No description available.

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

Resonance frequency detuning (RFD) is a piezoelectric-based vibration reduction approach that applies to systems experiencing transient excitation through the system*s resonance—for example, turbomachinery experiencing changes in rotation speed, such as on spool-up and spool-down. This technique relies on the inclusion of piezoelectric material and manipulation of its electrical boundary conditions, which control the stiffness of the piezoelectric material. Resonance frequency detuning exploits this effect by intelligently switching between the open-circuit (high stiffness) and short-circuit (low stiffness) conditions as the excitation approaches resonance, subsequently shifting the natural frequency to avoid this resonance crossing and limit the response. The peak response dynamics are then determined by the system*s sweep rate, modal damping ratio, electromechanical coupling coefficient, and, most importantly, the trigger (represented here in terms of excitation frequency) that initiates the stiffness state switch. This thesis identifies the optimal frequency-based switch trigger over a range of sweep rates, damping ratios, and electromechanical coupling coefficients. With perfect knowledge of the system, the optimal frequency-based switch trigger decreases approximately linearly with the square of the coupling coefficient. Furthermore, phase of vibration at the time of the switch has a very small effect; switching on peak strain energy is marginally optimal. In practice, perfect knowledge is unrealistic and an alternate switch trigger based on an easily measurable parameter is necessary. As such, this thesis also investigates potential methods using the open-circuit piezoelectric voltage response envelope and its derivatives. The optimal switch triggers collapse to a near linear trend when measured against the response envelope derivatives and, subsequently, an empirical control law is extracted. This control law agrees well with and produces a comparable response to that of the optimal control determined using perfect and complete knowledge of the system.

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.

Structural topology optimization has been extensively studied in aeronautical, civil, and mechanical engineering applications in order to improve performance of systems. This thesis focuses on an optimal design of damping treatment using topology optimization, and the reduction of computational expense of the topology optimization procedure. This thesis presents mainly two works on topology optimization. In the first work, topology optimization is implemented to optimally design damping treatments in unconstrained-layer damping material. Since the damping effect relies on the placement of damping treatment, and the weight of damping material may be an important factor, the placement of damping material is optimally determined using topology optimization with an allowable maximum. Unconstrained-layer plate and shell structures are modeled. The damping layer on the unconstrained-layer structures is considered as the design domain. Using topology optimization, the damping layer is designed numerically, and then experimentally validated by comparing the damping effects. In the numerical example, the topological damping treatment usually provides much higher damping effects compared to other approaches such as strain energy distribution (SED) and an evolutionary structural optimization (ESO). In the second work, a numerical algorithm, named as reducible design variable method (RDVM) topology optimization, is proposed in order to efficiently reduce the computational expense. Since it usually requires thousands to millions of design variables and up to hundreds of iterations in topology optimization, the major difficulty is its computational expense. The RDVM topology optimization is implemented into static (minimization of compliance) and dynamic (maximization of the fundamental resonance frequency) problems. The RDVM significantly reduces computing time, as confirmed by numerical examples. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2011-07-08 10:10:20.606

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.

Vibration control is a large branch in control research, because all moving systems may induce desired or undesired vibration. Due to the limitation of passive system's adaptability and changing excitation input, vibration control brings the solution to change system dynamic with desired behavior to fulfill control targets. According to preference, vibration control can be separated into two categories: vibration reduction and vibration amplification. Lots of research papers only examine one aspect in vibration control. The thesis investigates the control development for both control targets with two different control applications: vehicle suspension and ocean wave energy converter. It develops control methods for both systems with simplified modeling setup, then followed by the application of a novel mechanical motion rectifier (MMR) gearbox that uses mechanical one-way clutches in both systems. The flow is from the control for common system to the control design for a specifically designed system. In the thesis, active (model predictive control: MPC), semi-active (Skyhook, skyhook-power driven damper: SH-PDD, hybrid model predictive control: HMPC), and passive control (Latching Control) methods are developed for different applications or control performance comparison on single system. The thesis also studies about new type of system with switching mechanism, in which other papers do not talk too much and possible control research direction to deal with such complicated system in vibration control. The state-space modeling for both systems are provided in the thesis with detailed model of the MMR gearbox. From the simulation, it can be shown that in the vehicle suspension application, the controlled MMR gearbox can be effective in improving vehicle ride comfort by 29.2% compared to that of the traditional hydraulic suspension. In the ocean wave energy converter, the controlled MMR WEC with simple latching control can improve the power generation by 57% compared to the passive MMR WEC. Besides, the passive MMR WEC also shows its advantage on the passive direct drive WEC in power generation improvement. From the control development flow for the MMR system, the limitation of the MMR gearbox is also identified, which introduces the future work in developing active-MMR gearbox by using an electromagnetic clutch. Some possible control development directions on the active-MMR is also mentioned at the end of the thesis to provide reference for future works. / Master of Science / Vibration happens in our daily life in almost all cases. It is a regular or irregular back and forth motion of particles. For example, when we start a vehicle, the engine will do circular motion to drive the wheel, which causes vibration and we feel wave pulses on our body when we sit in the car. However, this kind of vibration is undesirable, since it makes us uncomfortable. The car manufacture designs cushion seats to absorb vibration. This is a way to use hardware to control vibration. However, this is not enough. When vehicle goes through bumps, we do have suspension to absorb vibration transferred from road to our body. The car still experiences a big shock that makes us feel dizzy. On the opposite direction, in some cases when vibration becomes the motion source for energy harvesting, we would like to enhance it. Hardware can be helpful, since by tuning some parameters of an energy harvesting device, it can match with the vibration source to maximize vibration. However, it is still not enough due to low adaptability of a fixed parameter system. To overcome the limitation of hardware, researches begin to think about the way to control vibration, which is the method to change system behavior by using real-time adjustable hardware. By introducing vibration control, the theory behind that started to be investigated. This thesis investigates the vibration control theory application in both cases: vibration reduction and vibration enhancement, which are mentioned above due to opposite application preferences. There are two major applications of vibration control: vehicle suspension control and ocean wave energy converter (WEC) control. The thesis starts from the control development for both fields with general modeling criteria, then followed by control development with specific hardware design-mechanical motion rectifier (MMR) gearbox-applied on both systems. The MMR gearbox is the researcher designed hardware that targets on vibration adjustment with hardware capability, which is similar as the cushion seats mentioned at the beginning of the abstract. However, the MMR cannot have capability to furtherly optimize system vibration, which introduces the necessity of control development based on the existing hardware. In the suspension control application, the control strategy introduced successfully improve the vehicle ride comfort by 29.2%, which means the vehicle body acceleration has been reduced furtherly to let passenger feel less vibration. In the WEC application, the power absorbed from wave has been improved by 57% by applying suitable control strategy. The performance of improvement on vibration control has proved the effect on further vibration optimization beyond hardware limitation.