CONCEPTS FOR WAVE-EXCITED OFFSHORE STRUCTURES

A study of the resultants of the inertia and drag-force intensities in duced by waves on offshore structures is made. The relationships betwe en these resultants and the corresponding modal forces that govern the structural response are examined, and information and concepts are re ported that elucidate the main factors that control such forces. The d emonstration that the inertia and drag components of the modal forces can be expressed in terms of the sea-surface kinematics is a distingui shing feature of the study. More specifically, it is demonstrated that , in deep waters, the inertia modal force is particularly influenced b y the horizontal water-particle displacement evaluated at the still-wa ter level. The corresponding drag modal force is shown to be controlle d by the square of the vertical water-particle displacement computed a t the same level. The analyses for the wave excitations presented in t his paper advance the understanding of their characteristics and are p otentially useful for the development of efficient design-oriented pro cedures for offshore platforms. Analyses for the wave-induced structur al response are also presented that further enhance the usefulness of the reported information and concepts.