41 research outputs found

    Estudo teórico e experimental da aplicação de meios porosos cerùmicos em LHP e CPL

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    Tese (doutorado) - Universidade Federal de Santa Catarina, Centro TecnolĂłgico, Programa de PĂłs-Graduaçao em Engenharia MecĂąnica, FlorianĂłpolis, 2010O controle tĂ©rmico na indĂșstria eletrĂŽnica tem crescido em importĂąncia devido Ă  contĂ­nua diminuição de tamanho e ao aumento na potĂȘncia dos componentes. Nestas aplicaçÔes, buscam-se dispositivos eficientes de transferĂȘncia de calor, capazes de transferir grandes cargas de calor com uma diferença mĂ­nima de temperatura. Neste contexto, os tubos de calor (Heat Pipes - HPs), os tubos de calor em forma de circuito (Loop Heat Pipes - LHPs) e as bombas capilares (Capillary Pumping Loops - CPLs) sĂŁo alternativas confiĂĄveis e viĂĄveis para a dissipação de calor. Os evaporadores capilares da maioria dos LHPs e CPLs utilizam meios porosos feitos de metal ou de plĂĄstico. Neste trabalho, um meio poroso cerĂąmico Ă© proposto para aplicaçÔes em LHPs e CPLs. O desempenho do meio poroso cerĂąmico como evaporador capilar Ă© analisado teĂłrica e experimentalmente. Primeiramente, Ă© feita uma anĂĄlise teĂłrica de transferĂȘncia de calor e de massa de um evaporador capilar plano com uma estrutura porosa formada por uma ou duas camadas com propriedades diferentes. O meio poroso tem formato de um disco e Ă© instalado entre os canais de lĂ­quido e de vapor. Um fluxo de calor externo Ă© aplicado Ă  superfĂ­cie superior da estrutura porosa onde ocorre a evaporação do fluido de trabalho. A transferĂȘncia de calor e de massa Ă© modelada usando as equaçÔes macroscĂłpicas de conservação da energia e da massa. O fluido Ă© assumido incompressĂ­vel, prevalece o equilĂ­brio tĂ©rmico local e a Lei de Darcy Ă© usada para modelar o fluxo viscoso dentro do meio poroso. Os modelos desenvolvidos permitem verificar o efeito das variĂĄveis de projeto no desempenho do evaporador capilar tais como fluidos de trabalho, dimensĂ”es, permeabilidade, raio mĂ©dio de poros e condutividade tĂ©rmica do meio poroso. Para as anĂĄlises experimentais, testes de desempenho de dois LHPs, um utilizando acetona e o outro ĂĄgua como fluidos de trabalho, foram realizados para potĂȘncias de atĂ© 25 W. AlĂ©m disso, testes de desempenho de um CPL usando ĂĄgua foram realizados para potĂȘncias de atĂ© 30 W. O meio poroso cerĂąmico utilizado possui 50% de porosidade, distribuição de raio de poro entre 1 e 3E-6 m e uma permeabilidade de 1,5 E-14 m2. Considerando uma temperatura de operação limite de 100 °C e regime permanente, os LHPs foram capazes de transferir atĂ© 15 W para ĂĄgua e 25 W para acetona, enquanto que o CPL foi capaz de transferir atĂ© 30 W. Apesar do bom desempenho dos sistemas de bombeamento capilar avaliados, observou-se que mais pesquisas ainda sĂŁo necessĂĄrias, buscando otimizar as propriedades termofĂ­sicas do meio poroso cerĂąmico e melhorar o projeto dos LHPs e do CPL

    Hydration and thermal decomposition of cement/calcium-sulphate based materials

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    FSI-mallien soveltaminen modernien risteilylaivojen kansivarustelurakenteiden tuuliherÀtteisen vÀrÀhtelyn ennustamisessa

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    Recent market trends in the cruise industry aim to provide traditionally land-based attractions on cruise liners. This leads to the integration of special architectural features, such as water parks and amusement rides, in way of the cruise ships’ upper decks. Deck amusements are ideally lightweight structures that comprise of slender beams which aims to reduce the added weight on top decks. To ensure safety it is critical to understand the influence of wind loading introduced by Vortex-Induced Vibration (VIV) on the dynamic structural response. This thesis aims to determine the differences between one- and two-way coupled Fluid-Structure Interaction (FSI) analyses in the context of ship deck outfitting structures subjected to VIV. Accordingly, a large deck amusement structure is idealized as an aluminum portal frame, subject to a constant head wind. Transient one- and two-way coupled FSI simulations, based on Reynolds-Averaged Navier-Stokes (RANS) fluid dynamics model and linear elastic 3D FEA, are conducted using the commercial CFD software STAR-CCM+. Results are assessed and compared against quasi-static and quasi-dynamic beam element idealizations solved by NX Nastran. The investigation carried out reveals that vortex shedding remains at the original shedding frequency in the one-way coupled solution. However, the two-way coupled simulation demonstrates a clear lock-in of the vortex shedding to the portal frame’s natural frequency. Consequently, the dynamic loading experienced by the portal frame is significantly increased and the structure experiences resonant vibration when full two-way FSI coupling is considered. Neither the one-way coupled nor the quasi-dynamic analysis are able to capture these effects.ViimeisimmĂ€t suuntaukset risteilymarkkinoilla pyrkivĂ€t tuomaan laivoille elĂ€myksiĂ€, jotka ovat aiemmin olleet mahdollisia vain maissa. TĂ€mĂ€ on johtanut ennennĂ€kemĂ€ttömien rakenteiden, kuten vesipuistojen ja huvipuistolaitteiden integroimiseen modernien risteilyalusten ylĂ€kansille. Kyseiset rakenteet ovat ideaalisesti mahdollisimman kevyitĂ€ sekĂ€ koostuvat pitkistĂ€ ja suhteellisen ohuista palkeista, minkĂ€ tarkoituksena on vĂ€hentÀÀ ylimÀÀrĂ€istĂ€ painoa laivan ylĂ€kansilla. Riskien minimoimiseksi on ÀÀrimmĂ€isen tĂ€rkeÀÀ ymmĂ€rtÀÀ, miten jatkuva tuulikuormitus ja siitĂ€ johtuva pyörreherĂ€tteinen vĂ€rĂ€htely vaikuttavat rakenteiden dynaamiseen vasteeseen. TĂ€ssĂ€ diplomityössĂ€ selvitetÀÀn, kuinka yhteen ja kahteen suuntaan kytketyt neste-rakenne -vuorovaikutusanalyysit eroavat laivan kansivarustelurakenteiden tuuliherĂ€tteisen vĂ€rĂ€htelyn ennustamisessa. TĂ€tĂ€ varten suuri huvipuistorakenne on idealisoitu alumiinisena palkkikaarena, joka altistuu vakionopeuksiselle vastatuulelle. Rakenne analysoidaan aikariippuvaisilla yhteen ja kahteen suuntaan kytketyillĂ€ neste-rakenne -vuorovaikutussimulaatioilla. Virtausmallinnus perustuu Reynolds-keskiarvoistettuihin Navier-Stokes -yhtĂ€löihin ja rakennemalli lineaariselastiseen 3D-elementtimenetelmÀÀn. Simulaatiot lasketaan kĂ€yttĂ€en numeerista virtauslaskentaohjelmaa STAR-CCM+. Tuloksia arvioidaan ja verrataan kvasistaattisen ja kvasidynaamisen palkkielementtimallien kanssa. Palkkielementtimallit ratkaistaan kĂ€yttĂ€en kaupallista NX Nastran -ratkaisijaa. Diplomityön tulosten perusteella pyörteiden irtoaminen sĂ€ilyy alkuperĂ€isellĂ€ taajuudella laskettaessa yhteen suuntaan kytketyllĂ€ analyysilla. Kahteen suuntaan kytketty analyysi osoittaa, ettĂ€ pyörteiden irtoaminen lukkiutuu kaarirakenteen ominaistaajuudelle. TĂ€mĂ€n johdosta rakenteen dynaaminen kuormitus kasvaa merkittĂ€vĂ€sti ja palkkikaari vĂ€rĂ€htelee resonanssissa. Yhteen suuntaan kytketty laskenta tai arvioidut yksinkertaisemmat menetelmĂ€t eivĂ€t kykene mallintamaan nĂ€itĂ€ ilmiöitĂ€

    Contactless excitation for electric machines: high temperature superconducting flux pumps

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    With the intensification of global warming and climate change, the pace of transformation to a neutral-emission society is accelerating. In various sectors, electrification has become the absolute tendency to promote such a movement, where electric machines play an important role in the current power generation system. It is widely convinced that electric machines with very high power density are essential for future applications, which, however, can be hardly achieved by conventional technologies. Owing to the maturation of the second generation (2G) high temperature superconducting (HTS) technologies, it has been recognized that superconducting machine could be a competitive candidate to realize the vision. One significant obstacle that hinders the implementation of superconducting machines is how to provide the required magnetic fields, or in other words, how to energise them appropriately. Conventional direct injection is not suitable for HTS machines, because the current leads would bridge ambident temperature to the cryogenic environment, which can impose considerable heat load on the system and increase the operational cost. Thus, an efficient energisation method is demanded by HTS machines. As an emerging technology that can accumulate substantial flux in a closed loop without any physical contact, HTS flux pumps have been proposed as a promising solution. Among the existing developed HTS flux pumps, rotary HTS flux pumps, or so-called HTS dynamo, can output non-zero time-averaged DC voltage and charge the rest of the circuit if a closed loop has been formed. This type of flux pump is often employed together with HTS coils, where the HTS coils can potentially work in the persistent current mode, and act like electromagnets with a considerable magnetic field, having a wide range of applications in industry. The output characteristics of rotary HTS flux pumps have been extensively explored through experiments and finite element method (FEM) simulations, yet the work on constructing statistical models as an alternative approach to capture key characteristics has not been studied. In this thesis, a 2D FEM program has been developed to model the operation of rotary HTS flux pumps and evaluate the effects of different factors on the output voltage through parameter sweeping and analysis of variance. Typical design considerations, including the operating frequency, air gap, HTS tape width, and remanent flux density have been investigated, in particular, the bilateral effect of HTS tape width has been discovered and explained by looking at the averaged integration of the electric field over the HTS tape. Based on the data obtained from various simulations, regression analysis has been conducted through a collection of machine learning methods. It has been demonstrated that the output voltage of a rotary HTS flux pump can be obtained promptly with satisfactory accuracy via Gaussian process regression, aiming to provide a novel approach for future research and a powerful design tool for industrial applications using rotary HTS flux pumps. To enhance the applicability of the proposed statistical models, an updated FEM program has been built to take more parameters into account. The newly added parameters, namely the rotor radius and the width of permanent magnet, together with formerly included ones, should have covered all the key design parameters for a rotary HTS flux pump. Based on data collected from the FEM model, a well-trained semi-deep neural network (DNN) model with a back-propagation algorithm has been put forward and validated. The proposed DNN model is capable of quantifying the output voltage of a rotary HTS flux pump instantly with an overall accuracy of 98% with respect to the simulated values with all design parameters explicitly specified. The model possesses a powerful ability to characterize the output behaviour of rotary HTS flux pumps by integrating all design parameters, and the output characteristics of rotary HTS flux pumps have been successfully demonstrated and visualized using this model. Compared to conventional time-consuming FEM-based numerical models, the proposed DNN model has the advantages of fast learning, accurate computation, as well as strong programmability. Therefore, the DNN model can greatly facilitate the design and optimization process for rotary HTS flux pumps. An executable application has been developed accordingly based on the DNN model, which is believed to provide a useful tool for learners and designers of rotary HTS flux pumps. A new variant inspired by the working principles of rotary HTS flux pumps has been proposed and termed as stationary wave HTS flux pumps. The superiority of this type is that it has a simple structure without any moving components, and it utilises a controllable current-driven electromagnet to provide the required magnetic field. It has been demonstrated that the origin of the output voltage is determined by the asymmetric distribution of the dynamic resistance in the HTS tape, for which the electromagnet must be placed at such a position that its central line is not aligned with that of the HTS tape. A numerical model has been built to simulate the operation of a stationary wave HTS flux pump, based on which the output characteristics and dynamic resistance against various parameters have been investigated. Besides, accurate and reliable statistical models have been proposed to predict the open circuit voltage and effective dynamic resistance by adapting the previously developed machine learning techniques. The work presented in this PhD thesis can bring more insight into HTS flux pumps as an emerging promising contactless energisation technology, and the proposed statistical models can be particularly useful for the design and optimization of such devices

    Study of the mechanisms involved in the regulation of O2 consumption kinetics during exercise.

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    Lors d’un exercice Ă  une intensitĂ© au-dessous du seuil ventilatoire 1 (V1), la rĂ©ponse fondamentale de la cinĂ©tique de la consommation de dioxygĂšne (V̇ O2) s'Ă©lĂšve de maniĂšre mono- exponentielle, atteignant un Ă©tat stable aprĂšs quelques minutes. Cependant, lors de l'exercice Ă  une charge de travail constante au-dessus de V1, la cinĂ©tique de V̇ O2 est caractĂ©risĂ©e par un dĂ©but de l’état stable retardĂ© et une deuxiĂšme augmentation de V̇ O2 superposĂ©e Ă  la rĂ©ponse initiale de V̇ O2.Cette augmentation lente de V̇ O2 est appelĂ©e la composante lente (V̇ O2sc). Il a Ă©tĂ© proposĂ© que cet excĂšs de V̇ O2, reflet de l'inefficacitĂ© musculaire, provienne principalement des muscles exercitant; cependant, Ă  ce jour, les mĂ©canismes putatifs Ă  cette augmentation sont toujours mal compris. Plusieurs thĂ©ories ont Ă©tĂ© proposĂ©es, parmi lesquels : a) la combinaison de processus liĂ©s Ă  la fatigue nĂ©cessitant un recrutement supplĂ©mentaire de fibres pour compenser les fibres dĂ©jĂ  fatiguĂ©es, et b) l'influence potentielle des diffĂ©rents profils mĂ©taboliques de diffĂ©rentes populations de types de fibres. Le but de cette thĂšse est de clarifier et de nourrir le dĂ©bat sur les causes de V̇ O2sc, en particulier pour ces deux derniers paradigmes. Trois expĂ©rimentations ont Ă©tĂ© rĂ©alisĂ©es pour mesurer la concordance et les interfĂ©rences de diffĂ©rentes cinĂ©tiques de fibres musculaires et la fatigue musculaire avec la V̇ O2sc. Les rĂ©sultats de cette thĂšse sont les suivants : 1) Lors d’un exercice difficile, l'altĂ©ration des propriĂ©tĂ©s neuromusculaires des extenseurs du genou (reflĂ©tant les processus de fatigue) n’a Ă©tĂ© significativement rĂ©duite qu’aprĂšs 20-30 min d'exercice, alors que la V̇ O2sc avait fini de croitre. Ce rĂ©sultat suggĂšre qu'une relation temporelle entre la fatigue et la V̇ O2sc ne semble pas exister et, par consĂ©quent, le dĂ©veloppement de la fatigue n'est pas une condition essentielle pour le dĂ©veloppement de la V̇ O2sc. 2) La fonction neuromusculaire Ă©valuĂ©e Ă  l’aide d’une stimulation double (Ddb, 100 Hz) pendant l'exercice d'extension du genou n'a pas Ă©tĂ© altĂ©rĂ©e dans le domaine difficile. En revanche, dans le domaine intense, la diminution significative de la force maximale et du taux maximal de dĂ©veloppement de la force lors de la Ddb, reflĂ©taient des processus de fatigue et Ă©taient partiellement corrĂ©lĂ©es au dĂ©veloppement de V̇ O2sc relatif. Par consĂ©quent, les rĂ©sultats suggĂ©raient que la V̇ O2sc dans les domaines difficiles et intenses n'est pas le produit d'un mĂ©canisme identique. 3) Afin de construire une nouvelle courbe combinant les principes de Henneman et de superposition, les trois courbes de transitions (repos-modĂ©rĂ©e, modĂ©rĂ©e-difficile et difficile-intense) ont Ă©tĂ© alignĂ©es dans le temps et sommĂ©es. Les rĂ©sultats ont montrĂ© que globalement les paramĂštres de la cinĂ©tique de la courbe reconstruite n'Ă©taient pas significativement diffĂ©rents d'une transition depuis le repos Ă  un exercice d'intensitĂ© intense. Cela suggĂšre que le recrutement supplĂ©mentaire de fibres n'Ă©tait pas prĂ©sent et que l'apparition de V̇ O2sc est au moins liĂ©e, sinon le rĂ©sultat, des diffĂ©rentes propriĂ©tĂ©s mĂ©taboliques des fibres musculaires. Ces rĂ©sultats Ă©vidence, lors de l'exercice chez l'homme, que les processus de fatigue reprĂ©sentĂ©s par des altĂ©rations des propriĂ©tĂ©s neuromusculaires ne sont pas une condition sine qua non pour le dĂ©veloppement de la V̇ O2sc dans le domaine difficile, et que l'apparition du V̇ O2sc pourrait ĂȘtre le iĂ©tĂ©s mĂ©taboliques des fibres musculaires. -- Below the gas exchange threshold (GET), the fundamental response of O2 consumption (V̇ O2) kinetics rises monoexponentially, reaching a steady state after a few minutes. However, at a constant work rate exceeding the GET, the response is characterized by a delayed onset and a second rise in V̇ O2 superimposed on the initial V̇ O2 response. This slowly developing rise in V̇ O2 is termed the slow component (V̇ O2SC). This excess of V̇ O2, a reflection of muscle inefficiency, has been proposed to arise primarily from the exercising muscles; however, to date, the putative mechanisms are poorly understood. Several theories have been proposed, including the combination of fatigue-related processes requiring additional fiber recruitment to compensate for the already fatigued fibers and the potential influence of the different metabolic profiles of different fiber-type populations. The aim of this thesis is to clarify and nourish the debate on the causes of the V̇ O2SC, especially for these last two paradigms. Three different experiments were performed to measure the concordance and interferences of different kinetics of muscle fibers and muscle fatigue with the V̇ O2SC. The findings of this thesis are as follows: 1) During exercise at heavy intensity, the alteration in the neuromuscular properties of the knee extensors (reflecting fatigue processes) was significantly reduced after only 20-30 min of exercise, while the V̇ O2SC was stable. The results suggest that a temporal relationship between fatigue and the V̇ O2SC does not appear to exist; therefore, the development of fatigue is not an essential requirement to elicit the V̇ O2SC. 2) Neuromuscular function assessed through doublet stimulation (Ddb, 100Hz) during knee extension exercise was not altered in the heavy domain. In contrast, in the severe domain, the significant diminution in maximal force and maximal rate of force development during the Ddb, reflected fatigue processes and were partially correlated with the development of the relative V̇ O2sc. Therefore, the results suggest that the V̇ O2sc in the heavy and severe domains is not the product of an identical mechanism. 3) After constructing a new kinetics curve combining the Henneman and superposition principles, the three different intensity curves (moderate, heavy and severe) were time aligned and summed. The results showed that overall kinetics parameters from the reconstructed curve were not significantly different from one transition to severe-intensity exercise. This suggests that additional fiber recruitment was not present and that the appearance of the V̇ O2sc is at least related to, if not the result of, the different metabolic properties of muscle fibers. These results provide evidence in exercising humans that fatigue processes portrayed by alterations in neuromuscular properties are not a sine qua non for the development of the slow component in the heavy domain, and that, the appearance of the V̇ O2sc could be the result of the different metabolic properties of muscle fibers

    Modelling and Simulation of Human-Environment Interactions

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    Computational models provide intelligent environmental decision support systems to understand how human decisions are shaped by, and contribute to changes in, the environment. These models provide essential tools to tackle the important issues raised by climate change, including migrations and conflicts due to resource scarcity (e.g., water resources), while accounting for the necessity of co-managing ecosystems across a population of stakeholders with diverse goals. Such socio-environmental systems are characterized by their complexity, which is reflected by an abundance of open questions. This book explores several of these open questions, based on the contributions from over 50 authors. While several books account for methodological developments in modeling socio-environmental systems, our book is unique in combining case studies, methodological innovations, and a holistic approach to training the next generation of modelers. One chapter covers the ontological, epistemological, and ethical issues raised at the intersection of sustainability research and social simulation. In another chapter, we show that the benefits of simulations are not limited to managing complex eco-systems, as they can also serve an educational mission in teaching essential rules and thus improve systems thinking competencies in the broader population
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