Shape memory polymers (SMPs) are a relatively new class of active materials that can store a temporary shape and return to the original configuration upon application of a stimulus such as temperature. This shape changing ability has led to increased interest in their use for biomedical and aerospace applications. A major challenge, however, in the advancement of these applications is the ability to accurately predict the material behavior for complex geometries and boundary conditions. This work addresses this challenge by developing an experimentally calibrated and validated constitutive model that is implemented as a user material subroutine in Abaqus ? a commercially available finite element software package. The model is formulated in terms of finite deformations and assumes the SMP behaves as a thermoelastic material, for which the response is modeled using a compressible neo-Hookean constitutive equation. An internal state variable, the glassy volume fraction, is introduced to account for the phase transformation and associated stored deformation upon cooling from the rubbery phase to the glassy phase and subsequently recovered upon heating. The numerical implementation is performed such that a system of equations is solved using a Newton-Raphson method to find the updated stress in the material. The conductive heat transfer is incorporated through solving Fourier's law simultaneously with the constitutive equations. To calibrate and validate the model parameters, thermomechanical experiments are performed on an amorphous, thermosetting polyurethane shape memory polymer. Strains of 10-25% are applied and both free recovery (zero load) and constrained displacement recovery boundary conditions are considered for each value of applied strain. Using the uniaxial experimental data, the model is then calibrated and compared to the 1-D experimental results. The validated finite element analysis tool is then used to model biomedical devices, including cardiovascular tubes and thrombectomy devices, fabricated from shape memory polymers. The effects of heat transfer and complex thermal boundary conditions are evaluated using coupled thermal-displacement analysis, for which the thermal material properties were experimentally calibrated.

Inflatable wings provide an innovative solution to unmanned aerial vehicles requiring small packed volumes, such as those used for military reconnaissance or extra-planetary exploration. There is desire to implement warping actuation forces to change the shape of the wing during flight to allow for greater control of the aircraft. In order to quickly and effectively analyze the effects of wing warping strategies on an inflatable wing, a finite element model is desired. Development of a finite element model which includes woven fabric material properties, internal pressure loading, and external wing loading is presented. Testing was performed to determine material properties of the woven fabric, and to determine wing response to static loadings. The modeling process was validated through comparison of simplified inflatable cylinder models to experimental test data. Wing model response was compared to experimental response, and modeling changes including varying material property models and mesh density studies are presented, along with qualitative wing warping simulations. Finally, experimental and finite element modal analyses were conducted, and comparisons of natural frequencies and mode shapes are presented.

Šiame darbe buvo analizuojama programinė įranga skirta diskretizuoti sritį į baigtinius elementus. Analizuotos MATLAB sistemos ir COMSOL programos diskretzavimo galimybės. Sukurta programa sujungianti COMSOL ir MATLAB, kuri leidžia diskretizuoti sritį į baigtinius elementus. / In this work was done study of software for domain discretization by finite elements. Created program that connects MATLAB and COMSOL, which allows domain discretization by finite elements.

By using the finite element method to solve the appropriate momentum and energy equations the friction factors and Nusselt numbers for fully developed laminar flow were determined for one- and two-dimensional flow systems. The Nusselt numbers were determined for domain boundaries subjected to a constant heat flux (H1) or a constant surface temperature (T) around the computational boundaries and in the axial directions. C++ programs, that were rewritten and extended from previous programs, were used to solve the laminar flow and to determine the values. The required wall shear stresses and heat fluxes were directly obtained for a duct as part of the primary finite-element solution; these values were then used to determine the Nusselt number and friction factor for the specific duct. The computations were performed for circular-, annular-, trapezoidal-, rectangular- and triangular ducts. Special emphasis was placed on trapezoidal ducts since only a limited number of studies have been performed on trapezoidal duct shapes and none of these studies employed the finite element method. Excellent agreement was found when the determined values were compared with the values reported in the literature. In general, the agreement of the values improved as the number of elements was increased. It was, therefore, concluded that the methods used in this study yielded friction factors and Nusselt numbers that are very accurate and usable. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2009.

By using the finite element method to solve the appropriate momentum and energy equations the friction factors and Nusselt numbers for fully developed laminar flow were determined for one- and two-dimensional flow systems. The Nusselt numbers were determined for domain boundaries subjected to a constant heat flux (H1) or a constant surface temperature (T) around the computational boundaries and in the axial directions. C++ programs, that were rewritten and extended from previous programs, were used to solve the laminar flow and to determine the values. The required wall shear stresses and heat fluxes were directly obtained for a duct as part of the primary finite-element solution; these values were then used to determine the Nusselt number and friction factor for the specific duct. The computations were performed for circular-, annular-, trapezoidal-, rectangular- and triangular ducts. Special emphasis was placed on trapezoidal ducts since only a limited number of studies have been performed on trapezoidal duct shapes and none of these studies employed the finite element method. Excellent agreement was found when the determined values were compared with the values reported in the literature. In general, the agreement of the values improved as the number of elements was increased. It was, therefore, concluded that the methods used in this study yielded friction factors and Nusselt numbers that are very accurate and usable. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2009.

In dieser Arbeit entwickeln wir einen Löser für elliptische Randwertprobleme. Dazu diskretisieren wir ein Randwertproblem mittels der Methode der finiten Elemente und erhalten ein Gleichungssystem. Mittels Gebietszerlegungstechniken unterteilen wir das Gebiet der Differentialgleichung und können Teilprobleme des Randwertproblems definieren. Durch die Gebietszerlegung wird eine Hierarchie von Zerlegungen definiert, die wir mittels eines Gebietszerlegungsbaumes festhalten. Anhand dieses Baumes definieren wir nun einen Löser für das Randwertproblem. Dabei berechnen wir die verschiedenen Matrizen des Lösers durch den sogenannten HDD-Algorithmus (engl. hierarchical domain decomposition). Die meisten der zu erstellenden Matrizen sind dabei vollbesetzt, weshalb wir sie mittels Hierarchischer Matrizen approximieren. Mit Hilfe der Hierarchischen Matrizen können wir die Matrizen mit einem fast linearen Aufwand erstellen und speichern. Der Aufwand der Matrixoperationen ist ebenfalls fast linear. Damit wir die Hierarchischen Matrizen für den HDD-Algorithmus verwenden können, müssen wir die Technik der Hierarchischen Matrizen erweitern. Unter anderem führen wir eingeschränkte Clusterbäume, eingeschränkte Blockclusterbäume und die verallgemeinerte Addition für Hierarchische Matrizen ein. Zusätzlich führen wir eine neue Clusterbaum-Konstruktion ein, die auf den HDD-Algorithmus zugeschnitten ist. Die Kombination des HDD-Algorithmus mit Hierarchischen Matrizen liefert einen Löser, den wir mit einem fast linearen Aufwand berechnen können. Der Aufwand zur Berechnung einer Lösung sowie der Speicheraufwand ist ebenfalls fast linear. Des Weiteren geben wir noch einige Modifizierungen des HDD-Algorithmus für weitere Anwendungsmöglichkeiten an. Zusätzlich diskutieren wir die Möglichkeiten der Parallelisierung, denn durch die Verwendung der Gebietszerlegung wird das Randwertproblem in unabhängige Teilprobleme aufgeteilt, die sich sehr gut parallelisieren lassen. Wir schließen die Arbeit mit numerischen Tests ab, die die theoretischen Aussagen bestätigen.

Η σύγχρονη γεννήτρια, ή αλλιώς εναλλακτήρας, είναι σύγχρονη μηχανή η οποία μετατρέπει μηχανική ενέργεια σε εναλλασσόμενη ηλεκτρική ενέργεια. Η σύγχρονη μηχανή, χρησιμοποιούμενη ως γεννήτρια, είναι η σπουδαιότερη μηχανή για την παραγωγή ηλεκτρικής ενέργειας και αποτελεί το επίκεντρο κάθε σταθμού παραγωγής ηλεκτρικής ενέργειας. Σκοπός της παρούσας διπλωματικής εργασίας είναι η μελέτη της συμπεριφοράς της σύγχρονης γεννήτριας στη μόνιμη κατάσταση λειτουργίας αναλύοντας τα είδη των σύγχρονων παραμέτρων που προκύπτουν, καθώς επίσης και η μελέτη και ο προσδιορισμός των απωλειών στην ονομαστική κατάσταση λειτουργίας. / The synchronous generator is a type of synchronous machine, which converts mechanical energy into alternating electrical energy. When the synchronous machine is used as a generator, it is the most important machine for the production of electrical energy and it constitutes the epicentre for each station which produces electrical energy. The scope of this present thesis is the study of the behavior of synchronous machine in the steady-state of operation analyzing the types of synchronous parameters and synchronous quantities, as well as the study and determination of losses in the nominal situation of operation. The steady-state tests suggested in this thesis are required for analyzing the performance of a synchronous machine under normal operating conditions.

Σκοπός της διατριβής είναι η πρόβλεψη των συζευγμένων ηλεκτρομηχανικών ιδιοτήτων ενός πολυμερούς ενισχυμένου με νανοσωλήνες άνθρακα σε επίπεδο στρώσης υλικού (μικροκλίμακα), χρησιμοποιώντας δεδομένα και αναλύσεις ατομικής και υποατομικής κλίμακας. Αρχικά γίνεται η πρόβλεψη των μηχανικών ιδιοτήτων των νανοσωλήνων χρησιμοποιώντας μια προσέγγιση που συνδυάζει εξισώσεις μοριακής μηχανικής και ανάλυση με πεπερασμένα στοιχεία. Στη συνέχεια γίνεται πρόβλεψη των ηλεκτρικών ιδιοτήτων των νανοσωλήνων χρησιμοποιώντας τη μέθοδο Ισχυρού Δεσμού (ή Δέσμιας Κατάστασης). Ο συνδυασμός των δυο αυτών παρέχει πληροφορίες για τη συζευγμένη ηλεκτρομηχανικής απόκριση των νανοσωλήνων άνθρακα. Τέλος, γίνεται ανάλυση της μικροδομής ενός νανοσυνθέτου υλικού και πώς αυτή μεταβάλεται υπό την επίδραση μηχανικού φορτίου. Ο συνδυασμός όλων των αναπτυχθέντων προτύπων οδηγεί στην πρόβλεψη της συζευγμένης ηλεκτρομηχανικής συμπεριφοράς του νανοσυνθέτου υλικού. Τα μοντέλα που αναπτύχθηκαν καθώς και οι προβλέψεις τους επιβεβαιώθηκαν σε αντιπαράθεση με θεωρητικές προβλέψεις και πειραματικές μετρήσεις άλλων διακεκριμένων ερευνητών. / The goal of this thesis is the prediction of the coupled electromechanical response of carbon nanotube doped polumer in ply-level (microscale), using minimal input from atomic and subatomic analyses. First, the mechanical properties of carbon nanotubes are predicted using an approach that combines molecular mechanics and finite element analysis. Next, the electrical properties of carbon nanotubes are predicted using the tight-binding method. The coupling of these two models leads to the prediction of the electromechanical response of individual carbon nanotubes. Finally, the microstructure of a nanocomposite is analyzed, along with the effects of strain. All these models, when combined, predict the coupled electromechanical response of the nanocomposite. All models and predictions have been successfully correlated with theroetical predictions and experimental measurements of other researchers, found in the open literature.

Bien que son utilisation requière plus de paramètres que les méthodes traditionnelles la méthode des éléments finis est de plus en plus utilisée pour la conception, des ouvrages géotechniques. Son utilisation nécessite notamment la définition du champ initial des contraintes qui reste très difficile à estimer et mesurer.Ce travail de thèse est une contribution à une meilleure connaissance de l'état initial des contraintes dans une pente. La thèse comporte des études numériques et expérimentales.Les études numériques évaluent, dans un premier temps, la variation des résultats des calculs par la méthode des éléments finis induite par l'incertitude sur l'état initial des contraintes. Dans un deuxième temps, la distribution des contraintes suite à la modélisation d'une pente au moyen du logiciel CESAR-LCPC est étudiée. L'influence des paramètres géologiques, géométriques et mécaniques sur le champ initial des contraintes est étudiée.L'objectif de l'étude expérimentale est de mesurer, avec des capteurs de pression totale fonçables, les contraintes horizontales dans une pente. La campagne expérimentale opte pour un suivi de la relaxation des contraintes horizontales jusqu'à la stabilisation des mesures. Des essais en laboratoire, réalisés au CEREMA à Aix en Provence, incluent des essais œdométriques à mesure de K0 qui donnent des valeurs du coefficient de pression des terres au repos mesuré en laboratoire. Les difficultés liées à la mesure du coefficient de pression des terres au repos et les paramètres qui peuvent l'influencer (nature des terrains, variations de teneur en eau, etc.) sont discutés / Though the finite element method requires more input data than traditional methods, it is increasingly used for the design of geotechnical structures. Its use needs to define initial stresses, which are difficult to estimate or to measure.This thesis is a contribution to a better understanding of the initial stresses in a slope. It consists of both numerical and experimental studies.The numerical studies focus on two issues. At first, they assess the effects of initial stresses on the results of calculations using finite element methods. Secondly, the distribution of stresses in a slope is analysed, using CESAR-LCPC finite elements software. The influence of geological, geometric and mechanical parameters on the state of stresses is studied.The objective of the experimental studies is to measure the lateral stresses in a slope using push-in total stress cells. The stresses are measured continuously in order to estimate the stresses in the ground after the dissipation of the effects of installation procedure. Laboratory tests made at CEREMA in Aix-en-Provence include “K0 oedometer tests” which provide measures of the coefficient of earth pressure at rest. The difficulties associated with the measurement of the coefficient of earth pressure at rest and the parameters that can influence it (type of soil, geometry of soil mass, water content ...) are discussed

Made available in DSpace on 2014-06-11T19:30:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-12-20Bitstream added on 2014-06-13T19:40:18Z : No. of bitstreams: 1 silva_rm_dr_ilha.pdf: 2780916 bytes, checksum: 6decfae89e48d3addc3e2f3c8889ff34 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho é apresentada a modelagem analítica baseada nas equações de Maxwell e a modelagem numérica baseada no Método da Simulação de Cargas (MSC) e no Método dos Elementos Finitos (MEF) empregados no cálculo do campo eletromagnético quase-estático em linhas de transmissão. O método dos elementos finitos consiste numa adaptação do método residual de Galerkin. Ele é atualmente considerado um método matemático para a solução de equações diferenciais parciais, entre as quais se inclui a Equação de Poisson, Equação de Laplace, Equação de Helmholtz, Navier-Stokes, etc. Esse é um método de aproximação de problemas contínuos em domínios fechados onde o contínuo se divide em um número finito de partes, ou elementos, cujo comportamento se especifica mediante um número finito de parâmetros associados a certos pontos característicos denominados nós. Os nós são os pontos de união de cada elemento com seus adjacentes. A solução do sistema completo segue as regras dos problemas discretos. O sistema completo se forma pela associação dos N elementos. As incógnitas do problema deixam de ser funções matemáticas e passam a ser o valor dessas funções nos n nós. O comportamento no interior de cada um dos N elementos passa a ser definido a partir do comportamento dos n nós, mediante adequadas funções de interpolação ou funções de forma. A precisão do método depende da forma do elemento da malha bidimensional, ou seja, se ele é triangular ou quadrilateral, por exemplo. Além disso, a quantidade de pontos de integração e conseqüentemente a base polinomial do elemento finito, podem ser explorados para aumentar a precisão dos resultados. A base do método dos elementos finitos são as funções de mapeamento, e suas derivadas. No método de Galerkin as funções de mapeamento são igualadas às funções de forma originando os elementos... / In this research is presented a mathematical modeling based on Maxwell's equations and numerical modeling based on Charge Simulation Method (CSM) and the Finite Element Method (FEM) for calculating the quasi-static electromagnetic field in transmission lines. The finite element method is an adaptation of Galerkin residual method. It’s currently considered a mathematical method for solving partial differential equations, among which includes the Poisson equation, Laplace equation, Helmholtz equation, Navier-Stokes, etc. This is an approximation method of continuing problems in closed domains where the continuous is divided into a finite number of parts or elements whose behavior is specified by a finite number of parameters associated with certain characteristic points called nodes. The nodes are union points of each element with its adjacent. The solution of the entire system follows the rules of the discrete problems. The complete system is formed by the association of N elements. The unknowns of the problem, mathematical functions, become the value of these functions on n nodes. The behavior within each of elements N is now defined from the behavior of n nodes, using appropriate interpolation functions or shape functions. The method precision depends on the shape of two-dimensional mesh element, i.e., if it is triangular or quadrilateral. Moreover, the number of integration points and therefore the polynomial finite element basis, can be exploited to increase the accuracy of the results. The basis of the finite element method are the mapping functions and their derivatives. In the Galerkin method the mapping functions are matched to the shape functions form the isoparametric. Finally, from above definitions, simply refer to the tables of numerical integration, showing how the elements are integrated, and use them in the rest of the numerical modeling