Unsteady viscous flow with non linear free surface around oscillating SWATH ship sections

Ship motion problem is approached exploiting the assumption of linearity and subdividing forces acting on the hull in different components; in this paper the focus is on the radiation problem. A fully viscous solver, based on the numerical solution of the Navier-Stokes equation through the finite volume technique, is used to calculate radiation forces on hull surface, with non linear free surface evaluated through the volume of fluid method. Radiation forces are the most influenced by viscous effects, especially for particular hull geometries as SWATH ships. OpenFOAM libraries are used to solve the unsteady flow around one circular and two SWATH two dimensional sections forced to heave in calm water. The comparison with experiments evidence a very good agreement of the forces measured over a wide frequency range including irregular frequencies.