Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references. Also available in electronic version.

Thesis (M.S.)--Rochester Institute of Technology, 2006. / Typescript. Includes bibliographical references (leaves 132-137).

This study investigates energy harvesting characteristics from a spinning device that consists of a proof mass that is supported by two orthogonal elastic structures with the piezoelectric material. Deformation in the piezoelectric structures due to vibration of the proof mass generates voltages to power electrical loads. The governing equations for this electromechanically coupled device are derived using Newtonian mechanics and Kirchhoff's voltage law. The case where the device rotates at a constant speed and is subjected to sinusoidal base excitation is examined in detail. The energy harvesting behavior is investigated for devices with identical piezoelectric support structures (called tuned devices). Closed-form expressions are derived for the steady state response and power harvested. For nonzero rotation speeds, these devices have multifrequency dynamic response and power harvested due to the combined vibration and rotation of the host system. The average power harvested for one oscillation cycle is calculated for a wide range of operating conditions to quantify the devices' performance. Resonances do not occur for cases when the base excitation frequency is fixed and the rotation speed varies. For cases of fixed rotation speed and varying base excitation frequency, however, resonances do occur. The number and location of these resonances depend on the electrical circuit resistances and rotation speed. Resonances do not occur at speeds or frequencies predicted by resonance diagrams, which are commonly used in the study of rotating system vibration. These devices have broadband speed energy harvesting ability. They perform equally well at high and low speeds; high speeds are not necessary for their optimal performance. The impact of the chosen damping model on energy harvesting characteristics for tuned devices is investigated. Two common damping models are considered: viscous damping and structural (hysteretic) damping. Closed-form expressions for steady state dynamic response and power harvested are derived for models with viscous and structural damping. The average power harvested using the model with structural damping behaves similarly at high speeds and low speeds, and at high resistances and low resistances. For the viscous damping model, however, the average power harvested is meaningfully different at high speeds compared to low speeds, and at high resistances compared to low resistances. The characteristics of devices with nonidentical piezoelectric support structures (called mistuned devices) are investigated numerically. Similar to spinning tuned devices, mistuned devices have multifrequency dynamic response and power harvested. In contrast to tuned devices, high amplitude average power harvested occurs near speeds and base excitation frequencies predicted by resonance diagram.

Made available in DSpace on 2014-06-11T19:27:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-09-26Bitstream added on 2014-06-13T20:35:23Z : No. of bitstreams: 1 prazzo_ce_me_ilha.pdf: 1585012 bytes, checksum: 3ddb6b2bb4fddee99d49636888c24ded (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Esse trabalho discute o uso dos materiais piezelétricos, mais especificamente, o Polyvinylidene Fluoride (PVDF) e o Lead Zirconate Titatane (PZT) na análise modal experimental (AME) de estruturas mecânicas. Materiais piezelétricos, também chamados de materiais inteligentes, têm se consolidado como uma nova tecnologia que mostra um grande potencial de aplicação em diferentes áreas da engenharia. Esse tipo de material exibe um acoplamento entre multi-domínios físicos, como por exemplo o acoplamento eletro-mecânico, o térmo-magnético, etc. O acoplamento eletro-mecânico produz um deslocamento elétrico quando o material é sujeito a uma tensão mecânica (efeito direto) e um deformação mecânica quando esse material é submetido a um campo elétrico (efeito inverso). Assim, principalmente por conta desses efeitos, seu uso no campo da análise modal experimental torna-se uma interessante questão a ser investigada. A incorporação de novas tecnologias nos testes estruturais pode agregar novos conhecimentos e avanços tanto na análise modal baseada na relação entrada-saída da estrutura, quanto na mais recente técnica, a análise modal baseada apenas na resposta das mesmas. Os conceitos teóricos para o desenvolvimento são apresentados e discutidos neste trabalho, onde é mostrada a análise modal de uma viga utilizando tanto sensores e atuadores convencionais quanto os produzidos com materiais inteligentes. Os testes de análise modal da viga foram feitos utilizando diferentes combinações de sensores e atuadores e isso pode mostrar as diferenças da estimativa de modos utilizando materiais piezelétricos. Também é apresentada a formulação da relação entre os modos em deslocamento e os modos com diferença de inclinação obtidos com materiais piezelétricos e, finalmente, uma comparação dos resultados obtidos pelas diferentes técnicas. Os testes apresentados mostram... / This work discusses the use of piezoelectric materials, more specifically, Polyvinylidene Fluoride (PVDF) and Lead Zirconate Titanate (PZT) for experimental modal analysis (EMA) of mechanical structures. Piezoelectric materials also called smart materials have becoming a consolidated new technology that shows a large potential of application for different engineering areas. These materials exhibit a multi physics domain field coupling like mechanical and electrical coupling domains, thermal and magnetic coupling and etc. The electro-mechanical coupling domains of the material produces an electric displacement when the material is subject to a mechanical stress (direct-effect) and a mechanical strain when the material is submitted to an electric field (inverse effect). So, mainly due to these effects, the use in the experimental modal analysis field appears to be an interesting issue to be investigated. The incorporation of this new technology in the structural tests might aggregate new acknowledgments and advances in the well consolidated input-output based modal analysis techniques as well as in the more recent output only-based modal analysis. This work aims to present some contribution in this area by using piezoelectric sensors, instead of the conventional ones like accelerometers for modal analysis of mechanical structures. The theoretical concepts and background for the developing of the work are presented and discussed, it is also presented the modal analysis of a beam like structure using conventional sensors/actuators and piezoelectric materials. The modal analysis tests of the beam are conducted using different kinds of sensors/actuator and they give some insight of the difference of the estimated modes shapes by using piezoelectric materials. It is also presented a formulation that shows the relation between... (Complete abstract click electronic access below)

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, Cape Town,1999 / Smart structures technology featuring a network of sensors and actuators, real-time control capabilities, computational capabilities and host material will have tremendous impact upon the design, development and manufacture of the next generation of products in diverse industries. The idea of applying smart materials to mechanical and structural systems has been studied by researchers in various disciplines. Among the promising materials with adaptable properties such as piezoelectric polymers and ceramics, shape memory alloys, electrorheological fluids and optical fibers, piezoelectric materials can be used both as sensors and actuators because of their high direct and converse piezoelectric effects. The advantage of incorporating these special types of material into the structure is that the sensing and actuating mechanism becomes part of the structure by sensing and actuating strains directly. This advantage is especially apparent for structures that are deployed in aerospace and civil engineering. Active control systems that rely on piezoelectric materials are effective in controlling the vibrations of structural elements such as beams, plates and shells. The beam as a fundamental structural element is widely used in all construction. The purpose of the present project is to derive a set of approximate governing equations of smart composite beams. The approximate analytical solution for laminated beams with piezoelectric laminae and its control effect will be also presented. According to the review of the related literature, active vibration control analysis of smart beams subjected to an impulsive loading and a periodic excitation are simulated numerically and tested experimentally.

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, Cape Town, 2002 / Distributed Piezoelectric Actuator (DPA) is one kind of actuator in the smart technology field. Firstly, DPA is one kind of solid-state actuator, and can be embedded in the structure. Secondly, it can be controlled by the electrical signal with high bandwidth and high precision. So it can be applied in the many different fields, such as high-resolution positioning, noise and vibration detection and shape control. Up to now, all of the DPA theory investigations and the product designs are based on applying the approximate electrical field. And only the rectangular shape DPA has been studied. The accurate distribution and intensity of electrical and mechanics field, and the numerical imitation for the DPA products with rectangular and other shapes have never been discussed and studied. Therefore, the development of DPA to be used in the micro application, such as in the Micro Electro-Mechanical System (MEMS), has been limited. This thesis has developed the analytical analysis models for two types of DPA elements and the part circular shape DPA element. The MathCAD and MATLAB program have been used to develop the analytical models. The ABAQUS program has also been used to compare the results between the analytical models and Finite Element Method (FEM). Finally, the accuracy and reliability of analytical models have been proved by results comparison between the analytical models, FEM and the product testing data from the industry. This thesis consists of five chapters. Chapter 1 is the introduction of smart structure. The characterizations of constituent materials, including the piezoelectric material and matrix epoxy material have been discussed in Chapter 2. In Chapter 3, the analytical models for two type of DPA element have been developed and the comparisons have also been completed. The analytical models for part circular shape DPA element have been developed in Chapter 4. The conclusions and recommendations are included in Chapter 5.

Desde o final da década de 1980 até os dias atuais a utilização de materiais inteligentes em sistemas de controle de vibrações e em problemas de conversão de energia mecânica em energia elétrica tem sido amplamente investigada. Entre os materiais inteligentes destacamos os piezelétricos, apresentando acoplamento entre os domínios elétrico e mecânico. Em casos de controle passivo de vibrações utiliza-se o efeito piezelétrico direto e a energia de vibração é dissipada em um circuito elétrico passivo. Apesar de não utilizarem uma fonte externa de energia, a faixa de frequências onde o controlador passivo tem bom desempenho é limitada em relação aos controladores ativos. Em problemas de controle ativo de vibrações o efeito piezelétrico inverso é utilizado. Neste caso, uma tensão elétrica de controle é aplicada aos piezelétricos para a atenuação de vibrações. Os sistemas híbridos de controle (ativo-passivo) associam circuitos passivos e uma fonte de tensão elétrica. Nesse caso, os efeitos piezelétricos direto e inverso são utilizados simultaneamente. Espera-se que a parte ativa do sistema híbrido necessite de menor potência elétrica de atuação (se comparado com um controlador ativo) além do sistema híbrido proporcionar melhor resposta estrutural que o sistema passivo isoladamente. Entretanto, os controladores ativos e híbridos apresentam desvantagens relacionadas com complexidades de uma lei de controle, necessidade de equipamentos externos e podem exigir elevada potência de atuação. Os controladores semi-passivos surgiram como uma alternativa aos pontos negativos dos controladores passivos, ativos e híbridos. Uma técnica semi-passiva chamada SSD (synchronized switch damping) consiste no chaveamento do material piezelétrico entre a condição de circuito aberto e a condição de curto-circuito (SSDS) ou a uma indutância (SSDI), em momentos específicos da vibração da estrutura. Em geral, a conversão eletromecânica de energia é amplificada assim como o efeito shunt damping. Dessa forma, os circuitos semi-passivos, assim como os passivos, têm sido utilizados tanto como controladores de vibração quanto em problemas de coleta piezelétrica de energia. O objetivo deste trabalho é avaliar o desempenho de controladores piezelétricos passivos, semi-passivos, ativos e híbridos na atenuação de vibrações e também em problemas aeroelásticos. O modelo piezoaeroelástico é obtido com um modelo por elementos finitos (placa de Kirchhoff) eletromecanicamente acoplado que associado a um modelo aerodinâmico não-estacionário (método de malha de dipolos) resulta um modelo piezoaeroelástico. Casos de excitação harmônica de base, entrada impulsiva e também condição de flutter são estudados. / From the late 1980s until the present date, the use of smart materials as actuators in vibration control systems and as conversers of mechanical energy into electricity has been widely investigated. Among these smart materials, the piezoelectric ones stand out, presenting a coupling between the electrical and mechanical domain. In passive vibration control, the direct piezoelectric effect is used and vibration energy is dissipated (or harvested) in a passive circuit. Although no external power source is required, the frequency bandwidth in which passive controllers have good performance is limited when compared to active controllers. In active vibration control problems, the inverse piezoelectric effect is used. In this work, a voltage source is applied on the piezoceramic patches in order to attenuate vibration. Hybrid (active-passive) vibration controllers combine passive shunt circuits with the voltage source. In this case, the direct and inverse piezoelectric effects are used simultaneously. It is expected that the active part of the hybrid system will require less energy (when compared to an active controller) and a better structural response will be obtained than the purely passive system. Nevertheless, the active and hybrid controllers present disadvantages such as complexity of a control law, require external equipment and potentially require large amounts of energy. The semi-passive controllers are a recent alternative to the drawbacks of passive, active and hybrid controllers. A semi-passive technique called SSD (synchronized switch damping) consists of using an electronic switch that the piezoelectric element is briefly switched to an electrical shunt-circuit that can be a simple short-circuit (SSDS), or a small inductance (SSDI) at specific times in the structure\'s vibration cycle (Mohammadi, 2008). In general, the electromechanical energy conversion is enhanced as well as the shunt effect damping. Therefore, the switching techniques, as well as the passive circuits, have been used both in vibration control problems and in piezoelectric energy harvesting problems. The goal of this work is to assess the performance of passive, semi-passive, active and hybrid piezoelectric controllers to attenuate vibration in aeroelastic problems. The aeroelastic model is obtained by combining an electromechanically coupled finite element model (Kirchhoff\'s plate) with an unsteady aerodynamic models (the doublet-lattice method and Roger\'s model). The case studies are carried out on an elastic wing response to a base excitation, impulse force, and the flutter condition.

Impedance-based Non-Destructive Evaluation for Additive Manufacturing (INDEAM) is rooted in the field of Structural Health Monitoring (SHM). INDEAM generalizes the structure-to-itself comparisons characteristic of the SHM process through introduction of inter-part comparisons: instead of comparing a structure to itself over time, potentially-damaged structures are compared to known-healthy reference structures. The purpose of INDEAM is to provide an alternative to conventional nondestructive evaluation (NDE) techniques for additively manufactured (AM) parts. In essence, the geometrical complexity characteristic of AM processes combined with a phase-change of the feedstock during fabrication complicate the application of conventional NDE techniques by limiting direct access for measurement probes to surfaces and permitting the introduction of internal defects that are not present in the feedstock, respectively. NDE approaches that are capable of surmounting these challenges are typically highly expensive. In the first portion of this work, the procedure for impedance-based NDE is examined in the context of INDEAM. In consideration of the additional variability inherent in inter-part comparisons - as opposed to part-to-itself comparisons - the metrics used to quantify damage or change to a structure are evaluated. Novel methods of assessing damage through impedance-based evaluation are proposed and compared to existing techniques. In the second portion of this work, the INDEAM process is applied to a wide variety of test objects. This portion considers how the sensitivity of the INDEAM process is affected by defect type, defect size, defect location, part material, and excitation frequency. Additionally, a procedure for studying the variance introduced during the process of instrumenting a structure is presented and demonstrated. / Doctor of Philosophy / Impedance-based Non-Destructive Evaluation for Additive Manufacturing (INDEAM) is a quality control approach for detecting defects in structures. As indicated by the name, impedance-based evaluation is discussed in this work in the context of qualifying additively manufactured (3D printed) structures. INDEAM fills a niche in the wider world of nondestructive evaluation techniques by providing a less expensive means to qualify structures with complex geometry. Complex geometry complicates inspection by preventing direct, physical access to all the surfaces of a part. Inspection approaches for parts with complex geometry suffuse a structure with energy and measure how the energy propagates through the structure. A prominent technique in this space is CT scanning, which measures how a structure attentuates x-rays passing through it. INDEAM uses piezoelectric materials to both vibrate a structure and measure its response, not unlike listening for the dull tone of a cracked bell. By applying voltage across a piezoelectric patch glued to a structure, the piezoelectric deforms itself and the bonded structure. By monitoring the electrical current needed to produce that voltage, the ratio of applied voltage to current draw---impedance---can be calculated, which can be thought of as a measure of how a system stores and dissipates energy. When the applied voltage oscillates near a resonant frequency of a structure (the pitch of a rung bell, for example) the structure vibrates much more intensely, and that additional movement dissipates more energy due to viscosity, friction, and transmitting sound into the air. This phenomenon is reflected in the measured impedance, so by calculating the impedance value over a large range of frequencies, it is possible to identify many resonances of the structure. So, the impedance value is tied to the vibrational properties of the structure, and the vibration of the structure is tied to its geometry and material properties. One application of this relationship is called impedance-based structural health monitoring: taking measurements of a structure when it is first built as a reference, then measuring it again later to watch for changes that indicate emerging damage. In this work, the reference measurement is established by measuring a group of control structures that are known to be free of defects. Then, every time a new part is fabricated, its impedance measurements will be compared to the reference. If it matches closely enough, it is assumed good. In both cases, impedance values don't indicate what the change is, just that there was a change. A large portion of this work is devoted to determining the types and sizes of defects that can be reliably detected through INDEAM, what effect the part material plays, and how and where the piezoelectric should be mounted to the part. The remainder of this work discusses new methods for conducting impedance-based evaluation. In particular, overcoming the extra uncertainty introduced by moving from part-to-itself structural health monitoring comparisons to the part-to-part quality control comparisons discussed in this work. A new method for mathematically comparing impedance values is introduced which involves extracting the resonant properties of the structure rather than using statistical tools on the raw impedance values. Additionally, a new method for assessing the influence of piezoelectric mounting conditions on the measured impedance values is demonstrated.

An elasticity solution is presented for the static equilibrium equations of an axisymmetric composite cylinder under loadings due to embedded piezoelectric laminae. The solution is used to study both uniform and non-uniform distributions of the piezoelectric effect and results are verified using the finite element method. A cylindrical truss element actuator is developed based upon this analysis and shown to be useful in damping vibrations of truss-type structures. It has also been shown that by varying the distribution of the piezoelectric effect. spatially, modal actuators capable of actuating specific modes of axial vibrations in a bar can be developed. Finally, the effects of a piezoelectric patch have been investigated. The axial forces generated at the fixed ends of a cylinder are demonstrated to be proportional to the length of the patch. / Master of Science

This dissertation investigates the fundamental behavior of multifunctional materials for energy conversion. Multifunctional materials exhibit two or more functional properties, such as electrical, thermal, magnetic etc. In this dissertation, the emphasis is on understanding the principles for energy conversion from one domain to another (e.g. thermal to electrical; or mechanical to electrical) by utilizing nanomaterials and nanostructured materials such as carbon nanotubes, shape memory alloy (SMA), and flexible piezoelectric materials. Carbon nanotubes (CNTs) are known for their unique electrical and thermal properties. Development of solid-state suspended CNT sheets having extremely low heat capacity per unit area opens an opportunity for utilizing thermoacoustic phenomenon (electrical to thermal to acoustic energy conversion) that results in sound generation over a wide range of frequencies. Detailed theoretical modeling and experiments were conducted for understanding the acoustics generation from multi-wall carbon nanotubes (MWNTs) sheets. The sound pressure level (SPL) of CNT-based thermoacoustic projector (TAPs) is proportional to the frequency and hence the performance reduces in low frequency (LF) region which could be used for noise cancellation, SONAR and oceanography applications. Extensive analytical modeling in conjunction with experiments were conducted involving structure-fluid-acoustic interaction to determine the operational physical behavior of TAPs. Numerical model combines all the controlling steps from power input to acoustic wave generation to the propagation in outer fluid media. Power input to the computational domain is used to determine the frequency dependent thermal diffusive length which governs the generation of TA wave. MWNT yarns/fibers/threads were also designed to harvest ocean wave energy (mechanical to electrical energy conversion). These yarn-based harvesters electrochemically convert tensile or torsional mechanical energy into electrical energy without requiring an external bias voltage. Harvesters were developed by spinning sheets of forest-drawn MWNTs into high-strength yarns. SMA wires exhibit two unique properties: thermally induced martensite to austenite phase transformation and super-elasticity (stress-induced martensitic transformation). These properties were implemented for developing the low-grade thermal energy harvesters (thermal to electrical energy conversion). More than half of the energy generated worldwide is lost as unused thermal energy because of the lack of efficient methodology for harnessing the low-grade heat. A systematic study is presented here that takes into account all the key steps in thermal to electrical conversion such as material optimization, thermal analysis and electrical conditioning to deliver the efficient harvester. Next using thin sheets of piezoelectric materials, strain energy harvesting from automobile tires is studied (strain to electrical conversion. Flexible organic piezoelectric material was utilized for transduction in the harvester for continuous power generation and simultaneous sensing of the variable strain experienced by tire under different driving conditions. Using sensors mounted on a real tire of a mobile test rig, measurements were conducted on different terrains with varying normal loads and speeds to quantify the sensitivity and self-powered sensing operation. / Doctor of Philosophy / This dissertation studies the potential of carbon nanotubes yarns and sheets, piezoelectric sheets and shape memory alloy wires for energy conversion applications. Multiwalled carbon nanotubes (MWNTs) are known for their unique electrical and thermal properties. Large surface area, solid state self-suspended carbon nanotube sheets having extremely low heat capacity per unit area were utilized for design of thermoacoustic projectors operating over a wide range of frequencies. Detailed numerical modeling and experiments were conducted for understanding the acoustics generation from MWNT sheets. Another potential application for MWNT yarns is in ocean wave energy harvesting, where these yarn based harvesters convert tensile mechanical energy into electrical energy. Harvesters were developed by spinning sheets of MWNTs into high-strength yarns. SMA exhibits unique phase change behavior on mechanical and thermal loading, which were utilized for converting low-grade thermal energy into electrical energy. At low temperature gradients, where there is lack of methodologies for converting thermal energy into electrical energy, SMA wire-based energy harvesters are shown to provide ultra-high power density. Extensive experimentation in conjunction with multi-physics modeling is conducted to provide understanding of energy losses occurring during the thermal to electrical conversion. Lastly, this dissertation investigates the mechanical to electrical conversion using organic piezoelectric materials. Self-powered strain sensing mechanism for autonomous vehicle will provide new capabilities in monitoring the dynamics and allow developing additional automated controls to assist the driver performance.