Numerical confirmation of cloaking phenomenon on an array of floating bodies and reduction of wave drift force

When multiple floating bodies are situated closely, hydrodynamic interactions among bodies are expected to be large and complex. These hydrodynamic interactions should be taken into account not only in hydrodynamic forces of first order in the incident-wave amplitude but also in time-averaged steady forces of second order which are called the wave drift force. In this paper, it is shown that the wave drift force on a floating body can be reduced to almost zero at a specific wavenumber, by placing extra supporting columns in a way of surrounding the floating body and utilizing the 'cloaking' phenomenon. Furthermore to reduce the wave drift force for a wider range of wave frequencies, we propose to control the parameters of outer surrounding columns such as draft and distance from the inner floating body at each frequency. These parameters of surrounding columns are optimized in this paper by a genetic algorithm so as to minimize the total scattered-wave energy. For numerical computations with high accuracy, the wave interaction theory combined with higher-order boundary-element method is adopted and the integral with respect to the azimuth angle in the formula of wave drift force is analytically performed.