Integrated Design Development
of a Low Motion
Semisubmersible Hull Form
Contents
• The Semisubmersible as a Deepwater Concept
• Hull Form Development and Optimization
• Hull Motion and Structural Verification
• Platform Features
– Hull
– Topsides
– Mooring and Riser System
• Conclusions
The Semisubmersible as a Deepwater Concept
• System components adaptable to ultra-deep water • Concept supports wide range of topside payloads • Track record of proven design and fabrication and methods • Proven offshore installation methods with minimal risk • Quayside Hook-up and Commissioning
Advantages
Limitations
• Currently, the concept is limited to applications with subsea wells
Hull Form Development
CONSTRUCTION TRANSPORTATION INSTALLATION OPERATION
-
Functional Requirements
Practical Aspects
Hull Form Optimization
Design Verification
TOPSIDES DRILLING PAYLOAD RISERS HULL
-
OPTIMIZED MOTIONS AND STEEL WEIGHT -
ANALYSIS MODEL TESTING
-
Work Flow Path
Functional Requirements
Basis Range of Application Location Gulf of Mexico Adaptable to other regions
Water Depth 1830 m > 3000 m
Topsides 100 KBOPD 150 MMSCFD Drilling 26,000 Tonnes
Can be re-configured for larger topsides (>40,000 Tonnes)
Riser System Steel Catenary Risers: 6 Production 2 Test 2 Water Injection 2 Export 18-inch Maximum Dia. 4,500 Tonnes vertical load
Flexibility to accommodate additional risers and/or larger diameter
Basic Requirements
Practical Considerations
Draft Limitation Operating Draft (Max.) = 27.5m
• Structural efficiency • Stability / tow-out draft • Deck Installation
Column Configuration Four-column and Six-Column configurations studied Six-column solution selected:
• Structural benefit from reduced deck span • Improved rectangular deck layout (safety, piping, etc.) • Increased flexibility for deck construction
Ring Pontoon Omni Directional Motion Response
Transit Draft (Min.) = 12m • Flexibility for Deck Integration • Access to yards
Hull Form Optimization
Variables • Draft • Columns (number, size,
spacing, shape, inclination)
• Pontoon (length, aspect ratio, bilge radius, shape)
• Cross bracing / ring pontoon configuration
Constraints • Target motion RAOs • Heave natural period • Motion/Acceleration at Riser
Attachment • Minimum GM • Deck area requirement • Minimum trimming ballast • Pontoon span / depth ratio • Maximum Draft • Transit draft
SOLVER
HULL WEIGHT MODEL
MOTION RESPONSE
MODEL
Cycle III-Operating
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.010
0 5 10 15 20 25 30 35 40
Period (sec)
Ang
ular
Mot
ion
(rad
/ m
)
Pitch, Hdg=0Roll, Hdg=90
Cycle III-Operating
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0 5 10 15 20 25 30 35 40
Period (sec)
Hea
ve (m
/m)
CG, Hdg=0CG, Hdg=90
Pontoon Weight Coefficients
Pontoon Aspect Ratio
Volu
met
ric W
eigh
t Coe
ff. (
t/m3)
Draft = 22.5 mDraft = 27.5 mDraft = 32.5 m
OPTIMIZED HULL
Hull Form Optimization
• Morison Element formulation for heave pitch and roll motion
• Added mass and inertia (wave) forces calculated assuming hull as an assembly of slender Morison elements
• Closed-form equations for pre-integrated forces along longitudinal, transverse and vertical slender members
• Motions are de-coupled by calculating angular motions about an estimated center of rotation
• Special treatment (added mass corrections) at connections between elements and element ends to obtain reasonable correlation with results from 3-D radiation / diffraction analysis
h_toc
H_taper * (draft_r - Hp) draft_r
Hp
Wpo
Xpon_Ytrans * Yi
Yi
Xsp + Dco
Db_Dt * Dco Db_Dt * Dci
Cant
rad_col * Dcorad_col * Dci
Xsp
Xsp/3 Xsp/3
Ysp/2
Wpi
Dco
Wpx
pon_Xtrans * XspDci
Motion Response Model
Example of Hull Idealization
Pontoon Weight Coefficients
Pontoon Aspect Ratio
Volu
met
ric W
eigh
t Coe
ff. (
t/m3)
Draft = 22.5 mDraft = 27.5 mDraft = 32.5 m
Hull Form Optimization
Pontoon Aspect Ratio
a/b = 2 a/b = 3
Volu
met
ric W
eigh
t Coe
ffici
ent
Increasing Draft
• Steel Weights defined on a volumetric basis
• Correlated to actual and preliminary designs
• Adjustments for draft / column (tank vent) height
• Adjustments for pontoon height and aspect ratio
Steel Weight Calculation:
Hull Motion And Structural Verification
• Motion Response Prediction • Comparison to Production Semi’s and MODU’s • Model Testing • Structural Verification
Hull Form - Key Features
• Six-columns • Ring Pontoon • Pontoon Shaped to Reduce
Motion and Provide Omni-directional Response
• Enlarged Center Column and Pontoon Section
• Pontoon Aspect Ratio Maximizes Added Mass Contribution
• Pontoons Consist Entirely of Flat Plate Construction
• Columns Rounded to Reduce Wave Run-up
Motion Characteristics
Heave Rao Pitch / Roll Rao
0.0000
0.0010
0.0020
0.0030
0.0040
0.0050
0.0060
0.0070
0.0080
0.0090
0.0100
0 5 10 15 20 25 30
Period (seconds)
Rol
l/Pitc
h A
mpl
itude
(rad
/ m
)
Roll (Beam Seas)Pitch (Head Seas)
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
0 5 10 15 20 25 30Period (seconds)
Hea
ve A
mpl
itude
(m/m
)
0 deg (Head) 45 deg (Quartering)
90 deg (Beam)
Motion Performance Comparison
HEAVE MOTION @ CG, Hdg=90 (Beam Seas)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
5 6 7 8 9 10 11 12 13
Tz (sec)
Sig.
Hea
ve /
Hs
(m/m
)
KBR Drilling and Production Semi
Production Semi 2
5th Generation Drilling Semi
Production Semi 1
Heave Rao Heave Response
100-YR HURRICANE
Heave RAO, Hdg = 90 (Beam Seas)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0 5 10 15 20 25 30
Period (sec)
Hea
ve (m
/m)
KBR Drilling and Production Semi
Production Sem 2
Typical 5th Generation Drilling Semi
Production Semi 1
Motion Performance Comparison
Roll Rao Pitch Rao Pitch RAO, Hdg = 0 (Head Seas)
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.010
0 5 10 15 20 25 30
Period (sec)
Pitc
h (ra
d/m
)
KBR Drilling and Production SemiTypical Production Semi5th Generation Drilling Semi
Roll RAO, Hdg = 90 (Beam Seas)
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.010
0 5 10 15 20 25 30
Period (sec)
Rol
l (ra
d/m
)
KBR Drilling and Production SemiTypical Production Semi5th Generation Drilling Semi
Motion Performance Comparison
Heave Acceleration at Riser Porch #2, Hdg=45
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
5 7 9 11 13
Tz (sec)
Sig.
Hea
ve.A
cc'n
/ H
s [
(m/s
^2)/m
]
Production Semi #1
Production Semi #2
KBR Drilling and Production Semi
Vertical Acceleration At Riser Porch Locations
Heave Acceleration at Riser Porch #1, Hdg=45
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
5 7 9 11 13
Tz (sec)
Sig.
Hea
ve.A
cc'n
/ H
s [
(m/s
^2)/m
]
Production Semi #1
Production Semi #2
KBR Drilling and Production Semi
Model Test Verification
Heave Rao Correlation
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
0 5 10 15 20 25 30
Period (sec)
Hea
ve A
mpl
itude
(m/m
)
DIFFRACTION ANALYSISModel Test (soft mooring)Model Test (full mooring)
Structural Design Process
Hull Framing and Scantling Calculations
Global Hull FE Model (Patran): •Shell & Bulkhead Plating •Pontoon & Column Web Frames •Column Deck Flat Plating & Girders •Shell and Bulkhead Stiffeners (“Lumped”) •“Dummy” Members for Risers Porches, Fairleads, etc.
Static and Mooring/Riser Loads (Patran): •Hull Dead Weight and Operational Loads, including Ballast
•Topsides Dead Weight and Operational Loads
•Mooring Line & Riser Tensions
Global Topsides Model (Patran): •Primary Transverse Trusses •Primary Longitudinal Trusses •Primary Deck Girders and Plating
Hydrodynamic Analysis (WADAM)
•Various Wave Headings & Periods •Map Wave Pressures and Inertial Loads onto Global FE Model
Determine Design Waves
•“Squeeze-Pry” Load between the Pontoons •Global Torsional Moment •Longitudinal Shear Force between Pontoons
Global Strength Analysis (SESAM) •Stillwater + Hydrodynamic Loads •Yield Checks •Buckling Checks (SESAM-Platework)
Fatigue Analysis (SESAM)
•“Screening” Level Stochastic Fatigue Analysis using a Blanket SCF and one or more S-N Curves with G.o.M Scatter Diagram •Detailed Fatigue Analysis of Critical Areas using Refined FE Models (e.g. “t” x “t”)
123,239
210,135
262,672
368,602360,927
322,958
Hull Structure
Web Frames
Transv. Bhd. Plating, Stiff & Girders
Shell Plating & Stiff.
Long. Bhd. Plating & Stiff.
Typical Pontoon Framing • Scantlings in accordance with Class Rules (confirmed by Global Strength and Fatigue Analysis).
• Shell Plate Thickness Limited to 22 mm, except 30 mm in way of cross pontoon connections.
• Plate thickness and stiffener size variations minimized (8 plates sizes and 7 stiffener sizes, excluding local reinforcement at foundations).
• Option for bulb or angle stiffeners. • Frame Spacing: 2400 - 2950 mm. • Stiffener Spacing: 640-750 mm. • 355 MPa (50 ksi) Materials.
Hull Structural Design
Global Structural Model
• Hull design has adequate strength and meets stress/buckling criteria using reasonable plating and stiffener sizes
• All areas have fatigue in excess of 200 years (based on Gulf of Mexico Criteria)
• Castings used in “corner” region to provide sufficient fatigue life Casting Detail
Moorings
Risers
Drilling Derrick
Accommodation & Utilities
Platform Configuration
TOPSIDES
Process Capacity: 100 KBOPD 150 MMSCFD Dimensions 60 x 96 x 14m Number of Decks: 2 Operating Weight: 26,000 tonnes
HULL Overall Length………...112 m Overall Breadth………..95.2 m Height (t.o. column)…..43.4 m Draft……………………..27.5 m Air Gap (to deck)..…….18.3 m
Process Facility
PF1CVOID
PF1BBALLAST
PF1ABALLAST
PF2ABALLAST
PF4BBASE OIL
PF3ABALLAST
PF5BBALLAST
PF4ADRILL
WATER
PF5ABALLAST
PF6ABALLAST
ACCESS SHAFTW.T.DOOR
SF1CVOID
SF1BBALLAST
SF1ABALLAST
SF2ABALLAST
SF4BBALLAST
SF3ABALLAST
SF4ABALLAST
SF5ABALLAST
SF6ABALLAST
ACCESS SHAFTW.T.
DOOR
CF1DVOID
PA1CVOID
PA1BBALLAST
PA1ABALLAST
PA2ABALLAST
PA4BBALLAST
PA3ABALLAST
PA5BBALLAST
PA4ABALLAST
PA5ABALLAST
PA6ABALLAST
ACCESS SHAFT
ACCESS SHAFTELEV.SHAFT
P6BBALLAST
S6BBALLAST
SF2BBALLAST
PF2BFUEL OIL
PA2BBALLAST
PUMPROOM
UTIL.SHAFT
ELEV.SHAFT
PUMPROOM
UTIL.SHAFT
ELEV.SHAFT
PUMPROOM
UTIL.SHAFT
ELEV.SHAFT
PUMPROOM
UTIL.SHAFT
SA1ABALLAST
SA2ABALLAST
SA4ABALLAST
SA3ABALLAST
SA5ABALLAST
SA6ABALLAST
SA1BBALLAST
SA2BFUEL OIL
SA4BBASE OIL
SA5BBALLAST
SA1CVOID
CA1DVOID
SF5BBALLAST
Lower Hull Plan
CROSS PONTOONS (VOID TANKS)
PUMP ROOM (TYP)
ACCESS TUNNELS
FLUID STORAGE TANKS (TYP)
Transverse Section At Corner Columns
ACCESS SHAFT
BALLAST TANK
PUMP ROOM
VOID
VOID
EQPT ROOM
CHAIN JACK
FAIRLEAD
VOID
PIPING/UTILITY CHASE
CROSS PONTOON
CHAIN LOCKERS
CHAIN PIPES
Transverse Section At Center Column
ACCESS TUNNEL
VOID VOID
BALLAST TANK
BALLAST TANK
BULK TANKS
CHEMICAL STORAGE
MUD TANKS DRILLING
FLUID STORAGE
COLUMN STORAGE CAPACITIES
Barite/Bentonite…………425 m3 (15,000 ft3)
Cement……………………340 m3 (12,000 ft3)
Liquid Mud……………….4,000 bbls
Drilling Fluid (Brine)……4,000 bbls
Chemical Storage……….4,500 bbls
Topsides Configuration Alternatives
• Integrated Deck – Stiffened Plate “Box” Deck – Floatover or Lifted Construction
• Modular Deck – Truss Structure – Lifted in 4,000 ton modules or
larger
INTEGRATED “BOX” DECK
MODULAR DECK
Modular Deck Configuration
PROCESS MODULE
UPPER DECK
LOWER DECK
MEZZANINE DECK
PROCESS MODULE
Topsides - Upper (Weather) Deck
QUARTERS
RISER RACK
PIPE RACK
PIPE RACK SUBSTRUCT.
POWER GEN.
GAS COMPRESSION
CEMENTING/ SACK STORAGE
DERRICK
FLARE
16.8 m 16.8 m 19.75 m 19.75 m 22.1 m
96 m
60 m
LAYDOWN/ UTILITIES
FLASH GAS
BOOSTER PUMPS
Topsides - Lower (Production) Deck
QUARTERS
MUD PITS
MUD PUMPS
UTILITIES
MANIFOLD
OIL PROCESS
AREA
WATER TREAMENT
UTILITIES
MCC/ SWITCHGEAR
GAS TREATMENT
Hull - Deck Interface
BOX BEAM
FE Model
Modular Deck Construction
Mooring And Riser System
EXPORT RISERS
PRODUCTION, INJECTION & TEST RISERS
MOORINGS
UMBILICALS
RISER PORCHES
Mooring System
SCR Interface - Production Lines
SCR FLEX JOINT/BASKET
CLEAR DECK AREA FOR VERTICAL ACCESS
FIXED PIPING
TO MANIFOLD
CHAIN JACK
CHAIN BASKET
MESSENGER CHAIN
TOPSIDES
SCR LAYOUT CONCEPT
INSTALLATION SET-UP
Summary
• The semisubmersible hull form provides low motion characteristics within normal draft limits and using a relatively simple hull geometry.
• Motion response verified by analysis and model testing
• Structural design and analysis to verify hull weight and construction.
• Efficient and functional deck layout.
• Flexibility to accommodate alternative deck construction methods.
• Flexibility to accommodate riser system
Integrated Design Development
of a Low Motion
Semisubmersible Hull Form
Thank You
Contacts
For further information on our designs and services please contact: Singapore Office: 39, Pandan Road, Singapore. 609281 Tel.: +65 91093201 +65 68539106 Malaysia Office: 11, Jalan 14/2, Taman Tar, Ampang, Salangor, Kuala Lumpur. 68000 Tel.: +60 342665601 Mob.: +60 123210824 +60 178810807 Irvine Engineering Pte Ltd - Registered Address: 60 Paya Lebar Road, #08-43 Paya Lebar Square, Singapore. 409051 Tel.: +65 68539106
Dubai Office: Jumeirah Lake Towers, P.O. Box: 643593, Cluster C, Goldcrest Executive Tower Office 706, Dubai. UAE. Tel.: + 971 4 447 0897 Fax: + 971 4 447 0896 Mob.: + 971 567451923 (Main Company Contact)