Analysis of acoustic scattering mechanism of a near-bottom suspended elastic sphere

Based on the two-dimensional circumferential decomposition method, this study focuses on the efficient numerical calculation of the three-dimensional scattering sound field for a near-bottom target in a non-axisymmetric background field. The method is applied to study the acoustic scattering mechanism of a near-bottom suspended elastic sphere target. The expressions for calculating far-field sound pressure in the two-dimensional finite element model of the near-bottom axisymmetric target are provided based on the ray acoustic superposition theory of the four-path coupling model between the seabed and the target. Taking into account the combined influence of the additional echo introduced by the interface, the frequency-angle spectrum and frequency-height spectrum of the elastic sphere target are computed, and an accurate predictive formula for the bright-dark alternating interference fringes of the coupled scattering sound field is presented. Through analysis of both numerical and experimental results, the propagation law of target mirror reflection, elastic waves excited in the elastic target body, and seabed reflection waves coupling with each other, as well as their influence on the total field, are explained when the glancing angle and suspension height of the target change. Moreover, the mechanism of intensity fluctuation in the target scattering sound field caused by changes in suspension height and glancing angle is discussed. The results indicate that increasing the grazing angle and suspension height will reduce the spacing between peaks of adjacent resonance peaks in the target spectrum, and that the interference fringe calculation formula for the sound field coupled between the seabed and the target can better predict the target scattering spectral information.