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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Enhancement of Natural Convection Heat Transfer within Closed Enclosure Using Parallel Fins

Gdhaidh, Farouq A.S., Hussain, Khalid, Qi, Hong Sheng 03 1900 (has links)
Yes / A numerical study of natural convection heat transfer in water filled cavity has been examined in 3-D for single phase liquid cooling system by using an array of parallel plate fins mounted to one wall of a cavity. The heat generated by a heat source represents a computer CPU with dimensions of 37.5∗37.5mm mounted on substrate. A cold plate is used as a heat sink installed on the opposite vertical end of the enclosure. The air flow inside the computer case is created by an exhaust fan. A turbulent air flow is assumed and k-ε model is applied. The fins are installed on the substrate to enhance the heat transfer. The applied power energy range used is between 15 - 40W. In order to determine the thermal behaviour of the cooling system, the effect of the heat input and the number of the parallel plate fins are investigated. The results illustrate that as the fin number increases the maximum heat source temperature decreases. However, when the fin number increases to critical value the temperature start to increase due to the fins are too closely spaced and that cause the obstruction of water flow. The introduction of parallel plate fins reduces the maximum heat source temperature by 10% compared to the case without fins. The cooling system maintains the maximum chip temperature at 64.68°C when the heat input was at 40W that is much lower than the recommended computer chips limit temperature of no more than 85°C and hence the performance of the CPU is enhanced.
82

A Variation of Positioning Phase Change Materials (PCMs) Within Building Enclosures and Their Utilization Toward Thermal Performance

Abuzaid, Abdullah Ibrahim 26 April 2018 (has links)
Recently, buildings have been receiving more serious attention to help reduce global energy consumption. At the same time, thermal comfort has become an increasing concern for building occupants. Phase Change Materials (PCMs), which are capable of storing and releasing significant amounts of energy by melting and solidifying at a given temperature, are perceived as a promising opportunity for improving the thermal performance of buildings. This is because they use their thermophysical properties and latent heat while transforming state (or phase) as a feature for thermal energy storage systems to reduce overall energy demand, specifically during peaks hours, as well as to improve thermal comfort in buildings. This research aims to provide an overview of opportunities and challenges for the utilization of PCMs in the Architecture, Engineering, and Construction (AEC) sector, a broader understanding of specifically promising technologies, and a clarification of the effectiveness of different applications in building enclosures design especially in exterior walls. The research discusses how PCMs can be incorporated within building enclosures effectively to enhance building performance and improve thermal comfort while reducing heating and cooling energy consumption in buildings. The major objectives of the research include studying the properties of PCMs and their potential impact on building construction, clarifying PCMs selection criteria for building application, identifying the effectiveness of utilizing PCMs on saving energy, and evaluating the contribution of utilizing PCMs in building enclosures to thermal comfort. The research uses an exploratory quantitative approach that contains three main stages: 1) a systematic literature review, 2) laboratory experiments, and 3) validation to meet the goal of the research. Finally, by extrapolating results, the research ends with a practical assessment of application opportunities and how to effectively utilize PCMs in exterior walls of buildings. / PHD / With the growing concern of energy savings and selecting the most efficient way to provide thermal comfort for buildings’ users, buildings need to be constructed with an effective utilization method of materials and systems. Phase Change Materials (PCMs) have the ability to moderate temperatures within a specific range. They can be applied to reduce the energy used in buildings and improve thermal comfort. This is because they absorb heat when materials melt and release it when materials solidify. This research studies the properties of PCMs and their potential impact on building construction and clarifies PCM selection criteria for building applications. Also, the research illustrates the impacts of utilizing PCMs in different positions within an external wall on energy savings and thermal comfort. The research uses an exploratory quantitative approach that contains three main stages: 1) a systematic literature review, 2) laboratory experiments, and 3) validation to meet the goal of the research. Finally, the research ends with a practical assessment of application opportunities and how to effectively utilize PCMs in exterior walls of buildings.
83

Geophysical Study at Old Stone Fort State Archaeological Park, Manchester, Tennessee

Yerka, Stephen Jay 01 December 2010 (has links)
The Old Stone Fort State Archaeological Park covers over 800 acres within Manchester, Tennessee, and is owned and managed by the Tennessee Division of State Parks. The central archaeological site within the park boundary is The Old Stone Fort mounds that enclose about 50 acres on a plateau above the convergence of the Big Duck and the Little Duck Rivers. The hilltop enclosure dates to the Middle Woodland Period, and radiocarbon dates obtained at the site range from the first to the fifth century A. D. Because of its size and apparent complexity, previous investigations of the site have been quite limited in areal exposure. Many questions remain as to the overall structure of the site, including the relationship of built and natural features, the presence of any structures or other anthropogenic features, and the occurrence of presence of any domestic remains. This research project utilizes detailed digital topographic survey, geographical information system (GIS) analysis, geophysical survey, limited re-excavation of previously investigated portions of the site, and manual coring to locate and characterize archaeological deposits within the enclosure and mounds. Magnetometer, resistance, electromagnetic susceptibility, conductivity, and ground penetrating radar techniques were used during the investigations. Geophysical data, using these instruments, were collected over the same area in many cases. All together 20,000 m2 were examined during the project. Results indicate potential archaeological features and deposits within the plateau interior. Analysis suggests the presence of several geophysical anomalies potentially associated with prehistoric use of the site, especially within the Eastern Gateway complex. One such anomaly, or complex of anomalies, represents a possible structure. Historic archaeological deposits are also indicated by the geophysical data. Excavations at the site were limited to minimize impact. In a re-excavated trench, a lens of black shale within the stone mound construction may indicate a building stage not previously observed at Old Stone Fort. A second excavation confirmed a ditch feature detected in the geophysical survey. Archaeological deposits located during the survey are interpreted as evidence of sustained use of the ceremonial site during the Middle Woodland Period by local corporate groups to maintain and intensify membership for individuals who were settled in nucleated villages throughout most of the year.
84

Vapour Diffusion Control in Framed Wall Systems Insulated with Spray Polyurethane Foam

Smith, Rachel Cecilia January 2009 (has links)
The Intergovernmental Panel on Climate Change (IPCC) estimates that buildings account for 40% of the global energy use. The IPCC believes substantial improvements to building efficiency can be implemented easily by improving building enclosures through increased levels of insulation, optimizing glazing areas and minimizing infiltration of outside air.<br><br> Building enclosure design encompasses a wide range of parameters but the transport of heat, air and moisture through the enclosure is of primary importance. In predominantly cold Canadian climates, adequate thermal insulation, effective air barriers, and proper moisture control are crucial for energy savings and durability of the structure.<br><br> For decades, standard construction practice in Canada dictated a polyethylene sheet behind the interior drywall layer to serve as a vapour barrier for assemblies with traditional fibre-based cavity insulation. If the polyethylene sheet was sealed carefully enough it had the added benefit of reducing air leakage. Unfortunately, vapour barriers place the emphasis on the wrong moisture transport mechanism; air leakage can have 10 times or greater the wetting potential than vapour diffusion. Regardless, code enforcement personnel continued (and continue in some areas) to require vapour barriers in all climates, all assemblies, and all occupancies. To do so, they overrule the provision in Part 5 of The National Building Code of Canada that states vapour barriers are not required if it can be shown that the uncontrolled vapour diffusion will not affect the operation of the building and systems, or the health and safety of the occupants.<br><br> Foam plastic insulations perform better than fibre-based insulation in terms of the combined resistance to transmission of heat, air and vapour. This research investigated several types of open cell and closed cell spray polyurethane foam insulation in a variety of assembly configurations both in lab tests and hygrothermal simulations. The simulations were extrapolated to seven Canadian climate categories and three levels of interior relative humidity. The goal was to determine which spray polyurethane foam applications required the addition of a dedicated vapour barrier layer beyond what the foam itself could provide.<br><br> The moisture content of the oriented strand board sheathing layer (OSB) in the tested and modelled assemblies was used as the performance evaluation point because during wintertime vapour drives, the wood sheathing is the most likely condensing surface. Prolonged high moisture content (greater than 20%) in wood and wood products in wall assemblies leads to mould growth and decay. By this measure, if the wood sheathing moisture contents stay within the safe range (less than 19%) a vapour barrier is not necessary. The results are presented in Table 7-4.<br><br> The performance of assemblies containing closed cell spray foam was excellent for all climates and humidity levels. Their performance was equivalent to traditional wall assemblies incorporating a polyethylene sheet vapour barrier. The performance of assemblies with open cell spray foam was equivalent to traditional wall assemblies containing no vapour barrier. Open cell spray foam and fibreglass batt both require additional vapour control layers with all but the mildest Canadian climates with the lowest interior humidities. However, in those mild climates with low interior humidities, the only vapour control layer required was a medium permeance latex paint with primer.<br><br>
85

Vapour Diffusion Control in Framed Wall Systems Insulated with Spray Polyurethane Foam

Smith, Rachel Cecilia January 2009 (has links)
The Intergovernmental Panel on Climate Change (IPCC) estimates that buildings account for 40% of the global energy use. The IPCC believes substantial improvements to building efficiency can be implemented easily by improving building enclosures through increased levels of insulation, optimizing glazing areas and minimizing infiltration of outside air.<br><br> Building enclosure design encompasses a wide range of parameters but the transport of heat, air and moisture through the enclosure is of primary importance. In predominantly cold Canadian climates, adequate thermal insulation, effective air barriers, and proper moisture control are crucial for energy savings and durability of the structure.<br><br> For decades, standard construction practice in Canada dictated a polyethylene sheet behind the interior drywall layer to serve as a vapour barrier for assemblies with traditional fibre-based cavity insulation. If the polyethylene sheet was sealed carefully enough it had the added benefit of reducing air leakage. Unfortunately, vapour barriers place the emphasis on the wrong moisture transport mechanism; air leakage can have 10 times or greater the wetting potential than vapour diffusion. Regardless, code enforcement personnel continued (and continue in some areas) to require vapour barriers in all climates, all assemblies, and all occupancies. To do so, they overrule the provision in Part 5 of The National Building Code of Canada that states vapour barriers are not required if it can be shown that the uncontrolled vapour diffusion will not affect the operation of the building and systems, or the health and safety of the occupants.<br><br> Foam plastic insulations perform better than fibre-based insulation in terms of the combined resistance to transmission of heat, air and vapour. This research investigated several types of open cell and closed cell spray polyurethane foam insulation in a variety of assembly configurations both in lab tests and hygrothermal simulations. The simulations were extrapolated to seven Canadian climate categories and three levels of interior relative humidity. The goal was to determine which spray polyurethane foam applications required the addition of a dedicated vapour barrier layer beyond what the foam itself could provide.<br><br> The moisture content of the oriented strand board sheathing layer (OSB) in the tested and modelled assemblies was used as the performance evaluation point because during wintertime vapour drives, the wood sheathing is the most likely condensing surface. Prolonged high moisture content (greater than 20%) in wood and wood products in wall assemblies leads to mould growth and decay. By this measure, if the wood sheathing moisture contents stay within the safe range (less than 19%) a vapour barrier is not necessary. The results are presented in Table 7-4.<br><br> The performance of assemblies containing closed cell spray foam was excellent for all climates and humidity levels. Their performance was equivalent to traditional wall assemblies incorporating a polyethylene sheet vapour barrier. The performance of assemblies with open cell spray foam was equivalent to traditional wall assemblies containing no vapour barrier. Open cell spray foam and fibreglass batt both require additional vapour control layers with all but the mildest Canadian climates with the lowest interior humidities. However, in those mild climates with low interior humidities, the only vapour control layer required was a medium permeance latex paint with primer.<br><br>
86

Concurrent fire dynamic models and thermomechanical analysis of steel and concrete structures

Choi, Joonho 21 October 2008 (has links)
The objective of this study is to formulate a general 3D material-structural analysis framework for the thermomechanical behavior of steel-concrete structures in a fire environment. The proposed analysis framework consists of three modeling parts: fire dynamics simulation, heat transfer analysis, and a thermomechanical stress analysis of the structure. The first modeling part consists of applying the NIST (National Institute of Standards and Technology) fire dynamics simulator (FDS) where coupled Computational Fluid Dynamics (CFD) with thermodynamics are combined to model the fire progression within the steel-concrete structure. The goal is to generate the spatial-temporal (ST) solution variables (temperature, heat flux) on the surfaces of the structure. The FDS-ST solutions are generated in a discrete numerical form. Continuous FDS-ST approximations are then developed to represent the temperature or heat-flux at any given time or point within the structure. An extensive numerical study is carried out to examine the best ST approximation functions that strike a balance between accuracy and simplicity. The second modeling part consists of a finite-element (FE) transient heat analysis of the structure using the continuous FDS-ST surface variables as prescribed thermal boundary conditions. The third modeling part is a thermomechanical FE structural analysis using both nonlinear material and geometry. The temperature history from the second modeling part is used at all nodal points. The ABAQUS FE code is used with newly developed external user subroutines for the second and third simulation parts. The main objective is to describe the nonlinear temperature-dependency of the specific heat of concrete materials, especially high-strength concretes, that drastically affects their transient thermal solution. New algorithms are also developed to apply the continuous FDS-ST surface nodal boundary conditions in the transient heat FE analysis. The proposed modeling framework is applied to predict the temperature and deflection of the well-documented Cardington fire tests and to predict the time-to-collapse of the recent Oakland bridge fire caused by a fuel-truck accident.
87

Vybrané aspekty vlivu bezobratlých herbivorů na složení travinného společenstva

HRUBÁ, Karolína January 2018 (has links)
The first part of my thesis is focused on observation of the leaf damage by invertebrate herbivores during season. I examined how the selected traits affect the palatability of plant species. In the next project, I investigated the effect of herbivory and gaps on seedling establishment. And finally, in the last part, I studied the effect of herbivory of terrestrial gastropods on competitive relationships among selected species.
88

War machines of the charitable city : fundraising and the architecture of territory in Paris

Franklin, Rosalind Ethelline January 2018 (has links)
This dissertation explores the entangled territorialities of charitable fundraising, redressing the under-theorisation of the praxis as a social construct and a transformative spatial process. It approaches fundraising from an etiological perspective, drawing on French continental theory, particularly the work of Michel Serres and of Deleuze and Guattari, as well as concepts arising from literature in relational geographies and in business studies. Unlike many scholarly accounts, which obscure the fact that this property-challenged, property-desiring practice relies on the hospitality of others in order to extract and transfer resources, this study argues that the trait of interloping is crucial to fundraising’s expansive colonisation of urban space. Seizing on the notions of minor architecture and itinerant territoriality, it thinks through fundraising’s habits, inhabitations and habitats. By doing so, it reveals a form of nomadic war machine specialised in crafting parasitic architectures that invade urban territories to constitute a territory of its own. That this state-authorised territory has become an obligatory passage point within contemporary networked societies says much about how power is forged through the intersection of political, moral-economic and socio-affective parameters. Moreover, in uncovering a hint of revanchism against the property-owning classes, this research points to the usual affective politics emerging at a time of state metamorphosis and protracted economic uncertainty. This conceptual work provides entry for an ethnographic exploration of the charitabilisation of urban life within the context of austerity in contemporary Paris. Evidence collected from interviews, participant observation, video, photography, maps, drawings and extant literature is used to illuminate fundraising’s polydimensional strategies and widespread yet minimally disruptive appropriations and expropriations. While other authors have documented the movement of fundraising in France from utter marginalisation to mainstream to strategic importance, this study traces the political and territorial machinations of the powerful Parisian network of non-profit leaders, association executives, heads of fundraising agencies, management consultants, lawyers, and government officials who lead the push for a more generous France. The continuities, tensions, and contradictions between this group’s production of space and the realities of on-the-street fundraising are explored through a series of case studies. The views presented highlight ways in which fundraisers induce and take advantage of breaches in prevailing articulations of space, time and citizen-bodies to fortify more-than-capitalist urban logics. Collectively, they render visible the temporalities, hotspots, technologies, imaginaries, schemes, and hypocrisies informing an aggressive incrementalism. The new view of Paris imparted foregrounds the enterprising, contested and geographically uneven process of cultivating the habit of ceding property, both in the sense of subjectivities and of material rights. This dissertation’s conceptual and empirical strands make it possible to apprehend how minoritarian actors become dominant. Extending the minoritarian’s right to temporally hold power and property is shown to involve continuously testing and exploiting the affordances of relations. Displayed and analysed are the contamination of ideals and the breaking of pacts within fundraising’s moral pursuit of wealth transference. Such promiscuities ought to be regarded as, this study emphasizes, a form of preparedness for the city to come.
89

Pós-efeitos da sincronização em campo e a fase de atividade do roedor subterrâneo tuco-tuco (Rodentia: Ctenomyidae) / Aftereffects of field entrainment and the activity phase of the subterranean rodent tuco-tuco (Rodentia: Ctenomyidae)

Barbara Mizumo Tomotani 09 December 2011 (has links)
Os tuco-tucos de Anillaco (Ctenomys cf. knighti) são roedores subterrâneos noturnos quando colocados em ciclo claro-escuro no laboratório. Com o interesse de se investigar o quanto um animal subterrâneo se expõe à luz, foi realizado um experimento de observação contínua em campo durante as horas claras do dia. Três indivíduos, um em cada estação, foram observados em uma arena semi-natural. Essas observações revelaram que os tuco-tucos não apenas saíam freqüentemente durante as horas claras do dia, como também apresentavam atividades robustas de forrageamento e remoção de terra de seus túneis. Uma vez que não se tinha conhecimento da atividade abaixo da terra ou durante à noite, foram examinados os pós-efeitos do arrastamento em campo para se investigar se o ritmo estaria sincronizado em campo e o quanto da atividade observada correspondia à atividade total do animal. Os pós-efeitos foram acessados pela transferência dos animais observados diretamente da arena para condições constantes. Surpreendentemente os animais exibiram uma atividade robusta concentrada na fase correspondente à noite ambiental sem transientes e sem traços da atividade diurna previamente observada em campo. Esse padrão foi observado em outros 10 animais trazidos dessa vez diretamente do campo e colocados em condições constantes. Além disso, não foram observadas diferenças na fase de atividade de animais com e sem acesso a rodas de atividade. Portando, nosso estudo com esses animais subterrâneos pode contribuir com elementos ecológicos nas discussões recentes sobre o significado da atividade diurna em animais que são noturnos segundo a fase do oscilador / South American subterranean rodents (Ctenomys cf. knighti), commonly known as tuco-tucos, display robust, nocturnal, wheel-running rhythms under a light-dark condition. To verify whether these subterranean and nocturnal animals ever expose themselves to light in the field, individual animals were continuously observed during light hours in a semi-natural enclosure that was constructed in their natural habitat. Observations during different seasons revealed that tuco-tucos not only emerged aboveground during daylight hours but also that their light exposure was due to robust diurnal activities of foraging and soil removal. Because of the lack of access to these animals´ subterranean and nocturnal activities in the field, the aftereffects of field entrainment were examined instead to verify the contribution of the previously observed diurnal behaviors to the total daily activity. This examination was achieved by transferring the observed animals from a field enclosure to constant laboratory conditions. Surprisingly, tuco-tucos exhibited robust activity concentrated in the phase corresponding to the external night without any trace of transients or of the diurnal activity that was observed in the enclosure. This pattern was also replicated when the aftereffects of the field entrainment of other animals trapped directly from the field were measured in the laboratory. Furthermore, no difference was detected in the activity measured with and without access to a running wheel. Our study of a wild subterranean species in its natural habitat can contribute novel ecological elements to the recently debated issue of the meaning of day-activity displayed by nocturnal rodents in the field
90

Visualising Interval-Based Simulations

Pawlik, Amadeusz, Andersson, Henry January 2015 (has links)
Acumen is a language and tool for modeling and simulating cyber-physical systems. It allows the user to conduct simulations using a technique called rigorous simulation that produces results with explicit error bounds, expressed as intervals. This feature can be useful when designing and testing systems where the reliability of results or taking uncertainty into account is important. Unfortunately, analyzing these simulation results can be difficult, as Acumen supports only two ways of presenting them: raw data tables and 2D-plots. These views of the data make certain kinds of analysis cumbersome, such as understanding correlations between variables. This is especially true when the model in question is large. This project proposes a new way of visualising rigorous simulation results in Acumen. The goal of this project is to create a method for visualising intervallic values in 3D, and implement it in Acumen. To achieve that, every span of values is represented as a series of overlapping objects. This family of objects, which constitutes an under-approximation of the true simulation result, is then wrapped inside a semi-translucent box that is a conservative over-approximation of the simulation result. The resulting implementation makes for a combination of mathematical correctness (rigour), and mediation of intervals in question. It enables the user to explore the results of his rigorous simulations as conveniently as with the existing, non-rigorous simulation methods, using the 3D visualisation to simplify the study of real-life problems. To our knowledge, no existing software features visualisation of interval-based simulation results, nor is there any convention for doing this. Some ways in which the proposed solution could be improved are suggested at the end of this report

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