SciELO Brasil - Scientific Electronic Library Online
(53.052 recursos)
SciELO (Scientific Electronic Library Online) is an electronic library covering a selected collection of Brazilian scientific journals. The objective of the site is to implement an electronic virtual library, providing full access to a collection of serial titles, a collection of issues from individual serial titles, as well as to the full text of articles. The project envisages the development of a common methodology for the preparation, storage, dissemination and evaluation of scientific literature in electronic format.
Mostrando recursos 1 - 20 de 165
1.
Dynamic optimization for the trajectory planning of robot manipulators in the presence of obstacles - Saramago,Sezimária F. P.; Steffen Júnior,Valder
This paper presents an approach to the solution of moving a robot manipulator with minimum cost along a specified geometric path in the presence of obstacles. The main idea is to express obstacle avoidance in terms of the distances between potentially colliding parts. The optimal traveling time and the minimum mechanical energy of the actuators are considered together to build a multiobjective function. A simple numerical example involving a Cartesian manipulator arm with two-degree-of-freedom is described.
2.
Modeling, optimizing and simulating robot calibration with accuracy improvement - Motta,José Maurício S. T.; Mcmaster,R. S.
This work describes techniques for modeling, optimizing and simulating calibration processes of robots using off-line programming. The identification of geometric parameters of the nominal kinematic model is optimized using techniques of numerical optimization of the mathematical model. The simulation of the actual robot and the measurement system is achieved by introducing random errors representing their physical behavior and its statistical repeatability. An evaluation of the corrected nominal kinematic model brings about a clear perception of the influence of distinct variables involved in the process for a suitable planning, and indicates a considerable accuracy improvement when the optimized model is compared...
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Kinematic analysis and modelling of biped locomotion systems - Silva,Filipe Miguel Teixeira Pereira da; Machado,José Antônio Tenreiro
This paper presents the kinematic study of robotic biped locomotion systems. The main purpose is to determine the kinematic characteristics and the system performance during walking. For that objective, the prescribed motion of the biped is completely characterised in terms of five locomotion variables: step length, hip height, maximum hip ripple, maximum foot clearance and link lengths. In this work, we propose four methods to quantitatively measure the performance of the walking robot: energy analysis, perturbation analysis, lowpass frequency response and locomobility measure. These performance measures are discussed and compared in determining the robustness and effectiveness of the resulting locomotion.
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Application of a Pid+fuzzy controller on the motion control system in machine tools - Lacerda,H. B.; Belo,E. M.
This work deals with an hybrid PID+fuzzy logic controller applied to control the machine tool biaxial table motions. The non-linear model includes backlash and the axis elasticity. Two PID controllers do the primary table control. A third PID+fuzzy controller has a cross coupled structure whose function is to minimise the trajectory contour errors. Once with the three PID controllers tuned, the system is simulated with and without the third controller. The responses results are plotted and compared to analyse the effectiveness of this hybrid controller over the system. They show that the proposed methodology reduces the contour error in a...
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Linear-quadratic optimal control of descriptor systems - Müller,Peter C.
In recent years the analysis and synthesis of (mechanical) control systems in descriptor form has been established. This general description of dynamical systems is important for many applications in mechanics and mechatronics, in electrical and electronic engineering, and in chemical engineering as well. This contribution deals with linear mechanical descriptor systems and its control design with respect to a quadratic performance criterion. Here, the notion of properness plays an important role whether the standard Riccati approach can be applied as usual or not. Properness and non-properness distinguish between the cases if the descriptor system is exclusively governed by the control...
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Formulação probabilística para análise de tabuleiros de pontes rodoviárias com irregularidades superficiais - Silva,José Guilherme Santos da; Roehl,João Luís Pascal
Apresenta-se uma metodologia de análise com o objetivo de avaliarem-se os efeitos de irregularidades superficiais no tabuleiro sobre o comportamento de pontes rodoviárias submetidas à passagem de veículos. A resposta do sistema veículo-estrutura é obtida no domínio da freqüência segundo modelo probabilístico. Simula-se o tabuleiro das pontes com modelo de elementos finitos unidimensionais com massas discretizadas nos nós, o veículo por um sistema de massas, molas e amortecedores, e as irregularidades da pista são definidas por modelo não-determinístico com base na densidade espectral do perfil do pavimento. O carregamento é constituído por uma sucessão infinita de veículos igualmente espaçados deslocando-se...
7.
Geometric nonlinear dynamic analysis of plates and shells using eight-node hexahedral finite elements with reduced integration - Azevedo,Ricardo Lessa; Awruch,Armando Miguel
This work presents a geometric nonlinear dynamic analysis of plates and shells using eight-node hexahedral isoparametric elements. The main features of the present formulation are: (a) the element matrices are obtained using reduced integrations with hourglass control; (b) an explicit Taylor-Galerkin scheme is used to carry out the dynamic analysis, solving the corresponding equations of motion in terms of velocity components; (c) the Truesdell stress rate tensor is used; (d) the vector processor facilities existing in modern supercomputers were used. The results obtained are comparable with previous solutions in terms of accuracy and computational performance.
8.
Modeling and control of multibody system with flexible appendages - Soares,Álvaro Manoel de Souza; Góes,Luiz Carlos Sandoval; Souza,Luiz Carlos Gadelha de
The objective of this work is to describe the design and the implementation of an experiment to study the dynamics and the active control of a slewing multi-link flexible structure. The experimental apparatus was designed to be representative of a flexible space structure such as a satellite with multiple flexible appendages. In this study we describe the design procedures, the analog and digital instrumentation, the analytical modeling together with model validation studies carried out through experimental modal testing and parametric system identification studies in the frequency domain. Preliminary results of a simple positional control where the sensor and the actuator...
9.
Curving simulation and stability of a creep-controlled wheelset for high speed rail-vehicles - Meisinger,Reinhold
Higher travel speeds of rail vehicles will be possible by developing sophisticated top performance bogies having creep-controlled wheelsets. In this case the torque transmission between the right and the left wheel is realized by an actively controlled creep coupling. To investigate hunting stability and curving capability the linear equations of motion are written in state space notation. Simulation results are obtained with realistic system parameters from industry and various controller gains. The advantage of the ?creep-controlled wheelset" is discussed by comparison the simulation results with the dynamic behaviour of the special cases ?solid-axle wheelset" and ?loose wheelset" (independent rotation of...
10.
Vibration analysis for Bearing outer race condition diagnostics - Shiroishi,J.; Y. Li,S. Liang; Danyluk,S.; Kurfess,T.
This paper investigates defect detection methodologies for rolling element bearings through vibration analysis. Specifically, the utility of a new signal processing scheme combining the High Frequency Resonance Technique (HFRT) and Adaptive Line Enhancer (ALE) is investigated. The accelerometer is used to acquire data for this analysis, and experimental results have been obtained for outer race defects. Results show the potential effectiveness of the signal processing technique to determine both the severity and location of a defect. The HFRT utilizes the fact that much of the energy resulting from a defect impact manifests itself in the higher resonant frequencies of a...
11.
Investigação para detecção automática de falhas têxteis - Proença,Claudia Belmiro; Conci,Aura; Segenreich,Solly A.
Este trabalho apresenta uma aplicação de Dimensão Fractal (DF) e técnicas de segmentação de imagens na inspeção industrial automática. Foi desenvolvido um sistema para a indústria têxtil objetivando a detecção de defeitos. A indústria têxtil se particulariza por ter um tipo de produção que torna inviável a utilização das técnicas de extração de características morfológiocas, usualmente empregadas em sistemas de controle de qualidade baseados na visão. Basicamente o sistema implementado compara dados obtidos de imagens digitalizadas, as características destes dados dependem do método selecionado. Dois tipos de métodos podem ser usados: métodos de segmentação e dimensão fractal. Para implementação no...
12.
Critical aspects on the behavior of material from the mechanical tool-workpiece interaction in single point diamond turning - Jasinevicius,Renato Goulart; Duduch,Jaime Gilberto; Porto,Arthur José Vieira; Purquério,Benedito Morais
Some material aspects such as grain size, purity and anisotropy exert an important influence on surface quality, especially in single point diamond turning. The aim of this paper is to present and discuss some critical factors that can limit the accuracy of ultraprecision machining of non-ferrous metals and to identify the effects of them on the cutting mechanism with single point diamond tools. This will be carried out through observations of machined surfaces and chips produced using optical and scanning electron microscopy. Solutions to reduce the influence of some of these limiting factors related with the mechanism of generation of...
13.
BEM/FEM non-linear model applied to transient analysis with viscous damping - Coda,Humberto Breves; Venturini,Wilson Sérgio
In this article a two-dimensional transient boundary element formulation based on the mass matrix approach is discussed. The implicit formulation of the method to deal with elastoplastic analysis is considered, as well as the way to deal with viscous damping effects. The time integration processes are based on the Newmark rhoand Houbolt methods, while the domain integrals for mass, elastoplastic and damping effects are carried out by the well known cell approximation technique. The boundary element algebraic relations are also coupled with finite element frame relations to solve stiffened domains. Some examples to illustrate the accuracy and efficiency of the...
14.
Thermal radiation in combustion systems - Pessoa-Filho,José Bezerra
A numerical procedure for solving the nongray radiative transfer equation (RTE) in two-dimensional cylindrical participating media is presented. Nongray effects are treated by using a narrow-band approach. Radiative emission from CO, CO2, H2O, CH4 and soot is considered. The solution procedure is applied to study radiative heat transfer in a premixed CH4-O2, laminar, flame. Temperature, soot and IR-active species molar fraction distributions are allowed to vary in the axial direction of the flame. From the obtained results it is possible to quantify the radiative loss in the flame, as well as the importance of soot radiation as compared to gaseous...
15.
Escoamento turbulento na saída de um duto curvo de seção retangular divergente: estudo experimental - Indrusiak,Maria Luiza Sperb; Möller,Sergio Viçosa
Neste trabalho é apresentado o estudo experimental do escoamento turbulento em um duto curvo simulando parte de uma caldeira de uma usina termoelétrica. As cinzas resultantes da queima de carvão mineral, transportadas pelos gases da combustão, incidem sobre o economizador, localizado após um duto curvo, e provocam erosão dos tubos, levando a falhas que provocam a parada da unidade. A distribuição do escoamento após a curva favorece a erosão na região próxima à parede côncava do duto. A solução clássica para redistribuição do escoamento em curvas são as chapas direcionadoras. No caso presente elas não são aplicáveis, pois a erosão...
16.
On the development of an unstructured grid solver for inert and reactive high speed flow simulations - Silva,Luis Fernando Figueira da; Azevedo,João Luiz F.; Korzenowsk,Heidi
An unstructured grid Euler solver for reactive compressible flow applications is presented. The method is implemented in a cell centered, finite volume context for unstructured triangular grids. Three different schemes for spatial discretization are implemented and analyzed. Time march is implemented in a time-split fashion with independent integrators for the flow and chemistry equations. The capability implemented is tested for inert flows in a hypersonic inlet and for inert and reactive supersonic flows over a 2-D wedge. The results of the different schemes are compared with each other and with independent calculations using a structured grid code. The strengths and...
17.
Experimental analysis of the flow between stay and guide vanes of a pump-turbine in pumping mode - Mesquita,André L. Amarante; Ciocan,G. D.
An experimental study was conducted in a pump-turbine model in pumping mode, in order to characterize the flow field structure in the region between stay and guide vanes, using mainly the laser-Doppler anemometry in a two-color and back-scattered light-based system. The structure of the steady and unsteady flow was analyzed. The measurements were performed at three operation points. The obtained data provide appropriate boundary conditions and a good base of validation for numerical codes, and for the understanding of main loss mechanisms of this complex flow.
18.
Model for subchannel friction factors and flow redistribution in wire-wrapped rod bundles - Carajilescov,Pedro; Fernandez y Fernandez,Elói
The fuel element of LMFBR consists of a bundle of rods wrapped with an helical wire as spacer, surrounded by an hexagonal duct. In the present work, a semi-empirical model is developed to calculate bundle average and subchannel based friction factors and flow redistribution. The obtained results were compared to experimental data and they were considered satisfactory for wide range of geometrical parameters.
19.
Pressure drop coefficients for elliptic and circular sections in one, two and three-row arrangements of plate fin and tube heat exchangers - Bordalo,Sérgio Nascimento; Saboya,Francisco Eduardo Mourão
The objective of the present work is the experimental determination of pressure drop coefficients (loss coefficients) for elliptic and circular sections in one, two and three-row arrangements of plate fin and tube heat exchangers. The experiments permitted to correlate the dimensionless loss coefficient with the flow Reynolds number in the rectangular channel formed by the plate fins. The experimental technique consisted of the measurement of the longitudinal pressure distribution along the flow channel, for several values of air mass flow rate. The total number of data runs, each one characterized by the flow Reynolds number, was 216. The present geometry...
20.
A high frequency electronic transducer for multiphase flow measurements - Belo,Francisco Antônio; Moura,Luiz Felipe Mendes de
This paper describes an electronic transducer for multiphase flow measurement. Its high sensitivity, good signal to noise ratio and accuracy are achieved through an electrical impedance sensor with a special guard technique. The transducer consists of a wide bandwidth and high slew rate differentiator where the lead inductance and stray capacitance effects are compensated. The sensor edge effect is eliminated by using a guard electrode based on the virtual ground potential of the operational amplifier. A theoretical modeling and a calibration method are also presented. The results obtained seem to confirm the validity of the proposed technique.
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