Scielo RSS http://bibliotecadigital.uns.edu.ar/rss.php?pid=0327-079320120022&lang=pt vol. 42 num. 2 lang. pt http://bibliotecadigital.uns.edu.ar/img/en/fbpelogp.gif http://bibliotecadigital.uns.edu.ar http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200001&lng=pt&nrm=iso&tlng=pt The present paper describes a novelty approach to detect structural changes in the generating units of Itaipu power plant. The methodology is based solely on output time series measured in the rotating electric machine. The method deals with the application of time-series analysis through auto-regressive moving average models (ARMA) and statistical modeling for the linear prediction of damage diagnosis. In order to illustrate the procedure proposed is employed a simplified mathematical model regarding shaft radial vibrations in the generating unit 18A of Itaipu power plant. Several parameters variations are imposed in the system to simulate real damages conditions in the electrical machine. The approach is also evaluated with experimental data. The efficacy, advantages and drawbacks of the proposed method are demonstrated through these numerical and experimental tests. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200002&lng=pt&nrm=iso&tlng=pt Mobile manipulators operating in field environments will be required to manipulate large loads, and to perform such tasks on uneven terrain which may cause the system to reach dangerous tipover instability. Therefore, this paper presents a method for finding the Maximum Allowable Dynamic Load (MADL) of geometrically nonlinear flexible link mobile manipulators with stability consideration. Moment-Height Stability (MHS) criterion is used as an index for the system stability. The dynamic model for links in most mechanisms has often based on small deflection theory but for applications like light-weight links, high-precision or high speed, it is necessary to capture the deflection caused by nonlinear terms. Hence, the equations of motion are derived taking into account the nonlinear strain-displacement relationship. Then, a method for determination of the maximum allowable loads is described. In order to verify the effectiveness of the presented algorithm, several simulation studies and experiments are carried out and the results are discussed. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200003&lng=pt&nrm=iso&tlng=pt This paper is devoted to describe the analysis of unsteady boundary layer flow and heat transfer of a viscous, incompressible micropolar fluid having temperature-dependent viscosity and thermal conductivity over a non-isothermal horizontal stretching sheet. The fluid viscosity and the thermal conductivity are assumed to vary as inverse linear functions of temperature. The unsteady boundary layer equations for the momentum, angular momentum and thermal energy are simplified using suitable transformations. The resulting system of nonlinear ordinary differential equations is solved numerically by employing a shooting technique with fourth order Runge-Kutta integration scheme. The effects of the various parameters on the velocity, microrotation and temperature profiles are presented graphically. In addition, tabulated results for the skin-friction coefficient, Nusselt number and couple stress at the plate are presented and discussed. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200004&lng=pt&nrm=iso&tlng=pt The spectrophotometric method for the determination of cuprous ions in solution presented by Anwar et al. (2000), has since been analyzed and improved, especially with regard to interference from iron and ion species commonly found in acid mine drainage (AMD). The reduction of cupric ions in the presence of ferrous ions, not considered by Anwar et al., renders this method unfeasible for cuprous ion determination. In the absence ferrous ions, the method is simple, fast, economic, accurate and very reliable for total copper determination, even for copper concentrations as low as 5 mg/L. Iron concentrations > 5 g/L produce less than 3% error in determination of copper concentrations of 50 mg/L. Typical AMD ion concentrations do not interfere, except for aluminum which interferes significantly at ten times (x10) AMD concentration http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200005&lng=pt&nrm=iso&tlng=pt In this paper, a real-time application of a Leak Detection and Isolation (LDI) algorithm for a plastic pipeline is presented. This LDI algorithm is fed with flow and pressure signals coming from sensors placed at the ends of the pipeline. It uses a flow observer based on a model obtained from the Method of Characteristics, and it is designed in order to assure an acceptable real-time leak isolation by taking into account various practical difficulties. In particular it incorporates an adaptation law for the friction coefficient in order to compensate for possible variations. The whole scheme is successfully tested on a plastic pipeline prototype, transporting water and built as a possible benchmark. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200006&lng=pt&nrm=iso&tlng=pt The performance of an electrocoagulation (EC) system with aluminium and iron electrodes for removing heavy metal ions (Cd2+, Cu2+, Cr3+, Sr2+ and Zn2+) present in synthetic produced water on laboratory scale was studied systematically. Experimental parameters such as applied current, flow effluent and sacrificial electrodes were investigated in order to understand their influence on the EC process. Increasing the current density accelerated the electrocoagulation process, but made it less efficient. Cd2+, Cu2+, Sr2+ and Zn2+ showed similar removal rates, under similar conditions, indicating a uniform electrochemical behavior. The study gave indications on the removal mechanisms of the investigated metals. Cd2+, Cu2+ and Zn2+ ions are hydrolyzed and co-precipitated as hydroxides. Cr4+, was proposed to be reduced first to Cr3+ at the cathode before precipitating as hydroxide. The process expenditure was estimated and reported showing the viability of this process as a green alternative, obtaining modest costs using Fe electrodes. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200007&lng=pt&nrm=iso&tlng=pt Process control represents an important tool for meeting product quality, process safety and environmental regulation. Different control strategies have been recently proposed in the literature; however, internal model control (IMC) has received great attention. Fractional calculus represents a fast growing field involving non-integer order derivatives. The aim of this work is the application of fractional calculus to develop generalized internal model control loops transfer functions, which is presented in two different approaches: firstly, the process model is considered perfect, i.e., equal to the internal model; secondly, the internal model is described by fractional transfer function. Simulation results showed that the proposed generalization could successfully control an industrial oven and a biochemical reactor described by fractional models, allowing better results when compared to integer order IMC. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200008&lng=pt&nrm=iso&tlng=pt The effect of different cooking methods (grilling, frying, steaming and microwave cooking) was investigated on proximate composition, cooking loss (CL), color and protein solubility (PS) of golden grey mullet (Liza aurata) fillet. Fillet's protein and ash contents significantly increased after cooking with all methods, compared to raw fillet. Higher protein content was related to microwave method, followed by fried, grilled and steamed, respectively. All treatments showed increase in protein and ash contents. Decrease in moisture and increase in fat contents was the most prominent changes in proximate composition. After cooking, PS of fillets decreased with decreasing pH with the minimum solubility was observed at a pH range 5-6 indicating the isoelectric point (PI) of fillets. Microwaved sample showed the lowest solubility compared to other cooking methods. All cooking processes reduced L* value and increased b* value. Fried and microwaved samples had significant differences in a* value compared to other treatments. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200009&lng=pt&nrm=iso&tlng=pt A numerical study on the buildup and propagation of planar detonation waves in H2 + Air combustible mixtures, based on the use of unsteady Euler equations coupled with source terms to account for rates controlled chemical activity, is presented. The computer solver works with 13 chemical species and 33 different one step reactions of a H2-O2 - N2 combustion mechanism. The detonation process is initiated via the energy provided by an igniter which acts as a driver of a shock tube driving through a combustible mixture a blast (or strong shock), accompanied by exothermic chemical changes. It is shown that for each equivalence ratio of the combustible mixture, the detonation can only be triggered if the igniter energy deposition equals or exceeds a computed minimum value. When the igniter energy deposition is less than this minimum, the combustion zone start to decouple from the blast front and if that energy is diminished even more, the combustion could not take place. A particular way of generating sustained overdriven detonations, is also considered. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200110&lng=pt&nrm=iso&tlng=pt In this paper to study the thermoelastic behavior of a gas turbine blade, a computer code based on Conjugate Heat Transfer method was developed to solve the coupled external flow field and the internal temperature field inside a gas turbine blade. An interpolation method based on the 3D shape functions was used to calculate the correct temperature values at the boundaries to determine the stress field. For the materials with temperature dependent mechanical and physical properties, the thermal stresses exhibit a nonlinear behavior. In these cases, an analytic solution for the energy and equilibrium equations to obtain the temperature distribution and the stress field, knowing K(T), α(T), E(T) would be impossible and the numerical schemes should be employed instead. The results show that the stress for the materials with temperature dependent properties is higher than that for the cases where the blade material properties are constant with temperature. Further, the temperature field and the flow field obtained by the present method were compared to the available experimental findings. The results show a good agreement. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200111&lng=pt&nrm=iso&tlng=pt This paper treats on grindability differences of mineral mixtures to achieve a preliminary selective particle size contrast by comminution in order to improve further sorting operation. Quartz and calcite had been chosen as example of binary system. The theoretical basis for this work was inspired by the optimization study carried out by Ray and Szekely (1973), through an algebraic model based on evolution of log-normal distribution of particle size during comminution. On the other hand, the present work has described grindability differences through the classical Rosin-Rammler size distribution. The study of the evaluation of binary mixture differences was realized by sieving analyses and the estimation of Rosin-Rammler sharpness and median diameter. An objective function was conceived stressing the relationship between the expended energy in the grinding process and the optimum residence time. It is possible to use the results as a background for grinding optimization system, since that the penalty function inside objective function can be adequately calibrated as far as technical and economic impacts on further sorting separations are concerned. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200112&lng=pt&nrm=iso&tlng=pt A mathematical model was developed to describe mass transport in polymeric films based on modifications of Fick's law in a continuous macroscopic approach. The purpose of this work was specifically to model the transport of water vapor and oxygen in polymeric films at the pore level, based on physical aspects of the condensation process and the morphology and connectivity of the porous medium, with two-dimensional pore networks representing pore spaces. Using a Pore scale discrete model, we found that the pore-level distributions of liquid (condensate) and vapor as transport phenomena occurred. The vapor and oxygen diffusivities ranged from 4.22×10-6 to 3.16×10-7 cm²/s and from 3.66×10-6 to 2.86×10-7 cm²/s, respectively. Also, the vapor and oxygen permeabilities ranged from 2.61×10-3 to 3.83×10-4 nD (1nD=10-21m²) and from 6.77×10-3 to 1.35×10-3 nD, respectively. The transport properties obtained by the model were compared with the corresponding results for chitosan films obtained in previous experimental studies, showing a partial agreement. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200113&lng=pt&nrm=iso&tlng=pt This paper evaluates the production of fatty acids ethyl esters from corn oil and ethanol. The reaction was carried out applying low-frequency high-intensity ultrasound (25 kHz) under atmospheric pressure and ambient temperature. Response surface methodology (RSM) was used to evaluate the influence of alcohol to oil molar ratio and catalyst concentration (sodium hydroxide) on the yield of corn oil into ethyl esters. Analysis of the operating conditions by RSM showed that the most important operating condition affecting the reaction was the ethanol to oil molar ratio. Results showed low yield of corn oil into ethyl esters. The highest yield observed was of 62.9% after 30 minutes of reaction. The best operating condition was obtained applying an alcohol to oil molar ratio of 4.5 and a catalyst to oil molar ratio of 0.010. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200114&lng=pt&nrm=iso&tlng=pt In this study, the performance of a "kraft" black liquor recovery boiler was analyzed using WinGEMS, a commercial simulator software. The operational variables and design parameters of a pulp industrial unit in southeastern Brazil provides the input data used in setting up the material and energy balance equations in the simulator program. The simulations allowed the prediction of thermal efficiency as a function of solid content in the liquor, in which an increase of 10% in steam generation was obtained when dry solids were increased from 72% to 100%, the latter being a hypothetical operational condition. This study also determined that in spite of making accurate predictions about the temperature profile along the recovery boiler, WinGEMS does not correctly predict the profile of combustion gases when burning eucalyptus black liquor. http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200115&lng=pt&nrm=iso&tlng=pt Carrying out regression analysis for gas leakage of pressure-relief valve (PRV) to get accurate leakage flow and changing trend of leakage will be helpful in assessing the reliability of PRV. Classic support vector regression (SVR) is an excellent regression model, and has been widely used in various fields. However, standard SVR model does regression only using leakage data without elements closely related to the leakage considered. In this paper a regression model based on support vector regression plus (SVR+) is put forward to perform leakage regression of PRV, in which particle swarm optimization (PSO) is used to select optimum parameters of SVR+, termed PSO_SVR+. The experimental results demonstrate that the proposed model taking the difference of inlet pressure and outlet pressure of PRV as hidden information can access a more favorable regression precision than SVR can provide. Meanwhile this article also investigates effects of PSO and Genetic Algorithm on the performance of regression model (SVR+ or SVR) http://bibliotecadigital.uns.edu.ar/scielo.php?script=sci_arttext&pid=S0327-07932012002200116&lng=pt&nrm=iso&tlng=pt The interactions between Bovine Serum Albumin (BSA) and three flavonols, galangin, kaempferol and quercetin were studied by means of fluorescence spectroscopy. The fluorescence intensity of BSA exhibits remarkable decrease along with appreciable blue-shift of its maximum emission wavelength upon addition of the three compounds, respectively. The respective binding constant Ka and number of binding sites of each compound were calculated, and the quenching mechanism was proposed. Based on the values of thermodynamic parameters, the binding of each compound proceeds spontaneously with BSA. The binding distance between each and BSA was obtained by Foerster's dipole-dipole non-radiation energy transfer mechanism.