Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-09-25T11:56:53Z No. of bitstreams: 1 MARCOS ANTÔNIO AMARAL LINS - TESE (PPGEP) 2013.pdf: 2840885 bytes, checksum: 13b6f2695a2ffd6be9d615430752bc2d (MD5) / Made available in DSpace on 2018-09-25T11:56:53Z (GMT). No. of bitstreams: 1 MARCOS ANTÔNIO AMARAL LINS - TESE (PPGEP) 2013.pdf: 2840885 bytes, checksum: 13b6f2695a2ffd6be9d615430752bc2d (MD5) Previous issue date: 2013-07-05 / Para muitos gêneros alimentícios, o processo de transferência de calor é essencial para se chegar à condição de consumo humano. O presente trabalho teve como objetivo estudar o fenômeno da difusão transiente de calor em alimentos pastosos contidos em recipientes cilíndricos. O estudo apresenta soluções para a equação de difusão com condição de contorno do primeiro tipo. Foram desenvolvidas ferramentas analíticas (otimizador acoplado à solução analítica) para a descrição da difusão de calor em produtos pastosos com as formas mencionadas. As ferramentas analíticas foram validadas através de dados obtidos por simulação numérica tanto para o cilindro infinito quanto para o finito. Os erros cometidos com as ferramentas desenvolvidas no cálculo da difusividade térmica aparente para os dados simulados são aceitáveis quando o sensor de temperatura é colocado na região mais interna do cilindro. Os resultados obtidos para a difusividade térmica aparente de agar gel, purê de tomate e creme custard são compatíveis com os resultados encontrados na literatura para esses produtos. O software Finite Cylinder First Kind foi desenvolvido, validado e aplicado aos dados do purê de tomate, creme custard e agar gel para várias posições no interior do cilindro finito onde estes gêneros alimentícios se encontravam. Todos os resultados obtidos por otimização e simulação tiveram uma excelente concordância com os resultados experimentais. O método numérico se mostrou mais eficiente do que o analítico, na descrição do processo de difusão de calor nos produtos estudados, devido sua versatilidade de permitir a obtenção da solução da equação de difusão considerando a difusividade térmica variável com a temperatura local. / For many foodstuffs, the process of heat transfer is essential to reach the condition human consumption. The present work aims to study the phenomenon of transient diffusion of heat in pasty foodstuffs contained in cylindrical containers. The study presents solutions for the diffusion equation with boundary condition of the first kind. Analytical tools were developed - optimizer coupled to the analytical solution - to describe the diffusion of heat into products with the forms mentioned. Analytical tools were validated using data obtained by numerical simulation for both the cylinder the infinite and finite. The tools developed minimize errors in calculating the thermal diffusivity for the simulated data are acceptable when the temperature sensor is placed in the innermost region of the cylinder. The results obtained for the thermal diffusivity of agar gel, tomato puree and cream custard are consistents with the results found in the literature for these products. The software finite cylinder first kind was developed, validated and applied to data of tomato puree, cream custard and agar gel for various positions within the finite and infinite cylinder filled with these foodstuffs. All results obtained by simulation and optimization had an excellent agreement with the experimental results. The numerical method is more efficient than the analytical description of the heat diffusion process in the products, due to their versatility that allows obtaining the solution of the diffusion equation considering the thermal diffusivity varies with local temperature.

Submitted by Lucienne Costa (lucienneferreira@ufcg.edu.br) on 2017-12-12T20:48:31Z No. of bitstreams: 1 JAIR STEFANINI PEREIRA DE ATAÍDE – TESE (PPGEP) 2014.pdf: 4947088 bytes, checksum: 8019d110744376ffaadc9a31152768ad (MD5) / Made available in DSpace on 2017-12-12T20:48:31Z (GMT). No. of bitstreams: 1 JAIR STEFANINI PEREIRA DE ATAÍDE – TESE (PPGEP) 2014.pdf: 4947088 bytes, checksum: 8019d110744376ffaadc9a31152768ad (MD5) Previous issue date: 2014-10-24 / O aumento na demanda por produtos alimentícios por parte da população requer uma indústria alimentícia moderna e de qualidade, na qual se faz necessário avaliar e ter conhecimento profundo, dentre outras coisas, das propriedades termofísicas dos alimentos, principalmente daqueles submetidos a uma tecnologia de conservação pelo uso do calor. Neste estudo, o fenômeno da difusão transiente de calor foi estudado em gêneros alimentícios pastosos contidos em recipientes com forma geométrica arbitrária. Dessa forma, tem-se o intuito de disponibilizar as análises das implicações da consideração de uma difusividade térmica constante (ou dependente da temperatura média) no estudo de transferência de calor durante a pasteurização de produtos cuja forma possa ser obtida pela revolução de áreas planas. Em adição, propôs que a difusividade térmica seja uma função da temperatura local no interior do produto, possibilitando uma maior precisão na descrição da transferência de calor. Para isso, foi discretizada e resolvida numericamente a equação de difusão escrita em coordenadas generalizadas, através do método dos volumes finitos, com uma formulação totalmente implícita, para condições de contorno de primeiro tipo. O código computacional foi desenvolvido em FORTRAN, usando o estúdio CVF 6.6.0, na plataforma Windows XP. As ferramentas numéricas foram validadas através de dados obtidos na literatura para o cilindro infinito. Para comprovação da eficiência do método de pasteurização realizou-se análises físico-químicas e microbiológicas antes e após o tratamento térmico. A análise e comparação dos resultados mostraram que ocorre uma redução dos micro-organismos totais, sem proporcionar tanta alteração nutricional, particularmente no valor proteico das polpas, proporcionando segurança alimentar com um menor gasto energético. Bem como, uma vez conhecida a expressão da difusividade térmica em função da temperatura local, é possível definir o tempo necessário para que o alimento acondicionado em um recipiente com uma geometria qualquer e simetria de revolução, entre em equilíbrio térmico com uma temperatura previamente definida, através de simulações. Dessa forma, torna-se desnecessário a realização de experimentos a cada vez que um novo recipiente for utilizado para acondicionar o produto. / The increase in demand for food products by the population requires a modern and quality food industry, where it is necessary to evaluate and have deep knowledge, among other things, the thermophysical properties of foods, especially those subjected to a conservation technology by use of heat. In this study, the phenomenon of transient heat diffusion was studied in pasty foodstuffs in containers of arbitrary geometric shape. Thus, it has been the aim of the analysis of the implications of an account (or dependent on the average temperature) to study the transfer of heat during pasteurisation of products whose shape can be obtained by the flat areas provide thermal diffusivity constant revolution. In addition, proposed that the thermal diffusivity is a function of the local temperature inside the product, providing greater precision in the description of the heat transfer. For it was discretized and numerically solved the diffusion equation written in generalized coordinates by the finite volume method with a fully implicit formulation for boundary conditions of the first kind. The computer code was developed in FORTRAN, using the CVF Studio 6.6.0 on Windows XP platform. The numerical tools were validated using data from the literature for the infinite cylinder. To prove the efficiency of the pasteurization method was carried out physicochemical and microbiological before and after heat treatment analysis. The analysis and comparison of the results showed that a reduction in total micro-organisms occurs, without providing much nutritional changes, particularly in the pulp protein value of providing food security to a lower energy expenditure. And, once known the thermal diffusivity of the expression depending on the local temperature, it is possible to set the time required for the food packed in a container with any geometry and symmetry of revolution, comes into thermal equilibrium with a previously set temperature, through simulations. Thus, it becomes unnecessary to perform experiments each time a new container is used for packaging the product.

L’objectif ultime de ce travail de thèse est d’évaluer la possibilité de valider et d’optimiser un processus de fabrication en utilisant la simulation numérique en tenant compte des incertitudes irréductibles sur le procédé, les matériaux et la géométrie du produit fabriqué. La prise en compte des incertitudes nécessite de quantifier les effets des variations des paramètres du modèle sur les sorties de celui-ci, en propageant ces variations via la simulation numérique pour évaluer leurs effets sur les sorties. Dans ce travail nous avons proposé une procédure pour déterminer le seuil de sensibilité du modèle numérique afin de construire des plans d’expériences numériques cohérents avec ce seuil. Nous avons également montré que, compte tenu des incertitudes sur les matériaux et la géométrie du produit, il est possible d’optimiser certains paramètres du procédé pour contrôler les effets des incertitudes sur les variations dimensionnelles et morphologiques du produit. Pour cela, nous avons proposé une procédure d’optimisation basée sur un algorithme NSGA-II et une méta-modélisation du procédé. L’application à l’emboutissage d’une tôle en U, retour élastique inclus, montre qu’il s’agit d’un problème de conception robuste pour lequel nous obtenons l’ensemble des compromis entre l’écart à la moyenne et l’écart type d’une fonction « performance » du procédé correctement choisie. Finalement l’analyse de ces résultats nous permet de quantifier le lien entre la notion de robustesse d’une solution optimisée du procédé et les critères de mesure de la qualité du produit / The ultimate objective of this thesis is to evaluate the possibility to validate and optimize a manufacturing process using numerical simulation and taking into account the irreducible uncertainties in the process, materials and geometry of manufactured product. Taking into account the uncertainties requires quantifying the effects of variations of model parameters on the outputs, by propagating these variations via computer simulation to assess their effects on the outputs. In this work, we have proposed a procedure to determine the sensitivity threshold of the numerical model to build numerical Design of Experiments consistent with this threshold. We have also shown that, given the uncertainties in the materials and the geometry of the product, it is possible to optimize certain process parameters to control the effects of uncertainties on the dimensional and morphological variations of the product. For this, we have proposed an optimization procedure based on NSGA-II algorithm and a meta-modeling of the process. The application for deep drawing of a U-shaped sheet metal part, springback included shows that it is a robust design problem for which we get all the compromise between the deviation from the mean and standard deviation of a "performance" depending on the process correctly chosen. Finally, the analysis of these results allows us to quantify the relationship between the notion of robustness of an optimized solution of the process and criteria for measuring the quality of the product

No description available.

Fluid-structure interaction (FSI) as the name suggests, is the study of dynamic interaction of both fluid and structure motions. Fluid-structure interaction exists in almost all engineering and science fields. Moreover, the random loading caused by fluid motions in uncertain environment conditions present new challenges to the designers. The objective of the present research work is to develop efficient and robust finite element models to solve fluid structure interaction problems effectively. A key advantage of the displacement based FE M is the flexibility and easiness in modifying the existing efficient numerical solvers, and can also be extended easily to a number of problems. The research work carried out in this thesis can be divided into three parts. In the first part, development of displacement based Lagrangian FE models for acoustic fluids is presented. Here, the displacement fields of the 2-D and 3-DFEs are derived based on the consistently assumed constrained strain fields satisfying irrotationality and incompressibility constraints simultaneously. These elements’ behaviour, in terms of number of zero energy modes, non-zero spurious modes, and the integration order is studied. The inf-sup test is carried out on all the elements to examine the performance of each formulated element. Next, a new class of FEs based on Legendre polynomials is presented. The node point locations in this case are obtained by calculating the zero’s of equation(1- ξ2)L’n(ξ) =0,where,Ln is the Legendre polynomial of order n in one dimension. In the second part, the development of a spectral layer element for studying wave propagation in acoustic fluids is presented. Laplace transform based spectral finite element formulation is developed for studying acoustic wave propagation. The partial differential equations(PDE)are converted to ordinary differential equations(ODE) by taking Laplace transform. The Laplace damping parameter is introduced for easy handling of the numerical Laplace transform(NLT).This Laplace damping parameter removes the “wraparound”problem which is present in shortwave guides due to periodicity of the Fourier transform. Later, a technique is developed through which SFEM stiffness matrix can be added to the FEM dynamic stiffness matrix in the frequency domain. Finally, Uncertainty analysis is carried out to understand the effect of randomness in the design parameters on the system response variability. Here, standard uncertainty analysis procedure called Monte Carlo simulation (MCS) is considered first and later Polynomial chaos expansion(PCE). In this analysis, the gravitational forces, bulk modulus of the fluid, and Young’s modulus of the structure are considered as random input variables in the study. The randomness in the system output is measured in terms of coefficient of variation for each random variable considered.

Main topic of this thesis are magnetic fluids. These are specific type of fluids which can simplistically be considered as Bingham fluids. Main issues regarding the magnetic fluids mentioned in this thesis are: rheological properties of the magnetic fluids, behaviour of the magnetic fluids and the use of the magnetic fluids in industrial applications. Main goal is to apply Binghams model on the the magnetic fluids assuming that this model can be applied with a good accuracy. Equations which describe behaviour of the Bingham fluids are constructed. Some assumptions which have to be respected to use this analytical equations for magnetic fluids are formulated. Flow of bingham fluid is analytically solved in some simplificated cases with consideration of laminar flow. Analytical results are confronted with numerical ones obtained from CFD software Fluent for the purpose of verification.

Los suelos blandos originan diversos problemas en el momento de las construcciones, como en las cimentaciones de distintas edificaciones u otras obras civiles. Estos tipos de suelos necesariamente tienen que ser analizados y tratados correctamente, pues, estos originan problemas a corto y largo plazo. En las décadas posteriores se han desarrollado métodos para mejorar el terreno, uno de estos métodos consiste en la construcción, sobre el suelo blando, de elementos verticales rígidos que se llaman inclusiones rígidas. Cuyo principal meta, es la mejora sobre el suelo blando, bajo bases o cimentaciones de estructuras y malos rellenos, permitiendo el desarrollo de las edificaciones con mayor velocidad y disminuyendo los asentamientos de forma sustancial. Al aplicarse esta técnica sobre el terreno blando, se disminuye el asentamiento vertical, ya que al colocarse una capa de reparto que distribuye toda la carga de la estructura se transfiere todo el peso a las inclusiones, minimizando la carga sobre el terreno blando y por consecuente el asentamiento. Como parte de esta tesis presentaremos dos métodos para estudiar el asentamiento de edificaciones que descansan sobre un suelo blando mejorado con la técnica de inclusiones rígidas. El desarrollo de la solución es completamente analítico, pero los análisis de elementos finitos se utilizan para verificar la validez de algunas suposiciones, como un modelo geométrico simplificado, la distribución de la carga con la profundidad y las condiciones de contorno. El perfil del suelo se divide en secciones horizontales independientes, y el equilibrio de las tensiones y la compatibilidad de las deformaciones se presentan en las direcciones vertical y horizontal. La solución se presenta desarrollando un análisis numérico (Plaxis) comparándolo con el método analítico (Combarte) y se puede implementar fácilmente en una hoja de cálculo. / The soft soils cause various problems at the time of construction, as in the foundations of different buildings or other civil works. These types of soils necessarily have to be analyzed and treated correctly, as these cause short and long term problems. In the last decades methods have been developed for the improvement of the land, one of these methods consists of the introduction or construction in the soft soil of rigid vertical elements that are called inclusions. Its main application is in soils under large landfills or foundations of structures, allowing the construction of buildings with greater speed and decreasing settlements considerably. By applying this technique on the soft ground, vertical settlement is reduced, since by placing a distribution layer that distributes the entire load of the structure, all the weight is transferred to the inclusions, minimizing the load on the soft ground and consequently settlement. As part of this thesis we will present two methods to study the settlement of buildings that rest on a soft soil improved with the technique of rigid inclusions. The development of the solution is completely analytical, but the finite element analyzes are used to verify the validity of some assumptions, such as a simplified geometric model, the distribution of the load with the depth and the boundary conditions. The floor profile is divided into independent horizontal sections, and the balance of the stresses and the compatibility of the deformations are presented in the vertical and horizontal directions. The solution is presented by developing a numerical analysis (Plaxis) comparing it with the analytical method (Combarieu) and can be easily implemented in a spreadsheet. / Tesis

[pt] Esta dissertação estuda o comportamento dinâmico não linear de colunas de perfuração de poços de petróleo. A coluna de perfuração é uma estrutura longa, flexível e esbelta, responsável pela perfuração propriamente dita. Seus elementos e funções são apresentados e uma análise numérica é realizada posteriormente. Foi desenvolvido um programa utilizando o software MATLAB (marca registrada) para simulação numérica do comportamento dinâmico das colunas pelo método dos elementos finitos que utiliza a formulação corotacional para implementação da não linearidade geométrica. A discretização da estrutura utiliza um elemento de viga com seis graus de liberdade por nó aplicando a formulação de viga de Euler-Bernoulli. Para solução do sistema de equações não lineares resultante utiliza-se o método de Newton-Raphson. Além disso, o método de Newmark é utilizado para integração no tempo das equações de movimento do problema. Um modelo com molas lineares é proposto para representar o contato entre a parede do poço e a coluna. A metodologia proposta e as funcionalidades do programa desenvolvido são avaliadas e seus resultados são comparados com algumas soluções analíticas ou numéricas de exemplos disponíveis na literatura. Esses resultados conferem confiabilidade na análise de problemas de coluna de perfuração, que apresentam as séries temporais de deslocamentos e esforços em toda a coluna e os modos de flambagem gerados. Os resultados obtidos demonstram que a coluna é muito sensível a qualquer mudança de condição de contorno, o que corrobora com a complexidade do problema. Assim, o trabalho fornece uma base razoável para desenvolvimentos posteriores, que permitam a análise de toda a coluna de perfuração acoplada. / [en] This work studies the nonlinear dynamic behavior of oil well drillstring, which is a long slender flexible structure responsible for the drilling. Its elements and functions are presented, and numerical analyses are performed later. The work develops a computational code using the software MATLAB (trademark) for the numerical simulation of the column s dynamic behavior using the finite element method. The corotational formulation is used for the implementation of geometric nonlinearity. The structure s discretization uses a beam element with six degrees of freedom per node and employs the Euler-Bernoulli s beam formulation. The Newton-Raphson method is responsible for solving the nonlinear system of equations. In addition, the solution procedure uses the Newmark s method for the time integration of the problem s movement equations. A linear setup spring model is proposed to represent the contact between the borehole wall and the column. The proposed methodology and computational code capabilities are evaluated by comparing some results to analytical or numerical results of examples available in the literature. These results give reliability to analyze drillstring problems, which present the displacements and forces time series of the whole column and the buckling modes generated. The results show that the column is very sensitive to any boundary condition changing, which corroborates the complexity of the problem. Hence, the work proposes a reasonable basis for further developments, allowing the entire coupled drillstring analysis.

<div>On rectangular meshes, the simplest spectral element method for elliptic equations is the classical Lagrangian <i>Q</i>^k finite element method with only (<i>k</i>+1)-point Gauss-Lobatto quadrature, which can also be regarded as a finite difference scheme on all Gauss-Lobatto points. We prove that this finite difference scheme is (<i>k</i> + 2)-th order accurate for <i>k</i> ≥ 2, whereas <i>Q</i>^<i>k</i> spectral element method is usually considered as a (<i>k</i> + 1)-th order accurate scheme in <i>L²</i>-norm. This result can be extended to linear wave, parabolic and linear Schrödinger equations.</div><div><br></div><div><div>Additionally, the <i>Q^k</i> finite element method for elliptic problems can also be viewed as a finite difference scheme on all Gauss-Lobatto points if the variable coefficients are replaced by their piecewise <i>Q^k </i>Lagrange interpolants at the Gauss Lobatto points in each rectangular cell, which is also proven to be (<i>k</i> + 2)-th order accurate.</div></div><div><br></div><div><div>Moreover, the monotonicity and discrete maximum principle can be proven for the fourth order accurate Q2 scheme for solving a variable coefficient Poisson equation, which is the first monotone and high order accurate scheme for a variable coefficient elliptic operator.</div></div><div><br></div><div><div>Last but not the least, we proved that certain high order accurate compact finite difference methods for convection diffusion problems satisfy weak monotonicity. Then a simple limiter can be designed to enforce the bound-preserving property when solving convection diffusion equations without losing conservation and high order accuracy.</div><div><br></div></div>

In this thesis, we first propose a new scalar auxiliary variable (SAV) approach for general dissipative nonlinear systems. This new approach is half computational cost of the original SAV approach, can be extended to high order unconditionally energy stable backward differentiation formula (BDF) schemes and not restricted to the gradient flow structure. Rigorous error estimates for this new SAV approach are conducted for the Allen-Cahn and Cahn-Hilliard type equations from the BDF1 to the BDF5 schemes in a unified form. As an application of this new approach, we construct high order unconditionally stable, fully discrete schemes for the incompressible Navier-Stokes equation with periodic boundary condition. The corresponding error estimates for the fully discrete schemes are also reported. Secondly, by combining the new SAV approach with functional transformation, we propose a new method to construct high-order, linear, positivity/bound preserving and unconditionally energy stable schemes for general dissipative systems whose solutions are positivity/bound preserving. We apply this new method to second order equations: the Allen-Cahn equation with logarithm potential, the Poisson-Nernst-Planck equation and the Keller-Segel equations and fourth order equations: the thin film equation and the Cahn-Hilliard equation with logarithm potential. Ample numerical examples are provided to demonstrate the improved efficiency and accuracy of the proposed method.