compréhension du écoulement de jeu et le bruit de large bande associé, une campagne de recherche a été menée au LMFA. En ce qui concerne l'écoulement de jeu, cette campagne de recherche comprend une expérience avec des technologies de mesure avancées, un calcul zonal LES et une série de calculs RANS / URANS. L'expérience et les simulations considèrent une configuration simple de l'écoulement de jeu à un faible nombre de Mach. Les résultats expérimentaux et numériques sont analysés de façon systématique et approfondie dans la présente étude. Enfin, des efforts sont déployés pour la modélisation et la prédiction du bruit à large bande avec des résultats expérimentaux et numériques. On observe dans l'expérience un système à multiple-tourbillon, avec une tourbillon de jeu intense. Les différentes analyses sur les caractéristiques d'écoulement montrent un bon accord entre l'expérience et le ZLES dans la région du écoulement de jeu. L'approche zonale (RANS-LES) s'avère être un outil puissant pour fournir une description détaillée du écoulement de jeu, avec un coût de calcul limité. Cependant, les calculs RANS et URANS surestiment globalement la diffusion de la tourbillon. En outre, l'oscillation du tourbillon de jeu est étudiée en utilisant des champs instantanés de PIV et l'amplitude d'oscillation est évaluée. La réponse dynamique de la tourbillon de jeu est également étudiée avec URANS aux fréquences choisies. Deux modèles de prédiction du bruit en champ lointain, correspondant à deux sources acoustiques différentes, sont reformulés et mis en oeuvre avec les données de champ proche des simulations numériques. Ces prédictions sont comparées aux mesures à champ lointain. En utilisant les données ZLES, le modèle de l’écoulement de jeu sur-estime le bruit généré dans la région de jeu. Le modèle de bruit de bord de fuite est implémenté avec les données ZLES et les données RANS et fournit une très bonne prédiction dans une large bande de fréquenceThe tip-leakage flow is a common flow feature in turbomachines. It originates from the relative motion between the blade tip and the end-wall, and the pressure difference across the blade. The tip-leakage flow is extremely complex for its three-dimensional unsteady nature, and its existence leads to many unfavourable effects, such as aerodynamic performance losses and noise emissions. These issues have motivated extensive experimental and numerical researches from both aerodynamic and aeroacoustic points of view. In order to improve the understanding of the tip-leakage flow and its associated broadband noise, a research campaign has been carried out at LMFA. Regarding the tip-leakage flow, this research campaign includes an experiment with advanced measurement technologies, a zonal LES computation and a series of RANS/URANS computations. Both the experiment and the simulations consider a single-airfoil configuration at low Mach number. Experimental and numerical results are analysed systematically and thoroughly in the current study. Finally, efforts are put on the broadband noise modelling and prediction based on the experimental and numerical results. A multi-vortex system with an intense tip-leakage vortex is observed in the experiment. The various analyses of the flow characteristics show a good agreement between the experiment and the ZLES in the blade tip region. The zonal (RANS-LES) approach proves itself to be a powerful tool to provide a detailed description of the tip-leakage flow, with a limited computational cost. However, the RANS and URANS computations globally over-estimate the diffusion of the tip-leakage vortex. Furthermore, the random oscillation of the tip-leakage vortex is investigated using PIV instantaneous flow fields and the wandering amplitude is evaluated. The dynamic response of the tip-leakage vortex is also studied with URANS at selected frequencies. Two far-field noise prediction models, corresponding to two different acoustic sources, are reformulated and implemented with the near-field data from the numerical simulations. These predictions are compared to the far-field measurements. Using the ZLES data as input, the blade-tip self-noise model is found to over-estimate the noise generated in the blade-tip region. The trailing-edge noise model is implemented with the time-averaged ZLES and the RANS near-field data, and yields a very good prediction within a broad range of frequency
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Chaudhry, Udey. "Tip leakage flow, heat transfer and blade lifting in a jet engine turbine." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/94499.
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An existing Navier-Stokes code (MEFP) was used to calculate developing flow and heat transfer in turbine tip gaps. Successful calculations of the heat transfer to a model turbine blade tip were obtained with a Prandtl mixing length turbulence model. The calculations revealed details of the flow development including recirculation and reattachment on the blade tip surface. The calculated heat transfer distributions were in good agreement with experimental data. A combined solution of the energy equation in the tip gap flow and in the rotor blade tip gave tip temperature distributions.
An independent computational study, using the same numerics as MEFP but a separate new computer program, was also performed to investigate the numerical accuracy of heat transfer calculations for fully developed flow.
A literature survey of gas turbine blade materials and factors influencing turbine tip blade life was performed. Approximate temperature ranges for the significant blade life reduction mechanisms, hot corrosion, oxidation, and melting were determined. calculations for typical jet engine conditions, In the present a maximum tip temperature of 1488 K was predicted which would lead to high oxidation rates for present day turbine blade alloys.M.S.
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Huang, Xujing. "Quantitative information flow of side-channel leakages in web applications." Thesis, Queen Mary, University of London, 2016. http://qmro.qmul.ac.uk/xmlui/handle/123456789/12864.
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It is not a secret that communications between client sides and server sides in web applications can leak user confidential data through side-channel attacks. The lower lever traffic features, such as packet sizes, packet lengths, timings, etc., are public to attackers. Attackers can infer a user's web activities including web browsing histories and user sensitive information by analysing web traffic generated during communications, even when the traffic is encrypted. There has been an increasing public concern about the disclosure of user privacy through side-channel attacks in web applications. A large amount of work has been proposed to analyse and evaluate this kind of security threat in the real world. This dissertation addresses side-channel vulnerabilities from different perspectives. First, a new approach based on verification and quantitative information flow is proposed to perform a fully automated analysis of side-channel leakages in web applications. Core to this aim is the generation of test cases without developers' manual work. Techniques are implemented into a tool, called SideAuto, which targets at the Apache Struts web applications. Then the focus is turned to real-world web applications. A black-box methodology of automatically analysing side-channel vulnerabilities in real-world web applications is proposed. This research demonstrates that communications which are not explicitly involving user sensitive information can leak user secrets, even more seriously than a traffic explicitly transmitting user information. Moreover, this thesis also examines side-channel leakages of user identities from Google accounts. The research demonstrates that user identities can be revealed, even when communicating with external websites included in Alexa Top 150 websites, which have no relation to Google accounts.
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Roberts, Jennifer Jean. "Natural CO₂ fluids in Italy : implications for the leakage of geologically stored CO₂." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/11805.
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A principle concern for engineered CO2 storage is long-term security. Surface leakage (‘seepage’) of injected CO2 to the surface is economically and environmentally undesirable. Italy is a region of intense natural CO2 degassing; 308 CO2 seeps are catalogued which exhibit different surface characteristics, and a number CO2 rich reservoirs were discovered when drilling for hydrocarbons. These seeps and reservoirs provide excellent natural analogues for seeps that might arise from breached carbon stores. This thesis explores the geological controls on the crustal plumbing of CO2 fluids to model the processes governing CO2 seep locations and distribution, and characteristics; and their consequences on human health risk. Risk of human death from accidental CO2 poisoning at all seep types is low (10-8 yr-1) and several factors influence risk of human mortality. Seeps distribute on two spatial scales; on a local scale (<5 km) seeps are clustered and aligned with subsidiary geologic structures, while on large scales seep clusters are discrete, and align with regional structures. Within clusters, seep locations are influenced by fault maturity, the presence of lithological boundaries and seep manifestation, which is determined by the flow properties of the outcropping lithology and local topography. Sealing and seeping CO2 reservoirs are identified, and their geological characteristics compared. Italian reservoirs successfully retain large CO2 columns at a range of reservoir conditions. Reservoirs which have hydrostatic pressure conditions in the overburden, determined from well logs, are located close to surface CO2 seeps and recent extensional faults. Where there is significant overpressure above hydrostatic in the overburden, there are no seeps present above the reservoir structure. Overpressure of reservoir fluids may enhance fluid flow rates but is not a necessary condition for CO₂ leakage. Geothermal conditions influences the style of leakage at depths and towards the surface. Total CO2 degassing from dry Italian CO2 seeps is 3.5 ± 0.5 Mt(CO2)yr-1. It would take thousands of years for the effectiveness of a commercial scale store to be significantly reduced if it leaks to form a single seep with the mean flux rates modeled in Italy. If a seep cluster develops, the storage effectiveness will reduce more rapidly, and could negate engineered CO₂ storage as a climate mitigation strategy. The research presented in this thesis contributes to a body of knowledge which directly informs site selection procedure for carbon storage and maximise the long term storage potential for CCS. Thorough scientific understanding of the geological processes governing fluid escape is crucial to assure the scientific, political and public communities that safe, long-term carbon storage can be realised as an effective climate mitigation technology.
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Manzi, Daniel. "Determinação de parâmetros do modelo pressão-vazamento para setor de distribuição de água da cidade de Piracicaba, SP." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/18/18138/tde-26112015-161053/.
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A redução das perdas em sistemas de distribuição de água tem se tornado, além de uma questão ética, um determinante da eficiência e mesmo da sobrevivência das concessionárias destes serviços. A quantificação e determinação da natureza das vazões perdidas, que possuem relação íntima com as pressões de operação, são aspectos que ainda merecem análises mais profundas e práticas. Os parâmetros do modelo pressão-vazamento permitem o detalhamento das perdas físicas e foram obtidos por meio de calibrações para um setor de distribuição de água da cidade de Piracicaba, SP, em padrões hidráulicos distintos - sob hipótese de consumo noturno nulo (vazão mínima noturna), descargas de rede, patamares de pressão e sob consumo diurno dirigido pela pressão através de curvas encontradas na literatura e propostas. Os resultados obtidos indicaram que os valores dos parâmetros do modelo pressão-vazamento não são fixos, mas variam conforme o padrão hidráulico de operação da rede. Estudos acerca do parque de hidrômetros e seus desvios de indicação também foram realizados, em conjunto com uma análise das vazões típicas de abastecimento residencial, e apontaram para fortes erros de medição em razão do uso de reservatórios domiciliares.Losses reduction on water supply networks came to be, beyond the ethical question, a condition for efficiency and even survival of enterprises which develop those services. Quantification and determination of the nature of leakage, which are closely related to operational pressure, are aspects which still claim for deeper and more practical analysis. Parameters to the pressure-leakage model allows to detail physical losses at one given system, and they were obtained throughout employment of distinct hydraulic patterns - minimal night flow (no usage), network flush situations, pressure levels and day usage driven by pressure from curves found on lectures and author\'s propositions - when proceeding calibration at a water supply section at the Piracicaba city, SP. Achieved results have shown that pressure-leakage model parameters values are not constant, but really change according to network\'s operational hydraulic pattern. Studies concerning section\'s water flow meters and its measuring deviation were also done, and joined to an analysis of typical patterns of home usage flows; they have pointed to huge metering errors because of employment of home reservoirs.
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Farge, Talib Z. "The effect of tip leakage, backswept blades and inlet distortion on centrifugal compressor flow." Thesis, University of Liverpool, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304987.
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Novakovic, Christopher. "Computing and estimating information leakage with a quantitative point-to-point information flow model." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5900/.
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Information leakage occurs when a system exposes its secret information to an unauthorised entity. Information flow analysis is concerned with tracking flows of information through systems to determine whether they process information securely or leak information. We present a novel information flow model that permits an arbitrary amount of secret and publicly-observable information to occur at any point and in any order in a system. This is an improvement over previous models, which generally assume that systems process a single piece of secret information present before execution and produce a single piece of publicly-observable information upon termination. Our model precisely quantifies the information leakage from secret to publicly-observable values at user-defined points - hence, a "point-to-point" model - using the information-theoretic measures of mutual information and min-entropy leakage; it is ideal for analysing systems of low to moderate complexity. We also present a relaxed version of our information flow model that estimates, rather than computes, the measures of mutual information and min-entropy leakage via sampling of a system. We use statistical techniques to bound the accuracy of the estimates this model provides. We demonstrate how our relaxed model is more suitable for analysing complex systems by implementing it in a quantitative information flow analysis tool for Java programs.
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AbdelMeguid, Hossam Saadeldin. "Pressure, leakage and energy management in water distribution systems." Thesis, De Montfort University, 2011. http://hdl.handle.net/2086/4905.
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A fast and efficient method to calculate time schedules for internal and boundary PRVs and flow modulation curves has been developed and implemented. Both time and flow modulation can be applied to a single inlet DMA. The time modulation methodology is based on solving a nonlinear programming problem (NLP). In addition, Genetic Algorithms (GA) has been proposed and investigated to calculate the optimal coefficients of a second order relationship between the flow and the outlet pressure for a PRV to minimize the background leakage. The obtained curve can be subsequently implemented using a flow modulation controller in a feedback control scheme. The Aquai-Mod® is a hydraulic device to control and modulate the outlet pressure of a PRV according to the valve flow. The controller was experimentally tested to assess its performance and functionality in different conditions and operating ranges. The mathematical model of the controller has been developed and solved, in both steady state and dynamic conditions. The results of the model have been compared with the experimental data and showed a good agreement in the magnitude and trends. A new method for combined energy and pressure management via integration and coordination of pump scheduling with pressure control aspects has been created. The method is based on formulating and solving an optimisation NLP problem and involves pressure dependent leakage. The cost function of the optimisation problem represents the total cost of water treatment and pumping energy. Developed network scheduling algorithm consists of two stages. The first stage involves solving a continuous problem, where operation of each pump is described by continuous variable. Subsequently, the second stage continuous pump schedules are discretised using heuristic algorithm. Another area of research has been developing optimal feedback rules using GA to control the operation of pump stations. Each pump station has a rule described by two water levels in a downstream reservoir and a value of pump speed for each tariff period. The lower and upper water switching levels of the downstream reservoir correspond to the pump being “ON” or “OFF”. The achieved similar energy cost per 1 Ml of pumped water. In the considered case study, the optimal feedback rules had advantage of small number of ON/OFF switches, which increase the pump stations lifetime and reduce the maintenance cost as well.
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Danias, George Carleton University Dissertation Engineering Aeronautical. "Contributions to the study of tip leakage flow in a planar cascade of turbine blades." Ottawa, 1987.
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Ma, Ruolong. "Unsteady Turbulence Interaction in a Tip Leakage Flow Downstream of a Simulated Axial Compressor Rotor." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/28060.
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The unsteady behavior of a tip leakage flow downstream of a simulated axial compressor rotor has been studied. The Virginia Tech low speed linear cascade wind tunnel was adapted to model the unsteady tip leakage flow produced by a rotor operating in the vortical wakes of a set of stator vanes. The cascade, consisting of 8 GE rotor B blades, has adjustable tip gap, inlet angle of 65.1 degrees, turning angle of 11.8 degrees and solidity of 1.076. The cascade Reynolds number, based on blade chord, was 393,000. A moving end wall was used to simulate the relative motion between rotor and casing, and vortex generators attached to the moving end wall were used to produce an idealized periodic unsteady vortical inflow similar to that shed by the junction of a row of inlet guide vanes.
Measurements of the vortical inflow to the cascade produced by the generators and of the mean blade loading at the mid span are presented. The periodic and aperiodic behavior of the tip leakage flow downstream of the cascade, produced by this vortical disturbance, is also presented using phase and time averaged 3-component turbulence and pressure fluctuation measurements. These measurements are made for tip gap from 0.83% to 3.3% chord and streamwise locations from 0.772% to 1.117% blade spacing axially downstream of the cascade.
The phase averaged inflow measurements reveal that the inflow produced by the vortex generators consists of a pair asymmetric counter-rotating vortices embedded in a thin (4.6% chord) endwall boundary layer. The vortices extend some 7.4% chord from the end wall. Their strength is about two orders smaller than the typical circulation of the tip leakage vortices produced by the cascade.
Phase averaged single point three component hot-wire measurements downstream of the cascade reveal that the vortical inflow is, however, capable of producing significant large scale fluctuations in the size, strength, structure and position of the tip leakage vortex. These effects increase in magnitude with increase of tip gap. For small tip gaps these effects appear to be due to simple superposition between the inflow vortices and the tip leakage vortex. However for larger tip gaps these effects appear primarily a consequence of the inflow vortices interfering with the shedding of circulation from the blade tip. The fact that the circulation fluctuation is consistent with the inviscid unsteady loading prediction suggests that the inviscid response may be a major mechanism for generating the tip leakage unsteadiness.
Although there is large periodic fluctuation in the tip leakage flow disturbed by the inflow, there is a larger aperiodic component. Two point correlation measurements and linear stochastic estimation are used to reveal the structure of this aperiodic part for a tip gap of 3.3% chord. The aperiodic fluctuation, containing most of the turbulence energy, is found appearing to be organized structures in large scale, and making the estimated instantaneous velocity field significantly different from the phase averaged periodic velocity field.
Phase averaged pressure fluctuation measurements made using a microphone in the tip leakage vortex downstream of the cascade reveal that there are significant periodic fluctuating pressure waves and intense mean square fluctuation of the aperiodic fluctuating pressure. They are consistent with the measured periodic flow and aperiodic flow field respectively. These microphone measurements are validated using fluctuating pressure gradient estimates determined from the hot-wire measurements.Ph. D.
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Balasubramanian, Venkat Krishnan. "Design Automation Flow for Voltage Adaptive Light Vth Hopping for Leakage Minimization in Sequential Circuits." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352490620.
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Teeluckdharry, Sahil. "An experimental investigation of leakage flow paths in soil surrounding leaks in water distribution systems." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/24917.
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Over the last few decades, water stress has been imminent in most municipalities around the world. The problem of water losses from pipelines is a major concern due to the increasing demands. Leakage is normally responsible for a large percentage of water losses in distribution systems and results in enormous wastage of valuable resources and energy. Leaks may be developed in many forms and locations in the system and active leak detections are required to find and repair damaged pipes. Few studies have been done on the soil-leak interaction in real pipeline systems. Recent research have shown that the high velocity water jets entering the surrounding soil causes a fluidisation zone outside leaks. The fluidised zone of soil and water is responsible for dissipating most of the energy of the water jet from the pipe leak and thus, limiting the leak's ability to reach soil surface. In municipalities where active leak detections are not implemented, it is easier for municipalities to detect leaks if they appear on the surface and thus, it is crucial to understand the routes of water leaks and the factors causing them to appear above the ground. This study investigated the soil-leak interaction focusing mainly on factors affecting leakage flow paths in water distribution systems. An experimental set up was designed and built to study the different factors in a controlled environment. A series of experiments were performed where water jets from manufactured circular leaks were released in different trench set ups. Three main variables were investigated namely flow rate, leak orientation and in-situ soil to start understanding the movement of the leak flow as a preliminary study. The volumetric moisture content were measured using EC-5 moisture sensors at different locations in the tank to analyse the movement of leakage water and iPERLS smart water meters were used to measure the flow of water through the walls of the trench. The results of the experiments showed how much leakage water is actually lost through the side and bottom walls. The volumetric moisture content readings indicated the movement of the leak in the tank. The results of the study indicated that leak orientation has the greatest influence on the paths of the leaks. Also, the flow rate had to be increased to a very high value so that the leak appears above the sand surface. The permeability of the in-situ soil was found to have the least effect on the leakage flow paths.
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Sethapati, Vivek Venkata. "Computational Fluid Flow Analysis of the Enhanced-Once through Steam generator Auxiliary feedwater system." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/77020.
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The once through steam generator (OTSG) is a single pass counter flow heat exchanger in which primary pressurized water from the core is circulated. Main Feedwater is injected in an annular gap on the outer periphery of the steam generator shroud such that it aspirates steam to preheat the feedwater to saturation temperature. An important component of the OTSG and enhanced once through steam generator (EOTSG) is the auxiliary feedwater system (AFW), which is used during accident/transient scenarios to remove residual heat by injecting water through jets along the outer periphery of the heat exchanger core directly on to the tubes at the top of the OTSG. The intention is for the injected water, which is subcooled, to spread into the tube nest and wet as many tubes as possible. In this project, the main objectives were to use first principles Computational Fluid Dynamics to predict the number of wetted tubes versus flow rate in the EOTSG at the AFW injection location above the top tube support plate. To perform the fluid analysis, the losses in the bypass leakage flow and broached hole leakage flow were first quantified and then used to model a 1/8th sector of the EOTSG. Using user defined functions (UDF), the loss coefficients of the leakage flows were implemented on the 1/8th sector of the EOTSG computational model to provide boundary conditions at the bypass flow and leakage flow locations With this method, the number of tubes wetted in the sector of EOTSG for various AFW flow rates was found. Results showed that the number of wetted tubes was in very close agreement to that predicted by experimental-analytical methods by the sponsor, AREVA. With the maximum flow rate of 65 l/s a total of 318 tubes were wetted and the percentage of tubes wetted with broached holes was 8.7%.
The analysis on the bypass leakage flow showed that the loss coefficients was a function of the mass flow rate or the flow Reynolds number through the gap and it increased as the Reynolds number increased from 300 to 1600. The experimental and computational loss coefficients agree to within 15% of each other. In contrast, the constant loss coefficient of 1.3 used by AREVA was much higher than that obtained in this study, particularly in the low Reynolds number range. As the Reynolds number approached 3000, the loss coefficients from this study approached the value of 1.3. This value of the loss coefficient was implemented for the bypass flow leakage in the 1/8th sector of the EOTSG model.
The analysis on the broached hole leakage flow was performed using a single hole, five holes, and one, two, four and eight rows of broached holes in order to characterize the loss coefficients. The one hole and five hole computational models were validated with experiments. The computational models showed the presence of voids in the leakage flow through the tube support plate (TSP), which were not observed (visually) in the experiments. The characterization of the broached hole leakage in the one, two and four rows showed that the loss coefficient of the control broached hole increased as the number of rows increased. These results indicated that for the same height of water on the TSP, the resistance to leakage flow increased as the number of tubes increased. They also indicated that leakage flow through the broached holes was not solely a function of the height of water above the TSP but also the surrounding geometrical topology and the flow characteristics. However, the analysis done for eight rows showed that the loss coefficient became constant after a certain number of rows as the loss coefficient differed by only 5% from the results of the four rows. From these results it was determined that the loss coefficient asymptotes to an estimated value of 4.0 which was implemented in the broached hole leakage flow in the 1/8th sector of the EOTSG.
Computational models of the 1/8th sector of the EOTSG were implemented with the respective loss coefficients for the bypass and leakage flows. Results showed that as the AFW flow rate increased, the percentage wetted tubes increased. The data matched closely with AREVA's experimental-analytical model for flow rates of 14.5 l/s and higher. It was also deduced that complete wetting of the tubes is not possible at the maximum AFW flow rate of 65 l/s.Master of Science
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Behr, Thomas. "Control of rotor tip leakage and secondary flow by casing air injection in unshrouded axial turbines /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17283.
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Holzinger, Felix [Verfasser]. "Coupling of tip leakage flow and blade vibration in transonic compressors : Mechanism and countermeasures / Felix Holzinger." Aachen : Shaker, 2018. http://d-nb.info/1159835063/34.
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Simon, Helene A. "Influence of the implant location on the hinge and leakage flow fields through bileaflet mechanical heart valves." Thesis, Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-04012004-192539/.
Full textAbstract:
Thesis (M.S.)--Chemical Engineering, Georgia Institute of Technology, 2004.Sambanis Athanassios, Committee Member ; Sotiropoulos Fotis, Committee Member ; Yoganathan Ajit, Committee Chair. Includes bibliographical references (leaves 239-243).
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Simon, Hélène A. "Influence of the implant location on the hinge and leakage flow fields through bileaflet mechanical heart valves." Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04012004-192539/unrestricted/helene%5Fsimon%5Fa%5F200405%5Fmast.pdf.
Full textAbstract:
Thesis (M.S.)--Chemical Engineering, Georgia Institute of Technology, 2003.Sambanis Athanassios, Committee Member ; Sotiropoulos Fotis, Committee Member ; Yoganathan Ajit, Committee Chair. Includes bibliographical references (leaves 239-243).