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: Les travaux présentés dans cette thèse traitent du contrôle de systèmes dynamiques soumis à des excitations harmoniques et transitoires en utilisant des absorbeurs de type Nonlinear Energy Sink (NES). Plusieurs aspects ont été développés : la conception et la réalisation d'un nouveau design pour le NES cubique, l'étude de la location et du transfert irréversible d'énergie sur un NES bistable et le développement d'un critère de conception pour un NES à Vibro-Impact (VI). Dans un premier temps, un critère de conception est proposé pour le NES à raideur cubique. Le design proposé est basé sur des ressorts coniques ou des ressorts à pas variable. Un mécanisme à raideur négative est aussi introduit pour supprimer la partie linéaire et avoir une raideur cubique pure. Dans un deuxième temps, le concept du NES est validé expérimentalement par des essais statiques et des essais dynamiques. Une analyse de sensibilité est aussi menée sur la longueur des ressorts précontraints, elle dénote parfois un état bistable de l'oscillateur. Ensuite, le NES bistable ainsi obtenu est étudié plus en détail. Ce type d'absorbeur s'avère être très robuste pour différents types d’excitation. Des études expérimentales sont aussi menées afin d'explorer le comportement dynamique. Enfin, un critère de conception est proposé pour le NES à Vibro-Impact. Des calculs analytiques détaillés sont proposés pour contrôler les vibrations sous différentes excitations. L'étude expérimentale montre une bonne cohérence avec les résultats théoriques. / The work presented in this thesis deals with the passive control of dynamics systems subjected to harmonic and transient excitations using a Nonlinear Energy Sink (NES). Several research aspects have been developed: design theory and experimental study of a novel NES, efficient Targeted Energy Transfer (TET) of bistable NES and design criteria for optimally tuned Vibro-Impact (VI) NES. Firstly, a design criterion intended to provide optimal nonlinear stiffness is proposed. Then a novel design of NES system yielding cubic stiffness with conical springs or variable pitch springs and negative stiffness mechanism is developed. Secondly, the experimental procedures for static and dynamic test are presented and applied to validate the concept of NES system. Then a sensitivity analysis is performed with respect to the pre-compressed length of springs. Thirdly, the optimal design of the above device with negative stiffness (termed as bistable NES) is studied. This type of NES is proved to work robustly for different types of excitation, and experimental study of semi-active control are explored. Finally, design criteria for optimally tuned VI NES are studied. Detailed analytical calculations of clearance to control the vibration under different excitations are proposed. A good correspondence between theoretical and experimental results is observed.

The target of the research is to employ the autoresonant control technique in order to maintain the nonlinear oscillation mode at resonance (i.e. ultrasonic vibration at the tip of a drill bit at a constant level) during vibro-impact process. Numerical simulations and experiments have been executed. A simplified Matlab-Simulink model which simulates the ultrasonically assisted machining process consists of two parts. The first part represents an ultrasonic transducer that contains a piezoelectric transducer and a 2-step concentrator (waveguide). The second part reflects the applied load to the ultrasonic transducer due to the vibro-impact process. Parameters of the numerical models have been established based on experimental measurements and the model validity has been confirmed through experiments performed on an electromechanical ultrasonic transducer. The model of the ultrasonic transducer together with the model of the applied load was supplemented with a model of the autoresonant control system. The autoresonant control intends to provide the possibility of self-tuning and self-adaptation mechanism for an ultrasonic transducer to maintain its resonant regime of oscillations automatically by means of positive feedback. This is done through a signal to be controlled (please refer to Figure 7.2 and Figure 7.3) transformation and amplification. In order to examine the effectiveness and the efficiency of the autoresonant control system, three control strategies have been employed depending on the attributes of the signals to be controlled . Mechanical feedback control uses a displacement signal at the end of the 2nd step of the ultrasonic transducer. The other two control strategies are current feedback control and power feedback control. Current feedback control employs the electrical current flowing through the piezoceramic rings (piezoelectric transducer) as the signal to be controlled while power feedback control takes into account both the electrical current and the power of the ultrasonic transducer. Comparison of the results of the ultrasonic vibrating system excitation with different control strategies is presented. It should be noted that during numerical simulation the tool effect is not considered due to the complexity of a drill bit creates during the Ultrasonically Assisted Drilling (UAD) process. An effective autoresonant control system was developed and manufactured for machining experiments. Experiments on Ultrasonically Assisted Drilling (UAD) have been performed to validate and compare with the numerical results. Two sizes of drill bits with diameters 3mm and 6mm were applied in combination with three autoresonant control strategies. These were executed during drilling aluminium alloys with one fixed rotational speed associated with several different feed rates. Vibration levels, control efforts, feed force reduction were monitored during experiments. Holes quality and surface finish examinations supplement analysis of the autoresonant control results. In addition, another interesting research on the investigation of the universal matchbox (transformer) has been carried out. Introducing a varying air gap between two ferrite cores allows the optimization of the ultrasonic vibrating system, in terms of the vibration level, effective matchbox inductance, voltage and current level, phase difference between voltage and current, supplied active power etc (more details please refer to Appendix I).

The power plant and aerospace industries have been facing a huge loss, due to structural failure. The structural failure occurs due to the presence of the crack in it. Hence, it becomes necessary to monitor the structural health under operating condition. Most of the techniques, for structural health monitoring are used for a specific purpose. Some of these techniques require structure dismantling, which is very much expensive and time consuming. So the vibration based structural health monitoring is advantageous, compared to other techniques. Most of the vibration based Structural Health Monitoring (SHM) approaches, use linear vibration theory. But, these linear vibration based procedures, have inherently low sensitivity to crack. Since crack introduces nonlinearities in the system, their merits in damage detection need to be investigated for SHM. In this thesis, the problem is focused on studying nonlinear dynamics of cracked structures for Structural Health Monitoring. For this, simulations and experiments are performed. The new procedure for the simulation is developed using Matlab-Simulink. It uses the numerical approximation for dynamic compliance operators and a nonlinear model of cracks contact faces interaction to study the dynamic behaviour of the cracked bar. Furthermore, the finite element model of the cracked cantilever bar with crack- tip plasticity is developed and the dynamic behaviour of the elasto-plastic bar is studied. Additionally, numerous experiments are performed to study the dynamics of cantilever bar with the fatigue crack in it. The results from Matlab-Simulink simulation shows the distribution of higher harmonics generated along the bar length, as a function of distance from the crack. In finite element simulation, comparison is made between the resonance frequency of cracked cantilever bar with and without crack-tip plasticity. It is found that, there is decrease in resonance frequency of the cracked bar with cracked tip plasticity, when compared with the resonance frequency of cracked bar without crack-tip plasticity. This reduction in resonance frequency is due to the crack-induced plasticity near the crack tip which affects the overall stiffness of bar. In experiments, the response is measured at four different points on the cracked cantilever bar at a given resonant frequency of excitation at lower and higher vibration amplitude. For lower vibration amplitude, it is found that the response obtained near the vicinity of the crack shows the presence of higher harmonics of resonant frequency, which disappears in the response obtained far away from the crack. For higher vibration amplitude, it is found that the response obtained near the vicinity of the crack shows the presence of higher harmonics along with the low frequency component. This low frequency component causes modulation, which leads to the generation of side band frequencies near the resonant frequency. The occurrence of low frequency component and side band frequencies is due to the vibro-impact behaviour of crack. The amplitude of these side band frequencies and higher harmonics are reduced in the response obtained far away from the crack. This indicates that crack-induced nonlinearity has a localized effect on the dynamics of bar. It is also observed that the magnitude of low frequency component is proportional to the magnitude of resonant frequency of excitation. This indicates that crack behaves like a signal modulator, detector of low frequency component and amplifier as the magnitude of low frequency component is proportional to the magnitude of resonant frequency excitation. From the Matlab-Simulink simulation and experimental results, it is concluded that crackinduced nonlinearity affects the dynamic behaviour of the cracked bar significantly, which will be effective in structural health monitoring. Keywords: vibro-impact, crack, dynamic compliance, harmonics, modulator, detector, amplifier, crack-tip plasticity, resonance frequency, structural health monitoring.

L'objectif de cette étude est de caractériser le bruit de graillonnement des boîtes de vitesses automobiles, qui résulte des chocs entre les pignons au niveau des rapports non engagés, sous l'effet des fluctuations de vitesses imposées par le moteur. Outre les paramètres de conception de la boîte de vitesses et les conditions de fonctionnement, les paramètres qui gouvernent la réponse dynamique des pignons fous sont les couples de traînée et les caractéristiques des contacts qui gouvernent les chocs entre dents. Un modèle numérique non linéaire a été élaboré pour caractériser la réponse dynamique d'un pignon fou. Il permet d'identifier le seuil d'excitation au-delà duquel le phénomène de graillonnement apparaît et de qualifier la très grande diversité de comportements dynamiques susceptibles d'être observés, en fonction du niveau d'excitation adimensionnée, du jeu de denture et du coefficient de restitution des chocs entre dents. Les paramètres inconnus ont été identifiés expérimentalement, grâce à l'exploitation d'un banc d'acyclisme et l'implémentation de codeurs optiques sur les pignons menant et fou. Des essais en réponse libre amortie ont permis de discriminer les différentes sources de dissipation(roulements, palier du pignon fou, barbotage, etc.) et de valider les modèles permettant d'identifier le couple de traînée s'exerçant sur chaque pignon fou. D'autres essais en régime de fonctionnement stationnaire ont permis de décrire le coefficient de restitution des chocs entre les pignons, sa dispersion et sa variation avec la vitesse d'impact. Les mesures effectuées sous une excitation maîtrisée ont permis de caractériser le comportement dynamique du pignon fou et de valider les hypothèses retenues et les résultats numériques obtenus par le modèle non linéaire, recalé à partir des paramètres préalablement identifiés. Enfin, l'analyse du transfert entre les impulsions générées au niveau des pignons et la réponse vibratoire du carter a permis d'évaluer expérimentalement et numériquement le critère qui qualifie le bruit de graillonnement rayonné par la boîte de vitesses. La mise en oeuvre du modèle numérique permet d'analyser l'influence des paramètres de conception de la boîte de vitesses et de proposer des solutions qui minimisent le graillonnement, pour l'ensemble des rapports de la boîte et des conditions de fonctionnement.

[pt] Uma linha de pesquisa de grande interesse no estudo de colunas de perfuração de poços de petróleo aponta para a necessidade de se aumentar a taxa de penetração (ROP) na perfuração em rochas duras. Procurando suprir tal necessidade, este trabalho tem como objetivo estudar mecanismos e propor um novo dispositivo, utilizando as próprias vibrações geradas na coluna durante a perfuração. As várias formas de vibrar da coluna são, geralmente, indesejadas durante a perfuração. Porém, é possível utilizar algumas destas formas de vibrar para melhorar a eficiência do processo de perfuração. Inicialmente, avalia-se a influência das vibrações torcional e axial na ROP. Posteriormente, estuda-se a perfuração na ressonância e alguns aspectos e cuidados no uso desta nova técnica de perfuração, que vem sendo desenvolvida por empresas do setor. Por fim, é desenvolvido um novo dispositivo de perfuração, chamado de perfuração com martelo em ressonância ou perfuração percussiva- rotativa auto-excitada. Este dispositivo tem como premissa usar a vibração axial gerada no processo de corte, para criar uma carga harmônica na broca e excitar uma massa de aço (martelo). Desenvolve-se um modelo com vibro-impacto e atrito seco, representando o martelo e a resistência da rocha, respectivamente. Faz-se aqui, um estudo numérico e uma validação experimental do movimento percussivo de um modelo que representa a broca com este novo dispositivo. Os resultados mostram que a melhor forma do dispositivo operar é impactando a cabeça da broca, em condição de período-1, com um impacto por ciclo de forçamento. Adicionalmente, os parâmetros do experimento são identificados e os resultados numérico-experimental são comparados, mostrando que são similares. / [en] An area of interest in the study of drillstrings is due to the device of increasing the rate of penetration (ROP) in hard rocks. Trying to supply such necessity, this work aims to study mechanisms and to propose a new device, using vibrations generated in the drillstring itself. The various forms of drillstring vibrations are generally regarded as detrimental in the question. However, it is possible to use some of these vibrations forms in such a way as to enhance drilling performance. Initially, the influence of the torsional and axial vibrations in ROP is analyzed. Next, the resonance drilling, that is being developed by companies in this area, and some aspects and cares in the use of this new drilling technique are studied. At the end, a new drilling device, called resonance hammer drilling or self excited percussive rotary drilling, is developed. This device has as premise to use the axial vibration due to the cutting process, to generate a harmonic load at the bit and to excite a steel mass (hammer). A model with vibro-impact and dry friction is developed, representing the hammer and the resistance of the medium, respectively. It is presented a numeric study and an experimental validation of the percussive motion of the model, that represent the bit. The results show that the best way of the hammer to operate is impacting the bit head, in period-1 condition, ie, with one impact per cycle. Moreover, the experimental parameters are identified and since the numerical-experimental results are similar, the model used is validated.

[pt] Nesta Tese, o design robusto, com um modelo incerto de um sistema de vibro-impacto eletromecânico é feito. O sistema é composto de um carrinho, cujo movimento é aciondo por um motor de corrente contínua e um martelo embarcado neste carrinho. O martelo é ligado ao carrinho por um mola não linear e por um amortecedor linear, de modo que existe um movimento relativo entre eles. Uma barreira linear flexível, colocada fora do carrinho, restringe aos movimentos do martelo. Devido ao movimento relativo entre o martelo e a barreira, impactos podem ocorrer entre estes dois elementos. O modelo metemático desenvolvido para sistema leva em conta a influência do motor no comportamento dinâmico do sistema. Alguns parâmetros do sistema são incertos, tais como a rigidez e os coeficientes de amortecimento da barreira flexível. O objetivo da Tese é realizar uma otimização deste sistema eletromecânico com respeito a parâmetros de projeto, a fim de maximizar a potência de impacto sob a restrição de que a potência elétrica consumida pelo motor seja menor do que um valor máximo. Para escolher os parâmetros de projeto no problema de otimização, uma análise de sensibilidade foi realizada a fim de definir os parâmetros mais sensíveis do sistema. O problema de otimização é formulado no âmbito de otimização robusta, devido à presença de incertezas no modelo. As distribuições de probabilidades das variáveis aleatórias são construídas através do Princípio da Máxima Entropia e estatísticas da resposta estocástica do sistema são calculadas pelo método de Monte Carlo. O conjunto de equações não-lineares é apresentado, e um integrador temporal adaptado é desenvolvido. O problema de otimização não-linear estocástico com restrição é resolvido para diferentes níveis de incertezas e também para o caso determinístico. Os resultados são diferentes e isto mostra a importância da modelagem estocástica. / [en] In this Thesis, the robust design with a uncertain model of a vibro-impact eletromechanical system is done. The electromechanical system is composed of a cart, whose motion is excited by a DC motor (motor with continuous current), and an embarked hammer into this cart. The hammer is connected to the cart by a nonlinear spring component and by a linear damper, so that a relative motion exists between them. A linear flexible barrier, placed outside of the cart, constrains the hammer movements. Due to the relative movement between the hammer and the barrier, impacts can occur between these two elements. The developed model of the system takes into account the influence of the DC motor in the dynamic behavior of the system. Some system parameters are uncertain, such as the stiffness and the damping coefficients of the flexible barrier. The objective of the Thesis is to perform an optimization of this electromechanical system with respect to design parameters in order to maximize the impact power under the constraint that the electric power consumed by the DC motor is lower than a maximum value. To chose the design parameters in the optimization problem, a sensitivity analysis was performed in order to define the most sensitive system parameters. The optimization is formulated in the framework of robust design due to the presence of uncertainties in the model. The probability distributions of random variables are constructed using the Maximum Entropy Principle and statistics of the stochastic response of the system are computed using the Monte Carlo method. The set of nonlinear equations are presented, and an adapted time domain solver is developed. The stochastic nonlinear constrained design optimization problem is solved for different levels of uncertainties, and also for the deterministic case. The results are different and this show the importance of the stochastic modeling. / [fr] Dans cette Thèse, nous étudions l optimization robuste avec un modèle incertain d un système étrectromécanique avec vibro-impact. Le système életromécanique est contitué d un chariot dont le mouvement est généré par un moteur à courant continu, et d un mateau embarqué dans ce chariot. Le Marteau est relié au chariot par un resort non linéaire et par un amortisseur linéaire, de façon qu un mouvement relative existe entre eux. Une barrière flexible linéaire, placée à l extérieur du chariot limite les mouvements du Marteau. En raison du mouvement relative entre le Marteau et la barrière, des impacts peuvent se produire entre ces deux éléments. Le modèle du système dèveloppé prend en compte l influence du moteur à courant continu dans la comportement dynamique du système. Certains paramètres du système sont incertains, tells que les coefficients de rigidité et d amortissement de la barreire flexible. L objectif de la Thèse est de réaliser une optimization de ce système életromécanique en jouant sur les paramètres de conception. Le but est de maximizer la puissance d impact sous la contrainte que la puissance électrique consommée par le moteur à courant continu soit inférieure à une valeur maximale. Pour choisir les paramétres de conception dans le probléme d optimisation, une analyse de sensibilité a été réalisée afin de definir les paramètres du système les plus sensibles. L optimisation est formulée dans le cadre de la conception robuste em raison de la présence d incertitudes dans le modele. Les lois de probabilités des variables aléatoires du problème sont construites em utilisant le Principle du Maximum d Entropie. Les statistiques de la réponse stochastique du système sont caçculées em utilisant la méthode de Monte Carlo. L emsemble de équations non linéaires est presente, et um solveur temporel adapte est développé. Le probléme d optimisation non linéaire stochastique est résolu pour différents niveaux d incertitudes, ainsi que pour le cas déterministe. Les résultats sont différents, ce qui montre l importance de la modélisation stochastique.