No description available.

No description available.

<p> A brief comparison between the ROM models is made in this study.</p>

System Dynamics has been applied to various fields in the natural and social sciences. There still remain countless problems and issues where understanding is lacking and the dominant theories are event-oriented rather than dynamic in nature. One such research area is the application of the traditional systems engineering process in new technology development. The Navy has been experiencing large cost overruns in projects dealing with the implementation of new technologies on complex ship systems. We believe that there is a lack of understanding of the dynamic nature of the technology development process undertaken by aircraft-carrier builders and planners. Our research effort is to better understand the dynamics prevalent in the new technology development process and we use a dynamic modeling technique, namely, System Dynamics in our study. We provide a comprehensive knowledge elicitation process in which members from the Newport News Shipbuilding, the Naval Sea Command Cost Estimating Group, and the Virginia Tech System Performance Laboratory take part in a group model building exercise. We build a System Dynamics model based on the information and data obtained from the experts. Our investigation of the dynamics yields two dominant behaviors that characterize the technology development process. These two dynamic behaviors are damped oscillation and goal seeking. Furthermore, we propose and investigate four dynamic hypotheses in the system. For the current structure of the model, we see that an increase in the complexity of new technologies leads to an increase in the total costs, whereas a increase in the technology maturity leads to a decrease in the total costs in the technology development process. Another interesting insight is that an increase in training leads to a decrease in total costs. / Master of Science

Este trabalho apresenta e compara alguns meios para o estudo do comportamento dinâmico de uma lavadora de roupas de eixo vertical durante o processo de extração de água das roupas, também conhecido como centrifugação. Os três métodos utilizados para estudar o comportamento dinâmico de uma lavadora de roupas de eixo vertical foram: analítico, experimental e simulação através de multicorpos. O interesse nesta etapa é devido ao fato dos problemas de vibração de uma lavadora ocorrerem principalmente durante a centrifugação. A modelagem de uma lavadora de roupas durante a etapa de centrifugação permite a obtenção de seu comportamento dinâmico bem como de suas principais características. Um outro tópico estudado neste trabalho foi o fenômeno de deslocamento da lavadora, um dos principais motivos de reclamação dos usuários de lavadoras de roupa automáticas. / This work presents and compares some ways to study the dynamic behavior of a vertical axis washing machine during the water extraction process, also called spinning stage. The three methodologies used to study the dynamic behavior of a vertical axis washing machine area: analytical, experimental and simulation using Multi Body System. The interest in this stage is due to the fact that the main vibration problems of an automatic washing machine occur in the spinning cycle. Since the unbalance force that causes the vibration problems is centrifugal in nature, this makes intuitive sense as the rotational speed of the basket is the largest during the spin extraction cycle. Thus, modeling the washing machine during the spinning cycle allow us to get its dynamic behavior as well as the main characteristics of this behavior. Another topic studied in this work was the walking phenomenon, the main complaint of the users.

Made available in DSpace on 2017-07-21T19:25:46Z (GMT). No. of bitstreams: 1 Regiane Siqueira.pdf: 5314044 bytes, checksum: c87c036209bfc1afaae749bad20579fb (MD5) Previous issue date: 2015-04-16 / This study proposes to analyze mathematical models that describe the dynamics of populations, namely, sets of organisms that may or may not belong to the same species but have similar behavior as relates to their dynamics. It is specially treated with models of cell populations that consider the delay time, which are described by dierential equations with delay. The analysis is realized in two mathematical with models, the rst describes the interaction of tumor cells with the immune system. It is considered that the immune system is constituted by resting cells and hunting cells, as well as, the resting cells become cells hunting but the conversion is not straightforward, requiring shaping by delayed dierential equations. The second describes a model for treatment of cancer by chemotherapy where there is metastasis of a primary to a secondary focus by tumor cells. We observe the interactions between normal and tumor cells as being competitive for the available resources, and it is thought the chemotherapy agent as a predator in normal and cancer cells. Metastasis can occur with a delay time, which leads to delayed dierential equations. Next study is a model for treating of brain tumor by chemotherapy. We propose a system of coupled dierential equations that model brain tumour with treatment by chemotherapy, which considers interactions among the glial cells, the glioma, the neurons, and the chemotherapeutic agents. We study the conditions for the glioma growth to be eliminated, and identify values of the parameters for which the inhibition of the glioma growth is obtained with a minimal loss of healthy cells. / Neste trabalho, propoe-se analisar modelos matematicos que descrevem a dinâmica de populações, ou seja, conjuntos de organismos que podem ou n~ao pertencer a mesma espécie, porem possuem comportamento semelhante no que refere-se a sua dinâmica. São tratados de forma especial os modelos de populações de celulas onde considera-se o tempo de retardo, isto e, aqueles descritos por equações diferenciais com atraso. Primeiramente e realizada a análise em dois modelos matemáticos, o primeiro descreve a interação das células tumorais com o sistema imunologico. Considera-se que o sistema imunologico e constituído por células de repouso e células de caça, sendo que as de repouso se convertem em celulas de caça, mas a conversão não e imediata, havendo necessidade de modelar por equações diferencias com atraso. O segundo descreve um modelo para tratamento do câncer por quimioterapia, onde ha metástase de um foco primário para um foco secundário pelas células tumorais. Observa-se as interações entre as células normais e tumorais como sendo competitivas para os recursos disponiveis, e e pensado no agente de quimioterapia como um predador em ambas as celulas, normais e cancer genas. A metastase pode ocorrer com um tempo de retardo, o que da origem a equações diferencias com atraso. Em seguida e descrito um modelo para o tratamento de um tumor cerebral por quimioterapia. E proposto um sistema de equações diferenciais ordinarias para modelar o tumor no cerebro em tratamento por quimioterapia, que considera as interações entre as celulas da glia, o glioma, os neurônios e os agentes quimioterapicos. Analisa-se as condições para o crescimento do glioma a ser eliminado, e identica-se os valores de parâmetros para os quais a inibição do crescimento do glioma e obtida com um mínimo de perda de células saudáveis.

Na sociedade atual as estruturas de linhas de transmissão são consideradas componentes essenciais do sistema de infraestrutura urbana. Sua função é a de transmitir a eletricidade gerada nas fontes de produção até o consumidor através de uma rede de distribuição. Este tipo de estruturas por sua extensão, exposição e variações topográficas, se mostram vulneráveis ao carregamento dinâmico de ventos originados a partir tormentas elétricas, tais como downbursts e tornados. No Brasil tem-se observado nos últimos tempos um aumento de acidentes neste tipo de estrutura, principalmente devido à incidência de fortes ventos. No presente trabalho estuda-se o comportamento dinâmico de um trecho de linha de transmissão da empresa Eletrobrás FURNAS quando submetido à ação de ventos provenientes de downburst. Na pesquisa foram identificados os principais modelos analíticos disponíveis na literatura que oferecem o campo de velocidades horizontais e verticais médias e a componente flutuante. Com base e alguns dos modelos identificados na revisão bibliográfica, implementou-se um programa computacional capaz de simular todas as componentes do campo de velocidades de um downburst em movimento. A partir do programa implementado foi realizado um estudo paramétrico onde identificou-se a combinação de variáveis do evento que provoca a maior energia cinética armazenada. Finalmente é apresentada uma revisão estrutural dos montantes da torre central da linha modelada, através da análise da relação demanda/capacidade na altura da coluna. Dos resultados obtidos, pode-se concluir que a combinação de variáveis que provoca os resultados de forças internas mais críticos varia em relação a cada componente da linha considerado. O estudo de sensibilidade das variáveis envolvidas nos modelos implementados revelou que existe um incremento monotônico crescente da energia cinética armazenada com o aumento dos parâmetros e para a maioria dos casos, exceto quando =500 . Da flutuação e sua influência no comportamento dinâmico na linha analisada, conclui-se que a consideração das flutuações na resposta dinâmica dos cabos condutores e para-raios pode ser desprezada, fato que foi comprovado através dos valores obtidos na inclinação das linhas de tendência realizadas. / Transmission Lines (TL) are considered one of the essential components of the urban infrastructure. Their role is to transmit electricity from sources of production to the distribution system and then to consumers. This type of structure for its length, exposure and topographical variations, show themselves vulnerable to dynamic loading winds originated from electrical storms such as tornadoes and downbursts. In Brazil, it has been observed recently, an increase in the accidents of this type of structure, primarily due to incidence of strong winds. In the present research, is analyzed the dynamic behavior of a transmission line system of Eletrobras Furnas Company when subjected to downburst. In the investigation, the main analytical models available in the literature that offer the wind field of horizontal and vertical speeds and the fluctuating component were identified. Based on some of the models identified in the literature review, was implemented a computer program capable of simulating all components of the velocity of a moving downburst. Based on the implemented program was conducted a parametric study in order to identify the combination of variables that causes the greatest kinetic stored energy. Finally is presented a structural review of the columns of the central tower of the system, by examining the demand/capacity relationship. Regarding to the parametric study, it was found that the combination of variables which causes the most critical internal forces varies for each component of the line considered. The sensibility study of the variables involved the models used in this study revealed that there is a growing monotonic increase in the stored energy with the accretion of and 1.parameters for most of the cases, except when 0=500 . Analyses conducted using the fluctuations in the mean wind field reveal that the resonant response of the conductor and ground wire cables can be neglected, a fact that was confirmed by the values obtained from the slope of the trend lines held.

While wind energy has witnessed faster growth than any other renewable energy source in recent years, two issues—the decreasing availability of large land expanses for new wind farms and transmission difficulties arising from siting wind farms in remote regions far from load centers—have slowed down this growth considerably. Siting wind turbines offshore places the generating capacity closer to population and load centers; thus, reducing grid congestion. Also, at offshore sites, one can expect higher wind speeds, decreased turbulence, and reduced noise and visual impact constraints. Offshore wind turbines that have been built thus far have had foundations (such as monopiles or jacket structures) that have extended to the seabed. Such offshore wind turbines have thus been confined to shallow waters closer to the shore. Sites farther offshore provide better wind resources (i.e., less turbulence and smoother, stronger winds) while also reducing visual impact, noise, etc. However, deeper waters encountered at such sites make bottom-supported turbines less economical. Wind turbines mounted atop floating platforms are, thus, being considered for deeper water offshore sites. Various floating platform concepts are under consideration; the chief differences among them arise from the way they provide stability to counter the large mass of the rotor-nacelle assembly located high above the mean water level. Of these alternative concepts, the spar buoy platform is a deep draft structure with a low center of gravity, below the center of buoyancy. Reliability analysis of a spar buoy-supported floating offshore 5MW wind turbine based on stochastic simulation is the subject of this study. Environmental data from a selected deepwater reference site are employed in the numerical studies. Using time-domain simulations, the dynamic behavior of the coupled platform-turbine system is studied; statistics of tower and rotor loads as well as platform motions are estimated and critical combinations of wind speed and wave height identified. / text

Na sociedade atual as estruturas de linhas de transmissão são consideradas componentes essenciais do sistema de infraestrutura urbana. Sua função é a de transmitir a eletricidade gerada nas fontes de produção até o consumidor através de uma rede de distribuição. Este tipo de estruturas por sua extensão, exposição e variações topográficas, se mostram vulneráveis ao carregamento dinâmico de ventos originados a partir tormentas elétricas, tais como downbursts e tornados. No Brasil tem-se observado nos últimos tempos um aumento de acidentes neste tipo de estrutura, principalmente devido à incidência de fortes ventos. No presente trabalho estuda-se o comportamento dinâmico de um trecho de linha de transmissão da empresa Eletrobrás FURNAS quando submetido à ação de ventos provenientes de downburst. Na pesquisa foram identificados os principais modelos analíticos disponíveis na literatura que oferecem o campo de velocidades horizontais e verticais médias e a componente flutuante. Com base e alguns dos modelos identificados na revisão bibliográfica, implementou-se um programa computacional capaz de simular todas as componentes do campo de velocidades de um downburst em movimento. A partir do programa implementado foi realizado um estudo paramétrico onde identificou-se a combinação de variáveis do evento que provoca a maior energia cinética armazenada. Finalmente é apresentada uma revisão estrutural dos montantes da torre central da linha modelada, através da análise da relação demanda/capacidade na altura da coluna. Dos resultados obtidos, pode-se concluir que a combinação de variáveis que provoca os resultados de forças internas mais críticos varia em relação a cada componente da linha considerado. O estudo de sensibilidade das variáveis envolvidas nos modelos implementados revelou que existe um incremento monotônico crescente da energia cinética armazenada com o aumento dos parâmetros e para a maioria dos casos, exceto quando =500 . Da flutuação e sua influência no comportamento dinâmico na linha analisada, conclui-se que a consideração das flutuações na resposta dinâmica dos cabos condutores e para-raios pode ser desprezada, fato que foi comprovado através dos valores obtidos na inclinação das linhas de tendência realizadas. / Transmission Lines (TL) are considered one of the essential components of the urban infrastructure. Their role is to transmit electricity from sources of production to the distribution system and then to consumers. This type of structure for its length, exposure and topographical variations, show themselves vulnerable to dynamic loading winds originated from electrical storms such as tornadoes and downbursts. In Brazil, it has been observed recently, an increase in the accidents of this type of structure, primarily due to incidence of strong winds. In the present research, is analyzed the dynamic behavior of a transmission line system of Eletrobras Furnas Company when subjected to downburst. In the investigation, the main analytical models available in the literature that offer the wind field of horizontal and vertical speeds and the fluctuating component were identified. Based on some of the models identified in the literature review, was implemented a computer program capable of simulating all components of the velocity of a moving downburst. Based on the implemented program was conducted a parametric study in order to identify the combination of variables that causes the greatest kinetic stored energy. Finally is presented a structural review of the columns of the central tower of the system, by examining the demand/capacity relationship. Regarding to the parametric study, it was found that the combination of variables which causes the most critical internal forces varies for each component of the line considered. The sensibility study of the variables involved the models used in this study revealed that there is a growing monotonic increase in the stored energy with the accretion of and 1.parameters for most of the cases, except when 0=500 . Analyses conducted using the fluctuations in the mean wind field reveal that the resonant response of the conductor and ground wire cables can be neglected, a fact that was confirmed by the values obtained from the slope of the trend lines held.

abstract: The stability of nanocrystalline microstructural features allows structural materials to be synthesized and tested in ways that have heretofore been pursued only on a limited basis, especially under dynamic loading combined with temperature effects. Thus, a recently developed, stable nanocrystalline alloy is analyzed here for quasi-static (<100 s-1) and dynamic loading (103 to 104 s-1) under uniaxial compression and tension at multiple temperatures ranging from 298-1073 K. After mechanical tests, microstructures are analyzed and possible deformation mechanisms are proposed. Following this, strain and strain rate history effects on mechanical behavior are analyzed using a combination of quasi-static and dynamic strain rate Bauschinger testing. The stable nanocrystalline material is found to exhibit limited flow stress increase with increasing strain rate as compared to that of both pure, coarse grained and nanocrystalline Cu. Further, the material microstructural features, which includes Ta nano-dispersions, is seen to pin dislocation at quasi-static strain rates, but the deformation becomes dominated by twin nucleation at high strain rates. These twins are pinned from further growth past nucleation by the Ta nano-dispersions. Testing of thermal and load history effects on the mechanical behavior reveals that when thermal energy is increased beyond 200 °C, an upturn in flow stress is present at strain rates below 104 s-1. However, in this study, this simple assumption, established 50-years ago, is shown to break-down when the average grain size and microstructural length-scale is decreased and stabilized below 100nm. This divergent strain-rate behavior is attributed to a unique microstructure that alters slip-processes and their interactions with phonons; thus enabling materials response with a constant flow-stress even at extreme conditions. Hence, the present study provides a pathway for designing and synthesizing a new-level of tough and high-energy absorbing materials. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2017