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Optimization of newton-raphson methods in RC nonlinear analysis
(1989) Araújo, José Milton de
The Newton-Raphson method is used for the nonlinear analysis of reinforced concrete structures. Three extrapolation formulas for displacements are developed in order to accelerate the convergence of the iterative scheme. The computing time and the number of necessary iterations for each proposed alternative are compared.
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Wave propagation in jettied entrance channels. II: observations
(1991) Melo Filho, Eloi; Guza, Robert
Field measurements of surface gravity waves along the center line of the straight, 1 km long, 8 m deep, 250 m wide Mission Bay entrance channel (bounded by rubble-mound jetties) are compared to a model developed in a companion paper by Melo and Guza. The observations show a rapid downchannel decay of wave energy. Additionally, the observed ratio of significant wave heights between any two stations along the channel axis is rather constant despite the different wave and current conditions encountered. The model, with all empirical coefficients determined with existing parameterizations, agrees qualitatively well with these observations. These model results are insensitive to the details of the motions and dissipation occurring within the jetties so long as an appropriate amount of energy is lost at these lateral boundaries. The wave height on the center line of a wide channel with highly absorptive jetties is controlled by diffraction. In fact, the observations and model results on the center line at Mission Bay are similar to previously published simplified models with the jetties replaced by strips of appropriate bottom dissipation and also to the decay along the center line of a breakwater gap with the gap width equal to the entrance channel width.
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Wave propagation in jettied entrance channels. I: models
(1991) Melo Filho, Eloi; Guza, Robert
A model for the propagation of sea and swell waves in a channel bounded by rubble-mound jetties is presented. The model combines elements of earlier work on waves normally incident on a breakwater with a modified diffraction model based on the linear mild-slope equation. For grazing-angle (relative to the jetty axis) wave incidence, a parabolic approximation to the governing equation is used to obtain numerical solutions for monochromatic long waves propagating down the channel. An initially plane wave evolves into a spatially complex pattern as dissipation occurs along the jetties and energy is drawn from the channel interior by diffraction. Comparisons of the model to field observations are presented in a companion paper.
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Local and average transport coefficients for the turbulent flow in internally ribbed tubes
(1992) Almeida, Jorge Alberto; Mendes, Paulo Roberto de Souza
Heat transfer coefficients and pressure drop data were determined experimentally for the turbulent flow in circular ducts equipped with internal transverse ribs, that is, ribs normal to the flow. Both fully developed and entrance region results were obtained. Also, both local and per-cycle average heat transfer results were determined. The naphthalene sublimation technique was employed in the experiments. The effects of rib height, rib spacing, and Reynolds number were investigated. The friction factor is shown to increase with rib height and to decrease with rib spacing in the range investigated. The local heat transfer results revealed, for most cases investigated, that the film coefficient in a cycle increases in the axial direction up to a maximum value. Then it decreases mildly up to a local minimum, increasing from this axial position to the" end of the cycle.
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On stochastic finite elements for structural analysis
(1994) Araújo, José Milton de; Awruch, Armando Miguel
This paper considers the stochastic finite element analysis of structures resulting from random spatial variability of material properties, when they are subjected to loads of deterministic nature. Direct Monte Carlo simulation, Monte Carlo with Neumann expansion of the stiffness matrix and Taylor series expansion combined with the classical finite element approach are applied and compared with respect to accuracy and computational efficiency. Dynamic and non-linear problems are also included.
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An objective cracking criterion for the analysis of concrete dams
(1996) Araújo, José Milton de; Awruch, Armando Miguel
Cracking analysis by the finite element method may be accomplished using a continuum damage theory, but results are strongly affected by the adopted finite element mesh. A reduced tensile strength has been proposed in order to obtain objective results; however this approach may still be dependent on the adopted finite element mesh. An alternative model for concrete cracking, which is independent of the finite element mesh and especially suitable for the analysis of concrete dams, is proposed in this work.
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Experimental observation of chaotic motion in a rotor with rubbing
(1998) Piccoli, Humberto Camargo; Webber, Hans Ingo
This paper presents an application for chaotic motion identification in a measured signal obtained in an experiment. The method of state space reconstruction with delay co-ordinates with the dynamic evolution described by a map is used. Poincar e diagrams, correlation dimensions and Lyapunov exponents are obtained as tools for deciding about the existence of chaotic behaviour. The method is applied to measurements of the lateral displacement of a vertical rotor experiencing rubbing and in some signals chaos is observed. The work concludes that the possibility of chaotic motion is well determined with the observation of Poincar ́e diagrams and computation of Lyapunov exponents. Correlation dimensions computations, strongly influenced by noise, are not convenient tools for investigation of chaotic behaviour in signals generated by mechanical systems.
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Probabilistic finite element analysis of concrete gravity dams
(1998) Araújo, José Milton de; Awruch, Armando Miguel
A methodology for the probabilistic analysis of concrete gravity dams is presented, Concrete properties and seismic excitation are considered as random variables. The seismic excitation is considered as a non-stationary stochastic process which is artificially generated. Concrete properties have random variations over the spatial domain. Structural response is obtained employing the finite element method to solve the equations of motion of the coupled system dam-reservoir-foundation. Structural safety is evaluated with respect to the main failure modes (cracking, concrete crushing and sliding at the dam-foundation interface) using the Monte Carlo method.
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Cracking safety evaluation on gravity concrete dams during the construction phase
(1998) Araújo, José Milton de; Awruch, Armando Miguel
The cracking phenomenon in concrete gravity dams during the construction phase is analysed in this work. Stresses due to the self-weight of the dam, thermal gradients, creep and drying shrinkage are computed, taking into account the different stages of the construction process. A twodimensional constitutive model considering time dependent and temperature dependent mechanical properties is adopted for the concrete. Safety against cracking is obtained using a criterion independent of the finite element mesh.
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Considerações sobre a hidráulica de canais fluviais e de canais de maré
(1998) Melo Filho, Eloi
Este trabalho apresenta uma contribui- ção no sentido de inserir o tópico canais de maré no escopo da hidráulica de canais tradicional. As peculiaridades próprias dos escoamentos em canais fluviais e em canais de maré são discutidas e comparadas tanto do ponto de vista físico quanto do matemático. Alguns tópicos específicos são tratados em detalhe: as equações de Saint-Venant são comparadas às equações de Águas Rasas; uma abordagem alternativa à tradicional para escoamentos permanentes em canais fluviais é apresentada; a possibilidade de ocorrência de escoamentos super-críticos em canais de maré é analisada e algumas propriedades peculiares às ondas de cheias e às ondas de maré são revisadas e discutidas.
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On the measurement of directional wave spectra at the southern Brazilian coast
(1999) Alves, Jose Henrique Gomes de Mattos; Melo Filho, Eloi
The detailed reconstruction of the directional spectrum of wind waves from measurements of the wave field is an essential requirement for several applications, including the numerical modeling of wave evolution. Three reconstruction techniques that provide estimates of the directional distribution function D f ;u ; given the one-dimensional frequency spectrum, are compared using data from a coastal locality at the southern Brazilian coast. The techniques are the maximum entropy method (MEM), the Fourier Expansion Method using a cos2 type function (FEMcos) and the Fourier Expansion Method using a sech type function (FEMsech). The main patterns of the wave climate at the study site are qualitatively assessed. Three main sea states, including swell, transition between local sea and swell, and directionally bimodal wind sea, are identified. Time series from three events associated with the main sea states provide test cases for inter comparison of the three reconstruction techniques. Maximum entropy estimates of D f ;u provide results that are more consistent than those obtained from the two FEM techniques in all cases considered. q1999 Elsevier Science Ltd. All rights reserved.
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Metodologia para obtenção de modelos de vida útil em estrutura marítima de concreto com idade avançada
(2000) Guimarães, André Tavares da Cunha; Helene, Paulo Roberto do Lago; Quarcione, Valdecir Angelo
Esse trabalho tem por objetivo o desenvolvimento de método para a obtenção de modelos de durabilidade em estruturas de concreto armado localizadas em ambiente marítimo. Este método foi desenvolvido realizando-se medições de profundidades de ataque de anidrido carbônico, íons cloreto e sulfato na estrutura de concreto do cais do Terminal de Conteiners localizado no complexo portuário da cidade do Rio Grande – RS, construção essa com 22 anos de idade. A partir das profundidades de ataque dos agentes agressivos e da idade da estrutura pesquisada são elaborados modelos em forma de ábacos onde obtém-se valores de cobrimentos das barras de aço em função da vida útil estabelecida em projeto para zona de névoa, zona de respingo e zona de maré. Os resultados obtidos são consistentes, sendo a aplicação do método indicada para outros ambientes litorâneos, permitindo a obtenção de dados em diversos locais ao longo da costa brasileira e a geração de modelos mais precisos no futuro. Para tal, é indispensável a padronização dos métodos de pesquisa para que dados de diversas trabalhos possam ser confrontados.
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O módulo de deformação longitudinal do concreto
(2000) Araújo, José Milton de
Neste trabalho é feito um estudo sobre a correlação existente entre o módulo de deformação longitudinal do concreto e sua resistência à compressão. Diversos resultados experimentais disponíveis na bibliografia são utilizados para testar a validade de algumas fórmulas de projeto. Em particular, são analisadas as fórmulas propostas pelo CEB, pelo ACI e a fórmula proposta no projeto de reformulação da norma brasileira NBR-6118. Do estudo realizado, conclui-se que a fórmula do CEB é a que melhor representa a correlação entre o módulo de deformação longitudinal e a resistência à compressão do concreto.
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A avaliação da erodibilidade dos solos sob o enfoque geotécnico – pesquisas e tendências
(2000) Bastos, Cezar Augusto Burkert; Milititsky, Jarbas; Gehling, Wai Ying Yuk
A erodibilidade, particularizada como a susceptibilidade a erosão hídrica por fluxo superficial concentrado, é uma das propriedades de comportamento dos solos de maior complexidade pelo grande número de variáveis intervenientes. Estudada por diferentes áreas do conhecimento (Agronomia, Hidráulica, Geologia de Engenharia e Engenharia Geotécnica), tem no meio geotécnico a maior lacuna na sua quantificação e entendimento dos mecanismos envolvidos. O artigo traz uma revisão das pesquisas geotécnicas referentes a avaliação da erodibilidade dos solos destacando os avanços recentes e tendências futuras.
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Proposta metodológica de um banco de dados geotécnicos para uso em Sistema de Informações Geográfica (SIG) e sua aplicação no município de Porto Alegre, RS
(2000) Valente, Antônio Luís Schifino
Este trabalho apresenta uma proposta metodológica de estruturação de um banco de dados digital para armazenamento, fácil consulta e visualização de parâmetros e informações sobre o meio físico de interesse na Geotecnia. A estruturação do banco de dados visa também a sua conexão a um Sistema de Informações Geográficas (SIG), com a finalidade de introduzir uma componente espacial às informações armazenadas. Para área teste é escolhido o município de Porto Alegre (RS).
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Grau de saturação do concreto: um importante fator na difusão de cloretos
(2001) Guimarães, André Tavares da Cunha; Helene, Paulo Roberto do Lago
Em pesquisas anteriores [5, 6] observam-se altos teores cloretos (2%/cimento) na superfície externa de elementos de concreto armado localizados em ambiente marítimo e em zona predominantemente de névoa. Entretanto a frente de ataque por cloretos está em uma profundidade baixa para a classe de concreto utilizada. Por observações, suspeita-se da influência do teor de umidade sobre a difusividade de cloretos. Sendo assim, é desenvolvido ensaio com o objetivo de avaliar a variação do coeficiente de difusão dos cloretos com a variação do teor de umidade da pasta de cimento. Conclui-se que o Grau de Saturação (GS)(percentual do teor de umidade da pasta de cimento em relação a absorção máxima) tem grande influência sobre a difusividade de cloretos da pasta de cimento endurecida, sendo que esse fator deve ser levado em conta na previsão de vida útil de uma estrutura de concreto armado.
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Three-dimensional simulation of high compressible flows using a multi-time-step integration technique with subcycles
(2001) Teixeira, Paulo Roberto de Freitas; Awruch, Armando Miguel
An algorithm to simulate three-dimensional high compressible flows using the finite element method and a multi-time-step integration technique with subcycles is presented in this work. An explicit two-step Taylor–Galerkin scheme is adopted to integrate in time the continuum equations. When explicit schemes are used, the time-steps must satisfy the CFL stability conditions. If the smallest critical time-step is adopted uniformly for the whole domain, the integration scheme may consume a large amount of CPU time. Multi-time-step integration techniques are very suitable in these cases because elements and nodes are separated into several groups and a different time-step is assigned to each group. In this way, each group of elements is integrated with a time interval which is much closer to the critical time-steps of the elements in the group. This results in great computational savings, mainly when element sizes and properties are very different, leading to significant differences in the local critical time-step values. Multi-time-steps integration techniques are also very useful in transient problems, taking into account that at the end of each subcycle, values of the unknowns at the same time level are obtained. The multi-time-step algorithm is applied to analyze the supersonic flow (Mach=8.5) past a sphere immersed in a non-viscous flow, and the results and computational performance are compared with those obtained when a uniform time-step is used over the whole domain.
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Estimativa da suscetibilidade potencial à erosão laminar devido a fatores naturais: uma proposta metodológica e sua aplicação no município de Porto Alegre (RS)
(2001) Valente, Antônio Luís Schifino; Koppe, Jair Carlos; Risso, Alfonso; Bastos, Cezar Augusto Burkert; Striedler, Adelir José; Dias, Regina Davison
Este trabalho apresenta uma proposta metodológica para estimativa, por meio de técnicas de geoprocessamento, da suscetibilidade potencial à erosão laminar devido a fatores naturais. O método utiliza a integração de dados referentes a aspectos naturais do meio físico, considerados na Equação Universal de Perdas dos Solos. Por meio de um Sistema de Informações Geográficas (SIG), em especial, o software IDRISI, são cruzadas informações sobre erosividade da chuva, erodibilidade do solo e fator topográfico. Para a determinação do fator topográfico são utilizadas técnicas de modelagem digital do terreno e o método proposto por Risso & Chevallier [13]. Como resultado é apresentado o mapa da suscetibilidade potencial à erosão laminar devido a fatores naturais, na escala 1:50.000, para o município de Porto Alegre (RS).
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Probabilistic analysis of reinforced concrete columns
(2001) Araújo, José Milton de
The subject of this work is the probabilistic finite element analysis of reinforced concrete columns. Concrete properties are represented as homogeneous Gaussian random fields. The yield stress and position of steel reinforcement, dimensions of the column cross-section and axial load are considered as random variables. The Monte Carlo method is employed to obtain expected values and standard deviations of the rupture load. The partial safety factors method is used for columns design and structural safety is evaluated by means of the reliability index, which is obtained through simulations. The effects of main parameters on the reliability index are investigated. It is shown that the correlation length of random fields for concrete properties may have a significant effect on reliability. Therefore, simplified procedures, which do not consider spatial variations of concrete properties are inappropriate for safety analysis.
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Measurement and modeling of wind waves at the northern coast of Santa Catarina, Brazil
(2001) Alves, Jose Henrique Gomes de Mattos; Melo Filho, Eloi
Directional measurements of wind-wave spectra made during the year of 1996 are used in a preliminary investigation of the wind-wave climate and its transformation at the São Francisco do Sul island, northern coast of the Santa Catarina state. Four major sea states and associated meteorological conditions are identified through analyses of joint distributions of observed wave parameters. Transformations of these main sea-state patterns due to refraction and shoaling are investigated through a numerical modeling approach that allows the reconstruction of the wave field within extensive coastal areas, using single point measurements of the wave spectrum in shallow waters. Cross-validation of measured and reconstructed spectra at the study site yield consistent results, suggesting that the proposed methodology works well for the São Francisco do Sul coast.