The interaction of waves (generated by numerous causes, e.g., wind and earthquakes) with structures makes marine hydrodynamics. Thus, the integrity of the structures depends on the understanding of the interfacial mechanics, which is far more complex than either the waves or flow about bluff bodies for a large number of reasons: turbulence, separation, in-line and transverse forces, empirical equations (e.g., Morison's equation), empirical nature of the lift, drag, and inertia coefficients based on relatively low-Reynolds number experiments (carried out with purely sinusoidal oscillations in a large U-shaped water tunnel or on offshore platforms with large scatter), three-dimensionality and the omnidirectionality of the interaction, flow-induced vibrations, proximity of the bodies, breaking of the waves, refraction, diffraction, reflection, the ever present and ever elusive damping, and myriads of other occurrences limit our ability to design structures with reasonable confidence, as evidenced by occasional failures. With the realization of the fact that the subject phenomena are complex beyond our capacity to fully observe, measure, or to compute, even in the era of nanotechnology and quantum computing, we discuss waves and wave–structure interactions separately but with a keen interest in each simultaneously. This chapter discusses only the most important characteristics of the ocean waves and serves as an integral part of the rest of the topics covered.

Surface gravity waves

As noted by Billingham and King (2000), “Whenever we see or hear anything, we do so because of the existence of waves.” In this chapter our emphasis is on the interaction of currents and design waves with offshore structures. It is rather remarkable that progressive linear gravity waves represent the first approximation of more fundamental and advanced versions of waves, aptly described by Wehausen and Laitone (1960); Phillips (1977); LeBlond and Mysak (1978); Geernaert and Plant (1990); Sarpkaya (1992); Komen et al. (1994); Malenica et al. (1995); Sawaragi (1995); Young (1999); Goda (2000); Lavrenov (2003); Janssen (2004); Sarpkaya (2006a); Svendsen (2006); Holthuijsen (2007) and many others.