Hydrodynamics of unconventional SWATH vessels in waves

Abstract

The motion responses of unconventional Small Water-plane Area Twin Hull (SWATH) vessels are unique in the sense that viscosity has significant non-linear effects on their hydrodynamic parameters. The parametric optimization of the hull shape of these vessels to reduce the total resistance in waves yields an interesting hull form where viscous effects become significant and this kind of problem is generally more difficult to solve. This study aims to investigate the motion response of these special kind of ships in waves using both numerical and experimental approach with some theoretical simplifications to better understand the hydrodynamics of the ship. The two modes of motion of interest in this study are heave and pitch motions which were chosen in order to focus on the degrees of freedom which significantly contributes to the resistance of the ship in head waves. The vessel under investigation is an unmanned surface vessel (USV) proposed to be used to monitor a team of autonomous underwater vehicles. A scaled version of this model is built and some experiments were conducted at the MIT towing tank at zero speed. Additionally, the numerical methods are implemented using 2D and 3D potential flow solvers. As this is an ongoing project, the results obtained so far including the study of the effects of the inertial characteristics of the ship on the response amplitude operator (RAO) are presented.