Sea Surface Effects on Sound Scattering in the Persian Gulf Region Based on Empirical Relations

In this paper, sound scattering from the sea surface in the Persian Gulf region is investigated. Chapman-Harris and Ogden-Erskine empirical relations coupled with perturbation theory are implemented. Based on the Ogden and Erskine＇s experiments, sound scattering from the sea surface has three different regimes in which two mechanisms of surface roughness and subsurface bubble clouds are involved. Ogden-Erskine＇s scattering relation which consists of perturbation theory and Chapman-Harris＇s scattering terms are verified by the experimental data of Critical Sea Tests 7. Subsequently, wind speed in the Persian Gulf is provided based on three data bases of Arzanah station, ERA40, and PERGOS. Accordingly, surface scattering strength in the Persian Gulf region is calculated at different grazing angles, frequencies and provided wind speeds. Based on the resulted values of scattering strength, scattered intensity from the sea surface is also studied. These studies indicate that both scattering strength and scattered intensity generally increase as grazing angle, frequency and wind speed increase.

A Significant Look at the Effects of Persian Gulf Environmental Conditions on Sound Scattering Based on Small Perturbation Method

The main goal of this paper is to investigate sound scattering from the sea surface, by Kuo＇s small perturbation method （SPM）, in the Persian Gulf＇s environmental conditions. Accordingly the SPM method is reviewed, then it is demonstrated how it can accurately model sound scattering from the sea surface. Since in Kuo＇s approach, the effects of surface roughness and sub-surface bubble plumes on incident sounds can be studied separately, it is possible to investigate the importance of each mechanism in various scattering regimes. To conduct this study, wind and wave information reported by Arzanah station as well as some numerical atmospheric models for the Persian Gulf are presented and applied to examine sound scattering from the sea surface in the Persian Gulf region. Plots of scattering strength by Kuo＇s SPM method versus grazing angle for various frequencies, wave heights, and wind speeds are presented. The calculated scattering strength by the SPM method for various frequencies and wind speeds are compared against the results of critical sea tests 7 （CST-7）. The favorable agreement achieved for sound scattering in the Persian Gulf region is indicative of the fact that the SPM method can quite accurately model and predict sound scattering from the sea surface.

Sound scattering from underwater elastic spherical shell covered with multilayered medium approximated acoustic cloak

The anechoic performance and mechanism of underwater elastic spherical shell covered with coating are studied at low frequencies.The acoustic cloak is anisotropic material,which can be designed with homogeneous isotropic materials on the basis of effective medium approximation theory.The analytic expression of scattering acoustic field from the shell covered with multilayered medium is formulated and the scattering form function,resonance mode,acoustic field distribution are computed,the scattering characteristics and mechanism of transmission are analyzed.The results show that the direction of sound transmission inside the multilayered medium is changed,the acoustic field is deflected gradually,and the acoustic energy flux is guided around the target,which reduces the scattering intensity at low frequencies,the acoustic intensity of target＇s surface is very weak.Excepting the first resonance peak in spectrum produced by the zero order partial wave,the other resonance modes of elastic spherical shell are not excitated and the multilayered medium can suppress the resonance of the spherical shell effectively.

Ocean circumstance effects on the sound scattering of thermocline

This paper is based on the proven statement that sound scattering in shallow sea de pends mainly on thermocline, and is to analyze the contribution from sound scattering by plankton, and the effects of waves and other parameters of oceanic condition, on fluctuations of travelling time and amplitude of received signals. The results showed that the effect of plankton density distribution only appeared as a background interference. And main component of in terference is come from wind wave and swell.

An experimental study on the sound scattering of the ship's wakes

The experiments for the sound scattering of the ship wakes are introduced in this article. The wakes are detected in both horizon and vertical in lake trials and its traces are shown in display model A or B, Its size and sound scattering strength are measured also. The scattering signals are analysed with the instananeous frequency sequence statistics methods

Acoustic radiation force on a multilayered sphere in a Gaussian standing field

We develop a model for calculating the radiation force on spherically symmetric multilayered particles based on the acoustic scattering approach.An expression is derived for the radiation force on a multilayered sphere centered on the axis of a Gaussian standing wave propagating in an ideal fluid,The effects of the sound absorption of the materials and sound wave on acoustic radiation force of a multilayered sphere immersed in water are analyzed,with particular emphasis on the shell thickness of every layer,and the width of the Gaussian beam.The results reveal that the existence of particle trapping behavior depends on the choice of the non-dimensional frequency ka,as well as the shell thickness of each layer.This study provides a theoretical basis for the development of acoustical tweezers in a Gaussian standing wave,which may benefit the improvement and development of acoustic control technology,such as trapping,sorting,and assembling a cell,and drug delivery applications.

Pentamode-Based Coding Metasurface for Underwater Acoustic Stealth

Coding metasurface draws amounts of research interests due to its potential for achieving sophisticated functions in wave manipulation by using simple logical unit cells with out-of-phase responses. In this paper, we present a novel acoustic coding metasurface structure for underwater sound scattering reduction based on pentamode metamaterials. The metasurface is composed of two types of hexagonal pentamode unit cells with phase responses of 0 and π respectively. The units are arranged in random 1-bit coding sequence to achieve low-scattering underwater acoustic stealth effect. Full-wave simulation results are in good accordance with the theoretical expectation. The optimized arrangement resulted in the distribution of scattered underwater acoustic waves and suppression of the far field scattering coefficient over a wide range of incident angles. We show that pentamode-based coding metasurface provides an efficient scheme to achieve underwater acoustic stealth by ultrathin structures.

Development of a New Target Simulator

The.functions of a general target simulator are too few to provide the sonar equipmentand sonar signal-Processing algorithm with a set of integrated experimental data. In this paper anew universal target simulator is developed based on the sound scattering theory. It can produceintegrated simulated data for the various existing sonar equipment and the usual sonar signalprocessing algorithms. The means and efficiency of detection of sonar equipment are improvedby this new simulator In the meantime, this new device stimulates the research on sonar signalprocessing algorithms.

STUDY OF WING SHIELDING EFFECT OF PROPELLER AIRCRAFT

The calculation of wing shielding effect starts from solving Ffowcs Williams and Hawkings equation without quadrupole source in time domain. The sound scattering of the wing and fuselage which are surrounded by a multi propeller sound field is modeled as a second sound source. A program is developed to calculate the acoustical effects of the rigid fuselage as well as wings with arbitrary shape in motion at low Mach number. As an example, the numerical calculation of the wing shielding of Y12 aircraft with an approximate shape is presented. The result manifests clearly the shielding effect of the wing on the fuselage and the approach is more efficient than that published before.

Modification to first-order Born approximation for improved prediction of scattered sound from weakly scattering objects

When deriving the Fourier diffraction theorem based on the first-order Born approximation,the difference between wave number of the scattering object and that of the surrounding medium is ignored,causing substantial errors in sound scattering prediction.This paper modifies the Born approximation by taking into account the amplitude and phase changes between the scattering object and the water due to the wave number difference.By changing the radius and center position of the sampling circle in the Fourier domain,accuracy of the predicted sound scattering is improved.With the modified Born approximation,the computed far-field directional pattern of the scattered sound from a circular cylinder is in good agreement with the rigorous solution.Numerical calculations for several objects with different shapes are used to show applicability and effectiveness of the proposed method.

Theoretical analysis for sound wave scattering by parallel cylindrical tubes in boilers

Although the sonic soot cleaning techniques have been applied in boilers in power plants, petrochemical works and general industries world wide, most of the correlated basic problems have not been well solved yet. By using Helmholtz integral equation, sound wave scattered by heat-exchanger tubes is numerically calculated. Sound field distribution characteristics on the tube surfaces and around the tube group is obtained. The results can be applied to the development of sonic soot cleaning techniques in boilers.

Sound pulse scattering from an edge of thick elastic plates:experimental and numerical investigations

A sound pulse scattering from an edge of thick plates is experimentally and numerically investigated. Beside the edge diffracted signal, waves radiated by the plate that are excited from the plate edge are also detected in the diffraction process. The phenomena are examined by the elastic plate theory and agrecment is observed. The finite difference method (FDM) is used in the numerical calculation. Field distribution around the plate edge and fields at certain points as functions of time are displayed. Comparison is made with experiments. It is found that the grid size of FDM formulation may affect accuracy of computation significantly, but the results show the same phenomena as that measured in experiments.

SCATTERING OF SOUND FROM A PAIR OF FINITE CYLINDERS——A PRELIMINARY STUDY APPLICABLE TO SOUND INTENSITY TECHNIQUE

In this paper, it is studied that the scattering effect is caused by microphones itself, on both wave magnitude and phase. The experimental method was found difficult to do this. We will apply the Boundary Element Method(BEM) to the problem and explain the results obtained. The numerical method seems to be a powerful tool in this situation.

Time-Harmonic Acoustic Scattering in a Complex Flow:A Full Coupling Between Acoustics and Hydrodynamics

For the numerical simulation of time harmonic acoustic scattering in a complex geometry,in presence of an arbitrary mean flow,the main difficulty is the coexistence and the coupling of two very different phenomena:acoustic propagation and convection of vortices.We consider a linearized formulation coupling an augmented Galbrun equation(for the perturbation of displacement)with a time harmonic convection equation(for the vortices).We first establish the well-posedness of this time harmonic convection equation in the appropriatemathematical framework.Then the complete problem,with Perfectly Matched Layers at the artificial boundaries,is proved to be coercive+compact,and a hybrid numerical method for the solution is proposed,coupling finite elements for the Galbrun equation and a Discontinuous Galerkin scheme for the convection equation.Finally a 2D numerical result shows the efficiency of the method.