Radiated waves and rotational flows generated by cylindrical Oscillating Water Columns.

This paper is concerned with the radiated wave and the rotational flow fields generated by the forced oscillations of the water columns within surface-piercing hollow cylinders. The present study utilised Open Foam as the viscous flow solver to numerically model the forced oscillations. An investigation of the radiated waves in the fields near the water columns confirms two distinct nonlinear characteristics. These are progressively reduced amplitude and progressively reduced phase difference. An evaluation of the rotational flow fields around the mouths of the water columns helps explain their origins. This study confirms that the nonlinear characteristics in the near-field are physically caused by the formation and motion of vortex ring at the bottom edge of the cylinder. Interestingly, the progressively reduced amplitude is not evident in the far-field. All these new findings support the confirmation regarding the appropriateness of linear radiation theory and the implication of the vortex motion on the effective draft of a fixed cylindrical Oscillating Water Column (OWC). • Wave radiations generated by forced oscillations of water columns are studied. • Near-field radiated waves have progressive reductions in amplitude and phase difference. • Vortex formation and motion cause nonlinear characteristics in near field. • Far-field radiated waves exhibit insignificant progressive amplitude reductions. • Location of vortex closest to the mouth affects the effective draft of water column. [ABSTRACT FROM AUTHOR]