RECONSTRUCTION OF LAYERED ELASTIC BOTTOM CHARACTERISTICS BY THE FREQUENCY DEPENDENCE OF SOUND REFLECTIVITY

2001 ◽  
Vol 09 (04) ◽  
pp. 1475-1484 ◽  
Author(s):  
VLADIMIR N. FOKIN ◽  
MARGARETE S. FOKINA
Keyword(s):  
Frequency Dependence ◽  
Half Space ◽  
Simulated Data ◽  
Elastic Half Space ◽  
Ocean Bottom ◽  
Sediment Layer ◽  
Elastic Bottom ◽  
Sea Bottom ◽  
Sound Reflection ◽  
Grazing Angles

The relation between the sound reflection losses measured at fixed grazing angles and the characteristics of the sediment layer and underlying half-space is considered. Based on this relation, a method of the reconstruction of the sea bottom characteristics is developed for a ocean bottom consisting of a single sediment layer overlaying a semi-infinite elastic half-space. Using this bottom model, the reconstruction of the characteristics of a layered elastic bottom is performed from the numerically simulated data with induced synthetic error.

RESONANCES OF ACOUSTIC WAVES INTERACTING WITH AN ELASTIC SEABED

2001 ◽  
Vol 09 (03) ◽  
pp. 1079-1093 ◽  
Author(s):  
MARGARETE S. FOKINA ◽  
VLADIMIR N. FOKIN
Keyword(s):  
Reflection Coefficient ◽  
Half Space ◽  
Acoustic Waves ◽  
Elastic Half Space ◽  
Exact Expression ◽  
Ocean Bottom ◽  
Sediment Layer ◽  
Resonance Theory ◽  
Space Characteristic ◽  
Exact Calculations

An exact expression for the reflection coefficient is obtained with the Thomson–Haskell technique for the geoacoustical model of an ocean bottom consisting of an elastic homogeneous sediment layer overlying an elastic half-space. Characteristic equations for explicit determination of the position of each individual resonance contribution to the reflection coefficient are derived. Analytical expressions for the angular and frequency resonance positions are found. The resonance expression for the reflection coefficient is written in the form of a sum of resonance terms. Comparison between resonance theory and exact calculations for the elastic layer covering the elastic half-space is presented. The results of resonance formalism show excellent agreement with exact theory in all the cases.

An estimate of the properties of Love-type surface waves in a frictionally bonded layer

1979 ◽  
Vol 69 (2) ◽  
pp. 305-317
Author(s):  
Richard K. Miller
Keyword(s):  
Experimental Data ◽  
Frequency Dependence ◽  
Surface Waves ◽  
Half Space ◽  
Elastic Layer ◽  
Coulomb Friction ◽  
Analytical Approach ◽  
Elastic Half Space ◽  
High Frequencies ◽  
The Earth

abstract An approximate analytical approach is presented for determining the attenuation, dispersion, and intensity of motion at depth associated with Love-type surface waves in an elastic layer bonded by Coulomb friction to an elastic half-space. It is found that the dispersion curves are only slightly affected by a small amount of slip at the interface, but that the level of attenuation in the system increases considerably with the amplitude of motion. The results for the frequency dependence of the attenuation in the system are in basic agreement with experimental data on the attenuation of Love waves in the Earth (Jackson, 1971). The results for the intensity of motion at depth indicate a deterioration of bonding at high frequencies.

The efficiency of application of virtual cross-sections method and hypotheses MELS in problems of wave signal propagation in elastic waveguides with rough surfaces

2016 ◽  
pp. 3564-3575 ◽  
Author(s):  
Ara Sergey Avetisyan
Keyword(s):  
Half Space ◽  
Cross Sections ◽  
Classical Method ◽  
Signal Propagation ◽  
Elastic Half Space ◽  
Layered Systems ◽  
Surface Layers ◽  
Inhomogeneous Surface ◽  
Wave Signal ◽  
The Impact

The efficiency of virtual cross sections method and MELS (Magneto Elastic Layered Systems) hypotheses application is shown on model problem about distribution of wave field in thin surface layers of waveguide when plane wave signal is propagating in it. The impact of surface non-smoothness on characteristics of propagation of high-frequency horizontally polarized wave signal in isotropic elastic half-space is studied. It is shown that the non-smoothness leads to strong distortion of the wave signal over the waveguide thickness and along wave signal propagation direction as well.  Numerical comparative analysis of change in amplitude and phase characteristics of obtained wave fields against roughness of weakly inhomogeneous surface of homogeneous elastic half-space surface is done by classical method and by proposed approach for different kind of non-smoothness.

Guided Surface Waves on an Elastic Half Space

1971 ◽  
Vol 38 (4) ◽  
pp. 899-905 ◽  
Author(s):  
L. B. Freund
Keyword(s):  
Wave Propagation ◽  
Surface Wave ◽  
Surface Waves ◽  
Half Space ◽  
Body Wave ◽  
Three Dimensional ◽  
Elastic Half Space ◽  
Normal Displacement ◽  
Rigid Barrier ◽  
Wave Disturbances

Three-dimensional wave propagation in an elastic half space is considered. The half space is traction free on half its boundary, while the remaining part of the boundary is free of shear traction and is constrained against normal displacement by a smooth, rigid barrier. A time-harmonic surface wave, traveling on the traction free part of the surface, is obliquely incident on the edge of the barrier. The amplitude and the phase of the resulting reflected surface wave are determined by means of Laplace transform methods and the Wiener-Hopf technique. Wave propagation in an elastic half space in contact with two rigid, smooth barriers is then considered. The barriers are arranged so that a strip on the surface of uniform width is traction free, which forms a wave guide for surface waves. Results of the surface wave reflection problem are then used to geometrically construct dispersion relations for the propagation of unattenuated guided surface waves in the guiding structure. The rate of decay of body wave disturbances, localized near the edges of the guide, is discussed.

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