A numerical technique that employs a computational fluid dynamics (CFD) code is used to perform coupled fluid-structure interaction simulation of a wave energy device in order to assess power output in a 3D numerical wave flume. The current method determines the motion of the buoy from the dynamic solution of the fluid flow problem and the dynamic buoy motion problem rather than prescribing the motion of the buoy. The power output of the device is calculated for different wave conditions. The technique was expanded for an array of two buoys to determine the interference between them. (C) 2007 Elsevier Ltd. All rights reserved.