Alternate treatments of jacobian singularities in polar coordinates within finite-difference schemes

Jacobian singularities of differential operators in curvilinear coordinates occur when the Jacobian determinant of the curvilinear-to-Cartesian mapping vanishes, thus leading to unbounded coefficients in partial differential equations. Within a finite-difference scheme, we treat the singularity at the pole of polar coordinates by setting up complementary equations. Such equations are obtained by either integral or smoothness conditions. They are assessed by application to analytically solvable steady-state heat-conduction problems.

Properties of individual YBCO layers in a two-layered design for energy-efficient digital data cables

We are developing two-layered Yttrium Barium Copper Oxide (YBCO) thin film structures for energy efficient data links for superconducting electronics and present the results of their property measurements. High temperature superconductors (HTS) are advantageous for the implementation of energy-efficient cables interconnecting low temperature superconductor-based circuits and other cryogenic electronics circuits at higher temperature stages. The advantages of the HTS cables come from their low loss and low dispersion properties, allowing ballistic transfer of low power signals with very high bandwidth, low heat conduction and negligible inter-line crosstalk. The microstrip line cable geometry for typical materials is a two-layered film, in which the two superconducting layers are separated by an insulation layer with a minimized permittivity. We have made a proof of concept design of two YBCO films grown by pulsed laser deposition and then assembled into a sandwich with uniform insulating interlayer of tens of micrometers thick. We report on results obtained from such systems assembled in different ways. Structural and electromagnetic properties have been examined on individual films and on the corresponding sandwich composite. © 2013 IEEE.

Análise numérica de evaporadores do tipo Roll-Bond usados em refrigeradores domésticos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Um algoritmo para a construção de superfícies potenciais de falha em sólidos tridimensionais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise termoelástica experimental e computacional por elementos finitos da parede externa em concreto armado de um forno de cozimento de anodo

Nesta dissertação foi desenvolvido um estudo sobre o comportamento de uma estrutura em concreto armado submetida a elevadas variações térmicas. A estrutura analisada consiste na parede externa de um forno de cozimento de anodo utilizado na produção de Alumínio, e está submetida a variações térmicas de cerca de 125C devido à própria operação do forno. As motivações principais para o estudo foram a ocorrência de grandes deformações e o surgimento de fissuras na estrutura, o que poderia provocar a inutilização do forno. O objetivo do trabalho foi a investigação das causas destas patologias, assim como o estabelecimento de propostas para reforço da estrutura. Para isso, foram realizados estudos experimentais e computacionais do comportamento da estrutura. Inicialmente, a estrutura foi monitorada utilizando-se transdutores de deslocamento e sensores de temperatura (termopares), conectados a um sistema de aquisição de dados para obtenção e armazenamento automática das amostras ao longo do tempo. Em seguida, foram desenvolvidos modelos computacionais em Elementos Finitos com auxilio do programa computacional Algor, para determinação da distribuição de temperatura e as correspondentes tensões e deformações de origem térmica na estrutura. Nestes estudos, foram realizadas análises estacionárias e transientes de condução de calor, seguidas de análises de tensões de origem térmica. Como conclusão do estudo, tem-se que a metodologia proposta para a solução do problema foi bastante satisfatória, solucionando o problema de forma precisa, porém econômica.

Aplicação da computação simbólica na resolução de problemas de condução de calor em cilindros vazados com condições de contorno convectivas

Pós-graduação em Engenharia Mecânica - FEG

A local-global scheme for tracking crack path in three-dimensional solids

This paper aims to contribute to the three-dimensional generalization of numerical prediction of crack propagation through the formulation of finite elements with embedded discontinuities. The analysis of crack propagation in two-dimensional problems yields lines of discontinuity that can be tracked in a relatively simple way through the sequential construction of straight line segments oriented according to the direction of failure within each finite element in the solid. In three-dimensional analysis, the construction of the discontinuity path is more complex because it requires the creation of plane surfaces within each element, which must be continuous between the elements. In the method proposed by Chaves (2003) the crack is determined by solving a problem analogous to the heat conduction problem, established from local failure orientations, based on the stress state of the mechanical problem. To minimize the computational effort, in this paper a new strategy is proposed whereby the analysis for tracking the discontinuity path is restricted to the domain formed by some elements near the crack surface that develops along the loading process. The proposed methodology is validated by performing three-dimensional analyses of basic problems of experimental fractures and comparing their results with those reported in the literature.

Transferência de calor inversa do método convencional e do otimizado de lubri-refrigeração na retificação plana tangencial

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Termodinâmica de um conjunto de partículas em um bilhar bidimensional dependente do tempo: um gás bidimensional simplificado

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Existence of Solutions for Abstract Non-Autonomous Neutral Differential Equations

In this paper we discuss the existence of mild and classical solutions for a class of abstract non-autonomous neutral functional differential equations. An application to partial neutral differential equations is considered.

EXISTENCE OF SOLUTIONS FOR A FRACTIONAL NEUTRAL INTEGRO-DIFFERENTIAL EQUATION WITH UNBOUNDED DELAY

In this article, we study the existence of mild solutions for fractional neutral integro-differential equations with infinite delay.

A swirler stabilized combustion chamber for a micro-gas turbine fuelled with natural gas

Micro-gas turbines are a good alternative for on-site power generation, since their operation is very reliable. The possibility of operating with various fuels increases versatility and, as a result, the usage of these devices. Focusing on a performance improvement of a tri-fuel low-cost micro-gas turbine, this work presents investigations of the inner flow of its combustion chamber. The aim of this analysis was the characterization of the flame structure by the temperature field of the chamber inner flow. The chamber was fuelled with natural gas. In the current chamber, a swirler and a reversed flow configuration were utilized to provide flame stabilization. The inner flow investigations were done with numerical analysis, which were compared to experimental data. The analysis of the inner flow was done with numerical simulations, which used the RSM turbulence model. A β-PDF equilibrium model was adopted to account for the turbulent combustion process. Different models of heat transfer were compared. Thermal radiation and specially heat conduction in the liner walls played significant roles on results.

Comparative theoretical analysis of continuous wave laser cutting of metals at 1 and 10 um wavelength

We present a derivation and, based on it, an extension of a model originally proposed by V.G. Niziev to describe continuous wave laser cutting of metals. Starting from a local energy balance and by incorporating heat removal through heat conduction to the bulk material, we find a differential equation for the cutting profile. This equation is solved numerically and yields, besides the cutting profiles, the maximum cutting speed, the absorptivity profiles, and other relevant quantities. Our main goal is to demonstrate the model’s capability to explain some of the experimentally observed differences between laser cutting at around 1 and 10 μm wavelengths. To compare our numerical results to experimental observations, we perform simulations for exactly the same material and laser beam parameters as those used in a recent comparative experimental study. Generally, we find good agreement between theoretical and experimental results and show that the main differences between laser cutting with 1- and 10-μm beams arise from the different absorptivity profiles and absorbed intensities. Especially the latter suggests that the energy transfer, and thus the laser cutting process, is more efficient in the case of laser cutting with 1-μm beams.

A new boundary condition solved with B.I.E.M.

Among the classical operators of mathematical physics the Laplacian plays an important role due to the number of different situations that can be modelled by it. Because of this a great effort has been made by mathematicians as well as by engineers to master its properties till the point that nearly everything has been said about them from a qualitative viewpoint. Quantitative results have also been obtained through the use of the new numerical techniques sustained by the computer. Finite element methods and boundary techniques have been successfully applied to engineering problems as can be seen in the technical literature (for instance [ l ] , [2], [3] . Boundary techniques are especially advantageous in those cases in which the main interest is concentrated on what is happening at the boundary. This situation is very usual in potential problems due to the properties of harmonic functions. In this paper we intend to show how a boundary condition different from the classical, but physically sound, is introduced without any violence in the discretization frame of the Boundary Integral Equation Method. The idea will be developed in the context of heat conduction in axisymmetric problems but it is hoped that its extension to other situations is straightforward. After the presentation of the method several examples will show the capabilities of modelling a physical problem.

Simulation of Temperatures and Stresses during Construction of a RCC Dam

Se describen las variaciones de temperaturas y de tensiones durante la construcción de presas de hormigón compactado. The curing of concrete is an exothermic process. The heat of hydration generated induces temperature increases in the concrete, which will disappear in the long term by heat conduction in the concrete mass and thermal exchanges with the environment. The problem is of particularly interest for large concrete masses, as is the case of dams, because the time involved in the heat diffusion process grows with the square of the dimensions and a hotter dam interior implies the possibility of cracking the exposed surfaces of the dam. The Cuira dam, currently being built in Venezuela using roller compacted concrete, is a 134 m high, arch-gravity dam. In support of the design, different strategies were analysed, including various combinations of cooling of the water and the aggregate in order to achieve acceptable results. The calculations were conducted with Abaqus, taking into account all the necessary mechanical and thermal characteristics, as well as the relevant non-linearities. The analyses led to the conclusion that no cooling was required, even taking into account the stress state imposed by an early and rapid filling of the reservoir.