A Numerical Study of the Roll Damping for Double-Symmetric Bodies

Roll damping is essential for describing properly the motions of a ship, particularly when operating in rough sea conditions, being determinant for parametric or synchronous roll phenomena. Roll damping is a complex process of energy transfer from the hull to the water, which affects the amplitude of motion. Roll damping is dominated by viscous effects as well as by the interaction of the ship with the free surface. Numerical simulations of the free roll decay are carried out in this paper for a double-symmetric floating hull with one or two bilge keels based on an unsteady viscous flow solver. The numerical solutions reported in here are computed with the ISIS-CFD viscous flow solver, part of the Numeca FineTM/Marine suite. Turbulent flow is simulated by solving the unsteady equations of flow. Closure to the turbulence is achieved through the Shear Stress Transport (SST hereafter) based Detached Eddy Simulation (DES), which provides the accuracy of LES for highly separated flow regions and a computational efficiency of RANS in the near-wall region. Free roll decay is studied for various initial roll angles at a given advancing speed of the main hull. The influences of the bilge keel surface and initial roll angle on the roll damping coefficient are discussed.