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Dec 2007

Volume 122, Issue 6, pp. 3133-EL235

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Reconstruction of Rayleigh–Lamb dispersion spectrum based on noise obtained from an air-jet forcing

Eric Larose, Philippe Roux, and Michel Campillo

J. Acoust. Soc. Am. Volume 122, Issue 6, pp. 3437-3444 (2007); (8 pages) | Cited 10 times

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The time-domain cross correlation of incoherent and random noise recorded by a series of passive sensors contains the impulse response of the medium between these sensors. By using noise generated by a can of compressed air sprayed on the surface of a plexiglass plate, we are able to reconstruct not only the time of flight but the whole wave forms between the sensors. From the reconstruction of the direct A0 and S0 waves, we derive the dispersion curves of the flexural waves, thus estimating the mechanical properties of the material without a conventional electromechanical source. The dense array of receivers employed here allow a precise frequency-wavenumber study of flexural waves, along with a thorough evaluation of the rate of convergence of the correlation with respect to the record length, the frequency, and the distance between the receivers. The reconstruction of the actual amplitude and attenuation of the impulse response is also addressed in this paper.
Show PACS
43.40.Dx Vibrations of membranes and plates
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.50.Yw Instrumentation and techniques for noise measurement and analysis
43.40.Ph Seismology and geophysical prospecting; seismographs

Response variance prediction for uncertain vibro-acoustic systems using a hybrid deterministic-statistical method

R. S. Langley and V. Cotoni

J. Acoust. Soc. Am. Volume 122, Issue 6, pp. 3445-3463 (2007); (19 pages) | Cited 2 times

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Imperfections during the manufacturing process can cause significant variations in the noise and vibration levels exhibited by nominally identical structures. Any response calculations employed during the design process should ideally take account of these uncertainties and predict the expected range in performance. Recently a hybrid method has been developed to predict the ensemble average response of a built-up system by combining a deterministic model of parts of the system with a statistical model of other components [ Shorter, P. J., and Langley, R. S. (2005) J. Sound. Vib., 288, 669–700 ]. In this paper the method is extended to predict the ensemble variance of the response. Expressions are derived for the variance of the vibrational energies in the statistical components, and for the variance of the cross spectrum of the response of the deterministic components, which augment the mean values of these quantities predicted by the original theory. The method employs a nonparametric model of uncertainty, in the sense that the statistical components are taken to carry diffuse wave fields, and this obviates the requirement for a detailed description of the system uncertainties. The method is validated by application to a range of coupled plate structures, and good agreement with detailed Monte Carlo simulations is found.
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43.40.Qi Effect of sound on structures, fatigue; spatial statistics of structural vibration
43.20.Ks Standing waves, resonance, normal modes
43.40.Dx Vibrations of membranes and plates
43.20.Bi Mathematical theory of wave propagation
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