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COB143 METODOLOGÍA PARA LA PREVENCIÓN DE PROBLEMAS DINÁMICOS EN OPERACIONES DE MECANIZADO.
José Antonio Sánchez Galíndez, Mª Helena Fernandes, José Ignacio Llorente, Luis N. Lòpez de Lacalle & Joseba Pérez Bilbatua.
Departamento de Ingeniería Mecánica, Escuela Técnica Superior de Ingenieros Industriales C/ Alameda de Urquijo s/n, 48013 Bilbao, España – email: impsagaj@bi.ehu.es
The basis of a methodology for the prediction of chatter vibrations in metal cutting operations are presented in this paper. The methodology uses time-domain simulation of the cutting process. A model for the prediction of cutting forces has been developed. In order to do this, the main existing cutting force models are reviewed, selecting a mechanics of oblique cutting approach for implementing the methodology. The most relevant features of dynamic characterization of machine-tools are then commented on. After this, the existing methods for cutting process dynamic simulation are studied, leading to the conclusion that time-domain simulation is the best approach if effects such as non-linearities of the process are to be taken into account. An extension of the existing models, that allows the three-dimensional dynamics of the process to be taken into account is proposed. Finally, the results obtained during the first stage of the implementation of the methodology are shown. .
Keywords: Mecanizado, Fresado, Chatter, Vibración, Simulación
COB160 Determinação do comportamento vibratório do motor de indução de gaiola por meio de elementos finitos / Determination of THE SQUIRREL-CAGE INDUCTION MOTOR vibrational behavior BY FINITE ELEMENTS
C.G.C.Neves, N.Sadowski & R.Carlson
GRUCAD-DEEL-CTC-UFSC
CEP 88049-900 - Florianópolis - SC – Brasil - Email: guilherm@grucad.ufsc.br
Many others phenomena occur simultaneously in a electric rotating machine besides the classical electro-mechanical energy conversion. One part of the energy amount is converted in losses and dissipated thermally; however, another much smaller, but equally important, is irradiated as noise to environment. In this paper a Finite Element numerical model is used to investigate the squirrel-cage induction motor vibrational behavior. This model allows to calculate the windings and bars currents, the magnetic forces and motor structure dynamic response. Firstly, the Finite Element method is employed to discretize the electromagnetic field equations and the b - method is used to discretize the time derivatives of the field and external circuit equations. The magnetic forces acting on the squirrel-cage induction motor stator are obtained by a method based on the Maxwell’s Stress Tensor. From it, the harmonic composition of the magnetic forces is evaluated. The second step in this work consists in proceeding with the mechanical FEM to obtain the natural and forced response of the stator mechanical structure.
Keywords: Vibrações, Forças Magnéticas, Tensor de Maxwell, Método de Elementos Finitos, Motor de Indução de Gaiola, Ressonâncias. - Vibration, Magnetic Forces, Maxwell’s Stress Tensor, Finite Element Method, Squirrel-cage Induction Motor, Ressonances.
COB167 Análise das vibrações de origem magnética no MRC por meio de simulação e procedimentos experimentais/ ANALYSIS OF SWITCHED RELUCTANCE MOTOR magnetic caused vibrations BY SIMULATION AND EXPERIMENTAL PROCEDURES
C. G. C. Neves, N. S. Soeiro, N. Sadowski & R. Carlson
GRUCAD-DEEL-CTC-UFSC, CEP 88049-900 Florianópolis - SC – Brasil - Email: guilherm@grucad.ufsc.br
The switched reluctance motor (SRM) presents short pitch concentrated windings and doubly salient structure. These characteristics provide this machine with certain advantages like simple and robust motor and converter structures, good efficiency and high speed capability. Despite of this positive attributes the SRM does exhibit higher levels of vibration than most competing drives, like induction and permanent magnet motors. Firstly, in this paper electromagnetic FEM analysis is applied to the SRM magnetic structure in order to obtain the electromagnetic forces pattern. From this the harmonic composition of the radial forces is evaluated. The second step in this work consists in proceeding with the Experimental Modal Analysis (to obtain the natural frequencies); mechanical FEM are also used to evaluate the natural frequencies and the mode shapes which define the dynamic of the mechanical behavior of the mechanical structure of SRM. Finally with Rotational Experiments, the SRM is driven by its converter and is possible to verify the vibrations.
Keywords: Vibrações, Forças magnéticas, Tensor de Maxwell, Método de Elementos Finitos, Análise Modal Experimental, Motor de Relutância Chaveado, Experimentos Rotacionais, Ressonâncias.
Vibration, Magnetic Forces, Maxwell’s Stress Tensor, Finite Element Method, Experimental Modal Analysis, Switched Reluctance Motor, Rotational Experiments, Ressonances.
COB216 ISOLAMENTO DE VIBRAÇÕES EM BAIXA FREQÜÊNCIA EM UM SISTEMA DE ALAVANCA / VIBRATION ISOLATING IN LOW FREQUENCY SYSTEMS USING A LEVER
Fábio Meneghetti Ugulino de Araújo, Seyyed Said Dana,
Clivaldo Silva de Araújo & José Calazans de Castro
Departamento de Engenharia Mecânica, Universidade Federal da Paraíba, Campus I,
CEP 58.059-900 João Pessoa - PB – Brasil – e-mail: meneghet@elogica.com.br
Mechanical vibration has brought discomfort and distress for human beings, and it has contributed a great deal of damage to structural integrity of machines and structures. Consequently, insulating precision equipment from even slight vibration of the base, and reducing its malicious effects, have been the object of constant study and research. In this paper a model is designed to isolate the vibration of the base in low frequencies, by employing the principals of active control, while using a lever system. First the response of the uncontrolled simulated model is obtained. Furthermore the response of the model is obtained by subjecting it to active control utilizing sensors, amplifiers, motor, and a system to convert a rotational position of the motor to longitudinal distance. A new analysis compares the performance of the controlled system with respect to the uncontrolled one. The controlled system is improved by introducing a compensator.
Keywords: Vibração, Isolamento, Controle Ativo, Compensador / Vibration, Isolating, Active Control, Compensator.
COB429 USING THE PSEUDO-INVERSE TECHNIQUE TO PREDICT RANDOM EXCITATION FORCES FROM ACCELERATION RESPONSE MEASUREMENTS
Paulo S. Varoto1 & Kenneth G. Mcconnell2
1Depto de Engenharia Mecânica, EESC-USP São Carlos SP, Brasil, 2Department of Aerospace and Mechanics, Iowa State University, Ames, IA, USA, E-MAIL: varoto@sc.usp.br
This article investigates the inverse problem of predicting random forces from acceleration responses using the pseudo-inverse technique. It is shown that a commonly accepted assumption of input signals being uncorrelated is untrue. Under this assumption, only real valued acceleration auto spectral densities are used to solve for the unknown random forces in the pseudo-inverse technique. Experimental results show that acceleration cross spectral densities must be used in addition to auto spectral densities when solving the inverse problem for random forces. These cross spectral densities are complex functions of the excitation frequency and thus, they carry the phase information required to establish the correlation between time variables.
Keywords: Force identification, random loads, inverse problems
COB437 CONTROLE DE VIBRAÇÕES EM EDIFÍCÍOS ATRAVÉS DE PÊNDULOS SUSPENSOS /VIBRATION CONTROL IN TALL BUILDINGS USING A SUSPENDED PENDULUM
Luciana do Val de Azevedo, Romulo de Freitas Paixão & Seyyed Said Dana
Pos-Graduação em Engenharia Mecânica- Centro de Tecnologia - UFPB, CEP 58059-900, João Pessoa, Paraiba, Brasil,
E-mail contact@ct.ufpb.br
Excessive vibration in structures can be attenuated by active or passive dissipative mechanisms. Though active controle systems have grown substantially recently, however the passive systems still represent the major ways for reduction of amplitudes in vibration of structures. Their use still brings low cost simplified and relatively easy implemented devices. In this work a study of efficiency of synchronized oscillators acting passively to reduce the amplitude of vibration of tall buildings subjected to random vibration is presented. It is shown that the efficiency of control system designed for optimal work depends principally on the amount of the inherent damping in structural configuration. In the systems with low structural damping the effect of introducing damping by an auxiliary system is high, and the efficiency becomes a considerable factor. In other hand the effect of auxiliary system diminishes when the damping in principal system is already high.
Keywords: Vibração, isolamento , oscilados sintonizados, Vibration Isolation
COB439 CONTROLE ATIVO DE VIBRAÇÕES COM ATUADORES PIEZOELÉTRICOS/ACTIVE CONTROL OF VIBRATION USING PIEZOELECTRICS ACTUATORS
Simplício Arnaud da Silva, Seyyed Said Dana & Clivaldo Silva de Araújo
Departamento de Tecnologia Mecânica, Universidade Federal da Paraíba, Campus I, CEP 58.073-420 - João Pessoa - Pb - Brasil
E. Mail: arnaud@ct.ufpb.br
Transient noise control has been applied in variety of devices, machines , and structures. In this paper an active control approach that reduces transient noise transmission through a double plate in a circular duct is presented. Two circular pieces of piezoelectric material are is used in the plate as an actuator to induce a moment in the plate. The same procedure is applied to use a circular piezoelectric material as a sensor. A special configuration consisting of two circular plates are used as a plant to control transient noise using a dynamic feedforward controller. In the experiment the forward traveling wave is captured by the first plate containing a piezoelectric sensor. This information is used to as feedforward signal. A special electronic circuit is used to perform as the feedforward controller. A transient pressure pulse is used to excite the first plate, and reductions of up to 20 dB are observed at the second plate placed downstream of the first place, when the controller is active.
Keywords: Controle ativo, Controle de ruído, Piezoelétrico/Active Control, Noise Control, Piezoelectric
COB468 Interação Rotor-Estrutura de Fundação através de mancais hidrodinâmicos / Interaction Rotor-Foundation Structure through hydro-dynamics bearings
Katia Lucchesi C. Dedini & Paula Frassinetti Cavalcante
Departamento de Projeto Mecânico- Faculdade de Engenharia Mecânica - UNICAMP
Cep 13085-970 Campinas- S.P-Brasil E- mails : katia@dpm.fem.unicamp.br, pplegal@dpm.fem.unicamp.br
This paper presents a methodology for the analysis of the foundation behaviour and its influence on the whole system (rotor-bearings-foundation), using a mathematical approach to determine its modal parameters such as modal mass, damping factor and natural frequency. The analysis of the complete system is done applying the discretization of the foundation and rotor by finite element method. The evaluation of the foundation modal parameters is done by the analysis of the structure frequency response function, obtained by Fourier Transform. Afterwards the analysis of the system frequency response function is done and analytical results are showed.
Keywords: Fundação em concreto, Rotor, Parâmetros modais / Concrete Foundation, Rotor, Modal Parameters
COB681 A TIME DOMAIN METHOD FOR INPUT FORCE RECONSTRUCTION
Gino Genaro* & Domingos Alves Rade**
* Graduate Student in Mechanical Engineering. E-mail: ggenaro@ufu.br
** Assistant Professor. E-mail: domingos@ufu.br, Federal University of Uberlândia - Department of Physical Sciences
Campus Santa Mônica - CEP 38400-902 - Uberlândia - MG - Brazil.
This paper addresses the problem of indirect force reconstruction from the dynamic responses of the structure. A time domain method is proposed which is based on the equations of motion in the modal space requiring, as experimental data, the acceleration time responses of the structure when acted upon by the forces to be identified and a set of eigensolutions (natural frequencies, mode shapes, modal damping factors and generalized masses). After the basic formulation is presented, numerical applications to a simple test structure are shown to demonstrate the effectiveness of the method. Some key points are also examined, such as the effect of the incompletness of experimental data and measurement noise upon the performance of the method. The numerical results reveal that the method can be accurate and well adapted to real-world applications.
Keywords: Indirect force reconstruction, force measurement, system identification, inverse problems, vibrations/identificação indireta de forças, medição de forças, identificação de sistemas, problemas inversos, vibrações.
COB682 ESTIMAÇÃO DE FUNÇÕES RESPOSTA EM FREQÜÊNCIA EM AMBIENTES RUIDOSOS / FREQUENCY RESPONSE FUNCTIONS ESTIMATION IN NOISY ENVIRONMENTS .
Marcus Antônio Viana Duarte*, Domingos Alves Rade** & Leandro Afonso da Silva***
* Departamento de Engenharia Mecânica, E-mail: mvduarte@ufu.br
**Departamento de Ciências Físicas, E-mail:domingos@ufu.br
*** Departamento de Engenharia Mecânica, E-mail: lafonsos@ufu.br, Universidade Federal de Uberlândia - UFU - Uberlândia
CEP 38400-902 Uberlândia, Brasil
In this paper, the estimation of frequency response functions (FRFs) from vibration tests is addressed. The main objective of the reported study is to evaluate the performance of some of the currently used frequency response function estimators under experimental conditions in the field, where inescapable uncontrolled perturbations are present in the test environment. A vibration testing procedure was carried out in laboratory, where two random forces were applied simultaneously. The first one played the role of the main test excitation force, which was accounted for in the input-output model used for estimation, whilst the second one was introduced to take into account the uncontrolled inputs, which were not considered in the theoretical model. Under these conditions, the frequency response functions obtained by using the classical estimators H1, H2 as well as three other estimators based on the concept of instrumental variable, Hc, Hx and Hy were compared to the corresponding ones obtained without the uncontrolled input, so as to evaluate the quality of the estimates provided by each estimator.
Keywords: Estimação, Funções de Resposta em Freqüência, Variáveis Instrumentais, Ensaios Dinâmicos
Estimation, Frequency Response Functions, Instrumental Variables, Dynamic Testing
COB849 ANÁLISE DO COMPORTAMENTO DINÂMICO DE VIGAS CONTENDO JUNTAS PARAFUSADAS/ ANALYSIS OF DYNAMIC BEHAVIOUR OF BEAMS WHITCH BOLTED JOINTS.
João Alberto de Oliveira & Araildo Lima da Silva
Departamento de Engenharia Mecânica, Faculdade de Engenharia - UNESP - Guaratinguetá
CEP 12500-000 Guaratinguetá, Brasil - E-mail: Joalboli@ feg.unesp.br
This work is devoted to investigation of dynamic behaviour of bolted joints. Both damping ratio and natural frequency of vibration are studied in function of the variation the physicals parameters of the joint, bolt tightening torque and the surface finish. The values of natural frequencies w n and displacements amplitudes q(t) for beams studied are calculated using specialized softwares and applied for calculations of damping ratio by method of the logarithmic decrement. The experimental results are analyzed and compared with relation of damping ratio and natural frequency of vibration in the first mode.
Keywords: Bean; bolted joint; damping ratio; logarithmic decrement; natural frequency of vibration.
COB955 IDENTIFICAÇÃO DE DEFEITOS TIPO PITTING EM UM MOTOREDUTOR DE VELOCIDADE / IDENTIFICATION OF PITTING ERROS IN GEARBOXES
Jorge Nei Brito, Alexandre Albuquerque Pinto & Carlo Ehardt Teatini
Departamento de Mecânica - Fundação de Ensino Superior de São João del Rei - FUNREI, CEP 36.300-000 São João del Rei, Brasil
E-mail: demec @ csa.funrei.br
This work presents a methodology to identify the influence of the active involute profile of helical gear caused by pitting on motor-gearbox. Power spectrum density and wave forms were obtained with and without pitting, in order to determine its behavior on motor-gearbox.
Keywords: Motoredutor, vibração, freqüência de engrenamento, pitting e engrenagem. Gearbox, vibration, gear mesh, pitting and gear.
COB1155 WAVELETS TRANSFORM FOR IDENTIFICATION OF VIBRATING MECHANICAL SYSTEMS
Victor Florin Poterasu
Theoretical Mechanics Departament, Technical University "Gh. Asachi" Iasi, Bd. Copou 22, RO - 6600 Iasi, Romania
The paper proposes an identification method for the mechanical and structural systems based on wavelets family. The advantages of using wavelets for system identification are that good localization and hierarchical multi-resolution can be achieved in both time and frequency domain. Consequently, the system model with multiple coupled modes can be identified (by wavelet based identification techniques) more efficient and accurately, especially for wideband (transient) and nonstationary signals. After a presentation of wavelets transform and identification procedure, the paper studies a simulated vibrating system formed by discrete masses, springs and dampers.
Keywords: Mechanical Vibrations, Wavelets Transform, Multi-resolution, Identification.
COB1179 CONTROLE DE ESTRUTURAS COM NÃO-LINEARIDADES CÚBICAS E QUADRÁTICAS SOB CARGAS HARMÔNICAS / CONTROL OF STRUCTURES WITH CUBIC AND QUADRATIC NONLINEARITIES UNDER HARMONIC LOADS
Osvaldo Casares Pinto & Paulo Batista Gonçalves
Departamento de Engenharia Civil, Pontifícia Universidade Católica - PUC-Rio - CEP 22453-900 Rio de Janeiro, RJ
E-mail: paulo@civ.puc-rio.br
Under extreme environmental loading such as wind, earthquakes and waves, flexible structures like tall buildings, long bridges and offshore platforms tend to develop large vibrations, possibly resulting in extensive damage. This paper studies a methodology for the active control of flexible structures, in order to limiting the amplitude of oscillations to be within safe allowable bounds. The method is based on nonlinear optimal control, using an indicial formulation and state feedback control. General polynomial representation of the control law up to the third order are presented. This methodology is applied to sdof systems with quadratic and cubic nonlinearities, with a computer code implemented to control up to the fifth order. Strongly nonlinear systems subjected to simple harmonic excitations are tested. Numerical results indicate that the control algorithm can be efficient in systems susceptible to chaotic vibrations, escape from a potential well or dynamic jumps.
Keywords: Active structural control, nonlinear systems, escape from a potential well, chaotic vibrations (controle estrutural ativo, não-linearidades, escape de um vale potencial, vibrações caóticas).
COB1362 VIBRAÇÕES INDUZIDAS EM MOTORES C.C. POR FALHAS NOS CIRCUITOS ELETRÔNICOS RETIFICADORES DE CORRENTE E DE CONTROLE DE VELOCIDADE / INDUCED VIBRATION IN DC ELECTRIC MOTORS BY CURRENT AND SPEED RECTIFIERS DEFECTS
Márcio Tadeu de Almeida, Alexandre Augusto Simões
Departamento de Engenharia Mecânica, Escola Federal de Engenharia de Itajubá - EFEI - Itajubá CEP 37.500.000, Brasil
E-mail: simoes@iem.efei.rmg.br
This paper presents in a simple way, the technics used to identify defects on the rectyfing current eletronics circuits and on the speed control of the direct current motors, through the vibration analisys. The system is described both by the DC control firing Cards and the DC control comparitor card, explaining about the main faults that can occur in this components. It is also shown a case history where the applying of the vibration diagnostic helped with success to detect the fault. Finally a short conclusion is presented with the main identified frequencies on the vibration spectrums when the circuits fails.
Keywords: Vibrações, Motores CC, Retificadores, Vibration, Rectifier.
COB1378 HIGH FREQUENCY MODELS FOR ACTIVE COMPOSITE BEAMS CONTAINING PIEZOELECTRIC SENSORS AND ACTUATORS
A. M. B. Braga1 , A. L. Gama2 , O. Macedo Neto1 & Luís P. F. de Barros1
1 Departamento de Engenharia Mecânica, PUC-Rio, 22453-900, Rio de Janeiro, RJ
2 Departamento de Engenharia Mecânica, UFF, 24210-000, Niterói, RJ
The problem addressed in this paper is that of modeling the dynamic response of laminate, composite beams excited by distributed piezoelectric actuators. In particular, we are interested in the high frequency range, where traditional approximate beam models, such as the Classical Laminate or the First Order Shear Deformation theories, fail in providing accurate representation of the electromechanical structural response. To avoid this shortcoming, Reddy's layerwise laminate theory is employed. Through compar- isons with exact, wave-dispersion analytical results, it is shown that this approach allows us to properly simulate the high-frequency range of the active beam's dynamic response.
Keywords: Structural Acoustics - Smart Structures - Composite Structures - Piezoelectric Materials - Vibrations
COB1411 ANÁLISE DE SENSIBILIDADE PARA DETERMINAÇÃO DE PONTOS DE MEDIÇÃO DE VIBRAÇÕES OTIMIZADOS / SENSIBILITY ANALYSIS TO IDENTIFY THE OPTIMAL POINTS OF VIBRATION MEASUREMENTS
Luiz de Paula do Nascimento
Departamento de Engenharia Mecânica, Faculdade de Engenharia - UNESP - Ilha Solteira
Av. Brasil Centro, 56 - CEP 15.385-000 - Ilha Solteira - SP - Brasil, E-mail: depaula@ feis.unesp.br
The sensibility analysis can be used to simulate and predict the vibratory behaviour of the systems. A particular interest is to obtain relationships among the parameters and the behaviour of the systems. Therefore, this work presents a sensibility analysis of response of the system with respect to the variations of its dynamical parameters, in order to identify the better points of vibration measurements. This technique is very important in monitoring, control and fault detection since it permits to obtain a great quantity of information of the state of the machine with a reduced number of sensors. The analysis was carried out by using a mathematical model developed with the finite elements method. An example of application of this technique in a Francis turbine of vertical shaft is presented.
Keywords: Modelagem, sensibilidade, vibrações, monitoramento / Modelling, sensibility, vibration, monitoring.