scholarly journals Dispersion Curves of Transverse Waves Propagating in Multi-Layered Soils from Experimental Tests in a 100 m Deep Borehole

Geosciences ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 207
Author(s):  
Angelo Aloisio ◽  
Ferdinando Totani ◽  
Rocco Alaggio ◽  
Gianfranco Totani
Keyword(s):  
Lamb Waves ◽  
Direct Methods ◽  
Experimental Tests ◽  
Dispersion Curves ◽  
Layered Soils ◽  
Deep Borehole ◽  
Transverse Waves ◽  
Seismic Engineering ◽  
Geotechnical Investigations ◽  
Hyperbolic Dispersion

The estimate of the velocity of shear waves (Vs) is essential in seismic engineering to characterize the dynamic response of soils. There are various direct methods to estimate the Vs. The authors report the results of site characterization in Macerata (Italy), where they measured the Vs using the seismic dilatometer in a 100 m deep borehole. The standard Vs estimation originates from the cross-correlation between the signals acquired by two geophones at increasing depths. This paper focuses on the estimate of the dependence of Vs on the wavenumber. The dispersion curves reveal an unexpected hyperbolic dispersion curve typical of Lamb waves. Interestingly, the contribution of Lamb waves may be notable up to 100 m depth. The amplitude of surface waves decrease rapidly with depth; still, their influence may be essential up to depths considered unusual for standard geotechnical investigations, where their effect is generally neglected. Accordingly, these waves may bias the outcomes of the standard Vs estimations, which ignore frequency-dependent phenomena. The paper proposes an enhancement of the accepted procedure to estimate Vs and addresses the importance of Lamb waves in soil characterization.

Dielectric and Mechanical Loading Effects of a Fluid on Lamb Waves Propagating in an Immersed Piezoelectric Plate

2005 ◽  
Vol 21 (3) ◽  
pp. 179-186 ◽  
Author(s):  
C.-H. Yang ◽  
Y.-A. Lai
Keyword(s):  
Lamb Waves ◽  
Piezoelectric Plate ◽  
Dispersion Curves ◽  
Partial Wave Analysis ◽  
Theoretical Treatment ◽  
Fluid Loading ◽  
Wave Analysis ◽  
Sensor Applications ◽  
Dielectric Loading ◽  
Loading Effects

AbstractThis research is focused on exploring the fluid loading effects on the dispersion curves of Lamb modes propagating in a piezoelectric plate. A theoretical treatment based on a partial wave analysis is developed to model the dispersion curves of Lamb modes propagating in an X-LiNbO3 plate loaded by a fluid with combined mechanical/dielectric properties. In particular, the mode-shifting characteristics caused by the fluid loading as a function of the propagation orientation are illustrated with numerical examples. Finally, for the case of water as an immersing fluid, individual attributions of the mechanical and dielectric loading effects causing the mode-shifting are analyzed. It is found that the dielectric loading effect dominates the mode-shifting while the mechanical density loading can be neglected while Lamb waves propagate in an X-LiNbO3 plate immersing in water. The current results provides useful information for the applications of acoustic plate mode (APM) devices used in liquid sensor applications.

Noncontact Evaluation of Defects in Thin Plate With Multimodes Lamb’s Waves and Wavelet Transform

2002 ◽  
Author(s):  
Morimasa Murase ◽  
Koichiro Kawashima
Keyword(s):  
Group Velocity ◽  
Thin Plate ◽  
Wavelet Transformation ◽  
Velocity Dispersion ◽  
Lamb Waves ◽  
Group Velocity Dispersion ◽  
Dispersion Curves ◽  
Contact Method ◽  
Intact Specimen ◽  
Time Frequency

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.

scholarly journals Multiple zero group velocity Lamb modes in an anisotropic plate: propagation along different crystallographic axes

2019 ◽  
Vol 97 (10) ◽  
pp. 1064-1074
Author(s):  
Soufien Karous ◽  
Souhail Dahmen ◽  
Mohamed Shili Bouhdima ◽  
Morched Ben Amor ◽  
Christ Glorieux
Keyword(s):  
Group Velocity ◽  
Lamb Waves ◽  
Iodic Acid ◽  
Transverse Waves ◽  
Cutoff Frequencies ◽  
Crystallographic Planes ◽  
Zero Group ◽  
Crystallographic Axes ◽  
Symmetric And Antisymmetric Modes ◽  
Lamb Mode

This paper studies the propagation of symmetric and antisymmetric Lamb waves along a 1 mm thick iodic acid plate (HIO3) in the 1–50 MHz frequency range. The Lamb mode propagation along three crystallographic planes was theoretically investigated, for two mutually orthogonal propagation directions. Several frequencies were found that correspond to Lamb modes with zero group velocity (ZGV) and non-null phase velocity values. The first symmetric Lamb mode, S1, was found to possess only one ZGV point, regardless of the propagation direction; higher order symmetric and antisymmetric modes with up to four ZGV points were found, depending on the propagation plane. The dependence of the ZGV frequencies on each elastic constant (c11, c13, c33, c55) of the HIO3 plate material was also investigated by changing the constant values by 5% and 10%. It was found that c33 and c55 affect the number of the ZGV points, while c11 and c13 affect the frequency of the ZGV points. The existence and frequencies of the ZGV points are strongly dependent on the proximity of standing longitudinal and transverse waves at nearby cutoff frequencies.

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

2014 ◽  
Vol 14 (07) ◽  
pp. 1450024 ◽  
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.

Stopband edges in the dispersion curves of Lamb waves propagating in piezoelectric periodical structures

1988 ◽  
Vol 53 (19) ◽  
pp. 1806-1808 ◽  
Author(s):  
A. Alippi ◽  
F. Craciun ◽  
E. Molinari
Keyword(s):  
Lamb Waves ◽  
Dispersion Curves

scholarly journals Improving ultrasonic imaging of aluminum plates using phase modulation

2020 ◽  
Vol 15 (3) ◽  
pp. 1-5
Author(s):  
Rafael Mateus Tischer ◽  
Ricardo Tokio Higuti ◽  
Vander Teixeira Prado ◽  
Claudio Kitano
Keyword(s):  
Phase Modulation ◽  
Lamb Waves ◽  
Dead Zone ◽  
Ultrasonic Imaging ◽  
Experimental Tests ◽  
Ultrasonic Signal ◽  
Signal Phase ◽  
Ultrasonic Signals ◽  
Aluminum Plates ◽  
Image Simulations

Ultrasonic imaging using arrays is a widespread technique used in medical imaging, with increasing use in industry. Conventional techniques use amplitude information from the ultrasonic signals to produce the images. These amplitude images can be produced with high quality, but can also present limitations regarding dead zone, artifacts and detection of far reflectors. Coherence images based on the signal phase have been explored in some works, and produce an image that indicates the presence of a defect. In this work we explore he effect of phase modulation of the ultrasonic signal and its effect on the corresponding coherence image. Simulations and experimental tests in an aluminum plate using Lamb waves and a linear piezoelectric array show that the phase modulation hasadvantages over coherence images without phase modulation for defect indication.

Lamb Wave-Based Damage Location Detection Method of Composite Plate

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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