Nonlinear wave effect of the slow-drift motion of a floating body

The slow drift motion of a floating body in a two-dimensional wave field has been investigated using a time-domain, fully nonlinear numerical model with nonreflective open boundaries. Preliminary computations were conducted for incident bichromatic waves, in which wave theories with different orders were applied in generating the waves required. The results show that the use of low-order theories generates undesirable free waves, and that fourth-order terms contribute markedly to low-frequency input. The motion of a rectangular floating body in response to nonlinear bichromatic waves was computed. The numerical results for small-amplitude incident waves agree reasonably well with the second-order approximation for both the steady and difference-frequency (Delta sigma) components in the body's motion. For relatively large waves, however, the 2 Delta sigma component becomes predominant compared with the Delta sigma component. The motion of the body in irregular waves with different wave parameters has also been presented in order to discuss the validity range of a second-order approximation. Copyright (C) Elsevier Science Limited.