Scielo RSS <![CDATA[Journal of the Brazilian Society of Mechanical Sciences and Engineering]]> http://www.scielo.br/rss.php?pid=1678-587820120003&lang=en vol. 34 num. 3 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<b>Study of water entry of circular cylinder by using analytical and numerical solutions</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300001&lng=en&nrm=iso&tlng=en Water impact phenomenon in the case of a circular cylinder is an important issue in offshore industry where cross members may be in the splash zone of the incident wave. An analytical method as well as a numerical solution are employed to study the water entry problem of a circular section. The procedure for derivation of the analytical formulas is demonstrated step by step. The volume of fluid (VOF) simulation of the water entry problem is also performed to offer comparison of the results of the linearized analytical solution with a fully nonlinear and viscous fluid flow solution. To achieve this, the FLOW-3D code is utilized. Some consideration has also been given to the points of intersection of the free surface and the body, where the singularities exist in the free surface deformation and velocities, as predicted by the linear theory. These singularities appear to be avoided in the real fluid by the formation of jets which quickly break up into sprays under the action of surface tension. Slamming force, free surface profile, impact force, pressure distribution and evolution of intersection points are also presented and comparisons of the obtained results against the results of previous studies illustrate favorable agreements. <![CDATA[<b>Vapor chamber heat sink with hollow fins</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300002&lng=en&nrm=iso&tlng=en A new vapor chamber heat sink with maximum fin efficiency is presented. The fins are hollow, so the vapor generated at the base flows up to the top of the fins. As a result, the heat sink is practically isothermal. A prototype of the hollow fin vapor chamber heat sink was built and tested. The prototype presented 20% less overall thermal resistance than conventional pin fin heat sinks with the same mass and volume. A theoretical model for the heat sink thermal resistance was developed and the agreement between the model and the experimental data is fair. <![CDATA[<b>Selection of optimal process parameters for minimizing burr size in drilling using Taguchi's quality loss function approach</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300003&lng=en&nrm=iso&tlng=en The exit burr in drilling degrades the precision of products and causes additional cost of deburring. Therefore, it is essential to minimize burr size at the exit of holes in drilling at the manufacturing stage. Taguchi's quality loss function approach, a multi-response optimization method, has been employed to determine the best combination values of cutting speed, feed, point angle and lip clearance angle for specified drill diameters to simultaneously minimize burr height and burr thickness during drilling of AISI 316L stainless steel workpieces. The experiments were planned as per L9 orthogonal array and multi-response signal to noise (S/N) ratio was applied to measure the performance characteristics. Analysis of means (ANOM) and analysis of variance (ANOVA) were performed to determine the optimal levels and to identify the level of importance of parameters. The confirmation tests with the optimal levels of parameters were carried out to illustrate the effectiveness of Taguchi optimization. <![CDATA[<b>Slip-line metal cutting model with negative rake angle</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300004&lng=en&nrm=iso&tlng=en A small dead region is seen in front of the rake face of the tool during cutting with negative rake. The lack of knowledge about the stagnant region in the cutting with negative rake requires researching new models. In this work, cutting mechanism of the metal cutting with negative rake angle tools and the stagnation zone formation were studied. A model was generated from the experimental work by usage of the Dewhurst and Collins' matrix technique for solving the slip-line problem numerically. This model was applied at negative rake angles from 0º to -70º. All slip line angles in the slip line model that consist of three regions were resolved with the help of the experimental data. Variation of the dead metal zone and slip line regions with negative rake angle was determined. Effects of the negative rake angle on the cutting and thrust forces were investigated according to the cutting speed. <![CDATA[<b>Optimization of end milling parameters under minimum quantity lubrication using principal component analysis and grey relational analysis</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300005&lng=en&nrm=iso&tlng=en Machining is the major reliable practice in accomplishment of metal cutting industries. The accelerated growing competition demands top superior and large quantity with low cost products. Metal working fluids have significant fragment of manufacturing cost and causes ecological impacts and health problems. This work attempts to advance a competent machining alignment with no ecological impacts. The prediction of quality characteristics and enhancement of machining field are consistently accepting great interest in machining sectors to compress the accomplishment costs. In this paper, GA based ANN prediction model proposes to envisage the quality characteristics of surface roughness and tool wear. The comparison of predicted and experimental values acknowledges the precision of the model. The end milling experiments are conducted beneath minimum quantity lubrication. This paper as well deals with the multiple objective optimization with principal component analysis, grey relational analysis and Taguchi method. ANOVA was carried out to determine each parameter contribution percentage on quality characteristics. The results show that cutting speed is the most influencing parameter followed by feed velocity, lubricant flow rate and depth of cut. The confirmation tests acknowledge that the proposed multiple-objective methodology is able in determining optimum machining parameters for minimum surface roughness and tool wear. <![CDATA[<b>Flexural-torsional vibration analysis of axially loaded thin-walled beam</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300006&lng=en&nrm=iso&tlng=en The present paper considers the flexure-torsion coupled vibrations of axially loaded thin-walled beams with arbitrary open cross section, by means of an exact solution. The effects of axial force, warping stiffness and rotary inertia are included in the present formulations. In the case of simply supported thin-walled beam, a closed-form solution for the coupled natural frequencies of free harmonic vibrations was derived by using a general solution of the governing differential equations of motion based on Vlasov theory. The method is illustrated by its application to two test examples, to demonstrate the effects of bending-torsion coupling and axial force on the dynamic behavior of thin-walled beams. Compared with those available in the relevant literature, numerical results demonstrate the accuracy and effectiveness of the proposed method. <![CDATA[<b>Bending investigation on carbon fiber/epoxy composites nano-modified by graphene</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300007&lng=en&nrm=iso&tlng=en An extreme conditions situation, e.g. pre-salt deep sea exploration, requires new materials with even better performance. Nanotechnology is the new paradigm that can lead to the development of these new super materials. The effect of graphene pileups dispersion into carbon fiber/epoxy composites was investigated experimentally. The dispersion process was based on sonication and high shear mixing. XRD and SEM indicate that although the dispersion process can lead to exfoliated nanostructures, there is a saturation limit for the epoxy system, around 0.5 wt. %. The addition of graphene to carbon/epoxy composites seems to have no influence into stiffness, as the slopes of the stress-strain curves were near constant for all specimen tested. The bending strength, however, was heavily influenced by formation of graphene pileups into epoxy matrix and its dispersion around the carbon fibers. The increase on bending strength from 623.01±70.16 MPa (control samples) to 1259.92±61.73 MPa for 0.5 wt. % graphene addition represents an average improvement of 102%. This can be attributed to changes on failure mechanism, moving from intra-laminar failure to a mix failure mode where inter- and intra-laminar failure are combined in a zigzag pattern. A possible explanation for such behavior is the formation of strong bonds at the fiber/matrix surroundings due to nanostructures formation. <![CDATA[<b>Determining the viscous behavior of non-Newtonian fluids in a flume using a laminar sheet flow model and Ultrasonic Velocity Profiling (UVP) system</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300008&lng=en&nrm=iso&tlng=en The flow of non-Newtonian fluids in rectangular open channels has received renewed interest over the past number of years especially as large flumes are being used to transport tailings in countries like Chile. The effect of yield stress on the flow behavior is complex and not yet fully understood. The Ultrasonic Velocity Profiling (UVP) technique has been used to construct velocity profiles of non-Newtonian fluids flowing in a 10 m by 300 mm wide tilting flume. The contour maps were integrated to show that the velocity profiles were indeed correct. The thin film flow models available in the literature have been tested in terms of flow depth and Reynolds number. The measured profiles also show the influence of the side walls on the general flow features as the distance from the centre increases. The results reported herein span the laminar, transition and turbulent flow regions. As far as can be ascertained, it is the first time that this technique has been used to measure velocity profiles in opaque non-Newtonian fluids for open channel flow. It is shown here that, under appropriate conditions, the velocity profile and flow depth can be used to obtain the viscous properties of the fluids tested. Excellent correspondence between the rheological parameters inferred from the velocity profile measurements and that from the tube viscometry was obtained. <![CDATA[<b>Experimental investigation of the enhanced oil recovery process using a polymeric solution</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300009&lng=en&nrm=iso&tlng=en Enhanced oil recovery methods are becoming an important source of oil production of wells that have already been explored and, by these methods, of increase of the total volume of oil extracted. An important example is the injection of polymeric solutions after the injected water has reached the breakthrough point. In the present work an experimental apparatus was built in order to test the ability of enhanced oil recovery of polymeric solutions, composed by Xanthan Gum (XG) dissolved in distilled water. This apparatus consists of an idealized porous media made with small spheres inserted in a cylindrical cell and then filled with oil with the same viscosity as the petroleum found in Campos Basin (Rio de Janeiro, Brazil). As displacing fluid, we tested polymeric solutions of different concentrations of Xanthan Gum and these non-Newtonian fluids were characterized using a rotational rheometer. The resulting characterization has shown that increasing the concentration, not only the level of viscosity, but also the elasticity of the fluid increases. The shear-thinning behavior of the solution can be well captured by a power-law model. For higher concentrations the shear-thinning feature of the Xanthan Gum solution is more pronounced. We conducted an experimental procedure to mimic enhanced oil recovery process by first injecting water until the breakthrough point. Increasing the polymer concentration, the extra amount of oil recovered also increase. Theoretical and heuristic analyses show that in the shear dominated regions, the Xanthan Gum polymeric solutions do not increase pore efficiency, but increase sweep efficiency, while the extensional character of the polymeric solution seems to indicate that in extensional dominated regions the polymeric solutions play an important role on the oil recovery efficiency from both perspectives: pore and sweep efficiencies. <![CDATA[<b>In-flight collision avoidance controller based only on OS4 embedded sensors</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300010&lng=en&nrm=iso&tlng=en The major goal of this research was the development and implementation of a control system able to avoid collisions during the flight for a mini-quadrotor helicopter, based only on its embedded sensors without changing the environment. However, it is important to highlight that the design aspects must be seriously considered in order to overcome hardware limitations and achieve control simplification. The controllers of a UAV (Unmanned Aerial Vehicle) robot deal with highly unstable dynamics and strong axes coupling. Furthermore, any additional embedded sensor increases the robot total weight and therefore, decreases its operating time. The best balance between embedded electronics and robot operating time is desired. This paper focuses not only on the development and implementation of a collision avoidance controller for a mini-robotic helicopter using only its embedded sensors, but also on the mathematical model that was essential for the controller developing phases. Based on this model we carried out the development of a simulation tool based on MatLab/Simulink that was fundamental for setting the controllers' parameters. This tool allowed us to simulate and improve the OS4 controllers in different modeled environments and test different approaches. After that, the controllers were embedded in the real robot and the results proved to be very robust and feasible. In addition to this, the controller has the advantage of being compatible with future path planners that we are developing. <![CDATA[<b>The use of an axisymmetric formulation of the Finite Volume Method for the thermal analysis of the retina and ocular tissues following implantation of retinal prosthesis</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300011&lng=en&nrm=iso&tlng=en This study analyzes the heat transfer in human eyes following implantation of retinal prostheses using an axisymmetric formulation of the Finite Volume Method. The model used consisted of a vertex centered unstructured grid finite volume method in an edge-based data structure and an explicit time integration. The results of the finite volume thermal analysis in ocular tissues were determined in the presence of two types of retinal implants: subretinal and epiretinal. For the subretinal device, the maximum temperature reached in the retina was 36.78°C (309.78 K) and the irreversible thermal damage occurred at 200 days. In the case of the epiretinal implant, the maximum temperature reached at the retinal/chip interface was 36.92°C (309.92 K) and the irreversible thermal damage occurred at 180 days. Our results indicate that tin spite of its higher dissipation power, the epiretinal implant produces thermal damages similar to that caused by the subretinal implant. The computational tool which was developed was able to effectively calculate temperature profiles and thermal damage values to retinal implants and is also capable to calculate temperature profile in any other geometry of interest, for example with other types s of external thermal source like laser beans. <![CDATA[<b>A study of convective flux schemes for aerospace flows</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300012&lng=en&nrm=iso&tlng=en This paper presents the effects of some convective flux computation schemes on boundary layer and shocked flow solutions. Second-order accurate centered and upwind convective flux computation schemes are discussed. The centered Jameson scheme, plus explicitly added artificial dissipation terms are considered. Three artificial dissipation models, namely a scalar and a matrix version of a switched model, and the CUSP scheme are available. Some implementation options regarding these methods are proposed and addressed in the paper. For the upwind option, the Roe flux-difference splitting scheme is used. The CUSP and Roe schemes require property reconstructions to achieve second-order accuracy in space. A multidimensional limited MUSCL interpolation method is used to perform property reconstruction. Extended multidimensional limiter formulation and implementation are here proposed and verified. Theoretical flow solutions are used in order to provide a representative testbed for the current study. It is observed that explicitly added artificial dissipation terms of the centered scheme may nonphysically modify the numerical solution, whereas upwind schemes seem to better represent the flow structure. <![CDATA[<b>Proper orthogonal decomposition for model reduction of a vibroimpact system</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000300013&lng=en&nrm=iso&tlng=en The application that inspires this work is the percussion drilling. This problem has impacts and presents uncertainties. In this first analysis the focus is on the construction of an efficient reduced-order model to deal with the nonlinear dynamics due to the impacts. It is important to have an efficient reduced-order model to perform the stochastic analysis. The simplified full model is constructed using the finite element method, and three different bases are used to construct the reduced-order models: LIN-basis (composed by the normal modes of the associated linear problems), PODdir-basis (obtained through proper orthogonal decomposition -direct method) and PODsnap-basis (obtained through proper orthogonal decomposition -snapshot method). The shapes of the elements of LIN-basis, PODdir-basis, and PODsnap-basis are compared. One important conclusion is that the information necessary to represent the details of a vibroimpact dynamics, measured by the proper orthogonal values, is more than the usual 99% recommended.