Coupled Surge-Heave Motions of a Moored System. II: Stochastic Analysis and Simulations

Analyses and simulations of the coupled surge-and-heave motions of a nonlinear, moored, experimental, submerged structure subjected to random waves are presented here. The random wave excitations examined include periodic waves with additive noise and narrow-band random waves. Characteristic experimental results include noisy subharmonic and superharmonic responses, and transition behaviors among multiple coexisting responses. This investigation applies a systematic, stochastic analysis procedure to further the deterministic study presented in Part I. Good agreement between the analytical predictions and experimental results is shown. Effects of random perturbations in waves on nonlinear response phenomena are examined, especially for the cases of multiple responses coexisting with chaos. It is found that chaotic responses are sensitive and of weak strength compared to other coexisting responses, and the system response trajectories mainly stay in the stronger, periodic attracting domains. Numerical results indicate perturbation-induced response transitions leading to very large-amplitude response beyond the experimental model limitations.