In the modern dynamic engineering field, experimental dynamics is an important area of study. This area includes structural dynamics, structural control, and structural health monitoring. In experimental dynamics, methods to obtain measured data have seen a great influx of research efforts to develop an accurate and reliable experimental analysis result. A technical challenge is the procurement of informative data that exhibits the desired system information. In many cases, the number of sensors is limited by cost and difficulty of data archive. Furthermore, some informative data has technical difficulty when measuring input force and, even if obtaining the desired data were possible, it could include a lot of noise in the measuring data. As a result, researchers have developed many analytical tools with limited informative data. Subspace identification method is used one of tools in these achievements. Subspace identification method includes three different approaches: Deterministic Subspace Identification (DSI), Stochastic Subspace Identification (SSI), and Deterministic-Stochastic Subspace Identification (DSSI). The subspace identification method is widely used for fast computational speed and its accuracy. Based on the given information, such as output only, input/output, and input/output with noises, DSI, SSI, and DSSI are differently applied under specific assumptions, which could affect the analytical results. The objective of this study is to observe the effect of assumptions on subspace identification with various data conditions. Firstly, an analytical simulation study is performed using a sixdegree-of-freedom mass-damper-spring system which is created using MATLAB. Various conditions of excitation insert to the simulation test model, and its excitation and response are iv analyzed using the subspace identification method. For stochastic problems, artificial noise is contained to the excitation and followed the same steps. Through this simulation test, the effects of assumption on subspace identification are quantified. Once the effects of the assumptions are studied using the simulation model, the subspace identification method is applied to dynamic response data collected from large-scale 12-story buildings with different foundation types that are tested at Tongji University, Shanghai, China. Noise effects are verified using three different excitation types. Furthermore, using the DSSI, which has the most accurate result, the effect of different foundations on the superstructure are analyzed.

No description available.

Electric propulsion motors have emerged as a promising solution to address greenhouse gas emissions from Internal Combustion Engines (ICEs). While electric propulsion motors offer numerous advantages over Internal Combustion Engines (ICEs), they also pose certain challenges. Electric motors are prone to high-frequency tonal noise, which can be annoying to customers and become a quality concern in noise-sensitive automotive applications. The ongoing effort to increase the speed of electric propulsion motors for enhanced power density can have an adverse impact on rotors. This is due to the fact that the stress induced in the rotor is quadratically proportional to its speed. This concern becomes particularly significant for motors that rely on air barriers and thin bridges to enhance their electromagnetic performance. The thesis makes a contribution to address these challenges. First, the acoustic noise mitigation methods at the transmission stage are investigated. Then, acoustical materials are experimentally validated for their capacity to mitigate acoustic noise at the transmission stage. Then, experimental modal analysis is conducted to find out the modal characteristics of a stator-housing assembly. The mode shapes and modal frequency are compared with finite element results to evaluate the fidelity of the finite element model. Then, an equivalent damage approach is used to employ accelerated fatigue analysis for a rotor using constant amplitude load cycles. Finally, a thermomechanical fatigue analysis workflow is developed for a rotor to overcome the limitations of the constant amplitude load cycle approach, with an additional computational cost. / Thesis / Doctor of Philosophy (PhD)

Ce travail de thèse porte sur l'élaboration d'un matériau composite à matrice thermodurcissable incorporant des renforts nanométriques et/ou une phase élastomère, permettant d'améliorersa rigidité, son amortissement et sa résilience. Pour cela, nous avons réalisé des formulations baséessur des matrices époxyvinylester, renforcées ou non par une phase élastomère et chargées de montmorillonite ou de sépiolite. Nous avons étudié leurs propriétés visco-élastiques par analyse modaleexpérimentale et leurs propriétés à l'impact par des essais d'impact par chute de masse. Nous avonsdéterminé la microstructure des composites fabriqués en nous appuyant sur la diffraction des rayonsX et des observations en microscopie électronique. Des modèles d'homogénéisation, fondés sur lemodèle de H ALPIN -T SAI et adaptés aux matériaux composites étudiés, ont été développés afin dedisposer d'un outil permettant de relier explicitement la rigidité des composites à leur morphologie.Une analyse paramétrique approfondie a permis de déterminer les caractères morphologiques lesplus influents et d'évaluer la performance des procédés de mise en œuvre au regard des renforcements mécaniques obtenus. Expérimentalement, l'incorporation de montmorillonite ou de sépiolite a conduit à une augmentation significative du module élastique et la présence d'une phase élastomère dans la résine a permis de doubler l'amortissement et d'augmenter la résilience. Finalement, les formulations les plus performantes ont été retenues pour la fabrication de composites renforcés de fibres de verre. L'amélioration des propriétés mécaniques se retrouve, dans une moindre mesure, dans lesprototypes réalisés. La pertinence de l'utilisation de ces matériaux à l'échelle industrielle a été évaluée. / This thesis focuses on the development of a thermosetting matrix composite incorporating nanoscale reinforcements and/or an elatomeric phase to improve its stiffness, damping and resilience.To do so, we made formulations based on epoxy vinyl ester matrices, filled or not by an elastomeric phase, and reinforced with montmorillonite or sepiolite. Their viscoelastic properties were studied usingexperimental modal analysis and their impact properties were investigated using drop weight impacttesting. The microstructure of these composites was examined using X-ray diffraction and electronmicroscopy observations.Homogenization models based on H ALPIN -T SAI model and adapted to the studied composites were developed to provide a tool able to explicitly link the stiffness of the material to its morphology.A detailed parametric analysis allowed to determine the most influential morphological characteristics and to assess the efficiency of the process regarding the mechanical stiffening obtained.Experimentally, the incorporation of montmorillonite or sepiolite led to a significant increase in the elastic modulus and, with the presence of an elastomeric phase in the resin, the damping was doubled and the resilience was increased.Finally, the most efficient formulations were used to manufacture glass fibers reinforced composites.The improvement in mechanical properties was found, to a lesser extent, for the manufactured prototypes.The relevance of the use of these materials on an industrial scale was evaluated.

Apresenta-se um estudo analítico e experimental do fenômeno de interação entre excitadores eletrodinâmicos e a estrutura em ensaios de vibração e discutem-se causas e efeitos desta interação na qualidade dos resultados obtidos. Inicialmente, realizam-se simulações numéricas que contemplam as características mecânicas e eletromagnéticas do excitador. Definido o modelo para o excitador, realizam-se simulações de teste com estruturas, dos quais obtêm-se as forças de entrada e funções de resposta em freqüência (FRFs) estimadas que serão comparadas às FRF reais da estrutura. Posteriormente, considera-se a inclusão de graus de liberdade rotacionais aos modelos do excitador e da estrutura. Finalmente, as simulações de testes com múltipla excitação têm como objetivo principal o de observar os fenômenos de queda de força de excitação e seus efeitos sobre as FRFs estimadas. Com os resultados experimentais verificam-se os principais fenômenos da interação excitador / estrutura observados nas simulações numéricas tais como a queda da força de excitação e a influência da dinâmica do conjunto excitador / amplificador na resposta da estrutura. Através dos resultados experimentais obtidos com uma viga metálica observam-se os principais efeitos previstos pelas simulações. Ainda, comparam-se as alterações nos dados obtidos com outros métodos de excitação tais como, martelo impulsivo e excitação em malha fechada. Testes realizados com diferentes estruturas, como um pneumático e um chassi tubular, vêem complementar os dados obtidos até então para excitação com um único excitador. Os testes realizados com a finalidade de validar os modelos que incluem graus de liberdade rotacionais mostram que tais grandezas não podem ser negligenciadas, principalmente no que se referem aos testes com excitação via base, em que o item de teste é montado diretamente sobre o excitador. Ainda, verificam-se os resultados obtidos com diversos estimadores de FRFs em ensaios com acréscimo de ruído aos sinais de entrada e saída. Os resultados experimentais realizados com dois excitadores mostram os mesmos efeitos observados nas simulações, em geral uma redução na queda da força de excitação e uma melhor distribuição de energia pela estrutura. / An analytical and experimental study of the interaction between electrodynamic exciters and the structure under test is presented, and the causes and effects of this interaction on the obtained data quality are discussed. Initially, some numerical simulations are performed concerning the shaker\'s mechanical and electrical features. Once the shaker model is defined, some tests with structures were simulated in order to obtain the input forces and the estimated frequency response functions to be compared with the measured FRFs. Afterwards, the rotational degrees of freedom were included in the shaker and structure models. Ending this section, tests with multiple input forces were simulated. The experimental results confirm most of the phenomena observed in the simulation section, such as the input force drop-off and the influence of the shaker / power amplifier assembly on the structure\'s response. The tests conducted with a steal beam confirmed the effects predicted by the simulations. Therefore, these results are compared with others, obtained from alternative methods such as impact test and closed loop shaker tests. Tests with structures like a truck tyre and a tubular chassis complement the assessment of single input tests. The tests performed with the objective of validating the models considering rotational degrees of freedom show that these quantities cannot be neglected, mainly when base driven tests are concerned. Also, the efficiency of FRF estimators applied to shaker tests, in the presence of noise on the input and output channels is verified experimentally. The multiple input tests corroborate the effects observed in the simulations, in general, a reduction of the droopoff on the force and an improvement on the input energy distribution on the structure.

Findings from a project involving rotating equipment defect detection using the Algorithm of Mode Isolation (AMI) are presented. The prototypical system evaluated is a rotating shaft, supported by hydrodynamic bearings at both ends, with one disk mounted to the shaft. Shaft cracks and bearing wear are the two equipment defects considered. An existing model of the prototypical system from the literature, termed the simplified model. is modified to simulate the presence of a transverse shaft crack at mid-span. This modified model is termed the standard model. Ritz series analysis, in conjunction with a previously published description of the compliance related to the presence of a transverse shaft crack, is used to describe the decrease in shaft stiffness associated with the crack. The directional frequency response function (dFRF) is shown in the literature to provide benefits over the standard frequency response function (FRF) in both system identification and shaft crack detection for rotating equipment. The existing version of AMI is modified to process dFRFs and termed Two-Sided AMI. The performance of Two-Sided AMI is verified through system identification work using both the simplified model and a rigid rotor model from the literature. The results confirm the benefits of using the dFRF for system identification of isotropic systems. AMI and Two-Sided AMI are experimental modal analysis (EMA) routines, which estimate modal properties based on a frequency domain expression of system response. Eigenvalues and associated modal residues are the modal properties considered in the present work. Three defect detection studies are fully described. In the first, the simplified model is used to investigate bearing wear detection. Various damage metrics related to the eigenvalue and the residue are evaluated. The results show that residue-based metrics are sensitive to bearing wear. Next, the standard model is used in an in-depth investigation of shaft crack detection. When a shaft crack is present, the standard model is time-varying in both the fixed and moving coordinate systems. Therefore, this analysis is also used to evaluate performing EMA on non-modal data. In addition to continuing the evaluation of various xiv damage metrics, the shaft crack study also investigates the effects of noise and coordinate system choice (fixed or moving) on shaft crack detection. Crack detection through EMA processing of noisy, non-modal data is found to be feasible. The eigenvalue-based damage metrics show promise. Finally, the standard model is used in a dual-defect study. The system is configured with both a shaft crack and a worn bearing. One defect is held constant while the magnitude of the other is increased. The results suggest that AMI is usable for defect detection of rotating machinery in the presence of multiple system defects, even though the response data is not that of a time-invariant system. The relative merits of both input data types, the FRF and the dFRF, are evaluated in each study.

Apresenta-se um estudo analítico e experimental do fenômeno de interação entre excitadores eletrodinâmicos e a estrutura em ensaios de vibração e discutem-se causas e efeitos desta interação na qualidade dos resultados obtidos. Inicialmente, realizam-se simulações numéricas que contemplam as características mecânicas e eletromagnéticas do excitador. Definido o modelo para o excitador, realizam-se simulações de teste com estruturas, dos quais obtêm-se as forças de entrada e funções de resposta em freqüência (FRFs) estimadas que serão comparadas às FRF reais da estrutura. Posteriormente, considera-se a inclusão de graus de liberdade rotacionais aos modelos do excitador e da estrutura. Finalmente, as simulações de testes com múltipla excitação têm como objetivo principal o de observar os fenômenos de queda de força de excitação e seus efeitos sobre as FRFs estimadas. Com os resultados experimentais verificam-se os principais fenômenos da interação excitador / estrutura observados nas simulações numéricas tais como a queda da força de excitação e a influência da dinâmica do conjunto excitador / amplificador na resposta da estrutura. Através dos resultados experimentais obtidos com uma viga metálica observam-se os principais efeitos previstos pelas simulações. Ainda, comparam-se as alterações nos dados obtidos com outros métodos de excitação tais como, martelo impulsivo e excitação em malha fechada. Testes realizados com diferentes estruturas, como um pneumático e um chassi tubular, vêem complementar os dados obtidos até então para excitação com um único excitador. Os testes realizados com a finalidade de validar os modelos que incluem graus de liberdade rotacionais mostram que tais grandezas não podem ser negligenciadas, principalmente no que se referem aos testes com excitação via base, em que o item de teste é montado diretamente sobre o excitador. Ainda, verificam-se os resultados obtidos com diversos estimadores de FRFs em ensaios com acréscimo de ruído aos sinais de entrada e saída. Os resultados experimentais realizados com dois excitadores mostram os mesmos efeitos observados nas simulações, em geral uma redução na queda da força de excitação e uma melhor distribuição de energia pela estrutura. / An analytical and experimental study of the interaction between electrodynamic exciters and the structure under test is presented, and the causes and effects of this interaction on the obtained data quality are discussed. Initially, some numerical simulations are performed concerning the shaker\'s mechanical and electrical features. Once the shaker model is defined, some tests with structures were simulated in order to obtain the input forces and the estimated frequency response functions to be compared with the measured FRFs. Afterwards, the rotational degrees of freedom were included in the shaker and structure models. Ending this section, tests with multiple input forces were simulated. The experimental results confirm most of the phenomena observed in the simulation section, such as the input force drop-off and the influence of the shaker / power amplifier assembly on the structure\'s response. The tests conducted with a steal beam confirmed the effects predicted by the simulations. Therefore, these results are compared with others, obtained from alternative methods such as impact test and closed loop shaker tests. Tests with structures like a truck tyre and a tubular chassis complement the assessment of single input tests. The tests performed with the objective of validating the models considering rotational degrees of freedom show that these quantities cannot be neglected, mainly when base driven tests are concerned. Also, the efficiency of FRF estimators applied to shaker tests, in the presence of noise on the input and output channels is verified experimentally. The multiple input tests corroborate the effects observed in the simulations, in general, a reduction of the droopoff on the force and an improvement on the input energy distribution on the structure.

La prestation vibroacoustique est une question primordiale pour les constructeurs de véhicules, qui sont contraints par des lois ainsi que par des besoins commerciales: d'une part, un grand nombre de normes existe, visant à régler les niveaux vibratoires et acoustiques que les occupants d'un véhicule peuvent supporter, d'autre part le constructeur est intéressé à garantir un haut degré de confort pour que son produit soit compétitif. L'industrie du poids lourds comporte des spécificités par rapport à d'autres secteurs industriels, et surtout par rapport au marché des véhicules légers: non seulement l'architecture d'un véhicule industriel est unique, mais en plus ce qui caractérise les poids lourds par rapport à d'autres véhicules terrestres est la grande diversité des configurations disponibles. Une bonne connaissance des mécanismes de transmission des vibrations et du bruit, ainsi que du bilan de leurs sources, permette de fixer des règles de conception plus rigoureuses pour les composants. Par ailleurs, la connaissance des influences des paramètres architecturaux d'un camion sur les prestations vibroacoustiques donne une meilleure clé d'interprétation pour prédire les caractéristiques qu'un composant du véhicule doit avoir. Actuellement ces vérifications sont largement basées sur des essais, soit subjectifs (estimations par des techniciens experts) soit objectifs (acquisitions par microphones et accéléromètres). Cette pratique est très coûteuse car, pour prendre en compte la diversité des camions, il faut tester un grand nombre de véhicules. Pour franchir ces limitations, le prototypage virtuel - au lieu des essais physiques - doit être renforcé. Les méthodologies numériques sont déjà utilisées au sein du Groupe Volvo, mais les outils disponibles sont considérés en partie inappropriés pour les besoins de calcul des prestations NVH. Les activités de cette thèse ont été réalisées dans le cadre du service Noise and Driveline Vibration, qui est responsable de l'estimation du confort acoustique perçu par les occupants du camion, dans toutes ces conditions d'utilisation. Les travaux de thèse sont concentrés sur le comportement du châssis comme composant principale; le châssis est la principale voie de transfert des vibrations depuis le moteur vers la cabine. En outre, une attention particulière sera donnée à l'effet des accessoires sur le comportement dynamique du châssis, bien que peu d'intérêt sera porté sur la signature vibratoire des accessoires mêmes. / The vibroacoustic performance is a matter of primary concern for modern vehicle manufacturers, that are constrained by health and safety legislation as well as by commercial needs: on the one hand, a number of norms exists regulating the level of vibration and noise that vehicle occupants can tolerate, but on the other hand a manufacturer is also interested in guaranteeing a high level of comfort in order to keep products competitive. The commercial vehicle industry presents some peculiarity with respect to other vehicle manufacturing businesses, and especially to the more known car industry: not only the architecture of a commercial vehicle is a class of its own, but what differentiates the most trucks from other ground vehicles are the configuration diversity and customization. A deep knowledge of the vibration and noise transmission mechanisms in trucks as well as source breakdown allows defining more rigorous and strict component specifications. Furthermore, the comprehension of the sensitivity of truck architecture parameters on vibroacoustic features provides even deeper means to assess the needed properties for a component to be installed on a vehicle. At present the verification is largely based on tests, both subjective (assessment by experimented test engineers) and objective (microphone and accelerometer acquisitions). This practice is extremely expensive, since, in order to take into account the large diversity of trucks, a large number of vehicles has to be tested. To overcome this limit, virtual testing - as opposed to physical testing - should be strengthened. Numerical methods are already largely used in the Volvo Group, but the available tools are considered partly unfit to the NVH demands and inappropriate with respect to their specific needs. The activities of the current thesis have been developed in the framework of the Interior Noise and Driveline Vibration group, which is responsible for the estimation of the acoustic comfort perceived by driver and passengers in all driving conditions and vehicle uses. This thesis will focus on the behaviour of the chassis as a primary component. The chassis is the main transfer path for engine-induced vibrations transmitted to the cabin. Besides, a peculiar attention will be given to the effect the chassis equipment components have on the chassis dynamics, even though limited interest will be put on the investigation of the dynamic signature of the equipment itself.

The diploma thesis deals with determination of modal parameters for machine tool manage-ment. Experimental modal analysis is performed and a new method for determining the damping and stiffness of the machine tool guidance is proposed. A mathematical model for the calculation of signals using state equations was created and the damping stiffness was determined using hysteresis curves.

[pt] Nas últimas décadas, perfis pultrudados de polímeros reforçados com fibra (PRF) vêm despertando grande interesse na indústria civil devido a sua alta relação entre resistência e peso e sua aplicabilidade em ambientes agressivos. Apesar de apresentar grande resistência às intempéries, a degradação dos PRF foi notada após anos de exposição em campo. A utilização de ensaios não destrutivos (END) se mostra como uma boa alternativa para avaliar a integridade deste material, havendo especial interesse para controle de qualidade de baixo custo em campo. Dessa forma, este trabalho utilizou ensaios de vibração livre com duas técnicas de excitação por impulso para detectar danos em polímeros reforçados com fibra de vidro envelhecidos em câmaras com elevada temperatura, umidade e salinidade. Através da avaliação das frequências naturais e amortecimentos, foi observado o impacto das condições ambientais na integridade do material, resultado corroborado pela variação das propriedades elásticas obtidas através da resposta dinâmica acústica. / [en] In the last decades, pultruded profiles of fiber-reinforced polymers (FRP) have been attracting great interest in the civil industry due to their high strength-to-weight ratio and their applicability in aggressive environments. Despite showing great resistance to weathering, the degradation of FRP was noticed after years of exposure in the field. The use of non-destructive techniques (NDT) has been shown to be a good alternative to evaluate the integrity of this material, with special interest for low-cost quality control in the field. Thus, this work used free vibration tests with two impulse excitation techniques to detect damage in glass fiber reinforced polymers aged in chambers with high temperature, humidity and salinity. Through the evaluation of natural frequencies and damping, the impact of environmental conditions on the integrity of the material was observed, a result corroborated by the variation of elastic properties obtained through the acoustic dynamic response.