EE - Artigos Publicados em Periódicos
URI permanente para esta coleçãohttps://rihomolog.furg.br/handle/1/513
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Resultados da Pesquisa
- ItemOn stochastic finite elements for structural analysis(1994) Araújo, José Milton de; Awruch, Armando MiguelThis 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.
- ItemAn objective cracking criterion for the analysis of concrete dams(1996) Araújo, José Milton de; Awruch, Armando MiguelCracking 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.
- ItemProbabilistic finite element analysis of concrete gravity dams(1998) Araújo, José Milton de; Awruch, Armando MiguelA 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.
- ItemCracking safety evaluation on gravity concrete dams during the construction phase(1998) Araújo, José Milton de; Awruch, Armando MiguelThe 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.
- ItemLocal and average transport coefficients for the turbulent flow in internally ribbed tubes(1992) Almeida, Jorge Alberto; Mendes, Paulo Roberto de SouzaHeat 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.
- ItemExperimental observation of chaotic motion in a rotor with rubbing(1998) Piccoli, Humberto Camargo; Webber, Hans IngoThis 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.
- ItemWave propagation in jettied entrance channels. II: observations(1991) Melo Filho, Eloi; Guza, RobertField 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.
- ItemWave propagation in jettied entrance channels. I: models(1991) Melo Filho, Eloi; Guza, RobertA 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.
- ItemConsiderações sobre a hidráulica de canais fluviais e de canais de maré(1998) Melo Filho, EloiEste 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.
- ItemOn the measurement of directional wave spectra at the southern Brazilian coast(1999) Alves, Jose Henrique Gomes de Mattos; Melo Filho, EloiThe 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.