Orca Offshore performed critical transport and installation analyses for Centrica’s self-installing gas platform in the Dutch North Sea. The F3-FA platform has a suction pile foundation resting on a temporary barge so it can be relocated, providing significant cost savings across three to four fields. Because of the size of the piles and the location close to wave zone, large hydrodynamic loads would be acting on the piles. For the success of the project, it was crucial to know these loads at an early stage.
Orca Offshore used Bentley’s MOSES application to carry out motion and stability analysis, multi-body dynamic analysis, structural spectral analysis, and support scale model tests for this moveable platform. This type of self-installing platform is designed to reduce costs and environmental impact, achieved through the reuse of the platform and the fact that everything is recovered from the seabed after removal of the platform.
Calculating hydrodynamic loads was crucial to determining pile size – 15 meters high and 15 meters in diameter. The loads determined how to size the steel work as well. MOSES determined those loads and the wave clearances required to confirm the structural strength of the platform. The use of MOSES reduced the amount of steel required in the platform and for sea fastening and proved that this unique, reusable platform concept would work.
MOSES determined the loads using a five-body model. A verification model test confirmed the results. After confirming the accuracy of the MOSES analysis, Orca Offshore used MOSES to confirm the structural strength of the complete platform during transport and installation. This was done using the MOSES spectral structural solver in the frequency domain. Using this method, the structural loading could be derived accurately without undue conservatism.