FPSO/FLNG mooring system evaluation by Gaidai reliability method

Abstract

Floating production storage and offloading unit (FPSO) is an offshore vessel, producing, storing natural gas or crude oil, prior to oil shuttle tanker transport. The equivalent of natural gas is known as floating liquefied natural gas (FLNG). Robust prediction of the extreme mooring hawser tensions, during FPSO operations, is an important design and engineering reliability and safety concern. Excessive mooring hawser tensions may occur during certain types of offloading operations, posing potential operational risks. In this study, ANSYS-AQWA-software package has been used to model vessel dynamics, subjected to hydrodynamic wave loads, acting on FPSO or liquefied natural gas (LNG) vessel, under actual in situ environmental conditions. Experimental validation of the numerical results has been briefly discussed as well.

This study presents novel multi-dimensional reliability method, based on Monte Carlo simulations (or alternatively on measurements). Proposed methodology provides accurate failure or damage risks assessment, utilizing available underlying dataset efficiently. Described approach may be well utilized at the vessel design stage, while selecting optimal vessel’s parameters, minimizing potential FPSO mooring hawser tensions. The aim of this study was to benchmark state of the art Gaidai reliability method, proposed recently; this novel methodology opens up the possibility to predict simply and efficiently failure or damage risks for non-linear multi-dimensional dynamic offshore energy system as a whole.

Key advantage of the suggested methodology is its multi-dimensionality (with unlimited number of system dimensions/components/processes, all having different physical dimensions), while classic reliability methods typically are not covering dimensions higher than two.