L’objet de cette thèse est d’étudier différents dispositifs d’amortissement de vibrations en basses fréquences des aubes de rotor de soufflante ("fan") d’un turboréacteur. Les solutions étudiées utilisent des pastilles piézoélectriques, liées à l’aube et connectées à un circuit électrique passif ou semi-passif. Dans la première partie, il s’agit de mettre en pratique le modèle électromécanique développé dans la thèse de Julien Ducarne, puis de l’étendre au cas tridimensionnel par l’utilisation de la méthode des éléments finis. Ce modèle de comportement prend en compte le couplage entre une structure mécanique quelconque et des pastilles piézoélectriques planes ou courbes. Par la suite, un modèle réduit à faible nombre de degrés de liberté est construit, ce qui permet après résolution de prédire l’efficacité des dispositifs amortissants. Deux techniques, nommées "shunt" et "switch" sont appliquées au cas d’une aube fan. La première consiste à utiliser un circuit électrique résistif ou résonant. La seconde, encore à l’état de recherche, comporte un circuit muni d’un interrupteur synchronisé aux oscillations de la structure, ce qui produit un amortissement analogue à celui d’un frottement sec. La modélisation et l’optimisation électrique de ces circuits, issus de différents travaux antérieurs, ne font l’objet que d’un rappel dans ce mémoire. Une procédure d’optimisation est développée pour pouvoir trouver les géométries et les emplacements des pastilles qui maximisent le couplage électromécanique. Deux algorithmes différents (recuit simulé et recherche avec liste taboue) sont utilisés et mis en interaction avec les outils de calcul éléments finis pour trouver des solutions optimisées. Afin de valider sur un cas industriel l’ensemble des travaux sur les dispositifs piézoélectriques, une campagne d’essai est menée sur une aube fan de CFM56-7b. Les niveaux d’atténuation mesurés et ceux prévus par le modèle sont ensuite comparés. La seconde partie est consacrée à l’évaluation de l’effet des nonlinéarités géométriques sur la dynamique d’une structure tournante. Initialement prévue pour être intégrée à la partie shunt piézoélectrique, ceci afin de pouvoir estimer l’efficacité de ce dernier lorsque la structure tourne et vibre en grande amplitude, l’étude n’a pas été poursuivie et constitue une partie sans lien avec les techniques de réduction de vibrations. Néanmoins, les résultats obtenus en 1D, ainsi que la méthode de prise en compte des nonlinéarités dans le cas 3D viennent compléter et enrichir les différentes études actuelles menées sur le sujet, raison pour laquelle ce chapitre a été ajouté à ce mémoire. La détermination des caractéristiques dynamiques modales et leurs évolutions en fonction de certains paramètres de fonctionnement de l’aube constituent l’objet de cette partie. Plusieurs modèles sont développés et comparés pour pouvoir juger de la présence et de l’importance des divers phénomènes non linéaires dans la réponse forcée d’une poutre en rotation. / Vibration reduction of a turbojet fan blade with piezoelectric patches connected to a passive or semipassive electrical circuit, commonly called "shunt", is addressed in this study. The purpose of this work is to present a method for maximizing the performance of piezoelectric shunts. To validate the model, 2 experiments on a CFM56-7b fan blade are then done. To improve the damping level, a key issue is the optimization of the whole system, in terms of location and size of the piezoelectric patches and electric circuit components choice. It was shown these two optimizations, mechanical and electrical, can be realized separately. Moreover, it is proved the only parameters to maximize are the modal electromechanical coupling factors, which characterize the energy exchanges between the mechanical structure and the piezoelectric patches for a given mode. Since the optimal value of the electric circuit parameters are known as functions of the coupling factors and the system structural characteristics, they can be evaluated in a second step. Thus, the mechanical optimization consists in maximizing the coupling factors by optimizing the patches positions and dimensions, i.e. finding the best design. To fulfill this requirement and in order to manage a complex geometry, a 3D finite element formulation of the coupled electromechanical problem is derived from the one developed by Julien Ducarne during his Ph.D. thesis. A reduced order model of the discretized problem is then obtained by expanding the mechanical displacement unknowns vector onto the short-circuit eigenmodes to get the modal electromechanical coupling factors. However, when the optimization aims to reduce the vibration level with several patches, the main concern arises from the huge number of possible designs to test. For that reason, a method is proposed to cut back simulations time as well as to cope with the many local minima. This method consists in splitting up the optimization procedure in two steps. In the first one, the influence of patches on the structural eigenmodes is neglected. Therefore, an analytic coupling indicator, based on the eigenmodes of the naked host structure, can be defined and gives rise to a first approximate optimization using a simulated annealing algorithm. Then, the solutions of the first step are used as a starting point for a second optimization, working with the tabu search algorithm and where eigenmodes are computed for each new tested design.

A research report submitted to the Faculty of Civil and Environmental Engineering, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. 13 October, 2016 / A Passive Auto-Tuning Mass Damper with Pulley connections (PATPD) is a vibration control device that consists of a box filled with silica sand on roller supports. The silica sand provides the mass of the damper. The PATPD is connected to the structure to be controlled by a group of ropes and pulleys; it is free to move in any translational direction. The pulleys and rope transfer a driving force to the damper, caused by the movement of the structure. The mass provides an inertial force which, in addition to the driving force of pulleys, dissipates energy providing the vibration control of the structure. Firstly, the test model underwent ‘PATPD Efficiency tests’ where the model was subjected to free translational, torsional and coupled vibration both with and without damper. This procedure was then repeated for forced harmonic excitation and the control effect for both analysed. These tests aimed to demonstrate the effectiveness of the PATPD at controlling structural vibrations. The results indicate that the PATPD provided at least 99% reduction to first natural frequency Power Spectral Density (PSD) peak for all tests, with relatively minimal increases for others. The model then underwent ‘Parameter Tests’ where the damper characteristics were changed and test procedure above repeated. These tests aimed to investigate the effect of the property changes of the PATPD on its ability to control free and forced vibration. The results indicate that (a) the PATPD provided significant reduction to first natural frequency PSD peak for all tests and (b) the properties of the PATPD affected the amount of control provided to the structure thus optimization of the PATPD could result in improved control effect. The models’ ‘Dynamic Properties’ namely model mass and stiffness were changed and test procedure repeated. These tests aimed to demonstrate the auto-tuning or adaptivity of the PATPD in its ability to control free and forced vibration. The results indicate that for all tests performed the PATPD provided significant reduction to first natural frequency PSD peak for all tests, with relatively minimal increases for others. The PATPD worked over a wide frequency band and was able to adapt to frequency changes providing significant control effect. Additional forced vibration tests under specific frequencies close to and far away from the models’ natural frequency demonstrates PATPD adaptability and efficiency. In addition tests under random excitation (as could be expected for earthquake loading) demonstrated PATPD positive control effect, adaptability and efficiency. / MT2017

Orientador: João Eduardo Guarnetti dos Santos / Banca: José Antônio Poletto Filho / Banca: Eduardo Carlos Bianchi / Resumo: Com o crescimento da mecanização na agricultura, cresceu também o numero de acidentes, e como consequência, tem-se o aumento da preocupação com a saúde dos operadores do setor agrícola. Alguns dos fenômenos inerentes do funcionamento das máquinas e ferramentas agrícolas é a vibração e o ruído, os quais podem causar problemas a saúde ocupacional dos operadores . A vibração que é emitida pelos motocultivadores e outros equipamentos mecânicos, se propaga nas mãos e braços, e por todo o corpo do operador, podendo provocar lesões passíveis de serem qualificadas como doenças profissionais. Assim como, o ruído gerado por essas máquinas afetam o bem-estar dos operadores. O presente trabalho teve como objetivo mensurar e analisar os níveis de vibração e o ruído que são transmitidos aos operadores de motocultivadores nas condições operacionais em campo. Para essa avaliação, variou-se a marcha, rotação e o tipo de ferramenta. Os dados experimentais foram analisados estatisticamente e tecnicamente, sendo utilizada as normas vigentes ISO 5349 (2001) e NHO 10 (2013) para avaliação da vibração e NR 15 (2014) para avaliação do ruído. Baseado nos resultados constatou-se que os níveis de vibração foram preocupantes, para todas as condições, já que não permitem a exposição de 8 horas de trabalho, quanto a frequência, deve-se atentar as situações em baixa rotação, por apresentarem concentração de energia de vibração com frequências prejudiciais ao ser-humano. Os resultados de ruído mostraram que... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: With the increase of mechanization in agriculture, the number of accidents also increased, and as a consequence, there has been an increase in the concern with the health of agricultural operators.Some of the inherent phenomena of the operation of agricultural machines and tools is vibration and noise, which can cause occupational health problems for operators. The vibration that is emitted by the motorcultivadores and other mechanical equipment, spreads in the hands and arms, and by the whole body of the operator, being able to cause lesions that can qualify as occupational diseases. As well as, the noise generated by these machines affect the well-being of the operators. The aim of the present work was to measure and analyze the vibration and noise levels that are transmitted to the operators of motor cultivators under field operating conditions. For this evaluation, the gait, rotation and type of tool were varied.The experimental data were analyzed statistically and technically, with current regulation ISO 5349 (2001) and NHO 10 (2013) for vibration evaluation and NR 15 (2014) for noise assessment. Based on the results it was verified that the vibration levels were worrisome, for all the conditions, since they do not allow the exposure of 8 hours of work, as for the frequency, one must consider the situations in low rotation, because they present concentration of energy of vibration with frequencies detrimental to the human being. The noise results showed that for low rota... (Complete abstract click electronic access below) / Mestre

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During phonation, the vocal folds collision during the glottal closure is considered to be a risk factor for pathological development. This thesis is aimed at designing a dependable finite element analysis (FEA) model of the vocal folds for frequency and dynamic analysis and for calculating the impact stress between the vocal folds during glottal closure. A three-dimensional model with irregular geometry and a layered structure was designed. The measured viscoelastic properties of the vocal-fold mucosa and the transverse isotropic elastic properties of the vocal fold muscle are applied to the model. The boundary conditions are assumed to be fixed on lateral, anterior and posterior surfaces based on anatomical structure analysis. This model is symmetrical about the right and left vocal folds.The frequency and dynamic characters are presented using the software ABAQUS. The FEA model is validated by both experimental modal analysis (EMA) model results and in-vivo experimental results from the literature.In the vibration analysis, the eigenfrequency and eigenmode of the FEA model are determined. The model results compare well with the experiments performed on a silicone vocal fold model. The eigenmodes show the vibration direction at different excitation frequencies. In the closure process, the closure and collision dynamic results are obtained. The results show that: (1) the closure process is independent of the subglottal pressure; (2) the glottal opening amplitude and closing velocity vary approximately linear with the subglottal pressure; (3) the maximum impact stress occurs on the mid area of the inferior surfaces; (4) the impact stress is approximately linear with the subglottal pressure; and (5) the impact stress will cause vocal fold tissue damage when the subglottal pressure is over 800 Pa.It is anticipated that the model will help to identify voice disorders such as vocal-fold paralysis and vocal-fold nodules.

Masters Research - Master of Engineering (Research) / This thesis considers a number of related problems in the area of passive and semi-active vibration control of piezoelectric laminates. The thesis consists of three main parts. The first part of the thesis develops a mathematical model of a physical resonant system-piezoelectric laminated simply supported beam. It is essential to have a good understanding of the physical system so that the associated problems with passive and semi-active shunt damping can be addressed. The second part of the thesis is concerned with problems related with current passive shunt damping techniques using a single piezoelectric laminate. One of the current problems with multiple mode techniques is determining the correct resistive damping for each resonant mode. Therefore, a systematic method is presented for determining the optimal resistance elements by minimizing the H2 norm of the damped system. After the design process, shunt circuits are normally implemented using discrete resistors, capacitors and virtual inductors (Riordan Gyrators). The difficulty in constructing the shunt circuits and achieving reasonable performance has been an ongoing problem. A new approach to implementing piezoelectric shunt circuits is presented. A “synthetic impedance”, consisting of a voltage controlled current source and digital signal processor (DSP) system, is used to synthesize the terminal impedance of a required shunt network. The third part of the thesis is concerned with the semi-active vibration control of piezoelectric laminated. This part addresses a number of associated problems with the current passive shunt damping schemes. The foremost being the complexity of the shunt circuits required to dampen multiple modes. They generally act to minimize structural vibration at a specific frequency – which are rarely stationary. Therefore, a new broadband semi-active shunt technique for controlling multiple modes has been developed. The “negative capacitor” controller is proposed theoretically, and then validated experimentally. The negative capacitor is simular in nature to a passive shunt damper as it uses a single piezoelectric transducer to dampen multiple modes of a flexible structure.

Future NASA plans to launch large space strucutres solicit the need for effective vibration control schemes which can solve the unique problems associated with unwanted residual vibration in flexible spacecraft. In this work, a unique method of input command shaping called impulse shaping is examined. A theoretical background is presented along with some insight into the methdos of calculating multiple mode sequences. The Middeck Active Control Experiment (MACE) is then described as the testbed for hardware experiments. These results are shown and some of the difficulties of dealing with nonlinearities are discussed. The paper is concluded with some conclusions about calculating and implementing impulse shaping in complex nonlinear systems.

Vibration suppression of beams traversed by moving loads, using optimal Tuned-Mass-Damper (TMD) systems, is investigated. This study is performed on two different geometrical shapes of the beam, namely, uniform homogenous straight beam, and the uniform homogenous curved beam. Initially, three different models of the moving load on a straight beam were developed using the APDL coding in ANSYS©, a commercially available software. Results obtained from the numerical simulation of either a single moving load or a moving mass on the straight beam were compared and validated with those reported in literature. A comprehensive parameter sensitivity analysis was carried out on the beam traversed by moving load with and without the presence of random base excitation and the effects of different beam parameters on the dynamic response of the system were closely examined. Vehicles travelling on suspension bridges induce undesirable vibration, which must be suppressed to a great extent. A half-car planar model moving on a straight beam is considered to study the suppression of vibration and parameter optimization. Attempt is made to design an optimal TMD system to suppress the induced vibration of the bridge due to the moving vehicle, considerably. Furthermore, the effect of non-symmetrical and side-way motion of vehicles on bridges has been considered when both the torsional and flexural vibrations of the bridge-vehicle have been present. Optimum values of the double-acting TMDs parameters have been found to suppress the combined flexural and torsional vibrations of the supporting beam structure. Similar work has been carried out on a uniform homogenous curved beam traversed by either a moving load or a half-car planner model. The effects of the beam curvature angle and the type of loading are closely studied. Optimum values of the two TMDs were obtained to suppress the combined flexural and torsional vibrations of bridges traversed by traveling vehicles. / UOIT

This thesis presents results from experimental and numerical investigations of the hydrodynamic forces on a rigid cylinder moving with prescribed orbits in uniform flow. The hydrodynamic forces are measured in both in-line (IL) and cross- ow (CF) directions. The measurements are processed to nd excitation and added mass coeffcients at discrete frequencies. The numerical simulations are used to illustrate the vortex shedding modes and are compared with the experimental results. The hydrodynamic coeffcients obtained from the harmonic forced motion experiments of a rigid cylinder do not always represent forces on a cross section of a exible beam. The orbits used in the forced motion experiments are therefore extracted from the measured motions of cross sections of a exible pipe under uniform and shear flows. Both periodic and observed orbits within a time window are applied as prescribed motions. Higher order displacement components are present in such orbits. IL response amplitudes from combined IL and CF response are larger than pure IL response amplitudes. The hydrodynamic coefficients obtained from the periodic experiments are often larger than those obtained from the pure IL tests. Higher order displacement components are more common in the IL direction than in the CF direction, and higher order IL displacement components will cause larger hydrodynamic forces in both directions. The hydrodynamic coefficients obtained from periodic motion tests are adequate for representing quasi-periodic observed motions. For chaotic observed motions, periodic orbits will yield hydrodynamic coefficients with larger uncertainties. Results from numerical analyses using large eddy simulation (LES) indicate that this method can be used to identify vortex shedding patterns and predict hydrodynamic forces under certain Re numbers and orbits.

The present study proposes a simple and relatively complete displacement field, which, with the finite element formulation, can be employed in the analyses of the free vibration of circular and annular plates, the vibration with preloading in the radial direction, which is studied quite often, and the vibration with preloading under twisting, which has not yet appeared in the literature. The present results of the free vibration and the vibration under compressive stresses for circular and annular plates with different boundary conditions and various aspect ratios will be compared with those by ANSYS and other research. From the comparisons, we know that the present method does not need a fine mesh to get accurate natural frequencies of the plates. As to the vibration for the bar or tube with pretorsional loading, coupled vibration modes in the r-z plane and £c direction, it can be revealed by the present method, and the appearance of these vibration modes may be due to the coupling terms from the proposed displacement field. Also, these vibration modes have not been shown before.