Simulation of a transient bounded beam incident on an immersed isotropic plate for the reconstruction of lamb waves dispersion curves either in complex frequency and real slowness or in real frequency and complex slowness

2001 ◽  
Author(s):  
A. Bernard
Keyword(s):  
Isotropic Plate ◽  
Lamb Waves ◽  
Dispersion Curves ◽  
Complex Frequency ◽  
Real Frequency ◽  
Beam Incident

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.

scholarly journals Guided waves in a fluid-loaded transversely isotropic plate

2002 ◽  
Vol 8 (2) ◽  
pp. 151-159 ◽  
Author(s):  
F. Ahmad ◽  
N. Kiyani ◽  
F. Yousaf ◽  
M. Shams
Keyword(s):  
Guided Waves ◽  
Isotropic Plate ◽  
Transversely Isotropic ◽  
Dispersion Curves ◽  
Dispersion Relations ◽  
Normalized Frequency ◽  
Transversely Isotropic Plate ◽  
Second Mode ◽  
Symmetric And Antisymmetric Modes

Dispersion relations are obtained for the propagation of symmetric and antisymmetric modes in a free transversely isotropic plate. Dispersion curves are plotted for the first four symmetric modes for a magnesium plate immersed in water. The first mode is highly damped and switches over to the second mode when the normalized frequency exceeds 12.

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 Stellar dynamics in the periodic cube

2021 ◽  
Vol 507 (4) ◽  
pp. 4840-4851
Author(s):  
John Magorrian
Keyword(s):  
Stellar Dynamics ◽  
Equal Mass ◽  
Linear Perturbation ◽  
Complex Frequency ◽  
Dynamical Friction ◽  
Linear Evolution ◽  
Real Frequency ◽  
Alternative Expression ◽  
Self Consistent ◽  
Consistent Response

ABSTRACT We use the problem of dynamical friction within the periodic cube to illustrate the application of perturbation theory in stellar dynamics, testing its predictions against measurements from N-body simulations. Our development is based on the explicitly time-dependent Volterra integral equation for the cube’s linear response, which avoids the subtleties encountered in analyses based on complex frequency. We obtain an expression for the self-consistent response of the cube to steady stirring by an external perturber. From this, we show how to obtain the familiar Chandrasekhar dynamical friction formula and construct an elementary derivation of the Lenard–Balescu equation for the secular quasi-linear evolution of an isolated cube composed of N equal-mass stars. We present an alternative expression for the (real-frequency) van Kampen modes of the cube and show explicitly how to decompose any linear perturbation of the cube into a superposition of such modes.

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 Lamb Waves Topological Imaging of Multiple Blind Defects in an Isotropic Plate

2019 ◽  
Vol 24 (2) ◽  
pp. 320-326 ◽  
Author(s):  
Wen-Fa Zhu ◽  
Hai-Yan Zhang Zhang ◽  
Meng-Yun Xu ◽  
Guo-Peng Fan
Keyword(s):  
Lamb Wave ◽  
Isotropic Plate ◽  
Lamb Waves ◽  
Mode Conversion ◽  
Image Resolution ◽  
Imaging Method ◽  
Wave Fields ◽  
Face To Face ◽  
Element Simulation ◽  
Reference Medium

The study investigates the feasibility of the Lamb wave topological imaging method for detecting multiple blindholes in an isotropic plate. The topological imaging method is performed based on the computations of two wave fields, a forward and an adjoint, in the defect-free reference medium using different emitting sources. The image is computed by multiplying the forward and adjoint wave fields together and integrating them over time or frequency. The interferences of multimode aliasing and the scattering effect can thus be eliminated at the defectfree positions with an improved image resolution. To investigate the physical mechanism, the refocusing process of the multimode Lamb waves at the defect positions is presented by a face-to-face comparison between the snapshots of the forward and adjoint wave fields using the finite element simulation. The Lamb wave topological imaging method is numerically and experimentally verified to identify multiple blind-holes in an isotropic aluminium plate. The results demonstrate that the topological imaging method enables the suppression of the sartefacts resulting from the mode conversion and achieve high-resolution imaging of the blind defects

Sign in / Sign up

Export Citation Format

Share Document