Universidade
Federal do Rio Grande

Navegando por Autor "Rocha, Luiz Alberto Oliveira"

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An original procedure to determine transverse permeability using a multilayer reinforcement in RTM
(2010) Oliveira, Cristiano Peres; Souza, Jeferson Avila; Isoldi, Liércio André; Rocha, Luiz Alberto Oliveira; Amico, Sandro Campos; Silva, Rafael Diego Sonaglio da
Resin Transfer Molding (RTM) is a manufacturing process for polymer composites parts for a variety of uses. The numerical simulation of the resin flow into the mold can be used to minimize costs related to mold design and the manufacturing process itself. However, to obtain realistic results, accurate information about the resin and the reinforcement media are necessary. In the multilayer RTM, distinct porous media layers are stacked to obtain a final composite with better performance. For the numerical simulation of the multilayer RTM, transverse permeability (Kzz) data are necessary. This work proposes an original methodology to determine the transverse permeability in multilayer RTM composites, assuming that the in-plane permeabilities (Kxx and Kyy) are known and using this information, combined with experimental data obtained during mold filling. The motivation of this study is the fact that the transverse permeability is usually not available in the literature, being referred to as a difficult parameter to be directly determined using experiments.
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Análise de malhas para geração numérica de ondas em tanques
(2012) Gomes, Mateus das Neves; Isoldi, Liércio André; Santos, Elizaldo Domingues dos; Rocha, Luiz Alberto Oliveira
Este trabalho apresenta uma metodologia para a geração numérica de ondas em tanques e também um estudo de malhas a serem utilizadas em simulações numéricas da propagação de ondas regulares bidimensionais em tanques. São testados dois tipos de geração e refinamento de malhas. Assim busca-se encontrar uma malha independente que forneça resultados com acurácia e com menor esforço computacional. Foram realizadas simulações numéricas da geração de ondas através do pacote FLUENT® , que é baseado no Método de Volumes Finitos (MVF). Foi empregado o modelo multifásico Volume of Fluid (VOF) para reproduzir a propagação da onda no tanque. Esses resultados poderão ser utilizados em trabalhos futuros, principalmente no estudo numérico de dispositivos para conversão de energia das ondas do mar em energia elétrica, como por exemplo, os dispositivos de coluna de água oscilante (OWC) e de galgamento.
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Análise numérica da geometria de aletas inseridas em cavidades dirigidas em escoamento com transferência por convecção forçada
(2016) Aldrighi, Eliciana Sias; Rocha, Luiz Alberto Oliveira; Santos, Elizaldo Domingues dos
O presente trabalho apresenta um estudo numérico de escoamento laminar em três cavidades quadradas aletadas sob o efeito de convecção forçada. O escoamento proposto é assumido bidimensional, laminar e permanente. Objetiva-se através do Design Construtal a obtenção de geometria ótima da aleta de forma a maximizar a transferência de calor entre o fluido que escoa no interior da cavidade e a aleta aquecida, para alguns números de Reynolds (ReH = 10; 50; 100 e 1000). Para isto é fixada a relação das dimensões externas da cavidade (H/L = 1) e variação da geometria da aleta entre seu comprimento e altura (H1/L1) para a otimização da troca térmica. Todas as simulações são realizadas com número de Prandtl fixo (Pr = 0,71). A relação entre a área da cavidade e a aleta é considerada fixa ( = 0,05). As equações de conservação de massa, quantidade de movimento e energia foram resolvidas através de um código comercial de dinâmica dos fluidos computacional (CFD - do inglês: Computational Fluid Dynamics) baseado no método dos volumes finitos. O Design Construtal permitiu um significativo aumento de desempenho térmico, o maior número de Nusselt (NuH) foi obtido para a aleta inserida na superfície lateral direita da cavidade com H1/L1 = 2,0 com ReH = 1000, mostrando que o desempenho térmico depende da geometria. Como esperado, a geometria tem forte influência sobre o NuH para todos os ReH avaliados.
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Análise numérica do comportamento mecânico sob flexão de placas finas de material compósito laminado reforçado por fibras
(2013) Helbig, Daniel; Real, Mauro de Vasconcellos; Rocha, Luiz Alberto Oliveira; Santos, Elizaldo Domingues dos; Isoldi, Liércio André
A crescente necessidade de estruturas com propriedades mecânicas superiores impulsiona o desenvolvimento de novos tipos de materiais, dentre os quais se destacam os materiais compósitos laminados reforçados por fibras. Placas finas construídas com estes materiais possuem diversas vantagens em comparação com as fabricadas com materiais de construção mecânica convencionais como o aço: altas relações rigidez/peso e resistência/peso; alta resistência à fadiga; e excelente resistência à corrosão. Portanto, a aplicação destes elementos estruturais é cada vez mais frequente em diversas áreas da engenharia, especialmente em estruturas navais e offshore. Neste contexto, o presente trabalho analisa numericamente o comportamento mecânico de placas finas fabricadas com diferentes tipos de materiais compósitos (Vidro-E / Epóxi, Boro / Epóxi, Tecido de Vidro / Epóxi e Boro / Alumínio) em comparação com o comportamento mecânico de uma placa de Aço. Os resultados mostraram que é possível obter com uma placa de material compósito reforçado por fibras um comportamento mecânico semelhante, ou até melhor, que o de uma placa de aço.
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Análise teórica da influência de perfis sobre a potência de uma Turbina Wells empregada em dispositivos de conversão de energia das ondas
(2013) Dias, Gustavo da Cunha; Santos, Sonia Magalhães dos; Santos, Elizaldo Domingues dos; Rocha, Luiz Alberto Oliveira; Olinto, Cláudio Rodrigues
O presente trabalho apresenta um estudo teórico a respeito da influência de diversos perfis aerodinâmicos (NACA0012, NACA0015, NACA0018, NACA0020 e NACA0021) sobre a potência e torque gerados em uma turbina Wells. Em todos os casos avaliados, o rotor possui um raio da turbina rt = 245 mm e uma razão de aspecto de AR = 0.7. O objetivo principal é obter uma recomendação teórica a respeito de qual perfil aerodinâmico pode ser empregado para os rotores de pequenos dispositivos de conversão de energia das ondas do mar em energia elétrica, mais especificamente coluna de água oscilante com potências inferiores a 1kW. Para realizar a estimativa da potência e torque foram utilizadas recomendações teórico experimentais da literatura. Os resultados indicaram que o melhor perfil aerodinâmico (NACA0021) é capaz de conduzir a uma potência mecânica de aproximadamente 319 W, apresentando um desempenho 36 % superior ao perfil NACA0020, que conduziu aos piores resultados.
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Analytical modeling and numerical optimization of the biosurfactants production in solid-state fermentation by Aspergillus fumigatus
(2014) Castiglioni, Gabriel Luis; Stanescu, George; Rocha, Luiz Alberto Oliveira; Costa, Jorge Alberto Vieira
This is an experimental, analytical and numerical study to optimize the biosurfactants production in solid-state fermentation of a medium containing rice straw and minced rice bran inoculated with Aspergillus fumigatus. The goal of this work was to analytically model the biosurfactants production in solid-state fermentation into a column fixed bed bioreactor. The Least-Squares Method was used to adjust the emulsification activity experimental values to a quadratic function semi-empirical model. Control variables were nutritional conditions, the fermentation time and the aeration. The mathematical model is validated against experimental results and then used to predict the maximum emulsification activity for different nutritional conditions and aerations. Based on the semi-empirical model the maximum emulsification activity with no additional hydrocarbon sources was 8.16 UE·g-1 for 112 h. When diesel oil was used the predicted maximum emulsification activity was 8.10 UE·g-1 for 108 h.
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Computational modeling applied to the study of wave energy converters (WEC)
(2014) Seibt, Flávio Medeiros; Letzow, Max; Gomes, Mateus das Neves; Souza, Jeferson Avila; Rocha, Luiz Alberto Oliveira; Santos, Elizaldo Domingues dos; Isoldi, Liércio André
The employment of numerical methods to solve engineering problems is a reality, as well as, the worldwide concern about the need of renewable and alternative energy sources. Thus, this work presents a computational model capable of simulating the operating principle of some Wave Energy Converters (WEC). To do so, the device is coupled in a wave tank, where the sea waves are reproduced. The Finite Volume Method (FVM) and the Volume of Fluid (VOF) model are adopted. The results showed that the converter's operating principle can be numerically reproduced, demonstrating the potential of computational modeling to study this subject.
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Computational modeling of a regular wave tank
(2009) Gomes, Mateus das Neves; Olinto, Cláudio Rodrigues; Rocha, Luiz Alberto Oliveira; Souza, Jeferson Avila; Isoldi, Liércio André
This paper presents two different numerical methodologies to generate regular gravity waves in a wave tank. We performed numerical simulations of wave generation through the FLUENT® package, using the Volume of Fluid (VOF) multiphase model to reproduce the wave propagation in the tank. Thus it was possible to analyze two methods for generating regular waves that could be used in future work, especially in the study of devices of energy conversion from ocean waves into electrical energy.
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Computational modeling of an oscillating water column device for the Rio Grande coast
(2009) Gomes, Mateus das Neves; Isoldi, Liércio André; Olinto, Cláudio Rodrigues; Rocha, Luiz Alberto Oliveira; Souza, Jeferson Avila
This work presents the computational modeling of a converter of wave energy in electrical energy. The converter is Oscillating Water Column (OWC) type, submitted to the wave climate of Rio Grande city. The numerical simulation was performed using FLUE)T® package and employing the multiphase Volume of Fluid (VOF) model in the wave generation and in the interaction between the wave and the converter device. The computational domain was represented by a wave tank coupled with the OWC device. This domain allows the behavior analysis to be performed when the device is subjected to the incidence of regular waves. The waves were molded to represent the characteristics of the Rio Grande coastclimate. Results demonstrate that the OWC converter can be successfully used to convert the Rio Grande's coast wave energy in useful electrical energy.
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Constructal design aplicado a placas com furos elípticos sob flambagem.
(2013) Correia, Anderson Luis Garcia; Silveira, Thiago da; Silva, Caio César de Castro da; Rocha, Luiz Alberto Oliveira; Real, Mauro de Vasconcellos; Santos, Elizaldo Domingues dos; Isoldi, Liércio André
Placas são elementos amplamente empregados na engenharia estrutural. Em muitas situações é necessária a existência de perfurações nestas placas. Sabe-se ainda que elementos estruturais esbeltos submetidos a cargas de compressão axial podem falhar de maneira súbita, com uma tensão inferior à tensão de escoamento do material, devido a um fenômeno de instabilidade conhecido como flambagem. Nesse artigo, a Teoria Constructal será utilizada para otimizar geometricamente placas finas perfuradas, submetidas a compressão uniaxial, tendo como objetivo obter a dimensão ótima do furo que maximize a carga crítica de flambagem. Para isso diversas simulações numéricas foram realizadas, utilizando um modelo computacional baseado no Método dos Elementos Finitos (MEF). Observou-se que para todos os valores de Ø (relação entre o volume do furo e o volume da placa) analisados, a placa que apresenta melhor desempenho sob compressão uniaxial é a que possui a maior relação H/L (relação entre a altura e o comprimento da placa). No que diz respeito à análise individual de cada placa, a que obteve o maior acréscimo percentual no valor de carga crítica de flambagem em relação a uma placa sem furo foi a placa 1 (H/L = 1.00), chegando a 198.98%. A placa que apresentou o menor acréscimo percentual foi a placa 4 (H/L = 0.25), com 7.72%. Ao realizar uma comparação global entre as placas, a que obteve o melhor desempenho foi a placa 1 (H/L = 1.00), apresentando uma carga crítica máxima de flambagem 176.85% maior que a carga crítica máxima na placa de pior desempenho, placa 4 (H/L = 0.25).
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Constructal design applied to the elastic buckling of thin plates with holes
(2013) Rocha, Luiz Alberto Oliveira; Isoldi, Liércio André; Real, Mauro de Vasconcellos; Santos, Elizaldo Domingues dos; Correia, Anderson Luis Garcia; Lorenzini, Giulio; Biserni, Cesare
Elastic buckling is an instability phenomenon that can occur if a slender and thin plate is subjected to axial compression. An important characteristic of the buckling is that the instability may occur at a stress level that is substantially lower than the material yield strength. Besides, the presence of holes in structural plate elements is common. However these perforations cause a redistribution in plate membrane stresses, significantly altering their stability. In this paper the Bejan’s Constructal Design was employed to optimize the geometry of simply supported, rectangular, thin perforated plates subjected to the elastic buckling. Three different centered hole shapes were considered: elliptical, rectangular and diamond. The objective function was to maximize the critical buckling load. The degree of freedom H/L (ratio between width and length of the plate) was kept constant, while H0/L0 (ratio between the characteristic dimensions of the holes) was optimized for several hole volume fractions (φ). A numerical model employing the Lanczos method and based on the finite element method was used. The results showed that, for lower values of φ the optimum geometry is the diamond hole. For intermediate and higher values of φ, the elliptical and rectangular hole, respectively, led to the best performance.
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Constructal design applied to the optimization of heat transfer in a solid conducting wall
(2007) Marques, Crístofer Hood; Santos, Elizaldo Domingues dos; Rocha, Luiz Alberto Oliveira
The present paper applies Constructal Design to optimize the geometry of a Yshaped negative fin that intrudes a solid conducting wall with heat generation. The main goal is the minimization of the thermal global resistance between the solid wall and the negative fin, which removes energy from the wall. The optimization is achieved by varying the angle between the tributary branch of the Y-Shaped fin and the horizontal axis, as well as, by varying the ratio between the volume of the fin and the rectangular volume that circumscribes it (ψ), while the other geometric parameters are maintained fixed. Constructal Design led to a best configuration, with a thermal global resistance of 53%, 49% and 48% for ψ = 0.3, ψ = 0.4 and ψ = 0.5, respectively, smaller than the ones for the worst configuration.
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Constructal design de caminhos não-uniforme de alta condutividade térmica em forma de “y” para a refrigeração de corpos geradores de calor
(2014) Beckel, Cássia Cris; Horbach, Cristina Santos; Isoldi, Liércio André; Santos, Elizaldo Domingues dos; Rocha, Luiz Alberto Oliveira
Este estudo numérico utiliza o método Constructal Design para reduzir os pontos quentes de um sólido com geração de calor uniforme por unidade de volume através da transferência de calor por condução. A ideia é facilitar o acesso do fluxo de calor através de uma via em forma de “Y” empregando condutividades térmicas não-uniformes para a base e ramos do Y. A função objetivo consiste em minimizar o excesso de temperatura máxima adimensional de todo o sistema (materiais de alta e de baixa condutividade térmica). A configuração do sistema pode variar sujeita a duas restrições: o volume total e o volume das vias de alta condutividade. Materiais de várias condutividades e frações de áreas são estudados. Os resultados mostram a aplicabilidade do Constructal Design para a melhoria do desempenho térmico do sistema. Utilizando condutividades diferentes para a base e os ramos obteve-se uma melhora de mais de 30%. A geometria otimizada é aquela que melhor distribui as imperfeições, isto é, os pontos quentes (pontos de temperatura máxima), o que está de acordo com o princípio da ótima distribuição das imperfeições.
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Constructal design of a vortex tube for several inlet stagnation pressures
(2012) Marques, Crístofer Hood; Isoldi, Liércio André; Santos, Elizaldo Domingues dos; Rocha, Luiz Alberto Oliveira
The present paper shows a numerical study concerned with the geometrical optimization of a vortex tube device by means of Constructal Design for several inlet stagnation pressures. In the present study, it is evaluated a vortex tube with two-dimensional axisymmetric computational domain with dry air as the working fluid. The compressible and turbulent flows are numerically solved with the commercial CFD package FLUENT, which is based on the Finite Volume Method. The turbulence is tackled with the k-ε model into the Reynolds Averaged Navier-Stokes (RANS) approach. The geometry has one global restriction, the total volume of the cylindrical tube, and four degrees of freedom: d3/D (the ratio between the diameter of the cold outlet and the diameter of the vortex tube), d1/D (the ratio between the diameter of the inlet nozzle and the diameter of the vortex tube), L2/L (the ratio between the length of the hot exit annulus and the length of the vortex tube) and D/L (the ratio between the diameter of the vortex tube and its length). The degree of freedom L2/L will be represented here by the cold mass fraction (yc). In the present work it is optimized the degrees of freedom yc and d3/D while the other degrees of freedom and the global restriction are kept fixed. The purpose here is to maximize the amount of energy extracted from the cold region (cooling effect) for several geometries, as well as, investigate the influence of the inlet stagnation pressure over the optimal geometries. Results showed an increase of the twice maximized cooling heat transfer rate of nearly 330 % from 300 kPa to 700 kPa. Moreover, the optimization showed a higher dependence of (d3/D)o for the lower range of inlet pressures, while the optimization is more dependent of yc,oo for higher inlet stagnation pressures.
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Constructal design of a x-shaped cavity cooled by convection
(2014) Link, Fernanda Bichet; Rocha, Luiz Alberto Oliveira; Santos, Elizaldo Domingues dos; Isoldi, Liércio André
This paper applies Constructal design to study the geometry of a X-shaped cavity that penetrates into a solid conductive wall. The objective is minimizing the dimensionless maximal excess of temperature between the solid body and the cavity. There is uniform heat generation on the solid body. The cavity surfaces are cooled by convection heat transfer while the solid body is subjected to adiabatic conditions on its outer surfaces. The total volume and the cavity volume are fixed, but the lengths and thickness of the X-shaped cavity can vary. The emerged optimal configurations and performance are reported. The effect of the area fraction φ which denotes the ratio between the cavity area and the total area of the geometry, and the ratio between the length and thickness of the branch cavity, H1/L1, on the dimensionless maximal excess of temperature is numerically investigated. The results show that the dimensionless maximal excess of temperature θmax,min decreases approximately 60% when the cavity fraction increases from φ = 0.05 to 0.25. The results also show that the X-shaped cavity performs approximately 45% better when compared to a C-shaped cavity under the same thermal conditions. The optimal X-shaped cavity is also in accordance with the optimal distribution of imperfections principle.
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Constructal design of convective cavities inserted into a cylindrical solid body for cooling
(2015) Lorenzini, Giulio; Estrada, Emanuel da Silva Diaz; Santos, Elizaldo Domingues dos; Isoldi, Liércio André; Rocha, Luiz Alberto Oliveira
This work applies Constructal design to study numerically the geometry of cavities bathed by a fluid with constant heat transfer coefficient that are intruded into a cylindrical solid body. The objective is to minimize the maximum excess of temperature between the solid body and the ambient by morphing the cavity geometry. Internal heat generating is distributed uniformly into the solid body which has adiabatic conditions on the outer surfaces. The total volume and the volume of the cavities are fixed. The cavities are rectangular with variable aspect ratio. The optimized geometry and performance are reported as functions of the ratio between the volume of the cavities and the total volume, the number of cavities and the dimensionless parameter that accounts for the convective heat transfer, λ. The main results indicate that for fixed number of cavities, ϕc, and dimensionless parameter λ, there is an optimal number of cavities, No, that minimizes the maximum excess of temperature and this optimal number of cavities in general increases as ϕc and λ increases.
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Constructal design of isothermal x-shaped cavities
(2014) Lorenzini, Giulio; Biserni, Cesare; Link, Fernanda Bichet; Santos, Elizaldo Domingues dos; Isoldi, Liércio André; Rocha, Luiz Alberto Oliveira
This paper applies constructal design to study the geometry of a X-shaped cavity that penetrates into a solid conducting wall. The objective is to minimize the maximal dimensionless excess of temperature between the solid body and the cavity. There is uniform heat generation on the solid body. The total volume and the cavity volume are fixed, but the geometric lengths and thickness of the X-shaped cavity can vary. The cavity surfaces are isothermal while the solid body has adiabatic conditions on the outer surface. The emerged optimal configurations and performance are reported graphically. When compared to the Y- and C- and H-, the X-shaped cavity performs approximately 53% better than the Y-shaped cavity and 68% better than the C-shaped cavity for the area fraction φ = 0.05, while its performance is 22% inferior to the performance of the H-shaped cavity for the area fraction φ = 0.1. The results indicate that the increase of the complexity of the cavity geometry can facilitate the access of heat currents and improve the performance of the cavities.
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Constructal design of solid state fermentation bioreactors
(2009) Cunha, Daniele Colembergue da; Souza, Jeferson Avila; Costa, Jorge Alberto Vieira; Rocha, Luiz Alberto Oliveira
Constructal Design is applied to geometric optimization of an insulated wall bioreactor. The optimization of the bioreactor geometry allows that it to operate, below a certain temperature limit, without external cooling equipment. The possibility of using less equipment shows how geometric optimization can be used as a tool for the ecologically correct management of energy. For the geometric optimization, a mathematical model that represents the solid state fermentation by Aspergillus niger is validated and used to study a column fixed bed bioreactor with fixed volume. The model is solved numerically for an insulated wall bioreactor. According to Constructal Design the shape of the bioreactor is free to change subject to volume constraint and in the pursuit of better performance. The optimal ratio between the diameter and the length of the bioreactor, i.e., the ratio which corresponds to the optimal maximum temperature equal to 35 ºC, is calculated for several inlet velocities, volumetric flow rates and inlet air temperatures.
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Constructal design of T-shaped assemblies of fins cooling a cylindrical solid body
(2014) Lorenzini, Giulio; Biserni, Cesare; Corrêa, Roberta de Lima; Santos, Elizaldo Domingues dos; Isoldi, Liércio André; Rocha, Luiz Alberto Oliveira
This paper considers the numerical optimization of a T-shaped assembly of fins cooling a cylindrical solid body. The objective is to minimize the maximum excess of temperature between the solid cylindrical body and the ambient. Internal heat generation is distributed uniformly throughout the solid body. The assemblies of fins are bathed by a steady stream with constant ambient temperature and convective heat transfer. The outer surfaces of the cylindrical body are adiabatic. The total volume of the body and the total volume of the fins are fixed, but the lengths of the fins can vary. The initial simulations demonstrated that the optimal performance is achieved when the tributaries shape becomes slender and the stem thicker so that the system has more freedom to morph. However, when the number of assembly exceeds 2, the best configuration is the one that presents slender stems and shorter tributaries. The reason of this sudden change in behavior is that the tributaries length is limited by the presence of the neighbor assembly of fins: the system becomes “locked” and has no more freedom to morph. Finally, a digression on how the number of T-shaped fin assembly affects the configuration patterns concludes the paper.
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Constructal design of T-shaped cavity for several convective fluxes imposed at the cavity surfaces
(2013) Lorenzini, Giulio; Biserni, Cesare; Link, Fernanda Bichet; Isoldi, Liércio André; Santos, Elizaldo Domingues dos; Rocha, Luiz Alberto Oliveira
The purpose here is to investigate, by means of the constructal principle, the influence of the convective heat transfer flux at the cavity surfaces over the optimal geometry of a T-shaped cavity that intrudes into a solid conducting wall. The cavity is cooled by a steady stream of convection while the solid generates heat uniformly and it is insulated on the external perimeter. The convective heat flux is imposed as a boundary condition of the cavity surfaces and the geometric optimization is achieved for several values of parameter a = (2hA1/2/k)1/2. The structure of the T-shaped cavity has four degrees of freedom: L0/L1 (ratio between the lengths of the stem and bifurcated branches), H1/L1 (ratio between the thickness and length of the bifurcated branches), H0/L0 (ratio between the thickness and length of the stem), and H/L (ratio between the height and length of the conducting solid wall) and one restriction, the ratio between the cavity volume and solid volume (φ). The purpose of the numerical investigation is to minimize the maximal dimensionless excess of temperature between the solid and the cavity. The simulations were performed for fixed values of H/L = 1.0 and φ = 0.1. Even for the first and second levels of optimization, (L1/L0) ○○ and (H0/L0)○, the results revealed that there is no universal shape that optimizes the cavity geometry for every imposed value of a. The T-shaped cavity geometry adapts to the variation of the convective heat flux imposed at the cavity surfaces, i.e., the system flows and morphs with the imposed conditions so that its currents flow more and more easily. The three times optimal shape for lower ratios of a is achieved when the cavity has a higher penetration into the solid domain and for a thinner stem. As the magnitude of a increases, the bifurcated branch displaces toward the center of the solid domain and the number of highest temperature points also increases, i.e., the distribution of temperature field is improved according to the constructal principle of optimal distribution of imperfections.