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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Model-based control of plate vibrations using active constrained layer damping

Chantalakhana, Chak January 2000 (has links)
In this thesis, the author presents a numerical and experimental study of the application of active constrained layer damping to a clamped-clamped plate. Piezoelectric actuators with modal controllers are used to improve the performance of vibration suppression from the passive constrained layer damping treatment. Surface damping treatments are often effective at suppressing higher frequency vibrations in thin-walled structures such as beams, plates and shells. However, the effective suppression of lower frequency modes usually requires the additional of an active vibration control scheme to augment the passive treatment. Advances in the technologies associated with so-called smart materials are dramatically reducing the cost, weight and complexity of active structural control and make it feasible to consider active schemes in an increasing number of applications. Specifically, a passive constrained layer damping treatment is enhanced with an active scheme employing a piezoceramic (PZT) patch as the actuator. Starting with an established finite element formulation it is shown how model updating and model reduction are required to produce a low-order state-space model which can be used as the basis for active control. The effectiveness of the formulation is then demonstrated in a numerical study. Finally, in the description of the experimental study it is shown how modes in the frequency range from 0 to 600 Hz are effectively suppressed: the two lowest modes (bending and torsional) through active control, the higher modes (around ten in number) by the passive constrained damping layer. The study'S original contribution lies in the experimental demonstration that given a sufficiently accurate model of the plate and passive constrained damping layer, together with a suitable active feedback control algorithm, spillover effects are not significant even when using a single sensor and single actuator. The experimental traces show, in some instances, minor effects due to spillover. However, it can be concluded that the presence of the passive layer introduces sufficient damping into the residual modes to avoid any major problems when using only the minimum amount of active control hardware.
2

ANALYSIS AND SHAPE MODELING OF THIN PIEZOELECTRIC ACTUATORS

Mouhli, Makram 01 January 2005 (has links)
The field of smart materials is an increasingly growing area of research. In aerodynamics applications especially, transducers have to fulfill a series of requirements such as light weight, size, energy consumption, robustness and durability. Piezoelectric transducers, devices which transform an electrical signal into motion, fulfill many of these requirements. Specifically, piezoelectric composites are of interest due to their added toughness and ease of integration into a structure. Resulting composites have a characteristic initial curvature with accompanying residual stresses that are responsible for enhanced performance, relative to flat actuators, when the active material is energized. A number of transducer designs based on composites have been developed. Two of these piezoelectric composites called Thunder® and Lipca are analyzed. Thunder is a composite of steel, polyimide adhesive, PZT, polyimide adhesive, and aluminum; and Lipca is a composite of fiberglass epoxy, carbon/epoxy, PZT, and fiberglass epoxy.Room temperature shapes of circular and rectangular Thunder® and Lipca actuators are predicted by using the Rayleigh-Ritz model. This technique is based on the assumption that the stable geometric configuration developed in the actuator after manufacturing, is the configuration that minimizes the total potential energy. This energy is a function of the displacement field which can be approximated by two functions, a four term model, and a twenty-three term model. The coefficients in the models are determined by minimizing the total potential energy of the actuator. The actuator deformations are assumed to obey the Kirchhoff hypothesis and the actuator layers are assumed to be in the state of plane stress.The four coefficient model produces results not comparable to three-dimensional surface topology maps. The twenty-three coefficient model however, is shown to have generally good agreement with the data for all studied actuators. To quantify the difference, at the cross section of each actuator, a profile is fitted by using a quadratic equation obtaining regression coefficients above 99%. For all actuators, the error between experimental and the calculated centerline data is less than 6%. For the 6R model however, the error is approximately 25%. One of the possible reasons for the error may be the tolerance of the thickness of the PZT layer. By changing the PZT thickness ±6% of the nominal value, over predicts the experimental dome height by 20%. Another possible reason for the discrepancy is the thickness of the actuator, thicker than all actuators used in this study, which might contradict the validity of the thin actuator assumption. Furthermore, by calculating the side-length-to-thickness ratio, 115 in this case, as stated by Aimmanee & Hyer (2004), may cause instability, and could result in unexpected behavior.The neutral axis position, calculated by using a force balance at equilibrium under the assumption of pure bending, for all actuators used in this study is determined and compared to the ceramic layer position. The results indicated that for all Thunder® models the neutral axis is located below the ceramic layer indicating that the PZT wafer may be in total tension. For the Lipca C2 device however, the neutral axis is found to be above the ceramic layer, indicating that the piezoelectric layer may be in total compression.Strain fields are also predicted with contradicting results when compared to the theory that the ceramic is in tension in the Thunder actuators. The contradiction on the strain calculations can be explained by the manner the strain field is derived: by differentiating and squaring the high-order polynomials of the approximated displacement component losing accuracy when it comes to predicting normal and shear strains.The Rayleigh-Ritz technique can become a tool to perform parametric studies of the key elements for manufacturing to optimize specific features of the actuators.
3

Natural frequency based damage identification of beams using piezoelectric materials

Zhao, Shengjie 24 December 2015 (has links)
Following the studies of natural frequency based damage detection methods, an advanced technique for damage detection and localization in beam-type structures using a vibration characteristic tuning procedure is developed by an optimal design of piezoelectric materials. Piezoelectric sensors and actuators are mounted on the surface of the host beam to generate excitations for the tuning via a feedback process. The excitations induced by the piezoelectric effect are used to magnify the effect of the damage on the change of the natural frequencies of the damaged structure to realize the high detection sensitivity. Based on the vibration characteristic tuning procedure, a scan-tuning methodology for damage detection and localization is proposed. From analytical simulations, both crack and delamination damage in the beams are detected and located with over 20% change in the natural frequencies. Finite element method (FEM) simulations are conducted to verify the effectiveness of the proposed methodology. / October 2016
4

Analysis and research of an ultra-precision XY positioning stage

Huang, Bo-Tse 05 August 2004 (has links)
Abstract This paper reports about a precision positioning XY stage utilizing flexure hinges and piezoelectric actuators. XY stage was designed with the aim of reducing the stress-concentration of flexure hinges and the low interference between two actuating axes. Utilized the expression of matrix to figure out the properties of the bellow-type flexure hinges, and proved these by mathematical software. Experiments demonstrated that the stage actuated by a stairstep driving signal with maximum displacement 1.3£gm and interference 50nm along X axis; along Y axis with maximum displacement 0.8£gm and interference 11nm. The stage actuated by a ramp signal with maximum displacement 1.2£gm and interference 45nm along X axis; along Y axis with maximum displacement 0.9£gm and interference 35nm. The finite element method (FEM) was used to analyse the stress-concentration of the stage. and the simulated results were compared with the experiments. Referred to the testing results, the target object could be moved in the aimed position accurately.
5

Desenvolvimento de uma mesa angular rotativa para a usinagem de ultraprecisão / Development of a rotating tilt stage for the machining high precision

Burato, Carlos Umberto 07 February 2003 (has links)
Este trabalho trata do desenvolvimento de uma mesa angular rotativa, para o microposicionamento de peças anesféricas durante a usinagem de ultraprecisão, para atender as tolerâncias nanométricas. Este microposicionamento angular é alcançado com o emprego de atuadores piezelétricos. Por se tratar de um tipo de sistema com movimento de rotação, relata-se o problema encontrado para energizar os atuadores. Este problema é abordado mostrando a alternativa encontrada destacando pontos relevantes, como: a) energização através de anéis coletores deslizantes, de cobre revestidos em prata, fixados no diâmetro externo do dispositivo; b)isolação elétrica entre os anéis e a peça; c) ligação do cabo coaxial vindo dos atuadores piezelétricos; d) aterramento dos cabos coaxiais, utilizando apenas um anel coletor deslizante. Explica como acontece a transmissão do sinal de corrente elétrica do aparelho de controle para os anéis deslizantes e posteriormente aos atuadores piezelétricos, utilizando contatos através de escovas, com 65% de prata e 35% de grafite, com molas duplas para garantir a pressão do contato, fixadas numa base rígida externa ao dispositivo. Destaca-se que a confiabilidade no microposicionamento da peça está na preservação da transmissão de uma corrente elétrica de 50mA para os atuadores. Conclui que é possível realizar o microposicionamento angular da peça que está sendo trabalhada, durante a usinagem de ultraprecisão, garantindo assim suas tolerâncias nanométricas / This work deals with a rotating tilt stage. It considers the micropositioning of aspheric workpieces during high precision machining, in order to obtain nanometric accuracies. It defines this angular micropositioning with the use of piezoelectric actuators. The problem found to energize the actuators, because it is a rotating driving mechanism is discussed. The chosen solution is presented and import points are highlighted, such as: a) to energize through sliding ring collectors, of copper coated in silver, fastened to the external diameter of the device; b) electric isolation between the rings and the workpiece; c) connection of the coax cable of the piezoelectric actuators; d) to ground the coax cables, just using a sliding ring collector. The transfer of electric current of the control system to the sliding rings and piezoelectric actuators is explained. Contacts with 65% of silver and 35% of carbon, with double springs to guarantee the pressure of the contact, fastened to a rigid base are used. The reliability in the micropositioning of a workpiece depends on the preservation of the electric current of 50mA to the actuators. It is shown that it is possible to realize the angular micropositioning of workpiece, during high precision machining, guaranteeing nanometric accuracies
6

Estudo da intensificação da coalescência de emulsões de água em óleo com a aplicação de onda estacionária de ultrassom. / Study of the intensifying water in oil emulsions coalescence with the application of ultrasonic standing wave.

Atehortua, Carlos Mario Giraldo 14 August 2015 (has links)
Considerando que o petróleo quando extraído dos poços em águas profundas chega a ter teor de água superior a 50% e que antes de ser enviado à refinaria deve ter uma quantidade de água inferior a 1%, torna-se necessário o uso de técnicas de redução da quantidade de água. Durante a extração do petróleo formam-se emulsões de água em óleo que são muito estáveis devido a um filme interfacial contendo asfaltenos e/ou resinas ao redor das gotas de água. Nesse trabalho é apresentada a utilização de ondas estacionárias de ultrassom para realizar a quebra dessas emulsões. Quando gotículas de água com dimensões da ordem de 10m, muito menores que o comprimento de onda, são submetidas a um campo acústico estacionário em óleo, a força de radiação acústica empurra as gotículas para os nós de pressão da onda. Uma célula de coalescência com frequência central ao redor de 1 MHz, constituída por quatro camadas sendo uma piezelétrica, uma de acoplamento sólido, uma com o líquido e outra refletora, foi modelada empregando o método da matriz de transferência, que permite calcular a impedância elétrica em função da frequência. Para minimizar o efeito do gradiente de temperatura entre a entrada e a saída da cavidade da célula, quando está em operação, foram utilizados dois transdutores piezelétricos posicionados transversalmente ao fluxo que são excitados e controlados independentemente. Foi implementado um controlador digital para ajustar a frequência e a potência de cada transdutor. O controlador tem como entrada o módulo e a fase da corrente elétrica no transdutor e como saída a amplitude da tensão elétrica e a frequência. Para as células desenvolvidas, o algoritmo de controle segue um determinado pico de ressonância no interior da cavidade da célula no intervalo de frequência de 1,09 a 1,15 MHz. A separação acústica de emulsões de água em óleo foi realizada em uma planta de laboratório de processamento de petróleo no CENPES/PETROBRAS. Foram testados a variação da quantidade de desemulsificante, o teor inicial de água na emulsão e a influência da vazão do sistema, com uma potência de 80 W. O teor final de água na emulsão mostrou que a aplicação de ultrassom aumentou a coalescência de água da emulsão, em todas as condições testadas, quando comparada a um teste sem aplicação de ultrassom. Identificou-se o tempo de residência no interior da célula de separação como um fator importante no processo de coalescência de emulsões de água e óleo. O uso de desemulsificante químico é necessário para realizar a separação, porém, em quantidades elevadas implicaria no uso de processos adicionais antes do repasse final do petróleo à refinaria. Os teores iniciais de água na emulsão de 30 e 50% indicam que o uso da onda estacionária na coalescência de emulsões não tem limitação quanto a esse parâmetro. De acordo com os resultados obtidos em laboratório, essa técnica seria indicada como uma alternativa para integrar um sistema de processamento primário em conjunto com um separador eletrostático. / Considering that oil when extracted from the wells in deep water have water content greater than 50%, and that before to be sent to the refinery must have a quantity of water less than 1%, it becomes necessary to use water amount reduction techniques. During the oil extraction are formed water-in-oil emulsions that are highly stable due to an interfacial film containing asphaltenes and / or resins around the water droplets. This work presents the use of ultrasonic standing waves to perform that emulsion break. When water droplets with dimensions about 10m, much smaller than the wavelength, are placed in a standing acoustic field in oil, the acoustic radiation force pushes the water droplets to the pressure wave nodes. A coalescing chamber with frequency about 1 MHz, with four layers comprising a piezoelectric, a solid coupling, one with the liquid, and another reflector, was modeled using the matrix transfer method, that allows calculating the electrical impedance as a function of frequency. To minimize the effect of the temperature gradient between the inlet and the outlet of the chamber cavity, when it is operating, were used two groups of piezoelectric transducers positioned transverse to the flow which are excited and controlled independently. A digital controller has been implemented to adjust the frequency and the power of each transducer. The controller has as input the modulus and phase of electrical current of the transducer and as output the amplitude of voltage and the frequency. For developed cells, the control algorithm follows an specific resonance peak within the chambers cavity in the frequency range 1.09 to 1.15 MHz. Acoustic separation of water in oil emulsions was carried out on a laboratory oil processing plant. Tests were performed by varying the amount of the chemical demulsifier, the initial water content in the emulsion. The system flow rate was kept constant at 80 W using the control system. Residence time within the separation chamber was identified as an important factor in the water in oil emulsions coalescence process. The use of chemical demulsifier is required to perform the separation, however in large quantities, it implies the use of additional processes before the oil final transfer to the refinery. Initial water contents in the emulsion about 30 and 50% indicate that the use of the acoustic standing wave in the emulsion coalescence has not limitation on this parameter. According to the results obtained in laboratory, this technique would be indicated as an alternative to integrate a primary processing system together with an electrostatic separator.
7

Força de radiação acústica produzida por ondas estacionárias de ultrassom. / Acoustic radiation force generated by ultrasound standing waves.

Ramos, Tiago dos Santos 28 September 2017 (has links)
O estudo da força de radiação acústica é de extrema importância para compreender o fenômeno da levitação acústica, tendo em vista que ela é que permite a levitação de objetos no interior de uma cavidade acústica. A cavidade acústica é uma região do espaço delimitada pelas faces de um transdutor e de um refletor, onde é produzida uma onda estacionária de alta intensidade. Nesta técnica, conhecida como levitação por ondas estacionárias, pequenos objetos são aprisionados nos nós de pressão da onda estacionária. Além desta, também existe uma outra técnica de levitação onde não há a necessidade de se utilizar um refletor, técnica conhecida como levitação de campo próximo, na qual se tem apenas um transdutor e o objeto de face plana que se deseja levitar. Nesta técnica há uma pequena região com ar entre o transdutor e o objeto, sendo que a espessura da camada de ar é muito menor que o comprimento de onda. Neste trabalho foi feito um estudo numérico e experimental da força de radiação acústica em levitadores acústicos de onda estacionária e em levitadores de campo próximo. As simulações foram realizadas no software de elementos finitos COMSOL Mutiphysics. No estudo experimental foi utilizada uma balança eletrônica para medir a força de radiação acústica e uma câmera de alta velocidade para observar o comportamento oscilatório de objetos esféricos no interior da cavidade acústica. O estudo da força de radiação acústica resultou em três principais contribuições. A primeira contribuição está relacionada com a caracterização de efeitos não lineares em um levitador acústico, como o fenômeno de salto (jump phenomenon) e o fenômeno de histerese. A segunda contribuição está relacionada com o estudo numérico e experimental da força de radiação acústica que atua no refletor de um levitador acústico. Por último também foi feito um estudo da força de radiação acústica que atua no refletor para a região do campo próximo. Neste último estudo foi verificado que quando o diâmetro da face do transdutor é pequeno em comparação com o comprimento de onda, surge uma força atrativa sobre o refletor, e esta força pode ser utilizada para levitar um objeto plano em baixo da face do transdutor, sem haver necessidade de utilizar refletores. / The study of the acoustic radiation force is of high relevance to understand the acoustic levitation, since it is responsible for the levitation of small objects in the interior of an acoustic cavity. The acoustic cavity is the region delimited by the surfaces of the transducer and the reflector, where it is generated an acoustic standing wave field of high intensity. In this technique, called standing wave acoustic levitation, small objects are entrapped at the pressure nodes of the standing wave. In addition, there is also another levitation technique where there is no need to use a reflector. This technique is known as near-field levitation, in which there is only one transducer and the flat-faced object to be levitated. In this technique there is a small region with air between the transducer and the object, with the thickness of the air layer being much smaller than the wavelength. In this work, a numerical and experimental study of the acoustic radiation force in acoustic wave levitators and near-field levitators was done. The simulations were performed in the finite element software COMSOL Mutiphysics. In the experimental results, an electronic scale was used to measure the acoustic radiation force and a high speed camera was applied to observe the oscillatory behavior of spherical objects inside the acoustic cavity. The study of acoustic radiation strength resulted in three main contributions. The first contribution is related to the characterization of nonlinear effects in an acoustic levitator, such as the jump phenomenon and the hysteresis phenomenon. The second contribution is related to the numerical and experimental study of the acoustic radiation force that acts on the reflector of an acoustic levitator. Finally, a study of the acoustic radiation force that acts on the reflector for the near field region was also made. In this last study, it was verified that when the transducer is small in comparison with the wavelength, an attractive force appears on the reflector. This force can be used to levitate a flat object below the transducer face, without requiring a reflector.
8

Regulation of Hysteretic Systems with Preisach Representation

Wang, Li January 2009 (has links)
Piezoelectric actuators are well suited for high precision mechanical and electrical engineering applications. However, its performance in regulator configurations has been limited due to hysteresis. The hysteresis in these actuators means that multiple input states can result in the same output, which introduces a further design variable (initial state) in the regulation problem. It is proposed that certain initial states result in better regulation performance based on the structure of the Preisach model. These initial states are called “neutral states”. In this thesis, hysteresis and piezoelectric actuators are introduced as background information. The Preisach model is used in this work to describe the hysteresis behaviour of a customized shape control unit SS15 due to its convenient general structure and ability to model hysteresis. The representation tests are performed and a Preisach model is subsequently constructed and verified by comparing simulation and experimental results to ensure that the hysteresis inherent in the piezoceramic actuators of the SS15 is suitably described by this model. In order to evaluate the regulation performance for a given desired output, uniformly-distributed noise is injected at the input side of the SS15 in open- and closed-loop tests. It is demonstrated, by both simulation and experimental results, that the system output drifts less when it starts from the neutral state in open-loop tests. A PI regulator is implemented in the closed-loop tests. When the system is driven from the neutral state, both simulation and experimental results demonstrate that the system requires less control effort for closed-loop regulation.
9

Regulation of Hysteretic Systems with Preisach Representation

Wang, Li January 2009 (has links)
Piezoelectric actuators are well suited for high precision mechanical and electrical engineering applications. However, its performance in regulator configurations has been limited due to hysteresis. The hysteresis in these actuators means that multiple input states can result in the same output, which introduces a further design variable (initial state) in the regulation problem. It is proposed that certain initial states result in better regulation performance based on the structure of the Preisach model. These initial states are called “neutral states”. In this thesis, hysteresis and piezoelectric actuators are introduced as background information. The Preisach model is used in this work to describe the hysteresis behaviour of a customized shape control unit SS15 due to its convenient general structure and ability to model hysteresis. The representation tests are performed and a Preisach model is subsequently constructed and verified by comparing simulation and experimental results to ensure that the hysteresis inherent in the piezoceramic actuators of the SS15 is suitably described by this model. In order to evaluate the regulation performance for a given desired output, uniformly-distributed noise is injected at the input side of the SS15 in open- and closed-loop tests. It is demonstrated, by both simulation and experimental results, that the system output drifts less when it starts from the neutral state in open-loop tests. A PI regulator is implemented in the closed-loop tests. When the system is driven from the neutral state, both simulation and experimental results demonstrate that the system requires less control effort for closed-loop regulation.
10

Controlling Deformation in Elastic and Viscoelastic Beams Due to Temperature and Moisture Changes Using Piezoelectric Actuator

Kuravi, Ramachandra Srinivasa Chaitanya 2011 May 1900 (has links)
This thesis analyzes the implementation of surface bonded piezoelectric actuators to control or minimize the deformation in elastic or viscoelastic cantilever beams due to simultaneous heat and moisture diffusion. The problem is addressed in the context of linearized elasticity and linearized viscoelasticity. The constitutive equations are derived from the balance laws for mass, linear and angular momenta, energy, entropy and the second law of thermodynamics. The constitutive equations for linearized elasticity are then obtained as a consequence of small deformation assumption. The temperature and moisture induced deformation is introduced through the coefficient of thermal expansion CTE and coefficient of moisture expansion CME. The constitutive equations for linearized viscoelasticity are obtained by correspondence principle. The coupled temperature and moisture diffusion equations are obtained as a consequence of Clausius-Duhem inequality. The extent of coupling between heat conduction and moisture diffusion phenomena is studied by varying the ratio of their diffusivities and a non-dimensional coupling parameter. The effect of coupled unsteady heat conduction and moisture diffusion phenomena on the short and long term response characteristics of the beam such as displacement, stress and strain fields is studied. Based on these response characteristics, the magnitude of external actuating voltage required to minimize deformation is predicted. This is followed by a comparative study of the field variables in cases of actuated and unactuated beams. Four materials are chosen for this study; aluminium, epoxy, carbon fiber reinforced polymer with fiber volume fraction of 60 percent, and an epoxy-like viscoelastic material. The viscoelastic material is assumed to be thermorheologically simple. The shift factor is assumed to be a linear function of temperature and moisture fields. To address this problem numerically, a finite difference formulation is presented for the field equations and boundary conditions. This numerical scheme is validated by solving the problem of uniformly loaded cantilever beam and comparing the results with the analytical solution known a priori. The results obtained numerically are validated by comparison with experimental results. It is observed that the under the effect of external actuation, the stress and displacement fields are largely minimized in all four cases chosen for study. The bending in the unactuated viscoelastic beam is more pronounced than bending in the unactuated elastic beam. This is due to the softening of the material with time due to evolving temperature and moisture fields. However, relatively lesser external actuating voltage is necessary to minimize bending in the former case compared to the latter. The magnitude of actuating electric field required in the piezoelectric layer suggests a need to address the problem with in a non-linear framework, no such attempt is made in this study.

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