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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.
41

Damage Detection in Aluminum Cylinders Using Modal Analysis

Davis, Ivan Christopher 12 August 2002 (has links)
Many studies have attempted to detect structural damage by examining differences in the frequency response functions of a structure before and after damage. In an experimental setting, this variation can not be attributed solely to the addition of damage. Other sources of variation include testing and structure variation. Examples of testing variation include the error introduced by modal parameter extraction, measurement noise, and the mass loading of the accelerometer. Structure variability is due to slight differences in the supposedly identical structures. Dimensional tolerancing is one example. This study began with six "identical" undamaged aluminum cylinders, of which three were later damaged to varying extents. The frequency response functions of the undamaged and damaged cylinders were measured. Also, the frequency response function of the same undamaged cylinder was measured multiple times to investigate testing variation. The contributions of testing, cylinder, and damage variation to the differences between cylinder responses was elucidated by specifically examining their frequency response functions in two ways: comparing the natural frequencies and directly investigating the entire frequency response function. The curvature of the frequency response functions was then used to determined the presence, location, and severity of the imparted damage. / Master of Science
42

Transition in Particle-laden Flows

Klinkenberg, Joy January 2013 (has links)
This thesis presents the study of laminar to turbulent transition of particle laden flows. When a flow becomes turbulent, the drag increases one order of magnitude compared to a laminar flow, therefore, much research is devoted to understand and influence the transition. Previous research at the Linne Flow Centre at KTH has concentrated on the understanding of the bypass transition process of single-phase fluids. Though there are still questions, the principles of this process are now, more or less, known. However, little is known of the influence of particles on transition. While experiments in the 1960s already showed that particles can reduce the friction in turbulent channel flows significantly. The question explored in this thesis is whether this can be attributed to their influence on transition. The initial onset of transition has been investigated with both modal and non-modal linear stability analysis in a Poiseuille flow between two parallel plates. Particles are introduced as a second fluid and they are considered to be solid, spherical and homogeneously distributed. When the fluid density is much smaller than the particle density, ξ (≡ ρf/ρp) &lt;&lt; 1, an increase of the critical Reynolds number is observed. However, transient growth of streamwise vortices resulting in streaks is not affected by inclusion of particles. Particles with ξ ∼ 1 hardly seem to have an effect on stability. Although linear analysis shows that particles hardly influence the transient growth of disturbances, they might affect other (non-linear) stages of transition. To investigate such effects, the full Navier-Stokes equations for 3D Poiseuille flow between two parallel plates are numerically solved and particles are introduced as points with two-way coupling. For particles in a channel flow with ξ&lt;&lt;1, results show that the transition to turbulence is delayed for mass fractions ƒ (=mp N / ρf) larger than 0.1. For a mass fraction of ƒ=0.4 the initial disturbance energy needed to get a turbulent flow increases with a factor of four. Even if lower particle mass fractions ƒ are used, locally there could be large particle mass fractions. Therefore, the next step is to investigate the generation of local large particle mass fractions ƒ. Such particle clusters can be as large as the typical flow structures in the flow, like streak width and vortex size. Then they might change the flow field and (in)stability mechanisms. Numerical simulations of bypass transition in a boundary layer flow are used to determine whether particles cluster and where they tend to cluster. It is found that point particles with ξ&lt;&lt;1 and a large particle relaxation time tend to move in the low speed regions of the flow. In case of streaks, the low speed streaks are most favourable. For smaller particle relaxation times, particles act as tracers and do not have a preferential position and are homogeneously distributed. For particles with ξ∼1 the linear stability analysis showed no transition effect at any ƒ. However, one effect neglected until now is that of particle size. For particles with dimensions of the same order of magnitude of the flow disturbance, particles might influence the flow field. To investigate whether such particles migrate towards positions where they can affect transition some exploratory numerical simulations and experiments are performed. Numerically, the lateral migration of large particles (H/d=5) with ξ=1 in a 3D Poiseuille flow between two parallel plates is investigated. In laminar channel flow, large particles tend to move laterally due to shear to an equilibrium position. For a single large particle some key parameters for migration are identified: the size of the particle and the velocity of the fluid. When multiple particles are present, they tend to form particle trains. If particles are close, they influence each other and the equilibrium position shifts towards the wall, where the final position is dependent on the inter particle spacing. Also, not one steady equilibrium position is present, but particles move around an equilibrium position. Experimentally, migration of particles in bypass transition with ξ=1 is investigated to find out whether neutrally buoyant particles have a preferential position within streaks. The first results with tracer particles (d∼50μm) and few large particles (d∼200μm) do not show detectable preferential positioning. / <p>QC 20131030</p>
43

Evaluate Operational Modal Analysis and Compare the Result to Visualized Mode Shapes

Song, Baiyi January 2017 (has links)
The prototypes vibration test carried out for obtaining reliable information concerning machine’s dynamic properties in development process. Analysis results should be able to correlate with FE model to determine if some underlying assumptions (material properties &amp; boundary conditions) were correct. EMA used for extracting structure modal parameter under laboratory condition. However, EMA can generally not provide all required information concerning machine dynamic property. To simulate vibration in operating, it commonly requires the model based on dynamic properties of the machine under operating. Thus, vibration tests need carried out under operational condition. OMA is a useful tool for extracting information concerning dynamic properties of operating machine. This report concerns vibration test of part of mining machine under operating condition. Modal parameters extracted by two kinds of OMA methods. Results from OMA was compared with corresponding EMA results, illustrates reader the advantages of OMA.
44

Feasibility of use of four-post road simulators for automotive modal applications

Sharma, Balaji R. 06 August 2010 (has links)
No description available.
45

Analysis of fan blade attachment

Shingu, Patrick, Garcia Cabrera, Miguel January 2014 (has links)
This thesis work is based on the analysis of a fan blade attachment whereby a complete 3D model is presented by a partner company. The acceptability of a new design regarding the mechanical loads consisting of dividing the hub into two parts instead of using a solid hub is studied. From the model some critical parameters for the attachment of the blade with respect to the stresses are chosen such as the rotational speed, fillet size of the blade and the neck size of the blade. Parametric studies of these parameters are carried out in order to suggest the new design. Bearing in mind that a safety factor of 2 is the prerequisite, based on the analysis performed on ANSYS Workbench, it is suggested from the preliminary design that the axial fan can operate in two specific scenarios consisting of a rotational speed of 1771 rpm and a rotational speed of 1594 rpm. Using this set of parameters, a suggestion is drawn up on the blade fillet which will give lower stress. Blade fillet size of 30 to 35mm is recommended while a size of 45mm is recommended on the neck of the blade. A modal analysis is performed in order to find at what frequency will the model be vibrating and a lowest and critical frequency of 16.8 Hz is obtained. Finally, a fatigue analysis of some interesting areas is performed in order to determine the numbers of cycles before fatigue failure occur. It is recommended to use the rotational speed since these speeds have offered a High Cycle Fatigue results.
46

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

Souza Junior, Newton Vieira de. January 2015 (has links)
Orientador: Sérgio Kurokawa / Banca: Ailton Akira Shinoda / Banca: Júlio Borges de Souza / Banca: Carolina Goulart de Carvalho / Banca: Eduardo Coelho Marques da Costa / Resumo: 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 / Abstract: 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 / Doutor
47

Estudo e implementação do método de Ewins-Gleeson para identificação de parâmetros modais /

Mendonça, Willy Roger de Paula. January 2007 (has links)
Resumo: Estruturas e máquinas em regime operacional usualmente são submetidas a carregamentos dinâmicos ocasionados por vibração. Este fenômeno é em grande parte prejudicial, tendo em vista que podem causar falhas por fadiga, ruídos indesejáveis, etc. Com objetivo de minimizar e avaliar níveis de vibração em sistemas estruturais, técnicas de modelagem teórica e experimental vêm sendo utilizadas com freqüência. Dentre diferentes técnicas aplicadas à avaliação do comportamento dinâmico de estruturas, a análise modal figura como uma das principais.O presente trabalho tem como objetivo implementar um método de identificação de parâmetros modais no domínio da freqüência, de estruturas com vários graus de liberdade (MDOF). O método foi implementado em um ambiente computacional de baixo custo. O programa desenvolvido possibilita através de suas interfaces gráficas identificar os parâmetros modais de dados experimentais de uma estrutura metálica ensaiada, simular os modos de vibrar identificados da estrutura e permite de forma pratica que os usuários com poucos conhecimentos em análise modal interajam com todo o processo de análise dos dados experimentais. / Abstract: Structures and machines in operational regime are usually submitted to dynamic loads caused by vibration. This phenomenon is largely harmful, considering can cause cracks for fatigue, undesirable noises, etc. With objective of minimize and evaluate vibration levels in structural systems, techniques of theoretical and experimental modeling have been used frequently. Among different techniques applied to the evaluation of the dynamic behavior of structures, the modal analysis present as one of the main. The present work has as objective implements a method of identification of modal parameters in the domain of the frequency to structures with multi degrees of freedom (MDOF). The method should be implemented in a low cost software. The developed software had made possible through their graphic interfaces to identify the modal parameters of experimental data of a rehearsed metallic structure, to simulate the modes of vibration identified and make possible users with few knowledge in modal analysis interact with the whole the process of analysis of the experimental data. / Orientador: Mauro Hugo Mathias / Coorientador: Everaldo de Barros / Banca: Mauro Hugo Mathias / Banca: José Elias Tomazini / Mestre
48

Estudo das características modais de um modelo de aeronave em alumínio /

Oliveira Junior, Adelmo Fernandes de. January 2016 (has links)
Orientador: Mauro Hugo Mathias / Coorientador: Everaldo de Barros / Banca: José Elias Tomazini / Banca: Carlos D'Andrade Souto / Resumo: A análise modal experimental é uma das técnicas mais importantes na caracterização dinâmica de estruturas. No setor aeroespacial a analise modal experimental é conhecida como Ground Vibration Test (GVT). Na Força Aérea Brasileira, o órgão responsável para executar o GVT é o Laboratório de Ensaios de Vibração (LEVI) da Divisão de Integração e Ensaio (AIE) do Instituto de Aeronáutica e Espaço (IAE). Esta pesquisa foi realizada neste laboratório que possui as facilidades para a execução de GVT. O objetivo principal deste estudo foi aprimorar a metodologia de ensaio de análise modal aplicada a um modelo de aeronave em alumínio do tipo GARTEUR SM-AG-19. O estudo desenvolvido possibilita que em ensaios futuros os resultados sejam replicados, no intuito de avaliar a integridade do sistema de medição, levando em consideração aspectos da influência do torque na junta aparafusada entre a asa e a fuselagem. Para validar a metodologia os resultados obtidos neste estudo foram comparados com os resultados de dois estudos desenvolvidos no Brasil. A contribuição principal desta pesquisa é relacionada ao estudo do efeito da variação do torque na junta aparafusada entre a asa e a fuselagem sobre os parâmetros modais da estrutura / Abstract: The experimental modal analysis is one of the most important techniques in the dynamic characterization of structures. In the aerospace industry, the experimental modal analysis is known as Ground Vibration Test (GVT). In the Brazilian Air Force, the institution responsible for executing the GVT is the Laboratory of Vibration Testing (LEVI) of the Integration and Testing Division (AIE) of the Institute of Aeronautics and Space (IAE). This research was carried out on this laboratory that has the facilities to perform the GVT. The main objective of this study was to improve the modal analysis test methodology applied to an aluminium aircraft model named GARTEUR SM-AG-19. This study allows the results to be replicated in future tests in order to evaluate the integrity of the measurement system, taking into account aspects of the influence of the torque on the bolted joint between wing and fuselage. In order to validate the methodology the results obtained in this study were compared to the results of two studies developed in Brazil. The main contribution of this research is the study of the torque variation effect on the bolted joint between wing and fuselage on the modal parameters of the structure / Mestre
49

A quadratic non-linear elasticity formulation for the dynamic behaviour of fluid-loaded structures

Suliman, Ridhwaan January 2018 (has links)
This work details the development and implementation of a numerical model capable of solving strongly-coupled fluid-structure interaction problems involving long thin structures, which are common multi-physics problems encountered in many applications. In most fluid-structure interaction problems the deformation of the slender elastic bodies is significant and cannot be described by a purely linear analysis. We present a new formulation to model these larger displacements. By extending the standard modal decomposition technique for linear structural analysis, the governing equations and boundary conditions are updated to account for the leading-order non-linear terms and a new modal formulation with quadratic modes is derived. The quadratic modal approach is tested on standard benchmark problems of increasing complexity and compared with analytical and full non-linear numerical solutions. Two computational fluid-structure interaction approaches are then implemented in a partitioned manner: a finite volume method for discretisation of both the fluid and solid domains and the quadratic modal formulation for the structure coupled with a finite volume fluid solver. Strong-coupling is achieved by means of a fixed-point solver with dynamic relaxation. The fluid-structure interaction approaches are validated and compared on benchmark problems of increasing complexity and strength of coupling between the fluid and solid domains. Fluid-structure interaction systems may become unstable due to the interaction between the fluid-induced pressure and structural rigidity. A thorough stability analysis of finite elastic plates in uniform flow is conducted by varying the structural length and flow velocity showing that these are critical parameters. Validation of the results with those from analytical methods is done. An analysis of the dynamic interactions between multiple finite plates in various configurations is also conducted.
50

Multiple-Input Multiple-Output (MIMO) blind system identification for operational modal analysis using the Mean Differential Cepstrum (MDC)

Chia, Wee Lee, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW January 2007 (has links)
The convenience of Operational Modal Analysis (OMA), over conventional Experimental Modal Analysis (EMA), has seen to its increasing popularity over the last decade for the purpose of evaluating dynamic properties of structures. OMA features an advantage of requiring only output information, which is in tandem with its main drawback of lacking scaled modeshape information. While correctly scaled modeshapes can be assumed under a restrictive assumption of spectrally white inputs, in reality, input spectra are at best broadband in nature. In this thesis, an OMA method for Multiple-Input Multiple-Output (MIMO) applications in mechanical structures is developed. The aim is to separate MIMO responses into a collection of Single-Input Single-Output (SISO) processes (matrix FRF) using cepstral-based methods, under less restrictive and hence more realistic coloured broadband excitation. Existing cepstral curve-fitting techniques can be subsequently applied to give regenerated FRFs with correct relative scaling. This cepstral-based method is based on the matrix Mean Differential Cepstrum (MDC) and operates in the frequency domain. Application of the matrix MDC onto MIMO responses leads to a matrix differential equation which together with the use of finite differences, directly solves or identifies the matrix FRF in a propagative manner. An alternative approach based on whitened MIMO responses can be similarly formulated for the indirect solution of the matrix FRF. Both the direct and indirect approaches can be modified with a Taylor series approximation to give a total of four propagative solution sequences. The method is developed using relatively simple simulated and experimental systems, involving both impulsive and burst random excitations. Detailed analysis of the results is performed using more complicated Single-Input Multiple-Output (SIMO) and MIMO systems, involving both driving and non-driving point measurements. The use of the matrix MDC method together with existing cepstral curve-fitting technique to give correct relative scaling is demonstrated on a simulated MIMO system with coloured inputs. Accurate representation of the actual FRFs is achieved by the matrix MDC technique for SIMO set-ups. In MIMO scenarios, excellent identification was obtained for the case of simulated impulsive input while the experimental and burst random input cases were less favourable. The results show that the matrix MDC technique works in MIMO scenarios, but possible noise-related issues need to be addressed in both experimental and burst random input cases for a more satisfactory identification outcome.

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