Resumo em Inglês:

The purpose of this work is to define a new algorithm for converting a CSG representation into a B-Rep representation. Usually this conversion is done determining the union, intersection or difference from two B-Rep represented solids. Due to the lack of explicit representation of surface boundaries, CSG models must be converted into B-Rep solid models when a description based on polygonal mesh is required. A potential solution is to convert a CSG model into a voxel based volume representation and then construct a B-Rep solid model. This method is called CSG voxelization, conceptually it is a set membership classification problem with respect to the CSG object for all sampling points in a volume space. Marching cubes algorithms create a simple mesh that is enough for visualization purposes. However, when engineering processes are involved, a solid model is necessary. A solid ensures that all triangles in the mesh are consistently oriented and define a closed surface. It is proposed in this work an algorithm for converting CSG models into triangulated solid models through propagation based marching cubes algorithm. Three main new concepts are used in the algorithm: open boundary, B-Rep/CSG Voxelization mapping and constructive triangulation of active cells. The triangles supplied by the marching cubes algorithm need not be coherently oriented; the algorithm itself finds the correct orientation for the supplied triangles. The proposed algorithm restricts the exploration to the space occupied by the solid's boundary. Differently from normal marching cubes algorithms that explore the complete sampled space.

Resumo em Inglês:

The laminar fully developed free surface flow in a helical channel with finite pitch and rectangular section is modeled. The mass and momentum conservation equations are written in a local orthogonal system and solved numerically using the finite volume method. The free surface position, determined using the height of liquid method, compares favorably against the experimental data. The main and secondary velocity fields are determined as well as the friction factor for Reynolds number ranging from 352 to 856.

Resumo em Inglês:

A fast algorithm for inverse airfoil design using an efficient panel method for potential flow calculation is presented. The method employs linear vortex distributions on the panels and a consistent procedure for imposing the Kutta condition, thus eliminating the spurious aerodynamic loading that usually appears at a cusped trailing edge. The algorithm searches the airfoil ordinates attending to a given surface velocity distribution with fixed abscissas. It begins with a guessed starting shape and successively modifies it by an iterative process, such that the normal velocity vanishes and the calculated velocity distribution gradually approaches the required one. Each iteration is performed in two main steps: 1) the flow calculation step; 2) the geometrical marching step, where the calculated velocity distribution is compared with the required one and a transpiration model is applied to modify the current shape towards another one more close to the target shape. The geometrical marching is conducted by varying the panel slopes as a function of the normal velocity excess induced by the difference between the required and calculated velocities. A scheme is applied in order to close the body shape. Various test cases were carried out and are presented for the efficiency and robustness validation of the proposed inverse algorithm.

Resumo em Inglês:

The machining parameter settings installed at CNC EDM machines are developed under optimum process conditions. Standard workpiece and electrode materials are used traditionally by machine manufacturers to establish the EDM parameter settings. However, this is not the usual situation of the tooling industry, where many different grades of workpiece and tool electrode materials are used. Consequently, the customers are required to develop their own process parameters, which normally demand many experimental tests. According to the aforementioned argument an experimental investigation on the EDM of AISI P20 tool steel under finish machining has been carried out. The tests were performed with graphite and copper as tool electrodes. Important EDM electrical parameters that influence the process performance were investigated. The measured technological outputs were the material removal rate Vw, volumetric relative wear <FONT FACE=Symbol>J</FONT> and workpiece surface finish Ra . The main conclusions can be summarized as follows: the best results for material removal rate Vw were reached when EDM with negative graphite electrodes. Graphite and copper tools presented similar results of Vw for positive polarity. For graphite and copper tools the lowest values of volumetric relative wear were achieved for positive polarity. The best surface roughness Ra was obtained for copper electrodes under negative polarity.

Resumo em Inglês:

This work demonstrates that scratch test techniques can be used to provide a quick and cost effective evaluation of cutting fluids. Apparent coefficient of friction and specific energy for the scratch steel samples under several lubrication conditions provides a good indicator of cutting fluid performance. This is followed by evaluation of the surface finish and the cutting force of the ABNT NB 8640 steel with emulsion and synthetic cutting fluids, at 5% of concentrations, and neat mineral oil in the turning process. Comparative tests were carried out under dry and wet conditions. Results show that the linear scratch test was not efficient while the pendular scratch test was efficient tool in the classification of cutting fluids. The results can be transferred to conventional machining due to its dynamic nature.

Resumo em Inglês:

This paper presents a two-dimensional numerical simulation of flows around different bluff bodies, at Re = 100 and 200, using the Immersed Boundary (IB) method, as a sequence of a previous work. The force density term required by the IB method is obtained with the Virtual Physical Model (VPM). Simulations were carried out for two circular cylinders of different diameter in tandem, two cylinders of the same diameter in tandem and two cylinders placed in side by side arrangement. The configurations of seven cylinders in a 'V' arrangement, for angles of 40o < alpha < 180o, were also simulated. A configuration of 23 different bluff bodies, representing a transverse cut in a central tower of an offshore structure, has been also simulated and the results were compared with a single compact square, of equivalent size. The Strouhal number, the drag and the lift coefficients were also calculated. The Strouhal number is calculated using the Fast Fourier Transform (FFT) of the lift coefficient temporal distribution. Visualization of the vorticity and pressure fields and the streamlines are presented for each simulation showing the flow dynamics and patterns. It was possible to verify that the IB method with VPM is a powerful methodology to simulate flows in the presence of complex geometries.

Resumo em Inglês:

Crooked beams and plates with arbitrary initial geometric imperfections are optimized in order to improve their prebuckling response in the presence of uncertain loadings. A novel optimization approach is presented to simultaneously handle the two types of uncertainties: arbitrary initial imperfection patterns and arbitrary loadings. A remarkable improvement in the prebuckling response of optimal designs is achieved by reducing the level of prebuckling displacements measured in some appropriate norm, irrespective of the uncertain imperfection pattern or loading. Two different norms are proposed, each one applicable to the beam or to the plate problem. The definitions of appropriate norms allow for the use of a minimax optimization approach that can consider the arbitrariness of both geometric imperfections and loadings. It is shown that the minimax procedure leads to optimum structural designs, in terms of optimal stiffness distribution, that are at the same time insensitive to perturbations in the loading space and to the pattern of initial imperfections in structure.

Resumo em Inglês:

The use of cutting fluids is well recognized for several years. To cater the needs of state- of- art machining processes, several fluid formulations are available in the present day market. Of such available fluids, water-soluble fluids are dominant. Though, the need of cutting fluids is explored, the functionality of different ingredients of the fluid is not much investigated. The present work is an attempt to study the role of emulsifier on the properties and performance of cutting fluid. In the present part of the paper, estimation of basic properties and microbial contamination of the fluids with varying emulsifier contents is dealt.

Resumo em Inglês:

This paper describes some of the key experimental results and features obtained from a study on upward flow boiling of water in a vertical tube at sub-atmospheric pressures. The experiments were conducted at 250, 500 and 1000 mbar (abs) exit pressures. From the experimental results, several interesting features and effects were observed, namely, heat transfer coefficient maxima at around zero thermodynamic quality were observed for high inlet liquid subcoolings at low sub-atmospheric pressures, which were attributed to local thermal non-equilibrium instability (Jeglic and Grace, 1965). Such effects were also observed in boiling of pure hydrocarbons in vertical tubes (Kandlbinder, 1997; Urso et al., 2002) and were explained and explored quantitatively with a thermal non-equilibrium slug flow model (Barbosa and Hewitt, 2005) that associates vigorous bubble growth at sub-atmospheric pressures to the formation of large Taylor bubbles separated by subcooled liquid slugs.

Resumo em Inglês:

Travelling-wave dielectrophoretic phenomena involving cell detection and manipulation are very interesting for biomedical and biotechnological applications. However, electrohydrodynamic phenomena may interfere with the action of dielectrophoresis. The main goal of our study is to calculate the interplay of these effects. In so doing, we have been able to go beyond the order-of-magnitude estimations, which were available in the literature. In this framework we have taken into account the effects of using square signals, which calls for a calculation of the combined polarisability effects due to the superposition of different frequencies. Thermal gradients are also a triggering agent of electrohydrodynamic effects. We have undertaken the pertinent thermal simulations with a concern for the influence of different boundary conditions. The dynamics of the thermal fields were also assessed in order to estimate the characteristic times of electrohydrodynamic phenomena. All these results have been used in a study of the fluid flow pattern motion at different frequencies and its influence on the particle behaviour.

Resumo em Inglês:

The present work studies upwind schemes applied to the solution of aeronautical and aerospace problems. The Harten, the Frink, Parikh and Pirzadeh, the Liou and Steffen and the Radespiel and Kroll algorithms, all first order accurate in space, are studied. The Euler equations in conservative form, employing a finite volume formulation and a structured spatial discretization, in the two-dimensional space, are solved. A time splitting method and a Runge-Kutta method of five stages are used to perform the time march of the numerical schemes. The steady state physical problems of the supersonic flow along a ramp and around a blunt body configuration are studied. All algorithms are accelerated to the steady state solution using a spatially variable time step. This technique has proved excellent gains in terms of convergence ratio as reported in Maciel. The results have demonstrated that the Liou and Steffen scheme has presented the most critical solutions, in both example-cases, in relation to the others schemes and a more accurate solution, in terms of the determination of the stagnation pressure in the blunt body case, than the Harten and the Radespiel and Kroll schemes. In the ramp problem, the Harten scheme predicts the best pressure distribution along the ramp wall in comparison with theoretical results. In the blunt body problem, the Liou and Steffen scheme presents the highest value of Cp at the configuration nose in relation to the other schemes. Values of cL and cD have been accurately predicted by all schemes, except by the Harten scheme.

Resumo em Inglês:

This paper aims to present Galerkin Least-Squares approximations for flows of Bingham plastic fluids. These fluids are modeled using the Generalized Newtonian Liquid (GNL) constitutive equation. Their viscoplastic behavior is predicted by the viscosity function, which employs the Papanastasiou's regularization in order to predict a highly viscous behavior when the applied stress lies under the material's yield stress. The mechanical modeling for this type of flow is based on the conservation equations of mass and momentum, coupled to the GNL constitutive equation for the extra-stress tensor. The finite element methodology concerned herein, the well-known Galerkin Least-Squares (GLS) method, overcomes the two greatest Galerkin shortcomings for mixed problems. There is no need to satisfy Babuška-Brezzi condition for velocity and pressure subspaces, and spurious numerical oscillations, due to the asymmetric nature of advective operator, are eliminated. Some numerical simulations are presented: first, the lid-driven cavity flow of shear-thinning and shear-thickening fluids, for the purpose of code validation; second, the flow of shear-thinning fluids with no yield stress limit, and finally, Bingham plastic creeping flows through 2:1 planar and axisymmetric expansions, for Bingham numbers between 0.2 and 133. The numerical results illustrate the arising of two distinct unyielded regions: one near the expansion corner and another along the flow centerline. For those regions, velocity and pressure fields are investigated for the various Bingham numbers tested.