543
1
INTRODUCTIONANDMOTIVATION
Due to ever energy hunger economies of the world
thenaturalgastrademarkethasseenarapidgrowth
inthelast20years.(DavidA.Wood2012)Alsodueto
geographical and political reasons natural gas
industryhasbeenforcedtoprovideotherwaysthan
the pipe lines to deliver the commodity to required
markets.
Thus Liquefied Natural Gas Carrier ships have
born. First LNG carrier “Methane Pioneer” has left
Calcaseieu River on 25 January 1959 and she was a
tinyonecomparedtotoday’s standards only having
5034 tons deadweight. Growing market and
advantageofcost
inbulkcarriagealsoboostthesize
and change the characteristic of LNG carriers
(Starosta,2007).Today’sthebiggestLNGcarrierisa
giantofaship“Q”typeLNGcarrierswith345meters
lengthoverallandhasacargocapacityofa 266.000
cubicmeterswhichequalsto161.994.000
cubicmeters
of natural gas. This is the dynamic change in
shipping.
Buton theother handas this LNGtrade is done
via seaway since 1959 there are lots of already
constructedcoastalfacilitieswhichareusedtoaccept
thishighlyspecializedcargobut from smallerships.
Dueto
thegreatinitialbuildingcostsofsuchfacilities,
itisextremelyhardtoconstructnewterminalsfrom
scratch for every new breed of LNG carrier borns.
Thusitisbeenacceptedthatthispartofthetradeis
muchmorestatic.
The Mooring Pattern Study
for Q-Flex Type LNG
Carriers Scheduled for Berthing at Ege Gaz Aliaga
LNG Terminal
S.Nas,Y.Zorba&E.Ucan
DokuzEylulUniversityMaritimeFaculty,Turkey
ABSTRACT:EvergrowingenergyindustryrequireslargerquantitiesofLNGtobetransportedbybiggerships
betweenterminals.Everyday,newkindoflargevesselscreatedbynewtechnologies,andtheseareusedto
tradearound the globe. This isthe dynamic change inshippingindustry. But on theother hand
these new
vesselsneedtosafelyberthtoexistingterminalswhichwemayacceptasmorestaticpartofthetrade.
ThusthisstudybornbytherequestofEgeGazAliagaLNGTerminalmanagementtodetermineifitissafeto
berthtotheterminalbyanewbreed
oflargeLNGcarriertypenamedasQ‐FlexandQ‐Max.TransasBridge
SimulatorNTPRO5000serieswasusedinthisstudyforextensiveexperimentswhichhadbeensimulatedby
theuseofhookfunction.Duringthestudy,everyforceappliedtomooringhooksanddolphinsbytheship
lines
weredividedinto3dimensionsandthenmeasuredbysimulationexperiments.Withanalysisofthedata,
required hook and dolphins strengths were determined for the safe mooring arrangements. Upon the
completionofthestudyEgeGazAliagaLNGTerminalbecamethefirstsafeberthforQ‐Flextypevesselsin
the
MediterraneanandtheBlackSea.Andfinallyallexperimentswereconfirmedwithreallifeexperiencewhen
thefirstQ‐FlextypeLNGcarrierberthedtotheEgeGazAliagaLNGTerminal.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 8
Number 4
December 2014
DOI:10.12716/1001.08.04.08
544
Nevertheless with careful planning, study and
with the calculation of risks an existing terminal
mightbeevaluatedthatifithascorrectarrangements
andqualitiestoreceivethenewclassofshipsorthe
newrequirementsfortheterminaltosafelyacceptthe
shipswhichmightnotevenbeendiscovered
whenthe
terminalwasfirstplanned.
MostlyaboveriskanalysesforLNGterminalsand
shippingdependoncomputermodels(Er, 2007).
2
MOTIVATIONOFTHESTUDY
Thisstudyisbornbytherequestof Ege GazAliaga
LNGTerminalManagementtodetermineifitissafe
toberthtotheirexistingterminalbya new breed of
largeLNGcarriertypevesselnamedasQ‐Flex.
Aliaga LNG Terminal which one of the
two
existing LNG Terminals in Turkey is constructed
between1998and2002andhasstarteditsoperation
in2006. Strategic technical specifications of Ege Gaz
AliağaLNGTerminalarestatedbelow;
Ege Gaz Aliağa LNG Terminal has 2 full
containment LNG storage tanks, each with a
capacityof140000m
3
,
EgeGazAliağaLNGTerminal’smeteorologically
convenient position and direction allow for the
efficientpassingofshiptraffic,
Re‐gasification and send‐out capacity:6 bcm/y of
highpressure,
Jettydesign: CapableofhandlingthelargestLNG
carriersintheworldandhasa17meterdraft
Location of Ege Gaz Aliağa LNG Terminal is
showninFigure1.
Figure1.LocationofTheEgeGazAliağaLNGTerminal
ButasdescribedbelowfirstQ‐Flexvesselwasnot
even built in 2006. In detail, “Q” type LNG carriers
arethestateoftheartvesselswhicharedesignedto
be more efficient and clean than the regular LNG
carriers and first delivered to service in 2007. They
weredesigned
asmembranetypecarriersandhavea
capacity between 210.000 and 216.000 cubic meters
which makes them the world’s largest carriers until
theentryintoserviceoftheQ‐MaxtypeLNGcarriers.
Principal dimensions and the tonnages of the “Q”
typeLNGshipsareshowninTable1.
In
thecompletionofthisstudyitisrevealedthatif
the terminal is compatible with the Q‐Flex type
vessels without any new upgrade in terms of
equipmentorconstructionornot.
Table 1. Principal Dimensions and Tonnages of the “Q”
TypeLNGShips
_______________________________________________
“Q”TypeLNGShips Q‐Flex*
1
Q‐Max*
2
_______________________________________________
LOA315m.345m.
LBP302m.332m.
Breadth50m.53,8m.
Draught(Loaded) 12,50m.12,2m.
Draught(Ballast)9,60m.9,60m.
SeaSpeed(Loaded) 21,1Knots 20,1Knots
Capacity217.000m
3
265.940m
3
DWT109.502ton 130.128ton
GRT135.848163.922
_______________________________________________
*
1
M/VAlShamal(SamsungHICL)
*
2
M/VAlDafna(SamsungHICL)
3 METHODOLOGY
3.1
Theaimofthestudy
The main aim of this study is to find a reliable and
verifiable and risk free solution to determine the
requiredmooring pattern arrangements of a specific
terminal for safe maneuvers of a specific ship type
beforesuchaneventhappensinreality.
The term “mooring pattern” refers to the
geometric
arrangementofmooringlinesbetweenthe
ship and the berth (OCIMF, 2008). Manifolds
connectionandotherinterfacesarenotinthescopeof
thestudy.
Itshouldbenotedthattheindustryhaspreviously
standardized on the concept of a generic mooring
layout, taking into account Standard environmental
criteria. The
generic mooring layout is mainly
applicable to a “multi‐directional” environment and
to the design of ship’s mooring equipment. For
general applications, the mooring pattern must be
able to cope with environmental forces from any
direction. This can best be approached by splitting
theseforcesintoalongitudinal,lateralanda
vertical
component and then calculating how to most
effectivelyresistthem.
Theship’smooringlinesshouldbeabletoholdthe
ship in position with wind speeds of 60 knots
(31m/sec)(OCIMF.2008;18).QFlextypevesselhave
20 sets of mooring lines with
Ø44 mm. ultra high
molecular weight polyethylene. Each mooring line
has MBL of 137 tons. However, the SWL value of
terminal mooring arrangements should be not less
thanMBLoftheshipmooringline(OCIMF.2008;26).
3.2
PreparationforSimulationExperiment
Studies were prepared according to OCIMF (2008)
Mooring Arrangements Guide 3
rd
Edition, SIGTTO
“Prediction of Wind Loads on Large Liquefied Gas
Carriers”andvariousothersources.
545
Study was begun with the preparation of model
simulation of Ege Gaz Aliaga LNG Terminal and
development of area simulation. Q‐Flex Type LNG
carrier’sloaded andballasted models were supplied
fromTransasCompany.
Supplied model LNG 10, had been installed to
bridge simulator. During the verification test on the
LNG 10 model, mooring arrangement was found
inconsistentwithrealQ‐FlexTypeLNGcarrier.
In this context, simulation model’s mooring
arrangement was requested to be re‐developed by
Transas Company according to real Q‐Flex LNG
carrier’s mooring arrangements blueprint. Re‐
developed and corrected LNG 10 model had been
testedforre‐validation.
In the process, simulation model’s different
characteristicswerecomparedwiththerealshipand
aerodynamiccoefficientsofLNG10Modelhavebeen
found inappropriate. Simulation model’s
aerodynamic coefficients were requested to be re‐
developedbyTransasCompany.
Lastlyre‐developedandcorrectedmodelandarea
simulation were
installed to bridge simulator to be
used in project experiments. Also experience of
RasGas Company and Aliaga LNG Terminal
Management’s experts are consulted to confirm
reliabilityandvalidityofsimulationmodels.
Then the Transas Bridge Simulator NTPRO 5000
serieswasusedforextensiveexperimentswhichhad
beensimulatedbythe
useof“Hook”function.Every
force applied to mooring hooks and dolphins are
calculatedandrecorded.
3.3
ReliabilityofDatacollectionmethod
To analysis the data obtained from simulation
experimenthookfunction,themathematicalmodelof
the simulation is have to be examined according to
the “mathematical models technical description” of
Transas;
Theshipitselfis acontrolled object.The steering
gears are propellers, rudders, anchor and mooring
systemsetc.Thesemeanthe
forcesonshiphull.The
valueofforcesdirectlydependsonthecontrolvalue
changes.
Thoughactualshipmotioninrealworldcanonly
bedescribedwithconsiderationofadditionalexternal
forces. External forces deriving from wind, current,
waves, channel geometry (the influence of water
depth, walls, bottom inclination, etc.)
and the
presenceofotherobjects(movingorimmovable)are
showninFigure2.
Figure2.ExternalForcesontheShipModel
Thus, it is extremely important to consider the
environmentalconditionsusedformooringmodelin
thestudy.
Simulation’s mathematical wind model can be
expressedasfollows:Theairflowaroundtheshipis
consideredasuniformflowofconstantdirectionand
velocity.ThewindvelocityatgivenBeaufortnumber
is obtained
as average value of wind velocity at 6
meters height above the sea level. Formulas for
calculatingtheaerodynamicforcesandmomentsare
as follows; aerodynamic longitudinal force (F
xA),
aerodynamiclateralforce(F
yA),aerodynamicvertical
force(F
zA),vessel course (φ), relativewinddirection
(φ
w),andspeed(Vw)asshowninFigure3.
Figure3.WindForces
For the environmental conditions used in
simulation experiments, OCIMF’s Mooring
EquipmentGuidelinesThirdEdition(2008)istakenas
reference for Mooring Model Study in compliance
with the local meteorological data gathered and
verifiedfromvarioussources.
Wind :30m/sec
Current:0,1m/sec–004
0
Wave :0meters
As can be seen from above values the most
dominant and important environmental condition is
determined as wind. Even though the prevailing
wind inthe region is from NNE – NE, according to
multi‐directional environmental forces mentioned in
Mooring Equipment Guidelines, wind was taken
from
everyanglein10degreestepsfor180degree.
546
Relativeandtrue directionsofthe winds usedin
simulation experiments are shown in Figure 4. In
relation to the wind velocity, 30m/sec is the highest
possiblewindvelocitywhichcanbeappliedinBridge
Simulator,Thus60knotsofwindvelocitycouldn’tbe
reached in simulation experiments and the
highest
value,58,3knots(30m/sec)wasapplied.
Figure4.WindDirectionsUsedinSimulationExperiments
In simulation experiments, formulas for
calculatingtheaerodynamicforcecomponentsareas
follows(Transas,2003);
2
AAHwk AwkN AA N
FC dC ,A0.5VAA
FA=Aerodynamicforcecomponents
САH=Non‐dimensional aerodynamic force
components
φwk =Relativewindvelocity
dCA =The additional values of non‐dimensional
aerodynamic force components due to the
superstructures.
AN =The superstructure area projected to the
centralplaneandtothemidshipplane
ρA= Relativewindanglevelocity.
VA =Relativewindvelocity.
A = The above water hull area projected to the
centralplaneandtothemidshipplane.
AN = The superstructure area projected to the
centralplaneandtothemidshipplane.
Structural formulas for complete aerodynamic
characteristics calculating are defined by functions
representedbypartialsumsofFourierseries.
Coefficients are depended on the superstructure
area and above‐water hull area and are provided in
thedatabase
ofthesoftware.
Another important factor for mooring pattern
study is of course the mooring arrangement of ship
andtheterminal.
Forthereliabilityandvalidityofthestudy,areal
Q‐FlexTypevessel,M/TAlHuwaila’sdatawastaken
asareference in simulationexperimentsand datais
listed
below. They are used with same values in
experiments.
NumberofMooringRopes:10atbow10atafttotal
20piecesmooringropes.
TypeofMooringRopes: UltraHighMolecular
WeightPolyethylene
MBLofMooringRopes: 137tons(Max.BL)
Terminals mooring arrangements are also shown
in the
Figure 5 in relation to the Q‐Flex type LNG
carrier.Eachmooringlinefastenedtoahookon the
dolphins.Angles and distances of the mooring lines
wereautomaticallycalculatedbysimulationsoftware
whichaccepted the mooring pattern of the vessel as
genericmooringlayout.
Figure5.MooringModel
Transas software’s mooring model can be
describedasfollows:Themooringgearconsistsofthe
mooring lines and docking winches. Mooring line
diameter and type, winch type, choke positions are
takenintoaccount.
A mooring line is modeled as a weightless
stretchable thread without considering its special
configuration. The model describes
the influence of
mooring lines from the winch to the another ship’s
choke,bollardormooringring.Twowinchoperation
conditions are examined: constant length conditions
(“stop” conditions) and constant tension condition.
Thelastconditionsupposedtohaveconstantvalueof
the force at ship’s end of tow‐line. The
force is
considered to be directed along the tow‐line. Both
conditionsareusedinthisstudy.
547
3.4
MooringpatternsimulationExperimentsand
Analysis
Itwasdeterminedthattheballastedshipwithbigger
windeffectareaisalwaysgivinghighervalueresults.
Thusitwasconsideredthattheballastedshipmodel
wasbettersuitedtomeasuretherequiredstrengthof
mooringarrangementsoftheterminal.
Totally 20 ropes had been moored to hooks on
dolphins
forLNGmodel10andthen16tonsofforce
was applied to each one automatically. For start of
LNG10modelsimulationexperiment,equilibriumof
forcesonthehooksandequalizationofropelengths
werewaited.
Whenever an environmental condition was
changed, to acquire the correct data, equilibrium of
forcesonthehooksshouldbewaited.Toreducethe
waiting times “Fast Time Simulation” practice was
used.
First installed environmental condition was
current in the experiment. Current’s effects on the
hooks had been observed but found negligible for
recording. Thereupon wind was installed to
experiment from 000
0
relative direction with the
velocityof10m/sec.
When forces had been equalized wind velocity
wasincreasedto20m/sec.Afterthenewequilibrium
had been achieved, wind velocity was increased to
upper limit of Bridge Simulator, to 30m/sec.
Equilibrium of forces on hooks was waited when
30m/secvelocitywasreached.
Data
recorded after forces were equalized.
Equilibriumprocessofforcesonthehooksisshown
inFigure6.
Figure6.Equilibriumprocessofforcesonthehooks
Afterward wind direction had been started to
changeby10
0
stepsinclockwiserotation.Eachtime
oscillationshadbeenwaitedtoreachequilibriumand
then data of longitudinal, lateral and vertical forces
ontheeachhookwasrecorded.
During simulation experiments the force applied
to hooks separately identified as 3 different
components longitudinal, lateral and vertical.
Diagram of these
force components are shown in
Figure 7. As can be seen in Figure 6 longitudinal
forces’directiontowardstothebowofshipwastaken
as (‐) and direction towards to the stern of the ship
was accepted as (+). Lateral forces’ direction to the
terminal was taken as (
‐) and direction away from
terminalwasacceptedas(+).Verticalforces’upwards
direction was taken as (‐) and downwards direction
wasacceptedas(+).
Figure 7. Components and Directions of Forces on the
Hooks
In simulation experiments, each force component
occurredoneachhookfromeverywinddirectionwas
measured and recorded separately. Furthermore,
obtained data is shown in graphics. An example
graphicofthe#1hookisgiveninFigure8.
Figure8.ForceComponentsonthe#1Hook
3.5 MooringModelSimulationExperimentResults
Detaileddataofeachlongitudinal,lateralandvertical
forcecomponentoneverymooringhookismeasured.
Basedonthisdata,detailedtotallongitudinal,lateral
and vertical forces occurring on each dolphin were
calculated.
548
From this data because of environmental
conditions, the maximum occurred longitudinal,
lateral and vertical forces, on dolphins were
calculatedandshowninTable2.Asthelateralforces,
the maximum force of 139,3 tons occurred on M7
dolphin. As the longitudinal forces, the maximum
forceof109,1tonsoccurredon
B1dolphin.Asvertical
forces,themaximumforceof‐52,5tons occurredon
M7dolphin.
Table2.TotalForcesOccurredonDolphins
_______________________________________________
DolphinFORCESTotalSWL
Number Lateral Longi. Vertical
_______________________________________________
M1 125,8 ‐33,4 ‐33,43x150=450
M2 117,3 17,9 ‐34,43x150=450
M3 49,0 33,4 ‐16,83x150=450
B114,6 109,1 ‐34,32x150=300
B415,4 ‐100,1‐33,22x150=300
M6 85,1 ‐30,6 ‐36,73x150=450
M7 139,3 14,5 ‐52,53x150=450
M8 115,3 23,7 ‐38,43x150=450
_______________________________________________
Themaximumcalculatedforcevaluesthatcaused
byQ‐FlexBallastedLNGCarrierwhichisberthedat
Ege Gaz Aliaga LNG Terminal and under
environmental conditions of 30m/sec wind from
various directions and with a stable current of
0.1m/sec are compared with the SWL value of
terminalmooringarrangements.
4
CONCLUSIONS
According to the comparison between the existing
hooks’SWLsandtheforceswhichwillbeoccurredon
the hooks when Q‐Flex vessel berthed, it is
determined that mooring equipment are well
sufficientforsuchforces.
This study revealed that Ege Gaz Aliaga LNG
Terminal is well suited and a
safe berth for Q‐Flex
TypeLNGcarriers.Uponthecompletionofthestudy
EgeGaz Aliaga LNG Terminal became the first safe
berth for Q‐Flex type vessels in the Mediterranean
andthe Black Sea. And finally all experiments were
confirmedwithreallifeexperiencewhenthefirstQ‐
FlextypeLNGcarrierberthedtotheEgeGazAliaga
LNGTerminal(25.11.2011).
Also this study revealed that adequate bridge
simulation systems can be used to evaluate the
compatibility of the more static part of shipping
bussiness like terminals to more dynamic part of
shipping as ships reliabily, efficiently and without
taking any unnecessary risks in terms of mooring
patternandarrangementstudies.
ACKNOWLEDGEMENT
Authors gratefully acknowledge to Mr. Ibrahim
Akbal,GeneralDirectorofEgeGaz.
Authorsalsowouldliketogiveaspecialthankto
Mr.MasumGuven,ManagerofEgeGazAliagaLNG
TerminalandCapt.KhaledDjebbar,Marine
Support
&ProjectsManagerofRasGas.
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