Dissertations / Theses: 'Non smooth contact dynamics'

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Hedman, Stefan. "Smooth and non-smooth approaches to simulation of granular matter." Thesis, Umeå universitet, Institutionen för fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-50584.

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Granular matter is defined as a collection of particle grains, such as sand.This type of matter have different characteristics (solid, liquid and gas) depending on the energy level per grain. There are several approaches to modeling and numerical simulations of granular matter. They are used by different groups for different purposes, and the choice between the approaches is based on knowledge and tradition rather than what might be best for the purpose. The key questions are when to use what method and what physical quality is lost depending on the choice.Two regimes of discrete element granular simulations emerge: smooth and non-smooth. To compare the efficiency and physical quality of the two approaches, four physics softwares are examined including Bullet Physics, LMGC90, AgX and LIGGGHTS. Test scenes are setup in each software and the results are compared to each other or to the results of other work.The thesis is performed at UMIT Research Lab at Umeå University.

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Lapillonne, Suzanne. "Modélisation multi-échelles des laves torrentielles avec un modèle numérique couplé solide-fluide." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALI034.

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Les laves torrentielles sont des phénomènes géologiques d'écoulement rapides d'un mélange fluide solide dans le lit d'un torrent. Le risque associé à ces écoulements est important pour les communautés vivant dans les régions montagneuses. Pour améliorer la précision de la gestion du risque, il est important de pouvoir modéliser ces phénomènes de façon précise. Bien que la communauté de recherche autour des laves torrentielles soit enthousiaste aux approches numériques, seulement quelques modèles ont calibré et validé leurs modèles à plusieurs échelles en utilisant des données de terrains et des données expérimentales. Cette thèse vise à conceptualiser un modèle qui est à l'interface de la communauté des modélisateurs et de celle des experts de terrains. Pour ce faire, des données de terrains sont utilisées pour calibrer et valider un modèle précis et résolu dans la hauteur couplant à la fois un solveur de mécanique granulaire et de mécanique des fluides. Le modèle numérique utilise le solveur DualSPHysics, qui couple la méthode Smoothed Particles Hydrodynamics (SPH) avec une méthode de résolution des interactions solide-solide par la librairie ProjectChrono.Le travail présente d'abord une introduction avec un état de l'art de la recherche sur les laves torrentielles ainsi qu'une présentation de la méthode numérique employée. Ensuite, le travail est divisé en trois chapitres. Premièrement, un protocole pour l'exploration des données de terrains est présenté, de même que son application sur le torrent du Réal (Sud-Est de la France). Les données ainsi produites nourriront le modèle numérique. Dans un deuxième temps, nous présentons un modèle simplifié 2D de laves. Les laves y sont présentées comme un mélange de grains polydisperse et de fluide visqueux au comportement Newtonien. Ce modèle est d'abord validé à plusieurs échelles puis des laves de différentes concentrations solides sont étudiées. Enfin, un modèle plus complexe est ébauché en employant un fluide interstitiel non-Newtonien. Le travail montre que ce type de modèle est adapté pour l'exploration de la physique des laves
Debris flows, i.e. rapid movements of a mixture of solid and fluid on steep terrain, pose significant risks to inhabited mountainous areas. Accurate modelling is crucial for effective risk mapping and to define relevant mitigation strategies in these regions. While there's enthusiasm in the community for debris flow modelling, only few models have used surge-scale data from real field measurements for calibration and validation at various scales. This Ph.D. thesis aims to conceptualise a field-driven coupled solid-fluid model for alpine debris flow surges at the surge scale. The numerical modelling in this study employs the hybrid model DualSPHysics, which uses the Lagrangian Smoothed Particles Hydrodynamics (SPH) method for fluid modelling and fully couples it with the solid dynamics solver ProjectChrono.After an introduction of the state-of-the-art in debris flow research and a presentation of the numerical methods, the work is divided in three interlocked sections. First, we focus on field data exploration by presenting a protocol for the processing of debris flow surge data. The outputted data on debris flow surges, processed from the monitoring station of the Réal torrent (South East France) will then feed the numerical model.Secondly, a simplified model is introduced. The front of the surges are represented in 2D featuring polydisperse boulders and a viscous Newtonian fluid. The model is rigorously validated against experimental data and empirical considerations.Thirdly, the model increases in complexity by adding a non-Newtonian rheology to the interstitial fluid.The work shows that such models are able to represent debris flow motion with field-like features

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Phan, Thanh-Luong. "Etude des structures en maçonnerie du génie civil par la méthode des éléments discrets : apports de la méthode "Non Smooth Contact Dynamics"." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS243.

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La maçonnerie est une technique de construction très ancienne qui est toujours d'utilisation très répandue sous toutes les latitudes. Elle fait appel à deux éléments essentiels : des blocs et des joints, qui peuvent être éventuellement remplis de mortier. Le matériau obtenu peut être considéré comme continu ou discontinu, selon les propriétés relatives des blocs et des joints. Les blocs sont souvent en pierre, en brique crue ou cuite. Les mortiers sont généralement à base de chaux, de ciment ou d'un mélange de ces deux composants. Depuis l'apparition du béton au XIX° siècle, les calculs se sont concentrés sur des approches continues, et les techniques de conception des maçonneries ont peu bénéficié des avancées scientifiques, et du développement d'outils de calcul largement utilisés dans les bureaux d'études. Corrélativement à cette évolution, la maçonnerie a perdu des parts de marché de la construction, et les méthodes et moyens mis en œuvre pour la conception d'ouvrages en maçonnerie n'ont pas été suffisamment modernisés. Dans ce contexte, le présent travail a pour ambition de contribuer au calcul de structures maçonnées, considérées comme des structures discontinues, avec l'objectif de servir au monde de l'entreprise et de l'architecture.L'échelle d'étude de la structure ou du matériau : comportement général de l'ensemble bâti, comportement d'un panneau de maçonnerie, comportement de l'interface mortier - bloc, ou des contacts blocs-blocs dans le cas de maçonnerie à joints vifs, conduit à l'utilisation de divers cadres théoriques, et méthodes analytiques ou numériques correspondantes. Après une analyse des avantages et inconvénients de diverses méthodes disponibles, numériques ou graphiques, dans le domaine de la mécanique et de l'architecture (stéréotomie), nous présentons en détail la méthode Non Smooth Contact Dynamics. Cette méthode, initiée à la fin du XX° siècle, par Jean-Jacques MOREAU et Michel JEAN, décrit de façon théorique, les conditions de mise en place des efforts de contact entre corps solides, déformables ou rigides, en 2D et 3D, en présence de chocs, et en présence de grands déplacements, ou rotations. Les conditions de non interpénétration entre corps sont régies par un formalisme spécialement développé dans le cadre de l'analyse convexe. Nous avons retenu ce cadre théorique, et utilisé une chaine logicielle développée sur ses bases, pour modéliser des structures réalistes, c'est-à-dire tridimensionnelles, soumises à des chargements dynamiques, et qui sont modernes, dans la mesure où elles intègrent une géométrie complexe, performante (économie de matière et esthétique) et la mise en œuvre d'une précontrainte, avec prise en compte de son phasage.L'exemple de la structure de l'escalier de Ridolfi est utilisé comme support à l'examen de divers paramètres d'optimisation du calcul réalisé avec la plateforme ouverte LMGC90, permettant à l'utilisateur de maîtriser en détail les diverses phases du calcul non-linéaire conduit. Les paramètres du calcul dont nous avons testé l'influence sont : le pas de temps, le critère de convergence, le nombre d'itérations gérées par l'algorithme de Gauss-Seidel, le critère de rétrécissement, le coefficient de frottement entre blocs, et l'intensité de la précontrainte mise en place par post tension dans les câbles. L'expérimentation conduite sur un modèle physique en vraie grandeur, est reconstituée, dans ses différentes phases, sur maquette numérique, et la pertinence des résultats obtenus par simulation est discutée.Les travaux ont été réalisés au Laboratoire de Mécanique et Génie Civil de l'Université Montpellier II et du CNRS, et au Laboratoire de Génie de l'Environnement Industriel de l'Ecole des Mines d'Alès. Leur financement a été assuré par le Ministère de l'Education et de la Formation du Vietnam, ainsi que par ARMINES
Although it is an old construction technique, masonry is still world wide spread nowadays. It uses two main components: blocks and joints, which can be filled with mortar. The resulting material can be considered as continuous or discontinuous, according to the relative performances of the blocks and joints. The blocks are often made of stone, raw earth or brick. The mortars generally incorporate lime or cement or a mixture of those components. Since the discovery of modern concrete during the XIXth century, calculations have been performed in the framework of continuous methods, and the masonry design technics have not fully benefited from the scientific breakthrough, nor from the development of calculation tools used in design offices. Following this evolution, masonry lost some ground in the construction field, and methods and means used for the design of buildings have not been improved enough. In this context, the present work aims at contributing to the calculation of masonry structures, considered as discontinuous structures, with the ultimate goal to be of some use in the field of industry and architecture.The structure or material study scale: general behavior of the building, behavior of a masonry panel, or behavior of the bonding between the blocks and the mortar, or the block-block contacts for dry friction masonry, leads to the use of several theoretical frameworks, and associated analytical or numerical methods. After an analysis of the pros and cons of the different available methods, in the fields of mechanics and architecture (stereotomy), we will present in detail the Non Smooth Contact Dynamics method. This method, initiated at the end of the XXth century, by Jean-Jacques MOREAU et Michel JEAN, describes theoretically, the conditions of the development of contact forces between solids, whether able to support strains or rigid, in 2D or 3D, under the effects of shocks, large displacements or rotations. The conditions of no overlapping between the bodies are described by equations developed using the convex analysis concepts. We chose this theoretical framework, and used the software platform developed on these concepts, for modeling realistic structures that are modern, because they allow to take into account 3D structures with complex and efficient geometries (aesthetic point of view, economy of material), subjected to dynamical loads, and including the sequential set-up of pre-stressing technics.The example of the Ridolfi stair case is used as a support for the examination of several optimization parameters for the calculation performed on the LMGC90 open software, allowing the modeler to supervise in detail several steps of the performed non-linear calculations. The calculation parameters of which we have tested the influence are: the time step, convergence criterion, the iteration number considered in the Gauss-Siedel algorithm, the shrinkage criterion, the friction coefficient between blocks, and the pre-stressing strain applied in the post tension cables. The experiment carried out on a real size physical model is numerically simulated, and the consistency of the computed results is discussed.The work was carried out in the Mechanics and Civil Engineering Laboratory of the University of Montpellier II and the CNRS (French National Scientific Research Agency), and the Laboratory of Industrial Environment Engineering of Alès School of Mines. The funding was provided by the Ministry of Education and Training of Vietnam, and ARMINES

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Martin, Sylvain. "Contribution à la modélisation du frittage en phase solide." Thesis, Compiègne, 2014. http://www.theses.fr/2014COMP2144/document.

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Cette thèse traite de la modélisation du frittage à l’échelle du Volume Élémentaire Représentatif de la pastille de matériau. L’objectif est de développer des outils numériquesde compréhension des phénomènes physiques mis en jeu lors du frittage. Le domaine d’application ciblé est la fabrication du combustible nucléaire. Une approche multi-Échelle a été mise en oeuvre. Dans un premier temps une modélisation à l’échelle d’un empilement, basée sur la méthode des Éléments Discrets, a été adoptée. Différentes études utilisant cette approche ont été proposées dans la littérature ces dernières années. Tous ces travaux utilisent une méthode discrète explicite. Si certains résultats ont pu être validés expérimentalement,une des limites vient de l’utilisation des méthodes explicites dontle pas de temps critique est très petit. Afin d’augmenter le pas de temps, la masse des particules y est augmentée artificiellement de plusieurs ordres de grandeur. Or,il a été démontré que cette pratique conduit, dans certains cas, à une diminution du réarrangement des particules au sein de l’empilement. Dans cette thèse, une méthode Éléments Discrets implicite appelée Dynamique des Contacts a été adaptée au frittage. Elle permet l’utilisation d’un pas de temps très supérieur à celui des méthodes discrètes explicites et ne nécessite pas d’augmenter artificiellement la massedes particules. La comparaison entre la Dynamique des Contacts et la Méthode des Éléments Discrets explicite montre que notre approche conduit à une représentation plus fidèle du réarrangement. Une validation expérimentale par Microtomographie X ainsi qu’une étude paramétrique sur le frittage des poudres bidispersés sont également présentées pour montrer les possibilités de l’approche discrète appliquée au frittage.La seconde partie est consacrée à une modélisation à l’échelle de deux particules parla méthode des Éléments Finis. Ce modèle repose sur une approche mécanique et vise à représenter de façon plus précise le comportement de deux particules en contact. Les diffusions au joint de grains, en surface et en volume peuvent être représentées. Pour le moment, seules les diffusions en surface et au joint de grains ont été étudiées. Si certaines optimisations restent nécessaires pour que le code soit fonctionnel, plusieurs aspects apparaissent déjà déterminants, comme la courbure de la surface à proximité du joint de grains. A l’avenir, le modèle Dynamique des Contacts du frittage pourra être complété etamélioré grâce aux éléments apportés par le modèle mécanique à l’échelle du grain
This thesis deals with the simulation of the sintering of nuclear fuel on a pellet scale. The goal is to develop numerical tools which can contribute to a better understandingof the physical phenomena involved in the sintering process. Hence, a multi scale approach is proposed. First of all, a Discrete Element model is introduced. It aims at modeling the motion of particles on a Representative Elementary Volume scale using an original Discrete Element Method. The latter is a Non Smooth Method called Contact Dynamics. Recently, there have been numerous papers about the simulation of sintering using Discrete Element Method. As far as we know, all these papers use smooth methods. Different studies show that the results match well experimental data. However, some limits come from the fact that smooth methods use an explicit scheme which needsvery small time steps. In order to obtain an acceptable time step, the mass of particles have to be dramatically increased. The Non Smooth Contact Dynamics uses an implicit scheme, thus time steps can be much larger without scaling up the mass of particles. The comparison between smooth and non smooth approaches shows thatour method leads to a more realistic representation of rearrangement. An experimental validation using synchrotron X-Ray microtomography is then presented, followedby a parametric study on the sintering of bimodal powders that aims at showing the capacity of this model.The second part presents a mechanical model on the sub-Granular scale, using a Finite Element method. This targets a better understanding of the behavior of twograins in contact. The model is currently being developped but the first results already show that some parameters like the shape of the surface of the neck are very sensitive.In the future, the Non smooth Contact Dynamics model of sintering may be improvedusing the results obtained by the sub-Granular scale mechanical model

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Nhu, Viet-Hung. "Dialogues numériques entre échelles tribologiques." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0043/document.

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En tribologie, la modélisation numérique est aujourd'hui un outil indispensable pour étudier un contact afin de pallier les limites expérimentales. Pour comprendre de mieux en mieux les phénomènes mis en jeu, les modèles ne se situent plus à une seule échelle, mais en font intervenir plusieurs, rendant plus que jamais le concept de triplet tribologique incontournable. Travaillant avec cette philosophie et en se basant sur l'approche Non Smooth Contact Dynamics, dont nous rappelons les grandes lignes, nous proposons de franchir deux cas: proposer des modèles offrant des résultats quantitatifs et mettre en place les premières pièces d'une homogénéisation au niveau du contact (VER). Dans le premier cas, l'étude du couplage éléments finis/éléments discrets au sein d'une même simulation a pour but de proposer des modèles plus "réalistes". Même si l’interface utilisée est déjà présente au coeur du contact et ne va pas évoluer, elle permet de mettre en évidence l’utilisation d’outil de mesure permettant de lier le mouvement des particules aux instabilités dynamiques et permet d’avoir des résultats qualitatifs mais aussi quantitatifs puisque la comparaison avec les taux de contraintes expérimentaux sont en très bonne adéquation. Dans le second cas, le VER sous sollicitations tribologiques est étudié afin d'étendre les techniques d'homogénéisation aux problèmes de contact afin de s'affranchir de la description des interfaces aux grandes échelles en trouvant un moyen d'homogénéiser le comportement hétérogène de l'interface et de le faire dialoguer avec le comportement continu des corps en contact en faisant remonter, dans un sens, des grandeurs moyennées à l'échelle microscopique à l'échelle macroscopique des premiers corps et dans l'autre sens, se servir des données locales à l'échelle macroscopique comme conditions limites à l'échelle microscopique
In tribology, the numerical modeling has become an indispensable tool for studying a contact to overcome the experimental limitations. To have a better understanding of the phenomena involved, the models are no longer located at a single scale, but involve several ones, more than ever, making the concept of tribological triplet as a unavoidable concept. Working with this philosophy and approach based on the Non Smooth Contact Dynamics framework, which we remind some outlines, we propose to cross two steps~: model that can offer quantitative results and that implement the first ingredient to perform a homogenization at a contact level. In the first case, the study of coupling finite elements/discrete elements within the same simulation aims to propose models that are more "realistic". Even if the interface is already present in the contact and not going to evolves, it can highlight the use of measurement tool of spot particles via dynamic instabilities and allows to have not only qualitative results but also quantitative ones since the comparison with the experimental strain rates are in very good agreement. In the second case, the study of VER in tribological charges is performed to extend the homogenization techniques to contact problems in order to overcome the interface description on large scales by finding a way to homogenize the heterogeneous behavior of the interface and make a dialogue with the continue behavior of bodies in contact by send up, in a sense, average values of the microscopic scale to the macroscopic scale and in the other sense, use local data of the macroscopic scale as boundary conditions at the microscopic scale

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Cao, Hong-Phong. "Modélisation par éléments discrets rigides et/ou déformables des milieux granulaires et des troisièmes corps solides : Influence du comportement local sur le comportement global." Thesis, Lyon, INSA, 2011. http://www.theses.fr/2011ISAL0045/document.

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Les Méthodes par Eléments Discrets apparaissent comme les méthodes les plus appropriées pour modéliser le caractère divisé. De nombreux travaux ont permis de mieux comprendre leurs comportements, mais dans certain cas se pose la question de l'impact du choix de la description volumique ou des lois d'interaction sur le comportement global du milieu. Dans ce contexte, en se basant sur l'approche "Non Smooth Contact Dynamic" permettant naturellement de mixer les différentes formulations, nous nous proposons de comprendre et d'analyser l'influence de cette description. Pour cela, nous utilisons deux applications différentes liées aux comportement quasi-statique (QS) des milieux granulaires et comportement dynamique des interfaces tribologiques. Au niveau de l'étude QS est faite en utilisant des essais de compression biaxiale et de cisaillement. Contrairement aux approches classiques, des particules déformables sont utilisées ici. Les résultats obtenus sont comparés en utilisant des outils de mesure tels que la relation contrainte-déformation, la compacité... Les résultats montrent qu'il n'est pas possible à partir d'une description rigide de converger vers des modèles déformables et souligne l'importance d'effectuer une analyse complète en tenant compte de la déformation des particules. Au niveau de la modélisation d'une interface tribologique s'intéresse à l'influence des conditions limites, des descriptions des premiers corps et du troisième corps sur la rhéologie de l'interface. Dans chaque simulation, frottement macroscopique, profils de vitesse et de contrainte sont observés. Les différents modèles utilisés ont peu d'influence sur la valeur du frottement mais plus d'influence sur les profils de vitesse au travers de l'épaisseur de troisième corps. Ceci souligne l'importante du choix du modèle lors de l'étude de la rhéologie de l'interface et montre qu'il est difficile d'obtenir des résultats génériques et ceci aussi bien en modèles bi que tridimensionnel
The Discrete Element Methods are the most appropriate methods to model the divided feature of some media such as granular ones, masonries or contact interfaces... Many studies have provided a better understanding of their behavior, but in some cases the impact of both volume description (rigid or deformable) and interaction laws (elastic or plastic) is not negligible on the global behavior. The approach used here is based on the "Non Smooth Contact Dynamic" framework which mixes naturally the rigid and deformable formulations. One propose to analyze the influence of this description. For this purpose, two different applications are used, related to the quasi-static behavior of granular media and to the modelization of the tribological interface under dynamic solicitations.The study of quasi-static behavior of granular media is developed though biaxial compression test and shear test. Contrary to classical approaches, deformable particles are used. The results are compared using tools such as the stress-strain macroscopic relation, the compacity... They show that it is not possible to converge to deformable particle with a rigid description and underline the importance to performance full analyze with deformable description.The modeling of a tribological interface under dynamic solicitation focuses on the influence of boundary conditions, models of the first bodies and the third body on the rheology of the interface. In each simulation, the macroscopic friction, the velocity profile and stress profile are observed. The different models used have not a large influence on the friction value but a large influence on the velocity profiles. This underline the importance of the choice of the model when investigation are performed on the rheology of the third body

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Nhu, Viet Hung. "Dialogues numériques entre échelles tribologiques." Phd thesis, INSA de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-00876855.

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En tribologie, la modélisation numérique est aujourd'hui un outil indispensable pour étudier un contact afin de pallier les limites expérimentales. Pour comprendre de mieux en mieux les phénomènes mis en jeu, les modèles ne se situent plus à une seule échelle, mais en font intervenir plusieurs, rendant plus que jamais le concept de triplet tribologique incontournable. Travaillant avec cette philosophie et en se basant sur l'approche Non Smooth Contact Dynamics, dont nous rappelons les grandes lignes, nous proposons de franchir deux cas: proposer des modèles offrant des résultats quantitatifs et mettre en place les premières pièces d'une homogénéisation au niveau du contact (VER). Dans le premier cas, l'étude du couplage éléments finis/éléments discrets au sein d'une même simulation a pour but de proposer des modèles plus "réalistes". Même si l'interface utilisée est déjà présente au coeur du contact et ne va pas évoluer, elle permet de mettre en évidence l'utilisation d'outil de mesure permettant de lier le mouvement des particules aux instabilités dynamiques et permet d'avoir des résultats qualitatifs mais aussi quantitatifs puisque la comparaison avec les taux de contraintes expérimentaux sont en très bonne adéquation. Dans le second cas, le VER sous sollicitations tribologiques est étudié afin d'étendre les techniques d'homogénéisation aux problèmes de contact afin de s'affranchir de la description des interfaces aux grandes échelles en trouvant un moyen d'homogénéiser le comportement hétérogène de l'interface et de le faire dialoguer avec le comportement continu des corps en contact en faisant remonter, dans un sens, des grandeurs moyennées à l'échelle microscopique à l'échelle macroscopique des premiers corps et dans l'autre sens, se servir des données locales à l'échelle macroscopique comme conditions limites à l'échelle microscopique.

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Di, Stasio Jean. "The CD-Lagrange scheme, a robust explicit time-integrator for impact dynamics : A new singular mass formulation, and an extension to deformable-deformable contact." Thesis, Lyon, 2021. http://www.theses.fr/2021LYSEI029.

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Les pneumatiques sont complexes à simuler car les matériaux y sont hétérogènes, incompressibles et non-linéaires. De plus la géométrie descend jusqu’à l’échelle millimétrique pour les sculptures de la bande de roulement, ce qui requiert un maillage fin. Le modèle éléments finis présente donc un grand nombre de degrés de liberté, reliés par des équations non-linéaires. En dynamique, la simulation est d’autant plus compliquée avec des chocs. Néanmoins elle est cruciale dans le processus de conception pneumatique, où elle apporte une meilleur compréhension de la physique ceci sans tests réels. Les schémas explicites rendent possible les simulations de chocs, car ils résolvent facilement les non-linéarités avec un coup calcul bas. Associés à une formulation de contact précise , ils forment des schémas robustes, précis et efficaces pour la dynamique non-linéaire avec impacts. Ce travail vise à choisir et un tel schéma, et l’améliorer pour la simulation de chocs sur pneumatiques.La première partie est un benchmark identifiant le schéma CD-Lagrange. L’intégration temporelle est réalisée par le schéma de la différence centrée, et le contact imposé par multiplicateurs de Lagrange sur la vitesse. Deux possibilités d’amélioration sont identifiées. La première est d’atteindre un impact conservatif, seul instant où le schéma n’est pas symplectique. La seconde amélioration est d’étendre la formulation au contact déformable-déformable.La deuxième partie vise à atteindre la conservation de l’énergie à l’impact en adaptant la méthode de la masse singulière au CD-Lagrange. Une première formulation 1D est construite. Elle démontre une amélioration majeure du bilan d’énergie. Deux formulations 3D sont ensuite explorées.La troisième partie introduit les méthodes mortier dans le CD-Lagrange. Elles permettent de traiter un contact déformable-déformable de manière robuste, même en présence de friction et de grands glissements. Une technique d’accélération est proposée pour résoudre le problème de contact, ceci sans perte de précision
Tyres are complex structures to simulate. The materials are heterogeneous and incompressible with non-linear responses. The geometry goes to the millimetre scales for tread patterns. For a finite elements simulation a precise mesh is then required. The model has then a large number of degrees of freedom and non-linear material laws. In dynamics, the simulation becomes even more challenging especially with impacts. Nevertheless it is crucial in the tire design process because it brings a deeper comprehension of the tire and avoids test on real structures. The explicit time-integration make feasible the impact simulations. They handle easily the non-linearities with a very low computational cost for a time-step. Merged with a precise contact formulation, they form robust, accurate and efficient schemes for addressing impact simulations. This work aims to choose and improve an explicit scheme for non-linear dynamics with impacts. The first part is a benchmark for selecting a scheme and enhance its possibilities of improvement. The selected one is the CD-Lagrange: an explicit scheme based on central difference method, a contact enforcement by Lagrange multipliers, and a contact condition on velocity. Two mains improvements are identified and explored. Firstly, the energy conservation at impact would make the scheme symplectic for deformable bodies. Secondly the formulation must be enlarged to deformable–deformable contact. The second part aims then to achieve the conservation of energy by adapting the singular mass matrix to the CD-Lagrange. The formulation is firstly built in 1D, and shows a major improvement for the energy balance. Then two possible extensions are explored for the 3D cases. The third part presents the CD-Lagrange scheme with a mortar formulation for deformable-deformable contact. It handles with stability and accuracy large sliding and friction. An acceleration technique is proposed for solving the contact problem, without any loss of accuracy

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FERRANTE, ANGELA. "Computational strategies for discrete modeling of Cultural Heritage structures." Doctoral thesis, Università Politecnica delle Marche, 2021. http://hdl.handle.net/11566/287778.

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Lo scopo di questo lavoro di ricerca è presentare lo sviluppo di approcci discontinui e l'influenza della stereotomia per simulare il comportamento dinamico non lineare di strutture storiche in muratura di grandi dimensioni. Gli obiettivi sono quindi le valutazioni qualitative e quantitative dei diversi approcci esistenti e delle principali leggi costitutive, l'analisi e la calibrazione dei parametri meccanici e fornire forti indicazioni sul miglior livello di discretizzazione necessario per questo tipo di approcci. Pertanto, lo studio prevede l'utilizzo di schemi di integrazione temporale implicita ed esplicita per la dinamica strutturale, rispettivamente nel metodo della Dinamica di Contatto Non Regolare e Modello di Zona Coesiva implementati nel codice LMGC90©, dove i moti di scorrimento sono governati dalla condizione di impenetrabilità di Signorini e dalla legge di attrito di Coulomb, e nel Metodo degli Elementi Discreti con comportamenti coesivi e di resistenza a trazione dei giunti nel codice 3DEC©. Una serie di casi studio di strutture esistenti è stata rappresentata adottando quattro diversi modelli geometrici che andavano da quello più complesso, comprese le pareti in muratura a geometria piena e disordinata (a sacco), a quello più semplice, includendo le murature con singolo paramento come semplificazione delle opere murarie esistenti. I risultati numerici hanno evidenziato le modalità di cedimento dipendenti dalla forma, dimensione e tessitura della muratura e le modalità di danneggiamento progressivo sotto azioni dinamiche. Inoltre, gli approcci numerici presentati si sono dimostrati in grado di simulare grandi spostamenti e separazioni complete di blocchi, riprodurre comportamenti meccanici complessi e fare previsioni sulla valutazione di vulnerabilità degli edifici storici in muratura. I risultati discussi sono positivi e preziosi nell'ottica della preservazione del patrimonio culturale da danni futuri proponendo linee guida per il rinforzo e l'adeguamento sismico delle strutture.
The aim of this research work is to present the development of discontinuous approaches and the influence of stereotomy to simulate the nonlinear dynamic behavior of historical large-scale masonry structures. Thus, the objectives are the qualitative and quantitative evaluations on the different existing approaches and the main constitutive laws, the analyses and calibration of mechanical parameters, and providing strong indications on the best level of discretization needed for these kinds of approaches. Thus, the study involves the use of implicit and explicit time integration schemes for structural dynamics, respectively in the Non-Smooth Contact Dynamics method and Cohesive Zone Model implemented in the LMGC90© code, where sliding motions are governed by Signorini's impenetrability condition and dry-friction Coulomb's law, and in the Discrete Element Method with cohesive and tensional behaviors at the joints in the 3DEC© code. A set of case studies from real structures was represented adopting four different geometric models ranged from the most complex one, including the full geometry and multi-leaf masonry walls, to the simplest one, including the single-leaf walls as a simplification of the real masonry. The numerical results highlighted the failure modes depending on the shape, size and texture of the masonry and the modalities of progressive damage under dynamic actions. Moreover, the numerical approaches presented have proven to be capable of simulating large displacements and complete block separations, reproducing complex mechanical behaviors and making predictions on the vulnerability assessment of the historical masonry buildings. The results discussed are successful and valuable in view of preservation of the cultural heritage from future damages proposing guidelines for strengthening and seismic retrofitting of structures.

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Barton, David A. W. "Dynamics and bifurcations of non-smooth delay equations." Thesis, University of Bristol, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432681.

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Lamba, Harbir. "Impacting oscillators and non-smooth dynamical systems." Thesis, University of Bristol, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385474.

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Wiercigroch, Marian. "Engineering Dynamics of Non-Smooth Systems: Modelling, Analysis and Experimental Studies." Thesis, University of Aberdeen, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485669.

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Abstract. In this thesis we study the non-smoothness dynamical systems using a suite of numerical, analytical and experimental methods. First the concept of non-smoothness is introduced by dividing the global space into a finite number of smooth subspaces. If a dynamical system is linear in all these subspaces then an implicit global analytical solution can be given providing the time occurrences of non-smoothness are determined. Mathematically this leads to a set of strongly nonlinear algebraic equations. To illustrate the concept and demonstrate the methodology of solving the non-smooth dynamical systems, four different engineering problems are studied theoretically and on purpose built experimental rigs. Firstly, the impacting and frictional oscillators are investigated and the [mdings are used to study two engineering systems: ground moling and percussive ultrasonic drilling of hard materials. The governing dynamics is analysed and the results are used to maximise the progression rates. The second example comes from rotordynamics, where the nonlinear interactions between a rotor and its snubber ring are investigated. The results obtained from the developed mathematical model confronted with the experiments shown good correlation. The non-smoothness in the third problem relates to the opening and closing of a fatigue crack. In this study a novel fatigue testing rig was built and its mathematical model was developed. The results from the theoretical modelling correlate well with the experimental [mdings. In the last application, the dynamics of metal cutting focusing on the frictional chatter is investigated. It has been shown that the bifurcation analysis can be instrumental in choosing the system parameters to avoid chatter. The list of references includes the major works in the area followed by the publications constituting this thesis.

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Wang, Zhaoxin. "Dynamics of Mechanical System Involving Conformal and Non-conformal Contact." OpenSIUC, 2010. https://opensiuc.lib.siu.edu/theses/222.

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Effective prediction of mechanical system response containing rough surface contact requires a multi-scale modeling approach. A mechanical system model may involve a Finite Element (FE) or Lumped Parameter (LP) method. In either case the model must be capable of accounting for at least two scales. The macro-scale behavior, including metric or sub-metric, such as centimeter and millimeter scales, and micron-scale accounting for the surface roughness effects must be included simultaneously. It is the objective of this research to facilitate the multi-scale modeling of mechanical system containing rough surface contact, by developing approximate equation for contact of rough surfaces and demonstrating the inclusion of the approximate equations in FE and LP models of mechanical systems. The Approximate equations for conformal and non-conformal rough surfaces in contact are derived. The approximate equations constitute contact force-displacement equations based on statistical account of interaction between rough surfaces. The force-displacement relations are implemented in an FE model of a circular washer in a bolted joint, including the surface roughness effects. The equations also serve to account for the effect of roughness in the vibration interaction of a wavy surface with a nominally flat surface.

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Nguyen, Vincent. "Dynamics and Control of Non-smooth Systems with Applications to Supercavitating Vehicles." UNIVERSITY OF MARYLAND, COLLEGE PARK, 2012. http://pqdtopen.proquest.com/#viewpdf?dispub=3478974.

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Chong, Antonio. "Numerical modelling and stability analysis of non-smooth dynamical systems vie ABESPOL." Thesis, University of Aberdeen, 2016. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=231038.

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Hoang, Thi Minh Phuong. "Optimisation des temps de calculs dans le domaine de la simulation par éléments discrets pour des applications ferroviaires." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2011. http://tel.archives-ouvertes.fr/tel-00726199.

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La dégradation géométrique de la voie ballastée sous circulation commerciale nécessite des opérations de maintenance fréquentes et onéreuses. La caractérisation du comportement des procédés de maintenance comme le bourrage, la stabilisation dynamique, est nécessaire pour proposer des améliorations en terme de méthode, paramétrage pour augmenter la pérennité des travaux. La simulation numérique d'une portion de voie soumise à un bourrage ou une stabilisation dynamique permet de comprendre les phénomènes physiques mis en jeu dans le ballast. Toutefois, la complexité numérique de ce problème concernant l'étude de systèmes à très grand nombre de grains et en temps de sollicitation long, demande donc une attention particulière pour une résolution à moindre coût. L'objectif de cette thèse est de développer un outil de calcul numérique performant qui permet de réaliser des calculs dédiés à ce grand problème granulaire moins consommateur en temps. La méthodologie utilisée ici se base sur l'approche Non Smooth Contact Dynamics (NSCD) avec une discrétisation par Éléments Discrets (DEM). Dans ce cadre, une méthode de décomposition de domaine (DDM) alliée à une parallélisation adaptée en environnement à mémoire partagée utilisant OpenMP sont appliquées pour améliorer l'efficacité de la simulation numérique.

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Lee, Gordon. "The theoretical and numerical analysis of impact oscillators." Thesis, University of Bristol, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336875.

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Preclik, Tobias [Verfasser], and Ulrich [Akademischer Betreuer] Rüde. "Models and Algorithms for Ultrascale Simulations of Non-smooth Granular Dynamics / Tobias Preclik. Gutachter: Ulrich Rüde." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2014. http://d-nb.info/1075478987/34.

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Shahzamanian, Sichani Matin. "Wheel-rail contact modelling in vehicle dynamics simulation." Licentiate thesis, KTH, Spårfordon, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-127949.

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The wheel-rail contact is at the core of all research related to vehicle-track interaction. This tiny interface governs the dynamic performance of rail vehicles through the loads it transmits and, like any high stress concentration zone, it is subjected to serious damage phenomena. Thus, a clear understanding of the rolling contact between wheel and rail is key to realistic vehicle dynamic simulation and damage analyses. In a multi-body-system simulation package, the essentially demanding contact problem should be evaluated in about every millisecond. Hence, a rigorous treatment of the contact is highly time consuming. Simplifying assumptions are, therefore, made to accelerate the simulation process. This gives rise to a trade-off between accuracy and computational efficiency of the contact models in use. Historically, Hertz contact solution is used since it is of closed-form. However, some of its underlying assumptions may be violated quite often in wheel-rail contact. The assumption of constant relative curvature which leads to an elliptic contact patch is of this kind. Fast non-elliptic contact models are proposed by others to lift this assumption while avoiding the tedious numerical procedures. These models are accompanied by a simplified approach to treat tangential tractions arising from creepages and spin. In this thesis, in addition to a literature survey presented, three of these fast non-elliptic contact models are evaluated and compared to each other in terms of contact patch, pressure and traction distributions as well as the creep forces. Based on the conclusions drawn from this evaluation, a new method is proposed which results in more accurate contact patch and pressure distribution estimation while maintaining the same computational efficiency. The experience gained through this Licentiate work illuminates future research directions among which, improving tangential contact results and treating conformal contacts are given higher priority.

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Shahzamanian, Sichani Matin. "On Efficient Modelling of Wheel-Rail Contact in Vehicle Dynamics Simulation." Doctoral thesis, KTH, Spårfordon, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-181691.

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The wheel-rail contact is at the core of all research related to vehicletrackinteraction. This tiny interface governs the dynamic performanceof rail vehicles through the forces it transmits and, like any high stressconcentration zone, it is subjected to serious damage phenomena. Thus,a clear understanding of the rolling contact between wheel and rail is keyto realistic vehicle dynamics simulation and damage analysis. In a multi-body dynamics simulation, the demanding contact problemshould be evaluated at about every millisecond for several wheel-rail pairs.Hence, a rigorous treatment of the contact is highly time-consuming.Simplifying assumptions are therefore made to accelerate the simulationprocess. This gives rise to a trade-o between the accuracy and computationaleciency of the contact model in use. Conventionally, Hertz+FASTSIM is used for calculation of the contactforces thanks to its low computational cost. However, the elliptic patchand pressure distribution obtained by Hertz' theory is often not realisticin wheel-rail contact. Moreover, the use of parabolic traction bound inFASTSIM causes considerable error in the tangential stress estimation.This combination leads to inaccurate damage predictions. Fast non-elliptic contact models are proposed by others to tacklethis issue while avoiding the tedious numerical procedures. The studiesconducted in the present work show that the accuracy of these models iscase-dependent. To improve the accuracy of non-elliptic patch and pressure estimation,a new method is proposed. The method is implemented in an algorithmnamed ANALYN. Comparisons show improvements in patch and, particularly,pressure estimations using ANALYN. In addition, an alternative to the widely-used FASTSIM is developed, named FaStrip. Unlike FASTSIM, it employs an elliptic traction boundand is able to estimate the non-linear characteristic of tangential stressdistribution. Comparisons show more accurate estimation of tangentialstress and slip velocity distribution as well as creep forces with FaStrip. Ultimately, an ecient non-elliptic wheel-rail contact model consistingof ANALYN and FaStrip is proposed. The reasonable computationalcost of the model enables it to be used on-line in dynamics simulationand its accuracy can improve the damage predictions.

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Votsios, Vasilis. "Contact mechanics and impact dynamics of non-conforming elastic and viscoelastic semi-infinite or thin bonded layered solids." Thesis, Loughborough University, 2003. https://dspace.lboro.ac.uk/2134/11815.

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The thesis is concerned with the contact mechanics behaviour of non-conforming solids. The geometry of the solids considered gives rise to various contact configurations, from concentrated contacts with circular and elliptical configuration to those of finite line nature, as well as those of less concentrated form such as circular flat punches. The radii of curvature of mating bodies in contact or impact give rise to these various nonconforming contact configurations and affect their contact characteristics, from those considered as semi-infinite solids in accord with the classical Hertzian theory to those that deviate from it. Furthermore, layered solids have been considered, some with higher elastic modulus than that of the substrate material (such as hard protective coatings) and some with low elastic moduli, often employed as tribological coatings (such as solid lubricants). Other bonded layered solids behave in viscoelastic manner, with creep relaxation behaviour under load, and are often used to dampen structural vibration upon impact. Analytic models have been developed for all these solids to predict their contact and impact behaviour and obtain pressure distribution, footprint shape and deformation under both elastostatic and transient dynamic conditions. Only few solutions for thin bonded layered elastic solids have been reported for elastostatic analysis. The analytical model developed in this thesis is in accord with those reported in the literature and is extended to the case of impact of balls, and employed for a number of practical applications. The elastostatic impact of a roller against a semi-infinite elastic half-space is also treated by analytic means, which has not been reported in literature. Two and three-dimensional finite element models have been developed and compared with all the derived analytic methods, and good agreement found in all cases. The finite element approach used has been made into a generic tool for all the contact configurations, elastic and viscoelastic. The physics of the contact mechanical problems is fully explained by analytic, numerical and supporting experimentation and agreement found between all these approaches to a high level of conformance. This level of agreement, the development of various analytical impact models for layered solids and finite line configuration, and the development of a multi-layered viscoelastic transducer with agreed numerical predictions account for the main contributions to knowledge. There are a significant number of findings within the thesis, but the major findings relate to the protective nature of hard coatings and high modulus bonded layered solids, and the verified viscoelastic behaviour of low elastic modulus compressible thin bonded layers. Most importantly, the thesis has created a rational framework for contact/impact of solids of low contact contiguity.

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Clayton, Maya. "Econometric forecasting of financial assets using non-linear smooth transition autoregressive models." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/1898.

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Following the debate by empirical finance research on the presence of non-linear predictability in stock market returns, this study examines forecasting abilities of nonlinear STAR-type models. A non-linear model methodology is applied to daily returns of FTSE, S&P, DAX and Nikkei indices. The research is then extended to long-horizon forecastability of the four series including monthly returns and a buy-and-sell strategy for a three, six and twelve month holding period using non-linear error-correction framework. The recursive out-of-sample forecast is performed using the present value model equilibrium methodology, whereby stock returns are forecasted using macroeconomic variables, in particular the dividend yield and price-earnings ratio. The forecasting exercise revealed the presence of non-linear predictability for all data periods considered, and confirmed an improvement of predictability for long-horizon data. Finally, the present value model approach is applied to the housing market, whereby the house price returns are forecasted using a price-earnings ratio as a measure of fundamental levels of prices. Findings revealed that the UK housing market appears to be characterised with asymmetric non-linear dynamics, and a clear preference for the asymmetric ESTAR model in terms of forecasting accuracy.

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Dia, Seydou. "Modélisation d'un contact dynamique non-linéaire : application au développement et à l'optimisation de modalsens." Phd thesis, Université de Haute Alsace - Mulhouse, 2010. http://tel.archives-ouvertes.fr/tel-00683067.

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La tribologie et l'analyse non-linéaire du signal est le sujet de mon travail de thèse. Dans la nature, les phénomènes linéaires sont l'exception ; rares sont les systèmes réels qui obéissent exclusivement à des lois linéaires. A l'opposée, les non-linéarités sont impliquées dans tous les processus naturels (réactions chimiques, mécanique, économie, etc.). Les systèmes frottant en sont un des exemples les plus courants, avec des applications très variées. Dans les systèmes de freinage, le frottement se trouve être à l'origine de nombreux problèmes d'instabilités. Les types d'instabilités auxquelles on a affaire dans ce cas sont celles des vibrations induites par le frottement. C'est justement sur ces instabilités que repose le principe Modalsens; un capteur- une lamelle- vient frotter sur un échantillon et ce frottement génère la vibration de celui-ci : le post-traitement par analyse de Fourier du signal vibratoire permet de distinguer des composantes liées au relief, au frottement et à la compressibilité des aspérités. Dans le cas de la méthode Modalsens, l'analyse de Fourier, qui est un outil linéaire, agit comme des lunettes aux travers desquelles est observé le signal et qui filtrerait toutes les composantes non-linéaires. Notre contribution s'inscrit dans cette optique: mettre en place une méthode performante d'analyse non-linéaire pour permettre de mieux appréhender l'analyse du comportement dynamique de Modalsens et de dégager de nouveaux estimateurs pour la caractérisation des surfaces textiles. Partant de là, les résultats obtenus nous serviront à proposer une modélisation du contact sur matériaux fibreux.

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Svahn, Fredrik. "On the stability and control of piecewise-smooth dynamical systems with impacts and friction." Doctoral thesis, Stockholm : Skolan för teknikvetenskap, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11079.

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Jacob, de Cordemoy Aymeric. "Analyse de sensibilité et optimisation pour des problèmes de contact." Electronic Thesis or Diss., Pau, 2023. http://www.theses.fr/2023PAUU3038.

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L'analyse de sensibilité de problèmes décrits par des inéquations variationnelles est un domaine prometteur pour le traitement de problèmes de contrôle optimal et d'optimisation de forme en mécanique du contact. L'objectif de cette thèse est de mener une telle analyse sans utiliser les méthodes classiques de régularisation et/ou de pénalisation qui perturbent la nature non lisse des modèles physiques d'origine. Nous proposons alors une nouvelle méthodologie, basée sur des outils avancés issus de l'analyse convexe et non lisse, tels que l'opérateur proximal et le concept d'épi-différentiabilité du second ordre. Plus précisément, les modèles considérés sont ceux issus de la mécanique du contact, décrivant le contact entre des solides déformables qui se touchent sur des parties de leurs bords sans s'interpénétrer et qui peuvent éventuellement glisser l'un contre l'autre, provoquant ainsi des phénomènes de frottement. La condition de non-perméabilité peut être décrite par la loi de contact unilatéral de Signorini, tandis que le frottement peut être décrit par la loi de friction de Tresca. Ces deux lois se traduisent par des inégalités et/ou des termes non lisses dans les formulations variationnelles correspondantes. À l'aide de notre approche, nous procédons à une analyse de sensibilité de ces modèles et étudions ainsi des problèmes associés de contrôle optimal et d'optimisation de forme
Sensitivity analysis of problems described by variational inequalities is a promising field for the treatment of optimal control and shape optimization problems in contact mechanics. The objective of this PhD thesis is to carry out such analysis without using classical regularization and/or penalization procedures which perturb the non-smooth nature of the original physical models. Then we propose a new methodology, based on advanced tools from convex and non-smooth analyses, such as the proximal operator and the concept of second order epi-differentiability. More precisely, the models considered are those from contact mechanics, describing the contact between a deformable body with a rigid foundation without penetrating it, and possibly allows sliding modes which causes friction phenomena. The non-permeability condition can be described by the Signorini unilateral conditions, while the friction can be described by the Tresca friction law, both resulting in inequalities and/or non-smooth terms in the corresponding variational formulations. Using our approach, we perform a sensitivity analysis of these models and thus study associated optimal control and shape optimization problems

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Sundar, Sriram. "Impact damping and friction in non-linear mechanical systems with combined rolling-sliding contact." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1386245045.

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AHMED, RIZWAN. "Experimental Investigation Of Non-Linear Structural Dynamics of Shrouded Turbine Blade." Doctoral thesis, Politecnico di Torino, 2022. https://hdl.handle.net/11583/2972153.

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BRUZZONE, FABIO. "2D/3D Nonlinear and Non-Hertzian Tooth Deflection Analysis for Compliant Gear Dynamics." Doctoral thesis, Politecnico di Torino, 2020. http://hdl.handle.net/11583/2847142.

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Duran, Celio. "Modélisation du comportement dynamique non-linéaire et transitoire de turbomoteur avec multitouches rotor/stator." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0144.

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Cette thèse traite de la dynamique non-linéaire multi-contact des ensembles rotor/stator et s’applique en particulier aux tur-bomoteurs d’hélicoptère conçus par Turboméca, groupe Safran. L’amélioration des performances des turbines à gaz pousse les constructeurs à réduire les jeux fonctionnels rotor-stator no-tamment, tout en garantissant robustesse et fiabilité. Cela nécessite de développer des modèles les plus précis possible afin de prévoir et maîtriser des situations à risques telles que les interactions rotor/stator entre les parties fixes et tournantes déclen-chées principalement, dans le cas des turbomoteurs d’hélicoptère, par la perte d’aubes. La partie 1 présente une synthèse bibliographique des principaux phénomènes physiques rencontrés suite à une touche ro-tor/stator en s’appuyant sur l’expérimentation et le calcul. Un bilan sur les différents modèles numériques de gestion du con-tact frottant est détaillé. La dualité entre méthodes temporelles et fréquentielles est aussi abordée comme la méthode de la ba-lance harmonique et les schémas d’intégration temporelle de la famille de Newmark. Il est aussi décrit deux outils d’analyse fréquentielle : le spectrogramme pour analyser l’évolution d’un spectre fréquentiel dans le temps, le full-spectrum pour pren-dre en compte les précessions du rotor. La partie 2 se focalise sur des systèmes dynamiques académiques : un oscillateur forcé à double butées, un rotor de Jeffcott et un rotor à 3 disques avec tous deux une interaction disque/carter. Compte tenu du caractère transitoire du comportement des turbomoteurs, il s’agit de tester des méthodes d’intégration temporelle pas à pas et aussi des lois de contact. Il en ressort que la méthode de Newmark à accélération moyenne, et les lois de contact type « pénalité amortie » combinées à une régularisation de la raideur et de l’amortissement par une fonction arc tangente sont pertinentes. La modélisation de rotor en flexion en ré-gime transitoire et avec plusieurs touches possibles est réalisée avec la méthode des éléments finis et l’intégration des mé-thodes et techniques précédentes. L’ensemble de la modélisation est mise en œuvre sous l’environnement Matlab et se traduit au final par un logiciel nommé ToRoS (Touche Rotor-Stator). Le turbomoteur de l’Ardiden 1H fait l’objet de la dernière partie. Le logiciel ToRoS développé est utilisé pour prévoir la dyna-mique transitoire de sa turbine libre soumise à de multiples touches, consécutifs à un départ d’aubes. Les lois de contacts ap-pliquées dépendent du type de contact : disque/carter, labyrinthe/stator, palier/butée. Durant la descente en vitesse, la ligne d’arbre adopte, en fonction du niveau de balourd, de la vitesse de rotation, des paramètres du contact et du frottement, un comportement avec un contact quasi-permanent en précession directe
This PhD thesis deals with the nonlinear transient dynamic response of rotor/stator assemblies in the case of multi-contacts, it is applied on Turbomeca’s helicopter turbo-engine. In order to improve gas turbine performances, constructors have to reduce rotor/stator clearances, while continuing to maintain component’s reliability, durability and safety. It implies the development of models to predict and control unsafe situations as, rotor/stator interactions between fixed and rotating parts, mainly triggered by a blade-loss in helicopters turbo-engine case. The first part of this document is concerned with a bibliographical summary of the main physical phenomena observed after a rotor/stator interaction, this is supported by experiments and numerical calculations. A review of the various sliding contact numerical models is presented. The duality between time and/or frequency simulation response methods as, harmonic balance method vs Newmark time integration scheme is discussed. Then two numerical tools for frequency domain analysis are described: the spectrogram to analyze frequency spectrum as a function of the time, the full-spectrum for analyzing the rotor whirl motions. The second part is focused on the time response simulation of some academic systems: an excited oscillator with two end-stops, a Jeffcott rotor and finally a 3 disks rotor both subjected to disk/casing interactions. Given the transient behavior exhibited by turbo-engine rotors following a rotor/stator contact, the purpose is to test several step-by-step time integration scheme combined with different contact laws. This analysis has shown that the Newmark scheme with constant acceleration used with damped contact penalty laws combined to stiffness and damping coefficients smoothed by arctangent functions are relevant. The rotor bending modeling during transient motion considering possible multi-contacts with the stator is realized using the finite element method and the previously reviewed contact modeling methods. The simulation is implemented under Matlab environment and is named ToRoS. (Rotor/Stator Touch). Finally, the developed modeling is applied to the Ardiden 1H turbo-engine. The ToRoS software is used to predict the transient dynamic response of the free power turbine subjected to multi-contacts, after a sudden blade-loss which is modeled by a sudden unbalance. Contact laws are applied and depend on contact type and location: disk/casing, seals, thrust bearing. Depending on the mass unbalance level, the speed of rotation, the contact and friction parameters, the rotor can be in a quasi-permanent contact state in forward whirl while the rotation speed is running-down

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Cebulla, Thomas [Verfasser], Heinz [Akademischer Betreuer] Ulbrich, and Carlo L. [Akademischer Betreuer] Bottasso. "Spatial Dynamics of Pushbelt CVTs: Model Enhancements to a Non-smooth Flexible Multibody System / Thomas Cebulla. Gutachter: Heinz Ulbrich ; Carlo L. Bottasso. Betreuer: Heinz Ulbrich." München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1050025792/34.

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Ponthus, Nicolas. "Contact sec glisssant sous faible charge : de la topographie des surfaces à la dynamique des solides de l'interface." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC021/document.

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Cette thèse porte sur la dynamique, normale à l'interface, d'un contact sec en glissement stationnaire entre deux surfaces de topographies aléatoires, soumis à une faible charge normale. Dans ce contexte, le mouvement d'un patin sous son propre poids a été étudié expérimentalement. Des mesures par vibrométrie laser du déplacement et de la vitesse normale du patin ont confirmé que, lorsque la vitesse de glissement augmente, le patin transite entre un régime où le contact est permanent vers un régime dynamique où il subit décollements, chocs et rebonds.À basse vitesse, le mouvement normal résulte d'un filtrage géométrique des topographies. Les caractéristiques statistiques et spectrales de ce mouvement ont pu être décrites. Les influences de la rugosité, de la longueur de corrélation, de la largeur de bande du spectre de rugosité et de l'aire apparente de contact ont été identifiées et analysées. Ces résultats ont pu être reproduits par des modèles numériques, mais aussi analytiques en adaptant la théorie des valeurs extrêmes. Des modèles de type Bouncing Ball, dont l'excitation est supposée donnée par le processus de filtrage géométrique, ont également été mis en place. Ils reproduisent une large gamme d'observations en régime dynamique, de la transition aux vibro-impacts.Pour tester certaines hypothèses des modèles mis en place, un patin multi-voies original a été développé et a permis d'accéder à la localisation spatiale des micro-contacts transitoires entre surfaces antagonistes. On observe que les micro-contacts sont gouvernés par une longueur caractéristique à basse vitesse de glissement et par un temps caractéristique à haute vitesse. Les rotations du patin deviennent importantes à haute vitesse, modifiant la répartition des micro-contacts à la surface du patin
This PhD thesis addresses the issue of the dynamics, normal to the interface, of a dry steady-sliding contact between two random topographies under weak normal load. In this context, the motion of a slider under its own weight has been studied experimentally. Measurements, using a laser vibrometer, of the normal displacement and velocity of the slider confirm the existence of a transition, as the sliding speed increases, from a regime of permanent contact to a regime of lift-offs, shocks and rebounds.At low speed, the normal motion is due to a geometrical filtering of the topographies, the statistical and spectral properties of which have been described. The roles of the roughness, including its spectral breadth and correlation length, and of the apparent contact area have been identified and analyzed. Those results have been reproduced not only using numerical models, but also using analytical ones based on the extreme value theory. Bouncing-Ball-like models, the excitation of which is assumed to be given by the geometrical filtering, have also been implemented and match with a broad range of experimental observations in dynamical regime, from the transition to vibro-impacts.To test some of the hypothesis of the models, a new experimental multi-channel slider has been designed and has enabled access to the spatial localization of the transient micro-contacts between the antagonists surfaces. It has been shown that micro-contacts are governed by a characteristic length at low sliding speed and by a characteristic time at high speed. The rotational motion of the slider also increases with sliding speed, changing the micro-contact distribution along the surface of the slider

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Bondoky, Karim [Verfasser], Klaus [Gutachter] Janschek, and Stefanos [Gutachter] Fasoulas. "A Contribution to Validation and Testing of Non-Compliant Docking Contact Dynamics of Small and Rigid Satellites Using Hardware-In-The-Loop Simulation / Karim Bondoky ; Gutachter: Klaus Janschek, Stefanos Fasoulas." Dresden : Technische Universität Dresden, 2020. http://d-nb.info/122783313X/34.

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Hmid, Abdelhak. "Dynamique d’équipements avec des non linéarités de liaisons localisées : Application aux systèmes optiques d’éclairage." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI139.

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La thèse concerne la prévision du comportement dynamique non linéaire d’équipements optique. Les travaux de recherche menés se concentrent sur la simulation des phénomènes vibratoires en jeu, afin de prévoir la réponse harmonique de l’équipement. Ces travaux ouvrent ainsi la voie à des préconisations d’évolutions dans la conception mécanique du projecteur pour augmenter sa durabilité et le confort de vision. En effet les essais pratiqués montrent que de forts niveaux de vibrations endommagent les composants du projecteur et détériorent la stabilité du faisceau d’éclairage. Afin d’éviter de telles nuisances, la conception du projecteur doit être adaptée grâce à un modèle mécanique qui intègre des comportements non linéaires causés essentiellement par les liaisons pour prévoir le mieux possible les niveaux de vibrations du projecteur embarqué. L’état de l’art est réalisé sur les comportements dynamiques non linéaires, les modèles et méthodes de résolution associés, puis les estimateurs existants de quantification des non linéarités. Les essais d’analyse modale réalisés mettent en évidence la présence de phénomènes non linéaires dus à de multiples causes (jeux-butées, frottements, stick-slip, …) localisées dans les liaisons réflecteur-boitier. Les caractérisations expérimentales menées sur les liaisons, délivrent des boucles efforts-déflexion qui montrent différents types de comportement non linéaire, aident au choix des modèles les plus pertinents et au calage de leurs paramètres. Les limites de validité des modèles de calculs linéaires sont déterminées par des critères formulés empiriquement. Les modèles non linéaires de liaison sélectionnés sont intégrés dans un modèle réduit à un puis à deux degrés de liberté d’un projecteur. La réprésentativité du modèle est évaluée sur la base des analyses modales mesurées du projecteur. Les équations décrivent le comportement dynamique de projecteur et les non linéarités sous l’hypothèse de régime stationnaire. La méthode de balance harmonique associée à une technique de continuation par longueur d’arc résout rapidement les équations et détermine avec précision les réponses dynamiques établies. L’étude est complétée par l’analyse de stabilité selon la théorie de Floquet qui met en évidence la présence des branches de solutions stables ou instables. Enfin des réponses harmoniques sont calculées avec un modèle aux éléments finis du projecteur complet. Les calculs sont basés sur l’identification des modes qui reposent sur la répartition des masses dans la structure, la nature des liaisons. Des études d’influence sont réalisées. Les paramètres étudiés sont les raideurs et précontraintes de contact, le coefficient de frottement, l’amortissement introduit. Leurs impacts sur les niveaux des vibrations sont quantifiés ce qui amène au recalage du modèle éléments finis pour améliorer les résultats modaux du projecteur automobile et sa réponse harmonique forcée
The thesis deals with the prediction of nonlinear dynamic behavior of automotive headlamps. The attention is focused on building models to estimate the vibration behavior of lighting system to enhance its durability and comfort of vision. Vibration tests show that high levels of vibration damage projector components and degrade the stability of the illuminating beam. To avoid these issus, headlamps design must be adapted to include nonlinear phenomena provided from the joints connecting the reflector and housing subsets. The state of the art is performed on the non-linear dynamic behavior, models and methods and existing estimators quantifying nonlinearities. The modal tests performed demonstrate the presence of non-linear phenomena (clearance, friction, stick-slip, …) located in reflector-housing joints. Experimental investigations carried out on joints show different types of nonlinear behavior and help to identify the most important contact parameters (stiffness and damping). The limits of validity of the linear models are determined by empirically formulated criteria. Selected nonlinear models are integrated in a 1D-model reduced to one then two degrees of freedom of a projector. The representativeness of the model is evaluated basing of modal measurement of headlamp. The Harmonic Balance Method was used to calculate the periodic response. The algorithm calculates also the stability of the periodic solutions found, using Floquet theory, and follows stable or instable branches versus varying system parameters via the arc-length continuation technique. Finally, harmonic responses are predicted with a finite element model of the entire headlamp. The calculations are based on the identification of modes that are based on the weight distribution in the structures and joints proprities. Sensibility studies are carried out on stiffness and preloaded contact, coefficient of friction and damping. Impacts on the vibration levels were quantified that leads to update the finite element model and improve modal and harmonic results of headlamp

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Bichet, Lionel. "Mécanismes de transports dans la fissuration des matériaux hétérogènes : application à la durée de vie d’exploitation des centrales nucléaires." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTS001/document.

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Les propriétés du béton constituant les enceintes de confinement des centrales électronucléaires évoluent sous les effets de mécanismes de vieillissement résultant notamment de transferts couplés de chaleur et de masse au sein du matériau. Ces phénomènes peuvent être modélisés par des équations de transports moyennées : lois de Fick pour le transport d’espèces en solution et lois de Fourier pour la description de la diffusion thermique. Dans cette étude, les développements concernent la diffusion de la thermique dans un milieu hétérogène fissuré représentant un matériau cimentaire dégradé chimiquement. Le problème thermo-mécanique est traité à l'aide d'une approche multi-corps reliés par des lois d’interactions enrichies (zones cohésives). La diffusion thermique est écrite dans le formalisme cohésif-volumique en prenant en compte le couplage entre un état d'endommagement local de la zone cohésive et une conductivité homogénéisée. Afin d'optimiser les coûts de calculs, une étude est menée sur la dimension d'un volume élémentaire représentatif (VER). Pour cela, la méthode d'eigenerosion est étendue à la fissuration de milieux hétérogènes puis appliquée aux milieux cimentaires. La propagation de fissures sous chargement thermique est ensuite analysée dans des VERs de béton dégradés représentatifs des enceintes de confinement des centrales nucléaires après plusieurs années. Le vieillissement est modélisé par un taux de pré-dégradation initial entre le mortier et les granulats. Le développement de multi-fissures est relié au taux de pré-dégradation et la formation "d'écrans" à la diffusion de la thermique est mise en avant
During their confinement in a nuclear power plant, the mechanical properties of the constitutive materials of concrete change as a result of ageing. This is due to the transportation of chemical species at the microscopic level of the media. Firstly, this can be modelled with average equations. The Fick laws represent the evolution of chemical diffusion and the Fourier laws, the transportation of heat at a mesoscopic level. In this research, we will consider thermal evolution on a fractured media.This thermomechanical problem is solved with a staggered method. The mechanical contribution used an approach based on multi-bodies system linked with cohesive zone models. The thermal problem is based on the approximation of the heat transfer equation at the cohesive interface. This approach has been implemented and validated. The description of the heat trough the interface is composed with the definition of an homogenised conductivity and the local damage parameter. In order to optimize the computational cost with a good agreement of the crack propagation, a criterion is proposed for sizing a representative elementary volume (REV). The eigenerosion method is used, validated and extended to heterogeneous media. Two studies are carried out on the morphological properties on a cementious media. As a result of those studies, a minimal size for a REV is defined.Crack spread under thermal loads are investigated on a media representing the concrete of the containment of a nuclear power station. The ageing effect are taken into account as an initial damage between the mortar and the aggregates. These parameters are expressed in terms of rate of initial damage. A study is proposed for different values of this rate. As assumed, the development of multi-cracks is linked with the rate of initial damage and the creation of thermal border is proposed

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Meksi, Olfa. "Contribution à la caractérisation numérique et expérimentale des échanges thermiques externes des machines électriques totalement fermées et non ventilées avec introduction des données d’incertitudes." Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2367/document.

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En plus des aspects électrique, magnétique, vibro-acoustique et mécanique, les considérations thermiques doivent être prises en compte lors des phases de conception et d’optimisation des machines électriques. Ce mémoire se porte sur l’analyse et la simulation du comportement thermique des machines électriques Totalement Fermées et Non Ventilées (TFNV) et plus particulièrement sur le cas de la machine Synchro-réluctante (Synchrel), utilisée comme actionneur d’embrayage. Un modèle thermique détaillé (MTD), décrivant le comportement thermique de la machine Synchrel est conçu. Ce MTD proposé est construit grâce à une combinaison de la méthode à Constantes Localisées (CL) et d’une technique numérique de type Mécanique des Fluides Numériques (MFN). La première méthode est dédiée à la modélisation des transferts conductifs et radiatifs. La seconde permet de modéliser le mécanisme de refroidissement par convection naturelle autour de la machine Synchrel. Compte-tenu de l’importance du mode de refroidissement sur l’évolution des températures critiques, l’approche MFN peut apporter plus de précision. Par contre, elle nécessite des temps de calcul importants ce qui freine son utilisation. Afin de surmonter cette problématique, les résultats numériques obtenus pour des points de fonctionnement particuliers sont utilisés afin de définir des relations de corrélation analytiques. Cette analyse numérique est accompagnée d’une démarche expérimentale afin d’élaborer les corrélations expérimentales correspondantes. L’étude montre que les solutions numériques peuvent converger vers des solutions plus précises si l’on tient compte des données d’incertitudes introduites par cette approche. La deuxième problématique traitée est la détermination des Résistances Thermiques de Contact (RTCs) des machines électriques. Elles constituent des paramètres clefs dans la définition du MTD complet. La démarche de détermination des RTCs est basée sur deux approches d’identification paramétrique. La première est basée sur des observations expérimentales du comportement thermique de la machine. La seconde est basée sur une approche mathématique de réduction de modèle. Les valeurs déterminées sont cohérentes avec la littérature, bien que la machine Synchrel diffère en topologie, taille et puissance. En utilisant la corrélation d’origine numérique du phénomène de convection externe, le MTD complet est alors utilisé afin d’évaluer la variation de température due à l’erreur introduite par la MFN. En utilisant la corrélation expérimentale, le MTD complet est validé. Les approches d’identification paramétrique conduisent à la construction de deux modèles thermiques de second ordre de la machine. Ces modèles permettent la surveillance du comportement thermique du bobinage et du carter. Ces deux modèles simplifiés font montre d’une prédictibilité satisfaisante au regard de leur simplicité
In addition to electrical, magnetic, vibro-acoustic and mechanical aspects, thermal considerations must be taken into account during the design and optimization of electrical machines. This study focuses on the analysis and the simulation of the thermal behavior of Totally Enclosed Non Ventilated (TENV) electric machines, specifically a Synchro-reluctant motor (Synchrel) in the context of an automotive application : a clutch actuator. A detailed thermal model (MTD) describing the thermal behavior of the Synchrel machine is designed. This proposed MTD is based on a combination of the Lumped Parameter Thermal Network method (LPTN) and the Computational Fluid Dynamics (CFD) methods. The first method is dedicated to model the conductive and radiative heat transfers. CFD techniques are dedicated to model the cooling mechanism based on the natural convection around the Synchrel machine. Since the critical temperature is very sensitive to the cooling mode, the CFD approach is used in this study to provide more accurate results. On the other hand, it requires considerable computing time, which prevents its use in design studies based on optimization methods. In order to overcome this problem, only some numerical results obtained for particular operating points are used to define an analytical correlation based on the numerical calculation relations. This numerical analysis goes with an experimental approach in order to elaborate the corresponding experimental correlations. This study shows that numerical solutions can present a good accuracy, if uncertainty data introduced by this approach are taken into account. The second research problem addressed in this study is the determination of the Contact Thermal Resistances (RTCs), which are key parameters in the definition of the MTD. The determination procedure of the RTCs is based on two parametric identification approaches. The first one is experimental and based on some observations of the thermal behavior of the machine. The second one is based on a mathematical model reduction approach. The determined values are consistent with results from literature, although the Synchrel machine differs in topology, size and power. Using the numerical correlations, the MTD is used to evaluate the temperature deviation due to error terms introduced by the CFD approach. Then, using these experimental correlations, the MTD’s quality can be checked and approved. Parametric identification approaches lead to the construction of two secondorder thermal models of the machine. These models allow monitoring the thermal behavior of the winding and the casing. Both simplified models show satisfactory predictability with respect to their great simplicity

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Charles, Alexandre. "Dynamique des systèmes de solides rigides avec impacts et frottement." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4738/document.

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Avec en perspective l’application à la robotique ou à l’étude des milieux granulaires, nous discutons la formulation des problèmes de contacts avec frottement en dynamique et pour les systèmes constitués de solides rigides. L’approche usuelle est event driven et ne permet pas d’écrire de manière systématique un problème d’évolution. Ceci a motivé l’émergence d’une nouvelle approche dans le cas sans frottement que nous généralisons au cas avec frottement. Suivant le point de vue de Lagrange sur l’équation de la dynamique, nous mettons en exergue l’usage systématique des puissances virtuelles et de la dualité. Ce parti-pris suggère de mettre l’accent sur l’effort généralisé de réaction dans la formulation et non sur les forces de réactions locales dans le monde réel, comme il est usuel. Ce point de vue permet d’échapper à des pathologies connues sous le nom de paradoxe de Painlevé
In the view of robotics or granular media mechanics, we question the statement of the dynamical evolution problem for multibody systems with contacts and friction. The usual approach is event driven and does not allow to state an evolution problem in a systematic way. This matter of fact gave rise to a new approach in the frictionless case we generalize to the case with friction. Sticking to the point of view of Lagrange on the equation of the dynamics, we emphasize the systematic use of virtual powers and duality. This bias suggests to put emphasis on generalized reaction forces in the statement of the evolution problem and not on local reaction forces of the real world, as it is usual in practice. This point of view allows to escape from pathologies known as Painlevé paradox

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Saint-Cyr, Baptiste. "Modélisation des matériaux granulaires cohésifs à particules non convexes : Application à la compaction des poudres d'UO2." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2011. http://tel.archives-ouvertes.fr/tel-00660146.

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On s'intéresse à la modélisation des matériaux granulaires composé d'agrégats non convexes et cohésifs en vue d'application à la rhéologie des poudres d'UO2 . L'inﬂuence du degré de non-convexité des particules est analysé en termes de grandeurs macroscopiques (frottement interne et cohésion de Coulomb) et de paramètres micro-mécaniques tels que l'anisotropie de la texture et la transmission des efforts. Il apparaît en particulier que la compacité évolue d'une manière complexe avec la non-convexité et que la résistance au cisaillement augmente mais sature sous l'effet d'imbrication entre agrégats. Des modèles simples sont introduits pour décrire ces comportements en termes de paramètres micro-mécaniques. De même, des études systématiques par cisaillement, compaction uniaxiale et compression simple montrent que la cohésion interne augmente avec la non-convexité mais est fortement contrôlée par les conditions aux limites et l'apparition de bandes de cisaillement ou de concentrations de contraintes.

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Parikh, Jaimit B. "Theoretical Investigation of Intra- and Inter-cellular Spatiotemporal Calcium Patterns in Microcirculation." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/1927.

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Microcirculatory vessels are lined by endothelial cells (ECs) which are surrounded by a single or multiple layer of smooth muscle cells (SMCs). Spontaneous and agonist induced spatiotemporal calcium (Ca2+) events are generated in ECs and SMCs, and regulated by complex bi-directional signaling between the two layers which ultimately determines the vessel tone. The contractile state of microcirculatory vessels is an important factor in the determination of vascular resistance, blood flow and blood pressure. This dissertation presents theoretical insights into some of the important and currently unresolved phenomena in microvascular tone regulation. Compartmental and continuum models of isolated EC and SMC, coupled EC-SMC and a multi-cellular vessel segment with deterministic and stochastic descriptions of the cellular components were developed, and the intra- and inter-cellular spatiotemporal Ca2+ mobilization was examined. Coupled EC-SMC model simulations captured the experimentally observed localized subcellular EC Ca2+ events arising from the opening of EC transient receptor vanilloid 4 (TRPV4) channels and inositol triphosphate receptors (IP3Rs). These localized EC Ca2+ events result in endothelium-derived hyperpolarization (EDH) and Nitric Oxide (NO) production which transmit to the adjacent SMCs to ultimately result in vasodilation. The model examined the effect of heterogeneous distribution of cellular components and channel gating kinetics in determination of the amplitude and spread of the Ca2+ events. The simulations suggested the necessity of co-localization of certain cellular components for modulation of EDH and NO responses. Isolated EC and SMC models captured intracellular Ca2+ wave like activity and predicted the necessity of non-uniform distribution of cellular components for the generation of Ca2+ waves. The simulations also suggested the role of membrane potential dynamics in regulating Ca2+ wave velocity. The multi-cellular vessel segment model examined the underlying mechanisms for the intercellular synchronization of spontaneous oscillatory Ca2+ waves in individual SMC. From local subcellular events to integrated macro-scale behavior at the vessel level, the developed multi-scale models captured basic features of vascular Ca2+ signaling and provide insights for their physiological relevance. The models provide a theoretical framework for assisting investigations on the regulation of vascular tone in health and disease.

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Ji, Hongjun. "Systèmes dynamiques coopératifs appliqués en biologie." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS514.

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Ce travail de thèse est constitué de nouvelles applications de la théorie des systèmes dynamiques coopératifs à l'étude de modèles en Biologie. Un premier modèle réduit d'une dynamique compartimentalisée couplant l'hémodynamique et le métabolisme énergétique cérébral. Nous avons proposé l'étude d'une extension naturelle de ce modèle comprenant deux compartiments intracellulaires distincts, l'un représentant un neurone et l'autre un astrocyte en plus du compartiment extracellulaire (aussi appelé interstitiel) et du compartiment capillaire. Nous avons commencé par observer que ce système (et même une extension de ce système à N neurones et A astrocytes) est un système coopératif. On a pu alors appliquer les techniques développées par Hal L. Smith et démontrer (en toutes dimensions) que l'unique point stationnaire est asymptotiquement stable. Dans la suite, nous avons considéré une variante du système réduit de dimension 2 dans laquelle on considère une dynamique différentiable par morceaux qui présente un saut lorsque la variable x ou la variable y dépasse un certain seuil. Ce système par morceaux permet l'introduction d'une autorégulation induite par un retour des concentrations de lactate extracellulaire ou capillaire sur le flux sanguin capillaire. De nouveaux phénomènes dynamiques sont découverts et nous discutons de l'existence et de la nature de deux points d'équilibre, d'un segment attractif, d'un équilibre frontalier et d'orbites périodiques en fonction du flux sanguin capillaire. Dans le dernier chapitre, on considère, en contraste avec les chapitres précédents, un système dynamique forcé. Ce système dynamique modélise une population dont l'environnement varie périodiquement dans le temps. Nous appliquons notre théorème à l'exemple d'une dynamique de population d'insectes (moustiques) avec un stade juvénile exposé à une compétition quadratique et un stade adulte. Cette dynamique est sujette à un forçage périodique saisonnier. En particulier, dans les pays tempérés, les moustiques sont très rares en hiver et connaissent une croissance explosive après les premiers épisodes pluvieux de la saison chaude
This thesis work consists of new applications of the theory of cooperative dynamical systems to the study of models in Biology. A first model of compartmentalized dynamics coupling hemodynamics and cerebral energy metabolism. It has been proposed to study a natural extension of this model comprising two distinct intracellular compartments, one representing a neuron and the other an astrocyte in addition to the extracellular compartment (also called interstitial) and the capillary compartment. We began by observing that this system (even an extension of this system to N neurons and A astrocytes) is a cooperative system. It was then possible to apply the techniques developed by Hal L. Smith and demonstrate (in all dimensions) that the single stationary point is asymptotically stable. In the following, we have considered a variant of the reduced system of dimension 2 in which we consider a piecewise differentiable dynamic that has a jump when the variable x or the variable y exceeds a certain threshold. This piecewise system allows the introduction of an autoregulation induced by a feedback of the extracellular or capillary Lactate concentrations on the Capillary Blood Flow. New dynamical phenomena are uncovered and we discuss existence and nature of two equilibrium points, attractive segment, boundary equilibrium and periodic orbits depending of the Capillary Blood Flow. In the last chapter, we consider, in contrast with the preceding chapters, a forced dynamical system. This dynamical system models a population whose environment varies periodically over time. We apply our theorem to the example of a population dynamics of insects (for example mosquitoes) with a juvenile stage exposed to a quadratic competition and an adult stage. These dynamics are subject to a seasonal periodic forcing. In particular, in temperate countries, mosquitoes are very rare in winter and grow explosively after the first rainy episodes of the hot season

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Pezzotti, Simone. "DFT-MD simulations and theoretical SFG spectroscopy to characterize H-Bonded networks at aqueous interfaces : from hydrophobic to hydrophilic environments Structural definition of the BIL and DL: a new universal methodology to rationalize non-linear χ(2)(ω) SFG signals at charged interfaces, including χ(3)(ω) contributions What the Diffuse Layer (DL) Reveals in Non-Linear SFG Spectroscopy 2D H-Bond Network as the Topmost Skin to the Air-Water Interface Combining ab-initio and classical molecular dynamics simulations to unravel the structure of the 2D-HB-network at the air-water interface 2D-HB-Network at the air-water interface: A structural and dynamical characterization by means of ab initio and classical molecular dynamics simulations Spectroscopic BIL-SFG Invariance Hides the Chaotropic Effect of Protons at the Air-Water Interface Molecular hydrophobicity at a macroscopically hydrophilic surface Graph theory for automatic structural recognition in molecular dynamics simulations DFT-MD of the (110)-Co3O4 cobalt oxide semiconductor in contact with liquid water, preliminary chemical and physical insights into the electrochemical environment." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLE008.

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Améliorer notre connaissance de la structure de l'eau dans l'environnement spécial offert par une interface est essentiel pour la compréhension de nombreux phénomènes naturels et applications technologiques. Pour révéler cette structure interfaciale de l'eau, des techniques capables de fournir des informations microscopiques, de manière sélective, pour cette couche interfaciale (BIL) sont nécessaires. Dans le présent travail de thèse, nous avons donc étudié les interfaces aqueuses au niveau moléculaire, en couplant la modélisation théorique à partir de simulations DFT-MD avec les spectroscopies SFG et THz-IR. En développant de nouveaux protocoles/outils d'investigation associant simulations DFT-MD et spectroscopie SFG, en particulier pour la rationalisation plus complexe des interfaces chargées, nous avons fourni une compréhension globale de l'effet des conditions interfaciales d'hydrophilicité, de pH, de force ionique sur le réseau des liaisons-H formé dans la couche interfaciale BIL, sur ses signatures spectroscopiques et sur son impact sur les propriétés physico-chimiques. Nous avons montré pour la première fois que, dans des conditions suffisamment hydrophobes, l'eau interfaciale crée des réseaux des liaisons-H bidimensionnels, révélé expérimentalement par les spectres THz-IR. Le réseau-2D dicte la dynamique de l'eau interfaciale, le potentiel de surface, l'acidité de surface, la tension superficielle et la thermodynamique d'hydratation des solutés hydrophobes. Cet "ordre horizontal" aux interfaces hydrophobes est opposé à "l'ordre verticale" obtenu aux interfaces hydrophiles. Nous avons aussi révélé comment les ions et les conditions de pH modifient ces arrangements structuraux
Improving our knowledge on water H-Bonded networks formed in the special environment offered by an interface is pivotal for our understanding of many natural phenomena and technological applications. To reveal the interfacial water arrangement, techniques able to provide detailed microscopic information selectively for the interfacial layer are required. In the present thesis work, we have hence investigated aqueous interfaces at the molecular level, by coupling theoretical modeling from DFT-MD simulations with SFG & THz-IR spectroscopies. By developing new investigation protocols/tools, coupling DFT-MD simulations and SFG spectroscopy, in particular for the more complex rationalization of charged interfaces, we have provided a global comprehension of the effect of various interfacial conditions (hydrophilicity, pH, ionic strength) on the HB-Network formed in the interfacial layer (BIL), on its spectroscopic signatures and on its impact on physico-chemical properties. We have shown for the first time that, in sufficiently hydrophobic conditions, BIL interfacial water creates special 2-Dimensional HB-Networks, experimentally revealed by one specific THz-IR marker band. Such 2D-network dictates HBs and orientational dynamics of interfacial water, surface potential, surface acidity, water surface tension and thermodynamics of hydration of hydrophobic solutes. Such "horizontal ordering” of water at hydrophobic interfaces is found opposite to the “vertical ordering” of water at hydrophilic interfaces, while coexistence of the two orders leads to disordered interfacial water in intermediate hydrophilic/hydrophobic conditions. Both DFT-MD and SFG further revealed how ions & pH conditions alter these BIL-water orders

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Hegde, Abhijit. "Mechanics of cutting in granular media." Thesis, 2021. https://etd.iisc.ac.in/handle/2005/5828.

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Cutting is an important deformation process encountered during many instances in the engineering of infrastructure, such as trawling, trenching, and excavation. This thesis presents the results of an experimental program on the orthogonal cutting of granular materials, performed under plane strain conditions. The kinematics of granular materials, when subjected to large deformations, is understood through direct imaging and concomitant image analysis. Three suites of experiments were performed to understand the effects of boundary conditions, material systems, and other constraints on the mechanics of cutting. In the first suite of experiments, we perform cutting on two sets of granular materials, spherical glass beads and angular Cauvery delta sand. We vary the three main parameters of the orthogonal cutting problem, the rake angle/ angle of attack of the tool, the initial depth of cut with respect to the free surface of the granular ensemble, and the cutting speed. The overall deformation of the material reaches a steady state after an initial transient phase, which can be observed from the angle of the repose of the pile that forms in-front of the tool. Instantaneous velocity fields show a bifurcation of flow occurring at the tool tip which results in a velocity jump across planes whose direction coincides with the Coulomb failure surfaces. These velocity jumps manifest as regions of intense shear emanating from the tool tip and has a ``band" like appearance when the effective strain rate contours are plotted. The velocity profiles across the shear band assume a sigmoidal shape which can be fit using an error function and allows us to extract the length scale associated with this velocity jump. We observe that the normalized width of the shear band decreases as particle size increases. The width of the shear band for both granular materials was observed to be insensitive to changes in the rake angle, cutting speed, and also the initial depth of cut and hence is a material constant for a given system size. In some cases, we also observe multiple shear bands forming in the system which run parallel to one another and have similar thickness. The measured volumetric strain rate within the shear bands is much lower than the shear rate. The dilation angle measured is always less than the friction angle suggesting that plastic flow occurring within the shear bands is in a non-associative state. We further observe a dead zone of granular material at the tool interface. In the second suite of experiments, we use a suite of granular materials such as cylindrical steel beads, rice grains, clay aggregates, polystyrene beads, and smaller glass beads. At the ensemble level, we find that the volume of material removed during cutting increases linearly in time for all granular materials. At the meso-scale, we once again observe similar sigmoidal velocity profiles across the shear band and is further used to determine the shear band width of each granular material. We find the normalized width of the shear bands is a function of particle size. Upon re-scaling the velocity profiles for different granular materials by their corresponding shear band widths, they all collapse onto a single master curve given by the scaled error function. Thus, we witness a remarkable universality in the kinematics of granular materials at multiple length scales during orthogonal cutting. We further measure the temperature within the shear bands and observe a power-law relationship between the temperature and shear rate, with an exponent ~ 0.55, a significant deviation from the predictions of kinetic theory. In-order to further probe the origin of this inherent length scale at the meso-level, we measure the mean squared displacements of the particles in the shear bands and observe that the particles are not diffusive and hence conclude that the length scale corresponding to the shear bands does not have its origin in a diffusion like process. In the third suite of experiments, a series of constrained cutting experiments were carried out wherein we force the cut granular material to flow through narrow channels by placing a rigid constraint across the cutting tool. We study the formation and evolution of shear bands under such circumstances. By the addition of a constraint, we pin the shear bands between the tool tip and the constraint corner. The separation distance between the tool and the constraint has a direct consequence on the characteristics of the shear bands generated within the ensemble. As the separation between the tool and plate increases, we recover the behavior of unconstrained cutting. Within the channel, the flow fields are very similar to what is observed in vertical hoppers, though the motion of particles is directed against gravity. Like in hopper flows, we observe dead zones along the length of tool and constraint boundaries. We further measure the thickness of this boundary layer using the same error function fit and find that the thickness of the boundary layer is constant across the channel height and nearly symmetric at the two boundaries for small channel widths. As the channel width increases, the boundary layer thickness also increases and becomes asymmetric at the two boundaries. We also present the results of cutting carried out on a constrained granular ensemble, i.e. two granular chains with different numbers of beads. This addition of a constraint to the granular ensemble suppresses the formation of localized shear bands within the ensemble and the deformation is diffuse and homogeneous. The deformation also propagates to regions faraway from the tool. Lastly, we provide a numerical underpinning to the cutting experiments using contact dynamics simulations. As in the case of the experiments, we vary the rake angle, initial depth of cut, and cutting speed in simulation. We compare the simulation results with analytical solutions provided by a 2-D model of cutting. We compare the deformation fields obtained from the simulations with our experimental results and deduce the forces on the tool and along the shear band.
IISc, DBT

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Haikal, Ghadir. "A stabilized Finite Element formulation of non-smooth contact /." 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3362916.

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Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009.
Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3667. Adviser: Keith D. Hjelmstad. Includes bibliographical references (leaves 113-120) Available on microfilm from Pro Quest Information and Learning.

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Misra, Sambit. "Non-smooth dynamics and control of tapping mode atomic force microscopy /." 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3363041.

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Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009.
Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3751. Adviser: Harry Dankowicz. Includes bibliographical references (leaves 136-141) Available on microfilm from Pro Quest Information and Learning.

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Gotika, Priyanka. "Non-smooth Dynamics Using Differential-algebraic Equations Perspective: Modeling and Numerical Solutions." Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10226.

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This thesis addressed non-smooth dynamics of lumped parameter systems, and was restricted to Filippov-type systems. The main objective of this thesis was twofold. Firstly, modeling aspects of Filippov-type non-smooth dynamical systems were addressed with an emphasis on the constitutive assumptions and mathematical structure behind these models. Secondly, robust algorithms were presented to obtain numerical solutions for various Filippov-type lumped parameter systems. Governing equations were written using two different mathematical approaches. The first approach was based on differential inclusions and the second approach was based on differential-algebraic equations. The differential inclusions approach is more amenable to mathematical analysis using existing mathematical tools. On the other hand, the approach based on differential-algebraic equations gives more insight into the constitutive assumptions of a chosen model and easier to obtain numerical solutions. Bingham-type models in which the force cannot be expressed in terms of kinematic variables but the kinematic variables can be expressed in terms of force were considered. Further, Coulomb friction was considered in which neither the force can be expressed in terms of kinematic variables nor the kinematic variables in terms of force. However, one can write implicit constitutive equations in terms of kinematic quantities and force. A numerical framework was set up to study such systems and the algorithm was devised. Towards the end, representative dynamical systems of practical significance were considered. The devised algorithm was implemented on these systems and the results were obtained. The results show that the setting offered by differential-algebraic equations is appropriate for studying dynamics of lumped parameter systems under implicit constitutive models.

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Patterson, Colin. "Reducing the contact time of impinging droplets on non-wetting surfaces." Thesis, 2015. https://hdl.handle.net/2144/15707.

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This work examines the use of macro-textured surfaces to reduce the contact time between impinging liquid droplets and non-wetting surfaces. Six macro-texture geometries are evaluated for their impact on maximum deformation diameters and contact time. The geometries considered are a set of spokes extending radially out from the impact point. Spoke counts of n=1 to n=6 are evaluated. The six spoke geometry demonstrated the maximum reduction in contact time with a 49% measured contact time reduction compared to a flat plate. This study evaluates droplet impacts experimentally using high-speed video. Samples are traditionally machined aluminum surfaces made non-wetting though the use of the Leidenfrost effect. In conjunction with the experimental results, we develop an analytical model to predict the contact time reduction based solely on impact Weber number and texture geometry. Finally, this study considers the impact of the macro-texture geometries on the dispersion of daughter droplets. High spoke-count geometries were observed to produce more than one droplet per spoke. Here again we develop an analytical model to predict this phase doubling based on a quasi-steady-state Rayleigh Plateau instability approach.

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Ivan, Lucian. "Development of High-order CENO Finite-volume Schemes with Block-based Adaptive Mesh Refinement (AMR)." Thesis, 2011. http://hdl.handle.net/1807/29759.

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A high-order central essentially non-oscillatory (CENO) finite-volume scheme in combination with a block-based adaptive mesh refinement (AMR) algorithm is proposed for solution of hyperbolic and elliptic systems of conservation laws on body- fitted multi-block mesh. The spatial discretization of the hyperbolic (inviscid) terms is based on a hybrid solution reconstruction procedure that combines an unlimited high-order k-exact least-squares reconstruction technique following from a fixed central stencil with a monotonicity preserving limited piecewise linear reconstruction algorithm. The limited reconstruction is applied to computational cells with under-resolved solution content and the unlimited k-exact reconstruction procedure is used for cells in which the solution is fully resolved. Switching in the hybrid procedure is determined by a solution smoothness indicator. The hybrid approach avoids the complexity associated with other ENO schemes that require reconstruction on multiple stencils and therefore, would seem very well suited for extension to unstructured meshes. The high-order elliptic (viscous) fluxes are computed based on a k-order accurate average gradient derived from a (k+1)-order accurate reconstruction. A novel h-refinement criterion based on the solution smoothness indicator is used to direct the steady and unsteady refinement of the AMR mesh. The predictive capabilities of the proposed high-order AMR scheme are demonstrated for the Euler and Navier-Stokes equations governing two-dimensional compressible gaseous flows as well as for advection-diffusion problems characterized by the full range of Peclet numbers, Pe. The ability of the scheme to accurately represent solutions with smooth extrema and yet robustly handle under-resolved and/or non-smooth solution content (i.e., shocks and other discontinuities) is shown for a range of problems. Moreover, the ability to perform mesh refinement in regions of smooth but under-resolved and/or non-smooth solution content to achieve the desired resolution is also demonstrated.

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Bondoky, Karim. "A Contribution to Validation and Testing of Non-Compliant Docking Contact Dynamics of Small and Rigid Satellites Using Hardware-In-The-Loop Simulation." 2020. https://tud.qucosa.de/id/qucosa%3A73251.

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Spacecraft (S/C) docking is the last and most challenging phase in the contact closure of two separately flying S/C. The design and testing of S/C docking missions using software-multibody simulations need to be complemented by Hardware-In-The-Loop (HIL) simulation using the real docking hardware. The docking software multibody simulation is challenged by the proper modeling of contact forces, whereas the HIL docking simulation is challenged by proper inclusion of the real contact forces. Existing docking HIL simulators ignore back-reaction force modeling due to the large S/C sizes, or use compliance devices to reduce impact, which alters the actual contact force. This dissertation aims to design a docking HIL testbed to verify docking contact dynamics for small and rigid satellites by simulating the real contact forces without artificial compliance. HIL simulations of docking contact dynamics are challenged mainly by: I. HIL simulation quality: quality of realistic contact dynamics simulation relies fundamentally on the quality of HIL testbed actuation and sensing instrumentation (non-instantaneous, time delays, see Fig. 1) II. HIL testbed design: HIL design optimization requires a justified HIL performance prediction, based on a representative HIL testbed simulation (Fig. 2), where appropriate simulation of contact dynamics is the most difficult and sophisticated task. The goal of this dissertation is to carry out a systematic investigation of the technically possible HIL docking contact dynamics simulation performances, in order to define an appropriate approach for testing of docking contact dynamics of small and rigid satellites without compliance and using HIL simulation. In addition, based on the investigations, the software simulation results shall be validated using an experimental HIL setup. To achieve that, multibody dynamics models of docking S/C were built, after carrying out an extensive contact dynamics research to select the most representative contact model. Furthermore, performance analysis models of the HIL testbed were built. In the dissertation, a detailed parametric analysis was carried out on the available models’ design-spaces (e.g., spacecraft, HIL testbed building-blocks and contact dynamics), to study their impacts on the HIL fidelity and errors (see Fig. 1). This was done using a generic HIL design-tool, which was developed within this work. The results were then used to identify the technical requirements of an experimental 1-Degree-of-Freedom (DOF) HIL testbed, which was conceived, designed, implemented and finally utilized to test and validate the selected docking contact dynamics model. The results of this work showed that the generic multibody-dynamics spacecraft docking model is a practical tool to model, study and analyze docking missions, to identify the properties of successful and failed docking scenarios before it takes place in space. Likewise, the 'Generic HIL Testbed Framework Analysis Tool' is an effective tool for carrying out performance analysis of HIL testbed design, which allows to estimate the testbed’s fidelity and predict HIL errors. Moreover, the results showed that in order to build a 6DOF HIL docking testbed without compliance, it is important to study and analyze the errors’s sources in an impact and compensate for them. Otherwise, the required figure-of-merits of the instruments of the HIL testbed would be extremely challenging to be realized. In addition, the results of the experimental HIL simulation (i.e., real impacts between various specimen) serve as a useful contribution to the advancement of contact dynamics modeling.

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Roy, Durbar. "Experimental and Theoretical Insights into Impact Phenomena of Small Scale Liquid Interfacial Systems." Thesis, 2023. https://etd.iisc.ac.in/handle/2005/6128.

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This work explores impact phenomena experimentally and theoretically for various interfacial systems ranging from medical diagnostics to drop impacts on solids and immiscible liquids. We study a hitherto unexplored impact phenomenon during an ophthalmology procedure called Non-Contact Tonometry. Using high fidelity experiments and theoretical modeling, we show that noninvasive ocular diagnostics demonstrate a propensity for droplet generation and present a potential pathway for pathogen transmission. The air puff-induced corneal deformation and subsequent capillary waves lead to flow instabilities (Rayleigh–Taylor, Rayleigh–Plateau) that lead to tear film ejection, expansion, stretching, and subsequent droplet formation. Effective cooling is one of the significant application areas of impact systems. In the context of cooling problems, we provide new insights using ab initio scaling and boundary layer analysis of the integral and differential forms of the conservation equations. We have probed the limiting scaling regimes by incorporating the evap- orative effects at the liquid-vapor interface. The dependence of liquid film thickness and Nusselt number on various non-dimensional numbers has been explored. We then investigate the class of drop impact problems where we study impacts on solids, bio-inspired substrates, and immiscible liquid pools at low to moderate impact en- ergies. We explore impacts on glass, PDMS, and soft lithographically fabricated replicas of the lotus leaf and rose petals. Surprisingly, the rose petal and lotus leaf replicas manifest similar impact dynamics. The observation is extremely intriguing and counter-intuitive, as rose petals and their replicas are sticky in contrast to lotus leaves. Air entrapment in the micrometer features of bio-inspired surfaces prevents frictional dissipation of droplet kinetic energy, leading to contact edge recession and subsequent break-up modes of the droplet. We explore the air entrapment dynamics beneath an impacting droplet on an immiscible viscous liquid pool using high-speed reflection interferometry imaging and linear stability analysis. We have detected unique hydrodynamic topology in thin air film surrounding the central air dimple (peripheral disc). The pattern resembles spinodal and finger-like structures typi- cally found in various thin condensed matter systems. We attribute the formation of multi-scale thickness perturbations, associated ruptures, and finger-like protru- sions in the draining air film as a combined artifact of thin-film and Saffman–Taylor instabilities. We also investigate the air craters formed on the surface of the impact- ing droplet and attribute its formation to the rapid deceleration of the droplet due to viscous drag force. The droplet response to the external impulsive decelerating force induces oscillatory modes on the surface exposed to the air forming capillary waves that superimpose to form air craters of various shapes and sizes. We introduce a non-dimensional parameter, the ratio of the drag force to the capillary force acting on the droplet to characterize the air craters. Further, we generalize the local droplet response with a global response model for low-impact energies based on an eigenvalue problem. We represent the penetrating drop as a constrained Rayleigh drop problem with a dynamic contact line. The air-water interface dynamics are analyzed using an in-viscid droplet deformation model for small deformation amplitudes. The local and global droplet response theories conform and depict that the deformation profiles could be represented as a linear superposition of eigenmodes in a Legendre polynomial basis. We further study air layer dynamics beneath an impacting droplet on a heated surface at various surface temperatures at low impact energy. The air layer thickness profile consisting of the dimple and the peripheral disc has been measured using high-speed reflection interferometric imaging. We decipher that a Gaussian profile can approximate the dimple height profile characteristics. The dim- ple thickness profile has a weak dependence on the substrate temperature and is a function of impact energy in general. The air layer rupture time scale and rupture radius increase with an increase in the substrate temperature. We characterize the air layer profile as a Knudsen field and show that a unified treatment, including continuum and non-continuum mechanics, is required to understand the air layer dynamics. The asymmetric wetting of the substrate by the impacting droplet initi- ates in the peripheral disc region. In the non-continuum regimes in the peripheral air disc, we discover intriguing asymmetric interface perturbations. These perturbative structures cause asymmetric wetting/contact between the droplet and the substrate. The sub-micron length scales of the structures exist due to the asymptotic effects of capillary and Van-der Waals interaction in the disc region.

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Kim, Minjung active 21st century. "Ab initio simulation methods for the electronic and structural properties of materials applied to molecules, clusters, nanocrystals, and liquids." Thesis, 2014. http://hdl.handle.net/2152/25099.

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Computational approaches play an important role in today's materials science owing to the remarkable advances in modern supercomputing architecture and algorithms. Ab initio simulations solely based on a quantum description of matter are now very able to tackle materials problems in which the system contains up to a few thousands atoms. This dissertation aims to address the modern electronic structure calculation methods applied to a range of various materials such as liquid and amorphous phase materials, nanostructures, and small organic molecules. Our simulations were performed within the density functional theory framework, emphasizing the use of real-space ab initio pseudopotentials. On the first part of our study, we performed liquid and amorphous phase simulations by employing a molecular dynamics technique accelerated by a Chebyshev-subspace filtering algorithm. We applied this technique to find l- and a- SiO₂ structural properties that were in a good agreement with experiments. On the second part, we studied nanostructured semiconducting oxide materials, i.e., SnO₂ and TiO₂, focusing on the electronic structures and optical properties. Lastly, we developed an efficient simulation method for non-contact atomic force microscopy. This fast and simple method was found to be a very powerful tool for predicting AFM images for many surface and molecular systems.
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Dissertations / Theses on the topic 'Non smooth contact dynamics'

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