Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 325-341). Available also in a digital version from Dissertation Abstracts.

The purpose of this research work is to propose an improved method for real-time sensitivity analysis (SA) applicable to large-scale complex systems. Borrowed from the EventTracker principle of the interrelation of causal events, it deploys the Rank Order Clustering (ROC) method to automatically group every relevant system input to parameters that represent the system state (i.e. output). The fundamental principle of event modelling is that the state of a given system is a function of every acquirable piece of knowledge or data (input) of events that occur within the system and its wider operational environment unless proven otherwise. It therefore strives to build the theoretical and practical foundation for the engineering of input data. The event modelling platform proposed attempts to filter unwanted data, and more importantly, include information that was thought to be irrelevant at the outset of the design process. The underpinning logic of the proposed Event Clustering technique (EventiC) is to build causal relationship between the events that trigger the inputs and outputs of the system. EventiC groups inputs with relevant corresponding outputs and measures the impact of each input variable on the output variables in short spans of time (relative real-time). It is believed that this grouping of relevant input-output event data by order of its importance in real-time is the key contribution to knowledge in this subject area. Our motivation is that components of current complex and organised systems are capable of generating and sharing information within their network of interrelated devices and systems. In addition to being an intelligent recorder of events, EventiC could also be a platform for preliminary data and knowledge construction. This improvement in the quality, and at times the quantity of input data, may lead to improved higher level mathematical formalism. It is hoped that better models will translate into superior controls and decision making. It is therefore believed that the projected outcome of this research work can be used to predict, stabilize (control), and optimize (operational research) the work of complex systems in the shortest possible time. For proof of concept, EventiC was designed using the MATLAB package and implemented using real-time data from the monitoring and control system of a typical cement manufacturing plant. The purpose for this deployment was to test and validate the concept, and to demonstrate whether the clusters of input data and their levels of importance against system performance indicators could be approved by industry experts. EventiC was used as an input variable selection tool for improving the existing fuzzy controller of the plant. Finally, EventiC was compared with its predecessor EventTracker using the same case study. The results revealed improvements in both computational efficiency and the quality of input variable selection.

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This research reviews and extends the impedance-based structural health monitoring technique in order to detect and identify structural damage on various complex structures. The basic principle behind this technique is to apply high frequency structural excitations (typically higher than 30 kHz) through the surface-bonded piezoelectric transducers, and measure the impedance of structures by monitoring the current and voltage applied to the transducers. Changes in impedance indicate changes in the structure, which in turn can indicate that damage has occurred. Several case studies, including a pipeline structure, a composite reinforced aluminum plate, a precision part (gear), a quarter-scale bridge section, and a steel pipe header, demonstrate how this technique can be used to detect damage in real-time. A method to process impedance measurements to prevent significant temperature and boundary condition changes registering as damage has been developed and implemented. Furthermore, the feasibility of using the technique for high temperature structures and for condition monitoring of critical facilities subjected to a severe natural disaster has been investigated. While the impedance-based structural health monitoring technique indicates qualitatively that damage has occurred, more information on the nature of damage is necessary for remote structures. In this research, two different damage identification schemes have been combined with the impedance method in order to quantitatively assess the state of structures. One is based on a wave propagation modeling, and the other is the use of artificial neural networks. A newly developed wave propagation model has been developed and combined with the impedance method in order to estimate the severity of damage. Numerical and experimental investigations on 1-dimensional structures were presented to illustrate the effectiveness of the combined approach. Furthermore, to avoid the complexity introduced by conventional computational methods in high frequency ranges, multiple sets of artificial neural networks were integrated with the impedance-based health monitoring technique. By incorporating neural network features, the technique is able to detect damage in its early stage and to determine the severity of damage without prior knowledge of the model of structures. The dissertation concludes with experimental examples, investigations on a quarter-scale steel bridge section and a space truss structure, in order to verify the performance of the proposed methodology. / Ph. D.

A sensibilidade eletromecânica dos transdutores de eletretos poliméricos resulta em muitas aplicações na engenharia, que motivaram a produção industrial de um filme não homogêneo e eletricamente carregado, denominado filme eletromecânico ou EMFi (ElectroMechanical Film). Um dispositivo alternativo a este EMFi, produzido em nosso laboratório, foi o resultado de uma bolha de ar homogênea termoformada, unida por dois filmes de teflon FEP. Este dispositivo possui uma estrutura similar ao EMFi, mas permite cavidades homogêneas a serem predefinidas e distribuídas no momento em que o dispositivo é produzido, diferindo das células no EMFi com tamanhos diversos e dispersas no interior do filme industrial. A possibilidade de controlar a geometria das bolhas de ar tornou possível o desenvolvimento de um modelo, empregado como uma ferramenta de projeto. A resposta eletromecânica deste transdutor foi modelada e então apresentada neste trabalho. Este modelo analítico avalia o desempenho destes transdutores com somente uma bolha termoformada, para efeitos de simplificação, baseado em capacitores em série, em função da deformação mecânica e da carga elétrica retida no polímero. São representados dinamicamente com parâmetros elétricos e mecânicos, definidos à medida que operam como sensores ou atuadores, com respeito ao limites impostos pela aplicação especificada. O gráfico da resposta em freqüência mostra a freqüência de ressonância e a largura da faixa para meia-amplitude que determina o coeficiente de amortecimento que não pode ser obtido diretamente do modelo analítico. Este gráfico também permite comparar a freqüência natural obtida graficamente com aquela calculada pelo modelo, tornando mais confiável o modelo desenvolvido para o transdutor. Finalmente, melhorias na instrumentação e em condições mais adequadas para os testes são sugeridas, bem como métodos alternativos para trabalhos futuros. / The electromechanical sensibility of polymeric electrets transducers yields many engineering applications which have motivated industrial production of a non-homogeneous and electrically charged film, the so-called electromechanical film (EMFi). An alternative device for this EMFi that has been produced in our laboratory was a homogeneous thermo-formed air bubbles bonded with two teflon FEP films. This device has a structure similar to the EMFi, but allows the homogeneous voids to be pre-defined and distributed at the moment the device is produced, differing the EMFi voids with diverse sizes and dispersed into the industrial film. The possibility to control the air bubbles geometry makes possible the development of a model to be used as a design tool. The electromechanical response of this transducer has been modeled and is presented in this work. Such analytical model evaluates the transducers performance using just a single thermo-formed bubble for simplification purposes, based on series capacitors, which are function of the mechanical deformation and electrical charge trapped in the polymer. They are represented dynamically, with electrical and mechanical parameters being defined as they work as sensors or actuators, regarding the limits imposed by the specified application. A frequency response plot shows the resonance frequency and the bandwidth for the half amplitude, which determines the damper coefficient that cannot be obtained directly from the analytical model. This plot also allows comparison of the natural frequency obtained graphically with the calculated one using the model, making more reliable the transducer model developed. Finally, instrumentation improvements and more suitable test conditions are suggested, as well as alternative methods for future works.

A sensibilidade eletromecânica dos transdutores de eletretos poliméricos resulta em muitas aplicações na engenharia, que motivaram a produção industrial de um filme não homogêneo e eletricamente carregado, denominado filme eletromecânico ou EMFi (ElectroMechanical Film). Um dispositivo alternativo a este EMFi, produzido em nosso laboratório, foi o resultado de uma bolha de ar homogênea termoformada, unida por dois filmes de teflon FEP. Este dispositivo possui uma estrutura similar ao EMFi, mas permite cavidades homogêneas a serem predefinidas e distribuídas no momento em que o dispositivo é produzido, diferindo das células no EMFi com tamanhos diversos e dispersas no interior do filme industrial. A possibilidade de controlar a geometria das bolhas de ar tornou possível o desenvolvimento de um modelo, empregado como uma ferramenta de projeto. A resposta eletromecânica deste transdutor foi modelada e então apresentada neste trabalho. Este modelo analítico avalia o desempenho destes transdutores com somente uma bolha termoformada, para efeitos de simplificação, baseado em capacitores em série, em função da deformação mecânica e da carga elétrica retida no polímero. São representados dinamicamente com parâmetros elétricos e mecânicos, definidos à medida que operam como sensores ou atuadores, com respeito ao limites impostos pela aplicação especificada. O gráfico da resposta em freqüência mostra a freqüência de ressonância e a largura da faixa para meia-amplitude que determina o coeficiente de amortecimento que não pode ser obtido diretamente do modelo analítico. Este gráfico também permite comparar a freqüência natural obtida graficamente com aquela calculada pelo modelo, tornando mais confiável o modelo desenvolvido para o transdutor. Finalmente, melhorias na instrumentação e em condições mais adequadas para os testes são sugeridas, bem como métodos alternativos para trabalhos futuros. / The electromechanical sensibility of polymeric electrets transducers yields many engineering applications which have motivated industrial production of a non-homogeneous and electrically charged film, the so-called electromechanical film (EMFi). An alternative device for this EMFi that has been produced in our laboratory was a homogeneous thermo-formed air bubbles bonded with two teflon FEP films. This device has a structure similar to the EMFi, but allows the homogeneous voids to be pre-defined and distributed at the moment the device is produced, differing the EMFi voids with diverse sizes and dispersed into the industrial film. The possibility to control the air bubbles geometry makes possible the development of a model to be used as a design tool. The electromechanical response of this transducer has been modeled and is presented in this work. Such analytical model evaluates the transducers performance using just a single thermo-formed bubble for simplification purposes, based on series capacitors, which are function of the mechanical deformation and electrical charge trapped in the polymer. They are represented dynamically, with electrical and mechanical parameters being defined as they work as sensors or actuators, regarding the limits imposed by the specified application. A frequency response plot shows the resonance frequency and the bandwidth for the half amplitude, which determines the damper coefficient that cannot be obtained directly from the analytical model. This plot also allows comparison of the natural frequency obtained graphically with the calculated one using the model, making more reliable the transducer model developed. Finally, instrumentation improvements and more suitable test conditions are suggested, as well as alternative methods for future works.

In networked robot systems (NRS), robots and robotic devices are distributed in the environment; typically tasks are performed by cooperation and coordination of such multiple networked components. NRS offer advantages over monolithic systems in terms of modularity, flexibility and cost effectiveness, and they are thus becoming a mainstream approach to the inclusion of robotic solutions in everyday environments. The components of a NRS are usually robots and sensors equipped with rich computational and communication facilities. In this thesis, we argue that the capabilities of a NRS would greatly increase if it could also accommodate among its nodes simpler entities, like small ubiquitous sensing and actuation devices, home appliances, or augmented everyday objects. For instance, a domestic robot needs to manipulate food items and interact with appliances. Such a robot would benefit from the ability to exchange information with those items and appliances in a direct way, in the same way as with other networked robots and sensors. Combining such highly heterogeneous devices inside one NRS is challenging, and one of the major challenges is to provide a common communication and collaboration infrastructure. In the field of NRS, this infrastructure is commonly provided by a shared middleware. Unfortunately, current middlewares lack the generality needed to allow heterogeneous entities such as robots, simple ubiquitous devices and everyday objects to coexist in the same system. In this thesis we show how an existing middleware for NRS can be extended to include three new types of “citizens” in the system, on peer with the other robots. First, we include computationally simple embedded devices, like ubiquitous sensors and actuators, by creating a fully compatible tiny version of the existing robotic middleware. Second, we include augmented everyday objects or home appliances which are unable to run the middleware on board, by proposing a generic design pattern based on the notion of object proxy. Finally,we go one step further and include humans as nodes in the NRS by defining the notion of human proxy. While there exist a few other NRS which are able to include both robots and simple embedded devices in the same system, the use of proxies to include everyday objects and humans in a generic way is a unique feature of this work. In order to verify and validate the above concepts, we have implemented them in the Peis-Ecology NRS model. We report a number of experiments based on this implementation, which provide both quantitative and qualitative evaluations of its performance, reliability, and interoperability.

O principal objetivo do controle de vibrações é a sua redução ou minimização, através da modificação automática da resposta estrutural. Em muitas situações isto é necessário para promover a estabilidade estrutural, e para alcançar o alto desempenho mecânico necessário em diversas áreas técnicas, tais como a engenharia aeroespacial, civil e mecânica, bem como a biotecnologia, inclusive em escala micro e nano mecânica. Uma alternativa é o uso de estruturas inteligentes, que são o resultado da combinação de sensores e atuadores integrados em uma estrutura mecânica, e um método de controle adequado. O principal objetivo deste trabalho é o desenvolvimento de rotinas computacionais para a simulação, via método dos elementos finitos, do controle ativo de estruturas inteligentes de cascas, placas e vigas delgadas de material compósito laminado com camadas de material piezoelétrico como sensores e/ou atuadores. Caracterizam esta pesquisa a utilização do elemento GPL-T9 de três nós e seis graus de liberdade mecânicos por nó, mais um grau de liberdade elétrico por camada piezoelétrica, assim como a avaliação de dois métodos de controle, o Proporcional-Integral-Derivativo (PID) e o Regulador Quadrático Linear ou Linear Quadratic Regulator (LQR), incluindo o LQR Modal, e a otimização da localização de pastilhas piezoelétricas através de um Algoritmo Genético (AG). Várias aplicações são apresentadas e os resultados obtidos são comparados aos disponíveis na literatura especializada. / The main objective of vibration control is its reduction or even its minimization by the automatic modification of the structural response. Sometimes this is necessary to increase structural stability and to attain a high mechanical behavior in several areas such as aerospace, civil and mechanical engineering, biotechnology, including macro, micro and nanomechanical scales. An alternative is to use a smart structure, which results of the combinations of integrated sensors and actuators in a mechanical structure and a suitable control method. Development of a computational code to simulate, using finite elements, the active control in smart structures such as slender shells, plates and beams of composite materials with embedded piezoelectric layers acting as actuators and sensors is the main objective of this work. This research is characterized by the use of the GPL-T9 element with three nodes and six mechanical degrees of freedom and one electrical degree of freedom per piezoelectric layer, by the evaluation of two control methods, the Proportional Integral Derivative (PID) and the Linear Quadratic Regulator (LQR), including the Modal LQR, and, finally by the optimization of piezoelectric patches placement using a Genetic Algorithm (GA). Several examples are presented and compared with those obtained by other authors.

Orientador: Vicente Lopes Júnior / Banca: Amarildo Tabone Paschoalini / Banca: Marcelo Areias Trindade / Resumo: Este trabalho apresenta o estudo e desenvolvimento de técnicas para o monitoramento da integridade estrutural em sistemas inteligentes com sensores e atuadores piezelétricos acoplados. Os índices de sensibilidade estudados e utilizados no monitoramento da estrutura são: índice de falha métrica, calculado diretamente do sinal de impedância elétrica dos sensores/atuadores piezelétricos; índices do sensor, calculados com as normas de sistemas ou com as matrizes grammiana de observabilidade e os índices de entrada, calculados com as matrizes grammianas de controlabilidade. Tais índices são utilizados para detectar e localizar as falhas em aplicações numéricas e experimentais. As normas de sistemas e as matrizes grammianas de controlabilidade e observabilidade são obtidas através de um modelo numérico, como por exemplo, Método dos Elementos Finitos; ou um modelo identificado experimentalmente, via o método de realização para autossistemas, mais conhecido como ERA (Eigensytem Realization Algorithm). Em uma segunda etapa do procedimento proposto, as falhas são quantificadas utilizando Redes Neurais Artificiais, que foram treinadas com as normas de sistemas e com as matrizes grammianas. / Abstract: This work presents the study and development of Structural Health Monitoring techniques for application in intelligent systems with coupled piezoelectric sensors and actuators. The indices of sensitivity for structural monitoring are based on: root-means-square deviation index, directly calculated from electric impedance signal of the piezoelectric sensors/actuators; sensor indices, calculated from system norms or observability grammian matrix, and input index, calculated from controllability grammian matrix. Such indices are used for damage detection and location in numerical and experimental applications. System norms, controllability and observability grammian matrices are obtained through numerical model, as for instance, Finite Element Method; or by experimental identification technique, via Eigensytem Realization Algorithm (ERA). In the second stage of the proposed procedure, damages were quantified using Artificial Neural Networks, that were trained with systems norms and grammian matrices. / Mestre

This thesis work was conducted in the Department of Mechanical Engineering at the Cape Peninsula University of Technology (CPUT) and was submitted towards the partial fulfilment of the Masters Degree in Technology: Mechanical Engineering. / Recent years have witnessed a tremendous growth and significant advances in “smart” composites and “smart” composite structures. These smart composites integrate active elements such as sensors and actuators into a host structure to create improved or new functionalities through a clever choice of the active elements and/or a proper design of the structure. Such composites are able to sense a change in the environment and make a useful response by using an external feedback control system. Depending on their applications, smart composites usually make use of either the joint properties of the structure or the properties of the individual elements within the composites. The accumulation in the understanding of materials science and the rapid developments in computational capabilities have provided an even wider framework for the implementation of multi-functionality in composites and make “smart” composites “intelligent”.