Page 141 - Marine Structural Design

Chapter 6 offshore Structural Analysis 117

registered in a specific country, the relevant requirements of the flag state authority shall also
be followed.
The main difference between an ocean-going ship and a site-specific FPSO is:
An FPSO is stationed in a specific site using mooring and anchoring systems, and
subjected to site-specific environmental conditions,
The operating life for an FPSO may be equal to or longer than 20 years,
Risers are attached to the FPSO hulls through riser porches or I-tubes,
Topside facilities may impose requirements such as motiodgreen-waterhafety and the
standard of living quarter is higher,
An FPSO may have cyclic offloading offshore with a frequency of approximately once per
week,
An FPSO is designed to have no dry docking imposing stricter requirements for
inspectiodmaintenance and repair.
Design and analysis of an FPSO include the following aspects @ai et a1 2001):
Vessel hull configuration selection
Design load case definition
Stability and compartmentation
Global performance
Greenwater
Intact strength covering transit, temporary conditions, extreme operating conditions, and
survival conditions
Structural strength in damaged condition
Mooring and riser systems
Topside consideration
The design load cases include:
In-place operating condition: environmental loads of up to 100 year return period,
quarteringhead seas (turret moored) or all headings (spread moored) and various loading
conditions from topsides, risers and mooring systems.
Survival Conditions: 100 years return environmenthesponses, worst loading conditions
from topsides and damaged conditions (for strength and stability)
Transportation Conditions: 10 years return period or less, ballast loading condition, dry
topside and head seas.
Installation and hoop up: selected weather window(s), ballast tanks, dry topsides and
heading of up to quarter seas
In developing the design criteria, consideration should be given to site-specific services,
including the following factors that may influence the hull actions:
Site-specific environmental conditions
Effect of mooring system