Resumo em Inglês:

The main contribution from this paper includes the hydrodynamic modeling and morphological analysis of Lake Água Preta in Belém city, Pará State, Brazil. The lake bathymetry was taken through the data provided by COSANPA (the local sanitation and water supply company) dating back to 1975, and from a 2009 field study. Both bathymetries produced two terrain elevation models, which were used for morphological analysis and hydrodynamic simulations. The morphological analysis has revealed that, from 1975 to 2009, the annual mean rate of sedimentation varies between 23,065 and 29,081 m³/year. Through this result, the sedimentation time of Lake Água Preta, from 2009, has been calculated, which varies between 295 and 381 years, maintaining the same rate of sedimentation, water consumption and pumping. The hydrodynamic model simulated the depths and velocities, showing a slight flow with velocities ranging from 0 to 33 cm/s. This flow is established between water input and output of the lake, which is used as reservoir of Belém city.

Resumo em Inglês:

In this paper, we present a phase-field model with a grid based on the Finite-Difference Method, for improvement of computational efficiency and reducing the memory size requirement. The numerical technique, which is based on the temperature change of the pure material, enables us to use, in the initial steps of the computation, a very small computational domain. Subsequently, in the course of the simulation of the solidification process, the computation domain expands around the dendrite. The computation showed that the dendrite with well-developed secondary arms can be obtained with low computation time and moderate memory demand. The computational efficiency of this numerical technique, the microstructural evolution during the solidification, and competitive growth between side-branches are discussed.

Resumo em Inglês:

Despite the evidence of energy transmission tower collapses due to tornadic events in the Brazilian territory, no national study treats the issue under strictly structural focus. In this context, as a starting point, mechanical global actions due to an approximate mathematical model of a F3 tornado, compatible with the Brazilian threat on two towers, one guyed and one self-supported tower, are evaluated; these tower models are largely used in the Paraná-Uruguai River Basins, critical on such occurrences. Comparisons with actions foreseen in design are performed in order to obtain the critical loading situations. Usage of tornadic response spectrum practices is proposed and particular aspects of tornadic loads on tower structures are analyzed.

Resumo em Inglês:

Phenomenological models are an important branch in VIV (Vortex-Induced Vibrations) and in VIM (Vortex-Induced Motions) studies to complement the results achieved via CFD (Computational Fluid Dynamics), as the latter tool is not presently a suitable tool for intense use in engineering analysis, due to high computer power requirements. A phenomenological model for evaluating the VIM on monocolumn platforms is presented and its results are compared with experimental ones. The main objective is to present a parametric analysis, focusing on the physical significance of the modifications in parameter values. The following parameters are varied: aspect ratio (L/D), structural damping (ξ), fluid damping (γ) and Strouhal number (S). The results are presented in terms of: non-dimensional amplitudes of motion (A X/D and A Y/D), added mass coefficient (Ca) and periods of motion (T X and T Y). The phenomenological model is based on a time-domain, two degree-of-freedom structural model coupled with van der Pol wake oscillators. The governing equations are solved through fourth-order Runge-Kutta schemes.

Resumo em Inglês:

This paper presents a new methodology to deal with uncertainty mitigation using observed data, integrating the uncertainty analysis and the history matching processes. The proposed method is robust and easy to use, offering an alternative way to traditional history matching methodologies. The main characteristic of the methodology is the use of observed data as constraints to reduce the uncertainty of the reservoir parameters. The integration of uncertainty analysis with history matching naturally yields prediction under uncertainty. The workflow permits to establish a target range of uncertainty that characterize a confidence interval of the probabilistic distribution curves around the observed data. A complete workflow of the proposed methodology was carried out in a realistic model based on outcrop data and the impact of the uncertainty reduction in the production forecasting was evaluated. It was demonstrated that for complex cases, with a high number of uncertain attributes and several objective-function, the methodology can be applied in steps, beginning with a field analysis followed by regional and local (well level) analyses. The main contribution of this work is to provide an interesting way to quantify and to reduce uncertainties with the objective to generate reliable scenario-based models for consistent production prediction.

Resumo em Inglês:

The present study introduces a methodology for mapping the thermodynamic losses of vapor compression refrigeration systems which consists of a theoretical model that splits the coefficient of performance into four terms: (i) the coefficient of performance of an ideal cycle (Carnot), (ii) the efficiency of a real cycle running with an ideal compressor, (iii) the compression efficiency of a real compressor, and (iv) the cycling efficiency. In addition, measurements of the relevant variables at several positions along the refrigeration loop are also required, generating performance data not only for the whole unit but also for each one of the system components. The proposed methodology points out the thermodynamic losses of the refrigeration system, identifying opportunities for energy performance improvement. In addition, the methodology is suitable for comparing different refrigeration systems with respect to the same thermodynamic baseline. Albeit the methodology was originally developed for household refrigerators, it can be easily extended to any kind of vapor-compression refrigeration systems.

Resumo em Inglês:

This paper deals with the analysis of diffusion coupled with temporary retention motivated by the challenge to solve the problem of population spreading. Retention may be associated to colonization of the occupied territory in this case. The discrete approach was selected to deal with this problem due to its relative simplicity and straightforward mathematical treatment. Two types of problems are analyzed namely: symmetric spreading with temporary retention, and propagation with temporary retention. It is clearly shown that higher order differential terms must be included in the governing equations of diffusion and propagation to represent the temporary retention effect. Specifically third and fourth order terms are associated to the retention effect in propagation and diffusion processes respectively. Control parameters regulating the relative influence of the diffusion and the retention terms in the governing equations come up naturally from the analysis. After the appropriated operations the finite difference equations reduce to partial differential equations. The control parameters are kept in the partial differential equations. These parameters are essential in the governing equations to avoid uncontrolled accumulation of particles due to the retention effect. The diffusion-retention problem appearing in several physicochemical problems are governed by the same equations derived here. The current literature refers to several types of diffusion-retention problems, but all solutions assume the classical second order equation as the basic reference. A short analysis of the equilibrium conditions for diffusion-retention problems with a source helps to show the coherence of the theory. In order to explore the potentialities of the discrete approach the problem of asymmetric distribution is also analyzed.

Resumo em Inglês:

This paper reports an experimental investigation using adaptive control in a refrigeration system. This system is composed basically of a semi-hermetic compressor, concentric tubes heat exchangers, the condenser and evaporator, and thermostatic expansion valve (TXV). The refrigerant used in the refrigeration system was the HCFC-22 and also an AC frequency inverter was used to control the speed of the compressor. The temperatures were measured by PT-100 sensors and the pressures using piezoresistive pressure transducers. Data acquisition was implemented using the Labview software. An electronic card with analogical signal output was also used. These analogical signals were converted into digital through a Programmable Logic Controller (PLC) and then sent to the computer through a PC serial port. Tests were performed with a variable speed compressor in the range from 30 to 70 Hz and the experimental results showed that the highest performance (COP) was attained by working in the range of 50 Hz, using adaptive fuzzy control.

Resumo em Inglês:

Oxyacetylene flame cutting is a relevant and widespread industrial process. The basic principles of the process lie in rapid high-temperature oxidation of the cut metal. The kinetics of the process depends, among other things, on the composition of the cut metal, the activity of the reactants. In this present work, a report of the role of carbon on the kinetics of the process is made; effects of the activities of oxyfuel gases on the flame cutting process is also elucidated. This was done by investigation of the effects of carbon content and the cutting pressures on the cutting rates of steels by the oxyacetylene cutting process. Six 10mm steel rods of different wt% C were flame cut using different acetylene and oxygen pressures. The composition of the steel rods used ranged from 0.16 wt% C to 0.33 wt% C, the acetylene pressures used ranged from 3.45 x 10-2 N.m-2 to 5.52 x 10-2N.m-2, while oxygen pressure ranged from 2.76 x 10-1N.m-2 to 3.17 x 10-1 N.m-2. The result shows that the cutting rates decreased with carbon content of the steel as a result of reduction of iron oxide during decarburization reactions; however, cutting rates increased with the oxyfuel pressures as a result of increased activity of oxyfuel gases with increased pressure.

Resumo em Inglês:

In this work an analytical model based on the slab method was built to analyze the lubrication during cold rolling of aluminum strips. Some process variables were studied like the rolling speed, the cross-section reduction, and lubricant viscosity. Numerical results are presented for pressure variation and film thickness at the inlet and work zones. The loads necessary to separate the rolls are also estimated. Some experimental results are shown for the surface roughness of the rolled products. It is shown that analytical results are in good accordance to experimental results, and that rolling pressure, lubricant film thickness and surface roughness are strongly influenced by rolling conditions, especially the lubricant viscosity and the area reduction.

Resumo em Inglês:

Compacted Graphite Iron (CGI) is a good option for the manufacturing of engine blocks, because of the possibilities to decrease the wall thickness and to operate at higher pressures. However, due to its greater tensile strength and hardness compared with grey cast iron, the pearlitic CGI structure makes its machining more difficult. Thus, the aim of this paper is to investigate the improvements in CGI drilling achieved through the use of cutting fluids with EP additives. Experimental investigation of the influence of an EP additive on the drilling process was carried out using a CNC machine with 7.64 kW of power and maximum rotation of 5000 rpm. The cutting parameters were a cutting speed of 110 m/min, feed velocity of 350 mm/min and hole-depth of 20 mm. Three cutting fluids were analyzed, with and without EP additives. The results showed that the EP additive influenced the CGI drilling performance due to a layer comprised of sulphur (EP additive) and metal. Adhesion was avoided and the friction and wear behavior was improved.

Resumo em Inglês:

The machining of titanium alloys poses several inherent difficulties owing to their unique mechanical properties and cutting characteristics. Finite element (FE) simulations have reduced the burden of extensive experimental trials in understanding the deformation behavior and optimize the cutting process. The FE code relies on the qualitative nature of inputs such as material flow stress model, friction conditions, fracture criterions and the accuracy of the modeling process. The aim of this paper is to assess the performance of four material model sets of the Johnson-Cook (JC) constitutive equation in modeling the deformation behavior of Ti6Al4V alloy. The FE output at steady state conditions is compared with results from orthogonal cutting experiments on a tube of the work material. The effect of the parameters of the JC law and the capabilities of the constitutive equation are analyzed. The FE model is excellent in predicting the effective stress, strain and temperature, but produces marginal deviations in cutting force and chip morphology predictions and under predicts the feed forces. The material model constants computed through an evolutionary computational optimization process and those with conditions similar to machining produced good correlation with experiments.

Resumo em Inglês:

This work presents a study about the correlations between the characteristics of the acoustic waves and the mechanical properties of low carbon hot rolled steel bars, through the comparison between the wave velocity or attenuation and the tensile strength, yield point or elongation of the material. The aim is the possibility of using this technique to predict the production quality of ASTM A36 steels. Acoustic velocity and attenuation measurements by gain acquisition were carried out with the use of longitudinal waves and transducers of 5 and 15 MHz. Samples of hot rolled reinforcement steel bars with one inch diameter were used. A metallographic study of grain size and inclusion content was made along with chemical composition to verify the influence of these factors to the acoustic measurements. Results indicated that it is possible to use the presented methodology to estimate the mechanical properties, in especial, the tensile strength in steel rebars.