Ab-initio methods for calculating electronic structure represent an important field of material physics. The aim of this theses - within the project focused on developing the new method for calculating electronic states in non-periodic structures based on density functional theory, pseudopotentials, and finite elements methods - is to convert Kohn-Sham equations into the form suitable for discretisation, to suggest apropriate method for solving generalized eigenproblem resulting from this discretisation and to implement an eigenvalue solver (or to modify existing one). The thesis describes a procedure for converting the many-particle Schrödinger equation into generalized rank-k-update eigenvalue problem and discusses various methods for its solution. Eigensolver Blzpack, which makes use of the block Lanczos method, has been modified, integrated into the Sfepy framework (a tool for the finite element method calculation) and resulting code has been successfully tested.

In the first chapter of the thesis we present an introduction to the visco- plasticity and overview of the presented problems. The constitutive relation for Bingham fluid is derived and in the second chapter. Further there is demon- strated a procedure of proving existence and uniqueness with classical varia- tional method. This method is compared with the same process using modern implicit theory. The last chapter starts with summary of used problem formu- lations and used software. It is then followed by the main part with results of numerical simulations, both for the purpose of used formulations comparison and then verification of the preferred one in more complicated simulations. We expect a possible application of tested approaches on different materials. 1

Electrochemical machining (ECM) is a non-conventional manufacturing process, which uses electrochemical dissolution to shape any conductive metal regardless of its mechanical properties and without leaving behind residual stresses or tool wear. Therefore, ECM can be an alternative for machining difficult-to-cut materials, complex geometries, and materials with improved characteristics, such as strength, heat-resistance or corrosion-resistance. Notwithstanding its great potential as a shaping tool, the ECM process is still not fully characterised and its research is an on-going process. Various phenomena are involved in ECM, e.g. electrodynamics, mass transfer, heat transfer, fluid dynamics and electrochemistry, which occur in parallel and this can lead to a different material dissolution rate at each point of the workpiece surface. This makes difficult an accurate prediction of the final workpiece geometry. This problem was addressed in the first part of the present thesis by developing a simulation model of the ECM process in a two-dimensional (2D) environment. A finite element analysis (FEA) package, COMSOL multiphysics® was used for this purpose due to its capacity to handle the diverse phenomena involved in ECM and couple them into a single solution. Experimental tests were carried out by applying ECM on stainless steel 316 (SS316) samples. This work was done in collaboration with pECM Systems Ltd® from Barnsley, UK. The interest of studying ECM on stainless steels (SS) resides on the fact that the application of ECM on SS typically results in various different surface finishes. The chromium in SS alloys usually induces the formation of a protective oxide film that prevents further corrosion of the alloy, giving the metal the special characteristic of corrosion resistance. This oxide film has low electrical conductivity; hence normal anodic dissolution often cannot proceed without oxide breakdown. Partial breakdown of the oxide film often occurs, which causes pits on the surface or a non-uniform surface finish. Therefore the role of the ECM machining parameters, such as interelectrode gap, voltage, electrolyte flow rate, and electrolyte inlet temperature, on the achievement of a uniform oxide film breakdown was evaluated in this work. Experimental results show that the resulting surface finish is highly influenced by the over-potential and current density, and by the characteristics of the electrolyte, flow rate and conductivity. The complexity of experimentally controlling these parameters emphasised the need for the development of a computational model that allows the simulation of the ECM process in full. The simulation of ECM in a three-dimensional (3D) environment is crucial to understand the behaviour of the ECM process in the real world. In a 3D model, information that was not visible before can be observed and a more detailed realistic solution can be achieved. Hence, in this work a computer aided design (CAD) software was used to construct a 3D geometry, which was imported to COMSOL Multiphysics® to simulate the ECM process, but this time in a 3D environment. This enhanced simulation model includes fluid dynamics, heat transfer, mass transfer, electrodynamics and electrochemistry, and has the novelty that an accurate computational simulation of the ECM process can be carry out a priori the experimental tests and allows the extraction of enough information from the ECM process in order to predict the workpiece final shape and surface finish. Moreover, this simulation model can be applied to diverse materials and electrolytes by modifying the input ECM parameters.

Assessment of concrete buttress dams today consists of using analytical methods to investigate the stability in different failure modes. However, they simplify the problem at hand and neglect certain important features linked to geometry and thus not truthfully appraise the structures real stability.  This could be economically costly in assessments of both existing dam structures as this would eventually lead to unwarranted rehabilitation. The same can be said for dams under design.   Kalhovd dam is a concrete buttress dam that has recently undergone assessment where certain sections proved unstable in either failure mode. This study focused specifically on a buttress, numbered 49, of said dam which was deemed in the assessment to be unstable in the overturning and sliding failure mode.   The methodology used was to assess and compare stability for different methods of calculation, meaning analytical versus numerical analysis. The numerical analysis was performed with two-dimensional finite element analyses in a commercial FEM-software called ATENA which focuses on reinforced concrete structures. The numerical models made, were then probabilistically analysed by randomizing various material parameters to see their effect on stability. Some FEA models discarded the conventional way of modelling loads, as required by standards, to more realistically portray load actions on dams based on historical measurement.   Results from this study showed dissimilarity of stability for buttress 49 depending on which method of analysis was performed. Analytical methods proved to yield the most conservative results and concluded the structure unsafe, while including an accurate representation of the geometry in FEA models improved the stability such that it can be considered stable against load actions stated in guidelines.   Furthermore, material parameters randomized in the probabilistic analysis substantiated that various concrete variables had relatively little effect on structural overall strength in the most common failure modes.

NiTi alloys have been the focus of Shape Memory Alloys (SMA) research and applications due their excellent ductility and shape memory properties, and these alloys have been extensively used in automotive, aerospace, and in biomedical applications. The effects of machining on the surface integrity and the corresponding material and mechanical properties of alloys can be best studied by utilizing NiTi alloys as workpiece material since their physical and mechanical properties are highly microstructure dependent. However, due to very poor machining performance of NiTi shape memory alloys, no comprehensive or systematic investigation on this topic has been conducted by researchers as yet. The current study makes a substantial and unique contribution to this area by making the first and significant contribution to studies on machining performance of NiTi shape memory alloys, and by achieving improved surface integrity and machining performance using cryogenic applications, which give significant reductions of tool-wear, cutting forces, and surface roughness. The influence of machining process conditions, including dry, MQL, preheated, cryogenic machining, and the effects of prefroze cryo machining on surface integrity characteristics such as microhardness, phase transformation, phase transformation temperature, depth of plastically deformed layer have been examined extensively, and unique findings have been obtained. The effects of machining process conditions, in particular preheated and cryogenic machining conditions, on thermo-mechanical and shape memory characteristics were identified through thermal cycling and stress-strain tests. For the first time, orthogonal cutting of NiTi shape memory alloys has been carried out in this study to investigate surface integrity comprehensively. Surface integrity and machining performance are compared for dry and prefroze cryogenic cooling conditions under a wide range of cutting speeds. Stress-induced martensitic phase transformation and deformation twinning were found in prefroze cryogenic and dry cutting conditions respectively. The existing microstructure-based constitutive models were used and modified to predict machining-induced phase transformation and resulting volume fraction. The modified model was implemented in commercial FEM software (DEFORM-2D) as a customized user subroutine. The obtained results from simulation and orthogonal cutting tests were compared considering martensitic volume fraction during cutting with various cutting speeds. The model captured the experimental trend of volume fraction induced by various cutting speeds and process variables. Overall, FEM simulation of cutting process of NiTi was successfully presented.

Este estudo tem como principal objetivo a compreensão de dois dos principais métodos de otimização topológica disponíveis na literatura: o método SIMP e ESO. Estes métodos foram implementados computacionalmente utilizando a linguagem de programação FORTRAN 90. Utiliza-se o Método dos Elementos Finitos (MEF) como parâmetro de solução mecânica neste trabalho, adotando-se a formulação baseada em deslocamentos para elasticidade linear. Ademais, visando avaliar o efeito da não linearidade geométrica na topologia ótima obtida, utiliza-se também o MEF posicional, o qual baseia-se nas posições nodais para solução do sistema não linear. Em conjunto com este método, adota-se a lei constitutiva de Saint-Venant-Kirchhoff, visando considerar os efeitos não lineares. Desta maneira, avalia-se a eficiência dos resultados obtidos por meio da aplicação de exemplos presentes na literatura. Conforme esperado, conclui-se que para exemplos cuja resposta apresenta pequenos deslocamentos, ambas as soluções se sobrepõem. No entanto, em se tratando de problemas em que a não linearidade geométrica tem influência, como estruturas constituídas de baixa densidade, a técnica do MEF posicional apresenta relevância na solução ótima. / This study has as main objective the understanding of two main topology optimization methods available in the literature: the methods SIMP and ESO. These methods were implemented computationally using the FORTRAN 90 programming language. The finite element method (FEM) is used as the mechanical solution parameter in this work, adopting the displacement-based formulation for linear elasticity. In addition, in order to evaluate the effect of geometric non-linearity in the optimal topology obtained, the FEM positional-based formulation is used, which uses the nodal positions for solution of the non-linear system. In conjunction with this method, the constitutive law adopted is the Saint-Venant-Kirchhoff in order to consider the nonlinearity. Hence, benchmarks presented in the literature are used to evaluate the efficiency of the obtained results. As expected, we conclude that the examples subjected to small displacements have similar solutions for both linear and nonlinear behavior. However, when problems that undergo geometrically nonlinear behavior, such as the ones modelled with soft materials, the FEM positional-based formulation has significant influence in the optimal solution.

Les thèmes de recherche développés dans le mémoire d'HdR se rapportent à l'étude de l'endommagement des géomatériaux. Ils associent toujours des expériences et des modélisations pour répondre à des exigences industrielles. La première partie de l'exposé portera sur l'étude du comportement des bétons de fibres à ultra haute performance (BFUHP). Ce travail de recherche, réalisé à plusieurs échelles, a mis en évidence l'impact d'une hétérogénéité locale sur le comportement global d'une structure en béton. La deuxième partie a pour objet l'étude du comportement des barrières argileuses des centres de stockage de déchets industriels spéciaux. Ce travail de recherche a permis, entre autre, de définir pour l'argile un critère de flexion sans fissuration qui tient compte des conditions de mise en œuvre. Pour ces deux travaux de recherche, la démarche scientifique retenue, a conduit au développement d'expériences spécifiques souvent uniques et non-conventionnelles pour les matériaux étudiés (bitraction sur le béton et flexion sur l'argile). De plus, ce travail a utilisé des modélisations non usuelles dans lesquelles ont été intégrées les particularités relatives aux problèmes posés (couplages modèles d'inclusion et éléments finis, modélisations discrètes et matériaux cohérents). Dans les deux cas l'objectif était de maîtriser la mise en œuvre et le comportement jusqu'à la ruine des matériaux afin d'optimiser leurs performances mécaniques.

<p>I hydrocyklonaggregatet RADICLONE används kragade hål som tätningsyta mot cyklonen. Hålen ändrar form under tillverkning och i drift med läckage som följd. </p><p>Syftet med arbetet är att studera hur de kragade hålen deformeras vid tillverkning och med hjälp av en FEM-modell beräkna deformationer vid drift och tillverkning. Utifrån resultaten har åtgärder föreslagits för att reducera hålens ovalitet. </p><p>Det som påverkar hålen mest vid tillverkning är kragning och svetsning av bajonettfästen. Enskilt största påverkan sker vid svetsning av ledplåten. </p><p>FEM-analysen vid drift visar att deformationerna varierar över mantlarna och att de högsta spänningarna ligger som ringar kring mantlarna så att kragarna får ta upp en stor del av dessa. </p><p>För att komma till rätta med dessa problem har ett antal produktions- och konstruktionsförändringar föreslagits: </p><p>- Använda ovala dragringar vid kragning av hålen </p><p>- Flytta ledplåtens infästning från manteln till bottengaveln </p><p>- Sära på hålen - Använda tjockare plåt i mantel 2</p><p>- Förbättra cyklonens tätningsytor mot kragarna på mantel 2 och 3</p>

<p>Complex surface structures in nature often have remarkable optical properties. By understanding the origin of these properties, such structures may be utilized in metamaterials, giving possibilities to create materials with new specific optical properties. To simplify the optical analysis of these naturally developed surface structures there is a need to assist data analysis and analytical calculations with numerical calculations.</p><p>In this work an application tool for numerical calculations of optical properties of surface structures, such as reflectances and ellipsometric angles, has been developed based on finite element methods (FEM). The data obtained from the application tool has been verified by comparison to analytical expressions in a thorough way, starting with reflection from the simplest of interfaces stepwise increasing the complexity of the surfaces.</p><p>The application tool were developed within the electromagnetic module of Comsol Multiphysics and used the script language to perform post-process calculations on the obtained electromagnetic fields. The data obtained from this application tool are given in such way that easily allows for comparison with data received from spectroscopic ellipsometry measurements.</p>

<p><strong><p>Sammanfattning</p><p>Denna studie beskriver hur elever, i skolår fem, uttrycker hälsa utifrån Antonovsky´s begrepp KASAM, en känsla av sammanhang. Genom en kvalitativ intervjustudie med öppna intervjufrågor, i grupper om tre elever, har eleverna samtalat om vad hälsa innebär för dem. Syftet med studien var att få eleverna att sätta ord på sina egna tankar kring hälsa. Resultatet visar att de har ganska goda kunskaper om vad hälsa innebär. De sätter dock inte in denna kunskap, i en övergripande beskrivning kring vad som ger känsla av sammanhang, i den egna livssituationen.</p></strong></p>