Dissertations / Theses on the topic 'Thermal field model'

The research conducted at the department of Electrical Engineering of the University of South Florida campus in Tampa only covers the electrical aspect of electric drives. However, the performance of electric machinery is significantly impacted by temperature variation. The literature review shows three main control techniques in use today in electric drives namely, Scalar control, Direct Torque control and Field Oriented control. This thesis presents a temperature rise of rotor bars, stator winding, stator core and stator frame in a running three phase field-oriented controlled induction machine. A literature search shows that none of research has been carried out to investigate a thermal response of a field-oriented controlled induction motor. With this motivation, we were able to implement a lumped parameters thermal model of a three-phase field-oriented IM in MATLAB Simulink, which allows us to determine that rotor bars have the highest temperatures rising to 84 degrees Celsius. This confirms that rotors bars are the hottest part of a running IM as stipulated in literature.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1988.
Title as it appears in M.I.T. Graduate List, Feb. 1988: Electrical and thermal modulation of protein synthesis in cartilage--a model for electric field effects on biological tissues.
Bibliography: leaves 264-281.
by Laura A. MacGinitie.
Ph.D.

High Spectral Resolution Lidar (HSRL) is a backscatter lidar technique that employs an optical/spectral filter to distinguish between particulate (Mie) and molecular (Rayleigh) backscattered light. By separating the two types of returns, higher accuracy measurements are possible that will enable improved climate models, air quality measurements, and climate forecasting. A spaceborne HSRL instrument can provide great impact in these areas by enabling near-continuous measurements across the Earth, however the optical filter technology has typically been too complex for reliable long-duration space flight due to the need for complicated and costly electro-optic feedback loops, extra alignment detectors, and additional laser sources. Furthermore, these complexities limit the filter from use in other applications. In this research, a high-performance, ultra-narrowband interferometric optical filter with a specific thermo-optical behavior has been designed and built. The interferometer has been designed such that it can be reliably adjusted/tuned by simply monitoring and adjusting the temperature. The greatly reduced operational complexity was made possible through high-accuracy thermal characterization of the interferometer materials, combined with detailed Structural-Thermal-Optical-Performance (STOP) modeling to capture the complicated interactions between the materials. The overall design process, fabrication procedures, and characterization of the optical filter are presented.
Doctor of Philosophy
LiDAR (an acronym for Light Detection and Ranging) is a technology that can be used to measure properties of the atmosphere. It is similar to radar, but uses much smaller light waves rather than larger radio waves, enabling more detailed information to be obtained. High Spectral Resolution Lidar (HSRL) is a lidar technique that uses a high precision optical filter to distinguish between light that scatters from particulates (such as dust, smoke, or fog) and light that scatters from molecules (such as oxygen, nitrogen, or carbon dioxide) in the atmosphere. By separating the two types of backscattered light, higher accuracy measurements are possible that will enable improvements in climate models, air quality measurements, and climate forecasting. A spaceborne HSRL instrument can provide great impact in these areas by enabling near-continuous measurements across the Earth; however, the optical filter technology has typically been too complex for reliable long-duration spaceflight due to the need for complicated and expensive additional hardware. In this research, a high-performance HSRL optical filter that can be reliably operated by simply monitoring and adjusting the temperature has been designed, built, and tested. The greatly-reduced operational complexity has been made possible through a new process that enables more accurate prediction of the complicated interactions between the materials of the optical filter. This process is based on a combination of high-accuracy characterization of the materials and detailed structural-thermal-optical-performance (STOP) modeling. The overall design process, fabrication procedures, and characterization of the optical filter are presented.

A challenging aspect of modern global development is to provide desired thermal environment for building occupants with optimum consideration of energy and occupants health and satisfaction, both physically and psychologically. The variation of activity level, health condition, needs, clothing habit and staying time of different categories of occupants in hospitals makes it critical where comfort level should be optimized. Now-a-days, tremendous changing on climate makes even more challenging to maintain optimum level of indoor thermal environment at low energy cost. Thermal comfort can be assessed by the well-established PMV- PPD model, and studies on the correlation with AMV ratings from the occupants can help to understand the exact scenario of the thermal comfort. Therefore, this research aims to estimate the thermal comfort level of healthcare occupants, compare PMV-PPD values with AMV for different categories of occupants, and analyze optimum operative temperature for energy savings. A combination of objective measurements and a field study with a semi-structured interview on comfort perception, following ISO-7726, 7730, 8996, 9920, 10551 and ASHARE- 55 regulations, were conducted, where a total number of 56 occupants, including 35 patients, 5 visitors and 16 medical staffs were participated from a health care center of a hospital in Stockholm, Sweden. The data was collected during the summertime. Based on studied thermal environment, both PMV (-1.59 to 1.01) and AMV range (-2 to 1) considering gender, indicated health care center of studied hospital toward slightly cold, where occupants wanted warmer indoor environment. Patients more than 60 years were most sensitive on thermal comfort and overall patients were more sensitive for warm indoor climate than medical staff due to health condition and age. But male respondents were less sensitive than female. PMV and AMV with optimum operative temperature provides the clear idea about optimum thermal environment for the hospitals occupant. Identifying an optimum thermal environment could be a sustainable solution if and only if energy can be reduced.

In this thesis we provide a scheme for phase separation by accounting for diffusion, dynamic equations and consistency with thermodynamics. The constituents are two compressible fluids and, for the non-simple character of the mixture, an extra energy flux is allowed to occur. Since also thermal effects are included, the result is a whole set of evolution equations for the concentration, the velocity and the temperature which describes a non-isothermal Navier-Stokes-Cahn-Hilliard model for phase separation in a binary mixture with extra fluxes and within the Fourier heat theory. Alternative heat theories may be proposed for this Navier-Stokes-Cahn-Hilliard theory. Meanwhile the mixing problem is described graphically. Moreover the model may be generalized including a source term, and this doesn't affect the thermodynamic scheme. Then we describe and then compare two mathematical models for chemotactic processes: the pioneeristic Keller-Segel model and the hydrodynamic model by Chavanis and Sire. The first one is able to describe clusters or peaks, the second one involves inertial effects together with a friction force and leads to network patterns or filaments that are in good agreement with the experimental results. We analyze the linear stability of an infinite, stationary and homogeneous distribution of cells for determining the critical thresholds above which chemotactic collapse is allowed and cellular aggregation is reproduced. Then we discuss the differences between the two models, moreover we show the analogy between the instability criterion for biological populations and the Jeans instability criterion in an astrophysical setting. Finally we propose a different approach for the derivation of new diffuse interface models for tumour growth (with chemotaxis and active transport) based on the Cahn-Hilliard theory, combined with the (stationary) Darcy momentum equation.

Most physical ablation modalities for cancer treatment are focal and are based on thermal damage. Despite their regular clinical use as an alternative to surgical resection, their thermal principle of operation entails risks regarding the preservation of neighboring vital structures, such as large vessels, critical ducts or nerves. In addition, being focal, their use is unpractical in cases where multiple nodules are present or tumors are difficult to reach with the applicators. This thesis explores non-thermal electrical treatments which can be applied in a non-focal manner. Two treatments have been investigated: the first treatment, proposed by others a few years ago, is based on the permanent application of low magnitude alternating electric fields through surface electrodes. Here, this treatment has been in vivo studied to evaluate its efficacy as well as to discern whether it is non-thermally mediated. The second electrical treatment is based on the electroporation phenomenon and targets liver tumor nodules. Electroporation-based therapies employ brief high magnitude electric fields. These pulsed fields, alone or in combination with chemotherapeutic drugs, are able to kill cells by increasing their membrane permeability. Current electroporation-based therapies for internal tumors are local and are delivered through needle-shaped electrodes. Rather than using needle electrodes to treat liver tumors, here it is explored a novel treatment in which large plate electrodes are used to deliver the field across the whole liver in a non local fashion. The treatment aims at simultaneously destroying all tumors while preserving healthy tissue. Its efficacy is based on selectively enhancing the electric field over the tumors by infusing a solution with high electrical conductivity. The proposed treatment for liver tumors requires a high performance generator which is not currently available. The work presented here includes the design of a new generator topology able to fulfill the requirements.
La majoria del mètodes físics d'ablació tumoral es basen en produir dany tèrmic de manera focalitzada. Tot i ser considerats una alternativa habitual a la resecció quirúrgica, el principi tèrmic de funcionament, comporta un risc per la preservació d'estructures vitals adjacents a la zona de tractament, tals com grans vasos o nervis. A més, el fet de ser focals, fa impracticable la seva aplicació en cas de múltiples nòduls o tumors de difícil accés. Aquesta tesi explora tractaments elèctrics no basats en temperatura, capaços de ser aplicats de manera no focal. S'han investigat dos tractaments: El primer, proposat per altres fa pocs anys, està basat en aplicar permanentment camps elèctrics alterns de baixa magnitud a través d'elèctrodes superficials. Aquí, aquest tractament s'ha estudiat in vivo tant per avaluar la seva eficàcia com per discernir si aquesta resideix en la temperatura. El segon tractament es basa en el fenomen d'electroporació i persegueix el tractament de nòduls hepàtics. En els tractaments basats en electroporació, s’apliquen breus camps elèctrics de gran magnitud per tal de permeabilitzar la membrana cel·lular. Això permet la penetració d’agents quimioterapèutics o produeix directament la mort cel·lular. En lloc d'utilitzar, com és habitual, agulles per tal d'aplicar el tractament, aquí s'explora tractar tot el fetge de forma no localitzada, fent servir grans elèctrodes plans i paral·lels. Utilitzant solucions d'alta conductivitat elèctrica, es pretén magnificar selectivament el camp elèctric sobre els tumors, sent així capaços de destruir tots els tumors i alhora preservar el teixit sà. El tractament proposat per els tumors hepàtics, requereix d'un equip generador actualment no disponible. El presentat treball inclou el disseny d'una nova topologia de generadors capaç de complir amb els requisits.

Le champ électrique d'une puissance suffisante peut provoquer une augmentation de conductivité et perméabilité de la membrane cellulaire. L'effet est connu comme l'électroporation, attribuée à la création de voies aqueuses dans la membrane. Quantifier le transport de la matière dans le cadre d'électroporation est un objectif important. Comprendre ces processus a des ramifications dans l’extraction du jus ou l’extraction sélective des composés de cellules végétales, l'amélioration de l'administration de médicaments, et des solutions aux défis environnementaux. Il y a un manque de modèles qui pourraient être utilisés pour modéliser le transport de la matière dans les structures complexes (tissus biologiques) par rapport à l'électroporation. Cette thèse présente une description mathématique théorique (un modèle) pour étudier le transport de la matière et le transfert de la chaleur dans tissu traité par l’électroporation. Le modèle a été développé en utilisant les lois de conservation et de transport et permet le couplage des effets de l'électroporation sur la membrane des cellules individuelles au transport de la matière ou la chaleur dans le tissu. Une solution analytique a été trouvée par une simplification, mais le modèle peut être étendu avec des dépendances fonctionnelles supplémentaires et résolu numériquement. La thèse comprend cinq articles sur l'électroporation dans l'industrie alimentaire, la création de modèle pour le problème de diffusion, la traduction du modèle au problème lié à l’expression de jus, validation du modèle, ainsi que des suggestions pour une élaboration future du modèle. Un chapitre supplémentaire est dédié au transfert de la chaleur dans tissu
An electric field of sufficient strength can cause an increase of conductivity and permeability of cell membrane. Effect is known as electroporation and is attributed to creation of aqueous pathways in the membrane. Quantifying mass transport in connection with electroporation of biological tissues is an important goal. The ability to fully comprehend transport processes has ramifications in improved juice extraction and improved selective extraction of compounds from plant cells, improved drug delivery, and solutions to environmental challenges. While electroporation is intensively investigated, there is a lack of models that can be used to model mass transport in complex structures such as biological tissues with relation to electroporation. This thesis presents an attempt at constructing a theoretical mathematical description – a model, for studying mass (and heat) transfer in electroporated tissue. The model was developed employing conservation and transport laws and enables coupling effects of electroporation to the membrane of individual cells with the resulting mass transport or heat transfer in tissue. An analytical solution has been found though the model can be extended with additional dependencies to account for the phenomenon of electroporation, and solved numerically. Thesis comprises five peer-reviewed papers describing electroporation in the food industry, model creation for the problem of diffusion, translation of the model to the mathematically-related case of juice expression, model validation, as well as suggestions for possible future development, extension, and generalization. An additional chapter is dedicated to transfer of heat in tissue

In this thesis, we study the phenomenon of thermally induced polarisation using a combination of theory and computer simulation. Molecules of sufficiently low symmetry exhibit thermo-molecular orientation when subjected to a temperature gradient, leading to considerable electrostatic fields in polar liquids. Here, we first use non-equilibrium molecular dynamics simulations to study this interesting effect numerically. To this end, we propose an integration algorithm to impose a constant heat flux in simulations and show that it greatly improves energy conservation compared to a previous algorithm. We next investigate the thermal polarisation of water and find that truncation of electrostatic interactions can lead to severe artefacts, such as the wrong sign of polarisation and an overestimation of the electric field. We further show that the quadrupole-moment contribution to the electric field is significant and responsible for an inversion of its sign. To facilitate the theoretical description of electrostatic interactions, we propose a new dipolar model fluid as a perturbation of a Stockmayer fluid. Using this modified Stockmayer model, we provide numerical evidence for the recently proposed phenomenon of thermally induced monopoles. We show that the electrostatic field generated by a pair of heated/cooled colloidal particles immersed in such a solvent can be trivially described by two Coulomb charges. Finally, we propose a mean-field theory to predict the thermo-polarisation effect exhibited by our model fluid theoretically, and demonstrate near quantitative agreement with simulation results.

Les techniques de camouflage, mimétisme ou invisibilité ont récemment connu une forte émergence, qui se poursuit aujourd’hui avec l’apparition des méta-surfaces. C’est dans ce contexte que ce travail de doctorat a été réalisé, notamment avec un premier objectif d’étendre ces outils et concepts aux problèmes inverses du domaine de la diffusion de la chaleur. La suite du travail a concerné le rayonnement thermique, les méta-surfaces et les transformations de champ. Après avoir étendu les techniques de mimétisme au domaine de la conduction, nous avons résolu le problème inverse associé, qui consiste à camoufler des objets imposés en forme ou conductivité. Ce premier travail a permis de mettre en évidence les classes de transformation qui laissent invariantes les paramètres physiques, conférant ainsi plus de pragmatisme au domaine du mimétisme. Nous avons ensuite considéré le cas du rayonnement thermique, et démontré pour la première fois que les illusions par rayonnement étaient envisageables, en appui sur l’invariance du théorème de fluctuation/dissipation. Dans une deuxième étape, nous avons mis au point une nouvelle méthode pour calculer le rayonnement thermique par des objets de forme arbitraire, mettant en jeu des méta-surfaces inhomogènes, anisotropes, chirales et non locales. Nous montrons également comment tirer profit des méta-surfaces pour remplacer les capes volumiques tout en conservant la fonction de camouflage. Cette technique est particulièrement prometteuse pour les applications, même si elle reste intrinsèquement liée à l’éclairement. Des techniques similaires sont développées pour que soit facilité l’utilisation de transformations discontinues de l’espace
Mimetism, camouflage or invisibility have motivated numerous efforts in the last decade, which are now extended with metasurfaces. This PhD work fits this international context and was first focused on inverse problems in heat conduction before we address thermal radiation and metasurfaces, field transformation. After we generalize the mimetism techniques to heat diffusion, we solved the associated inverse problem which consists of the camouflage of given objects, that is, objects with shape or conductivity that are before hand chosen. The results allowed us to emphasize the class of transformations which hold the physical parameters, hence giving more pragmatism to the field of mimetism. Then we addressed the case of thermal radiation and proved for the first time that mimetism effects could also be controlled in this field, on the basis of the fluctuation/dissipation theorem. In a second step, we built an original technique able to predict the thermal radiation from objects of arbitrary shapes. This technique involves inhomogeneous, anisotropic, chiral and nonlocal metasurfaces. We also show how to take more benefits of metasurfaces in order to replace the bulk mimetism cloaks. We believe this technique to give again more push forward to the field, though the mimetism efficiency now relies on the illumination conditions. Similar techniques are further developed to allow a practical use of discontinuous space transformations. Eventually, field transformation is introduced to complete all these results

Modulation doped heterostructures have revolutionized the operation of field effect devices by increasing the speed of operation. One of the factors that affects the speed of operation of these devices is the mobility of the carriers, which is intrinsic to the material used. Mobility of electrons in silicon based devices has improved drastically over the years, reaching as high as 50.000cm2/Vs at 4.2K and 2600cm2/Vs at room temperature. However, the mobility of holes in p-type silicon devices still remains comparatively lesser than the electron mobility because of large effective masses and complicated valence band structure involved. Germanium is known to have the largest hole mobility of all the known semiconductors and is considered most suitable to fabricate high speed p-type devices. Moreover, it is also possible to integrate germanium and its alloy (Si1_zGex ) into the existing silicon technology. With the use of sophisticated growth techniques it has been possible to grow epitaxial layers of silicon and germanium on Si1_zGex alloy layers grown on silicon substrates. In tills thesis we investigate in detail the electrical properties of p-type germanium and n-type silicon thin films grown by these techniques. It is important to do a comparative study of transport in these two systems not only to understand the physics involved but also to study their compatibility in complementary field effect devices (cMODFET). The studies reported in this thesis lay emphasis both on the low and high field transport properties of these systems. We report experimental data for the maximum room temperature mobility of holes achieved m germanium thin films grown on Si1_zGex layers that is comparable to the mobility of electrons in silicon films. We also report experiments performed to study the high field degradation of carrier mobility due to "carrier heating" in these systems. We also report studies on the effect of lattice heating on mobility of carriers as a function of applied electric field. To understand the physics behind the observed phenomenon, we model our data based on the existing theories for low and high field transport. We report complete numerical calculations based on these theories to explain the observed qualitative difference in the transport properties of p-type germanium and ii-type silicon systems. The consistency between the experimental data and theoretical modeling reported in this work is very satisfactory.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.11.13 - прилади і методи контролю та визначення складу речовин. Національний технічний університет "Харківський політехнічний інститут", Харків, 2015 р. Дисертацію присвячено розробці методу теплового контролю металів при температурах понад 600 °С із використанням, у якості детектора теплового випромінювання, цифрового фотоапарата. На основі встановлених теоретичних положень методу розроблені програмні алгоритми обробки цифрових зображень, що дозволили: провести процедуру калібрування цифрового фотоапарата у діапазоні яскравісних температур 500…1800 °С та встановити калібрувальні залежності у вигляді математичних рівнянь; здійснити тепловий контроль металевих пластин, об'ємних металевих зразків та встановити присутні в них дефекти; вирішити додаткові задачі теплового контролю металів, а саме встановити значення питомої масової теплоємності металу; моделювати рівномірні температурні поля на поверхні металевих пластин; встановити розподілення коефіцієнта теплового випромінювання поверхні металевих пластин.
Thesis for granting the Degree of Candidate of Technical sciences in speciality 05.11.13 - devices and methods of testing and materials composition determination. - National Technical University "Kharkiv Politechnical Institute", Kharkiv, 2015. The dissertation is devoted to development of a thermal control metals method at temperatures above 600 °C using as thermal radiation detector, digital camera. On the basis of the established method of theoretical positions were developed software algorithms for digital image processing that allowed: to carry a digital camera calibration brightness temperature in the range of 500...1800 °C and set the calibration curve in the form of mathematical equations; perform thermal control of metal plates, bulk metallic samples and established the presence of defects; to solve additional tasks of thermal metals control, namely to establish the value of the specific heat capacity of the metal mass; simulate uniform temperature field on the surface of the metal plates; determine the distribution coefficient of thermal radiation from the metal plates surface.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.11.13 - прилади і методи контролю та визначення складу речовин. Національний технічний університет "Харківський політехнічний інститут", Харків, 2015 р. Дисертацію присвячено розробці методу теплового контролю металів при температурах понад 600 °С із використанням, у якості детектора теплового випромінювання, цифрового фотоапарата. На основі встановлених теоретичних положень методу розроблені програмні алгоритми обробки цифрових зображень, що дозволили: провести процедуру калібрування цифрового фотоапарата у діапазоні яскравісних температур 500…1800 °С та встановити калібрувальні залежності у вигляді математичних рівнянь; здійснити тепловий контроль металевих пластин, об'ємних металевих зразків та встановити присутні в них дефекти; вирішити додаткові задачі теплового контролю металів, а саме встановити значення питомої масової теплоємності металу; моделювати рівномірні температурні поля на поверхні металевих пластин; встановити розподілення коефіцієнта теплового випромінювання поверхні металевих пластин.
Thesis for granting the Degree of Candidate of Technical sciences in speciality 05.11.13 - devices and methods of testing and materials composition determination. - National Technical University "Kharkiv Politechnical Institute", Kharkiv, 2015. The dissertation is devoted to development of a thermal control metals method at temperatures above 600 °C using as thermal radiation detector, digital camera. On the basis of the established method of theoretical positions were developed software algorithms for digital image processing that allowed: to carry a digital camera calibration brightness temperature in the range of 500...1800 °C and set the calibration curve in the form of mathematical equations; perform thermal control of metal plates, bulk metallic samples and established the presence of defects; to solve additional tasks of thermal metals control, namely to establish the value of the specific heat capacity of the metal mass; simulate uniform temperature field on the surface of the metal plates; determine the distribution coefficient of thermal radiation from the metal plates surface.

Microwave processing of ceramics has seen a growth in research and development efforts throughout the past decade. One area of interest is the exploration of improved heating control through experiments and numerical modeling. Controlled heating may be used to counteract non-uniform heating and avoid destructive phenomena such as cracking and thermal runaway. Thermal runaway is a potential problem in materials with temperature dependent dielectric properties. As the material absorbs electromagnetic energy, the temperature increases as does its ability to absorb more energy. Controlled processing of the material may be achieved by manipulating the applied field. The purpose of this research is to model the interaction of the EM-field with a thin ceramic fiber to investigate possible mechanisms that may affect the heating process. The fiber undergoes microwave heating in a single-mode resonant applicator. Maxwell's equations for the fields within the cavity are solved using mode-matching techniques taking into account the field interaction of the fiber and an arbitrarily shaped coupling aperture. Effects of varying the aperture shape on the field distribution are explored. The coupled nature of the electromagnetic solution with the material's temperature-dependent properties, including an analysis of non-uniform heating, is also discussed.
Master of Science

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A preocupação com os chamados impactos ambientais urbanos fomentou um maior interesse nas pesquisas, principalmente aquelas voltadas para as análises climáticas, na escala urbana. A cidade por consequência de seu processo de organização e estruturação desenvolveu um clima totalmente particular, o clima urbano, isso é possível através da retirada da vegetação original e a inserção dos chamados equipamentos urbanos, como por exemplo, as vias impermeabilizadas, as construções, a verticalização, além da circulação de pessoas e veículos que irão contribuir para maior aquecimento da atmosfera local. Os materiais presentes no meio urbano vão apresentar diferentes valores de albedo, emissividade, absortividade e irradiação e consequentemente, estes condicionarão diferentes valores de temperatura de superfície e que influenciarão na temperatura do ar. O presente estudo tem por objetivo analisar o comportamento do clima urbano na cidade de Juiz de Fora- MG, onde foram trabalhadas 35 regiões urbanas, localizadas ao longo do curso do Rio Paraibuna. O estudo busca através da aplicação de um modelo geoespacial, interligar variáveis que possuem uma conexão direta com a temperatura de superfície e indireta com a temperatura do ar. Este conjunto de dados permitiu alcançar uma maior compreensão, viabilizou a espacialização e consequentemente uma visualização de como se distribuem as áreas e suas diferentes capacidades de criarem distintos campos térmicos na cidade.Além disso, para fins de validação do modelo, foi feita uma correlação estatística entre o modelo matemático proposto e a temperatura de superfície obtida na faixa do infravermelho termal. O modelo utilizado provou possuir consistência para ser adaptado a fim de ser replicado em diferentes cidades com especificidades térmicas além de ser viável a integração de outras informações e dados.
Concern about so-called urban environmental impacts has fostered greater interest in research, especially those focused on climate analysis, on the urban scale. The city as a result of its process of organization and structuring has developed a totally particular climate, the urban climate, this is possible through the removal of the original vegetation and the insertion of so-called urban equipment, such as waterproofed roads, constructions, verticalization, besides the circulation of people and vehicles that will contribute to greater warming of the local atmosphere. The materials present in the urban environment will present different values of albedo, emissivity, absorptivity and irradiation and consequently, these will condition different values of surface temperature and that will influence the air temperature. The present study aims to analyze the behavior of the urban climate in the city of Juiz de Fora- MG, where 35 urban areas were located along the course of the Paraibuna River. The study searches through the application of a geospatial model, interconnecting variables that have a direct coexistence with the surface temperature and indirect with the air temperature. This dataset allowed to reach a greater understanding, made possible the spatialization and consequently a visualization of how the areas are distributed and their different capacities to create different thermal fields in the city. In addition, for purposes of validation of the model, a statistical correlation was made between the proposed mathematical model and the surface temperature obtained in the thermal infrared range. The model used proved to have consistency to be adapted in order to be replicated in different cities with thermal specificities besides being feasible the integration of other information and data.

This thesis investigates the flow field of a twin-engine, medium lift utility helicopter numerically. The effects of the exhaust hot gases emerging from the engines are accounted for in the numerical study. The commercial computational fluid dynamics (CFD) software ANSYS Fluent is employed for the computations. While the effects of engines are included in the computations through simple inlet and outlet boundary conditions, the main and tail rotors are simulated by the Virtual Blade Model in a time-averaged fashion. Forward flight at four different advance ratios and hover in ground effect are studied. The temperature distribution around the tail boom is compared to available flight test data. Good agreement with the flight test data is observed.

Recently, remarkable advances have been made in the understanding of micro/nanoscale energy transport, opening new opportunities in various areas such as thermal management, data storage, and energy conversion. This dissertation focuses on thermally-sensed nanotopography using a heated silicon microcantilever and near-field thermophotovoltaic (TPV) energy conversion system. A heated microcantilever is a functionalized atomic force microscope (AFM) cantilever that has a small resistive heater integrated at the free end. Besides its capability of increasing the heater temperature over 1,000 K, the resistance of a heated cantilever is a very sensitive function of temperature, suggesting that the heated cantilever can be used as a highly sensitive thermal metrology tool. The first part of the dissertation discusses the thermal characterization of the heated microcantilever for its usage as a thermal sensor in various conditions. Particularly, the use of heated cantilevers for tapping-mode topography imaging will be presented, along with the recent experimental results on the thermal interaction between the cantilever and substrate. In the second part of the dissertation, the so-called near-field TPV device is introduced. This new type of energy conversion system utilizes the significant enhancement of radiative energy transport due to photon tunneling and surface polaritons. Investigation of surface and bulk polaritons in a multilayered structure reveals that radiative properties are significantly affected by polariton excitations. The dissertation then addresses the rigorous performance analysis of the near-field TPV system and a novel design of a near-field TPV device.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 126-130).
The world is facing the challenge of finding new renewable sources of energy - first, in response to fossil fuel reserve depletion, and second, to reduce greenhouse gas emissions. Ocean Thermal Energy Conversion (OTEC) can provide renewable energy by making use of the temperature difference between the surface ocean and deep ocean water in a Rankine cycle. An OTEC plant pumps huge volumes of water from the surface and nearly 1 km depth, and releases it at an intermediate depth. The effects of this enormous flux are crucial to understand since disruption of the ambient temperature stratification can affect the efficiency of the plant itself and of adjacent plants. This thesis aims to study the external fluid mechanics of offshore OTEC power plants, to assess their environmental impact and to help analyze whether OTEC plants can provide a sustainable source of energy. Although there has been interest in OTEC for several decades, so far primarily physical and analytical models have been developed. In this study numerical models are developed to model OTEC operating plants: integral models for the near and intermediate field and a large-scale ocean general circulation model. Two strategies in modeling OTEC plant discharge are used to analyze plume dynamics: the "Brute Force" approach, in which a circulation model, MITgcm, computes the near, intermediate and far field mixing; and the "Distributed Sources and Sinks" approach, in which the near and intermediate field are represented in the circulation model by sources and sinks of mass computed by integral models. This study concludes that the Brute Force modeling strategy is highly computationally demanding and sometimes inaccurate. Such simulations are very sensitive to model resolution and may require the use of unrealistic model parameters. The Distributed Sources and Sinks approach was found to be capable of modeling the plume dynamics accurately. This method can be applied to the study of adjacent OTEC power plant interaction, redistribution of nutrients, and propagation of contaminants.
by Mariana Rodríguez Buño.
S.M.

According to classical linearized resistive magnetohydrodynamics theory, pressuredriven modes are unstable in the reversed-field pinch (RFP) due to unfavorable magnetic field line curvature. The result is based on the assumption of an adiabatic energy equation where anisotropic thermal conduction effects are ignored as compared to convection and compression. In this thesis the effects of heat conduction in the energy equation have been studied. We have examined these effects on the linear stability of pressure-driven resistive modes using boundary value theory (Δ´ ) and a novel initial-value full resistive MHD code employing the Generalized Weighted Residual Method (GWRM). In the Δ´ method, a shooting technique is employed by integrating from the resistive layer to boundaries. The GWRM method, on the other hand, is a time-spectral Galerkin method in which the fully linearized MHD equations are solved. For detailed computations, efficiency requires the temporal and spatial domains to be divided into subdomains. For this purpose, a number of challenging test cases including linearized ideal MHD equations are treated. Numerical and analytical investigations of equilibria reveal that thermal conduction effects are not stabilizing for reactor relevant values of Lundquist number, S0, and normalized pressure, βθ, for tearing-stable plasmas. These studies show that growth rate scales as  γ~_ S0−1/5 , which is weaker than for the adiabatic case, γ~_ S0−1/3. A numerical study of optimized confinement for an advanced RFP scenario including ohmic heating and heat conduction, is also part of this thesis. The fully nonlinear resistive MHD code DEBSP has been employed. We have identified, using both Δ´ and GWRM methods, that the observed crash of the high confinement is caused by resistive, pressure-driven modes.

QC 20130503

In this work we developed a 3-D theoretical model for plasma-enhanced thermo-field emission from nanostructured cathodes in the absence of significant erosion. Our first studies indicated that very dense arrays of vertically-aligned carbon nanotubes (CNT) acting as electron emitters in vacuum could sustain the temperatures resulting from very high surface-averaged current densities such as those found in the cathode spots of arc discharges on non-refractory cathodes. A comparative study of the electron emission models for cold surfaces subjected to strong electric field revealed the existence of a simple relation between the inaccurate Fowler-Nordheim (F-N) equation and the accepted result provided by the theory of Murphy and Good (M-G). We therefore proposed a parametric equation for the emitted current density which was as convenient as the F-N equation but more accurate. The use of M-G theory has also provided an explanation for the tip cooling effect described in a previous study on the destruction of field emitting CNT. We identified the source of the tip cooling effect as the Nottingham effect. For very short emitters, this particular effect heats the surface and accelerates the destruction process and for long emitters, it creates a small isothermal zone at the emitter's tip which is destroyed when it reaches a critical temperature (approximately 1850 K according to our calculations). When combined to existing data on the emitter's length, its diameter, the applied voltage and the measured current, our model can provide the emitter's work function, its room temperature resistivity and the value of the thermal contact resistance between the emitter and its substrate. Another version of this model includes a calculation of the surface electric field in the presence of a non-thermal plasma. To this end we modified the model developed by Mackeown and obtained a general result for 3-D surfaces. This general expression requires the calculation of the ion flux enhancement factor which can be obtained by solving Laplace equation above the surface of interest. This simple approach allows us to describe how the ions are redistributed within the sheath towards the tip of the CNT where the surface field increases. These theoretical predictions were tested by developing simultaneously a fabrication process for a composite electrode matching the optimized design we suggested. Anodic aluminum oxide templates were used as substrates to grow CNT arrays. In order to facilitate their large scale use we modified a standard CNT production process to allow the direct use of as anodized commercial aluminum. Our resulting electrodes were then used as cathodes in low pressure gas discharges. The operating parameters of these discharges are different from the typical voltages and current densities found in glow discharges using as electrodes bare aluminum surfaces. In fact, due to the very low work function of the sharp and relatively ordered emission sites and the simultaneous presence of a ceramic template around them, our electrodes produced very diffuse attachment points for the plasma in a similar fashion as thermionic cathodes do for high pressure arcs. They also required lower (38-140 V) sustaining voltages than what is necessary to sustain a conventional glow discharge. Our electrodes also showed the ability to sustain these low voltage discharges for as much as 500 hours if their bulk temperature was maintained below 60 Celsius and if water vapour was added to the feed gas. Our experiments in nitrogen-water mixtures demonstrated the feasibility of producing large amounts of UV photons at an operating voltage (anode, grounded cathode) of 90-100 V. These results are very promising for future applications in lighting.
Dans le cadre de ce projet nous avons développé un modèle en 3-D pour l'émission électronique par effet thermo-champ stimulée par un plasma. Nos premiers résultats ont indiqué que des réseaux denses de nanotubes de carbone (NTC) agissant en tant qu'émetteurs dans le vide pouvaient supporter les températures résultant de densité de courant moyennes très élevées de l'ordre de celles présentes dans les taches cathodiques d'arcs opérant sur des cathodes non-réfractaires. Une étude comparative des modèles pour l'émission électronique pour les surfaces froides soumises à de forts champs électriques a révélé l'existence d'une relation simple entre l'équation imprécise de Fowler-Nordheim (F-N) et le résultat accepté fourni par la théorie de Murphy et Good (M-G). Nous avons donc proposé une équation paramétrique précise et simple pour la densité de courant émise. L'usage de la théorie de M-G a aussi fourni une explication pour l'effet de refroidissement à la pointe décrit dans une étude précédente sur la destruction de NTC émettant par effet de champ: l'effet Nottingham. Pour des émetteurs très courts, cet effet particulier chauffe la surface et accélère le processus de destruction et pour de longs émetteurs, il crée une petite zone isotherme à la pointe de l'émetteur qui est détruite lorsqu'elle atteint une température critique (approximativement 1850 K). Lorsque combiné à des données sur la longueur de l'émetteur, son diamètre, la tension appliquée et le courant mesuré, notre modèle peut fournir le travail de sortie de l'émetteur, sa résistivité à la température ambiante et la valeur de la résistance de contact thermique entre l'émetteur et son substrat. Une autre version de ce modèle inclut un calcul du champ électrique de surface en présence d'un plasma froid. À cette fin, nous avons modifié le modèle développé par Mackeown et obtenu un résultat général pour des surfaces en 3-D. Cette expression générale requiert le calcul du facteur d'amplification du flux ionique, lequel peut être obtenu en résolvant l'équation de Laplace au dessus de la structure d'intérêt. Cette approche simple nous permet de décrire comment les ions sont redistribués à l'intérieur de la gaine vers la pointe des NTC où le champ électrique augmente. Ces prédictions ont été testées en développant simultanément un procédé de fabrication pour une électrode composite correspondant au schéma optimisé que nous suggérions. Des patrons d'oxyde anodique d'aluminium furent utilisés en tant que substrats pour faire croître nos réseaux de NTC mais afin de faciliter leur usage à grande échelle nous avons modifié le procédé de production des NTC pour permettre l'usage directe d'aluminium commercial anodisé. Nos électrodes furent ensuite utilisées comme cathodes dans des décharges à basse pression. Les tensions et densités de courant mesurées sont différentes des valeurs typiques rencontrées dans les décharges électroluminescentes utilisant comme électrodes, des surfaces d'aluminium. En fait, en raison du très faible travail de sortie des sites d'émission pointus et relativement ordonnés et de la présence simultanée d'un patron de céramique autour d'eux, nos électrodes ont produit des points d'attachement très diffus pour le plasma d'une façon similaire à ce qui est observé pour des cathodes réfractaires chaudes telles que le tungstène. Les tensions d'opération, dans la plage 38-140 V, sont de beaucoup inférieures aux tensions observées avec des électrode d'aluminium (>200 V). Nos électrodes ont aussi démontré leur capacité de maintenir ces décharges à basse tension pour au moins 500 heures si leur température moyenne était maintenue sous 60 Celsius et si de la vapeur d'eau était ajoutée au gaz injecté. Nos expériences dans des mélanges d'azote et d'eau ont démontré la faisabilité de produire de larges quantités de photons UV pour un potentiel anodique (cathode mise à la terre) de 90-100 V. Ces résultats sont très prometteurs pour de futures applications en éclairage.

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Capes
Desenvolvemos neste trabalho um estudo teórico da aplicação da dinâmica de campo térmico sobre o modelo de Jaynes-Cummings. De acordo com a abordagem feita por Hashizume no artigo, A new perspective to formulate a dissipative ther mo eld dynamics aplicamos os mesmos conceitos para investigar o processo de relaxação envolvido no modelo de Jaynes-Cummings. Num primeiro momento, fi zemos uma revisão de alguns elementos primordiais para a compreensão de toda a discussão envolvida nessa dissertação. Em seguida, estudamos processos de relaxação em sistemas quânticos simples, para podermos, mais tarde, traçar um paralelo entre os resultados e estabelecer alguma relação com o que foi encontrado. Diante da dinâmica de campo térmico, mas conhecida como TFD (ThermoFieldDynamics), usamos uma abordagem feita por Hashiz um e colaboradores, e investigamos como o processo de relaxação se desenvolve mediante a representação via TFD.
We develop in this work, a the or etical study of the application of theThermo eld dynamics on the model of Jaynes-Cummings. According to the approach taken by Hashizu me in the article, A new perspective to formulate a dissipative thermo eld dynamics", we use the same concepts to investigate the relaxation process involved in model Jaynes-Cummings. In the rst moment, we did are view of some key elements to comprenção all the discussion involved in this dissertation. Then, we study relaxation processes in simple quantum systems, for we could later draw a parallel between the results and establish some relationship to what was found. Front the thermal eld dynamics, butknownas TFD, we use an approach made by Hashizu me and colaborators, and we investigated how the relaxation process it developed through there presentation via TFD.

L'effet Magnéto-Impédance Géante (MIG) se manifeste par une forte variation de l’impédance d’un conducteur ferromagnétique parcouru par un courant alternatif et soumis à un champ magnétique variable. Ces dernières années, de nombreuses activités de recherches ont porté sur l'accroissement de la sensibilité en champ de ces dispositifs. Les valeurs atteintes aujourd’hui permettent de réaliser un magnétomètre à très haute sensibilité. Cependant, peu d’études se sont intéressées aux effets de la variation de la température de MIG et à sa stabilité à long terme. Mon travail de thèse présente une étude détaillée de la sensibilité en température des magnétomètres MIG et des méthodes permettant de s’affranchir des fluctuations induites par la variation de cette température. Sur la base d’un modèle théorique, une étude analytique des fluctuations d’offset engendrées par les variations de température a été réalisée. Ce modèle prend notamment en compte les principaux mécanismes mis en jeu : supposés être la perméabilité magnétique et la résistivité électrique. À partir de cette modélisation, une technique de compensation pour les différents modes de fonctionnement a été proposée. Un prototype de magnétomètre basé sur un micro-fil MIG off-diagonal a été mis en œuvre afin de vérifier l’efficacité de la méthode proposée. Cette dernière met principalement en œuvre une double modulation en courant de l’élément sensible. Les résultats expérimentaux ont été comparés à la configuration classique (simple modulation) et aux valeurs attendues. Ils montrent d’une part l'efficacité de cette technique et d’autre part la cohérence des résultats obtenus. Soit une réduction importante des fluctuations d’offset en température, notamment aux très très basses fréquences (< 10-3 Hz) avec une dérive de -1,8 nT/K pour une variation en température de 24 K et une dérive de 130 pT/h sur 12 heures d’acquisition
The Giant Magneto-Impedance (GMI) effect is manifested by a strong variation in the impedance of a ferromagnetic conductor when an alternating current flows through it and it is submitted simultaneously to a variable magnetic field. Over the last few years, numerous research activities have been devoted to improving the field sensitivity of these devices. The values reached today make it possible to produce a very high sensitive magnetometer. However, only a few studies have investigated the temperature effects on the GMI material and its long-term stability. My thesis presents a detailed study of the temperature sensitivity of GMI magnetometers, and we proposed some methods to remedy the fluctuations induced by the temperature variation. Based on a theoretical model, an analytic study of the offset fluctuations generated by the temperature variations was carried out. This model takes into account the physic mechanisms involved when a temperature variation occurs, supposed to be the magnetic permeability and the electrical resistivity. From this modeling, a compensation technique for the different modes of operation has been proposed. Subsequently, a magnetometer prototype based on off-diagonal GMI wire was implemented to verify the effectiveness of the proposed method. The latter injects a double current modulation in the GMI sensitive element. The experimental results were compared to the classical configuration (simple modulation) and to the expected values. They show, on the one hand, the efficiency of this technique and, on the other hand, the coherence of the obtained results. A significant reduction in the GMI offset drift depending on temperature has been achieved, especially at very very low frequencies (< 10- 3 Hz) with a drift of - 1.8 nT/K for a temperature variation of 24 K, and a drift of 130 pT/h over 12 hours of acquisition

Thesis (MEng)--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: This study investigates the implementation of the finite volume numerical method applicable to non-orthogonal control volumes and the application of the method to calculate the thermo-flow field within the collector area of a solar chimney power generating plant. The discretisation of the governing equations for the transient, Newtonian, incompressible and turbulent fluid flow, including heat transfer, is presented for a non-orthogonal coordinate frame. The standard k - E turbulence model, modified to include rough surfaces, is included and evaluated in the method. An implicit solution procedure (SIP-semi implicit procedure) as an alternative to a direct solution procedure for the calculation of the flow field on nonstaggered grids is investigated, presented and evaluated in this study. The Rhie and Chow interpolation practice was employed with the pressurecorrection equation to eliminate the presence of pressure oscillations on nonstaggered grids. The computer code for the solution of the three-dimensional thermo-flow fields is developed in FORTRAN 77. The code is evaluated against simple test cases for which analytical and experimental results exist. It is also applied to the analysis of the thermo-flow field of the air flow through a radial solar collector. KEYWORDS: NUMERICAL METHOD, FINITE VOLUME, NON-ORTHOGONAL, k+-e TURBULENCE MODEL, SIP
AFRIKAANSE OPSOMMING: Die studie ondersoek die implementering van 'n eindige volume numeriese metode van toepassing op nie-ortogonale kontrole volumes asook die toepassing van die metode om die termo-vloei veld binne die kollekteerder area van 'n sonskoorsteen krag aanleg te bereken. Die diskretisering van die behoudsvergelykings vir die tyd-afhanlike, Newtonse, onsamedrukbare en turbulente vloei, insluitende hitteoordrag, word beskryf vir 'n nie-ortogonale koordinaatstelsel. Die standaard k - E turbulensiemodel, aangepas om growwe oppervlakrandvoorwaardes te hanteer, is ingesluit en geevalueer in die studie. 'n Implisiete oplossings metode (SIP-semi implisiete prosedure) as alternatief vir 'n direkte oplossingsmetode is ondersoek en geimplimenteer vir die berekening van die vloeiveld met nie-verspringde roosters. 'n Rhie en Chow interpolasie metode is gebruik tesame met die drukkorreksie-vergelyking ten einde ossilasies in die drukveld in die nie-verspringde roosters te vermy. Die rekenaarkode vir die oplossing van die drie dimensionele termo-vloeiveld is ontwikkel in FORTRAN 77. Die kode is geevalueer teen eenvoudige toetsprobleme waarvoor analitiese en eksperimentele resultate bestaan. Die kode IS ook gebruik om die termo-vloeiveld binne 'n radiale son kollekteerder te analiseer. SLEUTELWOORDE: NUMERIESE METODE, EINDIGE VOLUME, NIE-ORTOGONAAL, k - E TURBULENSIE MODEL, SIP

At present there are different reliability standards that are being used for carrying out reliability prediction. They take into consideration different factors, environments and data sources to give reliability data for a wide range of electronic components. However, the users are not aware of the differences between the different reliability standards due to the absence of benchmarks of the reliability standards that would help classify and compare between them. This lack of benchmark denies the users the opportunity to have a top-down view of these different standards and choose the appropriate standard based on qualitative judgement in performing reliability prediction for a specific system. To addres this issue, the benchmark of a set of reliability standards are developed in this dissertation. The benchmark helps the users of the selected reliability standards understand the similarities and differences between them and based on the evaluation criterion defined can easily choose the appropriate standard for reliability prediction in different scenarios. Theoretical reliability prediction of two electronic products in Bombardier is performed using the standards that have been benchmarked. One of the products is matured with available incident report from the field while the other is a new product that is under development and yet to enter in service. The field failure data analysis of the matured product is then compared and correlated to the theoretical prediction. Adjustment factors are then derived to help bridge the gap between the theoretical reliability prediction and the reliability of the product in field conditions. Since the theoretical prediction of the product under development could not be used to compare and correlate any data due to unavailability, instead, the accelerated life test is used to find out the product reliability during its lifetime and find out any failure modes intrinsic to the board. A crucial objective is realized as an appropriate algorithm/model is found in order to correlate accelerated test temperature-cycles to real product temperature-cycles. The PUT has lead-free solder joints, hence, to see if any failures occurring due to solder joint fatigue has also been of interest. Additionally, reliability testing simulation is a performed in order to verify and validate the performance of the product under development during ALT. Finally, the goal of the thesis is achieved as separate models are proposed to predict product reliability for both matured products and products under development. This will assist the organization in realizing the goal of predicting their product reliability with better accuracy and confidence.
För närvarande finns det olika tillförlitlighetsstandarder som används för att utföra tillförlitlighet förutsägelse. De tar hänsyn till olika faktorer, miljöer och datakällor för att ge tillförlitlighetsdata för ett brett spektrum av elektronikkomponenter. Men användarna inte är medvetna om skillnaderna mellan de olika tillförlitlighetsstandarder på grund av avsaknaden av riktmärken för tillförlitlighetsstandarder som skulle hjälpa klassificera och jämföra mellan dem. Denna brist på jämförelse förnekar användarna möjlighet att få en top-down bakgrund av dessa olika standarder och välja lämplig standard baserad på kvalitativ bedömning att utföra tillförlitlighet prognos för ett specifikt system. För att lösa detta problem, är riktmärket en uppsättning av tillförlitlighetsstandarder som utvecklats i denna avhandling. Riktmärket hjälper användarna av de utvalda tillförlitlighetsstandarder förstå likheter och skillnader mellan dem och på grundval av bedömningskriteriet definieras kan enkelt välja lämplig standard för pålitlighet förutsägelse i olika scenarier. Teoretisk tillförlitlighet förutsäga två elektroniska produkter i Bombardier utförs med hjälp av standarder som har benchmarking. En av produkterna är mognat med tillgängliga incidentrapport från fältet, medan den andra är en ny produkt som är under utveckling och ännu inte gå in i tjänsten. Analysen av den mognade produkten fält feldata jämförs sedan och korreleras till den teoretiska förutsägelsen. Justeringsfaktorer sedan härledas för att överbrygga klyftan mellan den teoretiska tillförlitlighet förutsägelse och tillförlitligheten av produkten i fältmässiga förhållanden. Eftersom den teoretiska förutsägelsen av produkt under utveckling inte kan användas för att jämföra och korrelera alla data på grund av otillgängligheten, i stället är det accelererade livslängdstest som används för att ta reda på produktens tillförlitlighet under dess livstid och reda ut eventuella felmoder inneboende till styrelsen . Ett viktigt mål realiseras som en lämplig algoritm /modell finns i syfte att korrelera accelererade provningen temperaturcykler på verkliga produkttemperatur cykler. PUT har blyfria lödfogar därmed att se om några fel inträffar på grund av löda gemensam trötthet har också varit av intresse. Dessutom är tillförlitlighet testning simulering en utförs för att verifiera och validera produktens prestanda under utveckling under ALT. Slutligen är målet med avhandlingen uppnås som separata modeller föreslås att förutsäga produktens tillförlitlighet för både förfallna och produkter under utveckling. Detta kommer att hjälpa organisationen att förverkliga målet att förutsäga deras tillförlitlighet med bättre noggrannhet och förtroende.

Combining computer fluid dynamic, CFD, models with finite element, FE, models to calculate temperature in fire exposed structures can reduce design temperatures in structures while still obtaining the level of structural fire safety stipulated by society. A better understanding of heat transfer and the concept of adiabatic surface temperatures, AST, the transition of data between models can be simplified and more accurate temperature predictions can be made.The thesis focuses on heat transfer calculations by employing AST in particular, and how this can be used as a means of coupling any CFD and FE-analysis code. The thesis presents a method for performing FE-analysis of the thermal response with input data calculated with the computer code FDS, Fire Dynamics Simulator. Parallel to this, the heat balance equation in FDS is tested and an alternate numerical algorithm is developed and tested.Firstly, a verification model is developed to test the radiative and convective part of the existing heat balance equation in FDS. An alternate numerical algorithm for calculation of the heat transfer at surfaces is developed as a more homogenous alternative for CFD codes.Secondly is a study on how to extract AST from an arbitrary point with direction in a CFD calculation using an infinitesimal surface. Instead of modeling numerous small surfaces for extracting AST, a post processor is developed to calculate AST independent of any modeled surface. For CFD codes, such as FDS that depend on a rectilinear grid, this enables calculation of AST in any direction, not only directions normal to the Cartesian planes.Finally, a comparison is made between different methods for calculating temperatures in steel with AST from numerical fire dynamics/modeling calculations. In this thesis there is a comparison between simplified Eurocode techniques, simple finite element analysis and advanced finite element analysis. This study shows the benefit of understanding heat transfer in numerical codes and to implement the concept of AST in a proper way.This way, the concept of combining numerical fire dynamics calculation with numerical (or simplified) thermal calculations can be better understood and implemented.
Godkänd; 2013; 20131010 (joasan); Tillkännagivande licentiatseminarium 2013-11-15 Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Joakim Sandström Ämne: Stålbyggnad/Steel Structures Uppsats: Thermal Boundary Conditions Based on Field Modelling of Fires Heat Transfer Calculations in CFD and FE Models With Special Regards to Fire Exposure Represented With Adiabatic Surface Temperatures Examinator: Professor Ulf Wickström, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Diskutant: Teknologie doktor, Lektor Stephen Welch, the University of Edinburgh, UK Tid: Torsdag den 5 december 2013 kl 13.00 Plats: F1031, Luleå tekniska universitet

Conselho Nacional de Desenvolvimento Científico e Tecnológico
Neste trabalho, utilizamos o formalismo de teorias quânticas de campos a temperatura finita, tal como desenvolvidas por Matsubara, aplicado a uma hamiltoniana de N campos escalares com autointeração quártica a N grande. Obtém-se uma expressão, na primeira aproximação quântica, para o coeficiente do termo quadrático da hamiltoniana ("massa quadrada"), renormalizado, como função da temperatura. A partir dela, estudamos o processo de quebra espontânea de simetria. Por outro lado, a mesma hamiltoniana é conhecida como modelo de Ginzburg-Landau na literatura de matéria condensada, e que permite o estudo de transições de fase em materiais ferromagnéticos. A temperatura é introduzida através do termo quadrático na hamiltoniana, de forma linear: é proporcional à diferença entre a variável de temperatura e a temperatura crítica. Tal modelo, porém, possui validade apenas na regi~ao de temperaturas próximas à criticalidade. Como resultado de nossos cálculos na teoria de campos a temperatura finita, observamos que, numa faixa de valores em torno da temperatura crítica, a massa quadrática pode ser aproximada por uma relação linear em relação à variável de temperatura. Isso evidencia a compatibilidade da abordagem de Ginzburg-Landau, na vizinhança da criticalidade, com respeito ao formalismo de campos a temperatura finita. Discutimos também os efeitos causados pela presença de um potencial químico no sistema.
In this work, we use the formalism of quantum field theories at finite temperature, as developed by Matsubara, applied to a Hamiltonian of N scalar fields with quartic self-interaction at N large. We get an expression in the first quantum approximation to the coeficient of the quadratic term of the Hamiltonian ("square mass"), renormalized as a function of temperature. From it, we study the process of spontaneous symmetry breaking. On the other hand, the same Hamiltonian is known as Ginzburg-Landau model in the literature of condensed matter, and allows the study of phase transitions in ferromagnetic materials. The temperature is introduced through the quadratic term in the Hamiltonian of the linear form: is proportional to the difference between the temperature and the critical temperature. This model, however, is valid only in the region of temperatures close to criticality. As a result of our calculations in the field theory at finite temperature, we observed that in a range of values around the critical temperature, the quadratic mass can be approximated by a linear relation with the temperature. This highlights the compatibility of the Ginzburg-Landau approach, in the vicinity of criticality with respect to the formalism of finite temperature field. We also discuss the effects caused by the presence of a chemical potential in the system.

Cette thèse aborde la problématique de la modélisation multiphysique en génie électrique, avec une application à l'étude des vibrations d'origine électromagnétique des cages de développantes. Cette étude comporte quatre parties : la construction de la densité de courant, le calcul des forces locales, le transfert de solutions entre maillages et la résolution des problèmes couplés. Un premier enjeu est de correctement représenter les courants, cette opération est effectuée en deux étapes : la construction de la densité de courant et l'annulation de la divergence. Si des structures complexes sont utilisées, l'imposition du courant ne peut pas toujours être réalisée à l'aide de méthodes analytiques. Une méthode basée sur une résolution électrocinétique ainsi qu'une méthode purement géométrique sont testées. Cette dernière donne des résultats plus proches de la densité de courant réelle. Parmi les nombreuses méthodes de calcul de forces, les méthodes des travaux virtuels et des forces de Laplace, considérées par la littérature comme les plus adaptées au calcul des forces locales, ont été étudiées. Nos travaux ont montré que bien que les forces de Laplace sont particulièrement précises, elles ne sont pas valables si la perméabilité n'est plus homogène. Ainsi, la méthode des travaux virtuels, applicable de manière universelle, est préférée. Afin de modéliser des problèmes multi-physiques complexes à l'aide de plusieurs codes de calculs dédiés, des méthodes de transferts entre maillages non conformes ont été développées. Les procédures d'interpolations, les méthodes localement conservatives et les projections orthogonales sont comparées. Les méthodes d'interpolations sont réputées rapides mais très diffusives tandis que les méthodes de projections sont considérées comme les plus précises. La méthode localement conservative peut être vue comme produisant des résultats comparables aux méthodes de projections, mais évite l'assemblage et la résolution de systèmes linéaires. La modélisation des problèmes multi-physiques est abordée à l'aide des méthodes de transferts de solutions. Pour une classe de problème donnée, l'assemblage d'un schéma de couplage n'est pas unique. Des tests sur des cas analytiques sont réalisés afin de déterminer, pour plusieurs types de couplages, les stratégies les plus appropriées.Ces travaux ont permis une application à la modélisation magnéto-mécanique des cages de développantes est présentée.

Increasing demands for low heat losses and energy intensity of a building influence energy calculations. Higher demands are placed on the accuracy of the calculations. An important part of the thermal engineering calculations is the determination of the correct boundary conditions. An important input factor is primarily the indoor and outdoor environment, and temperature is the most important parameter for these types of enviromnent. It is not always the temperature of the external environment, but the environment that is adjacent to the soil or to unheated or differently heated spaces. The possibilities of modeling temperatures below the object are described in the standard ČSN EN ISO 10211. This standard specifies details for a geometric model for the numerical calculation of heat flows to assess the total heat loss of buildings or parts thereof, as well as to derive linear and point heat transfer factors. Furthermore, to calculate minimum surface temperatures to assess the risk of surface condensation and to determine the surface temperature factors. These are two different computational models. Therefore, it would be appropriate to simplify these calculations by simplifying the boundary conditions, namely to conduct an isotherm at a certain level below the terrain, which will be considered as a boundary condition, which is also based on long-term experience with "frost-free" depth. This calculation would be unambiguous, clear and simple.

Considering the late in-vessel phase of an unlikely core melt down scenario in a light water reactor (LWR) with the formation of a corium pool in the lower head of the reactor pressure vessel (RPV) the possible failure modes of the RPV and the time to failure have to be investigated to assess the possible loadings on the containment. In this work, an integral model was developed to describe the processes in the lower plenum of the RPV. Two principal model domains have to be distinguished: The tem-perature field within the melt and RPV is calculated with a thermodynamic model, while a mechanical model is used for the structural analysis of the vessel wall. In the introducing chapters a description is given of the considered accident scenario and the relevant analytical, experimental, and numerical investigations are discussed which were performed worldwide during the last three decades. Following, the occurring physical phenomena are analysed and the scaling differences are evaluated between the FOREVER-experiments and a prototypical scenario. The thermodynamic and the mechanical model can be coupled recursively to take into account the mutual influence. This approach not only allows to consider the temperature dependence of the material parameters and the thermally induced stress in the mechanical model, it also takes into account the response of the temperature field itself upon the changing vessel geometry. New approaches are applied in this work for the simulation of creep and damage. Using a creep data base, the application of single creep laws could be avoided which is especially advantageous if large temperature, stress, and strain ranges have to be covered. Based on experimental investigations, the creep data base has been developed for an RPV-steel and has been validated against creep tests with different scalings and geometries. It can be stated, that the coupled model is able to exactly describe and predict the vessel deformation in the scaled integral FOREVER-tests. There are uncertainties concerning the time to failure which are related to inexactly known material parameters and boundary conditions. The main results of this work can be summarised as follows: Due to the thermody-namic behaviour of the large melt pool with internal heat sources, the upper third of the lower RPV head is exposed to the highest thermo-mechanical loads. This region is called hot focus. Contrary to that, the pole part of the lower head has a higher strength and therefore relocates almost vertically downwards under the combined thermal, weight and internal pressure load of the RPV. On the one hand, it will be possible by external flooding to retain the corium within the RPV even at increased pressures and even in reactors with high power (as e.g. KONVOI). On the other hand, there is no chance for melt retention in the considered scenario if neither internal nor external flooding of the RPV can be achieved. Two patents have been derived from the gained insights. Both are related to passively working devices for accident mitigation: The first one is a support of the RPV lower head pole part. It reduces the maximum mechanical load in the highly stressed area of the hot focus. In this way, it can prevent failure or at least extend the time to failure of the vessel. The second device implements a passive accident mitigation measure by making use of the downward movement of the lower head. Through this, a valve or a flap can be opened to flood the reactor pit with water from a storage reservoir located at a higher position in the reactor building. With regard to future plant designs it can be stated - differing from former presumptions - that an In-Vessel-Retention (IVR) of a molten core is possible within the reactor pressure vessel even for reactors with higher power
Für das unwahrscheinliche Szenario eines Kernschmelzunfalls in einem Leichtwasserreaktor mit Bildung eines Schmelzesees in der Bodenkalotte des Reaktordruckbehälters (RDB) ist es notwendig, mögliche Versagensformen des RDB sowie Versagenszeiträume zu ermitteln, um die daraus resultierende mögliche Belastung des Sicherheitsbehälters bestimmen zu können. In dieser Arbeit wird ein integrales Modell entwickelt, das die Vorgänge im unteren Plenum beschreibt. Dabei sind zwei prinzipielle Modellbereiche zu unterscheiden: Das Temperaturfeld in der Schmelze und im RDB wird mit einem thermodynamischen Modell berechnet, während für die Strukturanalyse des RDB ein mechanisches Modell verwendet wird. Zunächst werden das betrachtete Unfallszenario dargestellt und die bisher in den letzten drei Dekaden weltweit durchgeführten wesentlichen analytischen, experimentellen und numerischen Untersuchungen diskutiert. Anschließend werden die auftretenden physikalischen Vorgänge analysiert. Gleichzeitig werden Skalierungsunterschiede zwischen den in dieser Arbeit betrachteten Experimenten der FOREVER-Reihe und einem prototypischen Szenario herausgearbeitet. Das thermodynamische und das mechanische Modell können rekursiv gekoppelt werden, wodurch die wechselseitige Beeinflussung berücksichtigt werden kann. Insbesondere werden damit neben der Temperaturabhängigkeit der Materialparameter und den thermisch induzierten Spannungen im mechanischen Modell auch die Rückwirkungen der Behälterverformung auf das Temperaturfeld selber erfasst. Für die Kriech- und Schädigungssimulation werden in dieser Arbeit neue Verfahren angewendet. Durch die Entwicklung und den Einsatz einer Kriechdatenbasis konnte die bei sehr unterschiedlichen Temperaturen, Spannungen und Dehnungen ungeeignete Verwendung einzelner Kriechgesetze umgangen werden. Aufbauend auf experimentellen Untersuchungen wurde eine Kriechdatenbasis für einen RDB-Stahl entwickelt und an Hand von Kriechversuchen verschiedener Geometrie und Dimension validiert. Als Ergebnis lässt sich festhalten, dass das gekoppelte Modell prinzipiell in der Lage ist, die Behälterdeformation im Falle der skalierten FOREVER-Experimente exakt zu beschreiben bzw. vorherzusagen. Unsicherheiten bezüglich der Versagenszeit resultieren aus nicht exakt bekannten Materialparametern und Randbedingungen. Die wesentlichen Ergebnisse dieser Arbeit lassen sich wie folgt zusammenfassen: Aufgrund des thermodynamischen Verhaltens eines großen Schmelzesees mit inneren Wärmequellen erfolgt die höchste thermomechanische Belastung des RDB im oberen Drittel der Bodenkalotte. Dieser Bereich wird als heißer Fokus bezeichnet. Der untere Bereich der Kalotte weist hingegen eine höhere Festigkeit auf und verlagert sich deswegen bei entsprechender Belastung des RDB im wesentlichen senkrecht nach unten. Bei einer externen Flutung besteht auch bei hohen Innendrücken für einen Reaktor großer Leistung (KONVOI) die Möglichkeit, die Schmelze im RDB zurückzuhalten. Ohne interne oder externe Flutung besteht für das betrachtete Szenario keine Aussicht für eine Schmelzerückhaltung im RDB. Aus den gewonnenen Erkenntnissen wurden zwei Patente abgeleitet. Dabei handelt es sich um passiv wirkende Einrichtungen zur Schadensbegrenzung: Die erste reduziert durch Abstützen des unteren Kalottenzentrums die Maximalspannungen im hochbeanspruchten Bereich des heißen Fokus und kann damit ein Versagen verhindern oder zumindest verzögern. Die zweite Einrichtung ermöglicht die passive Auslösung einer Flutung, indem die Abwärtsbewegung der Kalotte zur Steuerung genutzt wird. Hierdurch kann beispielsweise ein Ventil geöffnet werden, um Wasser aus im Gebäude höher angeordneten Reservoirs in die Reaktorgrube zu leiten. Abweichend von bisherigen Annahmen kann im Hinblick auf die Entwicklung zukünftiger Baulinien festgehalten werden, dass eine Kernschmelzerückhaltung im Reaktordruckbehälter auch für Reaktoren größerer Leistung möglich ist

Considering the late in-vessel phase of an unlikely core melt down scenario in a light water reactor (LWR) with the formation of a corium pool in the lower head of the reactor pressure vessel (RPV) the possible failure modes of the RPV and the time to failure have to be investigated to assess the possible loadings on the containment. In this work, an integral model was developed to describe the processes in the lower plenum of the RPV. Two principal model domains have to be distinguished: The tem-perature field within the melt and RPV is calculated with a thermodynamic model, while a mechanical model is used for the structural analysis of the vessel wall. In the introducing chapters a description is given of the considered accident scenario and the relevant analytical, experimental, and numerical investigations are discussed which were performed worldwide during the last three decades. Following, the occurring physical phenomena are analysed and the scaling differences are evaluated between the FOREVER-experiments and a prototypical scenario. The thermodynamic and the mechanical model can be coupled recursively to take into account the mutual influence. This approach not only allows to consider the temperature dependence of the material parameters and the thermally induced stress in the mechanical model, it also takes into account the response of the temperature field itself upon the changing vessel geometry. New approaches are applied in this work for the simulation of creep and damage. Using a creep data base, the application of single creep laws could be avoided which is especially advantageous if large temperature, stress, and strain ranges have to be covered. Based on experimental investigations, the creep data base has been developed for an RPV-steel and has been validated against creep tests with different scalings and geometries. It can be stated, that the coupled model is able to exactly describe and predict the vessel deformation in the scaled integral FOREVER-tests. There are uncertainties concerning the time to failure which are related to inexactly known material parameters and boundary conditions. The main results of this work can be summarised as follows: Due to the thermody-namic behaviour of the large melt pool with internal heat sources, the upper third of the lower RPV head is exposed to the highest thermo-mechanical loads. This region is called hot focus. Contrary to that, the pole part of the lower head has a higher strength and therefore relocates almost vertically downwards under the combined thermal, weight and internal pressure load of the RPV. On the one hand, it will be possible by external flooding to retain the corium within the RPV even at increased pressures and even in reactors with high power (as e.g. KONVOI). On the other hand, there is no chance for melt retention in the considered scenario if neither internal nor external flooding of the RPV can be achieved. Two patents have been derived from the gained insights. Both are related to passively working devices for accident mitigation: The first one is a support of the RPV lower head pole part. It reduces the maximum mechanical load in the highly stressed area of the hot focus. In this way, it can prevent failure or at least extend the time to failure of the vessel. The second device implements a passive accident mitigation measure by making use of the downward movement of the lower head. Through this, a valve or a flap can be opened to flood the reactor pit with water from a storage reservoir located at a higher position in the reactor building. With regard to future plant designs it can be stated - differing from former presumptions - that an In-Vessel-Retention (IVR) of a molten core is possible within the reactor pressure vessel even for reactors with higher power.
Für das unwahrscheinliche Szenario eines Kernschmelzunfalls in einem Leichtwasserreaktor mit Bildung eines Schmelzesees in der Bodenkalotte des Reaktordruckbehälters (RDB) ist es notwendig, mögliche Versagensformen des RDB sowie Versagenszeiträume zu ermitteln, um die daraus resultierende mögliche Belastung des Sicherheitsbehälters bestimmen zu können. In dieser Arbeit wird ein integrales Modell entwickelt, das die Vorgänge im unteren Plenum beschreibt. Dabei sind zwei prinzipielle Modellbereiche zu unterscheiden: Das Temperaturfeld in der Schmelze und im RDB wird mit einem thermodynamischen Modell berechnet, während für die Strukturanalyse des RDB ein mechanisches Modell verwendet wird. Zunächst werden das betrachtete Unfallszenario dargestellt und die bisher in den letzten drei Dekaden weltweit durchgeführten wesentlichen analytischen, experimentellen und numerischen Untersuchungen diskutiert. Anschließend werden die auftretenden physikalischen Vorgänge analysiert. Gleichzeitig werden Skalierungsunterschiede zwischen den in dieser Arbeit betrachteten Experimenten der FOREVER-Reihe und einem prototypischen Szenario herausgearbeitet. Das thermodynamische und das mechanische Modell können rekursiv gekoppelt werden, wodurch die wechselseitige Beeinflussung berücksichtigt werden kann. Insbesondere werden damit neben der Temperaturabhängigkeit der Materialparameter und den thermisch induzierten Spannungen im mechanischen Modell auch die Rückwirkungen der Behälterverformung auf das Temperaturfeld selber erfasst. Für die Kriech- und Schädigungssimulation werden in dieser Arbeit neue Verfahren angewendet. Durch die Entwicklung und den Einsatz einer Kriechdatenbasis konnte die bei sehr unterschiedlichen Temperaturen, Spannungen und Dehnungen ungeeignete Verwendung einzelner Kriechgesetze umgangen werden. Aufbauend auf experimentellen Untersuchungen wurde eine Kriechdatenbasis für einen RDB-Stahl entwickelt und an Hand von Kriechversuchen verschiedener Geometrie und Dimension validiert. Als Ergebnis lässt sich festhalten, dass das gekoppelte Modell prinzipiell in der Lage ist, die Behälterdeformation im Falle der skalierten FOREVER-Experimente exakt zu beschreiben bzw. vorherzusagen. Unsicherheiten bezüglich der Versagenszeit resultieren aus nicht exakt bekannten Materialparametern und Randbedingungen. Die wesentlichen Ergebnisse dieser Arbeit lassen sich wie folgt zusammenfassen: Aufgrund des thermodynamischen Verhaltens eines großen Schmelzesees mit inneren Wärmequellen erfolgt die höchste thermomechanische Belastung des RDB im oberen Drittel der Bodenkalotte. Dieser Bereich wird als heißer Fokus bezeichnet. Der untere Bereich der Kalotte weist hingegen eine höhere Festigkeit auf und verlagert sich deswegen bei entsprechender Belastung des RDB im wesentlichen senkrecht nach unten. Bei einer externen Flutung besteht auch bei hohen Innendrücken für einen Reaktor großer Leistung (KONVOI) die Möglichkeit, die Schmelze im RDB zurückzuhalten. Ohne interne oder externe Flutung besteht für das betrachtete Szenario keine Aussicht für eine Schmelzerückhaltung im RDB. Aus den gewonnenen Erkenntnissen wurden zwei Patente abgeleitet. Dabei handelt es sich um passiv wirkende Einrichtungen zur Schadensbegrenzung: Die erste reduziert durch Abstützen des unteren Kalottenzentrums die Maximalspannungen im hochbeanspruchten Bereich des heißen Fokus und kann damit ein Versagen verhindern oder zumindest verzögern. Die zweite Einrichtung ermöglicht die passive Auslösung einer Flutung, indem die Abwärtsbewegung der Kalotte zur Steuerung genutzt wird. Hierdurch kann beispielsweise ein Ventil geöffnet werden, um Wasser aus im Gebäude höher angeordneten Reservoirs in die Reaktorgrube zu leiten. Abweichend von bisherigen Annahmen kann im Hinblick auf die Entwicklung zukünftiger Baulinien festgehalten werden, dass eine Kernschmelzerückhaltung im Reaktordruckbehälter auch für Reaktoren größerer Leistung möglich ist.

L’étude des phénomènes couplés thermo-hydro-mécaniques intéresse la communauté scientifique aujourd'hui confronté au problème du stockage des déchets. La modélisation est un outil essentiel pour prédire l'évolution complexe du milieu hôte et de ces déchets. Parmi les approches numériques existants, on distingue les approches de types éléments finis et les approches de type éléments distincts. Si la première, plus ancienne, a déjà donné lieu à de nombreux développement et applications, elle rend mal quelquefois la réalité du massif rocheux fracturé. Nous avons souhaité cette dernière approche en la rendant capable de modéliser les échanges thermiques convectifs liés à la circulation d'un fluide dans les fissures de roche. Nous suspectons en effet que ce phénomène peut être important si le gradient hydraulique est suffisamment élevé. Une étude bibliographique nous a permis de mettre en évidence les paramètres qui déterminent ce phénomène dont le principal est le coefficient de transfert thermique h entre la roche et le fluide. Les nombreuses formulations recensées ne sont pas totalement suffisantes à expliciter la réalité de ses effets. D’autres mesures, in situ et en laboratoire, s'avèrent nécessaires. Nous avons pu établir des expressions pour les termes d'échange thermique entre le fluide et la roche et à l'intérieur du fluide lui-même. Souhaitant donc modéliser le phénomène à l'aide d'une approche adaptée au milieu discontinu, notre choix s'est porte sur le logiciel UDEC (Universal Distinct Element Code) dont la structure permettait moyennant quelques modifications d'accueillir les développements envisagés. Les algorithmes de calcul sont basés sur les différences de vitesse entre les transferts thermiques convectifs et conductifs. Nous avons testé notre modèle dans le cas de l'écoulement d'un fluide froid entre 2 blocs. Dans le cas d'une modélisation thermohydraulique, les échanges thermiques calculés sont cohérents et s'accordent avec ceux calculés par une autre approche numérique. On observe en effet que la convection thermique croit avec l'ouverture hydraulique de la fracture, la vitesse du fluide et décroit avec sa viscosité. Des calculs thermo-hydromécaniques ont montré la nécessité d'alterner les calculs thermiques et les calculs hydromécaniques suffisamment fréquemment pour rendre compte de la réalité du couplage. Notre modèle a été utilisé à grande échelle et a permis également d'interpréter les anomalies thermiques mesurées sur le site géothermal du Cézallier

Mise en evidence de la possibilite d'etude des variations du parametre d'ordre, en fonction de la pression, de la temperature et du champ electrique, a partir de mesures de birefringence; confirmation de l'ordre de transition de rbh::(2)po::(4) et etude du diagramme de phases 3d de kh::(2)po::(4) au voisinage d'un point tricritique. Etude des proprietes electromecaniques de kh::(2)po::(4) par une nouvelle technique de diffraction simultanee neutron-gamma, dans le but de preciser la relation entre les variations du parametre d'ordre et les anomalies de la dilatation au voisinage de la transition; interpretation qualitative par un modele de type slater

碩士
元智大學
機械工程學系
96
Taiwan is populous in recent years, according to the statistics data of the Ministry Of Interior. Between 1997 and 2006, the population density of Taiwan is 618.7 persons per square kilometer. The security problems in public places are relatively important too. In accordance with the data of Fire Agency, from 1997 to 2006, there are 10% of building fire occurred in public places. Although there is merely 10%, yet the fires in public places are easy to be neglected and difficult to be controlled. If once there is a fire, it will often lead to great casualties and property losses. This thesis utilizes Fire Dynamic Simulator (FDS) field model to simulate the residential fire accident occurred in Wei Er Kang restaurant , and research heat transmission phenomenon、smoke flows、upper layer temperatures and change of CO concentrations. To aim at main influence factor of a fire scene, change all kinds of parameters, and analysis fire field under different conditions, such as main fire source position, fire sizes, sprinkler to be set up and size of opening and position, that effect to a fire scene. The results expect to be a reference for the design of fire fighting engineering.

碩士
元智大學
機械工程學系
98
During the past decades in Taiwan, there were many fire cases occurred in apartment buildings, and most of which were often illegally rebuilt with metal sheet. In recent years, despite the rapid economy development in Taiwan, there still standing a lot of this kind of houses in villages and towns. Due to lack of overall rebuild plan, the inner old electric wire and the improper use of electric devices, plus narrow street sidewalks parked with cars which prevented fire engine from entering, as well as dense population and residential environment, if the fire happened, it could often cause great casualties and property losses. This paper is using an attached townhouse fire in Yangmei township in 2008 for fire study. There are too much combustibles in the fire house, and because all house additions are reconstructed with metal sheets at third floors, the fire spread out rapidly without effective isolation. This study uses Fire Dynamics Simulator (FDS) software to analyze the physical phenomenon of the fire scene and to analyze the heat conduction, smoke flows, upper layer temperature, change of carbon monoxide (CO) concentrations, and by adjusting the parameters of the key factors to analyze the influence of different conditions in fire scene. The simulation result is expected to provide a reference for fire protection engineering of the residential buildings.

There is a growing need to improve the understanding of the behaviour of infrastructure in permafrost regions. Permafrost affects nearly half of the land surface in Canada, especially in the north. Further development of natural resources in northern Canada will provide socio-economic benefits to the region and its residents. Linear infrastructure, such as highways, is an important part of that development. The integrity of infrastructure in northern regions is negatively impacted by thawing and degradation of the underlying permafrost initiated by changes in both air and ground temperatures. Subsequent deformations due to settlement and lateral spreading can lead to potentially hazardous driving on highways. The author’s research focused on a section of highway embankment on Provincial Road (PR) 391 located 18 km north of Thompson, Manitoba. The purpose of the research was to further understanding of the thermal and deformation behaviour of an embankment subjected to degrading permafrost conditions. The author’s research consisted of laboratory testing, instrumentation installation, data monitoring, and numerical modelling. Laboratory tests on four-inch (101.6 mm) diameter Shelby tube samples characterized the soil at the site. Data were collected remotely via satellite, and included ground temperatures, pore water pressures, and displacements both laterally and vertically. Ground temperatures indicated a frost bulb, a region of frozen ground, under the embankment. Thermal models using TEMP/W simulated the current ground thermal regime and projections of future thermal behaviour of the embankment. Deformation numerical models using SIGMA/W incorporated changes in the size of the frost bulb over a freeze-thaw cycle to simulate the deformation behaviour of the embankment. The numerical models were compared with the collected data.

Cheng Bo-ki.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.
Includes bibliographical references (leaves 150-153).
Abstracts in English and Chinese.
Chapter chapter 1 --- Introduction --- p.10
Chapter chapter 2 --- Background & Literature --- p.15
Chapter 2.1 --- Why Environmental Design? --- p.15
Comfort and Energy --- p.15
"Our Problems: Energy, Environment, and Health" --- p.19
Chapter 2.2 --- Knowledge in Environmental Design --- p.27
What is Environmental Design? --- p.27
Current knowledge in Environmental Design: Thermal Performance --- p.30
Thermal Studies in Hong Kong --- p.37
Chapter 2.3 --- Summary and Propositions --- p.42
Chapter chapter 3 --- Scale Model Study --- p.47
Chapter 3.1 --- Test Modules Application --- p.47
Chapter 3.2 --- Research Methodology & Experimental Setup --- p.54
Testing Facility in CUHK --- p.54
Solarimeter Substitute --- p.58
Chapter 3.3 --- Experimental Series --- p.61
Chapter 3.3.1 --- Envelope Colour --- p.61
Chapter 3.3.2 --- Windows --- p.73
Chapter 3.3.3 --- Shading --- p.75
Chapter 3.3.4 --- Thermal Mass --- p.80
Chapter 3.3.5 --- Orientations --- p.83
Chapter 3.3.6 --- "Combined Effects ofThermal Mass, Windows and Orientations" --- p.85
Chapter 3.3.7 --- "Combined Effects ofThermal Mass, Shading and Orientations" --- p.88
Chapter 3.4 --- Summary of Experiments --- p.90
Chapter 3.5 --- Predicting Indoor Air Temperature --- p.93
Chapter 3.5.1 --- Development of Predictive Formulas --- p.93
Chapter 3.5.2 --- Parametric Study of Envelope Colour --- p.97
Chapter 3.5.3 --- Parametric Study of Window Shading --- p.100
Chapter chapter 4 --- Field Study --- p.104
Chapter 4.1 --- Description of Housing Unit: Concord-I Block --- p.104
Chapter 4.2 --- Experimental Setup --- p.105
Chapter 4.3 --- Result of Field Measurement --- p.108
Chapter 4.3.1 --- Perform ance of top-most floor --- p.108
Chapter 4.3.2 --- Performance of Individual Rooms --- p.109
Chapter 4.3.3 --- Effect of Orientation --- p.110
Chapter 4.3.4 --- Indoor Thermal Comfort --- p.113
Chapter 4.4 --- Summary of Field Measurement --- p.116
Chapter chapter 5 --- Thermal Performance Prediction --- p.118
Chapter chapter 6 --- Conclusion --- p.126
Appendix 1 --- p.131
Appendix 2 --- p.133
Appendix 3 --- p.140

The thermal field induced by arc welding has been the subject of numerous experimental, analytical and numerical studies in the past. However, few studies have focused on the effects of the local geometry and pipeline welding procedure on the transient thermal field at or near the vicinity of the weldline. The local geometry and welding procedures are often simplified in computational or analytical studies and normally disregarded in quantitative assessments. The objective of this thesis is to evaluate the significance of these effects in order to understand their possible influence on the weld quality, pipeline integrity and weldability. In this thesis, simplified analytical models are developed, compared against outcomes from previous investigations, and validated with data obtained from a full-scale experimental study completed by the candidate. The conducted research indicates that the effects of the weld preparatory geometry (which is within the industry acceptable variations) and pipeline welding procedures might have a significant impact on the thermal history, specifically at low heat inputs and no preheats, which are characteristic for pipeline girth welding. Therefore, the account of these effects is very important for the adequate evaluation of the weld quality and, potentially, the pipe integrity. The results presented in this thesis can be utilised in the quality control, advanced modelling procedures and other activities directed towards the further improvement of pipeline construction procedures.
Thesis (M.Phil.) -- University of Adelaide, School of Mechanical Engineering, 2015.

Increasing atmospheric CO2 and other greenhouse gasses coupled to the accelerated rate of global warming puts plants and ecosystems under the strain of a rapidly changing abiotic environment. Understanding the impacts of changing global climate is a strong focus of plant science and the establishment of more resilient crop variants is an important goal for breeding programs. Our understanding of plant responses and acclimation to abiotic conditions has improved substantially over the last decades but the combination of a complex abiotic environment and high biological diversity, both on molecular as well as on species level, leaves us still with a lot of uncertainties. The aim of this doctoral thesis was to establish a link between plant thermal responses and the carbon-nitrogen balance of plants. The work in this thesis focused on ecologically significant species of the boreal region: Picea abies, Pinus sylvestris and Betula pendula; and Betula utilis, which is one of the prominent tree species in the high altitudes of the Himalayas. The results presented demonstrate that sub-optimal temperatures combined with other abiotic factors can have additive effects that are not easily deducible from the effect of the two factors separately. Low nitrogen availability enhanced the negative effect of low temperature, while elevated CO2 enhanced plant growth under moderate increases in temperatures but under a more extreme temperature increase it exacerbated the negative effect of heat. I also show evidence that species, despite being grouped into the same functional group or inhabiting the same biome can have different thresholds to temperature and to shifts in the C/N balance of their environment and that these differences can, to some extent, be explained by their differential growth strategies. Furthermore, I demonstrate results supporting the hypothesis that the C-N fluxes between mycorrhizal fungi and tree are strongly dependent on the C and N in the environment, highlighting the significance of the tree-mycorrhiza associations in the C sequestration capacity of the boreal region. In this thesis I also present a generalised empirically based mathematical model that can describe the respiration-temperature response of plant functional types or biomes with high precision, giving a more accurate estimate of NPP when implemented in global climate models, and has the potential to incorporate the thermal acclimation of respiration, further increasing the precision of estimating carbon fluxes under future warming temperatures. My results provide novel insights into the interactive temperature-carbon-nitrogen responses of plants, taking a step towards better understanding the response of plants and forests to future climates.
Ökande atmosfäriskt CO2 och andra växthusgaser kopplade till den accelererande globala uppvärmningen utsätter växter och ekosystem för stressen av en snabbt förändrande abiotisk miljö. Att förstå påverkan av ett globalt klimat i förändring står i fokus inom växtforskning och utvecklandet av mer motståndskraftiga grödor är ett viktigt mål inom programmen för växtförädling. Vår förståelse av växters responser och acklimatisering till abiotiska förhållanden har förbättrats avsevärt under de senaste decennierna, men på grund av kombinationen av en komplex abiotisk miljö och stor biologisk mångfald, både på molekylär nivå såväl som på art-nivå, kvarstår en del frågetecken. Syftet med denna avhandling var att upprätta ett samband mellan växters responser på temperaturförändringar och kol-kvävebalansen hos växter. Arbetet i denna avhandling inriktades på ekologiskt betydande arter i den boreala regionen, Picea abies, Pinus sylvestris and Betula pendula; samt Betula utilis som är en av de framträdande trädarterna på höga höjder i Himalaya. Resultaten som presenteras visar att suboptimala temperaturer i kombination med andra abiotiska faktorer kan ha additiva effekter som inte enkelt kan härledas från effekten av de två faktorerna var för sig. Låg kvävetillgänglighet ökade den negativa effekten av låg temperatur, medan förhöjd CO2-halt förbättrade planttillväxt under måttliga temperaturökningar, men under en mer extrem temperaturökning förvärrades dock den negativa effekten av värme. Jag framför även bevis på att arter, trots att de grupperas i samma funktionella grupp eller finns inom samma biom, kan ha olika tröskelvärden beträffande temperatur och förskjutningar i C/N-balansen i sin miljö och att dessa skillnader, i viss utsträckning, kan förklaras av deras olika tillväxtstrategier. Vidare visar jag resultat som stöder hypotesen att C-N - flöden mellan mykorrhiza och träd är starkt beroende av C och N i miljön. Detta belyser i sin tur betydelsen av samarbetet mellan träd och mykorrhiza gällande kolbindningskapaciteten i den boreala regionen. I denna avhandling presenterar jag även en generaliserad empiriskt baserad matematisk modell som med hög precision kan beskriva respiration-temperatur svar av växtfunktionella typer eller biom, vilken ger en mer exakt uppskattning av NPP i globala klimatmodeller. Mina resultat åstadkommer nya insikter i de interaktiva temperatur-kol-kväve-responserna hos växter, och tar ett steg mot bättre förståelse för växters och skogars reaktion på framtida klimat.

碩士
國立成功大學
材料科學及工程學系碩博士班
101
In this study, a physical model and a mathematical model have been developed to analysis the flow field and thermal field in the funnel-type mold of thin slab continuous casting. In the physical model experiment, a 0.5 scale model is used to analysis the influences of flow field with three types of nozzle. In order to simulate the real situation of thin slab continuous casting, a cooling system is built around the water model to cool down the mold and grow the solidification shell in the water model. By using this cooling system, the change of flow characteristic with solidification shell can be observed. According to the experiment results, there are four swirls in the mold and the positions of the swirls change by using different nozzles. In the cooling experiment, the existence of solidification shell does not affect the formation of swirls in the mold. In the mathematical experiment, the commercial software ProCAST is used to simulate the process of physical model experiment. The simulate results of thermal field and flow field are compared with the results of physical model and then confirm this mathematical model is reliable. Finally, this mathematical model with the actual casting cooling conditions is employed to predict the actual flow field and the solidified layer thickness inside the mold.

Qi, Pengfei = 湍流熱對流中速度場結構函數和流動循環的實驗研究 / 齊鵬飛.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2011.
Includes bibliographical references (p. 65-69).
Abstracts in English and Chinese.
Qi, Pengfei = Tuan liu re dui liu zhong su du chang jie gou han shu he liu dong xun huan de shi yan yan jiu / Qi Pengfei.
Abstract --- p.i
摘要 --- p.ii
Acknowledgements --- p.iii
Contents --- p.iv
List of Figures --- p.vi
List of Tables --- p.X
Chapter Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- What is turbulence? --- p.1
Chapter 1.2 --- Why study turbulence and experimentally? --- p.2
Chapter 1.3 --- Turbulent Rayleigh-Benard convection --- p.4
Chapter 1.4 --- Basic equations and characteristic parameters --- p.S
Chapter 1.4.1 --- Continuity equation --- p.5
Chapter 1.4.2 --- Momentum equation (Navier-Stokes equation) --- p.5
Chapter 1.4.3 --- Energy equation --- p.7
Chapter 1.4.4 --- Averaged equations --- p.9
Chapter 1.4.5 --- Characteristic parameters --- p.10
Chapter 1.5 --- Statistical properties in small-scale turbulence --- p.13
Chapter 1.5.1 --- Phenomenological description and Kolmogorov hypotheses --- p.14
Chapter 1.5.2 --- Local structure of the velocity fluctuations --- p.15
Chapter 1.6 --- Large-scale circulation --- p.17
Chapter 1.7 --- Motivation and Organizations of this thesis --- p.19
Chapter 1.7.1 --- B059 scaling --- p.19
Chapter 1.7.2 --- Large-scale circulation --- p.19
Chapter 1.7.3 --- Organization of the thesis --- p.20
Chapter 1.8 --- Some words to my experiment and further expectation --- p.21
Chapter Chapter 2 --- Experimental apparatus and techniques --- p.27
Chapter 2.1 --- Rectangle cell --- p.27
Chapter 2.2 --- The power supply and cooler --- p.28
Chapter 2.3 --- Thermistor and multimeter --- p.29
Chapter 2.4 --- Particle image velocimetry (PIV) technology --- p.30
Chapter 2.4.1 --- Seeding particles --- p.31
Chapter 2.4.2 --- Light source and light-sheet optics --- p.33
Chapter 2.4.3 --- Imaging system --- p.34
Chapter 2.4.4 --- Control system --- p.34
Chapter 2.4.5 --- Analysis method --- p.35
Chapter Chapter 3 --- Small-scale properties in rectangular cell --- p.37
Chapter 3.1 --- Introduction --- p.37
Chapter 3.2 --- Experimental condition --- p.37
Chapter 3.3 --- Homogeneity --- p.39
Chapter 3.4 --- Isotropy --- p.40
Chapter 3.5 --- Scaling of structure function --- p.42
Chapter Chapter 4 --- Large-scale circulation --- p.51
Chapter 4.1 --- Introduction --- p.51
Chapter 4.2 --- Experimental condition and limitation --- p.54
Chapter 4.3 --- Statistical properties of large-scale circulation period --- p.56
Chapter 4.4 --- Scaling of the Reynolds number --- p.59
Chapter 4.5 --- Oscillation period --- p.60
Chapter Chapter 5 --- Conclusion --- p.63
Chapter 5.1 --- Small-scale properties in rectangular cell --- p.63
Chapter 5.2 --- Large-scale circulation --- p.63
Reference --- p.65

碩士
國立清華大學
物理學系
91
We develop an atmosphere model for neutron stars with strong magnetic fields.　The atmosphere is composed of pure hydrogen.　We assume it is fully ionized and the opacity considered is contributed from　the Thomson scattering and free-free　absorption.　The equation of state has incorporated Coulomb correction.　We have allowed an arbitrary magnetic field direction in our codes for solving the　radiation transfer equation. In this paper,we have performed a computation with a magnetic field of　10^12 G, effective temperature 10^6 K and surface gravity　g*=GM/(R*R)(1-2GM/(Rc^2))=10^13 cm/sec^2. The angle between the magnetic field and the surface normal is 90 degree. The computed emergent spectra exhibit a high degree of polarization, limb darkening, high-energy bumps, and cyclotron lines. In addition, the polarization also depends on the viewing angles. Our current work forms the basis for more comprehensive studies in the future.

Nowadays, simulation tools, like the finite element method, are essential to design and optimise sheet metal forming processes. These tools use constitutive models to describe the thermo-mechanical behaviour of the material and their success is inherently dependent on the quality of the models and, consequently, on its calibration. Recent calibration procedures rely on fullfield measurements, heterogeneous tests, and inverse analysis methods. The combination of these three elements leads to more information extracted from a single mechanical test when compared to classical procedures that use homogeneous tests. This new concept of calibration has the potential to reduce the number of tests required and simplify the process. This thesis contributes to the calibration process of thermo-mechanical constitutive models by proposing new calibration methodologies based on this new concept. An overview of four inverse methods, namely the Finite Element Model Updating (FEMU), the Constitutive Equation Gap Method, the Equilibrium Gap Method and the Virtual Fields Method (VFM) is the starting point for this work. Details on the algorithms and implementation of each method are given, as well as a discussion on strengths and weaknesses. A comparative study in the framework of infinitesimal strains, on linear elasticity and non-linear plasticity, under the same conditions, is presented. This overview shows that FEMU is the most straightforward method to implement. The comparative study also shows that the other three methods outperform it in terms of computational efficiency. The VFM presents a balanced response in terms of accuracy and computational efficiency when compared to the other methods. An additional analysis of the accuracy of VFM and FEMU for plasticity models within finite strains framework is also presented. The results indicate that FEMU is sensitive to the distribution of the strain values present in the database of the test. The strain values with more representation in the database have more impact on the calibration results. In the same conditions, the VFM shows a more robust response when compared to FEMU. Two heterogeneous tests are then evaluated as potential databases to combine with the VFM. The aim is to propose a single test calibration methodology for anisotropic plasticity models. The first test is a biaxial tension test of a cruciform specimen. Three cruciform geometries are analysed as potential candidates to combine with the VFM. The analysis of the geometries shows that the inclusion of geometric perturbations in the specimen creates additional heterogeneity and enhances the information of this test. Accurate results are reached for the calibration of two anisotropic plasticity models. The second heterogeneous test is a uniaxial standard test with an optimized specimen shape. The calibration results show a good description of the material behaviour for the loading direction. However, a test in a single loading direction seems insufficient to accurately calibrate an anisotropic plasticity model. Moreover, the sensitivity of the VFM to the number of virtual fields is revealed in this study. The last part of this work focuses on the calibration of thermo-elastoviscoplasticity models. A heterogeneous thermo-mechanical test performed on a Gleeble machine is proposed to generate the experimental database. The analysis of the test shows a considerable range of temperatures, strain values and strain-rates. A first methodology that combines the FEMU with this heterogeneous test is evaluated using virtual data. A detailed sensitivity analysis of the Johnson-Cook material parameters is performed. The simultaneous calibration of all the parameters in the model is achieved with reasonable success. In a second methodology, the test is coupled with the VFM to calibrate a modified version of the Johnson-Cook model. The experimental database is then generated for a high strength steel. The calibration results show that a reasonable description of the flow stress evolution is attained. Overall, the two methodologies are promising alternatives to classical procedures.
Atualmente, as ferramentas de simulação numérica, como o método dos elementos finitos, são essenciais para projetar e otimizar processos de estampagem de chapas metálicas. Estas ferramentas de simulação utilizam modelos constitutivos para descrever o comportamento termomecânico do material, estando o seu sucesso dependente da qualidade destes modelos e consequentemente da sua calibração. Os processos mais recentes de calibração têm como base medições de campo total, testes heterogéneos e métodos de análise inversa. A combinação destes três elementos permite extrair mais informação de um ensaio mecânico quando comparado com os procedimentos clássicos de calibração que usam testes homogéneos. Deste modo, este novo conceito de calibração tem o potencial de reduzir o número de testes necessários e simplificar o processo. Esta tese pretende assim contribuir para o processo de calibração de modelos termomecânicos propondo novas metodologias baseadas neste novo conceito. O ponto de partida para este trabalho é a revisão geral de quatro métodos inversos, designadamente o método Finite Element Model Updating (FEMU), o Constitutive Equation Gap Method, o Equilibrium Gap Method e o Virtual Fields Method (VFM). Os algoritmos e o processo de implementação de cada método são apresentados detalhadamente nesta revisão, assim como uma discussão dos pontos fortes e fracos de cada método. E também apresentado um estudo comparativo, considerando uma formulação para pequenas deformações, para modelos de elasticidade linear e plasticidade não linear, adotando as mesmas condições para cada método. Esta revisão mostra que o método FEMU é o método de análise inversa mais simples de implementar. O estudo comparativo mostra que os outros três métodos apresentam um desempenho superior em termos de eficiência computacional. Quando comparado com os outros métodos, o VFM apresenta uma resposta equilibrada em termos de precisão dos resultados de calibração e eficiência computacional. No seguimento desta revisão é apresentada uma análise á precisão do VFM e FEMU para modelos de plasticidade considerando uma formulação para grandes deformações. Os resultados obtidos indicam que o método FEMU é sensível à distribuição dos valores de deformação presentes na base de dados do teste heterogéneo, uma vez que os valores de deformação com maior representatividade na base de dados têm um impacto superior nos resultados da calibração. Para as mesmas condições, o VFM apresenta uma resposta mais robusta quando comparado com o FEMU. Dois testes heterogéneos são avaliados como potenciais bases de dados a combinar com o VFM. O objetivo desta avaliação é propor uma metodologia de um só teste para calibração de modelos anisotrópicos de plasticidade. O primeiro teste a ser estudado é um teste de tração biaxial de um provete cruciforme. São analisadas três geometrias para o provete como possíveis candidatas a combinar com o VFM. Esta análise mostra que a inclusão de perturbações geométricas na geometria do provete leva a um aumento da heterogeneidade e informação criada pelo teste. Além disso, os resultados obtidos com o teste biaxial na calibração de dois modelos anisotrópicos de plasticidade são bastante precisos. O segundo teste avaliado consiste num teste de tração uniaxial num provete com geometria otimizada. Os resultados da calibração com este provete mostram uma boa descrição do comportamento do material para a direção de carregamento. No entanto, os resultados indicam que um teste com apenas uma direção de carregamento é insuficiente para uma calibração precisa de um modelo anisotrópico de plasticidade. Além desta análise, este estudo também revela que o VFM é sensível ao número de campos virtuais selecionados. A última parte deste trabalho incide sobre a calibração de modelos de termoelasto-viscoplasticidade. E proposto um teste heterogéneo termomecânico realizado num equipamento de testes Gleeble para criar uma base de dados experimental. A análise deste teste mostra que são atingidas gamas consideráveis de temperatura, deformação e velocidade de deformação. A primeira metodologia proposta combina este teste heterogéneo e o método FEMU, a sua avaliação é efetuada usando uma base de dados virtual. Esta avaliação incluí a análise detalhada da sensibilidade de cada parâmetro do modelo Johnson-Cook. Os resultados mostram que a calibração simultâneo de todos os parâmetros pode ser alcançada com razoável sucesso através desta metodologia. Numa segunda metodologia proposta, o mesmo teste heterogéneo é usado juntamente com o VFM para calibrar uma versão modificada do modelo de Johnson-Cook. A base de dados experimental é gerada para um aço de alta resistência. Os resultados do processo de calibração mostram que é possível obter uma descrição razoável da tensão de escoamento do material. Globalmente, os resultados das duas metodologias mostram que estas são alternativas bastante promissoras aos métodos clássicos de calibração.
De nos jours, les outils de simulation, comme la méthode des éléments finis, sont devenus essentiels pour concevoir et optimiser les procédés de mise en forme des tôles métalliques. Ces outils utilisent des modèles pour décrire le comportement thermo-mécanique du matériau et leur succès dépend de façon intrinèque de la qualité du modèle et, par conséquent, de sa calibration. Les procédures récentes de calibration reposent sur des mesures de champ, des essais hétérogènes et des méthodes d’analyse inverse. La combinaison de ces trois éléments permet d’extraire davantage d’informations d’un essai mécanique par rapport aux procédures classiques, qui utilisent des essais homogènes. Ce nouveau concept de calibration a le potentiel de réduire le nombre d’essais requis et de simplifier l’identification des paramètres. Cette thèse contribue au processus de calibration des modèles de comportement thermo-mécanique en proposant de nouvelles méthodologies de calibration fondées sur ce nouveau concept. Un aperçu de quatre méthodes inverses, à savoir Finite Element Model Updating (FEMU), Constitutive Equation Gap Method, Equilibrium Gap Method et Virtual Fields Method (VFM) est le point de départ de ce travail. Les algorithmes et la mise en œuvre de chaque méthode sont détaillés et une discussion sur les points forts et les points faibles est menée. Une étude comparative dans le cadre des déformations infinitésimales, pour l’élasticité linéaire et la plasticité non linéaire, est présentée. Cet aperçu montre que la méthode FEMU est la plus simple à mettre en œuvre. L’étude comparative montre également que les trois autres méthodes la surpassent quand l’efficacité du calcul est considérée. La méthode VFM présente une réponse équilibrée au regard de la précision et de l’efficacité du calcul par rapport aux autres méthodes. Une analyse supplémentaire sur la précision des méthodes VFM et FEMU pour les modèles de plasticité dans le cadre de transformations finies est également présentée. Les résultats indiquent que la méthode FEMU est sensible à la distribution des valeurs des d´eformations présentes dans la base de données expérimentale. En effet, les valeurs de déformations les plus représentées ont un impact plus important sur les résultats de la calibration. Dans les mêmes conditions, la méthode VFM montre une réponse plus robuste par rapport à FEMU. Deux tests hétérogènes sont ensuite évalués en tant que bases de données potentielles à combiner avec la méthode VFM. L’objectif est de proposer une méthodologie de calibration à partir d’un test mécanique unique pour les modèles de plasticité anisotrope. Le premier essai est un test de traction biaxiale d’un échantillon cruciforme. Trois géométries sont analysées en tant que candidats potentiels à combiner avec la méthode VFM. L’analyse des géométries montre que l’intégration de perturbations géométriques dans l’échantillon crée une hétérogénéité supplémentaire et améliore les informations de ce test. Des résultats précis sont obtenus pour la calibration de deux modèles de plasticité anisotrope. Le second test hétérogène est un test standard de traction uniaxiale avec une forme d’échantillon optimisée. Les résultats de la calibration montrent une bonne description du comportement du matériau dans la direction de la force appliquée. Cependant, un test dans une seule direction de chargement semble insuffisant pour calibrer avec précision un modèle de plasticité anisotrope. De plus, cette étude révèle la sensibilitè de la méthode VFM au nombre de champs virtuels. La dernière partie de ce travail se concentre sur la calibration d’un modele de thermo-élasto-viscoplasticité. Un essai hétérogène en déformations et en température réalisé avec une machine Gleeble est proposé pour générer la base de données expérimentale. L’analyse de l’essai montre une gamme importante de températures, de valeurs de déformation et de vitesse de déformation. Une première méthodologie qui combine la méthode FEMU avec cet essai hétérogèene est évaluée à l’aide de données virtuelles. Une analyse de sensibilité détaillée des paramètres du modèle de Johnson-Cook est effectuée. La calibration simultanée de tous les paramètres du modèlle est réalisée avec un succès raisonnable. Dans une seconde méthodologie, le test est couplé avec la méthode VFM pour calibrer une version modifiée du modèle de Johnson-Cook. La base de données expérimentale est alors obtenue pour un acier à haute résistance. Les résultats de la calibration montrent qu’une description raisonnable de l’évolution de la contrainte d’écoulement est obtenue. Dans l’ensemble, les deux méthodologies sont des alternatives prometteuses aux procédures classiques.
Programa Doutoral em Engenharia Mecânica

The low thermal conductivity of gallium arsenide compared to silicon results in self-heating effects in GaAs MESFETs that limit the electrical performance of such devices for high power applications. To date, analytical thermal models of self heating in GaAs MESFETs are based on the assumption of a uniformly heated channel. This thesis presents a two dimensional analysis of the electrothermal effect of this device based on the two dimensional power density distribution in the channel under various bias conditions. The numerical simulation is performed using the finite difference technique. The results of the simulation of an isothermal MESFET without heat effects is compared with various one dimensional analytical models in the literature. Electro thermal effects into the two-dimensional isothermal MESFET model allowed close examination of the temperature profile within the MESFET. The large gradient in power distribution results in a localized heat source within the channel which increases the overall channel temperature, which shows that the assumption of a uniformly heated channel is erroneous, and may lead to an underestimation of the maximum channel temperature.
Graduation date: 1992

Modeling microbial inactivation has a great influence on the optimization, control and design of food processes. In the area of food safety, modeling is a valuable tool for characterizing survival curves and for supporting food safety decisions. The modeling of microbial behavior is based on the premise that the response of the microbial population to the environment factors is reproducible. And that from the past, it is possible to predict how these microorganisms would respond in other similar environments. Thus, the use of mathematical models has become an attractive and relevant tool in the food industry.

This research provides tools to relate the inactivation of microorganisms of public health importance with processing conditions used in nonisothermal and non-thermal food processing technologies. Current models employ simple approaches that do not capture the realistic behavior of microbial inactivation. This oversight brings a number of fundamental and practical issues, such as excessive or insufficient processing, which can result in quality problems (when foods are over-processed) or safety problems (when foods are under-processed). Given these issues, there is an urgent need to develop reliable models that accurately describe the inactivation of dangerous microbial cells under more realistic processing conditions and that take into account the variability on microbial population, for instance their resistance to lethal agents. To address this urgency, this dissertation focused on mathematical models, combined mathematical tools with microbiological science to develop models that, by resembling realistic and practical processing conditions, can provide a better estimation of the efficacy of food processes. The objective of the approach is to relate the processing conditions to microbial inactivation. The development of the modeling approach went through all the phases of a modeling cycle from planning, data collection, formulation of the model approach according to the data analysis, and validation of the model under different conditions than those that the approach was developed.

A non-linear ordinary differential equation was used to describe the inactivation curves with the hypothesis that the momentary inactivation rate is not constant and depends on the instantaneous processing conditions. The inactivation rate was related to key process parameters to describe the inactivation kinetics under more realistic processing conditions. From the solution of the non-linear ordinary differential equation and the optimization algorithm, safety inferences in the microbial response can be retrieved, such as the critical lethal variable that increases microbial inactivation. For example, for nonisothermal processes such as microwave heating, time-temperature profiles were modeled and incorporated into the inactivation rate equation. The critical temperature required to increase the microbial inactivation was obtained from the optimization analysis. For non-thermal processes, such as cold plasma, the time-varying concentration of reactive gas species was incorporated into the inactivation rate equation. The approach allowed the estimation of the critical gas concentration above which microbial inactivation becomes effective. For Pulsed Electric Fields (PEF), the energy density is the integral parameter that groups the wide range of parameters of the PEF process, such as the electric field strength, the treatment time and the electrical conductivity of the sample. The literature has shown that all of these parameters impact microbial inactivation. It has been hyphothesized that the inactivation rate is a function of the energy density and that above a threshold value significant microbial inactivation begins.

The differential equation was solved numerically using the Runge-Kutta method (ode45 in MATLAB ®). The lsqcurvefit function in MATLAB ® estimated the kinetic parameters. The approach to model microbial inactivation, whether when samples were subjected to nonisothermal or to non-thermal food processes, was validated using data published in the literature and/or in other samples and treatment conditions. The modeling approaches developed by this dissertation are expected to assist the food industry in the development and validation process to achieve the level of microbial reduction required by regulatory agencies. In addition, it is expected to assist the food industry in managing food safety systems through support food safety decision-making, such as the designation of the minimal critical parameter that may increase microbial inactivation. Finally, this dissertation will contribute in depth to the field of food safety and engineering, with the ultimate outcome of having a broad and highly positive impact on human health by ensuring the consumption of safe food products.

In this thesis, we investigate wave propagation and plasma equilibrium in MAGPIE, a helicon based linear plasma device constructed at the Australian National University, to study plasma-material interactions under divertor-relevant plasma conditions. We show that MAGPIE is capable of producing low temperature (1–8 eV) high density hydrogen plasma (2–3×10^19 m-3) with 20 kW of RF power when the confining magnetic field is converging. The original research herein described comprises: (1) Characterization of hydrogen plasma in MAGPIE, (2) Analysis of the RF compensation of double Langmuir probes, (3) Excitation, propagation and damping of helicon waves in uniform and non-uniform magnetic fields and (4) Steady-state force balance and equilibrium profiles in MAGPIE. We develop an analytical model of the physics of floating probes to describe and quantify the RF compensation of the DLP technique. Experimental validation for the model is provided. We show that (1) whenever finite sheath effects are important, overestimation of the ion density is proportional to the level of RF rectification and suggest that (2) electron temperature measurements are weakly affected. We develop a uniform plasma full wave code to describe wave propagation in MAGPIE. We show that under typical MAGPIE operating conditions, the helical antenna is not optimized to couple waves in the plasma; instead, the antenna’s azimuthal current rings excites helicon waves which propagate approximately along the whistler wave ray direction, constructively interfere on-axis and lead to the formation of an axial interference pattern. We show that helicon wave attenuation can be explained entirely through electron-ion and electron-neutral collisions. Results from a two-dimensional full wave code reveal that RF power deposition is axially non-uniform with both edge and on-axis components associated with the TG and helicon wave respectively. Finally, force balance analysis in MAGPIE using a two-fluid “Braginskii” type formalism shows that the electron fluid exists in a state of dynamic (flowing) equilibrium between the electric, pressure and thermal forces. The pressure gradient, driven by the non-uniform RF heating, accelerates the plasma into the target region to velocities close to the ion sound speed. From the measured axial plasma flux we find that the plasma column in MAGPIE can be divided into an ionizing and a recombining region. For the conditions investigated, a large fraction of the plasma created in the ionizing region is lost in the recombining region and only a small fraction reaches the end of the device. The equilibrium plasma density along the length of MAGPIE can be quantitatively explained using a 1D transport calculation which includes volumetric particle sources and magnetic compression. We show that the plasma is transported, by the electron pressure gradient, from under the antenna (0.5×10^19 m-3) into the target region where it reaches maximum density (2-3×10^19 m-3). Using the results herein presented, this thesis explores the relationship between the RF power deposition in MAGPIE, parallel plasma transport and the production of high density plasma in the target region.