RCAAP Repository

Conselho Nacional de Desenvolvimento Científico e Tecnológico

This thesis presents a computational framework for simulating three-dimensional two-phase flows based on adaptive strategies for space and time discretization. The method is based on the fronttracking method of Unverdi and Tryggvason (1992), and the discretization of the Eulerian domain is based on the SAMR strategy of Berger and Colella (1989). The time integration algorithm is based on the IMEX scheme, and the time step is calculated based on CFL criteria. The implementation of the Lagrangian framework relied on the GNU Triangulated Library (GTS), which provides a complete data structure and supporting functions for data access, remeshing tools and data output. The memoryless simplification algorithm of Lindstrom and Turk (1998) is used for surface remeshing, preserving the volume and shape of the interface. Nevertheless, additional tools for volume recovery were implemented, motivated by the non-conservative behaviour of the advection of the Lagrangian interface. This process may also induce some non-physical undulations on the Lagrangian interface, which was circumvented with the implementation of the TSUR-3D algorithm of Sousa et al. (2004). The methodology was applied to a series of rising bubble simulations, in which a single bubble rises in an initially quiescent liquid, and validated against experimental results (BHAGA; WEBER, 1981). The validation process consisted in comparing the terminal shape and Reynolds number, as well as the topology of the streamlines downstream of the bubble. Finally, the algorithm was applied to the simulation of two cases of bubbles rising in the wobbling regime, which is characterized by the continuous change in the bubble shape and complex patterns of vortex shedding. The use of adaptive mesh refinement strategies led to physically insightful results, which would not be possible in a serial code with a uniform mesh.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

This work aims to investigate the influence of titanium cabonitride and other microstructural elements, on the machinability of VP100 steel with 270 and 350 parts per million of titanium, have the VP20 ISO steel with comparator. Such a study is justified considering that the VP100 is a steel for plastic injection molds on the market whose recently released its machinability aspects have not yet been fully exploited, there is still a big gap in knowledge about this material to be investigated. The results are discussed considering initially, the variation of machining forces due to the variation of cutting speed, feed and depth of cut in turning tests. Next, are evaluated the volume of material removed, and the mean square roughness Rq values for each type of material machined and cutting condition applied, depending on the evolution of the tool wear used in milling tests. The performance of the tests was made from a statistical design of experiments, where the relevant variables on the parameters of both the chemical composition of alloys and their machinability, define the factors and responses of interest in research. The tools used were the same in all conditions tested, therefore not constituted in a process variable, and the use of cutting fluid, since all tests were performed dry. The VP20 ISO showed better performance in machining followed by the VP100 with 350 ppm titanium, and the VP100 with 270 ppm titanium had a worse performance. Significant differences were observed in the microstructure of materials such as quantity, size, shape and distribution of titanium carbonitrides in the two modes of VP100, which contributed to the differences in the behavior of materials in machining.

In metal machining one of the most important topic is the understanding of the chip formation process. Its analysis leads to the conclusion of how important is the phenomena involved during the generation of a new engineering surface. Since 1930 E. M. Trent, one of the most important researcher in metal cutting of all times, has encouraged the study of the tribological behaviour at the chip-tool interface. This has served as the mainspring towards technological improvements, such as the use of adequate cutting fluids and tool coatings more and more resistant, which aims to prolong tool lives. It is known from the surface engineering that different surface topographies present different tribological behaviour. The use of laser technology allows to alter the topography of the tool surfaces without affecting their mechanical properties. The main objective of the present work is to evaluate the influence of laser textured surfaces of coated cemented carbide cutting tools in the machinability of ABNT 1050 steel in turning operation. The tools were textured in three different stages, varying the texture geometry and the laser power over the rake face of triple coated (TiCN-Al2O3-TiN) cemented carbide tools. The textures were characterized by electronic interferometry and scanning electron microscopy (SEM). The machining tests were carried out in several cutting conditions (cutting speed and feed rate) and different lubri-cooling atmospheres (dry, MQL and flood cooling). The machinability was evaluated also in three different classificatory stages. In the first stage (using the same texture geometry and different laser parameters) the machining force components and the workpiece surface roughness were considered as the evaluating parameters. In the second stage (different texture geometry) only the machining force components were considered. Finally, in the third stage (using the best texture determined by the previous stages) the tool life was the evaluating parameter. The results showed that from the machinability evaluating parameters, only the tool life with flood cooling presented positive response of the laser texture on the tool rake face. Under the other two lubri-cooling atmospheres (dry and MQL) the results did not show significant differences in the behaviour of the evaluating parameters. Varying the cutting conditions did not modify these results. This work has thus contributed for the study of the laser-materia interaction showing that this new technology of tool texturing is viable and can improve tool lives and hence shop floor productivity.

The objective of this study was to investigate the nitriding possibility on AISI 4140 steel samples, through the electrical discharge machining (EDM) process. The tests were executed on die sinking EDM machine, with some adaptations. As dielectric fluid, it was used a deionized water and urea solution. As electrode tool it was used electrolytic copper. The characterization techniques used were the micrographic analysis, x-ray diffraction, laser interferometry, GDOES, nanoindentation and microhardness. The electrical discharges were photographed using high speed camera. The results showed the formation of a rich nitride layer with a thickness between 20 and 25 micrometers. A decay occurs in the concentration from the surface. There was a gain in hardness, but it was not detected any change in the elasticity modulus. The electrical discharges photographs revealed the interference of urea on the same, however there was no significant topography alteration. The proposed model for nitriding is based on the nitrogen insertion on the steel surface by ion implantation. Thus, it can be concluded that the use of electric discharges showed a viable method of nitriding. The technological potential of the process was explored with complementary studies.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

The numerical simulation of fluid flow involving complex geometries is greatly limited by the required spatial grid resolution. These flows often contain small regions with complex motions, while the remaining flow is relatively smooth. Adaptive mesh refinement (AMR) enables the spatial grid to be refined in local regions that require finer grids to resolve the flow. This work describes an approach to parallelization of a structured adaptive mesh refinement (SAMR) algorithm. This type of methodology is based on locally refined grids superimposed on coarser grids to achieve the desired resolution in numerical simulations. Parallel implementations of SAMR methods offer the potential for accurate simulations of high complexity fluid flows. However, they present interesting challenges in dynamic resource allocation, data-distribution and load-balancing. The overall efficiency of parallel SAMR applications is limited by the ability to partition the underlying grid hierarchies at run-time to expose all inherent parallelism, minimize communication and synchronization overheads, and balance load. The methodology is based on a message passing interface model (MPI) using the recursive coordinate bisection (RCB) for domain partition. For this work, a semi-implicit projection method has been implemented to solve the incompressible Navier Stokes equations. All numerical implementations are an extension of a sequential Fortran 90 code, called "AMR3D", developed in the work of Nós (2007) .The efficiency and robustness of the applied methodology are verified via convergence analysis using the method of manufactured solutions. Validations were performed by simulating an incompressible jet flow and a lid driven cavity flow.

The present work describes the development of a parallel distributed-memory implementation, of an octree data structure, linked to an adaptive Cartesian mesh to solve the Navier- Stokes equations. The Finite Volume Method was used in the spatial discretization where the diffusive terms approximated by the central differences method. The temporal discretization was accomplished using the Adams-Bashforth method. Both temporal and spatial discretizations are of second-order of accuracy. The immersed boundary method was employed to represent immersed solid bodies in the flow and the Velocity-pressure coupling is done using the fractional-step method of two steps. Results, for sequential and parallel simulations, are presented both for the adaptive octree mesh and for a rectilinear mesh. Moreover, all simulated results were obtained using a external solver for the Poisson equation, from the pressure correction, in the fractional-step method. The numerical results are compared with numerical and experimental data, and the agreement between the two is found to be good.

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

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior