Determination of Phase Velocity Dispersion Curves and Group Velocity in a Plate Using Backward Radiated Leaky Lamb Waves

Multimode’s Lamb waves in aluminum plates with various defects were excited by a Q-switched Nd:YAG laser. The Lamb waves past through the defects were received a laser interferometer. The received signals of the Lamb waves are processed by the wavelet transformation. The wavelet transformation is generally shown on the time-frequency domain. By dividing a propagation distance by the time, the group velocities are identified. In this way, group velocity dispersion maps of multimode’s Lamb waves are constructed with the received temporal signals. By changing the shape of the mother wavelet, Gabor function, we can identify the dispersion curves of the higher mode Lamb waves. The group velocity dispersion maps of a intact specimen agree well on theoretical dispersion curves of S0, A0, S1, A1, S2, A2, and A3 modes. The difference between the dispersion maps of the intact specimen and that with defects clearly visualizes the existence of defects. This non-contact method is effective for inspecting various defects in thin plate structures.

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Validation of Dispersion Curve Reconstruction Techniques for the A0 and S0 Modes of Lamb Waves

International Journal of Structural Stability and Dynamics ◽

10.1142/s0219455414500242 ◽

2014 ◽

Vol 14 (07) ◽

pp. 1450024 ◽

Cited By ~ 7

Author(s):

Lina Draudvilienė ◽

Renaldas Raišutis ◽

Egidijus Žukauskas ◽

Audrius Jankauskas

Keyword(s):

Phase Velocity ◽

Structural Changes ◽

Lamb Waves ◽

High Sensitivity ◽

Dispersion Curves ◽

Curve Reconstruction ◽

Informative Signal ◽

Zero Crossing ◽

Reconstruction Methods ◽

Phase Velocity Dispersion

The properties of ultrasonic Lamb waves, such as relatively small attenuation and high sensitivity to structural changes of the object being investigated, allow performing of non-destructive testing of various elongated structures like pipes, cables, etc. Due to the dispersion effect of Lamb waves, a waveform of the received informative signal is usually distorted, elongated and overlapping in the time domain. Therefore, in order to investigate objects using the ultrasonic Lamb waves and to reconstruct the dispersion curves, it is necessary to know the relationship between frequency, phase and group velocities and thickness of the plate. The zero-crossing technique for measurement of phase velocity of Lamb waves (the A0 and S0 modes) has been investigated using modelled dispersed signals and experimental signals obtained for an aluminium plate having thickness of 2 mm. A comparison between two reconstruction methods of Lamb wave phase velocity dispersion curves, namely, the two-dimensional fast Fourier transform (2D-FFT) and zero-crossing technique, along with the theoretical (analytical) dispersion curves is presented. The results indicate that the proposed zero-crossing method is suitable for use in reconstruction of dispersion curves in the regions affected by strong dispersion, especially for the A0 mode.

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Sensitivities of phase-velocity dispersion curves of surface waves due to high-velocity-layer and low-velocity-layer models

Journal of Applied Geophysics ◽

10.1016/j.jappgeo.2016.10.017 ◽

2016 ◽

Vol 135 ◽

pp. 367-374 ◽

Cited By ~ 7

Author(s):

Chao Shen ◽

Yixian Xu ◽

Yudi Pan ◽

Ao Wang ◽

Lingli Gao

Keyword(s):

Phase Velocity ◽

Surface Waves ◽

High Velocity ◽

Velocity Dispersion ◽

Dispersion Curves ◽

Low Velocity ◽

Phase Velocity Dispersion ◽

Low Velocity Layer ◽

High Velocity Layer ◽

Velocity Layer

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New techniques for the determination of surface wave phase velocities

Bulletin of the Seismological Society of America ◽

10.1785/bssa0580031021 ◽

1968 ◽

Vol 58 (3) ◽

pp. 1021-1034 ◽

Cited By ~ 2

Author(s):

S. Bloch ◽

A. L. Hales

Keyword(s):

Phase Velocity ◽

Rayleigh Waves ◽

World Wide ◽

Velocity Dispersion ◽

Cross Product ◽

New Techniques ◽

Phase Velocities ◽

Phase Velocity Dispersion ◽

The World

abstract A number of new techniques have been developed for the determination of phase velocities from the digitized seismograms from pairs of stations. One of these techniques is to Fourier analyze the sum (or difference) of the two seismograms after time shifting in steps to correspond to steps in phase velocity. The amplitude of the summed seismogram is a maximum for any particular period when both seismograms are in phase at that period. Another method is to pass both seismograms through a narrow bandpass digital filter centered at various periods and form the cross product of the filtered seismograms, after time shifting. The average of the resultant time series is a maximum when the two signals are in phase. The computer output is a matrix consisting of amplitudes or averages as a function of phase velocity and period. The phase velocity dispersion is determined from the contoured matrix. Using these techniques, interstation phase velocities of Rayleigh waves have been determined for the “World Wide Network Standard Stations” at Pretoria, Bulawayo and Windhoek. The method using cross-products is the most efficient.

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Lamb Wave-Based Damage Location Detection Method of Composite Plate

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.301-303.1260 ◽

2011 ◽

Vol 301-303 ◽

pp. 1260-1266

Author(s):

Li Shao Zhang ◽

Huan Guo Chen ◽

Jian Min Li ◽

Li Tian

Keyword(s):

Group Velocity ◽

Lamb Wave ◽

Composite Laminates ◽

Composite Plate ◽

Velocity Dispersion ◽

Lamb Waves ◽

Group Velocity Dispersion ◽

Dispersion Curves ◽

Damage Location ◽

The Difference

To understand more about Lamb waves on composite laminates damage detection features, the Lamb wave group velocity dispersion curves are calculated and plotted by using dichotomy method in MATLAB. The signal parameters are chosen according to Group velocity dispersion curves. The dynamic response signals of the composite plate are obtained by finite element method. Damage location is calculated by the actual group velocity of Lamb wave and time of flight of the difference signal before and after damage.

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Combining surface-wave phase-velocity dispersion curves and full microtremor horizontal-to-vertical spectral ratio for subsurface sedimentary site characterization

Interpretation ◽

10.1190/int-2016-0021.1 ◽

2016 ◽

Vol 4 (4) ◽

pp. SQ41-SQ49 ◽

Cited By ~ 8

Author(s):

Agostiny Marrios Lontsi ◽

Matthias Ohrnberger ◽

Frank Krüger ◽

Francisco José Sánchez-Sesma

Keyword(s):

Surface Wave ◽

Phase Velocity ◽

Velocity Dispersion ◽

Spectral Ratio ◽

Test Site ◽

Dispersion Curves ◽

Surface Velocity ◽

Wave Phase ◽

Phase Velocity Dispersion ◽

Wave Phase Velocity

We compute seismic velocity profiles by a combined inversion of surface-wave phase-velocity dispersion curves together with the full spectrum of the microtremor horizontal-to-vertical (H/V) spectral ratio at two sediment-covered sites in Germany. The sediment deposits are approximately 100 m thick at the first test site and approximately 400 m thick at the second test site. We have used an extended physical model based on the diffuse wavefield assumption for the interpretation of the observed microtremor H/V spectral ratio. The extension includes the interpretation of the microtremor H/V spectral ratio observed at depth (in boreholes). This full-wavefield approach accounts for the energy contribution from the body and surface waves, and thus it allows for inverting the properties of the shallow subsurface. We have obtained the multimode phase velocity dispersion curves from an independent study, and a description of the extracted branches and their interpretation was developed. The inversion results indicate that the combined approach using seismic ambient noise and actively generated surface-wave data will improve the accuracy of the reconstructed near-surface velocity model, a key step in microzonation, geotechnical engineering, seismic statics corrections, and reservoir imaging.

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