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Ocean Engineering 38 (2011) 1130–1140
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Ocean Engineering
0029-80
doi:10.1
$An
Symposn Corr
E-m
journal homepage: www.elsevier.com/locate/oceaneng
Heat flow analysis of an FPSO topside model with wind effect taken intoaccount: A wind-tunnel test and CFD simulation$
B.J. Kim, J.Y. Yoon, G.C. Yu, H.S. Ryu, Y.C. Ha, J.K. Paik n
The Lloyd’s Register Educational Trust Research Centre of Excellence, Pusan National University, Busan, Republic of Korea
a r t i c l e i n f o
Article history:
Received 16 July 2010
Accepted 5 May 2011
Editor-in-Chief: A.I. Incecikoffloading (FSPO) topside models subject to fire. It is motivated by the need to identify the fire loads on
FPSO topsides, taking into account the effects of wind speed and direction as well as the effects of
Available online 1 June 2011Keywords:
FPSO topsides
Fire
Heat flow
Wind effect
Risk assessment and management
Wind tunnel test
CFD simulations
18/$ - see front matter & 2011 Elsevier Ltd. A
016/j.oceaneng.2011.05.004
earlier version of this paper was present
ium, OMAE 2010 Conference, 6–11 June 201
esponding author. Tel.: þ82 51 510 2429; fax
ail address: [email protected] (J.K. Paik).
a b s t r a c t
The aim of this paper is to study the feasibility of a computational fluid dynamics (CFD) method to
examine the effect of wind on the thermal-diffusion characteristics of floating production storage and
geometry of the FPSO topsides. The results of a wind-tunnel test and CFD simulation undertaken for
these purposes on a 1/14-scale FPSO topside model of a VLCC class FPSO unit are reported here. In the
wind-tunnel test, the locations of the heat source of the fire are varied, as are the speed and direction of
the wind, and the temperature distribution is measured. CFD simulations, using the ANSYS CFX (2009)
program, were performed on the test model, with the results compared with the experimental results.
It is concluded that wind has a significant effect on the thermal-diffusion characteristics of the test
model and that the CFD simulations are in good agreement with the experimental results. The insights
developed in this study will be very useful for the fire engineering of FPSO topsides.
& 2011 Elsevier Ltd. All rights reserved.
1. Introduction
In the offshore industry, the production, processing, storageand transportation of hydrocarbons present an inherent risk offire and explosions. Floating production storage and offloading(FPSO) topsides, in particular, have a high probability of fireand explosion accidents being caused by the leakage of oil orgas (Cullen, 1990; HSE, 1999, 2003; Czujko, 2001; Paik andThayamballi, 2007).
Fig. 1 shows the total number of oil and gas leakage incidentson FPSOs installed in UK waters from 1994 to 2008 (Paik andCzujko, 2009; Paik, 2010), as recorded by the UK’s Health andSafety Executive (HSE). The increasing trend in such incidents isobvious. It is thus of paramount importance that risk assessmentsbe carried out and the management of fire and gas explosions beconsidered in the design, building and operation of FPSOs (Paikand Thayamballi, 2007).
The aim of the present paper is to study the feasibility ofapplying the computational fluid dynamics (CFD) method to theheat flow analysis of FPSO topsides subject to fire with the windeffect taken into account. It is motivated by the need to examinethe effects of wind speed and direction as well as the geometry of
ll rights reserved.
ed at the Alaa E. Mansour
0, in Shanghai, China.
: þ82 51 512 8836.
FPSO topsides on thermal diffusion during fire and gas explosionswithin the framework of risk assessment and management. Forthis purpose, wind-tunnel tests and CFD simulations were under-taken on a 1/14-scale FPSO topside model of a VLCC class FPSOunit. The wind speed and direction were varied in the wind-tunnel test to investigate their effects on the thermal diffusioncharacteristics of the specific heat-source locations associatedwith fire or gas explosions. The temperature distribution was alsomeasured. Details of the experimental and numerical results aredocumented herein.
2. The wind tunnel test
2.1. Test set-up
Fig. 2 shows the 1/14-scale test model of a VLCC class FPSOtopside in conjunction with a separation module comprising pipingand separation equipment. The dimensions of the acrylic andwood test model are 1400 mm (D)�2000 mm (W)�525 mm (H).The test model was simplified and scaled considering the limita-tions of the wind-tunnel test facility, i.e. the projected area of themodel had to be less than 5% of the cross section of the windtunnel. The experiment was conducted in a wind-tunnel testfacility the layout of which with the test model placed on aturntable is depicted in Fig. 3. Wind was supplied from the windtunnel, with the turntable rotated to change the wind direction.
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
0
5
10
15
20
25
30
35
40
45
50
8
67
14
17
21
27
1718
1315
1917
20
8
34
2
8
1415
27
16
23
31
33
29
23
43
9
23
12
3
12 2
Major
Significant
Minor
Year
Fig. 1. Total number of major, significant and minor releases of oil and gas on FPSOs from 1994 to 2008 (Paik and Czujko, 2009).
1400mm2000mm
525mm
Fig. 2. 1/14-scale test model of a VLCC class FPSO topside.
Turn table(D= 3m)
Suct
ion
type
blo
wer
Pitot tube
Thermo couple
Data logger
Thermor spot sensor(Infrared)
Heat source
Switch
Wind tunnel
Fig. 3. Layout of the wind tunnel test facility.
290mm
55m
m
Fig. 4. Type and dimensions of the heat source.
Table 1Heat source specifications used in the test.
Type Sheath heater
Material STS304
Diameter (mm) 55
Coil diameter (mm) 8
Length (mm) 290
Capacity (kW) 3
Maximum temperature (K) 1026
0 200 400 600 800Time (s)
294
394
494
594
694
794
894
994
1094
Tem
pera
ture
(K
)
0.0m/s
1.5m/s
2.0m/s
Fig. 5. The temperature versus time history measured on the surface of the heat
source, with varying wind speed.
B.J. Kim et al. / Ocean Engineering 38 (2011) 1130–1140 1131
The wind speed was kept constant during the test through asuction-type blower and by stabilizing the air streams.
During the test, a sheath heater was used as the heat sourceinstead of fire, which is efficient and safe for supplying heat in thewind-tunnel facility, as shown in Fig. 4. A cylindrical heater waschosen to resemble the fire around the pipes and cylindrical
B.J. Kim et al. / Ocean Engineering 38 (2011) 1130–11401132
vessels on FPSO topsides. The specifications of the heater aredetailed in Table 1 and the maximum temperature on the surfaceof the heater was 1026 K without wind, as shown in Fig. 5.
2.2. Test cases
Three parameters, wind direction, wind speed and heat sourcelocation, were varied, resulting in a total of eight cases, asindicated in Table 2. In terms of wind speed, moderate breezeconditions equivalent to Beaufort number 4 (Paik andThayamballi, 2007) were considered, and thus wind speeds of6.3 and 8.4 m/s were selected. Considering the scale effect of thetest model, these wind speeds correspond to 1.5 and 2.0 m/s,respectively. Two heat-source locations and three wind directionswere considered, as can be seen in Table 2 and Fig. 6.
Before conducting these test cases, a pre-test was performed toconfirm the accuracy and applicability of the heat source. The
A-R4 A-R3 A-R2
A-R1
200mm
Case I
A-F1 A-F2
A-F3
A-F4
200mm
Case III
Fig. 6. Monitoring points on each of the test cases for variou
Table 2Test cases considered in the wind-tunnel test.
Heat source
position
Wind
direction
Wind speed
(m/s)
Case I A Rear 1.5
2.0
Case II A Side 1.5
2.0
Case III A Front 1.5
2.0
Case IV B Front 1.5
2.0
temperature on the surface of the heater was measured by aninfrared thermometer, and the temperature versus time historiesare shown in Fig. 5. As can be seen in the figure, the temperaturerapidly rises, and increases gradually between 400 and 700 s.After 700 s a constant temperature is obtained. Through the pre-test it was confirmed that the heater generates temperatures ofup to 1000 K and retains an almost constant temperature after700 s on the surface of the heater during the test. It was alsofound that wind has little effect in terms of the temperature onthe surface of the heater.
2.3. Test results and discussion
The air temperature was measured by thermocouples at thevarious monitoring points illustrated in Fig. 6, with times up to800 s. A set of measured temperature versus time histories isshown in Fig. 7. The air temperature measured by the thermo-couples increases over time and tends to maintain a constanttemperature, even though a slight tremor can be observed atrelatively high temperature. Before data were collected thetemperature of the heat source and the air flow in the windtunnel were stabilized. Table 3 shows the whole test dataobtained by the wind-tunnel test. The temperature given inTable 3 is the average temperature after the temperature of theheat source is stabilized, i.e. the measured temperatures between771 and 800 s have been averaged.
2.3.1. Effects of wind speed
Fig. 7 shows the result of Case III. As previously noted, thetemperature initially increases over time and then retains aconstant temperature at all monitoring points. At the monitoringpoints A-F1 and A-F2 where the temperature is relatively high,the temperature rise on the effects of wind speed is noticeable.
A-S1
A-S2
A-S3
A-S4
200mm
Case II
B-F1B-F2
B-F3
B-F4
200mm
Case IV
s heat-source locations (arrows indicate wind direction).
0 200 400 600 800Time (s)
294
299
304
309
314
319
324
329
334
339
344
Tem
pera
ture
(K
)
Wind speed: 1.5m/s
Wind direction: Front
Heat source position: A
A-F1
A-F2
A-F3
A-F4
0 200 400 600 800Time (s)
294
299
304
309
314
319
324
329
334
339
344
Tem
pera
ture
(K
)
A-F1
A-F2
A-F3
A-F4
Wind speed: 2.0m/s
Wind direction: Front
Heat source position: A
Fig. 7. Temperature versus time history measured at monitoring points A-F1 to
A-F4 in Case III: (a) wind speed¼1.5 m/s and (b) wind speed¼2.0 m/s.
Table 3Average temperature (K) obtained by present wind tunnel test (t¼771–800 s).
Case no. Monitoring
point
Wind speed (m/s) Difference
1.5 (A) 2.0 (B) (B)�(A)
Case I A-R1 306.4 303.4 �3.0
A-R2 302.0 301.1 �0.9
A-R3 301.9 300.6 �1.3
A-R4 300.8 300.0 �0.8
Case II A-S1 307.4 305.4 �2.0
A-S2 388.2 373.0 �15.2
A-S3 319.7 319.1 �0.6
A-S4 308.7 309.6 0.9
Case III A-F1 317.5 327.7 10.2
A-F2 307.2 309.9 2.7
A-F3 300.7 300.2 �0.5
A-F4 301.3 300.7 �0.6
Case IV B-F1 319.4 334.9 15.5
B-F2 308.8 318.6 9.8
B-F3 303.2 309.1 5.9
B-F4 299.4 303.8 4.4
B.J. Kim et al. / Ocean Engineering 38 (2011) 1130–1140 1133
The average temperature at point A-F1 is 317.5 K for 1.5 m/s windspeed, and 327.7 K for 2.0 m/s wind speed. This results in atemperature increase of about 10.2 K at A-F1 as wind speedincreases from 1.5 to 2.0 m/s. In addition, the tremor in thetemperature at A-F1 also increases as the wind speed increases.At point A-F2, the temperature increases by 2.7 K. However, atA-F3 and A-F4 where the temperature is relatively low, very littletemperature change can be observed, as shown in Fig. 7 andTable 3. In Case IV, the test results are similar to Case III. Thetemperature increases by 15.5 K at B-F1, by 9.8 K at B-F2, by 5.9 Kat B-F3 and by 4.4 K at B-F4 as the wind speed increases from1.5 to 2.0 m/s.
Fig. 8 shows the result of Case II. At the monitoring point A-S2where the temperature is relatively high, the decrease of tem-perature is noticeable as the wind speed increases. The averagetemperature at A-S2 is 388.2 K for 1.5 m/s wind speed, and373.0 K for 2.0 m/s wind speed. The temperature decreases by15.2 K at A-S2 as the wind speed increases from 1.5 to 2.0 m/s.At A-S1 and A-S3, the temperature decreases by 2.0 and 0.6 K,respectively, as shown in Fig. 8 and Table 3. The tremor in the
0 200 400 600 800Time (s)
294
314
334
354
374
394
414
Tem
pera
ture
(K
)
Wind speed: 1.5m/sWind direction: Side
Heat source position: A
A-S1
A-S2
A-S3
A-S4
0 200 400 600 800Time (s)
294
314
334
354
374
394
414
Tem
pera
ture
(K
)
A-S1
A-S2
A-S3
A-S4
Wind speed: 2.0m/sWind direction: Side
Heat source position: A
Fig. 8. Temperature versus time history measured at monitoring points A-S1 to
A-S4 in Case II: (a) wind speed¼1.5 m/s and (b) wind speed¼2.0 m/s.
B.J. Kim et al. / Ocean Engineering 38 (2011) 1130–11401134
temperature at A-S2 also decreases as the wind speed increases.It seems that the tremor is due to the turbulence across thecylindrical shape of the heat source. In Case I, the temperaturealso tends to decrease as the wind speed increases from 1.5 to2.0 m/s, as summarized in Table 3. However, in this case, thetemperature change is relatively small even though the tempera-ture at each monitoring point is almost the same.
In summary, two different trends on the effects of wind speedhave been observed by the wind-tunnel test. In Cases I and II, thetemperature tends to decrease as wind speed increases; however,the temperature tends to increase with the increasing wind speedin Cases III and IV. In this regard, it is confirmed that effects ofwind speed are significant on thermal diffusion characteristics ofFPSO topsides subject to fire.
2.3.2. Effects of wind direction
It is clearly shown in Fig. 8 that the temperature at themonitoring point A-S1 is significantly lower than the temperatureat points A-S2 and A-S3. The location of A-S1, A-S2 and A-S3 are12.5, 32.5 and 302.5 mm away from the surface of the heatsource, respectively. Furthermore, the temperature at A-S1 islower than that at A-S4, which is 570 mm away from the surfaceof the heat source as shown in Fig. 6. This is evident that heatspreads in the direction of the wind, and does not spread againstthe wind hence the wind direction significantly affects theheat flow.
The effects of wind direction are investigated in Cases I–III. Thelocation of the heat source is identical for these cases and thewind direction is changed for each individual case as shown inTable 2. However, it is difficult to determine the effects of winddirection directly from the test results as the monitoring pointsfor each case are different. For this reason, the temperaturedistribution is investigated along the distance from the surfaceof heat source to the monitoring point for each case. Even thoughthe temperature cannot be compared directly at the samedistance from the heat source for each wind direction, it ispossible to figure out the tendency of temperature distributiondepending on the wind direction as shown in Fig. 9. According tothe present test results, heat transfer is better when the windcrosses the cylindrical heat source, i.e. in Case II, rather than whenthe wind blows in the direction of the cylindrical heat source,i.e. in Cases I and III as illustrated in Fig. 9. For Cases I and III, the
-100 0 100 200 300 400 500 600 700 800 900Distance from the surface of the heat source (mm)
290
300
310
320
330
340
350
360
370
380
390
400
Tem
pera
ture
(K
)
: Case I (wind direction = rear): Case II (wind direction = side): Case III (wind direction = front): Case IV (wind direction = front)
Hollow: wind speed = 1.5m/sSolid: wind speed = 2.0m/s
Fig. 9. Effects of distance from the heat source on temperature distribution.
wind direction is the same, but the temperature distribution isnot, i.e. a relative low temperature is observed in Case I comparedto Case III. By comparing Case I with Case III, it is easy to see thatthe effect of the geometry surrounding the heat source affects thethermal diffusion characteristics significantly.
In conclusion, it was observed that heat spreads in thedirection of the wind, and does not spread against the wind,and heat transfers better when the wind blows in the transversedirection of the cylindrical heat source rather than in the long-itudinal direction. This confirms that the effect of the winddirection is significant. The geometry of the heat source and thetest model generate different heat flows according to the winddirection, so the effects of wind direction should be consideredtogether with the effects of such geometry. Cautious attention isrequired to develop a CFD model for fire simulation on FPSOtopsides, i.e. the geometry of the fire area and surroundingsshould be taken into account.
Fig. 10. ANSYS CFX mesh modeling.
Inlet1.5m/s, 2.0m/s
Outlet
1.5m/s, 2.0m/sWall: Adiabatic
Wall: Adiabatic
4000mm3400mm
1300mm
Fig. 11. Boundary conditions applied for the CFD simulations.
Heat source(Solid)
Atmosphere(Fluid)
Fluid-Solid Interfaces
55m
m
B.J. Kim et al. / Ocean Engineering 38 (2011) 1130–1140 1135
2.3.3. Effects of heat source location
Effects of heat-source location are investigated by using theresults of Cases III and IV. The location of the heat source of CaseIV is shifted 550 mm from the location of Case III, i.e. to the leftdirection in Fig. 6. For wind speeds of 1.5 m/s, the temperaturedistribution for both Cases III and IV along the wind direction aresimilar as shown in Fig. 9. However, for 2.0 m/s of wind speed, thetemperature distribution in Case IV is higher than that of Case III.This illustrates that thermal diffusion is affected by the heat-source location depending on the wind speed. It is likely to becorrelated with the air flow between two cylindrical vessels, thatis, if the wind speed between two cylindrical vessels is increasedthe heat is transferred further away from the heat source.
8mm
Atmosphere(Fluid)
Fig. 13. Fluid–solid interface via CHT option applied for heat-source modeling.
344
354
364
374
384
394
404
pera
ture
(K
)
Wind direction: Side
Wind speed: 1.5m/s
Test
CFX(Cylinder)
CFX(Coil)
2.3.4. Effects of distance from the heat source
Fig. 9 shows the effects of distance from the heat source. In allcase tests it is shown that the temperature decreases withincreasing distance from the heat source. However, the degreeof decrease is not identical. As the distance increases from theheat source, the temperature decreases gradually in Cases III andIV, and rapidly in Case II. In addition, in Case I, the temperature isalmost the same even though the distance increases from the heatsource. This occurs because the temperature decrease is affectednot only by the distance from the heat source but also the windspeed and direction, as well as the surrounding geometry. There-fore, it is concluded that the effects of wind speed, wind direction,heat-source location and distance from the heat source as well asthe surrounding geometry should be taken into account on heat-transfer analysis during fire and gas explosions for the frameworkof risk assessment and management of FPSO topsides.
290mm
55m
m
290mm
55m
m
290mm
55m
m
Section A-A’
A’
ACylinder type
Coil type
55m
m
8mm
55m
m
8mm
20mm 10mm
Fig. 12. Heat-source modeling used for the CFD simulations.
Time(s)
294
304
314
324
334Tem Sensor point:A-S2
0 200 400 600 800
0 200 400 600 800
Time(s)
294
304
314
324
334
344
354
364
374
384
394
404
Tem
pera
ture
(K
)
Wind direction: Side
Wind speed: 1.5m/s
Sensor point:A-S3
Test
CFX(Cylinder)
CFX(Coil)
Fig. 14. Comparison of average temperature versus time histories obtained by the
present test and ANSYS CFX simulations for the two types of heat-source modeling
for Case II with a wind speed of 1.5 m/s: (a) at monitoring point A-S2 and (b) at
monitoring point A-S3.
Table 4Properties of heat-source material.
Material Density
(kg/m3)
Specific heat
capacity (J/kg K)
Maximum
temperature (K)
Thermal
conductivity
(W/mK)
STS304 8000 500 1026 21.5
B.J. Kim et al. / Ocean Engineering 38 (2011) 1130–11401136
3. CFD simulations
3.1. Mesh size and boundary conditions
ANSYS CFX (2009) program was used for the CFD simulations ofthe wind-tunnel test. Fig. 10 shows the mesh modeling. The meshwas tetrahedral, and the elements numbered around 650,000. Theboundary conditions for the CFD simulations are shown in Fig. 11.To deal with turbulence behavior, the shear stress transport (SST)option was employed, and the thermal energy option was applied tomodel the thermal-transfer behavior.
3.2. Heat-source modeling
As heat-source geometry plays an important role in thermaldiffusion simulations with wind, realistic geometry modeling isnecessary to obtain good simulation results. It is necessary to idealizethe geometry of the heat source for computational efficiency. In this
Fig. 15. Temperature distribution obtained from the ANSYS CFD simulations f
Fig. 16. Temperature distribution around the heat source obtained by ANSYS CFX
speed¼2.0 m/s.
Table 5Comparison of average temperatures (K) obtained by the present test and ANSYS
CFX simulations for the two types of heat source modeling for Case II with a wind
speed of 1.5 m/s (t¼771–800 s).
Monitoring
point
Test (A) CFX Difference
Cylinder (B) Coil (C) (A)�(B) (A)�(C)
A-S2 388.2 312.0 370.2 66.2 18.0
A-S3 319.7 300.5 317.6 19.2 2.1
regard, two types of heat-source modeling were considered, namely,cylinder- and coil-type modeling, as shown in Fig. 12.
The conjugate heat transfer (CHT) option (ANSYS CFX, 2009)was applied for the heat source. The CHT model is suitable forheat transfer and takes into account material properties. Table 4shows the properties of the heat source material for the CHTmodel. Fig. 13 shows the fluid–solid interface (FSI) mechanism forthis model (ANSYS CFX, 2009), in which the solid represents theheat source and the fluid is equivalent to the atmosphere in thewind tunnel. The total heat flux released from the heat sourceequaled the capacity of the heat source used in the test and aconstant heat flux was released during the overall analysis time.
3.3. CFD simulation results and discussion
Transient analysis was carried out to simulate the thermal-diffusion behavior of the ANSYS CFD method. For a total of 800 sa uniform time-step size, i.e. 0.04 s was used. Two types of heat-source modeling were applied in the ANSYS CFX simulations forCases II and III. It was observed that both heat-source models gavesimilar temperatures in the overall time domain at all monitoringpoints for Case II. However, this was not found for Case III. Fig. 14draws a comparison between the ANSYS CFX simulation and thetest results for Case II. Average temperature versus time historiesare plotted to see the overall trend and it is found that thecylinder-type modeling gives a lower temperature in overall timecompared to the average temperature obtained by coil-typemodeling and the test. It is also noted that the coil-type modelinggives good agreement with the test results. Table 5 compares theaverage temperatures after about 770 s. It demonstrates that the
or Case II and Case III (wind speed¼1.5 m/s): (a) Case II and (b) Case III.
simulation for Case II (Elevation view): (a) wind speed¼1.5 m/s and (b) wind
B.J. Kim et al. / Ocean Engineering 38 (2011) 1130–1140 1137
heat-source geometry has a large influence in thermal-transferbehavior and it is confirmed that the coil-type modeling issuitable for the ANSYS CFX simulations. Thus, the coil-typemodeling was adopted for the heat source modeling in the CFDsimulation study.
Fig. 15 shows the temperature distribution obtained by ANSYSCFX simulations for Cases II and III. As discussed in Section 2.3.1in terms of effects of wind speed, some remarkable insights areobserved from the wind-tunnel test results for both cases. Figs. 16and 17 represent cross sections of the A–A’ marked region inFig. 15. As shown in Fig. 16, the high temperature region behindthe heat source shrinks as the wind speed increases from 1.5 to2.0 m/s. However, for Case III, the high temperature regionspreads over the back side along the wind, and turns thin andlong as the wind speed increases from 1.5 to 2.0 m/s (see Fig. 17).These CFD simulation results confirm the experimental testresults in which the temperature around the heat source tendsto decrease for Case II, and increase for Case III as the wind speedincreases.
The effects of wind direction discussed in Section 2.3.2 can alsobe accounted for by these CFD simulation results. In other words,the fact that heat transfers better when the wind blows in thetransverse direction of the cylindrical heat source as in Case II ratherthan in the longitudinal direction of the heat source as in Case III is
Fig.. 17. Temperature distribution around the heat source obtained by ANSYS CFX
speed¼2.0 m/s.
Table 6Comparison of average temperatures (K) at various monitoring points after 770 s for C
Monitoring point Wind speed¼1.5 m/s
Test (a) CFX (b) (a
A-S1 307.4 321.7 �
A-S2 388.2 371.7
A-S3 319.7 313.4
A-S4 308.7 310.1 �
Table 7Comparison of average temperatures (K) at various monitoring points after 770 second
Monitoring point Wind speed¼1.5 m/s
Test (a) CFX (b) (a
A-F1 317.5 318.0 �
A-F2 307.2 308.5 �
A-F3 300.7 300.5
A-F4 301.3 301.1
demonstrated in Figs. 15–17. The temperature distribution aroundthe heat source for Case II is higher than that for Case III as shown inFigs. 16 and 17. The indicated maximum temperature in Case III is377 K, and in Case II is 330 K. Tables 6 and 7 show the comparison ofthe CFD simulation results and test results, and verify that the sametrend is found in both the wind-tunnel test results and the CFDsimulations.
Fig. 18 shows the temperature distribution around the heatsource obtained by ANSYS CFX simulations for Case I. Thetemperature measured by the test indicates that the temperaturearound the heat source tends to decrease as wind speed increases,and the measured temperature is relatively low compared to theother cases as shown in Fig. 9 and Table 3. The cause of suchtest results is clearly illustrated in Figs. 18 and 19. In other words,the heat flow is concentrated on a side of the heat sourceby vortices generated by the geometry around the heatsource. In this regard, heat does not transfer parallel to the heatsource, and the temperature at the monitoring point cannotincrease with increasing wind speed. It is also found that thetemperature distribution in the vortex area is very sensitive tothe location due to a turbulent heat flow. For example, thetemperature between points A-R1 and A-R10 or betweenpoints A-R2 and A-R20 defined in Fig. 20 is very different eventhough the two points are very close, as can be seen in the
simulation for Case III (Section view): (a) wind speed¼1.5 m/s and (b) wind
ase II.
Wind speed¼2.0 m/s
)�(b) Test (A) CFX (B) (A)�(B)
14.3 305.4 304.3 1.1
16.5 373.0 357.5 15.5
6.3 319.1 317.7 1.4
1.4 309.6 305.2 4.4
s for Case III.
Wind speed¼2.0 m/s
)�(b) Test (A) CFX (B) (A)�(B)
0.5 327.7 326.7 1.0
1.3 309.9 312.3 �2.4
0.2 300.2 300.0 0.2
0.2 300.7 301.1 �0.4
Fig. 18. Contour map of temperature distribution obtained from the ANSYS CFX simulations after 770 s for Case I: (a) wind speed¼1.5 m/s and (b) wind speed¼2.0 m/s.
Fig. 19. Vector component of heat flow in Case I with a wind speed of 1.5 m/s.
Fig. 20. Variation in temperature at the monitoring points in a turbulent heat flow
in Case I with a wind speed of 1.5 m/s.
0 200 400 600 800Time (s)
296
298
300
302
304
306
308
310
Tem
pera
ture
(K)
CFX(A-R1)
CFX(A-R2)
Test(A-R2)
Test(A-R1)
CFX(A-R2′)
CFX(A-R1′)
Wind direction: Rear
Wind speed: 1.5m/s
Fig. 21. Comparison of the temperature versus time histories obtained from the
CFD simulations and experiment for Case I with a wind speed of 1.5 m/s.
Table 8Comparison of average temperatures at various monitoring points after 770 s in
Case I with a wind speed of 1.5 m/s.
Monitoring
point
Test (A) CFX (B) Difference
(A)�(B)
A-R1 306.4 303.1 3.1
A-R10 (306.4) 304.9 1.5
A-R2 302.0 299.0 3.0
A-R20 (302.0) 299.4 2.6
B.J. Kim et al. / Ocean Engineering 38 (2011) 1130–11401138
comparison presented in Fig. 21. Table 8 compares the averagetemperatures at various monitoring points after 770 s. It isevident that effects of geometry are significant in heat-transferbehavior and cautious attention is required to develop CFDmodels for fire simulation on FPSO topsides. Figs. 22 and 23show the average temperature distribution along the distancefrom the center of the heat source obtained by the CFDsimulations and the tests after 770 s for Cases I and II, respec-tively. It can be seen that the CFD simulations are in good
agreement with the experimental results. However, moreattention is needed to verify the sensitivity of the measuringlocation in the CFD simulations in relation to the experimentaltests.
Fig. 24 shows the velocity distribution around the heatsource for Cases III and IV with a wind speed of 2.0 m/s, and aconsiderable increase in wind speed between two cylindricalvessels can be observed. Furthermore, the heat source locatedbetween two cylindrical vessels in Case IV intensifies the airflow as shown in Fig. 24(a). This is a major cause of thetemperature distribution along the distance from the heat
Tem
pera
ture
(K
)
0 100 200 300 400 500 600 700 800294
314
334
354
374
394
A-R2 A-R3 A-R4
Test(1.5m/s)
Test(2.0m/s)
CFX(1.5m/s)
CFX(2.0m/s)
Distance from the center of heat source (mm)
Fig. 22. Comparison of the ANSYS CFX CFD simulations with the experimental
results after 770 s for Case I.
0 100 200 300 400 500 600 700
294
314
334
354
374
394
414
434
Tem
pera
ture
(K)
Test(1.5m/s)
Test(2.0m/s)
A-S2
A-S3
A-S4
CFX(1.5m/s)
CFX(2.0m/s)
Distance from the center of heat source (mm)
Fig. 23. Comparison of the ANSYS CFX CFD simulations with the experimental
results after 770 s for Case II.
Fig. 24. Velocity distribution around the heat source obtained by ANSYS CF
B.J. Kim et al. / Ocean Engineering 38 (2011) 1130–1140 1139
source for Case IV being higher than that for Case III with awind speed of 2.0 m/s, as shown in Fig. 9.
Through comparisons of CFD simulations with the testresults, it can be concluded that these CFD simulations are inreasonably good agreement with the experimental results.However, as the CFD simulations are significantly affected bythe adequacy of their modeling techniques, and the resultingCFD computations may be completely inaccurate if the mod-eling techniques are not relevant.
4. Concluding remarks
The feasibility of the CFD method to the heat-flow analysisof FPSO topsides subject to fire with wind effects has beeninvestigated in this paper. The study reported herein wasprompted by the need for the risk assessment and managementof FPSO topsides subject to fire and gas explosions. Its focus wason investigating the effects of wind direction and speed ontemperature distribution using a FPSO topside model, for whichboth wind-tunnel tests and CFD simulations were conducted.A 1/14-scale FPSO topside model based on a VLCC class FPSOunit was employed to measure the temperature distribution withtime, arising from a sheath heater. The test was carried out in awind-tunnel test facility with the test model mounted on aturntable. ANSYS CFX CFD simulations were also performedfor the numerical investigation and to develop CFD modelingtechniques.
It is found that both the turbulence caused by wind speed anddirection and the geometrical features of FSPO topsides rendercomplex heat-flow characteristics. The effects of wind speed anddirection on the temperature of the heat source are significantlyassociated with time.
Although the CFD simulations reported here are in reason-ably good agreement with the experimental results, it isrecognized that the CFD simulations are significantly depen-dent on the modeling techniques used. It is thus essential thatthese techniques be validated through comparison with experi-mental results before CFD computations are conducted. In thisregard, it is strongly recommended that experimental results beobtained for use as a reference in such validation. Dealing withreal FPSO topsides, which are very large and have complexgeometries, is challenging in terms of CFD simulation methods.The scale effect is significant in association with explosions andfires in CFD simulations, and it is thus desirable that theaforementioned experimental results be obtained using full-scale test structures rather than small-scale test models.
X simulation with a wind speed of 2.0 m/s: (a) Case III and (b) Case IV.
B.J. Kim et al. / Ocean Engineering 38 (2011) 1130–11401140
Acknowledgments
This study was undertaken at the Lloyd’s Register EducationalTrust Research Center of Excellence at Pusan National University,South Korea. The results are part of Phase II of the Joint IndustryProject on Explosion and Fire Engineering of FPSOs (EFEF JIP). Thesupport of the EFEF JIP partners is acknowledged: Pusan NationalUniversity (Korea), Nowatec AS (Norway), Hyundai Heavy Industries(Korea), Daewoo Shipbuilding and Marine Engineering (Korea), theAmerican Bureau of Shipping (USA), the Korean Register of Shipping,Samsung Heavy Industries, the Health and Safety Executive (UK),ComputIT (Norway), and GexCon (Norway). The authors are alsopleased to acknowledge the support of the National ResearchFoundation funded by the Ministry of Education, Science and Tech-nology (Grant no.: K20902001780-10E0100-12510).
References
ANSYS CFX, 2009. User’s Manual of CFX-solver, Release 11.0. ANSYS Inc., Canonsburg,PA, USA.
Cullen, L., 1990. The Public Inquiry into the Piper Alpha Disaster. HMSO, London, UK.Czujko, J., 2001. Design of Offshore Facilities to Resist Gas Explosion Hazard.
CorrOcean ASA, Norway.HSE, 1999. Review of Analysis of Explosion Response. Offshore Technology Report,
OTO 1998/174, Health and Safety Executive, London, UK.HSE, 2003. Fire and Explosion Guidance, Part 1: Avoidance and Mitigation of
Explosions. Health and Safety Executive, London, UK.Paik, J.K., 2010. Explosion and Fire Engineering of FPSOs (Phase II)—Definition of
Fire and Gas Explosion Design Loads. Research Institute of Ship and OffshoreStructural Design Innovation, Pusan National University, Korea.
Paik, J.K., Czujko, J., 2009. Explosion and Fire Engineering of FPSOs (Phase I).Research Institute of Ship and Offshore Structural Design Innovation, PusanNational University, Korea.
Paik, J.K., Thayamballi, A.K., 2007. Ship-shaped Offshore Installations: Design,Building, and Operation. Cambridge University Press, Cambridge, UK.
