For ships, barges and similar long offshore structures roll natural period generally falls within the frequency range of a typical wave energy spectrum generally experienced by them. This causes dynamic amplification of rolling motion. For these structures the roll damping is highly nonlinear. Therefore it is of utmost importance that good estimation of roll damping is made for such structures. Linear radiation diffraction theory can not predict damping for roll motion as good as for other degrees of freedom. For ships and barges radiation damping (in case of roll) is generally quite small compared to the total damping in the system. Hence, additional damping needs to be added for solving roll motion equation.

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