DESIGN OF A SEMI-SUBMERSIBLE PRODUCTION AND DRILLING FACILITY FOR THE GULF OF MEXICO

DESIGN OF A SEMI-SUBMERSIBLE PRODUCTION AND DRILLING FACILITY FOR THE GULF OF MEXICO OCEN 407- Design of Ocean Engineering Facilities Ocean Engineering Program Texas A&M University Final Report May 9, 2007

TABLE OF CONTENTS LIST OF FIGURES...iii LIST OF TABLES...iv ACKNOWLEDGEMENTS...v NOMENCLATURE...vi ABSTRACT...vii EXECUTIVE SUMMARY...viii 1 INTRODUCTION...1 1.1 Literature Review...1 1.2 Objective...1 1.3 Industry Day...1 1.4 Environment...2 1.5 Design Criteria...2 1.6 Gantt Chart...2 2 REGULATORY COMPLIANCE...4 2.1 General Arrangements...4 2.2 Storage and Slop Tanks...4 2.3 Accommodations...4 2.4 Spill Containment...4 2.5 Fire Safety...4 2.6 Lifesaving Appliances and Equipment...4 2.7 Flood Survival Requirements...4 2.8 Helicopter Deck...4 2.9 Environmental/Global Loading...5 2.10 General Structural Strength...5 2.11 Thickness Requirement for Plating...5 2.12 Mooring System...5 2.13 Stability...5 3 GENERAL ARRANGEMENT AND HULL DESIGN...6 3.1 Option One...6 3.2 Option Two...6 3.3 Selected Design...7 3.4 Transport and Operational Design Cases...8 3.5 Lifeboats...8 4 WEIGHT, BUOYANCY, AND STABILITY...9 4.1 Weight Calculations...9 4.2 Buoyancy Calculations...12 4.3 Stability...13 4.3.1 Intact Stability...13 4.3.2 Damaged Stability...15 4.3.3 Special Cases...16 5 LOCAL AND GLOBAL LOADING...20 5.1 Introduction...20 5.2 Calculation and Application of Static Loads...20 5.2.1 Application of Weight Loading...21 5.2.2 Application of Buoyancy Loading...23 5.3 Calculation and Application of Live Loads...24 5.3.1 Squeeze and Pry Conditions...24 5.3.2 Hoop Stresses...28 6 GENERAL STRENGTH AND STRUCTURAL DESIGN...29 6.1 Approach...29 6.2 Boundary Conditions...30 6.3 Geometric Properties...30 6.4 Allowable Stress Criteria...32 TAMU Team Gulf of Mexico i Final Report

6.4.1 Stress Results for Still Water Case...32 6.4.2 Stress Results for Squeeze Case...34 6.4.3 Stress Results for Pry Condition...35 6.4.4 Stress Results for Hoop Stresses...36 6.4.5 Stress Results Summary...36 6.5 ABS Plating Criteria for Watertight Bulkheads...36 7 ENVIRONMENTAL LOADING...37 7.1 Global and Local Effects...37 7.2 Wind Loading...37 7.2.1 Global Effects...37 7.2.2 Local Effects...37 7.3 Wave Loading...38 7.3.1 Global Effects...38 7.3.2 Local Effects...39 7.4 Current Loading...39 7.4.1 Global Effects...39 7.4.2 Local Effects...39 8 MOORING AND STATION KEEPING...40 8.1 Design Criteria...40 8.1.1 Quasi-Static Requirements...40 8.1.2 Environmental Loading Applications...40 8.1.3 Maximum Offsets...40 8.1.4 Watch Circle Requirements...40 8.1.5 Corrosion Tolerances...40 8.2 Primary Design...41 8.2.1 Design Layout and Components...41 8.3 Primary Design Results...43 8.3.1 Operational Offsets...43 8.4 Alternative Design Options...44 9 HYDRODYNAMICS OF MOTIONS AND LOADING...47 10 COST ANALYSIS...48 11 SUMMARY AND CONCLUSIONS...49 12 REFERENCES...50 Appendix A: GMOOR Input/Output...51 Appendix B: StabCad Input/Output...57 TAMU Team Gulf of Mexico ii Final Report

LIST OF FIGURES Figure 1- Gantt Chart...3 Figure 2- Square Column Semi-submersible Layout...6 Figure 3- Circular Column Semi-submersible Layout...7 Figure 4- Final Design Layout...8 Figure 5- Ballast Tank Layout...11 Figure 6- Center of Gravity Calculation Axis Convention...12 Figure 7- Yaw Angle of Heel Axis...13 Figure 8- Square Column StabCad Model...14 Figure 9- Operating Intact Stability Plot...14 Figure 10- Floodable Compartments...15 Figure 11- Operating Damaged Stability Plot...15 Figure 12- Intact Stability Plot, Hull Transporting Case...17 Figure 13- Intact Stability Plot, Towing Case...17 Figure 14- Damaged Stability Plot, Towing Case...18 Figure 15- Intact Stability Plot, Survival Case...18 Figure 16- Damaged Stability Plot, Survival Case...19 Figure 17- Basic Hull Component Definition...21 Figure 18- Applied Weight Loading...22 Figure 19- Applied Buoyancy Loading...23 Figure 20 - Wave Direction and Wave Length for Squeeze/Pry...24 Figure 21- Squeeze Wave Loading Condition...25 Figure 22- Pry Wave Loading Condition...25 Figure 23 - Pressure Differential across Column for Squeeze Case...25 Figure 24 - Pressure Differential across Column for Pry Case...26 Figure 25- Load Application of Squeeze Condition...27 Figure 26- Load Application for Pry Case...27 Figure 27- Beam Bending Element Degrees of Freedom...29 Figure 28- Input and Output of Structural Analysis...29 Figure 29 - Structural Model Boundary Conditions...30 Figure 30- Cross Sectional (local) Sign Convention...31 Figure 31- Plate with Stiffener...31 Figure 32- Maximum Bending Stresses...33 Figure 33- Minimum Bending Stresses...33 Figure 34 - Maximum Combined Stress, Squeeze Condition...34 Figure 35 - Minimum Combined Stress, Squeeze Condition...34 Figure 36 - Maximum Combined Stress, Pry Condition...35 Figure 37 - Minimum Combined Stress, Pry Condition...35 Figure 38- Vessel Component Layout...38 Figure 39- Static Pretensions for Primary Mooring Design...42 Figure 40-3-D View of 12 Leg Mooring Spread...42 Figure 41- Primary Design Offset in 0 degree Direction 150 ft under 10 year Winter Storm Conditions...44 Figure 42- Primary Design Offset in 45 degree Direction 150 ft under 10 year Winter Storm Conditions...44 Figure 43- Primary Design Offset in 90 degree Direction 150 ft under 10 year Winter Storm Conditions...44 Figure 44-3-D View of 16 Leg Mooring Spread...45 Figure 45-3-D View of 12 Leg Semi Taut Mooring Spread...46 Figure 46-3-D View of a 16 Leg Semi Taut Mooring System...46 Figure 47-100 Year Hurricane JONSWAP Spectrum...47 Figure 48- GMOOR Intact Mooring Analysis Output...55 Figure 49- GMOOR Damaged Mooring Analysis Output...56 TAMU Team Gulf of Mexico iii Final Report

LIST OF TABLES Table 1- Weight, Center of Gravity, and Draft for Each Design Case...ix Table 2- Compliance with ABS Stability Requirements...x Table 3 - Maximum and Minimum Calculated Combined Stresses and Deflections...xi Table 4- Environmental Loads for a 100 Year Hurricane...xi Table 5- Vessel Response... xii Table 6- Maximum Operational and Survival Environmental Data...2 Table 7- Square Column Hull Dimensions, Preliminary Design...6 Table 8- Circular Column Hull Dimensions, Preliminary Design...7 Table 9- Hull Weight and Natural Period Comparison for Preliminary Designs...7 Table 10- Comparison of Environmental Loads for Preliminary Designs...7 Table 11- Square Column Hull Dimensions, Final Design...8 Table 12- Weights and Centers of Gravity of Various Vessel Components...9 Table 13- Primary Ballast Tank Dimensions...10 Table 14- Ballast Tank Fullness (Primary Tanks)...11 Table 15- Vessel Weight and Buoyancy Characteristics...12 Table 16- Vessels Weights, Drafts, and Air Gaps...13 Table 17- Stability Results, Special Cases...16 Table 18- Allowable and Actual KG Comparison...19 Table 19- Weights of Major Structural Components...21 Table 20- Applied Weight Loadings, Operating Condition...22 Table 21 - Applied Buoyancy Loadings, Operating Condition...23 Table 22 - Net Forces and Points of Application for Squeeze-Pry...26 Table 23 - Buoyancy Differentials for Squeeze-Pry...28 Table 24 - Boundary Conditions Stiffnesses...30 Table 25- Geometric Properties of Major Structural Components...31 Table 26- Dynamic Stresses in Major Structural Components...36 Table 27 - Maximum Stresses and Factors of Safety...36 Table 28- Required Plate Thickness...36 Table 29- Component Areas and Coefficients for Bow Side Seas...38 Table 30- Final Calculated Environmental Loads...39 Table 31- Selected Mooring Line Component Properties...41 Table 32- Results of Dynamic Testing on a 12 Leg Taut System with Polyester, 100 yr Storm Conditions...43 Table 33- Results of Dynamic Testing on a 12 Leg Taut System with Polyester, 10 yr Storm Conditions...43 Table 34- FOS Results from 150 ft Offset Test under 10 year Winter Storm Conditions...44 Table 35-16 Leg Taut Mooring System Components...45 Table 36- Results of Dynamic Testing on a 16 Leg Taut System with Polyester, 100 yr Storm Conditions...45 Table 37- Safety Factors for 16 Leg and 12 Leg Wire Mooring Systems, 100 yr Storm Conditions...45 Table 38- Safety Factors for 12 and 16 Leg Semi Taut Mooring Systems, 100 yr Storm Conditions...46 Table 39- Vessel Response Motion...47 Table 40- Cost Estimates for the Mooring Design Options...48 Table 41- Cost Estimate for the Proposed Semi-Submersible and Mooring Design...48 TAMU Team Gulf of Mexico iv Final Report

ACKNOWLEDGEMENTS The Gulf of Mexico design team would like to thank the following people for their invaluable assistance and guidance during the completion of this project. Dr. Robert Randall, TAMU Rod King, Lloyds Register (Visiting Industry Lecturer, Industry Review Panel, Organized Industry Day) Philip Poll, Houston Offshore Engineering (Visiting Industry Lecturer, Industry Review Panel) John Chianis, Houston Offshore Engineering (Visiting Industry Lecturer) Kent Longridge, Intermoor (Visiting Industry Lecturer, Industry Review Panel) Patrick Kelly, BP (Industry Day Speaker) Bob Harvie, Lloyds Register (Industry Day Speaker) Leonard Simek, Mustang Engineering (Industry Day Speaker) C. Loper, Wellstream (Industry Day Speaker) Mike Holcomb, Keppel Offshore Marine (Industry Day Speaker) Jan Wolter Oosterhuis, Dockwise (Industry Day Speaker) ConocoPhillips, Lloyds Register, Houston Offshore Engineering, Intermoor Peter Noble, ConocoPhillips Bill Kinney, Fluor (Industry Review Panel) Gengshen Liu, Aker Kaevrner (Industry Review Panel) Rick Rogers, Global Santa Fe (Industry Review Panel) Engineering Dynamics Inc. (StabCad Software) Global Maritime (GMoor Software) TAMU Team Gulf of Mexico v Final Report

NOMENCLATURE FPS E A cs t FS σ CG CB LCG TCG VCG GM ρ M Mac r Aw S(ω) RS T γ L k z s Floating Production System Modulus of Elasticity Area of Cross Section Thickness of Steel Factor of Safety Stress Center of Gravity Center of Buoyancy Longitudinal CG Transverse CG Vertical CG Metacentric Height Fluid density Mass Added Mass Coefficient Radius of Gyration Displaced Volume Area of Waterplane Energy Density Function Response Spectrum Vessel Draft Water weight density (64 pcf) Wave Length Wave number Depth above MWL Stiffener Spacing TAMU Team Gulf of Mexico vi Final Report

ABSTRACT The purpose of this design project is to research, analyze, and design a semi-submersible production platform with drilling facilities capable of producing 120,000 barrels of oil and 10,000,000 cubic feet of gas per day. This vessel must be able to operate in the environmental conditions found in the Gulf of Mexico. Forces due to wind, current, and waves are considered when designing for both maximum operating and survival conditions. The vessel s hull and mooring system are designed such that it can operate in a 10 year winter storm and will survive a 100 year hurricane. In order to determine the success of the vessel design, parameters such as maximum vessel offset, response natural frequencies, and damaged and intact stability are analyzed. The design of this vessel meets all applicable API and ABS regulations. Finally, a cost analysis is performed in order to choose the most economical design. The International Student Offshore Design Competition (ISODC) has established several rules that must be met by all entries. Each design team must produce a safe hull design which matches the production rates as given by industry. Also, each project is required to address eight areas of competency, five of which are fundamental and three are specialized. The competencies covered in this design project are: Fundamental Competencies: General Arrangement and Overall Hull Design Weight, Buoyancy and Stability Local and Global Loading Strength and Structural Design Cost Specialized Competencies: Hydrodynamics of Motions and Loading Wind and Current Loading Mooring/Station Keeping The semi-submersible production unit is located in the Gulf of Mexico in a water depth of 5500 feet. Information on the topsides, such as weights, centers of gravity, and arrangements were supplied by Houston Offshore Engineering (HOE). The design of the vessel s hull and mooring system, as well as an analysis of its stability, structural integrity, and station keeping is the responsibility of this design group. This report outlines the work done by the design group and the resulting semi-submersible design. TAMU Team Gulf of Mexico vii Final Report

EXECUTIVE SUMMARY Introduction The Gulf of Mexico team was asked to design a semi-submersible production platform with drilling capabilities that will operate in 5500 feet of water. The vessel will comply with American Petroleum Institute (API) Standards and American Bureau of Shipping (ABS) Rules. The eight competency areas addressed by this project are: Fundamental Competencies: General Arrangement and Overall Hull Design Weight, Buoyancy and Stability Local and Global Loading Strength and Structural Design Cost Specialized Competencies: Hydrodynamics of Motions and Loading Wind and Current Loading Mooring/Station Keeping General Arrangement and Overall Hull Design Two design options are considered in this report. The selected design utilizes four columns with square cross sections and has the following dimensions: Column height: 90 ft Column width: 53 ft Pontoon length: 273 ft Pontoon width: 53 ft Pontoon height: 50 ft Each pontoon contains four equally sized floodable compartments, while each column has five. Ballast tanks are located in the pontoons. The hull is sized and the ballast tanks are filled such that all stability requirements are met. TAMU Team Gulf of Mexico viii Final Report

Weight, Buoyancy, and Stability The weight and stability characteristics of the vessel were analyzed for four cases which will occur during the vessel s design life. These cases are: operational, hull transport, towing, and survival. The hull transport case addresses the fact that the hull is fabricated in Korea and the transported to the Gulf of Mexico via a semi submersible transport vessel. During this case only the unballasted hull is considered. After the hull is mated with the topsides, the vessel is towed to location. The dry weights of the topsides along with the unballasted hull are considered during this case. During the survival case, the dry weights of the topsides are used to reflect that production and drilling are halted and the vessel is evacuated. In addition, the ballast tanks are completely filled. The total weights, centers of gravity, and drafts for each case are shown below in Table 1. The draft for the hull transport case is 15.44 ft which is less than the 29.5 ft maximum vessel draft that semi submersible transport vessels can accommodate. The towing draft is 25.71 ft which is less than the 45 ft depth of the Corpus Christi ship channel. The air gap during the survival case of 63.66 ft is well above the 51.65 ft minimum air gap required to accommodate the maximum wave during a 100 year hurricane. Table 1- Weight, Center of Gravity, and Draft for Each Design Case Hull Transport Towing Operational Survival Weight (kips) 46095 76749 167226 168188 LCG (ft) 0.00 0.13 0.00 0.00 TCG (ft) 0.00-0.13 0.00 0.00 VCG (ft) 43.66 94.78 65.47 59.68 GM (ft) 516.74 250.01 17.69 23.11 Draft (ft) 15.44 25.71 75.00 76.34 Air Gap (ft) N/A 114.29 65.00 63.66 These weight characteristics were input into the stability analysis software (StabCad) in order to analyze the vessel s stability for each case. The output from StabCad is compared with TAMU Team Gulf of Mexico ix Final Report

the ABS regulations in Table 2. The table shows that all requirements are met for each case analyzed. Intact Damaged Table 2- Compliance with ABS Stability Requirements Criteria Requirement Hull Transport Towing Operating Survival Righting Moment Area/Heeling >1.3 19.47 5.23 1.66 3.30 Moment Area Positive Moment Arm from 0 to downflooding or 2nd intercept 1st intercept to 2nd intercept or downflooding Maximum Righting Moment Arm/Heeling Moment Arm Yes Yes Yes Yes Yes >7 N/A 33.50 7.54 9.91 >2 N/A 18.31 6.82 9.27 Local and Global Loading Local and global loads acting on the structure include weight, buoyancy, and pressure. The effect of these loads on the structure is determined using the finite element program Visual Analysis. The weight of the structure and the buoyancy of the pontoons and columns are treated as dead (static) loads. Weights are applied using uniform line loads for beam elements and as uniform pressures for the topside. In order to investigate the squeeze and pry effects that result from wave loading a static analysis is performed simulating a wave passing through the structure. One analysis considers the loading that occurs when the wave troughs are at the columns and the crest is at the middle of the deck. The second case considers wave crests at the columns and the trough at the middle of the deck. General Strength and Structural Design A structural analysis is performed using Visual Analysis. The columns, pontoons, and nodes are represented by beam bending elements while the topside is represented by a rigid plate. The objective is to determine the maximum stresses and where they occur. The minimum and maximum stresses as well as the maximum deflection for the still water, squeeze, and pry cases are shown in Table 3. The combined stresses for each case are less than the maximum combined TAMU Team Gulf of Mexico x Final Report

stress of 37 ksi required by ABS. In addition, ABS criteria are investigated and met for minimum thickness requirements to support the hoop stresses caused by water pressure. Environmental Loading Table 3 - Maximum and Minimum Calculated Combined Stresses and Deflections Operating Squeeze Pry σ max 11.9 15.6 16.6 ksi σ min -20-25 -27.2 ksi deflection 1.41 3.27 4.21 inches One of the most important parts of the design process is having a thorough understanding of the environment in which the designed structure is operating. As a result, there are three main environmental factors considered in the iterative design process of the Gulf of Mexico Semi- Submersible. These three factors, wind, wave and current loads are computed based on preliminary structural dimensions. Specifically, using AutoCad plan and profile drawings of a given topside arrangement with drilling capability and Solidworks renderings of the primary hull design, exposed surface areas were calculated and used to compute the appropriate environmental loadings. The environmental loads that result from a 100 year hurricane are shown in Table 4. Table 4- Environmental Loads for a 100 Year Hurricane Type of Load Bow Beam Quartering Wind (kips) 1462.3 1258.7 1814 Current (kips) 627.1 627.1 836.2 Wave (kips) 81.1 92.9 115.9 Total (kips) 2170.5 1978.7 2766.1 Each environmental loading is considered on a local and global scale in order to maximize design form and function. A perfect example of the applied considerations can be seen in the column design where square columns were implemented instead of circular columns. TAMU Team Gulf of Mexico xi Final Report

Mooring and Station Keeping Mooring analysis was performed using G-Moor. Testing is performed to determine safety factors, offsets, and line tensions. The optimal design meeting all requirements, both API and industry, is a 12 leg taut system using 10.27 inch polyester rope and 7 inch chain with 10 degree spacing between each line. This system is capable of moving within a 150 ft circle under operational conditions and withstanding the violent conditions of a 100 year hurricane with intact and damaged factors of safety of 1.73 and 1.26, respectively. The anchors used for the mooring system are 416.33 kip suction piles. The piles are 95 feet long with an outer diameter of 216 inches and a wall thickness of 1.65 inches. Hydrodynamics of Motions and Loading The heave and roll natural periods of the vessel are 23.86 and 42.65 seconds, respectively. These natural periods are higher than the 10 to 20 second range in which the majority of the wave energy exists in a 100 year hurricane. This indicates that the vessel s response will be relatively low. The heave and roll motions are calculated using RAOs supplied by Intermoor and are shown in Table 5. The RAOs supplied were calculated for a semi submersible with similar dimensions to the design presented in this report. Table 5- Vessel Response Heave Motion (ft) Roll/Pitch Motion (deg) Significant Maximum Max Allowable Significant Maximum Max Allowable 10 yr Winter Storm ±1.90 ±3.53-0.11 0.21 4 100 yr Hurricane ±6.85 ±12.75 ±16.00 0.42 0.79 10 Cost Analysis The cost of the final design is $225.8 million. This cost includes the cost of the hull and the cost of the mooring system. The final design cost does not include the cost of the risers, the topsides, the drilling unit, transportation to the drilling site, integration and hook-up at the drilling site, and commissioning of the semi-submersible. TAMU Team Gulf of Mexico xii Final Report

The cost of the hull includes the engineering, procurement, and fabrication. The cost of the hull is based on the weight of steel, including structural weight of the hull. The overall cost of the hull is $195.2 million. The cost of the mooring system is based on the line components and number of lines used in the design, suction anchors, and on hull mooring equipment, such as, fairleads, chain jacks, stoppers, the hydraulic units, and the control systems. The overall cost of the 12 leg taut mooring design is $30.7 million. This yields an overall vessel cost of $225.8 million. TAMU Team Gulf of Mexico xiii Final Report

1 INTRODUCTION 1.1 Literature Review As the offshore oil and gas industry grew in the second half of the last century, there was a large surge in the development of offshore oil and gas production. This began by building fixed offshore structures, such as steel jacket platforms. However, as the industry ventured into deeper waters to produce oil and gas, floating structures became more economically feasible. The precursor to the semi-submersible oil and gas platform was the submersible platform. This type of platform utilized a barge which supported the production facilities. The vessel was towed to the proper location and the barge was ballasted down until it rested on the ocean floor. These platforms were extremely useful in that after exhausting a well, the barge could be ballasted up and the vessel moved to the next location. However, they were limited by the water depths that they could hold the production facilities above water [1]. Early semi-submersibles were conversions of submersible platforms into permanently floating structures. The first true semi-submersible was the Blue Water Rig No. 1, which was converted in 1961 [2]. At first, semisubmersible platforms were used for only drilling purposes. However, at the end of the century semis were used for production as well as drilling. The first semi-submersible floating production system was the Hamilton Brothers Transworld 58, which was converted from a drilling unit to serve in the North Sea in 1975. After a period with few semi-submersibles built for the Gulf of Mexico, there has been recent upswing in new constructions. These include Shell Oil s NaKika (2003), BP s Thunder Horse (2005), BP s Atlantis (2006), and Independence Hub (under construction) [3]. Semi-submersibles have several advantages that make them desirable to the oil and gas industry. Firstly, they display low wave driven motions due to their small water plane areas. The columns and pontoons often contain ballast tanks that can be used to alter the draft as necessary to adjust for weather conditions. Also, semis are relatively easy to move, making them excellent vessels for drilling operations. 1.2 Objective The purpose of this project is to perform basic design of a semi-submersible production platform with drilling facilities, capable of producing 120,000 barrels of oil and 10,000,000 cubic feet of gas per day. This vessel will operate in the Gulf of Mexico in 5500 feet water depth. The extent of this project is the basic design of the vessel s hull and mooring system, which must meet API and ABS regulations. 1.3 Industry Day Industry day was held at the ConocoPhillips headquarters in Houston, Texas on February 9, 2007. Its purpose was to inform the senior design class of various topics relevant to the design, transportation, installation, and operation of a semi-submersible production facility. The topics presented were as follows: FPU Project Drivers by Patrick Kelly, BP Class of FPUs by Bob Harvie, Lloyd s Register Topsides Considerations by Leonard Simek, Mustang Engineering Riser Types and Construction by C. Loper, Wellstream Hull Construction by Mike Holcomb, Keppel Offshore Marine Hull Transportation by Jan Wolter Oosterhuis, Dockwise Industry day was extremely informative and helped the 2007 senior design class gain a better understanding of the principles of designing a semi-submersible production platform. The Gulf of Mexico team would like to thank the various members of industry for sharing their knowledge and ConocoPhillips for hosting the event. The Gulf of Mexico team would also like to thank Rod King with Lloyd s Register for arranging the schedule for industry day. TAMU Team Gulf of Mexico 1 Final Report

1.4 Environment The semi-submersible being designed is located in the Gulf of Mexico in a water depth of 5500 feet. Metocean data has been provided by Intermoor and Houston Offshore Engineering. The weather conditions in this region are generally mild with the exception of winter storms, hurricanes, and loop currents. Consideration of loop currents was not required in the design criteria; however, recent major hurricanes such as Ivan (2004), Katrina (2005) and Rita (2005) have driven an increase in the design wind speed and wave height during a hurricane event. This fact is important to the design in that the vessel must be able to operate in a 10 year winter storm and must survive a 100 year hurricane. The metocean conditions corresponding to both events are shown below in Table 6. The 100 year hurricane metocean design criteria shown match those recommended in API RP 95F, which was written in response to recent hurricane activity in the Gulf of Mexico [4]. Table 6- Maximum Operational and Survival Environmental Data Condition Max Operating Survival Environmental Component 10 Year Winter Storm 100 Year Hurricane Wind Speed, V w (1 hour mean at 10 m) 53.6 knots 93.3 knots Significant Wave Height, H s 28.9 ft. 48.9 ft. Maximum Wave Height, H max 54.9 ft. 92.9 ft. Peak Period, T p 12.3 sec. 14.9 sec. Current Surface Speed, V c 2.5 knots 3.4 knots 1.5 Design Criteria The hull design must meet the following requirements with minimum cost. Functional Requirements: The facility must produce 120,000 barrels of oil and 10 million standard cubic feet of gas per day. Drilling operations must be supported. Mooring must be active to access wells in a 150 ft diameter Constraints: 20 year design life Maximum heave of +/- 16 ft Maximum offset: o Intact: 5% of water depth o Damaged: 7% of water depth o Drilling: 2% of water depth Max combined pitch and roll: o Operating: 4 o Survival: 10 Minimum air gap: 5 ft 1.6 Gantt Chart In order to ensure that the Gulf of Mexico design team completed tasks on schedule, a Gantt chart was created, shown in Figure 1. It shows a timeline of when major tasks are to be finished and who is responsible for completing them. The major tasks are broken down into individual responsibilities as follows: Christopher Aurich - Loading Conditions and Cost Analysis Tyson Breedlove - Structural Analysis Eric Brown - Environmental Loads Sean Evans - Environmental Loads Ryan Koska - Vessel Stability Analysis and Motions Bryce Read - Graphics and Mooring Analysis TAMU Team Gulf of Mexico 2 Final Report

Figure 1- Gantt Chart TAMU Team Gulf of Mexico 3 Final Report

2 REGULATORY COMPLIANCE The vessel designed by this team must meet all American Bureau of Shipping (ABS) and American Petroleum Institute (API) guidelines [5]. This section outlines the regulations that apply to the design of a semisubmersible production platform with drilling capabilities. 2.1 General Arrangements The deck must have a crest clearance of 1.2 m (4 ft) or 10% of the combined storm tide, astronomical tide, and maximum wave crest above the mean low water level, whichever is less (ABS 3-2-3); Guardrails with a height of at least 1 m (39.5 in) must line the perimeter of all open decks, walkways, catwalks, and openings (ABS 3-8-17.3); and, Potential fuel sources must be separated from possible ignition sources by space separation, firewalls, or protective walls (ABS 3-3-5.1). 2.2 Storage and Slop Tanks Fuel storage tanks must be isolated from sources of vapor ignition and can not be located on landing areas; and, Crude storage tanks, slop tanks, and tanks storing flammable liquids with low flash points (less than 60 C) must be separated from sources of ignition by cofferdams at least 0.76 m (30 in) wide (ABS 3-3-5.7). 2.3 Accommodations Living quarters and other accommodation spaces must be located outside of hazardous areas; and They may not be located above or below crude oil storage tanks or process areas (ABS 3-3-5.3). 2.4 Spill Containment A coaming at least 150 mm (6 in) in height must surround fuel storage areas; 2.5 Fire Safety The following steps must be taken to reduce the risk of fires and subsequent damage (ABS 3-4-1): Bulkheads, linings, ceilings, and draft stop must be made of non-combustible material; Ventilation of accommodations and command centers are to be designed such that they prevent the ingress of flames or smoke from outside sources; Escape routes are to be readily accessible and exit doors must be operable from both sides; There must be at least two independent fire pumps (ABS 4-4-1); and, The fire main must be able to provide water to the two fire pumps at a rate of 616 gpm; 2.6 Lifesaving Appliances and Equipment A minimum of two means of escape from the facility are to be provided (ABS 3.2.2); and, The total capacity of lifeboats must be equal to twice the total number of people on the vessel (ABS 3-8- 15.5); 2.7 Flood Survival Requirements The maximum heel angle due to asymmetrical flooding should not exceed 30 (ABS 5-8-2-9.2). 2.8 Helicopter Deck The deck must support a minimum of 2010 N/m 2 (42 psf); Impact loading due to helicopter landings must be considered; and If the helipad is supported by a manned structure (quarters, control rooms, etc.) the impact loading is to be factored by 1.15. (ABS 3-2-2) TAMU Team Gulf of Mexico 4 Final Report

2.9 Environmental/Global Loading The minimum wind velocity for unrestricted offshore service for all normal drilling rigs should be no less than 70 knots. 2.10 General Structural Strength Allowable stress criteria: o σ max = σ y /F.S. (assume σ y = 55ksi) o Maximum combined stress (axial and bending): Static loadings: F.S. = 1.67, σ max = 33 ksi Combined loadings (static and environmental). F.S = 1.25 σ max =44 ksi o Dynamic Stress Ratio Must be less than 1.25 2.11 Thickness Requirement for Plating (ABS 3.2.2) Node: t > 0.56 inches Lower Column: t > 0.47 inches Middle Column: t > 0.42 inches Upper Column: t > 0.37 inches Pontoon: t > 0.54 inches 2.12 Mooring System Quasi-Static Pretensions: o 15 % to 20 % of the minimum break load at the fairleads Minimum Safety Factors: o Intact under dynamic loadings >= 1.67 o Damaged under dynamic loadings >= 1.25 Maximum Offsets: o Intact under dynamic loadings <= 5 % of the water depth o Damaged under dynamic loading <= 7 % of the water depth Watch Circle Requirements o Operation within a 150 ft radial circle Corrosion Tolerances: o Line within the splash zone should be increased by 0.25 in o Remaining line length should be increased by 0.125 in 2.13 Stability The following stability requirements must be satisfied: Intact Stability Requirements: For column-stabilized units, the area under the righting moment curve at or before the second intercept angle or the down flooding angle, whichever is less, is to reach a value of not less than 30% in excess of the area under the overturning moment curve to the same limiting angle. (ABS 3.3.1) Damage Assumptions: Damage is assumed to occur on the exposed outer portions of the columns on the periphery of the vessel; Damage is assumed to occur over a vertical distance of 3 m (10 ft) at any point between 5 m (16.4 ft) above and 3 m below the draft being analyzed. If this damage occurs at the meeting of two floodable compartments, both compartments are to be considered damaged; and TAMU Team Gulf of Mexico 5 Final Report

Damage to columns is assumed to penetrate a depth of 1.5 m (5 ft) horizontally. (ABS 3-3-1) Damage Stability Requirements: The righting moment curve is to have a minimum range between the first and second intercept of 7 degrees; and The righting moment curve is to reach a value of at least twice the heeling moment curve. (ABS 3-3-1) 3 GENERAL ARRANGEMENT AND HULL DESIGN During the design of the semi-submersible production platform, two different configurations were considered. The alternatives were analyzed and the better of the two was chosen as the team s final design. The two designs are discussed below. 3.1 Option One The first preliminary design considered by the Gulf of Mexico group is a four column semi-submersible with a ring pontoon. The pontoon and columns have rectangular cross-sections and have dimensions as shown in Table 7. Note that the column height does not include the height of the pontoons. The columns are spaced 220 feet apart, center to center. Both the columns and pontoons are made of steel with a 1 inch equivalent thickness. A diagram of this design can be seen in Figure 2. Table 7- Square Column Hull Dimensions, Preliminary Design Length (ft) Width (ft) Height (ft) Columns 56 56 112 Pontoons 276 56 50 Figure 2- Square Column Semi-submersible Layout 3.2 Option Two The second preliminary design considered by the Gulf of Mexico group is a four column semi-submersible with a ring pontoon. The pontoon and columns have circular cross-sections and have dimensions as shown in Table 8. Note that the column height does not include the height of the pontoons. The columns are spaced 220 feet apart, TAMU Team Gulf of Mexico 6 Final Report

center to center. The pontoons and columns are made of 1 inch equivalent thick steel. A diagram of this design can be seen in Figure 3. Table 8- Circular Column Hull Dimensions, Preliminary Design Length (ft) Width or Diameter (ft) Height (ft) Columns - 60 100 Pontoons 280 60 50 3.3 Selected Design Figure 3- Circular Column Semi-submersible Layout The two alternate preliminary designs were sized such that they satisfy all stability requirements and have heave natural periods of at least 20 seconds. This was done with the assumption that the mooring system is the same for both configurations, and thus the weight of the deck, risers, umbilicals, and mooring lines for both models are equal. The hulls were split into floodable compartments using the same method. A table comparing the hull weight, heave natural periods, and metacentric heights of both designs is shown in Table 9. It should be noted that these weights only include the structural steel for the columns and pontoons. In addition, a comparison of the environmental loads on each preliminary design is shown in Table 10. The tables show that the weight, natural period, and environmental forces are similar for both vessels. However, the metacentric height for the square column hull is more than 3 ft higher than that of the circular column vessel. In addition, circular columns are more difficult to manufacture than square columns. These factors led to the decision to choose the square column configuration as the selected design. Table 9- Hull Weight and Natural Period Comparison for Preliminary Designs Square Columns Circular Columns Weight (kips) 11188.3 10383.1 Natural Period (s) 23.93 25.32 GM (ft) 15.51 12.29 Table 10- Comparison of Environmental Loads for Preliminary Designs Square Columns Circular Columns Total Bow Force (kips) 2016.8 1898.8 Total Beam Force (kips) 1827.2 1704.8 Total Quartering Force (kips) 2562.7 2402.4 In order to meet all design requirements, the square column design is optimized. The final dimensions of the hull are shown below in Table 11. A layout drawing of this design is shown in Figure 4. TAMU Team Gulf of Mexico 7 Final Report

Table 11- Square Column Hull Dimensions, Final Design Length (ft) Width (ft) Height (ft) Columns 53 53 90 Pontoons 273 53 50 Figure 4- Final Design Layout 3.4 Transport and Operational Design Cases There are four distinct vessel configurations that exist during its design life. First, the hull is built in Korea and then transported to the Gulf of Mexico via a semi-submersible transport vessel. This configuration includes only the hull with empty ballast tanks and is referred to as the hull transport case. The hull is mated with the topsides in a port in the Gulf of Mexico and then the vessel is towed to location. This configuration consists of only the hull and topsides with empty ballast tanks. During normal operation, the permanent ballast tanks are filled (see Figure 10) and production takes place. During survival conditions, the vessel is evacuated, the drilling riser is pulled, and production is halted. In order to compensate for the loss of weight, the secondary ballast tanks are filled. 3.5 Lifeboats There must be enough lifeboats to accommodate at least twice the number of people on the vessel (ABS 3-8-15.5). The quarters on this vessel will house approximately 60 people. Thus, a total lifeboat capacity for 120 people is needed. TAMU Team Gulf of Mexico 8 Final Report

4 WEIGHT, BUOYANCY, AND STABILITY The weight, buoyancy, and stability characteristics of the selected vessel configuration are analyzed for four cases that exist during the life of the vessel. 4.1 Weight Calculations In order to analyze the stability and cost of the vessel, the total weight and the center of gravity must be calculated. The weight, location, and center of gravity characteristics of the deck as well as production and drilling facilities were supplied by Houston Offshore Engineering (HOE). HOE also provided the weights of the SCRs and umbilicals. A table of all weights and locations of vessel components is shown in Table 12. Each of the components is marked with a symbol (*** for example). The weights for each vessel condition, shown at the bottom of the table, use these symbols to indicate which components are used to calculate the vessel weight. Table 12- Weights and Centers of Gravity of Various Vessel Components ITEM W(air) LCG L-MOM TCG T-MOM VCG V-MOM (kips) (ft) (lb-ft) (ft) (lb-ft) (ft) (lb-ft) SCR - production riser (***) 535.00-10.00-5350 15.00 8025 140.00 18725 SCR - production riser (***) 550.00 10.00 5500 15.00 8250 140.00 19250 SCR - production riser (***) 355.00 15.00 5325 10.00 3550 140.00 12425 SCR - production riser (***) 365.00 15.00 5475-10.00-3650 140.00 12775 SCR - water injection riser (***) 855.00 10.00 8550-15.00-12825 140.00 29925 SCR - oil export riser (***) 680.00-15.00-10200 -10.00-6800 140.00 23800 SCR - gas export riser (***) 90.00-15.00-1350 10.00 900 140.00 3150 Umbilical (***) 120.00 10.00 1200 15.00 1800 140.00 4200 Deck primary+secondary steel weight (**) 10900.00 0.00 0 0.00 0 172.50 27250 Drilling Rig Weight (Operating) (") 9200.00 0.00 0 0.00 0 172.50 23000 Drilling Rig Weight (Dry) (**) 5401.00 0.00 0 0.00 0 172.50 13503 Facility & quarters weights (Operating) (") 17030.00 0.00 0 0.00 0 172.50 42575 Facility & quarters weights (Dry) (**) 13227.00 0.00 0 0.00 0 172.50 33068 Futures (***) 2000.00 0.00 0 0.00 0 151.67 46667 Company Reserve (**) 1000.00 0.00 0 0.00 0 151.67 23333 Diesel storage in hull (500 bbl.s)(not incl. in total system payload) (**) 126.00 80.00 10080-80.00-10080 130.00 5670 Hull Shell Steel (Appurtenances and Marine 13561.92 Systems - 35%) (*) 0.00 0 0.00 0 46.68 1740251 Column Structure Weight (*) 8089.92 0.00 0 0.00 0 95.00 647194 Pontoon Structure Weight (*) 17702.00 0.00 0 0.00 0 25.00 2655300 Node Structure Weight (*) 6741.60 0.00 0 0.00 0 25.00 1011240 Ballast Tank 1 (***) 4242.28-50.63-214765 110.00 466650 21.80 649934 Ballast Tank 2 (***) 4236.46-16.88-71490 110.00 466011 21.77 649170 Ballast Tank 3 (***) 4230.48 16.88 71389 110.00 465352 21.74 648383 Ballast Tank 4 (***) 4224.49 50.63 213865 110.00 464694 21.70 647595 Ballast Tank 5 (***) 4207.65 110.00 462842 50.63 213012 21.62 645378 Ballast Tank 6(***) 4204.62 110.00 462508 16.88 70953 21.60 644978 Ballast Tank 7 (***) 4201.23 110.00 462136-16.88-70896 21.58 644532 Ballast Tank 8 (***) 4197.85 110.00 461763-50.63-212516 21.57 644086 Ballast Tank 9 (***) 4202.27 50.63 212740-110.00-462250 21.59 644669 TAMU Team Gulf of Mexico 9 Final Report

Table 12- Weights and Centers of Gravity of Various Vessel Components (Continued) ITEM W(air) LCG L-MOM TCG T-MOM VCG V-MOM (kips) (ft) (lb-ft) (ft) (lb-ft) (ft) (lb-ft) Ballast Tank 10 (***) 4208.41 16.88 71017-110.00-462925 21.62 645479 Ballast Tank 11 (***) 4214.40-16.88-71118 -110.00-463584 21.65 646267 Ballast Tank 12 (***) 4220.39-50.63-213657 -110.00-464243 21.68 647056 Ballast Tank 13 (***) 4236.87-110.00-466056 -50.63-214492 21.77 649224 Ballast Tank 14 (***) 4240.26-110.00-466429 -16.88-71554 21.79 649669 Ballast Tank 15 (***) 4243.64-110.00-466801 16.88 71611 21.80 650114 Ballast Tank 16 (***) 4247.03-110.00-467173 50.63 215006 21.82 650559 Ballast (Survival) (****) 8564.02 0.00 0 0.00 0 46.82 1097734 Stored Chain (Vessel Centered) (***) 915.00 0.00 0 0.00 0 9.84 151118 Mooring, 3 legs (***) 2212.71 136.50 302035 136.50 302035 9.84 365444 Mooring, 3 legs (***) 2212.71 136.50 302035-136.50-302035 9.84 365444 Mooring, 3 legs (***) 2212.71-136.50-302035 136.50 302035 9.84 365444 Mooring, 3 legs (***) 2212.71-136.50-302035 -136.50-302035 9.84 365444 Total Weight Hull Dry (kips) (*) 46095 0.00 0 0.00 0 43.66 6053985 Total Weight Hull& Rig Dry (kips) (*+**) 76749 0.13 10080-0.13-10080 94.78 6156808 Total Operating (kips) (*+***+") 167226 0.00 0 0.00 0 65.47 18316719 Total Survival (kips) (all, except for ") 168188 0.00 0 0.00 0 59.68 19395449 Several guidelines were provided by HOE on the estimation of the hull weight. These are as follows: Structural Weight Estimate: o 8-9 pcf for columns o 12-14 pcf for nodes o 10-12 pcf for pontoons Appurtenances and Outfitting Weight Estimate: o 30% of hull structural weight Marine Systems Weight Estimate: o 5% of hull structural weight In order to keep the center of gravity as close to the z axis as possible and to achieve the needed drafts, ballast tanks were added to the vessel s pontoons. These tanks were split into two vertical sections, the bottom of which remains filled during the life of the vessel after installation and the top of which is filled in order to ballast down during extreme storm conditions. The dimensions of the primary ballast tanks are displayed in Table 13 and their layout is shown in Figure 5. Also shown are the secondary ballast tanks, which have the same width and length as the primary tanks, but are 5.5 feet tall. In order to satisfy stability and natural period requirements, the primary ballast tanks were filled to the levels shown in Table 14. In addition, the secondary ballast tanks are capable of offsetting a shift in the topsides center of gravity of up to 7.8 ft. The vessel s center of gravity is calculated with the following equations using the axis convention shown in Figure 6. Table 13- Primary Ballast Tank Dimensions Width 45 ft Height 44 ft Length 33.75 ft TAMU Team Gulf of Mexico 10 Final Report

Figure 5- Ballast Tank Layout Table 14- Ballast Tank Fullness (Primary Tanks) Tank 1 99.07 Tank 2 98.94 Tank 3 98.80 Tank 4 98.66 Tank 5 98.26 Tank 6 98.19 Tank 7 98.11 Tank 8 98.03 Tank 9 98.14 Tank 10 98.28 Tank 11 98.42 Tank 12 98.56 Tank 13 98.95 Tank 14 99.02 Tank 15 99.10 Tank 16 99.18 LCG = TCG = VCG = n i= 1 n i= 1 n i= 1 n i= 1 n i= 1 n i= 1 Wx i W i i Wy W i i Wz W i i i i (1) (2) (3) TAMU Team Gulf of Mexico 11 Final Report

Y X Figure 6- Center of Gravity Calculation Axis Convention The centers of gravity and buoyancy, as well as the metacentric heights for the four cases are shown in Table 15. Table 15- Vessel Weight and Buoyancy Characteristics Condition Draft (ft) LCB (ft) TCB (ft) VCB (ft) LCG (ft) TCG (ft) VCG (ft) GM (ft) Hull Transport 15.44 0.00 0.00 7.72 0.00 0.00 43.66 516.74 Vessel Towing 25.71 0.00 0.00 12.86 0.13-0.13 94.78 250.01 Operation 75.00 0.00 0.00 29.03 0.00 0.00 65.47 16.60 Survival 76.34 0.00 0.00 29.30 0.00 0.00 59.68 22.35 4.2 Buoyancy Calculations The total weight of the vessel is used to find its draft. This is done by calculating the volume of water that is displaced due to the weight of the vessel. For the hull transport and towing cases, it is assumed that the pontoons are not fully submerged. Thus the draft is found by dividing the displacement in cubic feet by the cross sectional area of the pontoons. The resulting draft is compared to the height of the pontoons in order to test the assumption that they are not fully submerged. For the operating case, the total volume of the pontoons is subtracted from the volume of water displaced, resulting in the volume of water that the columns displace. This volume is divided by the total cross sectional area of all four columns, which results in the height of the columns that are submerged. This height is added to the height of the pontoons in order to obtain the draft of the vessel. The weights, drafts, and air gaps for all cases are shown below in Table 16. It should be noted that the survival air gap is slightly lower than that of the operating condition. This is due to the fact that the secondary ballast tanks are completely filled in order to reduce tank sloshing and free surface effects on stability. This slightly overcompensates for the loss in vessel weight due to evacuation and the halting of production and drilling. This results in a reduction in the air gap of 1.34 ft. While this conflicts with the general concept that vessels would increase their air gaps during more severe weather, the survival air gap of 63.66 ft greatly exceeds the minimum required air gap of 51.65 ft. TAMU Team Gulf of Mexico 12 Final Report

Table 16- Vessels Weights, Drafts, and Air Gaps Hull Transport Towing Operating Survival Weight (kips) 46095 76749 167226 168188 Weight (L. tons) 20578 34263 74654 75084 Volume Displaced (ft 3 ) 720241 1199210 2612900 2627932 Draft (ft) 15.44 25.71 75.00 76.34 Air Gap (ft) N/A 114.29 65.00 63.66 4.3 Stability The stability of the vessel was analyzed with the computer software StabCad, using the center of gravity and draft information found in the weight and buoyancy calculations as input [6]. The StabCad model used in the stability analysis is shown in Figure 8. Both intact and damaged stability are considered as well as several special cases that exist before installation. The wind was applied in the direction that created the largest heeling moment arms. The resulting wind direction causes the vessel to heel about an axis 42 degrees from the x axis as shown in Figure 7. Wind Direction 42 Column 4 Y Column 1 X Column 3 Column 2 Figure 7- Yaw Angle of Heel Axis 4.3.1 Intact Stability StabCad is used to perform an intact stability analysis using the center of gravity and draft found using the weight calculation spreadsheet. Downflooding points are applied to the tops of the columns to simulate air vents. The program input and output can be found in Appendix B. The displacement calculated by the program is 96277.1 short tons and the downflooding angle is 22.92 degrees which is controlled by column 2. The center of buoyancy at the design draft of 75.00 feet is located at the center of the column arrangement, 29.03 feet above the keel. The metacenter is located 16.60 feet above the center of gravity. TAMU Team Gulf of Mexico 13 Final Report

Figure 8- Square Column StabCad Model According to ABS regulations the area under the righting moment curve at or before the second intercept angle or the downflooding angle, whichever is less, is to reach a value of not less than 30% in excess of the area under the overturning moment curve to the same limiting angle. In addition, the righting arm must remain positive between zero degrees and the downflooding angle. A plot of the righting and heeling moment arms, as output from StabCad, is shown in Figure 9. The area under the righting arm is approximately 66% larger than the area under the heeling arm. This combined with the fact that the righting arm is positive between zero degrees and the downflooding angle means that all intact stability requirements are met. Figure 9- Operating Intact Stability Plot TAMU Team Gulf of Mexico 14 Final Report

4.3.2 Damaged Stability StabCad is also used to perform a damaged stability analysis using the same center of gravity, draft, and downflooding points that were used for the intact stability analysis. The primary and secondary floodable compartments used for the columns and pontoons are shown below in Figure 10. ABS regulations specify that the angle between the first intercept of the righting and heeling moment arms and the second intercept or downflooding angle, whichever is less, must be at least 7 degrees. In addition, the righting arm must be a minimum of twice the heeling arm at, or before the downflooding angle. The plot of righting and heeling arms shows that the angle between their intersection and the downflooding angle is 7.54 degrees. The righting arm at the downflooding angle of 19 degrees is 4.64 feet, while the heeling arm is 0.68 feet, yielding a righting arm to heeling arm ratio of 6.82. This shows that all damaged stability requirements are met by this hull design. Figure 10- Floodable Compartments 7.54 Figure 11- Operating Damaged Stability Plot TAMU Team Gulf of Mexico 15 Final Report

4.3.3 Special Cases Stability analyses were performed for three special cases that occur during the design life of the vessel. First, the hull transport case is analyzed. A damaged stability analysis is not performed for this case due to the assumption that damage does not occur during the process and that the hull is tested for leaks before transporting it. A plot of the righting and heeling moment arms for the intact stability analysis is shown in Figure 12. The numerical results from the analysis, shown in Table 17, confirm that the hull meets all intact stability requirements. In addition, the hull has a draft of 15.44 ft, which satisfies the restriction that in order to load it on the semi-submersible transport ship its draft must be less than 29.53 ft (9 m). The center of gravity of the hull is located 43.66 ft above the keel. The second special case is the towing of the vessel to the operating location. In this condition, the vessel has a draft of 25.71 ft and a center of gravity 94.78 ft above the keel. Due to possibility of damage during this process, both intact and damaged stability analyses are performed for this case. Plots of the righting and heeling moment arm curves for intact and damaged stability are shown in Figure 13 and Figure 14, respectively. The numerical results are displayed in Table 17 and confirm that all stability requirements are met for this case. Finally, the vessel s intact and damaged stability is analyzed for the survival condition. In this configuration, the vessel has a draft of 76.34 ft and a center of gravity 59.68 ft above the keel. Plots showing the righting and heeling arm for both the intact and damaged stability analyses can be seen in Figure 15 and Figure 16. The fact that all stability requirements are met is shown by the numerical results displayed in Table 17. Intact Damaged Table 17- Stability Results, Special Cases Criteria Requirement Hull Transport Towing Survival Righting Moment Area/Heeling Moment Area >1.3 16.39 4.48 3.30 Positive Moment Arm from 0 to downflooding or 2nd intercept Yes Yes Yes Yes 1st intercept to 2nd intercept or downflooding >7 N/A 43.19 9.91 Maximum Righting Moment Arm/Heeling Moment Arm >2 N/A 18.5 9.27 TAMU Team Gulf of Mexico 16 Final Report

Figure 12- Intact Stability Plot, Hull Transporting Case Figure 13- Intact Stability Plot, Towing Case TAMU Team Gulf of Mexico 17 Final Report

Figure 14- Damaged Stability Plot, Towing Case Figure 15- Intact Stability Plot, Survival Case TAMU Team Gulf of Mexico 18 Final Report

Figure 16- Damaged Stability Plot, Survival Case Another method of confirming that the stability requirements are met for all cases is to compare the center of gravity with the allowable KG. The allowable KG is the maximum vertical center of gravity which gives the following results: Area under righting arm = 1.3* Area under heeling arm Range of stability from 1 st intercept to downflooding angle or 2 nd intercept = 7 If the vertical center of gravity of the vessel is less than the lowest allowable KG, then the vessel satisfies all stability requirements. This is the case with the semi-submersible design, as shown in Table 18. Table 18- Allowable and Actual KG Comparison Allowable KG (ft) Intact Damaged Actual KG (ft) Hull Transport 501.37 N/A 43.66 Towing 265.00 154.69 94.78 Operating 70.46 66.56 65.47 Survival 78.76 66.09 59.68 TAMU Team Gulf of Mexico 19 Final Report

5 LOCAL AND GLOBAL LOADING 5.1 Introduction Many different types of loadings act on the structure over its design life. It is important to estimate these loads on the structure and apply them to a structural model appropriately. For preliminary design, the loads are simplified as much as possible. Therefore, the loading conditions for still water operating conditions and for the worse case scenario of squeeze and pry are investigated. The most critical stresses are due to loads caused by the squeeze and pry conditions. In each condition, the loads on the structure can be classified into three categories: Load Categories: 1. Weights a. Steel b. Internal (equipment, etc.) c. Ballast tanks 2. Buoyancy a. On Columns b. On Pontoons 3. Pressure differential. a. On Pontoons b. On Columns c. Across columns (for squeeze-pry condition). For the still water condition, all loads are static. For the squeeze pry condition, buoyancy loads and pressure differentials are dynamic. There are also three loading conditions that are being considered. Load Conditions: 1. Still Water a. All loads are static 2. Squeeze a. Buoyancy is dynamic b. Pressure differentials exist across columns 3. Pry a. Buoyancy is dynamic b. Pressure differentials exist across columns The first loading condition considered is the structure in still water. This is defined by ABS as a static load case, since it does not include any environmental loads such as wave loadings. Then the squeeze and pry loading conditions are tested. This constitutes the worst case scenario due to environmental conditions. The squeeze and pry conditions are environmental loading cases in which a large wave propagates through the structure, causing the stresses to be magnified. The squeeze-pry condition is explained in more detail in section 5.3.1. 5.2 Calculation and Application of Static Loads Static loads are defined as loads that do not change with time and are at rest. Weight is the most definite static load. Buoyancy is treated as quasi-static load in the still water condition. However, during the squeeze and pry conditions, the buoyancy is no longer constant and must be recalculated. TAMU Team Gulf of Mexico 20 Final Report

5.2.1 Application of Weight Loading The dead loads in the structure include the weights of the steel, equipment, ballast tanks, and topsides. The equipment weights in the pontoons, nodes and columns are estimated based on estimates used by Houston Offshore Engineering (HOE) and are calculated on a volumetric basis as follows (A diagram defining each component is shown in Figure 17): 8-9 lbs/ft 3 for columns. 12-14 lbs/ft 3 for pontoons. 10-12 lbs/ft 3 for nodes. Column Node Pontoon Figure 17- Basic Hull Component Definition This procedure for estimating the weights of the equipment is widely used within industry. Since the ballast tanks are located in the pontoons, their weights are added to the total weight of the ballast tanks. The internal weight of the topside includes the weights of the quarters, equipment, risers, drilling rig, and allowances for future equipment. The resulting weights within each structural component are as follows: Table 19- Weights of Major Structural Components Column Pontoon Node Topside W steel (kips) 12290 25275 8530 10900 W internal (kips) 1041-8851 32780 W Ballast (kips) - 67558 - - W total (kips) 13331 92834 17380 43680 %W structure 8% 56% 10% 26% W structure (kips) 167226 In the structural model, columns, pontoons and nodes are treated as beam elements, and the deck is treated as a rigid plate. This is a fairly accurate representation of the structure, with most errors occurring at the joints. TAMU Team Gulf of Mexico 21 Final Report

The first issue to address is how weights are applied to the structural model. For the columns, pontoons and beams, the loads are applied as line loads with magnitude w. The value of w is calculated according to equations (4) through (7). For the topside, the weight is distributed as a uniform pressure, w topside, over the surface of the topside. Values for w are shown in Table 20. These loads are constant throughout the analysis and are applied to the structural model as shown in Figure 18. w w W node node = (4) Lnode W pontoon pontoon = (5) Lpontoon w w W column column = (6) Lcolumn W topside topside = (7) Atopside Table 20- Applied Weight Loadings, Operating Condition w topside w node w column w pontoon w buoyancy 0.9 kips/ft 86.9 kips/ft 34.1 kips/ft 105.5 kips/ft 128.7 kips/ft Figure 18- Applied Weight Loading TAMU Team Gulf of Mexico 22 Final Report

5.2.2 Application of Buoyancy Loading Buoyancy loads are needed to balance the weight of the structure. The condition for a floating structure is that the buoyancy equals the total weight of the structure. The buoyancy acting on the column is calculated by multiplying the volume of the column by the specific weight of the water. This buoyancy load on the columns is applied as a single concentrated load at the bottom of each column. Since the column width and breadth are constant at 53 ft, the buoyancy in the columns becomes only a function of the draft, T. For the still water condition, the draft does not vary and therefore the buoyancy in the column is constant. However, for the squeeze and pry cases the drafts are varying due to the wave. Therefore, the buoyancy in the columns is not constant. This buoyancy load on the pontoon is applied as a uniform line load acting over the distance of pontoon with magnitude b pontoon. Using equation (10) the buoyancy of the pontoon is solved for as shown in equation (11). Values for the buoyancy loads are shown in Table 21. The application of these loads on the structure is shown in Figure 19. Buoyancy = W total (8) Bcolumn = columnγ water = 2809Tγ water (9) 4bpontoonLpontoon + 4Bcolumn = Wtotal (10) 4Bcolumn Wtotal bpontoon = 4L (11) pontoon Table 21 - Applied Buoyancy Loadings, Operating Condition b pontoon 128.7 k/ft B column 13483.2 k Figure 19- Applied Buoyancy Loading TAMU Team Gulf of Mexico 23 Final Report

5.3 Calculation and Application of Live Loads Live loads are dynamic loads that the structure experiences in its operating condition over the course of its design life. The biggest source of live loads is waves. As a wave passes through the structure, it creates a wave induced dynamic pressure, P d, as well as causing the draft to vary. Since the buoyancy is a function of the displaced volume, the buoyancy in the columns varies. Therefore, the live loads being considered are as follows: 1. Buoyancy in Columns, B column. 2. Force due to wave induced dynamic pressures across the columns. These dynamic forces cause bending stresses and hoop stresses to be magnified. The worst case scenarios for wave loadings are the squeeze and pry conditions. 5.3.1 Squeeze and Pry Conditions Imagine a wave with a wavelength equal to the diagonal of the structure as shown in Figure 20. For a wave of this wavelength, the crest of the wave is in the center while the trough is on the outer corners, and vice versa. This causes a squeezing and prying of the columns. The squeeze condition is when the wave trough is in the center of the pontoon and the columns are pulled inward, as shown in Figure 21. The pry condition is when the wave crest is in the center of the structure and the columns are pulled outward, as shown in Figure 22. Figure 20 - Wave Direction and Wave Length for Squeeze/Pry TAMU Team Gulf of Mexico 24 Final Report

Figure 21- Squeeze Wave Loading Condition Figure 22- Pry Wave Loading Condition Figure 23 - Pressure Differential across Column for Squeeze Case TAMU Team Gulf of Mexico 25 Final Report

Figure 24 - Pressure Differential across Column for Pry Case λwh cosh( d + z) P= λwz+ cos( kx ωt ) (12) 2 cosh( kd) P = P( z) P( z) (13) net 1 2 F = b P ( z) dz (14) net net z c zp net net ( z) dz = P z dz ( ) (15) The total force acting on the column due to the passing wave is calculated according to Equation (14) and the point of application, z c, is calculated according to Equation (15). Simpson s method is used to perform the numerical integration. The net force acting on the columns and the distance from the keel is shown in Table 22. Notice that, for the squeeze case, the net force is acting to push the columns inward, and is therefore inducing a moment into the pontoons. Further, for the pry case, the net force is acting to pull the columns outward. Yet, the force in the pry case is one order of magnitude less than that in the squeeze case. Table 22 - Net Forces and Points of Application for Squeeze-Pry Squeeze F net 13013 kips z c 26 ft Pry F net -1475 kips z c 27 ft TAMU Team Gulf of Mexico 26 Final Report

A wave propagating through the diagonal of the structure with a wavelength equal to the length between the diagonal causes a buoyancy differential in the columns, db. The force due to the buoyancy differential acts on the bottom of the columns, and is a function of the differential change of displaced volume, d. Since the cross section of the column is constant, the equation can be simplified as shown in equation (16). Therefore, the buoyancy from the pontoons remains constant, but the buoyancy from the columns varies. H db = d γwater = 2809 γwater (16) 2 Figure 25- Load Application of Squeeze Condition Figure 26- Load Application for Pry Case While the squeeze and pry conditions are important, they do not address dynamic hoop stresses in the columns and dynamic axial stresses in the pontoon. As observed in the squeeze and pry conditions, an oncoming wave also causes a pressure variation along the surface of the structure. The water pressure increases due to the wave passing through the structure. The pressure can be calculated according to equation (17) given below. This TAMU Team Gulf of Mexico 27 Final Report

pressure variation creates a time dependant hoop stress in the columns and a dynamic axial stress in the pontoons. These stresses are calculated and discussed in detail in section 6.4. = + = γη γ (17) kz P Phydro Pdyn e z Table 23 - Buoyancy Differentials for Squeeze-Pry B 8988.8 kips db 4494.4 kips 5.3.2 Hoop Stresses When a wave propagates through the structure, a dynamic component of the hoop stresses in the columns and the axial stresses in the pontoons is created. For this case, a 50 foot regular wave is used for the analysis. The hoop stress in the column is calculated according to Equation (18), and the axial stress in the pontoon is calculated according to Equation (20). The aspect ratio, α, is of importance and is calculated by Equation (21). Results for these stresses are tabulated in Section 5.7. AxP Axλ z σ column, static = = 2t 2t (18) AP x dyn σ column, dynamic = 2t (19) P λ( z2 z1) σ pontoon, static = = A A (20) σ dyn α = σ (21) static TAMU Team Gulf of Mexico 28 Final Report

6 GENERAL STRENGTH AND STRUCTURAL DESIGN The purpose of the structural analysis is to determine member stresses, identify stress concentrations, solve for deflections, and determine the plate thickness. Structural analysis is performed using the Visual Analysis software [7]. Visual Analysis uses a finite element method with cubic displacement functions to solve for deflections, stresses, and strains within a member. For this case, all structural members are represented as beam bending elements with 3 degrees of freedom at each node. Figure 27- Beam Bending Element Degrees of Freedom The structural model created in Visual Analysis is subsequently loaded with different load cases that are likely occur during the lifetime of the structure. The nature of these loads and how they are applied are discussed more in detail in Chapter 5. In addition, investigations are made into ABS requirements for the structure. These requirements include specifications for minimum thickness of plating and maximum/minimum bending stresses. 6.1 Approach The procedure for structural analysis is as follows: 1. Create a beam model of hull with simplified deck Determine section properties (E, A cs, I and S) using an equivalent thickness, t eqv. Determine boundary conditions. Vertical springs applied at bottom of node Horizontal springs applied at 16 feet above keel Simplify deck as rigid plate. 2. Perform hydrostatic analysis and record beam stresses. 3. Perform hydrodynamic analysis for regular wave. 4. Determine if ABS design criteria is met. 5. Compute dynamic stress ratio 6. Increase structural estimate in areas with high dynamic stress ratio (>1.25). Figure 28- Input and Output of Structural Analysis TAMU Team Gulf of Mexico 29 Final Report

6.2 Boundary Conditions Boundary conditions are needed to keep the model numerically stable. The boundary conditions for this model are the mooring lines for the vertical direction and a water plane spring for the horizontal direction. The mooring line springs are added at the fairleads, 16 feet above the keel. The stiffness of these springs is obtained through the force offset curves provided by GMOOR. The water plane stiffness is assumed to be the water plane stiffness (tons per inch immersion, TPI) divided by 100. The goal is to create a numerically stable but soft boundary condition (HOE). K = ( TPI)/100 (22) Table 24 - Boundary Conditions Stiffnesses 41 kips/ft k mooring k waterplane 410 kips/ft 6.3 Geometric Properties Figure 29 - Structural Model Boundary Conditions As indicated in Figure 28, the geometric properties of each structural member are essential for maintaining an accurate model. These properties are calculated in a spreadsheet and the results for each structural member are shown in Figure 29. The equations used to compute these values are shown below and the sign convention can be seen in Figure 30. It is important to understand the thickness being used is not the thickness of the outer layer of the steel but an equivalent thickness that includes the outer layer of the steel as well as the stiffeners. The method of computing this thickness is shown in Figure 31 and Equation (23). The stiffener spacing, s, is assumed using a typical value of 25 inches. TAMU Team Gulf of Mexico 30 Final Report

Figure 30- Cross Sectional (local) Sign Convention Figure 31- Plate with Stiffener t eqv A + A st+ A plate stiffener stiffener = = (23) s s 2 I ( 3 )/ z = b teqv b+ h 6 (24) I = h t b+ h (25) 2 (3 ) / 6 y eqv A = 2( b+ h) t (26) cs S S I eqv z z = (27) ymax I y y = (28) zmax Table 25- Geometric Properties of Major Structural Components Column Pontoon Node t 1 in t 1 in t 1 in Iz 1.72E+08 in 4 Iz 1.50E+08 in 4 Iz 1.72E+08 in 4 Iy 1.72E+08 in 4 Iy 1.64E+08 in 4 Iy 1.72E+08 in 4 Sz 5.39E+05 in 3 Sz 4.73E+05 in 3 Sz 5.39E+05 in 3 Sy 5.39E+05 in 3 Sy 5.47E+05 in 3 Sy 5.39E+05 in 3 A 2.54E+03 in 2 A 2.47E+03 in 2 A 2.54E+03 in 2 s 25 in s 25 in s 25 in TAMU Team Gulf of Mexico 31 Final Report

6.4 Allowable Stress Criteria The allowable stress criteria are defined as shown (ABS 3.2.2): Maximum combined stress (axial and bending): Static loadings (still water): F.S. = 1.67, σ max = 33 ksi Combined loadings (squeeze and pry): F.S = 1.25 σ max =44 ksi Dynamic Stress Ratio Must be less than 1.25 σ = σ y /F.S. (assume σ y = 55ksi) (29) It is important to understand how these stresses are being calculated in order to minimize them. The axial and bending stresses are calculated according to equation (30). Observation of this equation indicates that the stress is linearly proportional to the distance from the center axis (y,z) and inversely proportional to the cross sectional area, A x, and the moments of inertia, I y and I z. Therefore, by maximizing the cross sectional area and the moment of inertia the stress will be minimized. The hoop stress, σ z, is due to the hydrodynamic pressure, P. This pressure fluctuates when a wave propagates through the structure, adding a dynamic portion to the pressure. This, in turn, adds a dynamic stress. HOE recommends that dynamic stress ratio stays under 1.25. P M y M z x z y σ x = + (30) Ax Iz Iy AcsP Acsλz σ z = = (31) 2t 2t The combined axial and bending stresses for the still water case are calculated in Visual Analysis and shown in Figure 32 and Figure 33. The combined axial and bending stresses for the squeeze and pry conditions are shown in Figure 34 through Figure 37. For information on how squeeze and pry loads are calculated see Section 5.3.1. The hoop stresses are calculated in a spreadsheet and the results are listed in Table 26. For information on how the hoop stresses are calculated see Section 5.3.2. 6.4.1 Stress Results for Still Water Case The stresses through the columns and pontoons for the still water condition at a draft of 75 feet are shown in Figure 32 and Figure 33. The maximum and minimum stresses occur at the connection between the topside and the columns. Further, the stresses in the columns are 28 68 % greater than the stresses in the pontoons. The maximum deflection occurs at the top of the column and is found to be 1.41 inches. TAMU Team Gulf of Mexico 32 Final Report

Figure 32- Maximum Bending Stresses Figure 33- Minimum Bending Stresses TAMU Team Gulf of Mexico 33 Final Report

6.4.2 Stress Results for Squeeze Case For the squeeze case, the stresses in the columns and pontoons are greater than that of the still water case. This is due to the buoyancy differentials and the pressure differentials as explained in Section 5.3.1. Therefore, there are added loads acting on the structure. From Figure 34, notice that the maximum stress no longer occurs in the columns but in the pontoons. This is due to the moment that the pressure differential creates. Deflections are also greater than those in the still water case. The max deflection occurs at the top of the columns and is 3.27 inches. For the squeeze case, stresses are increased 25-30% and deflections are increased about 150%. Figure 34 - Maximum Combined Stress, Squeeze Condition Figure 35 - Minimum Combined Stress, Squeeze Condition TAMU Team Gulf of Mexico 34 Final Report

6.4.3 Stress Results for Pry Condition The pry condition represents the worse case scenario. Both maximum and minimum stresses are greater than those in the still water case by 25-36%. The maximum stresses occur in the pontoon rather than in the columns. However, the minimum stresses continue to occur in the columns. The deflection for this case is about 400% greater than the still water case, 4.17 inches. Figure 36 - Maximum Combined Stress, Pry Condition Figure 37 - Minimum Combined Stress, Pry Condition TAMU Team Gulf of Mexico 35 Final Report

6.4.4 Stress Results for Hoop Stresses As shown in Table 26, the greatest dynamic stress is occurring in the upper portion of the column. This is due to the relation between dynamic pressure of an oncoming wave and water depth. The dynamic component of pressure diminishes with depth. This results in a high dynamic stress ratio for the upper portion of the column. In this portion of the column, structural support will need to be increased. Table 26- Dynamic Stresses in Major Structural Components Design Head (ft) Dynamic Stress (ksi) Static Stress (ksi) Dynamic Stress Ratio Pontoon 92.67 2.64 9.91 0.27 Lower Column 74.67 5.83 15.53 0.38 Middle Column 56.81 6.26 10.09 0.62 Upper Column 39.11 6.73 4.7 1.43 6.4.5 Stress Results Summary In summary, the worst case scenario is for the pry condition. Table 27 shows that all the factors of safety are met for all cases. However, in further design, steps may need to be taken to decrease the maximum deflections. Table 27 - Maximum Stresses and Factors of Safety Operating Squeeze Pry σ y 55 55 55 ksi σ max 11.9 15.6 16.6 ksi FS 4.6 3.5 3.3 σ min -20-25 -27.2 ksi FS 2.8 2.2 2.0 deflection 1.41 3.27 4.21 inches 6.5 ABS Plating Criteria for Watertight Bulkheads ABS requires plating for a mobile offshore drilling vessel to meet a minimum thickness requirement that is a function of the aspect ratios, stiffener spacing, yield strength, and design head. The thickness of a water tight plate must not exceed: t = sk (qh) /525 + 0.06 in. (32) k = (3.075 α 2.077)/(α + 0.272) for 1 α 2 = 1.0 for α > 2 (33) This criterion was investigated in a spreadsheet and shown in Table 28. As seen, the thickness required does not exceed 1.00 inch at any location. Therefore, the design far exceeds the criteria. Table 28- Required Plate Thickness ABS Code, Plating (3-2-2) Node Lower Column Middle Column Upper Column Pontoon Design head, h (ft) 92.67 74.67 56.81 39.11 71.00 k (in) 1.00 0.99 0.99 0.99 1.00 Req'd plate thick (in) 0.40 0.36 0.32 0.28 0.40 Plate thickness used (in) 1.00 1.00 1.00 1.00 1.00 TAMU Team Gulf of Mexico 36 Final Report

7 ENVIRONMENTAL LOADING The analysis of the environmental loads on the production facility is an imperative step in the design process. Three important factors that are considered during this process are wind loads, wave loads, and current loads. Since the production facility is located in the Gulf of Mexico, it is not affected by swell waves. However, the Gulf of Mexico is highly prone to strong hurricanes that can easily reach strength of Category 5 with winds stronger than 135 knots. 7.1 Global and Local Effects As mentioned above, there are three factors considered in the semi-submersible design for the Gulf of Mexico. Each factor has a local and global effect on the semi-submersible which influences the design. Results from the local and global analysis have been implemented in the iterative design process in order to produce an effective and efficient semi-submersible. Global loads include the effect of a specific load on the entire assembly. Local load considerations are composed of load analyses on individual components that are directly affected by the corresponding load type. For example, the local analysis for wind loads concern the individual pieces of the topside and how they are affected independently. On a global effect, the wind loads can offset the whole structure while drilling and production is occurring creating loads on the mooring system. 7.2 Wind Loading 7.2.1 Global Effects Winds loads were calculated for three different faces of the structure: the bow (north face), the beam (east face), and the quarter (45 degree face). The quartering face gives the largest loads because at 45 degrees the wind encounters the greatest surface area. Quartering loads at various degrees other than 45 are also computed and used to establish an efficient mooring system for the semi-submersible platform as mentioned before. The winds loads are, by far, the largest loads that the structure endures as a whole. In turn, they have the greatest effect on the mooring analysis. The wind loads also have a major influence in offsetting the structure because the magnitude of force is so large. The final calculated wind loads can be found in Table 30. It is easily noticed that there is a difference in force magnitude when comparing bow and beam faces. As a result of surface area reduction of the topside components the beam wind loads are smaller. Table 29 is an excerpt from the spreadsheet used to calculate all loads, though here it is only the bow side data. Figure 38 displays the semisubmersible topside component sections used to calculate the necessary wind loads used for platform design. AutoCad plan and profile dimensioned drawings were used to calculate cross sectional areas for each wind exposed component. 7.2.2 Local Effects Topside components that are most affected by the wind loads are the cranes, flare boom, and drilling derrick. These components are areas of caution because their heights expose them to varying wind loads. Below is a detailed explanation of the process of calculating the wind loads. TAMU Team Gulf of Mexico 37 Final Report

Table 29- Component Areas and Coefficients for Bow Side Seas Component Area ft 2 C s Height Above MWL (ft) C h 1. Frame 1013.75 1.3 78.66 1.24 2. Compression Area 1859.63 1 122.48 1.38 3. Process Equip. Area 2499.69 1 125.96 1.39 4. Living Quarters 878.6 1 126.75 1.392 5. Power Area 1414.5 1 75.19 1.227 6. Process Area 2808.25 1 75.19 1.227 7. Deck 1116.59 1 104.66 1.328 8. Helipad 120.29 1 144.07 1.436 9. Railings 72.19 1.3 134.62 1.412 10. Boom 900.62 1.3 117.35 1.366 11. Cranes 2723 1.3 194.65 1.543 12. Derrick 4712.4 1.25 281.94 1.712 13. Front Columns 6748 1 31.83 1.035 14. Rear Columns 6748 1 31.83 1.035 Figure 38- Vessel Component Layout The shape coefficients, seen in Table 29, were chosen based on the specific shape of each component. The height coefficients were calculated using the following equation, taken from API 2SK codes [8]: y x x x 8 3 5 2 = 3 10 2 10 + 0.0063 + 0.8536 (34) This equation came from the line of best fit when the height coefficients were plotted against the respective height of the structure. Also seen in Table 29 are the heights of each component s centroid above the mean water level (MWL). This measurement was the x-value in Equation (34). The height coefficients, shape coefficients, and component areas were all multiplied together and then multiplied by the squared wind velocity to obtain the force. The final calculated wind loads can be found in Table 30 at the end of this section. 7.3 Wave Loading 7.3.1 Global Effects Wave loads are a major factor in the heave motion of the semi-submersible. Large heave motion and long natural periods can affect operation and production on the Gulf of Mexico semi-submersible. As mentioned before, TAMU Team Gulf of Mexico 38 Final Report

there are offset issues which are primarily from wind loads, but wave loading creates structure offsets as well. The wave loads, or mean wave drift force is a function significant wave height which have been calculated for bow, beam and quarter faces. 7.3.2 Local Effects Analysis of local wave loads mainly focuses on the columns of the submersible structure. The wave loads, like the wind loads, were calculated using equations given by API 2SK codes. The following 3 equations represent the equation for wave loading from the bow, beam, and quartering sides, respectively. y x x x y = 0.0009x 0.0942x + 4.7474x 19.283 (36) 3 2 y = 0.0004x 0.0489x + 3.0314x 7.8637 (37) = 0.0007 3 0.0857 2 + 4.5184 16.863 (35) 3 2 In these equations, the x-value is the significant wave height which is 48.9 feet. The output (y-value) is the mean wave drift force. The resulting forces can be found in Table 30. 7.4 Current Loading 7.4.1 Global Effects Depending on seasonal currents and operating drafts, the current loads affecting the semi-submersible contributes to offset motion. Current loading is a function of current velocity profile, exposed current area and current force and shape coefficients. The final calculated current loads can also be found in Table 30. 7.4.2 Local Effects Current loads affect both pontoons and columns in terms of drag force. The drag force varies with the current velocity profile, but for the operating draft range the current speed is constant. In the analysis, the wraparound theory was used here for currents as it was for wind loading. However, not only do currents wrap around and hit the back columns, they also wrap around and hit the front face of the back pontoon ( back meaning the columns and pontoon furthest away from the front-facing side) therefore increasing the current loads to higher values than if just the front face was in the analysis. The exact steps that were taken to calculate the current loads began with acknowledging that the current profile was constant throughout the entire draft of the semi-submersible. The next step included multiplying the total underwater area (including wrap-around area) and multiplying it by the shape coefficient which was the coefficient for a square column design. Then, similar to wind loading, this value was multiplied by the square of the current velocity to get a final force. As one can observe in Table 30, the forces for the bow and beam seas for current loading are the same because of the symmetry of the square hull design. Table 30- Final Calculated Environmental Loads Type of Load Bow Beam Quartering Wind (kips) 1390.5 1189.1 1719.8 Current (kips) 545.3 545.3 727 Wave (kips) 81.1 92.9 115.9 Total (kips) 2016.8 1827.2 2562.7 TAMU Team Gulf of Mexico 39 Final Report

8 MOORING AND STATION KEEPING The mooring analysis for this project was conducted using GMOOR [9]. Both intact and damaged conditions were tested for several different mooring systems in order to find the most cost effective solution for the vessel. 8.1 Design Criteria There are multiple criteria, set forth by industry standards and API codes, which must be met before the design can be installed. Due to the recent increase in hurricane activity, API codes have been updated to account for the extreme environmental conditions that can occur in the Gulf of Mexico. The criteria that must be met include scope of the mooring legs, pretension requirements, intact and damaged conditions under environmental loads, offsets, and watch circle requirements. 8.1.1 Quasi-Static Requirements Before environmental loading conditions can be applied to the mooring design the pretensions in each leg must meet API standards. For quasi-static design the pretensions must be 15% to 20% of the minimum break strength for the adjustable fairlead component. The factor of safety for this condition is between 5 and 6. 8.1.2 Environmental Loading Applications API standards require that the mooring system meet minimum safety factors for both intact and damaged situations under dynamic loadings. For dynamic loadings the factor of safety should be greater than 1.67 for intact mooring systems under the worst conditions. For damaged conditions, one line is broken in an iterative process through all of the legs to determine the highest tensions depending on the direction of the loading. From this a worst condition is found and a corresponding factor of safety that should be greater than 1.25. These loading conditions are tested on the bow at 0 degrees, the beam at 90 degrees, and at quartering at 45 degrees. 8.1.3 Maximum Offsets When the dynamic or environmental loads are applied the vessel is going to be offset from the origin. The requirements that must be met are going to be under the environmental loads. When the system is intact the offset should not be more than 5% of the water depth or within a range of 137.5 ft in a radial direction for the 5500 ft water depth for this design. When the system is damaged the offset should be not more than 7% of the water depth or within range of 192.5 ft in a radial direction. 8.1.4 Watch Circle Requirements The semi-submersible design is intended for both drilling and production. Because drilling is involved the vessel must be capable of excursions to drill and produce from multiple well heads. For this excursion drilling, a watch circle must be predetermined, or an area in which the vessel can move safely without damage to risers. Because the vessel is using steel catenary risers (SCR s), API requires that the watch circle remain within 5% to 10 % of the water depth. This equates to a range of 137.5 ft to 192.5 ft in the radial direction. For simplification the design is limited to a watch circle of 150 ft in the radial direction or 5.5% of the water depth. To allow for movement within the watch circle, chain is stored in onboard lockers as part of the adjustable fairlead component, which can be winched in or out depending on the amount of movement required. 8.1.5 Corrosion Tolerances To account for corrosion of chain, API requires the diameter of the chosen line component be increased. For lengths of line that are within the splash zone and thrash zone on hard bottom, the standards require a diameter increase of 0.2 to 0.4 mm (0.0079 to 0.0158 in) for every year of service. For the remaining length of the leg, the diameter increase can be reduced to 0.1 to 0.2 mm (0.004 to 0.0079 in) for every year of service. This diameter increase is only to be applied after strength analysis has been performed. For fatigue analysis the chain diameter for different periods of service life can be predicted assuming the corrosion rates can be predicted accurately. The corrosion rate will be dependent on the type of steel used in the TAMU Team Gulf of Mexico 40 Final Report

construction of the chain and the sea water environment the chain is exposed to. Due to these factors the corrosion rates are accelerated in the first few years of service life. As a result of these factors it is important to perform a fatigue analysis prior to accounting for added diameter size. When considering corrosion in wire it is important to look at the connections in the sockets. The corrosion at these points can be more extreme due to galvanized wire acting as an anode on adjacent components. When installing a permanent system API codes recommend isolating the wire electrically from the socket or isolating the socket from adjacent components. 8.2 Primary Design 8.2.1 Design Layout and Components The operational design chosen is a 12 leg taut system. The components of each line were chosen through an iterative process in order to meet minimum safety factor requirements and offsets. In Table 31 the components used on this mooring system are shown. Table 31- Selected Mooring Line Component Properties Component Type Diameter (in) Payout (ft) K4 Studless Anchor Chain 7 350 Polyester Line 10.27 7000 K4 Studless Adjustable Fairlead Chain 7 300 The first component in the table is placed at the anchor. The payout on this line was chosen based on requirements set forth within the API codes. Because suction anchors are going to be used and the system is designed as a taut system then 175 ft to 350 ft of anchor chain is required to keep the polyester mid line component off of the sea bed. The payout of component 1 is set at the maximum standard to account for any unpredicted environmental conditions that may occur in the Gulf of Mexico. The second component is placed between the anchor chain and fairlead chain. The polyester line was chosen because of the high tension capabilities and low weight, in comparison with steel wire. This component consists of most of the mooring leg because the goal is to minimize the weight on the vessel, thus increasing stability. The third component is the chain that is placed at the fairleads. This is the component that is adjustable and has enough length stored on board in lockers to allow for movement within the watch circle. The size of the adjustable component was set large due to larger tensions experienced at the fairleads. In Figure 39, shown below, is a top view of the 12 leg spread. The tensions on the lines are the pretensions that equate to the component factor of safety for the fairlead. The legs have been set at 10 degrees apart. Other spacings, such as 7.5 degrees and 15 degrees were tested and it was found that to maximize the effectiveness of the lines, 10 degree spacings were optimum. Figure 40 shows a 3-D representation of the mooring system design. TAMU Team Gulf of Mexico 41 Final Report

. Figure 39- Static Pretensions for Primary Mooring Design Figure 40-3-D View of 12 Leg Mooring Spread TAMU Team Gulf of Mexico 42 Final Report

8.3 Primary Design Results After checking to make sure that the static (no load) requirements were met. The environmental loads were applied for a 100 year hurricane using a batch file in G-MOOR. This chooses the worst conditions for damaged and intact situations and the direction of the loadings. The worst environmental conditions were determined to be at the quartering of the vessel at 45 degrees for intact and at the quartering at 45 degrees with line 10 broken. The results from the G-MOOR test are shown in Table 32. Table 32- Results of Dynamic Testing on a 12 Leg Taut System with Polyester, 100 yr Storm Conditions Condition Maximum Line Tension Safety Factor Maximum Offset (% of WD) Intact 3036.5 kips 1.53 1.0 % Damaged 3671.6 kips 1.26 1.4 % From the results of Table 32, it is seen that the safety factors for intact and damaged conditions meet the requirements of greater than 1.67 for intact and 1.25 for damaged and the offsets are not greater than the maximum allowable offsets of 5% of water depth for the intact case and 10% of water depth for the damaged case. The system was also checked under 10 year hurricane or in this case the operational conditions to assure that for drilling purposes the offsets were no greater than 2% of the water depth. The results from the 10 year storm or operational conditions are shown in Table 33. Table 33- Results of Dynamic Testing on a 12 Leg Taut System with Polyester, 10 yr Storm Conditions Condition Maximum Line Tension Safety Factor Maximum Offset (% of WD) Intact 1562.1 kips 1.53 0.32 % Damaged 1899.3 kips 1.89 0.36 % 8.3.1 Operational Offsets To access multiple wellheads, the mooring system chosen is capable of moving within a circular pattern with a radius of 150 ft. This is different than the offsets caused by the environmental conditions. The operational offsets are a result of line length adjustments. The mooring system design is capable of using the winches and chain jacks at the fairleads to pull in or let out line length to move within this 150 ft radius. In order for this to be accomplished, 250 feet of chain must be stored in chain lockers located beside the fairleads. To test this design the semi was offset in the 0 degree, the 45 degree, and 90 degree. If the design safety factors meet minimum requirements in these directions, the design will be capable of withstanding environmental loads from any position of offset. In Figure 41, Figure 42, and Figure 43 the offsets tested are shown. TAMU Team Gulf of Mexico 43 Final Report

Figure 41- Primary Design Offset in 0 degree Direction 150 ft under 10 year Winter Storm Conditions Figure 42- Primary Design Offset in 45 degree Direction 150 ft under 10 year Winter Storm Conditions Figure 43- Primary Design Offset in 90 degree Direction 150 ft under 10 year Winter Storm Conditions The results of the safety factors from the tested offsets are shown in Table 34. The safety factors met the minimum requirements showing that the rig is capable of moving within this 150 ft circle. Table 34- FOS Results from 150 ft Offset Test under 10 year Winter Storm Conditions Condition 12 Leg FOS under 150 ft offset Intact 3.00 Damaged 1.89 8.4 Alternative Design Options There are many other ways of testing the mooring capabilities for this vessel in the Gulf of Mexico. Five other design options were tested so as to choose the optimum design. The first option that was tested is a 16 leg taut system using polyester wire and chain, which is similar to the 12 leg taut system chosen for the design. The components for this design are shown in Table 35. The results from the dynamic testing are shown in Table 36. The factors of safety meet requirements and are more stable than the 12 leg system. The 16 leg system presents the capabilities of downsizing the components currently being used on the 12 leg taut system; however the added cost of anchor and fairlead installation may offset the need for the design. TAMU Team Gulf of Mexico 44 Final Report

Table 35-16 Leg Taut Mooring System Components Component Type Diameter (in) Payout (ft) K4 Studless Anchor Chain 5.25 350 Polyester Line 7.48 7000 K4 Studless Adjustable Fairlead Chain 5.25 300 Table 36- Results of Dynamic Testing on a 16 Leg Taut System with Polyester, 100 yr Storm Conditions Condition Maximum Line Tension Safety Factor Maximum Offset Intact 1314.48 kips 1.86 75.089 ft Damaged 2494.53 kips 1.46 96.99 ft Figure 44-3-D View of 16 Leg Mooring Spread The second option tested was a 12 leg taut system using jacket spiral strand wire instead of polyester line. Due to the large weight of chain and wire along with the extreme environmental conditions of the Gulf of Mexico, the safety requirements could not be met. This design option is insufficient and will not be used. The third option tested was a 16 leg taut system using jacket spiral strand wire in the place of polyester line. Similar to the 12 leg system using wire the 16 leg system with wire had the problem of the chain and wire being too heavy and the weather conditions being extreme. The safety requirements were not met and the design was determined to be insufficient and will not be used. The safety factors found for both the 12 and 16 leg systems using wire are shown in Table 37. Table 37- Safety Factors for 16 Leg and 12 Leg Wire Mooring Systems, 100 yr Storm Conditions Condition 12 Leg FOS 16 Leg FOS Intact 0.52 0.90 Damaged 0.19 0.81 The fourth option tested was a 12 leg semi taut system using chain and wire. This system, unlike the taut system, utilizes the weight of the lines as a restoring force. The system was tested under 100 year storm conditions and it was found that the offsets were more optimal than the taut systems but the semi taut system did not meet the minimum required factor of safety for the damaged case. A 3-D representation of the 12 leg semi taut system is shown in Figure 45. TAMU Team Gulf of Mexico 45 Final Report

Figure 45-3-D View of 12 Leg Semi Taut Mooring Spread The fifth option tested was a 16 leg semi taut system using chain and wire. This system like the 12 leg semi taut system utilizes the weight of the lines as a restoring force. The system was tested under 100 year storm conditions and it was found that the offsets were again more optimal than the taut systems but the damaged factor of safety did not meet minimum industry standards. A 3-D representation of the 16 leg semi taut system is shown in Figure 46 below. In Table 38 the factors of safety for both the intact and damaged cases for the 12 leg and 16 leg semi taut systems are shown. Figure 46-3-D View of a 16 Leg Semi Taut Mooring System Table 38- Safety Factors for 12 and 16 Leg Semi Taut Mooring Systems, 100 yr Storm Conditions Condition 12 Leg FOS 16 Leg FOS Intact 1.46 1.80 Damaged 0.07 0.17 TAMU Team Gulf of Mexico 46 Final Report

9 HYDRODYNAMICS OF MOTIONS AND LOADING In order to ensure that the vessel s motions as a response to the wave loading meets the requirements, the natural periods of the vessel are calculated. The JONSWAP spectrum energy density plot for the 100 year hurricane is displayed in Figure 47. The plot shows that the majority of the wave energy is between 10 and 20 second wave periods. A natural period of less than 10 seconds is not reasonable for a semi-submersible vessel, therefore the vessel s heave and roll natural period should be more than 20 seconds. 100 Year Hurricane JONSWAP Spectrum 0.5 0.4 S η (ft 2 *s) 0.3 0.2 0.1 0 0 5 10 15 20 25 T (s) Figure 47-100 Year Hurricane JONSWAP Spectrum The heave and roll natural periods are calculated to be 23.93 and 43.63 s, respectively. The following equations are used for this computation. (1 + M ac) M Theave ( ) 2π ρga = (38) w Troll ( ) = 2π ( 1+ ) 2 M M r ac ρ g GM L (39) Response amplitude operators (RAOs) for the heave and roll motions were supplied by InterMoor. These are used to calculate the motions that result from the vessel s wave loading with the following equations. The resulting heave and roll motions are shown in Table 39. RMS RAO S (40) 2 ( ) = Δ ω ( ( ω) Motion ) Significant Wave Response Motion = 2*RMS (41) Maximum Wave Response Motion = 3.72*RMS (42) Table 39- Vessel Response Motion Heave Motion (ft) Roll/Pitch Motion (deg) Significant Maximum Significant Maximum 10 yr Winter Storm 4.81 8.95 0.97 1.81 100 yr Hurricane 12.89 23.98 1.42 2.64 TAMU Team Gulf of Mexico 47 Final Report

10 COST ANALYSIS The cost analysis is based on cost per line for each of the design options that have been tested. Table 40 illustrates cost estimation for each of the design options. Table 40- Cost Estimates for the Mooring Design Options Mooring Design Unit Description Unit Price ($)/unit Price ($ Millions) 12 Leg Taut cost per line 12 1,068,900 12.8 16 Leg Taut cost per line 16 590,400 9.4 12 Leg Taut with Wire cost per line 12 8,046,300 96.6 16 Leg Taut with Wire cost per line 16 8,046,300 128.7 12 Leg Semi Taut cost per line 12 5,627,000 67.5 16 Leg Semi Taut cost per line 16 5,696,900 91.2 The cost estimate for the hull is based on the internal steel weight of each component (8 pcf for columns, 10 pcf for pontoons, and 12 pcf for nodes). The estimate for the hull does not include the cost of the risers, the topside equipment, drilling operations, transportation costs, integration, hook-up, and commissioning. The overall total cost which includes the hull, the suction anchors, the on-hull mooring equipment, and the mooring lines can be found in Table 41. Table 41- Cost Estimate for the Proposed Semi-Submersible and Mooring Design Unit Description Unit # Price ($)/unit Price ($ Millions) Suction Anchors cost per ton 2498.4 4500 11.2 Hull cost per short ton 16266.76 12000 195.2 On-Hull Mooring Equipment cost per line 12 550000 6.6 Total Cost 213 Mooring Line cost per line 12 1068909 12.8 Overall Total Cost 225.8 TAMU Team Gulf of Mexico 48 Final Report

11 SUMMARY AND CONCLUSIONS The recent rise in demand for deep water oil has led to an increase in the number of semi-submersible drilling and production vessels in service. Semi-submersibles have several advantages that make them desirable to the oil industry. Firstly, they display low wave driven motions due to their small water plane areas. The columns and pontoons often contain ballast tanks that can be used to alter the draft as necessary to adjust for weather conditions. Also, semi-submersibles are relatively easy to move, making them excellent vessels for drilling operations. The Gulf of Mexico team has designed a semi-submersible production and drilling vessel with the capability of producing 120,000 barrels of oil and 10,000,000 cubic feet of gas per day. The vessel has pontoons which are 273 feet long, 50 feet tall and 53 feet wide. The columns have a square cross-section and are 53 feet wide and 90 feet long. Intermoor and Houston Offshore Engineering provided the design group with environmental data for a 10 year return period winter storm and a 100 year hurricane. The semi-submersible is required to have the ability to produce in a 10 year winter storm and must survive a 100 year hurricane. The largest environmental load that the semi-submersible needs to allow for is a force of 2,562.7 kips on the quartering side of the structure caused by 100 year hurricane conditions. This includes forces due to wind, current, and waves. Structural analysis indicates that the worse case scenario occurs when a 50 foot wave propagates through the diagonal of the structure, squeezing and prying the columns. However, the estimated stresses for this case are sufficiently below ABS criteria for environmental loads. The maximum dynamic stress ratio due to a 50 foot wave is 1.4 and occurs at the upper portion of the column. StabCad was used to conduct both an intact and damaged stability analysis on the vessel during operational and towing conditions. In addition, an intact analysis was performed on the hull transport condition. In each case, the center of gravity was lower than the maximum allowable KG as given by ABS, which indicates that the vessel is stable during each stage of its design life, from transporting the hull to putting the rig into operation. Response amplitude operators (RAO's) provided by InterMoor and the JONSWAP wave spectrum were used to find the heave and roll responses of the semi-submersible. The maximum heave and roll responses during a 100 year hurricane are 12.75 feet and 2.64 degrees, respectively. Both roll and heave responses meet requirements given by HOE. Mooring analysis yielded an optimum design with a 12 leg taut system. The line system is composed of 7.25 inch chain and 10.27 inch polyester rope. The mooring spread was capable of moving within a 150 ft watch circle while maintaining minimum offsets of 1 % of the water depth intact and 1.4 % of the water depth damaged under environmental loadings. In the event 7.25 inch chain is unavailable then a 16 leg taut system ( was found to meet the minimum requirements and could be used for an elevated cost ($2.5 million), assuming the extra fairleads can be installed. The overall cost of the hull and mooring system is $225.8 million. The cost of the hull was based on its internal steel weight. The cost of the mooring was based on the number of legs and the thickness of the chain and polyester rope. The mooring system cost was $12.8 million. Other costs included in the cost estimation were the suction pile anchors that were sized by InterMoor and the cost of on hull mooring equipment such as chain jacks, fairleads, and stoppers. TAMU Team Gulf of Mexico 49 Final Report

12 REFERENCES [1] Creating New Opportunities and Challenges: Growing Support Industry. Minerals Management Service. May 24, 2005 <http://www.mms.gov/ooc/press/2005/press0524.htm> [2] Semi-submersible. Wikipedia. April 18, 2007 <http://en.wikipedia.org/wiki/semi-submersible> [3] Fales, Ray & Randall, Robert. Design of Offshore Oil and Gas Facilities. IMDC 2006 State of Art Report. 2006. page 32 [4] American Petroleum Institute. Interim Guidance for Gulf of Mexico MODU Design Practice- 2006 Hurricane Season (API RP95F), Washington D.C. 2006 [5] American Bureau of Shipping. Rules for Building and Classing Steel Vessels, Houston, TX. 2005. [6] Structural Dynamics, LLC. StabCAD, Version 4.3 SP1, 2003 [7] Integrated Engineering Software, Inc. Visual Analysis, Version 4.0 1.014, 2004 [8] American Petroleum Institute. Design and Analysis of Stationkeeping Systems for Floating Structures Third Edition (API RP 2SK), Washington D.C. 1997 [9] Global Maritime Consultancy, Ltd. Gmoor32, Version 9.406c, 2001 [10] AutoDesk, Inc. AutoCad Software, 2004 [11] The MathWorks, Inc. MATLAB, Version 7.2.0.232 (R2006a), 2006 TAMU Team Gulf of Mexico 50 Final Report

Appendix A: GMOOR Input/Output The mooring analysis was performed using GMoor compliments of Global Maritime and InterMoor. This program allowed for the mooring spreads to be designed, configured, and tested under environmental conditions to find the optimal mooring design. Input Files: Shown below is a basic example of the input file used to create the 12 line mooring spread. GMoor recognizes this file and uses it to configure the mooring spread. The data input includes the line numbers, the line lengths, the spacing of each line, the adjustable lengths of each line, and finally the line components and component properties. Spread File: "Gulf of Mexico" *CVF GOM-12line *NONE 2 2 0.00, 0.00, 0.00 *SLOPE 5500.00 0.00 75.00 12 1 1, 1, 5500.00, 35.00, 5500.00, 0.00, 1, 300.00 2, 1, 5500.00, 45.00, 5500.00, 0.00, 1, 300.00 3, 1, 5500.00, 55.00, 5500.00, 0.00, 1, 300.00 4, 1, 5500.00, 125.00, 5500.00, 0.00, 1, 300.00 5, 1, 5500.00, 135.00, 5500.00, 0.00, 1, 300.00 6, 1, 5500.00, 145.00, 5500.00, 0.00, 1, 300.00 7, 1, 5500.00, 215.00, 5500.00, 0.00, 1, 300.00 8, 1, 5500.00, 225.00, 5500.00, 0.00, 1, 300.00 9, 1, 5500.00, 235.00, 5500.00, 0.00, 1, 300.00 10, 1, 5500.00, 305.00, 5500.00, 0.00, 1, 300.00 11, 1, 5500.00, 315.00, 5500.00, 0.00, 1, 300.00 12, 1, 5500.00, 325.00, 5500.00, 0.00, 1, 300.00 1, 3 3, 300.00 "7 in K4 Studless Ch 347.77, 0.368280, 5800.00, 1.00, 0.49, 0.58, 2.40, 1.00, 20 0.714E+06, 0.00, 0.00, 0.00 0.00, 0.000000, 0.00, 1.00, 0.00, 0.00, 0.00 "10.24 Marlow Poly" 7000.00, 0.007930, 4536.00, 0.00, 0.11, 0.85, 1.20, 1.00, 20 0.891E+05, 0.00, 0.00, 0.00 0.00, 0.000000, 0.00, 1.00, 0.00, 0.00, 0.00 "7 in K4 Studless" 300.00, 0.368280, 5800.00, 1.00, 0.49, 0.58, 2.40, 1.00, 20 0.714E+06, 0.00, 0.00, 0.00 0.00, 0.000000, 0.00, 1.00, 0.00, 0.00, 0.00 The custom vessel file is used by GMoor as the main data file. This file contains the placement of the fairleads in relation to the vessel itself. This file also contains the environmental loading coefficients. These coefficients are factored in when loading conditions are applied within the program itself, to determine the effectiveness of the mooring spread. The vessel file contains 3 drafts so that GMoor can test within a range. TAMU Team Gulf of Mexico 51 Final Report

Custom Vessel File (CVF): /* NOTES * a) Things that need updating: * * - serial number??? * * - Drafts DONE * * - Vessel Data DONE * * - Wind/current force coeff. DONE * * - General Data: Licensee???? * * * * b) This file has updated response phase angles based * * on the comparison of phases between the existing * * (previous) Arctic I file and the Aleutian Key * * data file * * * * ==================================================== */ /* "GOM" semi-submersible drilling vessel * * Based on model of "Aleutian Key" semi-submersible * * Serialized for: Global Maritime Limited * * Vessel data at three drafts, two Thrusters defined * * Wind and Current coefficient data for two drafts * * regular wave data for two drafts * * All six RAOs for 0ø & 90ø headings at two drafts * * ===================================================== */ /* ------------------------- * * GENERAL DATA ( identity ) * * ------------------------- */ *GENERAL "GOM" /* Vessel name */ "TAMU" /* Licensee */ "2 February 2007" /* Issue date */ "GOM.PLN" /*.PLN file name */ "GM-100 060199" /* Serial Number */ "Sources of the data used to create this CVF, with validation" "and limitations, are contained in Report No.GM-33033-1198-37025 Rev1" /* ------------- * * Fairlead Data * ------------- */ *FAIRLEAD #NFAIRLEADS 12 #UNITS LENGTH METRES 34.4424, 42.0624, 3 42.0624, 42.0624, 3 42.0624, 34.4424, 3 42.0624, -34.4424, 3 42.0624, -42.0624, 3 34.4424, -42.0624, 3-34.4424, -42.0624, 3-42.0624, -42.0624, 3-42.0624, -34.4424, 3-42.0624, 34.4424, 3-42.0624, 42.0624, 3-34.4424, 42.0624, 3 /* ----------- * * Vessel Data * * ----------- */ *VESSEL #DRAFTS 19.812 22.86 25.908 #UNITS FORCE KN #DRAFT 1 /* 19.812m (65.00ft) */ 70807.41 /* Displacement - updated */ TAMU Team Gulf of Mexico 52 Final Report

1.80, 1.35, 0.0 /* mass Coefficients in : sway, surge, heave */ 0.0, 0.0, 28.1 /* radii of gyration for : pitch, roll, yaw */ 26.1, 13.0, 0.0 /* linear damping in : sway, surge, heave */ 0.0, 0.0, 0.46E6 /* quadratic damping in : pitch, roll, yaw */ #DRAFT 2 /* 22.86m (75.00ft) */ 73989.09 1.80, 1.35, 0.0 0.0, 0.0, 28.3 28.4, 14.2, 0.0 0.0, 0.0, 0.58E6 #DRAFT 3 /* 25.908m (85.00ft) */ 77170.77 1.80, 1.35, 0.0 0.0, 0.0, 28.4 30.7, 15.4, 0.0 0.0, 0.0, 0.70E6 /* --------------- * * Wind Force Data * * --------------- */ *WIND #DRAFTS 19.812 22.86 25.908 #UNITS FORCE KN #HEAD_INCR 22.5 /* changed from 15 - only have 9 coeff */ #HEAD_STEP 0 180 22.5 #DRAFT 1 /* 19.812m (65.00ft) */ /* Fx Fy Mxy */ 2.89 0.00 0.000 3.05 1.26 0.000 2.54 2.54 0.000 1.16 2.80 0.000 0.00 2.49 0.000-1.16 2.80 0.000-2.54 2.54 0.000-3.05 1.26 0.000-2.89 0.00 0.000 #YREFLECT #XREFLECT #DRAFT 2 /* 22.86m (75.00ft) */ /* Fx Fy Mxy */ 2.71 0.00 0.000 2.85 1.18 0.000 2.37 2.37 0.000 1.08 2.61 0.000 0.00 2.32 0.000-1.08 2.61 0.000-2.37 2.37 0.000-2.85 1.18 0.000-2.71 0.00 0.000 #YREFLECT #DRAFT 3 /* 25.908m (85.00ft) */ /* Fx Fy Mxy */ 2.53 0.00 0.000 2.66 1.10 0.000 2.21 2.21 0.000 1.00 2.43 0.000 0.00 2.15 0.000-1.00 2.43 0.000-2.21 2.21 0.000-2.66 1.10 0.000-2.53 0.00 0.000 #YREFLECT /* ------------------ */ /* Current Force Data */ TAMU Team Gulf of Mexico 53 Final Report

/* ------------------ */ *CURRENT #DRAFTS 19.812 22.86 25.908 #UNITS FORCE KN #HEAD_INCR 22.5 #HEAD_STEP 0 180 22.5 #DRAFT 1 /* 19.812m (65.00ft) */ /* Fx Fy Mxy */ 723.79 0.000 0.000 786.70 325.86 0.000 682.40 682.40 0.000 325.86 786.70 0.000 0.000 723.79 0.000-325.86 786.70 0.000-682.40 682.40 0.000-786.70 325.86 0.000-723.79 0.000 0.000 #YREFLECT #XREFLECT #DRAFT 2 /* 22.86m (75.00ft) */ /* Fx Fy Mxy */ 784.73 0.000 0.000 852.94 353.30 0.000 739.85 739.85 0.000 353.30 852.94 0.000 0.000 784.73 0.000-353.30 852.94 0.000-739.85 739.85 0.000-852.94 353.30 0.000-784.73 0.000 0.000 #YREFLECT #DRAFT 3 /* 25.908m (85.00ft) */ /* Fx Fy Mxy */ 845.67 0.000 0.000 919.17 380.73 0.000 797.31 797.31 0.000 380.73 919.17 0.000 0.000 845.67 0.000-380.73 919.17 0.000-797.31 797.31 0.000-919.17 380.73 0.000-845.67 0.000 0.000 #YREFLECT Output Input Files: A batch process is then run in GMOOR which first analyzes the intact mooring system for varying environmental loading directions. The output of this analysis, shown in Figure 48, gives the results for the environmental loading in the direction which causes the worst case. The program then analyzes the damaged condition. During this process, the GMOOR breaks each line one at a time and applies environmental loading from each direction for each broken line. It then outputs the worst case scenario, which can be seen in Figure 49. TAMU Team Gulf of Mexico 54 Final Report

Figure 48- GMOOR Intact Mooring Analysis Output TAMU Team Gulf of Mexico 55 Final Report

Figure 49- GMOOR Damaged Mooring Analysis Output TAMU Team Gulf of Mexico 56 Final Report