J. A. Souza

Numerical Study of the Effect of the Relative Depth on the Overtopping Wave Energy Converters According to Constructal Design

The conversion of wave energy in electrical one has been increasingly studied. One example of wave energy converter (WEC) is the overtopping device. Its main operational principle consists of a ramp which guides the incoming waves into a reservoir raised slightly above the sea level. The accumulated water in the reservoir flows through a low head turbine generating electricity. In this sense, it is performed a numerical study concerned with the geometric optimization of an overtopping WEC for various relative depths: d/λ = 0.3, 0.5 and 0.62, by means of Constructal Design. The main purpose is to evaluate the effect of the relative depth on the design of the ramp geometry (ratio between the ramp height and its length: H1/L1) as well as, investigate the shape which leads to the highest amount of water that insides the reservoir. In the present simulations, the conservation equations of mass, momentum and one equation for the transport of volumetric fraction are solved with the finite volume method (FVM). To tackle with water-air mixture, the multiphase model Volume of Fluid (VOF) is used. Results showed that the optimal shape, (H1/L1)o, has a strong dependence of the relative depth, i.e., there is no universal shape that leads to the best performance of an overtopping device for several wave conditions.

Resin Transfer Molding Process: Fundamentals, Numerical Computation and Experiments

Resin Transfer Molding (RTM) is one of the most widely known composite manufacturing technique of the liquid molding family, being extensively studied and used to obtain advanced composite materials comprised of fibers embedded in a thermoset polymer matrix. The fibrous reinforcement is considered a porous medium regarding its infiltration by the polymer resin. In this sense, this chapter aims to briefly discuss multiphase flow and heat transfer theory in RTM process, focusing on a multifluid model and the Control Volume/Finite Element (CV/FE) method. Finally, computational analysis was developed on the basis of ANSYS CFX® and PAM-RTM commercial software’s for the investigation of the fluid flow in RTM composite molding. In order to show the versatility and performance of the commercial codes, RTM experiments were carried under distinct injection pressure and fiber volume fraction conditions using plain-weave glass fiber cloth as the porous media. The transient numerical simulations provided information about volume fraction, pressure and velocity distribution of the phases (resin and air) inside the porous media.

Evaluation of mechanical properties of sandwich structures with polyethylene terephthalate and polyvinyl chloride core

Sandwich structures are comprised of two external faces/skins (usually made of synthetic fiber/resin) and a core, being lightweight and with high stiffness. These structures when based on a foam core are commonly processed using liquid molding techniques. In this study, the light resin transfer molding process is used to inject the polymeric resin (vinyl ester) into the porous cavity between the impermeable core and the mold walls. The main goal of the present work is to study the effect of different types of cores (polyvinyl chloride (PVC) and polyethylene terephthalate) and faces (glass fiber cloths or mats) on the mechanical characteristics of the sandwich structures. Specimens were subjected to flexural, flatwise and edgewise compression, and Shore-D hardness testing. General comparison between the different core materials indicated higher flatwise compressive, flatwise tensile and shear strength of the PVC. However, the effect of the core on the properties of the sandwich structure, e.g. flatwise compressive and edgewise compressive strength, was much less evident.

Design of Cooling Cavities by the Application of the Constructal Design

This paper develops a numerical study about the geometry of isothermal cavities in solid bodies with internal heat generation. The solid is constituted of a isotropic material, with low thermal conductivity, and adiabatic external surfaces. The cavity is used to dissipate the internally generated heat. An evolutionary algorithm is proposed, based on Constructal Theory, that builds a cavity able to maximize the heat transfer between the solid body and the ambient. Initial solid geometry (a squared fin) is divided into smaller squared elements (regions) that will be remove in order to build the cavity. First element is removed from the bottom center of the geometry and other elements are, at every step, removed so that minimize the hot spots in the solid domain. At every stage of the building process, thermal diffusion equation is numerically solved by the finite element method (FEM). The cavity construction must be flexible so that it freely progresses (evolves) in direction to the hot spots. Results show that the smaller the elements (resolution) used in the cavity construction the lower will be the maximum temperature. Besides that, present results are compare with similar works for cavities C, H, X e Y, presented in literature, showing that current methodology is very efficient in minimizing maximum solid internal temperature.

Numerical Analysis of the Resin Transfer Molding Process via PAM-RTM Software

This work aims to investigate the infiltration of a CaCO3 filled resin in fibrous porous media (resin transfer molding process) using the PAM-RTM software. A preform of glass fiber mat (fraction 30%), with dimensions 320 x 150 x 3.6 mm, has been used in rectilinear injection experiments conducted at room temperature and injection pressure 0.25, 0.50 and 0.75 bar. The polyester resin contain 0% and 40% CaCO3. The numerical results were evaluated by direct comparison with experimental data. The flat flow-front profile of the rectilinear flow was reached approximately half length of the mold. It was observed, that the both velocity infiltration and permeability have decreased with increasing the CaCO3 content, thus, increasing the time to processing of the composite material.

Resin transfer molding process: a numerical analysis

This work aims to investigate the infiltration of a CaCO3 filled resin using experiments and the PAM-RTM software. A preform of glass fiber mat, with dimensions 320 x 150 x 3.6 mm, has been used for experiments conducted at room temperature, with injection pressure of 0.25bar. The resin contained 10 and 40% CaCO3 content with particle size 38μm. The numerical results were evaluated by direct comparison with experimental data. The flat flow-front profile of the rectilinear flow was reached approximately halfway the length of the mold. It was observed, that the speed of the filling decreases with increasing CaCO3 content and,the higher the amount of CaCO3 in the resin, the lower the permeability of the reinforcement that is found. The reduction in permeability is due to the presence of calcium carbonate particles between the fibers, hindering the resin flow in the fibrous media. The computational fluid flow analysis with the PAM-RTM proved to be an accurate tool study for the processing of composite materials.

Resin Transfer Molding Process: A Numerical Investigation

In the processing of high performance composite materials, the RTM process has been widely used by many sectors of the industry. This process consists in injecting a polymeric resin through a fibrous reinforcement arranged within a mold. In this sense, this study aims to simulate the rectilinear infiltration of pure resin and filled resin (40% CaCO3) in a mold with glass fiber preform, using the PAM-RTM commercial software. Numerical results of the filling time and fluid front flow position over time were assessed by comparison with the experimental data and a good accuracy was obtained.

Análise Numérica da Influência da Forma da Câmara em um Dispositivo CAO para Conversão da Energia das Ondas do Mar em Energia Elétrica

Os oceanos represent am um dos maiores recursos naturais, pois apresentam expressivo potencial energético, podendo suprir parte da demanda energética mundial. Nas últimas décadas, alguns dispositivos destinados à conversão a energia das ondas dos oceanos em energia elétrica têm sido estudados. No presente trabalho, o princípio de funcionamento do conversor do tipo Coluna de Água Oscilante (CAO) foi estudado numericamente. A onda incide no interior da câmara hidro-pneumática da CAO, causando um movimento alternado da coluna de água, o qual produz um fluxo alternado de ar (compressão e descompressão) que passa por uma chaminé, onde existe uma turbina. Essa turbina é acoplada a um gerador elétrico, convertendo assim a energia das ondas em energia elétrica. O objetivo do presente estudo foi investigar a influência da forma geométrica da câmara sobre o fluxo alternado de ar que passa pela turbina do conversor CAO. Diferentes geometrias para a câmara hidro-pneumática foram analisadas, empregando um modelo computacional 3D. Os resultados mostraram que a geometria da câmara hidro-pneumática do conversor CAO e sua disposição em relação às ondas incidentes, apresentam influência direta na transformação da energia das ondas em energia elétrica. Dentre os casos analisados, um ganho de quase 7% no valor do fluxo total de ar que passa pela chaminé do dispositivo foi obtido.

Modelagem Computacional do Processo de Moldagem por Transferência de Resina (RTM) Aplicado a Hélices de Propulsão Naval

O presente trabalho mostra como a modelagem computacional pode auxiliar no processo de fabricação de Moldagem por Transferência de Resina (RTM) aplicado à produção de peças com geometrias complexas, como é o caso das hélices de propulsão naval. Este processo de fabricação de peças em material compósito consiste, basicamente, de um molde fechado e preenchido por um reforço fibro so no qual uma resina polimérica é injetada. A simulação numérica do processo de RTM, ou seja, do escoamento da resina através de meio poroso no interior do molde foi desenvolvida nos softwares GAMBIT e FLUENT, e foi aplicada nos estudo de uma hélice de propulsão naval. Por se tratar de uma peça de geometria complexa, a utilização da modelagem computacional como uma etapa preliminar à sua fabricação é de fundamental importância para a correta determinação dos pontos de saída de resina no molde. Assim, é possível projetar um molde eficiente, evitando custos extras relativos ao reprojeto do molde, ao desperdício de resina e também a um maior tempo de injeção. Os resultados obtidos neste trabalho evidenciam e comprovam estes aspectos.