Time domain prediction of motions of marine vehicles in waves

This paper presents an application of a boundary element method for the calculation of wave induced motions for a ship advancing in waves. The relevant surfaces have been described using a structured grid of flat quadrilateral panels. A desingularized approach has been adopted by placing Rankine singularities at a small distance from every panel center: inside the body and over the the free surface. The boundary element conditions are collocated at the panel centers. The boundary value problem is solved at each time step in terms of velocity potentials by using an eulerian time stepping scheme. The boundary conditions have been applied on the mean body wetted surface and the free-surface is considered at the calm water level. The velocity potential computed on the free-surface at a certain time-step allows to update the kinematic and dynamic boundary conditions. Once the current value of potential is obtained, the pressure on the mean hull surface has been calculated and forces and moments are given by the integration of pressure on the body. The major advantage of choosing the desingularized approach consists in reducing the computational effort, especially when non linear effects are considered. The adequacy of the numerical procedure and of the results has been verified for two and three dimensional cases. Different typologies of marine vehicles have been considered comparing the numerical output with experimental data, freely available in literature. In this paper examples for two cases are presented: the well-known modified Wigley hull, for which experiments on added mass and damping are also available, and the DTMB 5512 ship which was extensively tested at the University of Iowa.