Concepts for Wave-Excited Offshore Structures

A study of the resultants of the inertia and drag-force intensities induced by waves on offshore structures is made. The relationships between these resultants and the corresponding modal forces that govern the structural response are examined, and information and concepts are reported that elucidate the main factors that control such forces. The demonstration that the inertia and drag components of the modal forces can be expressed in terms of the sea-surface kinematics is a distinguishing feature of the study. More specifically, it is demonstrated that, in deep waters, the inertia modal force is particularly influenced by the horizontal water-particle displacement evaluated at the still-water level. The corresponding drag modal force is shown to be controlled by the square of the vertical water-particle displacement computed at the same level. The analyses for the wave excitations presented in this paper advance the understanding of their characteristics and are potentially useful for the development of efficient design-oriented procedures for offshore platforms. Analyses for the wave-induced structural response are also presented that further enhance the usefulness of the reported information and concepts.