Resumo em Inglês:

The steady-state aerodynamic characteristics of a new family of blunted leading edges immersed in a high-speed rarefied air flow are examined by using a Direct Simulation Monte Carlo (DSMC) Method. A very detailed description of the flow properties has been presented separately at the vicinity of the nose and adjacent to the afterbody surface of the leading edges by a numerical method that properly accounts for non-equilibrium effects that arise near the leading edges and that are especially important at high Mach number. Comparisons based on geometry are made between these new blunt configurations and round leading edge. Some significant differences between these leading edges are noted on the flowfield structure and on the aerodynamic surface quantities. It is found that the upstream effects have different influence on velocity, density, pressure and temperature along the stagnation streamline ahead of the leading edges. The analysis also shows that, despite the seeming advantages of the new blunt leading edge shapes, round leading edge still provides smaller stagnation point heating. Nevertheless, round leading edge provides larger total drag than the new blunt shapes under the range of condition investigated.

Resumo em Inglês:

The purpose of this work is to explain the concept of cutting fluids reasonable usage through the fluid minimum quantity in grinding processes. On that purpose, the development of a new nozzle and an own and adequate methodology should be required in order to obtain good results and compare them to the conventional methods. The analysis of the grinding wheel/cutting fluid performance was accomplished from the following input parameters: flow rate variation by nozzle diameter changes (three diameters values: 3mm, 4mm and 5mm), besides the conventional round nozzle already within the machine. Integral oil and a synthetic emulsion were used as cutting fluids and a conventional grinding wheel was employed. The workpieces were made of steel VC 131, tempered and quenched with 60HRc. Thus, as the flow rate and the nozzle diameter changes, keeping steady fluid jet velocity (equal to cutting velocity), attempted to find the best machining conditions, with the purpose to obtain a decrease on the cutting fluid volume, taking into consideration the analysis of the process output variables such as cutting strength, cutting specific energy, grinding wheel wear and surface roughness. It was verified that the 3mm diameter optimized nozzle and the integral oil, in general, was the best combination among all proposed.

Resumo em Inglês:

This paper presents an investigation into the solution of laminar mixed convective heat transfer in vertical elliptic ducts containing an upward flowing fluid rotating about a parallel axis. The coupled system of normalized conservation equations are solved using a power series expansion in ascending powers of rotational Rayleigh Number, Ratau - a measure of the rate of heating and rotation as the perturbation parameter. The results show the influence of rotational Rayleigh number, Ratau and modified Reynolds number, Re m on the temperature and axial velocity fields. The effect of Prandtl number, Pr, in the range 1 to 5, and eccentricity, e on the peripheral local Nusselt number are also reported. The mean Nusselt number is observed to be highest at duct eccentricity, e=0 for a given Prandtl number. However, results indicate insensitivity of peripheral local Nusselt number to Prandtl number at eccentricity, e=0.866, which is an important result to a designer of rotating vertical heat exchanger. The effect of eccentricity on the friction coefficient is also presented. The parameter space for the overall validity of the results presented is Ratau Re mPr<820.

Resumo em Inglês:

With the development of industrialized steel construction, new constructive elements have been brought not only to the market, but to the everyday construction site as well and, in this way professionals and users have questioned their efficiency. In respect to vibrations in floors, what can be detected is that floor structures are thinner and a decrease of the mass in the horizontal closing panels and the utilization of new materials and systems have led them to have lower natural frequencies, and so are nearer to the frequencies produced by walking. This decrease of mass of the closing panels also lead to a considerable weakness in terms of acoustical insulation, which can cause unfavorable conditions and discomfort. Thus, it becomes necessary to do detailed studies of the efficiency of the vibration and acoustical performance of the new systems to obtain the characterization and the qualification parameters in order to optimize their use. This study does a comparative evaluation of some kinds of horizontal and vertical closing systems in respect to the vibrational and acoustical insulation performance.

Resumo em Inglês:

In this work the turbulent flow of the Non-Newtonian Carreau-Yasuda fluid will be studied. A skin friction equation for the turbulent flow of Carreau-Yasuda fluids will be derived assuming a logarithmic behavior of the turbulent mean velocity for the near wall flow out of the viscous sub layer. An alternative near wall characteristic length scale which takes into account the effects of the relaxation time will be introduced. The characteristic length will be obtained through the analysis of viscous region near the wall. The results compared with experimental data obtained with Tylose (methyl hydroxil cellulose) solutions showing good agreement. The relations between scales integral and dissipative obtained for length, time, velocity, kinetic energy, and vorticity will be derived for this type of fluid. When the power law index approach to unity the relations reduces to newtonian case.

Resumo em Inglês:

The steady hydromagnetic flow in a porous medium of an incompressible viscous electrically conducting non-Newtonian fluid above an infinite rotating porous disk is studied with heat transfer. An external uniform magnetic field is applied perpendicular to the disk and a uniform injection or suction is applied through the surface of the disk. Numerical solutions of the nonlinear governing equations, which govern the flow and energy transfer, are obtained. The effect of the magnetic field, the suction and injection velocity and the characteristics of the non-Newtonian fluid on the velocity and temperature distributions are considered.

Resumo em Inglês:

Structural health monitoring (SHM) is related to the ability of monitoring the state and deciding the level of damage or deterioration within aerospace, civil and mechanical systems. In this sense, this paper deals with the application of a two-step auto-regressive and auto-regressive with exogenous inputs (AR-ARX) model for linear prediction of damage diagnosis in structural systems. This damage detection algorithm is based on the monitoring of residual error as damage-sensitive indexes, obtained through vibration response measurements. In complex structures there are many positions under observation and a large amount of data to be handed, making difficult the visualization of the signals. This paper also investigates data compression by using principal component analysis. In order to establish a threshold value, a fuzzy c-means clustering is taken to quantify the damage-sensitive index in an unsupervised learning mode. Tests are made in a benchmark problem, as proposed by IASC-ASCE with different damage patterns. The diagnosis that was obtained showed high correlation with the actual integrity state of the structure.

Resumo em Inglês:

The usual structural analysis models for telecommunication and transmission steel tower design tend to assume a simple truss behaviour where all the steel connections are considered hinged. Despite this fact, the most commonly used tower geometries possess structural mechanisms that could compromise the assumed structural behaviour. A possible explanation for the structure stability is related to the connections semi-rigid response instead of the initially assumed pinned behaviour. This paper proposes an alternative structural analysis modelling strategy for guyed steel towers design, considering all the actual structural forces and moments, by using three-dimensional beam and truss finite elements. Comparisons of the above mentioned design models with a third alternative, that models the main structure and the bracing system with 3D beam finite elements, are made for three existing guyed steel telecommunication towers (50m, 70m and 90m high). The comparisons are initially based on the towers static and dynamic structural behaviour later to be followed by a linear buckling analysis to determine the influence of the various modelling strategies on the tower stability behaviour.

Resumo em Inglês:

A well known phenomenon, the "built-up edge - BUE", occurs at the chip/tool interface when multiphase materials are machined at low cutting speeds. Under high compressive stresses, seizure prevents the material from sliding over the tool’s rake face. Although many reports have been published on the subject, studies of the BUE phenomenon have been marked by a lack of precision in determining its dimensions. This paper reports on a study of the BUE geometry of a SAE 12L14 steel machined at low speeds with and without a cutting fluid. Three quick-stop samples were prepared for each test condition (9 cutting speeds, with and without cutting fluid). The quick-stop samples were mounted perpendicularly in transparent acrylic resin to facilitate observation and the hardened resin sandpapered. The opposite face of the mounted sample was then ground to make the front and back faces parallel. After sandpapering and polishing, the samples were digitally photographed and their BUE geometries determined using an image analyzer. The measurements were done along the cutting width at five different points. It was found that the BUE dimensions varied considerably along the cutting width, and that the fluid reduced the BUE at the lowest cutting speed tested.

Resumo em Inglês:

The part 1 of this work presents a study about the use of the out-of-phase current pulses technology applied to the Double Wire MIG/MAG welding process with Insulated Potentials on welded coating. High-speed digital back-lighted images were recorded to evaluate the influence of the levels of out-of-phase current pulses on the behavior of both metallic transfer modes and voltaic arcs configurations. The results showed that, with the electrodes positioned side by side and the mean currents below the transition current, the out-of-phasing parameter setting reduces the deviations of the arcs and changes the paths of the droplets. However, no significant effect was noticed on bead finishing or arc stability.

Resumo em Inglês:

This paper presents a continuation of a study carried out on the use of the out-of-phase current pulses technology applied to the Double Wire MIG/MAG welding process with Insulated Potentials on welded coatings. In the first part it was reported how the level of out-phase pulsed current acts on arc configuration, droplet paths, bead finishing and arc stability. The objective now is to show the effect on the bead geometry caused by changes in arc and metal transfer. Beads were deposited on plate in a flat position and out-of-phase levels were varied. The results showed that, with the electrodes positioned side by side and mean currents below the transition current, the lag time between out-of-phase current pulses have a remarkable influence on the penetration profile of the weld bead.

Resumo em Inglês:

A new hybrid simulation method for room acoustics is presented. It is grounded on two well known numerical simulation techniques for room acoustics. The hybrid method takes geometric acoustics for granted and uses an improved version of the classical ray-tracing technique for computing the specular reflections and a slightly modified energy transition method for simulating the diffuse reflections. The impulse responses (IRs) are then computed by superposition of the specular and diffuse ones. The reverberant part of the IRs gains a much more realistic aspect than the one obtained from either ones method alone. Both the ray-tracing technique and the energy transition method are reviewed and some improved features are discussed. The sound source and the receiver modeling are presented, including a new method for simulating the head related transfer functions (HRTFs), and based on the wavelet technique, which provides a shorter time computation of the binaural impulse responses for auralization purposes. In a companion paper, entitled Hybrid method for numerical simulation of room acoustics: Part 2 - Validation of the computational code RAIOS 3, a validation of the method in an international inter-comparison with other softwares and measurements data is presented, showing the efficiency and the accuracy of the proposed hybrid method over non-hybrid ones.

Resumo em Inglês:

In the companion paper "Hybrid method for numerical simulation of room acoustics with auralization: Part 1- Theoretical and numerical aspects" a new hybrid method for numerical simulation of room acoustics, implemented by the software RAIOS 3, was presented. Here, the software itself and its main features are discussed. It will be shown that the proposed method actually results in very reliable and accurate predictions of the main acoustical parameters: T30, EDT, C80, D50, TS, G, LF and LFC. The performance of RAIOS 3 was assessed in an international intercomparison, coordinated by the Physikalisch-Technische Bundesanstalt, in Germany, where measured acoustical parameters where compared to those predicted by 9 different software. Due to the hybrid method proposed, the comparative results shown a very good agreement between the parameters predicted by our software and the measurements, even in a somewhat diffuse condition. In a statistical evaluation, the results obtained by the numerical code RAIOS 3, stayed among the top 10%. The strong dependency of the predicted acoustical parameters on reliable room data, especially absorption and diffusion coefficients, is also discussed.