Numerical investigation of submarine surface scattering and scaling effects under point forces excitation

Abstract

Underwater radiated noise (URN) is a critical factor in submarine stealth performance, with hydrodynamic loading acting as a major excitation source during high-speed cruising. This study investigates the role of non-compact hull surface scattering in shaping acoustic directivity patterns using a frequency-domain boundary element method (BEM). The method is validated against analytical solutions and applied to a DARPA Suboff subjected to multiple dipole excitations at the stern. Simulations were conducted across a range of Helmholtz numbers to assess frequency-dependent spatial directivity, and scaling analyses were performed to examine geometric similarity conditions. Results reveal that at low frequencies, directivity resembles the classical dipole figure-eight pattern, but when the wavelength becomes comparable to the hull dimensions, the non-compact boundary induces significant side lobes and compresses the main radiation lobe. Finally, these scattering effects persist into the far field in multi-scale configurations. The study confirms that spatial scale similarity can be preserved when source strength is scaled with the square of the geometric factor, but fixed-frequency evaluations expose scale-induced distortions in acoustic fields. These findings underscore the necessity of incorporating non-compact surface scattering into URN predictions, as neglecting such effects may result in inaccurate assessments of noise directivity in full-scale stealth evaluations.