An investigation of motions of catamarans in regular waves
The aim of this research is to develop computational tools to predict the large amplitude motions of a catamaran travelling with forward speed in waves. In this thesis, the results of theoretical and experimental investigations to predict the motions of catamarans in regular waves are presented. The motion problem of a catamaran travelling in waves has been formulated with the assumptions that the flow field is a potential flow. The solution of governing equations is determined by a set of initial-boundary conditions. In order to solve the motion problem, the exact boundary conditions have been simplified through linearisation by using the perturbation expansion technique. If the motion is steady and sinusoidal in time, the initial value problem can be precipitated out. Then, the initial-boundary value problem can be simplified to the boundary value problem. Solutions of the small amplitude motion problem of catamarans have been obtained by solving the two-dimensional Green function integral equations over the mean wetted body surface in the frequency domain. Numerical computations for three catamarans (ASR5061), Marintek and V-1 catamarans) travelling in the oblique waves have been carried out to compare with experimental measurements. For the low forward speed case, good comparisons between the calculated and experimental results have been obtained. When the forward speed increases, the linear frequency domain technique gives a gross overprediction of the motion responses for the heave and pitch modes at the resonance frequencies and the calculated resonance frequency is slightly higher than the experimental measurement. Generally better predictions are obtained in heave motions than in pitch motions.