scholarly journals Characteristics of Very Low Frequency Sound Propagation in Full Waveguides of Shallow Water

Sensors ◽  
2020 ◽  
Vol 21 (1) ◽  
pp. 192
Author(s):  
Nansong Li ◽  
Hanhao Zhu ◽  
Xiaohan Wang ◽  
Rui Xiao ◽  
Yangyang Xue ◽  
...  
Keyword(s):  
Shallow Water ◽  
Wave Speed ◽  
Sound Propagation ◽  
Sea Water ◽  
Bottom Topography ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Propagation Characteristics ◽  
Sea Bottom ◽  
Proposed Model

This work is concerned with the characteristics of very low frequency sound propagation (VLF, ≤100 Hz) in the shallow marine environment. Under these conditions, the classical hypothesis of considering the sea bottom as a fluid environment is no longer appropriate, and the sound propagation characteristics at the sea bottom should be also considered. Hence, based on the finite element method (FEM), and setting the sea bottom as an elastic medium, a proposed model which unifies the sea water and sea bottom is established, and the propagation characteristics in full waveguides of shallow water can be synchronously discussed. Using this model, the effects of the sea bottom topography and the various geoacoustic parameters on VLF sound propagation and its corresponding mechanisms are investigated through numerical examples and acoustic theory. The simulation results demonstrate the adaptability of the proposed model to complex shallow water waveguides and the accuracy of the calculated acoustic field. For the sea bottom topography, the greater the inclination angle of an up-sloping sea bottom, the stronger the leak of acoustic energy to the sea bottom, and the more rapid the attenuation of the acoustic energy in sea water. The effect of a down-sloping sea bottom on acoustic energy is the opposite. Moreover, the greater the pressure wave (P-wave) speed in the sea bottom, the more acoustic energy remains in the water rather than leaking into the bottom; the influence laws of the density and the shear wave (S-wave) speed in the sea bottom are opposite.

scholarly journals Researches on very low frequency acoustic signal propagation characteristics in different shallow elastic wedge bottoms

2019 ◽  
Vol 283 ◽  
pp. 02003
Author(s):  
Jun Zhu ◽  
Hanhao Zhu ◽  
Jun Tang ◽  
Guangxue Zheng
Keyword(s):  
Acoustic Signal ◽  
Low Frequency ◽  
Signal Propagation ◽  
Acoustic Energy ◽  
Propagation Characteristics ◽  
The Finite Element Method ◽  
Very Low Frequency ◽  
Extremely Low Frequency ◽  
Elastic Bottom ◽  
Sloping Bottom

Targeted at the issue of extremely low-frequency (<100Hz) acoustic propagation in complex shallow elastic bottom environments. The influence law of different complex elastic bottoms on the acoustic signal propagation at very low frequency by acoustic energy flux has been analyzed with the simulation, which is based on the finite element method. The elastic bottoms which have been studied are the shallow horizontal elastic bottom, and the up-sloping and the down-sloping elastic bottom. The results show that the acoustic signal propagating in the up-sloping and down-sloping elastic bottom environments is more complex than that propagating in the horizontal elastic bottom, and the acoustic energy leaking into those elastic bottoms has very different influence on the acoustic signal propagation, especially in the up-sloping bottom.

High‐resolution, three‐dimensional measurements of low‐frequency sound propagation in shallow water

1998 ◽  
Vol 103 (5) ◽  
pp. 3028-3028 ◽  
Author(s):  
George V. Frisk ◽  
Kyle M. Becker ◽  
Laurence N. Connor ◽  
James A. Doutt ◽  
Cynthia J. Sellers
Keyword(s):  
High Resolution ◽  
Shallow Water ◽  
Sound Propagation ◽  
Three Dimensional ◽  
Low Frequency ◽  
Frequency Sound ◽  
Dimensional Measurements

High-Resolution, Three-Dimensional Measurements of Low-Frequency Sound Propagation in Shallow Water

1998 ◽  
Author(s):  
George V. Frisk ◽  
Kyle M. Becker ◽  
Laurence N. Connor ◽  
James A. Doutt ◽  
Cynthia J. Sellers
Keyword(s):  
High Resolution ◽  
Shallow Water ◽  
Sound Propagation ◽  
Three Dimensional ◽  
Low Frequency ◽  
Frequency Sound ◽  
Dimensional Measurements

Effect of Guide’s Acoustic Parameters on Vertical Directivity of the Marine Ambient Noise

2014 ◽  
Vol 577 ◽  
pp. 1207-1210
Author(s):  
Chun Xia Meng ◽  
Hao Mu ◽  
Gui Juan Li
Keyword(s):  
Shallow Water ◽  
Sound Speed ◽  
Ambient Noise ◽  
Sound Propagation ◽  
Sea Water ◽  
Surface Boundary ◽  
Ray Theory ◽  
Directivity Characteristic ◽  
Acoustic Parameters ◽  
Equipment Performance

The vertical directivity characteristic of ambient noise is one inherent characteristic of the ocean in shallow water. And it includes the information of guide’s acoustic characteristic information. The marine guide is composed of sea water; seabed and surface boundary, there into, the acoustic parameters of seabed are hardly obtained exactly. In this paper, the model of vertical directivity for ambient noise is established. Based on the ray theory of sound propagation, the influence of guide’s acoustic parameters which include sound speed, density and attenuation coefficient on vertical directivity of marine ambient noise is simulated. The results are propitious to analysis and command the characteristics of ambient noise, and valuable to accelerate the exertion of acoustic equipment performance.

Detection of Objects Buried in the Sea Bottom with the Use of Parametric Echosounder

2013 ◽  
Vol 38 (1) ◽  
pp. 99-104 ◽  
Author(s):  
Eugeniusz Kozaczka ◽  
Grazyna Grelowska ◽  
Sławomir Kozaczka ◽  
Wojciech Szymczak
Keyword(s):  
Low Frequency ◽  
Point Of View ◽  
Acoustic Energy ◽  
Sidescan Sonar ◽  
Main Task ◽  
Sound Sources ◽  
Sea Bottom ◽  
Detection Of Objects ◽  
Beam Patterns

Abstract The paper contains results of a in situ research main task of which was to detect objects buried, partially or completely, in the sea bottom. Object detecting technologies employing acoustic wave sources based on nonlinear interaction of elastic waves require application of parametric sound sources. Detection of objects buried in the sea bottom with the use of classic hydroacoustic devices such as the sidescan sonar or multibeam echosounder proves ineffective. Wave frequencies used in such devices are generally larger than tens of kHz. This results in the fact that almost the whole acoustic energy is reflected from the bottom. On the other hand, parametric echosounders radiate waves with low frequency and narrow beam patterns which ensure high spatial resolution and allows to penetrate the sea bottom to depths of the order of tens of meters. This allows to detect objects that can be interesting, among other things, from archaeological or military point of view.

scholarly journals A Mathematical Model of Stratified Geophysical Fluid Flows Over Variable Bottom Topography

2020 ◽  
Vol 3 (3b) ◽  
pp. 112-137
Author(s):  
SI Iornumbe ◽  
T Tivde ◽  
RA Chia
Keyword(s):  
Mathematical Model ◽  
Shallow Water ◽  
Wave Motion ◽  
Wave Speed ◽  
Bottom Topography ◽  
Nonlinear Partial Differential Equations ◽  
Fluid Flows ◽  
Variable Bottom ◽  
Conservation Of Momentum ◽  
Model Equations

In this paper, a mathematical model of stratified geophysical fluid flow over variable bottom topography was derived for shallow water. The equations are derived from the principles of conservation of mass and conservation of momentum. The force acting on the fluid is gravity, represented by the gravitational constant. A system of six nonlinear partial differential equations was obtained as the model equations. The solutions of these models were obtained using perturbation method. The presence of the coriolis force in the shallow water equations were shown as the causes of the deflection of fluid parcels in the direction of wave motion and causes gravity waves to disperse. As water depth decreases due to varied bottom topography, the wave amplitude were shown to increase while the wavelength and wave speed decreases resulting in overturning of the wave. The results are presented graphically.

UNDERWATER CHARACTER AND HORIZONTAL PROPAGATION OF AIR-GUN SIGNALS

1998 ◽  
Vol 38 (1) ◽  
pp. 708
Author(s):  
J.D. Penrose ◽  
R.D. McCauley
Keyword(s):  
Shallow Water ◽  
Sound Propagation ◽  
Model Performance ◽  
Low Frequency ◽  
Propagation Model ◽  
Seismic Survey ◽  
Biological Research ◽  
Water Characteristics ◽  
Air Gun ◽  
Development Paths

This paper describes work carried out as part of an APPEA/ERDC supported project, Investigation of the Environmental Effects of Offshore Seismic Survey Activities. In this project biological research concerning the interaction of acoustic signals with marine organisms is linked to sound propagation studies focussed on frequencies, water characteristics and seabed types of relevance to offshore exploration practice. A key feature of the propagation component of the project concerns the extent to which lateral propagation of airgun signals in the water column may be adequately predicted.The study of acoustic propagation in the sea is an integral part of both scientific and defence enquiry. In recent years, the comparatively complex issue of propagation in shallow water, here considered as involving depths of 200 m or less, has received increasing attention. The literature concerning low frequency propagation in shallow water has features in common with seismic literature. Different emphases, however, notably concerning applications, the role of shear waves in solids and the geometry of the propagation environment have largely resulted in separate development paths being adopted by these two related fields. This paper summarises the range of modelling approaches available to predict shallow water propagation, some key issues influencing propagation and the influence of water and seabed parameters on model performance.An illustration of propagation model performance is provided in this paper by comparing the output from a normal mode model KRAKEN, with experimental data obtained using a mono-frequency source in shallow water in Cleveland Bay, Queensland. This offers an opportunity to assess propagation in a complex and, in acoustic terms, poorly classified environment. These results will be complemented in the conference presentation by airgun data obtained in Exmouth Gulf, Western Australia.

Sound Field Modeling with Bottom Reflective Parameters (P,Q) Based on Parabolic Equation

2020 ◽  
Vol 28 (04) ◽  
pp. 2050029
Author(s):  
C. J. Zhang ◽  
J. R. WU ◽  
Z. D. Zhao ◽  
L. Ma ◽  
E. C. Shang
Keyword(s):  
Sound Propagation ◽  
Transmission Loss ◽  
Low Frequency ◽  
Sound Field ◽  
Propagation Models ◽  
Acoustical Properties ◽  
Sea Bottom ◽  
Model Independent ◽  
The Mean ◽  
Parameter Coupling

Acoustical properties of the sea bottom can be described using geoacoustic (GA) models. Most existing propagation models use GA parameters as the bottom properties. It is difficult to obtain GA parameters for a layered bottom because of inter parameter coupling. These problems can be solved by inverting the model-independent reflective parameters P and Q. For a multilayered bottom, a sound field computation model, RamPQ, is developed using the mapping of GA and (P, Q) spaces. The mean square error of the transmission loss in numerical simulations and experimental data for low-frequency sound propagation are employed to validate RamPQ and demonstrate the performance of the model.

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