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The Volume 20, No 4, December 2015



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Active Control Experiment Study of a Flexible Beam with Multiple Time Delays

Chen Long-Xiang and Cai Guo-Ping


https://doi.org/10.20855/ijav.2015.20.4383


In this paper, active control for vibration of a flexible beam with multiple time delays is studied numerically and experimentally. Piezoelectric (PZT) patches are used as actuators, and foil gauges were used as sensors. Firstly the motion equation of a flexible beam with multiple time delays and Piezoelectric patches is presented and written into a state space form. Then the state equation is discretized and transformed into a standard form without any explicit time delay by a particular augmentation for state variables. So time-delay controller could be designed based on the standard state equation using the discrete active control method. Finally, numerical and experimental studies are presented to verify the validity of the time-delay processing method using the discrete optimal control method and the discrete variable structure control method, respectively. An experimental setup is constructed using DSP TMS320F2812. The numerical and experimental results show that the proposed time-delay controller is effective in suppressing the beam vibration. It is also applicable to both short- and long- time delays.


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Simulation of the Hysteresis Mathematic Model for the MR fluid damper Using A Hybrid Evolutionary Algorithm

Xue Xiaomin, Wu Xiaohong, Sun Qing and Zhang Ling


https://doi.org/10.20855/ijav.2015.20.4384


The developed MF dampers can be used for diverse applications, including structural vibration mitigation, shock absorption, and vibration control in various systems. This paper has firstly investigated the mechanical characteristics of the self-made MR damper through experimentation. Based on the test data, the damper is found to possess nonlinear hysteresis. Usually, various models, especially the Bouc-Wen model, are proposed to interpret the complex characteristics which have the capability to capture behavior of a wide class of hysteretic systems. However, the Bouc-Wen model consists of a set of multi-unknown parameters that need to be estimated simultaneously. It is a burdensome task to effectively identify the exact values of the parameters. In view of this, this paper proposes a novel hybrid evolutionary algorithm combining Genetic Algorithm with Particle Swarm Optimization (GA-PSO). By using the GA-PSO, the optimized result would be more effective and accurate than the traditional one, because it overcomes the drawbacks of low-speed convergence in GA and local optimization in PSO. Finally it is verified through a large amount of experimental data, which can estimate the multi parameters in the Bouc-Wen model efficiently and precisely. Also suggested are the implications of the present study on other nonlinear hysteretic models or other complex mathematical models.


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Vibrations of Circular Plate on Concentric Rigid Ring and Rotational and simply supported edge

L. Bhaskara Rao and C. Kameswara Rao


https://doi.org/10.20855/ijav.2015.20.4385


In this paper, the vibrations of a circular plate with a rotationally restrained edge that has concentric rigid ring support are studied. The influences of the rotational restraint parameter and radius of internal rigid ring support on the vibration of the plate's natural frequencies are investigated. Frequencies for the first three modes of vibration are obtained and plotted graphically. The cross-over radius and the optimum location point of internal rigid ring support are determined. The results presented in this paper are from exact analysis, and hence can serve as standard values for estimating the accuracy of results obtained from various approximate methods.


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Stability and Accuracy of Aeroacoustic Time-Reversal using the Pseudo-Characteristic Formulation

A. Mimani, C. J. Doolan and P. R. Medwell


https://doi.org/10.20855/ijav.2015.20.4386


This paper investigates the stability and accuracy of the aeroacoustic Time-Reversal (TR) simulation using the Pseudo-Characteristic Formulation (PCF). To this end, the forward simulation of acoustic wave propagation in 1-D and 2-D computational domain with a uniform mean flow was implemented using the PCF of the Linearised Euler Equations (LEE). The spatial derivatives in the opposite propagating fluxes of the PCF were computed using an overall upwind-biased Finite-Difference (FD) scheme and a Runge-Kutta scheme was used for time-integration. The anechoic boundary condition (ABC) was implemented for eliminating spurious numerical reflections at the computational boundaries, thereby modelling a free-space. The stability of 1-D forward and TR (with only time-reversed acoustic pressure as the input at the boundary nodes) simulations were analysed by means of an eigenvalue decomposition, wherein it was shown that opposite upwinding directions must be considered while using the overall upwind-biased FD scheme. Furthermore, the implementation of ABC was found to be crucial for ensuring the stability of the forward simulation over a large time duration and the 2-D TR simulations. The overall central Dispersion-Relation Preserving (DRP) FD schemes were however, found to be unstable and unsuitable for TR simulation. The accuracy of both the forward and the TR simulations using the PCF was assessed by comparing the simulation results against the corresponding analytical solutions of a spatially and temporally evolving Gaussian pulse. It was shown that numerically reversing the mean flow direction during TR (using the PCF) and only the time-reversed acoustic pressure as input at the boundaries is sufficient to accurately back-propagate the waves and localise the initial emission point of the pulse in 1-D or 2-D computational domain.


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Ball Bearing Fault Diagnosis using Supervised and Unsupervised Machine Learning Methods

V. Vakharia, V. K. Gupta and P. K. Kankar


https://doi.org/10.20855/ijav.2015.20.4387


This paper deals with the approach of using multiscale permutation entropy as a tool for feature selection for fault diagnosis in ball bearings. The coefficients obtained from the wavelet transformation of the vibration signals of the bearings are used for the calculation of statistical parameters. Based on the minimum multiscale permutation entropy criteria, the best scale is selected and statistical parameters such as crest factor, form factor, and permutation entropy are calculated. Finally, the faults are classified by considering the statistical parameters and permutation entropy as features in supervised and unsupervised machine learning methods, such as a support vector machine and self-organizing maps, respectively. Results revealed that the multiscale permutation entropy-based feature extraction techniques provide higher classification accuracy in comparison to the other methodologies that have been proposed in previous published works. The methodology proposed in this paper also gives good results for unsupervised learning methods, i.e. self-organizing maps.


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Free Vibration of the Damping Beam Using Co-simulation Method Based on the MFT

D. Q. Wang, C. J. Wu and R. C. Yang


https://doi.org/10.20855/ijav.2015.20.4388


The particle damping technique has been in development for several decades, and has been used successfully in many fields. However, it is difficult to predict its damping characteristics due to complex collisions and friction mechanisms, as well as high non-linear damping characteristics in dense particles. The focus of these current main achievements is centralized on the equivalent single degree of freedom (SDOF) system under free and forced vibration. In this paper, a brand new co-simulation approach for the continuum structure system based on the multiphase flow theory (MFT) of gas solid is developed by the COMSOL Multiphysics live link for MATLAB. A simple continuum structure system, (i.e., the cantilever particle damped beam) is made as an experiment. It is further shown that the damping capacity of a cantilever beam depends not only on the exerted location of the particle damper, but also the quantity of the filling. An experimental verification is performed, and an acceptable accordance is achieved between the theoretical results and the experimental data. It can be shown that the theoretical work in this paper is valid. The co-simulation method simplifies the complicated modelling problem, and offers the possibility to analyse the vibro-acoustic response prediction for complicated particle-damping composite structures.


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Study of Secondary Field Waves at Scattering of Nonlinearly Interacting Acoustic Waves by an Elongated Spheroid

Iftikhar B. Abbasov


https://doi.org/10.20855/ijav.2015.20.4389


The study and three-dimensional simulation of the field of the second harmonic wave at the scattering of nonlinearly interacting acoustic waves by an elongated spheroid are carried out in this work. The problem is presented in the elongated spheroidal coordinate system, and the foci of the spheroid coincide with foci of the spheroidal coordinate system. The description of the occurring wave processes is presented on the basis of the obtained relation for acoustic pressure of the second harmonic wave. The scattering diagrams for the acoustic pressure field of the second harmonic wave are presented, and three-dimensional models of a scattering diagram are created.


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