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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.
1

Thermal Management in Laminated Die Systems Using Neural Networks

Seo, Jaho 26 August 2011 (has links)
The thermal control of a die is crucial for the development of high efficiency injection moulds. For successful thermal management, this research provides an effective control strategy to find sensor locations, identify thermal dynamic models, and design controllers. By applying a clustering method and sensitivity analysis, sensor locations are identified. The neural network and finite element analysis techniques enable the modeling to deal with various cycle-times for the moulding process and uncertain dynamics of a die. A combination of off-line training through finite element analysis and training using on-line learning algorithms and experimental data is used for the system identification. Based on the system identification which is experimentally validated using a real system, controllers are designed using fuzzy-logic and self-adaptive PID methods with backpropagation (BP) and radial basis function (RBF) neural networks to tune control parameters. Direct adaptive inverse control and additive feedforward control by adding direct adaptive inverse control to self-adaptive PID controllers are also provided. Through a comparative study, each controller’s performance is verified in terms of response time and tracking accuracy under different moulding processes with multiple cycle-times. Additionally, the improved cooling effectiveness of the conformal cooling channel designed in this study is presented by comparing with a conventional straight channel.
2

Thermal Management in Laminated Die Systems Using Neural Networks

Seo, Jaho 26 August 2011 (has links)
The thermal control of a die is crucial for the development of high efficiency injection moulds. For successful thermal management, this research provides an effective control strategy to find sensor locations, identify thermal dynamic models, and design controllers. By applying a clustering method and sensitivity analysis, sensor locations are identified. The neural network and finite element analysis techniques enable the modeling to deal with various cycle-times for the moulding process and uncertain dynamics of a die. A combination of off-line training through finite element analysis and training using on-line learning algorithms and experimental data is used for the system identification. Based on the system identification which is experimentally validated using a real system, controllers are designed using fuzzy-logic and self-adaptive PID methods with backpropagation (BP) and radial basis function (RBF) neural networks to tune control parameters. Direct adaptive inverse control and additive feedforward control by adding direct adaptive inverse control to self-adaptive PID controllers are also provided. Through a comparative study, each controller’s performance is verified in terms of response time and tracking accuracy under different moulding processes with multiple cycle-times. Additionally, the improved cooling effectiveness of the conformal cooling channel designed in this study is presented by comparing with a conventional straight channel.
3

Avaliação do ciclo de vida e simulação termoenergética em unidade habitacional unifamiliar do Programa Minha Casa Minha Vida

Moraga, Gustavo Longaray January 2017 (has links)
Os edifícios são responsáveis por importantes impactos ambientais, principalmente, pelo seu longo ciclo de vida. Neste sentido, as edificações são potenciais redutoras de danos ambientais, já que as decisões sobre seu impacto podem ser feitas em projeto. No Brasil, o Programa Minha Casa Minha Vida (PMCMV) produziu mais de dois milhões de unidades de habitação, sendo um importante gerador de impactos. Foram realizadas pesquisas avaliando impactos sociais, urbanísticos e arquitetônicos do PMCMV, entretanto ainda existe escassez de estudos avaliando os impactos ambientais dessas edificações. Esta pesquisa utiliza a metodologia de Avaliação do Ciclo de Vida (ACV) para quantificar os impactos ambientais potenciais de uma casa do PMCMV. A metodologia considera três fases, com referência no estudo de caso de uma casa térrea situada na região metropolitana de Porto Alegre (sul do Brasil). A Fase 1 quantifica o uso de energia através de simulação termoenergética, testando envoltórias alternativas em comparação à original. A Fase 2 realiza a ACV preliminar, para verificar as contribuições de impacto mais relevantes em dois modelos selecionados. A Fase 3 desenvolve a ACV final com dados adaptados para a realidade brasileira. Os resultados demonstram que os impactos operacionais da edificação são os mais importantes ao longo do ciclo de vida de 50 anos, para as duas alternativas de envoltória avaliadas. Mesmo assim, os requerimentos incorporados da edificação podem representar impactos importantes, ultrapassando 40% em categorias como aquecimento global e depleção da camada de ozônio. O transporte de materiais de construção e matérias primas é um dos maiores causadores dos impactos incorporados. Além desse, a recorrência de manutenções mostra-se importante, assim como a durabilidade dos materiais de construção. A aplicação da ferramenta de ACV confirma sua importância como instrumento para a tomada de decisão, identificando processos mais relevantes na qualificação ambiental de edificações. / Buildings are responsible for expressive environmental impacts, especially for its long life-cycle. In fact, buildings are important potential reducers of environmental damages, because decisions concerning its future impacts can be made at design stage. In Brazil, “My House My Life” program (MHMLP) produced more than two million dwellings, generating significant impacts. Some of MHMLP impacts were already addressed, such as social, urban and architectural, however there is a lack on environmental impacts studies focused on these buildings. This research applies Life Cycle Assessment method to quantify potential environmental impacts of a MHMLP dwelling. Methodology considered three phases, using as reference the case study of a single-story house located at the metropolitan area of Porto Alegre (southern Brazil). Phase 1 quantifies energy use through thermal dynamic simulations, considering different encloses types in comparison to the original option. Phase 2 applies streamlined Life Cycle Assessment (LCA) framework to evaluate the most important contributions to the environmental impacts of the two previously selected models. In phase 3, LCA was developed considering data regionalization and adaptation to the Brazilian context. Results show that operational impacts are the most important ones on the 50 years dwelling life cycle, for both evaluated alternatives. Nevertheless, embodied impacts can represent more than 40% of total global warming and ozone depletion potential impacts. Transportation of raw and construction materials is one of the most important contributors to embodied impacts. Furthermore, recurrent embodied impacts are important, as well as construction materials durability. LCA application validates its importance as a framework to support decision-making, identifying hotspots on buildings environmental qualification.
4

Avaliação do ciclo de vida e simulação termoenergética em unidade habitacional unifamiliar do Programa Minha Casa Minha Vida

Moraga, Gustavo Longaray January 2017 (has links)
Os edifícios são responsáveis por importantes impactos ambientais, principalmente, pelo seu longo ciclo de vida. Neste sentido, as edificações são potenciais redutoras de danos ambientais, já que as decisões sobre seu impacto podem ser feitas em projeto. No Brasil, o Programa Minha Casa Minha Vida (PMCMV) produziu mais de dois milhões de unidades de habitação, sendo um importante gerador de impactos. Foram realizadas pesquisas avaliando impactos sociais, urbanísticos e arquitetônicos do PMCMV, entretanto ainda existe escassez de estudos avaliando os impactos ambientais dessas edificações. Esta pesquisa utiliza a metodologia de Avaliação do Ciclo de Vida (ACV) para quantificar os impactos ambientais potenciais de uma casa do PMCMV. A metodologia considera três fases, com referência no estudo de caso de uma casa térrea situada na região metropolitana de Porto Alegre (sul do Brasil). A Fase 1 quantifica o uso de energia através de simulação termoenergética, testando envoltórias alternativas em comparação à original. A Fase 2 realiza a ACV preliminar, para verificar as contribuições de impacto mais relevantes em dois modelos selecionados. A Fase 3 desenvolve a ACV final com dados adaptados para a realidade brasileira. Os resultados demonstram que os impactos operacionais da edificação são os mais importantes ao longo do ciclo de vida de 50 anos, para as duas alternativas de envoltória avaliadas. Mesmo assim, os requerimentos incorporados da edificação podem representar impactos importantes, ultrapassando 40% em categorias como aquecimento global e depleção da camada de ozônio. O transporte de materiais de construção e matérias primas é um dos maiores causadores dos impactos incorporados. Além desse, a recorrência de manutenções mostra-se importante, assim como a durabilidade dos materiais de construção. A aplicação da ferramenta de ACV confirma sua importância como instrumento para a tomada de decisão, identificando processos mais relevantes na qualificação ambiental de edificações. / Buildings are responsible for expressive environmental impacts, especially for its long life-cycle. In fact, buildings are important potential reducers of environmental damages, because decisions concerning its future impacts can be made at design stage. In Brazil, “My House My Life” program (MHMLP) produced more than two million dwellings, generating significant impacts. Some of MHMLP impacts were already addressed, such as social, urban and architectural, however there is a lack on environmental impacts studies focused on these buildings. This research applies Life Cycle Assessment method to quantify potential environmental impacts of a MHMLP dwelling. Methodology considered three phases, using as reference the case study of a single-story house located at the metropolitan area of Porto Alegre (southern Brazil). Phase 1 quantifies energy use through thermal dynamic simulations, considering different encloses types in comparison to the original option. Phase 2 applies streamlined Life Cycle Assessment (LCA) framework to evaluate the most important contributions to the environmental impacts of the two previously selected models. In phase 3, LCA was developed considering data regionalization and adaptation to the Brazilian context. Results show that operational impacts are the most important ones on the 50 years dwelling life cycle, for both evaluated alternatives. Nevertheless, embodied impacts can represent more than 40% of total global warming and ozone depletion potential impacts. Transportation of raw and construction materials is one of the most important contributors to embodied impacts. Furthermore, recurrent embodied impacts are important, as well as construction materials durability. LCA application validates its importance as a framework to support decision-making, identifying hotspots on buildings environmental qualification.
5

Avaliação do ciclo de vida e simulação termoenergética em unidade habitacional unifamiliar do Programa Minha Casa Minha Vida

Moraga, Gustavo Longaray January 2017 (has links)
Os edifícios são responsáveis por importantes impactos ambientais, principalmente, pelo seu longo ciclo de vida. Neste sentido, as edificações são potenciais redutoras de danos ambientais, já que as decisões sobre seu impacto podem ser feitas em projeto. No Brasil, o Programa Minha Casa Minha Vida (PMCMV) produziu mais de dois milhões de unidades de habitação, sendo um importante gerador de impactos. Foram realizadas pesquisas avaliando impactos sociais, urbanísticos e arquitetônicos do PMCMV, entretanto ainda existe escassez de estudos avaliando os impactos ambientais dessas edificações. Esta pesquisa utiliza a metodologia de Avaliação do Ciclo de Vida (ACV) para quantificar os impactos ambientais potenciais de uma casa do PMCMV. A metodologia considera três fases, com referência no estudo de caso de uma casa térrea situada na região metropolitana de Porto Alegre (sul do Brasil). A Fase 1 quantifica o uso de energia através de simulação termoenergética, testando envoltórias alternativas em comparação à original. A Fase 2 realiza a ACV preliminar, para verificar as contribuições de impacto mais relevantes em dois modelos selecionados. A Fase 3 desenvolve a ACV final com dados adaptados para a realidade brasileira. Os resultados demonstram que os impactos operacionais da edificação são os mais importantes ao longo do ciclo de vida de 50 anos, para as duas alternativas de envoltória avaliadas. Mesmo assim, os requerimentos incorporados da edificação podem representar impactos importantes, ultrapassando 40% em categorias como aquecimento global e depleção da camada de ozônio. O transporte de materiais de construção e matérias primas é um dos maiores causadores dos impactos incorporados. Além desse, a recorrência de manutenções mostra-se importante, assim como a durabilidade dos materiais de construção. A aplicação da ferramenta de ACV confirma sua importância como instrumento para a tomada de decisão, identificando processos mais relevantes na qualificação ambiental de edificações. / Buildings are responsible for expressive environmental impacts, especially for its long life-cycle. In fact, buildings are important potential reducers of environmental damages, because decisions concerning its future impacts can be made at design stage. In Brazil, “My House My Life” program (MHMLP) produced more than two million dwellings, generating significant impacts. Some of MHMLP impacts were already addressed, such as social, urban and architectural, however there is a lack on environmental impacts studies focused on these buildings. This research applies Life Cycle Assessment method to quantify potential environmental impacts of a MHMLP dwelling. Methodology considered three phases, using as reference the case study of a single-story house located at the metropolitan area of Porto Alegre (southern Brazil). Phase 1 quantifies energy use through thermal dynamic simulations, considering different encloses types in comparison to the original option. Phase 2 applies streamlined Life Cycle Assessment (LCA) framework to evaluate the most important contributions to the environmental impacts of the two previously selected models. In phase 3, LCA was developed considering data regionalization and adaptation to the Brazilian context. Results show that operational impacts are the most important ones on the 50 years dwelling life cycle, for both evaluated alternatives. Nevertheless, embodied impacts can represent more than 40% of total global warming and ozone depletion potential impacts. Transportation of raw and construction materials is one of the most important contributors to embodied impacts. Furthermore, recurrent embodied impacts are important, as well as construction materials durability. LCA application validates its importance as a framework to support decision-making, identifying hotspots on buildings environmental qualification.
6

Dynamic Probabilistic Risk Assessment of Nuclear Power Generation Stations

Elsefy, Mohamed HM January 2021 (has links)
Risk assessment is essential for nuclear power plants (NPPs) due to the complex dynamic nature of such systems-of-systems, as well as the devastating impacts of nuclear accidents on the environment, public health, and economy. Lessons learned from the Fukushima nuclear accident demonstrated the importance of enhancing current risk assessment methodologies and developing efficient early warning decision support tools. Static probabilistic risk assessment (PRA) techniques (e.g., event and fault tree analysis) have been extensively adopted in nuclear applications to ensure NPPs comply with safety regulations. However, numerous studies have highlighted the limitations of static PRA methods such as the lack of considering the dynamic hardware/software/operator interactions inside the NPP and the timing/sequence of events. In response, several dynamic probabilistic risk assessment (DPRA) methodologies have been developed and continuously evolved over the past four decades to overcome the limitations of static PRA methods. DPRA presents a comprehensive approach to assess the risks associated with complex, dynamic systems. However, current DPRA approaches are faced with challenges associated with the intra/interdependence within/between different NPP complex systems and the massive amount of data that needs to be analyzed and rapidly acted upon. In response to these limitations of previous work, the main objective of this dissertation is to develop a physics-based DPRA platform and an intelligent data-driven prediction tool for NPP safety enhancement under normal and abnormal operating conditions. The results of this dissertation demonstrate that the developed DPRA platform is capable of simulating the dynamic interaction between different NPP systems and estimating the temporal probability of core damage under different transients with significant analysis advantages from both the computational time and data storage perspectives. The developed platform can also explicitly account for uncertainties associated with the NPP's physical parameters and operating conditions on the plant's response and probability of its core damage. Furthermore, an intelligent decision support tool, developed based on artificial neural networks (ANN), can significantly improve the safety of NPPs by providing the plant operators with fast and accurate predictions that are specific to such NPP. Such rapid prediction will minimize the need to resort to idealized physics-based simulators to predict the underlying complex physical interactions. Moving forward, the developed ANN model can be trained under plant operational data, plants operating experience database, and data from rare event simulations to consider for example plant ageing with time, operational transients, and rare events in predicting the plant behavior. Such intelligent tool can be key for NPP operators and managers to take rapid and reliable actions under abnormal conditions. / Thesis / Doctor of Philosophy (PhD)
7

Contribution à l'évaluation in situ des performances d'isolation thermique de l'enveloppe des bâtiments / In situ assessment of the thermal insulation performance of building envelopes

Thébault, Simon Romain 27 January 2017 (has links)
Dans un contexte d’économie d’énergie et de réduction des émissions de gaz à effet de serre, de nombreux efforts ont été réalisés en France pour renforcer l’isolation de l’enveloppe des bâtiments afin de contribuer à réduire les consommations de chauffage. Toutefois, il arrive souvent que la performance thermique calculée avant construction ou rénovation ne soit pas atteinte sur le terrain (erreur de calcul, défauts de mise en œuvre, etc.). Or, pour pouvoir généraliser la construction de bâtiments à basse consommation et la rénovation, il faut pouvoir garantir aux maîtres d'ouvrage une performance réelle de leur bâtiment après travaux. Le fait de mesurer in situ la performance intrinsèque d'isolation thermique de l'enveloppe permet de contribuer à cette garantie. Il existe à l’échelle internationale de nombreuses méthodes basées sur le suivi des consommations et des conditions thermiques intérieures et extérieures. Certaines ont déjà fait leurs preuves sur le terrain, mais sont souvent soit contraignantes, soit peu précises. Et surtout, les calculs d’incertitude associés sont souvent rudimentaires. L’objectif de ce travail financé par le CSTB est de consolider scientifiquement une nouvelle méthode de mesure de la qualité d’isolation globale d’un bâtiment à réception des travaux (méthode ISABELE). Dans le premier chapitre, un état de l'art sur les méthodes existantes a été réalisé afin de dégager des pistes d'amélioration sur la base d'une synthèse comparative. La piste prioritaire identifiée porte sur le calcul d'incertitude (un point central du problème). La propagation des erreurs aléatoires par un approche bayésienne ainsi que des erreurs systématiques par une approche plus classique feront l'objet de la méthodologie globale proposée dans le second chapitre. L'une des importantes sources d'incertitude porte sur l'évaluation du débit d'infiltration. La caractérisation de cette incertitude et de l'impact sur le résultat de mesure fera l'objet du troisième chapitre, avec un comparatif de différentes approches expérimentales (règle du pouce, modèles aérauliques, gaz traceur). Enfin, une amélioration de la prise en compte de la dynamique thermique du bâtiment au cours du test sera proposée dans le dernier chapitre. Son fondement repose sur l'adaptation du modèle thermique inverse en fonction du bâtiment et des conditions du test. Pour cela, une sélection parmi une banque de modèles simplifiés est réalisée sur la base de critères statistiques et du principe de parcimonie. Ces différentes dispositions ont été testés sur une large série de mesures menées sur un même bâtiment à ossature bois (chalet OPTIMOB). La robustesse et la précision du résultat de mesure ont ainsi pu être légèrement améliorées. La méthode de calcul du débit d'infiltration, ni trop simple ni trop complexe, a pu également être validée. Enfin, le temps de mesure minimal nécessaire a pu être déterminé en fonction de la classe d'inertie du bâtiment. / The global context of energy savings and greenhouse gases emissions control led to significant efforts in France to boost the thermal insulation in buildings in order to reduce heating consumption. Nevertheless, the stated thermal performance before construction or refurbishment is rarely achieved in practice, for many reasons (calculation errors, defects in materials or workmanship, etc.). Yet, guaranteeing the real thermal performance of buildings on the spot is crucial to enhance the refurbishment market and the construction of energy efficient buildings. To do so, measurement techniques of the intrinsinc thermal insulation performance indicators are needed. Such techniques already exist worldwide, and consist in processing the measurement data from the indoor and outdoor thermal conditions and the heat consumption. Some of them have already proved themselves in the field, but are either binding or very imprecise. And above all, the related uncertainty calculations are often rough. The objective of this thesis funded by CSTB is to consolidate a novel measurement method of the thermal insulation quality of a whole building after reception of work (ISABELE method). In the first chapter, a state of the art of the existing methods allows to identify possible ways to pursue this goal from a comparative synthesis. The primary reflection is about the uncertainty calculation method (which is a central issue). The second chapter presents a global methodology to combine the propagation of random and systematic errors from bayesian and classical approaches. One of the most important uncertainty sources deals with the infiltration air flow evaluation during the test. The third chapter investigates the characterization of this uncertainty, as well as its impact on the final result, depending on the chosen experimental approach (rule of thumb, simplified aeraulic models, tracer gases). Lastly, an improvement of the inclusion of the bluiding thermal dynamics during the test will be proposed in the last chapter. The basis of this improvement is to adapt the inverse model according to the building type and the test conditions. To do so, the proposed algorithm selects a model form a variety of simplified greybox models based on statistical criteria and parcimony. All these contributions have been tested on a large serie of measurements on a same timber-framed building (OPTIMOB shed). The robustness and precision of the results have been slightly improved. The intial infiltration air flow calculation, neither too simple of too complicated, has also been validated. Finaly, a better ordrer of magnitude of the minimal test duration has been determined, depending on the building inertia.
8

Chiral Spin Textures for Unconventional Computing

Shiva Teja Konakanchi (20379624) 06 December 2024 (has links)
<p dir="ltr">The limitations of the traditional von Neumann computing architecture, particularly evident in the slowdown of Moore's law, have spurred the development of alternative domain-specific computing paradigms. This dissertation explores novel materials-physics based solutions for two promising alternatives: quantum computing and probabilistic computing, with a specific focus on leveraging magnetic spin textures and their unique properties. We demonstrate that magnetic spin textures, with their inherent topology and chirality, offer distinctive advantages in addressing key challenges in both computing paradigms. These textures' ability to couple with various degrees of freedom, such as electrical, thermal, mechanical, and optical, makes them particularly suitable for hybrid device implementations. Our work presents four contributions to the field.</p><p dir="ltr">First, we propose a novel approach of using skyrmions --- topologically protected rigid-object like spin textures --- to nucleate and braid Majorana modes in topological superconductor-magnetic multilayer heterostructures. We show analytically and numerically that skyrmion--vortex bound pairs can be braided in experimentally relevant timescales. Inspired by circuit quantum electrodynamics methods, we propose a novel readout scheme based on the dispersive coupling between vortex confinement states and Majorana bound states. This work paves the way for experimentally demonstrating the non-Abelian statistics of Majorana bound states, which might be a crucial step towards the development of fault-tolerant topological quantum computers.</p><p dir="ltr">Second, we study thermal relaxation mechanisms and timescales of spin-split chiral antiferromagnets. The class of spin-split antiferromagnets, including altermagnets, have recently emerged as excellent candidates for ultra-fast and low-energy spintronics applications. Due the lack of dipolar order, they are unaffected by stray fields. However, the spin-split bands still offer electrical control and readout of these antiferromagnets unlike the conventional antiferromagnets. While a lot of promising phenomena in these materials has already been experimentally demonstrated, thermal relaxation mechanisms of such magnets remain unexplored. Using reaction rate theories and statistical physics tools, we study the thermal dynamics of chiral antiferromagnets. We show that these materials thermally relax at ultra-fast picosecond-order timescales. Further, by building on the analogy between XY magnets and current biased Josephson junctions, we propose a novel approach to electrically tune the thermal barrier in chiral antiferromagnets. Although such chiral antiferromagnets may not be suitable for non-volatile memory type of applications, they emerge as promising candidates for the building blocks of probabilistic computers.</p><p dir="ltr">We then turn our attention to the strongly correlated quantum system of quantum spin liquids. We show that spin textures exchange coupled to a Kitaev spin liquid (KSL) can induce emergent gauge fields on the Majorana fermions in the spin liquid. These emergent gauge fields may trap zero energy modes if they are able to thread a net flux through the KSL. We derive analytical expressions for the gauge fields in the presence of spin textures and outline the conditions to obtain a net flux. Zero energy Majorana fermion modes trapped on such spin textures may eventually be used for fault tolerant quantum computing.</p><p dir="ltr">Finally, in the last project, we bring the quantum and probabilistic computing paradigms together by proposing a quantum two level system as a sensor for the building blocks of a probabilistic computer. we show that quantum spin defects such as Nitrogen vacancy centers (NV) can be used as novel probes for characterizing probabilistic bits. We show that various NV sensing protocols can be leveraged to create a complete picture of this nascent magnet based probabilistic bits including their energy barrier and attempt times.</p><p dir="ltr">Our findings suggest that magnetic spin textures, particularly their topological and chiral properties, could provide crucial solutions to current challenges in alternative computing platforms. This work bridges the gap between materials physics, device physics and the applications in alternative computing platforms.</p>

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