Dissertations / Theses on the topic 'Dynamic thermal behavior'

O presente trabalho analisou o ritmo climático da cidade de Descalvado - SP, por meio de dois episódios representativos do fato climático (de inverno e de primavera), bem como o comportamento térmico no interior de duas casas populares ocupadas, situadas na área urbana do município. Utilizou-se estação automática (CR10X - Campbell Scientific Inc.) que possibilitou a aquisição e o armazenamento dos dados meteorológicos, vinculando estes dados climáticos ao sistema de circulação atmosférica secundária. Dentro da abordagem Dinâmica do Clima, utilizou-se os conceitos de tipos de tempo afeito ao comportamento térmico das casas ocupadas. Os limites da zona de conforto propostos por GIVONI (1992) foram utilizados como referencial na análise do comportamento térmico das casas ocupadas. Os resultados demonstraram que as duas residências apresentaram comportamento térmico semelhante durante as possíveis situações de estresse de calor e frio. Conclui-se que, apesar de se tratar, do ponto de vista econômico, de moradias de baixo custo de construção, são casas que apresentaram adequado desempenho térmico.<br>The present work analyze the climatic rhythm Descalvado - SP, by using representative episodes of the climatic (winter and spring), as well as the thermal behavior of two occupied popular houses indoor, located in urban area of municipal district. Automatic station used (CR10X - Campbell Scientific Inc.) made possible acquisition and storage of meteorological data, correlating climatic data to the secondary atmospheric circulation system. Dynamic approach of Climate was used the concepts of Types of Time for obtaining thermal behavior of the occupied houses. Givoni\'s limits of comfort zone (1992) was used a reference in analysis of house\'s thermal performance. Results demonstrated that the two occupied houses presented similar thermal behavior during possible situation of heat and cold stresses. For conclusion, under economical point of view, although treating of low cost construction homes, they are houses that presented appropriate thermal performance.

L’objectif de ce travail de recherche est de concevoir un amplificateur de puissance sur la base de considérations électrothermiques. Il décrit la question du dynamique EVM et du « paquet long » lors de la conception de l’amplificateur avec des transistors bipolaires à hétérojonctions. Basé sur le comportement électrothermique du circuit, une méthode d’optimisation de l’EVM statique et dynamique est proposée. Un frontend RF complet (amplificateur de puissance + coupleur + interrupteur + amplificateur faible bruit) est conçu pour le dernier standard WLAN : le Wi-Fi 6. La distribution de temperature dynamique dans le circuit est analysée. Son effet sur les performances de la puce est quantifié. Enfin, une polarisation adaptative programmable a été conçue pour garder des performances optimales sur toute la plage de température. Les mesures du circuit montre tout l’effet bénéfique de cette compensation, permettant de garder le dynamique EVM en dessous de -47 dB sur la plage de température ambiante de -40 à 85°C<br>The aim of this work is to design a power amplifier based on electrothermal considerations. It describes the Dynamic Error Vector Magnitude challenge and long packet issue when designing a power amplifier with hetero-junction bipolar transistors. Based on the circuit electrothermal behavior, an optimization method of both the static and dynamic linearity is proposed. A complete RF front-end (PA + coupler + switch + LNA) is designed for the latest WLAN standard: the Wi-Fi 6. The dynamic temperature distribution in the circuit is analyzed. It’s impact on the performances is quantified. Finally, a programmable temperature dependent bias is designed to compensate for performance degradation. The measurements show a significant linearity improvement with this compensation, allowing the PA to maintain the DEVM lower than -47dB at 14.5 dBm output power, over a large ambient temperature range from -40°C to 85°C

Comportement dynamique des batiments. La forme modale et les techniques de reduction du modele. Transformation de cette forme lorsque le modele du batiment est simplifie, en une expression analytique simple; cette propriete est utilisee pour rechercher une correlation entre un nombre restreint de parametres descriptifs d'un batiment dont un parametre continu d'inertie et ses besoins de chauffage

La performance énergétique des bâtiments peut être estimée grâce à la réalisation de simulations de thermique dynamique qui prennent en compte différentes hypothèses conventionnelles telles que celles définies dans la réglementation thermique 2012 (météo, occupation, consignes de température, usages de la fenêtre et du volet par les occupants, etc.). Les retours d’expériences dans les bâtiments énergétiquement performants mettent en évidence des écarts importants de consommations énergétiques entre les prévisions et les mesures in situ ainsi que des surchauffes estivales. D’après la communauté scientifique, même s’il existe de multiples facteurs pouvant expliquer ces écarts, l’occupant semble être l’élément le plus impactant. En effet, son action sur la fenêtre et le volet modifie le renouvellement d’air et la gestion des apports solaires. L’usage mais aussi la typologie de la fenêtre et du volet affectent donc les consommations énergétiques et le confort. L’objectif de notre étude est l’analyse de l’évolution thermique d’appartements occupés afin d'établir un modèle comportemental de l’occupant réel permettant de quantifier l’impact des modifications architecturales sur le confort thermique et les performances énergétiques des bâtiments. L’objet d’étude est un ensemble de deux résidences situées sur la commune de Vauvert (Gard, France) construites en 1969. De caractéristiques constructives identiques et suite à des rénovations similaires (V.M.C., chaudières, fenêtres), l’une d’entre elles a été récemment isolée thermiquement par l’extérieur. Une analyse sur une année des conditions thermiques réelles, du comportement individuel de l’occupant et des consommations d’énergie est menée sur la base d’enquêtes et par une instrumentation in situ dans les séjours de 13 appartements occupés. Elle nous permet de définir un modèle comportemental de l’occupant soit 32 combinaisons d’usage de la fenêtre et du volet qui peuvent être regroupées selon trois profils d’occupants (l’occupant « expert », l’occupant « actif » et l’occupant « contre-productif »). La modélisation fine des paramètres nécessaires pour les simulations de thermique dynamique réalisées avec Pléiades+COMFIE, aide à la compréhension de l’impact des stratégies architecturales sur le confort et les consommations énergétiques des bâtiments en milieu méditerranéen. L’analyse thermique des deux résidences (isolée et non isolée) montre, en hiver, des niveaux similaires de consommation pour un confort réduit dans la résidence non isolée. Cependant, en été, lors de pics de température, des surchauffes apparaissent dans la résidence isolée. Le comportement de l’individu a ainsi un rôle essentiel dans la limitation de l’inconfort d’été. Les analyses des mesures in situ montrent que des stratégies permettant le rafraîchissement des appartements ne sont pas toujours mises en place par les occupants. Des solutions architecturales atténuant le comportement contre-productif de l’individu sont finalement évaluées<br>The current design of energy-efficient buildings used to be performed by dynamic thermal simulations using conventional hypotheses like those of the 2012 French thermal regulations (weather reports, occupancy, temperature set, operations of windows and shutters by occupants, etc...). However, feedback highlights a great difference in energy consumption between forecasts on the one hand and in situ measurements in winter as well as overheating in summer on the other hand. According to the scientific community, even if many factors can account for this gap, the inhabitants seem to play a major role in it as well. Indeed, by acting on their windows and shutters, they modify the renewal rate of fresh air and the management of solar contributions. As the matter of fact, the use and the type of windows and shutters affect the energy consumptions and the comfort. The aim of this study is to analyse the thermal evolution of occupied apartments in order to establish a behavioral model of the occupants. This will allow us to quantify the impact of architectural modifications on the thermal comfort and the energy performances of buildings.Two residential buildings are investigated in Vauvert (a city in southern of France). Both of them were built in 1969 using the same constructive techniques and have lately been renovated in a similar way (CMV, boilers, windows). The only difference is that on the facade of one of them an external thermal insulation has recently been installed. The analysis of the real thermal conditions, of the actual human behavior and of the amount of energy consumed is built on surveys and on an extensive year-round in situ instrumentation in the living rooms of 13 apartments. It allows us to define a behavioral model of occupants based on 32 different combinations in the operations of windows and shutters. We can divide them into three occupants' profiles (the “expert” occupant, the “active” occupant and the “counterproductive” occupant). Digital Pléiades+COMFIE simulations are made in order to validate this model. The refined modeling of the dynamic thermal simulation parameters helps to understand the impact on the thermal comfort and the energy consumption of different architectural strategies in the Mediterranean area.In winter the thermal analysis of the two residential buildings (insulated and non insulated) shows similar levels of consumption, but a lower level of thermal comfort in the non insulated case. However during temperature peaks in summer, overheating appears in the insulated dwellings, but human behavior is the key to limit occupants’ discomfort. The analysis of in situ measurements shows that strategies to cool down the apartments are not always implemented by occupants. Architectural solutions mitigating “counterproductive” occupants’ behavior are finally examined

[EN] The test for determining the resonance frequencies has traditionally been used to investigate the mechanical integrity of concrete cores, to assess the conformity of concrete constituents in different accelerated durability tests, and to ascertain constitutive properties such as the elastic modulus and the damping factor. This nondestructive technique has been quite appealed for evaluation of mechanical properties in all kinds of durability tests. The damage evolution is commonly assessed from the reduction of dynamic modulus which is produced as a result of any cracking process. However, the mechanical behavior of concrete is intrinsically nonlinear and hysteretic. As a result of a hysteretic stress-strain behavior, the elastic modulus is a function of the strain. In dynamic tests, the nonlinearity of the material is manifested by a decrease of the resonance frequencies, which is inversely proportional to the excitation amplitude. This phenomenon is commonly referred as fast dynamic effect. Once the dynamic excitation ceases, the material undergoes a relaxation process whereby the elastic modulus is restored to that at rest. This phenomenon is termed as slow dynamics. These phenomena (fast and slow dynamics) find their origin in the internal friction of the material. Therefore, in cement-based materials, the presence of microcracks and interfaces between its constituents plays an important role in the material nonlinearity. In the context of the assessment of concrete durability, the damage evolution is based on the increase of hysteresis, as a result of any cracking process. In this thesis three different nondestructive techniques are investigated, which use impacts for exciting the resonant frequencies. The first technique consists in determining the resonance frequencies over a range of impact forces. The technique is termed Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). It consists in ascertaining the downward resonant frequency shift that the material undergoes upon increasing excitation amplitude. The second technique consists in investigating the nonlinear behavior by analyzing the signal corresponding to a single impact. This is, to determine the instantaneous frequency, amplitude and attenuation variations corresponding to a single impact event. This technique is termed as Nonlinear Resonant Acoustic Single Impact Spectroscopy (NSIRAS). Two techniques are proposed to extract the nonlinear behavior by analyzing the instantaneous frequency variations and attenuation over the signal ring down. The first technique consists in discretizing the frequency variation with time through a Short-Time Fourier Transform (STFT) based analysis. The second technique consists of a least-squares fit of the vibration signals to a model that considers the frequency and attenuation variations over time. The third technique used in this thesis can be used for on-site evaluation of structures. The technique is based on the Dynamic Acousto- Elastic Test (DAET). The variations of elastic modulus as derived through NIRAS and NSIRAS techniques provide an average behavior and do not allow derivation of the elastic modulus variations over one vibration cycle. Currently, DAET technique is the only one capable to investigate the entire range of nonlinear phenomena in the material. Moreover, unlike other DAET approaches, this study uses a continuous wave source as probe. The use of a continuous wave allows investigation of the relative variations of the elastic modulus, as produced by an impact. Moreover, the experimental configuration allows one-sided inspection.<br>[ES] El ensayo de determinación de las frecuencias de resonancia ha sido tradicionalmente empleado para determinar la integridad mecánica de testigos de hormigón, en la evaluación de la conformidad de mezclas de hormigón en diversos ensayos de durabilidad, y en la terminación de propiedades constitutivas como son el módulo elástico y el factor de amortiguamiento. Esta técnica no destructiva ha sido ampliamente apelada para la evaluación de las propiedades mecánicas en todo tipo de ensayos de durabilidad. La evolución del daño es comúnmente evaluada a partir de la reducción del módulo dinámico, producido como resultado de cualquier proceso de fisuración. Sin embargo, el comportamiento mecánico del hormigón es intrínsecamente no lineal y presenta histéresis. Como resultado de un comportamiento tensión-deformación con histéresis, el módulo elástico depende de la deformación. En ensayos dinámicos, la no linealidad del material se manifiesta por una disminución de las frecuencias de resonancia, la cual es inversamente proporcional a la amplitud de excitación. Este fenómeno es normalmente denominado como dinámica rápida. Una vez la excitación cesa, el material experimenta un proceso de relajación por el cual, el módulo elástico es restaurado a aquel en situación de reposo. Este fenómeno es denominado como dinámica lenta. Estos fenómenos ¿dinámicas rápida y lenta¿ encuentran su origen en la fricción interna del material. Por tanto, en materiales basados en cemento, la presencia de microfisuras y las interfaces entre sus constituyentes juegan un rol importante en la no linealidad mecánica del material. En el contexto de evaluación de la durabilidad del hormigón, la evolución del daño está basada en el incremento de histéresis, como resultado de cualquier proceso de fisuración. En esta tesis se investigan tres técnicas diferentes las cuales utilizan el impacto como medio de excitación de las frecuencias de resonancia. La primera técnica consiste en determinar las frecuencias de resonancia a diferentes energías de impacto. La técnica es denominada en inglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Ésta consiste en relacionar el detrimento que el material experimenta en sus frecuencias de resonancia, con el aumento de la amplitud de la excitación. La segunda técnica consiste en investigar el comportamiento no lineal mediante el análisis de la señal correspondiente a un solo impacto. Ésta consiste en determinar las propiedades instantáneas de frecuencia, atenuación y amplitud. Esta técnica se denomina, en inglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Se proponen dos técnicas de extracción del comportamiento no lineal mediante el análisis de las variaciones instantáneas de frecuencia y atenuación. La primera técnica consiste en la discretización de la variación de la frecuencia con el tiempo, mediante un análisis basado en Short-Time Fourier Transform (STFT). La segunda técnica consiste en un ajuste por mínimos cuadrados de las señales de vibración a un modelo que considera las variaciones de frecuencia y atenuación con el tiempo. La tercera técnica empleada en esta tesis puede ser empleada para la evaluación de estructuras in situ. La técnica se trata de un ensayo acusto-elástico en régimen dinámico. En inglés Dynamic Acousto-Elastic Test (DAET). Las variaciones del módulo elástico obtenidas mediante los métodos NIRAS y NSIRAS proporcionan un comportamiento promedio y no permiten derivar las variaciones del módulo elástico en un solo ciclo de vibración. Actualmente, la técnica DAET es la única que permite investigar todo el rango de fenómenos no lineales en el material. Por otra parte, a diferencia de otras técnicas DAET, en este estudio se emplea como contraste una onda continua. El uso de una onda continua permite investigar las variaciones relativas del módulo elástico, para una señal transito<br>[CAT] L'assaig de determinació de les freqüències de ressonància ha sigut tradicionalment empleat per a determinar la integritat mecànica de testimonis de formigó, en l'avaluació de la conformitat de mescles de formigó en diversos assajos de durabilitat, i en la terminació de propietats constitutives com són el mòdul elàstic i el factor d'amortiment. Esta tècnica no destructiva ha sigut àmpliament apel·lada per a l'avaluació de les propietats mecàniques en tot tipus d'assajos de durabilitat. L'evolució del dany és comunament avaluada a partir de la reducció del mòdul dinàmic, produït com resultat de qualsevol procés de fisuración. No obstant això, el comportament mecànic del formigó és intrínsecament no lineal i presenta histèresi. Com resultat d'un comportament tensió-deformació amb histèresi, el mòdul elàstic depén de la deformació. En assajos dinàmics, la no linealitat del material es manifesta per una disminució de les freqüències de ressonància, la qual és inversament proporcional a l'amplitud d'excitació. Este fenomen és normalment denominat com a dinàmica ràpida. Una vegada l'excitació cessa, el material experimenta un procés de relaxació pel qual, el mòdul elàstic és restaurat a aquell en situació de repòs. Este fenomen és denominat com a dinàmica lenta. Estos fenòmens --dinámicas ràpida i lenta troben el seu origen en la fricció interna del material. Per tant, en materials basats en ciment, la presència de microfissures i les interfícies entre els seus constituents juguen un rol important en la no linealitat mecànica del material. En el context d'avaluació de la durabilitat del formigó, l'evolució del dany està basada en l'increment d'histèresi, com resultat de qualsevol procés de fisuración. En esta tesi s'investiguen tres tècniques diferents les quals utilitzen l'impacte com a mitjà d'excitació de les freqüències de ressonància. La primera tècnica consistix a determinar les freqüències de ressonància a diferents energies d'impacte. La tècnica és denominada en anglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Esta consistix a relacionar el detriment que el material experimenta en les seues freqüències de ressonància, amb l'augment de l'amplitud de l'excitació. La segona tècnica consistix a investigar el comportament no lineal per mitjà de l'anàlisi del senyal corresponent a un sol impacte. Esta consistix a determinar les propietats instantànies de freqüència, atenuació i amplitud. Esta tècnica es denomina, en anglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Es proposen dos tècniques d'extracció del comportament no lineal per mitjà de l'anàlisi de les variacions instantànies de freqüència i atenuació. La primera tècnica consistix en la discretización de la variació de la freqüència amb el temps, per mitjà d'una anàlisi basat en Short-Time Fourier Transform (STFT). La segona tècnica consistix en un ajust per mínims quadrats dels senyals de vibració a un model que considera les variacions de freqüència i atenuació amb el temps. La tercera tècnica empleada en esta tesi pot ser empleada per a l'avaluació d'estructures in situ. La tècnica es tracta d'un assaig acusto-elástico en règim dinàmic. En anglés Dynamic Acousto-Elastic Test (DAET). Les variacions del mòdul elàstic obtingudes per mitjà dels mètodes NIRAS i NSIRAS proporcionen un comportament mitjà i no permeten derivar les variacions del mòdul elàstic en un sol cicle de vibració. Actualment, la tècnica DAET és l'única que permet investigar tot el rang de fenòmens no lineals en el material. D'altra banda, a diferència d'altres tècniques DAET, en este estudi s'empra com contrast una ona contínua. L'ús d'una ona contínua permet investigar les variacions relatives del mòdul elàstic, per a un senyal transitori. A més, permet la inspecció d'elements per mitjà de l'accés per una sola cara.<br>Eiras Fernández, JN. (2016). Studies on nonlinear mechanical wave behavior to characterize cement based materials and its durability [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/71439<br>TESIS<br>Premiado

Sigma 3 grain boundaries play a large role in the microstructure of fcc materials in general, and particularly so in grain boundary engineered materials. A recent survey of grain boundary properties revealed that many of these grain boundaries possess very large mobilities, and that these mobilities increase at lower temperature, contrary to typical models of thermallyactivated grain boundary motion. Such boundaries would have a tremendous mobility advantage over other boundaries at low temperature, which may explain some observed instances of abnormal grain growth at low temperature. This work explains the boundary structure and motion mechanism that allows for such mobilities, and explores several of the unique factors that must be considered when simulating the motion of these boundaries. The mobilities of a number of boundaries, both thermally-activated and antithermal, were then calculated over a wide temperature range, and several trends were identified that relate boundary crystallography to thermal behavior and mobility. An explanation of the difference in thermal behavior observed in sigma 3 boundaries is proposed based on differences in their dislocation structure.

The aim of the research project is to evaluate the suitability of novel materials and structures, such as functionally graded cellular lattices and nanocomposite materials with carbon nanotube inclusions, to be adopted as potential fillers in aero-engine and general aero-structural designs for optimum light-weight performance and augmented energy dissipation. Potential benefits of tailoring the geometry of cellular cores employed in sandwich-like structures in order to achieve a desired thermo-mechanical performance have stimulated a wealth of research studies in the context of functional gradation applied to lattice materials. On such basis, the present dissertation investigates the mechanical properties and equivalent thermal conductivities of iso-volume periodic honeycomb concepts with 3- and 4-connectivities along the in-plane and out-of-plane principal directions. A centre-symmetric 3-connected hexagonal topology and a centre symmetric 4-connected cross-chiral topology are considered in the investigation, the latter conducted adopting both analytical techniques and finite element procedures. Results highlight how variations in cell topology, size and cell-wall thickness allow for a tailoring of the mechanical properties and relative density along the cellular tessellation, suggesting how dropping the assumption of periodicity of a cellular lattice in favour of a graded configuration might be a feasible design solution for achieving a desired mechanical/thermal response ill structural sandwich panels or core fillers. As case study, a band-graded cellular structure based on the family of hexagonal re-entrant topologies is investigated as potential core filler in an aerofoil model, resulting into a light-weight solution which optimizes the material layout within the fixed space of the aerofoil cross-section. In the second part of' the dissertation, an investigation of the nature of frictional damping in CNT-based polymer composites is presented, highlighting how dispersions of carbon nanotubes in a polymeric matrix could lead to consistent increases in energy dissipation under cyclic loading. Attention is focused on the relation between damping augmentation and design parameters, such as volume fractions of the constituents, nanotube aspect ratios alld particularly the interface shear strength governing the quality of stress transfer between carbon nanotubes and surrounding matrix.

Interest in the use of heat pipe technology for heat recovery and energy saving in a vast range of engineering applications has been on the rise in recent years. Heat pipes are playing a more important role in many industrial applications, especially in increasing energy savings in commercial applications and improving the thermal performance of heat exchangers. Computational techniques play an important role in solving complex flow problems for a large number of engineering applications due to their universality, flexibility, accuracy and efficiency. However, up to now, computational studies on heat pipes are still at an early stage due to the complexity of multiphase flow characteristics and heat and mass transfer phase changes. Therefore, the main objective of this study is to develop a CFD modelling that includes the complex physical phenomena of both the heat transfer processes of evaporation and condensation and the mass transfer process of phase change during the pool boiling and film condensation. In this thesis, two novel numerical models were developed in ANSYS FLUENT. In the first, a two-dimensional CFD model was developed to visualise the two-phase flow and the evaporation, condensation and heat transfer phenomena during the operation of a wickless heat pipe, that otherwise could not be visualised by empirical or experimental work. An in-house code was developed using user-defined functions (UDFs) to enhance the ability of FLUENT to simulate the phase change occurring inside the heat pipe. Three different fluids, water, R134a and R404a, were selected as the working fluids of the investigated wickless heat pipe. The cooling system of the condenser section was simulated separately as a three-dimensional CFD model of a parallel-flow double pipe heat exchanger to model the heat transfer across the condenser section's heat exchanger and predict the heat transfer coefficients. The overall effective thermal resistance along with the temperature profile along the wickless heat pipe have been investigated. An experimental apparatus was built to carry out a thermal performance investigation on a typical wickless heat pipe for the purpose of validating the CFD simulation. A theoretical model based on empirical correlations was developed to predict the heat transfer thermal resistances in the evaporator and the condenser section. The second model was developed to combine the two-dimensional CFD simulation of the wickless heat pipe and the three-dimensional CFD simulation of the condenser section's heat exchanger to simulate the two-phase flow phenomena of boiling and condensation and the cooling system of the condenser section through a comprehensive three-dimensional CFD model of a wickless heat pipe. Two fluids, water and R134a, were selected as the working fluids of the investigated wickless heat pipe. This model was validated using a transparent glass wickless heat pipe to visualise the phenomena of pool boiling and comparing the results with the three-dimensional CFD flow visualisation. This study demonstrated that the proposed CFD models of a wickless heat pipe can successfully reproduce the complex physical phenomena of both the heat transfer process of evaporation and condensation and the mass transfer process of phase change during the pool boiling that takes place in the evaporator section and the filmwise condensation that takes place in the condenser section. The CFD simulation was successful in modelling and visualising the multiphase flow characteristics for water, R134a and R404a, emphasising the difference in pool boiling behaviour between these working fluids. The CFD simulation results were compared with experimental measurements, with good agreement obtained between predicted temperature profiles and experimental temperature data.

The majority of structural studies on DNA have been carried out using fibre diffraction, while studies of its dynamics and thermal behaviour have been mainly performed in solution. When the DNA double helix is heated, it exhibits local separation of the two strands that grow in size with temperature and lead to their complete separation. This work has investigated various aspects of this phenomenon. The experiments reported in this thesis were carried out on films of oriented fibres of DNA prepared with the Wet Spinning Apparatus. Thus, sample preparation and characterisation are essential parts of the research. The structures of two forms of DNA, A and B, have been explored as a function of relative humidity at fixed ionic conditions. A method to eliminate traces of ever-present B-form contamination in A-form samples was established. The high orientation of the DNA molecules within the samples allowed us to investigate dynamical fluctuations and the melting transition of DNA using neutron scattering, which can provide the spatial information crucial to understand a phase transition, probing the static correlation length along the molecule as a function of temperature. The transition has been investigated for A and B-forms in order to understand its dependence on molecular configuration.Furthermore, after the first melting, denatured DNA films show typical glass behaviour. Their thermal relaxation has been explored using calorimetry.Neutron and X-ray inelastic scattering (INS and IXS) were used in the past to measure longitudinal phonons in fibre DNA, and the results shown disagreement. Recent INS measurements supported with phonon simulations have been crucial to understand the different dispersion curves reported to date. Experiments using INS and IXS have been carried out to continue with this investigation. Attempts to observe the transverse fluctuations associated to the thermal denaturing of DNA, never experimentally investigated before, have been made.

Un estudio numérico del comportamiento térmico y fluido-dinámico de flujos bifásicos, liquido-gas, en conductos es presentado. El análisis numérico es basado en dos diferentes modelos. El primer modelo es conocido como quasi-homogéneo, este modelo asume el flujo bifásico como una mezcla homogénea, que esta caracterizada por un flujo másico, una presión y una temperatura de mezcla. Estas tres variables son encontradas por medio de la resolución numérica de las ecuaciones de conservación de masa, momento y energía. Las velocidades de las fases gas y liquida pueden ser evaluadas a partir del flujo másico total de mezcla y de la distribución de una de las fases en el volumen, la cual es determinada mediante expresiones empíricas. Aunque el modelo quasi-homogéneo es capaz de dar buenos resultados en diferentes aplicaciones donde el flujo bifásico esta presente, este modelo no puede dar información de cada una de las fases independientemente. Sí el modelo quasi-homogéneo es aplicado considerando las restricciones con algunos configuraciones de flujo y el hecho de no incluir los términos de intercambio a través de la interfase, este modelo es capaz de convertirse en una buena herramienta de estimación del comportamiento térmico y fluido-dinámico en diferentes sistemas térmicos, donde el flujo bifásico esta presente. El segundo modelo es conocido como dos-fluidos, este modelo permite considerar que el liquido y el gas coexisten en un mismo volumen de control y que cada una de las fases esta caracterizada por tener una velocidad y una temperatura diferente. Este modelo tiene en cuenta las interacciones entre cada una de las fases y la interfase, así es capaz de reconocer la influencia de los intercambios de masa, momento y energía a través de la interfase. El modelo de dos-fluidos necesita más información empírica que el modelo quasi-homogéneo para cerrar y resolver el sistema de ecuaciones que lo caracteriza. <br/><br/>La simulación numérica ha sido desarrollada por medio de la técnica de los volúmenes finitos basada en una integración transitoria, unidimensional o bidimensional de las ecuaciones de continuidad de masa, momento lineal y energía. La presión, las velocidades, las temperaturas y la distribución de cada una da las fases al interior del conducto son obtenidas por medio de la resolución de las ecuaciones gobernantes.<br/><br/>Un método semi-implícito basado en el conocido método de corrección de presiones para resolver fluidos en una fase SIMPLE, ha sido empleado para resolver el acoplamiento entre la presión y la velocidad. Los algoritmos de resolución para cada uno de los modelos desarrollados en esta Tesis son detallados.<br/><br/>La verificación y validación de los modelos presentados en este trabajo se han realizado contra expresiones analíticas y datos experimentales obtenidos desde la literatura técnica o mediante la infraestructura experimental del CTTC. Una comparativa de resultados entre el modelo quasi-homogéneo y el modelo de dos-fluidos para un caso unidimensional es presentado. Además, dos casos reportados en la literatura han sido usados para comparar los resultados del modelo de dos-fluidos en dos dimensiones.<br/><br/><br/>Aplicaciones de los modelos desarrollados en esta Tesis son presentados con el propósito de mostrar las posibilidades ofrecidas por ellos para mejorar el diseño de diferentes equipos térmicos y evitar condiciones de trabajo no deseadas. Un intercambiador de calor del tipo de doble tubo es analizado, observando la influencia de diferentes parámetros sobre el comportamiento térmico y fluido-dinámico. La resolución numérica de un intercambiador del tipo aleta y tubo trabajando como un evaporador o un condensador ha sido comparado con datos experimentales, llegando a obtener un buen ajuste entre ellos. Finalmente, las condiciones de trabajo de un panel solar son optimizadas mediante la simulación numérica, con el objetivo de evitar alcanzar condiciones peligrosas que produzcan daños severos a la instalación.

Lors de la certification des moteurs d’avion, certains composants sont testés vis-à-vis de phénomènes balistiques. La soufflante doit ainsi résister à l’ingestion d’oiseaux et à la perte d’aubes sans compromettre les performances globales du réacteur. Les aubes de soufflante, et particulièrement leur bord d’attaque, subissent des déformations élevées à grande vitesse, des chargements non proportionnels et un auto-échauffement induit parla dissipation plastique. Compte tenu de leurs bonnes propriétés mécaniques spécifiques,les alliages de titane Ti-6Al-4V sont considérés comme des candidats prometteurs pour le bord d’attaque d’aubes de soufflante multi-composants. Dans ce travail, une campagne expérimentale a été menée sur un alliage de Ti-6Al-4V laminé comprenant des essais de traction, compression et cisaillement à plusieurs températures et vitesses de déformation(lentes et rapides), sous des trajets de chargements monotones et alternés. A partir des résultats obtenus, un modèle constitutif a été développé rendant compte des effets combinés de l’orthotropie, de l’asymétrie traction-compression, des écrouissages cinématique et isotrope non linéaires, de la vitesse et de l’adoucissement thermique. Les constantes ont été identifiées au moyen du logiciel Zset. Le modèle a ensuite été implémenté entant que procédure matériau utilisateur (Fortran) dans le code de calculs commercial par élément finis LS-DYNA. Les performances du modèle numérique ont alors été évaluées en menant des simulations numériques sur un élément de volume soumis à différents trajets de chargement ainsi que sur des éprouvettes utilisées pour la campagne expérimentale<br>During the aircraft engine certification, various components are tested against ballisticphenomena. The engine fan must accordingly resist bird strike and blade loss withoutcompromising the whole engine thrust performance. Fan blades, and particularly theirleading edge, undergo large deformation under high strain rate, non-proportional loadingpaths and plastic dissipation induced self-heating. Due to their high specific mechanicalproperties, Ti-6Al-4V titanium alloys are promising candidates for fan multi-componentblade leading edge. In this work, an experimental campaign has been carried out on acold rolled Ti-6Al-4V alloy comprising tension, compression and shear tests performed atvarious temperatures and (low and high) strain rates, under monotonic and alternatedloading paths. Based on these results, a constitutive model has been developed accountingfor the combined effects of orthotropy, strength differential, nonlinear kinematic andisotropic hardenings, strain rate hardening as well as thermal softening. Material constantshave been identified using Zset software. The model has been implemented asuser material (Fortran) subroutine into the commercial finite element computation codeLS-DYNA. The performances of the numerical model have then been estimated by conductingnumerical simulations considering a volume element under various loading pathsas well as the specimens used for the experimental campaign

Les structures en béton armé s'endommagent au cours de leur vie à cause de plusieurs facteurs : conditions thermiques, attaques chimiques, retrait, fluage, carbonatation, corrosion, etc. Ce processus d'endommagement débute dès les premiers jours de la vie de l'ouvrage et continue lors de son vieillissement. L'endommagement au jeune âge peut influencer significativement le comportement dynamique des structures en béton armé. En effet, la fréquence propre d'une structure, qui constitue un paramètre de dimensionnement, peut être fortement réduite à cause de cet endommagement. Afin de déterminer l'influence de l'endommagement dû aux effets du jeûne âge (0 à 28 jours) sur la réponse sismique d'une structure en béton armé, ce travail de thèse a combiné à la fois modélisations numériques et essais pseudo-dynamiques sur deux groupes de portiques en béton armé. Le premier groupe a été gardé en conditions endogènes (échanges hydriques avec l'extérieur empêchés) durant le jeune âge afin de limiter les effets du retrait de séchage (fissuration). Le second groupe a quant à lui été gardé en conditions non-endogènes (échange d'eau avec le milieu extérieur possible) similaires aux conditions de chantier, ce qui a induit un endommagement initial (fissurations) dû notamment à un retrait de séchage plus important. Les deux types de portiques ont été soumis à la fin de leur jeune âge au même chargement sismique au moyen d'essais pseudo-dynamiques. D'une part, ce manuscrit présente les résultats expérimentaux obtenus à travers la réalisation d'essais pseudo-dynamiques afin d'évaluer le comportement dynamique des portiques face à un séisme d'intensité modérée. Les structures ont été instrumentées en utilisant de la fibre optique, des capteurs de déplacement et de force ainsi que des vélocimètres et de la corrélation d'image. D'autre part, le modèle numérique en poutres multifibres qui a été développé pour les portiques et qui permet de suivre l'évolution de leur endommagement au jeune âge et de déterminer leur réponse lorsqu'ils sont soumis à un accident sismique est présenté. Dans ce modèle numérique, le retrait et les déformations thermiques du béton sont calculés avant d'être réinjectés dans un modèle d'endommagement couplé permettant de tenir compte des effets de fluage et de déformations mécaniques. Le modèle numérique a été validé en comparant ses résultats à ceux obtenus expérimentalement, ce qui a permis d'évaluer l'évolution de fréquences propres des deux types de structures au jeune âge ainsi que de quantifier leur différence de comportement dans le domaine non-linéaire. Les travaux menés dans le cadre de cette thèse ont donc permis de proposer un modèle complet pour les structures en béton armé qui peut être utilisé afin de suivre l'évolution de leur endommagement allant de leur réalisation à l'application d'un accident sismique et de quantifier leur vulnérabilité sismique<br>Reinforced Concrete (RC) structures get damaged over time due to many factors: thermal conditions, chemical attacks, shrinkage, creep, carbonation, corrosion, etc. This damaging process starts at early-age and continues with structure aging. Early age damage can have a significant impact on the dynamic behavior of reinforced concrete structures. In fact, the natural frequency of a structure, which is a design parameter can be highly reduced due to this damage. In order to quantify the impact of early-age damage (0 to 28 days) on the seismic response of a reinforced concrete structure, this thesis combined both numerical modeling and pseudo-dynamic tests on two types of RC portal frames. The first one was kept in endogenous conditions (water exchange with the surrounding environment was prevented) during its early age period in a way to limit drying effects leading to cracks. As for the second one, it was kept in non-endogenous conditions (possibility of water exchange with the surrounding environment) similar to construction site conditions, which induced an initial damage (cracks apparition) due to a more important drying shrinkage. Both types of RC portal frames were subjected after their early age period to the same seismic loading using pseudodynamic tests. On the one hand, this manuscript presents the experimental results obtained through the use of pseudodynamic tests in order to evaluate the behavior of the two types of RC structures under a moderate intensity earthquake. The structures were instrumented using optical fiber sensors, displacement and load sensors, velocimeters and monitored using Digital Image Correlation. On the other hand, the enhanced multifiber beam model that was developed for the portal frames in order to follow their early age damage and to determine their static and dynamic behavior while accounting for their early age effects is presented. In this numerical model, shrinkage and concrete thermal deformations are calculated and then introduced as inputs of a coupled damage model accounting for creep and mechanical deformations. Such model was validated by comparing its results to the ones obtained experimentally, which made it possible to evaluate the evolution of frequency content of the two types of structures during early age and to quantify their difference of behavior in the non-linear domain. Work conducted within this thesis thus allowed proposing a complete model for reinforced concrete structures that can be used in order to follow their damage evolution from casting until being subjected to a seismic load and to quantify their seismic vulnerability

Among technologies capable to produce electricity locally without contributing to GHG releases, building integrated PV systems (BIPV) could be major contributor. However, when exposed to intense solar radiation, the temperature of PV modules increase significantly, leading to a reduction in efficiency so that only about 14% of the incident radiation is converted into electrical energy. The high temperature also decrease the life of the modules, thereby making passive cooling of the PV components through natural convection a desirable and cost-effective means of overcoming both difficulties. An experimental investigation of heat transfer and fluid flow characteristics of natural convection of air in vertical and inclined open-ended heated channels is therefore undertaken so as provide reliable information for the design of BIPV. Two experimental set ups were developed and used during the present investigations; one located at the CETHIL laboratory in Lyon, the F-device and the other located at the University of New South Wales in Sydney, the R-device. Both channels consisted of two wide parallel plates each of which could be subjected to controlled uniform or non-uniform heat fluxes. The investigation has been conducted by analyzing the mean wall temperatures, measured by thermocouples and mean velocity profiles and turbulent quantity distributions of the flow, measured with a PIV system. Flow patterns close to the heated faces were also investigated. The study is particularly focused on the transition region from laminar to turbulent flow. Three different heating geometric arrangements are examined in the modified Rayleigh number range from 3.86 x 105 to 6.22 x 106. The first is a vertical channel with one wall uniformly heated while the other was unheated, the second was a vertical channel in which both walls were non-uniformly heated and the third is an inclined channel uniformly heated from above. In the vertical configurations the width-to-height channel aspect ratio was fixed at 1:15 and in the inclined ones at 1:16. It is shown that the flow is very sensitivity to disturbances emanating from the ambient conditions. Moreover, the propagation of vortical structures and unsteadiness in the flow channel which are necessary to enhance heat transfer, occurred downstream of the mid-channel section at Ra* = 3.5 x 106 for uniformly and asymmetrically heated channels inclined between 60° and 90° to the horizontal. Indeed, these unsteady flow phenomena appears upstream the location of the inflexion point observed in the temperature excess distribution of the heated wall. In the case of non-uniform heating on both sides of the channel, a stronger 'disruption mechanism' exists, which leads to enhanced mixing and increased Reynolds stresses over most of the width of the channel. Empirical correlations of average Nusselt number as a function of modified Rayleigh number were obtained for each configuration.

A study on shape memory alloy materials as vibration dampers is reported. An important component is the strain rate-dependent and temperature-dependent constitutive behavior of shape memory alloy, which can significantly change its energy dissipation capacity under cyclic loading. The constitutive model used accounts for the thermo-mechanical strain rate-dependent behavior and phase transformation. With increasing structural flexibility, the hysteretic loop size of shape memory alloy dampers increases due to increasing strain rates, thus further decreasing the response of the structure to cyclic excitation. The structure examined is a beam, and its behavior with shape memory alloy dampers is compared to the same beam with conventional dampers. Parametric studies reveal the superior performance of the shape memory alloy over the conventional dampers even at the resonance frequency of the beam-damper system. An important behavior of the shape memory alloy dampers is discovered, in that they absorb energy from the fundamental and higher vibration modes. In contrast, the conventional dampers transfer energy to higher modes. For the same beam control, the stiffness requirement for the shape memory alloy dampers is significantly less than that of the conventional dampers. Response quantities of interest show improved performance of the shape memory alloy over the conventional dampers under varying excitation intensity, frequency, temperature, and strain rate.

ZnO nanowires and nanorods are a new class of one-dimensional nanomaterials with a wide range of applications in NEMS. The motivation for this work stems from the lack of understanding and characterization of their thermomechanical behaviors essential for their incorporation in nanosystems. The overall goal of this work is to develop a fundamental understanding of the mechanisms controlling the responses of these nanostructures with focus on: (1) development of a molecular dynamics based framework for analyzing thermomechanical behaviors, (2) characterization of the thermal and mechanical behaviors in ZnO nanowires and (3) development of models for pseudoelasticity and thermal conductivity. The thermal response analyses show that the values of thermal conductivity are one order of magnitude lower than that for bulk ZnO due to surface scattering of phonons. A modified equation for phonon radiative transport incorporating the effects of surface scattering is used to model the thermal conductivity as a function of wire size and temperature. Quasistatic tensile loading of wires show that the elastic moduli values are 68.2-27.8% higher than that for bulk ZnO. Previously unknown phase transformations from the initial wurtzite (WZ) structure to graphitic (HX) and body-centered-tetragonal (BCT-4) phases are discovered in nanowires which lead to a more complete understanding of the extent of polymorphism in ZnO and its dependence on load triaxiality. The reversibility of the WZ-to-HX transform gives rise to a novel pseudoelastic behavior with recoverable strains up to 16%. A micromechanical continuum model is developed to capture the major characteristics of the pseudoelastic behavior accounting for size and temperature effects. The effect of the phase transformations on the thermal properties is characterized. Results obtained show that the WZ→HX phase transformation causes a novel transition in thermal response with the conductivity of HX wires being 20.5-28.5% higher than that of the initial WZ-structured wires. The results obtained here can provide guidance and criteria for the design and fabrication of a range of new building blocks for nanometer-scale devices that rely on thermomechanical responses.

Laser is an efficient and widely used heat source in metal processing suchas welding and additive manufacturing. It has some great advantages compared to the other conventional heat sources like electron beam and arc namely: ability of handling complicated joint geometries and producing large components. Laser beam welding encompasses many complex physical phenomena such asheat transfer, metal melting, flow and solidification, free surface deformation, evaporation and possibly vaporization. The aim of this research work istwo-fold: gain deeper process understanding and improve the model reliability. Deeper process understanding is sought on the effect of beam shaping on themelt pool. To achieve improved model reliability, a good support consists in using qualitative experimental data representing the process. Thus, 3D validation of the melt pool geometry is performed while it was usually 2D inprevious research works. Furthermore, a new calculation procedure for laser absorption is introduced. To conduct this research work, a Computational Fluid Dynamics approach is used. A solver, capable of tracking the deformation of the melt free surface, is developed in OpenFOAM. Concerning beam shaping, it is found that not only the melt pool size as previously known but also the melt flow pattern is modified through elongating the beam shape.This last result could not be revealed by former studies as the non-transparent media hinders optical observation. New in-process quantitative measurements performed by a project partner are used to test the model. Weaknesses of the former absorptivity models are highlighted, as well as the limitations of the proposed model. Finally, the results show that the proposed absorptivity model function of local surface conditions leads to much better agreement with experimental results compared to the former constant absorptivity model. The maximum discrepancy compared to the experimental measurement, which is observed for the melt pool depth, can indeed be reduced to about 10%.<br>Laser är en effektiv och allmänt använd värmekälla vid svetsning och additiv tillverkning. Den har några viktiga fördelar jämfört med andra konventionella värmekällor såsom elektronstråle och elektrisk ljusbåge, nämligen: den kan ofta användas till komplicerade svetsgeometrier, och den kan producera stora komponenter. Lasersvetsning involverar olika sammansatta fysikaliska fenomen såsom värmeöverföring, metallsmältning, flöde, stelning, ytdeformation, avdunstning och i vissa fall förångning. Syftet med mitt forskningsarbete är tvåfaldigt: att få en djupare processförståelse och att förbättra modellens tillförlitlighet. Fördjupad processförståelse eftersträvades för att förstå hur formen på laserstrålen påverkar svetssmältan. För att uppnå förbättrad modellsäkerhet behövs experimentella data av hög kvalitet som representerar processen. Således utfördes 3D-validering av smältgeometrin medan det vanligtvis var 2D i tidigare forskningsarbeten. Dessutom har en ny modell för laserabsorption föreslagits. I forskningen har numerisk strömningssimulering (Computational Fluid Dynamics) använts för att simulera processen och en numerisk lösare, som kan spåra deformationen av den rörliga smälta ytan, är utveckladi programvaran OpenFOAM. Beträffande laserstrålens utbredning visar resultaten att svetssmältans storlek och även svetssmältansflöde modifieras genom att laserstråleformen förlängs. Medan den förra är känd från tidigare experimentella studier upptäcktes den senare inte före denna studie eftersomdet icke-transparenta mediet hindrar optisk observation. Nya (in-process) kvantitativa mätningar utförda av en projektpartner har använts för att testa modellerna. Svagheter i den tidigare absorptionsmodellen framhävdes, liksom begränsningarna i den föreslagna modellen. Slutligen visade resultaten att den föreslagna modellen där laserabsorptionen är en funktion av lokala ytförhållanden ledde till en bättre overensstämmelse med mätningar jämfört med den tidigare modellen med konstant laserabsorbtion. Den maximala avvikelsen jämfört med experimentell mätning, som observerades med avseende på smältbassängsdjupet, kunde reduceras till cirka 10%.<br><p>Till licentiatuppsats hör 2 inskickade artiklar, som inte visas nu.</p>

Nuclear fuel performance is highly affected by the behaviour of fission gases, particularly<p>at elevated burnups, where large amounts of gas are produced and can<p>potentially be released. The importance of fission gas release was the motivation<p>for large efforts, both experimentally and theoretically, in order to increase our<p>understanding of the different steps of the process, and to continuously improve<p>our models.<p>Extensions to higher burnups, together with the growing interest in novel types<p>of fuels such as inert matrix fuels envisaged for the transmutation of minor actinides,<p>make that one is still looking for a permanently better modelling, based<p>on a physical understanding and description of all stages of the release mechanism.<p>Computer simulations are nowadays envisaged in order to provide a better<p>description and understanding of atomic-scale processes such as diffusion, but even<p>in order to gain insight on specific processes that are inaccessible by experimental<p>means, such as the fuel behaviour during thermal spikes.<p>In the present work simulation techniques based on empirical potentials have<p>been used, focusing in a first stage on pure uranium dioxide. The behaviour of<p>point defects was at the core of this part, but also the estimation of elastic and<p>melting properties.<p>Then, in a second stage, the study has been extended to the behaviour of helium<p>and xenon. For helium, the diffusion in different domains of stoichiometry<p>was considered. The simulations enabled to determine the diffusion coefficient and<p>the migration mechanism, using both molecular dynamics and static calculation<p>techniques. Xenon behaviour has been investigated with the additional intention<p>to model the behaviour of small intragranular bubbles, particularly their interaction<p>with thermal spikes accompanying the recoil of fission fragments. For that<p>purpose, a simplified description of these events has been proposed, which opens<p>perspectives for further work.<p>/<p>Les performances du combustible nucléaire sont fortement affectées par le comportement<p>des gaz de fission, et ce particulièrement lorsqu’un taux d’épuisement<p>élevé est atteint, puisque d’importantes quantités de gaz sont alors produites<p>et peuvent potentiellement être relâchées. Les enjeux, entre autre économiques,<p>liés au relâchement de gaz de fission ont donné lieu à d’importants efforts, tant<p>sur le plan expérimental que théorique, afin d’accroître notre compréhension des<p>différentes étapes du processus, et d’améliorer sans cesse les mod`eles. Les extensions<p>à des taux d’épuisements encore plus élevés ainsi que l’intérêt croissant pour<p>de nouveaux types de combustible tels que les matrices inertes, envisages en vue<p>de la transmutation des actinides mineures, font qu’à l’heure actuelle, le besoin<p>permanent d’une meilleure modélisation, basée sur une compréhension et une description<p>physique des différentes étapes du processus de relâchement de gaz de<p>fission, est toujours de mise.<p>Les simulations par ordinateur ont ainsi été considérée comme un nouvel angle<p>de recherche sur les processus élémentaires se produisant à l’échelle atomique, à la<p>fois afin d’obtenir une meilleure compréhension de processus tels que la diffusion<p>atomique ;mais aussi afin d’avoir accès à certains processus qui ne sont pas observables<p>par des voies expérimentales, tels que la le comportement du combustible<p>lors de pointes thermiques.<p>Dans ce travail, deux techniques, basées sur l’utilisation de potentiels interatomiques<p>empiriques, ont permis d’étudier le dioxyde d’uranium, dans un premier<p>temps en l’absence d’impuretés. Cette partie était principalement centrée sur le<p>comportement des défauts ponctuels, mais a aussi concerné différentes propriétés<p>élastiques, ainsi que le processus de fusion du composé.<p>Ensuite l’étude a été étendue aux comportements de l’hélium de du xénon. Pour<p>ce qui a trait à l’hélium, la diffusion dans différents domaines de stoechiométrie<p>a été considérée. Les simulations ont permis de déterminer le coefficient de diffusion<p>ainsi que le mécanisme de migration lui-même. Quant au xénon, outre les<p>propriétés de diffusion, l’intention fut de se diriger vers la modélisation des petites<p>bulles intragranulaires, et plus précisément vers leur interaction avec les pointes<p>thermiques, créées lors du recul des fragments de fission. Une description simplifiée de ce processus a été proposée, qui offre de nouvelles perspectives dans ce<p>domaine.<p><p><br>Doctorat en Sciences de l'ingénieur<br>info:eu-repo/semantics/nonPublished

Les modèles actuels utilisés pour la modélisation des tubes d'arme se concentrent uniquement sur les chargements mécaniques subis par la structure. Des travaux récents au sein de Nexter Systems ont permis de prendre en compte l'action du projectile sur la structure en plus de la pression des gaz, qui est, suivant les normes actuelles, le paramètre dimensionnant.Le but de ces travaux est d'étudier le comportement thermomécanique d'un tube d'arme lors d'une séquence de tir. Des expertises métallographiques ont mis en évidence le développement d'une zone affectée thermiquement au niveau de la peau interne du canon. Ces observations valident l'influence des sollicitations thermiques sur les matériaux et ont motivé le choix de prendre en compte ces dernières dans la modélisation des tubes d'arme. De plus, l'utilisation d'une loi de comportement offrant la possibilité de faire évoluer les propriétés des matériaux en fonction de la température a amélioré la pertinence et la fidélité des modèles numériques. Les résultats obtenus sont en accord avec les données expérimentales et les observations métallographiques. Les sollicitations thermiques sont prédominantes dans le cas de l'étude et sont responsables pour une grande partie de l'endommagement subis par le canon. En effet, l'élévation en température des matériaux engendre non seulement de fortes contraintes thermomécaniques mais aussi une détérioration des caractéristiques matériaux voire un effondrement des propriétés lorsqu'un seuil critique est dépassé. Les observations menées et les résultats numériques montrent la nécessité de prendre en compte les sollicitations thermiques dans le dimensionnement des tubes d'arme en particulier lorsque les températures atteintes lors des tirs en cadence sont élevées<br>Current models of gun tubes focus only on the mechanical loads experienced by the structure. Recent works in Nexter allow us to take into account the action of the projectile on the tube in addition to the gas pressure, which is the major parameter to design gun barrels according to current standards.The aim of this work is to study the thermomechanical behavior of a gun barrel during firing. Metallographic studies highlight the development of a heat affected zone at the inner surface of the tube. These observations show the influence of thermal stresses on the material and the requirement to consider them in the numerical analyses. Moreover, the use of thermomechanical constitutive equations, that allow us to change the mechanical and thermal properties of the materials as a function of temperature, has improved the accuracy and the reliability of the numerical analyses. The results are consistent with the experimental data and metallographic observations. Thermal stresses are predominant and are responsible for the major part of the damage endured by the barrel. Indeed, the rise of the material's temperature generates not only strong thermomechanical stresses but also a drop in the material properties or a sharp drop if a critical limit is exceeded. The numerical results and the observations highlight the need to take into account the thermal loads in the design of barrels especially when the temperatures reached during firing are high

Le but de ces travaux est de créer un modèle aérothermique, avec un temps de calcul court, d’un alternateur automobile intégré au sein d’une simulation complète d’un environnement sous-capot d’un véhicule. La prise en compte de leur influence au sein d'un comportement moteur est recherchée. Un modèle simplifié permettant la simulation du comportement aéraulique et thermique d’un alternateur a été développé. Il utilise une approche nodale afin de simuler les phénomènes thermiques et aérauliques du système. Différents algorithmes et une interface homme-machine permettent un paramétrage facile et rapide, et une implémentation automatique du modèle. En effet, le paramétrage du réseau nodal est fait automatiquement, l’utilisateur doit seulement rentrer les différents paramètres du système : dimensions, caractéristiques matériaux, pertes thermiques... Cela nous permet d’avoir aussi un modèle adaptable facilement à tout type d’alternateur. Le comportement aéraulique de l’alternateur est simulé via des coefficients de convection, intégrés au réseau nodal. Ces coefficients sont déterminés via des corrélations en fonction du nombre de Reynolds de l’écoulement. Pour chaque zone de l’écoulement d’air dans l’alternateur, ces corrélations ont été identifiées via une modélisation CFD de l’alternateur, lui-même validé par des essais aérauliques sur banc expérimental. Le modèle a été vérifié et validé via des essais expérimentaux thermiques. Il présente une erreur moyenne inférieure à 10%, et fonctionne sur l’ensemble des régimes d’utilisation. Il présente un temps de calcul de l’ordre de 2 minutes. Le modèle a été intégré dans une simulation simplifiée d’un environnement sous-capot. Une méthodologie de couplage a été développée, permettant l’intégration des données du modèle simplifié, au sein des simulations sous-capot. Ces simulations modélisent le comportement thermique des environnements sous-capot ainsi que le compartiment aéraulique. Les flux d’air sont simulés et le couplage du modèle simplifié permet d’intégrer l’influence thermique de l’alternateur, au sein de l’environnement sous-capot, ainsi que l’impact aéraulique de ce dernier. La méthodologie de couplage permet d’importer les valeurs de températures et de débits, estimées par le modèle simplifié, au sein du maillage d’une CAO de l’alternateur. Ces travaux sont en cours d’intégration dans les processus numériques du Groupe PSA. Différentes perspectives sont en cours d’étude, afin d’utiliser ce modèle sur d’autres éléments du sous-capot, ou d’autres machines tournantes, comme des moteurs électriques présents sur les véhicules hybrides et électriques<br>The objective of the thesis is to create a thermal model of an alternator, with a quickly time run. This model will integrate the influence of the alternator inside an under-hood simulation. A simplify model able to simulate the aerodynamic and thermal behaviour has developed. It use a nodal approach to simulate the aerodynamic and thermal behaviour. Different algorithms and an user’s interface able to a quickly set up and a automatically implementation. Indeed, the nodal, approach was realized automatically by the model, the user inform the dimensions of the alternator, the materials characteristics and the thermal losses. Thanks to we have a model that use with any automobile alternator. The aerodynamic of the alternator is simulate with convection coefficient via the nodal approach. These coefficients are estimated with correlations based on Reynolds of the flow. The CFD simulation of the alternator identified these correlations. The CFD model has been validate with an aerodynamics tests. The model is checked and validate by thermal tests. It has an average error lower than 10% and work to any regime of the use. The time run is equal to 2 minutes. The modal has been integrate inside an under-hood simulation. A coupling methodology has been developed to allow the integration of the data, like the temperatures and the flowrate was estimate by the simplify model, inside an under-hood simulation. The under-hood simulation modelling the aerodynamic and thermal behaviour of the engine compartment. Therefore, the coupling methodology allow integrating the aerodynamic and thermal influence of the alternator inside the compartment. The work is actually in progress inside the numerical processes of the PSA group. Many perspectives are studied, to use the model on other under-hood elements, or other electric machine, like the electric engines used inside the hybrid vehicles

L’amélioration continue de la performance énergétique des bâtiments a été accompagnée par un développement d’outils numériques de plus en plus performants et précis. Alors que la prise en compte des phénomènes liés aux bâtiments, aux systèmes et à la météorologie est bien maîtrisée, le comportement des occupants est modélisé de manière très simplifiée par des scénarii répétitifs et des lois déterministes. L’impact des occupants sur les consommations énergétiques dans les bâtiments performants est pourtant majeur, comme en témoigne les écarts récurrents entre les résultats prédits et mesurés. Le travail de thèse propose, par l’intermédiaire d’une plateforme multi-agents et de modèles stochastiques, une mise à jour de la prise en compte de la présence des occupants et de leurs comportements sur la gestion des ouvrants, des dispositifs d’occultation, de l’éclairage et de la température de consigne de chauffage. Le champ d’application de la plateforme concerne les bâtiments de bureaux et de logements, pour des opérations neuves et de rénovation. Les modèles de comportement des occupants sont idéalement issus de campagnes de mesures in situ, d’études de laboratoire ou d’enquêtes sociologiques. La plateforme proposée est alors co-simulée avec le logiciel EnergyPlus, afin d’étudier l’influence des modèles sur les performances énergétiques. Dans la perspective de garantie de performance énergétique, ce travail contribue à la mise à jour et à la fiabilisation des outils de prédiction<br>Continuous improvement of the building energy performance is associated with the development of increasingly efficient and accurate numerical tools. While the consideration of phenomena related to buildings, systems and weather is well mastered, occupants’ behaviours are modelled in a very simplified way by repetitive scenarios and deterministic laws. The impact of occupants on energy consumption in high-performance buildings is dominant, as evidenced by the recurring gaps between predicted and measured results. The thesis demonstrates, via a multi-agent platform and stochastic models, an update on the ability to model occupants’ presence, their behaviours on windows, occultation devices, artificial lighting and heating setpoint temperatures. The application of the platform applies to office and residential buildings, for new builds and refurbishments. Occupants’ behaviour models are ideally obtained from in situ surveys, laboratory studies or sociological works. The suggested platform is then co-simulated with the EnergyPlus software, to study the influence of the models on a buildings energy performance. In the perspective of energy performance guarantees, this work contributes to the updating and reliability of prediction tools

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>This study aimed to evaluate different alternatives for management of natural pasture. Vegetation dynamics was evaluated for a period of six years in a natural pasture, submitted along 16 years to fire and grazing treatments. Furthermore, we evaluated the production and behavior of beef heifers from 12 to 18 months of age, maintained on natural pasture under two grazing frequencies. In the first experiment, the treatments consisted of a combination of burning factors (presence or absence) and grazing (presence or absence), in concave and convex slope positions, in a completely randomized design with factorial arrangement of four treatments and two topographic positions. Rotational grazing was used, with intervals calculated by the thermal time (760 degree days) necessary for the emergence of four leaves of Paspalum notatum and Andropogon lateralis. Burning was performed at the end of winter in a bimodal fashion. The treatments excluded from disturbances had a behavior atypical due to a burning caused by a lightning leading vegetation to a succession process. The grazed treatments had a stable prevalence of Paspalum notatum, on concave slope and its association with Andropogon lateralis, in convex slope. Natural grassland proved to be resilient to burning and grazing. However, the use of burning and grazing on concave slope areas can cause a reduction in vegetation diversity. In the second experiment, we evaluated the effect of two defoliation intervals, 375 and 750 degree days (DD), on the productive performance of beef heifers maintained on natural pasture under rotational grazing in the growing season of 2010 and 2011. The experimental design was completely randomized with two treatments and three replications. We evaluated the forage mass, height, green material and dead material in pasture. The performance measurements in animals were evaluated stocking rate, average daily gain and gain/ha. The greatest height, mass of green material, dead material and forage mass were observed in 750 DD treatment. Treatment with 375 DD presented a higher percentage of green material in relation to herbage mass. The highest average daily gain and gain per area were observed in the treatment 375 DD. The shortest interval between grazing permits satisfactory performance in rearing of beef heifers, since the natural pasture is managed with green material above 1500 kg DM/ha and grazing periods lower than three days. In the third experiment were related parameters and performance of grazing animal and its ingestive behavior. Ingestive behavior of heifers was measured as times of grazing, ruminating and resting, bite rate, bites per feeding station, feeding stations per minute, displacement rates by stations and time. The multiple regression equations had coefficients of determination of 48, 68 and 89% for grazing time, average daily gain and gain/ha. The average temperature, day of occupation, number of bites/min and bits per season were the best predictors of ingestive behavior of beef heifers grazing on natural grassland.<br>Este trabalho teve por objetivo avaliar alternativas de manejo de pastagem natural. Foi avaliada a dinâmica da vegetação por um período de seis anos de uma pastagem natural, submetida ao longo de 16 anos a tratamentos de fogo e pastejo. Além disso, foram avaliadas a produção e o comportamento de novilhas de corte dos 12 aos 18 meses de idade, mantidas em pastagem natural sob duas frequências de desfolha. No primeiro experimento, os tratamentos foram constituídos da associação dos fatores queima (presença ou ausência) e pastejo (presença ou ausência), nas posições de encosta e baixada, num delineamento completamente casualizado com arranjo fatorial de quatro tratamentos e duas posições topográficas. O pastejo foi rotacionado, com intervalos calculados pela soma térmica acumulada (760 graus dia) necessária para o surgimento de quatro folhas das espécies Paspalum notatum e Andropogon lateralis. A queima foi realizada ao final do inverno de forma bimodal. Os tratamentos excluídos de distúrbios tiveram um comportamento atípico devido a uma queima provocada por um raio levando a vegetação a um processo de sucessão. Os tratamentos pastejados foram estáveis com um predomínio das espécies Paspalum notatum, na encosta e de uma associação desta com Andropogon lateralis, na baixada. A pastagem natural mostrou-se resiliente a queima e ao pastejo. Entretanto, o uso da queima e pastejo, em áreas de encosta, pode causar redução na diversidade da vegetação. No segundo experimento foi avaliado o efeito de dois intervalos entre desfolhas de 375 e 750 graus dia (GD), sobre o desempenho produtivo de novilhas de corte mantidas em pastagem natural sob pastoreio rotacionado, na estação de crescimento entre 2010 e 2011. O delineamento utilizado foi o inteiramente casualizado com dois tratamentos e três repetições. Foram avaliados a massa de forragem, altura, material verde e material morto na pastagem. As medidas de desempenho nos animais foram a carga animal, ganho médio diário e ganho/ha. As maiores altura, massa de material verde, material morto e massa de forragem total foram observados com 750 GD. No tratamento com 375 GD foi observado maior percentual de material verde em relação à massa de forragem. Os maiores ganho médio diário e ganho por área foram observados no tratamento 375 GD. O menor intervalo entre pastoreios permite desempenho satisfatório na recria de novilhas de corte, desde que a pastagem natural seja manejada com material verde superior a 1500 kg de MS/ha e com períodos de ocupação de no máximo três dias. No terceiro experimento, foram relacionados os parâmetros da pastagem e de desempenho animal com o comportamento ingestivo dos animais. O comportamento ingestivo das novilhas foi medido pelos tempos de pastejo, de ruminação e de ócio, taxa de bocados, bocados por estação alimentar, estações alimentares por minuto, taxas de deslocamento e tempo por estação. As equações de regressão múltipla apresentaram coeficientes de determinação de 48, 68 e 89% para tempo de pastejo, ganho médio diário e ganho/ha, respectivamente. A temperatura média, os dias de ocupação, número de bocados/min e bocados por estação foram os melhores preditores do comportamento ingestivo das novilhas de corte em pastagem natural.

Diese Arbeit befasst sich mit Hochleistungsdioden aus den Halbleitermaterialen Silizium und Siliziumkarbid. Analysiert werden die statischen und dynamischen Schalteigenschaften. Bei den SiC-Bauelementen handelt es sich um unipolare Schottky-Dioden und bei den Silizium-Dioden um bipolare pin-Dioden. Bei den SiC-Schottky-Dioden liegt der Schwerpunkt auf der Analyse des statischen Durchbruchverhaltens von Randstrukturen und auf der Untersuchung der Selbsterwärmung bei Einzel- und Mehrpulsbelastung. Bei den bipolaren Silizium-Dioden wird das Durchbruchverhalten bei niedrigen und hohen Stromdichten untersucht. Aus den Sperrcharakteristiken, die positiv und negativ differentielle Widerstandsäste aufweisen, lassen sich Schlussfolgerungen auf das dynamische Verhalten ziehen. Das Abschaltverhalten (reverse recovery) der mit Plasma überschwemmten Bauelemente wird zuerst im Hinblick auf den Einfluss von Strukturparametern untersucht, um die prinzipiellen Einflussgrößen zu erläutern. Dann folgen die Ergebnisse zur Filamentbildung, die bei den hohen Belastungen der Bauelemente während des Kommutierungsprozesses auftreten können. Die auftretenden Filamentstrukturen werden analysiert und - soweit möglich - Einflussgrößen herausgearbeitet. Schließlich wird noch auf den Einfluss von Randstrukturen auf das Filamentierungsverhalten, die als Inhomogenität in jedem Bauelement vorhanden sind, eingegangen.

The works contributes to the need to design more efficient heating and domestic hot water preparation systems. Dynamic building and simulation plays an important role in the development of domestic hot water (DHW) preparation systems for residential buildings, in order to evaluate and optimize the final energy and the DHW comfort. The case study of this work is a big multi-family building composed of 96 flats. District heating (DH) is used to heat up the water in the storage tank located in the technical room. A distribution system connects the storage to all the fresh water stations (FWS) located in each flat. The chosen approach is to simulate the building-level DHW preparation with a single heat exchanger (HX) which approximates the behaviour of all the HXs of the building. For this purpose, the simultaneity factor (fs) should be considered. First, a representative model of the FWS for each flat is implemented in Matlab/Simulink and tested with two different control strategies of the circulation pump and two different DHW profiles, derived either from standard EN16147 or created as a stochastic profile. From the flat-level model, a building-level model is derived. Four different building-level DHW profiles are used to evaluate the simultaneity factor, and so the peak load of the building, in order to size the HX for the whole building. The DHW profiles (and so the simultaneity factor) and the parametrization of the HX influence the results. Final energy and DHW comfort (i.e. the DHW temperature and the “waiting time” to reach this temperature) are compared in each case. The return temperature of the fluid sent back to the storage is also analysed. The development of the return temperature to the storage is influenced by the DHW profiles and the thermal capacity of the pipe.

Vor dem Hintergrund zukünftiger Sensoren, basierend auf dem piezoresistiven Effekt von einwandigen Kohlenstoffnanoröhren (SWCNT), werden in dieser Arbeit umfangreiche Ergebnisse zum mechanischen Verhalten von Grenzflächen zwischen SWCNTs und edlen Metallen am Beispiel von Pd und Au präsentiert. Im Fokus steht dabei die Synergie von rechnerischen und experimentellen Methoden Molekulardynamik (MD), nanoskalige Tests und Analytik , um (1) mit guter Genauigkeit maximale Kräfte von gezogenen SWCNTs, welche in Metall eingebettet sind, vorauszuberechnen und (2) einen wertvollen Beitrag zum Verständnis der zu Grunde liegenden Fehlermechanismen zu liefern. Es wurde ein MDModell eines in eine einkristalline Matrix eingebetteten SWCNTs mit Randbedingen eines Auszugsversuchs entwickelt. Mit diesem Modell können Kraft-Weg-Beziehungen und Energieverläufe für einen quasistatischen verschiebungsgesteuerten Auszugsversuch errechnet werden. Das Modell liefert kritische Kräfte bei Versagen des Systems. Des Weiteren können mit diesem Modell der Einfluss des SWCNT-Typus, der Einbettungslänge, der Temperatur, von intrinsischen Defekten und Oberflächengruppen (SFGs) auf das Grenzflächenverhalten untersucht werden. Zum Vergleich wurden kritische Kräfte experimentell durch in situ Auszugsversuche in einem Rasterelektronenmikroskop bestimmt. Es wurde eine sehr gute Übereinstimmung von rechnerischen und experimentellen Daten festgestellt. Der vorherrschende Fehler im Experiment ist der SWCNT-Bruch, jedoch wurden auch einige SWCNT-Auszüge beobachtet. Mit Hilfe der MD-Simulationen wurde gefunden, dass die SFGs als kleine Anker in der umgebenden metallischen Matrix wirken und somit die maximalen Kräfte signifikant erhöhen. Diese Grenzflächenverstärkung kann Zugspannungen verursachen, die genügend hoch sind, so dass SWCNT-Bruch initiert wird. Im Gegensatz dazu zeigten Simulationen von Auszugstests mit idealen SWCNTs nur kleine Auszugskräfte, welche meistens unabhängig von der Einbettungslänge des SWCNTs sind. Dieses Verhalten wird mit einer inkommensurablen Konfiguration der Kristallstrukturen an der Grenzfläche von SWCNTs und der einbettenden Edelmetalle interpretiert. Zur Qualifizierung der Existenz von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material wurden analytische Untersuchungen mittels Fluoreszenzmarkierung von Oberflächengruppen durchgeführt. In Übereinstimmung mit Literaturstellen zum gesicherten Nachweis von SFGs, bedingt durch technologische Behandlungen, weisen diese Experimente stark auf das Vorhandensein von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material hin. Demnach kann der dominante SWCNT-Bruch Fehler durch die Grenzflächenverstärkung auf Grund von SFGs erklärt werden<br>In the light of future sensors, that are based upon the piezoresistive effect of singlewalled carbon nanotubes (SWCNTs), this work presents comprehensive results of studies on the mechanical behavior of interfaces between SWCNTs and noble metals using the examples of Pd and Au. With this contribution, the focus is on a synergy between computational and experimental approaches involving molecular dynamics (MD) simulations, nanoscale testing, and analytics (1) to predict to a good degree of accuracy maximum forces of pulled SWCNTs embedded in a noble metal matrix and (2) to provide valuable input to understand the underlying mechanisms of failure. A MD model of a SWCNT embedded in a single crystalline matrix with pull-out test boundary conditions was developed. With this model, force-displacement relations and energy evolutions for a quasi-static displacement controlled test can be computed. The model provides critical forces for failure of the system. Furthermore, the influence of SWCNT type, embedding length, temperature, intrinsic defects and surface functional groups (SFGs) on the interface behavior can be studied using this model. For comparison, critical forces were experimentally determined by conducting pull-out tests in situ, inside a scanning electron microscope. A very good agreement of computational and experimental values was discovered. The dominant failure mode in the experiment was a SWCNT rupture, although several pull-out failures were also observed. From MD simulations, it was found that SFGs act as small anchors in the metal matrix and significantly enhance the maximum forces. This interface reinforcement can lead to tensile stresses sufficiently high to initiate SWCNT rupture. In contrast, pull-out test simulations of ideal SWCNTs show only small pull-out forces, which are mostly independent on SWCNT embedding length. This behavior is interpreted with an incommensurate configuration of crystal structures at the interface between SWCNTs and embedding noble metals. To qualify the existence of carboxylic SFGs on the used SWCNT material, an analytical investigation by means of fluorescence labeling of surface species was performed. In agreement with literature reports on the secured verification of SFGs due to necessary technological treatments, these experiments strongly indicate the presence of carboxylic SFGs on the used SWCNT material. Thus, the dominant SWCNT rupture failure is explained with an interface reinforcement by SFGs

Vor dem Hintergrund zukünftiger Sensoren, basierend auf dem piezoresistiven Effekt von einwandigen Kohlenstoffnanoröhren (SWCNT), werden in dieser Arbeit umfangreiche Ergebnisse zum mechanischen Verhalten von Grenzflächen zwischen SWCNTs und edlen Metallen am Beispiel von Pd und Au präsentiert. Im Fokus steht dabei die Synergie von rechnerischen und experimentellen Methoden Molekulardynamik (MD), nanoskalige Tests und Analytik , um (1) mit guter Genauigkeit maximale Kräfte von gezogenen SWCNTs, welche in Metall eingebettet sind, vorauszuberechnen und (2) einen wertvollen Beitrag zum Verständnis der zu Grunde liegenden Fehlermechanismen zu liefern. Es wurde ein MDModell eines in eine einkristalline Matrix eingebetteten SWCNTs mit Randbedingen eines Auszugsversuchs entwickelt. Mit diesem Modell können Kraft-Weg-Beziehungen und Energieverläufe für einen quasistatischen verschiebungsgesteuerten Auszugsversuch errechnet werden. Das Modell liefert kritische Kräfte bei Versagen des Systems. Des Weiteren können mit diesem Modell der Einfluss des SWCNT-Typus, der Einbettungslänge, der Temperatur, von intrinsischen Defekten und Oberflächengruppen (SFGs) auf das Grenzflächenverhalten untersucht werden. Zum Vergleich wurden kritische Kräfte experimentell durch in situ Auszugsversuche in einem Rasterelektronenmikroskop bestimmt. Es wurde eine sehr gute Übereinstimmung von rechnerischen und experimentellen Daten festgestellt. Der vorherrschende Fehler im Experiment ist der SWCNT-Bruch, jedoch wurden auch einige SWCNT-Auszüge beobachtet. Mit Hilfe der MD-Simulationen wurde gefunden, dass die SFGs als kleine Anker in der umgebenden metallischen Matrix wirken und somit die maximalen Kräfte signifikant erhöhen. Diese Grenzflächenverstärkung kann Zugspannungen verursachen, die genügend hoch sind, so dass SWCNT-Bruch initiert wird. Im Gegensatz dazu zeigten Simulationen von Auszugstests mit idealen SWCNTs nur kleine Auszugskräfte, welche meistens unabhängig von der Einbettungslänge des SWCNTs sind. Dieses Verhalten wird mit einer inkommensurablen Konfiguration der Kristallstrukturen an der Grenzfläche von SWCNTs und der einbettenden Edelmetalle interpretiert. Zur Qualifizierung der Existenz von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material wurden analytische Untersuchungen mittels Fluoreszenzmarkierung von Oberflächengruppen durchgeführt. In Übereinstimmung mit Literaturstellen zum gesicherten Nachweis von SFGs, bedingt durch technologische Behandlungen, weisen diese Experimente stark auf das Vorhandensein von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material hin. Demnach kann der dominante SWCNT-Bruch Fehler durch die Grenzflächenverstärkung auf Grund von SFGs erklärt werden.<br>In the light of future sensors, that are based upon the piezoresistive effect of singlewalled carbon nanotubes (SWCNTs), this work presents comprehensive results of studies on the mechanical behavior of interfaces between SWCNTs and noble metals using the examples of Pd and Au. With this contribution, the focus is on a synergy between computational and experimental approaches involving molecular dynamics (MD) simulations, nanoscale testing, and analytics (1) to predict to a good degree of accuracy maximum forces of pulled SWCNTs embedded in a noble metal matrix and (2) to provide valuable input to understand the underlying mechanisms of failure. A MD model of a SWCNT embedded in a single crystalline matrix with pull-out test boundary conditions was developed. With this model, force-displacement relations and energy evolutions for a quasi-static displacement controlled test can be computed. The model provides critical forces for failure of the system. Furthermore, the influence of SWCNT type, embedding length, temperature, intrinsic defects and surface functional groups (SFGs) on the interface behavior can be studied using this model. For comparison, critical forces were experimentally determined by conducting pull-out tests in situ, inside a scanning electron microscope. A very good agreement of computational and experimental values was discovered. The dominant failure mode in the experiment was a SWCNT rupture, although several pull-out failures were also observed. From MD simulations, it was found that SFGs act as small anchors in the metal matrix and significantly enhance the maximum forces. This interface reinforcement can lead to tensile stresses sufficiently high to initiate SWCNT rupture. In contrast, pull-out test simulations of ideal SWCNTs show only small pull-out forces, which are mostly independent on SWCNT embedding length. This behavior is interpreted with an incommensurate configuration of crystal structures at the interface between SWCNTs and embedding noble metals. To qualify the existence of carboxylic SFGs on the used SWCNT material, an analytical investigation by means of fluorescence labeling of surface species was performed. In agreement with literature reports on the secured verification of SFGs due to necessary technological treatments, these experiments strongly indicate the presence of carboxylic SFGs on the used SWCNT material. Thus, the dominant SWCNT rupture failure is explained with an interface reinforcement by SFGs.

Ce travail de recherche se situe dans le cadre du développement de la méthode des éléments de frontière (BEM) pour les milieux poreux multiphasiques. À l'heure actuelle, l'application de la BEM aux pr oblèmes des milieux poreux non-saturés est encore limitée, car l'expression analytique exacte de la solution fondamentale n'a pas été obtenue, ni dans le domaine transformé ni dans le domaine réel. Ceci provient de la complexité du système d'équations régissant le comportement des milieux poreux non-saturés. Les développements de la BEM pour les sols non-saturés effectués au cours de cette thèse sont basés sur les modèles thermo-hydro-mécanique (THHM) et hydro-mécanique (HHM) présentés dans la première partie de ce mémoire. Ces modèles phénoménologiques basés sur la théorie de la poromécanique et les acquis expérimentaux sont obtenus dans le cadre du modèle mathématique présenté par Gatmiri (1997) et Gatmiri et al. (1998). Après avoir présenté les modèles THHM et HHM, on établit pour la première fois les équations intégrales de frontière et les solutions fondamentales associées pour un milieu poreux non-saturé sous chargement quasi-statique pour les deux cas isotherme (2D dans le domaine de Laplace) et non-isotherme (2D et 3D dans les domaines de Laplace et temporel). Aussi, les équations intégrales de frontière ainsi que les solutions fondamentales 2D et 3D (dans le domaine de Laplace) pour le modèle dynamique couplé des sols non-saturés sont obtenues. Ensuite, les formulations d'éléments de frontière (BEM) basées sur la méthode quadrature de convolution (MQC) concernant les milieux poreux saturé et non-saturé sous chargement quasi-statique isotherme et dynamique sont implémentées dans le code de calcul " HYBRID ". Ayant intégrées les formulations de BEM pour les problèmes de propagation d'ondes ainsi que pour les problèmes de consolidation dans les milieux poreux saturés et non-saturés, il semble que nous ayons fourni à l'heure actuelle le premier code de calcul aux éléments de frontière (BEM) qui modélise les différents problèmes dans les sols secs, saturés et non-saturés. Une fois le code vérifié et validé, des études paramétriques portant sur des effets de site sismiques sont effectuées. Le but recherché est d'aboutir à un critère simple, directement exploitable par les ingénieurs, combinant les caractéristiques géométriques et les caractéristiques du sol, permettant de prédire l'amplification du spectre de réponse en accélération dans des vallées sédimentaires aussi bien que vides

Les garnitures mécaniques sont utilisées dans de multiples applications pour réaliser l'étanchéité autour d'arbres en rotation. Ces composants peuvent fonctionner efficacement pendant plusieurs années en conditions stables, mais leur durée de vie est significativement réduite lorsque les conditions varient. L'objectif de ce travail de recherche est de développer et d’utiliser un banc d'essais et code de calcul pour étudier l'impact de pulsations de pression, d’inversions de pression et du chargement dynamique résultant sur les performances de garnitures mécaniques ayant des faces mésalignées et présentant des défauts de planéité.Le solveur fluide d'un modèle numérique de garnitures mécaniques a été étendu aux conditions transitoires. Un module résolvant la dynamique des forces et des moments a été ajouté afin de prédire le déplacement axial et les déplacements angulaires de la face montée de manière flexible. Afin de caractériser les performances de garnitures, un banc d'essais générant des pulses de pression a été instrumenté et des méthodes de mesure de perte de volume d'huile et d'entrée d'eau mises en place.Des garnitures mécaniques à faces parallèles puis mésalignées, fonctionnant sous pulsations et inversions de pression, ont été testées expérimentalement et simulées. Seules de très faibles augmentations d'eau dans l'huile ont été observées, sans augmentation au cours du temps, et sans fuite d'huile mesurable. Les faibles valeurs d'entrées d'eau sont dues à la faible épaisseur de film et à la courte durée des inversions de pression. Une garniture mécanique expérimentale à fort défaut de planéité a aussi été testée. Contrairement aux autres paramètres, le défaut de planéité semble augmenter significativement la fuite et promouvoir les entrées d'eau et pourrait ainsi être à l'origine de certaines défaillances<br>Face seals are mechanical devices used to seal rotating shafts in numerous applications. While they can operate efficiently under steady conditions for years, they tend to fail prematurely when operating in severe, or rapidly varying conditions. The focus of this research work is the development and use of an experimental and a numerical method to investigate the impact of pressure pulses, pressure inversions and induced dynamic loading on the performance of mechanical face seals exhibiting face misalignment and waviness.The fluid solver of a state-of-the art face seal numerical model was extended to transient conditions and a module solving the dynamics for the axial and angular degrees of freedom of the flexibly-mounted stator added. A system-level experimental setup generating pressure pulses was instrumented and methods to characterise face seal performance in terms of oil volume loss and ingression of water outer-fluid selected and implemented.Face seals, with flat and misaligned faces, operating under pressure pulses and pressure inversions were experimentally tested and simulated. They show only slight increase of water in the oil, no increase over time, and no measurable oil leakage. The low water ingression is due to low film thickness combined with the short duration of pressure inversions. An exploratory face seal of high waviness was also experimentally tested. Contrary to the other parameters, the waviness appears to significantly increase the leakage and promote water ingression and could thus be at the origin of some seal failures

L'océan est le plus grand réservoir d'énergie solaire de notre planète. La quantité de chaleur qu'il est capable de stocker est modulée par sa circulation complexe, opérant sur une vaste gamme d’échelles allant du centimètre à la dizaine de milliers de kilomètres. Cette thèse s'intéresse à deux types de processus océaniques: les tourbillons de mésoéchelle, d'une taille de 100 à 300 km, et les fronts de sous-mésoéchelle, d'une taille inférieure à 50 km. L'idée communément admise est que les mouvements agéostrophiques de sous-mésoéchelle sont principalement confinés à la couche de mélange océanique de surface et sont faibles dans l'océan intérieur. Cette vision classique de la dynamique océanique repose sur l'hypothèse que l'océan intérieur est en équilibre quasi-géostrophique, empêchant la formation de forts gradients de densité en profondeur. Cette thèse remet en question ce paradigme en se basant sur des observations CTD in situ à haute résolution collectées par des éléphants de mer instrumentés, des images satellite d’élévation de la surface de l’océan, et des sorties de modèle à haute résolution dans le Courant Circumpolaire Antarctique.Les résultats indiquent que les mouvements agéostrophiques sont (i) générés par le champ tourbillonnaire de mésoéchelle via des processus defrontogenèse, et (ii) ne sont pas limités à la couche de mélange de surface ; bien au contraire, ils pénètrent dans l'océan intérieur jusqu'à 1000 m deprofondeur. Ces fronts agéostrophiques de sous-mésoéchelle sont associés à d'importants flux de chaleur dirigés de l'intérieur de l'océan vers la surface, d'une amplitude comparable aux flux air-mer.Cet effet peut potentiellement altérer la capacité de stockage de chaleur de l'océan et devrait être le plus fort dans les zones tourbillonnaires telles que le Courant Circumpolaire Antarctique, le Kuroshio et le Gulf Stream, les trois courants clefs du système climatique. Il apparaît ainsi que les fronts agéostrophiques de sous-mésoéchelle représentent une voie importante, mais encore largement méconnue, pour le transport de chaleur, de nutriments et de gaz entre l'intérieur et la surface de l'océan, avec des répercussions potentiellement majeures pour les systèmes biogéochimique et climatique<br>The ocean is the largest solar energy collector on Earth. The amount of heat it can store is modulated by its complex circulation, which spans a broad range of spatial scales, from centimeters to thousands of kilometers. This dissertation investigates two types of physical processes: mesoscale eddies (100-300 km size) and submesoscale fronts (£ 50 km size). To date, ageostrophic submesoscale motions are thought to be mainly trapped within the ocean surface mixed layer, and to be weak in the ocean interior. This is because, in the classical paradigm, motions below the mixed layer are broadly assumed to be in quasigeostrophic balance, preventing the formation of strong buoyancy gradients at depth. This dissertation introduces a paradigm shift; based on a combination of high-resolution in situ CTD data collected by instrumented elephant seals, satellite observations of sea surface height, and high-resolution model outputs in the Antarctic Circumpolar Current, we show that ageostrophic motions (i) are generated by the backgound mesoscale eddy field via frontogenesis processes, and (ii) are not solely confined to the ocean surface mixed layer but, rather, can extend in the ocean interior down to depths of 1 000 m. Deepreaching ageostrophic fronts are shown to drive an anomalous upward heat transport from the ocean interior back to the surface that is larger than other contributions to vertical heat transport and of comparable magnitude to air-sea fluxes. This effect can potentially alter oceanic heat uptake and will be strongest in eddy-rich regions such as the Antarctic Circumpolar Current, the Kuroshio Extension, and the Gulf Stream, all of which are key players in the climate system. As such, ageostrophic fronts at submesoscale provide an important, yet unexplored, pathway for the transport of heat, chemical and biological tracers, between the ocean interior and the surface, with potential major implications for the biogeochemical and climate systems

博士<br>元智大學<br>機械工程學系<br>94<br>This study evaluates aerosol dynamics in indoor flow field with different particle size. Various transport and removal mechanisms of aerosol dynamics, including fluid convection, Brownian motion, thermophoretic drift, and coagulation of aerosols, are simulated. There are two mathematical models in this study, Zone Model and Field Model. The zone model calculates the average aerosol behavior in indoor environment. The field model is based on the SIMPLE method. The SIMPLE method is applied to solve the momentum, energy, and aerosol concentration equations. The main scheme is based on a boundary layer type solution of sectional aerosol simulation that uses flow fields provided a computational dynamics code. This study evaluates the aerosol concentration distribution in indoor environment and investigates the effect of coagulation on the deposition velocity along indoor surfaces. The results will help us to control the aerosol deposition onto surfaces and improve the indoor air quality.

博士<br>國立臺灣大學<br>機械工程學研究所<br>94<br>Among the novel electronic cooling devices, miniature heat pipes (MHP) have been received attention in recent years. For understanding the thermal mechanism of MHPs completely, two types of MHPs have been investigated in this dissertation. One is a disk-shaped miniature heat pipe (DMHP) and the other is a multi-loop pulsating heat pipe (MLPHP). A mounting base integrated with DMHP is designed for laser diode TO can package. For understanding the temperature distribution and physical phenomenon of DMHP, a CFD model is made using the commercial code, Fluent 6.1.18. Combining the applications of this package and user defined C++ program, two-phase heat/mass transfer mechanism is built. The modeling results and the experimental data are reported and are in good agreement with each other. Mathematical modeling of the MLPHP is a contemporary problem that remains quite elusive. Simplifications and assumptions made in all the modeling approaches developed so far render them unsuitable for engineering design. In this dissertation, a more realistic modeling scheme is presented which proves considerable information for thought toward the next progressive step. At different operational conditions, the MLPHP experience bulk internal flow circulations. A time average model based on design parameters for predicting thermal performance has been developed, and from which the optimal suggestions could be provided. In addition, the non-linear auto-regressive moving average model with exogenous inputs (NARMAX) approach is employed to analyze the dynamics of the MLPHP. The nonlinearity would be represented in both time and frequency domains. High speed flow visualization for the MLPHP is provided. It is identified that there exists the bulk circulation flow that lasts longer and the local flow direction switch flow. Dispersed bubbles, vapor plugs and the transition flow patterns from the dispersed bubbles to the vapor plugs are the major flow patterns in the MLPHP. By increasing the heating power, vapor plugs observed became shorter and more uniformly dispersed due to the vapor plug deformation and breakup mechanism. Bubble sizes have unsymmetrical distributions among various tubes. The complex combined effects of bubble nucleation, coalescence and condensation are responsible for the oscillation flow in the MLPHP. From analyzing the effect of operational parameters on thermal performance of MLPHP, the vertical bottom heating mode is regarded as the optimal operational condition. In addition, a comprehensive description of the effect for each combination of conditions (charge ratio, heating power, heating mode, orientation) is provided by experiment.

碩士<br>國立交通大學<br>應用化學系所<br>95<br>This study investigates on obtaining a water model suited to long simulation time of macromolecules in solution and constructing a simulation system of aqueous solutions. Comparison between other models revealed that flexible three-center model has been already used in many large-scale simulation and it’s provided with experimental data. Because the model works well with short-range truncation suited to high-speed computation. It’s tested by comparing the structural, dynamic and thermodynamic properties of water in aqueous solution, at several temperature and density, with the other models and experimental data. Our program also was tested by calculation such properties and fitted these literature very well. Therefore, the aims of research divide into three parts: First is tested for many water properties comparing with literature；Second investigates on the structural and dynamic properties of brine solutions；the other simulates charged aqueous nanodroplets for different condition, which were different temperatures, the number of ions, the type of ion and the size of droplets, in vacuum and these nanodroplets were given some additional velocity ranging from 1 m/s to 200 m/s to observe two nanodroplets bumped into or merged each other or merged . Studies show that ionic solvation shell effects strongly on the water structure in aqueous solution, like Cl- anion makes water more slow meaning ionic solvation shells are rigid. Computation of Bond time correlation functions shows that Cl--water pair can hold longer than water-water pair. The rigidity can play an important role in charged aqueous nanodroplets. At several conditions, the nanodroplet including Cl- ions were stable. Giving two nanodroplets a velocity in a direction to overcome the surface energy of the droplet made a formation of bridge structure and giving more kinetic energy performed the merged process. To calculate the surface area and volume of a nanodroplet, there are the merged nanodroplet and a nanodroplet had the same number water molecules and ions of the merged nanodroplet, we use the molecular modeling software TINKER implemented the algorithms of solvent accessible surface. The result of computation can prove the merged nanodroplet is the stable structure.

The driving force behind research in alternative clean and renewable energy has been the desire to reduce emissions and dependence on fossil fuels. In the United States, ground vehicles account for 30% of total carbon emission, and significantly contribute to other harmful emissions. This issue causes environmental concerns and threat to human health. On the other hand, the demand on fossil fuel grows with the increasing energy consumption worldwide. Particularly in the United States of America, transportation absorbs 75% of this energy source. There is an urgent need to reduce the transportation dependence on fossil fuel for the purpose of national security. Polymer electrolyte membrane (PEM) fuel cells are strong potential candidates to replace the traditional combustion engines. Even though research effort has transferred the fuel cell technology into real‒world vehicle applications, there are still several challenges hindering the fuel cell technology commercialization, such as hydrogen supply infrastructure, cost of the fuel cell vehicles, on‒board hydrogen storage, public acceptance, and more importantly the performance, durability, and reliability of the PEM fuel cell vehicles themselves. One of the key factors that affect the fuel cell performance and life is the run‒time thermal and water management. The temperature directly affects the humidification of the fuel cell stack and plays a critical role in avoiding liquid water flooding as well as membrane dehydration which affect the performance and long term reliability. There are many models exists in the literature. However, there are still lacks of control‒oriented modeling techniques that describe the coupled heat and mass transfer dynamics, and experimental validation is rarely performed for these models. In order to establish an in‒depth understanding and enable control design to achieve optimal performance in real‒time, this research has explored modeling techniques to describe the coupled heat and mass transfer dynamics inside a PEM fuel cell. This dissertation is to report our findings on modeling the temperature dynamics of the gas and liquid flow in the porous media for the purpose of control development. The developed thermal model captures the temperature dynamics without using much computation power commonly found in CFD models. The model results agree very well with the experimental validation of a 1.5 kW fuel cell stack after calibrations. Relative gain array (RGA) was performed to investigate the coupling between inputs and outputs and to explore the possibility of using a single‒input single‒output (SISO) control scheme for this multi‒input multi‒output (MIMO) system. The RGA analyses showed that SISO control design would be effective for controlling the fuel cell stack alone. Adding auxiliary components to the fuel cell stack, such as compressor to supply the pressurized air, requires a MIMO control framework. The developed model of describing water transport in porous media improves the modeling accuracy by adding catalyst layers and utilizing an empirically derived capillary pressure model. Comparing with other control‒oriented models in the literature, the developed model improves accuracy and provides more insights of the liquid water transport during transient response.<br>text

Frictional measurements were made on natural fault gouge at seismic slip rates using a high-speed rotary-shear apparatus to study effects of slip velocity, acceleration, displacement, normal stress, and water content. Thermal-, mechanical-, and fluid-flowcoupled FEM models and microstructure observations were implemented to analyze experimental results. Slightly sheared starting material (Unit 1) and a strongly sheared and foliated gouge (Unit 2) are produced when frictional heating is insignificant and the coefficient of sliding friction is 0.4 to 0.6. A random fabric gouge with rounded prophyroclasts (Unit 3) and an extremely-fine, microfoliated layer (Unit 4) develop when significant frictional heating occurs at greater velocity and normal stress, and the coefficient of sliding friction drops to approximately 0.2. The frictional behavior at coseismic slip can be explained by thermal pressurization and a temperature-dependent constitutive relation, in which the friction coefficient is proportional to 1/T and increases with temperature (temperature-strengthening) at low temperature conditions and decreases with temperature (temperature-weakening) at higher temperature conditions. The friction coefficient, normal stress, pore pressure, and temperature within the gouge layer vary with position (radius) and time, and they depend largely on the frictional heating rate. The critical displacement for dynamic weakening is approximately 10 m or less, and can be understood as the displacement required to form a localized slip zone and achieve a steady-state temperature condition. The temporal and spatial evolution of hydromechanical properties of recovered from the Nankai Trough (IODP NanTroSEIZE Stage 1 Expeditions) have been investigated along different stress paths, which simulate the natural conditions of loading during sedimentation, underthrusting, underplating, overthrusting, and exhumation in subduction systems. Porosity evolution is relatively independent of stress path, and the sediment porosity decreases as the yield surface expands. In contrast, permeability evolution depends on the stress path and the consolidation state, e.g., permeability reduction by shear-enhanced compaction occurs at a greater rate under triaxialcompression relative to uniaxial-strain and isotropic loading. In addition, experimental yielding of sediment is well described by Cam-Clay model of soil mechanics, which is useful to better estimate the in-situ stress, consolidation state, and strength of sediment in nature.

碩士<br>國立臺北科技大學<br>有機高分子研究所<br>102<br>The study employs OIT (Oxidation Induction Time) methods of differential scanning calorimetry (DSC) to explore the performance of SIS type hot melt pressure sensitive adhesive (HMPSA) when adding various types of antioxidants to search for the proper type and appropriate dosage, etc. The results of OIT experiments show that the trade-plate 1010 (Tetra- [methylene- (3,5-di-tert-butyl-4-hydroxyphenyl) – propionate]methane) has the best effect when adding it alone . However, we find out combining 1010 with IRGAFOS168 (Tris (2,4-ditert-butylphenyl)phosphite) has better effect than using it alone. In addition ,We employ different molecular structures of SIS (styrene -isoprene- styrene tri-block copolymers), such as linear, asymmetric and radial types to be made into HMPSA. Then, to analyse the relationships about bonding properties, thermal properties and the rheological behaviors by using DSC, thermal gravimetric analysis (TGA), and rheometer. We conclude that HMPSA increased coating workability when radial structure of SIS was used. Moreover, the linear or asymmetric structures of SIS can be considered when products require holding power or heat resistance.

Thesis (M.S.) -- University of Tennessee, Knoxville, 2005.<br>Title from title page screen (viewed on August 31, 2005). Thesis advisor: Hairong Qi. Thesis advisor: Thomas G. Hallam. Document formatted into pages (ix, 89 p. : ill. (some col.). col. map). Vita. Includes bibliographical references (p. 84-88).

The prediction of the behaviour and spread of bushfires has always been fraught with a large number of unknowns,not the least of which has been the seemingly capricious nature of fire itself. Operational bushfire prediction systems, developed as they are using empirical methods, aim to predict the long-term mean spread of a bushfire based on its steady-state behaviour....

Small endothermic mammals have high mass-specific resting energy requirements, making their behavioural and metabolic adaptions to variation in thermal conditions and prey availability critical for survival. My project focuses on the relationships between daily and seasonal variation in thermal conditions and the activity and thermoregulatory energetics of small insectivorous bats and their prey. My findings highlight the sensitivity of bats and insects to environmental factors and the moderating effects of riparian habitats on nightly thermal conditions. My results also indicate the necessity of long-term sampling for monitoring bat populations because there is strong within site variation in activity levels depending on thermal conditions and season. The new information on torpor use by M. macropus changes the perception that torpor is only used extensively during winter in cold climates. Torpor apparently plays a large role in balancing the tight energy budget of small insectivorous bats even in mild climates. My findings contribute to ecology by providing new insight on the drivers of bat and insect activity and the thermal dynamics of a predator-prey system in different environmental conditions.

Tese de doutoramento em Sistemas Sustentáveis de Energia (SES), apresentada ao Departamento de Engenharia Civil da Faculdade de Ciências e Tecnologia da Universidade de Coimbra<br>Linear and point thermal bridges (LTBs and PTBs) increase the heat loss of a building envelope in winter conditions due to a concentration of heat fluxes, which depends on the properties of the material(s) and the geometrical characteristics of the thermal bridge. Furthermore, in these two-dimensional (2D) and three-dimensional (3D) junctions, the surface temperatures are normally significantly lower, which increases the risk of surface condensation and the occurrence of building pathologies. Therefore, it is of the utmost importance to evaluate LTBs and PTBs at the design stage of the building and assess their contribution to the energy performance of buildings. The steady-state analysis of the energy performance of buildings normally takes into account the LTBs, but the PTBs’ contribution tends to be neglected. Whole building dynamic simulation studies, however, usually only assume the one-dimensional (1D) heat transfer through the building envelope and fail to consider the multidimensional heat flows through the linear and point thermal bridges. However, it is very important to predict the thermal behaviour of LTBs and PTBs dynamically, since the influence of the thermal inertia of materials can be considered and high performance solutions can be chosen to reduce the thermal bridging effect. This will prevent the development of pathologies associated with thermal bridges and increase the overall energy performance of the building. Most studies on dynamic thermal bridging analysis use simplified techniques that do not give accurate information about the dynamic behaviour of linear and point thermal bridges. Therefore, more realistic models are required that can provide more accurate results and a better knowledge of the dynamic thermal bridges’ behaviour. The main goal set for this research was to analyse the dynamic effect of geometrical linear and point thermal bridges of buildings, such as 2D and 3D building corners, using the boundary element method (BEM) formulated in the frequency domain. For this, multidimensional numerical modelling tools were specially built to study the transient heat diffusion through LTBs and PTBs, using 2D and 3D BEM formulations. These tools enabled the computation of the temperature distribution and heat fluxes through the linear and point thermal bridges, over time. The numerical models were first verified against analytical schemes, known for regular geometries, and then were experimental validated using hot box measurements, simulating the dynamic thermal behaviour of a 2D and a 3D corner of a wooden building. Several numerical simulations of the transient heat transfer through 2D and 3D building corners were performed to illustrate the applicability of the proposed BEM models and to evaluate the thermal bridging effect over time. The influence of the constructive solutions and the external temperature variation on the dynamic thermal behaviour of LTB and PTB was also analysed. The importance of modelling linear and point thermal bridges dynamically was demonstrated. It was concluded that a static analysis underestimates the linear thermal transmittances and overestimates the wall’s surface temperature in the vicinity of the LTB. Moreover, the additional heat flow through the PTBs analysed was found to be significantly lower than the heat flow through the adjacent building elements and through the LTB junctions. However, the evaluation of the dynamic point thermal bridging effect in building envelope details can be very important when it comes to overcoming moisture condensation problems, since lower surface temperatures are registered in the vicinity of the PTBs under dynamic conditions. The dynamic behaviour of the linear and point thermal bridges clearly depends on the thermal properties of the materials and the position of the insulation layer.<br>As pontes térmicas lineares e pontuais (PTL e PTP) são caracterizadas por uma concentração dos fluxos de calor, que depende das suas características geométricas e das propriedades térmicas dos materiais. Esta concentração de fluxos é responsável pelo aumento das perdas de calor através da envolvente do edifício, durante a estação de aquecimento. Para além disso, nestas ligações bidimensionais (2D) e tridimensionais (3D), as temperaturas na superfície são normalmente significativamente mais baixas, aumentando o risco de condensações superficiais e a ocorrência de patologias no edifício. Por este motivo, é de extrema importância avaliar as PTL e PTP na fase de projeto dos edifícios, bem como determinar a sua contribuição no desempenho energético dos mesmos. A análise estática do desempenho energético de edifícios considera normalmente a existência de PTL, contudo a contribuição das PTP tende a ser desprezada. Por outro lado, os estudos de simulação dinâmica de edifícios, por norma, assumem apenas a transferência de calor unidimensional (1D) através da envolvente e não consideram os fluxos de calor multidimensionais que ocorrem através das PTL e PTP. No entanto, é muito importante prever o comportamento térmico dinâmico destas ligações, de modo a considerar a influência da inércia térmica dos materiais e assim ser possível escolher soluções construtivas de elevado desempenho que permitam reduzir o efeito da ponte térmica. Este tipo de análise permitirá prevenir o desenvolvimento de patologias associadas às pontes térmicas e aumentar o desempenho energético global do edifício. A maior parte dos estudos de análise dinâmica de PTL e PTP usam metodologias simplificadas e não fornecem informações precisas sobre o comportamento térmico dinâmico das mesmas. Logo, são necessários modelos mais realistas, que permitam obter resultados mais precisos e um maior conhecimento sobre o comportamento térmico dinâmico das pontes térmicas. O principal objetivo deste trabalho de investigação foi analisar o efeito dinâmico de pontes térmicas geométricas, lineares e pontuais, tais como os cantos 2D e 3D da envolvente de edifícios, através do Método dos Elementos de Fronteira (BEM) formulado no domínio da frequência. Para isso, foram desenvolvidas ferramentas de modelação numérica multidimensionais para o estudo da difusão de calor, em regime transiente, usando formulações 2D e 3D do BEM. Estas ferramentas permitiram calcular a distribuição de temperaturas e os fluxos de calor ao longo do tempo nas pontes térmicas lineares e pontuais. Os modelos numéricos foram primeiro verificados através de soluções analíticas, conhecidas para geometrias regulares. Posteriormente, estes modelos foram validados experimentalmente, através de medições realizadas numa hot box que simulam o comportamento térmico dinâmico de cantos 2D e 3D de um edifício em madeira. Foram realizadas várias simulações numéricas da transferência de calor transiente em cantos 2D e 3D de edifícios para ilustrar a aplicabilidade dos modelos BEM propostos e para avaliar o efeito das pontes térmicas ao longo do tempo. Foi ainda analisada a influência das soluções construtivas e da variação da temperatura exterior no comportamento térmico dinâmico das PTL e das PTP. A importância da modelação das pontes térmicas, em regime dinâmico, foi demonstrada. Este estudo permitiu concluir que uma análise estática subestima as transmissões térmicas lineares e sobrestima as temperaturas superficiais na PTL. Além disso, verificou-se que o fluxo de calor adicional através das PTP analisadas é significativamente menor do que o fluxo de calor que ocorre nos elementos construtivos adjacentes e nas PTL. No entanto, a avaliação do efeito dinâmico da PTP em pormenores construtivos da envolvente do edifício pode ser muito importante quando se trata de superar problemas de humidade, uma vez que, em condições dinâmicas, as temperaturas superficiais registadas nas PTP são mais baixas. O comportamento térmico dinâmico das pontes térmicas lineares e pontuais depende claramente das propriedades térmicas dos materiais e da localização da camada de isolamento.<br>Projecto "Slimframe” - POCI-01-0247-FEDER-003408) e Projecto “ClimTestE+” - POCI-01-0247-FEDER-003344 / LISBOA-01-0247-FEDER-003344