Model Summary |
 
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Model Summary |
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The moored vessel is approximately 340m in length, with a draft of 21m, and is situated in a water depth of 810m. The mooring system consists of eight lines connected to a turret. The angular spread between the lines is 45o. Each line is 1100m in length, of which 160m is chain of diameter 152mm and the remainder is wire of diameter 89mm. Mooring line pre-tension of each line is about 750kN. The anchoring radius from the turret centreline is 700m, with each fairlead 8m below the MWL. The horizontal distance between the turret centreline and the vessel CoG is 150m. In the finite element model of this system, the vessel is modelled using an assemblage of 19 beam elements; a snapshot of this arrangement is shown in the figure below. Of the 19 elements, 16 model the turret “carousel” to which the mooring lines are attached via hinges. There is 1 vertical element, and this is connected via a linear flex joint to the final, horizontal, element, which connects the turret to the CoG.
Schematic of Vessel and Turret
The only constraints applied to the mooring system are those at the mooring line anchor points; there are no other prescribed motions applied to the vessel or mooring lines. The vessel is subjected to wind, current and low frequency second order wave loads in order to identify the vessel response in surge, sway and yaw. These motions are subsequently combined with first order motions due to wave loading to simulate the combined vessel response.
In this analysis only one mooring line is considered, the most loaded line from Phase 1. A more detailed model incorporating more elements is employed in this case. The moored vessel is not included in the model, but the vessel motions from Phase 1 are combined with motions calculated from first order RAOs to give the combined vessel response.