Abstract
The problem of large amplitude, nonlinear, rolling in the presence of a stochastic beam sea has been approached several times in the past. However, most of the published work is devoted to the consideration of the case where the bandwidth of the excitation (input process) is greater than that of the rolling ship (output process). As a result the complex nonlinear roll dynamics cannot exhibit all its typical peculiarities and in particular no consideration is given to the very dangerous possibility of bifurcations and jumps of amplitude as precursors of an eventual degeneration to chaotic behaviour. This possibility was proposed long ago in the narrow band stochastic case and successively revealed experimentally in regular beam waves. In the meantime the possibility of bifurcations in the presence of stochastic excitation was confirmed together with the validity of Gaussian methods to this purpose. In this paper, the hypothesis of "artificial" narrow band sea spectrum is abandoned and the case of Pierson-Moskowitz case is analysed by means of the cumulant-neglect closure method. The strong effect of non linearities is highlighted together with the possibility of complex roll dynamics.
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