Resumo em Inglês:

The Energy-Rate method is an applied method to determine the transient curves and stability chart for the parametric equations. This method is based on the first integral of the energy of the systems. Energy-Rate method finds the values of parameters of the system equations in such a way that a periodic response can be produced. In this study, the Energy-Rate method is applied to the following forced Mathieu equation: y" + hy' + (1 - 2β + 2β cos (2rt)) y = 2β sin² (rt) This equation governs the lateral vibration of a microcanilever resonator in linear domain. Its stability chart in the β-r plane shows a complicated map, which cannot be detected by perturbation methods.

Resumo em Inglês:

An adaptive mesh strategy based on nodal re-allocation is presented in this work. This technique is applied to problems involving compressible flows with strong shocks waves, improving the accuracy and efficiency of the numerical solution. The initial mesh is continuously adapted during the solution process keeping, as much as possible, mesh smoothness and local orthogonality using an unconstrained nonlinear optimization method. The adaptive procedure, which is coupled to an edge-based error estimate aiming to equidistribute the error over the cell edges is the main contribution of this work. The flow is simulated using the Finite Element Method (FEM) with an explicit one-step Taylor-Galerkin scheme, in which an Arbitrary Lagrangean-Eulerian (ALE) description is employed to take into account mesh movement. Finally, to demonstrate the capabilities of the adaptive process, several examples of compressible inviscid flows are presented.

Resumo em Inglês:

In this work, aspects of discretization errors associated with finite volume (FV) and equivalent finite element (FE) modelling strategies are discussed within the framework of polymer melt flow. The computational approaches are based on the generalized Newtonian model in conjunction with Cross constitutive equation. The numerical examples illustrate one and two-dimensional fluid flows, in which the latter is discretized using structured quadrilateral elements / volumes. A study on the best strategy to compute non-linear viscosities at control volume boundaries is also presented for FV. Based on well established a posteriori error estimation techniques, it is demonstrated that, in this class of problems, FV discretization errors and differences between FE and FV solutions are greatly affected by the scheme used to compute the FV non-linear coefficients at the control volume surfaces. Simulations for rectangular channels show that FE yields smaller global errors then FV for velocity and temperature solutions.

Resumo em Inglês:

This work deals with the problem of minimizing the waste of space that occurs on a rotational placement of a set of irregular bi-dimensional small items inside a bi-dimensional large object. This problem is approached with an heuristic based on simulated annealing. Traditional " external penalization" techniques are avoided through the application of the no-fit polygon, that determinates the collision-free region for each small item before its placement. The simulated annealing controls: the rotation applied and the placement of the small item. For each non-placed small item, a limited depth binary search is performed to find a scale factor that when applied to the small item, would allow it to be fitted in the large object. Three possibilities to define the sequence on which the small items are placed are studied: larger-first, random permutation and weight sorted. The proposed algorithm is suited for non-convex small items and large objects.

Resumo em Inglês:

Fiber-metal laminates (FML) composed of alternating layers of unidirectional fiber-reinforced plastic (FRP) laminae and aluminum-alloy sheets offer some superior mechanical properties, compared with either conventional laminates consisting of only FRP laminae or high-strength monolithic aluminum alloys. The environmental factors can limit the applications of composites by deteriorating the mechanical properties during service. Usually, polymeric matrix absorbs moisture when exposed to humid environments and metals are prone to surface corrosion. On the other hand, FML laminates presents more resistance of moisture when compared with their constituents. Evaluation of shear properties is particularly important in the design of mechanically fastened parts and components, which are subject to parallel and opposing loads. In this work, the shear behavior was studied for Glare laminates and its constituents in dry and wet conditions.

Resumo em Inglês:

One of the most influential sources in machining affecting surface roughness is the instantaneous state of tool edge. The main objective of the current work is to relate the in-process immeasurable cutting edge deformation and surface roughness to a more reliable easy-to-measure force signals using a robust non-linear time-dependent modeling regression techniques. Correlation between wear propagation and roughness variation is developed throughout the different edge lifetimes. The surface roughness is further evaluated in the light of the variation in both the static and the dynamic force signals. Consistent correlation is found between surface roughness variation and tool wear progress within its initial and constant regions. At the first few seconds of cutting, expected and well known trend of the effect of the cutting parameters is observed. Surface roughness is positively influenced by the level of the feed rate and negatively by the cutting speed. As cutting continues, roughness is affected, to different extents, by the rather localized wear modes either on the tool nose or on its flank areas. Moreover, it seems that roughness varies as wear attitude transfers from one mode to another and, in general, it is shown that it is improved as wear increases but with possible corresponding workpart dimensional inaccuracy. The dynamic force signals are found reasonably sensitive to simulate either the progressive or the random modes of tool edge deformation. While the frictional force components, feeding and radial, are found informative regarding progressive wear modes, the vertical (power) components is found more representative carrier to system instability resulting from the edge's random deformation.

Resumo em Inglês:

In the present research work, the effect of several process parameters on the machining characteristics of pure titanium (ASTM Grade-I) has been reported. The machining characteristics that are being investigated are tool wear rate and the quality of the machined surface in terms of the surface finish. The mechanism of material removal was has also been correlated with the machining conditions. Four different process parameters were undertaken for this study; Tool material, abrasive material, grit size of the slurry used and power rating of the machine. The optimal settings of parameters are determined through experiments planned, conducted and analyzed using Taguchi method. The significant parameters are also identified and their effect on tool wear rate and surface roughness is studied. The results obtained have been validated by conducting the confirmation experiments.

Resumo em Inglês:

Turning is a widely used metal removal process in manufacturing industry that involves generation of high cutting forces and temperature. Lubrication becomes critical to minimize the effects of these forces and temperature on cutting tool and workpiece. The conventional cutting fluids employed in machining have certain limitations with regard to their use for ecological and economic reasons. Development of lubricants that are eco friendly is acquiring importance. In this context, application of solid lubricants has proved to be a feasible alternative to the conventional cutting fluids. In the present work, Boric Acid is used as a lubricant in turning process. Variations in cutting force, tool wear, tool temperature and surface roughness are studied under different machining conditions. The results indicate that there is considerable improvement in the machining performance with Boric Acid assisted machining compared to dry and wet machining.

Resumo em Inglês:

A numerical investigation was performed to evaluate distinct convective heat transfer coefficients for three discrete strip heat sources flush mounted to a wall of a parallel plates channel. Uniform heat flux was considered along each heat source, but the remaining channel surfaces were assumed adiabatic. A laminar airflow with constant properties was forced into the channel considering either developed flow or a uniform velocity at the channel entrance. The conservation equations were solved using the finite volumes method together with the SIMPLE algorithm. The convective coefficients were evaluated considering three possibilities for the reference temperature. The first was the fluid entrance temperature into the channel, the second was the flow mixed mean temperature just upstream any heat source, and the third option employed the adiabatic wall temperature concept. It is shown that the last alternative gives rise to an invariant descriptor, the adiabatic heat transfer coefficient, which depends solely on the flow and the geometry. This is very convenient for the thermal analysis of electronic equipment, where the components' heating is discrete and can be highly non-uniform.

Resumo em Inglês:

The aim of this work is to analyze the carbon monoxide (CO) transport in the human body submitted to several physical activity levels. A complete mathematical model of the human respiratory system was developed, considering the exchanges of CO, oxygen (O2) and carbon dioxide (CO2) in the lung, blood and tissues. The human body was divided in the following compartments: alveolar, pulmonary capillaries, arterial, venous, tissue capillary and tissues. The gas transport in the blood and tissues is represented by empirical equations. The physiological parameters were described in function of physical activity. The model was validated by comparing its results with experimental data of controlled CO exposition. The agreement was excellent. CO concentration curves for critical days of São Caetano do Sul city (SP, Brazil) atmosphere were used as model input. The simulation results for some physical activities show that the more intense the activity, the larger the blood carboxyhemoglobin (COHb) level variations. The COHb level was compared with a CO quality air criteria, which showed to be adequate for low and moderate physical activity levels.

Resumo em Inglês:

Restoring the internal lumen of arteries by employing an expandable mesh (stent) of metallic or polymeric material, known as angioplasty, is one of the most common procedure for treatment of the obstructive cardiovascular diseases. The stent for angioplasty have been extensively used in the treatment of the cardiovascular diseases. They should be flexible during the implant procedure and stiff when implanted into the blood vessel. These design criteria depend on the material, geometry and the technology used in the stents manufacturing. The objective of this work is to provide the optimized geometry of a stainless steel stent by means of the topological optimization technique. The general idea of this methodology is to simulate the implant process of a stent using the finite elements method, extract the sensitivities of its flexibility and stiffness and update its material distribution or topology in an iterative procedure. The algorithm for the numerical computation of the stent material distribution is based on the heuristics and in the Lagrangian of the optimization problem. The results show that the stent optimal topologies provided by this methodology have some advantages when compared with the traditional geometries of commercial stents.