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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.
61

Representação de linhas de transmissão trifásicas diretamente no domínio das fases por meio da matriz ABCD

Souza Junior, Newton Vieira de [UNESP] 24 November 2015 (has links) (PDF)
Made available in DSpace on 2016-05-17T16:51:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-11-24. Added 1 bitstream(s) on 2016-05-17T16:55:46Z : No. of bitstreams: 1 000864137.pdf: 1322861 bytes, checksum: d161e962603f1c90597c57338efb1e2d (MD5) / Este trabalho apresenta um modelo de linha de transmissão desenvolvido diretamente no domínio das fases a partir da representação por meio de quadripolos para linhas polifásicas. Deste modo, esse modelo de linha foi estruturado em função dos parâmetros longitudinais e transversais variáveis na frequência e por meio da matriz ABCD. Esta abordagem foi possível a partir da utilização implícita de uma matriz de transformação, variável em função da frequência utilizada nas transformações entre os domínios das fases e dos modos. A matriz de transformação é descrita explicitamente em função dos parâmetros longitudinais e transversais de uma linha trifásica. As grandezas modais da linha foram convertidas para o domínio das fases e resultando assim, em um modelo analítico desenvolvido diretamente no domínio das fases. O modelo proposto foi aplicado para simular uma linha trifásica em um plano de simetria vertical e também situações assimétricas envolvendo condições desequilibradas de carga, por exemplo: faltas fase-fase ou fase-terra e cargas desequilibradas. As simulações considerando condições assimétricas ou desequilibradas não são possíveis em muitos modelos no domínio do tempo e da frequência utilizando uma matriz real e constante. No entanto, a partir da utilização implícita de uma matriz de transformação variável na frequência, o modelo proposto tornou-se capaz de simular transitórios eletromagnéticos em condições assimétricas e desequilibradas. Um dos grandes atributos do modelo proposto consiste na inclusão e simulação de condições não-lineares de forma simplificada por meio de condições de contorno aplicadas aos sinais de entrada e saída das matrizes ABCD. Simulações no domínio do tempo e da frequência foram efetuadas durante o desenvolvimento deste trabalho, possibilitando a ampla análise das possíveis aplicações do modelo de linhas de transmissão proposto / This work presents a transmission line model developed directly in the domain of phases from representation through quadripolos for polyphase lines. Thus, the line model was structured as function of longitudinal and transverse parameters variable frequency and by means of ABCD matrix. This approach was possible from the implicit use of a transformation matrix, variable a function of frequency used in transformations between domains of the phases and modes. The transformation matrix is explicitly described as a function of the longitudinal and transverse parameters of a three-phase line. Modal line magnitudes were converted into the domain of the phases, resulting in an analytical model developed directly in the domain phase. The proposed model was applied to simulate a three-phase line without a vertical symmetry plane and also situations involving asymmetric unbalanced load conditions, for example: phase-to-phase or phase-ground and unbalanced loads. The simulations considering asymmetrical or unbalanced conditions are not possible in many models in the time domain and frequency using a real and constant matrix. However, from the implicit use of variable frequency transformation matrix, the model was able to simulate electromagnetic transients in asymmetrical manner and unbalanced. One of the major attributes of the model consists of the inclusion and non-linear simulation conditions in a simplified manner by means of boundary conditions applied to the input and output signals of ABCD matrices. The simulations in the time domain and frequency domain were made during the development of this work, enabling the comprehensive analysis of possible applications the lines proposed transmission model
62

Investigation of Mode Superposition as Modelling Approach for Crankshaft Torsion

Johansson, Jonas January 2018 (has links)
With tougher emission standards for heavy duty trucks, good control of the engine is of importance. By taking into consideration the torsional vibrations occurring in the crankshaft, the engine control can be improved. This could be done by implementing a torsion model that would give feedback to the engine control unit to reduce the cycle-to-cycle variations in the cylinders, which is partly due to the torsion in the crankshaft. It is therefore of interest to determine if a torsion model can be developed with a reduced computational complexity and still have sufficient accuracy. In this thesis a model was developed in Matlab for estimation of torsion in the crankshaft of an inline 6 cylinder diesel engine. By applying Newtons second law, the equations of motion that describe the torsional vibrations in the crankshaft were set up. The equations of motion were transformed using modal analysis and with the use of mode superposition it was investigated how reducing the number of vibrational modes in the model, affected the models accuracy in its estimation of torsion. Two model reductions were evaluated where the first three and four vibrational modes were used to calculate the torsional displacement between the flywheel and the cylinders. Using measured pressure curves for a number of operating points of the engineas input to the model, results were produced for different crank angle intervalsshowing deviations between the developed torsion models and a reference models estimation of torsion. Due to the damping approximation used in the model, high initial deviations could be found at certain operating points beforereducing the number of vibrational modes. These initial deviations weregreatest for the first two cylinders. Results from the model reductions showed that using the first three vibrational modes in the torsion model, is sufficient for estimating the torsional displacement between the flywheel and all cylinderswith an accuracy of within 0.1 degrees, with the exception of the first two cylinders for the early and late combustion interval.
63

Identificação dos parâmetros modais utilizando apenas as respostas da estrutura : identificação no domínio do tempo /

Nunes Junior, Odair Antonio. January 2006 (has links)
Orientador: João Antônio Pereira / Banca: Luiz de Paula do Nascimento / Banca: Domingos Alves Rade / Resumo: A Análise Modal envolvendo apenas as respostas da estrutura é ainda um desafio que requer o uso de técnicas de identificação especiais. Este trabalho discute a identificação baseada apenas na resposta utilizando um método de identificação no tempo, mais especificamente, o método Identificação Estocástica de Subespaço. É mostrado que uma estrutura vibrando excitada por forças não conhecidas, pode ser modelada como um modelo de espaço de estado estocástico. A partir da aplicação de técnicas numéricas robustas como fatorização QR e Decomposição em Valores Singulares para a matriz bloco de Hankel semi-infinita, contendo os dados de resposta, é obtida a estimativa dos estados do modelo. Uma vez que os estados são conhecidos, o sistema de matrizes é encontrado através da solução de um problema de mínimos quadrados. Encontrado o modelo matemático da estrutura, os parâmetros modais são estimados diretamente através da decomposição em autovalores. O trabalho apresenta ainda uma metodologia que utiliza a função densidade de probabilidade para identificar possíveis componentes harmônicos contidos nos sinais de respostas. Os sinais são filtrados em uma faixa de freqüência contendo um provável modo e é verificado se este corresponde a um modo natural ou operacional. A metodologia é avaliada com dados simulados e experimentais e os resultados obtidos mostraram-se promissores para identificação dos parâmetros modais de sistemas estocásticos lineares e invariantes no tempo, utilizando apenas as respostas. / Abstract: Modal analysis using output-only measurements is still a challenge in the experimental modal analysis community. It requires the use of special modal identification techniques. This work discusses the concepts involved in the output-only modal analysis and the implementation of the Stochastic Subspace Identification time domain method. It is shown that a vibrating structure excited by an unknown force can be modelled as a stochastic state space model. In this approach, the SSI method estimates the state sequences directly from the response data and the modal parameters are estimated by using the eigenvalues decomposition of the state matrix. The steps of the procedure are implemented using the well-known numerical linear algebra algorithms, Singular Value Decomposition and the QR decomposition. It also includes a methodology based on the Probability Density Function to identify harmonic components of the response signals. The signals are filtering in a range of frequency containing a mode, to verify if it is a natural or operational mode. The approach is evaluated with simulated and experimental data and the results have shown to be promising to identify the modal parameters of stochastic linear time-invariant systems, based only on the output data. / Mestre
64

Contribuição a teoria e pratica da analise modal acustica experimental / A contribution to the theory and practice of experimental acoustic modal analysis

Rossetto, Gustavo Dalben 22 August 2001 (has links)
Orientador: Jose Roberto de França Arruda / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-07-31T18:15:00Z (GMT). No. of bitstreams: 1 Rossetto_GustavoDalben_M.pdf: 4484828 bytes, checksum: b149e9723524115d4c39c2ea81d0c5bc (MD5) Previous issue date: 2001 / Resumo: Neste trabalho uma geometria simples (cavidade retangular) é usada para o estudo da metodologia aplicada na análise modal acústica. Modelos analítico e numérico são desenvolvidos para a comparação com os resultados experimentais. Três tipos de dispositivos de excitação do sistema acústico foram construídos. Um baseado num pistão conectado a um shaker, e outros dois usando um alto-falante do tipo driver. O primeiro atuador usando o driver é similar ao modelo desenvolvido por um projeto europeu, onde um tubo flexível com uma terminação instrumentada com um microfone é usado para a condução da excitação acústica. O segundo atuador baseado no uso do driver também usa um tubo flexível, mas este é instrumentado com dois microfones em sua terminação. O comportamento destes dois últimos atuadores em termos de aceleração de volume (essencial para a análise modal acústica experimental) e de potência ativa (necessária para Análise Estatística de Energia Experimental) sendo injetados no meio são investigados. A análise modal experimental da cavidade retangular é realizada e um método que utiliza a transformada de Fourier espacial multidimensional do campo de pressão medido é proposto para-a construção do campo de deslocamento de partícula para a visualização do modo acústico / Abstract: In the present work, a simple geometry (rectangular shallow cavity) is used to investigate the acoustic modal analysis methodology. Analytical and numerical models are developed for the comparison with the experimental results. Three types of excitation devices were constructed. One based on a shaker-driven piston and the other two using a driver loudspeaker. The first actuator based on a driver loudspeaker is similar to a model developed by an EEC project, where a flexible tube with a socket, instrumented with one microphone, at its termination is used to conduct the sound excitation. The second actuator based on a driver loudspeaker alse uses a flexible tube, but it is instrumented with two microphones in its socket instead of one. The behavior of these last two actuators in terms of volume acceleration (essential in the acoustic modal analysis) and active power (necessary for the Experimental Statistical Energy Analysis) being injected into the medium are investigated. The experimental modal analysis of the rectangular cavity is performed and a method using multi-dimensional spatial Fourier transforms of the array of pressure measurements is proposed for the construction of the partic1e displacement field for acoustic mode shape visualization / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica
65

Characterization of Vibration Test Fixtures using Modal Analysis

Hall, Melissa A. 04 October 2021 (has links)
No description available.
66

Dynamic investigation of vibratory screen response in a FEM environment

Harat, Robert Oliver January 2020 (has links)
Effective models of vibratory screens which can capture the true response characteristics are crucial in the understanding of faults and failures which occur in vibratory screens. However, the current available models are usually simplified and have limited validation to that of a physical screen. Much research has been conducted to optimise the screening efficiency of screens. The optimisation includes screen geometry, material processing of the screen and the dynamic response of the screen. These investigations have not been furthered to investigate the effects of different faults on the dynamic response of a vibratory screen. To model a vibratory screen which can replicate the dynamics of a physical vibratory screen it is important to create a model with enough complexity to capture the dynamics of the screen. The model of the screen was validated using both modal analysis and the transient response of the screen. The modal analysis was used to ensure that the physical characteristics of the model are consistent with that of the physical screen. Once this was completed, the second validation aimed to investigate if the model of the screen could capture transient faults which are measured experimentally. It was found that it was not possible to conclusively determine if the finite element methods model could Finally, an intelligent method was used to distinguishing between different faults and classifying them accordingly. The intelligent method was also trained using the FEM data and then used to classify the physical screen data. / Dissertation (MEng)--University of Pretoria, 2020. / Mechanical and Aeronautical Engineering / MEng / Unrestricted
67

STUDY ON DAMAGE ASSESSMENT OF STEEL PLATED STRUCTURES BASED ON LOCAL VIBRATION CHARACTERISTICS / 局所振動特性に基づく薄肉鋼構造物の損傷評価に関する研究

Sakhiah, Binti Abdul Kudus 26 March 2018 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21082号 / 工博第4446号 / 新制||工||1691(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 杉浦 邦征, 教授 KIM Chul-Woo, 教授 河野 広隆 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM
68

Application of Parametric NURBS Geometry to Mode Shape Identification and the Modal Assurance Criterion

Selin, Evan D. 12 April 2012 (has links) (PDF)
The dynamic characteristics of a part are highly dependent on geometric and material properties of the part. The identification and tracking of vibrational mode shapes within an iterative design process becomes difficult and time consuming due to the frequently changing part definition. Currently, visual inspection of analysis results is used as the means to identify the shape of each vibrational mode determined by the modal analysis. This thesis investigates the automation of the mode shape identification process through the use of parametric geometry and the Modal Assurance Criterion. Displacement results from finite element modal analysis are used to create parametric geometry templates which can be compared one to another irrespective of part geometry or finite element mesh density. Automation of the mode shape identification process using parametric geometry and the Modal Assurance Criterion allows for the mode shapes from a baseline design to be matched to modified part designs, giving the designer a more complete view of the part's dynamic properties. It also enables the identification process to be completed much more quickly than by visual inspection.
69

Modal Analysis of Composite Structures with Damping Material

Tremaine, Kellie Michelle 01 June 2012 (has links) (PDF)
The purpose of this study is to develop an analytical solution for modal analysis of actively damped orthotropic composite plates in bending and to verify it with experimental analysis. The analytical modal analysis solution for composite plate dynamics is derived using Euler theory. This analysis applies to structures with orthotropic lamina of uniform material properties at any lamination angle. The bending-extensional coupling can be neglected for plates that are symmetric or approximately symmetric, which allows an exact solution for natural frequency and mode shape to be obtained. An exact solution can be found for natural vibration and in general. The active control is modeled analytically by combining the Lagrange equation with the Ritz Assumed Mode method. This analysis produces a generalized coordinate vector that correlates the assumed mode to the particular amplitude of a particular case. The kinetic energy dissipated by the piezoelectric actuator from the system over one oscillation can be calculated from the generalized coordinate vector and the assumed mode. The equivalent damping ratio of the active control system is calculated as the ratio between the kinetic energy absorbed by the piezoelectric actuator from the system in one oscillation and the maximum strain energy of the system during that oscillation. A point mass on the plate, such as an accelerometer mass, can also be modeled as a single layer of uniform mass, that is an isotropic layer, by equating the potential energy of the point mass with the potential energy of the uniform mass layer. It is important to note that the mass of the isotropic layer is frequency dependent, and it has no effect on the plate stiffness. The analytical model is validated by comparison to experimental work. The samples studied were aluminum and composite plates of various lengths. The active control predictions were also validated using previous experimental work completed at California Polytechnic State University in San Luis Obispo. These cases included active control of an aluminum beam with a patch of piezoelectric material and an aluminum sailplane with a patch of piezoelectric material. Results indicate that while the analytical mode solutions are in good agreement with the experimental results, they are also systematically higher than the experimental results. The analytical active control solutions match previous work when the piezoelectric effects are linear. The main result of adding an active control system is approximately a 5-10% increase in modal frequencies and a 200-800% increase of damping ratio.
70

Modal interactions in the dynamic response of isotropic and composite plates

Hadian, Mohammad Jafar 12 October 2005 (has links)
Hamilton's principle and a third-order shear-deformation theory are used to derive a set of five coupled partial-differential equations governing the nonlinear response of composite plates. The reduction of these equations by using classical plate theory is discussed and the corresponding partial-differential equations governing both rectangular and circular plates are derived. Generalized Levy-type solutions are obtained for the problem of linear free vibrations and linear stability of shear-deformable cross-ply laminated plates. The governing equations are transformed into a set of first-order linear ordinary-differential equations with constant coefficients. The general solution of these equations is obtained by using the state-space concept. Then, the application of the boundary conditions yields equations for the natural frequencies and critical loads. However, a straightforward application of the state-space concept yields numerically ill-conditioned problems as the plate thickness is reduced. Various methods for overcoming this problem are discussed. An initial-value method with orthonormalization is selected. It is shown that this method not only yields results that are in excellent agreement with the results in the literature, but it also converges fast and gives all the frequencies and buckling loads regardless of the plate thickness. Further It is shown that the application of classical plate theory to thick plates yields inaccurate results. The influence of modal interactions on the response of harmonically excited plates is investigated in detail. The case of a two-to-one autoparametric resonance in shear-deformable composite laminated plates is considered. Four first-order ordinary-differential equations describing the modulation of the amplitudes and phases of the internally resonant modes are derived using the averaged Lagrangian when the higher mode is excited by a primary resonance. The fixed-point solutions are determined using a homotopy algorithm and their stability is analyzed. It is shown that besides the single-mode solution, two-mode solutions exist for a certain range of parameters. It is further shown that in the multi-mode case the lower mode, which is indirectly excited through the internal resonance may dominate the response. For a certain range of parameters, the fixed points lose stability via a Hopf bifurcation, thereby giving rise to limit cycle solutions. It is shown that these limit-cycles undergo a series of period-doubling bifurcations, culminating in chaos. Finally, the case of a combination resonance involving the first three modes of axisymmetric circular plates is studied. The method of multiple scales is used to determine a set of ordinary-differential equations governing the modulation of phases of the modes involved and that the excited mode is not necessarily the dominant one. Furthermore, it is shown that for a choice of parameters the multi-mode response loses stability through a Hopf bifurcation, resulting in periodically or chaotically modulated motions of the plate. / Ph. D.

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