Numerical analysis of primary conversion efficiency of oscillating water columns with multiple chambers

The authors investigate the primary conversion efficiency of Oscillating Water Columns (OWCs) with multiple water chambers and air chambers.Two-dimensional frequency-domain numerical models to estimate the primary conversion efficiency of a two-chamber OWC with two air chambersand a two chamber OWC with one air chamber are developed. The numerical results are compared with that of a conventional one chamber OWC with equivalent total chamber width and front opening. The wave induced force is calculated using the boundary element method based on the velocity potential theory. Assuming air to be an ideal gas, the air flow is calculated using an equation of state and the equations of conservation of mass and energy. Boundary integral equations are formulated to calculate the air pressure in the air chambers, the reflection coefficient and the primary conversion efficiency of each of the chambers as well as the combined efficiency. In addition, the behaviour of these physical quantities with the variation of the nozzle ratio, the relative water depth, the depth of the curtain wall and the width of the front-chamber are investigated using the calculated results.