<p>The objectives of this investigation were to experimentally and numerically assess the performance of a ball bearing supported turbocharger (TC). Turbochargers are mechanical devices used to improve the efficiency of modern engines. Using ball bearings improves the TC efficiency, and represents one of many evolving high-speed applications for ball bearings.</p> <p>The experimental objectives of this investigation were to design and develop a turbocharger test rig (TTR) to measure the shaft whirl of the rotating assembly and the axial and frictional loads experienced by the bearing cartridge. The TTR contains a ball bearing TC which was instrumented and operated under a variety of test conditions including rotational speeds up to 55,000 rpm. In order to measure the axial loads on the compressor and turbine sides, customized sensors were designed, fabricated and integrated into the TC housing. The anti-rotation (AR) pin, which normally prevents the bearing cartridge from rotating, was replaced with a custom-made sensor to measure frictional losses in the bearing cartridge.  These sensors were designed to minimally affect the operation of the TC. Proximity probes were initially installed on the compressor side and later on the turbine side to monitor shaft whirl using targets attached to the ends of the impellers. An assembly to record axial shaft motion with a proximity probe was also developed. Axial load and motion results indicated that the compressor side bears most of the axial load. As the backpressure or the speed of the TC increased the axial load also increased. Frictional measurements from the AR pin sensor demonstrated low power losses in the ball bearing cartridge. For certain shaft speed ranges, the data from the sensors illustrated periodic trends in response to subsynchronous whirl of the shaft.</p> <p>The numerical modeling objectives of this investigation were to characterize the dynamics of the ball bearing supported TC. In this TC, the compressor, turbine and shaft are supported by a bearing cartridge composed of back-to-back angular contact ball bearings. The cartridge is supported by squeeze film dampers (SFDs) and is prevented from rotation by the AR pin. To achieve the objectives, first an equivalent bearing model was developed to investigate the bearing dynamics and whirl of the TC rotating assembly. The TC bearing cartridge was modeled with a single deep groove ball bearing (DGBB) using the discrete element method. The SFD which supports the bearing was modeled with a bilinear spring and damper. A DGBB was used because it can support axial load in both directions. This model was then extended to include a flexible shaft represented by tetrahedral finite elements and supported by an ACBB cartridge. After this model was used to reproduce the whirl from the test rig, the bearing internal geometry and SFD properties were adjusted to determine their effect on shaft whirl. Wear and damage criteria were also developed to evaluate the simulation results. The best simulation result was obtained with a small clearance in the bearing and with a stiffer SFD. The clearance was necessary as the shaft and bearing deform at high speeds, preloading the bearing.</p> <p>The best simulation result was found to have reduced sliding and limited variation in contact force, which should lead to reduced friction and improved overall life. This study demonstrates the importance of taking the bearing system into account while designing a TC or other high speed mechanical system, as the bearing and SFD properties can have a significant impact on the system performance.</p>

<p dir="ltr">Reverse osmosis (RO) is emerging as the world’s leading desalination technology due to its superior energy efficiency and the shift towards renewable electrification. However, RO systems need to further improve efficiency, increase operating flux, reach higher salinities (>7.5% w.t.), and minimize component complexity. Treating RO as a dynamical system, this dissertation invents new processes for high-efficiency desalination that achieve milestones for low downtime and high final salinity. It also introduces modeling methods that include more detail (e.g. salt retention, time-varying salinity, concentration polarization, salt transport, temporal multi-staging, etc.) and the first use of certain optimization methods in RO.</p><p dir="ltr">Batch RO is an unsteady, pressure driven process that efficiently desalinates a saline feed volume over time by continuously recirculating the brine through the membrane module. A tank houses the concentrating feed and mediates the streams entering and leaving the membrane module. Most studies so far have concentrated on the high-pressure tank design that requires finite downtime at the end of each stroke. A scalable pressure exchanger batch RO (PX-BRO) configuration using atmospheric tanks that practically has zero downtime and produces permeate even while flushing is first described in this dissertation.</p><p dir="ltr">To achieve high recovery at nominal RO pressures, osmotically assisted RO processes have both sides of the membrane saline and the streams usually in counterflow. The first unsteady osmotically assisted process based on the high-pressure piston tank design, batch counterflow RO (BCFRO) is introduced which dramatically reduces the energy needs. To address the issue of high component count in spatial multi-staging, the first “temporally multi-staged” BCFRO process is also introduced. The new process uses the pressure ex- changer and atmospheric pressure tank design for scalability and operational flexibility.</p><p dir="ltr">For membranes with low salt rejection, it becomes imperative to integrate the salt trans- port dynamics for deciding operating and initial conditions. Trajectory optimization is used to match salinity and volume between stages of temporally multi-staged BCFRO. Treating the process as an optimal control problem, a framework for obtaining time varying flux pro- files that minimize the specific energy consumption is also developed. Both reduced order and discretized models are developed to analyze these new batch RO configurations.</p>

<p dir="ltr">Uncertainty quantification is a science and engineering subject that aims to quantify and analyze the uncertainty arising from mathematical models, simulations, and measurement data. An uncertainty quantification analysis usually consists of conducting experiments to collect data, creating and calibrating mathematical models, predicting through numerical simulation, making decisions using predictive results, and comparing the model prediction with new experimental data.</p><p dir="ltr">The overarching goal of uncertainty quantification is to determine how likely some quantities in this analysis are if some other information is not exactly known and ultimately facilitate decision-making. This dissertation delivers a complete package, including theory, algorithms, and applications of information field theory, a Bayesian uncertainty quantification tool that leverages the state-of-the-art machine learning framework to accelerate solving the classical uncertainty quantification problems specified by differential equations.</p>

<p dir="ltr">Acoustic guitar soundboard material selection is based on selective evaluations that have been developed over centuries. These traditional practices are not conducive to the guitar industry we experience today because the supply of traditionally acceptable soundboard wood has decreased greatly. The purpose of this research was to develop an objective wood selection metric to determine the sound quality of an acoustic guitar’s soundboard. The metric would replace the subjective evaluations traditionally used to select materials for acoustic guitar soundboards.</p><p dir="ltr">The acoustic properties of sound radiation coefficient, material’s speed of sound, resonance and damping and the material properties of longitudinal and radial elastic modulus, density, and specific modulus were used in an attempt to construct a material selection metric. These variables were selected because the literature review revealed that these were the most critical variables in determining sound quality. The gaps in the literature were testing and analyzing samples that represented the true dimensions of an acoustic guitar soundboard blank and forming the metric. The literature revealed that the previous experimental studies did not have the appropriate test sample dimensions that correspond to the test samples evaluated by the subjective methods.</p><p dir="ltr">The methodology was carried out by using the objective testing counterparts to the subjective assessments found in the literature review. Instrumented hammer tap testing collected data to determine damping and resonance frequencies. A three-point static bending test collected data for longitudinal and radial elastic modulus. Mass and dimension measurements were recorded to calculate density. Calculations were done to compute the acoustic properties and specific modulus of the test samples. These variables were put into a table and underwent statistical analysis in the form of predictor correlation and logistical regression. The experimental variables were modeled against the subjective evaluation of an expert on the usability of the test samples.</p><p dir="ltr">Statistical analysis proved that the dataset did not show any significant separation between “good” or “bad” test samples or a significant correlation between the usability of the test sample and the variables in the dataset. The methodology did not produce an objective material selection metric to determine the sound quality of an acoustic guitar’s soundboard. Future research should include a wider range of measured frequencies and the collection of time domain data.</p>

<p dir="ltr">This article-based research traces the evolution and advancements of vehicular aerodynamic concepts and emphasizes on the significance of vehicle aerodynamics for high-performance vehicles. The thesis further explores the scope of integrating advanced vehicle aerodynamic concepts into consumer vehicles. The thesis aims to point out the significant improvements achieved with the integration of active aerodynamic concepts in terms of both vehicle performance as well as efficiency figures for consumer vehicles. Additionally, exploring the scope for the development of these advanced active aerodynamic systems as third-party modifications is the secondary objective of the presented research. The thesis also highlights the development and integration of unique active aerodynamic systems featured in performance vehicles and analyzes the performance gains achieved using MATLAB program-based simulations supported by a graphical representation of analyzed output data. The study of Active aerodynamic systems for both performance/track-oriented and consumer vehicles remains to be the primary emphasis for the presented thesis.</p>

FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais / Esta Dissertação versa sobre a análise de confiabilidade de estruturas sujeitas a controle ativo e passivo de vibrações, com ênfase na aplicação dos métodos de confiabilidade de primeira ordem (FORM, First Order Reliability Method) e segunda ordem (SORM, Second Order Reliability Method). Esses são usados para calcular o índice de confiabilidade e, consequentemente, a probabilidade de falha de estruturas, considerando variáveis aleatórias modeladas segundo funções densidade de probabilidade. Três técnicas de controle são avaliadas: controle ativo empregando atuadores piezelétricos; controle passivo por absorvedores dinâmicos de vibrações e controle passivo baseado em atuadores piezelétricos conectados a circuitos shunt ressonantes. Para cada caso, são definidas funções de estado limite que descrevem limites operacionais e/ou requisitos de projeto, cuja avaliação é baseada em respostas obtidas por meio de modelos de elementos finitos das estruturas analisadas. Para cada uma das técnicas de controle, aplicações numéricas dos métodos FORM e SORM são realizadas considerando como estrutura principal uma treliça plana. Para efeito de avaliação da precisão das estimações de confiabilidade fornecidas por estes métodos, foram também utilizadas Simulações de Monte Carlo. A partir dos resultados, são discutidas as características específicas observadas para cada técnica de controle. Em específico, para duas delas foram identificados domínios de segurança e de falha de formas atípicas, em cujos casos, fica inviabilizado o uso dos métodos FORM e SORM. De modo geral, os resultados confirmam a importância e a conveniência de se aplicarem os métodos de análise de confiabilidade a estruturas sujeitas a procedimentos de controle de vibrações. / This dissertation is devoted to the reliability analysis of structures subjected to active and passive vibration control, with emphasis on the use of First Order Reliability Method (FORM) and Second Order Reliability Method (SORM). These methods are used to evaluate the reliability indices and the associated failure probability, considering that the random variables are modeled by probability density functions. Three techniques of vibration control are considered, namely: active control using PZT stack actuators, passive control based on dynamic vibration absorbers, and passive control based on piezoelectric transducers connected to resonant shunt circuits. For each technique, limit state functions are defined related to the operational limitations or design requirements. Their evaluation is made from structural responses obtained from finite element models. For each control technique, numerical applications of FORM and SORM are carried-out for a two-dimensional truss, defined as the structure of interest. To assess the accuracy of the reliability estimations provided by those methods, Monte Carlo Simulations are also performed. The numerical results enable to put in evidence specific characteristics of each control technique as related to reliability. Specifically, for two of them it is verified the occurrence of atypical geometrical forms of the safety and failure domains, which preclude the use of FORM and SORM. In general, the results confirm the importance and convenience of performing reliability assessment of structures subjected to vibration control procedures. / Dissertação (Mestrado)

O fenômeno de stick-slip, no processo de perfuração de poços de petróleo, é propiciado pela interação entre broca e formação rochosa e pode dar origem a grandes oscilações na velocidade angular podendo provocar danos irreparáveis ao processo. Neste trabalho, analisa-se o desempenho de leis de controle aplicadas à mesa rotativa (responsável por movimentar a coluna de perfuração), visando à redução de stick-slip e de oscilações da velocidade angular da broca. As leis de controle implementadas são do tipo PI (Proporcional-Integral), com parcelas de torque aplicado à mesa rotativa, proporcional e integral à velocidade da mesa, podendo ser com peso na broca constante ou variável. Para a coluna de perfuração, foi proposto um modelo em elementos finitos com função de forma linear. O torque na broca foi modelado segundo atrito de Coulomb pela forma não regularizada, curva esta ajustada pelos dados empíricos conforme propostas da literatura. Diversos critérios de desempenho foram analisados e foi observado que a minimização do desvio médio da velocidade angular em relação à referência propicia melhores condições de operação. Análises paramétricas dos ganhos de controle proporcional e integral foram realizadas, dando origem a curvas de nível para o desvio médio de velocidade angular na broca. A partir destas curvas, foram definidas regiões de estabilidade nas quais o desvio é aceitável. Estas regiões foram observadas serem maiores para menores pesos na broca e maiores velocidades angulares de referência e vice-versa. A adição do controle do peso na broca permitiu uma redução global dos níveis de desvio médio de velocidade angular, dando origem a um aumento das regiões de estabilidade do processo de perfuração. / The stick-slip phenomenon, in the process of drilling oil wells, due to the interaction between drill and rock formation can lead to large fluctuations in drill-bit angular velocity and, thus, cause irreparable damage to the process. In this work, the performance of control laws applied to the rotary table (responsible for moving the drill string) is analyzed, in order to reduce stick-slip and drill-bit angular velocity oscillations. The control laws implemented are based on a PI (Proportional-Integral) controller, for which the torque applied to the rotating table has components proportional and integral to table angular velocity with constant or variable WOB (Weight On Bit). For the drillstring, a finite element model with a linear interpolation was proposed. The torque on the drill-bit was modeled by a non-regularized Coulomb friction model, with parameters that were adjusted using empirical data proposed in literature. Several performance criteria were analyzed and it was observed that the minimization of the mean deviation of the drill-bit angular velocity relative to the target one would provide the best operating condition. Parametric analyses of proportional and integral control gains were performed, yielding level curves for the mean deviation of drill-bit angular velocity. From these curves, stability regions were defined in which the deviation is acceptable. These regions were observed to be wider for smaller values of WOB and higher values of target angular velocity and vice-versa. The inclusion of a controlled dynamic WOB reduced the levels of mean deviation of angular velocity, leading to improved stability regions for the drilling process.

Neste estudo se propõe o desenvolvimento de um modelo numérico para a ligação deslizante entre elementos sólidos bidimensionais, aplicável à simulação de sistemas deslizantes de isolação de base para estruturas. A formulação implementada é baseada no Método dos Elementos Finitos Posicional (MEFP) para análise dinâmica não linear geométrica de estruturas escrita na forma Lagrangeana total. Elementos triangulares planos e isoparamétricos de aproximação cúbica com matriz de massa completa são utilizados principalmente na elaboração da parte sólida dos dispositivos de ligação entre estruturas reticuladas e a base móvel. Esses elementos também poderm ser utilizados na modelagem da estrutura em si, porém, para esse fim, elementos finitos isoparamétricos de barra geral com massa distribuída por unidade de comprimento foram implementados. As equações de movimento são integradas no tempo aplicando o método de Newmark e o problema de deslizamento é resolvido com o algoritmo baseado na técnica dos multiplicadores de Lagrange, onde a restrição das posições de um nó escravo é feita em relação a uma sequência de superfícies mestres. Elementos de barra geral foram usados para simular as superfícies mestres de contato, o que aumenta as possibilidades de aplicações, incluindo mecanismos compostos apenas por barras gerais. Analisam-se exemplos disponíveis na literatura para a validação da formulação proposta e propõem-se aplicações diversas na engenharia das estruturas. / This study proposes the development of a numerical model for the sliding joint between two-dimensional solid elements, applicable to the simulation of sliding base isolation systems. The implemented formulation is based on the Positional Finite Element Method (PFEM) for geometrical nonlinear dynamic analysis of structures written in the total Lagrangian form. Plane and isoparametric triangular cubic approximation elements with full mass matrix are mainly used in the elaboration of the solid part of the devices of joints between reticulated structures and mobile base. These elements can also be used in the modeling of the structure itself, however, for that purpose, isoparametric elements of general bar with mass distributed per unit of length were implemented. The motion equations are integrated in time by applying the Newmark method and the sliding problem is solved with the algorithm based on the technique of Lagrange multipliers, where the constraint of the positions of a slave node is made in relation to a sequence of master surfaces. General bar elements were used to simulate the master contact surface, which increases the possibilities of applications, including mechanisms composed only of general bars. Analyze examples available in the literature for the validation of the proposed formulation and proposed diverse applications in the engineering of the structures.

Esta tese apresenta uma análise numérica do controle de vibrações estruturais através de cerâmicas piezelétricas em extensão conectadas a circuitos ativo-passivos compostos por resistência, indutância e fonte de tensão. Para tal, um modelo de elementos finitos de vigas sanduíche com três camadas elásticas e/ou piezelétricas foi desenvolvido. Realizou-se também uma modelagem dos componentes do circuito elétrico e seu acoplamento à estrutura gerando assim uma equação de movimento acoplada para a estrutura com elementos piezelétricos conectados aos circuitos elétricos. Uma análise harmônica das equações obtidas foi realizada para se obter uma avaliação preliminar dos efeitos causados pelos componentes elétricos do circuito na estrutura. Observou-se que os elementos passivos do circuito, resistência e indutância, tem não somente um efeito de absorvedor dinâmico de vibrações mas, também, promovem uma amplificação da autoridade de controle no caso de se atuar através da fonte de tensão. Usando a metodologia tradicional de projeto de absorvedores dinâmicos de vibrações, derivou-se expressões para os valores de resistência e indutância de modo a maximizar o desempenho passivo do sistema. Uma análise do efeito de incertezas das constantes piezelétricas e dielétricas da cerâmica piezelétrica considerada e dos componentes de resistência e indutância do circuito elétrico no desempenho do controle passivo e ativo-passivo de estrutura tipo viga cantilever foi realizada. O objetivo desta análise foi quantificar robustez e sensibilidade do controle proposto. Em sequida, um estudo de otimização dos valores de resistência e indutância do circuito elétrico em função da tensão elétrica de controle máxima a ser aplicada em uma placa com diversos atuadores piezelétricos foi realizado. Finalmente e também para a estrutura tipo placa, uma análise de incertezas da rigidez da cola na interface entre estrutura e atuadores piezelétricos e seus efeitos no desempenho do controle passivo e ativo-passivo foi realizada. / This work presents a numerical analysis of the structural vibration control using piezoelectric materials in extension mode connected to active-passive electric circuits composed of resistance, inductance and voltage source. For that, a finite element model for sandwich beams with three elastic or piezoelectric layers was developed. A modeling of the electric circuit dynamics and its coupling to the structure with piezoelectric elements was also done. A harmonic analysis of the resulting equations was performed to yield a preliminary evaluation of the effects caused by the electric circuit components on the structure. It was observed that the passive circuit components not only lead to a dynamic vibration absorber effect but also to an amplification of the control authority in case of actuation using the voltage source. Using the standard methodology for the design of dynamic vibration absorbers, expressions were derived for the resistance and inductance values that optimize the passive vibration control performance of the system. An analysis of the effect of uncertainties of piezoelectric and dielectric constants of piezoelectric ceramic and resistance and inductance components of the shunt circuit on the passive and active-passive control performance for a cantilever beam structure was performed. The objective of this analysis was to quantify robustness and sensitivity of the proposed control. Then, an optimization study of the values of resistance and inductance of the shunt circuit as a function of the maximum control voltage to be applied on a plate with several piezoelectric actuators was performed. Finally and also for the plate structure, an analysis of uncertainties in the stiffness of the adhesive interface between structure and piezoelectric actuators and their effects on the performance of passive control and active-passive was performed.

Les matériaux évolués tels que les matériaux composites ou les fibres de carbone sont de plus en plus utilisés dans l'industrie. Ils rendent les structures plus légères et plus résistantes mais en contrepartie, ils apportent de nouveaux problèmes de vibration. De nombreuses recherches sont ainsi en cours pour apporter des solutions afin d'éliminer les vibrations indésirables tout en restant compactes, légères, intelligentes et modulaires. Récemment, des techniques de contrôle non linéaires, dénommées en anglais S.S.D. (Synchronized Switch Damping) ont été proposées et validées. Ces méthodes font commutées un élément piézoélectrique collé à la structure mécanique à amortir sur un circuit électrique de manière synchronisée avec la déformation de celle-ci. Un effet amortissant peut ainsi être obtenu en utilisant l'énergie de vibration de la structure mécanique elle-même. Basée sur ces concepts, une nouvelle technique appelée S.S.D.E.T. (Synchronized Switch Damping with Energy Transfer) est proposée dans ce manuscrit. Cette méthode permet d'amortir une vibration en utilisant de l'énergie extraite à partir d'autres vibrations. Les résultats de ce travail de thèse sont présentés de la manière suivante. Premièrement, le principe et les lois de commande de la technique S.S.D.E.T. sont introduits. Ainsi, un modèle mathématique est établi et permet de vérifier les concepts proposés par simulation. Ensuite, des validations expérimentales menées sur différentes configurations sont décrites et démontrent l'augmentation de l'amortissement sur un système composé de deux structures mécaniquement indépendantes, sur un système composé d'une seule structure qui vibre selon plusieurs modes et sur une combinaison des deux précédents. Enfin, une extension de la technique S.S.D.E.T. est introduite dans un cadre d'échange d'énergie bidirectionnel. Celle-ci permet d'obtenir un amortissement privilégié sur un mode tout en conservant un contrôle correct des autres modes. / Advanced materials such as carbon fiber, composite materials et al. are more and more used in modern industry. They make the structures lighter and stiffer. However, they bring vibration problems. Researchers studied numerous methods to eliminate the undesirable vibrations. These treatments are expected to be a compact, light, intellectual and modular system. Recently, a nonlinear technique which is known as Synchronized Switch Damping (SSD) technique was proposed. These techniques synchronously switched when structure got to its displacement extremes that leading to a nonlinear voltage on the piezoelectric elements. This resulting voltage showed a time lag with the piezoelectric strain thus causing energy dissipation. Based on the developed SSD techniques, a new synchronized switch damping e.g. Synchronized Switch Damping with Energy Transfer (SSDET) was proposed in this document. This method damped the vibration by using the energy from other vibrating form. The objectives of the work reported in this document were threefold. The first one consisted of introduction of SSDET principle and developing its control law. This part aimed at establishing the mathematical model and verifying the proposed method by mathematical tools. Then, the experimental validations were carried out. Three experiments with different configurations demonstrated that SSDET can be implemented not only between structures but also vibrating modes in one structure. A SSDET scheme with multi-patches was also investigated for improving the damping. Finally, a bidirectional SSDET concept was introduced based on the original SSDET technique. This technique be regarded as a multimode control SSDET. Since it privileged the target vibration while keeps a decent control effect on the source vibration.