A three-dimensional transient numerical code ITU-WAVE based on potential theory and Neumann-Kelvin approximation is extended to take into account wave interaction in an array system using two and four truncated vertical cylinder arrays. ITU-WAVE panel code is validated against analytical array results before applied to power absorption from ocean waves for different array configurations. The effects of the separation distances between array system and heading angles on energy absorption in both sway and heave modes are studied by the support of numerical simulations which show sway mode has wider bandwidth than heave mode for energy absorption. It is also shown that wave interactions are stronger when the array systems are close and these wave interactions are reduced significantly and shifted to larger times when the separation distance is increased. The wave interaction is much stronger at the same separation distance and heading angle in heave mode than in sway mode. Numerical experience also shows that more power is absorbed in sway mode than in heave mode in both two and four array systems at any separation distances and heading angles when the bodies in array system have the same displacement in both sway and heave modes. (C) 2016 Elsevier Ltd. All rights reserved.