Current Issue : April - June Volume : 2014 Issue Number : 2 Articles : 5 Articles
In this paper,modal frequency estimation by using autocorrelation functions in both the time and frequency domains for structural\r\ndiagnostics is discussed.With popular structural health monitoring methods for periodic inspections such as with the ââ?¬Å?hammering\r\ntest,ââ?¬Â hearing is very useful for distinguishing differences between structural conditions. Hearing detects pitch and tone, and it is\r\nknown that the auditory process is related to wave periodicity calculated fromautocorrelation functions. Consequently, on the basis\r\nof the hammering test, modal frequencies can be estimated by autocorrelation, the same as hearing. In this paper, modal frequencies\r\nwere estimated by using autocorrelation for constant structural health monitoring under a nonstationary noise condition. First,\r\nfundamental modal frequencies were estimated by using the autocorrelation of the time domain which was inspired by pitch\r\ndetection of hearing. Second, higher modal frequency compositions were also analyzed by using autocorrelation in the frequency\r\ndomain as with tones discrimination. From the results by conducting scale-model experiments under unknown nonstationary\r\nnoise conditions, periods of fundamental modal frequency were derived by using periods histogram of autocorrelation functions.\r\nIn addition, higher modal frequency estimation under nonstationary noises was also discussed....
Utilization of biomass for green products is still progressing in the effort to provide alternative clean technology. This paper presents\r\nthe utilization of natural waste fibers frompaddy as acoustic material. Samples of sound absorbingmaterial frompaddy waste fibers\r\nwere fabricated.The effect of the fiber density, that is, the fiber weight and the sample thickness, and also the air gap on the sound\r\nabsorption coefficient is investigated through experiment. The paddy fibers are found to have good acoustic performance with\r\nnormal incidence absorption coefficient greater than 0.5 from 1 kHz and can reach the average value of 0.8 above 2.5 kHz. This\r\nresult is comparable against that of the commercial synthetic glass wool. Attachment of a single layer of polyester fabric is shown\r\nto further increase the absorption coefficient....
The problem of diffraction of a plane elastic wave by a gradient transversely isotropic layer is considered. Using the method of\r\noverdetermined boundary value problem in combination with the Fourier transform method, the system of ordinary differential\r\nequations of the second order with boundary conditions of the third type is obtained which is solved by the grid method. Results\r\nof calculations obtained using the above-mentioned technique for the case of piecewise linear profiles for the Young modulus of\r\nthe layer are given....
This paper describes the vibroacoustic coupling between the structural vibrations and internal sound fields of thin structures. In\r\nthis study, a cylindrical structure with thin end plates is subjected to the harmonic point force at one end plate or both end plates,\r\nand a natural frequency of the end plates is selected as the forcing frequency. The resulting vibroacoustic coupling is then analyzed\r\ntheoretically and experimentally by considering the dynamic behavior of the plates and the acoustic characteristics of the internal\r\nsound field as a function of the cylinder length. The length and phase difference between the plate vibrations, which maximize\r\nthe sound pressure level inside the cavity, are clarified theoretically. The theoretical results are validated experimentally through\r\nan excitation experiment using an experimental apparatus that emulates the analytical model.Moreover, the electricity generation\r\nexperiment verifies that sufficient vibroacoustic coupling can be created for the adopted electricity generating system to be effective\r\nas an electric energy-harvesting device....
Damping of vibrations is often required to improve both the performance and the integrity of engineering structures, for example,\r\ngas turbine blades. In this paper, we explore the possibility of using piezoelectric plates to control the multimode vibrations of a\r\ncantilever beam. To develop an effective control strategy and optimize the placement of the active piezoelectric elements in terms\r\nof vibrations amplitude reduction, a procedure has been developed and a new analytical solution has been proposed.The results\r\nobtained have been corroborated by comparison with the results from a multiphysics finite elements package (COMSOL), results\r\navailable in the literature, and experimental investigations carried out by the authors....
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