Introduction to Spar Buoy PlatformsIntroduction to Spar Buoy PlatformsAn Overview of Design AspectsAn Overview of Design Aspects

Presented by Dr. Presented by Dr. JokoJoko H. H. WidjajaWidjaja

atatNationalNational UniversityUniversity ofof Civil EngineeringCivil Engineering

Hanoi, Socialist Republic of VietnamHanoi, Socialist Republic of Vietnam

Presentation Presentation OutlinesOutlines

• Industrial Codes and StandardsIndustrial Codes and Standards•• Types of Spar Buoy Platforms in the WorldTypes of Spar Buoy Platforms in the World•• Prototypes of Spar Buoy Platforms (AIT Research)Prototypes of Spar Buoy Platforms (AIT Research)•• KikehKikeh Spar Buoy Platform in Asia (Arup and Spar Buoy Platform in Asia (Arup and TechnipTechnip))•• Design Philosophy and MethodologyDesign Philosophy and Methodology•• Spar Buoy Platform Spar Buoy Platform -- Structural Configuration; ModelsStructural Configuration; Models•• Weight Management and Hydrostatic StabilityWeight Management and Hydrostatic Stability•• Environmental Conditions: Criteria, Parameters and LoadsEnvironmental Conditions: Criteria, Parameters and Loads•• Design MethodsDesign Methods•• Response Motions Response Motions •• Vortex Induced Vibration (video)Vortex Induced Vibration (video)•• Summary of findingsSummary of findings

Industrial Codes and StandardsIndustrial Codes and Standards•• API RP API RP 22FPS ‘Recommended Practice for Planning, Designing and FPS ‘Recommended Practice for Planning, Designing and

Constructing of Floating Production Systems’, Constructing of Floating Production Systems’, 11st Ed., st Ed., 20012001//20112011•• API RP API RP 22SK ‘Recommended Practice for Design and Analysis of Station SK ‘Recommended Practice for Design and Analysis of Station

Keeping Systems for Floating Structures’, Keeping Systems for Floating Structures’, 22nd Ed. nd Ed. 19961996, , 20112011•• ISO ISO 1990119901--7 7 ‘Station Keeping Systems for Floating Offshore Structures and ‘Station Keeping Systems for Floating Offshore Structures and

Mobile Offshore Units’, Mobile Offshore Units’, 20052005•• NORSOK Standard NNORSOK Standard N--001 001 ‘Structural Design’, ‘Structural Design’, 20042004•• API RP API RP 22A WSD ‘Recommended Practice for Planning, Designing and A WSD ‘Recommended Practice for Planning, Designing and

Constructing of Fixed Offshore Platforms’, Errata and Supplement Constructing of Fixed Offshore Platforms’, Errata and Supplement 33, , 2121st st Ed., Ed., 20072007

•• AISC ‘Allowable Stress Design’, AISC ‘Allowable Stress Design’, 99th Ed., th Ed., 19881988•• API Bull API Bull 22V ‘Design of Flat Plate Structure’ V ‘Design of Flat Plate Structure’ 33rdrd Ed., Ed., 20042004•• API Bull API Bull 22U ‘Bulletin on Stability Design of Cylindrical Shells’ U ‘Bulletin on Stability Design of Cylindrical Shells’ 33rdrd Ed., Ed., 20042004•• API RP API RP 22T ‘T ‘‘Recommended Practice for Planning, Designing and ‘Recommended Practice for Planning, Designing and

Constructing of Tension Leg Platforms’Constructing of Tension Leg Platforms’22ndnd Ed. Ed. 19971997; ; 33rdrd Ed. Ed. 20112011

Spar Buoy PlatformsSpar Buoy Platforms

Source: Mustang, 2010

Types of Spar Buoy PlatformTypes of Spar Buoy Platform

ClassicClassic--SparSpar Truss Truss --SparSpar Cell Cell --SparSpar

AIT Research AIT Research –– Spar Buoy PlatformsSpar Buoy Platforms

Prototype Spar Buoy Platforms (Source: Prototype Spar Buoy Platforms (Source: ChanaChana S. AIT Thesis) S. AIT Thesis)

AIT Research AIT Research –– Spar Buoy PlatformsSpar Buoy Platforms

MorpethMorpeth SeastarSeastar TLPTLP(Source: (Source: AtlantiaAtlantia Offshore)Offshore)

MorpethMorpeth SeastarSeastar -- Spar PlatformSpar Platform(Source : (Source : AdisakAdisak K. AIT Thesis)K. AIT Thesis)

Malaysia Malaysia KikehKikeh Spar Buoy PlatformSpar Buoy Platform

Source: PETROMIN Source: PETROMIN 1414, April , April 20062006

Design PhilosophyDesign PhilosophyToTo avoid Resonant Motion by properly designing the platform natural avoid Resonant Motion by properly designing the platform natural period in view of environmental frequency content period in view of environmental frequency content

Dynamic response characteristics of a structure Dynamic response characteristics of a structure 1

1

TS / TW

DAF

= x

/xs

ResponseResponse controlled: controlled:

StiffnessStiffness DampingDamping MassMass

QuasiQuasi--staticstatic DynamicDynamic DynamicDynamic

Type of analysisType of analysis

Typical spectral wave of a sea state Typical spectral wave of a sea state

H

Tw (sec)

DAF

TS/TW

1

11--yr Scatter yr Scatter WavesWaves

Design storm Design storm WavesWaves

SwellsSwells

1

Fixed Fixed PltfPltf Floating Floating PltfPltf

General ConsiderationsGeneral ConsiderationsA. As per US Coast Guard or ABS: HYDROSTATIC STABILITYA. As per US Coast Guard or ABS: HYDROSTATIC STABILITY•• Intact and Damage Stability: Intact and Damage Stability: MetacentricMetacentric height > height > 11m above COGm above COG

B. AsB. As per API RP per API RP 22FPS: STRUCTURALFPS: STRUCTURAL• Project Phases: construction, Project Phases: construction, loadoutloadout, transportation, installation, , transportation, installation, drilling, indrilling, in--place and decommissioningplace and decommissioning•• System condition (Intact and Damaged Conditions): Dropped Object, System condition (Intact and Damaged Conditions): Dropped Object,

Boat Impact, etc.Boat Impact, etc.•• Environmental Events: extreme Environmental Events: extreme enviromentalenviromental. extreme load and extreme . extreme load and extreme

motion events motion events •• Structural Reserve Structural StrengthStructural Reserve Structural Strength•• Safety: Blast Overpressure and Fire Hazard, Escape Route with Muster Area, etc.Safety: Blast Overpressure and Fire Hazard, Escape Route with Muster Area, etc.•• Air Gap: minimum clearance of wave cress and BOS of Topside at Air Gap: minimum clearance of wave cress and BOS of Topside at

any roll positionany roll position•• Interface with other systems: with mooring system and risersInterface with other systems: with mooring system and risers•• Water tight compartment of hull for ballastingWater tight compartment of hull for ballasting•• Corrosion Protection: corrosion allowance and Corrosion Protection: corrosion allowance and cathodiccathodic protectionprotection•• Vortex Induced Vibration (VIV): use of helical strakeVortex Induced Vibration (VIV): use of helical strake

Design Methodology Design Methodology

Fatigue DesignFatigue Design

Transportation: Transportation: --Wet TowWet Tow-- Dry towDry tow

Installation of Hull: Installation of Hull: -- Heavy Lift VesselHeavy Lift Vessel-- SelfSelf--installed from barge or wet towinstalled from barge or wet tow

Installation of Topside:Installation of Topside:-- Heavy Lift Vessel Heavy Lift Vessel -- FloatFloat--over methodover method

In-place analysis: Time or Frequency

Domain

Vortex Induced Vibration (VIV) Assessment

Design ProcedureDesign Procedure

Environmental data

Structural Model

Topsides design

Mooring line design

ANSYS AQWA Computer Model

Selection of Wave Theory

A

Data input

Hull design

Analysis ProcedureAnalysis Procedure

Hydrostatic analysis (Free Floating)

Hydrodynamic analysis

Static/dynamic stability?

In-place analysis: Time or Frequency

Domain

Serviceability?

In-place Results

OK

No

No

• Offset displacement• RMS Acceleration

UC<1? No

A

OK

Spar Buoy Platform Spar Buoy Platform –– Structural ConfigurationStructural Configuration

Source: PETROMIN Source: PETROMIN 1414, April , April 20062006

• TopsideTopside••Hull: Hull: -- Hard Tank w/ Helical StrakesHard Tank w/ Helical Strakes

-- Mid Section (Stiffened cell or Mid Section (Stiffened cell or Truss with Heave plates)Truss with Heave plates)

-- Soft TankSoft Tank•• Mooring SystemMooring System•• Center Well (MoonCenter Well (Moon--pool)pool)

Helical Strakes

Source: PETROMIN Source: PETROMIN 1414, April , April 20062006

Prototype Spar Buoy ModelsPrototype Spar Buoy Models

Single Hull 3 - Hulls 4 - Hulls

Prototype Spar Buoy Prototype Spar Buoy Platforms Platforms –– Case StudyCase Study

200 m water depth

400 m water depth

600 m water depth

Parametric Dimension of Spar modelsParametric Dimension of Spar modelsParameters

Prototype Spar Buoy Platform ModelsSingle Hull 3- Hull 4-Hull

Topside Load (MT) 2,929 2,929 2,929

Topside Area (m2) 600 600 600

Free Board (m) 10 10 10

Cell Spar Diameter (m) 20.5 3@10 4@10

Cell Height (m) 60 60 60

Truss Structure Height (m) 60 60 60

Soft Tank Height (m) 5 5 5

Structure Weight (MT) 1,288 1,790 2.038

Sand Ballast (MT) 3,150 8,891 7,007

Water Ballast (MT) 5,773 10,606 7,297

Total Weight (MT) 13,170 24,216 19,271

Weight Management and COGWeight Management and COG

Mooring Tension

Base weight = Self-Weight + Topside

payload

Buoyancy Force

Reserve Buoyancy = Buoyancy capacity – Base weight > min % as shown below

• 15% of base weight for intact hull• 5% of base weight for damage hull

Hydrostatic Stability Hydrostatic Stability -- PhilosophyPhilosophy

Mooring Tension

Self-Weight + Topside payload

Buoyancy Force

• Location of COG and COB • Meta Centric Height (GM) from

COG ABOVE COB ( Pendulum action)

• Reserve Buoyancy (overboard)

Reserve Buoyancy Reserve Buoyancy –– zero trimzero trimItems Single Hull 3-Hulls 4-Hulls

Topside Load (MT) 2,929 2,929 2,929

Structure Weight (MT) 1,288 1,790 2.038

Ballast Sand (MT) 3,150 8,891 7,007

Vertical Force Component of Mooring Lines (MT)

8 x 25.89 = 207.13

12 x 25.89 = 310.68

8 x 25.89 = 207.13

Trial Ballast Water (MT) 16,186.86 10,295.32 16,374.86

Total weight 23,760 24,216 28,555

COG (m) from Chart Datum -54.575 -77.091 m -67.192

Buoyancy Volume (m3) 23,181.5 23,625 27,859

Displacement (MT) 23,181.5 23,625 27,859

COB (m) from Chart Datum -46.546 -60.346 -53.960

COB to COG (m) 8.029 16.745 13.232

Corrected Ballast Water (%) 69.00 % 43.80 % 58.07 %

Reserve Buoyancy (%) 12.70% 14.96% 16.92%

Hydrostatic StabilityHydrostatic Stability

( ) ( )( ) ( ) ( )1

cos / sinN

n m n n nH n Vn

IGM BM GB F y F x W GBV

θ θ θ=

= ± = + − + ± ∑

Fh

Fv

Fh

Fv

X

Y

Typical Restoring Moment of Typical Restoring Moment of Spread Mooring Line SystemSpread Mooring Line System

0.000E+00

6.106E+079.590E+07

1.253E+08 1.342E+08

2.333E+08

4.197E+08

1.388E+08

1.838E+08

2.371E+08

0.000E+00

5.000E+07

1.000E+08

1.500E+08

2.000E+08

2.500E+08

3.000E+08

3.500E+08

4.000E+08

4.500E+08

0 10 20 30 40 50 60 70 80 90

The Restoring Moment (kN-m) of 8 Spread Mooring Lines

Hydrodynamic StabilityHydrodynamic Stability

Dynamic stability criteria0.707 > Ts/Tw > 1.414

Structural heave period

Structural roll, pitch period

Free Floating Offshore Structures

Hydrodynamic StabilityHydrodynamic StabilityStation Keeping system for Floating Offshore Platforms

System heave period

System roll period

System pitch period

Strength Design of Spar Buoy PlatformsStrength Design of Spar Buoy Platforms

Prototype Spar Buoy ModelsPrototype Spar Buoy Models

Single Hull 3 - Hulls 4 - Hulls

Gravity and Environmental LoadsGravity and Environmental Loads

Wave + Current

Steady/Gust Wind

Mooring Tension

Self-Weight + Topside payload

Buoyancy Force

Environmental Design CriteriaEnvironmental Design Criteria• APIAPI RP RP 22FPS, FPS, 11stst Ed., Section Ed., Section 22..44..55: extreme : extreme 100100--year sea state year sea state

for FPS category for FPS category 1 1 for lifefor life--time > time > 5 5 yearsyears•• API RP API RP 22SK, SK, 22ndnd Ed.: extreme Ed.: extreme 100100--year sea state for permanent systemyear sea state for permanent system•• API RP API RP 22T, T, 22ndnd Ed.: extreme Ed.: extreme 100100--year sea state year sea state

Normal environmental sea state: appropriate return period storm (Normal environmental sea state: appropriate return period storm (10 10 years)years)

Sea State Design Parameters:Sea State Design Parameters:

•• Steady and Gust WindSteady and Gust Wind•• Wind driven WavesWind driven Waves•• WindWind--driven, tidal and circulation (oceanic) currentdriven, tidal and circulation (oceanic) current•• Tide and Water LevelTide and Water Level•• Joint Probability Statistics: wind, wave, swell, tide and currentJoint Probability Statistics: wind, wave, swell, tide and current

Design Wave HeightsDesign Wave HeightsDesign wave

Direction (from)N NE E SE S SW W NW

10-year return period (Tropical storm/Typhoon) – South Vietnam (100 09’ N Latitude)

Maximum wave height (m) 11.5 11.5 8.5 6.0 3.6 4.9 5.5 6.6Associated period (s) 8.2 11.6 8.6 12.9 12.8 8.7 8.1 6.9

10-year return period (Tropical cyclonic storm) – Myanmar (140 08’ N Latitude) Maximum wave height (m) 8.0 8.2 8.6 9.0 9.6 10.1 9.6 9.0Associated period (s) 8.6 8.7 8.6 9.1 9.4 9.9 9.4 9.1

10-year return period (Typhoon storm) – Thailand (100 10’ N Latitude)Maximum wave height (m) 6.16 6.46 6.07 5.39 4.68 4.22 4.22 4.61Associated period (s) 5.76 5.78 5.75 5.69 5.63 5.59 5.59 5.62

100-year return period (Tropical storm/Typhoon) – South Vietnam (100 09’ N Latitude)Maximum wave height (m) 17.7 17.7 13.1 9.3 5.5 7.6 8.5 10.2Associated period (s) 12.2 12.2 10.8 9.5 7.8 8.8 9.2 9.9

100-year return period (Tropical cyclonic storm) – Myanmar (140 08’ N Latitude) Maximum wave height (m) 13.8 14.1 14.4 15.3 15.6 15.6 15.6 14.5Associated period (s) 11.3 11.4 11.6 11.9 12.0 12.0 12.0 11.6

100-year return period (Typhoon storm) – Thailand (100 10’ N Latitude)Maximum wave height (m) 12.16 13.22 12.43 11.03 9.57 8.64 8.64 9.44

Associated period (s) 6.31 6.40 6.33 6.21 6.07 5.98 5.98 6.06

Waves and Swells at Gulf of Waves and Swells at Gulf of MotamanMotamanMyanmarMyanmar

Swell

Wind-driven Waves

Wave Scatter Diagram

Frequency (0.1 Hz)

Wav

e H

eigh

t (m

)

Location of Andaman SeaLocation of Andaman Sea

Schematic Forces on a Spar Buoy PlatformSchematic Forces on a Spar Buoy Platform

Wave Force

Current Force

Wind Force

GravityForce

Buoyancy Force

Mooring Tensions

Environmental LoadsEnvironmental LoadsMorisonMorison Equation or Diffraction TheoryEquation or Diffraction Theory

Source: DNV-RP-C205: Environmental condition and loads

Large body (Diffraction Theory)

• Hydrostatic force

• Steady drift force 1st order wave excitation

• Mean drift wave force 2nd order wave excitation

• Slow varying wave force

Slender member (Morison Equation)

• Hydrostatic force

• Morrison wave force

Hydrodynamic Force ModifiersHydrodynamic Force Modifiers

• Apparent Wave Period (AWP) • Load factor increase of 5% due to anodes• Wave kinematic factor taken 0.88 for extreme storm wave • No current blockage factor considered

Directional Current Speed ProfilesDirectional Current Speed Profiles

Current speed (m/s) Direction (from)

N NE E SE S SW W NW

10-year return period (Tropical cyclonic storm)

Surface (0% of water depth) 0.7 0.9 0.8 0.6 0.7 1.2 1.1 0.6

25% of water depth 0.5 0.7 0.6 0.4 0.5 0.9 0.9 0.4

Mid-depth 0.4 0.6 0.5 0.3 0.4 0.8 0.7 0.3

75% of water depth 0.4 0.5 0.4 0.3 0.4 0.7 0.7 0.3

1m above seabed 0.2 0.3 0.3 0.3 0.2 0.4 0.4 0.2100-year return period (Tropical cyclonic storm)

Surface (0% of water depth) 1 1.1 1 0.8 1 1.4 1.3 0.9

25% of water depth 0.6 0.8 0.7 0.5 0.6 1 1 0.5

Mid-depth 0.4 0.6 0.5 0.3 0.4 0.8 0.8 0.3

75% of water depth 0.4 0.5 0.5 0.3 0.4 0.8 0.7 0.3

1m above seabed 0.2 0.3 0.3 0.2 0.2 0.5 0.4 0.2

Directional Reference Wind SpeedsDirectional Reference Wind SpeedsDesign wind Speed(m/s) Remarks

10-year return period (Tropical cyclonic storm)

1-hour mean wind 19 Weibull Distribution

10-minute mean wind 21 Ditto

1-minute mean wind 23 Ditto

3-second gust wind 26 Ditto

100-year return period (Tropical cyclonic storm)

1-hour mean wind 32 Weibull Distribution

10-minute mean wind 35 Ditto

1-minute mean wind 40 Ditto

3-second gust wind 45 Ditto

Direction (from)

E NE N NW W SW S SE

0 45 90 135 180 225 270 315Factor 0.7 0.7 0.75 0.65 0.85 1 0.95 0.7

Equation of Motion for Floating Offshore Equation of Motion for Floating Offshore StructuresStructures

SimplifiedSimplified velocity model which ignores hydrodynamic damping term Cvelocity model which ignores hydrodynamic damping term CHH for stationary cylinder for stationary cylinder

RelativeRelative velocity model with Morison environmental velocity model with Morison environmental laodlaod shows the inclusion of entrained mass and shows the inclusion of entrained mass and hydrodynamic damping hydrodynamic damping

Random Waves Random Waves -- Steady Mean (Steady Mean (11st order) st order) & Low Frequency Waves (& Low Frequency Waves (22nd order)nd order)TheThe wave and current induced force for moored floating objects can only be determined from wave and current induced force for moored floating objects can only be determined from flow pressure field over the entire wet area of floating object.flow pressure field over the entire wet area of floating object.

From Bernoulli equation. the dynamic pressure is related to the squared velocity of flow particles. From Bernoulli equation. the dynamic pressure is related to the squared velocity of flow particles. The squared velocity can be expressed as the summation of a constant and oscillatory terms The squared velocity can be expressed as the summation of a constant and oscillatory terms which, respectively, represent steady mean wave and low frequency wave.which, respectively, represent steady mean wave and low frequency wave.

LinearLinear Diffraction WaveDiffraction WaveVelocityVelocity potential is considered as the sum of incident wave and diffracted (scattered) potential is considered as the sum of incident wave and diffracted (scattered) wave which should satisfy the Laplace equation and be subjected to boundary conditionswave which should satisfy the Laplace equation and be subjected to boundary conditions

BoundaryBoundary ConditionsConditions

Wave ForcesWave Forces

WaveWave pressure field and force on wetted area (S)pressure field and force on wetted area (S)

Where: Where: nnii is unit vector in is unit vector in ii directiondirection

Mooring Line SystemMooring Line System

Mooringtension

Mooring extension

Spread Mooring Line SystemsSpread Mooring Line Systems

Single Hull -8 3-Hull -12 4-Hull -8

NonNon--linear Material Property of Mooring Lineslinear Material Property of Mooring Lines

P(e)

(N)

synthetic fiber rope

y = 0.0032x5 - 1.1564x4 + 148.36x3 - 7176.8x2 + 242287x

y = - 1.156x4 + 148.3x3 - 7176.x2 + 24228x

0.00E+00

2.00E+06

4.00E+06

6.00E+06

8.00E+06

1.00E+07

1.20E+07

1.40E+07

1.60E+07

0.00E+00 2.00E+01 4.00E+01 6.00E+01 8.00E+01 1.00E+02 e

(Source: http:www.ead.anl.gov)

Suction PilesSuction Piles

Drag AnchorsDrag Anchors

Stiffness Matrix of Spar Buoy PlatformStiffness Matrix of Spar Buoy PlatformHydrostatic stiffness of Free Floating Structures

Aw = cut water plane areaxcg , ycg , zcg = position of Center of water plane area to Center of Gravityx , y , z = distance from the center of Aw with local axis X’. Y’ and Z’ρsw = mass density of seawaterg = gravitational acceleration

Surge - X

Sway - Y

Heave - Z

Roll - RX

Pitch- RY

Yaw- RZ

Stiffness Matrix of Spar Buoy PlatformStiffness Matrix of Spar Buoy PlatformSingle taut mooring line stiffness in global coordinate system

Translation Matrix from Mooring Tie-in point to COG

Y

X

Z

Stiffness Matrix of Spar Buoy PlatformStiffness Matrix of Spar Buoy Platform

Mooring line stiffness in Global axis (Spar Buoy Coordinate System with Origin at COG)

Global System stiffness can be determined using superposition concept as shown below.

Force Equilibrium of Spar Buoy PlatformsForce Equilibrium of Spar Buoy Platforms

Surge - X

Sway - Y

Heave - Z

Roll - RX

Pitch - RY

Yaw - RZ

FLOWCHARTFLOWCHART -- ANSYS AQWAANSYS AQWAData input AQWA solver Output

AQWA-LINE

AQWA-LIBRIUM

AQWA-FER

AQWA-NAUT

Geometry

Environmental parameter

Mooring tension and spread

Free floating static stability

Moored floating static stability

Frequency domain responses

Time history responses

Natural Period of Free Floating Spar Natural Period of Free Floating Spar Buoy ModelsBuoy Models

Single Hull

4-Hull3-Hull

RAO of Heave RAO of Heave Motion Motion –– 400400m WDm WD

Single Hull

4-Hull

3-Hull

RAO of Roll RAO of Roll Motion Motion –– 400400m WDm WD

RAO of Pitch RAO of Pitch Motion Motion –– 400400m WDm WD

3-Hull

4-Hull

Single Hull

Allowable Criteria (Operation Case)

Translation Displacement =10m

Rotation Angle = 5 Degree

Acc. = 0.07g = 0.686 m/s^2

Allowable Criteria (Storm Case)

Translation Displacement =14m

Rotation Angle = 10 Degree

Acc. = 0.15g = 1.471 m/s^2

Response Motion Response Motion –– 200200m W.D m W.D

Allowable Criteria (Operation Case)

Translation Displacement =20m

Rotation Angle = 5 Degree

Acc. = 0.07g = 0.686 m/s^2

Allowable Criteria (Storm Case)

Translation Displacement =28m

Rotation Angle = 10 Degree

Acc. = 0.15g = 1.471 m/s^2

Response Motion Response Motion –– 400400m W.D m W.D

Allowable Criteria (Operation Case)

Translation Displacement =30m

Rotation Angle = 5 Degree

Acc. = 0.07g = 0.686 m/s^2

Allowable Criteria (Storm Case)

Translation Displacement =42m

Rotation Angle = 5 Degree

Acc. = 0.15g = 1.471 m/s^2

Response Motion Response Motion –– 600600m W.D m W.D

• Pre-Tension is recommended less than 20% of MBL

Maximum Mooring Line Tensions Maximum Mooring Line Tensions T

ensi

on (M

T)

0

500

1,000

1,500

2,000

2,500

Model 1 (ton)

Model 2 (ton)

Model 3 (ton)

weight of structure 1,288 1,790 2,038

Weight of structure

WeightWeight of the Cellof the Cell--Spar Spar Buoy PlatformsBuoy Platforms

Acceptance CriteriaAcceptance CriteriaAsset (Spar Buoy Platform) phase In-place

Platform condition Intact

Environmental condition10-year sea state for operating storm case

100-year sea state for extreme storm case

Number of wave attack direction 8

Maximum mooring tension (API RP 2SK) 60% of MBL

Maximum offset5% of water depth for operating storm condition

7% of water depth for extreme storm condition

Maximum heave motion ± 4.8m

Maximum pitch/roll motion4 degrees for operating storm condition

7 degrees for extreme storm condition

RMS heave acceleration

0.315 m/s2 for 8 working hours

0.210 m/s2 for 16 working hours

0.140 m/s2 for 24 working hours

Ref.: HOE Recommendation (Bea, Gregg, Hooks, Riordan, Russell, & Williams),

Design Basis Design Basis –– Hull and Topside STRHull and Topside STR

•API RP 2A WSD, 21st Ed. Errata and Supplement 3, 2007, for tubular members

• AISC ASD 9th Ed.. 1988, for non-tubular members

• API Bull 2V, 3rd Ed., 2004, for plating design

• API Bull 2U, 3rd Ed., 2004, for shell design

Summary of FindingsSummary of Findings• Center of Buoyancy is above Center of Gravity, use trussed Spar

buoy platform type or to ballast soft tank• Reserve Buoyancy for intact condition >15% of base weight• COG shall be at close at possible to center line of platform• Structural configuration shall be symmetric as possible• Use double wall hull for upper part of hull against boat impact• Use heave plate to compensate heave motion (heave period is the

lowest period of Spar platform and close to sea state / swell period)• Mooring lines shall be light, strong, non-linear properties, non-

corrosive, durable, less maintenance, etc.; to be symmetric arrangement in use (Spread Mooring system)

• Mooring line vertical stiffness insignificantly affects heave period • Roll and pitch angles and displacement response for three hull (cell)

model are commonly larger than single- and four-hull models due to most probably by non symmetric structural configuration and spread mooring pattern

ThankThank youyou

AnyAny questionquestion??