Investigation of the Scale Effects on Roll Motion for The Ship Bettica Using Numerical Simulation

In this paper, we focus on analysing scale effects on the roll motion of the Italian ship Bettica using a numerical method. First, the roll decay motion of the ship is simulated at both the model scale and full scale, and the predicted results are compared with experimental data to validate the numerical strategy. The results show that there are scale effects that cause the difference in roll amplitudes between the model and the full-scale ship. To investigate the viscous effects on the roll damping components, forced roll simulations are carried out at the model scale and full scale, and the roll damping components (frictional, wave-making, eddy-making, bilge keel and lift components) are obtained. An analysis of these roll damping components indicates that the frictional component is influenced by scale effects, especially in the case of zero or low forward speed. We also show that the bilge keel component is affected by scale effects when the height of the bilge keels is reduced to a certain value below the boundary layer thickness. The velocity fields around the bilge keels are analysed to better understand the scale effects.