Dissertations / Theses on the topic 'Geometridae Behavior'

The magnetic behaviour in nanoscale structures is of great interest for the fundamental understanding of magnetisation processes and also has importance for wide ranging technological applications. This thesis examines mechanisms for the enhanced control of domain walls in these structures via focussed ion beam modifications to magnetic nanowires and through the inclusion of periodic geometrical modifications to the nanowires geometry. A detailed investigation into the effect of focussed ion beam irradiation on the structure of NiFe/Au bilayers was performed through x-ray reflectivity and fluorescence techniques. This analysis revealed the development of interfacial intermixing with low dose irradiation. This is associated with complex changes of the magnetic behaviour including a rapid decrease, followed by a recovery of the saturation magnetisation with low dose irradiation. This behaviour is attributed to changes in the local environment of the atoms at the interface; resulting in modifications to the magnetic moment on Ni and Fe. The development of an induced moment on Au and a change in the spin-orbit interaction is also suggested. Localised control of the magnetic properties in nanowires demonstrates the ability to manipulate domain walls in these structures. Here, irradiated regions provide pinning sites where the width and dose of the irradiated region give control over the pinning potential. The inclusion edge modulation to nanowires geometry provides additional control over their magnetic behaviour. The direct magnetisation reversal field of these structures is explained by an analytical model based on the torque on the spins following the modulated wire geometry. This model is scalable for different modulation parameters and combines with the effect of localised regions of orthogonal anisotropy along the wire; explaining the reversal behaviour over the entire parameter space. Domain wall mediated reversal in modulated wires was also investigated in these structures. The inclusion of modulation shows an improvement in dynamic properties by the suppression of Walker breakdown. This is due to the relationship between geometrical modulations and the periodicity of micromagnetic domain wall structural changes during the Walker breakdown process. The combination of this work shows a route to the optimisation of the dynamic properties whilst minimising the detrimental increase in the de-pinning field from the modulation.

The thermal properties of fabric are an important factor in the understanding of the thermo-physiological comfort of clothing. The principal aim of this research was to develop novel numerical methods, Graphical User Interface (GUI) plug-ins and experimental setup to evaluate the effective thermal conductivity and thermal resistance of different textile structures which has significant impact on the thermal comfort of clothing. The numerical methods also include the analysis of the effect of fibre orientation, thermal anisotropy of fibre, temperature dependent thermal conductivity and fibre volume fraction on the effective thermal conductivity and thermal resistance of textile fabrics. The research covers the development of geometrical models of woven, knitted, nonwoven and the composites fabric structures, evaluation of their thermal properties by using finite element method, creation of user friendly plug-ins and the extended application tools. Micro and mesoscopic scale modelling approaches were used to investigate the effective thermal conductivity and thermal resistance of textile structures. Various techniques, including scanning electron microscopy, x-ray microtomography and experimental method have been adopted to obtain the actual 3D dimensional parameters of the fabrics for finite element analysis. Research revealed that, the thermal anisotropy of fibres, fibres material orientation and temperature dependent thermal conductivity of fibre have significant impact on the effective thermal conductivity of fabrics because experimental and simulated results were highly correlated with the consideration of above mentioned factors. In addition a unique technique has been developed in modelling fabric coated by microencapsulated phase change material for temperature stable textile and clothing system. User friendly GUI plug-ins have been developed to generate both microscopic and mesoscopic scale models for finite element analysis. The plug-ins were developed by using Abaqus/CAE as a platform. The GUI Plug-ins enable automatic model generation and property analysis of knitted fabrics and composites. Apart from finite element analysis of various fabric structures, an experimental device has been developed for testing thermal conductivity of fabrics which is capable of testing small sample size within very short period of time. The device was validated by commercial available apparatus for testing of fabric thermal conductivity.

Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Engineering, 2007.
"May, 2007." Title from electronic dissertation title page (viewed 04/07/2008) Advisor, Erol Sancaktar; Committee members, Avraam I. Isayev, Sadhan C. Jana, Darrell H. Reneker, Shing-Chung Wong; Department Chair, Sadhan C. Jana; Dean of the College, George R. Newkome; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

O estudo do comportamento espectral de culturas agrícolas, por meio da radiometria de campo, contribui para a obtenção de uma maior precisão nos modelos gerados pelo sensoriamento remoto, quando utilizados na estimativa e análise de variáveis agronômicas de culturas. Tendo em vista que os sensores a bordo de satélites podem adquirir imagens sob diferentes ângulos de visada e em diferentes horários de passagem, torna-se necessário o conhecimento do efeito dessas variáveis sobre a resposta espectral das culturas. A presente pesquisa teve como objetivo avaliar a influência de três ângulos de visada (0º, 30º e 45º) e três horários de medição (10 horas, 12 horas e 14 horas), o que implica em diferentes ângulos de elevação solar, na resposta espectral da cultura de feijão, como também nas relações entre o índice de área foliar (IAF) e o Índice de Vegetação Diferença Normalizada (NDVI). O experimento foi conduzido na “Fazenda Areão”, pertencente à Escola Superior de Agricultura 'Luiz de Queiroz' (ESALQ/USP), Piracicaba, SP, de março a junho de 2005. O delineamento experimental foi o de blocos ao acaso, com parcelas subdivididas, constituído de três blocos, três tratamentos primários referentes aos horários de leitura e três tratamentos secundários relacionados ao ângulo de visada. Foram realizadas nove campanhas de medição no campo, com o espectroradiômetro SPECTRON SE-590. Dos fatores de reflectância (FR) determinados, simularam-se as bandas TM3 e TM4 e, a partir destes, foram gerados os índices de vegetação. De acordo com os resultados obtidos, concluiu-se que a variação do horário de medição não proporcionou variação significativa sobre os valores do FR nas bandas TM3 e TM4. Já a variação do ângulo zenital de visada influenciou significativamente, ao nível de 5 % de probabilidade, o FR nas bandas TM3 e TM4, para todos os dias de leitura. Quanto às relações IAF e NDVI, o modelo linear apresentou melhores ajustes, estatisticamente significativos (p≤0,05).
The study of the spectral behavior of crops, through field radiometry, contributes to a better precision in models generated by remote sensing, when they are used to estimate and analyze crops’ agronomic variables. Once sensors aboard of satellites are able to acquire images under different viewing angles and at different times of the day, it is necessary to understand the effect of such variables on the crops’ spectral response. The objective of this research was to evaluate the influence of the viewing angles (0º, 30º and 45º) and three radiometric acquisition times (10:00 a.m, 12:00 a.m and 2:00 p.m), related to different sun elevation angles, on the spectral behavior of bean crop, as well as on the relationship between Leaf Area Index (LAI) and Normalized Difference Vegetation Index (NDVI). The experiment was installed in the “Fazenda Areão”, of the ESALQ/USP, in Piracicaba, SP, from March to June, 2005. The experimental design was the randomized blocks, with split plots, with three blocks, three primary treatments (acquisition times) and three secundary treatments (viewing angles). Nine field campaigns were carried out with the SPECTRON SE-590 spectroradiometer. Bands TM3 e TM4 were simulated from the determined reflectance factors and, with these bands, vegetation indices were generated. According to the results, it was concluded that the variation on acquisition time did not lead to a significant variation on the reflectance factors in the TM3 and TM4 bands. On the other hand, the variation in the viewing angle significantly affected (p≤0,05) the reflectance factor in the TM3 and TM4 bands, for every day of measurement. Regarding the relationships between LAI and NDVI, the linear model showed the best fit (p≤0,05).

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Este trabalho teve o propósito de determinar o comportamento dos gases na seção de radiação de um combustor de ar que pertence a uma planta industrial. O corpo metálico do equipamento rompeu em seu primeiro ano de operação, devido a um problema conceitual em sua geometria. A fluidodinâmica computacional (CFD), por meio do método dos volumes finitos, foi utilizada para desenvolver um modelo tridimensional que pudesse reproduzir o perfil de temperatura e o comportamento do fluxo do ar de combustão no equipamento. Na simulação, através do uso do software ANSYS CFX, foram utilizados: (i) o modelo de turbulência Reynolds Stress Model (RSM); (ii) as malhas hexaédrica, tetraédrica e prismática; (iii) o modelo de radiação P-1; e (iv) o modelo de combustão Eddy Dissipation Concept (EDC). Como resultado, foram apresentadas quatro possíveis mudanças na geometria do combustor de ar que, caso adotadas, eliminariam os riscos de novas falhas e garantiriam a continuidade operacional da unidade de processo.
This paper has the objective to describe the behavior of the flow and temperature of the flue gas in the radiation section of the vessel used to preheat air in a combustor. The equipment failed in its first operational year, due to a conceptual problem in its geometry. The CFD code based on finite volume method was applied to simulate the physical model of combustor using the ANSYS CFX software, reproducing the main features of the preheater. The simulation had considered: (i) Reynolds Stress Model (RSM) as turbulence model, (ii) The meshes applied were the hexahedral, tetrahedral and prismatic, (iii) P-1 was used as the radiation model and (iv) Eddy Dissipation Concept (EDC) as combustion model. Through the simulation was possible to propose four different kind of combustor geometry modification, that the application of anyone of them would eliminate the risk of new failures, ensuring the unit production availability.

The morphological properties of rock fractures may have a significant influence on their hydromechanical behaviour. Fracture surface roughness could change the fluid flow regime from laminar to turbulent, while it causes the flow properties to deviate from cubic law for smooth channels due to a change in fracture equivalent hydraulic aperture. Different empirical (including the well known Joint Roughness Coefficient, JRC) and statistical methods have been proposed for surface roughness characterisation in an attempt to link them to the hydromechanical behaviour of fractures.This thesis aims to investigate the potential for assessment of fluid behaviour by studying its surface geometrical properties. D[subscript]R[subscript]1 and D[subscript]R[subscript]2, the 2D and 3D roughness parameters developed recently using Riemannian geometry, were used to correlate fracture geometry to its flow behaviour. Also, the 2D Riemannian isotropy parameter (I[subscript]R[subscript]2) was used to correlate surface roughness anisotropy with directionality in fluid flow behaviour along different directions.Numerical simulations in both 2D and 3D were performed assuming the laminar flow regime using FLUENT software. This assumption is, to a large extent, acceptable for situations where the height to length ratios of a fracture is very small. 2D analysis of synthetic profiles with different geometries demonstrated how a change in profile roughness can affect flow response, for example, the pressure drop. JRC flow channels developed in this work as combinations of pairs of JRC profiles were simulated numerically. The analysis results indicated that channels with a similar JRC average for the upper and lower walls but a different JRC profile number responded differently when they were subjected to fluid flow. Therefore, assuming special fluid properties, correlations developed using the pressure drop of a fracture can be estimated by its analogy to JRC flow channels.3D simulations of a corrugated plane were performed assuming different asperity height distributions, for fluid travelling along different directions with respect to surface geometry and at different shear displacements. No asperity contact and failure is assumed in the analysis performed in this work. D[subscript]R[subscript]2 analysis results of the corrugated plane indicated how fluid flow could be related to surface geometry. For instance, it was observed that the pressure drop was maximised along the direction of maximum roughness and reduced to its minimum along a perpendicular direction which shows anisotropy in fluid flow behaviour. Significant changes in pressure drop due to shear offset indicated the importance of fracture wall displacements with respect to each other. A detailed analysis of one synthetically generated surface, and also five surfaces with identical statistical parameters except their correlation distances being different, further confirmed the above concepts. This was followed by analysing a real rock like fracture which was studied elsewhere for fracture shear tests in the lab. Simulation of this surface was performed with particular interest in identifying the locations where the velocity magnitude reduced to nearly zero after the fracture was subjected to a shear offset corresponding to maximum shear stress. These areas were found to be very similar to the locations of asperity degradations as observed through lab experiments. The roughness analysis of the surface was in agreement with the correlation found between the mechanical and hydraulic behaviour of the surface.The results of this research demonstrate how detailed analysis of surface geometry could provide valuable information with respect to surface flow behaviour. Detailed discussions and interpretations of the results will be presented and various conclusions will be made.

Cette thèse introduit le concept de comportement géométrique d'un assemblage mécanique. Cette notion permet de rendre compte du caractère assemblable ou mobile d'un mécanisme sous la forme d'un système de relations algébriques entre les paramètres géométriques permettant de le décrire. Dans un premier temps, cette thèse montre l'intérêt de ce concept pour traiter des problèmes faisant intervenir plusieurs effets physiques et plusieurs scénarios d'utilisation. Ce chapitre est appliqué à l'étude de l'assemblabilité d'un treillis pyramidal de conception à 4 barres décrit par un modèle géométrique non cartésien issu de la littérature. Dans un second temps, après avoir constaté le manque de modèles adaptés permettant de représenter des mécanismes mobiles, ce travail en propose un non cartésien. Il détaille aussi une méthode de mise en équation afin de traduire la mobilité d'un mécanisme. Une application de ce modèle et de la méthode est également faite. Elle permet de résoudre localement le problème de la mobilité d'un mécanisme de Bennett. Enfin, la dernière partie de ce travail expose une solution pour associer et comparer deux objets décrits par des représentations non cartésiennes. Cette technique est utile pour comparer deux états physiques du même objet utilisé dans différents scénarios pour assurer le suivi d'une exigence géométrique. Elle peut également être utilisée pour associer des objets réels et des objets idéalisés pour traiter des problèmes de tolérancement

Since ancient times, master builders have used arches to cover large spans in masonry structures. As a consequence, nowadays the safety assessment of these structural elements plays a fundamental role in the conservation of built cultural heritage. Due to their frequent occurrence, support displacements are one of the primary sources of damage for masonry arches. Among the potential causes of support displacements, slow-moving landslides have received very little attention from the scientific community. The present thesis is motivated by the observation of extensive and severe damage in the arches of historic masonry churches exposed to slow-moving landslides. These phenomena produce a combination of vertical and horizontal supports displacements, whose effect on the arch structural behaviour has never been thoroughly investigated in the literature, especially in the framework of large displacements. In view of the above, this thesis aims at providing a full understanding of the mechanics of masonry arches subjected to large support displacements, with special attention to inclined displacements. The methodology used to accomplish this goal included both experimental tests and numerical analyses on a segmental scaled dry-joint masonry arch subjected to different combinations of horizontal and vertical support displacements. The numerical simulations were carried out in the framework of large displacements using two different numerical approaches based on finite element (FE) and rigid block (RB) modelling. A micro-modelling strategy was adopted, where the arch was modelled as an assemblage of voussoirs, very stiff and infinitely resistant in compression in the FE model and rigid in the RB model, interacting at no-tension friction interfaces. Preliminary numerical simulations, aimed at designing the experimental set-up and gaining a first insight in the arch response, were carried out considering the arch as a rigid-no tension structure. To this aim, a very large value of interface normal stiffness was adopted in the FE model. A large experimental campaign was performed on a 1:10 small-scale model built as a dry-joint assemblage of voussoirs made of a bicomponent composite material. The results of the tests allowed, for the first time in the literature, to accurately assess the effect of the direction of the imposed support displacements on the arch response in the framework of large displacements. The comparison between numerical and experimental results showed that the numerical models were not able to accurately predict the experimental response. To investigate this discrepancy, a sensitivity analysis on the effect of the interface normal stiffness on the FE predictions was performed. The results demonstrated that the difference between numerical and experimental results could be attributed due to the imperfections, and resulting deformability, of the joints of the physical model. A strategy to include imperfections in the numerical modelling, consisting in calibrating the interface normal stiffness based on the experimental results, was thus proposed and validated by performing further FE simulations, whose results were in very good agreement with the experimental evidence. Finally, to investigate the effect of geometrical imperfections on the arch response, a further experimental test was performed on a physical model made of bicomponent composite voussoirs exhibiting more imperfections. The test was simulated using a FE calibrated model to further validate the strategy proposed to model imperfections. The comparison between the experimental results for the two tested physical models showed that imperfections play a fundamental role in the response of small-scale arches to large support displacements. Furthermore, reducing the interface normal stiffness with respect to the large value adopted to model rigid interfaces proved to be an effective strategy to simulate the amount of imperfections of the experimental models.
Desde la antigüedad, los maestros constructores han utilizado el arco como elemento estructural para salvar grandes luces en estructuras de mampostería. En consecuencia, para la conservación del patrimonio arquitectónico es hoy en día de fundamental importancia la correcta verificación estructural de este tipo de elementos. Se ha observado frecuentemente que el desplazamiento de los apoyos es una de las principales causas de daño en arcos de mampostería. De entre las distintas causas que pueden provocar dicho desplazamiento, el deslizamiento de tierras ha recibido poca atención por parte de la comunidad científica. La presente tesis encuentra su motivación en el daño extenso y severo observado en los arcos de las iglesias de mampostería ubicadas en zonas expuestas a deslizamiento de tierras. Este fenómeno produce una combinación de desplazamientos verticales y horizontales, cuyo efecto en el comportamiento estructural de los arcos no ha sido investigado en profundidad, especialmente en lo relativo a grandes desplazamientos. Esta tesis aspira a contribuir al conocimiento del comportamiento mecánico de los arcos de mampostería sometidos a grandes desplazamientos de apoyos, con especial atención a los desplazamientos inclinados. La metodología utilitzada para dicho fin incluye ensayos experimentales y análisis numéricos en un modelo a escala de un arco de mampostería a junta seca. El modelo fue ensayado bajo diferentes combinaciones de desplazamientos horizontales y verticales en uno de sus apoyos. La simulación numérica fue desarrollada en el marco de grandes desplazamientos usando dos métodos numéricos diferentes: un modelo de elementos finitos (FE) y un modelo de bloques rígidos (RB). Los modelos fueron concebidos como un conjunto de dovelas rígidas con infinita resistencia a compresión en el modelo FE y como dovelas infinitamente rígidas en el modelo RB. En ambos modelos la interfaz entre dovelas fue modelada sin resistencia a tracción. Con el objetivo de diseñar la configuración experimental y adquirir una comprensión inicial de la respuesta del arco, se llevaron a cabo simulaciones numéricas preliminares en las cuales se consideró al arco estudiado como una estructura rígida. Para ello en el modelo FE del arco, la rigidez normal de la interfaz fue inicialmente caracterizada con un valor muy elevado. La campaña experimental fue llevada a cabo en modelos a escala 1:10. Los resultados de los ensayos experimentales permitieron, por primera vez en la literatura, un análisis preciso del efecto que tiene la dirección del desplazamiento impuesto en el comportamiento del arco en marco de grandes desplazamientos. La comparaci ón entre los resultados numéricos y experimentales mostró que los modelos numéricos no eran capaces de capturar de manera precisa la respuesta experimental. Para investigar esta discrepancia, se realizó un estudio de sensibilidad relativo al efecto de la rigidez normal de la interfaz sobre las predicciones del modelo FE. Los resultados demostraron que la diferencia entre los resultados numéricos y experimentales se debía a las imperfecciones de las juntas del modelo físico. Como consecuencia, se propuso la inclusión de imperfecciones en el modelo numérico. Para ello se calibró la rigidez normal de la interfaz según los resultados experimentales y el modelo se validó con nuevas simulaciones. Finalmente, con el fin de investigar el efecto de las imperfecciones en la respuesta del arco, se llevó a cabo otro ensayo con el mismo modelo experimental, pero añadiéndole imperfecciones. El ensayo fue simulado con un modelo calibrado FE. Los resultados obtenidos mostraron que las imperfecciones juegan un rol fundamental en la respuesta de arcos a pequeña escala con grandes desplazamientos en los apoyos. Además, la reducción de la rigidez normal de la interfaz con respecto al valor muy elevado inicialmente adoptado demostr ó ser una estrategia efectiva para simular las imperfecciones de los modelos experimentales.
Fin dall’antichità, i maestri costruttori hanno utilizzato gli archi per coprire grandi luci nelle strutture in muratura. Di conseguenza, ad oggi la valutazione della sicurezza di questi elementi strutturali gioca un ruolo fondamentale nella conservazione del patrimonio architettonico. A causa del loro frequente verificarsi, gli spostamenti degli appoggi sono una delle principali fonti di danno per gli archi in muratura. Tra le potenziali cause di questi spostamenti, le frane a cinematica lenta hanno ricevuto pochissima attenzione da parte della comunità scientifica. La presente tesi è motivata dall'osservazione di danni ingenti negli archi di chiese storiche in muratura interessate da frane a cinematica lenta. Questi fenomeni producono una combinazione di spostamenti verticali e orizzontali agli appoggi, il cui effetto sul comportamento strutturale dell'arco non è mai stato studiato a fondo in letteratura, soprattutto nell’ambito di grandi spostamenti. Alla luce di queste osservazioni, questa tesi si propone di fornire una piena comprensione della meccanica degli archi in muratura soggetti a grandi spostamenti degli appoggi, con particolare attenzione agli spostamenti inclinati. La metodologia utilizzata per raggiungere questo obiettivo ha incluso sia prove sperimentali che analisi numeriche su un arco ribassato in muratura di giunti a secco in piccola scala, in cui sono state applicate diverse combinazioni di spostamenti orizzontali e verticali in corrispondenza di un appoggio. Le simulazioni numeriche sono state eseguite nell’ambito dei gradi spostamenti utilizzando due diversi approcci numerici basati su una modellazione ad elementi finiti (FE) ed una modellazione a blocchi rigidi (RB). È stata adottata una strategia di micro-modellazione, in cui l'arco è stato modellato come un assemblaggio di blocchi, molto rigidi e infinitamente resistenti a compressione nel modello FE e infinitamente rigidi nel modello RB. In entrambi i modelli i blocchi erano collegati da interfacce senza resistenza a trazione. Simulazioni numeriche preliminari, finalizzate a progettare il set-up sperimentale e ad acquisire una prima conoscenza della risposta dell'arco, sono state eseguite considerando l'arco come una struttura rigida non resistente a trazione. A tal fine, nel modello FE è stato adottato un valore molto elevato di rigidezza normale delle interfacce. Un’ampia campagna sperimentale è stata eseguita su un modello in scala 1:10 costruito come un assemblaggio a secco di blocchi realizzati con un materiale composito bicomponente. I risultati delle prove sperimentali hanno permesso, per la prima volta in letteratura, di valutare con precisione l'effetto della direzione degli spostamenti imposti sulla risposta dell'arco nell’ambito dei grandi spostamenti. Il confronto tra i risultati numerici e sperimentali ha mostrato che i modelli numerici non erano in grado di cogliere in maniera accurata la risposta sperimentale, specialmente in termini di spostamento ultimo al collasso. Al fine di indagare le ragioni di questa discrepanza, è stata quindi eseguita un'analisi di sensitività relativa all’effetto della rigidezza normale delle interfacce sulle previsioni del modello FE. I risultati hanno dimostrato che la differenza tra risultati numerici e sperimentali poteva essere attribuita alle imperfezioni, e conseguente deformabilità, delle interfacce del modello fisico. Una strategia per includere le imperfezioni nella modellazione numerica, consistente nel calibrare la rigidezza normale delle interfacce sulla base dei risultati sperimentali, è stata quindi proposta e validata attraverso ulteriori simulazioni FE, i cui risultati si sono rivelati in ottimo accordo con le evidenze sperimentali. Infine, per indagare l'effetto delle imperfezioni geometriche sulla risposta dell'arco, è stata eseguita un’ulteriore prova sperimentale su un modello fisico costituito da blocchi dello stesso materiale composito bicomponente che presentavano però più imperfezioni. Al fine di validare ulteriormente la strategia proposta per modellare le imperfezioni, la prova sperimentale è stata simulata utilizzando un modello FE calibrato. Il confronto tra i risultati sperimentali per i due modelli fisici ha mostrato che le imperfezioni giocano un ruolo fondamentale nella risposta di archi in piccola scala a grandi spostamenti degli appoggi. Inoltre, ridurre la normale rigidezza dell'interfaccia rispetto al valore molto alto adottato per modellare interfacce rigide si è rivelata una strategia efficace per simulare la quantità di imperfezioni dei modelli sperimentali
Enginyeria de la construcció

Cette thèse a pour objectif de modéliser, par approches biométriques, l’évolution dans le temps du visage humain, en partant de l’âge enfant, jusqu’à un âge adulte. Ces travaux sur le vieillissement rentrent dans le cadre des activités de recherche du groupe biométrie du laboratoire LiSSi (UPEC).Comme il est connu, l’évolution des traits dues au vieillissement dépend deplusieurs facteurs intrinsèques ou extrinsèques, dont : la génétique, l’origine ethnique, le mode de vie, etc. En considérons les modèles paramétriques proposés dans cette thèse, nous exploitons entre autres, les similitudes des caractéristiques extraites chez des individus d’une même catégorie d’âge. Ces similitudes sont intégrées dans nos modèles afin de pouvoir estimer l’apparence faciale à un âge spécifique. Contrairement aux nombreuses études traitant les modèles prédictifs de vieillissement facial, cette thèse propose pour la première fois un modèle réversible permettant également le rajeunissement numérique de l’apparence du visage que nous appellerons, modèle de prédiction arrière d’apparence. Quant à la prédiction avant, notre contribution s’est orientée vers la proposition d’un modèle non-linaire paramétrique de vieillissement permettant de prendre en considération les facteurs accélérateurs de vieillissements liés au mode de vie des individus. De manière générale, nous nous sommes intéressés aux conséquences de certaines addictions de type (drogues, alcool,exposition au soleil, etc.), sur le vieillissement prématuré du visage. Par conséquent,nous avons proposé des modèles sensibles à certains de ces facteurs en se basant sur des analyses statistiques. Comme retombés socio-économiques, cette étude a pour objectif de sensibiliser les jeunes personnes par rapport aux dangers liés à la consommation excessives de certaines substances, voire à l’addiction à certaines pratiques.Les études que nous avons menées durant cette thèse, ont nécessité la constitution d’une base de données contenant plus de 1600 images faciales. Cette base de données a permis le développement 30 modèles de visages «Face Templates». Suite à cela, nous avons créé une base de données d’évaluation, appelée «Face Time-Machine (FaceTiM)». Constituée à partir de 120 sujets, cette base de données est mise à disposition des chercheurs afin qu’ils puissent reproduire les résultats que nous avons obtenus, évaluer les performances, et enfin contribuer à l’amélioration des modèles proposés
The main focus of this thesis is to model the evolution trajectory of human face from infancy to senility using the biometrics facial features.The manifestation of facial changes caused by ageing depends on different factors such as genetic, ethnicity and lifestyle. Nevertheless, individuals in the same age group share some facial similarities. These resemblances can be employed to approximate the facial appearance of an individual in the bygone or the forthcoming years.Unlike numerous studies dealing with predictive face ageing models, for the first time, this thesis proposes the first Backward Facial Ageing Model aiming at digitally rejuvenate an adult face appearance down to its early childhood. We also present the Forward Facial Ageing Model to predict the adult face appearance in its future by taking into account the naturalageing trajectory. The main purpose of Forward Facial Ageing Model is to have a base model for the supplementary ageing models such as behavioural models.In this thesis for the first time in face ageing studies, the effects of different lifestyle behaviours are integrated into the facial ageing models. The Behavioural Facial Ageing Models predict the feature of a young face in case of having the high-risk lifestyle habits. The main attempt of these models is to illustrate the adverse effects of unsafe lifestyle behaviourson the senility of the face, aiming to prevent the youth from becoming involved in these habits. The Facial Ageing Modeling Database, contains over 1600 facial images, is collected to construct the models and 30 Face Templates for the purpose of the face ageing studies.Besides, the Face Time-Machine Database from 120 subjects is created and published to testand evaluate the results. For the proposed approach face contour and different components are modified non-linearly based on an estimated geometrical model related to the trajectory of growth or ageing. Moreover, the face texture is adapted by mapping a Face Template to the estimated geometrical model. Then, the effects of each lifestyle habit are set up to the primal predictive model.The evaluations of the results indicate that the proposed models are remarkably accurate to estimate the correct face appearance of an individual in the target age. While the simulated facial images are realistic and have the appearance, geometrical and textural characteristics of the target age, the personal identity and details of the input face images are preserved

In this thesis we treat and solve various problems related to movement pattern detection by designing and implementing parallel algorithms using the GPU. We first propose a GPU pipeline based algorithm to report the ’Popular places’ pattern. Then, we study the problem of reporting all subtrajectory clusters of a trajectory. To measure similarity between curves we choose the Fréchet distance. Finally we solve the ’Flock pattern’. To this aim, we present two algorithms to solve two problems related with the ’Flock pattern’: finding the maximal sets of a family and intersecting two families of sets. The GPU parallel algorithms proposed to solve these two problems are later used for reporting flock patterns
En aquesta tesi tractem i resolem varis problemes relacionats amb el càlcul de patrons de moviment en bases de dades espai-temporals, dissenyant i implementant algoritmes paral·lels utilitzant GPUs. Primer, proposem un algoritme que utilitza els processos gràfics de la GPU per reportar el patró ‘Llocs Populars’. Després estudiem el problema de reportar tots els grups de subtrajectories d’una trajectòria. Per mesurar la similitud entre corbes hem triat la distancia de Fréchet. Finalment resolem el problema del patró ‘Ramat’. Amb aquest objectiu, presentem dos algorismes per resoldre dos problemes relacionats amb el patró ‘Ramat’: El problema de trobar tots els conjunts maximals de una família, i el problema de intersecar dos famílies de conjunts. Proposem algorismes paral·lels per resoldre els dos problemes que després s’utilitzen per reportar patrons ’Ramat’

La géométrie d'un assemblage est définie au travers de la géométrie de ses composants décrite dans la configuration nominale du produit, c'est à dire que les composants sont sans défauts et leurs positions relatives exactes. Dans la réalité, les géométries effectives des composants présentent des défauts géométriques, et leurs situations relatives ne sont pas exactes. Le travail doctoral consiste à prédire la conformité géométrique d'un assemblage aéronautique à partir des géométries de ses composants. A partir de la connaissance de la géométrie des composants avec défauts, une seconde étape vise à réaliser la simulation de l’assemblage de ces composants (propagation des défauts géométriques et couplage éléments finis) afin d’évaluer la conformité géométrique de l’assemblage, et en déduire les opérations à mener pour atteindre cette conformité. L’ensemble de la démarche sera appliqué à des nacelles aéronautiques
The assembly geometry is define through its components geometry described in their nominal configuration, in other words without geometrical deviations and with accurate relative positions. In fact, the real components geometries has geometrical deviations and their positions are not accurate. The doctoral work consists of predict the geometrical conformity of an aeronautical assembly from the geometries of its components. From knowledge of components geometry, a second step objective is to realise the simulation of assembly of this components (geometrical deviations propagation and finite elements coupling) in order to evaluate the geometrical conformity of the assembly, and to determinate the required operations in order to reach this conformity. The entire process will be applied on aeronautical nacelles

Foi realizada a validação de um programa de análise de elementos finitos não lineares já desenvolvido, PROAES_NL. Para tal, quatro exemplos encontrados na literatura foram resolvidos utilizando o programa e os resultados foram comparados com os valores apresentados em artigos publicados e também com os resultados obtidos com o software de elementos finitos ANSYS. O erro relativo entre os resultados obtidos utilizando o PROAES_NL e as duas outras fontes mencionadas anteriormente foi relativamente pequeno e o programa foi considerado validado. A teoria de cálculo de sensibilidades em estruturas com comportamento não linear desenvolvida por Santos [1] foi estudada, interpretada e traduzida para o domínio físico. As equações resultantes foram implementadas numericamente em linguagem Octave completando o código PROAES_NL usando apenas dados de pós-processamento de elementos finitos. Para validar as expressões de análise de sensibilidade utilizadas foram resolvidos cinco exemplos. Os resultados obtidos foram comparados com os valores obtidos pelo método das diferenças finitas e com os resultados apresentados por Santos [1]. O erro relativo entre o programa PROAES_NL e as fontes mencionadas anteriormente foi pequeno e as expressões de sensibilidade foram consideradas validadas. Além disso, é demonstrado que existe uma diferença entre o cálculo da análise de sensibilidades numa análise linear e numa análise não linear. As expressões de sensibilidades implementadas foram depois usadas para executar otimizações de topologia. O objetivo era verificar se haveria alguma diferença entre executar uma otimização de topologia utilizando análises lineares e não lineares. Embora alguns dos artigos estudados mostrem diferenças entre a configuração ótima obtida com análise linear e análise não linear, usando o programa PROAES_NL, a diferença foi visível em apenas um dos dois exemplos estudados. Durante a fase final deste trabalho, limitações na convergência da análise não linear resultaram em restrições na seleção dos parâmetros de otimização.

博士
南台科技大學
電子工程系
95
As CMOS devices have been scaled down, the channel length shrinks and the absolute value of threshold voltage becomes smaller due to the reduced controllability of the gate over depletion region by the increased charge-sharing from the source/drain. Therefore, the study of short-channel effects (SCEs) have assumed a significant role because both the threshold voltage roll-off at decreasing gate length as well as drain-induced barrier lowering (DIBL) at increasing drain voltage pose a serious challenge to the efforts for down-scaling the CMOS technology. Double-Gate (DG) MOSFETs seem to be a very promising option for ultimate scaling of CMOS technology. In this dissertation, a physical and analytical model is developed for short-channel effects (SCEs) in fully depleted double-gate (DG) MOSFETs. On the base of resultant solution for 2-D Poisson’s equation included in both silicon film and gate oxide regions, the physical and analytical model including threshold voltage, subthreshold swing, and 2-D electrostatic potential for the short-channel fully depleted symmetrical double-gate (SDG) MOSFETs is developed. These analytical results can be used to model of DG MOSFET’s. The results calculated by the model agree well with the simulation data without any fitting parameters. They are also extendable to high-k gate insulators for precisely predicting the fringing field effects with high-k gate dielectrics. To enhance the immunity against SCEs, a new structure called the dual-material gate (DMG) MOSFET has been proposed. In the DMG MOSFET, the work function of metal gate 1 (M1) is greater than metal gate 2 (M2) i.e., ＞ and hence, threshold voltage ＞ which has the inherent advantage of improving the gate transport efficiency by modifying the electric field pattern and the surface potential along the channel. Based on fully resultant 2-D potential solution, the physical and precisely analytical model for the short-channel fully depleted symmetrical dual-material double-gate (SDMDG) MOSFETs is successfully developed. The simulated results of the analytical model match well with those simulated by device simulator. Besides giving deep insight into the device physics, the analytical results are useful in compact modeling the threshold voltage of short-channel SDMDG MOSFET. As the channel lengths of MOSFETs push into the nanometer regime, short-channel effects (SCEs) become intensively significant and put a hard limit to MOSFET performance. The design of optimal DG devices will require new insights into the underlying physics, especially the quantum mechanics (QM) of the carriers confined in very thin (tsi ≦10 nm) Si films. Quantum-mechanical confinement of inversion-layer carriers significantly affects the threshold voltage and gate capacitance of highly scaled MOSFETs. In this dissertation, we present a physical threshold voltage model in subthreshold region, and use analytical solutions to give design insight regarding the quantum effects in symmetrical DG MOSFETs. Quantization effects on DG MOSFET scalability is also examined in the thesis. This thesis not only provides a simple and computation-efficient short-channel surface potential and threshold voltage analytical model, but also offers the basic designing guideline for fully-depleted DG MOSFET.

碩士
朝陽科技大學
營建工程系碩士班
96
This research used FLA3D, a numerical analysis software based on the finite difference method, to analyze the mechanical behaviors of Pao- Shan in construction stage, and 921 Chi-Chi earthquake. These numerical results were compared with monitoring identify the rational of analysis method in this study. From the numerical results, they are close to the monitoring results and plane strain (2D) results. Therefore, the numerical analysis is rational in this study, and it can be so long enough that the 3D results are close to 2D results. And then the mechanical behaviors of earth dam were discussed for various ratio of length and weight of dam and ratio of width and height of core. In order to identify the safety of the second reservoir of Pao-Shan under the strong earthquake, 921 Chi-Chi acceleration-time history was added on the base of the dam. The results show it is in safety state except for the crust surface on the downstream of the dam. In the influence evaluation of geometrical parameters, as the ratio of length and height≧4, the 3D effect is able to neglect. Natural vibration frequency will reduce with the length increasing of the dam and the frequency is mainly about 3Hz. As the ratio of core base-width and height≧0.9, it is less influential on the deformation. After seepage stage,the natural frequency is higher than that of before seepage stage. As the ratio of core increase, the frequency will reduce. As the ratio of the length and height is equal to 6, and the ratio of the core base-width is equal to 0.9, the natural frequency before seepage stage and the third one is after the highest. The second high one is before seepage stage and the third one is after earthquake and the smallest one is predominant frequency of the dam under Chi-Chi earthquake. The natural frequency of the core is lower than those of crusts on the upstream and downstream.

No
The shear viscosity of polymethylmethacrylate (PMMA) melt is particularly investigated by using a twin-bore capillary rheometer at four temperatures of 210, 225, 240, and 255 degrees C with different capillary dies. Experimental results show that the geometrical dependence of shear viscosity is significantly dependent on melt pressure as well as melt temperature. The measured shear viscosity increases with the decrease of die diameter at lower temperatures (210 and 225 degrees C) but decreases with the decrease of die diameter at higher temperatures (240 and 255 degrees C). Based on the deviation of shear viscosity curves and Mooney method, negative slip velocity is obtained at low temperatures and positive slip velocity is obtained at high temperatures, respectively. Geometrical dependence and pressure sensitivity of shear viscosity as well as temperature effect are emphasized for this viscosity deviation. Moreover, shear viscosity curve at 210 degrees C deviates from the power law model above a critical pressure and then becomes less thinning. Mechanisms of the negative slip velocity at low temperatures are explored through Doolittle viscosity model and Barus equation, in which the pressure drop is used to obtain the pressure coefficient by curve fitting. Dependence of pressure coefficient on melt temperature suggests that the pressure sensitivity of shear viscosity is significantly affected by temperature. Geometrical dependence of shear viscosity can be somewhat weakened by increasing melt temperature. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3384-3394, 2013

Improving the knowledge of the mechanics of small-scale structures is important in many microelectromechanical and nanoelectromechanical systems. Classical continuum mechanics cannot be utilised to determine the mechanical response of small-scale structures, since size effects become significant at small-scale levels. Modified elasticity models have been introduced for the mechanics of ultra-small structures. It has recently been shown that higher-order models, such as nonlocal strain gradient and integral models, are more capable of incorporating scale influences on the mechanical characteristics of small-scale structures than the classical continuum models. In addition, some scaledependent models are restricted to a specific range of sizes. For instance, nonlocal effects on the mechanical behaviour vanish after a particular length. Scrutinising the available literature indicates that the large amplitude vibrations of small-scale beams and plates using two-parameter scaledependent models and nonlocal integral models have not been investigated yet. In addition, no twoparameter continuum model with geometrical nonlinearity has been introduced to analyse the influence of a geometrical imperfection on the vibration of small-scale beams. Analysing these systems would provide useful results for small-scale mass sensors, resonators, energy harvesters and actuators using small-scale beams and plates. In this thesis, scale-dependent nonlinear continuum models are developed for the time-dependent deformation behaviour of beam-shaped structures. The models contain two completely different size parameters, which make it able to describe both the reduction and increase in the total stiffness. The first size parameter accounts for the nonlocality of the stress, while the second one describes the strain gradient effect. Geometrical nonlinearity on the vibrations of small-scale beams is captured through the strain-displacement equations. The small-scale beam is assumed to possess geometrical imperfections. Hamilton’s approach is utilised for deriving the corresponding differential equations. The coupled nonlinear motion equations are solved numerically employing Galerkin’s method of discretisation and the continuation scheme of solution. It is concluded that geometrical imperfections would substantially alter the nonlinear vibrational response of small-scale beams. When there is a relatively small geometrical imperfection in the structure, the small-scale beam exhibits a hardeningtype nonlinearity while a combined hardening- and softening-type nonlinearity is found for beams with large geometrical imperfections. The strain gradient influence is associated with an enhancement in the beam stiffness, leading to higher nonlinear resonance frequencies. By contrast, the stress nonlocality is related to a remarkable reduction in the total stiffness, and consequently lower nonlinear resonance frequencies. In addition, a scale-dependent model of beams is proposed in this thesis to analyse the influence of viscoelasticity and geometrical nonlinearity on the vibration of small-scale beams. A nonlocal theory incorporating strain gradients is used for describing the problem in a mathematical form. Implementing the classical continuum model of beams causes a substantial overestimation in the beam vibrational amplitude. In addition, the nonlinear resonance frequency computed by the nonlocal model is less than that obtained via the classical model. When the forcing amplitude is comparatively low, the linear and nonlinear damping mechanisms predict almost the same results. However, when forcing amplitudes become larger, the role of nonlinear viscoelasticity in the vibrational response increases. The resonance frequency of the scale-dependent model with a nonlinear damping mechanism is lower than that of the linear one. To simulate scale effects on the mechanical behaviour of ultra-small plates, a novel scale-dependent model of plates is developed. The static deflection and oscillation of rectangular plates at small-scale levels are analysed via a two-dimensional stress-driven nonlocal integral model. A reasonable kernel function, which fulfil all necessary criteria, is introduced for rectangular small-scale plates for the first time. Hamilton and Leibniz integral rules are used for deriving the non-classical motion equations of the structure. Moreover, two types of edge conditions are obtained for the linear vibration. The first type is the well-known classical boundary condition while the second type is the nonclassical edge condition associated with the curvature nonlocality. The differential quadrature technique as a powerful numerical approach for implementing complex boundary conditions is used. It is found that while the Laplacian-based nonlocal model cannot predict size influences on the bending of small-scale plates subject to uniform lateral loading, the bending response is remarkably size-dependent based on the stress-driven plate model. When the size influence increases, the difference between the resonance frequency obtained via the stress-driven model and that of other theories substantially increases. Moreover, the resonance frequency is higher when the curvature nonlocality increases due to an enhancement in the plate stiffness. It is also concluded that more constraint on the small-scale plate causes the system to vibrate at a relatively high frequency. In addition to the linear vibration, the time-dependent large deformation of small-scale plates incorporating size influences is studied. The stress-driven theory is employed to formulate the problem at small-scale levels. Geometrical nonlinearity effects are taken into account via von Kármán’s theory. Three types of edge conditions including one conventional and two nonconventional conditions are presented for nonlinear vibrations. The first non-classical edge condition is associated with the curvature nonlocality while the second one is related to nonlocal in-plane strain components. A differential quadrature technique and an appropriate iteration method are used to compute the nonlinear natural frequencies and maximum in-plane displacements. Molecular dynamics simulations are also performed for verification purposes. Nonlinear frequency ratios are increased when vibration amplitudes increase. Furthermore, the curvature nonlocality would cause the small-scale pate to vibrate at a lower nonlinear frequency ratio. By contrast, the nonlocal in-plane strain has the opposite effect on the small-scale system. The outcomes from this thesis will be useful for engineers to design vibrating small-scale resonators and sensors using ultra-small plates.
Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2021

In recent years, there has been an increase in interest in cellular materials for structural applications, especially cellular metals (e.g., metal foams made of aluminium and its alloys). These closed-cell and open-cell foams usually have complex cellular structures resulting from the foaming process and their mechanical properties are governed by their cellular structures and by the properties of the base material. However, their mechanical characterization is difficult and most of the times can result in the destruction of the foam specimen. In this study, X-ray microcomputed tomography (µCT) was used together with finite element modelling to develop numerical models to estimate the elastic moduli and evaluate the effects of processing of the information obtained with the µCT scans in the final results. Such a technique complements experimental testing and brings great versatility. In order to accomplish this task, different thresholding techniques (segmentation) were applied to the 2D slices, which are the result of µCT scans, with special focus on a manual global technique with the mass as a quality indicator. Then, some reconstruction algorithms (e.g. Marching Cubes 33) were used to create 3D tessellated models in the STL format, which were oversampled (excessive number of faces) and with errors. Therefore, a simplification/clean-up procedure was applied to solve those issues, being analysed in terms of mass maintenance, shape maintenance with the Hausdorff algorithm and face quality, i.e., face aspect ratio. Two different procedures were evaluated, with and without small structural imperfections, so that the impact of the procedures could be analysed as well as the effect of the presence of small defects. The results obtained were evaluated and compared to several analytical and theoretical models, models based on representative unit-cells and experimental results in terms of the relation between the relative density and the relative Young’s modulus. Results demonstrated that the developed procedures were very good at minimizing changes in mass and shape of the geometries while providing good face quality, i.e., face aspect ratio. The models were also shown to be able to predict the properties of metallic foams in accordance with the findings of other researchers. In addition, the process of obtaining the models and the presence of small structural imperfections were shown to have a great impact on the final results.
Nos últimos anos, tem-se verificado um aumento do interesse na área dos materiais celulares, mais especificamente metais celulares, para aplicações estruturais (por exemplo, espumas metálicas de alumínios e as suas ligas). Estas espumas de célula aberta e fechada têm, normalmente, uma estrutura celular complexa resultante do processo de espumação e as suas propriedades mecânicas dependem das suas estruturas celulares e das propriedades do material base. No entanto, a caracterização mecânicas destes materiais é difícil e resulta, regularmente, na destruição dos specimens de espuma. Neste estudo, Micro-Tomografia Computorizada de Raios-X (µCT) foi aplicada juntamente com modelação por elementos finitos para desenvolver modelos numéricos que conseguem estimar os módulos de elasticidade e avaliar os efeitos do processamento da informação obtida pelos scans de µCT nos resultados finais. Esta técnica complementa os procedimentos experimentais e traz uma grande versatilidade. Para se completar a tarefa proposta, diferentes métodos de segmentação foram aplicados às fatias 2D, que são resultantes dos scans de µCT, com especial atenção num método de segmentação manual global que utiliza a massa como indicador de qualidade. Depois disso, alguns algoritmos de reconstrução, por exemplo, Marching Cubes 33, foram aplicados para criar modelos 3D de faces triangulares no formato STL que demonstram sobreamostragem (excessiva quantidade de faces) e alguns erros. Por essa razão, um procedimento de simplificação/limpeza foi aplicado para resolver estes problemas, sendo analisados em termos de preservação de massa, preservação de forma com o algoritmo de Hausdorff e qualidade das faces, ou seja, razão de proporção. Dois procedimentos diferentes foram avaliados, um com e outro sem pequenos defeitos estruturais para que se consiga analisar não só o impacto do processamento dos modelos assim como o efeito da presença de pequenos defeitos. Os resultados obtidos foram comparados com vários modelos analíticos e teóricos, modelos baseados em células unitárias representativas e resultados experimentais com base na relação entre a densidade relativa e o modulo de Young relativo. Os resultados demonstraram que os procedimentos desenvolvidos são bons a preservar a massa e forma das geometrias deixando as faces com boa qualidade. Verificou-se também que os modelos foram capazes de prever as propriedades das espumas metálicas em concordância com o trabalho de outros investigadores. Adicionalmente, mostrou-se que o processo de obtenção dos modelos e a presença de pequenas imperfeiçoes estruturais tem um impacto relevante nos resultados finais.
Mestrado em Engenharia Mecânica

碩士
淡江大學
化學工程與材料工程學系碩士班
106
Due to its great potential and capability, the fiber reinforced thermoplastics (FRT) material and technology have been applied into industry recently. However, due to the microstructures of fiber inside plastic matrix are very complex, they are not easy to be visualized. The connection from microstructures to the final shrinkage/warpage is far from our understanding. In this study, we have performed a benchmark with three standard specimens based on ASTM D638 where those specimens have different gate designs. Due to the geometrical effect, the warpage behaviors are quite different for those three specimens. Although we expect long fiber reinforced to enhance strength, it causes one specimen warped downward and bended inward, another warped upward, and the other slightly upward at the same time. The difference might be due to the interaction of the entrance effect of molten plastic with fiber content to cause high asymmetrical fiber orientation distribution (FOD). We further studied that the asymmetrical FOD is introduced by the entrance effect from the sprue entrance of the part to the gate of each standard specimen. This entrance effect will cause the variation of FOD and further influence the fiber distribution and the bundle phenomena. Moreover, the experimental study is also performed to validate the simulation results. From short shot testing to the warpage and bending measurement for each individual model, overall, the tendency for both numerical simulation and experimental results is in a reasonable agreement. However, some deviation still existed which needs for further study. Furthermore, in the fiber length effect study experimentally, the longer fiber reinforced the less warpage. Also, the elongation and strength of injected parts can be enhanced significantly as fiber length increased. For example, from pure PP to FRP with 25 mm fiber inside, the strength can be increased from 20 N/mm2 to 140 N/mm2 .

O σχεδιασμός και η ανάπτυξη οικονομικών προϊόντων, με ταυτόχρονη ικανοποίηση των αναγκών για υψηλές επιδόσεις και ασφάλεια αποτελεί μια από τις μεγαλύτερες προκλήσεις για τους ερευνητές μηχανικούς και τη βιομηχανία. Ειδικότερα στους τομείς της κατασκευαστικής βιομηχανίας (αεροναυπηγική, ναυπηγική, αυτοκινητοβιομηχανία, διαστημική) των οποίων τα προϊόντα παράγονται σύμφωνα με τις τεχνολογίες αιχμής, επιζητείται από το μηχανικό να σχεδιάζει νέα προϊόντα με υψηλότερες επιδόσεις, χωρίς να αγνοεί την απαίτηση για μείωση του κόστους και του χρόνου ανάπτυξης αυτών. Η τάση αυτή βρίσκει εφαρμογή κατά κύριο λόγο στην αεροναυπηγική, όπου η μείωση του αξιοσημείωτου κόστους ανάπτυξης νέων αεροσκαφών, χωρίς υποβάθμιση της ασφαλούς και υψηλής ποιότητας τους, αποτελεί βασικό και μόνιμο στόχο. Ο κυριότερος παράγοντας που επιβαρύνει σημαντικά την ανάπτυξη νέων αεροσκαφών, τόσο από πλευράς κόστους, όσο και χρονικά, είναι οι πειραματικές δοκιμές πλήρους κλίμακας η μεγάλης κλίμακας σε συνθήκες λειτουργίας, οι οποίες επηρεάζουν σημαντικά το κόστος και το χρόνο ανάπτυξης. Οι συγκεκριμένες δοκιμές συμπεριλαμβάνονται στη διαδικασία του σχεδιασμού, με σκοπό να επαληθεύσουν τα αποτελέσματα των αντίστοιχων δομικών αναλύσεων. Η σημασία των πειραματικών δοκιμών και συγκεκριμένα εκείνων της πλήρους κλίμακας ενισχύεται από το γεγονός ότι επιβάλλονται κατά την πιστοποίηση από τις αρχές Αδειοδότησης, με δεδομένο ότι οι δομικές αναλύσεις της αντίστοιχης κλίμακας (πολύ μεγάλης η πλήρους) δεν παρέχουν ικανοποιητική αξιοπιστία. Η παραπάνω αδυναμία να εξαχθούν ικανοποιητικά αποτελέσματα από τις δομικές αναλύσεις οφείλεται σε δύο βασικά χαρακτηριστικά της ανάλυσης των κατασκευών μεγάλης κλίμακας. Η πρόβλεψη της αστοχίας στις αεροναυπηγικές και άλλες κατασκευές απαιτεί μη-γραμμική ανάλυση, λόγω αιτιών που σχετίζονται με τη συμπεριφορά υλικού (μη-γραμμική συμπεριφορά λόγω ελαστοπλαστικής συμπεριφοράς μεταλλικών υλικών η λόγω αστοχίας συνθέτων υλικών) ή με τη συμπεριφορά της δομής (γεωμετρική μη-γραμμικότητα, προβλήματα επαφής, κλπ/). Επιπρόσθετα, στις κατασκευές αυτές υπάρχει μεγάλη διαφορά κλίμακας μεταξύ των διαστάσεων της περιοχής έναρξης και αρχικής διάδοσης της τοπικής βλάβης με τις συνολικές διαστάσεις της δομής, οι οποίες σχετίζονται με την τελική αστοχία της κατασκευής. Η προσομοίωση με αριθμητικές μεθόδους, με έμφαση στη μέθοδο των Πεπερασμένων Στοιχείων, της δομικής συμπεριφοράς μεγάλης κλίμακας κατασκευών με τα παραπάνω χαρακτηριστικά, οδηγεί σε αριθμητικά πρότυπα εκατομμυρίων βαθμών ελευθερίας, τα οποία απαιτείται να επιλυθούν με μη-γραμμικές μεθόδους. Ο συνδυασμός του μεγέθους των προτύπων αυτών με το μη-γραμμικό χαρακτήρα τους, καθιστά το πρόβλημα δυσεπίλυτο έως σήμερα με χρήση συμβατικών μεθόδων και ουσιαστικά αποτελεί την αιτία μη-αξιοποίησης των εικονικών δοκιμών (αριθμητικών αναλύσεων), στην ελαχιστοποίηση ή και την ολοκληρωτική αποφυγή των εκτενών και δαπανηρών πειραματικών δοκιμών. Βάσει των ανωτέρω, σκοπός της παρούσας διατριβής είναι η ανάπτυξη νέων, αξιόπιστων και ολοκληρωμένων μεθοδολογιών για τη μη-γραμμική ανάλυση κατασκευών μεγάλης κλίμακας, με κύριο στόχο την ικανοποιητική πρόβλεψη τοπικών φαινομένων που συνδέονται με την έναρξη της βλάβης, αλλά και την ικανότητα να εκτείνονται έως την κατάλληλη κλίμακα (ίσως και την πλήρη), ώστε να καθίσταται δυνατός ο υπολογισμός της δομικής συμπεριφοράς της κατασκευής μέχρι την τελική αστοχία. Στη βάση αυτή, γίνεται ανάπτυξη νέων μεθοδολογιών δομικής μη-γραμμικής ανάλυσης και προτείνονται κατάλληλες τροποποιήσεις σε ήδη καθιερωμένες μεθόδους, με σκοπό την εφαρμογή τους σε κατασκευές μεγάλης κλίμακας. Λόγω των πλεονεκτημάτων που παρέχονται από την ταχεία και συνεχόμενη εξέλιξη των ηλεκτρονικών υπολογιστών (ταχύτητα, μνήμη, λογισμικό) και την ευρεία χρήση εμπορικών πακέτων που βασίζονται στη θεωρία των πινάκων (Πεπερασμένα Στοιχεία, Συνοριακά Στοιχεία, κλπ.), οι παραπάνω μεθοδολογίες χρησιμοποιούνται ευρέως στην πρόβλεψη της δομικής συμπεριφοράς των κατασκευών στη βάση της φιλοσοφίας της ‘εικονικής δοκιμής’. Με δεδομένο ότι οι αριθμητικές μέθοδοι επίλυσης μη-γραμμικών προβλημάτων σε κατασκευές μεγάλης κλίμακας δεν παρέχουν ικανοποιητικά αποτελέσματα, όπως προαναφέρθηκε, στην παρούσα εργασία αναζητήθηκαν εναλλακτικές μεθοδολογίες και τεχνικές, για την προσέγγιση του τεχνολογικού προβλήματος από τη σκοπιά του μηχανικού και προτάθηκαν αξιόπιστες λύσεις με δυνατότητα εφαρμογής σε βιομηχανικό περιβάλλον. Η διαδικασία που ακολουθήθηκε αποτελείται από τέσσερις βασικούς άξονες, την γραμμική αριθμητική ανάλυση των τάσεων ολόκληρης της δομής μεγάλης κλίμακας, τον έλεγχο για πιθανή εμφάνιση τοπικής μη-γραμμικής συμπεριφοράς, την τοπική ανάλυση αστοχίας (μη-γραμμική ανάλυση) και μια σειρά κατάλληλων τεχνικών για τον προσδιορισμό της συνεισφοράς των περιοχών με τοπική μη-γραμμικότητα στη δομική συμπεριφορά ολόκληρης της δομής. Όλα τα βήματα της διαδικασίας πραγματοποιήθηκαν στη βάση της μεθόδου των Πεπερασμένων Στοιχείων. Η γραμμική αριθμητική ανάλυση τάσεων της κατασκευής έγινε με χρήση αριθμητικών προτύπων που προσομοιώνουν ολόκληρη την κατασκευή, χωρισμένων σε τμήματα, ανάλογα με την γεωμετρική επαναληψιμότητα που πιθανώς εμφανίζει η γεωμετρία. Οι τάσεις που υπολογίστηκαν χρησιμοποιήθηκαν στην πρόβλεψη τα εμφάνισης τοπικής μη-γραμμικότητας με τη βοήθεια κατάλληλα ανεπτυγμένων κριτηρίων, ανάλογα με το είδος της μη-γραμμικότητας που μπορεί να εμφανιστεί. Οι περιοχές μη-γραμμικότητας που ανιχνεύονται, ταξινομούνται σε σειρά κρισιμότητας και ανάλογα με το κρίσιμο επίπεδο φορτίου καθεμιάς από αυτές, επεξεργάζονται τοπικά με μη-γραμμικές αναλύσεις για την προσομοίωση της έναρξης και εξέλιξης της τοπικής μη-γραμμικότητας. Για τον υπολογισμό της συνεισφοράς των μη-γραμμικών υποπεριοχών στη δομική συμπεριφορά ολόκληρης της κατασκευής, αναπτύχθηκαν κατάλληλες τεχνικές περιγραφής της τοπικής μη-γραμμικότητας και εισαγωγής τους στα δομικά χαρακτηριστικά του αριθμητικού προτύπου της ολικής κατασκευής. Για την προσομοίωση της εξέλιξης της τοπικής μη-γραμμικότητας, από την πρώτη ανίχνευση μέχρι την τελική εξέλιξη, η διαδικασία εκτελείται βηματικά και επαναληπτικά. Αποδεικνύεται ότι κάτω από συγκεκριμένες παραδοχές, οι μεθοδολογίες για τη δομική μη-γραμμική ανάλυση κατασκευών μεγάλης κλίμακας είναι εφικτό να παρέχουν αξιόπιστα αποτελέσματα αντίστοιχα με εκείνα των πειραματικών δοκιμών πλήρους κλίμακας. Ταυτόχρονα είναι και αποτελεσματικές, δεδομένου ότι έχουν αναπτυχθεί κατάλληλα, ώστε να εστιάζουν τους διαθέσιμους υπολογιστικούς πόρους μόνο στις κρίσιμες περιοχές, μέσω της κατά απαίτησης εφαρμογής τοπικών μη-γραμμικών αναλύσεων.
The design and development of low-cost products, with simultaneous fulfilment of the requirements for higher performance and safety, is one of the biggest challenges for the research engineers and the industry. Especially in the sectors of the structural industry (aeronautics, shipbuilding, automotive, space industry) where the products are being produced according to the latest achievements of the technology, the engineer is obliged to design new products with higher proficiency, without neglecting the need for lower cost and development time. This trend has great application mainly in the aeronautical industry, where the reduction of the remarkable cost for the development of a new aircraft, without downgrading the level of safety and the quality of service comprises the main target of the current research effort. The main factor that weighs down the development of new aircrafts, as far as the cost and the time is concerned, is the required experimental tests of the full / large scale under service loads, which affect significantly the development cost and the time to market. These tests are included in the design process, in order to verify the results of the corresponding structural analyses. The importance of the experimental tests and specifically these of the full scale level is amplified by the fact that they are being imposed during the certification process by the Airworthiness Authorities, since the structural analyses of the corresponding scale (full scale) do not provide adequate results. The above mentioned inability of the structural analyses of providing adequate results is based on two main characteristics of the large scale structures. Firstly, the failure prediction in aeronautical (among others) structures requires non-linear analysis, for reasons related to the material behaviour (non-linear behaviour due to composite material damage, elastoplastic behaviour of metallic materials) and the structural behaviour (geometrical non-linearity, contact problems). Secondly, in these structures there is great difference between the dimensions of the local damage initiation region and the dimensions of the whole structure, with the latter being related with the total collapse. The simulation with numerical methods, especially with the use of Finite Elements, of the structural behaviour of large scale structures with the above characteristics, leads to million DOFs (Degrees Of Freedom), whose solution requires non-linear numerical methods. The combination of the size of these models with their non-linear nature renders the problem non-solvable using conventional methodologies and is in fact the reason for the, up to now, not thoroughly utilization of virtual testing (numerical simulations), that would lead to the minimization of the number or even to the complete avoidance of the extensive and costly experimental tests. Based on the above, main objective of this Thesis is the development of new, reliable and integrated methodologies for the non-linear analysis of large scale structures, targeting mainly in the satisfactory prediction of phenomena related to the initiation of local damage, but also being able to evolute up to the appropriate scale (maybe full scale), in order to account the structural behaviour of the whole structure up to the total collapse. On this basis, innovative methodologies are being developed for the structural non-linear analysis and appropriate modifications are proposed for already well-established techniques, in order to be applied on large scale structures. Due to the advantages offered from the rapid and constant progress of computers (speed, memory, software) and the wide usage of commercial tools that are based on the matrix theory (Finite Elements, Boundary Elements), the above mentioned methodologies were developed based on the philosophy of ‘virtual testing’. Due to the fact that the numerical solution methods for non-linear problems in large scale structures are not able to provide adequate results, as mentioned previously, in the present work alternative methodologies and techniques were investigated, approaching the technological problem from the engineer’s view and reliable solutions applicable to an industrial environment were proposed. The procedure that was followed consists of four basic keystones: the linear numerical stress analysis of the whole structure, the check for possible local non-linear behaviour, the local damage analysis (non-linear analysis) and a series of appropriately configured sub-routines, able to redefine the contribution of the regions exhibiting local damage in the structural behaviour of the whole structure. All the routines of the proposed methodologies were accomplished using the commercial Finite Element code ANSYS. The linear numerical stress analysis of the structure was carried out with the use of numerical models simulating the whole structure, divided into suitable parts, based on the geometrical repeatability. The calculated stresses were utilized for the prediction of the local damage, using properly developed damage criteria, depending on the type of non-linearity. The corresponding regions detected, were classified according to the criticality level (critical load) and were elaborated with local analyses of non-linear nature for the simulation of local damage initiation. For the accumulation of the contribution of the local damage in the structural behaviour of the whole structure, appropriate techniques were developed for the description of the local damage and its incorporation in the structural features of the numerical model of the structure. For the determination of the damage evolution, from the first detection up to the final failure, the procedure was performed in an incremental and iterative way. It was proved, that under specific assumptions, the proposed methodologies simulating the non-linear phenomena of large scale structures are capable of providing accurate results, in accordance with those of the experimental tests of full scale level. Simultaneously, the proposed methodologies become also efficient, providing that they have been developed appropriately, in order to focus the available computer resources on the non-linearly behaving regions by the ‘on demand’ application of the non-linear analyses.