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1 INTRODUCTIONS
In the past centuries, Oil and Natural gas have
been developed, and being the most convenient
and high-quality resources for human. In 1859,
drilling was started for oil discovery in United
States, and now developed more than 3000m deep
sea. Even Technology development and drilling
are began in very low temperature and harsh
environment.[1,2]
Offshore plant means design, production,
installation, and operation of drilling equipments
such as Drillship, LNG-SPSO, or LNG-FSRU for
digging up crude oil, natural gas or other energy
in the deep sea instead of land.[3]
As the offshore plant market develops, the
market of offshore equipment is expected to
expand, too, but only a minimum number of
companies produce a portion of products in Korea
compare to the world market.
Recently, up to 55 ton level is being
commercialized in case of professional
manufacture in other country, however there is
none in Korea.
BOP(Blow out preventer) Gantry Crane is the
essential equipment of Drilling System Package
for Drillship/Rig. It is used to move BOP stack in
Drilling Platform using BOP Trolley.
In this research, as a domestic manufacturing
of BOP Gantry Crane which is an offshore plant
equipment, ANSYS is applied into analysis of
rolling and pitching due to wave, wind load due to
Drillship, and the crane's self-weight and
structural analysis was implemented. ANSYS is
used for optimal design of Crane to FSI analysis
and fatigue life evaluation.
2 BOP GANTRY CRANE MODELING
2.1 3D Modeling
(a) Detail model (b) Simplify model
Fig.1 3D modeling of CATIA
FSI Analysis and Fatigue Analysis of BOP Gantry Crane
Hyun Ji Kim1, Gwi Nam Kim
1, Chang Kweon Jeong
2, Yong Gil Jung
3 and Sun Shul
Huh3*
1. Department of Energy and Mechanical Engineering, Graduate
school of Gyeongsang National University, Tongyeong
City, Republic of korea. 2. DMC co.,LTd, Gimhae City, Republic
of korea.
3. Department of Energy and Mechanical Engineering, Gyeongsang
National University, Tongyeong City, Republic of korea.
[email protected], [email protected],
[email protected], [email protected], [email protected],
ABSTRACT : Oil and Natural gases have been developed, and being
the most convenient and high-quality resources for human. Offshore
plant means design, production, installation, and operation of
drilling equipments for natural energy in the deep ocean. BOP
Gantry Crane is the essential equipment of Drilling System Package
for Drillship/Rig. It is used to move BOP stack in Drilling
Platform using BOP Trolley. In this research, CFX analysis was used
to consider wind pressure, and structure analysis was used to
consider dynamic coefficient, rolling, pitching, self-weight. As a
result of crane analysis, even though it is a weight-lightened
model, it is observe that the pressure, deformation and stress
value caused by the wind load are stably maintained above those of
the previous model. Therefore, the structure is thought to be
safe.
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As shown in Fig. 1, 3D modeling made by
CATIA (detailed and simplified model) was used
to structural analysis. The structure analysis
consisted of structure situation, some small parts
like a bolt connection, a winch fix point and
simplified traveling part. Plates thickness, width,
vertical and height are 21.6m are 12 mm, 10.4 m,
5.7 m and 21.6 m, respectively.
2.2 Mesh
Mesh is a process creating a three dimensions
Geometry model to a finite element model
consisted of Element and Node. Mesh of high
density improves the result of structural accuracy,
however it increases analysis time and the mount
of a memory. Therefore, it is important to consist
of regular size Mesh overall because each Node
proceed the structure analysis as a value. Because
of the differences between the internal and
external reinforcing plate of the BOP Gantry
Crane, size of Mesh is applied differently as Mesh
sizing.
3 BOUNDARY CONDITION
BOP Gantry Crane operates on Drillship/Rig
at sea, so environment load should be applied
more than general land crane. Case 1 is FSI
analysis and Case 2 is structure analysis. Case 1
and Case 2 divided environmental conditions of
the BOP Gantry Crane are analyzed and results
are compared. In each case stress value,
deformation, fatigue life and safety factors are
evaluated.[4]
The safety factor is calculated by a standard of
a yield strength of 360 Mpa, DH-36.
3.1 Boundary condition of CFX Analysis
In order to apply wind load to a BOP Gantry
Crane, the analysis was conducted using the FSI
(Fluid-Structure Interaction) technique. [5]
The boundary condition is shown in Fig. 2
First, the fluid field was organized in the form of a
box, and air was set up to be inside the box. Next,
the fluid field plane at the front of the crane was
set up as the Inlet of 63 m/s, the plane facing it as
the Outlet, and all other planes as Openings. The
bottom of the fluid field and the surface of the
crane were set up as walls to enable the value of
the pressure resulting from the fluid to be drawn.
Mesh size is very important in a fluid analysis.
However, if the inside of the entire fluid field is
densely meshing, it will delay analyzing the part
which does not have a big impact on the structure.
Accordingly, the mesh in the area far away from
the structure was organized coarsely and that in
the area close to the structure was organized
densely using the edge sizing function.
Fig. 2 Boundary Condition of CFX Analysis
3.2 Boundary condition of Structure Analysis
Fig. 3 shows the structure analysis of the
boundary condition of BOP Gantry Crane. A is
import pressure due to wind from CFX analysis
result, B,C is working load, D is fix point, E is
acceleration of Rolling and Pitching. It makes two
kinds (case 1 and case 2) of structure analysis
result according to working environment of crane,
explained next sentence.
A is wind pressure from CFX analysis. Wind
load means the load that occurs on the structure
when wind hits the structure. BOP gantry crane is
occurred wind speed 63 m/s, 20 m/s according to
API 2C register of regulation when drillship
moved or crane worked. The wind pressure E on
the Drillship was applied with maximum wind
speed 63m/s toward -X direction.
B and C are working load (SWL). In order to
express 200 ton of operation load, multiplication
value 320 ton of dynamic figure 1.6 is applied to
the force as 160 ton for each on A, B parts of
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fixed part -Z direction (gravity direction) on in the
main winch.
D is Fix, Pin hole part in the bottom of crane
and C is connected with traveling device which
moves as the rail, so fixed support was applied.
E is Rolling & Pitching (Acceleration). BOP
Gantry Crane operates on Drillship/Rig so the
motion of Drillship should be applied on the
analysis model.
Fig. 3 Structure analysis boundary condition of BOP gantry
crane
Table 1. Rolling & Pitching degree of Drillship
Roll (degrees) Pitch (degrees)
13 8
X Y Z
Longitudinal
[m/s]
Transverse
[m/s]
Vertical
[m/s]
Flare L
(~35.4M) 1.0 3.0 3.0
Flare M
(~100.4M) 2.8 4.7 3.3
Flare T
(~165.4M) 4.5 6.4 3.6
Table 1 shows rolling and pitching values of
Drillship according to the height. due to height
21.6M of BOP gantry crane, Flare L value is
applied to consider rolling and pitching. So,
acceleration is applied to E as X, Y, and -Z
(reverse gravity direction).
F is Earth gravity. In order to put self-weight F
of the crane, standard earth gravity is applied as -
Z direction.
3.3 Fatigue analysis
A structure can be destroyed when the number
of the repeated mechanical and thermal load. We
call this situation Fatigue.[6,7]
The case of BOP Gantry Crane, Fatigue limit
curve is applied a Goodman curve suitable for
structure steel. A compressive load happens
overall so a repetitive analysis of compressive
load supply and removal is progressed. Fig. 4 is S-
N Curve of DH-36 Steel the most important for
fatigue analysis.
Fig . 4 S-N diagram of DH-36 steel [8]
4 RESULT
4.1 CFX analysis result
Fig. 5 shows the result of the wind load
analysis of BOP Gantry Crane. Fig. 5(a) is shown
in vector to express the movement and intensity of
the wind, and it can be seen in which direction
and at what intensity the wind moves when it hits
the structure. It is confirmed that more turbulence
is generated immediately after it hits the structure
than before, and the wind pressure also increases
greatly.
As shown in Fig. 5(b), the stream line where it
can be seen that much turbulence is generated
between the legs of the crane. Many reinforcing
plates were added for stable structural form, and it
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was confirmed that much turbulence was
generated.
Fig. 5(c) shows the contour result, and it
appears mostly at the front which directly faces
the wind. While it can be seen in the previous
model that the load is partially concentrated on
the front side of the crane, we can see that the
wind load is evenly acting on the surface in
totality through change in the gradient of the
structure legs.
As it can be seen from the overall observation
result, though reinforcing plates may be helpful in
the aspect of structural stability, it could be
confirmed that reinforcing plates rather increase
the stress applied to the structure by the wind if
only the amount of pressure generated is
compared. A conclusion was made whether the
structure was stable or not through a structural
analysis.
(a) Vector from Wind Direction
(b) Stream Line
(c) Contour
Fig. 5 CFX Analysis Result
4.2 Structure analysis result
Fig. 6 shows the structural analysis result of
the crane. Fig. 6(a) is the deformation, of which
the maximum value is about 32 mm. As most of it
is compressive load, it appears at the top of the
structure. It is presumed that the deformation has
increased as the plates used have become thinner.
However, as 32 mm is very small when the
structure total size of 21 m is considered and far
below the specified deformation (length/800), the
structure is thought to be safe.
Fig. 6(b) represents the stress value, and the
maximum stress value of 177 MPa has occurred at
the bottom of the reinforcing plates designed for
the structure. Fig. 6(c) shows maximum stress
point. The reason why the stress distribution has
been changed while the basic load of the structure
other than the wind load is the same is presumed
to be because of the change in the form of the
structure. However, there is no big change in the
maximum stress value in comparison to that of the
previous model. As the safety factor (2.03) is
higher than the specified safety factor (1.5), the
structure has been safety designed.
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(a) Total Deformation
(b) Equivalent Stress
(c) Maximum stress point
Fig. 6 Structure Analysis Result
4.3 Comparison with the analysis result of previous model.
In comparison to the previous model used 16
mm thick plates, 2 reinforcing plates and leg angle
was vertical. The new model used 12 mm thick
plates, 4 reinforcing plates and the leg has little
tilt angle.
Due to these reasons, the result of fluid
analysis showed generation of much turbulence
between the added reinforcing plates. [9]
Nevertheless, as a result of the structure analysis,
the stress values have been found almost similar
while the deformation has increased by 5 folds.
Even though the load has increased due to the
turbulence and deformation, the stress values are
thought to be almost similar thanks to the stable
structure, and the structure is thought to be stably
designed as, when compared, the safety factor is
found to be higher than the specified safety factor
of 1.5. The results of analysis and structure
comparison are put in order and shown in Table 2.
Table 2 FSI Analysis Result of Each Modeling
Previous
model
New
model
Thickness 16 mm 12 mm
Height 25 M 21 M
Reinforce Plate 2 4
Deformation 7 mm 36 mm
Stress 170 MPa 172 MPa
Safety Factor 2.12 2.09
4.4 Fatigue analysis result
To determine the number of use per day when
a 320 ton is applied on the crane, a fatigue
analysis is conducted. The result implies a
minimum cycle of 108300 of use while there is a
fracture occurred at the same point. And, except
of the minimum cycle point where fracture
occurred, structure cycle life is 1000000 which is
about 137 times of use per day if the structure is
objected to use for 20 years.
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5 CONCLUSION
In this paper, a fluid analysis and a structure
analysis have been conducted to evaluate the
stability of BOP Gantry Crane against external
environmental force, as well as the following
conclusions can be obtained through compared
with the model before the design change.
(1) As a result of the crane fluid analysis, it is
confirmed in the contour result that the stress
concentration phenomenon of the previous model
has been resolved. Therefore, much turbulence is
generated, which is thought to be because of the
reinforcing plates added for stability of the
structure.
(2) In order to the structural analysis crane, even
though it is a weight-lightened model having
deformation of 32 mm and stress value of 177
MPa in comparison to the previous model, we
could observe that the pressure, deformation and
stress value caused by the wind load are stably
maintained above those of the previous model.
Thus, it was confirmed that a safety factor is
higher than the specified safety factor was
maintained. Therefore, the structure is thought to
be safe.
(3) In according to comparison of the previous
model and the changed new model. Result of the
structural analysis and the stress values have been
found almost similar while the deformation has
increased by 5 folds. Even though the load has
increased due to the turbulence and deformation,
the stress values are thought to be almost similar
thanks to the stable structure, and the structure is
thought to be stably designed.
(4) As a result of fatigue analysis, minimum cycle
is almost 1,000,000 cycles higher than 250,000 of
regulation fatigue life. The maximum life was
measured same point of maximum stress. If the
crane is used during 20 years, it can used
4167time a month. From this study, we expected
that these results can be used for future BOP
Gantry Crane technology development for making
of actual model.
Conflict of Interests
The authors declare that there is no conflict of
interests regarding the publication of this paper.
Acknowledgements
This is the result of the study conducted as a Wide
Economic Region Leading Industry Fostering
Project of the Dong-nam Institute for Regional
Program Evaluation supported by the Ministry of
Knowledge Economy(No. A002201167), and the
Korea Institute for Advancement of Technology.
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