Milton Dias Júnior

Structural Health Monitoring in Smart Structures Through Time Series Analysis

This paper describes the application of a structural health monitoring technique based on electrical measurements obtained by piezoceramics (PZT) patches bonded in lightweight structures. The goal is to detect and locate imminent structural change occurrence with statistical confidence through a nondestructive evaluation test. Though the major focus in damage detection is given by monitoring electrical impedance in frequency-domain, the current research work applies a novel approach based on time-series. In such case, auto-regressive moving average with exogenous input (ARMAX) system identification models and statistical process control (SPC) charts are used for linear prediction to detect and locate damages. In order to compare the results, the classical damage metric chart obtained by frequency response from input–output data is described. The efficacy of the proposed approach is demonstrated through experimental tests.This paper describes the application of a structural health monitoring technique based on electrical measurements obtained by piezoceramics (PZT) patches bonded in lightweight structures. The goal is to detect and locate imminent structural change occurrence with statistical confidence through a nondestructive evaluation test. Though the major focus in damage detection is given by monitoring electrical impedance in frequency-domain, the current research work applies a novel approach based on time-series. In such case, auto-regressive moving average with exogenous input (ARMAX) system identification models and statistical process control (SPC) charts are used for linear prediction to detect and locate damages. In order to compare the results, the classical damage metric chart obtained by frequency response from input—output data is described. The efficacy of the proposed approach is demonstrated through experimental tests.

Damage detection in a benchmark structure using AR-ARX models and statistical pattern recognition

Structural health monitoring (SHM) is related to the ability of monitoring the state and deciding the level of damage or deterioration within aerospace, civil and mechanical systems. In this sense, this paper deals with the application of a two-step auto-regressive and auto-regressive with exogenous inputs (AR-ARX) model for linear prediction of damage diagnosis in structural systems. This damage detection algorithm is based on the monitoring of residual error as damage-sensitive indexes, obtained through vibration response measurements. In complex structures there are many positions under observation and a large amount of data to be handed, making difficult the visualization of the signals. This paper also investigates data compression by using principal component analysis. In order to establish a threshold value, a fuzzy c-means clustering is taken to quantify the damage-sensitive index in an unsupervised learning mode. Tests are made in a benchmark problem, as proposed by IASC-ASCE with different damage patterns. The diagnosis that was obtained showed high correlation with the actual integrity state of the structure.

Model-Based Identification of Rotor-Bearing System Parameters Employing Adaptive Filtering

Instability issues and excessive vibration amplitudes are common problems encountered in large rotating machinery applications. In order to predict problems and overcome them, reliable rotor models are required. In the previous decades there has been a great improvement on finite element modeling, which was extensively used in rotordynamics problems. However, there is a great difficulty when bearings have to be considered, and the unbalance present in the machine must be known for good response prediction. This paper proposes a method of bearing and unbalance parameter estimation from measured responses at the bearings and considering a Finite Element model of the shaft. The proposed algorithm utilizes the adaptive filtering technique known as the RLS filter employing the QR decomposition. Simulations were conducted and good results were achieved for both stationary and speed-dependent bearing parameters.

Insights on Centrifugal Pendulum Vibration Absorber: Part Two — Behaviour of a FWD Powertrain With a CPVA on its Clutch’s Flange

This work is the second and last part of a study whose aim is to present the vibrational aspects of a system with a centrifugal pendulum vibration absorber (i.e. CPVA). The aim of this work, specifically, is to develop a mathematical model of a front engine–front wheel drive powertrain to study gear rattle phenomenon, and to install on its clutch disk’s flange a CPVA in order to understand what are the effects of this device on the dynamics of this system.Results from the linear analysis show that the eigenfrequencies of the system vary with the engine speed. They oscillate between the eigenvalues of the system without the CPVA and, for regions away from the tuning frequency of the pendulum, which is the second order of rotation of the engine, the behaviour of the system remains the same. However, near the tuning frequency of the pendulum, the behaviour of the system varies very much, and the amplitude of vibration of the gearbox’s inner parts diminishes.Simulations of the powertrain without and with the nonlinear model of the studied device show that its presence reduces dramatically the vibrations inside the gearbox and its nonlinear character does not influence the effectiveness of this solution.Copyright

Automotive Powertrain Vibrations Running on Wide Open Throttle Engine Conditions

Powertrain vibrations is a great concern in the automotive industry, once they are related to many Noise, Vibration and Harshness (NVH) phenomena. These are very complex system once their dynamic behaviour, in many cases, involve the interaction between the combustion engine and the remaing components of the powertrain, such as the clutch, transmission, differential, etc. In this work a system approach is used. First, the torque generated by a four cylinder engine is obtained through the thermodynamic equations. Then, these torque curves for each cylinder are combined and used as the excitation of a simplified model of a front wheel drive powertrain. Finally, the influence of ignition angles on the combustion characteristics and on the order content of engine output torque is analyzed. Results show that significant changes may happen on the second and fourth order responses.© 2013 ASME

Insights on Centrifugal Pendulum Vibration Absorber: Part One — Dynamic Modeling and Behaviour of Eigenvalues and Eigenvectors Along Rotating Speed

An automotive powertrain is a system that is designed to transmit torque from the engine to the wheels of the vehicle, allowing it to move. The working principle of most of the vehicle engines is the internal combustion, which causes the torque generated by this engine to have important oscillatory components, which cause the powertrain to vibrate and generate noise, which is undesired.In order to control this vibration, among many engineering solutions is the centrifugal pendulum vibration absorber (CPVA), whose dynamic behaviour turns it is capable of reducing the amplitude of important order components of the powertrain. It is usually installed on the flywheel of the vehicle, although it is possible to install it in other parts, such as the clutch disk.Although the CPVA is an important type of passive vibration absorber, it was still not found in the literature a parametrized formulation which can be applied to any vibration absorber of this kind. For this reason, the aim of this work is to propose a formulation based on dimensionless parameters, which can be applied to any CPVA. With this formulation, the dynamic behaviour of a simple 2DOF torsional system with a CPVA, spinning at constant speed, is verified.It is important to mention that this work is the first part of a two part work. In the second part, this formulation is applied to a more complex system with a CPVA, and results are shown to be coherent with the analyses shown here.Copyright

NUMERICAL INVESTIGATION ON THE NONLINEAR BEHAVIOUR OF POWERTRAIN SYSTEMS: FOCUS ON CLUTCH MODIFICATIONS

Resumo: O trem de potencia ou driveline, que consiste no sistema que transfere potencia do motor ate as rodas, possui um comportamento nao-linear devido aos seus elementos (embreagem, engrenamentos, etc.). Para aplicacoes automotivas, os parâmetros da embreagem sao apropriadamente escolhidos para que haja coincidencia do torque fornecido pelo motor para a condicao de conducao encarada pelo motorista (ponto morto, marcha engatada, etc.). Esse elemento tambem atenua condicoes desgradaveis para o passageiro, que se manifestam por meio de ruido ou vibracao. Neste trabalho, simulacoes numericas serao realizadas para demonstrar a influencia das caracteristicas de atrito e rigidez desse elemento, dando sugestoes para lidar com o fenomeno em situacoes reais. Resumo: The powertrain or driveline, which consists on the system which transfers power from the engine to the wheels, has a nonlinear behavior due to its elements (clutch, gears, etc.). For automotive applications, clutch parameters are chosen properly to match the engine torque for the driving condition faced by the driver (neutral, engaged gear, etc.). This element also attenuates annoying conditions for the passenger, manifested by noise and vibration. In this work, numerical simulations will be carried out to demonstrate the influence of frictional and stiffness characteristics this element, giving hints to deal with the phenomenon in real situations. Palavras-chave: powertrain, nonlinear vibration, engineer