Broadband cloaking of multiple truncated cylinders in water waves using the arrangement defects

Cloaking based on scattering cancellation is investigated for a surface-piercing truncated cylinder surrounded by several annularly arranged small truncated cylinders in water waves. The cloaking condition of a body in water waves corresponds to the absence of scattered waves radiating to infinity; that is, the cloaked structure appears invisible to a far-field observer. The effects of three kinds of defects of the outer cylinders on cloaking are considered: a radial location defect, a circumferential location defect, and a size defect. The higher-order boundary element method is combined with the wave interaction theory to accurately study this wave-structure interaction problem. Both the scattered wave energy of the entire structure and the wave drift force on the inner cylinder are calculated and analyzed for the different defects. The symmetry of the defect effects and the cloaking-wavenumber offset caused by a radial position defect of the entire outer cylinder array are first identified. The radial location defect is successfully adopted to control the cloaking frequencies over a wide band.