Post on 01-Apr-2018
Design
Model Tests for the DP Systemof a Drilling Semi-Submersible
Jitendra Prasad and Hatem Elgamiel
Noble Drilling Services, Inc.
October 17-18, 2006
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Noble Corporation
Model Tests for the DP System of a Drilling Semi-Submersible
J. Prasad and H. Elgamiel
Noble Drilling Services, Inc
Sugar Land, TX.
Dynamic Positioning Conference, Houston October 17 and 18, 2006
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Presentation Outline:
Project OverviewObjectivesSemi-Submersible Parameters Theoretical BackgroundTest Set-Up and ResultsDiscussion of ResultsChallenges and Lessons Learned
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Project Overview• Outfitting an existing Drilling Semi-Submersible
with a DP-3 class system
•Semi-Submersible is currently in Shipyard
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Objectives
Model Test and Numerical Predictions were Performed to :
Ensure that DP system will perform as planned.Satisfy clients requirements.Cross check numerical model vs. physical testsComply with common industry practice
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Semi-Submersible Particulars
Pontoon length 105.00 m Pontoon width 16.00 m Pontoon height 12.25 m Pontoon spacing C-C 55.00 m Corner Column dimensions 13.6 x 14.6 m Middle Column dimensions 11.6 x 14.6 m Column spacing C-C longitudinally 33.50 m Column spacing C-C transversely 55.00 m Height to main deck 38.25 m Height to machinery deck 37.25 m Transit Displacement 38,137 tones Operating Displacement 58,000 tones
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- Thrusters Type: Rolls-Royce UUC 355 FP Diameter = 3.5 mMotor Speed = 720 rpmPower = 3750 kWThrust = 646 kN
- Control System and Software by Converteam(previously Alstom).
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- Model thrusters (8 replicas) were used torepresent prototype thrusters.
- Nautronix NMS6000 DPS control system and software was used for the model test to simulate prototype DPS.
- NMS6000 was modified to operate in model test environment at the scale factor chosen.
− λ = 1:50 to meet facility limitations and match model scale.
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• Environmental Conditions:
383.113.75.71-Yr Brazil
481.610.54.910-yr GoM WS
KnotsknotsTp (sec)Hs (m)
WindCurrent WaveEnvironment
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Theoretical Background
• Typical Thrust losses in DP system occur due to thruster-hull interactions and thruster-thruster interactions.
• Thruster-hull interactions depend on design, dimensions, hull shape, draft, etc.
• Thrust losses in a twin hull DP semi-submersible can reach up to 40-50% if the jet from one thruster is directed to the opposite hull.
• Frictional losses and Coanda effect have a large contribution on the performance of any DP system.
• These losses can be reduced if the thrust jet is directed away from the hull and other thrusters.
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Test Set-Up and Results- Calibration and Interaction Tests
Three sets of dual-axis load cells were used to measure thrustforces during thruster-hull and thruster-thruster interactiontests.
LC1
LC2
LC3
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0%
20%
40%
60%
80%
100%180
170160
150
140
130
120
110
100
90
80
70
60
50
40
3020
100-10-20
-30
-40
-50
-60
-70
-80
-90
-100
-110
-120
-130
-140
-150-160
-170 -180
% Total Thrust
T1
T3
+ Jet- Jet
0%
20%
40%
60%
80%
100% 170 160150
140130
120
110
100
90
80
70
60
50
4030
201000-10-20
-30-40
-50
-60
-70
-80
-90
-100
-110
-120
-130
-140-150
-160-170
% Total Thrust
One Thruster Operating (T1)
Two Thrusters Operating (T1 & T3)
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-Numerical Predictions:GoM 10-Yr Winter StormHs =4.9m , Tp = 10.5s
Wind = 48 knots, Current = 1.6 knots
0
500
1000
1500
2000
2500
3000
3500
4000
45000
1020
30
40
50
60
70
80
90
100
110
120
130
140
150160
170180
190200
210
220
230
240
250
260
270
280
290
300
310
320
330340
350
Total Available Thrust (Intact, kN)
Total Required Thrust (kN)
Total Available Thrust (1BB Down, kN)
Total Available Thrust (1Th Down, kN)
Wind, Wave, Current Collinear
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1000150020002500300035004000450050005500
180170 160
150140
130120
110
100
90
80
70
6050
4030
20100
-10-20-30
-40-50
-60-70
-80
-90
-100
-110
-120
-130-140
-150-160
-170-180
Available Thrust (kn)Required Thrust 1 Yr Brazil(kn)Required Thrust 10 Yr GOM (kn)
-Model Test:Tests were conducted at four headingsWind, Waves and Current are collinearAll thrusters operatingOutput from Motion Measurement device is used as position indicator
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Discussion of Results
1. Both numerical predictions and model test show available thrust is greater than required thrust.
2. Difference between numerical predictions and actual measurements can be attributed to estimation of percentage losses.
3. Model test limitations and large scale factor may also affect the test results.
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Challenges and Lessons Learned
• Interaction tests and propulsion tests are usually carried on large models (small scale factor). These scale factors are usually between 1:25 to 1:30. Model testing facility limitations may dictate the model size.
• Previous tests have shown that tilting the thrusters reduces losses and hull effects by about 15 to 20%. After the test, it was decided to use tilted thrusters to overcome any future increase in rig load or changes in environmental conditions.