Numerical and experimental investigation of motion characteristics of a travelling trimaran encountering a freak wave

A hybrid frequency-time domain model has been developed to investigate motion characteristics of a travelling trimaran encountering a freak wave. A deterministic wave train containing a freak wave was modelled in a towing tank at Marine Design and Research Institute of China for testing the model trimaran under the action of the freak wave. Comprehensive numerical simulations examine the effect of the encountering position of the trimaran with the freak wave, forward speed and the configuration of side hulls on heave and pitch motions of the trimaran excited by the freak wave. It is found that there exists a feature of phase leading of the heave and pitch time histories around the occurrence time of the freak wave as the encountering position moves astern. It is further demonstrated that different encountering positions of the trimaran with the freak wave crest can merely lead to slight difference for the maximum peak-trough values of the heave and pitch motions, respectively. The maximum peak-trough values of the heave and pitch motion of the trimaran encountering the freak wave crest with center of gravity (CG) at different forward speeds tend to increase and decrease respectively as the forward speed increases. The time history of pitch motion is found to exhibit a whole downshift as the side hulls move forward.