Illustrated examples are given of marine structures, taken from oil exploitation, floating wind production, and other offshore activities. Important parameters such as the Reynolds number and the Keulegan–Carpenter numbers are introduced and the concepts of large and small (or slender) bodies are defined. The separation between linear and nonlinear wave loads and responses is introduced. Finally a brief outline of the book is given.

This chapter applies to bodies that are small compared to the wave lengths, of dimensions similar or smaller than the wave amplitude. As a result separation cannot be neglected and semi-empirical methods are usually applied to formulate the wave and current loading. The Reynolds number is introduced and the different flow regimes, for a circular cylinder in current, are illustrated. The Morison equation is introduced and applied to the wave loading upon cylinders. Experimental values of the inertia and drag coefficients, vs the Reynolds and Keulegan-Carpenter numbers, are presented. The deficiencies of the Morison equations, in complex flows, are emphasized. Alternatives such as the independent flow-field formulation, or wake models, are introduced. The oscillatory lift force, in steady current, is introduced and the Strouhal number and reduced velocity are defined.