Today’s Standard Technology: the OWC

OWC is the abbreviation for Oscillating Water Column and describes a design which makes use of the wave motion in rising and falling water columns. Figure 5a shows how a typ­ical OWC functions. It consists of a chamber with two open­ings. One of these is on the side towards the incoming waves and lies beneath the water level. The water can en­ter the chamber through this opening, driven by the wave energy. The second opening allows the pressure to equal­ize with the surrounding air. The water column in the cham­ber moves up and down at the wave frequency, and thus “breathes“ air in and out through the second opening. This “breath” drives an air turbine. It is constructed in such a way that it converts the oscillating motion of the air column in­to continuous rotational motion (see the infobox “Operat­ing Principles of OWC Turbines“ on p. 89).

In principle, an OWC represents a simple motion-con­version device (Figure 5b): In order to drive the generator, it converts the strong force at low velocity of the wave mo­tion into a motion of the air column with a weak force but a high velocity. The essential aspect is that the low specif­ic mass of the air permits a high acceleration.

OWC systems have been in use for decades for the en­ergy supply of beacon buoys (Figure 6). They were invent­ed by the Japanese Yoshio Masuda. In an OWC buoy, a ver­tical pipe assumes the function of the chamber. It reaches down into the calmer water layers below the buoy. There­fore, the water column in the pipe is at rest relative to the waves outside – but it moves relative to the buoy, since the latter is raised and lowered by the wave motion. Like stan­dard OWCs, most buoys employ an air turbine. Such buoys have rather quickly become standard for applications that require limited power outputs. Some of them have survived more than twenty years of operation at sea.

Today’s Standard Technology: the OWC

FIG. 5 THE OWC PRINCIPLE

The power plant converts the oscillating motion of the water column into elec-trical energy (a). It acts like a step-up gear box (b).

 

(b)

 

(a)

 

OWC air flow

 

Today’s Standard Technology: the OWC

low force high velocity

 

Oscillating
water column

 

high force low velocity

 

image146image147

Подпись: FIG. 6 Подпись: AN OWC BUOY

Подпись: Air turbineimage148Подпись:Подпись:image149