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 wo rks have analysed this effect in a quasi-steady manner. based on the r ate of change of the added resistance in waves, with respect to a smal l steady forward velocity. In this paper the wave-drift damping coeffi cient is derived more directly, from a perturbation analysis where the low-frequency body oscillations are superposed on the diffraction fie ld. Unlike the case of body oscillations in calm water, where the damp ing due to wave radiation is asymptotically small for low frequencies, the superposition of oscillatory motions on the diffraction field res ults in an order-one damping coefficient. All three degrees of freedom are considered in the horizontal plane. The resulting matrix of dampi ng coefficients is derived from pressure integration on the body. and transformed in special cases to a far-field control surface.