ACOUSTIC WAVES IN OCEAN SEDIMENTS

Geophysics ◽  
1977 ◽  
Vol 42 (4) ◽  
pp. 715-725 ◽  
Author(s):  
Robert D. Stoll
Keyword(s):  
Acoustic Waves ◽  
Unconsolidated Sediments ◽  
Physical Parameters ◽  
High Attenuation ◽  
Viscous Losses ◽  
Dilatational Wave ◽  
Simple Extrapolation ◽  
Sediment Layers ◽  
Refracted Waves ◽  
Skeletal Frame

An acoustic model for unconsolidated sediments is used to study velocity, attenuation, and reflection in ocean sediments. The model predicts attenuation and wave velocity on the basis of physical parameters such as porosity, grain size, permeability, and effective stress. Two mechanisms for energy loss are included in the model; one accounts for intergranular losses in the skeletal frame and the other for viscous losses in the porewater as it moves relative to the frame. As a result, in certain sediments such as sands and silts, attenuation is found to vary in a manner quite different from the usual dependency on the first power of frequency that is almost universally assumed. Furthermore, the amplitudes of reflected and refracted waves at boundaries between water and sediment or between sediment layers become frequency dependent. In the immediate vicinity of such boundaries, a significant amount of energy may be lost owing to the generation of a second kind of dilatational wave with extremely high attenuation. The model is able to handle variations in a variety of different physical parameters such as overburden stress, fluid compressibility, and stiffness of the sediment frame owing to lithification. For this reason it is well suited for use in predicting changes in velocity and attenuation with depth in real sediments where nonhomogeneous changing conditions are the rule and simple extrapolation of experimental data is not possible.

Shallow near-surface effects

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. T221-T231 ◽  
Author(s):  
Christine E. Krohn ◽  
Thomas J. Murray
Keyword(s):  
Time Delay ◽  
Velocity Gradient ◽  
P Wave ◽  
Unconsolidated Sediments ◽  
P Waves ◽  
Large Computer ◽  
Near Surface ◽  
S Waves ◽  
High Attenuation ◽  
Pulse Broadening

The top 6 m of the near surface has a surprisingly large effect on the behavior of P- and S-waves. For unconsolidated sediments, the P-wave velocity gradient and attenuation can be quite large. Computer modeling should include these properties to accurately reproduce seismic effects of the near surface. We have used reverse VSP data and computer simulations to demonstrate the following effects for upgoing P-waves. Near the surface, we have observed a large time delay, indicating low velocity ([Formula: see text]), and considerable pulse broadening, indicating high attenuation ([Formula: see text]). Consequently, shallowly buried geophones have greater high-frequency bandwidth compared with surface geophones. In addition, there is a large velocity gradient in the shallow near surface (factor of 10 in 5 m), resulting in the rotation of P-waves to the vertical with progressively smaller amplitudes recorded on horizontal phones. Finally, we have found little indication of a reflection or ghost from the surface, although downgoing reflections have been observed from interfaces within the near surface. In comparison, the following have been observed for upgoing S-waves: There is a small increase in the time delay or pulse broadening near the surface, indicating a smaller velocity gradient and less change in attenuation. In addition, the surface reflection coefficient is nearly one with a prominent surface ghost.

scholarly journals The importance of sound velocity determination for bathymetric survey

ACTA IMEKO ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 46
Author(s):  
Pier Paolo Amoroso ◽  
Claudio Parente
Keyword(s):  
Sound Velocity ◽  
Acoustic Waves ◽  
Physical Parameters ◽  
Ligurian Sea ◽  
Data Set ◽  
Correct Operation ◽  
Column Temperature ◽  
Bathymetric Survey ◽  
Depth Measurement

Bathymetric surveys are carried out whenever there is a need to know the exact morphological trend of the seabed. For a correct operation of the echo sounder, which uses the principle of acoustic waves to scan the bottom and determine the depth, it is important to accurately determine the sound velocity in water, as it varies according to specific parameters (Density, Temperature, and Pressure). In this work, we want to analyse the role of sound velocity determination in bathymetric survey and its impact on the accuracy of depth measurement. The experiments are conducted on data set provided by “Istituto Idrografico della Marina Militare Italiana” (IIM), the official Hydrographic Office for Italy, and acquired in the Ligurian sea. In our case, the formulas of Chen & Millero (UNESCO), Medwin, and Mackenzie were applied. The introduction of errors on chemical-physical parameters of the water column (Temperature, Pressure, Salinity, Depth) simulating inaccurate measurements, produces considerable impacts on sound velocity determination and subsequently a decrease of the depth value accuracy. The results remark the need to use precise probes and accurate procedures to obtain reliable depth data.

scholarly journals Fiber optic sensors for environmental monitoring

2019 ◽  
pp. 527-530
Author(s):  
Leonid B. Likumovich ◽  
Andrei V. Medvedev ◽  
Oleg I. Kotov ◽  
Sergei I. Markov ◽  
Vladimir M Nikolaev
Keyword(s):  
Signal Processing ◽  
Optical Fibers ◽  
Acoustic Waves ◽  
Phase Modulation ◽  
Fiber Optic ◽  
Fiber Optic Sensor ◽  
Sensor Technology ◽  
Maximum Efficiency ◽  
Physical Parameters ◽  
Signal Processing Technique

Sensors discussed are designed to register acoustic waves and micro deformations in ground. Sensor technology is based on phase modulation that occurs in optical fiber when it is influenced by outside mechanical disturbance. In our paper we consider two possible ways of registration this phase modulation: fiber optic interferometer and mode to mode interference. These methods can be incorporated with various signal processing technique to obtain maximum efficiency of fiber optic sensor under the certain conditions. It is well known that optical fibers are widely used to transmit high band signals for long distances. In this case fiber sensitivity to environmental disturbances is a bad thing. But from other side the disturbances change propagating light properties (intensity, phase, polarization, etc.). This changes can be registered in the output light and after appropriate signal processing will give information about the parameters of the outside influence on the fiber. This is an idea in brief how optical fibers can be used as physical parameters sensors.

scholarly journals Nonlinear dynamical properties of solitary wave solutions for Zakharov-Kuznetsov equation in a multicomponent plasma

2021 ◽  
Vol 67 (6 Nov-Dec) ◽  
Author(s):  
U.M. Abdelsalam
Keyword(s):  
Solitary Wave ◽  
Acoustic Waves ◽  
Traveling Wave Solutions ◽  
Reductive Perturbation Method ◽  
Physical Parameters ◽  
Nonlinear Dynamical ◽  
Multicomponent Plasma ◽  
Wave Solutions ◽  
Laboratory Plasmas ◽  
Component Plasma

Using the reductive perturbation method, we have derived the Zakharov-Kuznetsov (ZK) equation for a multi-component plasma model consisting of electrons, positrons and the uid ions with positive and negative charges. The extended homogenous balance method has been applied to obtain the soliton solution in addition to many traveling wave solutions. various physical parameters have different effects on the profile of the solitary wave pulses which can show the propagation of the ion acoustic waves in laboratory plasmas and many astrophysical plasma systems as in Earth's ionosphere.

scholarly journals An Efficient Routing Protocol Based on Stretched Holding Time Difference for Underwater Wireless Sensor Networks

Sensors ◽  
2019 ◽  
Vol 19 (24) ◽  
pp. 5557 ◽  
Author(s):  
Zahid Wadud ◽  
Khadem Ullah ◽  
Abdul Baseer Qazi ◽  
Sadeeq Jan ◽  
Farrukh Aslam Khan ◽  
...  
Keyword(s):  
Energy Consumption ◽  
Routing Protocols ◽  
Acoustic Waves ◽  
Time Difference ◽  
Holding Time ◽  
Source Node ◽  
Delivery Ratio ◽  
Optical Waves ◽  
High Attenuation ◽  
Hidden Terminal

Underwater Wireless Sensors Networks (UWSNs) use acoustic waves as a communication medium because of the high attenuation to radio and optical waves underwater. However, acoustic signals lack propagation speed as compared to radio or optical waves. In addition, the UWSNs also pose various intrinsic challenges, i.e., frequent node mobility with water currents, high error rate, low bandwidth, long delays, and energy scarcity. Various UWSN routing protocols have been proposed to overcome the above-mentioned challenges. Vector-based routing protocols confine the communication within a virtual pipeline for the sake of directionality and define a fixed pipeline radius between the source node and the centerline station. Energy-Scaled and Expanded Vector-Based Forwarding (ESEVBF) protocol limits the number of duplicate packets by expanding the holding time according to the propagation delay, and thus reduces the energy consumption via the remaining energy of Potential Forwarding Nodes (PFNs) at the first hop. The holding time mechanism of ESEVBF is restricted only to the first-hop PFNs of the source node. The protocol fails when there is a void or energy hole at the second hop, affecting the reliability of the system. Our proposed protocol, Extended Energy-Scaled and Expanded Vector-Based Forwarding Protocol (EESEVBF), exploits the holding time mechanism to suppress duplicate packets. Moreover, the proposed protocol tackles the hidden terminal problem due to which a reasonable reduction in duplicate packets initiated by the reproducing nodes occurs. The holding time is calculated based on the following four parameters: (i) the distance from the boundary of the transmission area relative to the PFNs’ inverse energy at the 1st and 2nd hop, (ii) distance from the virtual pipeline, (iii) distance from the source to the PFN at the second hop, and (iv) distance from the first-hop PFN to its destination. Therefore, the proposed protocol stretches the holding time difference based on two hops, resulting in lower energy consumption, decreased end-to-end delay, and increased packet delivery ratio. The simulation results demonstrate that compared to ESEVBF, our proposed protocol EESEVBF experiences 20.2 % lesser delay, approximately 6.66 % more energy efficiency, and a further 11.26 % reduction in generating redundant packets.

scholarly journals Peculiarities of surface acoustic waves, propagation in structures with functionally graded piezoelectric materials, coating from different ceramics on the basis of PZT

2020 ◽  
Vol 10 (01n02) ◽  
pp. 2060017
Author(s):  
T. I. Belyankova ◽  
E. I. Vorovich ◽  
V. V. Kalinchuk ◽  
O. M. Tukodova
Keyword(s):  
Acoustic Waves ◽  
Piezoelectric Materials ◽  
Surface Acoustic Waves ◽  
Functionally Graded ◽  
Ferroelectric Ceramics ◽  
Physical Parameters ◽  
Coating Materials ◽  
Homogeneous Half Space ◽  
Functionally Graded Piezoelectric Materials ◽  
Piezoelectric Structure

A model of a piezoelectric structure with an inhomogeneous coating is considered. The structure is a homogeneous half-space made of PZT-5H ferroelectric ceramics with a functionally graded coating. The properties of coating vary continuously in thickness from parameters of one material to parameters of another material in a continuously nonmonotonic or piecewise-continuous manner. As coating materials, various combinations of ceramics of different stiffness based on PZT are considered. Using the example of the problem of the propagation of sh-waves in a piezoelectric structure, we studied the influence of the ratio of the physical parameters of the coating materials, the localization region, and the size of the transition zone of one material to another on the propagation features of surface acoustic waves (SAWs) and the structure of the wave field.

scholarly journals EXPRESS: Acoustic Steering Using Thermally Induced Optical Reflection of Sound (THORS)

2021 ◽  
pp. 000370282110046
Author(s):  
Daniel S. Kazal ◽  
An Ngo ◽  
Ellen L Holthoff ◽  
Brian Cullum
Keyword(s):  
Acoustic Waves ◽  
Laser Light ◽  
Local Density ◽  
Incident Angle ◽  
Physical Parameters ◽  
Thermal Gradients ◽  
Acoustic Frequency ◽  
Thermally Induced ◽  
Acoustic Reflection ◽  
Angle Of Reflection

Using the recently discovered THORS phenomenon, it is possible to generate optically induced, local density barriers in air by the absorption of intense, modulated laser light (the THORS phenomenon), which results in abrupt differences in compressibility of the air at these barriers that can efficiently reflect incident acoustic waves. In this note, we demonstrate the ability to optically manipulate and reflect acoustic waves in air as well as optimize the functional parameters (optical modulation and acoustic frequency) and characterize the effects of common physical parameters, including localized thermal gradients and incident angle of reflection on the efficiency of the resulting acoustic reflection. Finally, the ability to efficiently steer acoustic waves around a physical obstruction using THORS is also demonstrated.

Oblique ion acoustic excitations in an ultra-relativistic degenerate dense magnetoplasma

2017 ◽  
Vol 95 (7) ◽  
pp. 655-661 ◽  
Author(s):  
Ata-ur Rahman ◽  
A. Qamar ◽  
S. Naseer ◽  
S.N. Naeem
Keyword(s):  
Acoustic Waves ◽  
Nonlinear Propagation ◽  
Physical Parameters ◽  
Ion Acoustic Waves ◽  
Linear Dispersion ◽  
Ion Acoustic ◽  
Ion Acoustic Solitons ◽  
Arbitrary Amplitude ◽  
Pseudopotential Approach ◽  
Acoustic Excitations

The linear and nonlinear propagation of ion acoustic waves is considered in a degenerate magnetoplasma, composed of relativistic degenerate electrons and an inertial ion fluid. A linear dispersion relation is derived in the linear approximation. The Sagdeev pseudopotential approach is used to investigate the properties of arbitrary amplitude, obliquely propagating ion acoustic solitary waves. The expression for the lower and upper Mach numbers for the existence of magnetized ion acoustic solitons has also been derived. The significant influence on the properties of soliton structures of relevant physical parameters, such as the plasma number density, the obliqueness (the angle between soliton propagation direction and magnetic field), and the soliton speed is also investigated. At the end, analytical results are supplemented through numerical analysis by using typical representative parameters consistent with degenerate and ultra-relativistic magnetoplasmas of astrophysical regimes.

scholarly journals Bubbly Water as a Natural Metamaterial of Negative Bulk-Modulus

Crystals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 457 ◽  
Author(s):  
Luan
Keyword(s):  
Dispersion Relation ◽  
Acoustic Waves ◽  
Expansion Method ◽  
Effective Modulus ◽  
Effective Density ◽  
Effective Theory ◽  
Water Medium ◽  
Long Wavelength ◽  
High Attenuation ◽  
Wide Range

In this study, an oscillator model of bubble-in-water is proposed to analyze the effective modulus of low-concentration bubbly water. We show that in a wide range of wave frequency the bubbly water acquires a negative effective modulus, while the effective density of the medium is still positive. These two properties imply the existence of a wide acoustic gap in which the propagation of acoustic waves in this medium is prohibited. The dispersion relation for the acoustic modes in this medium follows Lorentz type dispersion, which is of the same form as that of the phonon-polariton in an ionic crystal. Numerical results of the gap edge frequencies and the dispersion relation in the long-wavelength regime based on this effective theory are consistent with the sonic band results calculated with the plane-wave expansion method (PWEM). Our theory provides a simple mechanism for explaining the long-wavelength behavior of the bubbly water medium. Therefore, phenomena such as the high attenuation rate of sound or acoustic Anderson localization in bubbly water can be understood more intuitively. The effects of damping are also briefly discussed. This effective modulus theory may be generalized and applied to other bubble-in-soft-medium type sonic systems.

Effect of Dust Ion Collision on Dust Ion Acoustic Solitary Waves for Nonextensive Plasmas in the Framework of Damped Korteweg–de Vries–Burgers Equation

2019 ◽  
Vol 74 (10) ◽  
pp. 861-867 ◽  
Author(s):  
Niranjan Paul ◽  
Kajal Kumar Mondal ◽  
Prasanta Chatterjee
Keyword(s):  
Acoustic Waves ◽  
Solitary Wave Solution ◽  
Perturbation Technique ◽  
Viscosity Coefficient ◽  
Travelling Wave ◽  
Physical Parameters ◽  
Charged Dust ◽  
Ion Acoustic ◽  
De Vries ◽  
Ion Collision

AbstractAnalytical solitary wave solution of the dust ion acoustic waves (DIAWs) is studied in the framework of the damped Korteweg–de Vries–Burgers (DKdVB) equation in an unmagnetised collisional dusty plasma consisting of negatively charged dust grain, positively charged ions, q-nonextensive electrons, and neutral particles. Using Reductive Perturbation Technique, the DKdVB equation is obtained for DIAWs. The effects of different physical parameters such as dust ion collision frequency parameter (\({\nu_{id0}}\)), viscosity coefficient (η10), the entropic index (q), the speed of the travelling wave (M0), and the ratio between the unperturbed densities of the electrons and ions (μ) on the analytical solution of DIAWs are observed. The results of the present article may have applications in laboratory and space plasmas.

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