Thesis (Ph.D.)--University of Western Australia, 2007.

Thesis (Ph.D.)--Rochester Institute of Technology, 2005. / Typescript. Includes bibliographical references (leaves 179-189).

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisors: Clinton N. Dawson and Yannis Kallinderis. Vita. Includes bibliographical references.

Thesis (Ph.D.)--Rochester Institute of Technology, 2006. / Typescript. Includes bibliographical references (leaves 270-275).

Orientador: José Luiz Gasche / Resumo: Compressores herméticos alternativos são amplamente utilizados em sistemas de refrigeração por compressão de vapor de pequeno e médio porte. O sistema de válvulas automáticas utilizadas para controlar os processos de sucção e descarga é um componente importante deste tipo de compressor. O estudo experimental ou analítico/numérico destes processos é bastante complexo devido, principalmente, à interação fluido-estrutura entre as válvulas e o escoamento de fluido refrigerante. Uma revisão de literatura mostra que este tema ainda merece muita atenção dos pesquisadores, em particular daqueles que necessitam de dados experimentais acurados para validação de metodologias numéricas. Este é o contexto deste trabalho, cujo objetivo é descrever a dinâmica do movimento de um modelo de válvula usada neste tipo de compressor. Sensores óticos foram utilizados para medir o deslocamento instantâneo de modelos de válvulas fabricadas em aço mola SAE 1070 com 0,4 e 0,5 mm de espessura. Os testes foram realizados para escoamentos com números de Reynolds variando de 1.500 a 19.000. A descrição da dinâmica da válvula foi apresentada pela sua amplitude, frequência, pressão máxima à montante do escoamento da válvula e pelo coeficiente de restituição no impacto entre a válvula e o assento. De uma maneira geral, identificamos que a dinâmica da válvula depende significativamente de sua rigidez, do valor de força de pré-carga que está sujeita e do número de Reynolds do escoamento que incide sobre sua sup... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Hermetic reciprocating compressors are widely used in small and medium size vapor compression refrigeration systems. An important component of this type of compressor is the automatic valve system used for controlling the suction and discharge processes. The experimental or analytical/numerical study of this system is complex due to the fluid-structure interaction between the valves and the refrigerant flow. A literature review suggests that this theme still deserves attention from the researchers, in particular for those who need accurate experimental data to validate numerical methodologies. We aim to describe the dynamics of a suction valve model used in this type of compressor. Optical sensors were used to measure the instantaneous displacement of a spring-steel SAE 1070 valve model with 0.4 and 0.5 mm thickness. The tests were performed for Reynolds number of the flow ranging from 1,500 to 19,000. We present the dynamic behavior of the valve by its amplitude, frequency, maximum upstream pressure of the valve, and coefficient of restitution of the impact between valve and seat. Generally, we identify that the valve dynamics depends significantly on its stiffness, precharging force and Reynolds numbers of the flow. The impact between valve and seat also significantly change the dynamics of the movement. / Mestre

La connaissance de la viscosité est un défi majeur dans les technologies de pointe (biomédical, pétrochimie, imprimerie, cosmétique, agroalimentaire, etc). Cette étude présente un capteur de viscosité qui exploite la vibration transversale forcée d’une poutre mince. L’amortissement induit par le fluide permet d’évaluer sa viscosité et sa masse volumique par la seule connaissance des caractéristiques à la résonance de la poutre (amplitude et fréquence). Cette mesure est réalisée par un circuit électromagnétique. Dans ce travail, la simulation numérique et l’étude expérimentale du viscosimètre sont réalisées en vue de mieux cerner les paramètres influençant le fonctionnement du capteur. Les différentes investigations menées dans ce travail sont d’une grande importance pour l’optimisation du viscosimètre d’une part. D’autre part, c’est une contribution à l’ensemble des études qui traitent de l’aspect du couplage fluide-structure-électromagnétisme. / Knowing the viscosity becomes increasingly a major challenge in leading-edge technologies (biomedical, petrochemical, printing, cosmetic, food industry, etc). This study presents a viscosity sensor based on a thin beam immersed in a newtonian fluid and subjected to transverse vibrations due to an electromechanical excitation system. The damped vibration can be used to evaluate the fluid viscosity and density by measuring the beam’s resonance characteristics (amplitude, frequency). This measurement is done by an electromagnetic feedback circuit. In this work, numerical model and experimental studies of the vibrating viscometer are conducted to better understand the influencing factors of the sensor’s operation. The different investigations carried out in this work are of great importance for the viscometer optimization on one hand. On the other hand, it’s a contribution to all studies dealing with the aspect of fluid-structure-electromagnetism coupling.

This work is focused on the numerical modelling of fluid-structure interaction in three dimensions. Both internal and external laminar flow around flexible bodies are considered. The fluid flow simulated is based on the incompressible Navier-Stokes equations and the general focus is on laminar Newtonian flow. The streamline upwind/ pressure stabilising Petrov-Galerkin (SUPG/PSPG) method is employed to achieve a stable low order finite element discretisation of the fluid, while the solid is discretised spatially by a standard Galerkin finite element approach. The behavior of the solid is governed by Neo-Hooke elasticity. For temporal discretisation the discrete implicit generalised-alpha method is employed for both the fluid and the solid domains. The motion of the fluid mesh is solved using an arbitrary Lagrangian-Eulerian (ALE) scheme employing a nonlinear pseudo-elastic mesh update method. The fluid-solid interface is modelled using a finite element interpolation method that allows for non-matching meshes and satisfies the required conservation laws. The resulting sets of fully implicit strongly coupled nonlinear equations are then decomposed into a general framework consisting of fluid, interface and solid domains. These equations are then solved using different solution techniques consisting of strongly coupled monolithic Newton and block Gauss-Seidel methods as well as a weakly coupled novel staggered scheme. These solvers are employed to solve a number of three dimensional numerical examples consisting of: External flow: o a soft elastic beam fixed at both ends o a thin cantilever plate.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Mingjun Wei / In this study, a global Proper Orthogonal Decomposition (POD)-Galerkin based Reduced Order model (ROM) is proposed. It is extended from usual fixed-domain problems to more general fluid-solid systems with moving boundaries/interfaces. The idea of the extension is similar to the immersed boundary method in numerical simulations which uses embedded forcing terms to represent boundary motions and domain changes. This immersed boundary method allows a globally defined fixed domain including both fluid and solid, where POD-Galerkin projection can be directly applied. However, such a modified approach cannot get away with the unsteadiness of boundary terms which appear as time-dependent coefficients in the new Galerkin model. These coefficients need to be pre-computed for prescribed periodic motion, or worse, to be computed at each time step for non-prescribed (e.g. with fluid-structure interaction) or non-periodic situations. Though computational time for each unsteady coefficient is smaller than the coefficients in a typical Galerkin model, because the associated integration is only in the close neighborhood of moving boundaries. The time cost is still much higher than a typical Galerkin model with constant coefficients. This extra expense for moving-boundary treatment eventually undermines the value of using ROMs. An aggressive approach is to decompose the moving boundary/domain to orthogonal modes and derive another low-order model with fixed coefficients for boundary motion. With this domain decomposition, an approach including two coupled low-order models both with fixed coefficients is proposed. Therefore, the new global ROM with decomposed approach is more efficient. Though the model with the domain decomposition is less accurate at the boundary, it is a fair trade-off for the benefit on saving computational cost. The study further shows, however, that the most time-consuming integration in both approaches, which come from the unsteady motion, has almost negligible impact on the overall dynamics. Dropping these time-consuming terms reduces the computation cost by at least one order while having no obvious effect on model accuracy. Based on this global POD-Galerkin based ROM with forcing term, an improved ROM which can handle the parametric variation of body motions in a certain range is also presented. This study shows that these forcing terms not only represent the moving of the boundary, but also decouple the moving parameters from the computation of model coefficients. The decoupling of control parameters provides the convenience to adapt the model for the prediction on states under variation of control parameters. An improved ROM including a shit mode seems promising in model adaptation for typical problems in a fixed domain. However, the benefit from adding a shit mode to model diminishes when the method is applied to moving-boundary problems. Instead, a combined model, which integrates data from a different set of parameters to generate the POD modes, provides a stable and accurate ROM in a certain range of parametric space for moving-boundary problems. By introducing more data from a different set of parameters, the error of the new model can be further reduced. This shows that the combined model can be trained by introducing more and more information. With the idea of the combined model, the improved global ROM with forcing terms shows impressive capability to predict problems with different unknown moving parameters, and can be used in future parametric control and optimization problems.

Submitted by Gabriel Biancolin Moimas (gabrielmoimas18@gmail.com) on 2018-06-18T11:47:19Z No. of bitstreams: 1 Dissertação.pdf: 13607292 bytes, checksum: 4574d9cd3135ad2562a9648fd1641465 (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-06-18T12:12:00Z (GMT) No. of bitstreams: 1 moimás_gb_me_ilha.pdf: 13607292 bytes, checksum: 4574d9cd3135ad2562a9648fd1641465 (MD5) / Made available in DSpace on 2018-06-18T12:12:00Z (GMT). No. of bitstreams: 1 moimás_gb_me_ilha.pdf: 13607292 bytes, checksum: 4574d9cd3135ad2562a9648fd1641465 (MD5) Previous issue date: 2018-05-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Compressores herméticos alternativos são amplamente utilizados em sistemas de refrigeração por compressão de vapor de pequeno e médio porte. O sistema de válvulas automáticas utilizadas para controlar os processos de sucção e descarga é um componente importante deste tipo de compressor. O estudo experimental ou analítico/numérico destes processos é bastante complexo devido, principalmente, à interação fluido-estrutura entre as válvulas e o escoamento de fluido refrigerante. Uma revisão de literatura mostra que este tema ainda merece muita atenção dos pesquisadores, em particular daqueles que necessitam de dados experimentais acurados para validação de metodologias numéricas. Este é o contexto deste trabalho, cujo objetivo é descrever a dinâmica do movimento de um modelo de válvula usada neste tipo de compressor. Sensores óticos foram utilizados para medir o deslocamento instantâneo de modelos de válvulas fabricadas em aço mola SAE 1070 com 0,4 e 0,5 mm de espessura. Os testes foram realizados para escoamentos com números de Reynolds variando de 1.500 a 19.000. A descrição da dinâmica da válvula foi apresentada pela sua amplitude, frequência, pressão máxima à montante do escoamento da válvula e pelo coeficiente de restituição no impacto entre a válvula e o assento. De uma maneira geral, identificamos que a dinâmica da válvula depende significativamente de sua rigidez, do valor de força de pré-carga que está sujeita e do número de Reynolds do escoamento que incide sobre sua superfície. O impacto entre válvula e assento também altera significativamente a dinâmica do movimento. / Hermetic reciprocating compressors are widely used in small and medium size vapor compression refrigeration systems. An important component of this type of compressor is the automatic valve system used for controlling the suction and discharge processes. The experimental or analytical/numerical study of this system is complex due to the fluid-structure interaction between the valves and the refrigerant flow. A literature review suggests that this theme still deserves attention from the researchers, in particular for those who need accurate experimental data to validate numerical methodologies. We aim to describe the dynamics of a suction valve model used in this type of compressor. Optical sensors were used to measure the instantaneous displacement of a spring-steel SAE 1070 valve model with 0.4 and 0.5 mm thickness. The tests were performed for Reynolds number of the flow ranging from 1,500 to 19,000. We present the dynamic behavior of the valve by its amplitude, frequency, maximum upstream pressure of the valve, and coefficient of restitution of the impact between valve and seat. Generally, we identify that the valve dynamics depends significantly on its stiffness, precharging force and Reynolds numbers of the flow. The impact between valve and seat also significantly change the dynamics of the movement.

Neste trabalho um método de partículas para simular a dinâmica de sólidos elásticos e interação fluido estrutura e implementado. O método e baseado no Moving Particle Semi-implicit (MPS), originalmente desenvolvido para escoamentos incompressíveis com superfície livre. A estratégia principal do MPS e substituir os operadores diferenciais das equações governantes por operadores diferenciais discretos em uma distribuição de nos irregulares, derivados de um modelo de interação entre partículas. Inicialmente são apresentados os detalhes da formulação do método e modelos constitutivos utilizados. Uma condição simplificada de fragmentação e proposta, assim como um algoritmo de detecção de contato, permitindo a fragmentação entre vários sólidos. No caso da interação fluido-estrutura, as partículas de superfície do solido são tratadas como partículas de fluido e as pressões destas partículas são calculadas pela resolução da equação de Poisson para a pressão, tal como as partículas de fluido. Desta forma, o acoplamento entre solido e fluido e realizado utilizando o deslocamento e velocidade do solido elástico, como condições de contorno do fluido, e a pressão na interface, obtida pela resolução do movimento do fluido, e aplicada ao movimento do solido elástico. São apresentados e detalhados os algoritmos de solido elástico, fragmentação, colisão e acoplamento fluido-estrutura. Validações qualitativas e quantitativas do método são realizadas para casos estáticos e dinâmicos sujeitos a diferentes condições de contorno, comparando os resultados numéricos obtidos pelo MPS, outros métodos numéricos, soluções analíticas e medições experimentais presentes na literatura. / In this work a particle method to simulate the dynamics of elastic solids and fluid-structure interaction is implemented. It is based on the Moving Particle Semi-implicit Method (MPS), which was originally developed for incompressible flows with free surface. The main strategy of the MPS is to replace the differential operators of the governing equations by discrete differential operators on irregular nodes, which are derived from a model of interaction between particles. Initially details of the method and constitutive equations are shown. A simplified condition of fragmentation and collision between solids are proposed to allow the investigation of fragmentation amount multiple solids. In case of fluid-structure interaction, the solid\'s surface particles are treated as a fluid particle and the pressures of the surface particles are computed by solving Poisson equation for the pressure, just as the fluid particles. Therefore, the coupling between solid and fluid is done by using the displacement and velocity of elastic solid as the boundary conditions of the fluid, and the pressure at the interface, which is obtained when solving the fluid motion, is used to calculate the motion of the elastic solid. The algorithms for elastic solid, fragmentation, collision and fluid-structure interaction are presented and detailed. The qualitative and quantitative validations of the method are carried out herein considering static and dynamic cases subjected to deferent boundary conditions by comparing the numerical results from MPS with other numerical, analytical and experimental results available in the literature.