Cloaking a circular cylinder in water waves

In the diffraction of water waves by fixed bodies, the scattered waves propagate outward in the far field and attenuate with increasing distance from the structure. 'Cloaking' refers to the reduction in amplitude or complete elimination of the scattered waves. The possibility of cloaking is of both scientific and practical interests. Cloaking is considered here for a circular cylinder on the free surface, surrounded by one or more additional bodies. Linearized time-harmonic motion is assumed. A numerical procedure is used to optimize the geometry of the surrounding bodies, so as to minimize the energy of the scattered waves. Values of the scattered energy are achieved which are practically zero at a specific wavenumber, within the estimated numerical accuracy. This provides tentative support for the existence of perfect cloaking, and conclusive evidence that structures can be designed to have very small values of the mean drift force. (C) 2013 Elsevier Masson SAS. All rights reserved.