A Discrete Element Method on a Chain Turret Tanker Exposed to Survival Conditions

The computation of low frequency mooring forces on a tanker exposed to survival conditions requires knowledge of the hydrodynamic excitation and reaction forces. The low frequency excitation is caused by wave drift forces. The reaction forces on the tanker are a combination of added mass forces, wave drift damping forces, viscous forces and damping forces due to interaction with the mooring chains. This paper describes further development of the simulation method for a single point moored tanker. The dynamic behaviour of the mooring chains are coupled to the turret moored tanker, by means of a discrete element method. The method is used to predict the behaviour of a moored tanker exposed to survival conditions in deep water. Calculations for a turret moored tanker with 12 anchor legs at 150 m water depth are compared to model tests. Based on the comparison, an extrapolation to a water depth of 350 m is presented and discussed.