Resumo em Inglês:

This paper presents basic concepts of inverse and optimization problems. Deterministic and stochastic minimization techniques in finite and infinite dimensional spaces are revised; advantages and disadvantages of each of them are discussed and a hybrid technique is introduced. Applications of the techniques discussed for inverse and optimization problems in heat transfer are presented.

Resumo em Inglês:

This paper presents and evaluates the concept and implementation of two distinct multi-sensor systems for the automated manufacturing based on parallel hardware. In the most sophisticated implementation, 12 processors had been integrated in a parallel multi-sensor system. Some specialized nodes implement an Artificial Neural Network, used to improve photogrammetry-based computer vision, and Fuzzy Logic supervision of the sensor fusion. Trough the implementation of distributed and intelligent processing units, it was shown that parallel architectures can provide significant advantages compared to conventional bus-based systems. The paper concludes with the comparison of the main aspects of the transputer and the DSP-based implementation of sensor guided robots.

Resumo em Inglês:

The objective of this work is to develop a film thickness and velocity measurement technique using laser intensity measurement in liquid film flow. This technique was developed for annular flow studies, but it has been scarcely used due to the equipment's complexity, as compared with other techniques. The laser technique uses the reflection of the laser beam in water interface and the attenuation of its intensity to determine the interface position. Thus, the relation between intensity and thickness must be obtained by calibration. A theoretical model was proposed for the optical phenomena present in the film thickness measurement and its results were compared with experimental results using a planar mirror. A controlled experiment was conducted using one-dimensional waves in a short channel where the wave frequencies were varied by changing the vibrator's frequency and the film thickness was modified by changing the liquid volume. The reference film thickness was obtained by the analysis of photographic data taken through the transparent channel walls, allowing the comparison to the results from the laser technique. The experimental results for the film thickness presented a good agreement with the reference thickness from photographic data. The interface wave propagation velocities were measured with good accuracy, showing good agreement with the theoretical data.

Resumo em Inglês:

In this paper, the dynamic simulation of constrained mechanical systems that are interconnected of rigid bodies is studied using projection recursive algorithm. The method uses the concepts of linear and angular momentums to generate the rigid body equations of motion in terms of the Cartesian coordinates of a dynamically equivalent constrained system of particles, without introducing any rotational coordinates and the corresponding rotational transformation matrix. Closed-chain system is transformed to open-chain by cutting suitable kinematical joints and introducing cut-joint constraints. For the resulting open-chain system, the equations of motion are generated recursively along the serial chains. An example is chosen to demonstrate the generality and simplicity of the developed formulation.

Resumo em Inglês:

This study investigates the potential of naturally occurring biodegradable fibers for use as building thermal insulation. The use of biodegradable building thermal insulation would alleviate the environmental problems presently associated with the disposal of currently used man-made non-biodegradable thermal insulations. The apparent thermal conductivity(lambda) for biodegradable coconut and sugarcane fiber were investigated in accordance with ASTM C 518 over the density ranges 40 kg/m³ to 90 kg/m³ and 70 kg/m³ to 120 kg/m³ for the test temperature ranges 13.2ºC to 21.8ºC and 18ºC to 32ºC, respectively. The experimental data were used to determine empirical equations for lambda variation with density and temperature for both coconut and sugarcane fiber. Comparison of l at 24ºC for coconut and sugarcane fiber were made with seven different conventional insulation from published data. The results indicated that the minimum lambda for both coconut and sugarcane fiber are within the range normally associated with building thermal insulation. The lambda variation with density and mean temperature for both coconut and sugarcane fiber were consistent with the behavior of loose-fill thermal insulation.

Resumo em Inglês:

This paper proposes a cascade controller with friction compensation based on the LuGre model. This control is applied to a pneumatic positioning system. The cascade methodology consists of dividing the pneumatic positioning system model into two subsystems: a mechanical subsystem and a pneumatic subsystem. This division allows the introduction of friction compensation at force level in the pneumatic positioning system. Using Lyapunov's direct method, the convergence of the tracking errors is shown under the assumption that the system parameters are known. Experimental results illustrate the main characteristics of the proposed controller.

Resumo em Inglês:

Omnidirectional vision systems can provide images with a 360° of field of view. For this reason, they can be useful to robotic applications such as navigation, teleoperation and visual servoing. An effective way to construct this type of vision system is by combining lenses and mirrors together resulting on a system that does not require the movement of the camera to the direction of attention of the robot. A typical construction is by mounting a convex mirror in front of a camera aligning the center of the mirror with the optical axis of the camera. The most common convex mirror shapes used are conic, parabolic, hyperbolic and spherical. In this work we present two types of mirror that were constructed: a spherical mirror, used in the initial tests, and a hyperbolic, used for actual robot tasks. The hyperbolic mirror was manufactured using an ultra-precision CNC machine. Additionally, a software was developed to create panoramic and perspective images from the image acquired by the system. This work shows the development of an omnidirectional vision system, presenting the formulation used to determine a suitable mirror shape, the mechanical solutions used to build a fully operational system, and the results of the developed algorithm.

Resumo em Inglês:

Despite its importance for designing evaporators and condensers, a review of the literature shows that heat transfer data during phase change of carbon dioxide is very limited, mainly for microchannel flows. In order to give a contribution on this subject, an experimental study of CO2 evaporation inside a 0.8 mm-hydraulic diameter microchannel was performed in this work. The average heat transfer coefficient along the microchannel was measured and visualization of the flow patterns was conducted. A total of 67 tests were performed at saturation temperature of 23.3°C for a heat flux of 1800 W/(m2°C). Vapor qualities ranged from 0.005 to 0.88 and mass flux ranged from 58 to 235 kg/(m2s). An average heat transfer coefficient of 9700 W/(m2°C) with a standard deviation of 35% was obtained. Nucleate boiling was found to characterize the flow regime for the test conditions. The dryout of the flow, characterized by the sudden reduction in the heat transfer coefficient, was identified at vapor qualities around 0.85. Flow visualization results showed three flow patterns. For low vapor qualities (up to about 0.25), plug flow was predominant, while slug flow occurred at moderated vapor qualities (from about 0.25 to 0.50). Annular flow was the flow pattern for higher vapor qualities.

Resumo em Inglês:

Flutter is an in-flight vibration of flexible structures caused by energy in the airstream absorbed by the lifting surface. This aeroelastic phenomenon is a problem of considerable interest in the aeronautic industry, because flutter is a potentially destructive instability resulting from an interaction between aerodynamic, inertial, and elastic forces. To overcome this effect, it is possible to use passive or active methodologies, but passive control adds mass to the structure and it is, therefore, undesirable. Thus, in this paper, the goal is to use linear matrix inequalities (LMIs) techniques to design an active state-feedback control to suppress flutter. Due to unmeasurable aerodynamic-lag states, one needs to use a dynamic observer. So, LMIs also were applied to design a state-estimator. The simulated model consists of a classical flat plate in a two-dimensional flow. Two regulators were designed, the first one is a non-robust design for parametric variation and the second one is a robust control design, both designed by using LMIs. The parametric uncertainties are modeled through polytopic uncertainties. The paper concludes with numerical simulations for each controller. The open-loop and closed-loop responses are also compared and the results show the flutter suppression. The perfomance for both controllers are compared and discussed.

Resumo em Inglês:

The crescent searches for the reduction in time production are a factor that stimulates the improvement of the existent manufacturing techniques (Von Steeg 2002 and Waurzyniak 2002). Nowadays, the new researched processes should make possible the fabrication of pieces in a smaller time with a better use of the material resources and equipments (Klein 2002). The present work has for objective to show the viability of a combined tool that makes possible to perform a punching followed by a broaching in only one operation. This combo allies the advantages of the forming processes production and machining in only one process for heavy duty jobs on thick metal sheets. In this work were tested different configurations of combined punches. The objective was to analyze which are the main parameters that can have influence on the useful life of the tool in this new process, i.e., diameter of the punches and geometric form of the teeth for broaching. The precision overall depth of the holes, the roughness and the level of metal chip generation were measured. The analysis of the obtained data showed that the process is viable once were obtained holes with superior quality to the conventional stamping processes.

Resumo em Inglês:

A new form to carry out stochastic identification of structures in operational conditions using a non recursive method, the statistic analysis and the wavelet transform, is presented. The statistic analysis contributed to select the best system order and to automation of computational procedures. In general the identification of low frequencies is a difficult task. The wavelet transform is an essential tool for compression of data making possible the complete identification including low frequencies. In addition it improves the computational efficiency. The study of four degrees of freedom simulated system is presented and the results are compared with the analytical modal parameters.

Resumo em Inglês:

In this paper, a study is made in the problem of the orbital control of an Earth´s satellite using the gravity of the Moon. The main objective is to study a technique to decrease the fuel consumption of a plane change maneuver to be performed in a satellite that is in orbit around the Earth. The main idea of this approach is to send the spacecraft to the Moon using a single impulsive maneuver, use the gravity field of the Moon to make the desired plane change of the trajectory, and then return the spacecraft to its nominal semi-major axis and eccentricity using a bi-impulsive Hohmann type maneuver. The spacecraft is assumed to start in a circular orbit in the plane of the lunar orbit around the Earth and the goal is to put it in a similar orbit that differs from the initial orbit only by the inclination. A description of the close approach maneuver is made in the three-dimensional space. Analytical equations based in the patched conics approximation are used to calculate the variation in velocity, angular momentum, energy and inclination of the spacecraft that realizes this maneuver. Then, several simulations are made to evaluate the savings involved.

Resumo em Inglês:

The mathematical modeling of the rolling process involves several parameters that may lead to non-linear equations of difficult analytical solution. Such is the case of Alexander's model (Alexander 1972), considered one of the most complete in the rolling theory. This model requires excessive computational time, which prevents its application in on-line control and supervision systems. In this paper, the representation of the cold rolling process through Neural Networks trained with data obtained by Alexander's model is presented. This representation is based in sensitivity factors obtained by differentiating a neural network previously trained. The representation allows to obtain equations of the process for different operation points with low computational time. On the other hand, the representation based in sensitivity factors has predictive characteristics that can be used in predictive control techniques. Through predictive model, it is possible to eliminate the time delay in the feedback loop introduced by measurements of the outgoing thickness, normally with X-ray sensors. The predictive model can work as a virtual sensor implemented via software. An example of the application to a single stand rolling mill is presented.

Resumo em Inglês:

This work aims to investigate the efficiency of digital signal processing tools of acoustic emission signals in order to detect thermal damages in grinding processes. To accomplish such a goal, an experimental work was carried out for 15 runs in a surface grinding machine operating with an aluminum oxide grinding wheel and ABNT 1045 Steel as work material. The acoustic emission signals were acquired from a fixed sensor placed on the workpiece holder. A high sampling rate data acquisition system working at 2.5 MHz was used to collect the raw acoustic emission instead of the root mean square value usually employed. Many statistical analyses have shown to be effective to detect burn, such as the root mean square (RMS), correlation of the AE, constant false alarm rate (CFAR), ratio of power (ROP) and mean-value deviance (MVD). However, the CFAR, ROP, Kurtosis and correlation of the AE have been presented more sensitive than the RMS.

Resumo em Inglês:

The Generalized Integral Transform Technique (GITT) is applied to the solution of the momentum equations in a hydrodynamically developing laminar flow of a non-Newtonian power-law fluid inside a circular duct. A primitive variables formulation is adopted in order to avoid the singularity of the auxiliary eigenvalue problem in terms of Bessel functions at the centerline of the duct when the GITT approach is applied. Results for the velocity field and friction factor-Reynolds number product are computed for different power-law indices, which are tabulated and graphically presented as functions of the dimensionless coordinates. Critical comparisons with previous results in the literature are also performed, in order to validate the numerical codes developed in the present work and to demonstrate the consistency of the final results.