- The interactions of a porous, vertical cylinder array with regular and irregular incident waves and its performance as a breakwater are investigated by numerical simulations and medium-scale experiments. The interaction theory is based on linear potential theory for N bottom-mounted vertical cylinders, and the porous effects are included through Darcy's law. The empirical relationship between the plate porosity and porous parameter obtained from the experiments of Cho and Kim (2008) is applied to the present problem. The numerical results agree well with the measured data for 4, 6 and 10 tightly connected porous cylinder cases. Both transmitted and reflected waves as well as wave run-up and exciting forces are significantly reduced due to wall porosity. The results show that the optimal design of seawater-exchanging breakwaters for a given sea state can be found through a systematic parametric investigation by controlling the size, number, porosity and arrangement of circular cylinders. by The International Society of Offshore and Polar Engineers.