Simulating the propagation of longitudinal ultrasonic waves in aerospace structural materials

Orientador: Auteliano Antunes dos Santos JuniorDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: Materiais compósitos são cada vez mais utilizados na indústria aeroespacial, por apresentarem baixa relação entre massa específica e resistência mecânica. Para a realização de ensaios não destrutivos utilizando o ultrassom, faz-se necessário conhecer a velocidade com que o som se propaga através desses materiais. Nem sempre é possível desenvolver protótipos reais durante o desenvolvimento de um projeto, por limitações construtivas e de custo; modelos virtuais são, pois, necessários. O objetivo deste trabalho é desenvolver modelos virtuais para avaliar a propagação de ondas em compósitos e compará-los com resultados experimentais. Uma liga de alumínio é usada inicialmente, de forma a calibrar o modelo e configurar alguns parâmetros de simulação. O material composto analisado é um laminado unidirecional, fabricado a partir de 97 camadas de material pré-impregnado (AS4/8552) da Hexcel¿. Utiliza-se o método dos elementos finitos para simular a geração, propagação e recepção de ondas ultrassônicas no modelo. O foco do estudo são ondas longitudinais de volume, embora a geração de ondas longitudinais criticamente refratadas (Lcr) também seja demonstrada. A razão é que o estudo é parte de uma pesquisa sobre o desenvolvimento de técnicas ultrassônicas para a medição de tensões em compósitos, utilizando Acustoelasticidade. A fim de permitir a medição da velocidade da onda ultrassônica em diferentes orientações, foi fabricado um corpo de prova em formato de prisma de base poligonal de 24 lados. O modelo numérico desenvolvido considera o caso ideal, onde as lâminas são perfeitamente coladas umas nas outras e não há problemas como delaminação ou vazios. Um modelo simplificado de cada lâmina foi admitido, de modo a utilizar uma malha menos refinada nas simulações e reduzir o gasto computacional. A fração volumétrica de reforço e matriz foi mantida. Um pulso de 1 MHz foi inserido no modelo e as discretizações no tempo e no espaço foram escolhidas de forma coerente. Simulações para o caso de 0º e 90º foram feitas e um modelo para os outros ângulos de orientação foi proposto. Os resultados mostram-se satisfatórios e indicam que, no futuro, o modelo simplificado adotado poderá ser estendido, levando em conta não conformidades e uma distribuição mais heterogênea das fibras, permitindo o desenvolvimento de ferramentas de inspeção aperfeiçoadasAbstract: The use of composite materials in the aerospace industry is increasing due to its low ratio between density and mechanical strength. To perform non-destructive testing using ultrasound, it is necessary to know the sound velocity in these materials. It is not always possible to manufacture physical prototypes during the development of a project because of time, construction limitation and cost; virtual models are therefore needed. The objective of this work is to develop virtual models to evaluate the wave propagation in composites and compare them with experimental results. Initially, an aluminum alloy is used in order to calibrate the model and configure some simulation parameters. The composite material analyzed is a unidirectional laminate, made from 97 layers of prepreg material (AS4/8552) from Hexcel¿. We use the finite element method to simulate the generation, propagation and reception of ultrasonic waves in the model. The focus of this study is the generation of longitudinal bulk waves, although the generation of Critically Refracted Longitudinal (Lcr) waves is also demonstrated. The reason is that the study is part of an ongoing research project on the development of ultrasonic techniques for measuring residual stress in composites, using acoustoelasticity. To enable the measurement of the ultrasonic wave velocity in different orientations, we manufactured a specimen in a prismatic shape (24-sided polygonal base). The numerical model consists of the ideal case, where the different materials are completely attached to each other and there are no problems such as delamination or voids. A simplified model of each layer was admitted, to use a less refined mesh in the simulations and reduce the computational cost. The volume fraction of reinforcement and matrix was maintained. A pulse of 1 MHz was inserted into the model and the discretization both in time and space was chosen consistently. Simulations for the case of 0° and 90° were made and a model for the other orientations was proposed. The results prove to be satisfactory and indicate that in the future, the simplified model adopted could be extended, taking into account nonconformities and a more heterogeneous distribution of the fibers, allowing the development of improved inspection toolsMestradoMecanica dos Sólidos e Projeto MecanicoMestre em Engenharia Mecânic

Distance Protection for Parallel and Double-Circuit HV Lines

Chránění paralelních a souběžných vedení je skutečně problematické z důvodů účinku vzájemné indukčnosti vedení v souběhu, odporu poruchy nebo rozložení zpětného proudu poruchy, které zkreslují impedanci jednofázové poruchy „viděné“ distanční ochranou. Proto současné numerické distanční ochrany nabízí kompenzační funkce, které je možno použít pro korekci charakteristik a výpočtu vzdálenosti poruchy pomocí lokátorů její charakteristice s dostatečnou odporovou rezervou a možnosti nastavení odpovídajícího režimu vypnutí. Tato práce se zabývá problémy, kterým čelí lokátor distanční ochrany při měření a výpočtu vzdálenosti místa jednofázové poruchy, a také mapuje současný stav řešení těchto problémů. Na základě výpočtu parametrů zadaného vedení bylo provedeno zhodnocení možných chyb při lokalizaci jednofázové poruchy a navrženo nastavení distanční ochrany určené k jeho chránění včetně nastavení parametrů určených pro kompenzaci výše uvedených negativních jevů. Bylo zjištěno, že zemnící lana a transpozice vedení přispívají k přesnosti lokátorů, protože nejmenší chyba byla zjištěna v transponovaném vedení se zemním lanem.The protection of parallel and double-circuit lines is actually challenging due to the effect of mutual coupling impedance, fault resistance and the current reversal phenomenon which distort the single-phase fault impedance ‘’seen’’ by the distance protection. However, numerical distance protections currently used provide compensation functions which can be used for the characteristic correction and computation of distance-to-fault location, because of their locator characteristics with enough resistive reserve and the possibility of setting an adequate tripping mode. This work explores the problems faced by the distance protection locator while measuring and calculating the location distance of a single-phase fault, and the current state of solutions adopted in solving those problems. Owing to the parameter calculations for the given transmission line, possible faults when localizing single-phase faults were evaluated, and a setting design was proposed for the effective line protection, including settings of parameters which compensate the above mentioned negative phenomena. It was found that the earth-wire and the line transposition, improve the accuracy of the locators, because the least error was found in the transposed line with earth wire.

Perspectives of the use of admittance matrix based state estimator in the treatment of faults in distribution networks

Orientador: Madson Côrtes de AlmeidaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: O desenvolvimento e a maturação de tecnologias de medição, comunicação e geração distribuída tem resultado em profundas transformações no setor de distribuição de energia, culminando na concepção das chamadas redes inteligentes. O arquétipo tradicional de medidores, no qual apenas o consumo mensal era contabilizado, começa a incorporar novas medidas tais como medições de tensão e potências com taxas de amostragem de algumas dezenas de minutos. Alinhado com essas tendências, há investimentos sendo feitos em todo o mundo para que esses medidores, chamados de inteligentes, sejam instalados em consumidores residenciais. Desta forma, a projeção para os sistemas de distribuição é que eles sejam mais ativos na gestão e controle de energia. Neste contexto, surgiram novas abordagens de estimação de estado específicas para sistemas de distribuição e a oportunidade da aplicação destes estimadores devido à modificação da concepção dessas redes. Com isso, dentre as possibilidade da utilização destes estimadores para solucionar problemas corriqueiros da distribuidora tem-se o de localização de falta. A utilização de algoritmos robustos de estimação de estado que possam ser aplicados ao problema de tratamento de faltas podem ajudar a melhorar os índices de qualidade de energia entregue ao consumidor, bem como a confiabilidade da rede. Nesse contexto, o foco deste trabalho é avaliar, sob condições de falta, a robustez do estimador de estado baseado em matriz de admitância e propor melhorias que viabilizem o uso desse estimador como núcleo de uma ferramenta dedicada à localização de faltas em redes modernas de distribuição de energia elétricaAbstract: The development and maturation of measurement, communication and distributed generation technologies have resulted in profound transformations in the energy distribution sector, culminating in the design of the so-called smart grids. The traditional archetype of energy meters, in which just monthly consumption are accounted, is in a transition to incorporate new measures in the form of voltage and power measurements with sample rates of a few tens of minutes. Aligned with these trends, there are investments being made around the world for these so-called smart meters to be installed in residential consumers. Therefore, the projection for distribution systems is that they are more critical in the management and control of energy. In this context, new approaches of state estimation specific for distribution systems have emerged as opportunities for the application of these estimators due to the modification of the design of this network. Thus, there is the possibility to use these estimators to solve common problems of the distribution such as fault location. The use of robust state estimation algorithms that can be applied to the problem of fault treatment can help to improve consumer power quality indices as well as network reliability. In this context, the focus of this work is to evaluate, under fault conditions, the robustness of the state estimator based on admittance matrix and to propose improvements that will make use of this estimator as the core of a tool dedicated to fault localization in modern distribution networks of electricityMestradoEnergia EletricaMestre em Engenharia Elétrica1695517CAPE

Experimental validation of model for fault by wear parameter identification in lubricated bearings

Orientador: Katia Lucchesi Cavalca DediniTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: Máquinas rotativas são utilizadas em uma vasta gama de processos industriais onde, de maneira geral, o aumento da eficiência está diretamente relacionado ao aumento da velocidade de rotação. Por este motivo, mancais hidrodinâmicos são comumente utilizados devido a sua elevada capacidade de carga e aplicabilidade a altas rotações. No entanto, este tipo de mancal pode inserir anisotropia no sistema ocasionando o surgimento de instabilidades fluído induzidas. Assim, rotores de grande porte são submetidos a testes de estabilidade na fase de comissionamento e ao longo de sua vida útil visando uma operação segura. O presente trabalho se insere neste contexto em duas vertentes. Primeiramente, é a apresentado um método para a identificação dos parâmetros de desgaste em mancais hidrodinâmicos (profundidade e posição angular); um dos problemas inerentes a este tipo de mancal. O método é baseado no ajuste das dFRFs (Directional Frequency Response Function) do modelo desenvolvido em função das curvas obtidas experimentalmente. A dFRF experimental é obtida através da aplicação, por um atuador magnético, de um ruído-branco, e pela medição do deslocamento do eixo nos mancais. A dFRF simulada é obtida a partir do modelo em elementos finitos do eixo contendo os coeficientes de rigidez e amortecimento dos mancais hidrodinâmicos, contemplando casos com ou sem falha por desgaste. A presença do desgaste apresenta grande influência nos termos cruzados da dFRF, devido à intensificação do caráter anisotrópico dos mancais, sendo estes mais eficazes na identificação dos parâmetros do desgaste se comparados à FRF em coordenadas físicas. As vantagens do método proposto são a aplicabilidade em sistemas reais e a robustez na identificação dos parâmetros de desgaste de mancais hidrodinâmicos. A segunda vertente do trabalho é a apresentação do método MOBAR (Multiple Output Backward Autoregressive Method) como uma alternativa na obtenção do fator de amortecimento de rotores sustentados por mancais lubrificados, podendo ser utilizado nos testes de comissionamento e manutenção preditiva. O método é baseado em um modelo autorregressivo que utiliza apenas a resposta transiente do sistema, obtida a partir da aplicação de uma força rotativa utilizando-se um atuador magnético. Com as modificações propostas neste trabalho, o método apresentou-se consistente na identificação dos parâmetros de amortecimento, enquanto que a duração dos testes experimentais é da ordem de segundos, reduzindo custos de paradas programadasAbstract: Rotating machines are used in a wide range of industrial processes and, in general, a higher efficiency is directly related to a higher rotational speed. For this reason, hydrodynamic bearings are frequently used due to its high load capacity and applicability to higher rotational speeds. However, this kind of bearing may introduce anisotropy in the system leading to the appearance of fluid-induced instabilities. Thus, large rotors are submitted to stability tests at the commissioning stage and during its operational life aiming a secure operation. The present work is inserted in this context in two segments. First, a method for wear parameters identification in journal bearings (depth and angular position) , one of the inherent problems of such bearings, is presented. The method is based in adjust the dFRFs (Directional Frequency Response Function) of the developed model as a function of the experimental obtained curves. The experimental dFRF is obtained through the application of a white noise, by a magnetic actuator, and the displacement measurements of the shaft in the bearings. The simulated dFRF is obtained from a finite element model of the shaft containing the stiffness and damping coefficients of the lubricated bearings, with or without wear. The presence of wear has a high influence in the crossed terms of the dFRF, due to the increase of the anisotropy in the bearings, being more suitable for the wear parameters identification than the FRF in physical coordinates. The advantages of the proposed method are its applicability in real systems and the robustness of the wear parameters identification in hydrodynamic bearings. The second segment of this work consists of presenting the MOBAR method (Multiple Output Backward Autoregressive Method) as an alternative to obtain the damping factor of journal bearing supported rotors, which can be applied in tests for commissioning and predictive maintenance. The method is based in an autoregressive model, which uses only the transient response of the system, obtained through the application of a rotational force using a magnetic actuator. With the modifications proposed in this work, the method has presented consistence in the damping factor identification, while the tests duration are in the order of seconds, reducing the costs of programmed stopsDoutoradoMecanica dos Sólidos e Projeto MecanicoDoutor em Engenharia Mecânica5553/11-3CAPE

Earth Fault Distance Computation Methods Based on Transients in Power Distribution Systems

The most common fault type in MV distribution network is single line to earth fault. The initial transients of earth faults are important especially for unearthed and compensated neutral networks. The earth fault transient signals consist of many different frequency components, which result from charging and discharging of the network capacitances. The transient components provide valuable information for fault location purposes. The charging component has higher amplitude and lower frequency than the discharge component and hence is more suitable to be used for fault location purposes. In this thesis, we discuss algorithms to locate an earth fault in unearthed or a compensated neutral MV networks using the information of the measured transient signal. The networks considered are assumed to be radially operated and they are modeled using Electromagnetic Transient Program-Alternative Transient Program (EMTP-ATP). Five types of fault location algorithms have been developed which are called general model (GM) algorithm, exact model (EM) algorithm, continuous wavelet transform (CWT) based method, multiple regression analysis (MRA) based method and artificial neural network (ANN). GM algorithm is developed based on a simplified model of symmetrical components while EM algorithm is developed with exact "pi"-model of symmetrical components. Both algorithms utilize the frequency of charging transient to estimate the fault distance. CWT based algorithm requires both voltage and current of transient signals to estimate the fault path inductance. MRA and NN algorithms were developed using the transient signal measured from the secondary side of the MV/LV distribution transformer. In addition, an algorithm to find a correct path towards the position of fault in network which has many branches is presented. The results from intensive simulations and experiments in actual distribution networks are also presented in this thesis. The results are analyzed using signal processing techniques. The algorithms apply continuous wavelet transform (CWT) to locate the dominant charge transient frequency and extract the specific coefficient corresponding to the charge transient frequency. In this thesis, the properties of Hilbert transformation (HT) are used to estimate the damping attenuation of the transient signal. Finally the performance of the proposed fault location algorithms is evaluated and the results are compared. Based on the simulation results, it is found that the proposed algorithms work at a reasonable level of accuracy. The results from real experiment data show that both CWT and GM algorithms have a comparable result

Fault Diagnosis for Intra-platoon Communications

Fault location (Engineering), Highway communications--Mathematical models, Traffic flow--Mathematical models, intelligent transportation systems

Issues In Fault Tolerant Control Of Vehicle Follower Systems

The aim of this report is to study issues concerning fault detection and identification in vehicle follower control. The report discusses various potential fault modes among sensors, and actuators used in the vehicle following experiments in cars. It deals with issues of fault detection of sensors and actuators for vehicle following applications.Automobiles--Automatic control, Fault location (Engineering)

Fault Detection And Tolerant Control For Lateral Guidance Of Vehicles In Automated Highways

In this dissertation, the problem of fault tolerant control of automobiles is addressed. The three main problems handled in the dissertation are tire burst, sensor fault detection and slip angle control. The tire burst and sensor faults are important failure modes for automated highways, whereas the slip angle control problem is important during severe maneuvers for enhancing the vehicle safety.Motor vehicles--Steering-gear--Automation, Motor vehicles--Automatic control, Fault location (Engineering), Fault-tolerant computing

Intelligent Sensor Validation And Sensor Fusion For Reliability And Safety Enhancement In Vehicle Control

This research project is concerned with sensor validation and sensor fusion as part of a five module hierarchical architecture for supervisory control. The goal is to enhance reliability and safety of the Intelligent Vehicle Highway System (IVHS) by taking into consideration the uncertainty of sensors and the system. Potential hazards are detected and feasible maneuvers are recommended within the upper modules of the architecture.Automotive sensors, Fault location (Engineering), Real-time control, Multisensor data fusion, Motor vehicles--Automatic control

Fault Detection And Identification With Application To Advanced Vehicle Control Systems: Final Report

This study reports on a preliminary design of a health monitoring system for automated vehicles. A new detailed nonlinear vehicle simulation which extends the current simulation is documented and will be used as a future testbed for evaluating the performance of the health monitoring system. A health monitoring system has been constructed for the lateral and longitudinal modes that monitors twelve sensors and three actuators. The approach is to fuse data from dissimilar instruments using modeled dynamic relationships and fault detection and identification filters.Automobiles--Automatic control, Fault location (Engineering), Express highways--Automation