Made available in DSpace on 2014-10-09T12:31:04Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:16Z (GMT). No. of bitstreams: 1 01377.pdf: 3916698 bytes, checksum: ed6e95533001fb610ab17e41a058b984 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:43:51Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:10Z (GMT). No. of bitstreams: 1 06767.pdf: 4710608 bytes, checksum: 0df801946c2e3b5907a9d77d5ff698e5 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

A retificação representa o processo mais utilizado na usinagem de peças para obtenção de altos níveis de qualidade superficial, dimensional e produtividade. Uma importante etapa da retificação consiste na preparação e condicionamento do rebolo para o corte, a dressagem. Durante a dressagem, a superfície da ferramenta de corte é alterada para obtenção de arestas cortantes de acordo com as especificações desejadas. O objetivo deste trabalho é desenvolver um método para inscrição de texturas na superfície do rebolo que proporcionem melhores condições de corte durante a retificação e, também, possibilite utilizar a retificação como processo para texturização superficial de peças. O método desenvolvido consiste em alterar controladamente a profundidade de dressagem utilizando um excitador eletromecânico fixado na base do dressador de uma retificadora cilíndrica CNC. A movimentação é controlada por um software desenvolvido para sincronizar o deslocamento longitudinal do dressador com ondas senoidais enviadas ao amplificador operacional do excitador. Desta forma, o dressador proporciona inscrição de texturas no rebolo durante a dressagem. O método foi experimentalmente avaliado e sua funcionalidade foi comprovada. Texturas diversas foram inscritas na superfície do rebolo, com até 15 \'mü\'m de profundidade. Com o uso da texturização de rebolos foi possível obter redução de até 20% da potência específica de corte, sem perda representativa da qualidade final da peça (rugosidade e cilindricidade) e mantendo a vida da ferramenta de corte, em comparação com retificação convencional. Em complemento, o método possibilitou criação de diversos padrões de texturas nas superfícies de peças retificadas, possibilitando utilizar a retificação como um processo de usinagem para este fim. / Grinding represents the most applied machining process to achieve best combination of surface and dimentional quality, also productivity. One important stage of the grinding process is to prepare and condition the grinding wheel surface for the cutting, the dressing operation. During the dressing, wheel surface is changed to acquire cutting specification required for the operation. The objective of this work is develop a method to texturing the grinding wheel surface for better grinding performance and, also, texturing of surfaces through normal grinding cutting. The method controlled changes the dressing depth using an electro-mechanical actuator fixed to the dressing tool base of a CNC grinding machine. The displacement of the dressing tool is controlled using the developed software. It is able to synchronize the longitudinal movement with generated sine waves sent to the operational amplifier of the actuator. Through this movement and control, the dressing tool is able to texture the grinding wheel. The method was experimentally evaluated and its functionally proved. It is possible to inscribe different texturing patterns in the wheel surface, with depth up to 15 \'mü\'m. Using texturized wheels, is possible to reduce up to 20% the grinding power, without representative losses with the machined workpiece quality (roughness and roundness) and tool life, compared to regular grinding. In addition, it is possible to transfer different textures patterns to the workpiece surface while cutting, enabling grinding s a machining process to produce workpiece patterns.

Orientador: Robson Pederiva / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T14:08:15Z (GMT). No. of bitstreams: 1 Martins_DiegoRodrigo_M.pdf: 7219918 bytes, checksum: 31c54119f27719f2488e9ea8f2a0126e (MD5) Previous issue date: 2013 / Resumo: O presente trabalho tem por objeto o estudo de sistemas de transmissão por correia serpentina com tensionador automático, que é uma aplicação automotiva utilizada em larga escala e cujo comportamento dinâmico apresenta grande influência sobre o funcionamento dos acessórios acionados pelo motor. O movimento do eixo de manivelas acionado pelo processo de combustão apresenta como característica a ocorrência de variações de velocidade e torque entregues aos acessórios pelo sistema de transmissão, contudo as flutuações de torque resultantes deste movimento são o principal mecanismo excitador do sistema de transmissão por correia. Níveis elevados de flutuação de torque podem aumentar o nível de tração dinâmica atuante na correia, fazendo com que esta venha a falhar devido à fadiga, ou produzir níveis de vibração torcional elevados nas polias dos acessórios, causando impacto direto em seus suportes. Através de modelos matemáticos é avaliado o comportamento do sistema de transmissão, considerando alguns fenômenos responsáveis por introduzir não linearidades neste. São avaliados, assim, os efeitos de tração inicial, frequências naturais, formas modais e respostas temporais do sistema. Paralelamente é estudado o comportamento de um sistema de transmissão real através da uma investigação experimental. São identificados seus parâmetros lineares através de técnicas de Análise Modal, bem como efeitos de variação destes parâmetros em função da velocidade de operação do sistema. É avaliada a composição em frequência da resposta do sistema quando em operação e também são realizados testes para detecção de não linearidades no sistema / Abstract: The objective of the present work is the study of a tensioner loaded belt drive system, which is a recurrent automotive application used in large scale and whose dynamic behavior has great influence on the functioning of various components powered by engine. Crankshaft motion, powered by internal combustion process, presents as characteristic the occurrence of variations on speed and torque delivered to accessory by belt drive, torque fluctuation due to this motion is the main excitation mechanism to belt drive systems though. High levels of torque fluctuation can increase belt dynamic tension making it amenable to fault due to fatigue or produce high levels of torsional vibration on accessory pulleys which has direct impact on its support structure. By means of mathematical models, systems behavior is evaluated, taking into account phenomena responsible for introducing nonlinearities. Initial tractive tension, natural frequencies, modeshapes and time responses of the system are evaluated. In parallel, it is studied the behavior of a real belt drive system through experimental investigation. Linear parameters are identified by Experimental Modal Analysis techniques, and its variation as function of system operating speed, as well. Frequency composition of system's response are evaluated and also are performed tests to detect nonlinearities / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

This PhD thesis is concerned with developing a methodology for early diagnosis of cancer by comparing the resonant frequencies in the amplitude spectra obtained during a vibration test using the AFM or, by comparing the stiffness properties of single cancerous and normal cells obtained using a resonant technique. As there is no reliable data in the literature to prove the existence of resonant frequencies of single cells, this work pioneers the search for resonant frequencies of related microspherical soft bodies using the AFM. Experiments to investigate the resonant behaviour of single cells depends on various parameters which are difficult to control; for example, the cell type, deciding at what stage the cell should be tested during the culturing process, determining the nucleus size, determining the cytoskeleton integrity and designing an appropriate vibration test setup among others. For this reason, agarose microspheres were selected to carry out preliminary work as these samples have similar properties to human cells and their resonances are affected by fewer variables. Although these micrometric spheres were tested under different conditions, no clear resonant behaviour was found at frequencies below 20 kHz and, only wide curves (interpreted as highly damped peaks of resonance) in the interval ranging from 20 kHz to 100 kHz were observed. By considering those curves as the quadrupole (Qp) vibration mode, approximate stiffness values for the agarose microspheres were found to be in between 37 kPa and 72 kPa. These values are similar to those obtained during an indentation test performed on the same samples whic¬¬h gave Young’s modulus values ranging from 10 kPa to 200 kPa. In order to gain a greater insight into the vibration test performed on microscopic samples, the research was extended to include agarose spheres of millimetric size. The characterization of these samples was carried out using an innovative purpose-built experimental setup. For the vibration test, a PZT based excitation device and a vibro-acoustic sensor were designed and constructed. The amplitude spectra of the vibration tests performed on millimetric samples consistently showed at least three peaks of resonance from which after the numerical simulation of the vibration test were interpreted as the quadrupole (Qp) and octupole (Op) vibration modes. Using this information, stiffness values for the samples ranging from 100 kPa to 700 kPa were calculated. In order to obtain the stiffness of the millimetric samples using a different technique, an experimental setup was constructed to perform a compression test. However, due to high viscoleasticity of the samples, it was not possible to obtain a standard compression curve necessary for their mechanical characterization. The results obtained from the tests on millimetric agarose samples demonstrate that spheres made of this material are able to provide measurable vibrational characteristics. Consequently, this methodology can be further implemented on micrometric samples and possibly on human cells to detect their resonant frequencies and equivalent stiffness values which can be used as a cancer marker. From the vibrational experiments on millimetric samples, it was noticed that the excitation mechanism plays an important role and for this reason future work is proposed to continue in this direction.

This dissertation forms part of a research project assigned to the University of Pretoria by Eskom (the primary electricity utility in South Africa). The project aims to address, amongst others, the limitations imposed by shaft runout on the usable frequency range of diagnostic data measured by eddy current proximity probes on turbogenerator shafts. This research includes an experimental investigation into the effects of artificially induced faults on a laboratory-scale rotor system, the development and analysis of a mathematical (numerical) model of this rotor system and the development of data processing techniques (including artificial intelligence) to determine the rotor’s condition, faults and diagnostic signal parameters from both the experimental and numerical results. Furthermore, a methodology is to be developed to perform runout compensation in an unsupervised manner. These techniques are then to be implemented for proximity probe vibration data measured on turbogenerators. As part of the research project, this dissertation specifically focuses on the development and rotor dynamic analysis of numerical (finite element) models of the experimental (laboratory-scale) rotor system (using finite element software MSC.Nastran), including gyroscopic effects, a nonlinear force model for the hydrodynamic journal bearing of the rotor system (capable of capturing oil whirl and oil whip instabilities) as well as simulated faults (such as unbalance and rotor-stator rubbing). Since MSC.Nastran does not have a built-in nonlinear hydrodynamic journal bearing model, a custom model of such a bearing was developed and incorporated into the finite element solver, further expanding its already powerful rotor dynamic modelling capabilities. Rotor dynamic analyses performed include the calculation of critical speeds (synchronous complex modes analysis), Campbell diagrams (asynchronous complex modes analysis), steady state frequency response due to unbalance (synchronous frequency response analysis) and nonlinear transient response during rotor run-up. Amongst others, this dissertation explores the seemingly largely unexplored/undocumented capability of finite element software MSC.Nastran to perform rotor dynamic analyses using rotor models constructed with three-dimensional elements. Software (MATLAB code) was also developed to perform post-processing of the simulation results as well as signal processing for investigating the spectral content of transient results. The support structure of the laboratory-scale rotor system was experimentally characterised and an experimental modal analysis was performed on the rotor (excluding its support structure) and its results used to update the finite element rotor models. The transient dynamic response of the experimental rotor system during run-up due to unbalance and rubbing was also analysed in order to validate the developed numerical rotor system models. The numerical results are found to be in good agreement with the experimental results. / Dissertation (MEng)--University of Pretoria, 2015. / Mechanical and Aeronautical Engineering / Unrestricted

Aujourd'hui, les outils de simulations numériques sont omniprésents dans l'industrie, que ce soit dans l'industrie aéronautique, aérospatiale, ferroviaire ou automobile.En effet leur utilisation limite la fabrication (souvent très couteuse) de prototype, et permettent ainsi de réduire les couts et d'accélérer la phase de conception d'un nouveau produit.Dans le cadre des applications acoustiques, il est souvent recommandé de calculer la réponse sur l'ensemble de la bande de fréquences d'intérêt.Les outils de simulation numérique sur une bande de fréquences impliquent généralement plusieurs calculs à fréquences fixes.Même si c'est un moyen simple et naturel pour répondre au problème posé, une telle stratégie peut facilement conduire à des calculs énormes. Cela est particulièrement vrai dans la gamme des moyennes fréquences, où la réponse est particulièrement sensible à la fréquence.Dans cette thèse, la PGD (Proper Generalized Decomposition), est appliqué pour trouver une représentation fonctionnelle distincte de la fréquence et de l'amplitude des inconnues de la TVRC (théorie variationnelle des rayons complexes) sur une bande de fréquences donnée.Ceci permet d'obtenir une réponse de haute qualité sur une large bande en moyennes fréquences, sans nécessité de discrétisation fine de la plage de fréquences considérées. En outre, la représentation PGD de la solution permet d'économiser une grande quantité d'espace en terme de stockage de données. Dans un second temps, la technique PGD a été étendue à la stochastique. / In many industrial contexts, such as aerospace applications or cars design, numerical prediction techniquesbecome more and more useful. They restrict the use of real prototypes to a minimum and make easier thedesign phase. In such industries and in the specific for acoustic, engineers are interested in computing theresponses of systems on frequency bands. In order to predict the vibration behavior of systems overfrequency bands, standard numerical techniques usually involve many frequency-fixed computations, atmany different frequencies. Although it is a straightforward and natural mean to answer to the posed problem,such a strategy can easily lead to huge computations, and the amount of data to store often increasessignificantly. This is particularly true in the context of medium frequency bands, where these responses havea strong sensitivity to the frequency. In this work PGD (Proper Generalized Decomposition), in a first time, isapplied to found a separate functional representation over frequency and space of the unknown amplitude ofVTCR (Variational Theory of Complex Rays) formulation on a reduced frequency space. This allows tocalculate an high quality mid-frequency response over a wide band without a fine frequency discretization,saving computational resources. Moreover the PGD representation of the solution allows to save a hugeamount of space in term of stored data. In a second time, PGD technique as been applied to extend itspeculiarity to mid-frequency wide band with uncertainty.

The first objective of the dissertation is to develop a suitable reduced order model capable of investigating the nonlinear mechanical behavior of von-Karman plates under electrostatic actuation. The second objective is to investigate the nonlinear static and dynamic behavior of rectangular microplates under small and large actuating forces. In the first part, we present and compare various approaches to develop reduced order models for the nonlinear von-Karman rectangular microplates actuated by nonlinear electrostatic forces. The reduced-order models aim to investigate the static and dynamic behavior of the plate under small and large actuation forces. A fully clamped microplate is considered. Different types of basis functions are used in conjunction with the Galerkin method to discretize the governing equations. First we investigate the convergence with the number of modes retained in the model. Then for validation purpose, a comparison of the static results is made with the results calculated by a nonlinear finite element model. The linear eigenvalue problem for the plate under the electrostatic force is solved for a wide range of voltages up to pull-in. In the second part, we present an investigation of the static and dynamic behavior of a fully clamped microplate. We investigate the effect of different non-dimensional design parameters on the static response. The forced-vibration response of the plate is then investigated when the plate is excited by a harmonic AC load superimposed to a DC load. The dynamic behavior is examined near the primary and secondary (superharmonic and subharmonic) resonances. The microplate shows a strong hardening behavior due to the cubic nonlinearity of midplane stretching. However, the behavior switches to softening as the DC load is increased. Next, near-square plates are studied to understand the effect of geometric imperfections of microplates. In the final part of the dissertation, we investigate the mechanical behavior of initially curved microplates. Microplates often experience an initial curvature imperfection, due to the micro fabrication process, which affects significantly their mechanical behavior. In this case a clamped-free-clamped-free microplate is considered. We validate the reduced order model by comparing the calculated static behavior and the fundamental natural frequency with those computed by a finite element model. As case studies, we consider two commonly encountered profiles of the initial curvature imperfection and study their effects on both the static and dynamic responses of the microplates. Next, an initially curved microplate made of silicon nitride is studied. The static behavior of the microplate is investigated when applying a DC voltage. Then, the dynamic behavior of the microplate is examined under the application of a harmonic AC voltage, superimposed to a DC voltage. Simulation results calculated by the reduced order model are compared with experimental data for model validation purpose, which show good agreement.

The aim of this work is to create complex virtual model of electromagnetic vibration generator. This model will include mechanical and electromagnetic subsystem and also the model of output circuit. Created model will be implemented in Matlab/Simulink enviroment and model parameters will be identified so that the compare of simulation and real results will be acceptable.

No description available.