In this note, the response of a Spar Platform is studied when subject to very high waves. The novelty of this paper consists in adopting the Quasi Determinism (QD) theory in its first formulation for the determination of the response of the structure. In fact, one of the peculiarities of QD theory is that it can be adopted under any boundary condition. The Spar Platform has been modeled as a two-dimensional 3-degree-of-freedom (3dof) rigid cylindrical floating body, moored to the seabed, floating in deep water. Further, it is supposed to be a slender body under the action of extreme waves neglecting any diffraction effect. Moreover, such a system is considered to be nonlinear, because of the nonlinear damping derived from the drag force and because of the stiffness of the moorings, which in the model have been studied as nonlinear springs. The non linear coupled set of differential equations of motion have been integrated in order to obtain the response of the structure by means of numerical methods commonly adopted in Literature. Thus, the response under the occurrence of very high wave crests is studied by using Quasi,Determinism theory and then the results compared and validated with those obtained through Monte- Carlo simulations.
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