waves the structure moves in phase with the standing wave. The out of phase vertical motion of the structure creates stronger vortices and therefore more energy dissipation. This difference in the phase angle between the vertical motion of the FB and the standing wave formed in front of the structure was observed by Tolba (1998) using video analysis. The reflection coefficient in all cases is less than 0.3 mainly due to the high energy dissipation. The high energy dissipation and low reflection for