Resumo em Inglês:

In this work, the performance of a spark ignition engine powered with hydrogen fuel was studied and compared with gasoline fuel. Hydrogen fuel was used, using a locally made stainless steel gaseous regulator which was designed and installed in engine. This regulator was located between the engine and the hydrogen fuel cylinder, and it is triggered by the suction pressure and hence it keeps the fuel supply lines open under negative pressure only, which exists under no leak conditions and when the engine is running. It was found that the engine runs smoothly with the regulator in place. Further, it was found that the brake power and the volumetric efficiency of the engine drop down when the engine is powered by hydrogen, while the specific fuel consumption is drastically improved (by almost one-third) when hydrogen is used as a fuel. Finally, the thermal efficiency remains almost the same in both cases of fuels.

Resumo em Inglês:

The calculation of forces in the kinematic pairs of mechanisms by inverse dynamics is usually performed without friction considerations. In practice, when examination of articulated mechanisms takes into account friction, the solution of the inverse dynamics results in a complex procedure. If a modular approach for the inverse dynamics is used, then exact solutions are available, but not necessarily are practical. For example, the analytical solution for a second-class first-type Assur group is a 16th degree equation. Previous researches proposed an approximated but practical (graphical) method to calculate the forces on the kinematic pairs taking into account the friction forces. In this article, an analytical interpretation of the Artobolevski approximated method is developed for the second-class Assur group with three rotational pairs. The final results for the reactions calculated with the implemented method present a good approximation with respect to the graphical solution. Future work should consider friction forces not only in second-class groups with rotational joints, but also in second-class groups with prismatic joints and high-class Assur groups.

Resumo em Inglês:

Gas combustion represents the second principal way of electricity generation due to its disposal, and smaller dimension and pollution capacity when compared with diesel engines. The conversion of natural gas in electricity is made through gas turbines, and the rotors of its compressors are components that present significant difficulty in its manufacture. This paper focuses on an optimization approach of the 5-axis milling of titanium blisks, based on all the CAD/CAM modeling chain. Special interest is pointed to the systematic analysis of the correlation between machining parameter and surface integrity properties. The experimental part of this work is composed by two tests. The first one analyses the roughing operation of a TiAl6V4 impeller when using a tool radial engagement of 30% and 68%. The second is the simultaneous 5 axes milling of a test-piece, a TiAl6V4 integral bladed disk (BLISK) section containing five blades, with which the best milling strategy for this purpose is sought. The results showed the fundamental importance of CAD modeling in order to achieve simultaneous 5 axes milling without intermittent feed speed. It was observed that milling a blade following its parametric curves in the BLISK axis direction is the best choice, among the strategies proposed.

Resumo em Inglês:

A simulation program based on a control volume analysis has been used in the evaluation of the (ε, NTU) relationship for coils of complex geometry and flow arrangement. The simulation program has been evaluated through simple geometry and flow arrangement coils. The program results compare very well with correlations for simple cross flow coils, and a number of rows up to four. It has also been determined that closed form correlations developed for coils of an infinite number of tube rows are inadequate for those with number of rows in the range between 5 and 10. In addition, it has been found that closed form (ε, NTU) correlations for cross flow coils with the same tube arrangement and number of rows might lead to inaccuracies higher than 10% in the evaluation of the effectiveness of coils of complex flow arrangement.

Resumo em Inglês:

The reduction of the fuel content of a monoethanolamine nitrate (MEAN) fueled explosive slurry was investigated. The work was performed in three phases. The first one involved the MEAN content reduction in a reference slurry from its initial value of 36 down to 24% by weight, the balance being filled with ammonium nitrate, the least expensive item in the slurry composition. This proved to be successful, leading to an overall cost reduction of 17%, while keeping the overall performance quite satisfactory. The second phase consisted in trying to bring the MEAN content down from 24 to 17%. Although this led to further cost reduction, the formulations, obtained by substituting part of the MEAN content by ammonium nitrate/fuel oil (ANFO), produced unsatisfactory results regarding ignition and densities. In the third phase, the Design of Experiments Technique was used to find formulations displaying not only lower cost, but also acceptable overall performance. This led to a raw material cost reduction ranging from 23 to 26% relative to the initial reference slurry formulation.

Resumo em Inglês:

Due to its good mechanical properties, the Compacted (Vermicular) graphite cast iron (CGI) has found a lot of applications in the automobilistic field. One of the applications is the production of high power diesel engine blocks that, due to the higher strength compared to the usual gray cast iron, allows the increase of the pressure inside the cylinder and, consequently, production of high level of energy. The result is the better fuel burning what decreases the fuel consumption and the pollutants' emission levels. However, when CGI replaces gray cast iron, the machining processes used to produce the components are more difficult, with lower tool lives and higher power consumption. Moreover, because usually the raw material to produce cast products of CGI is selected from scrap, some residual level of titanium is present. Thus, the goal of this work is to study the influence of the titanium content (in residual levels) in the turning operation performance with carbide tools, using two cutting speeds. The results show that the alloys with the highest titanium content generated the shortest tool life, but the titanium content influenced neither power consumption nor workpiece surface roughness. Attrition/adhesion was the main tool wear mechanisms verified in this work.

Resumo em Inglês:

This paper presents the development of a dynamic torque meter to be applied to rotating shafts using electronic transduction, strain gage, telemetry and LabView Graphic programming. A mathematical model was developed. The electronic transduction signal is transmitted by digital modulation from a remote transduction unit fixed to a shaft to a base station, sending the signal to a PC, by means of a VI (Virtual Instrument) developed in LabView. It can also be delivered to other units besides the PC. The use of digital modulation to transmit the radiofrequency signal, replacing conventional couplings, allows communication with a high signal/noise ratio. A clamp acts as sealant, protecting it from the environment and making it easier to install. The prototype can be used at situation that it is impossible to use flanges or sockets (the most of the industrial applications) and it is installed directly on the surface of the shaft. The use of superbatteries allows the remote unit to remain independent of a feed for several days, with long periods between maintenance. After thousands of experimental essays, the theoretical model seems to confirm the proposed idea. The system presented has a potential for high precision, low cost, long work life and easy maintenance.

Resumo em Inglês:

A drill-string is a slender structure that turns and drills into the rock in search of oil. There are many sources of uncertainties in this complex dynamical system. However, this article is concerned only with uncertainties in the weight-on-hook, which is the supporting force exerted by the hook at the top. A probabilistic model is constructed for the random variable related to the weight-on-hook using the Maximum Entropy Principle, and the random response of the system is computed through Monte Carlo simulations. The idea is to understand how the performance of the system (which is measured by the rate of penetration) is affected by the uncertainties of the weight-on-hook. The continuous system analyzed is discretized by means of the Finite Element Method and a computer code is developed to do the simulations.

Resumo em Inglês:

This work brings as its main contribution the study of the phenomenon of density currents in non-stratified reservoirs, with flows in steady regimes. Flows are analyzed for a wide range of Reynolds and Richardson numbers in the entrance of the reservoir. Based on this hypothesis, a hybrid numeric model is presented considering the Reynolds Transport's Equation - focusing on the conservation for volume, mass and momentum - with the intention of obtaining three-dimensional components of velocities, reduced acceleration of gravity and geometric characteristics of currents along the reservoir. It is possible to notice in the numeric simulations, mainly, the need of complementation of the model that refers to the inclusion of the entrainment coefficient and the analysis in the unsteady regime.

Resumo em Inglês:

Studies for a one-dimensional reactive flow in a LOX/LH2-rocket engine nozzle with regenerative cooling system were performed, using the finite volume method, co-located grids and the GCI estimator for the discretization errors evaluation. Five physical models were employed: two one-species ones (with constant and with variable thermophysical properties) and three multi-species ones (frozen, local equilibrium and non-equilibrium flows), for which different chemical schemes were studied. The main results are: GCI can be used for the evaluation of uncertainties related to compressible flows; there are not significant differences between numerical results for six and eight species schemes; the main features of the coolant flow are little influenced by the physical model adopted; the frozen flow model, otherwise, is the preferable one by providing the upper bound for the maximum heat flux and the maximum temperature of the wall, with lower CPU time.

Resumo em Inglês:

Extensive solidification simulations are conducted using finite difference method on an aluminium alloy casting. Orthogonal experimental array layout is considered for running experimental simulations. Microstructural parameter Secondary Dendrite Arm Spacing (SDAS) at three different locations was predicted as response variable, through solidification simulations by varying the process parameters. The input process variables are pouring temperature, insulation on riser and chill volume heat capacity. An Artificial Neural Network (ANN) model was developed to predict the response variable for varied input process variables. Through sensitivity analysis the influence of input process variables on output response was obtained. The results obtained from solidification simulations and ANN model are validated experimentally.

Resumo em Inglês:

In order to achieve better part quality in sheet metal forming the rate of the material flow into the die cavity must be efficiently controlled. This control is obtained using a restraining force supplied either by the blankholder tool, drawbeads or both. When the restraining force required is too high, the use of drawbeads is necessary, although excessive blank deformation may be produced. Some other disadvantages such as adjustment difficulties during die try-outs to determine the actual Drawbead Restraining Force (DBRF) may also be encountered. One way to solve these problems and to reduce the number of die try-outs - which are very much time consuming - is to introduce/define accurate enough drawbead concepts. The present study will make use of a method that has been developed using the similitude approach in order to understand the influence of the most important parameters on DBRF and to establish a pre-estimate DBRF theory. Data bases have been developed throughout Explicit Dynamic Finite Element Method (EDFEM) based simulations. The results are compared with experimental data bases provided by Nine (1978) and with the analytical model of Stoughton (1988) results. The average of absolute error with respect to experimental data bases was around 6% and, for the studied cases, the maximum discrepancy was found to be below 11%. For the analytical and experimental cases, the average of absolute error was approximately 5% and, for the studied cases, the maximum error was below 7%. In terms of precision, the predictions derived from this approach are adequate when compared with analytical and experimental results. For this reason, the approach has been validated and accepted as a contribution to STAMPACK®, a commercial explicit dynamic finite element based system for forming processes numerical simulation.

Resumo em Inglês:

Numerical simulations of viscous fingering instabilities in miscible displacements at high mobility-ratios are presented. Anisotropic dispersion and monotonic viscosity profiles are considered. The coupled set of partial differential equations is approximated by the semi-discrete SUPG stabilized finite element formulation plus a discontinuity capturing technique to improve stability around the moving sharp fronts. The pressure equation is discretized by the standard Galerkin method, and a post-processing scheme is used to improve the numerical evaluation of Darcy's velocity. In the resulting scheme all variables (concentration, pressure and velocity) are approximated by equal order linear triangular elements. A homogeneous channel and a radial system were studied. Complex nonlinear viscous fingering mechanisms for high mobility-ratio miscible displacements were observed.