nÃo hà / As grandes questÃes do mundo globalizado tÃm passado, necessariamente, pelos temas ligados à sustentabilidade, energia limpa, exploraÃÃo do meio ambiente de forma ecologicamente correta e inovaÃÃo tecnolÃgica para manter o planeta saudÃvel. Nesse contexto, a energia eÃlica vem se destacando, principalmente na regiÃo Nordeste do Brasil, pelo grande potencial dos ventos e as caracterÃsticas de renovabilidade e complementaridade com a energia das hidrelÃtricas. As torres, que representam parcela significativa do custo do sistema, tendem a crescer buscando ventos com maiores velocidade e permitindo a utilizaÃÃo de turbinas eÃlicas de maior capacidade de geraÃÃo, acentuando-se a sua importÃncia como elemento estrutural do sistema. O objetivo geral deste trabalho à formular um modelo de otimizaÃÃo de torres tubulares de aÃo, composta de segmentos em tronco de cone. Busca-se a soluÃÃo de peso mÃnimo, tendo como variÃveis de projeto os diÃmetros externos e as espessuras de chapa caracterÃsticas de cada segmento. RestriÃÃes relativas à resistÃncia, à estabilidade e rigidez sÃo impostas com base em normas brasileiras. RestriÃÃes relativas à frequÃncia natural, a limitaÃÃes de transporte e geomÃtricas sÃo tambÃm requeridas. O conjunto nacele/rotor à modelado como uma massa rÃgida fixada no topo da torre, sem rotaÃÃo, e o carregamento atuante na estrutura inclui os pesos da torre e do conjunto rotor/nacele, o efeito estÃtico da aÃÃo do vento sobre a torre e as pÃs do rotor. A concepÃÃo de anÃlise adota modelo de viga engastada na base e livre no topo e emprega uma formulaÃÃo nÃo linear geomÃtrica pelo MÃtodo de Elementos finitos usando um programa em C++. O modelo de otimizaÃÃo foi implementado no MATLAB e, devido à natureza discreta das variÃveis de projeto e Ãs descontinuidades de funÃÃes de restriÃÃo e de suas derivadas, utilizam-se algoritmos genÃticos na soluÃÃo. Buscas na vizinhanÃa das soluÃÃes discretas sÃo realizadas usando um algoritmo baseado em informaÃÃo de gradiente (fmincon do MATLAB). AplicaÃÃes para vÃrias alturas de torre sÃo feitas, incluindo comparaÃÃes com uma torre cilÃndrica para validaÃÃo do modelo. Os resultados sÃo analisados frente aos de outros modelos da literatura. Os conceitos de projeto de torre rÃgida e flexÃvel sÃo discutidos relaxando-se as restriÃÃes de rigidez e de frequÃncia. SoluÃÃes obtidas sÃo analisadas usando elementos de casca do programa de anÃlise ABAQUS para verificaÃÃo de tensÃes e deslocamentos / The main subjects of the globalized world have passed necessarily by issues related to sustainability, clean energy, environment exploration in an ecologically correct way, and technology innovation to maintain a healthy planet. In this context, the wind has been highlighting, especially in the Northeast of Brazil, because of the large wind potential and the characteristics of renewability and complementarily with hydropower energy. The towers represent significant portion of the cost of the system, tends to grow seeking greatest wind speeds and allowing the use of wind turbines with bigger production capacity, emphasizing its importance as a structural element of the system. The main objective of this work is to formulate an optimization model of tubular steel towers, composed of segments in truncated cone. The aim is a minimum weight solution, having outer diameters and plate thicknesses characteristics of each segment as design variables. Constraints related to strength, stability and stiffness are imposed based on Brazilian codes. Constraints related to natural frequency, the limitations of transport and geometry are also required. The nacelle/rotor conjunct is modeled as a rigid mass attached to the top of the tower, without rotation, and the loading acting on the structure includes the weights of the tower and the nacelle/rotor conjunct, the static wind effect on the tower and on rotor blades. The analysis model adopts cantilever beam and employs a formulation for geometric nonlinear finite element method using a C++ program. The optimization model was implemented in MATLAB and due to the discrete nature of the design variables and the discontinuities of the constraint functions and their gradients we use genetic algorithms in the solution. Searches in the neighborhood of the discrete solutions are performed using a gradient based algorithm (fmincon in MATLAB). Applications to several tower heights are made, including comparisons with a cylindrical tower to validate the model. The results are analyzed against others models in the literature. The concepts of rigid and flexible tower project are discussed relaxing their stiffness and frequency constraints. Solutions obtained are analyzed using shell elements of ABAQUS analysis program to check tensions and displacements

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Diversas formas de geraÃÃo de energia vÃm sendo desenvolvidas com o intuito de oferecer alternativas ecologicamente corretas. Na regiÃo Nordeste do Brasil e principalmente no Estado do CearÃ, a energia eÃlica vem se destacando devido ao grande potencial dos ventos da regiÃo. Para aumentar a potÃncia gerada, torres cada vez mais altas tÃm sido usadas em busca de ventos mais fortes. Vale ressaltar que o custo das torres, geralmente fabricados em aÃo, representa parcela importante (20 a 30%) do custo total do sistema de geraÃÃo eÃlico. Este trabalho apresenta duas formulaÃÃes para a otimizaÃÃo do projeto de torres tubulares para geradores eÃlicos de aÃo. A primeira considera uma torre de aÃo cilÃndrica prismÃtica, onde foi modelada segundo a teoria de viga clÃssica de Euler-Bernoulli. A segunda formulaÃÃo considera uma torre, composta de segmentos de troncos de cone, onde foram utilizados para anÃlise por elementos finitos clÃssicos de pÃrtico plano. As variÃveis de projeto que definem as estruturas sÃo os diÃmetros representativos dos segmentos e as suas espessuras. Na torre cilÃndrica este diÃmetro à Ãnico. O custo mÃnimo à procurado minimizando-se o peso da torre. As restriÃÃes dizem respeito ao comportamento estrutural (rigidez, resistÃncia e estabilidade de acordo com recomendaÃÃes de normas) e ao processo de fabricaÃÃo e transporte. O processo de fabricaÃÃo confere aos diÃmetros representativos de cada segmento uma natureza contÃnua, e em conseqÃÃncia da disponibilidade comercial, as espessuras das chapas possuem natureza discreta. As restriÃÃes relativas à verificaÃÃo da seguranÃa segundo as normas apresentam pontos com descontinuidades nas funÃÃes e nas suas derivadas. Estes dois aspectos, que dificultam a soluÃÃo do problema pelos mÃtodos clÃssicos de ProgramaÃÃo MatemÃtica, tÃm sido adequadamente tratados por algoritmos baseados na simulaÃÃo do processo de evoluÃÃo de Darwin e em princÃpios da genÃtica, os chamados Algoritmos GenÃticos (AGâs). Assim, algumas aplicaÃÃes da formulaÃÃo sÃo feitas e soluÃÃes sÃo obtidas usando AGâs. Os resultados obtidos sÃo comparados com soluÃÃes da literatura e soluÃÃes Ãtimas sÃo verificadas por meios de modelos de elementos finitos de cascas usando o software ABAQUS. / Different forms of energy generation have been developed with the intention of offering environmentally friendly alternatives. In the Northeast region of Brazil and especially in the state of CearÃ, wind energy has been increasing due to the large potential of wind in the region. To increase the power, increasingly high towers have been used to capture stronger winds. It is noteworthy that the cost of towers, generally made of steel, represents significant portion (20-30%) of the total wind power generation system costs. This work presents two approaches for optimizing the design of tubular towers for wind steel generators. The first considers a prismatic cylindrical steel tower, which is modeled by means of the classical Euler-Bernoulliâs beam theory. The second formulation considers a tower composed of segments of the trunks of cone. The analysis was run by finite element analysis. The design variables that define the structures are the diameters of representative segments and their thicknesses. In the prismatic cylindrical tower, this diameter is unique. The minimum cost is searched by minimizing the weight of the tower. Constraints related to the structural behavior (stiffness, strength and stability in accordance with recommendations of standards) and the manufacturing process and transportation are considered. The manufacturing process gives the diameters of each segment representing a continuous nature, and as a result of commercial availability, the thicknesses of the plates have a discrete nature. The constraints to ensure the safety of the structure followed the standards recommendations. They presented discontinuities in their functions and their derivatives. The discrete nature and the discontinuities hinder the solution of the problem by classical methods of mathematical programming. So, they had been adequately addressed by algorithms based on simulation of the process of Darwinian evolution and principles of genetics, called Genetic Algorithms (GA). Thus, some applications of the formulation are made and solutions are obtained using GAâs. The results are compared with solutions from literature, and the optimum solutions obtained are verified by shell finite elements models using the software ABAQUS.

Otimização estrutural é uma área relativamente nova que vem sendo cada vez mais explorada. Existem muitos métodos clássicos, e outros mais recentes vem surgindo para disputar em eficiência, confiabilidade e rapidez na obtenção de um resultado ótimo. Os algoritmos são classificados em algoritmos determinísticos, que utilizam a informação do gradiente, ou seja, usam os valores das funções e suas derivadas, e os meta-heurísticos, algoritmos de otimização aleatórios que são métodos probabilísticos não baseados em gradiente, ou seja, usam somente a avaliação da função objetivo. São apresentados dois algoritmos meta-heurísticos relativamente recentes: o Harmony Search, baseado na improvisação musical em busca da harmonia perfeita, e o Firefly Algorithm, que é inspirado no comportamento da luz dos vagalumes. Vários exemplos clássicos de treliças 2-D e 3-D considerando otimização paramétrica e de forma, com restrições de tensão, deslocamento, flambagem e frequência natural, são apresentados para demonstrar a eficiência dos métodos. Os resultados são comparados aos de outros autores usando diferentes métodos encontrados na literatura. Os resultados indicam que os algoritmos de otimização estudados neste trabalho são melhores ou tão eficientes quanto os demais. Por fim, os métodos são aplicados à estrutura de um projeto de engenharia adaptado. / Structural optimization is a relatively new area that has been increasingly exploited. There are many classical methods, and newer are emerging to compete on efficiency, reliability and speed in obtaining an optimal result. The algorithms are classified into deterministic algorithms, which use the gradient information, i.e., use the values of the functions and their derivatives, and meta-heuristic algorithms, random optimization methods which are probabilistic methods not based on gradient, i.e., they use only objective function evaluation. Two relatively recent meta-heuristics algorithms are presented, Harmony Search, based on musical improvisation in search of the perfect harmony, and Firefly Algorithm, which is inspired by the behavior of the light of fireflies. Several benchmarks of 2-D and 3-D trusses considering size and shape optimization, with stress, displacement, buckling and natural frequency constraints, are presented to demonstrate the effectiveness of the methods. The results are compared to the others authors using different methods found in the literature. The results indicate that optimization algorithms studied in this work are better than or as efficient as others. Finally, the methods are applied to the structure of an adapted engineering design.

O conteúdo deste trabalho trata da formulação para solução do problema de otimização estrutural com minimização de massa em estruturas unifilares, sujeitas a restrição de tensão, flambagem das barras isoladas e fadiga. São considerados três casos de otimização: paramétrica, de forma e dimensional. Os problemas de singularidades nas restrições de tensão e flambagem são evitados através de uma formulação que faz uso de programação inteira para solução do problema. Outra singularidade encontrada na otimização topológica é a singularidade na matriz de rigidez da estrutura. Este problema foi evitado através de uma formulação que considera a existência de matriz de rigidez regular como restrição do problema. O método de solução utilizado para resolver problema de otimização é o método dos algoritmos genéticos. As restrições do problema são impostas através da penalização da função objetivo. O método de solução mostrou-se adequado para solução dos problemas estudados. A formulação implementada é validada através da solução de problemas clássicos de otimização estrutural. Os resultados obtidos são comparados com a literatura onde verificou-se a coerência dos mesmos. Após realizar a validação, a formulação é utilizada em um estudo que tem como base uma estrutura real: uma torre de queima de gases (flare) oriundos do processo de extração e armazenagem de petróleo em uma unidade flutuante. Para o problema da torre as restrições foram determinadas com base em critérios de falha estabelecido na norma DNV. A otimização do flare permitiu minimizar a massa da estrutura sem que os critérios de falha fossem violados. Verificou-se que a metodologia proposta é adequada para solução com grande número de restrições e com diversos casos de carregamento. / The purpose of this work is the development of a methodology to solve the structural optimization problem of frame structures subject to stress, buckling of isolated members, and fatigue constraints. Three types of structural optimization problems are considered: sizing, shape and topological. The stress and buckling singularity problems are avoided by an integer design variable formulation, using integer programing to obtain the optimization problem solution. Another issue found in optimization problems is the stiffness matrix singularity. The proposed formulations include the linear system stability as a constraint in the optimization problem. A genetic algorithm is used to solve the general optimization problem. All constraints of the problem are included with a penalization equation. The results show that genetic algorithm is a good approach to solve the proposed formulation. The proposed formulation is tested for solving classical optimization problems. The obtained results are consistent with the literature. A real engineering problem is solved with proposed methodology: a gas burning tower (flare). In this problem, all constraints are based on failure criteria recommended by DNV standards. The structural optimization of this problem shows that structural mass minimization is possible without violating the failure criteria. It is observed that solution methodology deals successfully with problems with multiple constraints and load cases

Processos aleatórios de corrosão e fadiga reduzem lentamente a resistência de estruturas e componentes estruturais, provocando um aumento gradual nas probabilidades de falha. A gestão do risco de falha de componentes sujeitos a corrosão e/ou fadiga é feita através de políticas de inspeção, manutenção e substituição, atividades que implicam em custos, mas visam manter a confiabilidade em níveis aceitáveis, enquanto o componente permanecer em operação. Aparentemente, os objetivos economia e segurança competem entre si, no entanto, a redução de recursos para inspeção e manutenção pode levar a maiores e crescentes probabilidades de falha, implicando em maiores custos esperados de falha, ou seja, maior risco. A otimização de risco estrutural é uma formulação que permite equacionar este problema, através do chamado custo esperado total. Nesta Tese, a otimização de risco é utilizada no intuito de encontrar políticas ótimas de inspeção e manutenção, isto é, quantidades de recursos a serem alocadas nestas atividades que levem ao menor custo esperado total possível. Os processos de corrosão e fadiga são representados através de modelos em polinômios de caos, construídos de maneira inédita, com base em dados experimentais ou observados da literatura. Com base nestes modelos, os problemas de otimização de risco envolvendo processos de fadiga e corrosão são resolvidos para diferentes configurações de custos de falha e de inspeções. Verifica-se que as políticas ótimas de inspeção, manutenção e substituição podem ser bastante diferentes para configurações de custo distintas, e que a determinação destas políticas é bastante desafiadora, devido, dentre outros fatores, à grande quantidade de mínimos locais do problema de otimização em questão, causadas por descontinuidades e oscilações da função custo esperado total. / Random corrosion and fatigue processes reduce slowly but gradually the resistance of structures and mechanical components, leading to gradual increase in failure probabilities. Risk management for mechanical components subject to corrosion and fatigue is made by means of policies of inspection, maintenance and substitution. These activities imply costs, but are made to maintain the reliability at acceptable levels, while the component remains in operation. Apparently, economy and safety are competing objectives; however, reduction in inspection and maintenance spending may lead to larger failure probabilities, increasing expected costs of failure (risk). Risk optimization allows one to solve this problem, by means of the so-called total expected cost. In this Thesis, risk optimization is used in order to find the best inspection and maintenance policy, i.e., the proper amount of resources to allocate to such activities in order to obtain minimum total expected cost. Corrosion and fatigue are modeled by means of polynomial chaos expansions, using a novel approach developed herein and experimental or observed data obtained from the literature. These models are employed within two risk optimization problems, solved for different failure and inspection cost configurations. Results show that the optimal policies of inspection, maintenance and replacements can be very different, for different cost configurations, and that the solution of the associated risk optimization problems is a very challenging task, due to the large number of local minima, caused by discontinuities and fluctuations in the total expected costs.

[en] The present work is concerned with the optimal location of piping supports. A Weighted average of the stress resultants at specified points is used as the objective function to be minimized. ANSI piping codes are considered for the constrained functions. The minimization process is carried out using the conjugate gradient method on an interior penalty function. Numerical examples are presented at the end of the work. / [es] Se presenta el problema de localización de los soportes de una tuberia como un problema de optimización donde se busca minimizar una media ponderada de las tensiones que actúan en las bocas de los equipamientos ligados a la línea. La localización de estos soportes debe ser realizada de manera que los esfuerzos que actúan en la tubería debido a los varios cargamentos posibles estén dentro de los límites especificados por las normas ANSI. Para el proceso de optimización se hace uso del método de gradientes conjugados aplicado a una función de penalidad que trasforma el problema inicial con restricciones en uno sin restricciones. Por último se presentan algunos resultados numéricos.

The rapid development of the Internet of Things (IoT) and wireless sensor network (WSN) technologies enable easy access and control of a variety forms of information and data from numerous number of smart devices, and give rise to many novel applications and research areas such as smart home, machine type communications, etc. However due to the small sizes, sophisticated environment, and large number of devices in network, it is hard to directly power the devices from grid. Hence the power connectivity remains one of the major issues that needs to be addressed for related IoT applications. Wireless power transfer (WPT) and backscatter communications are provisioned to be prominent solutions to overcome the power connectivity challenge, but they suer strong efficiency limitation which becomes the barrier to universally popularize such technologies. On the other hand, network optimization is also a research focus of such applications which significantly affects the performance of the system due to the high volume of connected devices and different features. In this thesis we propose advanced techniques to overcome the challenges on the low efficiency and network design of the wireless information and power transfer systems. The thesis consists of two parts. In the first part we focus on the power transmitter design which addresses the low efficiency issue associated with backscatter communication and WPT. In Chapter 2, we consider a backscatter RFID system with the multi-antenna reader and propose a blind transmit and receive adaptive beamforming algorithm. The interrogation range and data transmission performance are both investigated under such configuration. In Chapter 3 we study wireless power transfer by the beamspace large-scale MIMO system with lens antenna arrays. We first present the WPT model for the beamspace MIMO which is derived from the spatial MIMO model. By constraining on the number of RF chains in the transmitter, we formulate two WPT optimization problems: the sum power transfer problem and the max-min power transfer problem. For both problems we consider two different transmission schemes, the multi-stream and uni-stream transmissions, and we propose different algorithms to solve both problems in both schemes respectively. In the second part we study the network optimization problems in the WPT and backscatter systems. In Chapter 4, we study the resource allocation problem for a RF-powered network, where the objective is to maximize the total data throughput of all sensors. We break the problem into two subproblems: the sensor battery energy utilization problem and the charging power allocation problem of the central node, which is an RF power transmitter that transmits RF power to the sensors. We analyze and show several key properties of both problems, and then propose computationally efficient algorithms to solve both problems optimally. In Chapter 5, we study the time scheduling problem in RF-powered backscatter communication networks, where all transmitters can operates in either backscattering mode or harvest-then-transmit (HTT) mode. The objective is to decide the operating mode of each transmitter and minimize the total transmission time of the network. We also consider both ideal and realistic transmitters based on different internal power consumption models for HTT transmitters. Under both transmitter models we show several key properties, and propose bisection based algorithms which has low computational complexity that solves the problem optimally. The results are then extended to the massive MIMO regime.

Abstract not available

The understanding of the masticatory apparatus including its functional and structural relationship with other components of the cranium increasingly requires an interdisciplinary approach. Recently, "traditional biological sciences" such as anatomy, comparative biology, anthropology and evolution have increasingly meshed with elements from other domains, such as mechanical engineering and material sciences, which has resulted in new and exciting paradigms to be explored. This is particularly true in the field of craniofacial biomechanics yet there are still many unexplored issues and numerous questions that remain unanswered. Numerical modelling in general and Finite Element Analysis (FEA) in particular, represent a numerical experimental procedure to generate such information. Originally derived from the field of structural engineering, FEA has steadily permeated its way into craniofacial biomechanics and has proven itself as a most useful scientific tool. The present study introduces an engineering-based workframe for applying FEA to craniofacial biomechanical research in a comprehensive manner to cover the entire analytical spectrum, from developing questions to providing their solutions. The study is composed of two major experimental parts addressing both the linear elastic and the non-linear behaviour of some biomaterials encountered in the craniofacial arena. In the first part I analysed mandibular biomechanics using linear elastic models while in the second part I used nonlinear discrete models to determine the optimal elastic properties of the cervical restorative materials. Modern humans have a number of anatomical features that set us apart from our ancestors. Amongst these perhaps the most striking is the emergence of a protruding chin, otherwise absent in other archaic humans and hominids. While it has been shown that the chin has its embryological origins in the postnatal remodelling of bone in the area around the mandibular symphysis which produces the midline keel in the form of an inverted �T� the functional significance of this novel evolutionary feature is still obscure. It is accepted that the mandible is optimally designed for resisting masticatory stress, whereby optimal is seen as maximual strength at the lowest biological cost. Here, I tested the currently most accepted theory, namely that the chin provides mechanical resistance to the mandible during mastication. In other words, I tested the hypothesis that a chinned mandible would be stiffer and hence experience lower strains when compared to a non-chinned counterpart under identical loadings. My functional analysis consisted firstly of three simple models which reproduce a simian shelf, a flat and a chinned symphysis, loaded using two unidirectional loadcases (torsion and wishboning) to represent a distortion similar to that which occurs in the mandible during mastication. Secondly, I developed complex geometrical models which incorporated the cortical bone, medullary bone and teeth. The models were then analysed using the same loadcases as those used for the first theoretical models. Additionally, I incorporated the coronal bending and also a coupled loadcase which simulated the complex deformation of the mandible during biting. The aim here was to test the hypothesis that the presence of a chin changed the strain pattern in the mastication-loaded mandible. The results were then interpreted using Frost�s mechanostat theory which relates in a more precise manner the mechanical loading environment to the adaptive response of the bone. My results showed that the calculated strain values for both the chinned and flat mandibles were within the normal bone maintenance levels of the mechanostat during molar biting. In other words, variation in bone strain magnitude across the mandible, which should differ between the chinned and the non-chinned mandibles if the hypothetical mechanical role of the chin is true, is similar in both forms. I concluded that the development of the human chin is thus unrelated to the functional demands placed upon it by mastication. I suggested a new functional demand associated with pronounced tongue activity during speech. I hypothesise that it is the resistance to stresses induced by strong, repetitive contractions of the tongue and perioral musculature during, phonation that shaped the modern human chin. I tested my hypothesis by loading the symphyseal region with two principal nonmasticatory, muscle systems; firstly, the tongue and secondly the peri-oral muscular curtain, anterior to the symphysis. My results suggested that the flat, non-chinned symphysis when subjected to speech-related genioglossal movements will undergo adaptive changes which would result in an optimised (chinned) shape, such as that found in the modern human symphysis. These results thus offer a new foundation to an old hypothesis and a solution to the longstanding controversy over the origin of the human chin. I conclude that forces generated by speech rather than those generated by mastication, shaped the chin in anatomically modern humans. Prompted by an earlier observation I further investigated the apparent cross-over distribution of strains on the mandibular corpora during mastication. In doing so, I tested the hypothesis that this cross-over may be linked with another particular anatomical feature of the mandible that of the postcanine cortical asymmetry, which appears to be stereotypical among anthropoids. The results of my study hence suggest that strain patterns within the human mandible are more complex than previously thought. Not only do strains differ between lingual and buccal aspects of working and non-working sides, but they also differ within these areas (i.e. from alveolus to corpus, to lower border regions). I conclude that postcanine cortical asymmetry may be a retained evolutionary trait rather than the result of masticatory biomechanics. In the second section of the thesis I introduced a different analysis regime which allows the prediction of fracture initiation and propagation. In this part I analysed the mechanics underlying the failure of the restorations placed in non-carious cervical lesions and suggested changes in the material properties of the restorations used to treat them. Non-carious cervical lesions (NCCL) include those entities characterised by the cervical loss of hard dental tissue that occurs in the absence of any carious process. To distinguish between lesions that occur due to excessive occlusal load and other non-carious cervical lesion (i.e. erosion and abrasion) the clinical term "abfraction" has been adopted. Although a common clinical issue, failure of restoration placed in these lesions has not been subjected to a rigorous biomechanical analysis. To determine which of the material�s parameters should be changed and to what extent, I employed a combined numerical approach. Here I introduced a novel approach in simulating the cracking of restorative materials and tooth tissues which is based on a simpler material formulation and can be used in an advanced nonlinear numerical analysis. The material model I used allows automatic crack insertion and growth and also uniquely accounts for the microdamage which precedes the instalment of macroscopic cracks. The first step was to balance the factors that may affect failure employing a linear analysis with a stress-based approach to failure. Here, the aim was to investigate the influence of lesion shape and depth as well as the direction of occlusal loading on the mechanical response of the cervical glass-ionomer cements restoration in a lower first premolar. This analysis showed that the direction of loading was the major contributor to the failure of the restoration. The next step was to apply this fracture model to the restorations of the NCCL in order to verify if the material is able to accurately simulate the location and type of mechanical failure. The data for this problem, i.e. the geometry and the loadcase were derived from the conclusions of linear analysis, that is I chose the "worst case scenario" as the upper boundary of material endurance. My results showed that under the action of para-functional loadings the GIC failed on the cervical margin. I also showed that prior to fracture the restorative material undergoes strain softening, which in turn introduces damage and weakens the materials involved. After successfully testing the proposed model, the final step was to determine which material properties and restorative techniques would be most reliable under given biomechanical conditions. The present work relied on the hypothesis that a more flexible material would partially buffer the local stress concentration and hence reduce the likelihood of mechanical failure of the restoration. My study, a first of its kind, proposes a radical approach to address the problems of material improvement, namely: numerical-based material optimisation engineering. That is, I aimed to identify the "most favourable" selection of elastic modulus or E value for the restorative material, which will allow it to survive under the unfavourable occlusal loading conditions that may prevail. Two filling techniques were considered; firstly a single bulk material, namely glass-ionomer (GIC) and secondly a layered technique. The latter consisted of a layer of GIC supporting a composite bulk restorative. I chose two thicknesses for the GIC layer, 50 and 150 microns. My results showed that the restorative materials currently used in cervical non-carious lesions are largely unsuitable in terms of resistance to fracture of the restoration mostly because of their relative high stiffness irrespective of the filling technique. The best results are obtained for a bulk filling with a 1GPa elastic modulus material case in which the tensile stresses are about 50% of the failure limit. This approach in determining the mechanical properties of the restorative is novel and unique so far in the dental literature. The direct benefit of this study was the improvement of the restorative material, as it can be engineered to withstand the conditions identified as major cause of failure. This is consonant with the call for new materials better tailored for some specific needs.

This dissertation aims to advance the field of structural optimization by creating and demonstrating new methodologies for the explicit inclusion of manufacturing issues. The case of composite aerospace structures was a main focus of this work as that field provides some of the greatest complexities in manufacturing yet also provides the greatest incentives to optimize structural performance. Firstly, the possibilities for modifying existing FEA based structural optimization methods to better capture manufacturing constraints are investigated. Examples of brick-based topology optimization, shell-based topology optimization, parametric sizing optimization and manufacturing process optimization are given. From these examples, a number of fundamental limitations to these methods were observed and are discussed. The key limitation that was uncovered related to a dichotomy between analytical methods (such as FEA) and CAD-type methods. Based on these observations, a new Knowledge-Based framework for structural optimization was suggested whereby manufacturing issues are integrally linked to the more conventional structural issues. A prototype system to implement this new framework was developed and is discussed. Finally, the validity of the framework was demonstrated by application to a generic composite rib design problem.