Effect of duct extension on pneumatic efficiency of Backward Bent Duct Buoy (BBDB)

Abstract

The Backward Bent Duct Buoy (BBDB) is a wave energy converter which works on the principle of the Oscillating Water Column theory. The air displaced due to the rising and falling water surface in the oscillating water column is used to drive an electric machine to generate power. A physical model of the prototype BBDB with a geometric scale of 1:8 made of acrylic glass of size 412 × 280 × 255 mm was tested in the wave flume at the Centre for Water Resources laboratory, Anna University to determine the pneumatic efficiency of BBDB. The pneumatic efficiency, which is the ratio of output power of the displaced air to the input power due to waves, is primarily dependent on the amplitude of oscillation of the water column in the vertical air chamber. The effect of increasing the length of the horizontal duct on pneumatic efficiency has been studied. It was found that the duct length affects the primary conversion efficiency considerably and longer ducts may not necessarily improve the efficiency. It was observed that the BBDB model with the duct length of 412 mm shows better primary conversion efficiency of 5.3% and the area of the orifice opening also has an effect on the pneumatic efficiency.

Keywords:

• wave energy converter
• BBDB
• pneumatic efficiency
• OWC
• froude scaling
• response amplitude operator (RAO)