RCAAP Repository

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Numerical simulations to predict erosion in cyclone separators due to the impact of particles were accomplished in this work. The predictions were performed through Computational Fluid Dynamics methods. The geometry investigated was similar to that of a second stage cyclone of a fluidized catalytic cracking unit. The numerical results were compared to experimental results available in the literature. The cyclone walls were made of acrylic with multiple coatings of drywall in the experiments. However, the implemented models to predict the erosion were developed for metallic materials. In this context, the validation was performed with cases in which the materials involved were the same as that used in the implemented models. The influence of the two-phase models, turbulence modelling, mesh resolution, dipleg presence and the models of particle/wall collision in erosion were evaluated after the validation. It was found that the turbulence modelling and mesh resolution were the most relevant factors in the erosion prediction, at least in the studied cases. Another relevant parameter is the friction factor, whose value significantly modifies the erosion rate. It was noticed that the interaction between the fluid and the particles reduces the erosion rate, even at low concentrations, as well as the interparticle collisions. Generally, the eroded regions were observed to match those from the experiments.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

In this work small and large-scale wear tests of polyurethane (PU) sliding against polyamide (PA) were carried out. In the large-scale tests, PU and PA samples were submitted to conditions similar to those found in oil and gas platform operations. The wear of these samples was measured using a coordinate measuring machine. Using the small-scale test configuration, the influence of contact geometry, sliding velocity, sliding stroke and contact pressure at the coefficient of friction (COF) and on the wear mechanisms was evaluated. In both test scales, the wear mechanisms of PA and PU samples were analyzed using a scanning electron microscope. The thermal behavior of PA samples was investigated using differential scanning calorimetry. The PA physic-chemical analysis was performed using X-ray diffraction and Raman spectroscopy and infrared spectroscopy for PU. In large-scale tests was observed that the outer cover of flexible riser pipes had a maximum wear rate of 0.016 mm/km, while in the liner this wear rate was 0.264 mm/km. It was also observed that variations in the hardness of PU liner lead to an important change on the wear mechanisms and, consequently, on the wear rate. The wear rate at large-scale was also strongly affected by the contact temperature. Due to the reduction of the contact temperature, a sharp reduction on the liner wear rate was observed. However, no significant variation in the rate of wear of PA riser cover was noticed. In small-scales tests, under the same sliding velocity and contact pressure observed in the field, the tribological wear behavior was changed. It was also observed that increasing the contact pressure or reducing the sliding stroke leads to a decrease the COF, while the sliding velocity only induced a change in this parameter if the contact temperature was significantly increased. Using test parameters in small scale which lead to a temperature rise in the tribocontact, it was possible to reproduce the tribological behavior observed in large-scale test.

The determination of the dynamic parameters of great or complex structures can be made using modal synthesis methods subdividing the complete structure in substructures. The employment of this method may be done by using analytical or experimental procedures. Generally speaking, poor eigenvalues and eigenvectors may be identified using experimental modal synthesis methods due to a normalization deficient process of the modal bases and to the low orthogonality condition of the identified bases. The contribution of this current work is about the improvement of the great or complex structures dynamic identification process by using the experimental modal synthesis method. The basis of this research methodology is the SMFR (Modal Synthesis with Residual Flexibilities) method and an identification of the physical matrices of the system by using the experimental FRF (Frequency Response Function), called ACS (Simultaneous Curve Fitting) method. These matrices contribute to the improvement of the orthogonality conditions and normalization of the experimental modal bases. Simultaneously, two new methods (CSME and CSMF) for the automatic choice of the used substructures modal bases in the modal synthesis process have been developed. The validation procedures of these methodologies were developed by using examples of numerical simulation and experimental models. Using CSMF method, it was possible to improve the modal choice process, automatizing and minimizing the interference of the user in the modal synthesis method. In the case of experimental data with high level noise, the recommended is the iterative method.

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The present work aims to present a model of fluid-structure interaction, which was implemented in IMERSPEC2D code, that is a numerical code that solves problems of flow over immersed bodies by using the pseudospectral Fourier method coupled with the immersed boundary method. Initially, it has been proposed a comparative analysis between two numerical methods: Finite Volume Method (FVM) and Fourier Pseudospectral Method (MPEFO) with and without the use of the Immersed Boundary Method (MFI). This first analysis includes verification and validation of both numerical codes, in order to determine the advantages and disadvantages of MPEFO compared to MVF. The second part is the implementation of a fluid structure interaction model in IMERSPEC2D code, this approach takes account the partitioned interaction model, by using the fourth order optimized Runge-Kutta method in both time advanced of the fluid and of the structure. Furthermore, it is proposed to non-dimensionalization of the equations that models the structural movement. These implementations yield results with more accuracy and low computational cost, by proving the applicability and potentiality of IMERSPEC methodology. Lastly, several applications have been held in drilling and extraction oil problems. These simulations are still two-dimensional, however, it is possible to observe interesting flow patterns into extraction pipes for different aspect ratios and Reynolds numbers.

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Universidade Federal de Uberlândia

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

This study investigated the machinability of Ti-6Al-4V alloy with newly developed cutting tools such as uncoated (T1 and T3) and coated (T2 and T4) cemented carbides, Polycrystalline Diamond (PCD) T5 and T6 inserts, Cubic Boron Nitride (CBN) T7,T8,T9 inserts, SiC Whiskers Reinforced Ceramic (T10) insert, and Al2O3 base (T11) and Si3N4 base nano-grain size ceramic (T12) inserts using various cooling environments such as high pressure coolant supplies at pressures of 7 MPa, 11 MPa and 20.3 MPa, argon enriched environment and conventional coolant flow at high speed machining conditions typical of finish turning operation. Tool life and failure modes, wear mechanisms, component forces generated, surface integrity, surface finish and chip form data were used to assess the performance of the different cutting tools and cooling environments investigated. PCD and carbide inserts gave the best performance, in terms of tool life, when machining Ti-6Al-4V alloy. In general coarser (T1 and T4) grain size carbides and PCD (T5) inserts gave the best overall performance in terms of lower wear rate hence longer tool life compared to finer grain (T2,T3 and T6) grades. Encouraging tool life can be achieved when machining with high pressure coolant supply relative to conventional coolant flow and in the presence of argon. Tool lives generally increased with increasing coolant pressure due to the ability of the high coolant pressure to reduce the tool-chip contact length/area and to lift the chip, thereby providing adequate lubrication at the tool-chip interface with consequent reduction in friction. Machining with T1, T4 and T10 inserts in presence of argon was only able to prevent chip ignition with no improvement in tool life, due probably to the suppression of the cooling and/or lubrication characteristics of argon gas when machining at cutting conditions investigated. Up to 8 fold improvement in tool life were achieved when machining with PCD inserts relative to carbide inserts under conventional coolant flow. All the grades of CBN inserts gave poor performance during machining due to accelerated nose wear and, in some cases, severe chipping of the cutting edge associated with a relatively high diffusion wear rate that tends to weaken the bond strength of the tool substrate. An increase in the CBN content tends to accelerate notch wear rate, consequently diminishing tool life under the cutting conditions investigated. Micron and nano-grain size ceramics did not demonstrate satisfactory performance in terms of tool wear rate and tool life, due to severe abrasive wear and chipping of the cutting edge, hence the poor machined surfaces generated. Nose wear was the dominating tool failure mode when machining with carbide, PCD and CBN (T7) inserts due to a reduction in tool-chip and tool-workpiece contact lengths and the consequent increase in both normal and shear stresses and temperature at the tool tip, while severe notching and chipping occurred when machining with CBN (T8 and T9) and micron grain size ceramics. Severe notching also occurred when machining with nano-grain ceramic inserts, often leading to catastrophic tool failure at speeds in excess of 110 m min-1. Machining with PCD tools gave lower cutting forces than carbides inserts. Surface roughness values generated with carbides, PCD and CBN inserts were generally within the 1.6 μm rejection criterion for finish machining and above 2 μm when machining with all grades of ceramics employed. Micrographs of the machined surfaces show that micro-pits are the main damage to the machined surfaces. Microhardness of the machined surfaces when machining with carbides varied randomly around the hardness values of the workpiece material prior to machining. Machining with PCD tools generally led to softening of machined surfaces. Increase in cutting speed generally led to increased hardness when machining with the larger grain size PCD (T5) tool using conventional coolant flow and with coolant pressures up to 11 MPa. No evidence of plastic deformation was observed on the machined surfaces and the surface integrity of the finish machined surfaces is generally in agreement with Rolls Royce CME 5043 specification.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior