A Discrete Element Method on a Chain Turret Tanker Exposed to Survival Conditions
Author A. Dercksen and J.E.W. Wichers (MARIN)
Title A Discrete Element Method on a Chain Turret Tanker Exposed to Survival Conditions
Conference/Journal Behaviour of Offshore Structures (BOSS), London
Year 1992

Abstract
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.

Wichers [1] showed that for a chain turret moored tanker the interaction forces between the mooring system and the tanker contribute significantly to the low frequency motions of the tanker. In [2] Huijsmans presented an approximate method to include the interaction forces due to high and low frequency motions of the chain turret moored tanker. Dercksen et al. [3] discussed an improved method for calculating the contribution of the hydrodynamic chain damping on the low frequency vessel motions.

This paper describes a further development of the simulation method described in [4]. The dynamic behaviour of the mooring chains will be coupled to the turret moored tanker, by means of a discrete element method. The method will be 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 will be compared to model tests. Based on the comparison, an extrapolation to a water depth of 350 m will be presented and discussed.

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