Numerical Study of Parametric Roll on a Fishing Vessel

Present research activity examines numerically the occurrence of parametric roll on a fishing vessel interacting with regular head-sea waves. The adopted solver is an efficient 3-D numerical Domain-Decomposition strategy for the seakeeping of a 6-dof vessel without and with small forward speed and possibly subjected to bottom-slamming and water-on-deck events. Here, the vessel has been assumed at rest and the excitation frequency is varied in the first parametric resonance zone and occurrence and features of the instability are examined in terms of nonlinearities of the incident waves and roll natural-to-incident wave frequency ratio. The analysis is performed both fully within the potential-flow theory and examining the effect on the parametric resonance of the viscous correction to the roll damping obtained from free-decay 3D model tests on the same ship. A system of four cables, horizontal in the mean configuration, will be used experimentally to limit the horizontal vessel motions. Here the numerical solver is used to analyze the influence of cable stiffness and of cable configuration on the vessel behavior and to help the design of the physical set up. The vessel has deep draft and high mean freeboard, these aspects work against the occurrence of bottom slamming and water-on-deck events. Without forward speed, no bottom slamming phenomena were observed while limited number of water-on-deck events with small amount of shipped liquid was recorded for the highest-frequency incident waves with largest steepnesses, among those causing parametric roll.