Hyrodyanics of FLNGThe University of Western Australia
Outline
Introduction
FLNG in side-by-side offloading
Subsea Gas Fields SBS offloading
3/28
and Production BV
12 March 2015
Comparison of Metocean conditions:
Prelude v North Sea
(a) FPSO at Prelude
and Production BV
Surge Motion (Horizontal forward)
0 5 10 15 20 25 30 35 40 45
a b s
0 5 10 15 20 25 30 35 40 45
a b s
0 5 10 15 20 25 30 35 40 45
a b s
0 5 10 15 20 25 30 35 40 45
a b s
and Production BV
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0 5 10 15 20 25 30 35 40 45
a b s
0 5 10 15 20 25 30 35 40 45
a b s
FPSO_180
Conclusion: For any wave height and period all motions of FLNG are considerably lower
than corresponding motion of an FPSO. Sometimes FLNG motions are 2-4 times
lower. Only exception is for roll motion in period range 23-35 sec. This range is of no
practical significance since wave energy beyond 22sec is minimal. Roll response of
FLNG is, in fact, excellent.
12 March 2015
and Production BV
Conclusion: Extreme Cyclonic conditions at Prelude are comparable to extreme Central North Sea but less severe
than Northern North Sea
1 yr 4.5 8.0 11.0
100 yr 11.6 13.0 16.0
10,000 yr 17.6 17.0 20.0
Significant Wave Height, Hs (m)
Prelude Metocean Conditions v North Sea conditions
Return Period Prelude Location Central N Sea Northern N Sea
FLNG FPSO FLNG FPSO FLNG FPSO
1 yr 0.13m 0.79m 0.79m 2.05m 1.66m 3.82m
100 yr 1.63m 3.68m 2.12m 5.30m 2.97m 7.70m
10,000 yr 2.99m 7.75m 3.37m 8.50m 5.00m 11.05m
Compare FLNG motions at Prelude with FPSO motions @ Prelude or N Sea
(combine Metocean conditions & RAOs)
12 March 2015
Conclusion: FLNG at Prelude would experience much lower motions in extreme cyclones than FPSO in the North Sea
An FLNG in South China Sea
150 km
= 6.1 Tcf
• FLNG concept designed to serve in South China Sea
FLNG
Length over all Loa m 392.00 289.00
Breadth B m 69.00 43.20
Draft T m 13.85 10.05 Displacement Δ ton. 320,804 95,951
Centre of gravity KG m 20.553 14.49
Radius of roll gyration Kxx m 25.35 14.04
Radius of pitch gyration Kyy m 91.36 85.13
SBS offloading
Coupled modelling of SBS system
Added mass + Damping coefficient
Motion equation of the vessel Dynamic equation of mooring line
Vessel motions, Mooring dynamics, Forces on fenders
Frequency domain
Time domain
1 2 0
F F F F
M a a
a M a
j i j j j
h t h t d
h t h t
Mooring &fenders
• Model tests in Wave Basin at Shanghai Jiao Tong University.
Dimensions of Wave Basin:
Depth of artificial bottom can
be adjusted from 0 to 10 m
Ability: waves, current, wind
13.0 2.5 10.0 0.81
W a v e e
le v a ti o n (
m )
a
0.0
0.5
1.0
1.5
2.0
2.5
P o w
u m
(m )^
Sea states: (SBS offloading)
Wave: Hs=2.5 m Wind: Vw=13.0 m/s Current: Vc= 0.81 m/s
Tp= 10.0 s
Surge
18/28
Results & discussion 1. Comparison of numerical simulations and experimental data.
FLNG Surge and Pitch motions: FLNG_Surge
-6
-5
-4
-3
-2
-1
0
1
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Time (s)
S u
rg e (
Frequency (rad/s)
S ep
ct ru
m (m
^2 s/
ra d
Experiments
Simulations
FLNG_Pitch
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Time (s)
P it
c h
Frequency (rad/s)
S ep
ct ru
m (d
eg ^2
s/ ra
LNG Carrier Surge and Pitch motions:
Surge spectrum
(identical standard deviation)
LNG_Surge
-8
-6
-4
-2
0
2
4
6
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Time (s) S
Frequency (rad/s)
S ep
ct ru
m (m
^2 s/
ra d
Experiments
Simulations
LNG_Pitch
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Time (s)
P it
c h
Frequency (rad/s)
S ep
ct ru
m (d
eg ^2
s/ ra
Results & discussion
Dynamic forces on mooring lines:
Time series
which is related to surge motions of FLNG
Mooring line 2
3000
3100
3200
3300
3400
3500
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Time (s)
F o
rc e (
k N
Frequency (rad/s)
Simulation results > experimental data
To investigate the influence of pretension and stiffness of hawsers
Pretension/kN Stiffness/kNm-1
Case1 300 83.47
Case2 150 83.47
Case3 0 83.47
Case4 150 58.43
Case5 150 33.39
Case6 150 8.35
-12
-8
-4
0
4
-10 -8 -6 -4 -2 0 2 4 6 8 10
Displacement in x direction (m)
D is
p la
Displacement in x direction (m)
D is
p la
Displacement in x direction (m)
D is
p la
As expected, relative motions get larger, as pretensions get smaller
2. Sensitivity study.
Case 1 Case 2 Case 3
The number of the response peaks get fewer, as pretensions get smaller
But, the maximum force on fender 1 increase, as pretensions get smaller
Fender 1
Time (s)
F o
rc e (
k N
Time (s)
F o
rc e (
k N
Time (s)
F o
rc e (
k N
Case 4 Case 5 Case 6
Relative motions get larger, as stiffness gets smaller
Stiffness/kNm-1
Case4 58.43
Case5 33.39
Case6 8.35
Displacement in x direction (m)
D is
p la
Displacement in x direction (m)
D is
p la
Displacement in x direction (m)
D is
p la
Numbers of response peaks decrease, as stiffness gets smaller
But, the maximum value keep almost the same in the three cases
Stiffness/kNm-1
Case4 58.43
Case5 33.39
Case6 8.35
Fender 1
Time (s)
F o
rc e (
k N
Time (s)
F o
rc e (
k N
Time (s)
F o
rc e (
k N
• Numerical model is established and calibrated with model tests.
• Collision times of fenders in the stern > those in the bow.
• Decrease of pretensions and stiffness leads to an increase of relative motions in
horizontal plane, but a reduction in collisions.
FLNG vessel
• FLNG at Prelude would experience much lower motions in extreme cyclones
than FPSO in the North Sea.
FLNG in side-by-side offloading