Analytical and experimental study of modified oscillating water column wave energy extraction systems

Numerous wave energy extraction devices have in the past, been proposed and modelled theoretically and physically. The power extraction of most devices occurs at a low efficiency. However, the primary deterrents to the utilization of these devices include the high capital cost per unit of generated power, the mechanical complexity in the harsh salt environment, the unworthiness in severe sea states, and the low efficiency in random sea states. The oscillating water column device appears to be one of the most promising wave energy extraction systems. It has no large external moving parts in contact with the sea and initial model tests show it to have a high wave to air conversion efficiency. The conventional oscillating water column device has a cavity or piston chamber having vertical walls situated in a wave zone. The impinging waves cause the water column to oscillate up and down. The vertical motion of the free surface in the cavity acts similarly to a reciprocating piston compressor. The reciprocating water surface pumps air through rectifying values into turbine devices. One weakness of the conventional oscillating water column device is its sensitivity to the frequencies of approaching waves. Initial oscillating water column small model tests heremore » at the Technical University of Nova Scotia indicated that if the sides of the chambers were not vertical but had a non-constant cross-sectional area in the vertical direction, the energy conversion was greater over a broader spectrum of approaching waves. In order to study this in greater detail, an analytical model was devised, and further larger physical models were constructed and tested.« less