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Thesis (Ph. D.)--University of Wisconsin--Madison, 1967. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

Made available in DSpace on 2014-06-11T19:23:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2003-08-29Bitstream added on 2014-06-13T19:09:40Z : No. of bitstreams: 1 carvalho_gb_me_ilha.pdf: 3399591 bytes, checksum: 93cf9ce80b863df9a4e44fe804f03aa6 (MD5) / O presente trabalho traz uma investigação experimental do escoamento em torno de um cilindro rotativo posicionado perpendicularmente à direção principal do escoamento, para números de Reynolds inferiores a 103. Os experimentos foram conduzidos em um túnel hidrodinâmico vertical, com seção de teste 146x146x500 mm e intensidade turbulenta da corrente livre inferior a 0,5%. O diâmetro do corpo de prova foi fixado em 6 mm, proporcionando um bloqueio sólido no interior da seção de testes pouco superior a 4%. A influência do número de Reynolds e da rotação específica do corpo de prova sobre a configuração do escoamento foi bastante estudada. A freqüência de emissão dos vórtices, necessária ao cálculo do número de Strouhal, foi determinada a partir da obtenção do sinal de velocidades, adquirido com o auxílio de um anemômetro de filme quente, ou através da técnica de contagem de fotogramas. Técnicas de visualização de escoamento foram, também, empregadas, em diferentes circunstâncias, tanto na análise qualitativa do escoamento, como para auxiliar o correto posicionamento das sondas de filme quente. Em vários ensaios, a visualização do escoamento por injeção de corante líquido a montante do corpo de prova foi utilizada, mostrando-se bastante eficiente, sobretudo no que concerne à qualidade das imagens obtidas. No entanto, esta técnica só possibilita a visualização de uma região bastante restrita do escoamento e, dependendo do posicionamento da agulha de injeção, diferentes configurações do escoamento podem ser observadas, dificultando a interpretação dos resultados. Para contornar esta situação, utilizou-se, também, a técnica de geração de bolhas de hidrogênio, que permite uma visão mais abrangente do campo de escoamento. De maneira geral, os resultados foram bastante satisfatórios quando comparados com a literatura, mostrando que a... . / This work presents an experimental investigation on the flow around a rotating cylinder positioned perpendicularly to the free stream, for Reynolds numbers up to 103. The experiments have been carried out inside a 146x146x500 mm test section of a vertical water tunnel, using a 6mm diameter cylinder, which has provided a lower than 4% blockage ratio inside the test section, under a less than 0.5% maximum free-stream turbulence intensity. The influence of both diameter-based Reynolds number and specific rotation of the cylinder on the flow configuration has been analyzed. The vortex shedding frequency, parameter necessary to evaluate the Strouhal number, has been determined from the velocity signal from hot film anemometer as well as directly through a framecounting technique. Two different methods of flow visualization, liquid dye and hydrogen bubble generation, has been also used under distinct circumstances, in order to provide a qualitative analysis of the flow, as well to obtain the correct location of the hot-film probes. In some experiments, flow patterns have been visualized by liquid dye injection upstream the test cylinder, propitiating a good image quality. Dye injection, however, allows for the visualization of a quite restricted area of the flow, in such a way that, depending on the needle location, several distinct flow configurations appear, making it very difficult the interpretation of the results. In order to mitigate those drawbacks, the technique of hydrogen bubble generation has also been employed, reaching for a far wider vision of the flow field. The achieved results have showed that the wake structure is strongly affected by the cylinder rotation, in such a way that the vortices generation can be totally inhibited for a values upper than 2, in the all range of the Reynolds number.

When a bluff body is placed in flow, vortices are shed downstream of the body. For the case of a bluff body with a circular cross-section (a cylinder) attached to a spring and a damper, when the frequency of vortex shedding is close to the natural frequency of the structure, the cylinder oscillates in a direction perpendicular to the flow. This is called Vortex Induced Vibration (VIV) and is a canonical problem in fluid-structure interactions. The majority of studies on VIV of a flexibly mounted rigid cylinder are for the cases where the flow direction is perpendicular to the long axis of the structure. However, in many engineering applications, such as cable stays in bridges, mooring lines of floating offshore wind turbines and undersea pipelines, the flow direction may not be perpendicular to the structure. The hypothesis is that the VIV in inclined cylinders is similar to a normal-incidence case, if only the component of the free stream velocity normal to the cylinder axis is considered. This is called the Independence Principle (IP). The IP neglects the effect of the axial component of the flow, which is legit for small angles of inclination, but not for large angles. In this Thesis, a series of experiments have been conducted on a flexibly-mounted rigid cylinder placed inclined to the oncoming flow with various angles of inclination (0° < θ < 75°) in a subcritical Reynolds number range of 500 – 4,000 to investigate how the angle of inclination affects VIV. In these experiments, a rigid cylinder was mounted on springs, and air bearings were used to reduce the structural damping of the system. The system was placed in the test section of a recirculating water tunnel and crossflow displacements were measured. Even at high angles of inclination, large-amplitude oscillations were observed. The IP was found to be valid for angles of inclination up to 55°. While for all inclinations the onset of lock-in was observed to be at the same normalized flow velocity, for angles of inclination larger than 55°, the lock-in region (the range of dimensionless flow velocities for which the cylinder oscillates with a large amplitude) was smaller. These results show that the influence of the axial component of the flow is non-negligible for angles of inclination larger than 55°.

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An investigation of the possible performance improvements of thin circular cylindrical shells through the use of the variable stiffness concept is presented. The variable stiffness concept implies that the stiffness parameters change spatially throughout the structure. This situation is achieved mainly through the use of curvilinear fibers within a fiber-reinforced composite laminate, though the possibility of thickness variations and discrete stiffening elements is also allowed. These three mechanisms are incorporated into the constitutive laws for thin shells through the use of Classical Lamination Theory. The existence of stiffness variation within the structure warrants a formulation of the static equilibrium equations from the most basic principles. The governing equations include sufficient detail to correctly model several types of nonlinearity, including the formation of a nonlinear shell boundary layer as well as the Brazier effect due to nonlinear bending of long cylinders. Stress analysis and initial buckling estimates are formulated for a general variable stiffness cylinder. Results and comparisons for several simplifications of these highly complex governing equations are presented so that the ensuing numerical solutions are considered reliable and efficient enough for in-depth optimization studies. Four distinct cases of loading and stiffness variation are chosen to investigate possible areas of improvement that the variable stiffness concept may offer over traditional constant stiffness and/or stiffened structures. The initial investigation deals with the simplest solution for cylindrical shells in which all quantities are constant around the circumference of the cylinder. This axisymmetric case includes a stiffness variation exclusively in the axial direction, and the only pertinent loading scenarios include constant loads of axial compression, pressure, and torsion. The results for these cases indicate that little improvement over traditional laminates exists through the use of curvilinear fibers, mainly due to the presence of a weak link area within the stiffness variation that limits the ultimate load that the structure can withstand. Rigorous optimization studies reveal that even though slight increases in the critical loads can be produced for designs with an arbitrary variation of the fiber orientation angle, the improvements are not significant when compared to traditional design techniques that utilize ring stiffeners and frames. The second problem that is studied involves arbitrary loading of a cylinder with a stiffness variation that changes only in the circumferential direction. The end effects of the cylinder are ignored, so that the problem takes the form of an analysis of a cross-section for a short cylinder segment. Various load cases including axial compression, pressure, torsion, bending, and transverse shear forces are investigated. It is found that the most significant improvements in load-carrying capability exist for cases which involve loads that also vary around the circumference of the shell, namely bending and shear forces. The stiffness variation of the optimal designs contribute to the increased performance in two ways: lowering the stresses in the critical areas through redistribution of the stresses; and providing a relatively stiff region that alters the buckling behavior of the structure. These results led to an in-depth optimization study involving weight optimization of a fuselage structure subjected to typical design constraints. Comparisons of the curvilinear fiber format to traditional stiffened structures constructed of isotropic and composite materials are included. It is found that standard variable stiffness designs are quite comparable in terms of weight and load-carrying capability yet offer the added advantage of tailorability of distinct regions of the structure that experience drastically different loading conditions. The last two problems presented in this work involve the nonlinear phenomenon of long tubes under bending. Though this scenario is not as applicable to fuselage structures as the previous problems, the mechanisms that produce the nonlinear effect are ideally suited to be controlled by the variable stiffness concept. This is due to the fact that the dominating influence for long cylinders under bending is the ovalization of the cross-section, which is governed mainly by the stiffness parameters of the cylindrical shell. Possible improvement of the critical buckling moments for these structures is investigated using either a circumferential or axial stiffness variation. For the circumferential case involving infinite length cylinders, it is found that slight improvements can be observed by designing structures that resist the cross-sectional deformation yet do not detract from the buckling resistance at the critical location. The results also indicate that bucking behavior is extremely dependent on cylinder length. This effect is most easily seen in the solution of finite length cylinders under bending that contain an axial stiffness variation. For these structures, the only mechanism that exhibits improved response are those that effectively shorten the length of the cylinder, thus reducing the cross-sectional deformation due to the forced restraint at the ends. It was found that the use of curvilinear fibers was not able to achieve this effect in sufficient degree to resist the deformation, but that ring stiffeners produced the desired response abmirably. Thus it is shown that the variable stiffness concept is most effective at improving the bending response of long cylinders through the use of a circumferential stiffness variation. / Ph. D.

Advanced combustion modes offer promising solutions for both emission reduction and efficiency improvement. The lower local equivalence ratio and lower peak temperature characterized by the advanced combustion mode significantly reduce the generation of the engine-out emissions (especially the soot and NOx). Although the advanced combustion mode enjoys extra-low emissions, some technical challenges prevent it from being widely applied in real practice. Combustion phasing control as auto-ignition and narrow load range are two main challenges to be addressed. The estimation and control techniques for Diesel engine targeting these two challenges are presented in four papers in this thesis. Accessing to the in-cylinder conditions is essential for a more detailed combustion estimation and further combustion control. Paper 1 and Paper 2 (Chapter II and Chapter III) introduce methods of estimating two critical in-cylinder conditions, the in-cylinder temperature and oxygen concentration. The system dynamic models are derived and the Extended Kalman filter (EKF) and smooth variable structure filter (SVSF) are utilized for the in-cylinder temperature and in-cylinder oxygen concentration estimation, respectively. The method of coordinated control for the intake conditions and the combustion process aiming at a fast and accurate combustion process response is proposed in paper 3 (Chapter IV). Disturbance rejection control in conjunction with sliding mode method is proposed to control the air- and fuel-path loop simultaneously. As an indicator to show the combustion quality and to avoid significant incomplete combustion, the unburned fuel is estimated in paper 4 (Chapter V) based on the oxygen concentration. Three filters are designed to estimate the trapped unburned fuel and their robustness against modeling errors are analyzed and compared theoretically. / Dissertation / Doctor of Philosophy (PhD) / To ultimately reduce the engine-out emissions and increase the thermal efficiency, advanced combustion modes provide promising solutions. However, several obstacles, including the narrow load range and difficulty of the combustion phasing control, prevent the advanced combustion from being widely applied in practice. To address these obstacles, detail estimation of in-cylinder gas conditions and robust control for air- and fuel-path are critical. This thesis focuses on the states estimation and control for Diesel engines aiming to address the obstacles laid by the advanced combustion modes. Four journal papers with different objectives compose this thesis. Paper 1 and Paper 2 (Chapter II and III, respectively) propose methods of estimation of the in-cylinder temperature and oxygen concentration. Paper 3 (Chapter IV) introduces the method of coordinated control of the intake conditions and the combustion process. The unburned fuel is estimated in paper 4 (Chapter V). The techniques introduced in the 4 papers are either validated through calibrated GT-Power simulations or experiments in a Diesel engine.

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