A escolha do propulsor é uma etapa-chave no projeto de um navio. Muito do que se espera qualitativamente do desempenho de uma embarcação implica em economia de energia, em condições de operação e habitabilidade adequadas à tripulação, e em baixo custo de manutenção dos elementos estruturais e dos equipamentos. Essas questões estão diretamente relacionadas ao aproveitamento de combustível pelo sistema propulsivo e à propagação de vibração, cabendo ao propulsor um papel significativo para a performance do navio em ambos os aspectos. Por esta razão, a dissertação propõe a avaliação de propulsores navais com respeito à excitação de vibração e à eficiência, quando atuando em esteira não uniforme. A dissertação inicia-se com uma abordagem resumida especificamente sobre os estudos já realizados sobre indução de vibração pelo propulsor focados nas chamadas forças de mancal. Em seguida, revisam-se os assuntos pertinentes ao projeto de propulsor, isto é, definição de sua geometria, de seus coeficientes de operação, e dos métodos teóricos e computacionais utilizados para estudar seu comportamento hidrodinâmico. A metodologia do trabalho fundamenta-se no estudo paramétrico da geometria do hélice, objetivando identificar a influência de cada um dos parâmetros de projeto do propulsor nos dois aspectos destacados no início. As diversas configurações geométricas são submetidas a campos de velocidades advindos de diferentes navios, que representam três grupos de embarcações (navios série 60, porta-containers e navios-tanque), com o intuito de verificar as diferentes tendências de comportamento possíveis. Para a execução computacional, elabora-se uma rotina encarregada de sistematizar o processo de alterações geométricas, encaminhar os numerosos casos à análise hidrodinâmica, realizar o processo de integração casco-hélice e o pós-processamento dos resultados. A análise hidrodinâmica citada é feita através do uso de um software comercial, que, baseado na teoria do escoamento potencial, aplica o método dos painéis para a resolução do escoamento ao redor do propulsor. Os esforços excitados pelo hélice são traduzidos em critérios objetivos, baseados na transmissão de vibração através do eixo, que, associados ao critério de eficiência propulsora e à restrição relativa à ocorrência de cavitação, avaliam os casos e identificam-se o comportamento dos parâmetros de projeto. Obtém-se, como conclusão, uma metodologia de avaliação aplicável em outros casos de propulsores e navios. / The propeller choice is a key-step of the ship design. The high quality of the vessel performance requires energy economy, appropriated operating and environmental conditions for the crew, and low maintenance costs of structural elements and equipment. These questions consider directly fuel consumption by the propulsion system and the transmitted vibration, regarding the propeller an important role in the ships performance about both attributes. For this reason, the evaluation of marine propellers, regarding the induced vibration and the propulsive efficiency under a non-uniform inflow, is proposed. The study begins with a briefly state of the art about the propeller induced vibration focused in bearing forces. Then, a propeller design overview is made about subjects such as geometry definition, operation coefficients, and theoretical and computed methods for studying its hydrodynamic behavior. The methodology is based on a parametric study of the propeller geometry, in order to identify the influence of each of the propeller design parameters in both aspects highlighted in beginning. The several geometric configurations are submitted to the wake fields from different ships, that represent three groups of vessels (60 series, containers and tankers), then different tendencies of behavior can be expected. For computational execution, a routine is in charge of systematizing the process of geometrical parameterization, send the cases to the hydrodynamic analysis, make the hull-propeller integration and post process the data. The hydrodynamic analysis is compelled by a HSVA® software, which applies the panel method in the propeller flow, based on potential flow theory. The propeller induced bearing forces are converted in objective criteria, based on vibration transmission through the shaft, which, combined with the propulsive efficiency criteria and the cavitation restriction, evaluate the propeller geometric configurations. As a conclusion, a propeller evaluation methodology applicable to another kind of propeller series and wake fields is obtained.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第14135号 / 工博第2969号 / 新制||工||1441(附属図書館) / 26441 / UT51-2008-N452 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 杉浦 邦征, 准教授 白土 博通, 准教授 宇都宮 智昭 / 学位規則第4条第1項該当 / Doctor of Engineering / Kyoto University / DFAM

A footbridge in Slussen is planned to be built and will connect the area of Gamla Stan with Sodermalm. As an increasing number of footbridges with large span tend to become more flexible and light these days, the corresponding dynamic problems due to decreased stiffness and mass draw much more attention. Specifically speaking, reduced stiffness and mass lead to smaller natural frequencies, which make the structure more sensitive to pedestrian-induced loading, especially in lateral direction. Fortunately, in this master thesis, only the vibration in vertical direction is focused due to that the footbridge in Slussen project uses enough lateral bracings to make sure that the safety of lateral vibration is kept at an acceptable level. In order to analyze dynamic response of the footbridge, the real footbridge structure is converted into a FE model by the commercial software LUSAS. In this thesis, four different kinds of critical standards are introduced, which are Sétra [8], Swedish standard Bro 2004 [9], ISO 10137 [5] and Eurocode respectively. By comparing these four criteria, Sétra and Eurocode are finally chosen to be the standard and guidelines for this project. They give the basic theories about how to model the pedestrian loading and provide critical values to check the accelerations in both vertical and lateral direction. By using FE software LUSAS, natural frequencies of the footbridge and the corresponding mode shapes can be calculated directly. Then, according to these results and relevant theories introduced by Sétra, the pedestrian loading can be modeled and the acceleration response of any specific mode can be obtained as well. Finally, based on the worst case with excessive acceleration, the methods to reduce dynamic response will be presented. Commonly, there are two ways to reduce acceleration response. One method is to increase the stiffness of the structure. However, the increased stiffness is always accompanied with increased mass of the structure. Because of this reason, the other way that installing dampers is widely used in recent years. In this thesis, the tuned mass dampers (TMDs) are introduced in detail as well as the information about the design principles of it. With important parameters known, TMDs can be added to the model to check how the accelerations can be reduced.

Interaction of fluctuating vortex shedding with blade vibration can lead to a new class of aeromechanical instability referred as Non-synchronous vibrations. Investigating a well-known case that shows similar NSV features such as a circular cylinder can develop the understanding of physics behind NSV. A common approach to further investigating the vortex induced vibration is to control the motion of the cylinder and allowing the response of the wake to the motion to be studied in isolation. It has been found very important to carefully match the experimental conditions between free and controlled vibration. Many of research in the field of vortex induced vibration apply a rigid cylinder mounted horizontally and moving transversely to the flow stream as a paradigm for understanding the physics behind this phenomenon. Regarding the difficulties of implementation of vertically moving cylinder in experimental study, vortex dynamic and lock-in behavior of eccentrically rotating cylinder is studied in this M.Sc. Thesis. The main focus of this research is to understand to what extend a general feature of free vortex-induced vibration can be observed in the case of eccentrically rotating cylinder. If the present case captures the essential characteristics of freely oscillating cylinder the results of the forced motion via eccentrically rotating cylinder can be applied to predict the motion of an elastically mounted body. To do so a CFD model is established to predict the response, vorticity structure in near wake, timing of vortex shedding and the range of lock-in region over specific parameter space of the introduced alternative case. A commercial CFD code, Ansys/CFX, was implemented to perform this numerical study. Existences of synchronization region, striking similarity in lift force coefficient and wake mode have been observed in the current study.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19994号 / 工博第4238号 / 新制||工||1656(附属図書館) / 33090 / 京都大学大学院工学研究科原子核工学専攻 / (主査)教授 功刀 資彰, 教授 佐々木 隆之, 准教授 横峯 健彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21352号 / 工博第4511号 / 新制||工||1702(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 八木 知己, 教授 清野 純史, 教授 高橋 良和 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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京都大学 / 新制・課程博士 / 博士(工学) / 甲第24293号 / 工博第5066号 / 新制||工||1791(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 八木 知己, 教授 KIM Chul-Woo, 教授 高橋 良和 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The resilience of power infrastructure against environmental challenges, particularly wind-induced vibrations, is crucial for ensuring the reliability and longevity of overhead power lines. This dissertation extends the development of the Mobile Damping Robot (MDR) as a novel solution for mitigating wind-induced vibrations through adaptive repositioning and energy harvesting capabilities. Through comprehensive experimental and numerical analyses, the research delineates the design, optimization, and application of the MDR, encompassing its dynamic adaptability and energy harvesting potential in response to varying wind conditions. The study begins with the development and validation of a linearized model for the MDR, transitioning to advanced nonlinear models that more accurately depict the complex interactions between the robot, cable system, and environmental forces. A global stability analysis provides crucial insights into the operational limits and safety parameters of the system. Further, the research explores a multi-degree-of-freedom system model to evaluate the MDR's efficacy in real-world scenarios, emphasizing its energy harvesting efficiency and potential for sustainable operation. Findings from this research show the clear promise for the development of the MDR with the consideration of the nonlinear dynamics in play between the robot, the cable, and the wind. This work lays a foundational framework for future innovations in infrastructure maintenance, paving the way for the practical implementation of mobile damping technologies in energy systems. / Doctor of Philosophy / Across the United States, over 160,000 miles of power lines crisscross the landscape, powering everything from small homes to large industrial complexes. These critical infrastructures, however, are constantly battered by the elements, particularly by strong winds capable of inducing Aeolian vibrations. Such vibrations lead to oscillations in the power lines due to wind forces, potentially causing severe structural damage, compromising public safety, and incurring considerable economic costs. In response to these challenges, various mitigation strategies have been employed. Traditional methods include regular inspections carried out by foot patrols, helicopters, or sophisticated inspection robots, though these approaches are notably resource-intensive and costly. Additionally, mechanical devices like Stockbridge dampers are utilized to dampen the vibrations, but they suffer from efficiency issues when misaligned with the vibration nodes. This dissertation extends the study to an innovative solution to overcome these limitations: a mobile damping robot designed to navigate along power lines and autonomously position itself at the points of highest vibration amplitude, thereby optimizing vibration dampening. This study delves into the feasibility and effectiveness of such a solution, supported by thorough numerical simulations. The aim is to demonstrate how this advanced approach could redefine maintenance strategies for power lines, enhancing their resilience against wind-induced vibrations and reducing the reliance on laborious inspection methods and static damping devices with limited efficiency.