Dissertations / Theses on the topic '3d nonlinear models'

This work presents the development of a three-dimensional lattice material model for wood and its application to timber joints including the potential strengthening benefit of second order effects. A lattice of discrete elements was used to capture the heterogeneity and fracture behaviour and the model results compared to tested Sitka spruce (Picea sitchensis) specimens. Despite the general applicability of lattice models to timber, they are computationally demanding, due to the nonlinear solution and large number of degrees of freedom required. Ways to reduce the computational costs are investigated. Timber joints fail due to plastic deformation of the steel fastener(s), embedment, or brittle fracture of the timber. Lattice models, contrary to other modelling approaches such as continuum finite elements, have the advantage to take into account brittle fracture, crack development and material heterogeneity by assigning certain strength and stiffness properties to individual elements. Furthermore, plastic hardening is considered to simulate timber embedment. The lattice is an arrangement of longitudinal, lateral and diagonal link elements with a tri-linear load-displacement relation. The lattice is used in areas with high stress gradients and normal continuum elements are used elsewhere. Heterogeneity was accounted for by creating an artificial growth ring structure and density profile upon which the mean strength and stiffness properties were adjusted. Solution algorithms, such as Newton-Raphson, encounter problems with discrete elements for which 'snap-back' in the global load-displacement curves would occur. Thus, a specialised solution algorithm, developed by Jirasek and Bazant, was adopted to create a bespoke FE code in MATLAB that can handle the jagged behaviour of the load displacement response, and extended to account for plastic deformation. The model's input parameters were calibrated by determining the elastic stiffness from literature values and adjusting the strength, post-yield and heterogeneity parameters of lattice elements to match the load-displacement from laboratory tests under various loading conditions. Although problems with the modified solution algorithm were encountered, results of the model show the potential of lattice models to be used as a tool to predict load-displacement curves and fracture patterns of timber specimens.

The thesis is devoted to the study of the elastic behavior of solid crystals in the presence of dislocation defects by a variational point of view. In the first part we consider a Geometrically nonlinear elastic model in the three-dimensional setting, that allows for large rotations. Adopting a core approach, which consists in regularizing the problem at scale epsilon>0 around the dislocation lines, we perform the asymptotic analysis of the regularized energy as epsilon tends to 0. We focus in particular on the leading order regime and prove that the energy rescaled by $eps^2|logeps|$ Gamma converges to the line-tension for a dislocation density derived by Conti, Garroni and Ortiz in a three-dimensional linear framework. The analysis is performed under the assumption that the dislocations are well separated at intermediate scale, this in fact will allow to treat individually each dislocation by means of a suitable cell formula. The nonlinear nature of the energy requires that in the characterization of the cell formula we take into account that the deformation gradient is close to a fixed rotation. In the second part we obtain the same Gamma-limit but starting from a nonlinear elastic model with mixed growth, that is we consider an elastic energy which is substantially quadratic far from the dislocations and sub-quadratic in the core region. This can be seen as another way of regularising the problem and allow us to slightly relax the diluteness condition of the admissible dislocation density and improve the compactness result obtained in the previous case.

Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Haj-Ali, Rami; Committee Co-Chair: Leon, Roberto; Committee Co-Chair: White, Donald; Committee Member: DesRoches, Reginald; Committee Member: Gentry, Russell. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Im Mittelpunkt dieser Arbeit stehen virtuelle 3D-Stadtmodelle, die Objekte, Phänomene und Prozesse in urbanen Räumen in digitaler Form repräsentieren. Sie haben sich zu einem Kernthema von Geoinformationssystemen entwickelt und bilden einen zentralen Bestandteil geovirtueller 3D-Welten. Virtuelle 3D-Stadtmodelle finden nicht nur Verwendung als Mittel für Experten in Bereichen wie Stadtplanung, Funknetzplanung, oder Lärmanalyse, sondern auch für allgemeine Nutzer, die realitätsnah dargestellte virtuelle Städte in Bereichen wie Bürgerbeteiligung, Tourismus oder Unterhaltung nutzen und z. B. in Anwendungen wie GoogleEarth eine räumliche Umgebung intuitiv erkunden und durch eigene 3D-Modelle oder zusätzliche Informationen erweitern. Die Erzeugung und Darstellung virtueller 3D-Stadtmodelle besteht aus einer Vielzahl von Prozessschritten, von denen in der vorliegenden Arbeit zwei näher betrachtet werden: Texturierung und Visualisierung. Im Bereich der Texturierung werden Konzepte und Verfahren zur automatischen Ableitung von Fototexturen aus georeferenzierten Schrägluftbildern sowie zur Speicherung oberflächengebundener Daten in virtuellen 3D-Stadtmodellen entwickelt. Im Bereich der Visualisierung werden Konzepte und Verfahren für die multiperspektivische Darstellung sowie für die hochqualitative Darstellung nichtlinearer Projektionen virtueller 3D-Stadtmodelle in interaktiven Systemen vorgestellt. Die automatische Ableitung von Fototexturen aus georeferenzierten Schrägluftbildern ermöglicht die Veredelung vorliegender virtueller 3D-Stadtmodelle. Schrägluftbilder bieten sich zur Texturierung an, da sie einen Großteil der Oberflächen einer Stadt, insbesondere Gebäudefassaden, mit hoher Redundanz erfassen. Das Verfahren extrahiert aus dem verfügbaren Bildmaterial alle Ansichten einer Oberfläche und fügt diese pixelpräzise zu einer Textur zusammen. Durch Anwendung auf alle Oberflächen wird das virtuelle 3D-Stadtmodell flächendeckend texturiert. Der beschriebene Ansatz wurde am Beispiel des offiziellen Berliner 3D-Stadtmodells sowie der in GoogleEarth integrierten Innenstadt von München erprobt. Die Speicherung oberflächengebundener Daten, zu denen auch Texturen zählen, wurde im Kontext von CityGML, einem international standardisierten Datenmodell und Austauschformat für virtuelle 3D-Stadtmodelle, untersucht. Es wird ein Datenmodell auf Basis computergrafischer Konzepte entworfen und in den CityGML-Standard integriert. Dieses Datenmodell richtet sich dabei an praktischen Anwendungsfällen aus und lässt sich domänenübergreifend verwenden. Die interaktive multiperspektivische Darstellung virtueller 3D-Stadtmodelle ergänzt die gewohnte perspektivische Darstellung nahtlos um eine zweite Perspektive mit dem Ziel, den Informationsgehalt der Darstellung zu erhöhen. Diese Art der Darstellung ist durch die Panoramakarten von H. C. Berann inspiriert; Hauptproblem ist die Übertragung des multiperspektivischen Prinzips auf ein interaktives System. Die Arbeit stellt eine technische Umsetzung dieser Darstellung für 3D-Grafikhardware vor und demonstriert die Erweiterung von Vogel- und Fußgängerperspektive. Die hochqualitative Darstellung nichtlinearer Projektionen beschreibt deren Umsetzung auf 3D-Grafikhardware, wobei neben der Bildwiederholrate die Bildqualität das wesentliche Entwicklungskriterium ist. Insbesondere erlauben die beiden vorgestellten Verfahren, dynamische Geometrieverfeinerung und stückweise perspektivische Projektionen, die uneingeschränkte Nutzung aller hardwareseitig verfügbaren, qualitätssteigernden Funktionen wie z.~B. Bildraumgradienten oder anisotroper Texturfilterung. Beide Verfahren sind generisch und unterstützen verschiedene Projektionstypen. Sie ermöglichen die anpassungsfreie Verwendung gängiger computergrafischer Effekte wie Stilisierungsverfahren oder prozeduraler Texturen für nichtlineare Projektionen bei optimaler Bildqualität. Die vorliegende Arbeit beschreibt wesentliche Technologien für die Verarbeitung virtueller 3D-Stadtmodelle: Zum einen lassen sich mit den Ergebnissen der Arbeit Texturen für virtuelle 3D-Stadtmodelle automatisiert herstellen und als eigenständige Attribute in das virtuelle 3D-Stadtmodell einfügen. Somit trägt diese Arbeit dazu bei, die Herstellung und Fortführung texturierter virtueller 3D-Stadtmodelle zu verbessern. Zum anderen zeigt die Arbeit Varianten und technische Lösungen für neuartige Projektionstypen für virtueller 3D-Stadtmodelle in interaktiven Visualisierungen. Solche nichtlinearen Projektionen stellen Schlüsselbausteine dar, um neuartige Benutzungsschnittstellen für und Interaktionsformen mit virtuellen 3D-Stadtmodellen zu ermöglichen, insbesondere für mobile Geräte und immersive Umgebungen.
This thesis concentrates on virtual 3D city models that digitally encode objects, phenomena, and processes in urban environments. Such models have become core elements of geographic information systems and constitute a major component of geovirtual 3D worlds. Expert users make use of virtual 3D city models in various application domains, such as urban planning, radio-network planning, and noise immision simulation. Regular users utilize virtual 3D city models in domains, such as tourism, and entertainment. They intuitively explore photorealistic virtual 3D city models through mainstream applications such as GoogleEarth, which additionally enable users to extend virtual 3D city models by custom 3D models and supplemental information. Creation and rendering of virtual 3D city models comprise a large number of processes, from which texturing and visualization are in the focus of this thesis. In the area of texturing, this thesis presents concepts and techniques for automatic derivation of photo textures from georeferenced oblique aerial imagery and a concept for the integration of surface-bound data into virtual 3D city model datasets. In the area of visualization, this thesis presents concepts and techniques for multiperspective views and for high-quality rendering of nonlinearly projected virtual 3D city models in interactive systems. The automatic derivation of photo textures from georeferenced oblique aerial imagery is a refinement process for a given virtual 3D city model. Our approach uses oblique aerial imagery, since it provides a citywide highly redundant coverage of surfaces, particularly building facades. From this imagery, our approach extracts all views of a given surface and creates a photo texture by selecting the best view on a pixel level. By processing all surfaces, the virtual 3D city model becomes completely textured. This approach has been tested for the official 3D city model of Berlin and the model of the inner city of Munich accessible in GoogleEarth. The integration of surface-bound data, which include textures, into virtual 3D city model datasets has been performed in the context of CityGML, an international standard for the exchange and storage of virtual 3D city models. We derive a data model from a set of use cases and integrate it into the CityGML standard. The data model uses well-known concepts from computer graphics for data representation. Interactive multiperspective views of virtual 3D city models seamlessly supplement a regular perspective view with a second perspective. Such a construction is inspired by panorama maps by H. C. Berann and aims at increasing the amount of information in the image. Key aspect is the construction's use in an interactive system. This thesis presents an approach to create multiperspective views on 3D graphics hardware and exemplifies the extension of bird's eye and pedestrian views. High-quality rendering of nonlinearly projected virtual 3D city models focuses on the implementation of nonlinear projections on 3D graphics hardware. The developed concepts and techniques focus on high image quality. This thesis presents two such concepts, namely dynamic mesh refinement and piecewise perspective projections, which both enable the use of all graphics hardware features, such as screen space gradients and anisotropic texture filtering under nonlinear projections. Both concepts are generic and customizable towards specific projections. They enable the use of common computer graphics effects, such as stylization effects or procedural textures, for nonlinear projections at optimal image quality and interactive frame rates. This thesis comprises essential techniques for virtual 3D city model processing. First, the results of this thesis enable automated creation of textures for and their integration as individual attributes into virtual 3D city models. Hence, this thesis contributes to an improved creation and continuation of textured virtual 3D city models. Furthermore, the results provide novel approaches to and technical solutions for projecting virtual 3D city models in interactive visualizations. Such nonlinear projections are key components of novel user interfaces and interaction techniques for virtual 3D city models, particularly on mobile devices and in immersive environments.

A new three-dimensional finite solid element (3D FE) model for dowel-type wood connections was developed using the concept of a beam on a nonlinear wood foundation, which addresses the intricate wood crushing behaviour under the connector in a dowel type connection. In order to implement the concept of wood foundation with solid elements, a 3D FE wood foundation model was defined within a prescribed foundation zone surrounding the dowel. Based on anisotropic plasticity material theory, the material model for the foundation zone was developed using effective foundation material constants that were defined from dowel-embedment test data. New 3D FE single nail connection models were developed that incorporated the wood foundation model. The 3D wood foundation model was justified and validated using dowel-embedment test data with a range of dowel diameters, from a 2.5-mm nail to a25.4-mm bolt. The connection models provided successful results in simulating the characteristics of load-slip behaviour that were experimentally observed. Based on the success of the single nail connection models, several applications of the3D FE connection models were investigated including statistical wood material models, bolted connection models and a multiple nail connection model. Throughout the application studies, discussion of the benefits and limitations of the new model approach using the 3D FE wood foundation are presented. Also, future areas of study are proposed in order to improve the 3D FE dowel-type wood connections models.

L'elaborato propone un metodo per la modellazione tridimensionale di interi edifici in muratura, con lo scopo di valutare le performance sismiche, mediante il programma di calcolo SAP2000. La metodologia proposta consente la modellazione di pareti in muratura simulandone il comportamento non lineare sotto azioni agenti nel piano ed allo stesso tempo permette di considerare la ripartizione delle azioni verticali e soprattutto orizzontali che avviene tra le pareti, dovuta alle zone di connessione, ai solai ed alla loro rigidezza a taglio nel piano. Per lo sviluppo del metodo di modellazione è stato utilizzato un edificio molto semplice. Successivamente la metodologia è stata applicata ad un caso più realistico sul quale si sono fatte anche considerazioni riguardo i diversi comportamenti della struttura in funzione della rigidezza dei solai.

L'objectif principal est de faire premiers pas vers la conception topologique de structures hétérogènes à comportement non-linéaires. Le deuxième objectif est d’optimiser simultanément la topologie de la structure et du matériau. Il requiert la combinaison des méthodes de conception optimale et des approches de modélisation multi-échelle. En raison des lourdes exigences de calcul, nous avons introduit des techniques de réduction de modèle et de calcul parallèle. Nous avons développé tout d’abord un cadre de conception multi-échelle constitué de l’optimisation topologique et la modélisation multi-échelle. Ce cadre fournit un outil automatique pour des structures dont le modèle de matériau sous-jacent est directement régi par la géométrie de la microstructure réaliste et des lois de comportement microscopiques. Nous avons ensuite étendu le cadre en introduisant des variables supplémentaires à l’échelle microscopique pour effectuer la conception simultanée de la structure et de la microstructure. En ce qui concerne les exigences de calcul et de stockage de données en raison de multiples réalisations de calcul multi-échelle sur les configurations similaires, nous avons introduit: les approches de réduction de modèle. Nous avons développé un substitut d'apprentissage adaptatif pour le cas de l’élasticité non-linéaire. Pour viscoplasticité, nous avons collaboré avec le Professeur Felix Fritzen de l’Université de Stuttgart en utilisant son modèle de réduction avec la programmation parallèle sur GPU. Nous avons également adopté une autre approche basée sur le potentiel de réduction issue de la littérature pour améliorer l’efficacité de la conception simultanée
High-performance heterogeneous materials have been increasingly used nowadays for their advantageous overall characteristics resulting in superior structural mechanical performance. The pronounced heterogeneities of materials have significant impact on the structural behavior that one needs to account for both material microscopic heterogeneities and constituent behaviors to achieve reliable structural designs. Meanwhile, the fast progress of material science and the latest development of 3D printing techniques make it possible to generate more innovative, lightweight, and structurally efficient designs through controlling the composition and the microstructure of material at the microscopic scale. In this thesis, we have made first attempts towards topology optimization design of multiscale nonlinear structures, including design of highly heterogeneous structures, material microstructural design, and simultaneous design of structure and materials. We have primarily developed a multiscale design framework, constituted of two key ingredients : multiscale modeling for structural performance simulation and topology optimization forstructural design. With regard to the first ingredient, we employ the first-order computational homogenization method FE2 to bridge structural and material scales. With regard to the second ingredient, we apply the method Bi-directional Evolutionary Structural Optimization (BESO) to perform topology optimization. In contrast to the conventional nonlinear design of homogeneous structures, this design framework provides an automatic design tool for nonlinear highly heterogeneous structures of which the underlying material model is governed directly by the realistic microstructural geometry and the microscopic constitutive laws. Note that the FE2 method is extremely expensive in terms of computing time and storage requirement. The dilemma of heavy computational burden is even more pronounced when it comes to topology optimization : not only is it required to solve the time-consuming multiscale problem once, but for many different realizations of the structural topology. Meanwhile we note that the optimization process requires multiple design loops involving similar or even repeated computations at the microscopic scale. For these reasons, we introduce to the design framework a third ingredient : reduced-order modeling (ROM). We develop an adaptive surrogate model using snapshot Proper Orthogonal Decomposition (POD) and Diffuse Approximation to substitute the microscopic solutions. The surrogate model is initially built by the first design iteration and updated adaptively in the subsequent design iterations. This surrogate model has shown promising performance in terms of reducing computing cost and modeling accuracy when applied to the design framework for nonlinear elastic cases. As for more severe material nonlinearity, we employ directly an established method potential based Reduced Basis Model Order Reduction (pRBMOR). The key idea of pRBMOR is to approximate the internal variables of the dissipative material by a precomputed reduced basis computed from snapshot POD. To drastically accelerate the computing procedure, pRBMOR has been implemented by parallelization on modern Graphics Processing Units (GPUs). The implementation of pRBMOR with GPU acceleration enables us to realize the design of multiscale elastoviscoplastic structures using the previously developed design framework inrealistic computing time and with affordable memory requirement. We have so far assumed a fixed material microstructure at the microscopic scale. The remaining part of the thesis is dedicated to simultaneous design of both macroscopic structure and microscopic materials. By the previously established multiscale design framework, we have topology variables and volume constraints defined at both scales

Bridge bearing is an essential component with the function of connecting the superstructure and substructure of the bridge, transmitting load and providing movability to the superstructure. Under dynamic conditions, the internal friction of bridge bearing dissipates the vibration energy and therefore reduces the dynamic response of the bridge. Meanwhile, bearing friction is considered to have possible contribution to some nonlinear dynamic behaviour of the bridge structure, which requires further investigation.However, bearing friction, in most cases, are ignored or considered roughly and implicitly as part of structural damping in current bridge designing codes and methods. Most previous research was also focusing on bearing friction’s effect under high-amplitude vibration conditions, such as earthquake or heavy wind load. Bearing friction’s effect under common low-amplitude vibration in SLS such as train-induced vibration and vehicle-induced vibration is less attended. Although the effect of such low-amplitude vibration is less significant to structural safety, it plays an essential role to the bridge’s traffic safety and comfort. Meanwhile, the cumulative effect of such vibration can significantly influence the life and durability of bridge bearings due to its high occurring frequency. Hence, a clearer understanding of bearing dynamic behaviour is required to improve the understanding of bridge and bearing dynamics.In this thesis, an advanced numerical tool is developed for dynamic analysis of bearing friction. A 3D pot bearing finite element that can be implemented in commercial FE software ABAQUS, is programmed based on the mathematical friction models developed in previous research and the Bouc-Wen hysteretic model. Numerical results that accord with the results of relevant friction tests are produced by the calibrated and validated bearing finite element, giving proof that the element is capable to reflect the dynamic friction response of bridge pot bearing in reality.The 3D shell numerical model of Banafjäl bridge located on the Bothnia Line in Norrland, Sweden, is built as a study case of bridge dynamic analysis in this thesis, with implementation of the newly developed bearing element. The feasibility of implementing the bearing element in bridge dynamic analysis is proven by the numerical results. The nonlinear influence of bearing friction on the dynamic response of bridge structure, especially the influence on structural damping properties, is discussed preliminarily. The analysis results show that with the consideration of bearing friction, the damping presents a clear amplitude-dependency, which accords the phenomenon reported in previous research.

Materially non-linear analysis of reinforced concrete frame structures with infill walls requires appropriate mathematical models to be adopted for the beams and the columns as well as the infill walls. This study presents a mathematical model for frame elements based on a 3D Hermitian beam/column finite element and an equivalent strut model for the infill walls. The spread-of-plasticity approach is employed to model the material nonlinearity of the frame elements. The cross-section of the frame element is divided into triangular sub regions to evaluate the stiffness properties and the response of the element cross-section. By the help of the triangles spread over the actual area of the section, the bi-axial bending and the axial deformations are coupled in the inelastic range. A frame super-element is also formed by combining a number of frame finite elements. Two identical compression-only diagonal struts are used for modeling the infill. The equivalent geometric and material properties of the struts are determined from the geometry of the infill and the strength of the masonry units A computer code is developed using the object-oriented design paradigm and the models are implemented into this code. Efficiency and the effectiveness of the models are investigated for various cases by comparing the numerical response predictions produced by the program with those obtained from experimental studies.

La valutazione della vulnerabilità degli edifici scolastici esistenti nei confronti dei terremoti è un’esigenza di primaria importanza per la società in Italia. Poiché, generalmente, strutture dello stesso tipo e medesimo periodo di costruzione presentano caratteristiche simili, è stato possibile evidenziare le vulnerabilità tipiche e specifiche per differenti layout architettonici individuabili in scuole dell’infanzia, primarie e secondarie di I grado. Inizialmente, per una stima rapida delle prestazioni degli edifici, è stata valutata la vulnerabilità sismica di ciascun edificio scolastico ubicato nel comune di Trecastelli, adottando modelli ad aste a plasticità concentrata ed analisi statiche non lineari. Successivamente, per quantificare l'effettiva influenza delle vulnerabilità rilevate sul comportamento globale, è stato scelto un edificio scolastico in c.a. e realizzati tre modelli corrispondenti ad altrettanti approcci di modellazione affetti da diverse limitazioni di rappresentazione dei fenomeni reali. Per tale scopo, sono stati impiegati approcci a plasticità concentrata, a plasticità diffusa (modellazione a fibre) e al continuo con elementi solidi. Il confronto dei risultati numerici ottenuti da analisi pushover ha mostrato l’inadeguatezza del modello a fibre nella rappresentazione dei problemi di taglio del caso studio. Diversamente, il modello a plasticità concentrata si è rivelato più aderente alla realtà di quello a fibre ma non abbastanza preciso da considerare sollecitazioni concomitanti di flessione, taglio e sforzo normale e l'interazione tra di esse nella risposta inelastica della struttura. Naturalmente, il modello realizzato con elementi solidi 3D per il calcestruzzo e 1D per l’armatura risulta molto più accurato nella descrizione dei meccanismi complessi e combinati che si sviluppano nei nodi. Infine, è stata valutata anche l'efficacia di un possibile intervento di rinforzo tramite CFRP limitandosi al confinamento dei nodi non confinati.
The vulnerability assessment of existing school buildings against earthquakes represents a priority concern for the society in seismic countries. Since structures belonging to the same type and construction period may share similar features, it was possible to point out typical and specific seismic vulnerabilities related to different school architectural layouts for buildings that host the lower levels of the Italian education system. Firstly, to estimate the performance of buildings in a fast way, the vulnerability of each school building belonging to the municipality of Trecastelli was assessed, adopting a lumped plasticity approach and a nonlinear static procedure. With the aim of quantifying the effective influence of these vulnerabilities detected on the global seismic behaviour, a RC school building was chosen and three different models were implemented correspond to as many different approaches affected by various limitations in the representativeness respect to the reality. The different modelling technique used follow the lumped plasticity, the distributed plasticity (fibre model) and the 3D Continuum FE approaches. Nonlinear static (pushover) analyses were performed to assess the global seismic behaviour of the structure. The comparison of the numerical results has shown that the fibre model is the least suitable mean to represent the shear problems of the case study. Instead, the lumped plasticity model is closer to reality than the previous one but not precise enough to consider the concomitance of bending, shear and axial force and the interaction between them in the inelastic response. Of course, the 3D Continuum model is much more accurate than other models to describe the mechanisms developed in the joint panels which are very complex and combined. Finally, the effectiveness of a possible CFRP local strengthening intervention for the case study limited to confine the unconfined beam-column joints was also considered.

The master thesis is focused on the simulation of the toroid coils in Ansoft Maxwell 3D software, which uses finite element method for electromagnetic field simulation. Firstly the process creation of the geometric model toroid coil with seventy-five threaded is presented. It is necessary to debug this model and prepare it for the mesh generation. Physical properties are assign to this model and it gives rise to the physical model. We will set boundaries, excitation current, core material, winding material and the parameters for the mesh generations. New material Kashke K4000 will be created in the materials library and subsequently we will define its BH curve on the basis of datasheet. Analysis is made in two modes. Direct currents (7,5A; 10A; 15A; 20A; 25A) and (non)linear materials are used in magnetostatic solution. Toroid coil is excited by current pulse in transient solution. In Ansoft Maxwell Circuit editor a source which generates current pulse will be created. This excitation will be assigned to the toroid coil as an extern source through a terminal. Core material is linear in the case of transient analysis, because Ansoft Maxwell 3D doesn´t allow to use nonlinear material in this solution. Settings are different in transient and in magnetostatic analysis. End time and time step are entered to solve this task in transient analysis. Time points are entered too. Flux density and electromagnetic field strength are calculated in these time points and later it will be possible to view the results. Calculated fields are shown as the pictures in this thesis. The procedure how to use a field calculator in the postprocessing is given as well. The achievements are summarized in the conclusion.

Prior to this study, to our best knowledge, no cast-in-place, older-type RC building has ever been subjected to near-field strong ground motions from three major earthquakes. This happened in an indirect way in Turkey over a time span of eleven years. Three identical buildings belonging to Ministry of Public Works and Resettlement (MPWR) that had been built to the same design templates, experienced March 13th 1992 Erzincan earthquake in Erzincan, November 12th 1999 Dü
zce earthquake in Bolu and May 1st 2003 Bingö
l earthquake in Bingö
l, respectively. The ground motion sensor stations were fortuitously nearby in an adjacent single-story building in Bolu and Bingö
l. The station in Erzincan was in a single-story building about 2 km away from the case study building but we assume that the record applies to the building there. These three data represent characteristics of near-field ground motions and the distance of the sensor stations to the nearest fault trace was less than 10 km. The buildings sustained varying degrees of damage during the earthquakes and their damage survey was employed through site investigations. Given that the damage information, input motions, design drawings and material properties of the buildings are all known, this provided an opportunity to predict the structural damage to these buildings by proper modeling using the tools of current computational performance assessment procedures. In this circumstance, three dimensional (3D) analytical models of the MPWR buildings have been performed. Bi-directional excitations have been applied to the models by nonlinear time history analyses (NTHA). The results illustrate that NTHA are capable of indicating the occurrence of shear failure in captive columns
however, they overestimate the global damage level for all buildings. The overestimation is more significant in Erzincan case where the building sustained a pulse-type motion without significant distress.

Cette thèse vise à étudier expérimentalement, analytiquement et numériquement, les conséquences de variations et d'oscillations hydrodynamiques à forte variabilité temporelle en milieux poreux partiellement saturés. Les problèmes que nous étudions comportent des surfaces libres tant à l'extérieur qu'à l'intérieur des milieux poreux, celles-ci étant définies comme des isosurfaces de pression d'eau égale à la pression atmosphérique (Pwater = Patm). Les différentes études expérimentales réalisées en laboratoire sont, respectivement : une expérience d'imbibition dans une boite à sable avec effets capillaires importants; la transmission d'oscillations de la surface libre à travers un massif sableux intercalaire dans un petit canal à houle (IMFT, Toulouse); l'étude de la dynamique et de la propagation des oscillations des niveaux d'eau dans un grand canal à houle (HYDRALAB, Barcelone), partiellement recouvert d'un fond sableux incliné, avec mesures de niveaux d'eau en pleine eau et sous le sable, et mesures du fond sableux (érosion/dépôts). Pour les études théoriques, nous avons développés des solutions analytiques linéarisées. Un exemple de problème traité analytiquement est: l'équation linéarisée de Dupuit-Boussinesq (D-B) transitoire à surface libre, en hypothèse d'écoulements plans et vidange/remplissage instantané : oscillations forcées, transmission et dissipation d'ondes à travers une boite à sable rectangulaire. Nous avons aussi développé une solution de l'équation faiblement non linéaire de Dupuit- Boussinesq (D-B) pour étudier le problème d'imbibition avec variation abrupte du niveau d'eau amont (suivi temporel du front de saturation). Nous avons pu étudier les différents types de problèmes transitoires liés aux expériences citées plus haut par simulation numérique. En particulier, nous avons simulé des écoulements partiellement saturés et insaturés, en coupe verticale, à l'aide d'un code de calcul (BIGFLOW 3D) qui résoud l'équation de Richards généralisée en régime transitoire. Nous avons ainsi étudié numériquement en régime non saturé, l'expérience d'imbibition dans un sable initialement sec à frontières verticales (IMFT sandbox), puis l'expérience de propagation d'ondes dans le grand canal à houle de Barcelone (laboratoire HYDRALAB) comportant une plage de sable inclinée, avec un couplage complètement intégré entre les zones micro-poreuse (sable) et “macro-poreuse” (pleine eau). Pour analyser les résultats de cette dernière expérience et les comparer aux simulations, nous avons utilisé plusieurs méthodes de traitement et d'analyse des signaux : analyse de Fourier (spectres de fréquences) ; ondelettes discrètes multi-résolution (Daubechies) ; analyses corrélatoires simple et croisée. Ces méthodes sont combinées avec des méthodes de préfiltrage pour estimer dérives et résidus (moyennes mobiles ; ondelettes multi-résolution). Cette analyse des signaux a permis de comprendre et quantifier la propagation à travers une plage de sable. Au total, les différentes approches de modélisation mis en oeuvre, associé à des procédures de calage en situation de couplage transitoire non linéaire ont permis de reproduire globalement les phénomènes de propagation de teneur en eau et de niveau d'eau dans les différentes configurations étudiées
This thesis aims at investigating experimentally, analytically and numerically, the consequences of hydrodynamic variations and oscillations with high temporal variability in partially saturated porous media. The problems investigated in this work involve “free surfaces” both outside and inside the porous media, the free surface being defined as the “atmospheric” water pressure isosurface (Pwater = Patm). The laboratory experiments studied in this work are, respectively: Lateral imbibition in a dry sand box with significant capillary effects; Transmission of oscillations of the free surface through a vertical sand box placed in a small wave canal (IMFT, Toulouse); Dynamics of free surface oscillations and wave propagation in a large wave canal (HYDRALAB, Barcelona), partially covered with sand, with measurements of both open water and groundwater levels, and of sand topography (erosion / deposition). For theoretical studies, we have developed linearized analytical solutions. Here is a sample problem that was treated analytically in this work: The linearized equation of Dupuit-Boussinesq (DB) for transient free surface flow, assuming horizontal flow and instantaneous wetting/drainage of the unsaturated zone: forced oscillations, wave transmission and dissipation through a rectangular sandbox. We also developed a weakly nonlinear solution of the Dupuit-Boussinesq equation to study the sudden imbibition (temporal monitoring of the wetting front). We have studied the different types of transient flow problems related to the experiments cited above by numerical simulation. In particular, we have simulated unsaturated or partially saturated transient flows in vertical cross-section, using a computer code (BIGFLOW 3D) which solves a generalized version of Richards’ equation. Thus, using the Richards / BIGFLOW 3D model, we have studied numerically the experiment of unsaturated imbibition in a dry sand (IMFT sandbox), and then, with the same model, we have also studied the partially saturated wave propagation experiment in the large Barcelona wave canal (HYDRALAB laboratory), focusing on the sloping sandy beach, with coupling between the micro-porous zone (sand) and the “macro-porous” zone (open water). To interpret the results of the latter experiment and compare them to simulations, we use several methods of signal analyzis and signal processing, such as: Fourier analysis, discrete multi-resolution wavelets (Daubechies), auto and cross-correlation functions. These methods are combined with pre-filtering methods to estimate trends and residuals (moving averages; discrete wavelet analyses). This signal analyzis has allowed us to interpret and quantify water propagation phenomena through a sandy beach. To sum up, different modeling approaches, combined with model calibration procedures, were applied to transient nonlinear coupled flow problems. These approaches have allowed us to reproduce globally the water content distributions and water level propagation in the different configurations studied in this work

碩士
國立臺灣科技大學
應用科技研究所
103
Unstable pelvic fracture represents a severe injury associated with high morbidity and mortality. In the past, several types of fixators were used to treat this unstable fracture, including external fixators, plates, sacral bars, iliosacral screws, and pre-tensed curved bar. However, the biomechanical performances of the above fixation techniques were mainly evaluated according to the outcomes of clinical applications, and only one of the fixation techniques was selected and evaluated. To our knowledge, there were few studies to analyze and compare the biomechanical performances of different pelvic fixation techniques. In addition, the past studies had investigated one of the fixation techniques by using finite element methods. However, there has been no study that investigated the biomechanical performances of the fixation techniques by using 3D nonlinear finite element models of spine-pelvis-femur complex. Thus, the purpose of this study was to analyze and investigate the biomechanical performances of different pelvic fixation techniques for the treatment of unstable pelvic fracture. Three-dimensional nonlinear finite element models of spine-pelvis-femur complex were developed to investigate the biomechanical performances of different pelvic fixation techniques by using ANSYS Workbench 14.5. Concurrently, the biomechanical experiment was developed to validate the numerical results. In this study, three types of the pelvic fixators were evaluated and discussed, including posterior iliosacral screws, sacral bars, and locking compression plate. The fixation stability, pelvic stress, and implant strength were obtained and used to evaluate the strength and limitation of each fixation technique. The results of this study showed that the posterior iliosacral screws had better fixation stability compared with the sacral bars and the locking compression plate. Additionally, the locking compression plate revealed higher stress concentration effects on the pelvis and the implants compared with others. We hope that the outcomes of this study could directly provide the surgical suggestion to orthopedic surgeons and help them to understand the biomechanics of different pelvic fixation techniques.

碩士
淡江大學
電機工程學系碩士班
103
This thesis presents a three-dimensional (3D) model building method and a model-based visual tracking method for an object-of-interest. The proposed methods can help robots to accomplish more difficult tasks, such as 3D pose estimation and robust visual tracking of a rigid object. The contents of this thesis are divided into two parts. The first part presents the design of a 3D computer-aided design (CAD) model building algorithm, which produces a 3D CAD model of a geometrical object to facilitate the subsequent visual tracking task. The second part presents the design of a CAD-model based object pose estimation algorithm to implement the function of robust 3D object tracking. We first used Microsoft Kinect to capture the point cloud data of an object-of-interest for extracting its planar features. Then, its 3D CAD model was produced by vertex information of the object found by using geometrical characteristics of the object planar features. Next, a robust CAD-model based visual tracking method was implemented by fitting the contour of the projection of the 3D CAD model to the object contour on the image plane, which also can provide 3D pose information of the object during the visual tracking task.