PS6-6.1

OPERATING MEMBRANE LNG CARRIERS—PARTIAL LOADINGCASES FOR 160 000M3 VESSELS AND BEYOND

EXPLOITATION DES NAVIRES METHANIERS A CUVESMEMBRANES—CAS DES REMPLISSAGES PARTIELS POUR

DES CAPACITES POUVANT ATTEINDRE 160 000 M3 ET PLUS

Joël TessierEngineering Manager

Laurent SpittaelDeputy Manager

GAZTRANSPORT & TECHNIGAZ46, Avenue des Freres Lumiere

78140 Trappes, France

ABSTRACT

LNG carriers are usually dedicated to long term contracts and the vessels involved areoperated either fully loaded or with a minimum cargo during the ballast return voyage.This minimum cargo is spread in all tanks for voyages of a small or medium length or isgrouped in one tank for long voyages.

Modifications of traditional LNG trades are appearing due to FPSO/FSRU and theirshuttle vessels and to spot cargoes.

To take into account these new trades and the related specific operating conditions,LNG vessels and FPSO/FSRU have to allow partial filling levels in their tanks.

Today, some membrane LNG carriers (the AMAN series built by N.K.K. shipyard inJapan) can already be operated without any filling limitation.

The range of filling levels authorized can be increased for vessels operating in zoneswhere limited sea states are encountered.

Recently, the results given by studies on liquid motion in LNG tanks made for FPSOand FSRU allowed for a better understanding of the phenomenon encountered in partialfillings in membrane tanks. Complementary studies have been made for LNG vesselswith a capacity of 160,000 m3 and more.

The results of these studies show that partial fillings are acceptable in membranetanks. This additional flexibility given to membrane LNG carriers allows fortransportation of any cargo volume up to the maximum vessel capacity.

RESUME

Les navires méthaniers sont généralement dédiés à des contrats de transport à longterme et sont alors opérés soit en charge à leur capacité maximum soit sur ballast avec leminimum de cargaison répartie sur l’ensemble des cuves pour des voyages de courte oumoyenne durée ou sur une seule cuve pour des voyages de longue durée.

PS6-6.2

De nouveaux marchés apparaissent pour le GNL: les FPSO/FSRU et leurs naviresnavettes et les livraisons SPOT.

Pour répondre à ces nouveaux marchés ainsi qu’aux conditions particulièresd’opération les navires méthaniers et les FPSO/FSRU doivent pouvoir être utilisés avecdes remplissages partiels.

Actuellement des navires méthaniers à cuves membranes (la série des AMANconstruits par NKK) ont déjà la possibilité d’être utilisés sans limitation de remplissages.

Les niveaux de remplissage autorisés peuvent être élargis pour des navires opérantdans des zones où la mer est soumise à des spectres de houle limités.

Ces dernières années des études de mouvement de liquide faites sur les FPSO etFSRU ont permis de mieux appréhender les remplissages partiels dans les cuvesmembranes. Des études complémentaires ont alors été réalisées sur des cuves de naviresméthaniers dont la capacité peut atteindre 160.000m3 et plus.

Les résultats de ces études montrent que des remplissages partiels sont acceptablesdans les cuves membranes. Cette nouvelle flexibilité offerte par les navires méthaniers àcuves membranes permet d'assurer le transport de toute cargaison de GNL de volumeégal ou inférieur à la capacité maximum du navire.

PS6-6.3

OPERATING MEMBRANE LNG CARRIERS—PARTIAL LOADINGCASES FOR 160 000M3 VESSELS AND BEYOND

1. INTRODUCTION

Tank partial loading are now more and more needed on board LNG Carriers due topresent and future markets.

In the past the partial filling level was not required but partial loading wasexperienced. The first experience for partial loading (end of years seventies) was onboard the LNG Carrier named BEN FRANKLIN. On this membrane LNG ship a onemonth voyage was done between Persian gulf and Gironde estuary in France through theCap with 6 tanks filled, at 80% of tanks height, with LPG having a higher density thanthe LNG (0.6 instead of 0.47) without any trouble.

In the middle of years eighties the tank partial loading was considered in case of theAustralian LNG Project. For this project due to the presence of typhoon in the area of theloading terminal the LNG Ships should be able to leave the loading berth under a shortnotice. At that time two solutions were studied for the GTT membrane LNG Carriers:

- a procedure for tank loading in order to be able at any time to continue or stop theloading and/or to transfer the cargo from tank to tank to reach conventionalacceptable filling level in all tanks (below 10% of tanks length or greater than 80% oftanks height) during the short notice,

- the possibility to accept any filling level inside tanks thanks to model tests done inGTT laboratory and computer analysis done by Lloyd's Register (LR).

At that time GTT got LR approval to load at any level a 125,000 m3 five tanksmembrane LNG Carrier.

As in general LNG Carriers are usually dedicated to long term contracts they arealways operated with tanks fully loaded or with minimum level of LNG inside tanksduring ballast voyage.

Today four LNG Carriers built by NKK Shipyard in Japan (the AMAN series) canalready be operated without any filling level limitation.

For LNG Ships under construction, range of filling levels is increased when they areoperated in zones where limited sea states are encountered.

Very recently , the results given by studies and tests on liquid motion in LNG tank,made for FPSO and FSRU up to 200,000m3 capacity with 4 or 3 tanks allowed for abetter understanding of the phenomenon encountered in partial fillings in membranetanks.

The result is such, today, that partial filling can be considered on membrane LNGCarriers. This is the reason of the partial filling levels study done on LNG Carriers withcapacities of 138,000 and 163,000 m3.

2. GENERAL CONCEPTION OF LNG VESSELS WITH MEMBRANE TANKS

Membrane LNG Vessels are generally designed with 4 tanks.Tanks are octagonalwith top chamfers equal at least to 30% of the tank height and lower chamfers dimensionsgovern mainly by the ship hull structure in general.

PS6-6.4

Up to now tank length is accepted up to 17% of ship length between perpendiculars.

The filling levels already approved are:

- lower than 10% of tank length,or

- greater than 80% of tank height.

For the upper filling levels, the liquid free surface is rectangular which avoid to havethe same liquid resonance frequencies in longitudinal and transversal ways (under pitchand roll).

The containment systems GTT MARK III and NO 96 are designed to withstand atleast the maximum pressure loads which can occur under the above approved fillinglevels.

The MARK III containment system presents the same resistance against liquidpressure loads on any location inside the tank.

In case of NO 96 the containment system is reinforced on the upper part of the tank(down to 70% of tank height) to be able to withstand the pressure loads due to liquidmotions inside tank (The reinforced area can be increased if needed in case of tank partialloading).

3. SHIP PROJECTS CONSIDERED

Two ship projects have been considered for the study concerning the tank partialfilling:

- one 138,100 m3 LNG Carrier under construction, with the membrane system GTTNO 96, in DAEWOO in KOREA,and,

- one 163,700 m3 LNG Carrier project design by GTT, with the membrane systemGTT MARK III, near the maximum size able to reach the Japanese main receivingLNG terminals.

3.1. Main characteristics of the 138,100 m3 LNG Carrier(See the ship arrangement in appendix 1.)

Main characteristicsLength overall 277.000 mLength between perpendiculars 266.000 mMoulded breadth 43.440 mDepth 26.000 mDesign draught 11.400 mNumber of tanks 4Capacity at 100% 138,100 m3

Displacement 100,132 tDesign speed 20.5 Knots

Tank N° 2 dimensionsCapacity at 100% 40,449 m3

Length 43.720 mBreadth 37.898 m

PS6-6.5

Height 26.758 mUpper chamfer 8.638 mLower chamfer 3.778 m

3.2. Main characteristics of the 163,700 m3 LNG Carrier(See the ship arrangement in appendix 2.)

Main characteristicsLength overall 292.000 mLength between perpendiculars 282.000 mMoulded breadth 44.800 mDepth 27.450 mDesign draught (arrival full loaded) 11.500 mNumber of tanks 4Capacity at 100% 163,700 m3

Displacement (arrival full loaded) 110,000 tDesign speed 19.5 Knots

Tank N° 2 dimensionsCapacity at 100% 47,458 m3

Length 47.940 mBreadth 39.100 mHeight 27.540 mUpper chamfer 8.290 mLower chamfer 4.210 m

4. METHODOLOGY USED FOR THE STUDY

4.1. Objective

This methodology is defined to study any LNG tank filling possibility from 0 to98.5% of tank height in conditions of the world-wide navigation. Subject ships are a138,100 m3 LNG carrier under construction in DAEWOO (Hull N° 2206) and a 163,700m3 LNG carrier designed by GTT.

The study is based on 1/70 scale liquid motion model tests results analysis. The liquidmotion model tests are performed in the GAZTRANSPORT & TECHNIGAZ laboratory.

4.2. General

The liquid motion is induced in tank model with different filling conditions and forseveral forced tank motions.

Tank N°2, of the two LNG carriers, is considered representative, as the most exposedtank of the biggest capacity.

Results of the sea-keeping analysis provided by using numerical code HYDROSTARhave allowed to determine forced tank motions as the excitation for the liquid motionsmodel tests.

The most severe world-wide environmental conditions are taken according to theNorth Atlantic all directions scatter diagram (Area 16) from the IACS working group orISSC.

PS6-6.6

The following conditions are considered:

− Five main wave-ship incidences (0°, 45°, 90°, 135° and 180°),Four intermediate wave-ship incidences (22.5°, 67.5°, 112.5° and 157.5°),

− Two ship’s speeds (Vmax – design ship’s speed – and 60%Vmax – reduced speed –),− Three intervals of the significant wave height associated with each mean apparent

wave period from the scatter diagram (HS∈[0 m, 5 m], HS∈[5 m, Hmax] and HS∈[0m, Hmax]).

The considered conditions are combined as following:

− Maximum ship’s speed is applied for all headings (from 0° to 180°),− Reduced speed is additionally considered for bow quarter headings (from 0° to 45°),− Significant wave height range from 0 m to maximum given in the wave table for

stern headings (from 90° to 180°), is associated with maximum ship’s speed,− Bow quarter headings (from 0° to 45°) are treated with significant wave height

limited on interval from 0m to 5m (for maximum ship’s speed) or from 5m till Hmax

(for reduced speed).

Serviceable navigation limit is determined according to direct computed maximumpermissible vertical acceleration on fore perpendicular for longitudinal and diagonaldirections or maximum permissible roll angle for transverse direction.

Tank is excited by a combination of sine motions which amplitudes and periodscorrespond to the ship motion response on navigation conditions. Longitudinal, transverseand diagonal directions are analysed for the case of tank resonant period. Additionally,double tank resonant period is considered for longitudinal and diagonal directions. Caseof ship’s maximum motions are treated even if being out of resonance.

The most critical cases observed in model testing is repeated by application ofirregular excitation in terms of time histories of relevant motions.

4.3. Procedure for determination of the sloshing model test conditions

- Step 1: determination of resonance area

Series of preliminary model tests have been performed in order to determineresonance area of subjected large-chamfered tank geometry. Optionally, results in Step 1could be obtained also by numerical simulation.

Tank excitation amplitudes are arbitrary chosen, according to the former testsexperience.

Test configuration was the following:

- Direction:- Longitudinal, excited in pitch at 3°- Transverse, excited in roll at 15°- Diagonal, excited in roll and pitch (respectively at 11° and 3°)

- Tank fillings:

- Several filling ratios from 10 to 95% of tank height (10, 30, 50, 70, 75, 80, 90 and95%)

PS6-6.7

- Step 2: determination of tank resonance curves

Tank resonant curves for filling ratios from 10 to 95% of tank height (longitudinal,transverse and diagonal directions) are determined according to the resonant frequenciesmeasured in Step1.

Supplementary, tank resonant frequency versus filling ratio curves are drawn outusing the theoretical formulations for prismatic tank:

- Resonant longitudinal frequency:

c

c

i

xi ·l4·lh

·g·thF

π

π

= for a rectangular tank

With:hi : liquid height (m)lc : length of free surface (m)

- Resonant Transverse frequency:

i

i

i

xi ·b4·bh

·g·th

Fπ

π

= for a rectangular tank

With:hi : liquid height (m)bi : width of free surface (m)

For transverse and diagonal directions actual breadth of the free surface is considered.

In case that magnitude of ship’s motion appears smaller than arbitrary chosen in Step1, tank resonant curve are interpolated between measured and theoretical one.

- Step 3: selection of filling ratios

Based on the assumption that for large chamfered tank geometry 70% of tank height(H) represents the lower corner of the upper chamfer, following filling ratios are testedfor filling above 70%:

1) Lower corner of upper chamfer, as discontinuity of the cross-section geometry(70%),

2) 90% of H, due to the most interactions with ceiling experienced with large chamfers,3) 95% of H, due to the impact pressure peak observed on previous tanks with

small upper chamfers,4) One intermediate upper chamfer level corresponding to the highest impact

pressure recorded in Step 1.

For filling levels lower than 70%:

5) 10% of tank length, corresponding to the maximum of the lower approvedfilling level,

6) 30% of H,7) 50% of H,8) Other intermediate filling levels between 10% of tank length and 70% of tank

height corresponding to the higher impact pressures recorded in Step.1 or to thehigher ship responses.

PS6-6.8

- Step 4: determination of wave frequency interval

Using the encounter frequency functional dependency of wave frequency, waveincidence and ship’s speed, characteristic curves are derived for following service cases:

1) Maximum ship’s speed (Vmax) for all headings (from 0° to 180°)2) Reduced ship’s speed (0.6Vmax) for bow quarter headings (from 0° to 45°)

For analysed range of fillings (10 to 98%), superposition of tank resonant curve andcharacteristic speed–heading curve resulted in wave frequency interval considered, foreach of listed service cases.

- Step 5: determination of worst navigation conditions

Environmental condition is defined according to the North Atlantic all directionsscatter diagram (Area 16) from the IACS working group or ISSC. Sea-state is representedby significant wave height (HS) and mean apparent or peak wave period (TMA or TP).

Wave period interval analysed [TMA,min, TMA,max] is derived directly from the wavefrequency interval determined in Step 4.

Criteria for the wave height limitation on extreme serviceable bound are followingship’s responses:

- maximum permissible vertical acceleration on fore perpendicular γFP,max

(for longitudinal and diagonal directions),- maximum permissible roll angle φmax

(for transverse direction).

Ship’s response on the wave of unit height (RAO-s) is computed for two loadingconditions (chosen among available from the loading plan, corresponding to the tankfillings height of 70% and of 20%), two ship’s speeds (Vmax and 0.6Vmax) and nineheadings (from 0 to 180°).

Each of the service cases are treated separately.

Vertical acceleration γFP (or roll angle φ) are derived from RAO-s, for each waveperiod from interval [TMA,min, TMA,max] iteratively over significant wave height HS, untilgiven criteria is satisfied. The highest significant wave height HS that gives acceptablevalue of vertical acceleration γFP ≤ γFP,max (or roll angle φ ≤ φmax) is associated withcorresponding wave period TMA, forming together representative sea-state couple.

- Step 6: computation of ship’s response

Ship’s motions relevant for this study are:

- Longitudinal direction : pitch, surge and heave- Transverse direction : roll, sway and heave- Diagonal direction : pitch, surge, roll, sway and heave

From ship’s response amplitude operators (RAO-s) computed in Step 5, maximumship’s motions are calculated for all represented sea-states and service cases.

Maximum ship’s motions are determined as maximum short-term value of the ship’sresponse at 1/10th level, with respect to the tank N°2 centre of gravity.

PS6-6.9

For relevant 5 d.o.f. motions, results are presented in following form:

- Amplitudes and phases of RAO as function of wave encounter frequenciesωe,

- Motion zero-crossing periods TZ as function of wave period (TMA or TP),- Maximum response amplitudes R1/10 as function of wave period

(TMA or TP),- Maximum response amplitudes R1/10 as function of corresponding zero-

crossing periods TZ.

Supplementary, for the test cases with recorded highest impact pressures,corresponding time-histories of relevant motions will be computed.

- Step 7: determination of tank liquid motion excitation

For each condition and tank filling selected in Step 3, following cases are treated:

1) Resonance

Maximum motion amplitudes corresponding to the tank resonant period TR or2⋅TR.

2) Maximum motion (if out of resonance)

Motion period TZ corresponding to the maximum motion amplitude.

Tank liquid motions excitation are determined as harmonic function combined ofrelevant motions (within the frames of the test equipment capacity) for consideredconditions:

1) Resonance

DIRECTION SHIP MOTION PERIOD SHIP SPEED

VmaxLongitudinal Pitch and Surge TR, 2⋅TR 0.6 Vmax

Transverse Roll or Sway TR Vmax

VmaxDiagonal Pitch, Surge and Roll TR, 2⋅TR 0.6 Vmax

Note: - Wave incidences corresponding to the diagonal direction are selectedas the most critical after the motion analysis completed (Step 6).

2) Maximum motion

DIRECTION SHIP MOTION LEADINGMOTION PERIOD SHIP

SPEED

Longitudinal Pitch and Surge Pitch TZ,θ Vmax

Transverse Roll or Sway Roll TZ,φ Vmax

Diagonal Pitch, Surge and Roll To be selected TZ,L..M. Vmax

Note: - Wave incidences corresponding to the diagonal direction are selectedas the most critical after the motion analysis completed (Step 6).

PS6-6.10

Pitch motion is generally considered as leading motion for longitudinal directionwhile roll motion is generally considered for transverse direction. For diagonal directionsleading motions are determined among relevant motions.

Motion amplitudes and periods are calculated in Step 6.

Phases between motions are taken from RAO-s computed in Step 5, for wave periodsTW corresponding to the tank motion period (TR or TZ).

Test cases with recorded highest impact pressures are repeated, applying correspondingirregular excitation calculated in Step 6.

4.4. Models testing

The tests consist in moving model tanks (1/70th scale) filled with water at ambientconditions in order to:

- Check the resonant period for a given filling ratio and amplitude,- Measure pressures at various locations for a given case (filling ratio, motions

amplitudes, periods and phases). Possible locations of pressure sensors are givenhereafter on the model tank sketch:

The test rig allows to perform in the same time three (3) various motions: Pitch byrotation around an axis, roll by rotation of a cylinder and surge by translation of acylinder within the first one. See picture below (top of next page):

PS6-6.11

The FROUDE similitude has been used for the tank motions.

Two (2) types of motions have been tested:

- Harmonic motions: With a fixed frequency for each motion and a fixed phasebetween motions if needed. The amplitude and frequency of motions are inaccordance to the hydrodynamic response of the ships,

- Irregular motions: With a time history file describing the motion of the tank ateach step of time.

PS6-6.12

4.4.1. Tests conditions

- External conditions:

- The tank is filled with water, at steady state ambient temperature- Atmospheric pressure- Harmonic or random excitations. The amplitude, frequency, phases are according

to the sea keeping analysis of the barges and the filling ratios selected.

- Instrumentation:

Six (6) pressure transducers have been used to record the impact pressures. They arelocated where impacts occur.

4.4.2. Tests procedure

The test programme is composed of:

- The determination of tanks resonant frequencies for various filling and variousleading motions (pitch, surge, sway, roll).As preliminary tank model tests havebeen performed before, the value of the liquid resonant frequency have beenestimated.

- An identification of the category of the resonant mode (standing wave, travellingwave, hydraulic jump etc…),

- Harmonic tests with the leading motion only. A measurement of the pressures onthe tank walls and comparison with the reference pressures of the LNG carriermodel,

- Harmonic tests with the leading motion plus possible other motions. Ameasurement of the pressures on the tank walls and comparison with thereference model pressures,

- Irregular motions for the worse cases with a time history file coming from thesea-keeping analysis.

4.4.3. Tests

Various filling ratios have been selected:

Once the filling ratios selected (high, low or intermediate levels), the tests begin by afrequency sweeping in order to get the resonant periods, then a recording of the impactpressures at these periods, with the maximum model tank motions.

- Detection / Recording

- a frequency sweeping is first done around the liquid resonance according to thepreliminary tank model tests and the area where the impact pressures occur areidentified,

- In the determined range, the step of the frequency sweeping is 0.01 Hz and thepressure transducers are located in the impact area,

- Once the resonant frequency is selected, the tests are carried out on a longduration so that at least two hundred (200) pressure impacts can be recorded forstatistical processing.

- Data processing

The data processing consists in:

PS6-6.13

- Identification of the category of the resonant mode (standing wave, travellingwave, hydraulic jump etc...),

- Calculating the statistical characteristics of the impact pressures:

- Pmax : Maximal Value of the N recorded impact pressures,- P10 : Mean of the 10 highest impact pressures,- PN/10 : Mean of the N/10 highest impact pressures,- PN/3 : Mean of the N/3 highest impact pressures.

N ≈ 200.

- Random motions

Time history files are provided to the test rig. The tank pressures are recorded duringthe tests in order to statistically analyse the impact pressures.

4.4.4. Tests results

The impact pressures are analysed through statistical tools in order to get pressurestatistical law F(pi) i.e probability (p ≥ pi) = F(pi), where p is the pressure. Knowing F,we can then determine the extreme possible value at 10-3 probability or P1/1000 by: F(pi) =10-3.

These laws are then used to evaluate the pressures P1/1000 , which are compared topressure references.

Hereafter the model tank is installed on the test rig (138,100 m3 LNG carrier tank N°2) with a 70% height filling level and a pitch motion. The location of the pressuretransducers can also be seen.

PS6-6.14

4.5. Criteria

The acceptability of the different filling levels on the two LNG carriers is based on acomparison of the two model tanks tests results with the reference results of the LNGcarrier model.

5. MODEL TESTING DATA AND RESULTS

5.1. Determination of test conditions

Typical values, tables and curves are given hereafter in case of model tank N° 2 of the138,100 m3 LNG carrier under pitching.

5.1.1 Resonance area

Filling level Pitch amplitude Pitch frequency

In % of tank height In degree In Hz

10 3 0.490

30 3 0.810

50 3 0.945

70 3 1.050

75 3 1.080

80 3 1.130

90 3 1.135

95 3 1.088

5.1.2. Resonance curves determined by calculation

In addition is added the curve of measured frequencies (below)

PS6-6.15

Theoritical and measured resonance frequencies in pitch on the tank n°2 model of the 138 100 m3 LNG carrier

0

0,2

0,4

0,6

0,8

1

1,2

0 20 40 60 80 100%H

Res

onan

ce F

requ

enci

es (H

z)

Fréquences Théoriques à f Fréquences réelles à f

5.1.3. Selection of filling levels

Under head sea (0°),

- Between 70 and 98% of tank height: 70, 80, 90 and 95%,- Under 70% of tank height: 50, 37, 30 and 27%.

PS6-6.16

5.1.4 Determination of wave frequency interval

0

2

4

6

8

10

12

14

16

18

0 0,5 1 1,5 2 2,5 3 3,5 4

Omega Wave Frequency

Om

ega

e E

ncou

nter

Fre

quen

cy

SPEED 20.5 knots

SPEED 12.3 knots

5.1.5. Determination of worst navigation conditions

- Global Wave Statistics – Zone 16 all directions – North Atlantic

TZ 4,5 5,5 6,5 7,5 8,5 9,5 10,5 11,5 12,5TmaHs

4,89 5,98 7,06 8,15 9,23 10,32 11,41 12,49 13,58sum

0,5 2 13 22 14 5 1 0 0 0 571,5 11 53 78 51 18 4 1 0 2162,5 4 31 77 80 44 15 4 1 2563,5 1 13 45 64 47 21 6 2 1994,5 4 21 37 34 18 7 2 1235,5 1 9 19 20 13 6 2 706,5 3 9 11 8 4 1 377,5 1 4 6 5 3 1 208,5 1 2 3 3 2 1 129,5 1 2 1 1 510,5 1 1 1 311,5 1 112,5 0Total 2 29 125 249 272 187 90 35 10 999

- Maximum permissible vertical acceleration on fore perpendicular

PS6-6.17

0

0.2

0.4

0.6

0.8

1

1.2

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Lambda (m) Wave length

Acc

eler

atio

n (m

/s²)

Angle 0 deg

- RAOs for the two different speeds and one loading condition (Tank filled at 70%of H)

PITCH - speed = 20.5 knots

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2Omega (rd/s)

Am

plitu

de (

dg/m

)

Speed = 20.5 knots Angle = 0 deg

Speed = 20.5 knots Angle = 45 deg

Speed = 20.5 knots Angle = 90 deg

Speed = 20.5 knots Angle = 135 deg

Speed = 20.5 knots Angle = 180 deg

Amplitude Wave = 1m

Waves Amplitude 1.0mSpeed 20.5 knots

PS6-6.18

PITCH - speed = 12.3 knots

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6Omega (rd/s)

Am

plitu

de (

deg/

m)

Speed = 12.3 knots Angle = 0 deg

Speed = 12.3 knots Angle = 45 deg

5.1.6. Computation of ship’s response (Loading condition: tanks filled above 70% of H)

Value 1/10 at COG Tank 2 Incidence 0 degree - SPEED 20.5 Knots

0

1

2

3

4

5

6

6 6,5 7 7,5 8 8,5 9 9,5 10 10,5 11 11,5 12 12,5 13

rTz(s)

V1/

10 (

dg

or

m)

V1/10 Pitch (dg)V1/10 Surge (m)Série3Resonance Tank 2

95%90%

70%

80%

Amplitude wave =

PS6-6.19

5.1.7. Determination of model tank liquid motion excitation(With two loading conditions: tank filled above or under 70% of H)

Tank fillinglevels in %Hand motions

Phase

in (°)

Frequency

In Hz

Frequency

In Hz

Amplitude

In (°)

Amplitude

In mmMotions Pitch Surge Pitch Surge

95 297.94 1.05 1.05 1.35 0 & 4.2995 302.57 0.837 0.837 5.32 0 & 890 332.54 1.1 1.1 0.90 0 & 3.7180 349.85 1.135 1.135 0.80 0 & 3.2770 322.16 1.087 1.087 1.03 0 & 3.8650 194 0.945 0.945 1.89. 4.7150 5 0.945 0.945 4.28 0 & 6.5730 349 0.809 0.809 4.93 0 & 10.7730 29 0.809 0.809 4.72 1737 325 0.875 0.875 5.56 0 & 9.8627 98 0.771 0.771 5.45 0 & 15.3

5.2. Results

Typical results are given hereafter in case of model tank N° 2 of the 138,100 m3 LNGcarrier under pitching plus surge.

Filling level (%)

Pressure in bar

95 90 80 70 50 37 30 27

Pmax 0.351 0.202 0.417 0.206 0.477 0.269 0.588 0.557P10 0.230 0.093 0.121 0.100 0.225 0.134 0.309 0.335

5.3. Conclusions

Taking into account the two GTT Membrane Systems:

- GTT MARK III offering the same resistance at any location inside the tanks,and- GTT NO 96 with possible reinforced insulation boxes to be installed at any

location inside tanks,

and the analysis of the results of the two model tank test campaigns, it appears that fillinglevels inside tanks between 10% of tank length up to 80% of tank height, of the two shipsstudied, could be considered in operation in addition to the conventional acceptablefilling levels (lower than 10% of tank length or greater than 80% of tank height).

138,100 M3 LNG CARRIER

GT&T No 96 System

163,700 M3 LNG CARRIER

266.00

2.802.802.802.802.80

32.8033.6044.8044.8056.80 39.20

Tank 121,935 m3

Tank 240,449 m3

Tank 340,449 m3

Tank 435,268 m3

27.8

4

38.98

43.40

32.7

5

26.0

0

3.20

GT&T MK III System

282.00

3.003.003.003.003.00

31.5437.3248.5448.5458.30 42.76

Tank 127,086 m3

Tank 247,458 m3

Tank 347,458 m3

Tank 441,740 m3

39.70

44.80

28.1

4

33.7

5

27.4

5

3.00