Ch ina Qua" En gineering . VoU ] . N o .1, pp.SI - 92.

China Ocean Press. 1999. Printed in P.R . Ch ina . 51

--

The Behaviour of LNG Carrier Moored to a Jetty Exposed to

Waves, Swell, Unsteady Wind and Current

JI Chunqun " and J . E. W. WICHERS' •

Abstract - Most term inals for tankers are piers and sea islands. while other types include sing le pointmoorings and multiple-bu oy mo or ings. The LNG and LP G carrier moored to the jetty is a very commontermi na l for transfer of gas in open seas . It is impo rtant to estimate the m otions and line tension s of theLNG carrier when it moor s to a jetty in metccean environ ment. Norm ally, the motions of the Lf';G carrierwould be restricted by the load ing arm. which is connected to LNG carrier's manifold . An example of125,000 003 LN G carrier mo ored to a jetty exposed to a set of environment co nditio ns is given. A

mat hemati cal model which is ba sed on th e equations of mot ion in the: tim e dom ain is used to the.analysisof LNG moor ed to an ofTshore jetty exposed to waves. swell, wind an d cu rrent. By mea ns of a time do­main computer program T ERM SIM computations are ca rried out to determ ine and op timize the lay-outand / or orienta tion of the jet ty an d mooring gear in term s of forces in moo ring lines and fend ers and the

en velope of motions of the loading arms. The purpose of this study is to determine the sensitivity o f the mo­oring system and ca rrier mot ion s to the com bina tion s of wind waves with an d without swell. steady windan d wind spectra . The results can be: consulted by the designe r in the design of jett ies.

Key words: mooring sys tem; dynam ic response; rim e domain analysis; f UY

I. Introduction

The worldwide increasing demand for liqu id natural gas (LN G) and liquid pet roleum gas(LPG) results in exten sive transport from gas plants to receiving countries, thus. new jellies arebeing designed or buill. Existing jellies are sometimes converted to receive carriers . For the de­sign of jellies computations ha ve to be carried out so that the se carriers can be moored safely toa jetty exposed to wind waves a nd curre nt . By means of the time do ma in computer programTERMSIM computations can be carried out to determine and optimize the lay- out and I ororientation of the jelly and mooring gear in terms of forces in mooring lines and fenders and theenvelope of motions of the loading arms. In this paper a 125,000 m3 LNG carrier is assumed tobe moored to a jelly and exposed to a set of environmental condition s. The pu rpose of thisstudy is to det ermine the sensitivity of the mooring system and carrier moti on s to the combina­tions of wind wa ves with and without swell. steady wind and wind spectra.

2. Calculation Model of Carrier and Jetty

The carrier will be a 125,000 m3 LNG carrier with spherical cargo tanks. T he principal di­mensions of the carrier ar e derived from OCIMF (1985). The particulars and stability data ofthe carrier are given in Table I. The general arrangement of the carrier is shown in Fig. 1. Thecarrier is moor ed to a jelly in water depth of 16 m. The lay-o ut o f the jelly and the mooring

, Associate Pro fessor. State Key Labo ra tory of Ocean Engineer ing. Shan gha i Jiaoto ng Unive rsity, Sha nghai 200030.

P. R. China

Vice President and General Manag er of MARI~ USA Inc. Mari time Resea rch Institu te Netherlands.

The Nether lands

82 11 Chunqun and J. E. W. WI CHERS

(

system is also given in F ig. I . The stern an d stern breasting lines are connected to bo llardsI'" and 2=. The spring lines are connected to bollards 3= and 4= and the bow brasting linesare connect ed to bollards 5= and 6= . The lines arc connected to the bollards at an elevation of 6m above still water level. T o bollards 3= and 4= fenders are attached . On each bollard twofenders are positioned 5 m apart from the centerline of the bollard at an elevation of 4 m ab ovestill water level. Each mooring line is a combi-Iine. A cornbi -Iine con sist s of a steel wire (56 mmin diameter) and a 20 m long nylon double braid ed ta il (l05 mm in diame ter). In tota l 14 linesare emp loyed. The posi tions of the fair lcad s and the manifold on the ca rr ier a re given in Table2. The p ositions of th e release hook s on the bo llard s an d the position of the fenders are given inFig . I .

Table J Particulars and sta bility data

Designation Magnitu de

Length between perpendiculars L" (m ) 274 .0

Breath B (m} 44.2

D epth mou ld D (m} 25.0

D raft T [m] 11.0

Di splace men t volum e yo 1m' ) 93253

Center of gravity above kee l KG (m) 10.2

M etacentric height GM (m) 10.4

Longitudinal rad ius of gyrat ion in air Kyy (m) 68.0

Transverse radius of gyra tio n in air Kn (m} 15.9

Vertical radius o f gyration in air K (m} 69.0zzRoll period T. (s) 11.9

Wind area frontal A, (m ' ) 1300

Wind area side As (m') 6600

Ta ble 2 Fai rlea ds and manifold position (corresponding to Fig. I)

Designa tion I X · (m) y ' (m) z; · {m), s

Fairleads

F, - 140 9.5 13.0

fi - 126 14.5 13.0

F, I - 90 21.5 13.0

F, 100 21.5 13.0

F, I 115 17.5 I 13.0

F,

M anifold

130

19.1

10.0

19.1

13.0

15

Notes: • - W. f. t. midship cross sec tion and center; • • - w . r. L water line .

3. Environmental Conditinns in the S imulation

Fo r this study a combination of weather conditions is ap plied. The purpose is to study thesensitivity of the carrier ' s moti ons to th e given environmental conditions , The definit ions of the

The Behaviour of L~G Carrier Moored to a Jetty

r.<I !

fI I 1 !" ' 0 tOO 60 '0 60 ' 0-x f f " fi ! I

90'+"

180· o· frb 858 1 8 8 '

.. +;1( E

~lf1.2 270·' 1,12

' 0.,; 13 .104~

Curren I

83

APdimensions in meter

140.&5

Fig. 1. Lay-out of jetty and mooring system.

FP

{",.".-- wave, wind and current direction with regard to the carrier are also given in Fig. I. As a stand­

ard case the following weather ca se is taken: JONSW AP wave spectrum with H, = 2.5 m andT, = 9 s (I35 0), a steady 15-second wind speed of 25.2 m I s (I35 0 ) and a steady current ve­locity of 1.5 m I s (I 80 0 ) . With respect to the sta ndard case the following parameters are ap­plied:

• Mean period (T, = 7 to II s) with H, = 2.5 m;• The APi-wind spectrum with a mean hourly wind speed of 20 m I s instead of a steady

15 s wind speed;The JONSWAP spectrum with H, = 2.0 m and T, = 9 s in association with a

Gaussian swell spectrum with H, = 0.5 m and T, = 17 s;• Computations (with the mean period T, = 9 s) are repeated , while the wind direction is

changed to 225 0 •

In simulatio ns the API wind spectrum, JONSWAP wave spectru m and Gaussian swell spec­trum are used as the input of environment condition. The corresponding formulas are given asfollows . A rev iew of the computer simulations is given in Table 3.

- A PI wind spectrum:2 - ~

S (£0) = (j v [I +.!.2 + ~ ] J

V 2" . f 2" fp p

( I)

in which OJ - frequency in rad I s of wind oscillation; S v - spectral den sity of wind speed inm' l s; V - hourly mean wind speed; J; - average fact or: 0_00 25 V; U v - turbulenceintensity. (jv = 0.164 V.

84 II Chunqun and J. E. W . WICHERS

- JONSWAP wave spectrum:

(2)

in which: y - peak parameter (y = 3.3); (J = 0.07 for OJ .; OJm • and (J = 0.09 for OJ > rom; OJm

- M odal frequency; " = 0.076 (g ' d/ U2) -0 12; U = mean wind speed (knots); g ­

acce lera tion of gravi ty (m / S2).

- Ga ussia n swell spectrum:

(' wi )' - stJ(-"'- - u'• e w,S (OJ) = ---'4__--,~-_

( O. IOJ -J 27<p

in which ' I - significa nt wave height in m; OJp = 27< / T,;. Tp - peak period in s."')

(3)

Table 3 Review of computations

Wave Swell Wind CurrentR un

case "WA H, T, "s H , T, "WI V.. VII'API Vc( .) (m) (5) ( . ) (m) (5) ( .) (m I 5) (m I 5) (m I 5)

I 135 2.5 I I 135 25.2 J.5

2 135 2.5 9 135 25.2 J.5

3 135 2.5 7 135 25.2 J.5

4 135 2.5 9 135 20.0 J.5

5 135 2.0 9 135 0.5 17 135 25.2 J.5

6 135 2.0 9 135 0.5 17 135 20.0 J.5

7 135 2.5 9 225 25.2 J.5

8 135 2.5 9 225 20.0 J.5

9 135 2.0 9 135 0 .5 17 225 25.2 1.5

10 135 2.0 9 135 0.5 17 225 20.0 J.5

The wind spee d as a function of heigh t above the mean water level and average time inter­val is approximated by the following power law:

( ) V ( Z)6V .. I , z =" .. 10 (4)

in which V.. ( I , z) - wind speed averaged over a time interval I as defined by" and p, z meterabove the mea n water level; V.. - wind speed averaged over one hour , 10 m ab ove sea level; "- guest fac tor referen ced to Vw ; P- height exponent.

T he factors in the power law for the wind profi les are shown in Table 4.

Table 4

The Behaviour of LNG Carrier Moo red to a Jetty

Factors in the power law of wind profiles

85

Avcrage time intervalFactors

I bour 10 min . I min 15 s 5 s 3 s

• 1.000 1.060 1.180 1.260 1.310 1.330

P 0.150 0.130 0.113 0.106 0.102 0 .100

4. Description of Computer Program TERMSIM

For computation s the time domain program TERMSIM (TERMinal SIMulation) is used.For the combined equations of wave frequency and low frequency motion reference is made byWihcers (1988). The program is well validated with model tests (Oortmerssen et al ., 1986). Thecarrier can be exposed to arbitrary weather conditon s. The frequency domain computed linearfirst order RAO 's (added mass, damping and wave forces) and the matrix of the quadratic sec­ond order wave drift force RAO's (incl. wave set- down in shallow water) are the input forconvolution integrals and retardation function (Oortrnerssen, 1976; Pinker, 1980). Thehydrodynamic data, i. e. the matrices of the added ma ss and damping, the RAO's of the waveforces and the matrix of the quadratic transfer functi on of the wave drift forces, a re computedby means of the 3-D potential theory progr am DIFFRAC.

Since for moored carriers the low frequency motions are resonance motion s, the values ofthe low frequency hydrodynamic reactive forces I moment are important. In order to predictcorrectly these motions, an experimentally determined database is used which contains the lowfrequency hydrodynamic viscou s (non-linear) coefficients for a large number of carriers, loadingco nditions and water depth I draft ratio (Wichers, 1988).

Further different wind spectrum formulation s can be applied. For the wind and currentloads the OCIMF data as given in Re ferences (OCIM F, 1985 and 1994) can be used .

Besides the non-linear load-elongation of the synthetic lines , the load-compression curve ofthe fenders is taken into account. Especially for the low frequency motions of the carrier the fric­tion between the shiphull side and the fenders is important. For the friction a Colomb frictioncoefficient k = 0.1 is taken int o account. The computations are carried out in the time domain.

For a carrier moored to a jetty the yaw and sway motions can be con sidered to be relat ivelysma ll; th is is in contradiction with carriers moored for instance by a hawser to a buoy (SPM) orin a spread mooring system. For a carrier moored to a jetty the equ at ion s of moti on ca n be sim­plified as follows:

m x I + L a " x , + L J R Ix (I - e) x , (r) d i I, -, ,-,

= F ""ind + r '" + Fdyn + F ....ave + F m oof

• (5)I I I I I '

m X 2 + L a ll x , + L J R ll (I -r)x , (d dt,-, ,-,

86 JI Ch unqun and J. E. w . WICH ER S

= FW1nd + r '" + r: + r '"" + F;oor;, , . ,

Tn X ) + L a" x , + L S R ,. (t - r) x , (r ) dr+c" x , + c 3S x :3.-, ,. ,

= F ...·ave + F IDoor., , .

/ .. x . + L a., x It + L S R " (t - r) x , (r) dt: + c .. x . + b x.. ..-, ,- , - ~

= r?" + F ffioo r•• • •

/ " x , + L a" < , + L S R " (t - t ) x , (r) di + c " x s +b " x ,.-, ' -I - ¢

= F .....ave + F moo r.

s , .

I ", x • + L a"" x , + L S R "" (t - r) x , (r) dr' a' .-,

- ¢

= F ",i.nd + r" + Fdrn + F v,avc + F

moo r

• • • • •

(6)

(8)

(9)

(10)

in which. m . I - tanker mass and moment of inertia: a" - matrix of the freq uency-indepen ­dent added mass coefficients fo r i = I to 6 and k = I to 6; b.. - viscou s roll dampingcoefficient: R" - matrix of the retardation functions; c" - m atri x of the hydr ostati c restoring

force coefficients: F ' =d - rela tive wind force in i directi on : F,e" - rela tive current force in• •

i direction; F~YU - dynamic current force contributions in i direction; FW

. "

c- first and sec-

• •ond order wave force registrat ions in i direct ion: F

moo, - mooring force due to fende rs and mo -

•oring lines in i direction (i = I . 2. 6).

Eac h computa tio n star ts with a tra nsien t lime of ha lf an hour fo llowed by the period of 3hours. for which the statistical result s are derived. As an exa mple time registra tions of the forcesin fender 3'" as comp uted during the ru ns of weather conditions 5 and 9 are present ed in Figs. 2a nd 3. During each simulation th e following signa ls are compu ted an d ana lyzed :

moti on s of manifold in surg e direct ion X,,,:moti ons of manifold in sway direction r eel;

moti ons of manifold in heave direction Z,el:roll moti on of carrier:pitch motion of ca rri er:

The Behavio ur of L~G Carrier Moored to a Jetty 87

108009600840072004800 6000

Time (s)360024001200

I j I

! rf'\I

T. I II 1

I. . -\ - j

.J I'I i· I: I

iI l ··t!1

rl! IIi f

1.1 ~ . II II r ,

I I' i I f ' I

"

,,I! ii

c0~.

'"-ec-;~

~-e

~

~.,o c... M...s M

c::0.;:: 0o -;

'" ee

'" "... N...'""0

0c::'" -;~ '"r'1

:=~

c-;Mec

0-;

0( -.~

(

Fig. 2. Fender force in weather condition case 5.

yaw motion of carrier;forces in lines I;± th rou gh 14;±;forces in fenders I"" through 4"".

5. Discussion of Results

The resu lts of computations in terms of mean, sta ndard devia tion and the maximum valuesare given in Tables 5 and 6. Some discussion s are given through application of parameters of

weather conditions.

5.1 Weather Conditions Case I , Case 2 and Case 3

Under weather cond itions ca se I, case 2 and case 3 the mean wave pe riod of the spectra isvaried . Referring to the valu es as given in Tables 5 and 6, noti ce the results of the signa ls of thesurge mo tions of the manifold , the forces in mooring lines an d the fo rces on the fenders. Themag ni tude of the mean stand ard deviation (a) and the maximum, except for the fender forces,clearly show tha t they incr ease with the incr ease of wave period. The rea son for th e increase ofthe surge motion and the line forces is the values of the matrix of the quadratic tr ansfer function(QT F) of the wave drift forces I m oment. As an example, the QTF of the mian diagon al of the

88

'"g'"M

csei

JI Chunqun and J . E. W. WI CH ER S

I....... " ... .. .. .. .. ..

I.. .. ... .. .. j

... .. .... .. ... .. . .. - . .. .. .. .. ... ...... .. .. ... « • ••• . '. I .. ... .. .... .. .. .

I ,.. . .. ....... ... .. ...... ..... ... ... .. I .......... .... .. .. .....

.. . .. .-.., .... .' - ...f. . .... ..

... .. ... ... . .. . ••1. . . ..- .- .!

I.. ..... ... .... .. . ..' --. -. .. . .. ..

.. . .. .. .. .. . ... . . . . .. . ..... .... .. j

" j .. .. .. . . . ... ... .. .. .. .. ..... ..... ...... .. III ! !.. . .. . . . . .. .....

j Ir, .. .. . j.. .. .

I... .. . . ....... .. ..... I

.. .... .. ..... .. ..f

..... .. I .. .. ..... ...., . ... I! !

I .. '. '1 .. . ..... ... .. ... . . .. ...

Ij,.. .. .. .. . .... ..... i ... .. ., . .. .. .. ... .. .. ,. .. .. .... .. ..

jItI I jl: .. . ..... .. i! . .. ......I

. '. ..i II

I · , I-,

J;.

I'.. [ .. .. .. .. ... . j .

... .. r I .. . .. .. r I.. ..

I ~j

I' i .. . . [ . .. . .. .. - . U- -I

o 1200 2400 3600 4800 6000

Time (s)7200 8400 9600 10800

Fig. 3. Fender force in weather condition case 9.

wave d rift force in x-direction und er 135 0 wave directions is given in Fig . 4. From Fig . 4 it canbe seen that tbe magnitude of the QTF increases fro m co = 0.75 rad / 5 tr, = 8.4 5) to w =

0.58 ra d / s tr, = 10.8 s) with approximately a maximum value at w = 0.48 rad / s tr, = 13.2s). The mea n wave drift force and the spectral density of the wave drift force are responsible forthe mean and low frequency motions. T hey can be de termined as follows :

in which

~

JF 'm~o =2 ' S S( (co) P (w. cot dio

lSF (II) = 8 · S: S [ (ei ) S , (w + II) T ' (w.o

w + II) dw

(11)

, 2 "T (ill + II . w) = p (w + II . ill) + Q' (w + II . ill );

II - frequency of low frequency secon d order force;r ' (ill + I'. ill). Q' (ill + II . w) - in- phase an d out- phase comp onen ts of the quadratic tran­sfer fun ction;

T (ill + II. w ) - amplitude of quadratic transfer function .

Table 5

The Behaviour of LN G Carrier M oored to a Jetty

Results of co mputa tions of mean va lue

89

( Weather co nditio ns

Signals Ru n Run Run R un Run Run R un R un Run Runcase case case case case case case case case case

I 2 3 4 5 6 7 8 9 10Xrcl (m) - 0. 53 - 0.49 -0.37 I - 0 .37 - 0.41 O .~ 9 - 0.42 - 0.37 I -0.38 - 0.31r., (m) - 0.11 I 0.004 0.04 0.03 -0.07 - 0. 10 -0.39 -0.20 0.46 0.30

2'd (m) 0.006 0.0 1 0.01 0 .01 0.0 1 0.00 0.03 - 0.02 0.04 I -0.03Roll ( . ) 0.01 0.03 0.04 0.02 0.02 0.00 - 0. 10 -0.07 -0.41 -0.09Pitch ( • ) 0.00 0.00 0.00 0.00 0.00 o.oo ooo 0.00 -0.46 0.00Y aw ( . ) 0.02 0.02 0.00 0.00 0.00 0.01 - 0.09 0.05 0.00 0.05

Line 1 / 2 (kN) 122 84 78 93 99 108 109 102 I 117 I 118Line 3 / 4 (kN) 177 127 109 126 138 137 148 134 156 150

Line 5 (kN) 147 107 94 II I 120 124 135 121 144 138Line 6 / 7 (k N) 236 214 191 190 199 178 210 203 201 182Line 8 / 9 (k N) 79 62 81 87 78 101 107 113 112 I II

Line 10 (kN } 179 148 135 147 158 160 24 1 194 256 209Line 11 /1 2 (kN ) 164 125 118 130 144 151 233 183 252 204Line 13 / 14<kN ) 197 166 152 160 172 168 248 203 259 213

Fender I (kN) 1061 938 839 822 940 816 196 342 130 322Fend" 2 (kN) 893 868 1132 740 785 658 140 265 78 226

Fe nd " 3 (kN) 1085 1107 1182 86 1 111 53 812 343 135 177 99Fend" 4 (kN} 1280 1213 500 958 1198 954 424 165 283 140

160

140

c.E 120-'"c.E 100..~ '"-., -c -::: 80" '1'.. 3-.~ 60-"..-e 40"=0-

20

0

/ r-.. ,......,1/ 1\/ / '" -,

i\.. 1\

/ \ - -I'. ./ I'... ./ r-,----

/ I

if , I II/ I

I Iilr) M C, -e- '" or; co 'D io .- '" '" '" C> co C'1 'n N ' 001

CM

C.,.

cicO

cicc

cie-,

cico

ci0> 0

~OJ

ci ci ci ci ci ci 0 0 ...; ~

Frequency (rad!s)

Fig . 4. Quadratic transfer function of wave drift force in .r-di rectic n (135 0 wa vs: directio n)

90 JI Cbunqun and J. E. W. WI CHERS

(,

Considering these formulas it is clear tha t the excitation will increase if the peak period ofth e wave spectrum increase from Tp = 8.4 s to 13.2 s, resulting in higher values of motions andline forces. At the high load level the compression force will be constant over a relatively lar gerange . For this reason it can be concluded tha t in most wea ther co ndi tions the ma ximum fenderforce will mostly remain at the same level.

5.2 Weather Conditions Ca se 2, Case 4 and Case 6

For wea ther conditions case 2, case 4 and case 6 the parameters wind spec tra and swellboth are applied . The wind direction is 135 0 • Also notice the results as mentioned above .

A comparison of the results for weather conditions case 2 an d case 4 (constan t wind speed25.2 m I s versus the mean hour of 20 m I s in combination with an API wind spec tru m) showsth at only the maximum values oCthe manifo ld moti ons and the line forces are 10 - 20% higherfor a wind spectru m. For th e fend er force the same ca n be concl uded as menti oned earlier. Froma co mparison of th e resul ts fo r weather conditions case 2 an d case 5 it can be concluded th at forthe forces in the mooring lines both the sta ndard deviation an d the maximum values aresignifican tly larger. In spi te of the lowerin g of th e sgnificant wave height. the effec t of the re­sulting action of the remaining waves. swell and wind coming from the same direct ion seems toca use the increase in line forces. A com pa rison of the resul ts fo r wea ther conditions case 5 andcase 6 lead s to the sa me co nclusions as drawn for the results for weather conditions case 2 andcase 4. For the fender force the same can be conclude d as mentioned above.

5.3 Weather Cond itions Case 7, Case 8, Case 9 and Case 10

For weather co nditions case 7, case 8, ca se 9 and case 10 the parameters wind spectra andswell bo th are applied. The wind direction, however, is changed to 225 0 In this co ndition thewind has the effect of pushing the carrier away fro m the jetty.

From the results it can be concluded that the standard deviation an d maximum values ofboth the motions of the manifold and the mooring line forces are significa ntly larger than thosefound under weather condition s case 2. case 4, case 5 and ca se 6. Owing to the cha nged wind di­rection , the carrier is less heavily pushed against the fender s as demonistr ated in Figs. 2 and 3.The result is th at th e effect of the friction between the hull and the fender will be smaller, re­sulting in significantly larger low frequency mot ions . The effect of larger motions induces highervalues of the for ces in th e m ooring lines. especially in the spring lines compared with weathercondit ions case 2, case 4, case 5 and case 6.

Tbe effect of the wind spectrum and the swell is not so significan t with regard to the stand­ard case as fou nd in the case of wind di rect ion 135 0 • This shows that it is important to consid­er wind direc tion in jetty design.

6 . Concl usions

From the study of the sensitivity of the mooring system and carrier moti ons to the combina­tions of waves with and witho ut swell , steady wind and wind spectra and with the wind direc­tions of 135 0 and 225 0 the following conclusions can be dr awn :

Ta ble 6

The Behavio ur of Lr-;G Carrier M o ored to a Jett y

Results o f comp utations of standard dev ia tion and maximum value

91

(Weather conditions

Signals Run Run Run Run Runcase I case 2 case 3 case 4 case 5

a Max. a Max. a M ax. a M ax. a Max.

X~I {m) 0.60 - 3.65 0.26 - 2.27 0.13 - 1.04 0.28 - 2.39 0.21 - 1.57

l"rc: l {m) 0.22 I - 1.23 0.17 - 0.8 0.08 0.35 0.17 - 0.90 0.18 - 0.9

Zn:J (m) 0.16 0.69 0.11 0.51 0.26 0.24 0.10 0.47 0.10 0.42

Roll « ) 0.31 - 1.36 0.27 - 1.16 0.14 0.62 0.28 1.57 0.27 -1.2Pitch ( 0 ) 0.25 1.06 0.14 0.6 0.07 - 0.16 0.14 0.60 0.13 - 0.58Yaw ( . ) 0.35 - 1.2 0.15 0.6 0.07 - 0.26 0.15 0.58 0 .25 - 0.82

Line I 1 2 (kl') 150 1785 63 511 24 180 65 610 92 847

Line 3 14 (kl') 192 1899 75 588 29 222 75 602 115 1066

Line 5 (kN) 158 1700 67 534 22 188 68 507 99 905

Line 6 / 7 (kN) 156 2385 53 789 23 312 57 871 43 528

Line 8 /9 (kN ) 92 1238 43 268 28 186 49 330 47 323

Line 10 (kN) 124 1029 55 465 32 239 56 481 86 588

Line 11 /1 2 (kN) IS:! 1542 64 421 36 246 65 437 105 866

Line 13 /1 4 (kN) 133 1142 56 580 31 263 58 612 85 552

Fender I (kN) 159" 55 22 1228 4948 747 3781 1150 4945 1318 4948

Fender 2 (kK) 1423 5097 1150 4945 719 3508 1066 4933 1197 4947

Fen der 3 (kN) 1511 4949 1269 4884 1137 4572 1124 4862 1435 4949

Fender 4 {kN) 1704 4949 1369 4902 1205 4672 1226 4879 1590 4949

Weather conditions

SignalsRun Ru n R un Run Run

case 6 case 7 ca se 8 case 9 case 10

a Max. a M ax. a Max. o M ax. a Max.

X", (m ) 0.23 - 1.65 0.60 - 3.1 0.69 - 3.45 0 .53 - 2.50 0.37 - 2.17

Y,., (m ) 0.19 -0.97 0.28 - 1.29 0.23 -1.03 0.26 - 1.38 0.25 - 1.38

z., (m } 0.10 0.40 0.09 0 .34 0.08 - 0.43 0.09 - 0.40 0.09 - 0.36Roll ( 0 ) 0.28 - 1.26 0.41 1.58 0.38 1.58 0.36 - 1.41 0.33 - 1.43

Pitch ( 0 ) 0.13 - 0.58 0.14 0.6 0.14 0.60 0. \4 - 0.59 0.13 - 0.58

Y aw (. ) 0.24 - 0.88 0.17 - 0.73 0.15 - 0 .62 , 0.20 - 0.73 0.21 - 0.87

Line I / 2 (kN) 93 962 87 711 82 837 92 668 93 1032

Line 3 / 4 (k-'I) 112 1059 91 691 81 677 104 959 III 1129

Line 5 (kN) 98 964 86 699 I 76 732 94 784 98 1060

Line 6 1 7 (kN) 48 552 128 1132 156 1466 108 I 1016 73 762Line 8 1 9 (kK) 50 I 394 99 I 802 113 I 1080 91 618 I 67 541

Line 10 (kN J 86 630 66 653 I 69 I 769 75 770 84 831

Line 11 /1 2 (kN) 106 I 990 80 92 1 72 584 97 I 845 102 933

Line 13 /1 4 (kN ) I 85 615 75 930 86 1126 79 912 86 865

Fen der I (kN) 227 4946 668 4947 828 4936 I 520 4889 8 11 4769

Fender 2 (kN) 1052 4949 554 4948 716 4941 I 389 4662 649 4570

Fender 3 (kN) 1250 4949 233 3930 457 4409 I 159 3887 406 4126

Fender 4 (kN) 1417 4949 I 272 I 3988 525 4587 I 215 4 110 517 4202

Table 6

The Behaviour of LJ'G Carrier M oo red to a Jetty

Results of computations of standard deviation and maximum value

YI

( 'A,.eather conditions

Signals Run R un RUD Ru n Runcase 1 case 2 case 3 case 4 case 5,

o Max. a Max. a M ax. a Max. a Max.

X.. (m) 0.60 - 3.65 0 .26 - 2.17 I 0.13 I - 1.04 0.28 - 2. 39 0.21 -1.57

r~1 (m) 0.21 -1.23 0.17 - 0.8 0.08 0.35 0.17 - O.YO 0.18 - 0.9

Z~I (m) 0.16 0.69 0.11 0.5 1 0.26 0.24 0.10 0.47 0.10 0.42Roll ( 0 ) 0.31 - 1.36 0.27 - 1.16 0.14 0.62 0.28 1.57 0.27 - 1.2

Pitch ( 0 ) 0.25 1.06 0.14 0 .6 0.07 - 0.26 0.14 0 .60 0.13 - 0.58

Yaw ( 0 ) 0.35 - 1.2 0.15 06 0.07 - 0.26 0.15 0.58 0.25 - 0 .82

Line 1 / 2 (kN) 150 1785 63 51 1 24 180 65 610 92 847

Line 314 (kN ) 192 18Y9 75 588 29 222 75 60 2 115 1066

Line 5 (k N) 158 1700 67 534 22 188 68 507 99 905

Line 6 / 7 (kN) 156 2385 53 789 23 312 57 871 43 528

Line 8 /9 (kN) 92 1238 43 268 28 186 49 330 47 323

Line 10 (kN) 124 1029 55 465 32 239 56 481 86 588

Line 11 /12 (kl' ) 152 1542 64 421 36 246 65 437 105 866

Line 13 / 14 (kN) 133 1142 56 580 31 263 58 612 85 552

Fender I (kN) 1590 5522 1228 4Y48 747 3781 1150 4945 1318 4948

Fender 2 (kN) 1423 5097 1150 4945 719 3508 1066 4933 1197 4947

Fen der 3 (kN) 1511 4949 1269 4884 1137 4572 1124 4862 1435 4949

Fen der 4 (k N) 1704 4949 1369 4902 1205 4672 1226 4879 1590 4949

Weath er co nditions

Signa ls Ru n Run R un R UD Runcase 6 case 7 case 8 case 9 case 10

a M ax. a Max. o Max. a M ax. a Max.

X... (m ) 0.23 - 1.65 0.60 - 3.1 0.69 - 3.45 0.53 - 2.50 0.37 - 2. 17

Y... {m } 0.19 - 0.97 0.28 - 1.29 0.23 - 1.03 0.26 - 1.38 0.25 -1.38

Z~I (m) 0.10 0.40 0.09 0 .34 0.08 - 0.43 0.09 -0 .40 0.09 - 0.36

Ro ll ( 0 ) 0.28 -1.26 0.4 1 1.58 0.38 1.58 0.36 - 1.4 1 0.33 - 1.43

Piteh (" ) 0.13 -0.58 0.14 0 .6 0.14 0.60 0.14 -0.59 0.13 - 0.58

Yaw ( 0 ) 0.24 - 0.88 0.17 -0.73 0.15 - 0.62 0 .20 I - 0. 73 0.21 -0.87

Line I / 2 (kN) 93 962 87 711 82 837 92 668 93 1032

Line 3 / 4 (kN ) 112 1059 91 69 1 81 677 104 959 I I I 1129

Line 5 (kN) 98 964 86 699 76 732 94 784 98 1060

Line 6 / 7 IkN) 48 552 128 1132 156 1466 108 1016 73 I 762

Line 81 9 (kN) 50 394 99 802 113 1080 I 91 618 67 I 541

Line 10 (kN) 86 630 66 653 69 769 75 770 84 831

Line 11/ 12 (kN) 106 990 80 92 1 72 584 97 845 102 933

Line 13 / 14 (kN} I 85 615 75 930 86 1126 79 I 912 86 865

Fender 1 (kN} 227 4946 I 668 4947 828 4936 520 4889 I 811 4769

Fender 2 (kN ) 1052 4949 554 I 4948 716 4941 389 4662 I 649 4570

Fend er 3 (kN ) 1250 4949 I 233 I 3930 457 4409 159 3887 I 406 4 126

f ender 4 (kN) I 1417 4949 I 272 I 3988 I 525 4587 215 I 41 10 I 517 4 202

92 JI Ch unq un and J . E. W. WI CHER S

i,

In weather conditions case I, case 2 and case 3, the values of mo tion s of th e manifold,and the for ces in the mooring line s and fenders increase with th e increase of the mean wave peri­od of th e spectra. Thi s increas es are caused by the qua ntita tive fo rm of th e quadratic transferfun ction of the wave drift forces. Since th e load-compression curve is cons tan t over a larg e com­pression range the ma ximum values of th e fender forces mostly remain at the same level.

- From a compari son of th e results for weather conditions case 2 and case 4 it ca n be con­cluded that owing to the wind spectrum, the maximum values of mani fold motions and lineforces are 10- 20% high er.

- Fro m a comparison of the resu lts for weather con ditions case 2, ca se 5 an d case 6 it canbe concluded that, in spite of the lower wave height, th e swell causes a significant increase ofboth the standard deviation an d th e maximum valu es of forces in the mooring lines.

- For weather condi tions case 7, ca se 8, case 9 and case 10 it can be concluded tha t bo ththe m oti ons of the manifold an d the forces in mooring lines are signifi cantly larger than thosefor weather conditions ca se 2, case 4, case 5 and case 6.

- The wind directions is an importa nt fact or affecting the arrangement of the orienta tionof the jetty . The force in m ooring lines and fenders could be affect ed by th e changing of wind di­rection.

This study sh ows tha t comp utations are necessary in the find ing and unde rs tanding of thesensitivity of resulting forces and mot ions to weather conditions for th e desi gn of a jett y.

References

OCIM F·Society of International Gas Tankers and Terminal Operators Ltd, 1985. Pred iction of wind loads on large lique­

fied gas carriers, Witherby and Co. Ltd.. London. England .Wichers, J. E. W.. 1988. Simulation M odel jJ r Single Buoy M oored Tankers. Ph. D . dissertation. D elft University of

Technology, The N etherlands.

Oortm erssen. G . van. J. A. Pinkster and H. H. van den Boom. 1986. Compute r Simulation of Moored Ship Behaviour,Joumal ofwaterwav, Port, Coastal and Ocean Engineering, AS CE, 112. 2.

Oortmerssen, G . van. 1976. The M otions ofa .t f cored Ship in H' a l·cs. Ph. D . dissertation . Delf Uni versity of Technology .Pink ster, J. A.. 1980. Lo ....· Frequency Second Or der W avt' Excit ing Forces on Float ing S tructures, Ph. D . dissertation.

D elft Un iversity of Technology.OCIMF, 1994. Rediction of u,"ind and Current Loads on VLCC s. Second Edition. Wither by and Co . Ltd.. London.

England .