Scielo RSS <![CDATA[Journal of the Brazilian Society of Mechanical Sciences]]> http://www.scielo.br/rss.php?pid=0100-738620020004&lang=pt vol. 24 num. 4 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<B>Hot tool temperature analysis though infrared images</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400001&lng=pt&nrm=iso&tlng=pt Textile manufacture occupies a prominent place in the national economy. Because of its importance researches have been made on the development of new materials, equipment and methods used in the production process. The cutting of textiles starts in the basic stage, to be followed by the process of the making of clothes and other articles. In the hot cutting of fabric, one of the variables of great importance in the control of the process is the contact temperature between the tool and the fabric. This work presents a technique for the measurement of the temperature based on the processing of infrared images. With this purpose, it was developed a system which is composed of an infrared camera, a framegrabber PC board and a software which analyses the punctual temperature in the cut area enabling the operator to achieve the necessary control of other variables involved in the process. <![CDATA[<B>On non-ideal and non-linear portal frame dynamics analysis using bogoliubov averaging method</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400002&lng=pt&nrm=iso&tlng=pt We apply the Bogoliubov Averaging Method to the study of the vibrations of an elastic foundation, forced by a Non-ideal energy source. The considered model consists of a portal plane frame with quadratic nonlinearities, with internal resonance 1:2, supporting a direct current motor with limited power. The non-ideal excitation is in primary resonance in the order of one-half with the second mode frequency. The results of the averaging method, plotted in time evolution curve and phase diagrams are compared to those obtained by numerically integrating of the original differential equations. The presence of the saturation phenomenon is verified by analytical procedures. <![CDATA[<B>On-site calibration of a phase fraction meter by an inverse technique</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400003&lng=pt&nrm=iso&tlng=pt The formal calibration procedure of a phase fraction meter is based on registering the outputs resulting from imposed phase fractions at known flow regimes. This can be straightforwardly done in laboratory conditions, but is rarely the case in industrial conditions, and particularly for on-site applications. Thus, there is a clear need for less restrictive calibration methods regarding to the prior knowledge of the complete set of inlet conditions. A new procedure is proposed in this work for the on-site construction of the calibration curve from total flown mass values of the homogeneous dispersed phase. The solution is obtained by minimizing a convenient error functional, assembled with data from redundant tests to handle the intrinsic ill-conditioned nature of the problem. Numerical simulations performed for increasing error levels demonstrate that acceptable calibration curves can be reconstructed, even from total mass measured within a precision of up to 2%. Consequently, the method can readily be applied, especially in on-site calibration problems in which classical procedures fail due to the impossibility of having a strict control of all the input/output parameters. <![CDATA[<B>Three-dimensional supersonic flow over a spike-nosed body of revolution</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400004&lng=pt&nrm=iso&tlng=pt The unsteady, viscous, supersonic flow over a spike-nosed body of revolution is numerically investigated by solving the Navier-Stokes equations. The time-accurate computations are performed employing an implicit algorithm based on the second-order time-accurate LU-SGS scheme with the incorporation of a subiteration procedure to maintain time accuracy. The characteristics of the flow field for a Mach number of 3.0, Reynolds number of 7.87 x 10(6)/m, and angles of attack of 5 and 10 degrees are described. Self-sustained asymmetric shock wave oscillations were observed in the numerical computations for these angles of attack. The main characteristic of the flow field, as well as its influence on drag coefficient is discussed. <![CDATA[<B>Welding current effect on diffusible hydrogen content in flux cored arc weld metal</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400005&lng=pt&nrm=iso&tlng=pt The application of flux cored arc welding (FCAW) has increased in manufacturing and fabrication. Even though FCAW is well known for its good capability in producing quality welds, few reports have been published on the cause of the relatively high diffusible hydrogen content in the weld metal and its relation with the ingredients used in the wire production and with the welding parameters (mainly welding current). This paper describes experiments where data obtained from weld metal diffusible hydrogen analysis, metal droplet collection, and high-speed recording of metal droplet transfer were used to evaluate the effect of welding current on diffusible hydrogen content in the weld metal. The results from gas chromatography analysis showed that weld metal hydrogen content indeed increased with welding current. A polynomial regressional analysis concluded that hydrogen increase with current was better described by a linear function with proportional constant of approximately 0.7 or 70%. Different from the GMA welding transfer behavior, statistical analysis showed only a small increase in metal droplet size with increasing current. The metal transfer mode remained in the globular range for currents between 100 and 150 A. The most surprising findings were with the high-speed cinematography recording. Observing the high speed movies, it was possible to see that at low current, "unmelted" flux sporadically touched the weld pool but at higher current, the flux remained touching the weld pool during the whole time of droplet formation and transfer. It is believed that since the flux has ingredients that contain hydrogen, hydrogen passes through the arc undisturbed, going to the weld bead intact and increasing the hydrogen content in the weld metal. Another important observation is regarding to droplet size. Droplet size increased with increasing current because forces from decomposed gases from the flux could sustain the droplets, retarding their transfer and allowing them to grow. <![CDATA[<B>Control of transients in water distribution networks by H<SUB><FONT FACE=Symbol>¥</SUB></FONT> Control</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400006&lng=pt&nrm=iso&tlng=pt In this work, a controller for regulating the transients in water distribution networks is established. The control technique is the H<FONT FACE=Symbol>¥</FONT> Control. The developed controller is applied to a water distribution network and the results of this application demonstrate that the technique allowed the establishment of a robust controller, capable of attenuating the disturbances in a suitable way, being effective in controlling the oscillations of the state variables in question. <![CDATA[<B>Optimal design of 3R manipulators by using classical techniques and simulated annealin</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400007&lng=pt&nrm=iso&tlng=pt In this paper, the optimum design of 3R manipulators is formulated and solved by using an algebraic formulation of workspace boundary. A manipulator design can be approached as a problem of optimization, in which the objective functions are the size of the manipulator and workspace volume; and the constrains can be given as a prescribed workspace volume. The numerical solution of the optimization problem is investigated by using two different numerical techniques, namely, sequential quadratic programming and simulated annealing. Numerical examples illustrate a design procedure and show the efficiency of the proposed algorithms. <![CDATA[<B>Experimental study applied to an industrial robot by using variable structure controllers and friction compensation</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400008&lng=pt&nrm=iso&tlng=pt Control of an industrial robot is mainly a problem of dynamics. It includes non-linearities, uncertainties and external perturbations that should be considered in the design of control laws. In this work, two control strategies based on variable structure controllers (VSC) and a PD control algorithm are compared in relation to the tracking errors considering friction. The controller's performances are evaluated by adding an static friction model. Simulations and experimental results show it is possible to diminish tracking errors by using a model based friction compensation scheme. A SCARA robot is used to illustrate the conclusions of this paper. <![CDATA[<B>Neutron tomography using projection data obtained by Monte Carlo simulation for nondestructive evaluation</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400009&lng=pt&nrm=iso&tlng=pt This work present the application of a computer package for generating of projection data for neutron computerized tomography, and in second part, discusses an application of neutron tomography, using the projection data obtained by Monte Carlo technique, for the detection and localization of light materials such as those containing hydrogen, concealed by heavy materials such as iron and lead. For tomographic reconstructions of the samples simulated use was made of only six equal projection angles distributed between 0º and 180º, with reconstruction making use of an algorithm (ARIEM), based on the principle of maximum entropy. With the neutron tomography it was possible to detect and locate polyethylene and water hidden by lead and iron (with 1cm-thick). Thus, it is demonstrated that thermal neutrons tomography is a viable test method which can provide important interior information about test components, so, extremely useful in routine industrial applications. <![CDATA[<B>Development of nano-meter motion control in Japan</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400010&lng=pt&nrm=iso&tlng=pt Production machines for next generation LSIs such as 4G-DRAMs and for large liquid crystal displays such as 0.5mx0.5m size, and information equipment such as magnetic hard disks and DVDs must have the positioning accuracy of a nano-meter order. To realize such a high degree of the positioning accuracy, not only precision machine elements and mechanisms but also high precision sensors, actuators and controller design techniques becomes crucial. This paper introduces recent topics of precision positioning and motion control technology in Japan. <![CDATA[<B>Testing and simulation of fractionary electromechanical rotative drives</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400011&lng=pt&nrm=iso&tlng=pt This paper concerns the development of drives that use electromechanical rotative motor systems. It is proposed an experimental drive test structure integrated to simulation softwares. The objective of this work is to show that an affordable model validation procedure can be obtained by combining a precision data acquisition with well tuned state-of-the-art simulation packages. This is required for fitting, in the best way, a drive to its load or, inversely, to adapt loads to given drive characteristics. <![CDATA[<B>Single axis controlled attraction type magnetic bearing</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400012&lng=pt&nrm=iso&tlng=pt This paper presents a new type of magnetic bearing with active control only in axial direction. The bearing uses two pairs of permanent magnets working in attraction mode to restrict the radial motion and a control system composed of two electromagnets, a gap sensor and a controller to keep the axis in a fixed axial position. The principle, the dynamic model for axial motion and the control system for this bearing are presented. Finally, by experiments conducted in a prototype, the effectiveness of the presented concept is shown. <![CDATA[<B>Understanding the complexity in low dimensional systems</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400013&lng=pt&nrm=iso&tlng=pt Complex System is any system that presents involved behavior, and is hard to be modeled by using the reductionist approach of successive subdivision, searching for ''elementary'' constituents. Nature provides us with plenty of examples of these systems, in fields as diverse as biology, chemistry, geology, physics, and fluid mechanics, and engineering. What happens, in general, is that for these systems we have a situation where a large number of both attracting and unstable chaotic sets coexist. As a result, we can have a rich and varied dynamical behavior, where many competing behaviors coexist. In this work, we present and discuss simple mechanical systems that are nice paradigms of Complex System, when they are subjected to random external noise. We argue that systems with few degrees of freedom can present the same complex behavior under quite general conditions. <![CDATA[<B>Escape in a nonideal electro-mechanical system</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400014&lng=pt&nrm=iso&tlng=pt In this work a particular system is investigated consisting of a pendulum whose point of support is vibrated along a horizontal guide by a two bar linkage driven from a DC motor, considered as a limited power source. This system is nonideal since the oscillatory motion of the pendulum influences the speed of the motor and vice-versa, reflecting in a more complicated dynamical process. This work comprises the investigation of the phenomena that appear when the frequency of the pendulum draws near a secondary resonance region, due to the existing nonlinear interactions in the system. Also in this domain due to the power limitation of the motor, the frequency of the pendulum can be captured at resonance modifying completely the final response of the system. This behavior is known as Sommerfeld effect and it will be studied here for a nonlinear system. <![CDATA[<B>Petri Net approach for modelling system integration in intelligent buildings</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-73862002000400015&lng=pt&nrm=iso&tlng=pt In this paper, a Petri Net approach is introduced for modelling and simulation of control strategies in Intelligent Building. In this context, it is claimed that integration with other building systems can be achieved in a more systematic way considering a mechatronic approach (i.e. multidisciplinary concepts applied to the development of systems). The case study is the Ambulatory Building of Medical School Hospital of University of São Paulo. Particularly, the developed methodology is applied to the elevator system and to the HVAC (Heating, Ventilation and Air Conditioning) system. It is shown that using this approach, the control systems could be integrated, improving performance.