Mehran Saadati-Nasab - Mechanical Engineering, Ferdowsi of Mashhad, Mashhad, Iran
Mohammad Passandideh-Fard - Mechanical Engineering, Ferdowsi of Mashhad, Mashhad, Iran,
Morteza Anbarsooz. - Mechanical Engineering, Advanced Technologies Engineering, Quchan, Iran

Various types of wave energy absorption equipment work based on a swing or a submerged buoy to a fixed reference. The efficiency of this equipment can vary based on the depth of water in which they are installed. One of the equipment that can effectively use both components of wave forces in x and y direction is Bristol cylinder which was first introduced by Evans from the University of Bristol in 1976 [1]. Evans provided a linear theory to predict the performance of this group of wave energy absorption equipment and indicated that, in theory, there is a possibility of 100% absorption for wave energy using the cylinder [1]. He also showed that passing waves can be eliminated and the total wave energy can be absorbed for certain values of the spring constant and damping factor in each frequency of incident wave. Recently, Heikkinen et al. [2], through providing a theoretical analysis based on potential flow theory, investigated the effect of various parameters such as height, wave periodicity, and the cylinder diameter on the cylindrical Bristol efficiency. Evans [3] and Davis [4] experimentally showed that linear theory quite loses its accuracy in calculating the Bristol cylindrical efficiency for waves with high sharpness. This is due to limiting assumptions of linear theory which ignore the effects of viscosity and assumes the non-rotating flow and linear waves.