NOISY NONLINEAR MOTIONS OF MOORED SYSTEM .1. ANALYSIS AND SIMULATIONS

Nonlinear responses of a submerged moored structure are investigated t aking into account the presence of environment random noise. Sources o f nonlinearity of the system include a quadratic Morison hydrodynamic damping and a geometrically nonlinear restoring force. The random pert urbations are modeled by a white-noise process to examine their effect s on nonlinear responses analytically and numerically. The analysis pr ocedure includes a generalized Melnikov process to study response stab ilities in a global sense and the Fokker-Planck equation to demonstrat e response characteristics from a probabilistic perspective. Rich nonl inear phenomena including bifurcations, coexistence of attractors, and chaos are identified and demonstrated. Probability density functions solved from the Fokker-Planck equation are used to depict (co)existing response attractors on the Poincare section and demonstrate their pro babilistic properties. Noise effects on responses are shown via a gene ralized Melnikov criterion and the probability density function. It is found that the presence of noise may expand the chaotic domain in the parameter space and also cause transitions between coexisting respons es.