Roll-Sway-Heave Coupling in Beam Waves

To have reliable results by applying the modern methods of Non-Linear dynamics, a realistic mathematical model of ship motions is needed. In this paper we discuss, on an experimental basis, the large amplitude roll motion modeling, an issue of great interest in the studies of ship capsizing. In particular, the coupling of roll motion with the other motions in the transversal plane, heave and sway, is analyzed by means of a parameter identification technique used to discuss the goodness-offit of different mathematical models to the experimental data and to obtain values for the coefficients. The results relative to a series of tests conducted in beam waves on the scale model of a small Roro vessel in different initial stability conditions indicate that: · the results in terms of motion amplitudes do not depend on the mooring arrangement; · the coupling of roll into sway and heave is needed to account for the observed motions; · the coupling of heave and sway into roll is not so important nor for roll motion simulation nor for the estimate of the roll motion coefficients; · the effective wave slope coefficient estimated is sensibly smaller than current IMO prescription.