Liquid Storage Tanks (LSTs) are essential infrastructure systems that are used in various municipal and industrial settings. They play a critical role in storing and transporting liquids such as drinking water, oil, and gas that are used in daily life. Failure of these structures due to their poor seismic performance can have devastating consequences including the release of the stored liquid and damage to the surrounding area with potentially irreversible environmental impacts. In addition, the damage caused to the tank structure can be extensive, resulting in significant financial losses. Furthermore, the disruption of services provided by the tank such as water supply, oil and gas storage can be considerable. It is therefore crucial to study the seismic behaviour of these structures and ensure their safety and reliability to minimize the potential damages. The aim of this study is to investigate the behavior of LSTs in terms of the contained liquid, the tank’s structure, and its supports when subjected to seismic excitations. To obtain accurate results, different numerical techniques are applied in different phases of the study, including the Finite Volume Method (FVM), Finite Elements Method (FEM), Volume of Fluids (VoF) method, and Smoothed Particles Hydrodynamic (SPH) method. These techniques allow for a detailed analysis of the behavior of the tank and its supports during seismic excitation, providing a comprehensive understanding of the performance of LSTs during earthquakes. In order to examine the reliability and accuracy of the numerical model, the first part of the study includes the validation of the developed numerical model through comparison of the model and experimental results. The validated numerical model is then used to obtain the hydrodynamic pressures at different locations on the roof of tanks subjected to base excitations. The effect of liquid impact and hydrodynamic pressures on the roof of LSTs can be significant, however, limited studies have been completed on this issue. In the second part of the study, Artificial Intelligence (AI) techniques such as Genetic Programming are used to formulate these pressure values so that the maximum pressure can be obtained using the tank characteristics such as size and fill depth by the relationship obtained based on the AI approach. In the third part of the study, the supporting structures of LSTs subjected to base excitations are analyzed, and their shear forces are extracted and compared with the National Building Code of Canada (NBC 2020) in order to evaluate the reliability of the code and discuss possible improvements. The results of this study can be used to evaluate and make improvements in standards and guidelines for the seismic design of LSTs, which can help ensure the safety and reliability of these crucial infrastructures during seismic events.

[pt] Com o advento dos campos do Pré-sal brasileiro, a indústria nacional de óleo e gás se concentra cada vez mais em vencer os desafios impostos na explotação desses novos reservatórios. A construção de poços nesse cenário passa por uma série de dificuldades que tem sido sistematicamente vencidas ao longo do tempo, de forma que o tempo de contrução dos poços passa por intenso processo de redução. A estimativa é que o tempo atual de construção dos poços foi reduzido pela metade desde que foram perfurados os primeiros poços e o próximo desafio da Petrobras é possibilitar que haja redução de tempo drástica na mesma proporção até o ano de 2020. Isso será possível apenas se novas técnicas forem desenvolvidas, pois acredita-se que os poços estejam sendo construídos próximo do limite de otimização das técnicas existentes até o momento. Os revestimentos de superfície necessitam ser assentados no topo da formação de sal, o que demanda comprimentos da ordem de 1000 m ou mais. Infelizmente, por questões de volumetria operacional do bombeio de cimento e resistência à fratura das camadas de solo iniciais, não há retorno de cimentação na fase de superfície para o leito marinho. Esse fato leva ao aparecimento de comprimentos livres desses revestimentos com cerca de 500 m. Como o revestimento condutor é perfurado e cimentado, as resitências de fundação do poço são suficientes para suportar as cargas axiais oriundas da instalação dos revestimentos e equipamentos submarinos instalados no poço, uma vez que essas são descarregadas no sistema condutorsolo. O tempo de construção de poços pode ser reduzido sistematicamente em cerca de 2 dias caso se utilizem as técnicas de base-torpedo ou jateamento para assentamento do condutor. No entanto, a resistência do sistema condutor-solo é insuficiente para suportar as cargas axiais instaladas no poço. Isso significa que o revestimento de superfície passa também a suportar as cargas axiais do poço, o que pode levar o mesmo a flambar de forma helicoidal com consequente aumento nos níveis de tensão e deslocamentos indesejáveis. A formulação analítica disponível para o cálculo desses parâmetros deve ser posta à prova para que haja segurança nos projetos que levem em conta inícios de poços alternativos, que embora mais econômicos, devem ainda possuir elevada confiança na integridade estrutural. O presente trabalho se dedicou a desenvolver de forma clara um procedimento numérico robusto utilizando FEA em software comercial, o Abaqus, para avaliar os efeitos de elevadas cargas axiais sobre o trecho livre do revestimento de superfície e avaliar as consequências da sempre inevitável flambagem. O objetivo final é alcançado, uma vez que as análises numéricas e uma superposição de formulações analíticas de simples utilização demonstram uma boa aderência entre si. Além disso, é constatada uma nítida tendência linear entre o fator de atrito e o deslocamento do SCPS. Tal tendência pode ser explorada em trabalhos futuros para incorporação nas formulações analíticas deste parâmetro invariavelmente negligenciado no equacionamento das mesmas. / [en] With the advent of the Brazilian Pre-salt oil fields, the national oil and gas industry focuses increasingly on winning the challenges in the exploitation of these new reservoirs. The well construction in this scenario involves a number of difficulties wich have been overcome consistently over time, so that it undergoes intense time reduction. The estimate is that the current time of well construction has been reduced by half since the first drilled wells and the next challenge Petrobras is willing to make is a drastic time reduction at this same rate until the year 2020. This will be possible only if new techniques are developed, as it is believed that the wells are being constructed near the limits of optimization of the current techniques. Surface casings need to be seated on the top of salt formation, which requires lengths on the order of 1000 m or more. Unfortunately, due to operating volumes related to the cement pumping volume capacity and fracture resistance of the initial soil layers, there is no return of cement to the mudline. This fact leads to free lengths of these casings with about 500 m. As the conductor casing is drilled and cemented, the well foundation resistances are sufficient to withstand the axial loads originated from the installation of additional casings and subsea equipment, since these are discharged into the conductor-soil system. The well construction time can be reduced systematically by about 2 days if using torpedo base or jetting techniques to seat the conductor. However, both soilresistance systems are insufficient to withstand axial loads installed in the well. This means that the surface casing also starts to bear axial loads of the well, which can lead to its helical buckling with a consequent increase in stress levels and undesirable displacements. The analytical formulation available for the calculation of these parameters should be put tho the test so safety can be taken into account for alternative well s foundation designs, which although more economical, should still have high reliability in the structural integrity. This work is dedicated to develop a robust numerical procedure using FEA in a commercial software, Abaqus, to evaluate the effects of high axial loads on the free length of the surface casing and the consequences of an always inevitable buckling. The ultimate goal is achieved, since the numerical analysis and a superposition of simple analytical equations demonstrate good adhesion to each other. Moreover, a clear linear dependency is found between the friction factor and the displacement of the top of the casing. This trend can be explored in future research for incorporation into analytical formulations of this parameter invariably neglected in addressing them.

The present master's thesis deals with numerical modeling of solid-state micrometrical-sized polymeric dye lasers, commonly denoted as microcavities. It is part of a large research initiative carried out in the optics group, at the MAP (Microelectronics and Applied Physics) department in KTH (Kungliga Tekniska Högskolan - Royal Technical School) and targeted towards the design and manufacturing of micro- and nano-scaled polymeric components for nano-photonics, primarily lasers. The finite element method (FEM) in frequency domain is used as a primary modeling tool through the simulation software COMSOL Multiphysics. Models for spontaneous emission, optical losses and gain are developed and demonstrated. A specic layout is studied: the double hexagonal microcavity. While it was expected to be a good candidate for a laser, the design shows unexpected properties making it useful for sensing applications. Finally, the transposition of models to time domain is initiated : a replacement solution for the lacking perfectly matched layer (PML) in Comsol is developed and demonstrated. Methods for modeling materials parameters in time domain are investigated, together with the possible use of a more suitable algorithm : finite dierences in time domain (FDTD) or Yee's scheme.

The objective of this research project was to create a Finite Element Routine for the Linear Analysis of Post-Tensioned beams using the program CALFEM® [20] developed at the division of Structural Mechanics in Lund University, Sweden. The program CALFEM and our own made files were written in MATLAB, an easy to learn and user-friendly computer language. The approach used in this thesis for analyzing the composite beam consists in embedding the steel tendons at the exact location where they intersect the concrete parent elements, without moving the concrete parent element nodes. The steel tendons are represented as one dimensional bar elements inserted into the concrete parent elements, which at the same time are represented as 8 node Iso-parametric plane elements. The theory presented in Ref. [4] served as basis for the modeling of the post-tensioned beams; however it only explained the procedure for modeling simple reinforced concrete beams, due to this we needed to make the appropriate adjustments so we could model post-tensioned beams. Assembly of the tendon stiffness into the concrete elements will depend on the bond interface between the steel and concrete, this bonding effect will be modeled using link elements; the stiffness of this link element used in the concrete-tendon interface will be the change in cohesion (between the grout or duct and the steel tendon) at the interface due to the relative slip between the concrete and the steel elements nodes. Loads (Distributed, Concentrated or Post-Tensioning) are applied directly into the concrete parent elements, and then from their resultant displacement the displacements and forces of all the steel tendon elements are obtained, this is done consecutively for all the post-tensioned tendons at every load increment. Four examples from different references and software programs are solved and compared with our results: (1) A simply reinforced cantilever plate. (2) A reinforced concrete beam, under the effect of a vertical concentrated load at mid-span. For this problem the force distribution along the steel reinforcement is obtained for two conditions, perfectly bonded and perfectly un-bonded, our results are compared with the ones obtained with the program SEGNID. (3) Consists of a continuous un-bonded post-tensioned beam with two spans, without stress losses on the tendon. The reactions at the supports and the concrete stress distribution at the location of the mid-support are obtained after the post-tensioning force is applied at both ends. (4) Consist on a un-bonded post-tensioned beam with stress losses on the tendons due to friction, wobbling and anchorage loss, under gradual loading and consecutive post-tensioning of two tendons, the results are compared with the ones reported using the program BEFE [5] developed at the University of Technology Graz, Austria. The results obtained using our program are very similar to the ones obtained with the other programs, including the more powerful curved embedded approach used by BEFE [5].

Florida's Department of Transportation requires design storm tide hydrographs for coastal waters surrounding tidal inlets along the coast of Florida. These hydrographs are used as open ocean boundary conditions for local bridge scour models. At present, very little information is available on the effect that tidal inlets have on these open coast storm tide hydrographs. Furthermore, current modeling practice enforces a single design hydrograph along the open coast boundary for bridge scour models. This thesis expands on these concepts and provides a more fundamental understanding on both of these modeling areas. A numerical parameter study is undertaken to elucidate the influence of tidal inlets on open coast storm tide hydrographs. Four different inlet-bay configurations are developed based on a statistical analysis of existing tidal inlets along the Florida coast. The length and depth of the inlet are held constant in each configuration, but the widths are modified to include the following four inlet profiles: 1) average Florida inlet width; 2) 100 meter inlet width; 3) 500 meter inlet width; and 4) 1000 meter inlet width. In addition, two unique continental shelf profiles are used to design the ocean bathymetry in the model domains: a bathymetry profile consistent with the west/northeast coast of Florida (wide continental shelf width), and a bathymetry profile similar to the southeast coast of Florida (narrow continental shelf width). The four inlet-bay configurations are paired with each of the bathymetry profiles to arrive at eight model domains employed in this study. Results from these domains are compared to control cases that do not include any inlet-bay system in the computational domain. The ADCIRC-2DDI numerical code is used to obtain water surface elevations for all studies performed herein. The code is driven by astronomic tides at the open ocean boundary, and wind velocities and atmospheric pressure profiles over the surface of the computational domains. Model results clearly indicate that the four inlet-bay configurations do not have a significant impact on the open coast storm tide hydrographs. Furthermore, a spatial variance amongst the storm tide hydrographs is recognized for open coast boundary locations extending seaward from the mouth of the inlet. The results and conclusions presented herein have implications toward future bridge scour modeling efforts. In addition, a hindcast study of Hurricane Ivan in the vicinity of Escambia Bay along the Panhandle of Florida is performed to assess the findings of the numerical parameter study in a real-life scenario. Initially, emphasis is placed on domain scale by comparing model results with historical data for three computational domains: an ocean-based domain, a shelf-based domain, and an inlet-based domain. Results indicate that the ocean-based domain favorably simulates storm surge levels within the bay compared to the other model domains. Furthermore, the main conclusions from the numerical parameter study are verified in the hindcast study: 1) the Pensacola Pass-Escambia Bay system has a minimal effect on the open coast storm tide hydrographs; and 2) the open coast storm tide hydrographs exhibit spatial dependence along typical open coast boundary locations.

Thin walled stiffened composite panels, which are among the most utilized structural elements in engineering, possess the unfortunate property of being highly sensitive to geometrical imperfections. Existing analysis codes are able to predict the nonlinear postbuckling behavior of a structure with specified imperfections. However, it is impossible to determine the geometric imperfection profile of a nonexistent composite panel early in the design. This is due to the variety of uncertainties that are involved in the manufacturing of these panels. As a mater of fact, due to the very nature of the manufacturing processes, it is hard to imagine that a given manufacturing process could ever produce two identical panels. The objective of this study is to introduce a new design methodology in which a manufacturing model and a convex model for uncertainties are used in conjunction with a nonlinear design tool in order to obtain a more realistic, better performing final design. First a finite element code for the nonlinear postbuckling analysis of stiffened panels is introduced. Next, a manufacturing model for the simulation of the autoclave curing of epoxy matrix composites is presented. A convex model for the uncertainties in the imperfections is developed in order to predict the weakest panel profile among a family of panels. Finally, the previously developed tools are linked in a closed loop design scheme aimed at obtaining a final design that incorporates the manufacturing tolerances information through more realistic imperfections. / Ph. D.

Optical Tomography is an imaging modality that enhances early diagnosis of disease through use of harmless Near-Infrared rays instead of conventional x-rays. The subsequent images are used to reconstruct the object. However Optical Tomography has not been effectively utilized due to the complicated photon scattering phenomenon and ill-posed nature of the corresponding image reconstruction scheme. The major method for reconstruction of the object is based on an iterative loop that constantly minimizes the difference between the predicted model of photon scattering with acquired images. Currently the most effective method of predicting the photon scattering pattern is the solution of the Radiative Transfer Equation (RTE) using the Finite Elements Method (FEM). However, the conventional FEM uses classical C0 interpolation functions, which have shortcomings in terms of continuity of the solution over the domain as well as proper representation of geometry. Hence higher discretization is necessary to maintain accuracy of gradient-based results which may significantly increase the computational cost in each iteration. This research implements the recently developed Isogeometric Approach (IGA) and particularly IGA-based FEM to address the aforementioned issues. The IGA-based FEM has the potential to enhance adaptivity and reduce the computational cost of discretization schemes. The research in this study applies the IGA method to solve the RTE with the diffusion approximation and studies its behavior in comparison to conventional FEM. The results show comparison of the IGA-based solution with analytical and conventional FEM solutions in terms of accuracy and efficiency. While both methods show high levels of accuracy in reference to the analytical solution, the IGA results clearly excel in accuracy. Furthermore, FE solutions tend to have shorter runtimes in low accuracy results. However, in higher accuracy solutions, where it matters the most, the IGA proves to be considerably faster. / Doctor of Philosophy / CT scans can save lives by allowing medical practitioners observe inside the patient's body without use of invasive surgery. However, they use high energy, potentially harmful x-rays to penetrate the organs. Due to limits of the mathematical algorithm used to reconstruct the 3D figure of the organs from the 2D x-ray images, many such images are required. Thus, a high level of x-ray exposure is necessary, which in periodic use can be harmful. Optical Tomography is a promising alternative which replaces x-rays with harmless Near-infrared (NIR) visible light. However, NIR photons have lower energy and tend to scatter before leaving the organs. Therefore, an additional algorithm is required to predict the distribution of light photons inside the body and their resulting 2D images. This is called the forward problem of Optical Tomography. Only then, like conventional CT scans, can another algorithm, called the inverse solution, reconstruct the 3D image by diminishing the difference between the predicted and registered images. Currently Optical Tomography cannot replace x-ray CT scans for most cases, due to shortcomings in the forward and inverse algorithms to handle real life usages. One obstacle stems from the fact that the forward problem must be solved numerous times for the inverse solution to reach the correct visualization. However, the current numerical method, Finite Element Method (FEM), has limitations in generating accurate solutions fast enough using economically viable computers. This limitation is mostly caused by the FEM's use of a simpler mathematical construct that requires more computations and is limited in accurately modelling the geometry and shape. This research implements the recently developed Isogeometric Analysis (IGA) and particularly IGA-based FEM to address this issue. The IGA-based FEM uses the same mathematical construct that is used to visualize the geometry for complicated applications such as some animations and computer games. They are also less complicated to apply due to much lower need for partitioning the domain. This study applies the IGA method to solve the forward problem of diffuse Optical Tomography and compare the accuracy and speed of IGA solution to the conventional FEM solution. The comparison reveals that while both methods can reach high accuracy, the IGA solutions are relatively more accurate. Also, while low accuracy FEM solutions have shorter runtimes, in solutions with required higher accuracy levels, the IGA proves to be considerably faster.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24226号 / 工博第5054号 / 新制||工||1789(附属図書館) / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 平山 朋子, 教授 岩井 裕, 教授 松原 厚 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

[pt] Hoje em dia, é crescente a utilização de expansores de pele, visando criar um excesso de pele localizado, com o qual pode-se corrigir imperfeições encontradas na pele de um paciente. Este processo, envolve um implante de uma bolsa de silicone sob a pele, sendo enchida vagarosamente, através da injeção de uma solução fluida salina. Obviamente, a pele se expande no mesmo formato da forma da bolsa implantada. Em estudos prévios já realizados, as propriedades viscoelásticas da pele expandida foram ignoradas. O objetivo deste trabalho, é modelar a pele expandida por um expansor axissimétrico e inicializar os estudos para expansores sem simetria, como um material viscoelástico, isotrópico e homogêneo. Para este fim, é utilizado o método dos elementos finitos. Na análise de elementos finitos, é usado um modelo viscoelástico linear, com três diferentes tipos de elementos, casca, membrana e elementos sólidos, procurando o melhor elemento para descrever o modelo. É realizado também, um estudo paramétrico, variando a espessura dos elementos e comparando seus resultados. Para a análise por elementos finitos, é utilizado o programa ABAQUS, sendo o método validado através de resultados numéricos já obtidos. No futuro, nossa intenção é modelar expansores de forma não axissimétricas e aplicar nosso trabalho em experimentos in- vivo. / [en] Nowadays, soft tissue expanders are being increasingly, used to create local skin flaps which can cover relatively large tissue defects. This involves inserting a silicon-rubber balloon (prosthesis) in its collapsed state under the subcutaneous tissue of the patient, closing the incision, and then inflating the balloon slowly with a saline fluid through a one way valve. The valve is part of the balloon prosthesis. Obviously, the skin expands in the form of a dome in unison with the balloon underneath it. In preliminary studies designed to evaluate the behavior of skin created by soft tissue expansion, the viscoelastic proprieties of skin were ignored. The objective of the present work is model skin as an isotropic homogeneous viscoelastic material using the finite element method for large deformation in axisymmetric expanders. In finite element analysis we are using a linear viscoelastic model with three different kinds of elements, solid, shell and membrane, looking for the best element to describe the model. We are also making a parametric study, varying the thickness of the elements and comparing the results. To develop this finite element analysis, we are using the ABAQUS program . The methods have been validated using results from previous experimental works . In the future, we intend to model non-axisymmetric expanders and apply this work to in-vivo experiments. / [es] En la actualidad, la utilización de expansores de piel está en franco crecimiento. El objetivo de esta utilización es crear un exceso de piel localizado, con el cual se pueden corregir imperfecciones encontradas en la piel de un paciente. Este proceso consiste en el implante de una bolsa de silicone bajo la piel, a través de la injección de una solución fluida salina. Obviamente, la piel se expande en el mismo formato de la forma de la bolsa implantada. En estudios previos, se ignoraron las propriedades viscoelásticas de la piel expandida. El objetivo de este trabajo es modelar la piel expandida por un expansor axisimétrico e inicializar los estudios para expansores sin simetría, como un material viscoelástico, isotrópico y homogéneo. Para este fin, se utiliza el método de los elementos finitos. En el análisis de elementos finitos, se utiliza un modelo viscoelástico lineal, con tres tipos diferentes de elementos, casca, membrana y elementos sólidos, buscando el mejor elemento para descrivir el modelo. Se realiza también un estudo paronétrico, variando la espesura de los elementos y comparando sus resultados. Para el análisis por elementos finitos, se utiliza el programa ABAQUS, y el método es evaluado a través de resultados numéricos obtenidos con anterioridad. En el futuro, nuestra intención es modelar expansores de forma no axisimétricas y aplicar nuestro trabajo en experimentos in- vivo.

[pt] A utilização da teoria clássica do contínuo, juntamente com modelos locais para as relações constitutivas, tem demonstrado inconsistência física na representação de problemas onde ocorrem localizações das deformações. Nesta tese, empregam-se teorias de contínuos generalizados para descrever de forma consistente o mecanismo de localização. Inicialmente, explora-se a estratégia que consiste de um modelo elastoplástico para o contínuo de Cosserat. Numa segunda fase, apresenta-se um refinamento da teoria, com a utilização do contínuo com microexpansão. Para os dois casos, discutem-se exemplos numéricos e, quando possível, analíticos.As teorias apresentadas são incorporadas em um p rograma de elementos finitos, que adota a filosofia de programação orientada a objetos. / [en] The use of a classical continuum theory, together with local models for the constitutive relations, leads to physical inconsistencies in the representation of strain localization.In this thesis, generalized continuum theories are used in order to describe consistently localization mechanisms.In a first stage, the micropolar theory is associated with an elasto-plastic model.In a second stage, a refinement of the micropolar theory is presented, for a microstretch continuum.For both approaches, numerical examples are discussed and, whenever is possible, analytical solutions are presented.The theories above were incorporated in a general-purpose finite element program, which was developed using the object-oriented programming approach.