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This thesis is to develop a new ocean-wave-energy acquisition system. This system is composed of a float plate, a buoy, a nearly resonant vibrator, a dynamotor, and an oil pressure system. The whole system can be divided into two sub-systems by its function: energy generation system or vibration reduction system. Each of them can generate energy from ocean wave and reduce the vibration of flow plate. After simplifying the dynamic model and optimization analysis, we will discuss with the influence of parameters on the amount of energy and the vibration reduction. Energy generation system want to the maximum power by optimizing system parameters (mass of the buoy, mass of the nearly resonant vibrator, the coefficient of spring, and the coefficient of generator). Here we will use four kinds of optimization methods. In the first three methods, we want to find the suitable parameters to make system to generate the maximum power at an operation of frequency wave. These three methods are different from the request of the relation phase of displacement between the buoy and the nearly resonant vibrator. The fourth method, we want to find the parameters of system, which can generate power evenly at each of frequency in a range of frequency wave motion. The work is done by searching for minimum variance of power. Vibration reduction system can reduce the vibration of float plate by optimizing parameter. After simplifying and making some assumptions, system can be simplified approximately to a vibration absorber at a specific frequency. There is no displacement at that frequency, but there are displacements on the other frequency of the operation range. In order to let system to apply properly in a range of frequency, we find the minimum one that is the maximum displacement in the range of frequency. After optimization design, we can get each result from these two sub-systems. From the first three methods of energy generation system, all energy distributes on the around of operation frequency. There are no frequencies on the others of the operation range. Moreover, the displacement of each body in this system is too large to apply. By the fourth method, energy-frequency curve is evenly on the operation range. Overall, the average of energy is larger than that of frequency of system whose design concept from first three methods. The displacements of each body in this system are small enough to apply. In vibration reduction system, we search the parameters in the optimization methods. The results show that vibration reduction just occurs around the operation frequency and the others in the range not

The precise control of spacecraft with flexible appendages is extremely difficult. The complexity of this task is magnified many times when several flexible spacecraft must be controlled precisely and collaboratively, as in formation flying. Formation flying requires a group of spacecraft to fly in a desired trajectory while maintaining both relative positions and velocities with respect to each other. This work enhances two current state-of-the-art formation flying algorithms, specifically leader-follower and virtual-structure architectures. First, a flexible satellite model is integrated into each of these architectures. Second, input shaping is used to generate the satellites desired trajectories, thereby enhancing the performance of the system. This dissertation addresses key issues regarding the application of command generation techniques to flexible satellites controlled with formation flying control architectures. The temporal tracking and the trajectory tracking of each architecture are examined as well as the vibration characteristics of the formation satellites. Design procedures for applying trajectory shaping for the leader-follower and virtual-structure architecture are developed. Experiments performed on a flexible satellite testbed verify key simulated results.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Liang-Wu Cai / X. J. Xin / Thin walled structures such as plates and shells have application in many fields of engineering because these structures are light weight and can support large loads when designed suitably. In real world, loads may cause these structures to vibrate which can be undesirable causing fatigue and failure of the structure. Such undesirable vibrations need to be reduced or eliminated. In this work, analytical studies of flexural wave propagation for idealized geometries are conducted and finite element method (FEM) is used to explore the effects of composite panel designs of finite size for the reduction of vibration transmission. In the analytical studies, the influence of the material properties on the reflection and transmission characteristics are explored for an infinite bi-material plate, and infinite plate with a strip inhomogeneity. In the analytical study of an infinite thin plate with a solid circular inclusion, the far and near field scattering characteristics are explored for different frequencies and material properties. All the analytical studies presented here and reported in the literature consider infinite plates to characterize the flexural wave propagation. Obtaining closed form solutions to characterize the flexural wave propagation in a finite plate with inclusions is mathematically difficult process. So, FEM is used to explore the composite panel designs. The understanding gained about the material properties influence on the flexural wave propagation from analytical studies helped with the choice of materials for FEM simulations. The concept of phononic crystals is applied to define the design variations that are effective in suppressing vibration transmission. Various design configurations are explored to study the effects of various parameters like scatterer’s material properties, geometry and spatial pattern. Based on the knowledge gained through a systematic parametric study, a final design of the composite sandwich panel is proposed with an optimum set of parameters to achieve the best vibration reduction. This is the first study focused on reducing vibration and wave transmission in composite rotorcraft fuselage panels incorporating the concept of phononic crystals. The optimum sandwich panel design achieved 98% vibration transmission reduction at the frequency of interest of 3000 Hz.

The objective of this study was to design and build an after-market suspension for the rear wheels of a manual wheelchair. Suspension for wheelchairs is important because it has been reported that the International Organization for Standards' requirements for vibration loads on wheelchair users (ISO 2631-1), are not meet by today's standard wheelchairs. Today's wheelchairs need to be able to absorb everyday shock loads, thereby minimizing the energy transmitted to the user. The chosen design is based around the concept of adding shock reduction material between the hub of the wheel, and the axel bolt that connects the wheel to the frame of the chair. The approach taken was to design a suspension system that resides between an oversized wheel bearing, and the axle. To do this, ball-race bearings with an inner diameter of 4" were chosen, and polyurethane rubber was used as the shock absorbing material. Pro-Mechanica, a finite element analysis program, was used to analyze the suspension system. Since the most common camber/tilt for wheelchair wheels is three degrees from the vertical, the anticipated loads were applied to the wheel at this angle. A prototype of the suspension system was constructed to verify that the design would work, but no tests were performed on it. This analysis showed that the suspension system should not fail when subjected to 10 times the static load. This load was considered large enough to encompass the forces that a wheelchair chair wheel is typically subjected to. There is room for further work in the area of weight reduction, and in the use of the suspension system on steeper wheel cambers.

Large area high throughput metrology plays an important role in several technologies like MEMS. In current metrology systems the parallel operation of multiple metrology probes in a tool has been hindered by their bulky sizes. This study approaches this problem by developing a metrology technique based on miniaturized scanning grating interferometers (μSGIs). Miniaturization of the interferometer is realized by novel micromachined tunable gratings fabricated using SOI substrates. These stress free flat gratings show sufficient motion (~500nm), bandwidth (~50 kHz) and low damping ratio (~0.05). Optical setups have been developed for testing the performance of μSGIs and preliminary results show 6.6 μm lateral resolution and sub-angstrom vertical resolution. To achieve high resolution and to reduce the effect of ambient vibrations, the study has developed a novel control algorithm, implemented on FPGA. It has shown significant reduction of vibration noise in 6.5 kHz bandwidth achieving 6x10-5 nmrms/√Hz noise resolution. Modifications of this control scheme enable long range displacement measurements, parallel operation and scanning samples for their dynamic profile. To analyze and simulate similar optical metrology system with active micro-components, separate tools are developed for mechanical, control and optical sub-systems. The results of these programs enable better design optimization for different applications.

Cette thèse CIFRE (Conventions Industrielles de Formation par la REcherche), en collaboration avec Safran Aircraft Engines, concerne la réduction des vibrations de flexion en basse fréquence d'une aube de rotor de soufflante en matériau composite. L'intérêt premier est de réduire les marges au flottement en augmentant l'amortissement des aubages pour permettre l'utilisation des moteurs dans des plages de fonctionnement à haut rendement actuellement inexploitées. Les autres avantages directement liés à la réduction de vibration sont l'augmentation de la durée de vie des pièces ainsi que la réduction du bruit du moteur. L'objet de cette étude, est d'étudier différents dispositifs d'amortissement de vibrations piézoélectriques, en basses fréquences, applicables à une aube de turbomachine fabriquée en matériaux composites. Les applications principalement visées sont des aubes de rotor de soufflante ou des pales de rotor non caréné ("open-rotor"), de géométrie élancée et complexe. Les solutions étudiées utilisent des éléments piézoélectriques couplés à un circuit électrique passif ou semi-passif. Le coeur de ce travail de thèse, encore un verrou scientifique à l'heure actuelle, est de proposer des solutions performantes qui intègrent les éléments piézoélectriques aux aubes de soufflante afin de respecter les contraintes aérodynamiques imposées pour ce type de structure, tout en augmentant l'amortissement sur un des premiers modes de vibration. Les performances de ce genre de dispositifs sont directement liées à une grandeur : le facteur de couplage électromécanique, qu'il s'agit de maximiser. Il dépend de toutes les caractéristiques de la structure : les matériaux utilisés (structure composite hôte, matériau piézoélectrique), mais surtout du placement et de la géométrie des éléments piézoélectriques. L'utilisation de matériaux piézoélectriques connectés à des circuits actifs, semi-passifs ou passifs a été largement étudiée mais les expériences traitent presque toujours de cas académiques de poutres ou de plaques. L'objectif est ici, pour le dispositif piézoélectrique développé, de pouvoir évaluer les performances des shunts en terme d'atténuation sur une structure massive faiblement amortie. Une partie du travail consiste ainsi à bâtir un modèle éléments finis prédictif de la structure composite couplée aux matériaux piézoélectriques, en vue de quantifier les performances du dispositif. Plusieurs solutions sont testées sur une structure simple pour évaluer l'influence sur les performances du dispositif, (1) du choix du matériau piézoélectrique, (2) du placement et de la géométrie des éléments piézoélectriques ainsi que (3) du circuit électrique dissipatif. Différentes solutions d'intégration à l'aube sont proposées et une méthode de caractérisation des propriétés des matériaux tissés est développée dans la perspective d'intégrer les matériaux actifs à la préforme du composite. Cette étude est à la fois numérique et expérimentale : un démonstrateur, utilisant une aube en matériaux composites est conçu puis testé en laboratoire pour valider les concepts proposés. / This thesis concerns the vibration reduction in the low frequency range of a composite fan blade of a turbojet engine with piezoelectric devices. The interest is to increase lifespan and avoid flutter phenomena by reducing the vibration amplitude. The purpose of this thesis is to study several shunted piezoelectric devices, in the low frequency range, that can be applied to a woven composite turbojet fan blade. The targeted applications are the LEAP fan blades or the “open-rotor” fan blade, both of them required to manage a complex geometry. The solutions investigated used piezoelectric elements coupled to a passive or semi-passive circuit. The core of this thesis, still a scientific obstacle at present, is to propose efficient solutions that integrate the piezoelectric elements to the fan blades in order to meet aerodynamic constraints for this type of structure, while increasing damping level on one of the first modes of vibration. The performances of such devices are directly related to a coefficient: the electromechanical coupling factor that requires to be maximized. This coefficient depends on all the features of the structure: materials used (host composite structure, piezoelectric material), but especially the placement and geometry of the piezoelectric elements. The use of piezoelectric material connected to active, semi-passive or passive circuits has been extensively studied but the experiences almost always deal with academic cases such as beams or plates. The aim is for the developed piezoelectric device, to evaluate the damping performance of a weakly damped massive structure.A part of the work is thus to develop a predictive finite element model of the structure coupled to the piezoelectric material to quantify the performance of the device. Several solutions are tested on a simple structure to evaluate the influence on the device performance of, (1) the choice of the piezoelectric material, (2) the placement and geometry of the piezoelectric elements, and (3) of the dissipative circuit. Various integration solutions in the blade are proposed and a method for characterizing the properties of woven materials is developed in the perspective of integrating the active materials in the composite preform.This study is both numerical and experimental: a demonstrator using a composite fan blade is designed and tested in the laboratory to validate the proposed concepts.

Constrained negative stiffness elements in volume concentrations (1% to 2%) embedded within viscoelastic materials have been shown to provide greater energy absorption than conventional materials [Lakes et al., Nature (London) 410, 565–567 (2001)]. This class of composite materials, called meta-materials, could be utilized in a variety of applications including noise reduction, anechoic coatings and transducer backings. The mechanism underlying the meta-material's behavior relies on the ability of the negative stiffness element to locally deform the viscoelastic material, dissipating energy in the process. The work presented here focuses specifically on the design of the negative stiffness elements, which take the form of buckled beams. By constraining the beam in an unstable, S-shaped configuration, the strain energy density of the beam will be at a maximum and the beam will accordingly display negative stiffness. To date, physical realization of these structures has been limited due to geometries that are difficult to construct and refine with conventional manufacturing materials and methods. By utilizing the geometric freedoms allowed by the Selective Laser Sintering (SLS) machines, these structures can be built and tuned for specific dynamic properties. The objective of this research was to investigate the dynamic behavior of SLS-constructed meso-scale negative stiffness elements with the future intention of miniaturizing the elements to create highly absorptive meta-materials. This objective was accomplished first through the development and analysis of a mathematical model of the buckled beam system. A characterization of the Nylon 11 material was performed to obtain the material properties for the parts that were created using SLS. Applying the mathematical model and material properties, a tuned meso-scale negative stiffness structure was fabricated. Transmissibility tests of the meso-scale structure revealed that the constrained negative stiffness system was able to achieve overall higher damping and vibration isolation than an unconstrained system. Quasistatic behavior of the system indicated that these elements would be ideal for implementation within meta-materials. Based on the results of the meso-scale system, a method to test a representative volume element for a negative stiffness meta-material was developed for future completion. / text

<p>Dynamic systems and robotic manipulators designed for time-optimal point-to-point motion are adversely affected by residual vibrations introduced due to the joint flexibility inherent in the system. Over the years, multiple techniques have been employed to improve the efficiency of such systems. While some techniques focus on increasing the system damping to efficiently dissipate the residual energy at the end of the move, several techniques achieve rapid repositioning by developing cleverly shaped input profiles that aim to reduce energy around the natural frequency to avoid exciting the resonant modes altogether. In this work, a numerical framework for constructing shaped inputs using a Versine basis function with peak acceleration constraint has been developed and improvements for the existing numerical framework for the Ramped Sinusoid basis function have been made to extend the range of values of the weighting function and improve the computational time. Performance metrics to evaluate the effectiveness of the numerical framework in minimizing residual vibrations have been developed. The effects of peak input acceleration and weighting function on the residual vibration in the system have been studied. The effectiveness of the method has been tested under multiple conditions in simulations and the results were validated by performing experiments on a two-link flexible joint robotic arm. The simulation and experimental results conclusively show that the inputs developed using the constrained numerical approach result in better residual vibration performance as compared to that of an unshaped input. </p>

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.