Resumo em Inglês:

The paper describes the implementation details and validation results for an agglomeration multigrid procedure developed in the context of hybrid, unstructured grid solutions of aerodynamic flows. The governing equations are discretized using an unstructured grid finite volume method, which is capable of handling hybrid unstructured grids. A centered scheme as well as a second order version of Liou’s AUSM+ upwind scheme are used for the spatial discretization. The time march uses an explicit 5-stage Runge-Kutta time-stepping scheme. Convergence acceleration to steady state is achieved through the implementation of an agglomeration multigrid procedure, which retains all the flexibility previously available in the unstructured grid code. The calculation capability created is validated considering 2-D laminar and turbulent viscous flows over a flat plate. Studies of the various parameters affecting the multigrid acceleration performance are undertaken with the objective of determining optimal numerical parameter combinations.

Resumo em Inglês:

The influence of the fiber used as reinforcement in resin matrix composite materials submitted to repeated low energy impacts is analyzed. The aramid, glass and carbon fiber composites were submitted to drop weight tests from 0.5m and from 1m. The number of impact events necessary to cause failure was recorded, and the fracture characteristics of each composite were analyzed by optical microscopy and X-rays radiography. The results obtained showed that carbon fiber composites have better performance than the glass and aramid composites. This behavior was partially attributed to the higher elastic energy absorption of carbon fibers that delays the propagation of delamination, and fiber breakage. The failure mode of glass fiber composites was dominated by the higher number of glass fibers per surface area of the composites. The worst behavior shown by aramid composites was attributed to the intrinsic anisotropy of aramid fibers.

Resumo em Inglês:

Traditional design criteria for electromagnetic valves are discussed. Performance criteria for them are also shown. A method for investigating the armature mass importance on the EFI performance is proposed. This method is based on energy losses of a mass-spring-damper system (MKsB). It was found a range of values in which the dynamic response can be improved. Results are verified and discussed.

Resumo em Inglês:

An universal closed-form solution of Lagrangian multipliers for the coast-arcs of optimum space trajectories in a Newtonian central force field is obtained by means of properties of generalized canonical systems and Sundman transformation. This closed-form solution, valid for all conics, is given as a function of a generalized anomaly.

Resumo em Inglês:

A simplified method is used to determine the optimum water content in the flue gases of charcoal gasifiers to be utilized as alternative fuels in the operation of engines and gas turbines for power generation. Computational models of plug flow reactors and well stirred reactors are employed to simulate the reaction and post-flame zones, adopting different chemical mechanisms. In the simulations reactants enter the reactors at 1000 K, 1 atm and equivalence ratio 0.25. It was observed that mixtures about 3% to 4% in volume of water vapor allow to obtain optimal operation characteristics, including high blowout limit, low ignition delay, maximum reaction zone temperature, high CO2 prodution and low thermal NO formation. It was observed that increasing water contents reduce significantly ignition times up to 3% in volume, while blowout mass flow rates increase continuously up to 6 % in volume, the maximum value considered. Formation of NO decreases continuously with humidity after the flame zone, while there are peaks of NO formation within the flame zone below 1% in volume. Higher water vapor content decreases the final temperatures below 1700 K, leading to a lower thermal efficiency. The method can be used to estimate optimum operational conditions with other input parameters.

Resumo em Inglês:

The properties of turbulence induced in a viscous fluid by oscillating a grid within it are investigated. Vertical and horizontal components of fluctuating velocities are measured using the Digital Particle Image Velocimetry technique (DPIV). Vertical profiles of turbulent kinetic energy k, obtained from the fluctuating velocities, are presented and compared with theoretical predictions obtained using the k-epsilon turbulence model.

Resumo em Inglês:

A numerical model to study the aerodynamic and aeroelastic bridge deck behavior is presented in this paper. The flow around a rigid fixed bridge cross-section, as well as the flow around the same cross-section with torsional motion, are investigated to obtain the aerodynamic coefficients, the Strouhal number and to determine the critical wind speed originating dynamic instability due to flutter. The two-dimensional flow is analyzed employing the pseudo-compressibility approach, with an Arbitrary Lagrangean-Eulerian (ALE) formulation and an explicit two-step Taylor-Galerkin method. The finite element method (FEM) is used for spatial discretization. The structure is considered as a rigid body with elastic restrains for the cross-section rotation and displacement components. The fluid-structure interaction is accomplished applying the compatibility and equilibrium conditions at the fluid-solid interface. The structural dynamic analysis is performed using the classical Newmark's method.

Resumo em Inglês:

In this paper a direct boundary element hypersingular formulation for three-dimensional potential problems is presented. It is shown that the integrals which arise in this formulation are Cauchy principal value integrals, i.e., divergent terms of the finite part integrals cancel one another. Since in the present formulation the collocation points are placed within boundary elements, free terms are computed by simple expressions. The resulting integrals are one-dimensional and regular, therefore can be evaluated by Gaussian quadrature. For the numerical implementation, both linear and quadratic isoparametric triangular and quadrangular elements were used. Numerical results are presented to show the efficacy of the proposed hypersingular formulation.

Resumo em Inglês:

The pneumatic conveying of solids in a gas stream is a recurrent process in petrochemical industries. However, due to practical limitations the majority of existing systems have capacities ranging from 1 to 400 tones per hour over distances less than 1000 m, mainly because of a high power consumption per transported unit mass. More specifically, to avoid the formation of dense structures such as dunes and plugs, which, depending on the characteristics of the material and on the availability of a pressure head from the carrier phase may cause a violent pressure surge or a possible line blockage, the system is preferably operated at homogeneous dispersed flow. To sustain such a flow regime high velocities are needed and, accounting for the resulting higher pressure drops, higher power consumption is demanded. An optimized pneumatic conveying system can be conceived with the help of adaptive control techniques. In the context described above, lower transport velocities are allowed if the formation of aggregates that precedes the transition to dense phase flow regimes are automatically detected and destroyed, thus, artificially stabilizing the light phase homogeneous flow regime. This work assesses the reduction in the necessary power that the application of such adaptive control technique could produce. Experimental results are presented for a 45 mm i.d. pneumatic conveying system used to transport Setaria Italica seeds. The instrumentation used to identify the flow regime is constituted of several pressure sensors installed along the transport line. The proposed control strategy is based on processing these signals through a neural network model to assess the flow condition and to mimic an optimized gain scheduled PID algorithm. Preliminary results show that reductions in power consumption can reach 50% when compared with classical non controlled transport.

Resumo em Inglês:

A visualization study and Quantitative velocity measurements have been performed in Taylor-Couette flow with a medium-gap (ç= 0.356), over a large range of Taylor numbers (2.1x10(4) < Ta < 1.1x10(11)), with the outer cylinder fixed and the inner cylinder rotating about its axis. Quantitative velocity measurements were carried out using the PHANTOMM flow tagging technique. Two techniques were used for visualization study: the PHANTOMM technique that allowed flow structure visualization from small to moderate Taylor numbers, and the Particle Streak Imaging, PSI (the flow was seeded with neutrally buoyant polystyrene micro spheres) that permitted the flow structure visualization from moderate to high Taylor numbers. The results illustrate the expected three-dimensional features of flow and presence of Taylor cells at low Taylor numbers. Our study examined the interplay between small and large scales present in the flow as well as showed the gradual transition to turbulence with increasing Taylor numbers. Taylor cells were found for Taylor numbers less than 1.13 x 10(10). At low Taylor numbers, the flow in the cells appeared to be a rotational laminar flow with a high degree of coherence. At higher Taylor numbers, the cells aspect became more irregular, and the flow inside them became turbulent. The Görtler instability developed inside Taylor cells and close to the inner cylinder wall. At the highest Taylor numbers, turbulence increased up to the point where no Taylor cells could be detected. For the flow in our study, at Ta = 1.13 x 10(10), the homogenization by turbulence spread across the gap, and the flow structure sharply changed its pattern as a toroidal vortex in helical motion developed in a thin layer on the inner cylinder wall. Instantaneous velocities, average velocities, angular-momentum ratio and spectral density function were computed for all ranges of Taylor numbers in the range studied. These quantitative results show the same conclusions as the ones presented by the visualization study

Resumo em Inglês:

This paper describes a nonlinear phenomenon in the dynamical behavior of a nonlinear system under two non-ideal excitations: the self-synchronization of unbalanced direct current motors. The considered model is taken as a Duffing system that is excited by two unbalanced direct current motors with limited power supplies. The results obtained by using numerical simulations are discussed in details

Resumo em Inglês:

In this work, the use of interval arithmetic is considered to increase robustness of geometric classification algorithms in B-Rep solid modeling systems. The classification algorithms, also known as incidence tests, are important to keep the consistency between topology and geometry in a solid model during the application of Boolean operations. An error in the incidence test has deep impact over the steps that follow the Boolean operations and can damage the result, generating an inconsistent solid. The interval arithmetic incorporates approximation errors, so that, it eliminates the need of defining a fixed tolerance to do the comparison between floating-point numbers. However, it is not possible to directly convert floating-point algorithms to interval arithmetic, so that, it is necessary to reformulate the entire algorithm. Another important step in the Boolean operation is the determination of intersection points where the use of interval arithmetic can have side effects as intervals with large dimensions, and may cause incidence tests failures. It is necessary to control the growth of the intervals based on the geometry and topology. This work will introduce the application of interval arithmetic to a B-Rep solid modeler.

Resumo em Inglês:

This study builds upon the J-Q approach to characterize constraint effects on cleavage fracture behavior of cracked structural components. Discussions emphasize features of current two-parameter fracture methodologies which extend the limits of applicability of single parameter fracture approaches when LSY effects prevail. Inclusion of the second parameter (Q) in failure assessment procedures leads to the construction of experimentally derived fracture toughness loci, rather than conventional, single-valued definitions of toughness. The plan of the article is as follows. First, the notion of crack tip constraint and its connection with SSY reference fields is introduced. This is followed by a brief description of the J-Q theory to define the hydrostatic parameter Q. The paper then addresses representative numerical solutions which provide J-Q trajectories for common fracture specimens under bend and tensile loading, including deep and shallow crack SE(B) and SE(T) specimens. These analyses, when taken together with previous works, provide a fairly extensive body of results against which the robustness of the J-Q methodology can be weighed.

Resumo em Inglês:

Interactions between parametric, self-, and externally excited vibrations are analysed in this paper. The physical model of the vibrating system consists of a non-linear spring with periodically changing stiffness of Mathieu type and a non-linear damping described by Rayleigh's term. This system is additionally forced by a harmonic force (ideal system), or by a non-ideal energy source represented by a direct current motor with limited power supply. The model of DC motor is considered in two variants, as a classical, in Kononenko's sense model, and a complete electro-mechanical system. Quantitative and qualitative differences of the considered models are compared and discussed in the paper.