Paulo Roberto de Freitas Teixeira

Geometrically nonlinear static and dynamic analysis of composite laminates shells with a triangular finite element

Geometrically nonlinear static and dynamic behaviour of laminate composite shells are analyzed in this work using the Finite Element Method (FEM). Triangular elements with three nodes and six degrees of freedom per node (three displacement and three rotation components) are used. For static analysis the nonlinear equilibrium equations are solved using the Generalized Displacement Control Method (GDCM) while the dynamic solution is performed using the classical Newmark Method with an Updated Lagrangean Formulation (ULF). The system of equations is solved using the Gradient Cojugate Method (GCM) and in nonlinear cases with finite rotations and displacements an iterative-incremental scheme is employed. Numerical examples are presented and compared with results obtained by other authors with different kind of elements and different schemes.

Constructal Design of Wave Energy Converters

The augmentation of energy demand and the Kyoto agreement to reduce the greenhouse gas emissions have increased the interest for the study of renewable energy [1]. The growth and interest in expanding the wave energy sector are based on its potential estimated to be up to 10 TW. Depending on what is considered to be exploitable, this covers from 15 to 66 % of the total world energy consumption referred to 2006 [2–4]. According to ref. [5] the wave energy level is usually expressed as power per unit length (along the wave crest or along the shoreline direction). Typical values for “good” offshore locations (annual average) range between 20 and 70 kW/m and occur mostly in moderate to high latitudes. In this sense, the southern coasts of South America, Africa, and Australia are particularly attractive for wave energy exploitation.

ESTUDO DO MODELO DE FONTE DE CALOR DE DISTRIBUIÇÃO GAUSSIANA NA APLICAÇÃO DE SIMULAÇÕES TÉRMICAS NUMÉRICAS DOS PROCESSOS DE SOLDAGEM TIG

Welding processes are considered a thermal-mechanical-metallurgical coupled issue. The most important boundary condition in the numerical thermal analysis is the heat source model. Although many studies have been carried out to propose different types of heat source models, the limitations of each model application have not been clearly specified. The Gaussian heat source is a model in which heat is generated over a surface; therefore, it may not be suitable to be applied to thick plates. In this study, the accuracy of the Gaussian heat source model is investigated in bead-on-plate welding by the TIG process. Analyses are performed by the ANSYS® software, considering the convection and the radiation phenomena. Several cases with different parameters of heat distribution, heat input and plate thickness have had their weld pool geometries analysed and compared with those obtained experimentally. Analyses of the influence of the radial distance from the center of the Gaussian heat source and the thickness of the plate on the bead width and the penetrated depth of the fusion zone boundary are presented. Results have shown the adequacy and the limitations of the Gaussian heat source model in the welding simulation. Keywords: welding process, numerical simulation, heat source model, ANSYS® software. RESUMO Os processos de soldagem sao considerados problemas termo-mecânico-metalurgicos acoplados. A condicao de contorno mais importante na analise termica numerica e o modelo de fonte de calor. Embora muitos estudos tenham sido realizados com o objetivo de propor diferentes tipos de modelos de fontes de calor, a limitacao da aplicacao de cada modelo nao e claramente conhecida. A fonte de calor Gaussiana e um modelo no qual o calor e gerado sobre uma superficie; por esta razao, ela nao e adequada para aplicacoes em chapas espessas. Neste estudo, e investigada a acuracia do modelo de fonte de calor Gaussiana em uma soldagem do tipo cordao sobre chapa pelo uso do processo TIG. As analises foram realizadas por meio do programa computacional ANSYS®, considerando os fenomenos de conveccao e de radiacao. Para diversos casos com diferentes parâmetros de distribuicao de calor, intensidades de fluxos de calor e espessuras de chapa, sao analisadas as geometrias transversais do cordao de solda e estas sao comparadas com aquelas obtidas experimentalmente. Sao apresentadas as analises das influencias da distância radial do centro da fonte de calor Gaussiana e das espessuras das chapas na largura e na penetracao do cordao de solda. Os resultados mostram a aplicabilidade e as limitacoes do modelo de fonte de calor Gaussiana na simulacao da soldagem. Palavras-chave: processo de soldagem, simulacao numerica, modelo de fonte de calor, programa computacional ANSYS®.

Regular and Irregular Wave Propagation Analysis in a Flume with Numerical Beach Using a Navier-Stokes Based Model

This paper describes the analysis of the propagation of regular and irregular waves in a flume by using Fluent® model, which is based on the Navier-Stokes (NS) equations and employs the finite volume method and the Volume of Fluid (VoF) technique to deal with two-phase flows (air and water). At the end of the flume, a numerical beach is used to suppress wave reflections. The methodology consists of adding a damping sink term to the momentum equation. In this study, this term is calibrated for three cases of regular incident waves (H = 1 m, T = 5, 7.5, and 12 s) by varying the linear and quadratic damping coefficients of the formulation. In general, while lower values of damping coefficients cause residuals on the free surface elevation due to wave interactions with the outlet boundary, reflection occurs on the numerical beach when higher values are used. A range of optimal damping coefficients are found considering one of them null. In one of these cases, temporal series of free surface elevation are compared with theoretical ones and very good agreement is reached. Afterwards, an irregular wave propagation, characterized by a JONSWAP spectrum, is investigated. Several gauges along the flume are evaluated and good agreement between the spectrum obtained numerically and the ones imposed at beginning of the flume is verified. This study shows the capacity of NS models, such as Fluent®, to simulate adequately regular and irregular wave propagations in a flume with numerical beach to avoid reflections.

A 3D Numerical Wave Tank for Coastal Engineering Studies

This paper presents the validation of active and passive, made by a dissipation beach, numerical absorbing methods implemented in RANS-VOF FLUENT® code for modelling long time series of wave propagation interacting with coastal structures. Verification of both numerical techniques was performed in 2D – wave flume, and 3D – wave tank, this one using a multiple active absorption wave makers. The active absorption wave maker allows maintaining the incident wave generation and the mean water level along the time. Good results were obtained for 2D and 3D applications for active absorption wave maker at the generation boundary and both numerical beach and active absorption at the end of the flume/tank.