Resumo em Inglês:

The present work implements the spectral finite volume scheme in a cell centered finite volume context for unstructured meshes. The 2-D Euler equations are considered to represent the flows of interest. The spatial discretization scheme is developed to achieve high resolution and computational efficiency for flow problems governed by hyperbolic conservation laws, including flow discontinuities. Such discontinuities are mainly shock waves in the aerodynamic studies of interest in the present paper. The entire reconstruction process is described in detail for the 2nd to 4th order schemes. Roe's flux difference splitting method is used as the numerical Riemann solver. Several applications are performed in order to assess the method capability compared to data available in the literature. The results obtained with the present method are also compared to those of essentially nonoscillatory and weighted essentially non-oscillatory high-order schemes. There is a good agreement with the comparison data and efficiency improvements have been observed.

Resumo em Inglês:

The purpose of this study was to develop new approaches for predicting transonic flutter and limit cycle oscillations (LCO) using computational methods. The TSD equation is separated into the in-phase and out-of-phase components through a nonlinear harmonic averaging method. It is then solved in the frequency domain to obtain the aerodynamic forcing function which is needed in the flutter and LCO analyses. To predict flutter, equations are developed using the concept of generalized coordinates. The flutter speed is determined by examining the frequency-domain matrix equation eigenvalues. Flutter characteristics of the AGARD I-445.6 wing are analyzed. Flutter speed and frequency are well predicted in subsonic speed, but are overestimated in supersonic flow. To predict limit cycle oscillations, the frequency-domain aerodynamic coefficients are used to obtain a nonlinear time-domain expression for the aerodynamic force. Limit cycle oscillation characteristics of the DAST ARW-2 wing are analyzed. The results show LCO for Mach numbers ranging from 0.915 to 0.940.

Resumo em Inglês:

This paper presents an analysis of design guidelines for steel-concrete composite beams, formed by concrete-filled cold-formed steel sections. The study is based on experimental results for connector resistance (push-out) and for four full-scale beam bending tests. The accuracy of analytical design equations is evaluated by comparing their predictions with experimental results. Model bias and model uncertainty of analytical design equations are evaluated. The uncertainty in design variables (steel and concrete resistance, dead and live loads, model errors) is taken into account, and reliability index of code-compliant beams is evaluated. Results show that the models for shear connector and for beam bending resistance are fairly accurate, and represent very little contribution to problem uncertainty and failure probabilities. Results show that for practical beam lengths, full material interaction is guaranteed, and failure is dominated by bending. Reliability indexes of the order of 2.2 to 2.8 are obtained, reflecting reliability of the design procedures studied. These values are low, in comparison to target reliability levels of 3.0 used in code calibration, and should be interpreted carefully in future code revisions.

Resumo em Inglês:

This article is concerned with finite element approximations for yield stress fluid flows through a sudden planar expansion. The mechanical model is composed by mass and momentum balance equations, coupled with the Bingham viscoplastic model regularized by Papanastasiou (1987) equation. A multi-field Galerkin least-squares method in terms of stress, velocity and pressure is employed to approximate the flows. This method is built to circumvent compatibility conditions involving pressure-velocity and stress-velocity finite element subspaces. In addition, thanks to an appropriate design of its stability parameters, it is able to remain stable and accurate in high Bingham and Reynolds flows. Numerical simulations concerning the flow of a regularized Bingham fluid through a one-to-four sudden planar expansion are performed. For creeping flows, yield stress effects on the fluid dynamics of viscoplastic materials are investigated through the ranging of Bingham number from 0.2 to 100. In the sequence, inertia effects are accounted for ranging the Reynolds number from 0 to 50. The numerical results are able to characterize accurately the morphology of yield surfaces in high Bingham flows subjected to inertia.

Resumo em Inglês:

Thermodynamic property data including specific enthalpy, specific entropy and specific volume were generated for the new refrigerant HFO-1234yf (2,3,3,3-tetrafluoroprop-1-ene) using the well-known Peng and Robinson cubic equation of state. A general approach applicable to any fluid based on the concept of departure functions has been applied. Data for saturated vapor pressure, saturated liquid density, ideal gas heat capacity at constant pressure and critical properties were obtained from the open literature. The predictive capability of the proposed calculation methodology has been validated with thermodynamic property data for HFC-134a (1,1,1,2-tetrafluoroethane), showing average deviations lower than 0.6%. A thermodynamic analysis of the new refrigerant in the light of thermodynamic properties of an idealized cycle was carried out so as to measure its performance with respect to that HFC-134a under the same evaporating and condensing pressure conditions.

Resumo em Inglês:

The problem of SLAM (simultaneous localization and mapping) is a fundamental problem in autonomous robotics. It arises when a robot must create a map of the regions it has navigated while localizing itself on it, using results from one step to increase precision in another by eliminating errors inherent to the sensors. One common solution consists of establishing landmarks in the environment which are used as reference points for absolute localization estimates and form a sparse map that is iteratively refined as more information is obtained. This paper introduces a method of landmark selection and clustering in omnidirectional images for on-line SLAM, using the SIFT algorithm for initial feature extraction and assuming no prior knowledge of the environment. Visual sensors are an attractive way of collecting information from the environment, but tend to create an excessive amount of landmarks that are individually prone to false matches due to image noise and object similarities. By clustering several features in single objects, our approach eliminates landmarks that do not consistently represent the environment, decreasing computational cost and increasing the reliability of information incorporated. Tests conducted in real navigational situations show a significant improvement in performance without loss of quality.

Resumo em Inglês:

The fluid flow over bodies with complex geometry has been the subject of research of many scientists and widely explored experimentally and numerically. The present study proposes an Eulerian Immersed Boundary Method for flows simulations over stationary or moving rigid bodies. The proposed method allows the use of Cartesians Meshes. Here, two-dimensional simulations of fluid flow over stationary and oscillating circular cylinders were used for verification and validation. Four different cases were explored: the flow over a stationary cylinder, the flow over a cylinder oscillating in the flow direction, the flow over a cylinder oscillating in the normal flow direction, and a cylinder with angular oscillation. The time integration was carried out by a classical 4th order Runge-Kutta scheme, with a time step of the same order of distance between two consecutive points in x direction. High-order compact finite difference schemes were used to calculate spatial derivatives. The drag and lift coefficients, the lock-in phenomenon and vorticity contour plots were used for the verification and validation of the proposed method. The extension of the current method allowing the study of a body with different geometry and three-dimensional simulations is straightforward. The results obtained show a good agreement with both numerical and experimental results, encouraging the use of the proposed method.

Resumo em Inglês:

The effective design of viscoelastic dampers as applied to real-world complex engineering structures can be conveniently carried out by using modern multiobjective numerical optimization techniques. The large number of evaluations of the cost functions normally combined with the typically high dimensions of finite element models of industrial structures makes multiobjective optimization very costly, sometimes unfeasible. Those difficulties motivate the study reported in this paper, in which a strategy is proposed consisting in the use of evolutionary algorithms specially adapted to multiobjective optimization of viscoelastic systems, combined with robust condensation and metamodeling. After the discussion of various theoretical aspects, a numerical application is presented to illustrate the use and demonstrate the effectiveness of the methodology proposed for the optimal design of viscoelastic constrained layers.

Resumo em Inglês:

At present, due to their properties, the tungsten carbide-cobalt (WC-Co) composite materials are in huge demand by industry to manufacture special tools, dies/molds and components under erosion. The powder metallurgy is the usual process applied to obtain WC-Co products, but in some cases this process is unable to produce tools of very complex shapes and highly intricate details. Thus, additional conventional and non-conventional machining processes are required. In this context, the electrical discharge machining (EDM) is an efficient alternative process. However, the EDM parameters have to be properly set for any different tungsten carbide-cobalt composition and electrode material to achieve an appropriate level of machining performance. In this work, a special grade of tungsten carbide-cobalt was used as workpiece and a copper-tungsten alloy as electrode. Experiments on important EDM electrical and non-electrical parameter settings with reference to material removal rate, electrode wear ratio and surface roughness were carried out under typical rough and finish machining. This paper contributes with an attempt to provide insightful guidelines to optimize electrical discharge machining of WC-Co composite materials using CuW alloy electrodes.

Resumo em Inglês:

The use of artificial neural networks for prediction in hard turning has received considerable attention in literature. An often quoted drawback of ANNs is the lack of a systematic way for the design of high performance networks. This study presents a DOE based approach for the design of ANNs of Radial Basis Function (RBF) architecture applied to surface roughness prediction in turning of AISI 52100 hardened steel. Experimental factors are the number of radial units on the hidden layer, the algorithm employed to calculate the spread factor of radial units and the algorithm employed to calculate radial function centers. DOE is employed to select levels of factors that benefit network prediction skills. Experiments with data sets of distinct sizes were conducted and network configurations leading to high performance were identified. ANN models obtained proved capable to predict roughness in accurate, precise and affordable way. Results pointed significant factors for network design and revealed that interaction effects between design parameters have significant influence on network performance for the task proposed. The work concludes that the DOE methodology constitutes a better approach to the design of RBF networks for roughness prediction than the most common trial and error approach.

Resumo em Inglês:

Grey cast iron (GCI) is the most common material used in diesel engine blocks. However, to increase the pressures in the combustion chamber when this kind of alloy is used, it is necessary to increase the block wall thickness, what raises its weight and, consequently, does not fulfill the requirements. Thus, the compacted graphite iron (CGI) appears as an alternative for such application. It has characteristics of heat conductivity and damping similar to the GCI, but with superior mechanical properties, making possible the manufacturing of lighter engines with better performance. However, the use of CGI presents as disadvantage its worse machinability, when compared with GCI, stimulating development of machining techniques and cutting tool materials. The goal of this work is to analyze the performance of two tool materials (carbide and ceramic Si3N4) in the finishing milling of the fire face of the engine block made of CGI. To reach this goal these two materials were compared in terms of wear mechanisms and tool life in different cutting speeds. The main conclusion was that, for conditions similar to those used in this work, carbide is better than ceramic in terms of tool life in the milling CGI.

Resumo em Inglês:

The radiative transfer phenomenon is modeled by an integro-differential equation known as Boltzmann equation. This equation describes mathematically the interaction of the radiation with the participating medium, i.e., a medium that may absorb, scatter and emit radiation. In this sense, this work presents a study regarding the estimation of radiative properties in a one-dimensional participating medium by using two optimization heuristic methods, namely Simulated Annealing and Differential Evolution. First, a review of these two optimization techniques is presented. The direct radiative transfer problem solution, which is required for both optimization techniques, is obtained by using the Collocation Method. Finally, case-studies are presented aiming at illustrating the efficiency of these methodologies in the treatment of inverse radiative transfer problems.