Navegando por Autor "Biserni, Cesare"

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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 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 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.