Longitude has been engaged to undertake an operability analysis of a semisubmersible accommodation unit operating on dynamic positioning (DP) in order to demonstrate that the vessel can remain on station near the Prelude FSLNG with an up time of 98% or more.
The analysis required a multi body dynamic simulation to be carried out. Time domain simulation was used meaning that a full time history is calculated for the movement of both vessels relative to each other. Operability was calculated based on the gangway limits in terms of the permissible extension, azimuth and elevation of the gangway.
The DP of the system is set to “track target” mode during operation meaning that the accommodation unit is able to track and follow the low frequency motions of the FSLNG. The analysis was therefore set up with accurate modelling of the turret system and moorings of the Prelude allowing the vessel to weather vane freely and with the accommodation vessel set up in the analysis to track the low frequency motions of the Prelude.
The analysis of a range of different seastates was able to show that the proposed accommodation vessel and gangways system would be capable to operate on site with the required 98% uptime.
