L. A. Isoldi

Constructal Design of Convective Y-Shaped Cavities by Means of Genetic Algorithm

In the present work constructal design is employed to optimize the geometry of a convective, Y-shaped cavity that intrudes into a solid conducting wall. The main purpose is to investigate the influence of the dimensionless heat transfer parameter a over the optimal geometries of the cavity, i.e., the ones that minimize the maximum excess of temperature (or reduce the thermal resistance of the solid domain). The search for the best geometry has been performed with the help of a genetic algorithm (GA). For square solids (H/L = 1.0) the results obtained with an exhaustive search (which is based on solution of all possible geometries) were adopted to validate the GA method, while for H/L ≠ 1.0 GA is used to find the best geometry for all degrees of freedom investigated here: H/L, t1/t0, L1/L0, and α (four times optimized). The results demonstrate that there is no universal optimal shape that minimizes the thermal field for all values of a investigated. Moreover, the temperature distribution along the solid domain becomes more homogeneous with an increase of a, until a limit where the configuration of “optimal distribution of imperfections” is achieved and the shape tends to remain fixed. Finally, it has been highlighted that the GA method proved to be very effective in the search for the best shapes with the number of required simulations much lower (8 times for the most difficult situation) than that necessary for exhaustive search.

Constructal design of T-shaped cavity for several convective fluxes imposed at the cavity surfaces

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.

Flow of Stresses: Constructal Design of Perforated Plates Subjected to Tension or Buckling

It is possible to state that improving systems configuration for achieving better performance is the major goal in engineering. In the past, the scientific and technical knowledge combined with practice and intuition has guided engineers in the design of man-made systems for specific purposes. Soon after, the advent of the computational tools has permitted to simulate and evaluate flow architectures with many degrees of freedom. However, while system performance was analyzed and evaluated on a scientific basis, system design was kept at the level of art [1].

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.

Constructal Design Applied to the Geometric Evaluation of an Oscillating Water Column Wave Energy Converter Considering Different Real Scale Wave Periods

The present work presents numerical study of the influence of geometry on the performance of an oscillating water column (OWC) wave energy converter by means of a constructal design. The main purpose is to maximize the root mean square hydrodynamic power of device, (Phyd)RMS, subject to several real scale waves with different periods. The problem has two constraints: hydropneumatic chamber volume (VHC) and total OWC volume (VT), and two degrees of freedom: H1/L (ratio of height to length of the hydropneumatic chamber) and H3 (OWC submergence). For the numerical solution it was used a computational fluid dynamic (CFD) code, based on the finite volume method (FVM). The multiphasic volume of fluid (VOF) model is applied to tackle with the water–air interaction. The results led to important theoretical recommendations about the design of OWC device. For instance, the best shape for OWC chamber, which maximizes the (Phyd)RMS, was achieved when the ratio (H1/L) was four times higher than the ratio of height to length of incident wave (H/λ), (H1/L)o = 4(H/λ). Moreover, the optimal submergence (H3) was achieved as a function of wave height (H) and water depth (h), more precisely given by the following relation: h − (3H/4) ≤ (H3)o ≤ h.

Computational modeling and constructal design method applied to the mechanical behavior improvement of thin perforated steel plates subject to buckling

Perforated steel plates are structural components widely employed in engineering. In several applications these panels are subjected to axial compressive load, being undesired the occurrence of buckling. The present work associates the computational modeling and the constructal design method to obtain geometries, which maximizes the mechanical behavior for these components. A numerical model was used to tackle with elastic and elasto-plastic buckling. Square and rectangular plates with centered elliptical cutouts were considered and several hole volume fractions and ratios between the ellipse axes (H0/L0) were taken into account. Stress limit improvements around 100% were achieved depending only on the cutout shape.

Constructal Design of Vortex Tubes

The vortex tube (also known as Ranque-Hilsch vortex tube) is a mechanical device which splits a compressed high-pressure gas stream into cold and hot lower pressure streams without any chemical reactions or external energy supply [1–3]. Such a separation of the flow into regions of low and high total temperature is referred to as the temperature (or energy) separation effect. The device consists of a simple circular tube, one or more tangential nozzles, and a throttle valve. Figure 15.1 depicts schematically two types of vortex tubes: Counter flow (Fig. 15.1a) and parallel flow (Fig. 15.1b). The operational principle of a counter flow vortex tube, which is the scope of the present work, Fig. 15.1a, consists of a high-pressure gas that enters the vortex tube and passes through the nozzle(s). The gas expands through the nozzle and achieves a high angular velocity, causing a vortex-type flow in the tube. There are two exits: the hot exit that is placed near the outer radius of the tube at the end away from the nozzle and the cold exit that is placed at the center of the tube at the same end as the nozzle. By adjusting a throttle valve (cone valve) downstream of the hot exit it is possible to vary the fraction of the incoming flow that leaves through the cold exit, referred as cold fraction. This adjustment affects the amount of cold and hot energy that leaves the vortex tube in the device exits.

ESTUDO DO POTENCIAL TÉRMICO DE TROCADOR DE CALOR SOLO-AR EM DOIS TIPOS DE SOLOS NO MUNICÍPIO DE RIO GRANDE (RS)

A engenharia contemporânea evolui no sentido do desenvolvimento de metodos e aplicacoes para utilizacao de energias renovaveis visando minimizar acoes danosas ao meio ambiente. O solo, por sua vez, desempenha importante papel no principio fisico de funcionamento do Trocador de Calor Solo-Ar (TCSA), pois ora cede, ora absorve o calor para o ar, que escoa no interior dos dutos. Consequentemente, as propriedades termofisicas do solo influenciam no desempenho termico do TCSA. Entao, o objetivo deste trabalho e estimar o desempenho termico do TCSA para dois diferentes perfis geotecnicos de solos considerados. Para isso, a modelagem computacional foi essencial para o desenvolvimento deste trabalho. Atraves dos resultados obtidos, foi constatado que, o TCSA, quando instalado em solo com caracteristica argilosa, apresenta melhor desempenho termico se comparado a uma instalacao em solo arenoso. Tambem se constatou que nem sempre o potencial de resfriamento e aquecimento do TCSA aumenta com a profundidade de instalacao do duto. O perfil geotecnico do solo tem influencia fundamental no desempenho do TCSA, sendo necessario considerar suas caracteristicas para um projeto adequado deste dispositivo. Dessa forma, a principal contribuicao deste trabalho consistiu no desenvolvimento de metodologia para avaliar distintos perfis de solo para modelagem de TCSA. Palavras-chave : Trocador de Calor Solo-Ar, propriedades termofisicas, potencial termico.

Constructal Design of Thermal Systems

Constructal theory and design accounts for the universal phenomenon of generation and evolution of design [1, 2]. Constructal theory has been used to explain deterministically the generation of shape in flow structures of nature (river basins, lungs, atmospheric circulation, animal shapes, vascularized tissues, etc.) based on an evolutionary principle of flow access in time. That principle is the Constructal law: “for a flow system to persist in time “to survive,” it must evolve in such way that it provides easier and easier access to the currents that flow through it” [2]. This same principle is used to yield new designs for electronics, fuel cells, and tree networks for transport of people, goods, and information [3]. The applicability of this method/law to the physics of engineered flow systems has been widely discussed in recent literature [4–7].

Numerical Analysis of Perforated Thin Plates Subjected to Tension or Buckling

Thin perforated plates are employed as structural members in many engineering applications. More specifically, in naval, marine and offshore structures these panels are used to make a way of access or to reduce the total weight of the structure. In several design situations these plates are subjected to axial forces. Besides, the presence of the perforation causes a change in the plates mechanical behavior. When the perforated plate is tensioned, regions of stress concentration are generated, and if the panel is subject a compressive load, there is a possibility to occur the buckling phenomenon. For these reasons, in this work a numerical study was accomplished, aiming to obtain the optimal geometry for the thin perforated plate subjected to tension or buckling. The computational models were developed in the ANSYS software and the geometric optimizations were based on the Constructal Design method. The results indicated an optimal geometry which can be up to 594 % superior considering the level of stress concentration, and there is an optimal geometry which presents a critical buckling load until 57.2 % superior. Moreover, these preliminary results show that additional researches into this subject are justified.