Numerical and experimental studies on cloaked arrays of truncated cylinders under different wave directions

The cloaking phenomenon in arrays of truncated surface-piercing cylinders under different wave directions is investigated by numerical and experimental methods. Two arrangements, consisting of an inner cylinder surrounded by either four or eight outer cylinders, are considered to confirm this cloaking phenomenon and to find the effect of the wave direction. The cloaking configurations of the cylinders for a certain wave frequency and a certain wave direction are determined via a real-coded genetic algorithm to minimize the scattered wave energy of the cylinder array. Experiments in a wave basin are designed to measure the free-surface elevation at multiple locations in the vicinity of the inner cylinder and the wave drift force on the inner cylinder at various wavenumbers under different wave directions. Both the wave drift force and the wave elevation show good agreement between the numerical and experimental results. It is found that the reduction in the wave drift force acting on the inner cylinder in a cloaking configuration is due to the improvement of the wave elevation in the vicinity of the inner cylinder. Furthermore, the effect of the wave direction on the cloaking phenomenon is significant for the configuration with four outer cylinders, but it is negligible for eight outer cylinders.