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Active Flutter Suppression Of A Smart FinKaradal, Fatih Mutlu 01 September 2008 (has links) (PDF)
This study presents the theoretical analysis of an active flutter suppression methodology applied to a smart fin. The smart fin consists of a cantilever aluminum plate-like structure with surface bonded piezoelectric (PZT, Lead- Zirconate-Titanate) patches.
A thermal analogy method for the purpose of modeling of piezoelectric actuators in MSC® / /NASTRAN based on the analogy between thermal strains and piezoelectric strains was presented. The results obtained by the thermal analogy were compared with the reference results and very good agreement was observed.
The unsteady aerodynamic loads acting on the structure were calculated by using a linear two-dimensional Doublet-Lattice Method available in MSC® / /NASTRAN. These aerodynamic loads were approximated as rational functions of the Laplace variable by using one of the aerodynamic approximation schemes, Roger& / #8217 / s approximation, with least-squares method. These approximated aerodynamic loads together with the structural matrices obtained by the finite element method were used to develop the aeroelastic equations of motion of the smart fin in state-space form.
The Hinf robust controllers were then designed for the state-space aeroelastic model of the smart fin by considering both SISO (Single-Input Single-Output) and MIMO (Multi-Input Multi-Output) system models. The verification studies of the controllers showed satisfactory flutter suppression performance around the flutter point and a significant improvement in the flutter speed of the smart fin was also observed.
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Evaluation of AASHTO design specifications for cast-in-place continuous bridge deck using remote sensing techniqueMehranipornejad, Ebrahim 01 June 2006 (has links)
This research project concerns the construction, testing, and remote health monitoring of the first smart bridge structure in Florida, the East Bay bridge in Gibsonton, Hillsborough County. The East Bay Bridge is a four span, continuous, deck-type structure with a total length of 120' and width of 55'. The superstructure consists of an 18'' cast-in-place reinforced concrete slab, and is supported on pre-stressed pile bents, each consisting of 5 piles. The smart sensors used for remote health monitoring are the newly emerged Fabry --Perot (FP) Fiber Optic Sensors, and are both surface-mounted and embedded in the concrete deck.Static and Dynamic testing of the bridge were performed using loaded SU-4 trucks, and a finite element model for the bridge was developed for the test cases using commercial software packages. In addition, the smart sensors were connected to a data acquisition system permanently installed on-site. This system could be accessed through regular phone lin
es, which permits the evaluation of the bridge behavior under live traffic loads.Currently, these live structural data under traffic loading are transmitted to Hillsborough County's bridge maintenance office to assist in the health evaluation and maintenance of the bridge.AASHTO LRFD Design Code has been investigated using analytical and laboratory test but no attempt has been made to verify its relative outlook with respect to Allowable Strength Design (ASD) and AASHTO Standard Specifications (LFD) in a real field test. The likely reason for could have been the lack of accurate and reliable sensing systems.The data collected as well as the analytical studies through out this research, suggest that current LRFD design specifications for deck-type bridges are conservative. The technology developed under this work will enable practical, cost-effective, and reliable systematic maintenance of bridge structures, and the study will provide a unique opportunity for future growth of this tech
nology in the state of Florida and in other states and finally, long term collected data can be used to keep the design codes in check.
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Controle ativo de vibrações e localização ótima de sensores e atuadores piezelétricos /Bueno, Douglas Domingues. January 2007 (has links)
Orientador: Vicente Lopes Júnior / Banca: Walter Katsumi Sakamoto / Banca: Alberto Luiz Serpa / Resumo: Este trabalho apresenta o projeto do regulador linear quadrático (LQR - do inglês Linear Quadratic Regulator) para atenuar vibrações em estruturas mecânicas. Estas estruturas, com atuadores e sensores acoplados, são denominadas estruturas inteligentes. Os projetos de controladores ativos são resolvidos utilizando desigualdades matriciais lineares (LMIs - do inglês Linear Matrix Inequalities). Assim, é possível projetar controladores robustos considerando incertezas paramétricas na planta a ser controlada. São utilizados atuadores e sensores piezelétricos (PZTs) para aplicações em estruturas flexíveis dos tipos vigas e placas e, também, atuadores de pilha para aplicações em estruturas do tipo treliça. O problema do posicionamento ótimo dos atuadores e sensores piezelétricos também é resolvido utilizando as normas de sistemas H2, H , Hankel e as matrizes grammianas de observabilidade e controlabilidade. O modelo matemático da estrutura inteligente é obtido a partir do Método dos Elementos Finitos e, também, utilizando o Método de Identificação de Subespaços através de dados experimentais. O problema de posicionamento ótimo dos atuadores e sensores e o controle ativo de vibração são apresentados em simulações numéricas e experimentais. Os resultados mostram que os controladores robustos aumentam o amortecimento estrutural minimizando as amplitudes de vibração. / Abstract: This work presents the Linear Quadratic Regulator design to vibration attenuation in mechanical structures. These structures are named Smart Structures because they use actuators and sensors electromechanically coupled. Active controller designs are solved using Linear Matrix Inequalities. So, it is possible to consider polytopic uncertainties. Piezoelectric actuators and sensors are used for applications in flexible structures as beams and plates and, also, stack actuators for applications in truss structures. Optimal placement problem of piezoelectric actuators and sensors also solved using H2, H , Hankel system norms and controllability and observability grammian matrices. The mathematical model of the smart structure is obtained through Finite Element Method and, also, through Numerical State Space of Subspace System Identification (Subspace Method) by experimental data. The optimal placement of actuator and sensor and the active vibration control is numerically and experimentally implemented. Results show that the robust controllers increase the structural damping minimizing magnitude of vibrations. / Mestre
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Implementing Impedance - Based Health MonitoringRaju, Vinod 11 December 1997 (has links)
This work is an experimental study of applying an impedance-based health monitoring technique to complex structures. The work is presented in three parts.
In the first part we consider effects of the following three factors on damage detection abilities: actuator excitation level, test wire length and ambient conditions (temperature, structural loading and vibration). It was concluded that increasing the applied voltage improves the signal to noise ratio and damage detection abilities. Test wire lengths under 30m do not affect damage detection abilities. The technique is able to distinguish and detect damage even with variations in temperature, structural loading and vibration.
In the second part we apply our health monitoring technique to a complex truss structure and a massive steel steam header. We discovered that with multiplexing (acquiring a single signal from distributed actuators) the actuators on the truss structure we could detect damage but with less location information. Damage detection on the steel pipe ended in inconclusive results. The use of this technique on massive structures needs further investigation.
Finally, we conducted a detailed experimental study of monitoring the integrity of composite-reinforced masonry structures. We developed a software package which enables even a casual user to determine if significant damage has occurred in these structures. The technique was successfully applied to detect damage (particularly due to delamination) in these composite-concrete structures. Most significantly, the technique was also able to detect damage well in advance of actual failure.
This work relies mainly on frequency response plots and damage metric charts to present the data and to arrive at any conclusions. While frequency response plots give a qualitative approach to the analysis, damage metric charts attempt to quantify the data. / Master of Science
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Vibration Control for Chatter Suppression with Application to Boring BarsPratt, Jon Robert Jr. 18 December 1997 (has links)
A mechatronic system of actuators, sensors, and analog circuits is demonstrated to control the self-excited oscillations known as chatter that occur when single-point turning a rigid workpiece with a flexible tool. The nature of this manufacturing process, its complex geometry, harsh operating environment, and poorly understood physics, present considerable challenges to the control system designer. The actuators and sensors must be rugged and of exceptionally high bandwidth and the control must be robust in the presence of unmodeled dynamics. In this regard, the qualitative characterization of the chatter instability itself becomes important. Chatter vibrations are finite and recognized as limit cycles, yet modeling and control efforts have routinely focused only on the linearized problem. The question naturally arises as to whether the nonlinear stability is characterized by a jump phenomenon. If so, what does this imply for the "robustness" of linear control solutions?
To answer our question, we present an advanced hardware and control system design for a boring bar application. Initially, we treat the cutting forces merely as an unknown disturbance to the structure which is essentially a cantilevered beam. We then approximate the structure as a linear single-degree-of-freedom damped oscillator in each of the two principal modal coordinates and seek a control strategy that reduces the system response to general disturbances. Modal-based control strategies originally developed for the control of large flexible space structures are employed; they use second-order compensators to enhance selectively the damping of the modes identified for control.
To attack the problem of the nonlinear stability, we seek a model that captures some of the behavior observed in experiments. We design this model based on observations and intuition because theoretical expressions for the complex dynamic forces generated during cutting are lacking. We begin by assuming a regenerative chatter mechanism, as is common practice, and presume that it has a nonlinear form, which is approximated using a cubic polynomial. Experiments demonstrate that the cutting forces couple the two principal modal coordinates. To obtain the jump phenomena observed experimentally, we find it necessary to account for structural nonlinearies. Gradually, using experimental observation as a guide, we arrive at a two-degree-of-freedom chatter model for the boring process. We analyze the stability of this model using the modern methods of nonlinear dynamics.
We apply the method of multiple scales to determine the local nonlinear normal form of the bifurcation from static to dynamic cutting. We then find the subsequent periodic motions by employing the method of harmonic balance. The stability of these periodic motions is analysed using Floquet theory.
Working from a model that captures the essential nonlinear behavior, we develop a new post-bifurcation control strategy based on quench control. We observe that nonlinear state feedback can be used to control the amplitude of post-bifurcation limit cycles. Judicious selection of this nonlinear state feedback makes a supplementary open-loop control strategy possible. By injecting a harmonic force with a frequency incommensurate with the chatter frequency, we find that the self-excited chatter can be exchanged for a forced vibratory response, thereby reducing tool motions. / Ph. D.
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Design and Analysis of Model Based Nonlinear and Multi-Spectral Controllers with Focus on Motion Control of Continuous Smart StructuresKim, Byeongil 14 December 2010 (has links)
No description available.
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Finite Element Analysis and Genetic Algorithm Optimization Design for the Actuator Placement on a Large Adaptive StructureSheng, Lizeng 29 December 2004 (has links)
The dissertation focuses on one of the major research needs in the area of adaptive /intelligent/smart structures, the development and application of finite element analysis and genetic algorithms for optimal design of large-scale adaptive structures. We first review some basic concepts in finite element method and genetic algorithms, along with the research on smart structures. Then we propose a solution methodology for solving a critical problem in the design of a next generation of large-scale adaptive structures -- optimal placements of a large number of actuators to control thermal deformations. After briefly reviewing the three most frequently used general approaches to derive a finite element formulation, the dissertation presents techniques associated with general shell finite element analysis using flat triangular laminated composite elements. The element used here has three nodes and eighteen degrees of freedom and is obtained by combining a triangular membrane element and a triangular plate bending element. The element includes the coupling effect between membrane deformation and bending deformation. The membrane element is derived from the linear strain triangular element using Cook's transformation. The discrete Kirchhoff triangular (DKT) element is used as the plate bending element. For completeness, a complete derivation of the DKT is presented. Geometrically nonlinear finite element formulation is derived for the analysis of adaptive structures under the combined thermal and electrical loads. Next, we solve the optimization problems of placing a large number of piezoelectric actuators to control thermal distortions in a large mirror in the presence of four different thermal loads. We then extend this to a multi-objective optimization problem of determining only one set of piezoelectric actuator locations that can be used to control the deformation in the same mirror under the action of any one of the four thermal loads. A series of genetic algorithms, GA Version 1, 2 and 3, were developed to find the optimal locations of piezoelectric actuators from the order of 10<SUP>21</SUP> ~ 10<SUP>56</SUP> candidate placements. Introducing a variable population approach, we improve the flexibility of selection operation in genetic algorithms. Incorporating mutation and hill climbing into micro-genetic algorithms, we are able to develop a more efficient genetic algorithm. Through extensive numerical experiments, we find that the design search space for the optimal placements of a large number of actuators is highly multi-modal and that the most distinct nature of genetic algorithms is their robustness. They give results that are random but with only a slight variability. The genetic algorithms can be used to get adequate solution using a limited number of evaluations. To get the highest quality solution, multiple runs including different random seed generators are necessary. The investigation time can be significantly reduced using a very coarse grain parallel computing. Overall, the methodology of using finite element analysis and genetic algorithm optimization provides a robust solution approach for the challenging problem of optimal placements of a large number of actuators in the design of next generation of adaptive structures. / Ph. D.
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[en] EFFECTS AND APPLICATIONS OF NON-HOMOGENEOUS STRAINS IN BRAGG GRATINGS / [pt] EFEITOS E APLICAÇÕES DE DEFORMAÇÕES NÃO HOMOGÊNEAS EM REDES DE BRAGGADRIANO FERNANDES PINHO 21 September 2005 (has links)
[pt] Redes de Bragg em fibras ópticas (RBF) são formadas por
modulações periódicas
introduzidas no índice de refração do núcleo de fibras
ópticas. Estes componentes
comportam-se como filtros espectrais de banda passante, ou
seja, quando iluminados por
um sinal óptico de banda larga, refletem apenas uma fina
fatia espectral de luz, cujo
centro, o comprimento de onda de Bragg, é proporcional ao
período espacial da
modulação no índice de refração. As RBF têm encontrado
aplicações importantes no
sensoriamento das mais diversas grandezas, sendo hoje
utilizadas em sistemas de
monitoramento para vários segmentos industriais, tais como
os setores de petróleo e gás,
construção civil e aeroespacial, que, estima-se, respondem
em conjunto por cerca de 70%
destas aplicações. Em diversas situações o sensoriamento
com RBF baseia-se em
medidas indiretas da grandeza de interesse, sendo
empregados mecanismos de
transdução que transformam variações do mensurando em
deformações na fibra óptica.
Nestes casos, um problema que deve ser tratado com atenção
é o acoplamento entre
temperatura e deformação, uma vez que as RBF são sensíveis
a estas duas variáveis. Não
raro, a alternativa é utilizar simultaneamente duas RBF
para obter-se a compensação de
temperatura na medida de deformação.
Este trabalho apresenta um estudo sobre deformações não
homogêneas em redes de
Bragg e discute aplicações de duas técnicas que podem ser
utilizadas como alternativas
para eliminar o efeito da temperatura no sensoriamento de
deformação com apenas uma
RBF. A primeira delas explora a birrefringência óptica
induzida na RBF por
carregamentos transversais à fibra óptica. A segunda
baseia-se nos efeitos sobre o
espectro refletido pela rede de Bragg quando submetida a
um campo de deformações
longitudinais não uniformes ao longo da direção axial da
fibra óptica. No trabalho são
apresentados protótipos e dispositivos que exploram tais
técnicas para a medida simultânea de pressão e
temperatura. Esses protótipos foram projetados com auxílio
de
ferramentas CAD e modelados utilizando-se o método de
elementos finitos em conjunto
com a teoria de modos acoplados da Rede de Bragg. As
previsões obtidas utilizando-se
estes modelos mostraram-se bastante próximas dos
resultados das implementações
experimentais dos protótipos, indicando que a metodologia
de modelagem desenvolvida
pode ser aplicada nos projetos de transdutores baseados
nas duas técnicas estudadas. / [en] Fiber Bragg gratings (FBG) are modulations in the
effective refractive index of
optical fibers, introduced in a small length along the
fiber core. Such components operate
as narrow band reflective filters, that is, when
illuminated by a broad-band light source,
they reflect a narrow spectral band centered at a specific
wavelength, the Bragg
wavelength. This wavelength is proportional to the spatial
period of the refractive index
modulation. Fiber Bragg gratings have find an increasing
number of applications as
sensors for different quantities, and today are being
employed as part of permanent, real
time monitoring systems in various industrial segments.
The oil and gas sector, together
with civil infrastructure and aeronautics and aerospace,
account for almost 70% of this
applications. In a number of situations, FBG sensing is
based on indirect measurements
of the quantity being monitored, and a transduction
mechanism is employed to transform
changes in the measured quantity in strain sensed by the
optical fiber. Since the FBG is
sensitive to strain and temperature, proper temperature
compensation is always
necessary. Usually, a second grating is employed to
simultaneously measure temperature
and strain, performing the required compensation.
This thesis presents a study on effects due to non-
homogeneous strains in the
Bragg grating and discusses application of two different
techniques, based on these
effects, to allow temperature compensated strain
measurement using a single FBG. The
first technique explores strain induced optical
birefringence when the fiber is loaded
transversely. The second technique is based on changes in
the spectral shape of the light
signal reflected by the grating when subjected to non
homogeneous axial strain fields.
Prototypes of pressure and temperature transducers based
on these techniques have been
developed. These prototypes have been designed by
employing CAD techniques and
modeled using the finite element method in conjunction
with the theory of coupled
modes for fiber Bragg gratings. Comparisons between
results provided by theoretical models and experimental
realizations of the prototypes are very close,
demonstrating that
the developed approach can be applied to design
transducers based on the discussed
techniques. Results obtained with the proposed pressure
and temperature sensors are also
encouraging indicating that the two techniques are
suitable for industrial applications.
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Controle de vibração em uma pá inteligente de helicóptero / Vibration control of a smart helicopter bladeGasparini, José Nilson 06 December 2004 (has links)
O objetivo deste trabalho é investigar o controle ativo de vibração em uma pá inteligente de helicóptero. O desenvolvimento de materiais inteligentes para trabalharem como sensores e atuadores apresentam uma nova alternativa no controle de vibração. A pá de helicóptero é modelada pelo método dos elementos finitos, considerando os movimentos de batimento, flexão no plano de rotação, estiramento axial e torção. O modelo da pá considera também ângulo de torção geométrica, não coincidência entre os eixos, elástico e do centro de gravidade das seções transversais e material isotrópico. O modelo matemático é desenvolvido, e nele é incorporado atuadores piezelétricos distribuídos ao longo da envergadura da pá. O controle ativo de vibração é baseado no controle individual da pá na condição de vôo pairado. As matrizes de elementos finitos são obtidas pelo método de energia e um procedimento de linearização é aplicado às equações resultantes. O carregamento aerodinâmico linearizado é calculado para a condição de vôo pairado e a representação no espaço de estados é usada para o projeto de um controlador. Usou-se a técnica de atribuição da autoestrutura por realimentação de saída no modelo de ordem reduzida, resultado da aplicação do método da expansão por frações parciais. As simulações do modelo em malha aberta e fechada, exibiu boas qualidades de resposta, o que mostra que o controle ativo é uma boa alternativa para a redução de vibrações em helicópteros. / The objective of this work is to investigate the performance of a smart helicopter blade. Developments on smart materials for both sensing and/or actuation have provided a novel alternative in vibration control. The helicopter blade is modeled by the finite element method, considering the motions of flapping, lead-lagging, axial stretching, and torsion. The blade model also considers a pretwist angle, offset between mass and elastic axes, and isotropic material. The helicopter blade mathematical model allows the incorporation of piezoelectric actuators distributed along the blade span. The active vibration control is based on the premise of individual blade control and the investigation is carried out for hovering flight condition the finite element matrices are obtained by energy methods and a linearization procedure is applied to the resulting expressions. The linearized aerodynamic loading is calculated for hover and the state-space approach is used to design the control law. The eigenstructure assignment by output feedback is used in the blade-reduced model resulting from the application of the expansion method by partial fractions. The simulations for open and closed-loop systems are presented, having exhibited good response qualities, which shows that output feedback is a good alternative for smart helicopter blade vibration attenuation.
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Técnicas para monitoramento de integridade estrutural usando sensores e atuadores piezoelétricos / Techniques for structural health monitoring using piezoelectric sensors and actuatorsMaio, Carlos Eduardo Bassi 24 March 2011 (has links)
A utilização de materiais piezoelétricos, na função de sensores e atuadores distribuídos, para o controle e monitoramento de vibrações estruturais tem um enorme potencial de aplicação nas indústrias aeronáutica, aeroespacial, automobilística e eletroeletrônica. O uso de sensores piezoelétricos integrados para monitoramento de integridade estrutural (ou detecção de falhas), em particular, tem evoluído bastante na última década. Por conseguinte, o número de técnicas utilizadas para esse fim são as mais variadas possíveis. Dentre elas estão às técnicas que avaliam o efeito dos danos em baixa freqüência usando parâmetros modais, em especial freqüências naturais e modos, ou em média-alta freqüência medindo-se a impedância/admitância eletromecânica. O objetivo dessa dissertação é desenvolver, com auxílio de um modelo 2D ANSYS em elementos finitos, uma análise de diferentes técnicas para detecção da posição e tamanho da delaminação em estruturas compósitas utilizando pastilhas piezoelétricas. Várias métricas e técnicas são avaliadas em termos de sua capacidade de identificar, com relativa acurácia, a presença, localização e severidade do dano. Os resultados mostram que ambas as técnicas modal e baseada na impedância são capazes de identificar a presença de danos do tipo delaminação, desde que as pastilhas piezoelétricas estejam próximas do dano. Também é mostrado que as técnicas baseadas na impedância parecem ser mais eficientes do que as modais para detecção da posição e tamanho da delaminação. / The use of piezoelectric materials in the function of distributed sensors and actuators for the control and monitoring of structural vibrations has enormous potential for application in the aeronautical, aerospace, automotive and electronics. The use of integrated piezoelectric sensors for structural health monitoring (or damage detection), in particular, has evolved greatly over the last decade. Consequently, the numbers of techniques used for this purpose are highly diverse. Among them are techniques that evaluate the effect of damages on low frequency modal parameters, especially natural frequencies and mode shapes, or on medium-high frequency measurements of electromechanical impedance/admittance. The objective of this dissertation is to perform, with the aid of a 2D ANSYS finite element model, an analysis of different techniques for the detection of position and size of a delamination in a composite structure using piezoelectric patches. Several metrics and techniques are evaluated in terms of their capability of identifying, with relative accuracy, the presence, location and severity of the damage. Results show that both modal and impedance-based techniques are able to identify the presence of the delamination-type damages, provided the piezoelectric patches are close enough to the damage. It is also shown that impedance-based techniques seem more effective than modal ones for the detection of delamination position and size.
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