Resumo em Inglês:

Here, we propose an extension of the Partition of Unit Finite Element Method (PUFEM) and a numerical procedure for the solution of J2 plasticity problems. The proposed method is based in the Moving Least Square Approximation (MLSA) and is capable of overcoming singularity problems, in the global shape functions, resulting from the consideration of linear or higher order base functions, in the classical PUFEM. The classical PUFEM employs a single constant base function and results in the so-called Sheppard functions. In order to avoid the presence of singular points, the method considers an extension of the support of the classical PUFEM weight function. Moreover, by using a single constant base function, the proposed method reduces in the limit, to the classical PUFEM. Since the support of the global shape functions do overlap, the method becomes closely related to the Element Free Galerkin (EFG) method. The most important characteristic of the proposed method is that it can be naturally combined with the EFG method allowing us to impose, in some limiting sense, the essential boundary conditions, avoiding the usage of the penalty and/or multiplier methods. In order to obtain higher order global shape functions a hierarchical enhancement procedure was implemented.

Resumo em Inglês:

This paper presents an experimental study aiming to identify the means to minimize the reduction of the overall performance of a gasoline engine when employing the Exhaust-Gas Recirculation (EGR) technique that reduces NOx emissions. The increase of the compression ratio and turbocharging was evaluated as a mean to recover the original performance. The formation of pollutants and the engine performance were verified at full and partial loads. The results show that the combination of exhaust gas recirculation with turbocharger or through an increase of the compression ratio enhance the relation between the engine performance and the emission of NO. However, the turbocharger seemed to be more sensitive to the negative effects of the EGR technology.

Resumo em Inglês:

Products developed at industries, institutes and research centers are expected to have high level of quality and performance, having a minimum waste, which require efficient and robust tools to numerically simulate stringent project conditions with great reliability. In this context, Computational Fluid Dynamics (CFD) plays an important role and the present work shows two numerical algorithms that are used in the CFD community to solve the Euler equations applied to typical aerospace and aeronautical problems. Particularly, unstructured discretization of the spatial domain has gained special attention by the international community due to its ease in discretizing complex spatial domains. This work has the main objective of illustrating some advantages and disadvantages of a centered algorithm and an upwind one using an unstructured spatial discretization of the flow governing equations. Numerical methods include a finite volume formulation and the Euler equations are applied to solve a supersonic flow over a ramp problem, a hypersonic flow over a blunt body problem, a hypersonic flow over a double ellipsoid problem and a supersonic flow over a simplified configuration of VLS problem. Convergence acceleration is obtained using a spatially variable time stepping procedure.

Resumo em Inglês:

A numerical study is reported on power law shaped leading edges situated in a rarefied hypersonic flow. The sensitivity of the heat flux and drag coefficient to shape variations of such leading edges is calculated by using a Direct Simulation Monte Carlo method. Calculations show that the stagnation point heating on power law leading edges with finite radius of curvature follows the same relation for classical blunt body in continuum flow; it scales inversely with the square root of the curvature radius at the nose. Furthermore, for those leading edges with zero or infinity radii of curvature, the heat transfer behavior is in surprising agreement with that for classical blunt body far from the nose of the leading edge.

Resumo em Inglês:

Evaporative cooling operates using water and air as working fluids. It consists in water evaporation, through the passage of an air flow, thus decreasing the air temperature. This system has a great potential to provide thermal comfort in places where air humidity is low, being, however, less efficient where air humidity is high. A way to solve this problem is to use dehumidifiers to pre-conditioning the process air. This paper presents a system that can be used in humid climates coupling desiccant dehumidification equipment to evaporative coolers. The paper shows, initially, the main characteristics of the evaporative cooling and of the adsorption dehumidification systems. Later on the coupled systems, in which occurs a dehumidification by adsorption in a counter flow rotary heat exchanger following the evaporate cooling of the air in evaporative coolers, are analyzed. The thermodynamic equations of state are also presented. Following, this paper analyzes some operation parameters such as: reactivation temperature, R/P relationship (reactivation air flow/ process air flow) and the thermodynamic conditions of the entering air flow. The paper shows the conditions for the best operation point, with regard to thermal comfort conditions and to the energy used in the process. In addition this paper presents an application of the system in different climate characteristics of several tropical and equatorial cities.

Resumo em Inglês:

Composites made by hand lay-up are directed influenced by some fabrication factors, e.g. the stacking sequence, fiber volume fraction, as well as the cure process This study takes into consideration an E-glass/epoxy plain weave woven fabric composite made by hand lay-up. After the stacking sequence is completed, three sets of plates are selected and each one is cured differently. The three selected cure processes are: cure on air, cure vacuum assisted, and cure under compression. A variance study based on stiffness from ASTM D 3039/3039M tensile tests is performed to check the statistical differences caused by the cure processes. Additionally, a microscopic analysis is performed to identify the voids formation rate. The coupling between macro and micro-mechanical analysis is done by a non-dimensional coefficient which is able to capture the rate of defects generated by each cure process.

Resumo em Inglês:

In this paper a flexible finite element computational tool developed to investigate fluid-structure interaction applications in two dimensions is described. We consider problems which can be modelled as a viscous incompressible fluid flow and a rigid body-spring system interacting nonlinearly with each other. The coupling is dealt with the use of an interface approach, in which each physics involved is solved with different schemes and the required information is transferred through the interface of both systems. This approach is, at least in principle, very flexible and computationally efficient as the best available scheme can be adopted to solve each physics. Here, a stabilized FEM considering the "ALE" (Arbitrary Lagrangian-Eulerian) formulation with Crank-Nicholson time-integration is employed for the fluid-dynamics analysis, and the Newmark Method is used for the structural dynamics. Several important tools were incorporated into our system including different possibilities for the mesh movement algorithm, the computational domain decomposition into regions with and without mesh deformation, and the remeshing strategy (either global or local) to keep the necessary mesh quality. As application we present a study of the forced lock-in phenomena and a preliminary investigation on the suppression (or at least the reduction) of the vortex induced vibrations (VIV) on a solid circular cylinder using an idealization of a periodic acoustic excitation.

Resumo em Inglês:

A new phenomenological model is introduced by applying established conceptual models for direct injection combustion to develop a mathematical description of events. The model has the capability to predict particulate mass output, as well as a particulate mass history over a single combustion event. The model was developed in a Matlab-Simulink environment to promote modularity. Results of particulate mass output from single cylinder laboratory engine, and six-cylinder vehicular engine were used to determine the validity of the predictions made. Although predicted values do not perfectly match measured values, there is certainly reasonable agreement.

Resumo em Inglês:

In this work simulations of incompressible fluid flows have been done by a Least Squares Finite Element Method (LSFEM) using velocity-pressure-vorticity and velocity-pressure-stress formulations, named u-p-omega and u-p-tau formulations respectively. These formulations are preferred because the resulting equations are partial differential equations of first order, which is convenient for implementation by LSFEM. The main purposes of this work are the numerical computation of laminar, transitional and turbulent fluid flows through the application of large eddy simulation (LES) methodology using the LSFEM. The Navier-Stokes equations in u-p-omega and u-p-tau formulations are filtered and the eddy viscosity model of Smagorinsky is used for modeling the sub-grid-scale stresses. Some benchmark problems are solved for validate the numerical code and the preliminary results are presented and compared with available results from the literature.

Resumo em Inglês:

The objective of the present study was verify the influence of specimen dimensions on polymerization contraction stress of a self-cure dental composite and investigate the influence of confinement (expressed by the ratio between the bonded and unbonded area of the composite, or 'C factor') and volume of the specimen on stress values. The composite was inserted between the flat surfaces two glass rods attached to a universal testing machine. Specimen dimensions were defined using glass rods with different diameters (2.5, 5, or 8 mm) and adjusting the distance between them (0.63, 0.83, 1.25 or 2.5 mm). An extensometer was used to keep specimen height constant. Force development was monitored for 30 min and the maximum value was used to calculate nominal stress (MPa). System deformation (compliance) was estimated in order to calculate stress values on an ideally rigid situation. Data were analyzed by ANOVA/Tukey test (alpha=0.05) and regression analysis. The interaction was significant (p<0.001). Differences in nominal stress for different heights were verified only for 5-mm and 8-mm diameter specimens. In general, lower heights produced higher stress values. Regression analysis using all the collected data showed a linear correlation between stress and 'C factor'. However, non-linear relationships were found when stress was plotted against 'C factor' or volume selecting specimens with similar same diameter. It was concluded that specimen dimensions influenced test results. However, neither 'C factor' nor volume can be considered reliable predictors of contraction stress values.

Resumo em Inglês:

This work presents a computational model for the viscous flow through rectilinear cascades of axial turbomachinery. The model is based on modifications of the classical Hess & Smith panel method. The viscous effect of the attached flow portion is introduced by means of normal transpiration velocities obtained from the boundary layer calculations on the airfoil contour. At the separated flow portion, fictitious velocities semi-empirical normal velocities are introduced assuming a constant pressure in the wake. When the separation is not detected, it is possible to simulate the effect of the small wake near the trailing edge by using an injected flow on a distance based on the Gostelow (1974) fairing-in procedure. The numerical model presents two iteration cycles: the first one to find the separation point, and the second one to accomplish the viscous-inviscid interaction, in which the transpiration velocities and the flow injection are submitted to a relaxation process in order to guarantee the convergence of the method. Results for the pressure distributions, flow turning angles and lift coefficients are compared with experimental data for the model validation.

Resumo em Inglês:

Standard caloric measurements on Shape Memory Alloys (SMAs) are usually carried out with the specimen in a state free of stress, by means of standard calorimeters. However, in its every application, the material is subjected to some load, being therefore necessary to investigate the influence of loading on the caloric behavior of SMAs, in order to take this into account when modeling their thermodynamic behavior. The present work investigates the influence of loading on the heat of transformation in SMAs. Experimental measurements were carried out on NiTi samples and a mathematical description of the observed behavior was developed. The theoretical results are in agreement with the experimental ones.

Resumo em Inglês:

In this article the invariance of the Novozhilov's mean rotation measures will be emphasize by the invariance of the determinant of the gradient of deformation tensor of continuum mechanics, or the invariance of the second principal invariant of the tensor (I + E)-1 W.

Resumo em Inglês:

Recently the bond strength of composite resin to tooth has received attention from researchers of dental materials. Limitations imposed by the biological substrate, such as the size of the specimen, fostered the development of a tensile test with small dimensions. Due to the reduced size of the specimens, the test is called microtensile test. The specialized literature has not presented standards for the test parameters and the relatively large scatter of published bond strength data probably reflects the lack of standards for the test parameters. The objective of this study is to evaluate how specimen geometry and loading conditions affect the estimation of bond strength. A numerical simulation of the test using a Finite Element Model was performed to determine the associated variations on the stress field imposed by variations in the geometry of the specimen and loading conditions. The Finite Element pre-processing and post-processing was performed on Patran® and the Finite Element processing was performed on Marc®. Results from numerical simulations show that geometrical parameters and loading conditions have a significant influence on the stress field. Some suggestions of standards for the microtensile test considering the non-uniform stress field are presented.

Resumo em Inglês:

This paper proposes the use of artificial neural networks to predict the flexural resistance and initial stiffness of beam-to-column steel joints using the back propagation supervised learning algorithm. Three types of steel beam-to-column joints were investigated: welded, endplate and bolted with top, seat and double web angles, respectively. The neural networks results proved to be consistent with experimental and design code reference values.

Resumo em Inglês:

Distribution of magnetic field during electromagnetic continuous casting of hollow billets of aluminum alloys is studied by the method of numerical simulation. Two-dimensional axis-symmetric finite element model including water-cooled core, outer mould, ingot, inner and outer induction coil has been established. Distribution of magnetic flux density is obtained by solving magnetic vector potential formulations. 1) In electromagnetic casting, inner and outer induction coil interact, magnitude and admeasurements of current affect directly distribution of magnetic flux density. 2) Magnetic flux density near interior surface of pipe wall is increased notablely by increasing appropriately frequency. 3) Phase difference affects the magnitude and direction of the gradient of magnetic flux density.