A NONLINEAR PROBABILISTIC METHOD FOR PREDICTING VESSEL CAPSIZING IN RANDOM BEAM SEAS

The capsizing of vessels in random beam seas is investigated using a s ingle degree-of-freedom model which is limited to the roll motion. Sev eral factors, including sea wave spectrum, nonlinear righting moment c haracteristics, and nonlinear damping, are taken into account in the a nalysis. A nonlinear probabilistic method is developed by combining id eas from modern nonlinear dynamics (specifically, the Melnikov functio n and the phase space area flux) and random vibrations. Conditions for the onset of vessel capsizing are obtained in terms of the sea state characteristics (significant wave height and characteristic wave perio d) and the vessel parameters (damping and stiffness coefficients). Ext ensive numerical simulations are carried out to demonstrate the validi ty of the analytical results. It is found that there exists an excelle nt correlation between the rate of phase space flux and the probabilit y of capsizing.