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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

[en] AN EXCURSION IN THE DYNAMICS OF FLEXIBLE BEAMS: FROM MODAL ANALYSIS TO NONLINEAR MODES / [pt] UMA EXCURSÃO NA DINÂMICA DE VIGAS FLEXÍVEIS: DE ANÁLISE MODAL A MODOS NÃO LINEARES

GUSTAVO BRATTSTROEM WAGNER 24 November 2022 (has links)
[pt] Vigas flexíveis são encontradas com cada vez mais frequência em diferentes indústrias, uma vez que novos projetos têm buscado por estruturas mais longas e leves. Isso pode ser uma consequência direta das novas demandas estruturais nos projetos, ou uma simples consequência do engajamento das indústrias em programas de redução de custo (utilização de menos materiais). Em geral, vigas flexíveis são modeladas sob hipóteses de grandes deslocamentos, grandes rotações, mas com pequenas deformações. Essas hipóteses permitem que o equacionamento da dinâmica de vigas flexíveis seja feito através de elementos finitos co-rotacionais. A formulação co-rotacional decompõe o movimento das estruturas flexíveis em duas partes: uma contendo o movimento de corpo rígido e outra com uma (pequena) deformação elástica. Dessa forma, a não-linearidade geométrica causada pelos grandes deslocamentos e rotações das seções transversais das vigas podem ser computadas de forma eficiente. Uma das inovações dessa tese é o uso direto das equações de movimentos geradas pelos elementos finitos co-rotacionais no cálculo dos modos normais não-lineares (MNNs). Até agora, a maioria das análises dinâmicas com elementos finitos co-rotacionais foram restritas à integração das equações de movimento. O conhecimento de MNNs é útil na análise de sistemas não-lineares pois permitem um detalhado entendimento das vibrações nos regimes não-lineares. Com eles, pode-se, por exemplo, prever comportamentos de enrijecimento/relaxamento, localização de respostas, interação entre modos, existência de isolas, etc. A definição de Rosenberg sobre MNNs como sendo soluções periódicas (não necessariamente síncronas) do sistema é adotado na tese. Os métodos do Balanço Harmônico e do Tiro são apresentados e utilizados no cálculo de soluções periódicas de sistemas não-lineares. Um procedimento de continuação numérica é implementado para computar os MNN eficientemente para diferentes níveis de energia. Exemplos numéricos mostram a capacidade do método proposto quando aplicado aos elementos finitos co-rotacionais. / [en] Flexible beams are becoming ubiquitous in several industrial applications, as new projects often aim for lighter and longer structures. This fact is directly related to the new challenging demands on structural performances, or it is a simple consequence of the engagement of industries in cost reduction programs (usage of less material). Flexible beams are usually modeled under the assumption of large displacements, finite rotations, but with small strains. Such hypotheses allow the equation of motion to be built using co-rotational finite elements. The co-rotational formulation decomposes the total motion of a flexible structure into two parts: a rigid body displacement and an elastic (small) deformation. This way, the geometric nonlinearity caused by the large displacements and rotations of the beam s cross sections can be efficiently computed. One of the novelties of this thesis is the direct usage of the equation of motion generated by a co-rotational finite element formulation in the computation of nonlinear normal modes (NNM). So far, most of the dynamic analyses with co-rotation finite element models were restricted to numerical integrations of the equation of motion. The knowledge of NNMs can be beneficial in the analysis of any nonlinear structure since it allows a thoroughly understanding of the vibratory response in the nonlinear regime. They can be used, for example, to predict a hardening/softening behavior, a localization of the responses, the interactions between modes, the existence of isolas, etc. The Rosenberg s definition of NNM as periodic solutions (non-necessarily synchronous motion) is adopted here. The Harmonic Balance method and the Shooting methods are presented and used to compute periodic solutions of nonlinear systems. A numerical path continuation scheme is implemented to efficiently compute NNMs at different energy levels. Numerical examples show the capability of the proposed method when applied to co-rotational beam elements.
42

Nonlinear dynamics of one-way clutches and dry friction tensioners in belt-pulley systems

Zhu, Farong 25 September 2006 (has links)
No description available.
43

[pt] ANÁLISE DINÂMICA NÃO LINEAR DE PÓRTICOS COM BASE ELASTO-PLÁSTICA SOB AÇÃO SÍSMICA / [en] NONLINEAR DYNAMIC ANALYSIS OF FRAMES WITH ELASTO-PLASTIC BASE UNDER SEISMIC EXCITATION

LUIS FERNANDO PAULLO MUNOZ 11 October 2016 (has links)
[pt] A resposta dinâmica de sistemas estruturais não lineares tem sido um item de grande interesse nas pesquisas em engenharia civil. Problemas onde há interação base flexível-estrutura são de grande importância na análise estrutural, já que a maioria das estruturas civis é apoiada sobre sistemas flexíveis (solo ou sistemas de apoio com dissipação de energia). Nesta área, o estudo de sistemas submetidos a ações sísmicas é um tópico relevante, já que estas solicitações têm um grande conteúdo de frequências, o que pode influenciar consideravelmente as respostas da estrutura. Neste contexto, o conhecimento da resposta em frequência de estruturas não lineares sob uma excitação de base é uma ferramenta útil para avaliar os potenciais efeitos de ações sísmicas sobre estes sistemas. Na presente tese é desenvolvida uma metodologia de análise não linear dinâmica de sistemas estruturais reticulados sob excitações de base, considerando não linearidade geométrica e apoios flexíveis, representados por molas unidimensionais, com comportamento elasto-plástico. Através de uma análise paramétrica é avaliada a variabilidade das respostas de sistemas esbeltos submetidos a ações sísmicas reais, sismos artificiais, assim como ações sísmicas sucessivas. O problema no espaço é resolvido pelo método dos elementos finitos. Para a análise em frequência, é apresentada uma metodologia baseada no método do balanço harmônico e no método de Galerkin, juntamente com técnicas de continuação para a obtenção das curvas de ressonância não lineares. O problema no tempo é abordado através da integração das equações de movimento pelos métodos de Runge-Kutta e Newmark, associado ao método de Newton-Raphson. / [en] The dynamic response of nonlinear structures has been a topic of interest in civil engineering research. Problems in which base-structure interaction is present have a great importance in structural analysis, since most structures rests on flexibel systems (soil or supports with dissipation). In this research area, the study of structures under the action of seismic loads represent a relevant topic, since this kind of excitations may excite several vibration modes and thus influence strongly the dynamic response. In this context, the prediction of the nonlinear structural behavior in frequency domain of structures under base excitation is a useful resource to assess the potential effects of sismic loads on these systems. In this thesis, a methodology for nonlinear dynamic analysis of plane frame structures under base excitation is presented considering geometric nonlinearity and elastic supports represented by elasto-plastic unidimensional springs. Trough a parametric analysis, the variability of the dynamic responses of slender structural systems under the actions of real earthquakes, synthetics earthquakes, as well as the action of multiple earthquakes is assessed. The structural systems here analyzed are discretized in space using a nonlinear finite element formulation. For the response in frequency domain, a scheme based on the Balance Harmonic Method and the Galerkin method, in conjunction with continuation methods, is formulated to obtain the nonlinear resonance curves. The nonlinear dynamic response in the time domain is calculated by direct integration of the equations of motion. For this, the Runge-Kutta method and the Newmark method in association with the iterative Newton-Raphson scheme are employed.
44

Analyse de structures vibrantes dotées de non-linéarités localisées à jeu à l'aide des modes non-linéaires / Analysis of vibrating structures with localized nonlinearities using nonlinear normal modes

Moussi, El hadi 17 December 2013 (has links)
Le travail de cette thèse a été réalisé dans le cadre d'une collaboration entre EDF R&D et le LMA de Marseille (CNRS). Le but était de développer des outils théoriques et numériques pour le calcul de modes non-linéaires de structures industrielles possédant des non-linéarités localisées à jeu. La méthode de calcul utilisée est une combinaison de la méthode d'équilibrage harmonique (EH) et de la méthode asymptotique numérique (MAN), appelée EHMAN. Elle est réputée pour sa robustesse sur les problèmes réguliers. L'enjeu de ce travail de thèse est de l'appliquer sur des problèmes non-réguliers régularisés de type butée à jeu pour lequel un grand nombre d'harmonique est nécessaire. Des améliorations ont été apportées à la méthode de base pour rendre effectif le traitement de modèles à "grand" nombre de degrés de liberté (DDL). Les développements réalisés pendant la thèse ont été capitalisés par la création de nouveaux opérateurs dans Code_Aster.Une étude approfondie d'un système à 2 degrés de liberté a permis de faire émerger quelques caractéristiques des systèmes non-linéaires à jeu. Celles-ci ont servi entre autre à établir une méthodologie pour l'étude de systèmes à grand nombre de DDL. Pour finir, la potentialité des modes non-linéaires comme outil de diagnostic vibratoire est démontrée avec l'étude d'un tube cintré de générateur de vapeur. Le calcul des modes non-linéaires a monté l'existence d'une interaction entre un mode hors-plan (basse fréquence) et un mode plan (haute fréquence) expliquant des régimes vibratoires non-standards. Ce résultat, impossible à obtenir avec les outils de l'analyse modale linéaire, est confirmé expérimentalement. / This work is a collaboration between EDF R&D and the Laboratory of Mechanics and Acoustics. The objective is to develop theoretical and numerical tools to compute nonlinear normal modes (NNMs) of structures with localized nonlinearities.We use an approach combining the harmonic balance and the asymptotic numerical methods, known for its robustness principally for smooth systems. Regularization techniques are used to apply this approach for the study of nonsmooth problems. Moreover, several aspects of the method are improved to allow the computation of NNMs for systems with a high number of degrees of freedom (DOF). Finally, the method is implemented in Code_Aster, an open-source finite element solver developed by EDF R&D.The nonlinear normal modes of a two degrees-of-freedom system are studied and some original characteristics are observed. These observations are then used to develop a methodology for the study of systems with a high number of DOFs. The developed method is finally used to compute the NNMs for a model U-tube of a nuclear plant steam generator. The analysis of the NNMs reveals the presence of an interaction between an out-of-plane (low frequency) and an in-plane (high frequency) modes, a result also confirmed by the experiment. This modal interaction is not possible using linear modal analysis and confirms the interest of NNMs as a diagnostic tool in structural dynamics.
45

Adaptive Suppression of Interfering Signals in Communication Systems

Pelteku, Altin E. 21 April 2013 (has links)
The growth in the number of wireless devices and applications underscores the need for characterizing and mitigating interference induced problems such as distortion and blocking. A typical interference scenario involves the detection of a small amplitude signal of interest (SOI) in the presence of a large amplitude interfering signal; it is desirable to attenuate the interfering signal while preserving the integrity of SOI and an appropriate dynamic range. If the frequency of the interfering signal varies or is unknown, an adaptive notch function must be applied in order to maintain adequate attenuation. This work explores the performance space of a phase cancellation technique used in implementing the desired notch function for communication systems in the 1-3 GHz frequency range. A system level model constructed with MATLAB and related simulation results assist in building the theoretical foundation for setting performance bounds on the implemented solution and deriving hardware specifications for the RF notch subsystem devices. Simulations and measurements are presented for a Low Noise Amplifer (LNA), voltage variable attenuators, bandpass filters and phase shifters. Ultimately, full system tests provide a measure of merit for this work as well as invaluable lessons learned. The emphasis of this project is the on-wafer LNA measurements, dependence of IC system performance on mismatches and overall system performance tests. Where possible, predictions are plotted alongside measured data. The reasonable match between the two validates system and component models and more than compensates for the painstaking modeling efforts. Most importantly, using the signal to interferer ratio (SIR) as a figure of merit, experimental results demonstrate up to 58 dB of SIR improvement. This number represents a remarkable advancement in interference rejection at RF or microwave frequencies.
46

Nuevas técnicas de simulación y optimización de circuitos osciladores y lazos de enganche en fase de microondas

Domínguez Mosquera, Jacobo 25 June 2009 (has links)
El objetivo de este trabajo es el desarrollo de técnicas para la simulación y optimización del diseño de circuitos osciladores y lazos de enganche en fase de microondas. La intención de estas técnicas es que puedan ser utilizadas por el diseñador para optimizar las prestaciones de este tipo de circuitos durante la etapa de diseño. Por este motivo, se ha intentado que en todo momento las técnicas puedan ser utilizadas en combinación con un programa comercial de simulación de circuitos de microondas.En el caso de los circuitos osciladores, inicialmente se han optimizado sus prestaciones cuando se utilizan como osciladores controlados por tensión. De esta forma, se han desarrollado una serie de técnicas que, en combinación con simulaciones en un programa comercial, permiten la linealización y extensión de la característica tensión-frecuencia. Mediante una técnica de control de estabilidad, se ha optimizado la respuesta dinámica del oscilador ante entradas variantes en el tiempo. En concreto, se ha aumentado la rapidez de respuesta eliminando transitorios lentos oscilantes que distorsionan la señal de salida deseada. Esta técnica se ha aplicado al caso particular de osciladores controlados por tensión utilizados para generar señales chirp, como puede ser en radares Frequency Modulated Continuos Wave (FMCW). Se ha analizado también el fenómeno del "injection-pulling", en el que una señal interferente desplaza la frecuencia de oscilación. Para ello, se ha desarrollado una formulación tipo transitorio de envolvente cuyos coeficientes pueden ser identificados mediante simulaciones de balance armónico en un simulador comercial. La técnica permite incrementar la robustez del circuito oscilador ante estas señales interferentes. Dados los problemas observados en el simulador comercial para simular la característica de ruido de fase en osciladores con estructuras acopladas, se ha desarrollado una técnica de simulación de ruido de fase que solventa estos problemas. La técnica obtiene la característica de ruido de fase a través de simulaciones de transitorio de envolvente en combinación con el uso de generadores auxiliares. Estas simulaciones pueden realizarse sin problemas usando un simulador comercial. Los resultados de todas las técnicas han sido corroborados mediante medidas en varios tipos de osciladores de microondas. Finalmente, se ha realizado un estudio preliminar para combinar el uso de series de Volterra con la técnica de transitorio de envolvente para la simulación de la respuesta transitoria de los osciladores.En el caso de los lazos de enganche en fase, se ha desarrollado un programa propio que realiza un análisis no lineal de lazos acoplados o "Coupled Phase-Locked Loops" (CPLL). Estos sistemas son utilizados en aplicaciones tales como en control de apuntamiento de antenas "phased-array". El programa, basado en una formulación tempo-frecuencial del sistema, permite la obtención de los rangos de operación del CPLL mediante una caracterización no lineal de los elementos que componen el lazo. Se delimitan los rangos de histéresis, y se analiza la variación de estos rangos en función de los parámetros del sistema. Se analiza la estabilidad de las soluciones estacionarias, teniendo en cuenta parámetros tales como el retardo del lazo. Mediante el control de la estabilidad y un análisis de tipo transitorio de envolvente, se optimiza la rapidez del sistema en el seguimiento de entradas moduladas. Finalmente, se analiza el ruido de fase, separando la perturbación en fase en distintas componentes. Esta separación permite clarificar el efecto del ruido en el control de apuntamiento de un array de antenas. Las predicciones de las técnicas han sido validadas mediante medidas en un sistema CPLL a 2 GHz. / The objective of this work is the development of techniques for the simulation and optimization of the design of microwave oscillator circuits and phase-locked loops. The intention of these techniques is that they can be used by the designer to optimize the features of these kinds of circuits during the design stage. For this reason, a lot of effort has been put along this thesis to ensure that the techniques can be used in combination with commercial microwave circuit simulators.In the case of the oscillator circuits, initially, their features have been optimized when used as voltage controlled oscillators (VCO). In this way, different techniques are proposed for the computer aided design of these circuits. The first technique allows setting the operation frequency band for specific values of the tuning voltage. The second technique imposes a linear frequency-voltage characteristic with the aid of an auxiliary generator. To follow this characteristic, the circuit is solved in terms of an ideal capacitance, synthesized, at a later stage, with the tuning varactor embedded in a linear network. In the third technique, the oscillator response to a sawtooth input, used to generate a chirp signal, is improved, eliminating spurious frequencies, not observable in steady state. To illustrate the techniques, a VCO operating in the C-band has been optimized and used to generate a chirp signal with low nonlinear frequency distortion. The injection-pulling phenomenon in oscillator circuits has been also analyzed. Injection pulling by interference signals is an undesired phenomenon in front-end oscillators, which causes a shift of the oscillation frequency and degrades the output spectrum. A semi-analytical formulation for the insightful analysis of injection-pulling phenomena in the presence of a modulated carrier or chirp signal is presented. The formulation enables an efficient analysis of interference problems difficult to simulate with harmonic balance or standard envelope transient. It allows the modification of the original design in order to reduce the injection pulling to the desired levels. The techniques have been applied to an oscillator at 6 GHz. Considering the problems found in commercial software to simulate the phase noise characteristic of coupled oscillator topologies, a numerical technique for the determination of the phase-noise spectrum of free-running oscillators is presented. The technique is based on envelope transient and can be applied to any commercial simulator on which this analysis method is available. The main advantage of the technique is that it allows simulating the near carrier phase noise spectrum, including possible resonances. The elements providing the oscillator phase-noise spectrum are obtained from envelope-transient simulations of low-computational cost. Comparisons are performed between the presented technique and other existing techniques, such as the carrier modulation approach. The technique has been successfully tested on the simulation of the near carrier phase noise spectrum of an oscillator circuit at 6.3 GHz. Finally, a preliminary study has been carried out to combine the use of Volterra series with the envelope transient technique for the simulation of oscillator transients.Regarding the phase-locked loops, in this thesis, harmonic-balance (HB) and envelope-transient formulations of coupled phase-locked loops (CPLLs) are presented. The CPLL has the added difficulty of its autonomous behavior since no reference oscillator is present. The new formulation takes into account the autonomy of the system, introducing a special set of state variables, which depend on the autonomous frequencies. The hysteresis phenomenon in CPLLs is analyzed in detail, efficiently obtaining the pull-in and hold-in ranges through HB. The pole analysis of the perturbed HB system enables an accurate prediction of instabilities and resonances. Due to the CPLL autonomy, there exists an inherent noise accumulation effect. This effect is taken into account, analyzing the perturbation in terms of accumulation and deviation components. The envelope formulation allows simulating the CPLL behavior in presence of modulation signals. The influence of the stability of the steady-state solution on the modulated signals is investigated. The simulation results have been successfully compared with the measurements in a manufactured CPLL system at 2 GHz.
47

Méthodologies de couplage fort des systèmes dynamiques : approches linéaires et non-linéaires

Barillon, Franck 29 March 2011 (has links)
Dans cette thèse, nous nous sommes intéressés au comportement vibratoire d’un véhicule soumis à une excitation moteur dans deux plages de régimes différentes : basses fréquences (0 – 50 Hz) et moyennes fréquences (200 – 800 Hz). Le but était de fournir des méthodologies numériques permettant de prendre en compte les phénomènes de couplage vibratoires existant entre les différents sous-systèmes constitutifs d’une caisse automobile.En basses fréquences, nous avons adopté une approche globale où chaque sous-système a été caractérisé séparément. Tout d’abord, le comportement de la caisse a été caractérisé expérimentalement et numériquement par une méthode jusqu’alors réservée au domaine aéronautique dite d’appropriation modale. Les résultats numériques ont alors été confrontés aux résultats expérimentaux. Par ailleurs, le comportement non-linéaire en amplitude et en fréquence des pièces de filtration moteur (SMO) a été déterminé sur banc de mesure. Un fort comportement non-linéaire a pu être constaté et ces caractérisations ont été exploitées en construisant des nappes raideur-fréquence-amplitude. Dans un second temps, des méthodes numériques permettant de réaliser l’assemblage non - linéaire de la caisse et du groupe moto – propulseur (GMP) via les pièces de filtration non linéaires ont été mises en place. Pour ce faire, nous avons développé une méthode dite de Balance Harmonique (HBM) qui permet de prédire la dynamique non-linéaire de systèmes complexes. Afin d’appliquer cette méthode à une structure industrielle, nous avons utilisé une méthode de condensation sur les degrés de liberté non-linéaires, technique bien adaptée aux cas de structures linéaires reliées localement par des éléments de liaison non-linéaires. Cette méthode a tout d’abord été validée sur un périmètre restreint comprenant un GMP relié à un bâti rigide par ses pièces de filtration. A cette occasion, des phénomènes non-linéaires importants ont été constatés expérimentalement. Un modèle numérique de GMP a été construit et l’utilisation de la méthode HBM a permis de retrouver ces constats. Enfin, après avoir réalisé l’assemblage non-linéaire des trois sous-systèmes GMP - SMO - Caisse, la structure a été excitée de plusieurs manières différentes : appropriation numérique non-linéaire et excitation réelle d’un GMP. En moyennes fréquences, nous avons présenté dans ce mémoire une étude importante pour le groupe Renault concernant la caractérisation des pièces de filtration en moyennes fréquences. Au cours de la thèse, une méthodologie numérique basée sur la méthode FBS permettant de déconfiner (ou découpler) une suspension moteur initialement reliée à un banc de mesure a été proposée. La faisabilité numérique du déconfinement a ainsi été démontrée. Cette méthode permet donc, en dépit de phénomènes de couplage avec le banc de mesure, d’obtenir le comportement vibratoire intrinsèque de la pièce. / In this thesis we studied the vibratory behaviour of a whole vehicle under engine excitation at low frequencies (0 – 50 Hz) and medium frequencies (200 – 800 Hz). The aim of the thesis was to provide numerical methodologies to take into account coupling effects between all the sub-systems constituting a whole car. In low frequencies, we used a global approach where each subsystem was characterized separately before coupling. First the car body was characterised both experimentally and numerically using a modal appropriation method that is commonly used in the aeronautic field. Numerical shapes of the modes were correlated to experimental shapes. In addition, the amplitude and frequency non linear behaviour of the engine mounts was measured on a test bench. A strong non linear behaviour was observed and stiffness – frequency – amplitude layers were constructed based on those data.Secondly, numerical methods were developed in order to calculate the coupled non linear response between the engine, the engine mounts and the car body. We used a harmonic balance method that allows calculating the non linear dynamics of complex mechanical systems. In order to apply this method to large industrial finite element models, a condensation method on non linear degrees of freedom was developed. This technique is well adapted to problems of linear structures linked together with localnon linear joints. This method was validated on the isolated engine linked to a bench by the engine mounts. Strong non linear phenomena on the rigid body modes of the engine were observed experimentally.A numerical model of the engine was developed and the HBM method allowed reproducing these non linear phenomena. Eventually, the non linear model of the whole vehicle was coupled and excited by different efforts. First we calculated the response of the assembly using the appropriation method. Then, the structure was excited by a real four – cylinder engine excitation.In medium frequencies, we presented an important study for the group Renault concerning the stiffness measurement of the engine mounts. A numerical methodology based on the FRF Based Substructuring(FBS) method was developed. This method was applied to uncouple an engine mount initially coupled to a test bench. The numerical feasibility of the method was proved and allowed to get the own vibratory behaviour of the engine mount despite coupling phenomena with the test bench.
48

Computational modeling and design of nonlinear mechanical systems and materials

Tang, Pengbin 03 1900 (has links)
Les systèmes et matériaux mécaniques non linéaires sont largement utilisés dans divers domaines. Cependant, leur modélisation et leur conception ne sont pas triviales car elles nécessitent une compréhension complète de leurs non-linéarités internes et d'autres phénomènes. Pour permettre une conception efficace, nous devons d'abord introduire des modèles de calcul afin de caractériser avec précision leur comportement complexe. En outre, de nouvelles techniques de conception inverse sont également nécessaires pour comprendre comment le comportement change lorsque nous modifions les paramètres de conception des systèmes mécaniques non linéaires et des matériaux. Par conséquent, dans cette thèse, nous présentons trois nouvelles méthodes pour la modélisation informatique et la conception de systèmes mécaniques non linéaires et de matériaux. Dans le premier article, nous abordons le problème de la conception de systèmes mécaniques non linéaires présentant des mouvements périodiques stables en réponse à une force périodique. Nous présentons une méthode de calcul qui utilise une approche du domaine fréquentiel pour la simulation dynamique et la puissante analyse de sensibilité pour l'optimisation de la conception afin de concevoir des systèmes mécaniques conformes avec des oscillations de grande amplitude. Notre méthode est polyvalente et peut être appliquée à divers types de systèmes mécaniques souples. Nous validons son efficacité en fabriquant et en évaluant plusieurs prototypes physiques. Ensuite, nous nous concentrons sur la modélisation informatique et la caractérisation mécanique des matériaux non linéaires dominés par le contact, en particulier les matériaux à emboîtement discret (DIM), qui sont des tissus de cotte de mailles généralisés constitués d'éléments d'emboîtement quasi-rigides. Contrairement aux matériaux élastiques conventionnels pour lesquels la déformation et la force de rappel sont directement couplées, la mécanique des DIM est régie par des contacts entre des éléments individuels qui donnent lieu à des contraintes de déformation cinématique anisotrope. Pour reproduire le comportement biphasique du DIM sans simuler des structures à micro-échelle coûteuses, nous introduisons une méthode efficace de limitation de la déformation anisotrope basée sur la programmation conique du second ordre (SOCP). En outre, pour caractériser de manière exhaustive la forte anisotropie, le couplage complexe et d'autres phénomènes non linéaires du DIM, nous introduisons une nouvelle approche d'homogénéisation pour distiller des limites de déformation à grande échelle à partir de simulations à micro-échelle et nous développons un modèle macromécanique basé sur des données pour simuler le DIM avec des contraintes de déformation homogénéisées. / Nonlinear mechanical systems and materials are broadly used in diverse fields. However, their modeling and design are nontrivial as they require a complete understanding of their internal nonlinearities and other phenomena. To enable their efficient design, we must first introduce computational models to accurately characterize their complex behavior. Furthermore, new inverse design techniques are also required to capture how the behavior changes when we change the design parameters of nonlinear mechanical systems and materials. Therefore, in this thesis, we introduce three novel methods for computational modeling and design of nonlinear mechanical systems and materials. In the first article, we address the design problem of nonlinear mechanical systems exhibiting stable periodic motions in response to a periodic force. We present a computational method that utilizes a frequency-domain approach for dynamical simulation and the powerful sensitivity analysis for design optimization to design compliant mechanical systems with large-amplitude oscillations. Our method is versatile and can be applied to various types of compliant mechanical systems. We validate its effectiveness by fabricating and evaluating several physical prototypes. Next, we focus on the computation modeling and mechanical characterization of contact-dominated nonlinear materials, particularly Discrete Interlocking Materials (DIM), which are generalized chainmail fabrics made of quasi-rigid interlocking elements. Unlike conventional elastic materials for which deformation and restoring forces are directly coupled, the mechanics of DIM are governed by contacts between individual elements that give rise to anisotropic kinematic deformation constraints. To replicate the biphasic behavior of DIM without simulating expensive microscale structures, we introduce an efficient anisotropic strain-limiting method based on second-order cone programming (SOCP). Additionally, to comprehensively characterize strong anisotropy, complex coupling, and other nonlinear phenomena of DIM, we introduce a novel homogenization approach for distilling macroscale deformation limits from microscale simulations and develop a data-driven macromechanical model for simulating DIM with homogenized deformation constraints.

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