  Trajectory of surface gravity waves in potential flow regime is affected by
the gravitational acceleration, water density, and seabed depth. While the
gravitational acceleration and water density are approximately constant, the
effect of water depth on surface gravity waves exponentially decreases as the
water depth increases. In shallow water, cloaking an object from surface waves
by varying the seabed topography is possible, however, as the water depth
increases, cloaking becomes a challenge since there is no physical parameter to
be engineered and subsequently affects the wave propagation. In order to create
an omnidirectional cylindrical cloaking device for finite-depth/deep-water
waves, we propose a multi-layered elastic plate that floats on the surface
around a to-be-cloaked cylinder. The buoyant elastic plate is made of
axisymmetric, homogeneous, and isotropic layers which provides adjustable
degrees of freedom to engineer and affect the wave propagation. We first
develop a pseudo-spectral method to efficiently determine the wave solution for
a multi-layered buoyant plate. Next, we optimize the physical parameters of the
buoyant plate (i.e. elasticity and mass of every layer) using a real-coded
evolutionary algorithm to minimize the energy of scattered-waves from the
object. We show that the optimized cloak reduces the energy of scattered-waves
as high as 99.2% for the target wave number. We also quantify the wave drift
force exerted on the structures and show that the buoyant plate reduces the
exerted force by 99.9%.

Fluid Dynamics