8/16/2019 En - FSO Mooring System
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SO and Shuttle Tanker in Tandem ConfigurationHydrodynamic
Analysis Finalized to the Structural
Verification of the SO Mooring System
Strength and Fatigue Verifications of an FSOmooring system have
been performed basingthe results on proper hydrodynamic
analysis(developed inside ANSYS-AQWA)and structuralanalyses
(developed inside ANSYS-Workbench)of the system and relevant
components .
Hs m) Tz s)
1 5 4 1
2 0 4.7
5 7
Sea-state assumed for the
Strength checks have been based on results obtained fromcontact
non-linear analysis performed of Finite ElementModel of Ecubier
ChainStopper under extreme load case(practicallythe chain minimum
breaking load).
Fatigue checks have been developed according to spectral
approach as required by DNVOS-E301(Position
Mooring),ana1ysisinott1oadingcondi1ion assuming proper S/N curve
data as reported in DNVRPHydrodynamic AnalysisThe FSO (109 .000
DWT),operated by Edison, is moored on theRospo MareOffshore Oil
Field. The FSO mooring is guarantees via6 chains connected to a
rotating turret, installed at the FSO bow.During the oil
offloadingoperation, the Shuttle Tanker(45.000 DWT)is moored, via
an hawser,at the FSOaft end .The offloading operation takes place
under proper sea conditions,with waves characterized by significant
height Hs) ad zero upcrossing period Tz). To each sea state,
consistent current and windhave been accounted for.
The hydrodynamic model (performed inside
ANSYS-AQWAsuite),simulating the FSO and the Shuttle Tanker (this
one moored, atits stern, to a Tug via a mooring cable), refers both
toaligned andmisaligned meteo conditions (current incoming at 50
degrees withrespect to wavedirection, wind incoming at 25 degrees
with respectto wavedirection).On the model FSO Shuttle Tanker
mooring lines), timedomain hydrodynamic analysis has been performed
for each definedsea-state , obtaining, for each mooring chain and
for the hawser
C203 (Fatigue Design of Offshore Steel Structures) .The assumed
hypothesis at the base of fatigue spectral approachis that the
stress range, S, is a random variable characterized by aprobability
density equal top(S) and that. for each sea-state, thenumber of
cycles having stress variation in the rangeof Sand S+dSis directly
related to nip(S), where niis the total number of cyclesof that
sea-state.
connecting FSO and Shuttle Tanker, theaxial tension as function
of Fig 1 - HydrodinamicModelofFSO MooringUnes Shutter
Tankertime.
In order to check the strength resistance of mooring
components(such as Chain Stoppers and Ecubier ) installed at the
rotatingturret, besides hydrodynamic analyses under offloading
conditions,also hydrodynamicanalyses of FSO in moored condition,for
extremestorm case (100 years return period), have
beenperformed.
Strength and Fatigue Verification ofChain-Stopper and
EcubierBased on results of hydrodynamic analysis performed for
bothextremeand offloadingconditions, strength and fatigue
verificationsof ChainStopper and Ecubier have beenperformed. Fig. 2
- Von Mises Stress distributionon cubier and ChainStopper
29 \N
