NUMERICAL MODELLING AND EXPERIMENTAL MEASUREMENT OF THE ACOUSTIC SCATTERING BY TWO ELASTIC SPHERES

摘要

Acoustic scattering by distributions of particles is of interest in the ultrasonic remote sensing of sediments in suspension. This paper describes detailed numerical modelling of the backscattering properties of two elastic spheres (made from stainless steel or Pyrex glass) for ka values up to 10, where k is the wavenumber and a is the sphere radius. The calculations were performed by using a combined finite element and boundary element method. The form functions of the two elastic spheres for incidence angles of 0°, 45° and 90° are given for sphere separations of 2.5a and 4a. The average form function over all angles of incidence shows reasonable agreement with form function predictions based on first order multiple scattering theory. As a parallel study, experimental measurements have been performed in a laboratory tank using a parametric array as the acoustic source. The measurements were performed on spheres 12.7 mm in radius over the frequency range from 20 kHz to 220 kHz. The agreement between the experimental and numerical results is very good over the frequency range of interest and indicates the potential of the numerical modelling approach for studying the scattering properties of multiple scatterers and multiple scattering effects.