Gangway motion evaluation of an accommodation vessel operating along a turret moored FPSO

摘要

A monohull accommodation vessel (UMS) is going to be designated toservice single point turret moored FPSO. A large offshore gangway isemployed to connect the FPSO and the UMS, transferring hundreds ofpersons every day. Two challenging issues are identified at currentstage of feasibility study. The first issue is to ensure adequate DPcapacity of UMS to follow up FPSO’s response, and yaw motion inparticular, because of weather vanning mooring system. The secondissue, the main objective of this paper, concerns gangway workabilityand safety, due to relative motions of two vessels, by considering thecomplexities and uncertainties introduced by hydrodynamicinteractions between two bodies. Indeed, due to the interaction effect,the motion characteristics like heave and roll of the vessels, especiallyfor UMS of smaller displacement are significantly modified andamplified according to our multi-body hydrodynamic analysis, which isa disadvantageous way for gangway operation. Hydrodynamicinteractions associated with the relative position of the vessels anddifferent scenarios, other than parallel side-by-side, were studied andpredicted hydrodynamics, motions and gangway responses are reported.The spectra analysis was carried out, according to long term wavescatter diagram. After having checked with various criteria, the resultsindicate that this operation service is feasible and that adequate up-timeis achieved. Furthermore, a 1:50 multi-body hydrodynamic model testwas conducted by MARINTEK, and an excellent agreement has beenobtained between experiment and numerical simulation. Bothsimulation and measurement accurately captured extra peaks in motionRAOs besides natural period of motion itself, which reflect the impactof multi-body interaction.