This paper studies second-order wave interactions with a large floating body in two dimensions by a time-domain method. In the numerical scheme adopted. a time-stepping scheme together with a suitable iterative procedure are used to solve the coupled fluidstructure equations, and a boundary integral equati.on method. based on Green's theorem is used to calculate the resultmg wave fIeld at each time step. The method is illustrated by numerical results obtained for the diffraction-radiation of Stokes second-order waves by a moored semi-submerged circular cylinder. For the case of a floating structure subjected to regular waves. pronounced secondorder wave effects on the motion responses and the hydrodynamic forces. as well as the corresponding free surface profiles are highlighted. In particular. the effect of mooring stiffness on the response behaviour of the floating cylinder is examined. In relation to conventional frequency-domain methods. the present method provides a relatively algebraically straightforward and computationally effective numerical algorithm for treating the secondorder diffraction-radiation problem.


In many offshore projects. predictions of hydrodynamic loads and responses for large. Fixed or floating structures have generally been obtained on the basis of Iinearized potential flow theory Which IS formally valid for the case of small amplitude sinusoidal waves. Over the past decade. hydrodynamic research has increasingly focused on the study of nonlinear wave-structure interactions in order to account for the effects of steep waves encountered in engineering applications. Theoretically. the nonlinear problem can be solved by two categories of method: one approach is a second-order frequency-domain solution based on the Stokes perturbation procedure (e.g. Molin. 1979; Eatock. Taylor and Hung. 1987; and Kim and Yue. 1989). and the other IS a full nonlinear solution to the resulting wave field by a time-stepping procedure (e.g. Vinje and Brevig. 1981; Isaacson. 1982; and Cointe. 1989).

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