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For a ship undergoing roll motion at a resonance frequency, the roll restoring moment and virtual moment of inertia counteract each other and only the damping moment resists the roll exciting moments. Hence, accurate computation of the roll damping moment improves the roll motion prediction. There are several methods to calculate the damping moment; however, most of them fail to consider the viscous effects, such as the potential theory-based method. The experimental measurements take into account the viscous effect; however, they are expensive. The Computational Fluid Dynamics (CFD) method is an alternative to accurately consider the viscous effect. In this study, a CFD approach based on harmonic exciting roll motion technique is adopted to compute the roll motion characteristics and damping coefficients at different conditions. The impact of appendages, Froude number, and degrees of freedom on roll motion characteristics and damping coefficients are investigated for the model scale and full scale to study the scale effects. The results at the model scale are compared against experimental measurements and good correlation was found. [ABSTRACT FROM AUTHOR]