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The immersed boundary (IB) methods are used to enforce boundary conditions on surfaces not aligned with the computational mesh in a numerical simulation. This methodology has been used as a practical approach to model flow problems involving complex and/or moving bodies. Despite the great advantages of the immersed boundary methodology, it is shown in this work that some difficulties and challenges are posed when it is used to simulate the flow past sharp geometries. In present work, two main objectives are proposed: first, to assess the accuracy and efficiency of IB methods in simulations of flows past immersed bodies with highly sharp corners or thin plates. Secondly, we implement a numerical method which is able to satisfy these flow conditions. The study was composed of four stages: First, an extensive bibliographic review was conducted in order to know and understand the different immersed boundary methods; in the second stage it was presented modifications in Multi-Direct Forcing method; further on, it was presented a local directional ghost cell approach. Finally, the methods are implemented and tested for a number of problems, the modified multi-direct forcing approach was validated for a uniform flow past a circular cylinder, a sphere and an airfoil NACA0012. The local directional ghost cell approach was employed to calculate a Poiseuille flow, an impulsively started flow past a flat plate and uniform flow around a circular cylinder between two parallels walls

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

The necessity of understand the physical mechanisms in flows over complexes geometries are something imperative on modern engineering. In this way, tools that allow the analysis and understanding of such flows are very important as well. In this work, a numerical tool that allows the transient analysis of flows over several types of complexes three-dimensional geometries is presented: the Fluids-3D code. Such code uses the Immersed Boundary Method for representing an immersed body into the flow. The Immersed Boundary method uses two independent domains in the solution of the flows over complex geometries: an eulerian domain, which is discretized using Finite Volume Method over a non-uniform mesh to integrate the Navier-Stokes equations, and a second-order approximation for time and space derivatives; the lagrangian domain is represented by a superficial unstructured mesh, composed by triangles. Such mesh can be imported by commercial mesh generators, or generators of files used in stereolithography (*.stl - Standard Tessellation Language). In the Immersed Boundary Method, the effects of an immersed body are imposed by a source term in the Navier-Stokes equations. In this work the Virtual Physical Model for modeling this term is used. Such model is in development in LTCM Laboratory of Heat and Mass Transfer and Fluid Dynamics. The Fluids- 3D code also counts with parallel processing capabilities. The results of flows over several kinds of complexes geometries, such as wall mounted cubes, automobile and aircraft prototypes are shown. These simulations have provided rich analysis of the flows. Others important contributions of the present work are the preparations of the code to the implementation of a graphical user interface, and the optimization of the parallelization process of the code as well.

Cogeneration is a broadly used tool to improve the performance of thermal systems by using combined cycles. In this sense, it is aimed to identify the amount of spare energy found in the turbine used to perform extra power in engines equipped either with waste-gate or twin flow. In this way, refrigerating power is used motor vehicle applications. For this purpose, a semiempirical model is used for the engine, as based on the Otto cycle. Consequently, considerations extracted from the thermodynamic laws are applied to the air and gas flow through the various auxiliary engine components leading to a model that permits to evaluate the behavior of the parameters that characterize the operating conditions of the engine. The models were validated according to experimental data extracted from the literature (Bermudez, 1995) for the engine operating under full charge condition. Based on simulated results, the liquid power (cogeneration power) of the turbo-compressor was calculated by considering that the discharge gases were reoriented to the waste-gate to expand in the turbine. Similarly, VGT turbines allow obtaining this eventual extra power by varying its effective flow area. Another important aspect that was evaluated in this dissertation is related to the availability of the extra energy during the operation of the engine. In this sense, it was observed that this extra power was available in the engine during 70% of its operation time, under the condition of open waste-gate.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

In this work, the effects of the aspect radio and inclination angle in the convection heat transfer inside a square cavity are analyzed through integral transformation. The numerical simulations were made in square and plane cavity in a fluid with constant and variable properties and identifying the effect of the temperature variations. Varying the geometry of the cavity and its inclination it was identified the most sensitive properties at the temperature variations, as well as the geometric combinations which optimize the convection heat transfer. The Generalized Integral Transform Technique (JLWW) was capable to simulate the physical phenomenon successfully, capturing recirculations in critical convective cases numerically. The correlations were established between the rate of convection heat transfer and the aspect radio and the inclination angle of the cavity.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Conselho Nacional de Desenvolvimento Científico e Tecnológico

The main goal of this work is the evaluation of the performance of high-speed steel (HSS) taps when machining grey cast iron at high cutting speeds in dry conditions and when using MQL (minimal quantity of lubrication). The performance of four types of high speed steel with and without coating was investigated. They are: conventional HSS; HSS with addition of vanadium (HSS-E); HSS obtained by powder metallurgy (HSS-PM) and conventional HSS with surface treatment of nitriding. These tool materials are used in two coated situation: with TiN and multi layer TiN/TiNAl. It was used two tapping system, one using the collet tapping chuck of the machine tool without axial compensation, and the other using a self rotation system with axial compensation. The tool life criteria were based on dimensional tolerances of the threads, on tool wear and also on catastrophic failure of the tool. Analysis in the scanning electron microscope and optical microscope were done to measure the wear land and to determine the type and mechanisms of wear. The results showed that the effect of the cutting speed depends on the coating and the main wear mechanisms were adhesion and abrasion. The best performance was achieved with the multi layer coating TiN/TiNAl. The torque during the tapping operation was also monitored and the results for both system of fixation are compared. It was also performed a statistical investigation of the effects of some parameters. The cutting speed was the most influent parameter on tool wear. The application of cutting fluid improved the performance for all conditions tested.

The oil and gas extraction in deep waters by Petrobras has been expanded progressively in the recent years. In this condition, oil and gas can be extracted by Jacket type and semi-submersible platforms, which are connected to the wells through flexible risers. These components are constituted of a multilayer system with internal and external coatings made of polymers. On inspection of these risers, scratches and a significant reduction of the riser protection layer were observed. These damages were found to be related to the relative movement of the pipe in the area of the touchdown point (TDP). In order to reduce this problem the risers have being coated externally with plaques of polyurethane. High chemical inertia and good mechanical and abrasion resistance characterize these materials. Besides, they allow the riser to have a good flexibility. Thus, the abrasive wear of these risers was reduced. However, optimizations still must be reached. Currently, the abrasive wear resistance of these materials is evaluated by means of abrasive wear tests according to the DIN 53.516 norm and the single-pass scratching technique, both at a temperature of 4ºC. The latter one is appropriate for testing polymeric riser protections but it does not simulate the repetitive action of hard particles acting against the plaques. In the present work, a new test rig for abrasive wear testing is presented, which is based on multiple interactions between indenters and plaques. So, the deep water wear conditions were simulated and the wear micromechanisms of different polyurethane materials were observed to be similar to those of field application. The wear rate results showed that wear in these materials is basically due to microcracking. It was also noticed that materials with a good wear performance have a high tearing elongation and strength and a high resilience. A correlation between abrasive wear and mechanical properties of five different types of polyurethane was proposed. The obtained equation showed no linear relation with these results, suggesting that terms of higher degree may be important.

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