Scielo RSS <![CDATA[Journal of the Brazilian Society of Mechanical Sciences and Engineering]]> http://www.scielo.br/rss.php?pid=1678-587820100001&lang=pt vol. 32 num. 1 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<B>An adaptive fuzzy dead-zone compensation scheme and its application to electro-hydraulic systems</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100001&lng=pt&nrm=iso&tlng=pt The dead-zone is one of the most common hard nonlinearities in industrial actuators and its presence may drastically compromise control systems stability and performance. Due to the possibility to express specialist knowledge in an algorithmic manner, fuzzy logic has been largely employed in the last decades to both control and identification of uncertain dynamical systems. In spite of the simplicity of this heuristic approach, in some situations a more rigorous mathematical treatment of the problem is required. In this work, an adaptive fuzzy controller is proposed for nonlinear systems subject to dead-zone input. The boundedness of all closed-loop signals and the convergence properties of the tracking error are proven using Lyapunov stability theory and Barbalat's lemma. An application of this adaptive fuzzy scheme to an electro-hydraulic servo-system is introduced to illustrate the controller design method. Numerical results are also presented in order to demonstrate the control system performance. <![CDATA[<B>A case study on testing CMM uncertainty simulation software (VCMM)</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100002&lng=pt&nrm=iso&tlng=pt Virtual Coordinate Measuring Machines (VCMMs) are software packages aimed at providing uncertainty estimates for tridimensional measurements. Since they deal with metrology data to derive uncertainty estimates, which are to be used for making decisions related to product quality, they must be evaluated. Although there are international standards to deal with software testing for metrology, the evaluation of VCMMs performance is still in the experimental stage. Here a testing framework was organized focusing on the definition of the test context, the test purpose, the performance criteria and the testing strategy, including the usability of the VCMM interface, which is a common focus in software engineering but not in tests of metrology applications. Experimentation and reference data were also used to check the adequacy of uncertainty estimates against measurement results. The executed tests show that it is possible to provide the necessary evidence of acceptable VCMM performance. It is also demonstrated that no single testing strategy is sufficient to provide the necessary evidence to validate the VCMM from the metrology standpoint. <![CDATA[<B>On the application of self-organizing neural networks in gas-liquid and gas-solid flow regime identification</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100003&lng=pt&nrm=iso&tlng=pt One of the main problems associated with the transport and manipulation of multiphase flow is the existence of flow regimes, which have a strong influence on important parameters of operation. An example of this occurs in gas-liquid chemical reactors in which maximum coefficients of reaction can be attained by keeping a dispersed-bubbly flow regime to maximize the total interfacial area. Another example is the pneumatic conveying of solids in which the regimes are associated with safety and energy consumption. Thus, the ability to identify flow regimes automatically is very important, specially to maintain multiphase systems operating according to design conditions. This work assesses the use of a self-organizing map (neural network) adapted to the problem of regime identification in horizontal two-phase flows. In order to achieve extensive results, two different types of two-phase flows were considered: gas-solid and gas-liquid. Tests were made to verify the performance of the neural network model, using data collected at the experimental facilities of the Thermal and Fluid Engineering Laboratory of the University of São Paulo at São Carlos. Results show that the neural network is capable of correctly identifying the regimes. The error percentage is bigger when analyzing the same regime with flow rates different from the one used as training data emphasizing the importance of training signals choice. <![CDATA[<B>Analysis of numerically simulated true strain on high stampability sheets</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100004&lng=pt&nrm=iso&tlng=pt The sheet metal forming is a manufacturing process widely used industrially. The quality and efficiency of the process is dependent on the correct choice of the process parameters and the correct understanding of the sheet metal behavior. The identification of the regions where stretching and/or deep drawing occurred during the forming process can aid the process through the tools design optimization. This work consisted of evaluating three punch models with varied geometries. The purpose of this work was to simulate different punch geometries using the ANSYS/LS_DYNA program and to compare the results with those reported in the literature. An evaluation was also made of the chosen program's response quality (validation). The material model chosen was the Barlat's model. The friction coefficient influence was also investigated. A comparison of the major true strain (ε1) obtained by simulation compared with the experimental results indicated that this material model is able to satisfactorily reproduce the major true strain found in practice for the DC 06 steel. <![CDATA[<B>Uncertainty calculation for hearing protector noise attenuation measurements by REAT method</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100005&lng=pt&nrm=iso&tlng=pt The objective of this paper is to quantify the uncertainty of hearing protector attenuation measurements and present the metrology study necessary for the accreditation of the Industrial Noise Laboratory (LARI) at The Federal University of Santa Catarina and Individual Protection Equipment laboratory (LAEPI) of NR consultancy Ltda. - Brazil for hearing protector noise attenuation procedures using the "Real Ear Attenuation at Threshold - REAT" method of the Brazilian National Institute of Metrology Standardization and Industrial Quality - INMETRO. A model for the calculation of measurement uncertainty was developed based on the document: "Guide to expression of uncertainty in measurement" published by the International Organization for Standardization, first edition, corrected and reprinted in 1995, Geneva, Switzerland. The uncertainty of each source of error was estimated and the overall uncertainty of the hearing protector noise attenuation measurement was calculated for each 1/1 octave band frequency and the results used in the single number (NRRsf - Noise Reduction Rating for subject fit) uncertainty calculation. It was concluded that the largest uncertainty is due to the determination of the subject hearing thresholds. <![CDATA[<B>Effects of milling condition on the surface integrity of hot forged steel</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100006&lng=pt&nrm=iso&tlng=pt This paper presents a study on the influence of milling condition on workpiece surface integrity focusing on hardness and roughness. The experimental work was carried out on a CNC machining center considering roughing and finishing operations. A 25 mm diameter endmill with two cemented carbide inserts coated with TiN layer were used for end milling operation. Low carbon alloyed steel Cr-Mo forged at 1200 ºC was used as workpiece on the tests. Two kinds of workpiece conditions were considered, i.e. air cooled after hot forging and normalized at 950 ºC for 2 h. The results showed that finishing operation was able to significantly decrease the roughness by at least 46% without changing the hardness. On the other hand, roughing operation caused an increase in hardness statistically significant by about 6%. The machined surface presented deformed regions within feed marks, which directly affected the roughness. Surface finish behavior seems to correlate to the chip ratio given the decrease of 25% for roughing condition, which damaged the chip formation. The material removal rate for finishing operation 41% greater than roughing condition demonstrated to be favorable to the heat dissipation and minimized the effect on material hardness. <![CDATA[<B>A finite element model for the ocean circulation driven by wind and atmospheric heat flux</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100007&lng=pt&nrm=iso&tlng=pt A finite element model for solving ocean circulation forced by winds and atmospheric heat fluxes is presented. It is vertically integrated 1 1/2 layer model which solves the motion and continuity hydrodynamic equations coupled with the advection-diffusion transport equation for temperature. A space-time Petrov-Galerkin formulation is used to minimize the undesirable numerical spurious oscillation effects of unresolved boundary layers solution of classical Galerkin method. The model is employed to simulate the circulation of the eastern South Pacific Ocean represented by a mesh covering the area between the equator and 30ºS and between the 70ºW to 100ºW. Monthly climatological data are used to determine the wind and heat fluxes forcing functions of the model. The model simulates the main features of observed sea surface temperature (SST) pattern during the summer months showing the upwelling along the coastal boundary with currents oriented northwestward and the presence of southward flows and warm water intrusion in offshore side. The calculated SST fields are compared with the mean observed SST showing that the coastal processes and the interaction with the equatorial band are physically better resolved. <![CDATA[<B>Nitrogen charge temperature prediction in a gas lift valve</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100008&lng=pt&nrm=iso&tlng=pt The operation of a class of retrievable gas-lift valves (GLV) is controlled by the axial movement of a bellows. One force acting on the bellows is due to the pressure exerted by the nitrogen gas contained in the GLV dome. It depends on the nitrogen temperature, which is influenced by both the production fluid and the injection gas temperatures in the well. This work investigated this dependence for a GLV installed in a side pocket mandrel tube. Three independent procedures were used for this purpose, comprising a compact thermal model, an experimental investigation with a thermal mockup and a numerical analysis. From these, a correlation for the nitrogen temperature was proposed, based on the local production fluid and injection gas temperatures, and on their convective coefficients with the mandrel tube surfaces. <![CDATA[<B>Static and free vibration studies on a pulley-belt system with ground stiffness</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100009&lng=pt&nrm=iso&tlng=pt The static and free vibration behavior of a pulley-belt system with ground stiffness is investigated using a nonlinear model based on Hamilton's principle. In the equilibriumanalysis a computational method based on boundary value problem solvers is adapted to obtain the numerical solution, whereas for free vibration analysis spatial discretization is done using the Galerkin's method to evaluate the natural frequencies and vibration modes. The study indicates that there is a considerable decrease in equilibrium deflection due to ground stiffness, especially when it is larger than the belt bending stiffness and this effect is more pronounced for higher values of belt bending stiffness. Equilibrium deflections change reasonably with static span tension variation, but are more sensitive to variations of speed and longitudinal stiffness. The natural frequencies of the pulley-belt system increase with ground stiffness, but this is primarily restricted to the lower modes; higher modes are insensitive to ground stiffness. <![CDATA[<B>Simultaneous buckling and fundamental frequency optimization of frames under uncertain loadings</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100010&lng=pt&nrm=iso&tlng=pt This work presents the optimization of a frame under uncertain loadings when two design criteria are taken simultaneously into account. The uncertainty relates to the applied loading and is inherent to the operation of structures since real structures are designed to sustain a large variety of load cases of practical relevance. The design criteria considered are two of the most important from a practical point of view: buckling load and natural frequency. The technique developed is based in convex modeling where a load space is defined and all the elements of that load space have equal probability of occurrence. The outcome of the technique is an optimal design for which one loading or several loadings of the load space are the most dangerous or harmful to the structure. On the other hand, it is guaranteed that all the other loadings contained in the load space are conservative in the sense that they are less harmful to the optimal design. <![CDATA[<B>Order of accuracy study of unstructured grid finite volume upwind schemes</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100011&lng=pt&nrm=iso&tlng=pt A detailed numerical study is presented of the order of accuracy of some proposed cell centered, finite volume schemes used for the solution of the 2-D gasdynamic equations on triangular unstructured grids. The schemes studied are based on a MUSCL-type linear reconstruction of interface properties, which seeks to achieve 2nd-order accuracy in space. They are also nominally flux-vector splitting-type schemes, and the results here presented use Liou's AUSM+ algorithm. The basic aspects effecting the scheme's order of accuracy are the form in which the reconstruction process is designed and the form in which the limiting process is performed. Two basic concepts are tested with regard to the reconstruction process, namely the use of 1-D-type and gradient-based reconstruction. The limiter can also be constructed as a 1-D-type limiter or as a truly multi-dimensional limiter. The schemes are tested on a linear convection-like model equation and the numerical solutions are compared to the analytical solution, for different mesh sizes, in order to assess the scheme's order of accuracy. For comparison purposes, the results obtained with a centered scheme are also presented. Second-order accuracy is shown to be only obtained for the centered scheme. The nominally 2nd-order upwind algorithms lead to actual orders of accuracy, which vary from 0.9 to 1.5. <![CDATA[<B>Multiobjective optimization techniques applied to engineering problems</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000100012&lng=pt&nrm=iso&tlng=pt Optimization problems often involve situations in which the user's goal is to minimize and/or maximize not a single objective function, but several, usually conflicting, functions simultaneously. Such situations are formulated as multiobjective optimization problems, also known as multicriteria, multiperformance or vector optimizations. Because multiobjective optimization problems arise in different scientific applications, many researches have focused on developing methods for their solution. Thus, there are several criteria that can be considered to solve such complex optimizations. This paper contributes to the study of optimization problems, by comparing some of these methods. The classical method, based on function scalarization, in which a vector function is transformed into a scalar function, is represented here by the weighted objectives and global criterion methods. A different approach involves hierarchical, trade-off and goal programming, which treats the objective functions as additional constraints. Some multicriteria optimization problems are given to illustrate each methodology studied here. The techniques are initially applied to an environmentally friendly and economically feasible electric power distribution problem. The second application involves a dynamics optimization problem aimed at optimizing the first three natural frequencies.