Numerical simulation of moored structure station keeping in level ice

This paper describes a 2D numerical model for the interaction between drifting level ice and a moored structure. The floating structure is treated as a rigid body kept on station by a mooring system, and it can only move in the horizontal plane. The ice-breaking process is modelled using a geometrical method that characterises the contact zones between the hull of moored structure and the ice sheet. Ice rotating and sliding processes are modelled semi-empirically using ship ice resistance formulations. The numerical model predicts the time history of both the ice forces and the global mooring forces as well as the dynamics of the floating structure. The proposed model is validated by comparison with field data. The simulation results obtained with this model are compared with full scale measurements and experimental data from model tests on the Kulluk platform conducted in the Beaufort Sea during the 1980s. The results show good agreement between the field measurements and the model tests. This model is also used to study the influence of turret position on the stability of a moored icebreaking tanker (MT Uikku) under typical varying ice drift speeds and directions. Based on the heading controller, which keeps the hull aligned with the drift ice direction, the effects of ice thickness, ice drift speed and global mooring stiffness on mooring forces and responses of the moored vessel are studied.

► We model ice force and dynamics of moored structures in horizontal plan.
► The simulated results of Kulluk coincide well with field measurements.
► There exists an optimal turret position for moored tanker.
► Ice thickness has a significant effect on ice resistance; Ice drifting speed affects dynamics of moored tanker;
► Mooring stiffness has influences on maximum mooring force.