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Tesis sobre el tema "Multi-Scale finite element method"

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Publicado: 7 de diciembre de 2024

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1

Balazi, atchy nillama Loïc. "Multi-scale Finite Element Method for incompressible flows in heterogeneous media : Implementation and Convergence analysis". Electronic Thesis or Diss., Institut polytechnique de Paris, 2024. http://www.theses.fr/2024IPPAX053.

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Cette thèse porte sur l'application d'une méthode d'éléments finis multi-échelles (MsFEM) pour résoudre les écoulements incompressibles dans des milieux multi-échelles. En effet, la simulation de l'écoulement dans un milieu multi-échelle comportant de nombreux obstacles, tel que le cœur d'un réacteur nucléaire, est un défi de taille. Afin de capturer avec précision les échelles les plus fines de l'écoulement, il est nécessaire d'utiliser un maillage très fin. Cependant, cela conduit souvent à des simulations difficiles à réaliser en raison du manque de ressources informatiques. Pour remédier à cette limitation, cette thèse développe une MsFEM non-conforme enrichie pour résoudre les écoulements visqueux incompressibles dans des milieux hétérogènes, basée sur la méthode classique des éléments finis non conformes de Crouzeix--Raviart avec des fonctions de poids d'ordre élevé. La MsFEM utilise un maillage grossier sur lequel de nouvelles fonctions de base sont définies. Ces fonctions ne sont pas les fonctions de base polynomiales classiques des éléments finis, mais résolvent les équations de la mécanique des fluides sur les éléments du maillage grossier. Ces fonctions sont elles-mêmes approximées numériquement sur un maillage fin, en tenant compte de tous les détails géométriques, ce qui confère à cette méthode son aspect multi-échelle. Une étude théorique de la MsFEM proposée est menée aux niveaux continu et discret. Tout d'abord, le caractère bien posé des problèmes locaux discrets impliqués dans la MsFEM a été démontré à l'aide de nouvelles familles d'éléments finis. Pour ce faire, une nouvelle famille d'éléments finis non conformes en trois dimensions sur les tétraèdres a été développée. En outre, la première estimation d'erreur pour l'approximation du problème de Stokes dans des milieux perforés périodiques à l'aide de cette MSFEM est établie, démontrant sa convergence. Cette estimation est basée sur la théorie de l'homogénéisation du problème de Stokes dans les domaines périodiques et sur la théorie usuelle des éléments finis. Au niveau numérique, la MsFEM pour résoudre les problèmes de Stokes et d'Oseen en deux et trois dimensions a été implémenté dans un cadre massivement parallèle dans FreeFEM. En outre, une méthodologie pour résoudre le problème de Navier-Stokes est fournie
This thesis is concerned with the application of a Multi-scale Finite Element Method (MsFEM) to solve incompressible flow in multi-scale media. Indeed, simulating the flow in a multi-scale media with numerous obstacles, such as nuclear reactor cores, is a highly challenging endeavour. In order to accurately capture the finest scales of the flow, it is necessary to use a very fine mesh. However, this often leads to intractable simulations due to the lack of computational resources. To address this limitation, this thesis develops an enriched non-conforming MsFEM to solve viscous incompressible flows in heterogeneous media, based on the classical non-conforming Crouzeix--Raviart finite element method with high-order weighting functions. The MsFEM employs a coarse mesh on which new basis functions are defined. These functions are not the classical polynomial basis functions of finite elements, but rather solve fluid mechanics equations on the elements of the coarse mesh. These functions are themselves numerically approximated on a fine mesh, taking into account all the geometric details, which gives the multi-scale aspect of this method. A theoretical investigation of the proposed MsFEM is conducted at both the continuous and discrete levels. Firstly, the well-posedness of the discrete local problems involved in the MsFEM was demonstrated using new families of finite elements. To achieve this, a novel non-conforming finite element family in three dimensions on tetrahedra was developed. Furthermore, the first error estimate for the approximation of the Stokes problem in periodic perforated media using this MSFEM is derived, demonstrating its convergence. This is based on homogenization theory of the Stokes problem in periodic domains and on usual finite element theory. At the numerical level, the MsFEM to solve the Stokes and the Oseen problems in two and three dimensions is implemented in a massively parallel framework in FreeFEM. Furthermore, a methodology to solve the Navier–Stokes problem is provided
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2

Adzima, M. Fauzan. "Constitutive modelling and finite element simulation of martensitic transformation using a computational multi-scale framework". Thesis, Swansea University, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678581.

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3

HUI, YANCHUAN. "Multi-scale Modelling and Design of Composite Structures". Doctoral thesis, Politecnico di Torino, 2019. http://hdl.handle.net/11583/2739922.

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4

Bettinotti, Omar. "A weakly-intrusive multi-scale substitution method in explicit dynamics". Thesis, Cachan, Ecole normale supérieure, 2014. http://www.theses.fr/2014DENS0032/document.

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Les matériaux composites stratifiés sont de plus en plus utilisés dans l'aéronautique, mais ils peuvent être sujets à large délaminage si soumis à impact. La nécessité d'effectuer des simulations numériques pour prédire l’endommagement devient essentielle pour l’ingénieur. Dans ce contexte, l'utilisation d'une modélisation fine semble préférable. En revanche, le coût de calcul associé serait prohibitif pour larges structures. Le but de ce travail consiste à réduire ce coût de calcul, en couplant le modèle fin, restreint à la zone active de délaminage, avec un modèle grossier appliqué au reste de la structure. En raison du comportement transitoire des problèmes d'impact, l'adaptabilité dynamique des modèles pour suivre les phénomènes évolutifs représente un point crucial de la stratégie de couplage. Des méthodes avancées sont utilisées pour coupler différents modèles. Par exemple, la méthode de Décomposition de Domaines, appliquée à l'adaptabilité dynamique, doit être combinée avec une stratégie de remaillage, considérée comme intrusive pour la mise en œuvre d'un logiciel pour Analyse à Eléments Finis. Dans ce travail, les bases d'une approche faiblement intrusive, la méthode de Substitution, sont présentés dans le domaine de la dynamique explicite. Il s’agît d’une formulation globale-locale, conçue pour appliquer un modèle grossier sur tout le domaine pour obtenir une réponse globale: ce pré-calcul est ensuite corrigé itérativement par l'application du modèle raffiné appliqué seulement où nécessaire. La vérification de la méthode de Substitution en comparaison avec la méthode de Décomposition de Domaines est présentée
Composite laminates are increasingly employed in aeronautics, but can be prone to extensive delamination when submitted to impact loads. The need of performing virtual testing to predict delamination becomes essential for engineering workflows, in which the use of a fine modeling scheme appears nowadays to be the preferred one. The associated computational cost would be prohibitively high for large structures. The goal of this work consists in reducing such computational cost coupling the fine model, restricted to the surroundings of the delamination process zone, with a coarse one applied to the rest of the structure. Due to the transient behavior of impact problems, the dynamic adaptivity of the models to follow evolutive phenomena represents a crucial feature for the coupling. Many methodologies are currently used to couple multiple models, such as non-overlapping Domain Decomposition method, that, applied to dynamic adaptivity, has to be combined with a re-meshing strategy, considered as intrusive implementation within a Finite Element Analysis software. In this work, the bases of a weakly-intrusive approach, called Substitution method, are presented in the field of explicit dynamics. The method is based on a global-local formulation and is designed so that it is possible to make use of the pre-fixed coarse model the meshes the whole structure to obtain a global response: this pre-computation is then iteratively corrected considering the application of the refined model only where required, in the picture of an adaptive strategy. The verification of the Substitution method in comparison with the Domain Decomposition method is presented
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5

Zhou, Zhiqiang. "Multiple-Scale Numerical Analysis of Composites Based on Augmented Finite Element Method". Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_dissertations/75.

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Advanced composites are playing a rapidly increasing role in all fields of material and structural related engineering practices. Damage tolerance analysis must be a critical integral part of composite structural design. The predictive capabilities of existing models have met with limited success because they typically can not account for multiple damage evolution and their coupling. As a result, current composite design is heavily dependent upon lengthy and costly test programs and empirical design methods. There is an urgent need for efficient numerical tools that are capable of analyzing the progressive failure caused by nonlinearly coupled, multiple damage evolution in composite materials. Such numerical tools are a necessity in achieving virtual testing of composites and other heterogeneous materials. In this thesis, an advanced finite element method named augmented finite element method (A-FEM) has been developed. This method is capable of incorporating nonlinear cohesive damage descriptions for major damage modes observed in composite materials. It also allows for arbitrary nucleation and propagation of such cohesive damages upon satisfactory of prescribed initiation and propagation criterion. Major advantages of the A-FEM include: 1) arbitrary cohesive cracking without the need of remeshing; 2) full compatibility with existing FEM packages; and 3) easy inclusion of intra-element material heterogeneity. The numerical capabilities of the A-FEM have been demonstrated through direct comparisons between prediction results and experimental observations of typical composite tests including 3-point bending of unidirectional laminates, open-hole tension of quasi-isotropic laminates, and double-notched tension of orthogonal laminates. In all these tests, A-FEM can predict not only the qualitative damage patterns but also quantitatively the nonlinear stress-strain curves and other history-dependent results. The excellent numerical capability of A-FEM in accurately accounting for multiple cracking in composites enables the use of A-FEM as a multi-scale numerical platform for virtual testing of composites. This has been demonstrated by a series of representative volume element (RVE) analyses which explicitly considered microscopic matrix cracking and fiber matrix interface debonding. In these cases the A-FEM successfully predicted the cohesive failure descriptions which can be used for macroscopic composite failure analyses. At the sublaminate scale, the problem of a transverse tunneling crack and its induced local delamination has been studied in detail. Two major coupling modes, which depends on the mode-I to mode-II fracture toughness ratio and cohesive strength values, has been revealed and their implications in composite engineering has been fully discussed. Finally, future improvements to the A-FEM so that it can be more powerful in serving as a numerical platform for virtual testing of composites are discussed.
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6

De, Mier Torrecilla Monica. "Numerical simulation of multi-fluid flows with the Particle Finite Element Method". Doctoral thesis, Universitat Politècnica de Catalunya, 2010. http://hdl.handle.net/10803/6872.

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La presencia simultánea de múltiples fluidos con diferentes propiedades ocurre en numerosos problemas medioambientales, procesos industriales y situaciones de la vida diaria. Algunos ejemplos son la interacción fluido-combustible en la extracción mejorada de petróleo, mezcla de polímeros, emulsiones en productos alimentarios, formación de gotas de lluvia en nubes, inyección en motores de combustión o reactores de columna de burbujas. A pesar de que los flujos de multi-fluidos son muy frecuentes, todavía suponen un reto tanto desde el punto de vista teórico como computacional. En el caso de fluidos inmiscibles, la dinámica de la interfase entre fluidos juega un papel determinante. El éxito en la simulación de estos flujos dependerá de la capacidad del método numérico de modelar con precisión la interfase y los fenómenos que tienen lugar en ella.
En este trabajo nos hemos centrado en entender la principios físicos básicos de los multi-fluidos y las dificultades que aparecen en su simulación numérica. Hemos extendido el Particle Finite Element Method (PFEM) a problemas de varios fluidos diferentes con el objetivo de explotar el hecho de que los métodos lagrangianos son especialmente adecuados para el seguimiento de todo tipo de interfases. Hemos desarrollado un esquema numérico capaz de tratar grandes saltos en las propiedades físicas (densidad y viscosidad), de incluir la tensión superficial y de representar las discontinuidades de las variables del flujo. El esquema se basa en desacoplar las variables de posición de los nodos, velocidad y presión a través de la linearización de Picard y un método de segregación de la presión que tiene en cuenta las condiciones de interfase. La interfase se ha definido alineada con la malla móvil, de forma que se mantiene el salto de propiedades físicas sin suavizar a lo largo del tiempo. Además, los grados de libertad de la presión han sido duplicados en los nodos de interfase para representar la discontinuidad de esta variable debido a la tensión superficial y a la viscosidad variable, y la malla ha sido refinada cerca de la interfase para mejorar la precisión de la simulación. Hemos aplicado el esquema resultante a diversos problemas académicos y geológicos, como el sloshingde dos fluidos, extrusión de fluidos viscosos, ascensión y rotura de una burbuja dentro de una columna de líquido, mezcla de magmas y fuentes invertidas (negatively buoyant jet).
The simultaneous presence of multiple fluids with different properties in external or internal flows is found in daily life, environmental problems, and numerous industrial processes, among many other practical situations. Examples arefluid-fuel interaction in enhanced oil recovery, blending of polymers, emulsions in food manufacturing, rain droplet formation in clouds, fuel injection in engines, and bubble column reactors, to name only a few. Although multi-fluid flows occur frequently in nature and engineering practice, they still pose a major research challenge from both theoretical and computational points of view. In the case of immiscible fluids, the dynamics of the interface between fluids plays a dominant role. The success of the simulation of such flows will depend on the ability of the numerical method to model accurately the interface and the phenomena taking place on it.

In this work we have focused on understanding the basic physical principles of multi-fluid flows and the difficulties that arise in their numerical simulation. We have extended the Particle Finite Element Method to problems involving several different fluids with the aim of exploiting the fact that Lagrangian methods are specially well suited for tracking any kind of interfaces. We have developed a numerical scheme able to deal with large jumps in the physical properties, included surface tension, and able to accurately represent all types of discontinuities in the flow variables at the interface. The scheme is based on decoupling the nodes position, velocity and pressure variables through the Picard linearization and a pressure segregation method which takes into account the interface conditions. Theinterface has been defined to be aligned with the moving mesh, so that it remains sharp along time. Furthermore, pressure degrees of freedom have been duplicated at the interface nodes to represent the discontinuity of this variable due to surface tension and variable viscosity, and the mesh has been refined in the vicinity of the interface to improve the accuracy of the computations. We have applied the resulting scheme to several academic and geological problems, such as the two-fluid sloshing, extrusion of viscous fluids, bubble rise and break up, mixing of magmatic liquids and negatively buoyant jets.
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7

Zhao, Kezhong. "A domain decomposition method for solving electrically large electromagnetic problems". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1189694496.

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8

Kimn, Edward Sun. "A parametric finite element analysis study of a lab-scale electromagnetic launcher". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39498.

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The purpose of the study is to better understand the factors that affect melt-wear in the armature-to-rail contact interface of an electromagnetic launcher (EML). In order to investigate the factors, the study uses finite element analysis (FEA) to vary parameters of a lab-scale EML at the Georgia Institute of Technology. FEA is used due to the complex nature of the system, which includes the geometry and various engineering aspects that the EML incorporates. The study focuses on an uncoupled analysis of the structural, electromagnetic (EMAG), thermal, and modal aspects. The reason for the uncoupled analysis was because the system was complex and there were computational limits. Also, by uncoupling the analysis fields, the way the parameters affected melt-wear could be viewed separately. The study varied the geometry of the armature, the stiffness of the rail system (compliance layer), and the material of the armature. The structural analysis was for the initial contact of the rail to the armature and found the von Mises stresses, contact area, and contact pressure. The EMAG analysis found the Lorentz forces in the system based on a current curve used in the lab-scale EML. The thermal analysis consisted of friction heating and Joule heating. The modal analysis was for the unstressed and pre-stressed armature. Based on the study conducted, it was found that aluminum would provide the best speeds due to its lighter mass, but lacked in the thermal resistance area. Tungsten provided the better thermal resistance, but lacked in the potential speed due to its heavier mass.
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9

Guney, Murat Efe. "High-performance direct solution of finite element problems on multi-core processors". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34662.

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A direct solution procedure is proposed and developed which exploits the parallelism that exists in current symmetric multiprocessing (SMP) multi-core processors. Several algorithms are proposed and developed to improve the performance of the direct solution of FE problems. A high-performance sparse direct solver is developed which allows experimentation with the newly developed and existing algorithms. The performance of the algorithms is investigated using a large set of FE problems. Furthermore, operation count estimations are developed to further assess various algorithms. An out-of-core version of the solver is developed to reduce the memory requirements for the solution. I/O is performed asynchronously without blocking the thread that makes the I/O request. Asynchronous I/O allows overlapping factorization and triangular solution computations with I/O. The performance of the developed solver is demonstrated on a large number of test problems. A problem with nearly 10 million degree of freedoms is solved on a low price desktop computer using the out-of-core version of the direct solver. Furthermore, the developed solver usually outperforms a commonly used shared memory solver.
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10

Schiava, D'Albano Guillermo Gonzalo. "Computational and algorithmic solutions for large scale combined finite-discrete elements simulations". Thesis, Queen Mary, University of London, 2014. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9071.

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In this PhD some key computational and algorithmic aspects of the Combined Finite Discrete Element Method (FDEM) are critically evaluated and either alternative novel or improved solutions have been proposed, developed and tested. In particular, two novel algorithms for contact detection have been developed. Also a comparative study of different contact detection algorithms has been made. The scope of this work also included large and grand scale FDEM problems that require intensive use of CPU; thus, novel parallelization solutions for grand scale FDEM problems have been developed and implemented using the MPI (Message Passing Interface) based domain decomposition. In this context a special attention is paid to the rapidly developing multi-core desktop architectures. The proposed novel solutions have been intensively validated and verified and demonstrated using various problems from literature.
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11

Chirputkar, Shardool U. "Bridging Scale Simulation of Lattice Fracture and Dynamics using Enriched Space-Time Finite Element Method". University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1313753940.

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12

Cady, Ralph. "An adaptive multi-dimensional Eulerian-Lagrangian finite element method for simulating advection-dispersion". Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184697.

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Advection-dispersion is generally solved numerically with methods that treat the problem from one of three perspectives. These are described as the Eulerian reference, the Lagrangian reference or a combination of the two that will be referred to as Eulerian-Lagrangian. Methods that use the Eulerian-Lagrangian approach incorporate the computational power of the Lagrangian treatment of advection with the simplicity of the fixed Eulerian grid. A modified version of a relatively new adaptive Eulerian-Lagrangian finite element method is presented for the simulation of advection-dispersion. Advection is solved by an adaptive technique that automatically chooses a local solution technique based upon a criterion involving the spatial variation of the gradient of the concentration. Moving particles (the method of characteristics; MOC) are used to define the concentration field in areas with significant variation of the concentration gradient. A modified method of characteristics (MMOC) called single-step reverse particle tracking is used to treat advection in areas with fairly uniform concentration gradients. As the simulation proceeds, the adaptive technique, as needed to maintain solution accuracy and optimal simulation efficiency, adjusts the advection solution process by inserting and deleting moving particles to shift between MMOC and MOC. Dispersion is simulated by a finite element formulation that involves only symmetric and diagonal matrices. Despite evidence from other investigators that diagonalization of the mass matrix may lead to poor solutions to advection-dispersion problems, this method seems to allow "lumping" of the mass matrix by essentially decoupling advection and dispersion. Based on tests of problems with analytical solutions, the method seems capable of reliably simulating the entire range of Peclet numbers with Courant numbers that range to 15.
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13

Ghurbal, Ehsan. "Un-weighted multi-criteria mesh and structural optimisation method with finite element analysis". Thesis, University of Huddersfield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273718.

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14

Dadvand, Pooyan. "A framework for developing finite element codes for multi-disciplinary applications". Doctoral thesis, Universitat Politècnica de Catalunya, 2007. http://hdl.handle.net/10803/6868.

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The world of computing simulation has experienced great progresses in recent years and requires more exigent multidisciplinary challenges to satisfy the new upcoming demands. Increasing the importance of solving multi-disciplinary problems makes developers put more attention to these problems and deal with difficulties involved in developing software in this area. Conventional finite element codes have several difficulties in dealing with multi-disciplinary problems. Many of these codes are designed and implemented for solving a certain type of problems, generally involving a single field. Extending these codes to deal with another field of analysis usually consists of several problems and large amounts of modifications and implementations. Some typical difficulties are: predefined set of degrees of freedom per node, data structure with fixed set of defined variables, global list of variables for all entities, domain based interfaces, IO restriction in reading new data and writing new results and algorithm definition inside the code. A common approach is to connect different solvers via a master program which implements the interaction algorithms and also transfers data from one solver to another. This approach has been used successfully in practice but results duplicated implementation and redundant overhead of data storing and transferring which may be significant depending to the solvers data structure. The objective of this thesis is to design and implement a framework for building multi-disciplinary finite element programs. Generality, reusability, extendibility, good performance and memory efficiency are considered to be the main points in design and implementation of this framework. Preparing the structure for team development is another objective because usually a team of experts in different fields are involved in the development of multi-disciplinary code. Kratos, the framework created in this work, provides several tools for easy implementation of finite element applications and also provides a common platform for natural interaction of its applications in different ways. This is done not only by a number of innovations but also by collecting and reusing several existing works. In this work an innovative variable base interface is designed and implemented which is used at different levels of abstraction and showed to be very clear and extendible. Another innovation is a very efficient and flexible data structure which can be used to store any type of data in a type-safe manner. An extendible IO is also created to overcome another bottleneck in dealing with multi-disciplinary problems. Collecting different concepts of existing works and adapting them to coupled problems is considered to be another innovation in this work. Examples are using an interpreter, different data organizations and variable number of dofs per node. The kernel and application approach is used to reduce the possible conflicts arising between developers of different fields and layers are designed to reflect the working space of different developers also considering their programming knowledge. Finally several technical details are applied in order to increase the performance and efficiency of Kratos which makes it practically usable. This work is completed by demonstrating the framework's functionality in practice. First some classical single field applications like thermal, fluid and structural applications are implemented and used as benchmark to prove its performance. These applications are used to solve coupled problems in order to demonstrate the natural interaction facility provided by the framework. Finally some less classical coupled finite element algorithms are implemented to show its high flexibility and extendibility.
El mundo de la simulación computacional ha experimentado un gran avance en los últimos años y cada día requiere desafíos multidisciplinares más exigentes para satisfacer las nuevas demandas. El aumento de la importancia por resolver problemas multidisciplinares hizo poner más atención a la resolución de estos problemas y a los problemas que éstos implican en el área de desarrollo de software. Los códigos convencionales de elementos finitos tienen varias dificultades para enfrentar se con problemas multidisciplinares. Muchos de estos códigos se diseñan y desarrollan para solucionar ciertos tipos de problemas, implicando generalmente un solo campo. Ampliar estos códigos para resolver problemas en otros campos del análisis, normalmente es difícil y se necesitan grandes modificaciones. Los ejemplos más comunes son: grados de libertad predefinidos para los nodos, estructura de datos capaz de guardar sólo una serie de variables definidas, lista global de las variables para todas las entidades, interfaces basadas en los dominios, capacidad del Input/Ouput para leer nuevos datos o escribir nuevos resultados y definición del algoritmo dentro del código. Un método común para resolver estos problemas es conectar varios modulos de calculo a través de un programa principal que implemente los algoritmos de la interacción y también transfiera datos de un modulo de calculo a otro. Este método se ha utilizado en la práctica con éxito, pero resulta en muchas duplicaciones del código y exceso de almacenamiento y tiempo de ejecución, dependiendo de la estructura de datos de los modulos de calculo. El objetivo de esta tesis es diseñar e implementar un marco general para el desarrollo programas de elementos finitos multidisciplinares. La generalidad, la reutilización, la capacidad de ampliación, el buen rendimiento y la eficiencia en el uso de la memoria por parte del codigo son considerados los puntos principales para el diseño e implementación de este marco. La preparación de esta estructura para un fácil desarrollo en equipo es otro objetivo importante, porque el desarrollo de un código multidisciplinar generalmente requiere expertos en diferentes campos trabajando juntos. Kratos, el marco creado en este trabajo, proporciona distintas herramientas para una fácil implementación de aplicaciones basadas en el método de los elementos finitos. También proporciona una plataforma común para una interacción natural y de diferentes maneras entre sus aplicaciones. Esto no sólo está hecho innovando, sino que además se han recogido y usado varios trabajos existentes. En este trabajo se diseña y se implementa una interface innovadora basada en variables, que se puede utilizar a diferentes niveles de abstracción y que ha demostrado ser muy clara y extensible. Otra innovación es una estructura de datos muy eficiente y flexible, que se puede utilizar para almacenar cualquier tipo de datos de manera "type-safe". También se ha creado un Input/Ouput extensible para superar otras dificultades en la resolución de problemas multidisciplinares. Otra innovación de este trabajo ha sido recoger e integrar diversos conceptos de trabajos ya existentes, adaptándolos a problemas acoplado.Esto incluye el uso de un intérprete, diversas organizaciones de datos y distinto número de grados de libertad por nodo. El concepto de núcleo y aplicación se utiliza para separar secciones del codigo y reducir posibles conflictos entre desarrolladores de diversos campos. Varias capas en la estructura de Kratos han sido diseñadas considerando los distintos niveles de programación de diferentes tipos de desarrolladores. Por último, se aplican varios detalles técnicos para aumentar el rendimiento y la eficacia de Kratos, convirtiendo lo en una herramienta muy útil para la resolución de problemas prácticos. Este trabajo se concluye demostrando el funcionamiento de Kratos en varios ejemplos prácticos. Primero se utilizan algunas aplicaciones clásicas de un solo campo como prueba patrón de rendimiento. Después, estas aplicaciones se acoplan para resolver problemas multidisciplinares, demostrando la facilidad natural de la interacción proporcionada por Kratos. Finalmente se han implementado algunos algoritmos menos clásicos para demostrar su alta flexibilidad y capacidad.
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15

Procopio, Adam T. Zavaliangos Antonios. "On the compaction of granular media using a multi-particle finite element model /". Philadelphia, Pa. : Drexel University, 2006. http://hdl.handle.net/1860/1297.

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16

Mayeur, Jason R. "Generalized continuum modeling of scale-dependent crystalline plasticity". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/39635.

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The use of metallic material systems (e.g. pure metals, alloys, metal matrix composites) in a wide range of engineering applications from medical devices to electronic components to automobiles continues to motivate the development of improved constitutive models to meet increased performance demands while minimizing cost. Emerging technologies often incorporate materials in which the dominant microstructural features have characteristic dimensions reaching into the submicron and nanometer regime. Metals comprised of such fine microstructures often exhibit unique and size-dependent mechanical response, and classical approaches to constitutive model development at engineering (continuum) scales, being local in nature, are inadequate for describing such behavior. Therefore, traditional modeling frameworks must be augmented or reformulated to account for such phenomena. Crystal plasticity constitutive models have proven quite capable of capturing first-order microstructural effects such as grain orientation, grain morphology, phase distribution, etc. on the deformation behavior of both single and polycrystals, yet suffer from the same limitations as other local continuum theories with regard to modeling scale-dependent mechanical response. This research is focused on the development, numerical implementation, and application of a novel, physics-based generalized (nonlocal) theory of single crystal plasticity. Two distinct versions of a dislocation-based micropolar single crystal plasticity theory are developed and discussed within the context of more prominent nonlocal crystal plasticity theories. The constitutive models have been implemented in the commercial finite element code Abaqus, and the size-dependent deformation of both single and polycrystalline metals have been studied via direct numerical simulation. A comparison of results obtained from the solution of several equivalent initial-boundary value problems using the developed models and a model of discrete dislocation dynamics has demonstrated the predictive capabilities of the micropolar theory and also highlighted areas for potential model refinement.
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17

Lallemant, Lucas. "Numerical homogenization of a rough bi-material interface". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41111.

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The mechanical reliability of electronic components has become harder and harder to predict due to the use of composite materials. One of the key issues is creating an accurate model of the delamination mechanism, which consists in the separation of two different bounded materials. This phenomenon is a very challenging issue that is investigated in the Nano Interface Project (NIP), in which this thesis is involved. The macroscopic adhesion force is governed by several parameters described at different length scales. Among these parameters, the roughness profile of the interface has a pronounced influence. The main difficulty for an accurate delamination characterization is then investigating the effects of this roughness profile and the modifications it implies for the overall cohesion. The objective of the NIP is to develop an interface model for the numerical testing of electronic components in a finite element software. The problem is that a direct modeling of all the mechanisms described previously is really expensive in term of computation time, if possible at all. This difficulty is increased by the huge mismatch of the mechanical properties of the materials in contact. A scale transition method is therefore required, which is provided by homogenization. The idea is to consider the delamination at a wider scale. Rather than modeling the whole roughness profile, the adhesion at the interface will be described by homogenized, or macroscopic, parameters extracted from a representative model at the micro-scale, the RVE. This thesis will deal with the determination of these homogenized parameters.
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18

Kim, Kyusang. "The Atomic-scale Finite Element Method for Analyzing Mechanical Behavior of Carbon Nanotube and Quartz". Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/34851.

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The mechanical behavior of discrete atoms has been studied with molecular dynamics whose computational time is proportional to the square of the number of atoms, O(N2). Recently, a faster algorithm, Atomic-scale Finite Element Method (AFEM) with computational time proportional to the number of atoms, O(N), had been developed. The main idea of AFEM, compared with conventional finite element method is to replace nodes with atoms and elements with electric forces between atoms. When interpreting a non-linear system, it is necessary to use an iteration scheme.

A simulation of molecular dynamics based on the Verlet's method was conducted in order to validate AFEM in one dimension. The speed of AFEM was investigated in one and two dimensional atomic systems. The results showed that the computational time of AFEM is approximately proportional to the number of atoms, and the absolute computation time appears to be small. The frameworks of AFEM not only for multi-body potential but also pair potential are presented. Finally, AFEM was applied to analyze and interpret the mechanical behavior of a carbon nanotube and a quartz. The buckling behavior of carbon nanotube showed a good agreement with the results illustrated in the original literature.


Master of Science
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19

Mello, Frank James. "Weak formulations in analytical dynamics, with applications to multi-rigid-body systems, using time finite elements". Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/32854.

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20

Lepenies, Ingolf G. "Zur hierarchischen und simultanen Multi-Skalen-Analyse von Textilbeton". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1231842928873-71702.

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Die Arbeit widmet sich der Simulation und der Prognose des Materialverhaltens des Hochleistungsverbundwerkstoffes Textilbeton unter Zugbeanspruchungen. Basierend auf einer hierarchischen mechanischen Modellbildung (Multi-Skalen-Analyse) werden die Tragmechanismen des Verbundwerkstoffes auf drei Strukturebenen abgebildet. Damit lassen sich die den Verbundwerkstoff charakterisierenden mechanischen Kenngrößen aus experimentell ermittelten Kraft-Verschiebungs-Abhängigkeiten ableiten. Diese Kenngrößen sind mit heutiger Messtechnik nicht direkt experimentell bestimmbar. Es wird ein Mikro-Meso-Makro-Prognosemodell (MMM-Prognosemodell) für Textilbeton entwickelt, das basierend auf der Simulation des Mikrostrukturverhaltens das makroskopische Materialverhalten prognostiziert. Die Grundlage dafür bildet die qualitative und quantitative Bestimmung der Verbundeigenschaften zwischen der Filamentbewehrung und der einbettenden Matrix. Für das Verbundverhalten von Rovings in einer Feinbetonmatrix wird, ausgehend von einer Rovingapproximation mit superelliptischem Querschnitt, die partielle Imprägnierung des Rovings und die daraus resultierende Verbundwirkung identifiziert und simuliert. Auf Grundlage der mikro- und mesomechanischen Modelle sowie der Kalibrierung und Verifizierung des MMM-Prognosemodells durch die Simulation von Filament- und Rovingauszugsversuchen wird das makroskopische Zugverhalten von Textilbeton mit Mehrfachrissbildung prognostiziert. Die numerischen Ergebnisse werden durch die Ergebnisse der experimentellen Dehnkörperversuche validiert. Das MMM-Prognosemodell für Textilbeton wird im Rahmen einer hierarchischen Multi-Skalen-Analyse auf Zugversuche von Textilbetonbauteilen angewendet. Weiterhin wird die Verstärkungswirkung einer Textilbetonschicht an Stahlbetonbauteilen unter Biegebeanspruchung zutreffend simuliert. Es wird das nichtlineare Bauteilverhalten abgebildet, wobei die Bauteildurchbiegung, die effektiven Rovingbeanspruchungen und die Beanspruchungen der Filamente im Roving abgebildet werden
The present work deals with the simulation and the prediction of the effective material behavior of the high performance composite textile reinforced concrete (TRC) subjected to tension. Based on a hierarchical material model within a multi scale approach the load bearing mechanisms of TRC are modeled on three structural scales. Therewith, the mechanical parameters characterizing the composite material can be deduced indirectly by experimentally determined force displacement relations obtained from roving pullout tests. These parameters cannot be obtained by contemporary measuring techniques directly. A micro-meso-macro-prediction model (MMM-PM) for TRC is developed, predicting the macroscopic material behavior by means of simulations of the microscopic and the mesoscopic material behavior. The basis is the qualitative and quantitative identification of the bond properties of the roving-matrix system. The partial impregnation of the rovings and the corresponding varying bond qualities are identified to characterize the bond behavior of rovings in a fine-grained concrete matrix. The huge variety of roving cross-sections is approximated by superellipses on the meso scale. The macroscopic behavior of TRC subjected to tension including multiple cracking of the matrix material is correctly predicted on the basis of the micro- and meso-mechanical models. The calibration and verification of the MMM-PM is performed by simulations of roving pullout tests, whereas a first validation is carried out by a comparison of the numerical predictions with the experimental data from tensile tests. The MMM-PM for TRC is applied to tensile tests of structural members made of TRC. Furthermore, a steel-reinforced concrete plate strengthened by a TRC layer is accurately simulated yielding the macroscopic deflection of the plate, the mesoscopic stress state of the roving and the microscopic stresses of the filaments
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21

Kirkhope, Kenneth J. (Kenneth James) Carleton University Dissertation Engineering Mechanical. "Evaluation of stress intensity factors in multi-cracked thick-walled cylinders using finite element methods". Ottawa, 1988.

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22

Oliver, Serra Albert. "Local scale air quality model system for diagnostic and forecasting simulations using the finite element method". Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/326752.

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Air pollution is an important topic with a great social impact; it is related with public health, environment and ecology, and climate change. Scientists have developed several models in the last thirty years, and regional air quality operational systems are used routinely by governments and agencies. Efforts have also been done to simulate the air quality in the local scale; main models are Gaussian and Puff models, that are based on a Lagrangian approach. In contrast with these models, in this thesis we have developed a system using an Eulerian approach. This model is specifically designed for regions with complex orography where the Lagrangian models have problems computing the trajectory of the particles. This model can be used for diagnostic or prediction simulations. Air quality operational systems depend on the orography, meteorological data, and emission data. Air quality models use processors to incorporate these data into the model. The data can come from numerical weather prediction systems, experimental data, or databases. In this thesis we have developed processors, specifically designed for the local scale, to incorporate these data into our system. To incorporate the orography, we have developed a mesh generation algorithm suitable for complex terrain discretization; it also allows to insert layers that can match the regional models. A wind field model has also been used; it can interpolate a three-dimensional wind field from some station measurements using a log-linear vertical wind profile, or can interpolate it from a numerical weather prediction system. Once an interpolated wind field is computed, a mass-consistent model is applied to ensure null divergence and impermeability in the terrain. The wind field is modified to take into account the injection of the pollutants into the atmosphere. Briggs studied the trajectory of the plume rise giving some empirical equations that will be used in our model. Briggs' equations describe the trajectory in a plane; our model will modify this trajectory adapting it to the ambient wind field. This modification allows the plume rise to surround the mountains or channel into the valleys. The transport and reaction of pollutants in the atmosphere is then computed using an splitting method, so the transport and the chemical reactions are computed independently. To solve the transport of pollutants we have used a finite element method stabilized using least squares. The chemical reaction is simulated using simplified models such as RIVAD, or more complex ones such as CB05. To obtain more accurate results we have used adaptation. An error indicator has been used to adapt the mesh to the solution. To adapt the mesh to the concentration distribution of all the species is very demanding, for this reason we have used a multimesh method where every chemical specie has its own mesh where we solve the transport and the chemical reactions are simulated in a common mesh. The system developed in this thesis has diagnostic and forecasting capabilities. For this reason we present two different applications. The first one is a diagnostic application in La Palma island (Spain), where wind measurements are given, and SO2 and NO2 emissions from a stack are considered. The topography of the island is real, from a digital elevation model, but the wind field measurements, and the stack location and emissions, are simulated. The second application is a forecasting application data from the CMAQ benchmark test. It is located in the surrounding of Pineville Kentucky. In this application we have used all the data from CMAQ and the chemical reaction model CB05.
La contaminació atmosfèrica té gran impacte social; està relacionada ambla salut pública, l'ecologia, el medi ambient i el canvi climàtic. En els últims trenta anys, els científics han desenvolupat diversos models que els governs i les agències mediambientals utilitzen diàriament. També s'han fet esforços per simular la qualitat de l'aire en l'escala local. Els models principals són els models Gaussians i Puff, que es basen en una descripció Lagrangiana. En contrast amb aquests models, en aquesta tesi s'ha desenvolupat un sistema que utilitza una descripció Euleriana. Aquest model està dissenyat específicament per a les regions amb topografia complexa on els models Lagrangians tenen problemes calculant la trajectòria de les partícules. El model presentat en aquesta tesi pot ser utilitzat tant pel diagnòstic com per la predicció. Els sistemes operatius utilitzats actualment depenen de l'orografia, de dades meteorològiques i de dades d'emissió. Per tal d'incorporar aquestes dades, els models de qualitat de l'aire han desenvolupat diferents preprocessadors. Les dades poden venir dels sistemes numèrics de predicció meteorològics, de dades experimentals o de bases de dades. En aquesta tesi hem desenvolupat preprocessadors dissenyats específicament per a l'àmbit local, per tal d'incorporar aquestes dades al nostre sistema. Per incorporar l'orografia, hem desenvolupat un algoritme de generació de malles adequat per terreny complex; l'algoritme també ens permet inserir capes que poden coincidir amb la dels models regionals. S'ha desenvolupat un model de càlcul de camp de vent; a partir de les dades s'interpola un camp de vent tridimensional fent servir un perfil log-lineal vertical del vent, o s'interpola a partir dels resultats d'un sistema de predicció meteorològica. Quan s'ha calculat el vent interpolat, es fa servir un model de massa consistent per obtenir un camp de vent definitiu on s'ha imposat divergència zero i impermeabilitat del terreny. El camp de vent s'ha de modificar per tenir en compte la injecció dels contaminants a l'atmosfera. Briggs va estudiar la trajectòria de l'elevació de la ploma i va trobar equacions empíriques que utilitzarem en el nostre model. Les equacions de Briggs descriuen la trajectòria de la ploma en un pla vertical; el nostre model modificarà aquesta trajectòria adaptant-la al camp de vent ambiental. Aquesta modificació permet que l'elevació de la ploma rodegi les muntanyes o s'acanali a les valls. El transport i la reacció de contaminants a l'atmosfera es calcula utilitzant un mètode de "splitting", de manera que el transport i la reacció química es calculen de forma independent. Per resoldre el transport de contaminants, hem utilitzat el mètode d'elements finits estabilitzat amb mínims quadrats. La reacció química es simula mitjançant models simplificats com el model RIVAD, o més complexes com el CB05. Per obtenir resultats més precisos hem adaptat la malla a la solució utilitzant un indicador d'error. Haver d'adaptar la malla a la distribució de la concentració de totes les espècies contaminants és molt exigent i per aquest motiu hem utilitzat un mètode "multimesh" on cada espècie química té la seva pròpia malla on resolem el transport i les reaccions químiques es simulen en una malla comú. El sistema desenvolupat en aquesta tesi té capacitats de diagnòstic i pronòstic. Per aquesta raó es presenten dues aplicacions diferents. La primera és una aplicació de diagnòstic a l'illa de la Palma (Espanya), on es disposa de mesures de vent, i de les emissions de SO2 i NO2 d'una xemeneia. La topografia de l'illa és real, a partir d'un model digital del terreny, però les dades del camp de vent, la ubicació de la xemeneia i el valor de les emissions són simulades. La segona aplicació és una aplicació de predicció fent servir els resultats del benchmark del CMAQ. Es simula una zona a Pineville Kentucky. En aquesta aplicació hem utilitzat totes les dades del CMAQ i el model químic CB05.
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23

Wang, Dong. "A micro-scale method to associate the fatigue properties of asphalt binder, mastic and mixture". Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/38667.

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The fatigue damage is one of the most common distresses observed on the asphalt concrete pavement. The initiation and propagation of the fatigue damage is a complicated phenomenon and very difficult to detect. In order to thoroughly understand the fatigue of asphalt concrete, the behaviors of the key components of asphalt concrete under cyclic loading are investigated respectively. A new experiment method is developed to test the performances of asphalt binder, mastic and mixture under cyclic loading, which provides a tool to unify the fatigue test method for both binding medium and asphalt mixture. Using the new fatigue test method, the effects of loading magnitude, temperature and loading rate to the performance of the asphalt binder under cyclic loading are estimated. Mastic and mixture specimens are prepared by adding fillers and controlled-size aggregates into the asphalt binder. The effects of filler content to the performance of mastic specimen are discussed. The differences between the test results of mastic and mixture are compared and analyzed. Incorporated with the new fatigue test, x-ray tomography system is used in this study to: 1. Analyze the structure change of the mastic specimen before and after the fatigue test. 2. Compare the void content differences between the mastic and mixture specimens. 3. Reconstruct the 3-D internal structures of mastic and mixture specimens to build up the digital specimens. The digital specimens are used in the fatigue simulation of the asphalt binder, mastic and mixture specimens based on the finite element method. The asphalt binder, filler and aggregate are treated as different materials. Damage parameter is introduced to model the degradation of elastic modulus of the asphalt binder caused by fatigue damage. Direct cyclic analysis available in ABAQUS is used to obtain the response of the material after large number of loading cycles. The basalt fibers are dispersed into the asphalt binder and mastic specimens, the effects of the basalt fiber to the performances of the binder and mastic at low temperature are analyzed using both experimental and FEM modeling methods.
Ph. D.
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24

Yoshimura, Ryokei. "Global-scale electromagnetic induction : a new three-dimensional forward simulator using an edge-based finite element method". 京都大学 (Kyoto University), 2002. http://hdl.handle.net/2433/149993.

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Kaya, Deniz. "Pricing a Multi-Asset American Option in a Parallel Environment by a Finite Element Method Approach". Thesis, Uppsala universitet, Matematiska institutionen, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-155546.

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There is the need for applying numerical methods to problems that cannot be solved analytically and as the spatial dimension of the problem is increased the need for computational recourses increase exponentially, a phenomenon known as the “curse of dimensionality”. In the Black-Scholes-Merton framework the American option pricing problem has no closed form solution and a numerical procedure has to be employed for solving a PDE. The multi-asset American option introduces challenging computational problems, since for every added asset the dimension of the PDE is increased by one. One way to deal with the curse of dimensionality is threw parallelism. Here the finite element method-of-lines is used for pricing a multi-asset American option dependent on up to four assets in a parallel environment. The problem is also solved with the PSOR method giving a accurate benchmark used for comparison. In finance the put option is one of the most fundamental derivatives since it is basically asset-value insurance and a lot of research is done in the field of quantitative finance on accurate and fast pricing techniques for the multi-dimensional case. “What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.” Norbert Wiener “As soon as an Analytical Engine exists, it will necessarily guide the future course of the science. Whenever any result is sought by its aid, the question will then arise – by what course of calculation can these results be arrived at by the machine in the shortest time?” Charles Babbage
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26

Seriacopi, Vanessa. "Evaluation of abrasive mechanisms in metallic alloys during scratch tests: a numerical-experimental study in micro-scale". Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-12032018-144239/.

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The abrasion can have some approaches, such as: (i-) the manufacturing processes and the production of different surface features and finishing of workpieces and components; and (ii-) in terms of the wear and failure, which occur in tools materials. The present thesis consists in developing a numerical model by Finite Element Method (FEM) validated by experimental tests, aiming to evaluate microstructural influences on the abrasion of metallic alloys. Therefore, objectives are related to define rules focused on ductile material design to obtain cutting resistance. Regardless of their applications, the abrasive micro-mechanism depends on mechanical and damage properties of the materials and their microstructure. A simplified abrasion study is developed considering a single abrasive over a microstructure to evaluate from ploughing to cutting. Thus, scratch tests are performed in micro-scale, applying different ranges of constant normal force. Moreover, the specimen characterization was conducted using optical and electronic microscopy techniques, optical interferometry, conventional hardness, and instrumented indentation. By the developed numerical approach, the results were: (a-) in terms of apparent coefficient of friction (COF), the found numerical and experimental mismatches are assigned to the effects of adhesion, anisotropy, grain boundaries and twinning, for instance, which were not taken into account on the modelling; (b-) the hard precipitates have a prevailing effect over the matrix regarding the apparent COF, whereas the matrix effect is dominant of the soft precipitates on the COF behavior; (c-) as a consequence of the reduced strain energy and tangential load, the local COF decreased when the abrasive scratches the hard precipitates; (d-) regarding the depth of penetration and removed volume, the numerical results are in accordance with the experimental results; (e-) there is not a remarkable micro-mechanism transition using the approach of the dimensional wear coefficient as a function of normal load, which indicates that several abrasive micro-mechanisms can occur in a single scratching; however, a predominance of a certain micro-mechanism can be observed; (f-) hard precipitates often decreases the local depth of penetration and, as a consequence, they cause the reduced of removed volume and increased the local specific energy; (g-) considering the studied range of the normal load, soft precipitates follow the matrix mass removal behavior, but these particles can show fluctuations of the local specific energy in the less severe abrasion; and, finally, (h) the map of the abrasive resistance x deformed hardness/attack angle is an important tool to point out the dominant ductile or brittle effect on the microstructure (mechanical properties); and it delineates frontiers for the abrasive micromechanisms.
A abrasão pode ser tanto tratada do ponto de vista de processos de manufatura e geração de características superficiais distintas em peças e componentes, quanto pode ser abordada em termos de desgaste e falha em diferentes ferramentas aplicadas em processos de fabricação. A presente tese remete ao desenvolvimento de um modelo numérico pelo Método dos Elementos Finitos (MEF), validado por ensaios experimentais, com o objetivo de avaliar influências de aspectos microestruturais na abrasão de ligas metálicas. Portanto, o objetivo desta tese é focado na construção de regras que auxiliem no projeto de materiais dúcteis para terem resistência ao corte. Independentemente da aplicação, os estudos da ocorrência dos micro-mecanismos de abrasão incorporam propriedades mecânicas e de dano dos materiais e suas fases. A avaliação do micro-sulcamento ao micro-corte foi realizada a partir de um estudo simplificado de abrasão, considerando o riscamento de microestruturas por um único abrasivo. Dessa forma, ensaios de riscamento em micro-escala aplicando força normal constante dentro de uma faixa específica. Em adição, as caracterizações das amostras são realizadas a partir de técnicas de microscopia óptica e eletrônica, interferometria óptica, dureza convencional e indentação instrumentada. Por meio da abordagem numérica desenvolvida, os principais resultados obtidos foram: (a-) in termos de coeficiente de atrito aparente (COF), as divergências numérica e experimental encontradas foram decorrentes principalmente do efeito da adesão, anisotropia, contornos de grão e maclação que não foram levadas em conta na simulação; (b-) os precipitados duros tendem a ter efeito predominante sobre a matriz no que diz respeito ao COF aparente, ao passo que a influência da matriz é predominante sobre o comportamento dos precipitados moles; (c-) como consequência das reduções de energia de deformação e força tangencial, o COF local tende a ser diminuído quando o abrasivo passa por precipitados duros durante o riscamento; (d-) os resultados numéricos de profundidade de penetração média e volume removido total são consistentes com os resultados experimentais; (e-) não há uma transição marcante de micro-mecanismo em função de coeficiente de desgaste dimensional em função da carga, indicando uma predominância de um certo micro-mecanismo em um dado risco e, não ocorrendo transições bruscas; (f-) precipitados duros, em geral, diminuem a profundidade de penetração local e, assim, eles reduzem o volume removido e aumentam a energia específica; (g-) para a faixa de força normal avaliada, os precipitados moles seguiram o comportamento de remoção de material de sua matriz, mas podem apresentar oscilações na energia específica local nas condições menos severas de abrasão; e, por fim, (h-) o mapa de resistência à abrasão x dureza após deformação/ângulo de ataque é uma importante ferramenta para definir efeitos dominantes de propriedades mecânicas (dúctil e frágil) na microestrutura submetida à abrasão, e faz o delineamento de fronteiras de micro-mecanismos abrasivos.
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27

Steinigen, Frank, Jan-Uwe Sickert, Andreas Hoffmann, Wolfgang Graf y Michael Kaliske. "Tragwerke aus Textilbeton - numerische Strukturanalyse". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-78053.

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Der Beitrag gibt einen kompakten Überblick zur Leistungsfähigkeit und Anwendbarkeit der in den Teilprojekten D2-Numerische Simulation, E3-Sicherheitsbeurteilung und E4-Numerische Langzeitprognose des Sonderforschungsbereichs 528 entwickelten Algorithmen und Programmlösungen. Die gezeigten Methoden sind praxistauglich aufbereitet und stehen zur Anwendung für die Analyse des Kurz- und Langzeit-Tragverhaltens von Textilbetonstrukturen zur Verfügung
The paper provides a compact summary of the ability and applicability of the algorithms and software packages developed in the project parts D2-Numerical Simulation, E3-Reliability Assessment und E4-Numerical Long-term Prognosis of the Collaborative Research Centre 528. The presented methods are prepared for practical use and are available for the analysis of the short- and longterm load-bearing behaviour of textile reinforced concrete structures
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28

Lepenies, Ingolf G. "Zur hierarchischen und simultanen Multi-Skalen-Analyse von Textilbeton". Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A23636.

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Die Arbeit widmet sich der Simulation und der Prognose des Materialverhaltens des Hochleistungsverbundwerkstoffes Textilbeton unter Zugbeanspruchungen. Basierend auf einer hierarchischen mechanischen Modellbildung (Multi-Skalen-Analyse) werden die Tragmechanismen des Verbundwerkstoffes auf drei Strukturebenen abgebildet. Damit lassen sich die den Verbundwerkstoff charakterisierenden mechanischen Kenngrößen aus experimentell ermittelten Kraft-Verschiebungs-Abhängigkeiten ableiten. Diese Kenngrößen sind mit heutiger Messtechnik nicht direkt experimentell bestimmbar. Es wird ein Mikro-Meso-Makro-Prognosemodell (MMM-Prognosemodell) für Textilbeton entwickelt, das basierend auf der Simulation des Mikrostrukturverhaltens das makroskopische Materialverhalten prognostiziert. Die Grundlage dafür bildet die qualitative und quantitative Bestimmung der Verbundeigenschaften zwischen der Filamentbewehrung und der einbettenden Matrix. Für das Verbundverhalten von Rovings in einer Feinbetonmatrix wird, ausgehend von einer Rovingapproximation mit superelliptischem Querschnitt, die partielle Imprägnierung des Rovings und die daraus resultierende Verbundwirkung identifiziert und simuliert. Auf Grundlage der mikro- und mesomechanischen Modelle sowie der Kalibrierung und Verifizierung des MMM-Prognosemodells durch die Simulation von Filament- und Rovingauszugsversuchen wird das makroskopische Zugverhalten von Textilbeton mit Mehrfachrissbildung prognostiziert. Die numerischen Ergebnisse werden durch die Ergebnisse der experimentellen Dehnkörperversuche validiert. Das MMM-Prognosemodell für Textilbeton wird im Rahmen einer hierarchischen Multi-Skalen-Analyse auf Zugversuche von Textilbetonbauteilen angewendet. Weiterhin wird die Verstärkungswirkung einer Textilbetonschicht an Stahlbetonbauteilen unter Biegebeanspruchung zutreffend simuliert. Es wird das nichtlineare Bauteilverhalten abgebildet, wobei die Bauteildurchbiegung, die effektiven Rovingbeanspruchungen und die Beanspruchungen der Filamente im Roving abgebildet werden.
The present work deals with the simulation and the prediction of the effective material behavior of the high performance composite textile reinforced concrete (TRC) subjected to tension. Based on a hierarchical material model within a multi scale approach the load bearing mechanisms of TRC are modeled on three structural scales. Therewith, the mechanical parameters characterizing the composite material can be deduced indirectly by experimentally determined force displacement relations obtained from roving pullout tests. These parameters cannot be obtained by contemporary measuring techniques directly. A micro-meso-macro-prediction model (MMM-PM) for TRC is developed, predicting the macroscopic material behavior by means of simulations of the microscopic and the mesoscopic material behavior. The basis is the qualitative and quantitative identification of the bond properties of the roving-matrix system. The partial impregnation of the rovings and the corresponding varying bond qualities are identified to characterize the bond behavior of rovings in a fine-grained concrete matrix. The huge variety of roving cross-sections is approximated by superellipses on the meso scale. The macroscopic behavior of TRC subjected to tension including multiple cracking of the matrix material is correctly predicted on the basis of the micro- and meso-mechanical models. The calibration and verification of the MMM-PM is performed by simulations of roving pullout tests, whereas a first validation is carried out by a comparison of the numerical predictions with the experimental data from tensile tests. The MMM-PM for TRC is applied to tensile tests of structural members made of TRC. Furthermore, a steel-reinforced concrete plate strengthened by a TRC layer is accurately simulated yielding the macroscopic deflection of the plate, the mesoscopic stress state of the roving and the microscopic stresses of the filaments.
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29

Assaad, Al Ayoubi Nazih. "Multi-scale modeling of fiber orientation in coupled fiber-reinforced viscous polymer systems". Electronic Thesis or Diss., Ecole centrale de Nantes, 2024. http://www.theses.fr/2024ECDN0008.

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Les thermoplastiques renforcés par des fibres courtes ont acquis une notoriété croissante en ingénierie, notamment dans les applications automobiles. La prédiction précise de l'orientation des fibres est cruciale car elle influence les caractéristiques mécaniques. Les travaux de recherche antérieurs dans ce domaine ont mis en exergue la complexité inhérente à l'orientation des fibres au sein d'un écoulement. La majorité des simulations industrielles s'appuient sur des modèles macroscopiques qui font usage de quantités préalablement moyennées et d'approximations de fermeture, engendrant fréquemment des inexactitudes dans la prédiction de l'orientation des fibres. Afin de relever ce défi, la présente étude propose une nouvelle approche reposant sur la résolution de l'équation de Fokker-Planck à l'échelle mésoscopique.La méthode des éléments finis (MEF) est utilisée pour calculer l'orientation des fibres, permettant une représentation plus précise du comportement des fibres. Le tenseur d'orientation ainsi calculé est intégré aux équations de Stokes, engendrant un modèle multi-échelle de l'interaction entre les fibres et l'écoulement environnant, ce qui enrichit considérablement notre compréhension de cette dynamique complexe. Finalement, un modèle d'écoulement à deux phases est étudié, reproduisant fidèlement des situations réelles telles que le processus de surmoulage. En exploitant ce modèle multi-échelle, cette étude vise à améliorer la précision des simulations dans les applications industrielles, offrant de nouvelles perspectives pour l'optimisation des processus et la conception
Thermoplastics reinforced with short fibers have gained prominence in engineering, notably in automotive applications. Accurate prediction of fiber orientation is crucial, as it profoundly influences mechanical characteristics. Previous research in this field has highlighted the complexity of fiber orientation within a flow. Most industrial simulations rely on macroscopic models that use pre-averaged quantities and closure approximations, often resulting in inaccuracies in predicting fiber orientation. To address this challenge and enhance accuracy, this study presents a novel approach based on resolving the Fokker-Planck equation at the meso-scale level, offering a more detailed and accurate model for predicting fiber orientation.In this work, the finite element method (FEM) is used to compute fiber orientation, providing a more precise representation of fiber behavior. Subsequently, the computed orientation tensor is integrated into the Stokes equations, creating a multi-scale fiber-flow model which enhances our understanding of the dynamic interaction between fibers and the surrounding flow. Furthermore, the research extends its scope to develop a two-phase flow model, reflecting real-world scenarios such as overmolding process. By leveraging the multi-scale model, this work aims to improve the accuracy of simulations in industrial applications, providing valuable insights for process optimization and design
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30

Jamond, Olivier. "Propagation numérique de zones critiques dans un pneumatique par approches multi-modèles". Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2011. http://www.theses.fr/2011ECAP0020/document.

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Ces travaux se sont attachés au développement, à l’implémentation et à la validation d’une stratégie numérique pour la simulation de l’évolution d’un endommagement localisé susceptible de conduire à l’apparition, puis à la propagation de fissures dans une structure complexe, incompressible. Nous avons abordé cet objectif général en procédant par étapes.Dans un premier temps, nous avons développé une méthodologie numérique innovante pour la propagation de fissures dans le cadre de la mécanique de la rupture fragile. Cette méthodologie a deux caractéristiques importantes : incluant l’enrichissement Heaviside de la méthode XFEM dans le cadre de modélisation Arlequin, cette méthodologie permet de ne pas remailler la structure initiale, au cours de la propagation de la fissure. Attachant un patch Arlequin local en fond de la fissure qui se propage, elle permet d’approcher, avec la précision nécessaire, le comportement local des champs mécaniques. Cette méthodologie a été implémentée et testée numériquement. Dans un deuxième temps, nous avons étendu cette méthodologie pour la prise en compte de l’endommagement par fatigue. Dans l’approche développée, l’initiation et la propagation de fissures sont pilotées par l’évolution du champ d’endommagement. Un modèle heuristique représentatif, fournissant les incréments de propagation d’une fissure à partir des champs d’endommagement et de contraintes au voisinage de sa pointe, est proposé. En utilisant des modèles physiques représentatifs des difficultés liées à la problématique d’initiation et de propagation de fissures, sous l’effet d’un endommagement par fatigue, nous avons montré, à travers des essais numériques, une faisabilité globale de notre approche. Dans un troisième temps, nous nous sommes intéressés à la prise en compte de la contrainte d’incompressibilité dans une modélisation Arlequin. L’intégration de cette contrainte pose pour la formulation Arlequin continue et/ou discrète des questions spécifiques : comment gérer la double contrainte dans la zone de couplage en continu et en discret ?, comment traiter les éléments partiellement incompressibles ? Des réponses sont données et étayées théoriquement et/ou numériquement. Enfin, nous avons proposé un ensemble de procédures pratiques, permettant d’évaluer, de manière générale et performante, une intersection de maillages tridimensionnels. Ces développements, nécessaires à la mise en œuvre opérationnelle du cadre Arlequin dans des codes industriels, sont validés par des résultats de calculs Arlequin 3D
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31

Rukavina, Tea. "Multi-scale damage model of fiber-reinforced concrete with parameter identification". Thesis, Compiègne, 2018. http://www.theses.fr/2018COMP2460/document.

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Dans cette thèse, plusieurs approches de modélisation de composites renforcés par des fibres sont proposées. Le matériau étudié est le béton fibré, et dans ce modèle, on tient compte de l’influence de trois constituants : le béton, les fibres, et la liaison entre eux. Le comportement du béton est analysé avec un modèle d’endommagement, les fibres d'acier sont considérées comme élastiques linéaires, et le comportement sur l'interface est décrit avec une loi de glissement avec l’extraction complète de la fibre. Une approche multi-échelle pour coupler tous les constituants est proposée, dans laquelle le calcul à l'échelle macro est effectué en utilisant la procédure de solution operator-split. Cette approche partitionnée divise le calcul en deux phases, globale et locale, dans lesquelles différents mécanismes de rupture sont traités séparément, ce qui est conforme au comportement du composite observé expérimentalement. L'identification des paramètres est effectuée en minimisant l'erreur entre les valeurs calculées et mesurées. Les modèles proposés sont validés par des exemples numériques
In this thesis, several approaches for modeling fiber-reinforced composites are proposed. The material under consideration is fiber-reinforced concrete, which is composed of a few constituents: concrete, short steel fibers, and the interface between them. The behavior of concrete is described by a damage model with localized failure, fibers are taken to be linear elastic, and the behavior of the interface is modeled with a bond-slip pull-out law. A multi-scale approach for coupling all the constituents is proposed, where the macro-scale computation is carried out using the operator-split solution procedure. This partitioned approach divides the computation in two phases, global and local, where different failure mechanisms are treated separately, which is in accordance with the experimentally observed composite behavior. An inverse model for fiber-reinforced concrete is presented, where the stochastic caracterization of the fibers is known from their distribution inside the domain. Parameter identification is performed by minimizing the error between the computed and measured values. The proposed models are validated through numerical examples
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32

Ireland, David John. "Dielectric Antennas and Their Realisation Using a Pareto Dominance Multi-Objective Particle Swarm Optimisation Algorithm". Thesis, Griffith University, 2010. http://hdl.handle.net/10072/365312.

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Antennas utilising a dielectric medium are technologies that have become popular in modern wireless platforms. They offer several desirable features such as high efficiency, electrically small and resistance to proximity detuning. Being a volumetric radiator however, realising a final, commercially competitive solution, often requires the use of a computational optimisation algorithm. In the realm of antenna design the practice of optimisation typically involves an automated routine consisting of a heuristic algorithm and a forward solving engine such as the finite element method (FEM) or finite difference time domain (FDTD) method. The solving engine is used to derive a post-processed performance value typically referred to as an objective or fitness function, while the heuristic method uses the objective function data to determine the next trial solution or solutions that approach a design goal. Nowadays, commercially viable antenna platforms are not characterised by a single performance value, but rather, a series of objective functions that are often inherently conflicting. Thus, an increase in one objective function results in a decrease in another. The optimisation algorithm is therefore required to seek a solution dictated by the preferences of the designer. Classical literature dominantly featured preference articulation, a priori, where the set of objectives are transformed into a scalar using a predefined preference arrangement. Contemporary theory implements the articulation a posteriori, where the complete set of compromise solutions are sought by the optimisation algorithm. It is hypothesised that modern multi-objective optimisation (MOO) theory, using a posteriori preference articulation, can be more useful for contemporary antenna design. By treating the objectives as individual dimensions in a mathematical space, it allows for independent, simultaneous optimisation. At the time of writing this dissertation, all commercial simulation software that include an optimisation algorithm use a predefined preference to the performance criteria. Thus, where a large set of equally potential solutions exist, only one final solution is delivered. This thesis examines two novel dielectric antenna technologies and uses modern MOO theory to obtain new solutions that supersede their prototypes. Taking a commercial perspective by optimising the electromagnetic performance and the physical size of the antenna simultaneously, it is hypothesised this allows an unprecedented insight into the inherent tradeoffs of practical antenna configurations.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
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33

Gasperini, David. "A multi-harmonic finite element method for the micro-Doppler effect, with an application to radar sensing". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0026.

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Nous proposons une méthode de résolution par éléments finis et en domaine fréquentiel de problèmes de diffraction d'ondes au sein de domaines dont les frontières se déforment au cours du temps. Le problème original est exprimé sous forme faible, puis approché par une formulation simplifiée basée sur des développements asymptotiques valides lorsque l'amplitude des déformations est faible. Nous introduisons alors des développements en séries de Fourier de certaines grandeurs géométriques, ainsi que de la solution dans le cas de mouvements périodiques. Cela permet ainsi d'obtenir une formulation multi-harmonique couplée du problème de diffraction initial. Une méthode de résolution standard par éléments finis, couplée avec un solveur itératif, est alors appliquée afin de résoudre le système résultant. En vue d'accélérer la solution du système linéaire, définie sur des sous-espaces de Krylov, nous proposons un préconditionneur diagonal par bloc, indispensable à la convergence de la méthode pour les problèmes hautes fréquences. L'efficacité de la méthode présentée est enfin illustrée à travers une application à la détection radar pour l'industrie automobile
A finite element method in the frequency domain is proposed for solving wave scattering problems with moving or, more generally, deforming boundaries. First, the original problem is rewritten as an equivalent weak formulation set in a fixeddomain. Next, this formulation is approximated as a simpler weak form based on asymptotic expansions when the amplitude of the movements or the deformations is small. Fourier series expansions of some geometrical quantities under the assumption that the movement is periodic, and of the solution are next introduced to obtain a coupled multi-harmonic frequency domain formulation. Standard finite element methods can then be applied to solve the resulting problem and a block diagonal preconditioner is proposed to acceleratethe Krylov subspace solution of the linear system for high frequency problems.The efficiency of the resulting method is demonstrated on a radar sensing application for the automotive industry.A finite element method in the frequency domain is proposed for solving wave scattering problems with moving or, more generally, deforming boundaries. First, the original problem is rewritten as an equivalent weak formulation set in a fixeddomain. Next, this formulation is approximated as a simpler weak form based on asymptotic expansions when the amplitude of the movements or the deformations is small. Fourier series expansions of some geometrical quantities under the assumption that the movement is periodic, and of the solution are next introduced to obtain a coupled multi-harmonic frequency domain formulation. Standard finite element methods can then be applied to solve the resulting problem and a block diagonal preconditioner is proposed to acceleratethe Krylov subspace solution of the linear system for high frequency problems.The efficiency of the resulting method is demonstrated on a radar sensing application for the automotive industry
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34

Bhamare, Sagar D. "High Cycle Fatigue Simulation using Extended Space-Time Finite Element Method Coupled with Continuum Damage Mechanics". University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352490187.

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35

Zhang, Wenlong. "Forward and Inverse Problems Under Uncertainty". Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEE024/document.

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Cette thèse contient deux matières différentes. Dans la première partie, deux cas sont considérés. L'un est le modèle plus lisse de la plaque mince et l'autre est les équations des limites elliptiques avec des données limites incertaines. Dans cette partie, les convergences stochastiques des méthodes des éléments finis sont prouvées pour chaque problème.Dans la deuxième partie, nous fournissons une analyse mathématique du problème inverse linéarisé dans la tomographie d'impédance électrique multifréquence. Nous présentons un cadre mathématique et numérique pour une procédure d'imagerie du tenseur de conductivité électrique anisotrope en utilisant une nouvelle technique appelée Tentomètre de diffusion Magnéto-acoustographie et proposons une approche de contrôle optimale pour reconstruire le facteur de propriété intrinsèque reliant le tenseur de diffusion au tenseur de conductivité électrique anisotrope. Nous démontrons la convergence et la stabilité du type Lipschitz de l'algorithme et présente des exemples numériques pour illustrer sa précision. Le modèle cellulaire pour Electropermécanisme est démontré. Nous étudions les paramètres efficaces dans un modèle d'homogénéisation. Nous démontrons numériquement la sensibilité de ces paramètres efficaces aux paramètres microscopiques critiques régissant l'électropermécanisme
This thesis contains two different subjects. In first part, two cases are considered. One is the thin plate spline smoother model and the other one is the elliptic boundary equations with uncertain boundary data. In this part, stochastic convergences of the finite element methods are proved for each problem.In second part, we provide a mathematical analysis of the linearized inverse problem in multifrequency electrical impedance tomography. We present a mathematical and numerical framework for a procedure of imaging anisotropic electrical conductivity tensor using a novel technique called Diffusion Tensor Magneto-acoustography and propose an optimal control approach for reconstructing the cross-property factor relating the diffusion tensor to the anisotropic electrical conductivity tensor. We prove convergence and Lipschitz type stability of the algorithm and present numerical examples to illustrate its accuracy. The cell model for Electropermeabilization is demonstrated. We study effective parameters in a homogenization model. We demonstrate numerically the sensitivity of these effective parameters to critical microscopic parameters governing electropermeabilization
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36

Zeng, Sai. "Knowledge-based FEA Modeling Method for Highly Coupled Variable Topology Multi-body Problems". Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4772.

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The increasingly competitive market is forcing the industry to develop higher-quality products more quickly and less expensively. Engineering analysis, at the same time, plays an important role in helping designers evaluate the performance of the designed product against design requirements. In the context of automated CAD/FEA integration, the domain-dependent engineers different usage views toward product models cause an information gap between CAD and FEA models, which impedes the interoperability among these engineering tools and the automatic transformation from an idealized design model into a solvable FEA model. Especially in highly coupled variable topology multi-body (HCVTMB) problems, this transformation process is usually very labor-intensive and time-consuming. In this dissertation, a knowledge-based FEA modeling method, which consists of three information models and the transformation processes between these models, is presented. An Analysis Building Block (ABB) model represents the idealized analytical concepts in a FEA modeling process. Solution Method Models (SMMs) represent these analytical concepts in a solution technique-specific format. When FEA is used as the solution technique, an SMM consists of a Ready to Mesh Model (RMM) and a Control Information Model (CIM). An RMM is obtained from an ABB through geometry manipulation so that the quality mesh can be automatically generated using FEA tools. CIMs contain information that controls the FEA modeling and solving activities. A Solution Tool Model (STM) represents an analytical model at the tool-specific level to guide the entire FEA modeling process. Two information transformation processes are presented between these information models. A solution method mapping transforms an ABB into an RMM through a complex cell decomposition process and an attribute association process. A solution tool mapping transforms an SMM into an STM by mimicking an engineers selection of FEA modeling operations. Four HCVTMB industrial FEA modeling cases are presented for demonstration and validation. These involve thermo-mechanical analysis scenarios: a simple chip package, a Plastic Ball Grid Array (PBGA), and an Enhanced Ball Grid Array (EBGA), as well as a thermal analysis scenario: another PBGA. Compared to traditional methods, results indicate that this method provides better knowledge capture and decreases the modeling time from days/hours to hours/minutes.
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37

Tang, Jianning. "A study of oxide scale deformation and surface roughness transformation in hot strip rolling". Access electronically, 2006. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20061204.162042/index.html.

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38

Ramos, Tiago André Cirne. "Numerical simulation of multi-stage hydroforming process of tubular parts". Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14409.

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Mestrado em Engenharia Mecânica
Tubular hydroforming process is characterized by the plastic forming of metallic tubular components through the conjugation of compressive axial feeding and internal pressure. A proper definition of these parameters, known as loading path, allows the plastic forming of more complex parts, with variable thicknesses distributions. Additionally, the final part has excellent surface finishing and mechanical properties that may be adjusted towards the specified application. In terms of industrial products, tubular hydroforming plays a crucial role in automobile and aerospace industries, as an attractive process for production of lightweight structures, where structural stiffness is not compromised when compared to conventional forming processes. For that purpose, the use of numerical simulation based on finite element analyses, with the comprehension and prediction of the instabilities associated to the process (necking and wrinkling), is of maximum relevance. In this work, two benchmarks are taken into account: (i) a bulge tube with axisymmetric geometry, and (ii) a T-shaped tube. By defining the models in a numerical analysis environment by finite elements, using Abaqus software, loading paths with multiple stages, as well sensitivity analyses towards the type and mesh refinements applied, are conducted in order to evaluate the effects of the instabilities previously mentioned. In both benchmarks, it's also evaluated the influence of a longitudinal weld line by defining the weld bead and heat affected zone (HAZ) by means of their mechanical properties. The presence of this type of weld line is neglected in most of the research works in literature as a measure of simplification, which may lead to misleading results regarding the case when compared to those experimentally obtained.
Os processos de hidroformagem tubular caracterizam-se pela conformação plástica de estruturas metálicas tubulares através da conjugação de deslocamentos axiais de punções compressão e pressão interna. A correcta conjugação destes dois parâmetros permite que peças complexas, de espessuras variáveis, sejam obtidas. Adicionalmente, permite a obtenção de um excelente acabamento superficial, onde as propriedades mecânicas podem ser variáveis e ajustáveis consoante a aplicação em causa. Em termos de aplicabilidade a nível industrial, a hidroformagem tubular desempenha um papel crucial na indústria automóvel e aeroespacial, como sendo um processo atractivo no desenvolvimento de componentes estruturais mais leves sem perda de resistência estrutural quando comparado com processos convencionais. Nesta ótica, o recurso à simulação numérica para melhor compreensão e previsão de instabilidades inerentes ao processo (estricção e enrugamento) revela-se de máxima importância. No âmbito do presente trabalho, dois casos de estudo são abordados: (i) uma estrutura axissimétrica de secção circular variável, e (ii) um tubo em forma de T. Na definição dos modelos num ambiente de análise numérica por elementos finitos, recorrendo ao software Abaqus, curvas de carregamento de múltiplas etapas, assim como análises de sensibiblidades, no que toca a refinamento e tipo de malhas aplicadas, são conduzidas para averiguar os efeitos nas instabilidades referidas. Em ambos os casos de estudo são avaliadas a influência da consideração de um cordão de soldadura longitudinal, ao definir as propriedades mecânicas do material na zona do cordão e na zona afectada pelo calor. A presença de um cordão de soldadura é desprezada na maior parte das simulações da literatura por efeito de simplificação numérica, o que pode levar a aproximações mais grosseiras comparativamente com os resultados obtidos experimentalmente.
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39

Wilmes, Andre Antoine Renaud. "Development of a multi-physics molecular dynamics finite element method for the virtual engineering design of nano-structures". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/39966.

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The rise of technologically promising two-dimensional materials, particularly graphene, has further accelerated the already fast-paced progress in nano-synthesis techniques across all scales. While single atom devices are controllably manufactured, scalable techniques, such as chemical vapour deposition, have brought materials with tuneable nano-structures to the structural engineering scales. Hence, unprecedented design spaces for tailoring material properties at multiple, and previously unattainable, length scales have arisen and continue to expand. Therefore, materials modelling communities must follow the integration of the physics, chemistry and synthesis fields, while accelerating their efforts towards an integrated virtual engineering design and simulation environment. The latter is of pivotal technological significance because future developments of novel materials and devices inherently require virtual designing and optimisation to remain economically feasible. This work proposes and pursues a materials modelling landscape where state of the art methodologies are readily integrated across the scales. A mathematically rigorous molecular dynamics finite element, with novel theoretical attributes, is developed for readily implementing any MD force field, including reactive and fluctuating charge-dipole potentials, within an FEM-legacy numerical platform of solvers. Novel boundary conditions are presented for accurately capturing bending deformations in structures, discrete or continuum, which modularly achieve property homogenisation across differing scales and physical representations; thereby constituting an ideal bridging formulation for multi-scale and multi-physics integration. Numerical implementations of the proposed formulations are achieved within minutes using a network-theory-inspired code generator which presents novel strategies for meshing a priori unknown element topologies with motif-detection algorithms. This work demonstrates the feasibility of an integrated modelling methodologies landscape and achieves a virtual engineering design and simulation environment, which is shown to be versatile and applicable from the smallest scales, for resolving the electromechanical behaviours in potential nano-device designs, to the larger scales where material nano-structures are virtually tested to deduce properties of engineering interest, such as graphenes fracture toughness.
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40

Rempler, Hans-Uwe [Verfasser] y Wolfgang [Akademischer Betreuer] Ehlers. "Damage in multi-phasic materials computed with the extended finite-element method / Hans-Uwe Rempler. Betreuer: Wolfgang Ehlers". Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2012. http://d-nb.info/1028801238/34.

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41

Li, Tianyu. "On the Formulation of a Hybrid Discontinuous Galerkin Finite Element Method (DG-FEM) for Multi-layered Shell Structures". Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/82962.

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A high-order hybrid discontinuous Galerkin finite element method (DG-FEM) is developed for multi-layered curved panels having large deformation and finite strain. The kinematics of the multi-layered shells is presented at first. The Jacobian matrix and its determinant are also calculated. The weak form of the DG-FEM is next presented. In this case, the discontinuous basis functions can be employed for the displacement basis functions. The implementation details of the nonlinear FEM are next presented. Then, the Consistent Orthogonal Basis Function Space is developed. Given the boundary conditions and structure configurations, there will be a unique basis function space, such that the mass matrix is an accurate diagonal matrix. Moreover, the Consistent Orthogonal Basis Functions are very similar to mode shape functions. Based on the DG-FEM, three dedicated finite elements are developed for the multi-layered pipes, curved stiffeners and multi-layered stiffened hydrofoils. The kinematics of these three structures are presented. The smooth configuration is also obtained, which is very important for the buckling analysis with large deformation and finite strain. Finally, five problems are solved, including sandwich plates, 2-D multi-layered pipes, 3-D multi-layered pipes, stiffened plates and stiffened multi-layered hydrofoils. Material and geometric nonlinearities are both considered. The results are verified by other papers' results or ANSYS.
Master of Science
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42

Hassard, Patrick. "Dual-scale modelling of two-dimensional flow in porous media". Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/211518/1/Patrick_Hassard_Thesis.pdf.

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The standard approach to modelling fluid flow through a porous medium was developed decades ago, when computational resources were insufficient to feasibly simulate the flow directly. In this thesis, the feasibility of such flow simulation with modern computing power is demonstrated via the development of three accurate and efficient dual-scale models of porous media flow. An important outcome of the research is that the new dual-scale modelling framework accurately and efficiently simulates flows with a range of Reynolds numbers through a variety of heterogeneous porous media.
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43

Zhou, Changwei. "Approche couplée propagative et modale pour l'analyse multi-échelle des structures périodiques". Thesis, Ecully, Ecole centrale de Lyon, 2014. http://www.theses.fr/2014ECDL0040/document.

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La dynamique d’une structure peut être vue aussi bien en termes de modes (ondes stationnaires) qu’en termes d’ondes élastiques libres. Les approches modales sont largement utilisées en mécanique et de nombreuses techniques de réduction de modèles (Model Order Reduction - MOR) ont été développées dans ce cadre. Quant à la dynamique des structures périodiques, les approches propagatives sont majoritairement utilisées, où la périodicité est exploitée en utilisant la théorie de Bloch. Pour les structures périodiques complexes, plusieurs techniques MOR sur la base d’onde ont été proposées dans la littérature. Dans ce travail, une approche couplée propagative et modale a été développée pour étudier la propagation des ondes dans les structures périodiques. Cette approche commence par la description modale d’une cellule unitaire (échelle mésoscopique) en utilisant la synthèse modale (Component Mode Synthesis - CMS). Par la suite, la méthode propagative - Wave Finite Element Method (WFEM) est appliquée sur la structure (échelle macroscopique). Cette méthode est nommée “CWFEM” pour CondensedWave Finite Element Method. Elle combine les avantages de la CMS et WFEM. La CMS permet d’analyser le comportement local d’en extraire une base réduite. La WFEM exploite la périodicité de la structure d’en extraire les paramètres de propagation. Ainsi, l’analyse de la propagation des ondes dans la structure à l’échelle macroscopique peut être réalisée en prenant en compte l’échelle mésoscopique. L’efficacité de la CWFEM est illustrée par de nombreuse applications aux structures périodiques monodimensionnelle (1D) et bidimensionnelle (2D). Le critère de réduction optimale assurant la convergence est discuté. Les caractéristiques de propagation dans les structures périodiques sont identifiées: bande passante, bande interdite, la directivité marquée (wave beaming effects), courbe de dispersion, band structure, surface des lenteurs... Ces propriétés peuvent répondre au besoin de conception des barrières vibroacoustiques, pièges à ondes. La CWFEM est ensuite appliquée pour étudier la propagation des ondes dans des plaques perforées et plaques raidies. Une méthode d’homogénéisation pour déterminer le modèle équivalent de la plaque perforée est proposée. Les comportements à haute fréquence tels que la directivité marquée sont également prédits par CWFEM. Trois modèles de plaques avec perforations différentes sont étudiées dans ce travail. Une validation expérimentale est effectuée sur deux plaques. Pour la plaque raidie, l’influence des modes internes sur la propagation globale est discutée. La densité modale est estimée, en moyenne et haute fréquences, pour une plaque raidie finie, où une bonne corrélation est obtenue en comparant les résultats à l’issue des analyses modales
Structural dynamics can be described in terms of structural modes as well as elastic wave motions. The mode-based methods are widely applied in mechanical engineering and numerous model order reduction (MOR) techniques have been developed. When it comes to the study of periodic structures, wave description is mostly adopted where periodicity is fully exploited based on the Bloch theory. For complex periodic structures, several MOR techniques conducted on wave basis have been proposed in the literature. In this work, a wave and modal coupled approach is developed to study the wave propagation in periodic structures. The approach begins with the modal description of a unit cell (mesoscopic scale) using Component Mode Synthesis (CMS). Subsequently, the wave-based method -Wave Finite Element Method (WFEM) is applied to the structure (macroscopic scale). The method is referred as “CWFEM” for Condensed Wave Finite Element Method. It combines the advantages of CMS and WFEM. CMS enables to analyse the local behaviour of the unit cell using a reduced modal basis. On the other hand, WFEM exploits fully the periodic propriety of the structure and extracts directly the propagation parameters. Thus the analysis of the wave propagation in the macroscopic scale waveguides can be carried out considering the mesoscopic scale behaviour. The effectiveness of CWFEM is illustrated via several one-dimensional (1D) periodic structures and two-dimensional (2D) periodic structures. The criterion of the optimal reduction to ensure the convergence is discussed. Typical wave propagation characteristics in periodic structures are identified, such as pass bands, stop bands, wave beaming effects, dispersion relation, band structure and slowness surfaces...Their proprieties can be applied as vibroacoustics barriers, wave filters. CWFEM is subsequently applied to study wave propagation characteristics in perforated plates and stiffened plate. A homogenization method to find the equivalent model of perforated plate is proposed. The high frequency behaviours such as wave beaming effect are also predicted by CWFEM. Three plate models with different perforations are studied. Experimental validation is conducted on two plates. For the stiffened plate, the influence of internal modes on propagation is discussed. The modal density in the mid- and high- frequency range is estimated for a finite stiffened plate, where good correlation is obtained compared to the mode count from modal analysis
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44

Chung, Johnny. "Determination of Thermal Conductivity of Wood Exposed to Fire based on Small Scale Laboratory Trials for Finite Element Calculations". Thesis, Luleå tekniska universitet, Byggkonstruktion och brand, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-63264.

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This study describes an approach to determine the thermal conductivity of wood at elevated temperatures. The aim is to be able to use the developed conductivity as input in structural elements in finite element calculations. The conductivity of pine wood and glue laminated timber with different densities and moisture contents have been evaluated where small scale one-dimensional laboratory trials have been carried out in a cone calorimeter. Steel temperatures were measured behind the exposed wood samples. Obtained temperatures from the experimental trials have been compared with back calculated steel temperatures in the finite element program TASEF (Temperature Analysis in Structures Exposed to Fire). In the back calculations the conductivity at 100 °C, 300 °C and 500 °C was altered in order to achieve a best fit steel temperature curve as the measured ones during the experimental trials. At 20 °C the conductivity was taken from the literature. Between these temperature levels the conductivity was assumed to vary linearly. The dehydration of the moisture content in the wood samples have been considered by including it in the specific volumetric enthalpy, i.e. the integral over temperature of the density and specific heat as input in the temperature calculation program TASEF. Regarding the thermal degradation, recommended formulas in Eurocode 5: Design of timber structures – Part 1-2: General – Structural fire design, have been applied. The final back calculated conductivity values of the studied pine wood at specific temperatures (20 °C, 100 °C, 300 °C och 500 °C) were determined by the cone calorimeter test to be as follows; 0.09 W/mK, 0.07 W/mK, 0.05 W/mK and 0.35 W/mK. Comparing with presented conductivity of wood in Eurocode 5 the developed conductivity in this study are generally lower. Derived conductivity values from the back calculations in TASEF have been reconsidered for the glue laminated timber by taken account of differences in density and moisture content. By using a developed conversion factor, so called “conductivity ratio”, new conductivity values could be obtained which then has been used as an input in TASEF. As a result, good similarities between calculated steel temperatures and measured steel temperatures could be seen. The implemented method, consisting of simple one-dimensional laboratory trials for determining the thermal conductivity is deemed to be promising.  However, further studies are needed to be done in order to increase the accuracy of the method.
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45

Binti, Shamjuddin Amnani. "Swelling and disintegration of multi-component polymeric structures". Thesis, University of Leicester, 2018. http://hdl.handle.net/2381/43072.

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This thesis aims to develop an understanding about swelling and disintegration of multi-component polymeric structures such as pharmaceutical tablets. The thesis presents a model for the diffusion-driven water uptake, swelling deformation and subsequent disintegration of polymer matrix drug-delivery devices. Hygroscopic swelling occurs when a dry tablet enters a humid environment and absorbs water molecules. The modification of tablet structures changes the release profile of the drug in the desired manner. The previous research mostly focused on transport problems related to drug release. This study contributes an understanding of the mechanical behaviour of hydrophilic polymer release matrix materials which are treated as continuum. Modelling of the swelling problem involves concurrent large deformation of the polymer network and diffusion of the solvent through the network. A coupled diffusion-deformation model was created to study the relation between both physics. The coupled diffusion-deformation model was utilised to consider disintegration of polymer matrix through the inclusion of swelling agents. Two cases were presented to illustrate the application of the model: swelling-controlled and immediate-release drug delivery systems. This study used COMSOL Multiphysics®, a finite element commercial software to perform the analysis. Various physical modules: structural mechanics, chemical transport and mathematics were combined for solving coupled diffusion-deformation-damage boundary value problems. The numerical results were validated using existing experimental data from the literature. The model parameters were varied to investigate their sensitivity to the solution. Higher solvent concentration gradient in the matrix produced higher swelling strain, thus increased local stress. Disintegrability was measured by the time taken for the maximum principal stress to reach a given failure. Higher coefficient of water diffusion allows higher amount of water ingression into the matrix. Higher coefficient of hygroscopic swelling generates higher local swelling strain. This study facilitates in understanding the complex phenomena in the application of drug release formulation.
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46

Oravec, Peter. "Analýza uložení zadního kola formulového vozidla". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400877.

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This diploma thesis is focused on Formula Student upright analysis using final element method. The main goal is to review an effect of different boundary conditions on stress and deformation. Nowadays, the topologic optimization is a commonly used tool for design process of the upright, to create the lightest and the most rigid design possible. Boundary conditions, which should approximate reality really well, are one of inputs to topological optimization.
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47

Doyeux, Vincent. "Modélisation et simulation de systèmes multi-fluides. Applications aux écoulements sanguins". Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY017/document.

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Dans ce travail, nous développons un cadre de calcul dédié à la simulation d'écoulements à plusieurs fluides. Nous présentons des validations et vérifications de ces méthodes sur des problèmes de capture d'interfaces et de simulations de bulles visqueuses.Nous montrons ensuite que ce cadre de calcul est adapté à la simulation d'objet rigides en écoulement.Puis, nous étendons ces méthodes à la simulation d'objets déformables simulant le comportement des globules rouges : les vésicules. Nous validons aussi ces simulations.Enfin nous appliquons les précédents modèles à des problèmes ouverts de microfluidique tels que la séparation d'une suspension dans une bifurcation microfluidique et la rhéologie en milieu confiné
In this work, we develop a framework dedicated to the simulation of multi-fluid systems. We present validations and verifications of these methods on interface capture problems and viscous bubbles simulations.We then show that this framework is well fitted for the simulation of the rigid bodies flow.Next, we extend these methods to the simulation of deformable objects reproducing the behavior of red blood cells: the vesicles. We also validate these simulations.Finally, we apply the previous models to open micro-fluidic problems such as the splitting of a suspension at a bifurcation and the rheology in a confined environment
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48

Buchmann, Thies Joachim. "3D multi-scale finite element analysis of the present-day crustal state of stress and the recent kinematic behaviour of the northern and central Upper Rhine Graben /". Berlin : Logos-Verl, 2008. http://d-nb.info/990771296/04.

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49

Lau, Chi Keung. "Scale effects in tests on footings". Thesis, University of Cambridge, 1988. https://www.repository.cam.ac.uk/handle/1810/245006.

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This dissertation presents an investigation of the effects of stress, and of absolute and relative particle size, in tests on vertically loaded footings. Two granular materials, namely, a silica rock flour and a Chatelet flint grit, which differed in nominal diameter by a factor of 50 but were otherwise practically similar in all other grain characteristics were used in this work. A comprehensive series of triaxial tests under a wide range of cell pressures was carried out to quantify the stress and absolute particle size effects. Model footing tests were also performed by pushing a rigid circular punch axisymmetrically into the flat surface of a cylindrical soil model either under 1-g (gravity) with surcharge or under elevated g in a centrifuge. The 1-g and centrifuge test series were used to study the scale effects on the surcharge term Ng and the self-weight term Nγ of the Terzaghi bearing capacity equation, respectively. Parameters varied were punch diameter, particle size and surcharge or g level. Two theoretical analyses were attempted based on the finite element method and the method of characteristics. Using the Schofield Soil Model, the finite element analysis can give a reasonable order of magnitude prediction for the settlement of the footing under working load conditions. When the effect of reducing angle of shearing with increasing stress was taken into account together with the change of geometry due to footing penetration, the angles of shearing inferred from the method of characteristics fall within ±20 of those measured in triaxial compression tests. Distortion due to violating the scaling law by not conserving the ratio of particle size to model dimension was not considered to be significant. Distortion due to violating the constitutive soil behaviour by varying the absolute particle size was found to be significant due to differences in grain crushing, but this can be accounted for effectively by the new style of calculations developed in the thesis.
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50

Calixto, Tainan Khalil Leite 1990. "Otimização topológica evolucionária multiescala aplicada a problemas de elasticidade linear". [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265763.

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Orientador: Renato Pavanello
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-28T11:58:24Z (GMT). No. of bitstreams: 1 Calixto_TainanKhalilLeite_M.pdf: 15775150 bytes, checksum: e5e4d45becc32f922a1fd31b8f9bd3ab (MD5) Previous issue date: 2015
Resumo: A utilização de materiais de alta performance se tornou uma realidade em diversos campos da engenharia, como na indústria automotiva e aeroespacial, devido aos avanços nas técnicas de manufatura aditiva. Por outro lado, sabe-se que a otimização topológica estrutural é uma ferramenta de desenvolvimento de estruturas com ampla aplicação industrial. Dentre os vários métodos de otimização topológica existentes, a otimização estrutural evolucionária tem se destacado pela sua versatilidade, podendo ser utilizada em diversos tipos de problemas de engenharia. Na tentativa de combinar esses campos, este trabalho consiste no estudo do método de otimização evolucionária BESO (Bi-directional Evolutionary Structural Optimization) aplicado a sistemas bidimensionais multiescala a fim de se projetar as topologias ótimas, em ambas as escalas, de uma estrutura. A análise do modelo multiescala é feita através do método da homogeneização, onde o padrão do material microestrutural é considerado periódico. O algoritmo implementado pode buscar dois objetivos distintos: a minimização da flexibilidade média, que resulta na maximização da rigidez global; ou a maximização da frequência fundamental. Resultados numéricos do algoritmo são apresentados para o projeto de materiais, onde apenas a microestrutura é otimizada, e de estruturas, na qual otimiza-se as topologias nas duas escalas. Para a análise do desempenho do método de otimização multiescala, são propostos um índice de eficiência estrutural e uma metodologia de fabricação de estruturas periódicas
Abstract: High-performance materials utilization became a reality in many fields of actual engineering, such as in automotive and aerospace industries, due to advances in additive manufacturing techniques. In the other hand, structural topology optimization is a powerful tool for the structure development with wide industrial application. Among the various optimization methods, evolutionary structural optimization stands out for its versatility and it can be used in many engineering problems. As an attempt to combine these fields, this work intends to study the Bi-directional evolutionary Structural Optimization method applied to two-dimensional multi-scale systems in order to design the optimal topologies of structures in both scales. The analysis of multi-scale model is made using the homogenization method, where the pattern of the micro-structural material is considered periodic. The implemented algorithm can use two different objective function: mean compliance minimization, which results in maximizing the global stiffness; or fundamental frequency maximization. Numerical results are presented for material design, where only the micro structure is optimized, and for structural design, in which the topologies in both scales are optimized. Deepening the study in multiscale optimization, it is proposed an index to analyse the structural efficiency and also a manufacturing methodology of periodic structures
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
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