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vol. 34 num. 1 lang. en<![CDATA[SciELO Logo]]>http://www.scielo.br/img/en/fbpelogp.gif
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<![CDATA[<b>Numerical prediction of bed-load and surface deformation on a granular bed sheared by a turbulent boundary-layer</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100001&lng=en&nrm=iso&tlng=en
The entrainment of solid particles by a fluid flow is frequently found in nature and in industry. A better knowledge of this is of importance to understand the physical nature of the phenomenon and to improve industrial processes. Bed-load occurs if the shear stresses exerted by the fluid on the granular bed are bounded to some limits: a mobile granular layer takes place over the fixed part of the bed. When the fluid is a liquid, the thickness of this mobile layer is a few grain-diameters. Under these conditions, an initially flat granular bed may be unstable, giving rise to ripples and dunes. Some examples are the dunes seen in deserts, but also the ripples appearing in petroleum pipelines conveying sand. This article presents a mathematical model for the prediction of bed-load under a turbulent boundary-layer of a liquid, and its numerical implementation. The model, kept as simple as possible, focuses on the mobile layer of the granular bed, reducing then the computation domain. It is able to capture the pertinent physics involved, such as the growing of instabilities on the granular bed, so that, if employed together with the stability analysis of Franklin (2010), it selects and predicts the evolution of most unstable modes.<![CDATA[<b>A transformation of variables technique applicable to the boundary element method to simulate a special class of diffusive-advective potential problems</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100002&lng=en&nrm=iso&tlng=en
This paper describes a novel Boundary Element Technique developed for application to one-dimensional and a class of two-dimensional diffusive-advective potential problems. It is based on transformation of variable procedure to establish an integral equation inverse sentence, dealing only with boundary variables, using a fundamental solution associated with a diffusive problem. To apply the technique described here, the original differential equation is rewritten and flow potential functions are employed to contract terms which appear in the original equation, giving as a result an equivalent equation expressed in terms of the derivative of the product of two functions. This new form of the governing equation, together with the proposed transformation of variables is quite convenient for the application of the boundary element methodology: a very simple discretization procedure arises; the resulting algorithms require low CPU time and the numerical results are quite accurate.<![CDATA[<b>Laser beam welding tempered 300M ultrahigh mechanical strength steel</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100003&lng=en&nrm=iso&tlng=en
AISI 300M ultrahigh strength steel has been used in a number of high demanding applications, such as the VLS Brazilian rocket project. This work intends to propose laser beam welding, with subsequent tempering, as a possible route for the fabrication of engineering pieces of this steel. A 2 kW fiber laser was used to produce welded coupons for metallographic, hardness and tensile strength tests. It has been shown that convenient laser parameters for a 3 mm thick plate are 50 mm/s welding speed and 1200 W laser power. However, both welded materials and heat-affected zones presented high hardness and negligible plastic deformation. In order to produce useful engineering parts, it was suggested a tempering treatment for 2 hours at temperatures of 200 or 400ºC. Tensile mechanical testing has shown that welded and tempered coupons presented both yield and maximum strengths comparable to the unwelded material. On the other hand, a maximum elongation of about 4% was obtained, in comparison with 12% from the bulk sample.<![CDATA[<b>Determination of the relative position between grinding wheel and a cylindrical workpiece on a 7 axis grinding machine by acoustic emission</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100004&lng=en&nrm=iso&tlng=en
The contact between grinding wheel and workpiece in the grinding process is recognized by acoustic emission (AE). Two acoustic emission monitoring systems (MS) were integrated into a 3 axis CNC grinding machine. A laptop allows the signal acquisition and visualization. The acquired AE RMS signals from the contact between tool and workpiece are analyzed permitting to establish the most suitable AE monitoring system to recognize the contact in a particular grinding machine. In a second experimental setup the selected MS was installed on a 7 axis tool grinding machine at an industrial partner. At this partner, the relative position between grinding wheel and workpiece was previously determined manually. This procedure has a direct influence on the results depending on the technical skills of the operator. The automation of this activity supported by acoustic emission has led to satisfactory results regarding the relative position between grinding wheel and workpiece and contributed to the setup time reduction.<![CDATA[<b>Modeling and optimization of cylindrical grinding of Al/SiC composites using genetic algorithms</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100005&lng=en&nrm=iso&tlng=en
The Al/SiC composites have received more commercial attention than other kinds of Metal Matrix Composites (MMCs) due to their high performance. However, a continuing problem with MMCs is that they are difficult to machine, due to the hardness and abrasive nature of the SiC particles. Grinding is often the method of choice for machining Al/SiC composites to acquire high dimensional accuracy and surface finish in large scale production. Based on the full factorial design (3(4)), a total of 81 experiments, each having a combination of different levels of variables, are carried out to study the effect of grinding parameters such as wheel velocity, work piece velocity, feed and depth of cut on the responses such as tangential grinding force, roughness and grinding temperature. Modeling and optimization place a vital role in controlling any process for improved product quality, high productivity and low cost. In the present work, experimental results are used to calculate the analysis of variance (ANOVA) which explains the significance of the parameters on the responses. Based on the results of ANOVA, a mathematical model is formulated using multiple regression method. A genetic algorithm (GA) based optimization procedure has been developed to optimize the grinding parameters for maximum material removal by imposing constraints on roughness. This methodology would be useful for identifying the optimum grinding parameters in order to achieve the required material removal rate (MRR).<![CDATA[<b>Modelling and optimization of the surface roughness in the dry turning of the cold rolled alloyed steel using regression analysis</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100006&lng=en&nrm=iso&tlng=en
Surface quality of the machined parts is one of the most important product quality indicators and one of the most frequent customer requirements. The average surface roughness (Ra) represents a measure of the surface quality, and it is mostly influenced by the following cutting parameters: the cutting speed, the feed rate, and the depth of cut. Quantifying the relationship between surface roughness and cutting parameters is a very important task. In this study regression analysis was used for modelling and optimization of the surface roughness in dry single-point turning of the alloyed steel, using coated tungsten carbide inserts. The experiment has been designed and carried out on the basis of a three-level full factorial design. The linear, the quadratic and the power (non-linear) mathematical models were selected for the analysis. Obtained results are in good accordance with the experimentally obtained data, confirming the effectiveness of regression analysis in modelling and optimization of surface roughness in the turning process. The general conclusion is that the surface roughness has a clear downward trend with the cutting speed increase and decrease in the feed rate and the depth of cut.<![CDATA[<b>Modelling and analysis of cutting force and surface roughness in milling operation using TSK-type fuzzy rules</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100007&lng=en&nrm=iso&tlng=en
The present paper discusses on development of fuzzy rule based models (FRBMs) for predicting cutting force and surface roughness in milling operation. The models use TakagiSugeno-Kang-type (TSK-type) fuzzy rule to study the effect of four (input) cutting parameters (cutting speed, feed rate, radial depth of cut and axial depth of cut) on outputs (cutting force and surface roughness). The appropriate FRBM is arrived after a thorough investigation of different structures of rule-consequent function. A combined approach of genetic algorithm and multiple linear regression method is used to determine the rule-consequent parameters. Performance analysis of models by comparing with experimental data implies its potential towards practical application. Analysis of the influence of various input parameters on different outputs is carried out based on FRBMs and experimental data. It suggests that the cutting force becomes higher with increasing feed rate, axial depth of cut and radial depth of cut and lower with increase in cutting speed, whereas surface finish is improved with increase in cutting speed and gets poorer with increase in radial depth of cut.<![CDATA[<b>Geometrically non-linear analysis of inclined elastic rods subjected to self-weight</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100008&lng=en&nrm=iso&tlng=en
The behavior of inclined slender elastic rods subjected to axial forces and distributed load is discussed in this paper. Mathematical models and numerical solutions are developed for small and large displacements. A double-hinged boundary condition is assumed and the analysis is carried out for different values of non-dimensional weight (distributed load) and angle of inclination. The mathematical formulation results from considering geometrical compatibility, equilibrium of forces and moments and constitutive relations. For large displacements, a set of six first order non-linear ordinary differential equations with boundary conditions prescribed at both ends is obtained. This two-point boundary value problem is numerically integrated using a three-parameter shooting method. When small displacements are assumed the problem simplifies and a power series solution may be conveniently employed. The results for both simulations are presented, compared and discussed.<![CDATA[<b>Finite element validation on adhesive joint for composite fuselage model</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100009&lng=en&nrm=iso&tlng=en
A novel fabrication miniature composite fuselage structure consisted of a woven composite laminated with an adhesively bonded butt joint under axial compression loading is numerically simulated in this research. A Finite Element Analysis (FEA) via ABAQUS/Explicit was utilized to capture the complete compressive response that predicts the crushing behaviour and its mechanical strength from initial compression loading until its final failure mode. A woven C-glass fibre/epoxy 200 g/m² composite laminated (908) with the orthotropic elastic material properties is modelled as a continuum composite layup in the proposed numerical model. The adhesively bonded joint progression is considered using cohesive element technology that allows the correct accounting for the energy involved in the crushing process. The capability of the bonded joint to withstand axial crushing impact from debonding failure was examined. This proposed model was used to observe the crushing load and collapse modes under axial compression impact. The results that were extracted and computed from the FE modelling have shown a good agreement with the experimental test.<![CDATA[<b>Application of design of experiments to plasma Arc Welding Process</b>: <b>a review</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100010&lng=en&nrm=iso&tlng=en
Design of Experiment commonly referred to as DOE is one of the extensively used methods for experimental study of many manufacturing processes in engineering. DOE is a statistical approach in which a mathematical model is developed through experimental runs. DOE predicts possible output based on the input parameters of the experimental setup. In the present study, a review is made on DOE techniques that have been employed for various welding processes by other researchers. This study predominantly focuses on the usage of Response Surface Method, Taguchi's method and Factorial method in Welding.<![CDATA[<b>Implementation of acoustic materials to the VLS-1 Fairing</b><b> - </b><b>a sensitivity analysis using SEA</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100011&lng=en&nrm=iso&tlng=en
Satellite launchers are submitted to severe acoustic loads mainly during lift-off where SPL achieve, at the upper parts, values within the range of 140-160 dB. Such an excitation can damage embedded elements, if energy attenuation measures are not adopted. In view of managing the PLF vibro-acoustic environment, numerical techniques are applied to predict elasto-acoustic behavior. This manuscript presents a numerical study on the design of acoustic insulation for the VLS-1 fairing compartment. An excitation profile based on the literature is applied on a SEA coupled model of this structural-acoustic system and absorbing materials are added to the model. Two parameters of the absorbing material layer are analyzed: thickness and covered area. Two NCT modeling approaches are used to simulate the effect of blanketing the VLS-1 fairing: acoustic materials Biot's parameters, given by the manufacturer, and material samples absorption coefficient, measured in a Kundt Tube. Results show that an increase in the blanket thickness from 7.62 to 12.7 cm results in a TL of 1.7 dB OSPL, while variations of up to 3.0 dB OSPL are calculated if the fairing cavity blanketed area varies from 30% to 100%.<![CDATA[<b>Dimensional analysis and empirical correlations for heat transfer and pressure drop in condensation and evaporation processes of flow inside micropipes</b>: <b>case study with carbon dioxide (CO2)</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100012&lng=en&nrm=iso&tlng=en
In this paper, the experimental results of the convection heat transfer coefficient and pressure drop values during condensation and evaporation of CO2 were obtained at different operating conditions for flow inside micropipes. Reynolds number (ReD) ranged between 2000 and 15000. The dimensional analysis technique was utilized to develop correlations for Nusselt numbers and pressure drops. A comparison between experimental and correlated results was carried out. The results showed that for the condensation process, the bias errors were 5.25% and 0.4% for pressure drops and Nusselt number respectively. Consequently, Average Standard Deviation (ASD) values reached 17.94% and 4.62% for both respectively. On the other hand, for the evaporation process, the Nusselt number error was 3.8% with an ASD of 4.14%. The correlations presented in the present work can be used in calculating pressure drops and heat transfer coefficients for phase change flows in mini and micro tubes. It helps to enhance design calculations of heat exchangers, condensers and evaporators<![CDATA[<b>An edge-based unstructured mesh formulation for high speed tridimensional compressible flow simulation</b>]]>
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782012000100013&lng=en&nrm=iso&tlng=en
Numerical simulation of realistic compressible flows is very important and requires accurate and flexible tridimensional formulations, which should furthermore be robust and efficient. In this work we describe the development of a computational tool for numerical simulation of inviscid compressible 3-D fluid flow problems. This tool uses as the main building block an edge-based Galerkin FEM (Finite Element Method) together with a MUSCL (Monotonic Upstream-centered Schemes for Conservations Laws) approach to get a higher-order scheme with LED (Local Extremum Diminishing) property. The code is particularly developed for the simulation of supersonic and hypersonic flow regimes and several important (sometimes unavoidable) numerical procedures incorporated to increase its robustness are described. Some aspects related to the adoption of an edge-based data structure and other implementation issues are also described. Finally, some numerical model problems are analyzed and compared with results found in the literature demonstrating the effectiveness of the developed tool.