Papers by Keyword: Eigen-Frequencies

Abstract: The image of a semi-circular blockage and location in the uniform and stepped pipe was reconstructed by measuring the eigen-frequency shift of the resonance and anti-resonance frequencies of multi-sine acoustic waves. In this study we have used different boundary conditions from previous works of Wu and Fricke [1] and De Salis and Oldham [2] to determine the blockage cross-sectional area and position. The results agreed with real fractional cross sectional area and position in the both continuous and stepped pipes. New approach showed a better quality of reconstructed image with small ripple number and the false dummy blockage signal was also reduced. The present method of blockage image reconstruction is a noninvasive nondestructive and can meet the integrity evaluation implementation for all types of transmission pipeline

Abstract: Extrinsic resonance effects observed in a low-frequency subresonant mechanical spectrometer are reported. High resolution of the mechanical spectrometer enables precise measurement of small values of the mechanical loss tangent ( tanϕ = 1- 2 × 10-4) and the apparent high values of the loss tangent detected for extrinsic resonance effects in the vicinity of the eigen frequencies of the spectrometer. Forced oscillations can be used as a ‘signal quality test’ to validate the quality of exponentially damped harmonic oscillations in the resonant mode.