Acoustic scattering from a solid aluminum cylinder in contact with a sand sediment: Measurements, modeling, and interpretation

Abstract

Understanding acoustic scattering from objects placed on the interface between two media requires incorporation of scattering off the interface. Here, this class of problems is studied in the particular context of a 61 cm long, 30.5 cm diameter solid aluminum cylinder placed on a flattened sand interface. Experimental results are presented for the monostatic scattering from this cylinder for azimuthal scattering angles from 0 degrees to 90 degrees and frequencies from 1 to 30 kHz. In addition, synthetic aperture sonar (SAS) processing is carried out. Next, details seen within these experimental results are explained using insight derived from physical acoustics. Subsequently, target strength results are compared to finite-element (FE) calculations. The simplest calculation assumes that the source and receiver are at infinity and uses the FE result for the cylinder in free space along with image cylinders for approximating the target/interface interaction. Then the effect of finite geometries and inclusion of a more complete Green's function for the target/interface interaction is examined. These first two calculations use the axial symmetry of the cylinder in carrying out the analysis. Finally, the results from a three dimensional FE analysis are presented and compared to both the experiment and the axially symmetric calculations.

Rayleigh scattering of a cylindrical sound wave by an infinite cylinder

“…From Eqs. (7), (8), and (20) it follows that the effect of bearing variation on the relative change in the sum is of order 1 þOðj 2 ðkaÞÞ with and without the cylinder since p in;1 þp in;2 ¼ 2H ð1Þ 0 ðkbÞ þ Oðk 2 a 2 Þ and…”

“…In view of Eq. (20), the coefficients A n in the exact solution for the scattered field are proportional to ðkaÞ 2n for n ! 1.…”

“…(9)- (11) and approximately in Eqs. (18)- (20), and (22). Equations (36)-(38) can be readily simplified by taking into account that ka 2 =b ka ( 1 and using the approximate form of the A n coefficients.…”

“…In underwater acoustics, such problems can arise in dense multi-scatterer configurations, 6 radiation by finite sources, [7][8][9][10] target classification, [11][12][13] source localization, 14 scattering suppression, 15,16 and when calculating the radiation and scattering of sound due to objects located near the ocean surface 17,18 or the seafloor. [19][20][21] No simple analytic solutions are readily available for such problems, and numerical methods have to be used. This is the motivation for the present study.…”

Performance of Time Reversal Based Underwater Target Detection in Shallow Water

“…Meanwhile, mid-frequencies are currently used to detect sea mines at the bottom of the seabed in shallow seas. The Applied Physics Lab (APL) at the University of Washington in the United States of America conducted research on the scattering of sound waves from a 1∼2 m-long target [6,7]. In the study, frequencies of 1∼30 kHz are used to conduct comparative research between actual test data and simulation data on the scattering of sound waves in various cylindrical objects.…”