Resumo em Inglês:

System identification consists of the development of techniques for model estimation from experimental data, demanding no previous knowledge of the process. Aeroelastic models are directly influence of the benefits of identification techniques, basically because of the difficulties related to the modelling of the coupled aero- and structural dynamics. In this work a comparative study of the bilinear dynamic identification of a helicopter blade aeroelastic response is carried out using artificial neural networks is presented. Two neural networks architectures are considered in this study. Both are variations of static networks prepared to accomodate the system dynamics. A time delay neural networks (TDNN) for response prediction and a typical recurrent neural networks (RNN) are used for the identification. The neural networks have been trained by Levemberg-Marquardt algorithm. To compare the performance of the neural networks models, generalization tests are produced where the aeroelastic responses of the blade in flapping and torsion motions at its tip due to noisy pitching angle are presented. An analysis in frequency of the signals from simulated and the emulated models are presented. In order to perform a qualitative analysis, return maps with the simulation results generated by the neural networks are presented.

Resumo em Inglês:

Brazilian territory is situated on an intraplate region with low seismic activity, and so, it is important to answer an old question that remains unanswered: "Should standard building structures in Brazil be guaranteed by a seismic resistant design?" In this way , a methodology is described and used to evaluate the annual failure probability of a structure model subjected to ground motions compatible with a defined provincial seismicity; the model strength is taken as the maximum shear and overturning moment at the base. One considers five different structure models for each Brazilian state capital city and evaluates the annual failure probability which provides arguments to answer the above question.

Resumo em Inglês:

This paper reports the construction of an axisymmetric nonpremixed piloted jet burner, with well-defined initial and boundary conditions, known as the Delft burner, to assess turbulence-chemistry interaction in non-premixed turbulent flames. Detailed experimental information is described, involving hot-wire anemometry, thin-wire thermocouples and chemiluminescence visualization measurements. Radial profile of the axial mean velocity indicates excellent agreement between flow patterns developed within Delft installation and the one described herein. Chemiluminescence emissions from CH and C2 free-radicals were acquired with a CCD camera. Tomography reconstruction analysis was utilised to compare radical emissions and temperature spatial distributions. There was a strong dependence between temperature and CH/C2 emissions. This is an indication that these radicals can be used in flame front studies.

Resumo em Inglês:

Latent energy storage systems find applications in many engineering fields, including industrial refrigeration plants, air conditioning installations, recovery of heat in industrial processes, etc. To tackle the design of such systems, it is necessary to have correlations to account for the heat transfer during the melting and solidification of the phase change material (PCM). This work describes and analyzes the results obtained from the numerical simulation of pure water melting and solidification in the interior of tubes, which are typically present in ice banks of air conditioning systems. The shown results consider natural convection, accounting for the inversion in the water density. In the melting process, the considered initial conditions followed the classical Stefan and Neumann approach. The presented simulation results include the evolution of the phase change interface, and of the temperature, density and streamlines fields. Correlations for the Nusselt number and for the melted material volume as functions of time have been proposed.

Resumo em Inglês:

Mufflers are widely used for exhaust noise attenuation in vehicles and machinery. Recent advances in modeling procedures for accurate performance prediction have led to the development of modeling methods for practical muffler components in commercial design. Muffler designers need simple and fast modeling tools, especially in the preliminary design evaluation stages. Finite Element and Boundary Element methods are often used to provide valid results in a wide range of frequencies. However, these methods are time-consuming, its use needs highly trained personnel and the commercial software is usually quite expensive. Therefore, plane wave based models such as the transfer matrix method (TMM) can offer fast initial prototype solutions for muffler designers. In this paper, the principles of TMM for predicting the transmission loss (TL) of a muffler are summarized. The method is applied to different muffler configurations and the numerical predictions are compared with the results obtained by means of an experimental set up. Only stationary, non-dissipative mufflers are considered. The limitation of both the experimental method and the plane wave approach are discussed. The predicted results agreed reasonably well with the measured results in the low frequency range where the firing engine frequency and its first few harmonics are the main sources of noise.

Resumo em Inglês:

Turbulence parameters are derived from results of numerical simulation of gas-solid flow in circulating fluidized bed (CFB). A two fluid model with constant viscosity is applied considering an Eulerian continuum approach for both phases. An analysis is performed using a direct numerical integration of balance equations without an explicit use of any turbulence model for both phases. Even though velocity fluctuations of lower scales are eliminated by the considered computational mesh, fluctuations of larger scales are detected and analyzed. The results show that the Reynolds stresses behave according to the expected for a turbulent flow, and a reasonable agreement is found regarding literature experiment. Following the literature, granular temperature is derived from the Reynolds stresses, and qualitatively matches the expected behavior as described by the kinetic theory of granular flow. Finally, it is seen that solid's phase turbulence is captured using the present approach.

Resumo em Inglês:

This work aims at finding out the threshold to burning in surface grinding process. Acoustic emission and electric power signals are acquired from an analog-digital converter and processed through algorithms in order to generate a control signal to inform the operator or interrupt the process in the case of burning occurrence. The thresholds that dictate the situation of burn and non-burn were studied as well as a comparison between the two parameters was carried out. In the experimental work one type of steel (ABNT-1045 annealed) and one type of grinding wheel referred to as TARGA model 3TG80.3 - NV were employed.

Resumo em Inglês:

Nature is full of nonlinearities, responsible for a great variety of responses in natural systems. Physiological rhythms constitute a central characteristic of life, which is motivating the analysis of dynamical aspects related to natural systems. Natural rhythms could be either periodic or irregular over time and space and, each kind of dynamical behavior may be related to both normal and pathological physiological functioning. This review article presents an overview of nonlinear dynamics and chaos concepts useful for the analysis of biomedical system. After that, it is presented an overview of dynamical aspects related to different biomedical systems. Cardiovascular rhythms, brain rhythms, cellular and molecular rhythms are discussed from a dynamical approach pointing some characteristics of normal and pathological responses.

Resumo em Inglês:

This work presents the equations for the components of the volumetric error of a Coordinate Measuring Machine (CMM) considering thermal influences. These equations were applied to a moving bridge CMM and combines homogeneous transformations, regression techniques and least squares algorithm. The magnitudes of both the geometric errors and its thermally induced variations were collected by means of a Laser interferometric system, a mechanical square and an electronic level. Simultaneously, temperature values were monitored using T-type Copper-Constantan thermocouples. From the proposed model, components of the volumetric errors were synthesized. Results are discussed and compared to the ones obtained from measurement sets of a ring gauge. It was verified that the model presented an excellent ability to predict volumetric error of the CMM. Errors of about 10µm in magnitude were reduced by at least 75%, while for errors greater than 10µm, the efficiency of the model was 90%.

Resumo em Inglês:

An algorithm based on gradient techniques, proposed in a companion paper, is applied to numerical analysis of optimal low-thrust limited-power trajectories for simple transfer (no rendezvous) between coplanar circular orbits in a central Newtonian gravity field. The proposed algorithm combines the main positive characteristics of two well-known methods in optimization of trajectories: the steepest-descent method and the direct second variation method. The analysis is carried out for various radius ratios and transfer durations. The results are compared to the ones provided by a linear analytical theory. The performance of the proposed algorithm shows that it is a good tool in determining optimal low-thrust limited-power trajectories between close circular coplanar orbits in a Newtonian central gravity field.

Resumo em Inglês:

In the present work, the mechanical behavior of stress corrosion cracking phenomenon is described. Such phenomenon presents strong complexity due to metallurgic and electrochemical aspects. A methodology for modeling both SSR (Slow Strain Rate) and CL (Constant Load) tests based upon thermodynamics of continuum solids and elastoplastic damage is proposed. In this macroscopic approach, besides the classical variables (stress, total strain, plastic strain), an additional scalar variable related to the damage induced by stress corrosion is introduced. An evolution law depending on the corrosive environment parameters is proposed for this damage variable. The model accounts for the stress corrosion effect through a reduction of the mechanical resistance of the material induced by the damage variable. The model prediction is compared with the curves obtained experimentally in different acid solutions at room temperature showing a good agreement. The alloy/environment system studied here is an AISI 304 austenitic stainless steel in acid aqueous solution containing sodium chloride.

Resumo em Inglês:

Energy consumption, air pollution and industrial waste have received special attention from public authorities in recent years. The environment has become one of the most important subjects in the context of modern life, for its deterioration impacts the quality of life populations. Driven by pressure from environmental agencies, politicians have drawn up ever stricter laws aimed at protecting the environment and preserving energy resources. All these factors have led industry, research centers and universities to focus their efforts on researching alternative production processes, creating technologies to minimize or avoid the production of environmentally aggressive residues. Up to a few years ago, the main objective of manufacturing plants was to produce goods aimed at satisfying technological and economic aspects. Green, or "dry" machining and Minimum Quantity Lubricant (MQL) machining have caught the attention of researchers and technicians in the area of machining as an alternative to traditional fluids. Thus, this work proposes to explore the MQL concept in the grinding operation. Although its advantages allow one to predict a growing range of applications for MQL, the variables of influence to be considered and the effects on the results of the process have so far been little studied. Grinding involves several input parameters but, to date, little attention has been focused on the form and quantity of cutting fluid applied to the process. The condition and rate of cutting fluid applied directly influences some of the process's output variables. This work, therefore, analyzes the behavior of the MQL technique under different lubrication and cooling conditions, developing an optimized fluid application methodology based on the creation of a special nozzle through which a minimum amount of oil is pulverized in a compressed air stream. The evaluation of the technical performance of MQL in grinding, using aluminum oxide and superabrasive CBN (cubic boron nitride) grinding wheels, consisted of an experimental analysis of the behavior of the tangential cutting force, G ratio, roughness and residual stress. The results presented herein allowed us to evaluate the behavior of the MQL technique in the grinding process, thus contributing toward an environmentally friendly technology.

Resumo em Inglês:

Robot Calibration is a term applied to the procedures used in determining actual values that describe the geometric dimensions and mechanical characteristics of a robot or multibody structure. A robot calibration system must consist of appropriate robot modeling techniques, accurate measurement equipment, and reliable model parameter determination methods. For practical improvement of a robot's absolute accuracy, error compensation methods are required that use calibration results. Important to robot calibration methods is an accurate kinematic model that has identifiable parameters. This parameterized kinematic model must be complete, continuous and minimal. This work concerns to the implementation of techniques to optimize kinematic models for robot calibration through numerical optimization of the mathematical model. The optimized model is then used to compensate the model errors in an off-line programming system, enhancing significantly the robot kinematic model accuracy. The optimized model can be constructed in an easy and straight operation, through automatic assignment of joint coordinate systems and geometric parameter to the robot links. Assignment of coordinate systems by this technique avoids model singularities that usually spoil robot calibration results.

Resumo em Inglês:

This paper describes the dynamical behavior of a nonlinear flexible beam (cubic nonlinearities considered) connected to a dc motor (responsible for the slewing motion) when the angular displacement of the slewing axis and its derivatives are considered to be of a harmonic type and the system is excited near a resonance (present due to the nonlinear contribution).