By “oscillating water column”, we understand the water contained below a waterair interface inside a hollow structure with a submerged opening where the OWC water is communicating with the water of the open sea (see Figures 4.2, 4.5 or 7.1). Two kinds of interaction are considered: the radiation problem and the excitation problem. The radiation problem concerns the radiation of waves caused by an oscillating dynamic air pressure above the interface. The excitation problem concerns the oscillation caused by an incident wave when the dynamic air pressure is zero. Comparisons are made with wave-body interactions. Wave-energy extraction by OWCs is also discussed. Finally, the case in which several OWCs and several oscillating bodies are interacting with waves is considered (see Figure 7.1).

Many of the wave-energy converters which have, so far, been investigated in several countries are of the type with an OWC. The power take off may be hydraulic machinery, but pneumatic power take off, using air turbines, is more common. In the latter case there is a dynamic air pressure above the water surface inside the OWC chamber. In such a case the OWC may be referred to as a “periodic surface pressure” or an “oscillating surface-pressure distribution”. It is this kind of OWC which is the subject of study in the present chapter. When Eqs. (4.22)–(4.28) were discussed, one OWC as indicated in Figures 4.2 and 4.5 was considered. In Figure 7.1 two OWCs are indicated: one is in a floating structure, and the other is in a fixed structure. As with an oscillating body (cf. Chapter 5), with an OWC two kinds of interaction are considered.