Wave-drift damping of floating bodies

Wave-drift damping results from low-frequency, oscillatory- motions of a floating body, in the presence of an incident wave field. Previous works have analysed this effect in a quasi-steady manner, based on the rate of change of the added resistance in waves, with respect to a small steady forward velocity. In this paper the wave-drift damping coefficient is derived more directly, from a perturbation analysis where the low-frequency body oscillations are superposed on the diffraction field. Unlike the case of body oscillations in calm water, where the damping due to wave radiation is asymptotically small for low frequencies, the superposition of oscillatory motions on the diffraction field results in an order-one damping coefficient. All three degrees of freedom are considered in the horizontal plane. The resulting matrix of damping coefficients is derived from pressure integration on the body, and transformed in special cases to a far-field control surface.