Investigating the Scattered Wave due to Dipoles of an Operating Propeller by a Weighting-Iteration Method

Abstract

The main objective of this paper is to investigate the scattered waves from a ship hull due to the dipoles (i.e. unsteady forces) of an operating propeller. As the marine propeller is free from cavitation, the noise generated by such a ship is mainly due to the dipoles. According to the literature, only the radiation due to the dipoles of the operating propellers has been discussed, with no particular investigation into scattering. The unsteady forces of a propeller include three components: the axial thrust, the tangential torque force, and the radial force; but the radial force is generally omitted, because it is much smaller than the first two. This paper considers both the reflected noise from the free surface and the scattered noise from the ship's hull and applies the Discrete Wave Equation to predict acoustic pressure at both the far and near fields. For computation of the scattering problem, the study employs a weighting-iteration method in the time domain, which can solve the scattering problem with complex geometry. Finally, this research computes the dipole noise of a container ship radiated by the propeller and scattered from the ship's hull with a soft free surface.