DESIGN OF A FLOATING PRODUCTION STORAGE AND OFFLOADING VESSEL FOR

OFFSHORE INDONESIA

Eric Allen Dallas Dees Sean Hicks

Robert Hollibaugh Toby Martin

Terry Starling

OCEN 407 Design of Ocean Engineering Facilities Ocean Engineering Program

Texas A&M University

Final Report

15 May 2006

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TABLE OF CONTENTS

LIST OF FIGURES .......................................................................................................................5 LIST OF TABLES .........................................................................................................................7 ACKNOWLEDGEMENTS.............................................................................................................8 ABSTRACT.....................................................................................................................................9 EXECUTIVE SUMMARY ...........................................................................................................10

Content.................................................................................................................................10 Competency Areas ..............................................................................................................10 Regulatory Compliance ......................................................................................................11 General Arrangement and Overall Hull Design ..............................................................11 Weight, Buoyancy, and Stability .......................................................................................12 Global Loading/Environmental Loading..........................................................................13 Mooring and Station Keeping............................................................................................13 Hydrodynamics of Motions and Offloading .....................................................................14 Cost.......................................................................................................................................15

NOMENCLATURE.....................................................................................................................16 INTRODUCTION........................................................................................................................18

Background .........................................................................................................................18 Purpose.................................................................................................................................18 Team Organization .............................................................................................................18

Project Contract...........................................................................................................18 Student Schedules.........................................................................................................19 Gantt Chart ..................................................................................................................21

Field Trip .............................................................................................................................21 Environment ........................................................................................................................21

Geographic Location ...................................................................................................21 Wave Data....................................................................................................................22 Wind Data ....................................................................................................................23 Current Data ................................................................................................................24

Design Criteria ....................................................................................................................25 REGULATORY COMPLIANCE ..............................................................................................26

Design Considerations ........................................................................................................26 Mooring................................................................................................................................26 Stability ................................................................................................................................27 Environmental Loading .....................................................................................................27 Safety ....................................................................................................................................27

GENERAL ARRANGEMENT...................................................................................................28 WEIGHT, BUOYANCY, AND STABILITY ............................................................................30

Static Stability .....................................................................................................................30 Weight of Hull .....................................................................................................................31 Regulatory Compliance ......................................................................................................33 Fully Loaded Condition......................................................................................................34 50% Loaded Condition.......................................................................................................36

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20% Loaded Condition.......................................................................................................38 Damaged Stability ...............................................................................................................40

GLOBAL LOADING AND GENERAL STRUCTURAL STRENGTH ................................41 Topsides ...............................................................................................................................41 Lightship ..............................................................................................................................42 Tanks ....................................................................................................................................43 Still Water Buoyancy ..........................................................................................................45 Hogging/Sagging Buoyancy................................................................................................45 Visual Analysis Results.......................................................................................................47

WIND AND CURRENT LOADING..........................................................................................55 MOORING/STATION KEEPING.............................................................................................59

Mooring Weighted Objectives ...........................................................................................59 Environment .................................................................................................................60 Structure Modification .................................................................................................60 Weathervaning and Loads on Mooring Lines..............................................................60 Optimization of Storage ...............................................................................................61 Offloading, Tandem and Parallel ................................................................................61 Mooring Line Length and Risers .................................................................................61

Mooring Considerations .....................................................................................................62 Offset ............................................................................................................................62 Line Tension.................................................................................................................62 Weather Directionality.................................................................................................62 Mooring Geometry.......................................................................................................63 Hull Interference ..........................................................................................................63 Installation Cost...........................................................................................................63 Anchors ........................................................................................................................63 SESAM Software Package – Mimosa ..........................................................................64

Design ...................................................................................................................................64 8 Line Catenary System ...............................................................................................64

General Arrangement......................................................................................... 64 Line Tensions..................................................................................................... 64 Line on Bottom .................................................................................................. 65 Anchor................................................................................................................ 65

12 Line Grouped Catenary System ..............................................................................65 General Arrangement......................................................................................... 65 Line Tensions..................................................................................................... 66 Line on Bottom .................................................................................................. 66 Anchor................................................................................................................ 67

Design Comparison .............................................................................................................67 Collinear Weather: Case 1 .........................................................................................67 Non-Collinear Weather: Case 2 .................................................................................68 Non-collinear Weather: Case 3 ..................................................................................68 Cost Comparison .........................................................................................................69

HYDRODYNAMICS OF MOTIONS AND OFFLOADING ..................................................70 COST.............................................................................................................................................75 SUMMARY ..................................................................................................................................76

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REFERENCES.............................................................................................................................77 APPENDIX ...................................................................................................................................79

MIMOSA Output................................................................................................................79 Mooring Input (.mos)..........................................................................................................85 Anchor Selection Chart ......................................................................................................86 Stab-CAD Input File...........................................................................................................87

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LIST OF FIGURES

Figure 1: FPSO Location, West Natuna Sea................................................................................ 22 Figure 2: Annual % Occurrence of Significant Wave Height ..................................................... 23 Figure 3: 100 and 1 Year Return Significant Wave Height......................................................... 23 Figure 4: Annual % Occurrence of Wind Direction .................................................................... 24 Figure 5: 100 and 1 Year Return Wind Speed............................................................................. 24 Figure 6: 100 and 1 Year Return Current .................................................................................... 25 Figure 7: General Ship Layout..................................................................................................... 28 Figure 8: Belanak FPSO .............................................................................................................. 31 Figure 9: StabCAD Model ........................................................................................................... 32 Figure 10: StabCAD Model Showing Internal Tanks ................................................................. 33 Figure 11: Stability Curve............................................................................................................ 33 Figure 12: Intact Curve - Fully Loaded ....................................................................................... 34 Figure 13: Damaged Curve - Fully Loaded ................................................................................. 35 Figure 14: Cross Curves of Stability - Fully Loaded................................................................... 36 Figure 15: Intact Diagram - 50% Loaded .................................................................................... 37 Figure 16: Damaged Condition - 50% Loaded............................................................................ 37 Figure 17: Cross Curves of Stability - 50% Loaded .................................................................... 38 Figure 18: Intact Stability Curve for 20% Loaded....................................................................... 39 Figure 19: Damaged Stability Curve - 20% Loaded.................................................................... 39 Figure 20: Cross Curves of Stability - 20% Loaded .................................................................... 40 Figure 21: Damaged Stability Curve - Unstable Condition......................................................... 41 Figure 22: Topside Loads ............................................................................................................ 41 Figure 23: Lightship Loads.......................................................................................................... 42 Figure 24: 100% Load ................................................................................................................. 43 Figure 25: 50% Loaded Tanks..................................................................................................... 44 Figure 26: 20% Loaded Tanks..................................................................................................... 44 Figure 27: 100% Load - Still Water Buoyancy ........................................................................... 45 Figure 28: 50% Load - Still Water Buoyancy ............................................................................. 45 Figure 29: 20% Load – Still Water Buoyancy............................................................................. 45 Figure 30: Hog/Sag Buoyancy Forces ......................................................................................... 46 Figure 31: Still Water Bending Moment (SWBM)...................................................................... 48 Figure 32: Still Water Shear Forces............................................................................................. 48 Figure 33: Total Moment ............................................................................................................. 49 Figure 34: Total Shear Forces...................................................................................................... 49 Figure 35: Distribution Factor M................................................................................................. 50 Figure 36: Distribution Factor, F1................................................................................................ 51 Figure 37: Distribution Factor, F2................................................................................................ 51 Figure 38: Wave Induced Moment Envelope (WIBM) ............................................................... 52 Figure 39: Wave Induced Shear Force Envelope ........................................................................ 52 Figure 40: I = 1942 m4 - Hog/Sag Deflections............................................................................ 53 Figure 41: I = 1942 m4 - Still Water Deflections......................................................................... 54 Figure 42: I = 3400 m4 - Hog/Sag Deflections ............................................................................ 54 Figure 43: I = 3400 m4 - Still Water Deflections......................................................................... 55

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Figure 44: Mean Drift Force Curve for Bow Seas....................................................................... 57 Figure 45: Mean Wave Drift Force for Beam Seas ..................................................................... 57 Figure 46: Mean Wave Drift Force for Quartering Seas ............................................................. 58 Figure 47: Stevpris Mk5 Drag Embedment Anchor (Vyrhof 2000)............................................ 63 Figure 48: 3 – Dimensional Projection of 8 Line System............................................................ 64 Figure 49: Maximum Line Tensions for 8 Line System.............................................................. 65 Figure 50: 3 – Dimensional Projection of 12 Line System.......................................................... 66 Figure 51: Maximum Line Tensions for 12 Line System............................................................ 66 Figure 52: Colinear: Case 1 - Vessel Weathervaning................................................................. 67 Figure 53: Non-Collinear: Case 2 - Vessel Weathervaning........................................................ 68 Figure 54: Non-Collinear: Case 3 - Vessel Weathervaning........................................................ 69 Figure 55: Wave Spectrum .......................................................................................................... 71 Figure 56: RAO's for Heave ........................................................................................................ 72 Figure 57: Response Spectrum .................................................................................................... 72 Figure 58: RAO's for Roll............................................................................................................ 73 Figure 59: Wave Height Probability ............................................................................................ 74 Figure 60: Wind Speed Probability............................................................................................... 74

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LIST OF TABLES Table 1: Student Schedules.......................................................................................................... 19 Table 2: Gantt Chart..................................................................................................................... 21 Table 3: Design Environmental Conditions................................................................................. 25 Table 4: Vessel Dimensions......................................................................................................... 29 Table 5: Vessel Storage Capabilities ........................................................................................... 29 Table 6: Loading Conditions ....................................................................................................... 30 Table 7: Vessel Ratios ................................................................................................................. 30 Table 8: Vessel Lightship ............................................................................................................ 31 Table 9: Hull Weight Calculation ................................................................................................ 32 Table 10: Topside Loads.............................................................................................................. 42 Table 11: Lightship Loads ........................................................................................................... 43 Table 12: Tank Volumes and Weight .......................................................................................... 43 Table 13: Tank Loading............................................................................................................... 44 Table 14: Simpson Rule Analysis................................................................................................ 46 Table 15: Sag/Hog Wave Model.................................................................................................. 47 Table 16: Wind Force Height Coefficients.................................................................................. 56 Table 17: Wind Force Shape Coefficients ................................................................................... 56 Table 18: Environmental Loads Spreadsheet ............................................................................... 58 Table 19: Bow, Beam, and Quartering Sea Forces for 100 Year Storm...................................... 59 Table 20: Mooring Weighted Objectives Table........................................................................... 60 Table 21: Collinear Environmental Forces .................................................................................. 67 Table 22: Non-Collinear Case 2 - Environmental Forces............................................................ 68 Table 23: Non-Collinear Case 3 - Environmental Forces............................................................ 69 Table 24: Summary of 8 and 12 Line Systems ............................................................................ 69 Table 25: Mooring System Cost .................................................................................................. 70 Table 26: Vessel Natural Periods................................................................................................. 70 Table 27: Cost Breakdown............................................................................................................ 75

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ACKNOWLEDGEMENTS Team Indonesia would like to thank all who have been cooperating and supporting the Texas A&M University Ocean Engineering senior design course. Dr. Robert E. Randall, Texas A&M University Rod King, ConocoPhillips Nick Heather, ConocoPhillips Barbara Stone, Sea Engineering Vidar Aanesland, APL Inc., Turret Mooring Systems Tom Fulton, InterMoor, Mooring Systems Dave Walters, 2H Offshore, Riser Systems Chris Desmond and Alwyn McLeary, Lloyd’s Register Americas Inc., Classification and Integrity of Permanent Mooring Systems Aker Kvaerner, Pusnes AS, Offshore Loading Systems Yong Luo, SBM-IMODCO, FPSO Turret Moorings Tim Colton, ConocoPhillips, General Shipbuilding Chuck Steube, ConocoPhillips, FPSO Project Drivers Ian Simpson, American Bureau Shipping, Class of FPSO Hulls Det Norske Veritas (DNV), MIMOSA Software Engineering Dynamics Inc. (EDI), StabCAD Software G. Liu, Technip

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ABSTRACT ConocoPhillips has sponsored a design competition for a Floating, Production, Storage, and Offloading system. This system will operate off the Indonesian coast in the west Natuna Sea in 100 meters of water. The purposes of this FPSO design includes onsite processing of well production, providing onsite storage for stabilized product, showing high operability with consideration to a stable work platform, maintaining efficient offtake capabilities, and providing suitable exposed location survival capabilities. The key considerations in design for the FPSO consist of safe and efficient hull design, matching values for the production, storage, and offloading limits, recognizing the impact of hull deflections, and matching the mooring system to the dynamic motions, and loading conditions. The efficiency of the hull design includes finding adequate storage capacity, choosing reliable offloading systems, and accommodating topsides footprint and arrangement. The dynamic motions used with the mooring system include survival conditions, and normal plant operation conditions. The FPSO must produce during a one year storm in normal plant operation conditions, and the FPSO‘s survival condition is a one hundred year storm. The match in production is equivalent to the total fluids vs. stabilized product, 370 kbbls/day vs. 190 kbbls/day, and includes the possibility of shut ins. Storage production follows a 10 day rule where the vessel stores 10 days of production. Then offloading production is matched through the environmental conditions, and the type of offloading system. The impacts of the hull deflections contain the movement of topside modules, structures, piping, and the spacing between bulkheads. Finally, to set the mooring system, FPSO hull dynamics, offtake tanker efficiency, hull survival, and environmental directionality are considered. This mooring system is being designed to be resilient and compliant, have vessel motion within a given watch circle, provide a stable point for riser transfer, and safely moor in an extreme environment. To accomplish these goals six software suites were used, namely, Microsoft Excel, Word, Power Point, SESAM, StabCAD, and Visual Analysis. Three load vessel load states of twenty, fifty, and one hundred percent were evaluated.

SESAM software was used to calculate the mooring loads and mooring component specifications needed to keep the vessel within specified watch circles in stable and damaged states. Outputs from the mooring calculations were then used to calculate the Response Amplitude Operators (RAO) of the vessel. These frequency response spectrums were then compared to the frequencies of the environment to see if any dangerous responses of the vessel were possible. Results indicated that applied environmental frequencies were not in the range to cause resonance of the structure.

StabCAD, a vessel stability program, was used to calculate intact and damaged stability conditions for the vessel. The vessel was first input into the program by graphical means. Next, by using the drafts of the three loading conditions stability curves were calculated and used to interpret the stability condition of the vessel. Finally, tanks were simulated as damaged and stability curves were again calculated and evaluated. Final resulted for both intact and damaged conditions were satisfactory to provided guidelines.

Visual Analysis is a Structural analysis program used to model structures and the way that they react to applied loads. Using Visual Analysis, the general strengths of the vessel were evaluated. Initially, the vessel was modeled as a beam and subjected to three environmental states, namely hog, sag, and still water conditions caused by long period waves for the three vessel load conditions. Resulting deflections due to the imposed conditions were then compared to provided guidelines. Finally, the moment of the beam was adjusted to meet the hog, sag, and still water deflections required.

Offloading of finished product will be completed using a tandem method. Tandem offloading was deemed to be the safest and most efficient method due to the single point mooring of the vessel. The primary advantage of tandem offloading is the ability of the receiving vessel to weathervane with the FPSO, thus reducing the mooring loads and limiting the possibility of collisions. Also of concern is the varying size of the receiving vessels and their effects on the FPSO were a side by side offloading method to be used. Final analysis indicates that the FPSO is stable in three levels of loading, namely twenty, fifty, and one hundred percent. General strengths of the vessel were evaluated and found to be acceptable to deflection limits and frequency response to the environment. Mooring analysis results suggest that twelve and eight line single point mooring configurations are both applicable to the Indonesia location. Further analysis by cost indicates that the twelve line system is the less expensive of the two and thus the system that has been chosen.

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EXECUTIVE SUMMARY

Content The report is divided up into nine descriptive sections.

• Regulatory Compliance

• General Arrangement

• Weight, Buoyancy, and Stability

• Wind, Wave, and Current

• Global Loading

• General Structural Strength

• Environmental Conditions

• Mooring and Station Keeping

• Hydrodynamics of Mooring

• Offloading

• Cost

Additional subsections were added to each section to go into more specific explanation of each

section. Numerical results for each section can be seen in each respective section referenced.

Competency Areas

Eight areas of competency are addressed and are listed as follows:

• General Arrangement and Overall Hull Design

• Weight, Buoyancy and Stability

• Local and Global Loading

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• Wind and Current Loading

• Strength and Structural Design - General

• Mooring/Station Keeping

• Hydrodynamics of Motions and Offloading

• Cost

Regulatory Compliance The final design complies with API RP 2SK (1995), ABS (2000), MODU (2001), OCMIF

(1994), and MARPOL 73/78 (1978) rules for mooring and ship structure. General data for the

environmental loads including one, ten, and one hundred year wind, wave, and current

conditions are supplied by ConocoPhillips. From this information, the team calculates the ships

characteristics, and the response from the applied loads of the environment. Analyzing the

information with the computer programs MIMOSA, and SESAM does allow the calculation of

the loadings on the vessel and thus the required loads that the mooring would need to support

were found.

General Arrangement and Overall Hull Design General arrangements takes into consideration overall dimensions of the vessel as well as the

particular arrangement of processing equipment, tanks, accommodations, and overall hull design

which was provided by ConocoPhillips. The Floating Production Storage and Offloading

(FPSO) vessel has sixteen product tanks with a total storage volume of 263,720 m3, and a

product volume of 1.66 million barrels of oil to facilitate product storage. ConocoPhillips

requires the design to meet specific performance criteria concerning production and storage. The

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FPSO must produce 190 kbbls/day, and handle 370 kbbls/day under normal environmental

conditions. Ballasting is made possible by twelve L shaped tanks totaling 123,520 m3 of volume.

Next the overall hull design starts with the length between perpendiculars as 301 meters, breadth

is 58 meters, and the depth at keel equals 30.9 meters. The draft of the vessel varies depending

on the amount of product, and ballast that is being held. The fully loaded condition, 50% loaded

condition, and 20% loaded condition have corresponding drafts of 20.3, 16.1, and 15.1 meters.

Weight, Buoyancy, and Stability Weight distribution and stability for the vessel was calculated using Microsoft Excel. Central to

these calculations were centers of buoyancy and centers of gravity, and how these measurements

coincided with each other. For a fully loaded condition, the vessel’s VCG, VCB, TCG, TCB,

LCG, and LCB are 19.42, 10.14, 0.4, 0.0, 151.73, and 153 meters respectively. The weight of

the steel hull was to be determined by using Class Rules discussed in class (Heather 2006). First

a similar vessel in the same region was chosen to use as a scale model. This scale model

contains transverse, longitudinal, and wing tank bulkheads that allow the surface area of steel

making up the hull to be found. Next, the hull weight of the scaled vessel is divided by the

surface area of the hull to give an average weight per unit area. Then, the average weight per

unit area is multiplied by the surface area of the vessel, to get the steel hull weight. After

calculations the weight of the steel hull is 40,708 metric tons. Next, the lightship weight that

includes topside, hull, hull outfittings, hull machinery mooring system, accommodations, flare

tower, electronics, and offloading equipment equals 84,947 metric tons. The displacement under

a full load is given as 348,257 metric tons, and the displaced volume under a full load is 339,762

m3.

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Global Loading/Environmental Loading Global Loading addresses the loading of the ship structure. The first load to be considered is the

weight of the tanks, with product or other liquid inside, and is then applied to the structure

through the locations of the tanks centers of gravity. Then the lightship weights and topsides

weights are added through the same procedure. Finally the structure is subjected to a hogging,

sagging, and still water buoyancy force that act along the ships entire length. The values being

used for the extreme weather peak period, significant wave height, wind speed, and current speed

are 11.2 seconds, 5.3 meters, 24 meters per second, and 0.9 meters per second. These

environmental parameters will give a total bow and beam environmental load of 1336, and 6931

kilonewtons.

Mooring and Station Keeping A weighted objectives table is used to explain the justification of using an external turret, and

can be found in the mooring, and offloading section of the report. The software package used for

the mooring analysis is Mimosa. Mimosa uses frequency domain techniques to calculate wave

frequency, low frequency vessel motions, and mooring tensions. The weight of the entire

mooring system is 13,459 metric tons, and the diameters of the 12 mooring lines are 84

millimeters.

Strength and Structural Design-General A general arrangement of the vessel was supplied by ConocoPhillips, and the vessel is evaluated

for its structural strength using Visual Analysis structural evaluation software. Initial results were

then analyzed and revised to match regulatory requirements. Using ABS classification guidelines

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for the fundamentals of global loading, the still water and dynamic bending forces, shear forces,

and moment of inertia are found, and then compared to the requirements given by ABS codes.

The parameters calculated for the fully loaded condition, in a 100 year storm, include the still

water bending moment, 3x107 kN-m, and the maximum deflection in the hog or sag condition.

In this case the deflections are 48 centimeters for the sagging wave, and 33 centimeters for the

hogging wave. In order to get the deflections within the limits set, the moment of inertia had to

be equal to 3400 m4 instead of the minimum moment of inertia given by ABS equaling 1950 m4.

Hydrodynamics of Motions and Offloading Hydrodynamics of a vessel determines how it reacts to applied forces, and in this case, whether

they are from the environment or an offloading vessel. For the hydrodynamic characteristics of

the vessel, SESAM software suite is being used. Wave data is modeled as a JONSWAP spectrum

from environmental data provided by ConocoPhillips. The resulting spectrum is inputted into

SESAM, which calculates the response amplitude operators, or RAO’s, for the vessel. These

RAO's were then compared to the natural frequencies of the vessel for resonance analysis. For

this vessel the roll, pitch, and heave natural periods are 13.2, 12.6, and 12.7 seconds. The

calculated RAO of the vessel is 0.6 rad/sec, which is well out of the range of the vessel’s natural

frequencies. Offloading of the vessel is possible by two methods, side by side and tandem. The

preferred type is tandem due to the weathervaning advantages. Then for tandem offtake, there

are limits that have to be met in order to offload. The vessel can offload product when the

significant wave height is 2 meters, and there is a 10 knot wind. However, the vessel must

disconnect when the significant wave height is 2.5 meters combined with a 20 knot wind. One

criterion states that the FPSO must operate through a one year storm 95% of the time. According

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to the environmental data, the significant wave height in a one year event is 0.75 meters, and the

wind speed equals 16.52 knots. Therefore the design allows offloading productivity to increase.

Cost The cost of a project is a primary factor in the actual implementation of a concept. In this case,

ConocoPhillips provided a factored cost spreadsheet. Cost factors included hull steel, hull

outfitting, electrical, offloading system, mooring, initial startup marine costs, risers, topsides,

transportation, installation, and towing to site. Due to its competitive cost and its location, China

was chosen as the contractor of choice. Total cost of the vessel is $957 million for a vessel fully

assembled in China, shipped to location, moored with a twelve line system, and set up for

operation.

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NOMENCLATURE L Longitudinal Length of Vessel

Lbp Length between Perpendiculars

B Breadth of Vessel

D Depth of Vessel

T Draft of Vessel

kbbls Kilo-barrels

LCB Longitudinal Center of Buoyancy

LCG Longitudinal Center of Gravity

VCB Vertical Center of Buoyancy

VCG Vertical Center of Gravity

TCB Transverse Center of Buoyancy

TCG Transverse Center of Gravity

SA Total Structure Surface Area of Vessel

ABS American Bureau of Shipping

API American Petroleum Institute

MODU Mobile Offshore Drilling Unit

KG Center of Gravity

SC Simpson’s Coefficient

FB Force of Buoyancy

Mt Total Bending Moment

Msw Still Water Bending Moment

Mwave Wave Induced Bending Moment

Vt Total Shear Force

Vsw Still Water Shear Force

Vwave Wave Induced Shear Force

Cb Block Coefficient

∆ Molded Displacement

Mws Sagging Moment

Mwh Hogging Moment

Fwp Positive Shear

Fwn Negative Shear

I Moment of Inertia

SM Section Modulus

fp Allowable Shear Stress

Vhr One Hour Average Wind Velocity

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α Time Factor

Vt Wind Velocity for the Average Time Interval, t

Ch Height Coefficient

Cs Shape Coefficient

Fw Wind Force

A Surface Area

Fφ Oblique Force

Fx Bow Force

Fy Beam Force

Vc Current Velocity

Fc Current Force

Cc Current Force Coefficient

HS Significant Wave Height

VS Maximum Surface Current

VW Maximum Wind Velocity

Ts Maximum Spectral Period

S.F. Safety Factor

S(ω) JONSWAP Energy Spectrum

RAO Response Amplitude Operator

E Modulus of Elasticity

f Frequency

fp Peak Frequency

σ sigma

A Amplitude

ω Angular Frequency

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INTRODUCTION

Background Through the late 1950’s, offshore oil and gas production was associated with fixed platforms in water depths of 150 feet or less. Going offshore, well production was limited, with post single stage separation liquid production being sent to shore based treatment and storage facilities through short shallow water submarine pipelines. Ocean going tankers, generally ranging from 10,000 to 60,000 dwt in size provided the market an economical method of transporting the stabilized crude and products. These vessels were loaded, and offloaded at fixed shoreside tanker berthing facilities. Recently in the offshore oil industry, there has been an increasing demand for oil recovery in increasingly undeveloped areas of the world. A relatively recent answer to this demand has been the Floating Production Storage Offloading System. Advantages of the FPSO include resilience to a range of environments, mobility, lifespan, and lack of outside dependence. Areas that FPSO’s have been established in include the North Sea, off the coast of Africa, and in the Indian Ocean. These environments range from calm to the most severe sea conditions know. As with any oil production system, an FPSO has to be relatively stationary in the area of its wells for it to be productive; this requires a mooring system that effectively keeps the vessel in a required area, which is the emphasis of the design.

Purpose The purpose of this project is to analyze data supplied by ConocoPhillips and come to a practical design conclusion. Material that will be taken into consideration for the design is the General arrangement of the hull and process modules, global loading of the structure, wind and current loading, mooring and station keeping, hydrodynamics of motions and offloading, cost, weight, buoyancy, overall stability, and regulatory compliance. The final design and report was presented to a panel of judges for critique and actual workability of the design.

Team Organization Team Indonesia has a class and work schedule for each team member is seen below. All meetings outside of class were based upon this schedule. Project Contract Meetings

• Members will attend all stated meetings on time, absences will be addressed prior to meetings • Conversation will be limited to the project material • Meetings will begin with a recap and update on the previous meetings assignments and decisions • Responsibility for the meeting notes will be rotated among members every week • Meeting notes will be typed out following the meeting • Major decisions will not be made unless at least three members are present • Meetings will be limited to half an hour at a time • Discordant issues will be resolved before a meeting is dismissed

Team • Team members will respect the opinions of teammates • Project work load will be distributed evenly • Leadership will be shared throughout team • Team members will be alerted to trouble a member might have with an assignment • Assignments will be finished by agreed deadlines, any possible late assignments and other team members

will be notified well in advance • Critique of work will be constructive • Communication between members is a priority

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Student Schedules Table 1: Student Schedules

x - indicates in classwork - indicaties at work

Monday Bobby Dallas Eric Sean Terry Toby Tuesday Bobby Dallas Eric Sean Terry Toby8:00 AM 8:00 AM X X X9:00 AM X X X X X X 9:00 AM X X X

10:00 AM 10:00 AM X X X11:00 AM X 11:00 AM X X X12:00 PM Work X 12:00 PM X X X X1:00 PM X X Work Work 1:00 PM X Work2:00 PM X X Work Work 2:00 PM X X Work3:00 PM X Work Work 3:00 PM X X Work4:00 PM X X X X 4:00 PM X X5:00 PM X X X X 5:00 PM X Work X6:00 PM 6:00 PM Work7:00 PM 7:00 PM Work8:00 PM 8:00 PM Work9:00 PM 9:00 PM Work

10:00 PM 10:00 PM11:00 PM 11:00 PM12:00 AM 12:00 AM

Wednesday Bobby Dallas Eric Sean Terry Toby Thursday Bobby Dallas Eric Sean Terry Toby8:00 AM 8:00 AM X X X9:00 AM X X X X X X 9:00 AM X X

10:00 AM X X X X X X 10:00 AM X X11:00 AM X X X X X X 11:00 AM X X12:00 PM Work X 12:00 PM X X X X1:00 PM X X Work Work 1:00 PM X X X X2:00 PM X X Work Work 2:00 PM X X X X3:00 PM X Work Work 3:00 PM X X X X4:00 PM X X X X 4:00 PM X5:00 PM X X X X 5:00 PM Work X6:00 PM 6:00 PM Work7:00 PM Work 7:00 PM Work Work8:00 PM Work 8:00 PM Work Work9:00 PM Work 9:00 PM Work Work

10:00 PM Work 10:00 PM Work11:00 PM Work 11:00 PM Work12:00 AM Work 12:00 AM Work

Team Indonesia Student Schedules

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Friday Bobby Dallas Eric Sean Terry Toby Saturday Bobby Dallas Eric Sean Terry Toby8:00 AM 8:00 AM9:00 AM X X X X X X 9:00 AM

10:00 AM X X X X X X 10:00 AM11:00 AM X X X X X X 11:00 AM12:00 PM Work X 12:00 PM1:00 PM X Work X 1:00 PM2:00 PM X Work 2:00 PM3:00 PM X Work 3:00 PM4:00 PM 4:00 PM5:00 PM Work 5:00 PM Work6:00 PM Work 6:00 PM Work7:00 PM Work Work 7:00 PM Work Work8:00 PM Work Work 8:00 PM Work Work9:00 PM Work Work 9:00 PM Work Work

10:00 PM Work 10:00 PM Work11:00 PM Work 11:00 PM Work12:00 AM Work 12:00 AM Work

Sunday Bobby Dallas Eric Sean Terry Toby8:00 AM9:00 AM

10:00 AM11:00 AM12:00 PM1:00 PM2:00 PM3:00 PM4:00 PM5:00 PM Work6:00 PM Work7:00 PM Work8:00 PM Work9:00 PM Work

10:00 PM11:00 PM12:00 AM

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Gantt Chart Table 2: Gantt Chart

Eric AllenDallas DeesSean Hicks

Robert HollibaughToby Martin

Terry StarlingGroup

3rd 4th 1st 2nd 3rd 4th 1st 2nd 3rd 4th 1st 2nd 3rd 4th 1st 2ndIdentify Design TopicsConduct ResearchDesign Drawing (Solid Works)Examine Codes and RegulationsEnvironmental ConditionsProgress Report #1 DueWeight, BuoyancyBallast and Tank ArrangementEnvironmental LoadsProgress Report #2 DueMooring Analysis (MIMOSA)Stability Analysis (StabCAD)Analyze RAO'sBending Moments & Shear (Visual Analysis)Progress Report #3 DueMidterm Report DueRevised Midterm Report DueSNAME/MTS PresentationCost AnalysisNatural PeriodsVessel Damage StabilityDeflections and Hull StrengthHydrodynamics of OffloadingVessel SafetyDraft ReportRevised Draft ReportFinal PresentationFinal Report

January February March April May

Field Trip The field trip to ConocoPhillips headquarters in Houston, Texas was the starting point to the whole design project. The trip was lead by Rod King who is working with ConocoPhillips as a consultant. As a whole, many different aspects in designing an FPSO were brought to the team’s attention. The individual companies that attended, and their specialization in the industry include APL Inc., Turret Mooring Systems; InterMoor, Mooring Systems; 2H Offshore, Riser Systems; Lloyd’s Register Americas Inc., Classification and Integrity of Permanent Mooring Systems; Pusnes AS, Offshore Loading Systems; SBM-IMODCO, FPSO Turret Moorings; ConocoPhillips, General Shipbuilding; ConocoPhillips, FPSO Project Drivers; and the American Bureau Shipping, Class of FPSO Hulls.

Environment Geographic Location The environmental data for this design project was provided by ConocoPhillips. The data was taken from the Indonesian waters of the West Natuna Sea located within the South China Sea, in 100 meters of water. The exact

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location of the datum can be viewed below, coordinates: 4o 14’ 00” North Latitude and 106o 16’ 00” East Longitude.

Figure 1: FPSO Location, West Natuna Sea www.ict-silat.com/ Indonesia_map1.JPG Wave Data The wave conditions appear to display a high probability of occurrence in the North East direction, though a significant probability lies in the opposite direction. In the North East and South South West directions, probabilities of occurrence are 30% and 13%, respectively. The probability of wave headings in between the North East and South South West directions are considerably lower (1% at lowest). A rosette illustrating these findings is displayed below, in Figure 2.

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Figure 2: Annual % Occurrence of Significant Wave Height

Like Figure 2 above, Figure 3 below shows predominant wave action to the North East. The highest magnitude of significant wave heights occurs to the North East with 100 and 1 year return conditions of 5.3 m and 2.9 m, respectively. Directions orthogonal and opposite of the North East encounter waves in the 2 m and 1 m range for 100 and 1 year return periods. Relatively benign wave conditions should be expected at this location.

Figure 3: 100 and 1 Year Return Significant Wave Height Wind Data Similar to the waves, this location experiences a high probability of wind occurring to the North East and the South South West, ranging from 18% to 16%. Directions orthogonal to the NE and SSW only experience wind 1% to 3% of the year. Below in Figure 4, an illustration of these findings is displayed.

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Figure 4: Annual % Occurrence of Wind Direction Although the probability of occurrence is low in the North West and South East Directions, there are considerable wind velocities affecting these directions. The highest wind speeds occur in the North North East with magnitudes of 24 m/s and 16.8 m/s for 100 and 1 year return conditions.

Figure 5: 100 and 1 Year Return Wind Speed Current Data Unfortunately, there is no data available explaining the directionality of current conditions. However, there is enough evidence from the wind and wave data to believe the current will follow the same directional trends. The largest current velocities occur in the North East and South West directions with magnitudes of 0.9 m/s and 0.8 m/s

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for 100 and 1year return conditions. Also, the North North West and South South East directions can expect current velocities of 0.7 m/s and 0.6 m/s and 0.6 m/s and 0.5 m/s during 100 and 1year return conditions, respectively.

Figure 6: 100 and 1 Year Return Current A summary of the 100 and 1 year return conditions can be seen below, in Table 3. Table 3: Design Environmental Conditions Return Wind Current Hs PeriodPeriod (m/s) (m/s) (m) (sec)

1 16.8 0.8 2.9 9.1100 24 0.9 5.3 11.1

Design Criteria ConocoPhillips tasked Team Indonesia to design a FPSO to operate off the Indonesian coast and submit the design as a final report. The design Team Indonesia submits will follow performance criteria established by ConocoPhillips. The environment where the FPSO operates causes various loads on the vessel and mooring, and universal codes control the response. Team Indonesia’s design will follow the ABS codes for vessel displacements due to environmental loads and API 2SK codes for mooring response. Additionally, cost, safety, and constructability factor in the final design and should be addressed in the final report. All decisions made during the design must be explained and validated in the submitted report. ConocoPhillips requires the design to meet specific performance criteria concerning production and storage. The FPSO must produce 370 kbbls per day under normal environmental conditions, and, for storage, ConocoPhillips follows a “10 day rule” where the vessel stores 10 days worth of supply. The design will consider several configurations depending on the environmental loads on the vessel; for example, small storage tanks increase the vessel’s flexibility under environmental loads. The environment affects all facets of design; the FPSO design must follow environmental code requirements and ConocoPhillips requirements. The FPSO must produce during environmental conditions up to a 1 year storm, at which point ConocoPhillips shuts in the vessel, and the FPSO must survive a 100 year storm. During storms the vessel will experience bending and twisting; ABS codes limit how much the vessel can displace. Designs may consider different approaches to mitigate loads and deflections. Weathervaning, for example, allows the vessel to orient itself in the direction of the least amount of load, and both the hull size and strength limit deflections. Finally, the turret’s location, whether internal or external, depends on environmental loads.

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REGULATORY COMPLIANCE There are several sources/publications of regulations that outline the design aspects of FPSO vessels. These sources include the American Bureau of Ships (ABS), the American Petroleum Institute (API), the Oil Companies Marine International Forum (OCMIF), and the Protocol of 1978 relating to the International Convention for the Prevention of Pollution (MARPOL 73/78).

Design Considerations For the design of the FPSO there are several design criteria that must be met. They are as follows:

• Production o Rate (Total Fluids vs. Stabilized Product = 370 kbbls/day vs. 190 kbbls/day) o Impact of Shut-ins

• Storage o 10 Day Rule o More Tanks vs. Larger Tanks

• Offloading o Weather o Shuttle/Offtake Tankers

• Hull Deflections o Hog (+0.5 m) o Sag (-0.5 m) o Rack (+/- 5°)

The FPSO must also be able to maintain production in 1 year storm condition and be able to survive 100 year storm conditions on location. To design this vessel satisfactorily there are regulations that must be met in each design area.

Mooring In the area of designing the mooring system, the team has to meet the design criteria outlined by recommended practice, API RP 2SK. These guidelines state that the minimum Factors of Safety for intact and damaged conditions for the mooring lines are as follows:

• Factor of Safety = MBL/Max Line Tension o Intact conditions = 1.67 o Damage conditions (1-line broken) = 1.25

The guidelines also define the maximum watch circle offset for both intact and damaged conditions in order to maintain riser integrity. The maximum watch circle offset is as follows:

• Watch Circle offset o Max. Intact Offset < 8% of W.D. o Max. Damaged (1-line broken) Offset < 12% of W.D.

Maximum Offset = Mean + Dynamic Therefore, for our location with 100 meter water depth, the maximum intact offset is 8 meters and the maximum damaged offset is 12 meters.

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Stability In the area of vessel stability the team must meet criteria from MARPOL 73/78 regulations and ABS Class Rules for Ships and Mobile Offshore Drilling Unit (MODU) regulations. The MARPOL 73/78 regulations state set the following limits:

• MARPOL 73/78 – requirements for tank vessels (damage) o Limit 1: Right Arm at Max RA (A) > 0.1m o Limit 2: Angle from Equilibrium (D) to RAzero (B) or DF (C) > 20 deg o Limit 3: Absolute Angle at Equilibrium (D) < 25 deg o Limit 4: Area from Equilibrium (D) to RAzero (B) or DF (C) > 0.0175 M-Rad

The ABS MODU regulations state the following requirements:

• ABS/IMO MODU 1989– requirements for drill ships (intact / damage) o Intact Condition: Wind = 100 knots o Sufficient residual dynamic stability (measured from righting and heeling curves) o Damage Condition: Wind = 50 knots o Final waterline should not submerge any non-watertight openings o 2nd Intercept must be 7 degrees past 1st intercept o Within extent of weather tight integrity, righting moment reaches a value 2x healing moment (both

measured at the same angle).

Environmental Loading In the area of designing to handle the environmental loading on location, the team must meet regulations outlined by API 2SK (1995), OCMIF (1994), and ABS (2000). These sources outline various equations and coefficients to use in the calculation of wind, wave, and current forces induced by environmental conditions.

Safety For floating installations, ABS (2000) gives general guidelines regarding fire protection and personnel safety. Plans for seven fire protection systems need to be submitted with the design. These plans include a firewater system, deluge systems (water spray for process equipment), foam systems (for crude storage tanks), fixed fire fighting systems, paint lockers and flammable material storerooms, fire control and life saving equipment plan, and a fire and gas detection and alarm system. Spill containment for open and closed drain systems are to be provided in areas subject to hydrocarbon liquid or chemical spills. Containment utilizes curbing or drip edges at deck level, recessed drip pans, and containment of floor gutters, firewalls or protective walls. Open drain piping subjected to rainwater or other liquid accumulation should be self draining, cleanout or flushing connections are to be provided, and all open drains should lead to one final disposal location. The sealing of open drains should be permitted except when flammable liquids could be present in the system, of which a seal is to be provided to prevent vapor release. When an open drain system is subjected to an applied pressure, a liquid seal is to be provided on each drain header. Finally, when pumping systems are used to remove liquids from hazardous areas or from drain tanks mentioned above, branch suctions from safe and hazardous areas are to be arranged so that such areas cannot be pumped simultaneously. For closed drain systems, the drain vessel is to be provided with pressure relief valves which are sized to handle the maximum flow of gas or liquid that could occur under a blocked outlet condition. These drains from vessels containing non toxic, non flammable liquids, can be connected to a open drain piping system is sized to accommodate these additional drains. ABS also gives general lifesaving requirements using lifesaving appliances and equipment. First lifeboats of an approved type are to be provided, with a total capacity to accommodate twice the total number of people on board

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the subject unit. They are required to be installed on at least two sides of the installation, in safe areas in which there will be accommodation for 100%, in case one of the stations becomes inoperable. Next, inflatable life rafts of an approved type are to be provided onboard such that their total capacity is sufficient to accommodate the total number of people expected onboard the facility. Life rafts are to be placed in or next to areas where personnel might be working, in sufficient quantity to hold the maximum number of people that might be present in the working are at any one time. Also at least four life buoys of an approved type, with floating water lights, are to be provided. One ring life buoy is to be placed in a suitable rack on each side of the structure in an acceptable location. Multi-level structures may require the placement of additional life buoys. At least one life jacket of an approved type is to be provided for each person on a manned facility. Life preservers/ work vests are to be stored in readily accessible locations. In addition, life jackets numbering the same quantity as the maximum aggregate capacity of each life boat station must be stored next to the life boat station. When personnel baskets are used to transfer personnel from the facility to work boats, or vice versa, a work vest is to be provided and kept with the personnel basket for each person riding in the basket.

GENERAL ARRANGEMENT The general arrangement and specifics of our vessel was supplied by ConocoPhillips, the layout of which can be seen in Figure 7. Not included in the layout is the specific mooring design to be used.

Figure 7: General Ship Layout The overall design of the vessel reflects the refining and storage purpose of the vessel. The box shaped hull and minimum amount of machinery space facilitates the large amount of storage required after processing; optimization of the large expanse deck space facilitates the room needed for the topside processing modules. General dimensions

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for the hull can be seen in Table 4. Note that there is 1.5 meters of clearance between the hull and mooring lines in still water conditions. Table 4: Vessel Dimensions

Vessel Dimensions DimensionLOA (Length Overall)--meters 308.0LBP (Length Between Perpendiculars)--meters 301.0Breadth, molded--meters 58.0Depth at Centerline--meters 30.4Depth at Side--meters 29.4Camber--meters 1.0Double Bottom Depth--meters 3.0Ballast Wing Tank Width--meters 3.5Bilge Radius--meters 2.3

In addition to the vessel dimensions, we were given the number of tanks specified for use and the subsequent volume of the tanks. Table 5 details the tank types and values of the tank specifics. As can be seen, the majority of the tank space, approx. 1.6 million bbl, is used for final storage of the stabilized product. Table 5: Vessel Storage Capabilities

Vessel Storage CapacitiesStabilized Product Total for 16 tanks--cu mtrs 263,720Off-Spec Product Total for 2 tanks--cu mtrs 32,160Slops Total for 2 tanks--cu mtrs 9,330Produced Water Total for 2 tanks--cu mtrs 8,640Diesel Fuel (2 tanks@2100 + 2 tanks@450)--cu mtrs 5,100Crude Fuel Oil Total for 2 tanks--cu mtrs 5,180Process Fresh Water Total for 2 tanks--cu mtrs 2,650Potable Water Total for 2 tanks--cu mtrs 250Bulk Lube Oil Total for 2 tanks--cu mtrs 40Bulk Hydraulic Oil Total for 2 tanks 20Ballast Tank Total for 12L shaped tanks--cu mtrs 123,530Totals 450620

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WEIGHT, BUOYANCY, AND STABILITY

Static Stability Our vessel is statically stable in three states of evaluation, namely at full capacity, fifty percent capacity, and twenty percent capacity. Table 6: Loading Conditions

Table 7 details the initial locations of centers of gravity, centers of buoyancy, draft, metacentric height, draft, and weight factors. At our initial state, no ballast added to any of the three loading states, the vessel was stable in all three states except the ten percent loading. Although initially stable, an offset of five degrees to either port or starboard will upset the vessel, thus the full amount of ballast is used for the initial stability analysis. In addition to the vessel stability characteristics we have included the body ratios in table 7. Table 7: Vessel Ratios

- L/B B/D L/DActual 5.19 1.97 10.24Ideal 4.5 - 6.0 1.7 - 2.3 8.0 - 13.0

As can be seen, the body ratios of the vessel are within the ideal range of values. Next we look at the lightweight of the vessel. The lightweight of the vessel includes the topsides, hull weight, and accommodations weight, tandem offloading system, hull machinery weight, turret weight, electric and electronic weight, and miscellaneous weight. Table 8 details the weights of the vessel lightweight.

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Table 8: Vessel Lightship Vessel Lightship weight (mt) LCG (m) Long Moment (m4) VCG (m) Vert Moment (m4)

Hull Steel 40,708 159.86 6,507,581 16.79 683,487Hull Outfitting 3,380 158.23 534,817 33.13 111,979Accommodations Weight 800 277.47 221,976 38.33 30,664Tandem Offload Sys 120 5.00 600 34.40 4,128Hull Machinery weight 780 203.53 158,753 16.38 12,776Electric and Electronic Weight 610 154.88 94,477 32.77 19,990Misc 162 165.80 26,860 30.40 4,925mooring 13,459 301.00 4,051,159 30.40 409,154Topsides (Wet) 24,928 172.81 4,307,808 44.48 1,108,797FPSO Lightship 84,947 15,904,030 2,385,900

Weight of Hull The estimation of the steel weight is scaled from an existing ship in a similar region. The scaled vessel used, “Belanak” (shown below), is a similar size FPSO also located in the South Natuna Sea.

Figure 8: Belanak FPSO

http://www.jraymcdermott.com/projects/Belanak-FPSO__90.asp From class rules, the steel weight of the hull can be estimated by adding the hull weight of the scale vessel with the topside weight for the scaled version, then divide that by the surface area of the hull to give a weight per unit area. Then by multiplying this average weight per unit area of by the existing vessel’s surface area, and then subtracting the model ship’s topside weights, the existing vessel’s hull weight can be found (Heather, 2006). Websites give the characteristics of the hull, number of bulkheads, weight of the topsides, and hull weight for the Belanak (Muellar, 2006; ConocoPhillips, 2006; McDermott, 2006). Then using the process described above, the hull weight was found, as shown below, in Table 9.

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Table 9: Hull Weight Calculation Use CurrentlyExisting Vessel In Region Team IndonesiaBelanak

Double Side Hull Configuration Double Side Hull ConfigurationL = 285 m L = 308.0 mB = 58 m B = 58.0 mD = 26 m D = 30.9 mBulkheads Bulkheadstransverse 2 transverse 9.0outer 2 outer 2.0longitudional 2 longitudional 2.0

SA = 65716 m2 SA = 76299.7 m2

Wtopsides = 31000 mt Wtopsides = 24928 mtHull Weight = 28085 st = 25531.82 mtAVG Weight = 0.8602 mt/m2 Hull Weight = 40708.39 mt

StabCAD analysis was performed on the FPSO design using a draft of 19.66 meters for the fully loaded condition. The fully loaded displacement is 337,846 metric tons. Analysis was done on intact and damaged models. Damaged analysis was done with two adjacent ballast tanks compromised. Figure 9 is the complete StabCAD model including the internal tanks that can not be seen. Figure 10 is the StabCAD model with out the external barge showing the internal tanks and the top side equipment.

Figure 9: StabCAD Model

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Figure 10: StabCAD Model Showing Internal Tanks

Regulatory Compliance Regulatory compliance is required for the FPSO. ABS MODU (2000) regulations were used for intact and damaged stability. ABS MODU requires that the intact wind velocity be 100 knots and the damaged wind velocity be 50 knots. The second intercept of the righting arm must be at least 7 degrees past the second intercept for damaged conditions. Additional calculations needed to satisfy ABS MODU were needed for further stability analysis. The area under the righting arm above the heeling arm to the left of the downflooding angle is called area A. The area under the heeling arm and between the righting arm and the downflooding angle is area B and the small area between the zero angle of inclination and the righting arm and the heeling arm is area C. Each respective area can be seen in figure 11. ABS MODU stability rules require that the sum of area A and B must be greater than the sum of area B and C multiplied by 1.4. Additionally, area A multiplied by 1.4 needs to be greater than area B.

Figure 11: Stability Curve

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StabCAD uses ABS MODU as a guide in its stability calculations; other regulations can be considered using StabCAD’s results. Load Line and MARPOL regulations are both used for damaged stability and are similar in that they both require the righting arm at the maximum righting angle be greater than .1 meter and the angle between the two intercepts of the righting arm and the heeling arm to be at least 20 degrees. Differences in the three regulatory guidelines is that Load Line is more stringent by requiring the absolute angle of equilibrium to be less than 15 degrees, where MARPOL only requires it to be less than 25 degrees. Load Line also requires that the distance between the vessel’s center of gravity and metacenter be greater than zero. MARPOL, however, uses a different approach by requiring the area from equilibrium to the downflooding angle be greater than 0.0175 meter-radians.

Fully Loaded Condition Figure 12 shows the intact curve which gives the righting arm, heeling arm, and downflooding angle for a vessel with fully loaded product tanks. Area A, as described above, is 3.036. Area B is .695 and area C is .022. Area A plus area B is 3.722 and area B plus area C multiplied by 1.4 is .9534 and is less than 3.722, which is in compliance with ABS MODU rules. Area A multiplied by 1.4 is 4.288 and is greater than area B which also complies with ABS MODU rules. The downflooding angle is 20.3 degrees which is less than the maximum allowed 25 degrees.

Figure 12: Intact Curve - Fully Loaded Figure 13 below has the same information as the intact curve above only for a situation where two adjoining ballast tanks have been damaged. In a damaged condition the downflooding angle must be greater than the first intercept between the righting arm and the heeling arm, other wise the ship will sink. The distance from keel to center of gravity, KG, in a damaged condition must be less than the maximum allowed KG. In this situation the KG is 19.05 meters and the maximum allowable KG is 21.35 meters.

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Figure 13: Damaged Curve - Fully Loaded Figure 14, shown below, is a plot of the cross curves of stability for the vessel. The righting arm for the vessel is plotted against the draft for each angle of heel. The vessel’s righting arm is positive for 0 to 60 degrees of heel at drafts from 0 to 19 meters. With a heeling arm of 65 degrees the righting arm becomes less than 0 with drafts less than 2.5 meters and greater than 18 meters, this is dangerous as it means the vessel will try to flip instead of turning right side up. In severe environmental conditions where large vessel motions are possible the draft must be kept at less than 18 meters. The situation where the draft is less than 2.5 meters is highly unlikely as the ship when completely empty has a draft of more than 12 meters.

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Figure 14: Cross Curves of Stability - Fully Loaded 50% Loaded Condition The vessel’s stability was also determined when the product tanks were 50% and 20% full. The same rules for stability apply for the 50% and 20% loaded conditions that were used for the fully loaded condition. Figure 15 is the intact diagram for a 50% loaded condition. BY visually analyzing the graph is apparent that the rules for the ABS-MODU stability requirements are satisfied. Area A and area B together are much larger than 1.4 times area B and Area C. Additionally area A is much larger than 1.4 times area B.

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Figure 15: Intact Diagram - 50% Loaded Figure 16 is the diagram for the damaged situation at 50% loading. Two adjacent ballast tanks were damaged and then the stability was analyzed. The two tanks that were chosen were the two tanks that caused the lowest allowable center of gravity. As with the fully loaded condition the downflooding angle must be larger than the intersection of the righting arm and the heeling arm.

Figure 16: Damaged Condition - 50% Loaded

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Figure 17 shows the cross curves of stability for the 50% loading condition. The important point to note is that there is a positive moment arm until the vessel is at a 50 degree heeling angle. It is doubtful that the vessel will ever be at a 50 degree angle but at any angle less than 50 degrees the ship will right itself.

Figure 17: Cross Curves of Stability - 50% Loaded

20% Loaded Condition

Stability analysis was also performed when the vessel’s product tanks were only 20% loaded. The analysis was not performed when the tanks were empty due to damage that can occur to machinery that is run dry, thus tanks are not allowed to be completely empted but a small amount of product is left in the bottom of the tanks, 20% in this case. Figure 18 shows the intact stability curve for the 20% loaded case. Again by visually analyzing the figure the ABS-MODU rules are satisfied. Areas A and B are much larger than 1.4 times areas B and C and area A is much larger than 1.4 times area B.

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Figure 18: Intact Stability Curve for 20% Loaded Figure 19 shows the damaged stability curve for the 20% loaded situation. The important point is that the down flooding angle is still greater than the intersection of the righting arm and the heeling arm. Thus, the vessel will stay afloat when two adjacent ballast tanks are damaged.

Figure 19: Damaged Stability Curve - 20% Loaded

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Figure 20 shows a plot of the cross curves of stability for the 20% loading condition. As with the fully loaded and the 50% loaded conditions, the righting arms are all positive to an angle of 50 degrees. As highly improbable as it may seem, even if the vessel is tilted to 50 degrees under any of the loading situations it will right itself.

Figure 20: Cross Curves of Stability - 20% Loaded Damaged Stability An additional stability case to consider would be worst case scenario damage case. In Stab-CAD tanks were damaged and allowed to flood progressively until in the damaged stability curve the down flooding angle was less than the intersection of the righting arm and the heeling arm, as seen in Figure 21. All but the two forward ballast tanks had to be damaged before the vessel would become unstable. The vessel remained stable even when the two aft ballast tanks were left undamaged and the rest were damaged. Only when the port forward and the starboard forward tanks are left intact and the rest of the tanks are damaged does the vessel become unstable.

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Figure 21: Damaged Stability Curve - Unstable Condition

GLOBAL LOADING AND GENERAL STRUCTURAL STRENGTH

Topsides The FPSO is subjected to 4 main types of loads. These include the topsides, lightship, tanks, and buoyancy forces. The first load shown is the wet topside weights, and remains constant.

Figure 22: Topside Loads These loads were given by ConocoPhilips, shown in Table 10 below. The equipment and structure weights include module supports, piping, electrical, control, and instrumentation. The longitudinal center of gravity is taken from the aft of the FPSO with the vector forward. Then the loads with similar longitudinal center’s of gravity were added together, and applied to the beam.

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Table 10: Topside Loads Eqpt/Struct** Operate Fluid Total Total

Module Weight Weight Weight LCG Weight(mt) (mt) (mt) (m) (kN)

P1 241 197 438 249 4297P2 881 1002 1883 219 18472P3 2271 734 3005 189 29479P4 1701 628 2329 159 22847P5 1078 0 1078 129 10575P6 1804 0 1804 99 17697

S1 213 0 213 249 2090S2 1628 0 1628 219 15971S3 2268 737 3005 189 29479S4 1683 527 2210 159 21680S5 2068 565 2633 129 25830S6 2038 420 2458 99 24113S7 287 14 301 69 2953S8 79 0 79 39 775

PR1 54 0 54 249 530PR2 259 38 297 219 2914PR3 294 16 310 189 3041PR4 284 14 298 159 2923PR5 294 16 310 129 3041PR6 182 25 207 99 2031PR7 194 34 228 69 2237Flare 154 6 160 40 1570

Totals 19955 4973 24928 244544 Next, the lightship values are shown below, in Figure 23.

Lightship

Figure 23: Lightship Loads The lightship loads consist of a uniformly distributed hull weight across the length of the vessel, hull out fittings, employee accommodations, tandem offloading system, hull machinery weight, electric and electronics, external mooring system weights, and other miscellaneous weights. Below in Table 11, these values are listed.

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Table 11: Lightship Loads

Next, the tank loads were calculated using values given by ConocoPhilips, as shown below, in Table 12.

Tanks Table 12: Tank Volumes and Weight

Liquid (100% Full) Volume (m3) SG Density (kg/m3) Weight (mt)Stabilized Product Total for 16 tanks--cu mtrs 263720 0.94 940 247896.8Off-Spec Product Total for 2 tanks--cu mtrs 32160 0.94 940 30230.4

Slops Total for 2 tanks--cu mtrs 9330 0.94 940 8770.2Produced Water Total for 2 tanks--cu mtrs 8640 1.032 1032 8916.48

Diesel Fuel (2 tanks@2100 + 2 tanks@450)--cu mtrs 5100 0.9 900 4590Crude Fuel Oil Total for 2 tanks--cu mtrs 5180 0.9 900 4662

Process Fresh Water Total for 2 tanks--cu mtrs 2650 1 1000 2650Potable Water Total for 2 tanks--cu mtrs 250 1 1000 250Bulk Lube Oil Total for 2 tanks--cu mtrs 40 0.9 900 36

Bulk Hydraulic Oil Total for 2 tanks 20 0.9 900 18Ballast Tank Total for 12L shaped tanks--cu mtrs 123530 1.025 1025 126618.25

Total Fluid Weight: 434638.13 Figures 25, 26, and 27, below, give the weight distribution, as modeled in Visual Analysis, for the 100%, 50%, and 20% loaded conditions.

Figure 24: 100% Load

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Figure 25: 50% Loaded Tanks

Figure 26: 20% Loaded Tanks Table 13 below, gives the numbers used for the distributed loads on the hull. Table 13: Tank Loading Length from 100% Load 50% Load 20% Load

Aft (m) (kN-m) (kN-m) (kN-m)289.4 -301 30 30 30270 - 274.7 5488 5488 5488

227.8 - 267.8 12348 8609 7341187.2 - 227.8 12449 12367 13292147.8 - 187.2 12348 8609 7341107.8 - 147.8 10663 7767 700467.8 - 107.8 12555 8713 738242.8 - 67.8 12513 8478 6945

32.05 - 42.8 13139 15404 1767025.6 - 32.05 12093 14811 1753012.8 - 25.6 2911 5347 7782

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Still Water Buoyancy For each of the 100% (Figure 28), 50% (Figure 29), and 20% (Figure 30) buoyancy cases below, the corresponding drafts are 20, 16, and 15 meters respectively.

Figure 27: 100% Load - Still Water Buoyancy

Figure 28: 50% Load - Still Water Buoyancy

Figure 29: 20% Load – Still Water Buoyancy

Hogging/Sagging Buoyancy Next, these loads are combined with the induced wave corresponding to the loading condition, shown below, in Figure 31. These waves were modeled as a cosine wave function in both a hog and sag condition. The hog condition is where the wave crest is in the middle of the ship while a sag condition corresponds to the wave crest being at both the aft and stern ends of the ship. The wave height used, 5.3 meters, corresponds to the wave height in the 100 year storm.

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0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

0 50 100 150 200 250 300

Length Along Ship (m)

Forc

e (k

N-m

)

100% Load(sag)

100% Load(hog)

50% Load(sag)

50% Load(hog)

20% Load(sag)

20% Load(hog)

Figure 30: Hog/Sag Buoyancy Forces The loads above were modeled with a wavelength equal to that of the ship. To model the wave condition correctly the total combined force of the still water buoyancy for each load condition must be equal to the total force for each hog, and sag loading condition. In each of the cases above this occurs, and was confirmed using a Simpson’s Rule analysis. The analysis for the fully loaded condition in the hog and sag is shown below, in Table 14. Table 14: Simpson Rule Analysis

Draft (m) Draft (m) Simp100% Sag 100% Hog Coeff

0 22.7 13209.6 17.4 10118.6 1 13209.6 10118.618.8 22.3 12999.6 17.7 10328.6 4 51998.5 41314.237.6 21.9 12754.7 18.1 10573.5 2 25509.4 2114756.4 21.3 12433.9 18.7 10891.3 4 49735.7 43565.475.3 20 11664.1 20 11664.1 2 23328.2 23328.294.1 18.7 10891.3 21.3 12433.9 4 43565.4 49735.7112.9 18.1 10573.5 21.9 12754.7 2 21147 25509.4131.7 17.7 10328.6 22.3 12999.6 4 41314.2 51998.5150.5 17.4 10118.6 22.7 13209.6 2 20237.2 26419.2169.3 17.7 10328.6 22.3 12999.6 4 41314.2 51998.5188.1 18.1 10573.5 21.9 12754.7 2 21147 25509.4206.9 18.7 10891.3 21.3 12433.9 4 43565.4 49735.7225.8 20 11664.1 20 11664.1 2 23328.2 23328.2244.6 21.3 12433.9 18.7 10891.3 4 49735.7 43565.4263.4 21.9 12754.7 18.1 10573.5 2 25509.4 21147282.2 22.3 12999.6 17.7 10328.6 4 51998.5 41314.2301 22.7 13209.6 17.4 10118.6 1 13209.6 10118.6

Sum = 5.60E+05 5.60E+05TOTAL AREA = 3.51E+06 3.51E+06

SW AREA = 3.51E+06

L (m) FB (kN-m) S.C*FB Sag S.C*FB (Hog)FB (kN-m)

Below, in Table 15, a numerical representation of the hog and sag condition is shown.

47

Table 15: Sag/Hog Wave Model

Length 100% Load 100% Load 50% Load 50% Load 20% Load 20% LoadFrom Aft Sag Hog Sag Hog Sag Hog

L (m) FB (kN-m) FB (kN-m) FB (kN-m) FB (kN-m) FB (kN-m) FB (kN-m)0 13210 10119 10877 7786 10294 7203

18.8 13000 10329 10667 7996 10084 741337.6 12755 10573 10422 8241 9839 765756.4 12434 10891 10101 8559 9518 797575.2 11664 11664 9331 9331 8748 874894 10891 12434 8559 10101 7975 9518

112.8 10573 12755 8241 10422 7657 9839131.6 10329 13000 7996 10667 7413 10084150.5 10119 13210 7786 10877 7203 10294169.3 10329 13000 7996 10667 7413 10084188.1 10573 12755 8241 10422 7657 9839206.9 10891 12434 8559 10101 7975 9518225.7 11664 11664 9331 9331 8748 8748244.5 12434 10891 10101 8559 9518 7975263.3 12755 10573 10422 8241 9839 7657282.1 13000 10329 10667 7996 10084 7413301 13210 10119 10877 7786 10294 7203

Visual Analysis Results Three different loading conditions are analyzed and include fully loaded crude, 50 percent loaded crude, and 20 percent loaded crude. From ABS Rules for Building and Classing Steel Vessels 2005, it is shown that

t sw waveM M M= + And t sw waveV V V= + Where, Mt, the total bending moment, is to be considered as the maximum algebraic sum of the still water bending moment, Msw, and the wave induced bending moment, Mwave. Additionally Vt, the total shear force, is the maximum sum of the still water shear force, Vsw, and the wave induced shear force Vwave. From definition, the still water bending and shear force calculation, determining the bending moment and hull girder shear force values along the vessel’s entire length, are to be submitted together with a distribution of the lightship weights. So for each of the three loading conditions, the total still water moment and still water shear values can be found by combining the lightship, topsides, tanks, and still water buoyancy loads. Also the total moment and total shear value can be found by combining the lightship, topsides, and hog or sag buoyancy loads. Then these loads are factored into Visual Analysis using an equation combination, and then analyzed to get the results below.

48

0

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000

30,000,000

35,000,000

0 50 100 150 200 250 300

Length Along Ship (m)

SWB

M (k

N-M

) SWBM100%

SWBM50%

SWBM20%

Figure 31: Still Water Bending Moment (SWBM)

-500,000

-400,000

-300,000

-200,000

-100,000

0

100,000

200,000

300,000

400,000

0 50 100 150 200 250 300

Length Along Ship (m)

Shea

r Fo

rce

(kN)

SW100%

SW50%

SW20%

Figure 32: Still Water Shear Forces

49

0

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000

30,000,000

35,000,000

40,000,000

0 50 100 150 200 250 300 350

Length Along Ship (m)

Tota

l Mom

ent (

kN-m

)

Mt 100%(hog)

Mt 100%(sag)

Mt 50%(hog)

Mt 50%(sag)

Mt 20%(hog)

Mt 20%(sag)

Figure 33: Total Moment

-500,000

-400,000

-300,000

-200,000

-100,000

0

100,000

200,000

300,000

400,000

500,000

0 50 100 150 200 250 300

Length along Ship (m)

Tota

l She

ar (k

N)

100%(hog)

100%(sag)

50%(hog)

50%(sag)

20%(hog)

20%(sag)

Figure 34: Total Shear Forces

50

Next, in order to find the wave induced moment and shear force, the values for total moment and total shear are subtracted by the stillwater moment and shear forces. Then these values are applied to the ABS 3.5.1, and 3.5.2 envelopes obtained by the following equations: 2 3

1 1 ( 0.7) 10ws bM k C L B C x −= − + Sagging Moment 2 3

2 1 10wh bM k C L BC x −= Hogging Moment Where k1 and k2 are 110 and 190 respectively, C1 is 10.75 for a ship length of 300 < L <= 350 meters, L is the length of vessel, B is breadth of vessel, and

1.025b

wl

CLB dΔ

= ABS 11.3

Where ∆ is the molded displacement, Bwl is the greatest breadth at the summer load line, and d is the draft. Then the wave bending moment along the length L, can be obtained by multiplying the midship with the value of the distribution factor M shown in the figure below.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.2 0.4 0.6 0.8 1.0

Distance From Aft End in terms of L

M

Figure 35: Distribution Factor M Then the envelopes of maximum shearing forces induced by the waves, may be obtained by the following ABS 3.5.3 equations 2

1 1 ( 0.7) 10wp bF kF C LB C x −= + Positive Shear 2

2 1 ( 0.7) 10wn bF kF C LB C x −= − = Negative Shear

51

Where k equals 30, F1 and F2 are the distribution factors, below in Figures 37 and 38.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Distance From Aft in Terms of L

F 1

Figure 36: Distribution Factor, F1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Distance From Aft in Terms of L

F 2

Figure 37: Distribution Factor, F2

52

-15,000,000

-10,000,000

-5,000,000

0

5,000,000

10,000,000

15,000,000

0 50 100 150 200 250 300

Length Along Ship (m)

WIB

M (k

N-m

)ABS WAVEMOMENT(sag)ABS WAVEMOMENT(hog)VISA 100%(sag)

VISA 100%(hog)

VISA 50%(sag)

VISA 50%(hog)

VISA 20%(sag)

VISA 20%(hog)

Figure 38: Wave Induced Moment Envelope (WIBM)

-100,000

-80,000

-60,000

-40,000

-20,000

0

20,000

40,000

60,000

80,000

100,000

120,000

0 50 100 150 200 250 300

Length Along Ship (m)

Shea

r (kN

)

ABSSHEAR (+)

ABSSHEAR (-)

VISA 100%(sag)

VISA 100%(hog)

VISA 50%(sag)

VISA 50%(hog)

VISA 20%(sag)

VISA 20%(hog)

Figure 39: Wave Induced Shear Force Envelope

53

Figures 39 and 40, above, clearly indicate that the wave induced moment, and wave induced shear force for each case is well within the envelope, meeting the ABS 3.7.1 specifications. Next, the hull girder section modulus and hull girder moment of inertia must be found. The required hull girder section modulus for 0.4L amidships is to be greater than the value obtained by the equation below

t

p

MSMf

=

Where Mt stands for the largest total moment seen in the sagging condition for the 100% load and is equivalent to 3.76 x 107 kN-m, and fp is the nominal permissible bending stress, given by ABS 3.7.1, equaling 17.5 kN/cm2. Therefore the section modulus is to be greater than 215 m3. Next the hull girder moment of inertia, is found by ABS 3.7.2 and shown as

*33.3

L SMI =

Where L stands for the length of the ship, and the moment of inertia should not be less than the value calculated. In the case where the sagging condition is combined with a full load, the moment of inertia should be greater than 1942 m4. Next the section modulus and moment of inertia were inserted into Visual Analysis to find the deflections of the hull.

-90

-80

-70

-60

-50

-40

-30

-20

-10

00 50 100 150 200 250 300

Length along Ship (m)

Def

lect

ion

(cm

)

100%hog

100%sag

50%hog

50%sag

20%hog

20%sag

Figure 40: I = 1942 m4 - Hog/Sag Deflections

54

-80

-70

-60

-50

-40

-30

-20

-10

00 50 100 150 200 250 300

Length Along Ship (m)

Def

lect

ion

(cm

)

SW100%Load

SW 50%Load

SW 20%Load

Figure 41: I = 1942 m4 - Still Water Deflections Figures 41 and 42, above, clearly indicate that some of the deflections are greater than the limits of plus or minus 50 centimeters for the hog and sag condition (King 2006). The largest deflection shown is the fully loaded sagging condition equaling 85 centimeters. Therefore in order to decrease the deflections, the section modulus and moment of inertia are increased until the deflections get within the limits. After many trials the new section modulus and moment of inertia equal 376 m3, and 3400 m4 respectively. The new deflection values can be seen below, in Figures 43 and 44.

-60

-50

-40

-30

-20

-10

00 50 100 150 200 250 300

Length Along Ship (m)

Def

lect

ion

(cm

)

100%hog

100%sag

50%hog

50%sag

20%hog

20%hog

20%sag

Figure 42: I = 3400 m4 - Hog/Sag Deflections

55

-45

-40

-35

-30

-25

-20

-15

-10

-5

00 50 100 150 200 250 300

Length Along Ship (m)

Def

lect

ion

(cm

)

sw100%

sw50%

sw20%

Figure 43: I = 3400 m4 - Still Water Deflections Now all of the deflection, for each load case, in the hog and sag condition, meet the limits. Now the largest deflection is still the fully loaded sag condition, but the value is 48 centimeters.

WIND AND CURRENT LOADING The wind loading is based on a 1 hour average wind speed based on another time interval: t hrV Vα= Where, Vt is the wind velocity for the average time interval t, α is the time factor from Table 16, and Vhr is the one hour average wind velocity. The first step for calculating the wind load was to first find the surface areas of the different components of the FPSO affected by the bow and beam winds. This includes the projected area of each column. Also a blocked in projected area was used for the several deck housings instead of calculating each individual unit. However when this was done a Cs factor of 1.10 should was used. Isolated structures such derricks and cranes were calculated individually. In addition the open truss work commonly used for derrick mast and booms was approximated by using 60 percent of the projected block area from one of the faces. These areas were calculated for the appropriate hull draft of 24 meters from the given operating conditions. Additionally, areas were separated into smaller areas based on 15.3 meter increments above sea level. However the areas that were less than 15.3 meters in height used the height coefficient, Ch, associated with that body’s centroid. The height and shape coefficients can be found in Tables 16 and 17.

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Table 16: Wind Force Height Coefficients Over not Exceeding (m) Ch

0.0 - 15.3 1.0015.3 - 30.5 1.2330.5 - 46.0 1.4046.0 - 61.0 1.5261.0 - 76.0 1.62

Table 17: Wind Force Shape Coefficients Exposed Areas CsCylindrical Shapes 0.5Hull (surface above waterline) 1Deck House 1Isolated Structures 1.5Under Deck Areas (smooth surfaces) 1Under Deck Areas (exposed beams and girders) 1.3Rig Derrick 1.25 Next, the actual wind load calculations for both bow and beam seas were calculated by

2( )w w s h wF C C C A V= ∑ Where Fw is the wind force in Newton’s, Cw is a predetermined constant of 0.615 N-s2/m4, Cs and Ch are the shape and height coefficients respectively, A is the surface area of each unit in square meters, and Vw is the design wind speed in meters per second. The wind load calculations for oblique seas were calculated using the following equation.

2 2

2 2

2cos 2sin1 cos 1 sinx yF F Fφ

φ φφ φ

⎡ ⎤ ⎡ ⎤= +⎢ ⎥ ⎢ ⎥+ +⎣ ⎦ ⎣ ⎦

Where Fφ is the force in Newton’s due to an oblique environment, Fx and Fy is the force on the bow due to a bow environment or the force on the beam due to a beam environment, and φ is the direction of the approaching environment in degrees off of the bow. Next, the current loading was calculated in a similar way to the wind loading in that the steps included finding the surface areas, determining drag coefficients, and finally determining the current load. The current load calculation for the ship shape hull is approximated by: 2

c c cF C SV= Where Fc is the current force in Newton’s, Cc is the current force coefficient on the bow and beam equaling 2.89 or 72.37 Nsec2/m4 respectively, S is the wetted hull surface area in square meters including appendages, and Vc is the design current speed in meters per second. Next similar to wind loading, the current loading for oblique seas were calculated by:

2 2

2 2

2cos 2sin1 cos 1 sinx yF F Fφ

φ φφ φ

⎡ ⎤ ⎡ ⎤= +⎢ ⎥ ⎢ ⎥+ +⎣ ⎦ ⎣ ⎦

Where Fφ is the current force in Newton’s due to an oblique environment, Fx and FY is the current force on the bow due to a bow environment or the force on the beam due to a beam environment, and φ is the direction of the current

57

approaching environment in degrees off of the bow. Finally the wave loading can be found by finding the interaction between the ocean wave and the floating structure. First order forces, which oscillate ate the wave frequencies, induce first order motions that are also known as high frequency or wave frequency motions. Second order forces with frequencies below wave frequencies induce second order motions that are also known as low frequency motions. The steady component of the second order force is known as the mean wave drift force. Figures 45, 46, and 47, below, displays the mean drift force curves for bow, beam, and quartering seas can be seen.

Figure 44: Mean Drift Force Curve for Bow Seas

y = 0.0009x3 - 0.0942x2 + 4.7474x - 19.283R2 = 0.9994

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40 45

Significant Wave Height (ft)

Mea

n W

ave

Dri

ft F

orce

(Kip

s)

Figure 45: Mean Wave Drift Force for Beam Seas

58

y = 0.0004x3 - 0.0489x2 + 3.0314x - 7.8637R2 = 0.9993

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40 45 Figure 46: Mean Wave Drift Force for Quartering Seas Table 18, below, shows the spreadsheet used for environmental loads. Table 18: Environmental Loads Spreadsheet

24.000 alpha 1.180

Cs Ch A(Bow) AChCs Cs Ch A(Beam) AChCs

Hull above W L 1.000 1.23 835.2 1027.3 1.000 1.230 3130.4 3850.4T opSides 1.000 1.400 575.0 805.0 1.000 1.230 380.0 467.4

Accom 1.000 1.400 357.0 499.8 1.000 1.400 2268.0 3175.2Hull Bot tom 1.000 1.230 29.0 35.7 1.000 1.400 540.0 756.0

1.000 1.400 100.0 140.01.000 1.230 119.0 146.41.500 1.520 240.0 547.21.500 1.400 120.0 252.0

1796.2 6897.400Sum(CsChA) 2367.8 Sum(CsChA) 9334.6

Fwx 1167.9 Fwy 4604.2

T heta 45.0Fwq 3848.1

0.9002.890 SVc2 25772.580 SVc2 25772.580 T heta 45.000

72.370 Fc(kN) 74.483 Fc(kN) 1865.162 Fc(kN) 1293.09631818.000

17.400

T otal Force(kN) 1,302 6,819 5,345Mean Wave Drift Force 60.1 349.5 203.7Current 74.5 1865.2 1293.1W ind 1167.9 4604.2 3848.1

Total Environm e ntal Force sForce(kN) Bow Seas Beam Seas Quartering Seas

Force(kN) 60.1 349.5 203.7

Quartering Seas (Sway) y=1E-5x^4-0.0003x^3-0.0638x^2+4.0954x-7.2682Height (ft ) Bow Seas Beam Seas Quartering Seas

Beam Seas y=2E-5X^4-5E-5X^3-0.1433X^2+7.3983*X-8.9346

Quartering Seas (Surge) y=0.9366x+1.2207

Cubic Spline Curve Fit t ing Formulae [x=Hs(ft ), y=Force (kips)]Bow Seas y=9.63ln(x)-14

Cs(Bow Sea)Csy(Beam Sea)W eted Area

Me an W ave Drift Force

Force(Kips)

C urre nt ForceCurrent Speed Vc(m/s) Bow Seas Beam Seas Oblique Environment

Bow Se as Be am Se as

Force(kN)Quartering Seas

Wind Force

W ind Speed Vw(m/s)

Proje cte d Are as m ^2 (Above W ate r Line )

59

This spreadsheet is inaccurate due to the fact that the wave drift force was calculated for a drill ship of dissimilar dimensions. Therefore Froude scaling was used to obtain a more accurate approximation, shown below.

FPSO

Drillship

LL

λ =

3

, ,FPSO Drift Drillship DriftF F xλ= Therefore, the new drift forces for bow seas equal 428 kN. Below, in Table 19, the 100 year environmental loadings, for the vessel, can be seen. Table 19: Bow, Beam, and Quartering Sea Forces for 100 Year Storm

Total Environmental Forces

Force (kN)Bow Seas

Beam Seas

Quartering Seas

Wind 1,168 4,604 3,848Current 74 1,865 1,293Mean Wave Drift Force 60 350 204Total Force (kN) 1,302 6,819 5,345

MOORING/STATION KEEPING

Mooring Weighted Objectives When considering the mooring of our FPSO two primary types of mooring were considered, spread, and single point mooring. Within single point mooring there are two means of mooring, internal and external turrets. The three types of mooring usually use either catenary or semi-taught mooring lines. After considering the possibilities and ramifications of each, we decide that the external turret was the best choice. The weighted objectives table, Table 20, below, was used to qualify our choice of an external turret design. Nine conditions were considered for the table; they are listed as follows and referenced in the weighted objectives table. Each case has been assigned a factor of importance by which the particular objectives will be weighted for each mooring type.

1. Environmental applicability 2. Ship structure modification 3. Weathervaning ability 4. Loads on mooring lines 5. Optimization of product storage 6. Tandem offloading 7. Parallel offloading 8. Length of mooring lines and risers 9. Cost

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What conclusions did our team draw from the weighted objectives? We considered each of the objectives with respect to the applicability of the three types of mooring available to us. Table 20: Mooring Weighted Objectives Table

Applicability Score Applicability Score Applicability Score1. Environmental applicability 1 0.2 4 0.8 5 1 1 0.2

2. Ship structure modification 2 0.05 2 0.1 3 0.15 4 0.2

3. Weathervaning ability 3 0.1 5 0.5 5 0.5 0 0

4. Loads on mooring lines 4 0.05 4 0.2 4 0.2 2 0.1

5. Optimization of product storage 5 0.1 3 0.3 5 0.5 5 0.5

6. Tandem offloading 6 0.1 3 0.3 3 0.3 0 0

7. Parallel offloading 7 0.1 3 0.3 3 0.3 5 0.5

8. Length of mooring lines and risers 8 0.1 3 0.3 4 0.4 4 0.4

9. Cost 9 0.2 2 0.4 3 0.6 5 1Total 1 3.2 3.95 2.9

Most Favorable (5...1) Least Favorable

Objective Importance Factor

Case Internal Turret External Turret Spread MooringMooring types

Environment As can be seen in the environmental section of our report, the wind, wave, and currents of our area are not confined to any principle direction, instead they are constantly varying in direction. Internal and external turrets are effective in this type of an area because they have the ability to weathervane according to the dominant force factor. A spread mooring design, however, is a stationary concept and thus is subject to whatever force conditions might arise no matter the direction. The result is that a spread mooring system is ideal for a highly directional environment, any change in the directionality of the environment and the vessel would be in danger of breaking loose of its mooring. With this in mind we immediately rejected the spread mooring concept. This decision was further reinforced later on with further considerations of the other stated objectives in the weighted chart. Structure Modification Structure modification is only applicable were we to alter an existing vessel to accept some type of mooring system. For the internal turret major modifications would be necessary to strengthen the vessel’s internal structure to be able to accept and support the internal turret. For an external turret additional deck space and substructure stiffening will have to be added to compensate for the added stresses, whereas a spread moored vessel will have to undergo only moderate structural modifications. Weathervaning and Loads on Mooring Lines The location of the turret on the vessel plays a significant part in the vessel’s response to the surrounding environmental conditions, namely the vessel’s ability to weathervane and stresses applied to mooring lines. An external turret makes for an excellent weathervaning pivot due to the entire ship being located behind the turret. Internal turrets on the other hand do not weathervane as easily. With the internal turret located anywhere between the bow and the midship, an increase in deck forward of the turret adds more resistance to the weathervaning motion. In addition, if the turret is placed far enough back of the bow the more likely thrusters will be needed to assist in vessel movement. Increased difficulty in movement makes the vessel more susceptible to extended exposure to environmental loads, which in turn increases the load on the mooring system. However, an internal turret is not without its advantages. The closer the turret is to the midship the less likely the vessel is to pitch which results in less dynamic loading on the upper ends of the mooring lines. The external turret, on the other hand, reacts to the environment in just the opposite way. Instead it is more susceptible to pitch induced vertical motions which some experts have estimated to increase the end line load by as much as twenty percent that of an internal turret.

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Optimization of Storage Storage of crude is a major factor when deciding the feasibility of building an FPSO to fit a particular location. With an external turret as well as a spread moored vessel, there is not a decrease in the storage capability of the vessel. However when an internal turret is used, the amount of storage is reduced substantially. Take our vessel for example. There are sixteen tanks spaced on the longitude of the vessel. Each tank is forty feet long and three tanks are spaced along the width of the vessel. A diagram of the ship can be seen in the vessel layout in figure 1. Were an internal turret to be installed, a minimum of three tanks would have to be removed to capacitate the turret. The loss of volume would be close to twenty percent of the storage space. The only way to compensate for the lost storage would be to increase the length of the vessel to compensate for the displaced tanks. A change in vessel dimensions would in turn incur increased structural loads around the turret and increased longitudinal moments in the vessels structure when in a static, hog or sag states. Offloading, Tandem and Parallel Once the FPSO is producing, offloading becomes an issue. Two methods of offloading are presently used between shuttle tankers and FPSO’s, namely tandem and parallel. Both methods are particular in their mooring techniques. Tandem mooring uses hawsers to connect the shuttle tanker to the stern of the FPSO while keeping the two at a distance. Once the shuttle tanker is moored to the FPSO, a flexible conduit is used to transfer the crude. As for parallel offloading the shuttle tanker and FPSO moor together in a parallel orientation and the crude is offloaded via a flexible conduit. The primary difference between the tow offloading methods is the orientation of the risers and mooring lines to the shuttle tanker. With spread mooring a shuttle tanker is not free to move relative to the FPSO thus the two must be firmly moored to each other, otherwise the shuttle tanker runs the risk of running over and possibly damaging mooring lines. In comparison, a turret equipped FPSO has the ability to offload using either method while still weathervaning in response to loading conditions. Mooring Line Length and Risers Mooring line lengths for an FPSO are particular to the water depth and the mooring type either taught or catenary. Let us first look at spread mooring. Spread mooring requires sets of mooring lines attached to the quadrants of the vessel usually in a catenary fashion. This requires lines to be, as a rule of thumb, at least six times the depth of the water. In addition, but not particular to spread mooring, since the FPSO is in shallow water more line must be laid on the sea floor to increase the restoring force of the catenary system. As for using a taught line system, spread mooring seems to be associated with catenary mooring instead. As for internal and external turrets, the mooring can be either taught or catenary. The difference arises when considering the angle that the catenary lines approach the chain table. With the external turret the lines connect to the chain table below the keel whereas the external turret connects to above the deck of the vessel and has to stay clear of the moving vessel. Both turrets and the spread mooring can be accommodated when dealing with the mooring lines. Trouble arises when designing the risers. Two types of risers are used, rigid steel and flexible risers. These risers can be configured in a number of ways. Rigid risers are usually used in deeper water applications where more flexibility comes with longer risers, not to mention less expense. Flexible risers are better used in the shallower waters, due to their flexibility over shorter lengths and resilience to fatigue. The lay out of flexible risers is usually in a lazy “S” configuration. Simply put, the risers have flotation devices attached to take up the slack needed for flexing due to vessel motion. How do risers affect the choice of a turret? For a spread moored vessel the risers attach to a manifold on the side of the vessel and drop over the side of the vessel. As for the turret systems the risers connect through the center of the turret. This is where the external turret is a better choice than the internal turret and spread mooring. The extra height of the external turret allows for more favorable riser connection conditions. In contrast internal turrets are constructed to pass through the deck and hull of a ship and be placed within the internal structure of the vessel. Risers and mooring lines are then connected at the bottom of the internal turret, the chain table of which is near flush

62

with the keel of the vessel. When mooring in 100 meters of water an extra vertical 30 meters makes a significant difference in the track of mooring lines and risers. Cost As with any project, companies like to know the financial impact of optional methods. For our three mooring we will consider two significant cost factors associated with the three choices. First, the mooring lines for all three vessels will be approximately similar, minor differences will come with mooring line and riser lengths due to mooring line lengths and location. Second, initial cost of the vessel will be significantly affected if a turret system is selected over a spread system. The additional structure, turret stack, and possible increased length of the structure necessary for a turret system will add substantial expenses. Mooring Considerations The mooring system for the FPSO was designed to meet certain regulations and guidelines. The criteria for design are as follows:

• Maintain station in 100 year return weather conditions o Significant wave height, HS = 5.3 m o Maximum surface current, VS = 0.9 m/s o Maximum wind velocity, VW = 24 m/s o Maximum spectral period, TS = 11.1 seconds

• Maximum offset (API RP 2SK) o Intact: offset < 8% water depth o Damaged: offset < 12% water depth

• Safety Factor (API RP 2SK) o Intact: S.F. = 1.67 o Damaged (1 line broken): S.F. = 1.25

• Anchor Load (Drag Embedment – API RP 2SK) o Intact: S.F. = 1.5 o Damaged: S.F. = 1.0

• Minimize project cost Line Tension The maximum tension in the mooring lines is related to the stiffness or looseness of the system and the magnitude of environmental forces acting on the vessel. Safety factors for intact and damaged conditions have been developed to ensure correct sizing of chain in order to reduce the risk of system failure. The safety factor is equivalent to the breaking strength of a line divided by the maximum tension in the line. Safety factors cannot fall below 1.67 and 1.25 in intact and damaged conditions, respectively. For the damaged case, the second most loaded line, during intact conditions, was broken. The system was then reanalyzed to determine line tensions and offsets. Offset Environmental forces such as wind, current, and waves contribute to the offset of the FPSO. The offset, or displacement of the vessel from the geometric center, is important to the design of the system because of riser constraints. Damage to the risers is expected if excessive translation occurs. Due to a water depth of 100 meters, the mooring system is limited to an 8 meter intact offset and a 12 meter damaged offset. Weather Directionality In the case of a weathervaning vessel, various wind, wave, and current headings impact the bow of the vessel differently. Adhering to ABS rules, three different environmental heading combinations need to be examined, in

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order to determine the design conditions. The first case is collinear environment, where wind, wave, and current are 00 off the bow. The second case is when wind and current is 300 out of phase from the waves. The third case is when current and wind is 900 and 300 out of phase with the waves. In the case of the weather conditions, in the West Natuna Sea, the predominant weather direction is to the North East. Although weather conditions, in the West Natuna Sea, are predominantly to the North East, weather can be expected from multiple directions, throughout the year. Mooring Geometry The two most numerous mooring types are catenary and taut. Catenary utilizes a zero degree line angle with the seafloor at the anchor. Catenary lines greatly reduce vertical loads on the anchor. Catenary systems generally spread over a large seafloor area. Taut systems reduce vessel motions but increase line tensions. Also this type of system decreases the seafloor spread and amount of line length. Hull Interference External turret-moored vessels run the risk of mooring line interference with the hull. An appropriate combination of fairlead-chain angle and horizontal and vertical turret extension is necessary to avoid hull interference. Non-weather conditions need to be examined to determine the dimensions necessary to calculate hull clearance. This is so because no line slacking occurs in the lines closest to the bow of the vessel, when no weather is present Installation Cost The design of a FPSO system becomes a mounting cost as the design process progresses. One area of design that has much leniency for cost optimization is the mooring system. Some factors that drive the cost of a mooring system are number and length of chains, number and type of anchors, and cost of installing different mooring solutions. Anchors Different anchors serve different mooring systems. Drag embedment anchors are used for catenary systems and utilize the resistance of soil for support; thus, vertical loads must be minimized. It is recommended that an anchor scope of 6 – 8 times the water depth be used. Semi-Taut systems can tolerate much smaller anchor scopes (3 – 5 times the water depth) but require vertically tolerant anchors. Driven or suction pile anchors are commonly used with this type of system. For this type of anchor, the anchor tensions in both intact and damaged conditions need to be examined. Adhering to API rules, safety factors of 1.5 and 1.0 are used for intact and damaged conditions. The limiting condition should be used as the ultimate holding capacity of the anchor. The ultimated holding capacity should then be used to determine the appropriate anchor size. For the design of this system, a Stevpris Mk5 drag embedment anchor was chosen (see Soil Conditions). An illustration of this type of anchor can be seen in Figure 47.

Figure 47: Stevpris Mk5 Drag Embedment Anchor (Vyrhof 2000) (Vryhof anchor manual 2000)

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Soil Conditions The characteristics of the soil at the design location are necessary to the design of the anchors. For drag embedment anchors, the resistance of the soil to lateral loads affects the depth of installation and the anchor fluke area. Sand and hard clay reduces the anchor size, whereas, very soft clay increases the anchor size. The specific location for the anchor installation was found to have soil characteristics common to medium clay. A Vryhof anchor manual was provided by Dr. Randall, which contains charts that relate anchor size to soil conditions and anchor loads. It was found that a Stevpris Mk5 performed exceptionally well, in soil conditions similar to the design location. According to the Vryhof manual, for a Stevpris Mk5 anchor, the fluke/shank angle should be set at 320 for optimal performance in medium clay. SESAM Software Package – Mimosa The mooring analysis program mimosa was used to perform the analysis of the different mooring designs. The program allows the user to perform such calculations as maximum offsets, environmental loads, line tensions, geometry, etc. that are essential to a viable design solution. A file containing the particulars for the design FPSO vessel, as well as the wave force coefficients, was provided to us by Technip. The wave force coefficients, wind force coefficients, and the mass of our vessel was input into another file by Team Indonesia. Also a mooring file, containing mooring line particulars, was created by Team Indonesia, as an input file for Mimosa.

Design Two different design options have been analyzed:

• 8 line – spaced 450 apart • 12 line – 4 groups (900 apart) with 3 lines spaced 150 apart

8 Line Catenary System General Arrangement This system has 8 lines comprised of R4 – Grade, stud link steel chain. Each line is spaced 450 apart. The lines extend 800 meters horizontally from the fairleads to the anchors. Each line is 814 meters long and 111 millimeters thick, with a breaking strength of 9690 kN. An iterative process was used, adjusting the line length and diameter until offsets, safety factors, and line on bottom were optimized. There is also 1.5 m of hull clearance. A 3 – Dimensional illustration of this system is represented in Figure 48, below.

Figure 48: 3 – Dimensional Projection of 8 Line System Line Tensions

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Mooring responses were analyzed for the 100 year environment in both intact and damaged conditions. Every line in this system had maximum line tensions less than the allowable tensions, associated with the intact and damaged conditions. During intact conditions, the maximum line tension was 5108 kN, with a safety factor of 1.90. During damaged conditions, the maximum line tension was 7009 kN, with a safety factor of 1.38. Figure 49, below, depicts the intact and damaged line tensions.

Figure 49: Maximum Line Tensions for 8 Line System Line on Bottom A sufficient amount of line length lying on the seafloor is required to maintain a zero degree angle with the anchor, as required of a catenary system, to allow for drag embedment anchors. Chain sizes less than 111 mm were insufficiently heavy to maintain line on bottom. Line on bottom values of 150 m and 33 m were found for intact and damaged conditions, respectively. This system remains catenary in all conditions, thus allowing for the use of a drag embedment anchor. Anchor Soil conditions were needed for the installation site, in order to select the appropriate anchor. The design anchor load was determined by calculating the anchor load for the most heavily loaded line during intact and damaged conditions. The intact condition anchor load was found to be the limiting design feature. A 692 tonne design load was calculated, including a safety factor of 1.5, requiring the use of a Stevpris Mk5 – 15 metric tonne anchor. 12 Line Grouped Catenary System General Arrangement This system has 12 lines comprised of R4 – Grade, stud link steel chain. There are four groups containing three lines, spaced 150 apart. The lines extend 800 meters horizontally from the fairleads to the anchors. Each line is 814 meters long and 84 millimeters thick. Line lengths and chain sizes were optimized to ensure proper offsets, safety factors, and line on bottom. There is also 1.5 m of hull clearance. A 3 – Dimensional illustration of this system is represented in Figure 50, below.

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Figure 50: 3 – Dimensional Projection of 12 Line System Line Tensions Mooring responses were analyzed for the 100 year environment in both intact and damaged conditions. Every line in this system had maximum line tensions less than the allowable tensions, associated with the intact and damaged conditions. During intact conditions, the maximum line tension was 2945 kN, with a safety factor of 1.84. During damaged conditions, the maximum line tension was 3768 kN, with a safety factor of 1.44. Figure 51, below, depicts the intact and damaged line tensions.

Figure 51: Maximum Line Tensions for 12 Line System Line on Bottom Chain sizes less than 84 mm were insufficiently heavy to maintain line on bottom. Line on bottom values of 97 m and 30 m were found for intact and damaged conditions, respectively. This system remains catenary in all conditions, thus allowing for the use of a drag embedment anchor.

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Anchor The design anchor load was determined by calculating the anchor load for the most heavily loaded line during intact and damaged conditions. The intact condition anchor load was found to be the limiting design feature. A 408 tonne load was calculated, including a safety factor of 1.5, requiring the use of a Stevpris Mk5 – 8.5 tonne anchor.

Design Comparison Design solutions were obtained for both possible designs. Both systems were analyzed at depths of 100 meters, line lengths of 814 meters, and anchor to fairlead distances of 800 meters. Both systems were analyzed with the 100 year weather conditions. For the computation of forces affecting the bow, the collinear and two non-collinear conditions were considered. For the non-collinear cases, the environmental headings were adjusted until there were zero net sway forces. Then a fixed external moment was added resulting in a zero net yaw component. This method is necessary to simulate the weathervaning of an externally turreted vessel. Collinear Weather: Case 1 The first weather combination examined is the collinear case, where wind, waves, and current are all coming from the same direction. The vessel will weathervane such that all weather components are impacting the bow head on. Figure 53 and Table 20, below, summarizes the bow headings and total external forces affecting the vessel.

Figure 52: Colinear: Case 1 - Vessel Weathervaning Table 21: Collinear Environmental Forces

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Non-Collinear Weather: Case 2 The first non collinear case involves the wind/waves 300 out of phase with the current. The vessel fully weathervanes, when the wind/wave heading is 70 port of the bow and the current heading is 230 starboard of the bow, shown below in Figure 54. Below, in Table 21, is a summary of the forces subjected on the bow by the design weather conditions.

Figure 53: Non-Collinear: Case 2 - Vessel Weathervaning Table 22: Non-Collinear Case 2 - Environmental Forces

Non-collinear Weather: Case 3 The second non collinear case involves the wind and current 300 and 900, respectively, out of phase with the waves. The vessel fully weathervanes, when the wind heading is on the bow, the current is 600 port of the bow, and the waves are 300 starboard of the bow, shown below in Figure 55. Below, in Table 22, is a summary of the forces subjected on the bow by the design weather conditions.

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Figure 54: Non-Collinear: Case 3 - Vessel Weathervaning Table 23: Non-Collinear Case 3 - Environmental Forces

The case 2 environmental loading provides the most extreme static external vessel forces, with 1878 kN. Thus, case 2 is used as the design environmental condition. Both systems appear to perform similarly, when subjected to the design environmental conditions. Table 23, below, clearly shows that both systems exhibit sufficient strength, limited excursion, and sufficient line length on bottom. Table 24: Summary of 8 and 12 Line Systems

no. Line Chain Pre- break line on Anchor Max line on Total anchor Max line on Total anchorof Length Diam. Tens. strength bottom size Tens. bottom Offset S.F. tension Tens. bottom Offset S.F. tension

lines (m) (mm) (kN) (kN) (m) (mt) (kN) (m) (m) (mt) (kN) (m) (m) (mt)12 814 84 1340 5433 354 15.0 2945 97 √ 7.52 √ 1.84 √ 272 3768 30 √ 9.49 √ 1.44 √ 3678 814 111 2487 9690 356 8.5 5108 150 √ 6.68 √ 1.90 √ 462 7009 33 √ 10.74 √ 1.38 √ 683

Dimensions DamagedIntact

Cost Comparison Another way in which the two systems are compared is the overall cost. In order to do this, the line masses for each system were calculated and priced accordingly. In addition, the cost of the anchors is calculated. The 8 line system requires 15 metric tonne anchors whereas the 12 line system requires 8.5 metric tonne anchors. Below, in table 24, the results for the cost of each system are displayed.

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Table 25: Mooring System Cost

8 Line System 12 Line SystemExternal Turret $25,000,000 $25,000,000

Mooring Lines @ $2.50/kg $4,395,600 $3,785,100Anchors @ $42,000 $336,000 $504,000

Total $29,731,600 $29,289,100Cost Difference

Cost

$442,500 The 12 line system cost $442,500 less than the 8 line system. If the cost of installation is not taken into account, then the 12 line system appears to be the cheaper design. Because of the nearly identical scope and performance of the two systems, the driving factor for choosing the 12 line system is cost.

HYDRODYNAMICS OF MOTIONS AND OFFLOADING Hydrodynamics control the vessel’s operability; too much motion endangers workers and stops operation. Therefore, a complete analysis of the vessel’s response to an input function must be done before a vessel is put into operation. Hydrodynamics is the physics of how an object in water responds to an applied dynamic force. The input function is usually a wave spectrum, and the vessel’s natural periods control the response. Length, width, depth, weight, and other physical ship characteristics determine the frequencies which are presented in table 26, below. Table 26: Vessel Natural Periods

TN Time (s)Heave Natural Period 12.7

Roll Natural Period 13.2Pitch Natural Period 12.6

For the input function, the JONSWAP spectrum was used to model the sea state. JONSWAP uses the significant wave height, peak period, and the equation below to generate wave data that a numerical model, Sesam PostRep in this case, uses to generate the Response Amplitude Operators (RAO). Below, in Figure 56, the JONSWAP spectrum is shown.

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Figure 55: Wave Spectrum The RAO is not the actual response to the wave function, but the amplification factors to an input function; i.e., values greater than one amplify the input, and values less than one attenuate. Therefore, both the vessel characteristics and environment concern operators. The RMS equation below shows how the actual response is determined. Designers want to avoid resonance, when the vessel frequency matches the wave frequency, because this generates the maximum response and leads to catastrophe. The peak frequency to avoid is 0.6 rad/sec. Below is the root mean square response equation.

( )2( )RMS RAO Sω ω= Δ × ×∑

Of all the six degrees of freedom the vessel can move, Heave, Pitch, and Roll are the most important, and Heave most important of the three and is presented below. Heave is the vertical motion the vessel experiences due to an incoming wave; next of importance is pitch, the longitudinal rotation about the axis perpendicular to heave; and roll is the transverse rotation about the axis perpendicular to pitch. The initial calculations considered the waves incoming dead on the bow. This scenario is the most important to analyze because it is most likely to occur. The single point mooring system allows the vessel to orient itself in the direction of incoming waves. In this position, the heave and pitch will be at a maximum.

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Figure 56: RAO's for Heave According to Figure 57, above, the RAO for heave looks safe; the peak frequency is greater than the peak frequency of the incoming wave spectrum, and the vessel avoids resonance in the one year storm conditions.

Figure 57: Response Spectrum

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After the analyzing the dead on bow direction for incoming waves, subsequent analysis rotated the incoming wave spectrum at 22.5 intervals until 90 degrees. At 90 degrees, heave will be at its lowest values and roll at the maximum, Figure 59, below, shows.

Figure 58: Response for Roll Offloading of our vessel is possible by two methods, side by side and tandem. The type chosen is tandem due to the weathervaning advantages. For tandem offtake, there are limits that have to be met in order to offload. The vessel can offload product when the significant wave height is 2 meters, and there is a 10 knot wind. However, the vessel must disconnect when the significant wave height is 2.5 meters combined with a 20 knot wind. One criterion states that the FPSO must operate through a one year storm 95% of the time. Figure 59, below, demonstrates that the significant wave height as a cumulative annual probability.

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0.00

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Figure 59: Wave Height Probability Below, Figure 61 below shows that annual wind speed probability.

0.00000.05000.10000.15000.20000.25000.30000.35000.40000.45000.50000.55000.60000.65000.70000.75000.80000.85000.90000.95001.0000

0 2 4 6 8 10 12 14 16

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Figure 60: Wind Speed Probability According to our environmental data, the significant wave height in a one year event is 0.75 meters, and the wind speed equals 16.52 knots. Therefore the design allows offloading during a one year storm condition 100% of the time, without disconnecting, and this meets the criteria given.

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COST Vessel cost calculations were estimated using a spreadsheet supplied by Mr. Rod King. Cost factors were divided up into twelve areas that can be seen in table 25 in addition to a cost comparison between ship yards in three nations, namely Japan, Korea, and China. Table 27: Cost Breakdown

Japan Korea ChinaHull Steel 116.11 108.37 73.54Hull Outfitting 20.79 18.76 13.18Hull Machinery 1.05 0.94 In outfittingOutfitting 1.35 1.20 In outfittingAccomodations 23.2 20.9 15.6Offloading System 3.50 3.50 3.50Marine Cost 75 75 75Mooring System (8 Line) 29.73 29.73 29.73(12 Line) 29.29 29.29 29.29Topsides 620 620 620Contingency 112.80 111.32 105.58Transportation/Installation 20 20 20Total(12) 1,023.09 1,009.28 955.69Total(8) 1,023.53 1,009.72 956.13

Cost ($MM)Description

Total cost estimations of the vessel are estimated from 956.13 to 1023.53 millions of dollars. Major cost factors include the mooring system, hull steel, topsides, and contingency cost. Other major costs are constant across the three contractors, namely the contingency allowance, transportation\allowance, and offloading system. Included in table 25 are separate cost cases for twelve and eight line systems, each of which has been accounted for in separate totals noted by the number of lines. Mooring cost are affected by the cost of both the anchors and chains. Chains for the twelve line system were 84 mm and 111 mm for the eight line system both of which are R4 grade chains. Cost for a lower chain grade chain was relatively the same as that of R4 so the higher grade R4 chain was used. Anchor cost was taken at $42,000 per anchor. The difference between the two systems came to a total of $442,500 which is relatively negligible considering the overall cost. Yet, the cheaper system was chosen as the final design to be incorporated. Common factors between the three contractors include the topsides, transportation (since the three nations are relatively in the same area), offloading system and marine cost (trials, classification etc.) and thus limiting the competing amount between the three contractors. Otherwise China is consistently the cheapest contractor available and our final decision with a total cost of $956.13 million.

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SUMMARY This design report for a Floating Production, Storage and Offloading (FPSO) vessel in the West Natuna Sea in Indonesia looks at several design competencies which include: regulatory compliance (API-2SK, ABS, MODU, OCMIF, and MARPOL 73/78), mooring, stability, environmental loading, hydrodynamics, cost, and safety. This vessel was designed through collaboration between the senior design class and ConocoPhillips. The overall vessel characteristics and general arrangement were given. The vessel has a length 308 meters, a breadth 58 meters, and is 30.4 meters from deck to keel. The FPSO must produce 370 kbbls per day under normal environmental conditions, and for storage ConocoPhillips follows a “10 day rule” where the vessel stores 10 days worth of supply. The performance constraints of this design were given that the vessel must be able to maintain production on location under the stresses endured in one year storm conditions and must be able to survive on location in one hundred year storm conditions. The main focus of this design was on the mooring system. The design will consider several configurations depending on the environmental loads on the vessel; for example, small storage tanks increase the vessel’s flexibility under environmental loads. The environment this vessel is subjected to is considered benign. The wind wave and current loading has a high probability of being unidirectional from Northeast to Southwest under normal operating conditions. This would suggest that a fixed mooring system would be applicable. However, under storm conditions the directionality of these forces can change enough to cause them to be more prominent on the beam versus the bow, thus leading to the decision to use a single point mooring system to allow for weathervaning. The design team has looked at several arrangements of the tanks and of the mooring system. These different configurations were evaluated under three different loading conditions: full, 50% full, and 20% full. There were also a few constants throughout the design: the lightship hull weight which was determined to be 40,708 metric tons, and the draft for each of the loading conditions where the tank fullness was offset by the ballast tanks to keep the operating draft within a range of 15 to 20 meters. Two mooring solutions have been analyzed: an 8 line system where the lines are space 45° apart, and a 12 line system where the lines are grouped into 4 groups spaced 90° apart with the individual lines spaced 15° apart. The 8 line system is comprised of R4 Grade, stud link steel chain. Each line is 814 meters long and 84 millimeters thick. The 12 line system is comprised of R4 Grade, stud link steel chain as well. Each line is 814 meters long and 111 millimeters thick. The lines in both systems extend 750 meters horizontally from fairleads to anchors. Both systems were analyzed under conditions where the environmental forces were unidirectional and under conditions where the environmental forces came from different directions. The decision on which system to use was based on a weighted objectives table which took several aspects of the design into consideration, especially cost. After this evaluation the 12 line system was selected for use.

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REFERENCES American Bureau of Shipping. Rules for Building and Classing Steel Vessels. 7 vols. Port City Press, Inc.

Baltimore, Maryland, 1981. American Bureau of Shipping. Guide for Building and Classing Floating Production, Storage and Offloading

Systems. 7 vols. American Bureau of Shipping. New York, NY, 1996. American Bureau of Shipping. Guide for Building and Classing Facilities on Offshore Installations. 7 vols.

Houston, TX, 2000. American Bureau of Shipping. Guide for Building and Classing Facilities on Offshore Installations. 7 vols.

Houston, TX, 2000. American Bureau of Shipping. Rules for Building and Classing Mobile Offshore Drilling Units 2001.. 7 vols.

Houston, TX, 2000. American Petroleum Institute (API 2SK).Recommended Practice for Design and Analysis of Station keeping Systems for Floating Structures. First Edition. June, 1995. American Petroleum Institute. Recommended Practice for Design, Analysis, and Maintenance of Moorings for Floating Production Systems. American Petroleum Institute. Washington, DC, 1993. American Petroleum Institute. Analysis of Spread Mooring Systems for Floating Drilling Units. American

Petroleum Institute. Washington, DC, 1987. American Petroleum Institute. Recommended Practice for Design and Analysis of Station keeping Systems

For Floating Structures. First Edition. American Petroleum Institute. Washington, DC, 1995. Bauer. “Stability Curve.” Online posting. 2003 ConocoPhillips. “J. Ray McDermott wins contract from Conoco offshore Indonesia.” Online Posting. 15 May. 2006.

<http://www.gasandoil.com/goc/contract/cox14158.htm>. Heather, Nick. Interview. Structure and Weight –Estimating. February 2006. Heather, Nick. Interview. Fundamentals of Global Loading. February 2006. King, Rod. Interview. Cost Spreadsheet. February 2006. Marpol 73/78. Requirement for Tanked Vessels. United States, 1973 – 1978. McDermott, J. “Belanak FPSO.” Online Posting. 5 May. 2006.

<http://www.jraymcdermott.com/projects/Belanak-FPSO__90.asp>. Microsoft Excel. Vers. 2003. 1985 – 2003 Mimosa. Vers. 5.7-03. 2004. Mueller, John. “Belanak Hull Betokens Gas Breakthrough.” Online Posting. 25 Apr. 2006.

<http://www.oilonline.com/news/features/aog/20031001.Belanak_.12636.asp>. “Natuna Sea, Indonesia.” Map. 20 Mar. 2006. < http://www.ict-silat.com/ Indonesia_map1.JPG>.

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Oil Companies International Marine Forum. Prediction of Wind and Current Loads of VLCCs. 2nd Edition. 1994. Det Norske Veritas. MIMOSA Mooring Analysis Software, Version 5.7. November 2004. Autodesk, Inc. AutoCAD Software, 2004. Integrated Engineering Software, Inc. Visual Analysis, Version 4.0 1.014, 2004. Vryhof. Anchor Manual 2000. 2000. Ed. Netherlands, 1999

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APPENDIX

MIMOSA Output

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81

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84

85

Mooring Input (.mos)

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Anchor Selection Chart

(Vyrhof 2000)

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Stab-CAD Input File ALPID 3D View 0.707 0.707 -0.424 0.424 0.800 1 ALPID Global XY Pl 10.000 10.000 ALPID Global YZ Pl 10.000 10.000 ALPID Global XZ Pl 10.000 10.000 ALPREF 3D View 0.0 0.0 0.75 1 STBOPT 0 CALC ME ME PTPT KGPAR 51.5 25.6 1.4 CFORM 0. 22. 1. CROSS DF 1. 20. 1. 0. 60. 5. 0. 19.63 *INTACT 0. 35. 1. *DAMAGE 0. 80. 5. DRAFT 19.67 19.63 0. USER USER DWNFLD BALLAST TANK1 374 DWNFLD BALLAST TANK2 377 DWNFLD BALLAST TANK3 378 DWNFLD BALLAST TANK4 379 DWNFLD BALLAST TANK5 380 DWNFLD BALLAST TANK6 381 DWNFLD BALLAST TANK7 382 DWNFLD BALLAST TANK8 383 DWNFLD BALLAST TANK9 384 DWNFLD BALLAST TANK10 385 JOINT 1 0.000 0.000 0.000 JOINT 2 0.000 29.000 0.000 JOINT 3 0.000-29.000 0.000 JOINT 4 0.000 29.000 30.400 JOINT 5 0.000-29.000 30.400 JOINT 6 301.000 29.000 0.000 JOINT 7 301.000-29.000 0.000 \/\/\/\/\/\/\/\/\/\/\/\//\/\/\/\/\/\\/\/\// PANEL BRG 13 14 11 12 PANEL BRG 183 7 3 5 10 PANEL BRG 5 3 2 4 PANEL BRG 2 6 184 9 4 PANEL BRG 9 12 11 10 5 4 PANEL BRG 3 7 14 13 6 2 PANEL BRG 7 182 14 PANEL BRG 183 182 7 PANEL BRG 13 181 6 PANEL BRG 181 184 6 \/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\//\ BODY 1 .95OIL TANK 1 PANEL T1 15 18 19 22 PANEL T1 20 19 18 17 PANEL T1 16 15 22 21 PANEL T1 17 18 15 16 PANEL T1 21 22 19 20

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PANEL T1 21 20 17 16 BODY 2 .95OIL TANK 2 PANEL T2 20 24 23 19 PANEL T2 26 25 21 22 PANEL T2 25 24 20 21 PANEL T2 26 23 24 25 PANEL T2 22 19 23 26 PANEL T2 22 21 20 19 BODY 3 .95OIL TANK 3 PANEL T3 23 24 27 28 PANEL T3 30 25 26 29 PANEL T3 29 28 27 30 PANEL T3 26 23 28 29 PANEL T3 25 24 23 26 PANEL T3 30 27 24 25 \/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\ BODY 50 .95FORWARD STORE PANEL FST 9 12 11 10 179 178 PANEL FST 183 182 181 184 177 176 PANEL FST 183 176 179 10 PANEL FST 179 176 177 178 PANEL FST 184 9 178 177 PANEL FST 12 181 182 11 PANEL FST 11 182 183 PANEL FST 10 11 183 PANEL FST 9 184 181 PANEL FST 12 9 181 END