Made available in DSpace on 2014-06-11T19:27:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-09-30Bitstream added on 2014-06-13T18:31:09Z : No. of bitstreams: 1 caldiron_l_me_ilha_prot.pdf: 995296 bytes, checksum: dc02ada2316a49ff3c8fd3dca71338ba (MD5) / Neste trabalho são otimizadas rotinas computacionais de um método de estimação de rigidez de mancais de máquinas através de um processo de ajuste de modelo, utilizando a análise de sensibilidade. Este método consiste em utilizar a análise de sensibilidade dos autovalores com relação à variação da rigidez dos mancais de um rotor. A eficácia e a robustez do método são analisadas através de simulações teóricas, bem como através de dados experimentais obtidos de um rotor de rotação variável e rigidezes dos mancais ajustáveis. O modelo matemático de ajuste do sistema é desenvolvido pelo método dos elementos finitos e o método de ajuste converge empregando-se um processo iterativo. Este método de ajuste baseia-se na minimização da diferença entre autovalores experimentais e autovalores obtidos com o modelo matemático de ajuste a partir de valores de rigidez dos mancais previamente adotados. A análise é feita com o rotor em diversas velocidades de rotação para verificar a influência do efeito giroscópio, e em diversas condições de valores da rigidez dos mancais para analisar o método quando aplicado em rotores flexíveis e em rotores rígidos. O desempenho do método é analisado com resultados teóricos e experimentais. / In this work, computational routines of estimation method of stiffness bearing of machine via a model updating process are optimized, using the sensitivity analysis. This method consists of using the eigenvalue sensitivity analysis, relating to the stiffness bearing variation of a rotor. The efficacy and the robustness of the method are analyzed through the theoretical simulations, as well as, based on the experimental data obtained of a test rotor with variable rotating speeds and adjustable bearing stiffness values. The mathematical model system is developed by the finite element method and the method of adjustment should converge employing an iterative process. The method of adjustment is based on the minimization of the difference between experimental eigenvalues and eigenvalues obtained via mathematical model from previously adopted stiffness bearing values. The analysis is made by using the rotor in different rotating speeds in order to check the influence of the gyroscopic effect, and in several conditions of the stiffness bearing values to analyze the method when applied on flexible and rigid rotors. The performance of the method is analyzed through theoretical and experimental results.

Este trabalho apresenta metodologias para a construção e a sintonia de estimadores de estados não-lineares visando aplicações práticas. O funcionamento de um estimador de estados não-linear está calcado em quatro etapas básicas: (a) sintonia; (b) predição; (c) atualização da matriz de covariância de estados; (d) filtragem e suavização dos estados. As principais contribuições deste trabalho para cada uma destas etapas podem ser resumidas como segue: (a) Sintonia. A sintonia adequada da matriz de covariância do ruído de processos é fundamental na aplicação dos estimadores de estado com modelos sujeitos a incertezas paramétricas e estruturais. Sendo assim, foi proposto um novo algoritmo para a sintonia desta matriz que considera dois novos métodos para a determinação da matriz de covariância dos parâmetros. Este algoritmo melhorou significativamente a precisão da estimação dos estados na presença dessas incertezas, com potencialidade para ser usado na atualização de modelos em linha em práticas industriais. (b) Predição. Uma das etapas mais importantes para a aplicação do estimador de estados é a formulação dos modelos usados. Desta forma, foi mostrado como a formulação do modelo a ser usada em um estimador de estados pode impactar na observabilidade do sistema e na sintonia das matrizes de covariância. Também são apresentadas as principais recomendações para formular um bom modelo. (c) Atualização da matriz de covariância dos estados. A robustez numérica das matrizes de covariância dos estados usadas em estimadores de estados sem e com restrições é ilustrada através de dois exemplos da engenharia química que apresentam multiplicidade de soluções. Mostrou-se que a melhor forma de atualizar os estados consiste na resolução de um problema de otimização sujeito a restrições onde as estimativas fisicamente inviáveis dos estados são evitadas. Este também preserva a gaussianidade dos ruídos evitando que estes sejam mal distribuídos. (d) Filtragem e suavização dos estados. Entre as formulações estudadas, observou-se também que a melhor relação entre a acuracidade das estimativas e a viabilidade de aplicação prática é obtida com a formulação do filtro de Kalman estendido sujeita a restrições (denominada Constrained Extended Kalman Filter - CEKF), uma vez que esta demanda menor esforço computacional que a estimação de horizonte móvel, apresentando um desempenho comparável exceto no caso de estimativas ruins da condição inicial dos estados. Como uma solução alternativa eficiente para a estimação de horizonte móvel neste último caso, foi proposto um novo estimador baseado na inclusão de uma estratégia de suavização na formulação do CEKF, referenciado como CEKF & Smoother (CEKF&S). / This work presents approaches to building and tuning nonlinear state estimators aiming practical applications. The implementation of a nonlinear state estimator is supported by four basic steps: (a) tuning; (b) forecast; (c) state covariance matrix update; (d) states filtering and smoothing. The main contributions of this work for each one of these stages can be summarized as follows: (a) Tuning. An appropriate choice of the process-noise covariance matrix is crucial in applying state estimators with models subjected to parametric and structural uncertainties. Thus, a new process-noise covariance matrix tuning algorithm is presented in this work which incorporates two new methods for the parameter covariance matrix computation. The algorithm has improved significantly the state estimation accuracy when the presence of such uncertainties, with potential to be applied in on-line model update in industrial practice. (b) Forecast. One of the most important stages in applying state estimators is the used model formulation. In this way, it has been shown that the model formulation to be used in state estimator can impact on the system observability and noisecovariance matrices tuning. In this work it is also presented the main recommendations to formulate an appropriated model. (c) State covariance matrix update. The numerical robustness of the state covariance matrices used in unconstrained and constrained state estimators is illustrated by two chemical engineering examples tending to multiple solutions. It has been shown that the best technique to update the states consists in solving an optimization problem subjected to constraints, since it prevents from physically unfeasible states. It also preserves the noise gaussianity preventing from bad noise distribution. (d) States filtering and smoothing. Among the studied formulations, it was also noticed that the better relationship between performance and practical application is obtained with an extended Kalman filter formulation subjected to constraints (called Constrained Extended Kalman Filter - CEKF) because it requires small computational effort than MHE with comparable performance, except in case of poor guesses of the initial state. As an efficient solution for moving horizon estimation in the last case, it was proposed a new estimator based on the addition of a smoother strategy into the CEKF formulation, referred as CEKF & Smoother (CEKF&S).

Knowledge about the dynamic behaviour is a basic condition for a secure operation of modern machine tools. Hence numerical methods predicting the dynamic properties are gaining in importance. Usually for complex and coupled structures, the results of dynamic property calculation are yet insufficient. Therefore Finite Element model updating is a tool to improve the hypothetical factor of the analysis. Within the present thesis Finite Element modelling is performed using the example of the “Scherenkinematik”, a machine tool based on hybrid-kinematics. Initially the results of an Experimental Modal Analysis are evaluated by identifying Modal parameters and deriving possible structural modifications. In the second part of the thesis, the machines Finite Element model is created using the FEA-Software ANSYS. Afterwards the Finite Element model updating is performed by coupling ANSYS and the CAE-Software FEMtools. Therefore two approaches are formulated and tracked. It turns out, that there is no improvement of the analytical and experimental models correlation, neighter with nor without a steady reduction of the search domain needed for mode coupling. It is reasoned, that the characteristics and the results of an Finite Element updating process are affected by the quality of the model at start time and the approach as well as the technique chosen for model updating and parameter modification. Therefore the CAE-Software FEMtools is suitable to only a limited extent for Finite Element updating of strongly coupled mechanical structures as a result of the sensitivity analysis used for parameter modification.

The economic and technologic development experienced by the society in the last decades has caused the demand of a new type of faster and more comfortable transport. This type of demand has been covered by the air transport, the road transport and the railway transport. This situation where the society demands an improvement in her quality of life is the best situation for the birth of the high speed trains. Different studies carried out in the transport field have demonstrated that for distances between four hundred and one thousand of kilometres, the high speed trains provide a lower travelling times than the rest of the transports. These types of high speed trains have increased the axle loads and the average speeds, thus generally a dynamic analysis is required by the ERRI in all the railway bridges when the train speed is higher than 200 Km/h. Besides, when the train speed is going to be higher than 200 Km/h, the vibrations induced in the bridge can reduce the service life of the vehicles and structure, and generally, this fact leads to become the dynamic effect in the principal factor to take into account in order to design the structure. Therefore, an important knowledge in railway bridges dynamic is required to not to oversize the structures with the consequent economic cost. The purpose of this thesis is to study the possibility of accurately predicting the dynamic response of an existing railway bridge, subjected to the high speed train Gröna Tåget, implementing a simplified 2D finite element model with the aid of the program Abaqus. The bridge chosen is the Lögdeälv Bridge, a two spans composite bridge, located along the Bothnia Line (the new Swedish high-speed line), between the localities of Nordmaling and Rundvik. The measured eigenfrequencies due to bending modes of vibration are used for updating the model and then, these frequencies and the accelerations measured are used to compare and validate the different 2D updated models. The parameters used to update the models are; the damping coefficient of the structure, the mass and the stiffness of the bridge, and the supports stiffness. Finally it is concluded that the best model is achieved when the rotational support stiffness is modified in the two extremes supporters of the bridge.

Finite Element Model Updating has recently arisen as an issue of vast importance on the design, construction and maintenance of structures in civil engineering. Many algorithms have been proposed, developed and enhanced in order to accomplish the demands of the updating process, mainly to achieve computationally efficient programs and greater results.The present Master Thesis proposes two new algorithms to be used in Finite Element Model Updating: the Bees Algorithms (BA) and the Artificial Bee Colony algorithm (ABC). Both were first proposed in 2005, are based on the foraging behaviour of bees and have been proved to be efficient algorithms in other fields. The objective of this Master Thesis is, thus, to implement and to test these two newalgorithms in Finite Element Model Updating for a cantilever beam. The Finite Element Model and the algorithms are programmed, followed by the extraction of the experimental frequencies and the updating process. Results, comparison of these two methods and conclusions are given at the end of this report, as well as suggestions for further work.

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To obtain predictive modeling of a spacecraft, the author investigates the effects of adding cables to a simple structure with the goal of developing an understanding of how cables interacting with a structure. In this research, the author presents predictive and accurate modeling of a cable-harnessed structure by means of the Spectral Element Method (SEM). A double beam model is used to emulate a cable-harnessed structure. SEM modeling can define the location and the number of connections between the two beams in a convenient fashion. The proposed modeling is applied and compared with the conventional FEM. The modeling approach was compared to and validated by measurement data. The validated modeling was implemented to investigate the effect of the number of connections, of the spring stiffness of interconnections, and of mass portion of an attached cable. Damping has an important role in structural design because it reduces the dynamic response, thereby avoiding excessive deflection or stress, fatigue loads, and settling times. Experimental results with some specimens indicate a clear change of damping on the main structure with the inclusion of cable dynamics. The author investigated the modification of the damping of the host structure induced by various attached cables. The identification of a damping matrix is performed using measured data. The effect of the flexibility of a cable harness on damping is observed through experiments with various types of cables. The effect of the number of connections on damping is also investigated by changing the number of connections. Moreover, to overcome the sensitivity to noise in measured data of damping matrix identification approach, various methods are compared with a simulated lumped model and real test results. An improved damping matrix identification approach is proposed and can generate the unique damping matrix over the full frequency range of interest. / Ph. D.

This thesis presents a novel method for the correlation of FEM results to experimental test results known as the "Load updating method." Specifically, the load updating method uses the math model from the FEM and the strains measured from experimental or flight test data as inputs and then predicts the loads in the FEM which would result in strains that would correlate best to the measured strains in the least squared sense. In this research, the load updating method is applied to the analysis of a complex frame structure whose validation is challenging due to the complex nature of its structural behavior, load distributions, and error derived from residual strains. A FEM created for this structure is used to generate strain data for thirty-two different load cases. These same thirty-two load cases are replicated in an experimental setup consisting of the frame, supporting structure, and thirty actuators which are used to load the frame according to the specifications for each of the thirty-two load conditions. A force-strain matrix is created from the math model in NASTRAN using unit loads which are separately applied to each load point in order to extract strain results for each of the locations of the seventy-four strain gages. The strain data from the structural test and the force-strain matrix is then input into a Matlab code which is created to perform the load updating method. This algorithm delivers a set of coefficients which in turn gives the updated loads. These loads are applied to the FEM and the strain values extracted for correlation to the strains from test data. It is found that the load updating method applied to this structure produces strains which correlate well to the experimental strain data. Although the loads found using the load updating method do not perfectly match those which are applied during the test, this error is primarily attributed to residual strains within the structure. In summary, the load updating method provides a way to predict loads which, when applied to the FEM, would result in strains that correlate best to the experimental strains. Ultimately, this method could prove especially useful for predicting loads in experimental and flight test structures and could aid greatly in the Federal Aviation Administration (FAA) certification process. / Master of Science / The research presented in this thesis provides a new way for correlating data obtained during structural testing with results obtained from computer analysis known as the finite element method (FEM). During the process of certifying an aircraft structure with the FAA, it is important to be able to demonstrate that the results obtained for a given structure with a computer model matches the results produced by a real world experiment within a reasonable tolerance. Traditionally, differences between these two results have been accounted for by adjusting the model within the computer until its results match those from the test. However, in this research the loads which are applied on the computer model are changed instead until loads are found which produce results in the computer models that match those from testing. This method, known as the load updating method, therefore provides a way to predict loads on a structure where the loads are unknown such as a flight test article. Here, the ability of the load updating method to predict loads on a complex three dimensional frame structure is explored and the accuracy of the results studied by comparing the results to those from a structural test whose loads are known. It was found that the load updating method does indeed predict unknown loads to a reasonable accuracy and could aid future design efforts immensely.