A hybrid realizable k - epsilon/laminar computational fluid dynamics method consisting of the realizable k - epsilon model, laminar model, volume of fluid Geo-reconstruct surface capturing method, and motion-based zonal mesh update method, is presented to study the hydrodynamics of floating oscillating water columns (OWCs). This method is capable of precisely capturing water elevations and motions of the OWC device structure. The simulations of the prototype model are established and dimensionless comparisons are performed with experiments. The results show that the movement of the OWC device structure shows little scale effect with or without the consideration of air compressibility and depends only on the Froude number. Test cases are conducted on the pneumatic power of a floating OWC at prototype scale, showing that pneumatic power increases with increasing incident wave height for a heaving OWC. (C) 2020 Elsevier Ltd. All rights reserved.