Hydrodynamic Study of Free Standing Drilling Risers under Typhoon Generated Swell

Abstract A Free Standing Drilling Riser (FSDR) is a modification to drilling risers that enables rapid disconnection in an event of a typhoon. Air cans were installed to keep the drilling riser standing upright at its original location whilst the drilling rig sails away to safety. This mechanism can be used during a typhoon event as pulling back the whole riser string is a time exhaustive procedure. Typhoon occurring from distant seas can generate strong long period swell. Despite numerous studies on FSDR mechanism, the effect of typhoon generated swell on FSDR have not been reported. The objective of this paper is to study the hydrodynamic response of the FSDR mechanism under typhoon generated swell. Four sensitivity analysis based on swell height, swell period, wind wave height and wind wave period were conducted in Orcaflex10.1c finite element modelling software. The results shown that FSDR mechanism were reliable under typhoon generated swell. With the increase in swell height and swell period, the FSDR hydrodynamic response (lateral displacement, bending moment and von Mises stresses) increases. Since the disconnected FSDR was located out of the wave impact zone, increase in wind wave height and period have little to no effect on the hydrodynamic response.