浮体を用いた LNG タンクのスロッシング防止に関する研究 185

LNG

* ** *** ****

Experimental and Numerical Study of an Anti-Sloshing Floating Device for Membrane-Type LNG Tanks by Makoto Arai, Member Ryosuke Suzuki, Member Naohiko Kishimoto, Member Takahiro Ando, Member

Summary

Recent developments with offshore terminals and floating liquefied natural gas production, storage and offloading (FLNG)

applications have included the new requirement that the storage tanks be able to handle unrestricted filling with LNG. If membrane-type tanks are used in such new systems, the occurrence of sloshing in the half-load condition becomes one of the most important design issues. In this paper, we propose a simple anti-sloshing floating device to be installed inside a liquid cargo tank. By setting the device on the free surface of the liquid cargo, the original free surface is divided into two or more sub-surfaces, and resonant sloshing of the liquid can be avoided by changing the natural frequency of its motion. This floating device can follow the liquid height change in the tank during loading and unloading operations of the liquid cargo, a feature that is especially preferable in FLNG applications. We examine the performance of the proposed anti-sloshing device by a series of model experiments and numerical simulations, which indicate that the device's performance is very promising.

1.

Floating LNG (FLNG) FLNG

FLNGLNG

1) )

LNG

FLNG

2.

***

*******

25 2 28

浮体を用いた LNG タンクのスロッシング防止に関する研究

正会員　荒　井　　　誠＊　　　　正会員　鈴　木　良　介＊＊　　

正会員　岸　本　直　彦＊＊＊　　正会員　安　藤　孝　弘＊＊＊＊

原稿受理　平成 25 年 2 月 27 日

　日本船舶海洋工学会論文集　第 17 号　 2013 年 6 月　 186

2. 1

Fig.1 ( )

Fig. 1 Excitation generator.

900mm 600mm225mm 2

50mm 50mm 0.5

Fig.2I

3 I T2 5

Table 1 2

2

Fig. 2 Floating bodies.

Table 1 Dimensions of floating bodies. Float type I-1 I-2 I-3 T-1 T-2

Depth of float [mm] 150 300 450 300 300

Draft, d [mm] 75 150 225 150 150

Breadth of float, b [mm] 30 30 30 30 30

Breadth of horizontal plate, b1 [mm] - - - 120 210

2. 2

3

10mm

Fig.3

h B Db d

cb1

(xc, yc)xc yc

150mm 0.4Hz2.1Hz 4.2

Fig. 3 Definition of variables for the tank and float.

3.

3. 1

2

(1)

(2)

x yu v x y p

fx fy H

(3)

3)

3. 2

0yv

xu

xfxp

yuv

xuu

tu 1

yfyp

yvv

xvu

tv 1

vxHu

tH

D

B

h

d

b

c

D

B

hCx

CzyC

xC

cb1

浮体を用いた LNG タンクのスロッシング防止に関する研究 187

mxmypdxmgym 2cos (4)

m p

(x, y)

(1)~(3)

u v p H 3)

4) (4)

4.

4. 1

4. 1. 1

75mm(I-1 )Fig.4

10mmFig.3

0.8Hz 11.6Hz 2

Fig.4=1

Fig. 4 Comparison of the amplitude of liquid surface motion (with Type I-1 float and without float, h=50%D, =1deg.,

d=75 mm, yc=150 mm).

4. 1. 2

Fig4

Fig.5 3

(f) Fig.6

Fig. 5 Amplitude of liquid surface motion (Type I-1 float, h=50%D, =1deg., d=75 mm, yc=150 mm).

(a) f= 0.645Hz (b) f= 0.74Hz

(c) f=1.42Hz Fig. 6 Free surface deformation in a tank with float (Type I-1

float, h=50%D, =1deg., d=75 mm, yc=150 mm).

Fig. 7 Comparison of the measured and computed liquid surface

displacement at the tank corner (Type I-1 float, h=50%D, =1deg., d=75 mm, yc=150 mm).

y

0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

Am

plitu

de o

f liq

uid

surf

ace

mot

ion

[mm

]

Frequency of excitation [Hz]

Num.Cal.

Exp.

0

50

100

150

200

250

300

350

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

Am

plitu

de o

f liq

uid

surf

ace

mot

ion

[mm

]

Frequency of excitation [Hz]

No floats (Exp.)With a float (Num.Cal.)No floats (Num.Cal.)With a float (Exp.)

Without float (Num.cal.)

With float (Num.cal.)

Without float (Exp.)

With float (Exp.)

Am

plitu

de o

f flu

id su

rfac

e m

otio

n [m

m]

　日本船舶海洋工学会論文集　第 17 号　 2013 年 6 月　 188

Fig.6(a) 0.645Hz

Fig.6(b) Fig.5 2(0.74Hz)

25)

U U

Fig.6(c) 2

11/2

1Fig.7

Fig.8

Fig.5 3

1

Fig. 8 Amplitude of float motion (Type I-1 float, h=50%D, =1deg., d=75 mm, yc=150 mm).

4. 1. 3

150mmI-2 120mm 210mmT-1 T-2 Fig.9

1.3 1.4Hz2

3

Fig. 9 Comparison of the amplitude of liquid surface motion (Type I-2, Type T-1 and Type T-2 floats, h=50%D,

=1deg., d=75 mm, yc=150 mm).

Fig.9 T IU

1I-2 T-1 T-2 T

U

1

T-1 Fig.101.3 1.4Hz

Fig.9

Fig. 10 Amplitude of float motion (Type T-1 float, h=50%D, =1deg., d=75 mm, yc=150 mm).

I-1 2

1 Fig.11

U 2I-1 2 U

(0.74Hz) Fig.12(a) 2U 3

0

10

20

30

40

50

60

70

80

0 0.5 1 1.5 2

Ampl

itude

of li

quid

surf

ace

mot

ion

[mm

]

Frequency of excitation [Hz]

I-shaped float (Num.Cal.)120mm (Num.Cal.)210mm (Num.Cal.)I-shaped float (Exp.)120mm (Exp.)

I-shaped float (Num.Cal120mm (Num.Cal.)210mm (Num.Cal.)I-shaped float (Exp.)120mm (Exp.)

I-2 float (Num. cal.)T-1 float (Num. cal.)T-2 float (Num. cal.)I-2 float (Exp.)T-1 float (Exp.)T-2 float (Exp.)

05

1015202530

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

Am

plitu

de o

f flo

at m

otio

n [ m

m]

Frequency of exitation [Hz]

Num.Cal.

Exp.Num. cal.

012345678

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

Ampl

itude

of f

loat

mot

ion

[mm

]

Frequency of excitation [Hz]

Num.Cal.

Exp.

Num. cal.

Exp.

浮体を用いた LNG タンクのスロッシング防止に関する研究 189

Fig.12(a) 2 1 1

1.4Hz (1.7Hz )Fig.12(b)

15mm

Fig. 11 Comparison of the amplitude of liquid surface motion between one float and two floats cases

(Type I-1, h=50%D, =1deg., d=75 mm, yc=150 mm).

(a) U-tube mode (0.74Hz) (b) 1st mode (1.72Hz)

Fig. 12 Free surface deformation with multiple floats (Type I-1, two floats, h=50%D, =1deg., d=75 mm, yc=150 mm)

4. 2

Fig.13 70% I-1

5.96m 8.35

Fig.13

Fig.14 Fig.13Fig.14

(a) Without float

(b) With float Fig. 13 Change of liquid surface displacement in time

(Experiment, type I float, d=50mm, h=70%D).

(a) Without float

(b) With float Fig. 14 Change of liquid surface displacement in time (Numerical simulation, Type I float, d=50mm, h=70%D).

3

2

Fig.9 1.3 1.4Hz

0

10

20

30

40

50

60

70

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

Am

plitu

de o

f liq

uid

surf

ace

mot

ion

[ mm

]

Frequency of exitation [hz]

the No. of float=1 (Num.Cathe No. of float=2 (Num.Cathe No. of float=1 (Exp.)the No. of float=2 (Exp.)

No. of float=1 (Num. cal.)No. of float=2 (Num. cal.)No. of float=1 (Exp.)No. of float=2 (Exp.)

　日本船舶海洋工学会論文集　第 17 号　 2013 年 6 月　 190

5. 5. 1

Table 2 Dimensions of tank and float.

Tank breadth, B 60.0m 60.0m Tank height, D 40.0m 40.0m Initial liquid level, h 20.0m(50%) 20.0m(50%)

Center of rotation (xc,zc)[m] (30.0,10.0) (30.0,10.0)

Float breadth, b 4.0m Float draft, d 5.0m

Fig. 15 Relation between RAO of liquid surface motion and frequency of sea waves.

4

FLNGFLNG

FLNG

Walden 6)

60% 0.091Hz 0.14HzFig.15

critical frequencyTable 2

50% Fig.151

1

U

5. 2

5. 2. 1

FLNG

FLNG 7), 8) Table 3FLNG

Fig.16 VLCCFig.16

LNG3

1.5m 85m9)

Table 3 Principal dimensions of the designed ship in full load

condition.

Length between perpendiculars, Lpp 340m

Breadth, B 65m

Draft, d 15.5m

Displaced volume, V 2.9×105m3

Fig. 16 Loading condition of LNG tanks.

5.96m

10.16sec (6) ISSC

(6)

10),11)

5. 3

} /2exp{-0.44/ ) 2

(2

0.11)( 45-2 TTTH VVVV

02468

1012141618

0 0.05 0.1 0.15 0.2 0.25

Am

plitu

de o

f liq

uid

s urf

ace

mot

ion

[m]

Frequency of excitation [Hz]

No floats

With a float

Critical frequency

Without float

With float

浮体を用いた LNG タンクのスロッシング防止に関する研究 191

Table 250%

Fig.17

Fig.17

Fig.18 Fig.18h=30%, 50%, 70% 3000

(a) Without float

(b) With I-shaped float Fig. 17 Comparison of the liquid surface displacement at the left

side in the tanks with and without a float (H1/3=5.96m, T1/3=10.16s).

5. 4 Fig.18 I

Fig.19Fig.20 Fig.20(a) 30%

I 2 I 11/2

T50% 70% T 2

(a) h=30%D

(b) h=50%D

(c) h=70%D

Fig. 18 Number of exceedance of liquid surface displacement at left side wall (I-shaped float, H1/3=5.96m, T1/3=10.16s).

050

100150200250300350400

12 16 20 24 28 32 36 40

Num

ber o

f exc

eeda

nce

Liquid height [m]

Without a floatWith an I-shaped float

Top of the tankInitial liquid height

Without float

With one I-shaped float

050

100150200250300350400

20 24 28 32 36 40

Num

ber o

f exc

eeda

nce

Liquid height [m]

Without a float

With an I-shaped float

Top of the tankInitial liquid height

Without float

With one I-shaped float

Initial liquid heightTop of the tank

050

100150200250300350400

28 30 32 34 36 38 40

Num

ber o

f exc

eeda

nce

Liquid height [m]

Without a float

With an I-shaped float

Without float

With one I-shaped float

　日本船舶海洋工学会論文集　第 17 号　 2013 年 6 月　 192

(a) One T-shaped float (b) Two I-shaped floats (c) Two T-shaped floats

Fig. 19 Examined floats and float arrangements.

Fig.21I 1 T 2

T 2

FLNG LNG

1

(a) One I-shaped float (b) Two T-shaped floats

Fig. 21 Comparison of the float displacements. (H1/3=5.96m, T1/3=10.16s, h=50%D)

(a) h=30%D

(b) h=50%D

(c) h=70%D Fig. 20 Comparison of the number of exceedance of liquid

surface displacement at left side wall between different float arrangements (H1/3=5.96m, T1/3=10.16s).

0

50

100

150

200

250

300

350

400

12 16 20 24 28 32 36 40

Num

ber o

f exc

eeda

nce

Liquid height [m]

An I-shaped floatA T-shaped floatTwo I-shaped floatsTwo T-shaped floats

Initial liquid height Top of the tank

One I-shaped floatOne T-shaped floatTwo I-shaped floatsTwo T-shaped floats

Top of the tankInitial liquid height

0

50

100

150

200

250

300

350

400

20 24 28 32 36 40

Num

ber o

f exc

eeda

nce

Liquid height [m]

Without a floatAn I-shaped floatTwo T-shaped floats

Without float

One I-shaped float

Two T-shaped floats

Initial liquid height Top of the tank

050

100150200250300350400450

28 30 32 34 36 38 40

Num

ber o

f exc

eeda

nce

Liquid height [m]

Without a floatAn I-shaped floatTwo T-shaped floats

Without float

One I-shaped float

Two T-shaped floats

浮体を用いた LNG タンクのスロッシング防止に関する研究 193

6.

1) Arai, M, Bogaert, H., Graczyk, M., Ha, M.K., Kim, W.S., Lindgren, M., Martin, E., Noble, P., Tao, L., Valle, O., Xiong, Y.: Report of Committee V.2, Natural Gas Storage and Transportation, Proceedings of 18th International Ship and Offshore Structures Congress, Volume 2, pp. 67-112, 2012.

2) Arai, M., Suzuki, R., Ohta, Y. and Wang, X.: Study of an anti-sloshing floating device for membrane-type LNG tanks, Proceedings of IMDC 2012, 11th International Marine Design Conference, Vol.2, p.p. 554-565, 2012

3) Arai, M., Cheng, L. Y., Kumano, A., Miyamoto, T.: A Technique for Stable Numerical Computation of Hydrodynamic Impact Pressure in Sloshing Simulation, Journal of the Society of Naval Architects, Japan, Vol.191, pp.299-307, 2002.

4) 1975

5)

C 67 657 pp.204-211, 2001

6) 1992

7) FPSO4

, p.p.79-84, 2004 8) - LNG-FPSO -

74 2 p.p.152-161, 2009 9) 4 1983 10) Wang, X. and Arai, M.: A Study on Coupling Effect

between Seakeeping and Sloshing for Membrane-type LNG Carrier, International Journal of Offshore and Polar Engineering, Vol.21, No.2, p.p.1-8, 2011.

11) Wang, X. and Arai, M.: Research on Computational Method of Coupled Ship Motions and Sloshing, Journal of the Japan Society of Naval Architects and ocean Engineers, Vol.14, pp.97-104, 2011.