1 Copyright © 2012 by ASME
Proceedings of the 31th International Conference on Ocean, Offshore and Arctic Engineering
OMAE2012
June 10-15, 2012, Rio de Janeiro, Brazil
OMAE2012-83728
EXPERIMENTAL STUDY OF THE COUPLED HYDRODYNAMICS OF A DP BARGE
OPERATING CLOSE TO A FPSO
Daniel P. Vieira Numerical Offshore Tank – TPN
University of São Paulo São Paulo, SP, Brazil
Eduardo A. Tannuri Numerical Offshore Tank – TPN
University of São Paulo São Paulo, SP, Brazil
João Luis B. Silva Petrobras
Engineering Division Rio de Janeiro, RJ, Brazil
Marcos D. Ferreira Petrobras
Research Center - CENPES Rio de Janeiro, RJ, Brazil
ABSTRACT
The coupled hydrodynamic of a DP Barge operating close to
a FPSO is evaluated. Experimental tests in a wave basin were
performed to obtain the system dynamic behavior for several
relative positions and environmental incidences. Two small
scale models with factor 1:48 were tested in three different
relative positions, five incidence angles and two irregular seas.
The industry experience in operating barges was used to
provide the insight to select these configurations. The DP
Barge model was equipped with a dynamic positioning (DP)
system, in order to keep its position relative to the FPSO. The
FPSO model uses a scaled spread mooring system. Motions for
DP Barge only were also obtained. Discussions are centered in
reduction or amplification of DP Barge motions due the FPSO
presence. Results are presented in terms of motions significant
amplitude and RAO curves. A numerical model was evaluated
and its results compared with the experiments. Some
considerations, problems and conclusions about the operation
were also obtained. These discussions complement the study
presented by Vieira et al. (2011), which explored this operation
numerically. A companion paper (Tannuri et al., 2012) will
discuss the effects of the hydrodynamic coupling on the DP
performance of the barge.
KEYWORDS
Coupled hydrodynamics, Dynamic Position, Crane Barges,
Floating Production Storage and Offloading.
INTRODUCTION
Everyday several operations are carried out in Brazilian
offshore oil fields. These operations can range from a simple
crew transfer up to a complex replacement of large equipment.
Most of these operations need certain proximity between two or
more vessels. Here, a dynamic positioned (DP) crane barge
operating close to a FPSO is studied, see for instance Figure 1.
Figure 1 – Sketch of DP Barge operating close to a FPSO.
The barge first order motions may cause unacceptable
oscillations of the equipment and high tensions in the lifting
2 Copyright © 2012 by ASME
cable. In this case, there is no physical link between the floating
units, the motions coupling are provided just by the presence of
a modified wave field among the floating bodies, and here
named “hydrodynamic coupling”. This problem was
analytically modeled and extensively discussed in Newman
(2001) and in Chakrabarti (2000). Some numerical approaches
can be seen, for example, in Inoue & Ali (2003), Clauss &
Jacobsen (2005) and Lewandowski (2008).
Vieira et al. (2011) presented a numerical evaluation for the
system here analyzed and the main conclusions were that the
DP Barge motions were reduced in some situations and
amplified in others, but in all cases these motions were different
from those predicted for the vessel alone. Very reduced motions
were observed when the DP Barge is sheltered by FPSO from
wave incidences. Thus, to explore this problem in depth,
experimental tests were carried out using scaled models (1:48)
in waves to obtain the coupled behavior of the floating units.
Discussions are focused on reduction or amplification of
DP Barge motions due the FPSO presence. Results are
presented in terms of motions significant amplitude and RAO
curves always in the full scale. A numerical model was
evaluated and its results compared with the experiments. Some
considerations, problems and conclusions about the operation
were also obtained. This paper also presents some problems
obtained in an attempt to reproduce the experimental tests in the
numerical models and uses these problems as an introduction to
future work. A companion paper (Tannuri et al., 2012) will
discuss the effects of the hydrodynamic coupling on the DP
performance of the barge.
EXPERIMENTAL TESTS
The experimental tests were carried out in LabOceano
Wave Basin (Rio de Janeiro, Brazil). The tank dimensions are
40 m long, 30 m wide and 15 m deep. Multidirectional wave
maker flaps are disposed along one side of the tank and passive
absorbers are disposed along the others.
Models were scaled using 1:48 factor and their main
properties are presented in Table 1. A Qualisys optical system
was used to obtain time series from each test. The DP Barge
model was provided with a scaled DP system used to keep the
distance from FPSO. The FPSO model was moored using a
scaled spread mooring system.
Table 1 – Scaled Model Properties
Model Scale
(1:48)
Full Scale
(1:1)
Model Scale
(1:48)
Full Scale
(1:1)
LOA 2.54 121.9 5.03 241.53 m
LBP 2.54 121.9 4.78 229.25 m
B 0.64 30.5 0.81 38.97 m
D - - 0.42 20.06 m
T 0.11 5.2 0.28 13.21 m
0.15 1.67E+04 0.97 1.07E+05 m³
Δ 0.15 1.71E+04 0.99 1.09E+05 t
KG 0.16 7.53 0.20 9.77 m
Ixx 0.01 2.04E+06 0.08 2.04E+07 t.m²
Iyy 0.09 2.31E+07 1.56 3.97E+08 t.m²
Izz 0.09 2.40E+07 1.62 4.14E+08 t.m²
Tp Heave 1.15 8 1.52 10.5 s
Tp Roll 1.18 8.2 1.70 11.8 s
Units
DP Barge FPSO
The DP Barge model was tested alone in nine different
wave incidence angles: 135, 150, 160, 170, 180, 190, 200, 210
and 225 degrees. Figure 2 shows the orientation of incidence
angles.
Figure 2 – Orientation of incidence angles.
The coupled analysis considered three relative positions
between vessels. In all relative positions the minimum distance
between vessels was defined in the DP system as 20 meters. In
the Inclined Case the angle between the DP Barge and the
FPSO longitudinal axis was 45 degrees. Relative positions are
presented in Figure 3.
DP Barge
FPSO
225°
135°
157.5°
202.5°
180°
DP
Barge
FPSO
FPSO
(a)
(b)
(c)
Figure 3 – Relative positions and wave incidence. Caption:
(a) Parallel Case, (b) Transverse Case and (c) Inclined Case.
3 Copyright © 2012 by ASME
As an example, Figure 4 shows an Inclined Case test:
Figure 4 – Experimental tests in LabOceano Wave Basin
(Rio de Janeiro, Brazil).
Each test was performed using two different JONSWAP
irregular seas, with peak period Tp=8s. Figure 5 and Figure 6
show the sea elevation and the power spectral density for each
irregular sea. The waves present 1m and 2m significant height,
respectively.
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
-1
0
1
t [s]
Sea E
levation [
m]
0 2 4 6 8 10 12 14 16 18 200
0.7
1.4
Wave Period [s]
PS
D [
m²s
]
Std.Dev. = 0.2916 Hs = 1.166m Tp = 8s
Average = 0.001 Max. = 0.992 Min. = -1.136 Std.Dev. = 0.292
Figure 5 – Sea Elevation and Power Spectral Density for
Irregular Sea number 1 (Hs=1m)
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000-2
-1
0
1
2
t [s]
Sea E
levation [
m]
0 2 4 6 8 10 12 14 16 18 200
1
2
3
4
5
Wave Period [s]
PS
D [
m²s
]
Average = 0.015 Max. = 2.181 Min. = -2.006 Std.Dev. = 0.540
Std.Dev. = 0.5458 Hs = 2.183m Tp = 7.837s
Figure 6 – Sea Elevation and Power Spectral Density for
Irregular Sea number 2 (Hs=2m)
Results in frequency domain were obtained using Fourier
Series Analysis as presented in Chakrabarti (1994).
NUMERICAL MODEL
A numerical model, evaluated by boundary element method
code WAMIT (Wamit Inc., 2006), was compared with
experimental results. The wet surface presented in Figure 7 was
designed in computer-aided design (CAD) software called
MULTISURF. This software can communicate directly to the
WAMIT to generate the mesh for computational evaluation. The
mesh was generated using higher-order method. A convergence
test was carried out using panel size 2, 5, 10 and 20 meters. The
decrease in panel size did not present significant differences in
numerical results. Thus, a 5-meter panel size was used to
improve the time expended in simulation.
Figure 7 – DP Barge wet surface.
A coupled model was also obtained using WAMIT
multibody module, as described in Vieira et al. (2011). It will be
seen that the multibody analysis was not reliable with
experimental tests. In this case, the DP Barge presented a very
large yaw drift, which is not compatible with WAMIT analyses,
once WAMIT evaluates the motions for a static relative position
between vessels. The numerical analyses require a time domain
simulation using WAMIT coefficients evaluated for several
other positions that need to be updated for each time step. This
simulation was not carried out here. But some tests that did not
present significant drift motions were compared with the
numerical model. Viscous damping forces in the free surface
between vessels were not considered because the distance
between them was considered large enough.
DP BARGE ONLY - NUMERICAL AND EXPERIMENTAL
RESULTS
Figure 8 shows the Response Amplitude Operator obtained
in tests for the DP Barge vessel only. The RAO curves are
compared with the numerical model described above. For the
considered incidences, only the surge, heave and pitch RAOs
presented significant motions. Figure 8 shows the RAO
obtained for the two analyzed seas and all wave incidences, and
the columns contain the surge, pitch and heave RAOs,
respectively.
It is possible to see a good agreement between numerical
model and experimental results. Some few cases, such as the
pitch RAO for 135 and 225 degrees, presented a discrepancy
between numerical and experimental results, mainly for the tests
carried out with the irregular sea number 2. For these two
incidence angles the DP Barge presented a significant yaw drift,
which the linear numerical model cannot reproduce.
For the tested incidence angles, yaw drifts increase as these
angles moves from 180 degrees. As expected, the largest yaw
drifts were observed for 135 and 225 degrees. Figure 9 shows
the trace plot for those tests, and the large yaw drift can actually
be verified.
4 Copyright © 2012 by ASME
Response Amplitude Operator
13
5 d
eg
5 10 150
0.5
1
1.5
RA
O S
UR
GE
[m
/m]
T [s]
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O S
WA
Y [
m/m
]
T [s]
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O H
EA
VE
[m
/m]
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O R
OLL [
deg/m
]
T [s]
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O P
ITC
H [
deg/m
]
T [s]
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O Y
AW
[deg/m
]
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eg
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O S
UR
GE
[m
/m]
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WA
Y [
m/m
]
T [s]
5 10 150
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O H
EA
VE
[m
/m]
T [s]
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1.5
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O R
OLL [
deg/m
]
T [s]
5 10 150
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1
1.5
2
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O P
ITC
H [
deg/m
]
T [s]
5 10 150
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O Y
AW
[deg/m
]
T [s]
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eg
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O S
UR
GE
[m
/m]
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O S
WA
Y [
m/m
]
T [s]
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O H
EA
VE
[m
/m]
T [s]
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1
1.5
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O R
OLL [
deg/m
]
T [s]
5 10 150
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RA
O P
ITC
H [
deg/m
]
T [s]
5 10 150
0.5
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O Y
AW
[deg/m
]
T [s]
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eg
5 10 150
0.5
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1.5
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O S
UR
GE
[m
/m]
T [s]
5 10 150
0.5
1
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O S
WA
Y [
m/m
]
T [s]
5 10 150
0.5
1
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RA
O H
EA
VE
[m
/m]
T [s]
5 10 150
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1
1.5
2
2.5
RA
O R
OLL [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
2.5
RA
O P
ITC
H [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
2.5
RA
O Y
AW
[deg/m
]
T [s]
18
0 d
eg
5 10 150
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1
1.5
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O S
UR
GE
[m
/m]
T [s]
5 10 150
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O S
WA
Y [
m/m
]
T [s]
5 10 150
0.5
1
1.5
RA
O H
EA
VE
[m
/m]
T [s]
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0.5
1
1.5
2
2.5
RA
O R
OLL [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
2.5
RA
O P
ITC
H [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
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RA
O Y
AW
[deg/m
]
T [s]
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eg
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1
1.5
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O S
UR
GE
[m
/m]
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1
1.5
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O S
WA
Y [
m/m
]
T [s]
5 10 150
0.5
1
1.5
RA
O H
EA
VE
[m
/m]
T [s]
5 10 150
0.5
1
1.5
2
2.5
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O R
OLL [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
2.5
RA
O P
ITC
H [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
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RA
O Y
AW
[deg/m
]
T [s]
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0 d
eg
5 10 150
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1
1.5
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O S
UR
GE
[m
/m]
T [s]
5 10 150
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1
1.5
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O S
WA
Y [
m/m
]
T [s]
5 10 150
0.5
1
1.5
RA
O H
EA
VE
[m
/m]
T [s]
5 10 150
0.5
1
1.5
2
2.5
RA
O R
OLL [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
2.5
RA
O P
ITC
H [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
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O Y
AW
[deg/m
]
T [s]
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0 d
eg
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1
1.5
RA
O S
UR
GE
[m
/m]
T [s]
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0.5
1
1.5
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O S
WA
Y [
m/m
]
T [s]
5 10 150
0.5
1
1.5
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O H
EA
VE
[m
/m]
T [s]
5 10 150
0.5
1
1.5
2
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O R
OLL [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
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O P
ITC
H [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
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O Y
AW
[deg/m
]
T [s]
22
5 d
eg
5 10 150
0.5
1
1.5
RA
O S
UR
GE
[m
/m]
T [s]
5 10 150
0.5
1
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O S
WA
Y [
m/m
]
T [s]
5 10 150
0.5
1
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O H
EA
VE
[m
/m]
T [s]
5 10 150
0.5
1
1.5
2
2.5
RA
O R
OLL [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
2.5
RA
O P
ITC
H [
deg/m
]
T [s]
5 10 150
0.5
1
1.5
2
2.5
RA
O Y
AW
[deg/m
]
T [s]
Figure 8 – Surge, Heave and Pitch RAO of DP Barge only.
Caption: (line) Num. / (×) Exp. Wave 1 / (•) Exp. Wave 2.
-100 -80 -60 -40 -20 0 20 40 60 80
-80
-60
-40
-20
0
20
40
60
80
X (m)
Y (
m)
Barge trace plot
-100 -80 -60 -40 -20 0 20 40 60 80
-80
-60
-40
-20
0
20
40
60
80
X (m)
Y (
m)
Barge trace plot
225o
135o
Figure 9 – Trace plot for Wave number 2, 135° and 225°.
DP BARGE OPERATING CLOSE TO FPSO -
EXPERIMENTAL RESULTS
Figure 10 present heave significant amplitude for each
incidence angle. The figure illustrates the shielding effect
caused by FPSO presence. For the angles in which the DP
Barge is sheltered by FPSO (202.5° and 225°) heave motion is
smaller than for the angles in which the DP Barge is unsheltered
(135° and 157.5°).
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
135 157.5 180 202.5 225
Sign
ific
ant
Am
plit
ud
e (
m)
(deg)
Parallel
Tranverse
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
135 157.5 180 202.5 225
Sign
ific
ant
Am
plit
ud
e (
m)
(deg)
Parallel
Tranverse
Figure 10 – Heave Significant Amplitude Vs Incidence
Angle (up) Wave number 1 ; (down) Wave number 2.
Figure 11 presents pitch significant motions for each
analyzed incidence angle. The shielding effect can also be
visualized. The same trend can be obtained for the other
degrees of freedom.
5 Copyright © 2012 by ASME
0
0.2
0.4
0.6
0.8
1
1.2
1.4
135 157.5 180 202.5 225
Sign
ific
ant
Am
plit
ud
e (
de
g)
(deg)
Parallel
Tranverse
0
0.2
0.4
0.6
0.8
1
1.2
1.4
135 157.5 180 202.5 225
Sign
ific
ant
Am
plit
ud
e (
de
g)
(deg)
Parallel
Tranverse
Figure 11– Pitch Significant Amplitude Vs Incidence Angle
(up) Wave number 1; (down) Wave number 2.
The following analysis presents an evaluation from the DP
Barge point of view. Three cases were tested for DP Barge head
seas and three cases were tested for DP Barge bow-quartering
seas.
Figure 12 shows three different tests with head seas wave
incidence, and Figure 13 presents the influence of FPSO
presence in DP Barge motions for those head seas cases. In both
parallel and inclined cases, heave and pitch motions were
amplified. Heave motions were amplified in up to five times
comparing the inclined case with DP Barge only.
Barge
FPSO
DP Barge only Parallel 180deg
Barge
FPSO
Inclined 135 deg
Figure 12 – Head seas cases
0
0,2
0,4
0,6
0,8
1
1,2
wave 1 wave 2 wave 1 wave 2
Heave Pitch
Sign
ific
ant
Am
plit
ud
e (
m o
r d
eg) DP Barge only (b =
180deg)Parallel (b = 180deg)
Inclined (b = 135deg)
Figure 13 – Heave and Pitch Significant Amplitude for DP
Barge head seas.
Figure 14 shows the cases with bow-quartering seas, and
Figure 15 presents the influence of FPSO in DP Barge motions
for those tests. In this case, just the heave and roll motions were
amplified. Pitch motion did not present significant differences.
Roll motions were amplified four times for inclined case in
irregular sea number 1. Transverse case was the worst
configuration for heave motions.
Barge
FPSO
DP Barge only Transverse 135deg
Barge
FPSO
Inclined 180 deg Figure 14 – Bow-quartering seas cases
0
0,5
1
1,5
2
2,5
wave 1 wave 2 wave 1 wave 2 wave 1 wave 2
Heave Roll Pitch
Sign
ific
ant
Am
plit
ud
e (
m o
r d
eg) DP Barge only (b =
225deg)
Transverse (b = 135deg)
Inclined (b = 180deg)
Figure 15 – Heave, Roll and Pitch Significant Amplitude for
DP Barge bow-quartering seas
6 Copyright © 2012 by ASME
Figure 16 presents a comparison between coupled and
uncoupled tests for sheltered and unsheltered configurations. It
is possible to see how the FPSO presence amplifies the RAO
for unsheltered configuration in all range of periods studied and
reduces the RAO for sheltered configuration in periods from 7s
up to 9.5s. This figure is also an example of shield effect.
5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 100
0.2
0.4
0.6
0.8
1
1.2
1.4
RA
O H
EA
VE
[m
/m]
T [s]
DP Barge only
DP Barge+FPSO (unsheltered)
DP Barge only
DP Barge+FPSO (sheltered)
FPSO
DP Barge
Figure 16 – Heave RAO obtained with irregular sea number
1. Caption: red - β = 135deg / blue - β = 225deg
Similar results of amplified RAO curves were obtained in
Clauss & Jacobsen (2005) for analyzing the relative motions of
a crane operating close to a barge, confirming that these
motions alterations are easily found in the literature.
DP BARGE OPERATING CLOSE TO FPSO -
PRELIMINARY NUMERICAL RESULTS
Figure 17 presents a comparison between numerical and
experimental results. The numerical model presented a good
agreement for this configuration. In this case the DP Barge did
not have significant yaw drifts. However, in cases in which the
yaw drifts were larger than 5 degrees, it was not possible to
reproduce this good agreement.
In this figure, both in heave and pitch numerical curves it is
possible to see several peaks as the curve rises. These peaks
appear due to the several couplings of the system twelve
degrees of freedom. But its peaks arise from the linear nature of
the numerical solution. In experimental data these peaks do not
occur, just a small deflection was obtained for heave curves
about 8s period. The non-linear characteristics of damping
effects can explain this difference.
To obtain more reliable curves from numerical models a
time domain simulation will be run in future work. Inoue & Ali
(2003) presents a numerical model that can predict motions
with accuracy for a LNG operating in parallel and tandem
configurations. This evaluation must be considered in a future
work.
5 10 150
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
RA
O H
EA
VE
[m
/m]
T [s]
5 10 150
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
RA
O P
ITC
H [
deg/m
]
T [s] Figure 17 - Heave and Pitch RAO for Inclined Case (β =
180deg). Legend: (–) Num. / (×) Exp. Wave 1 / (•) Exp. Wave
2.
CONCLUSIONS AND NEXT TASKS
A scaled model test was performed with a DP Barge
simulating an operation close to a FPSO platform. The
hydrodynamic interference was achieved and several examples
of amplified and reduced motions due the FPSO presence were
presented.
Parallel case was the best configuration according to the
obtained results. Shielding effect must be considered in
operation design to reduce motion and amplify operational
window.
Both uncoupled and coupled numerical model were
provided and compared with experimental data. Significant
differences were obtained mainly in coupled cases. These cases
require a more extensive study which will be presented in a
future work using time domain simulations.
NOMENCLATURE
B Beam
D Depth
Hs Significant wave heigth
Ixx Moment of inertia about x axis
Iyy Moment of inertia about y axis
Izz Moment of inertia about z axis
KG Vertical distance between keel and center of
gravity
LBP Length between perpendiculars
7 Copyright © 2012 by ASME
LOA Length over all
T Draft
Tp Wave peak period
Tp Heave Heave resonant period
Tp Roll Roll resonant period
Wave Incidence
Δ Displacement
Volume
ACKNOWLEDGMENTS
Authors thank Petrobras, the University of São Paulo and
the Numerical Offshore Tank team for discussions and supports,
particularly Msc. Eng. Edgard Borges Malta for his consulting.
The first author thanks the National Petroleum Agency (ANP)
for financial support. The second author thanks the CNPq,
under the processes 302544/2010-0.
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