Experimental investigation of scattering from randomly rough elastic cylinders

Abstract

Acoustical backscattering from randomly rough infinitely long elastic cylinders surrounded by a fluid medium is examined. The cylinder radius is allowed to vary along its lengthwise axis creating one-dimensional rotationally symmetric roughness. Using recently published rough cylinder formulations [T.K. Stanton, J. Acoust. Soc. Am., 92, 1641-1664 (1992) and T.K. Stanton and D. Chu, J. Acoust. Soc. Am., 92, 1665-1678 (1992)], explicit expressions are derived for the backscattered field for a laboratory pulse-echo environment: spherically spreading directional source and receiver with arbitrary beam patterns. Efficient numerical integration algorithms are developed to solve for the backscattered field from a specified surface profile. Experimental measurements from dense elastic (stainless steel) cylinders immersed in water are presented to quantitatively illustrate the effects of small scale surface roughness (δs/a = 0.0131 where δ is the surface rms roughness and a is the mean cylinder radius) for 4.5 < ka < 70 where k is the acoustic wavenumber. The actual target surface profile is well described and used as an input in the numerical simulations. Agreement is found between measurements and simulation predictions both in the mean field levels and the field fluctuations over a wide range of frequencies.