A Comparison of Seismic and Hydroacoustic Measurements at Very Low Frequencies in Different Shallow Water Areas

1986 ◽  
pp. 653-662 ◽  
Author(s):  
B. Schmalfeldt
Keyword(s):  
Shallow Water ◽  
Low Frequencies ◽  
Hydroacoustic Measurements

Experimental Study of Slow-Drift Ship Motions in Shallow Water Random Waves

2011 ◽  
Author(s):  
Carl Trygve Stansberg ◽  
Trygve Kristiansen
Keyword(s):  
Spectral Analysis ◽  
Shallow Water ◽  
Transfer Functions ◽  
Second Order ◽  
Ship Motions ◽  
Random Wave ◽  
Random Waves ◽  
Low Frequencies ◽  
Wave Basin ◽  
Drift Forces

Slowly varying motions and drift forces of a large moored ship in random waves at 35m water depth are investigated by an experimental wave basin study in scale 1:50. A simple horizontal mooring set-up is used. A second-order wave correction is applied to minimize “parasitic” long waves. The effect on the ship motion from the correction is clearly seen, although less in random wave spectra than in pure bi-chromatic waves. Empirical quadratic transfer functions (QTFs) of the surge drift force are found by use of cross-bi-spectral analysis, in two different spectra have been obtained. The QTF levels increase significantly with lower wave frequencies (except at the diagonal), which is special for finite and shallow water. Furthermore, the QTF levels frequencies at low frequencies increase significantly out from the QTF diagonal. Thus Newman’s approximation should preferrably not be used in these cases. Using the LF waves as a direct excitation in a “linear” ship force analysis gives random records that compare reasonably well with those from the cross-bi-spectral analysis. This confirms the idea that the drift forces in shallow water are closely correlated to the second-order potential, and thereby by the second-order LF waves.

Sediment sound speed inversion at low frequencies in shallow water

2017 ◽  
Vol 142 (4) ◽  
pp. 2621-2621
Author(s):  
Zoi-Heleni Michalopoulou
Keyword(s):  
Shallow Water ◽  
Sound Speed ◽  
Low Frequencies

Weak quadratic interactions of two-dimensional waves

1971 ◽  
Vol 50 (1) ◽  
pp. 107-132 ◽  
Author(s):  
Young Yuel Kim ◽  
Thomas J. Hanratty
Keyword(s):  
Shallow Water ◽  
Deep Water ◽  
Wave Train ◽  
Water Layer ◽  
Rate Of Change ◽  
Two Dimensional ◽  
Low Frequencies ◽  
Resonant Interactions ◽  
Water Layers ◽  
Phase Angles

This paper reports on weak quadratic interactions which can occur with two-dimensional waves on shallow water layers and in the capillary-gravity range on deep water layers. It supplies experimental support of theoretical predictions for resonant interactions, but, perhaps of more significance, it explores in detail interactions which occur under conditions near resonance.Waves of approximately sinusoidal form are introduced on the surface of water in a long rectangular tank. For deep water a rapid distortion in the sinusoidal wave and sometimes additional crests are observed because of energy exchange among the first, second and third harmonics at frequencies where both surface tension and gravity are important (7·5–13 c/s). An even greater exchange of energy can be observed on shallow water layers at low frequencies. For example, a wave train with seven secondary crests can be observed when the wave maker is operated at 3·04 c/s in a water layer of 0·65 cm.Measured amplitudes and phase angles of the Fourier components of the wave train are described by a system of equations using only quadratic interactions among participating harmonics. The exchange of energy among Fourier components under certain conditions is explained in terms of the rate of change of relative phase angles of the different harmonics.

Predictability of acoustic intensity in shallow water at low frequencies using parabolic approximations

1991 ◽  
Vol 89 (4B) ◽  
pp. 1896-1896 ◽  
Author(s):  
R. J. Cederberg ◽  
W. L. Seigmann ◽  
M. J. Jacobson ◽  
W. M. Carey
Keyword(s):  
Shallow Water ◽  
Acoustic Intensity ◽  
Low Frequencies

Using Ambient Noise to Inverse Geo-Acoustic Parameters

2012 ◽  
Vol 588-589 ◽  
pp. 851-855
Author(s):  
Chun Xia Meng ◽  
Gui Juan Li ◽  
Liang Zhang
Keyword(s):  
Shallow Water ◽  
Ambient Noise ◽  
Theoretical Study ◽  
Ocean Surface ◽  
Ray Theory ◽  
Acoustic Parameters ◽  
Low Frequencies ◽  
Research Results ◽  
Noise Data ◽  
Stratified Ocean

This paper presents a theoretical study of the vertical coherence of ocean ambient noise as the source is the windy ocean surface on the ray theory. At low frequencies less than 2 kHz, the sensitivity of stratified fluid seabed to the vertical coherence of ambient noise in shallow water is analyzed under the condition of distance-irrespective stratified ocean. Using ambient noise data from Chinese north shallow water seabed geo-acoustics parameters are obtained, and the research results show that the inverted method is effective.

scholarly journals Horizontal Refraction of Acoustic Waves in Shallow-Water Waveguides Due to an Inhomogeneous Bottom Structure

2021 ◽  
Vol 9 (11) ◽  
pp. 1269
Author(s):  
Andrey Lunkov ◽  
Danila Sidorov ◽  
Valery Petnikov
Keyword(s):  
Shallow Water ◽  
Parabolic Equations ◽  
Acoustic Waves ◽  
Sound Propagation ◽  
Transmission Loss ◽  
Three Dimensional ◽  
Transitional Region ◽  
Wave Effect ◽  
Low Frequencies ◽  
Horizontal Refraction

Three-Dimensional (3-D) sound propagation in a shallow-water waveguide with a constant depth and inhomogeneous bottom is studied through numerical simulations. As a model of inhomogeneity, a transitional region between an acoustically soft and hard bottom is considered. Depth-averaged transmission loss simulations using the “horizontal rays and vertical modes” approach and mode parabolic equations demonstrate the horizontal refraction of sound in this region, even if the water column is considered homogeneous. The observed wave effect is prominent at low frequencies, at which the water depth does not exceed a few acoustic wavelengths. The obtained results within the simplified model are verified by the simulations for a real seabed structure in the Kara Sea.

Shallow water bottom scattering strength at low frequencies

1995 ◽  
Vol 97 (5) ◽  
pp. 3385-3385 ◽  
Author(s):  
Peter G. Cable ◽  
Mike Steele ◽  
James O’Connor
Keyword(s):  
Shallow Water ◽  
Low Frequencies ◽  
Scattering Strength ◽  
Water Bottom
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