The Fatigue Assessment For Bilge Box Structures Of A Cylindrical Floating Accommodation Platform

FAU(Floating Accommodation Unit) is an auxiliary Accommodation unit, which can both provide service of living facilities for Marine fixed facilities, Spar platform, FPSO(floating production, storage offloading), such as accommodation, food, entertainment, warehousing, and offer auxiliary support for the whole process of oil and gas field development, gradually becomes one of the hot spots in the marine engineering equipment building market.Fatigue is one of the most important failure modes in ship and offshore structures. Fatigue strength assessment of ship and offshore structures has always been the concern of the ship and ocean engineering for many years. At present, further research and exploration has been made for fatigue strength assessment of ship, the Column-Stabilized semi-submersible and jack-up platform structures, while the research of fatigue strength assessment for cylindrical platform structures less relatively. The cylindrical platform, including accommodation unit, has special structures different from other types of platforms, which have many toe ends in horizontal ring stringers. Due to the high dynamic loads, the stresses in those structures are more likely to concentrate then lead to fatigue damage, especially that closed to draft waterline. The research target of this paper is a cylindrical floating accommodation platform, which is converted from a FPSO. In order to reduce the heave motion amplitude, a new ring skirt bilge structure offering greater damping has been added to the original bilge box structures. The new bilge structures has a significantly larger radius than main hull, which can effectively reducing heave amplitude, as well suffered huge dynamic load and bending moment from waves. So fatigue damage are easy to generated in the connection structures between the main hull and bilge box. As an accommodation unit, it’s particularly more important to guarantee platform of life and property safe, and very imperative to check the fatigue strength.The paper aims to a cylindrical accommodation platform building in shipyard. Based on DNV-rules (fatigue design of offshore steel structures and fatigue assessment of ship structures), fatigue strength assessment of newly added bilge box structures and stringer toe ends closed to draft waterline was carried out using simplified fatigue analysis method combined with spectrum analysis method by SESAM software. The fatigue life of the structures was calculated to provide the reference for the design and construction of cylindrical accommodation platform, which has important significance to practical engineering.