FPSO Design Document. Marie C. McGraw Roberto J. Meléndez Javier A. Ramos

Transcription

1 FPSO Design Document Marie C. McGraw Roberto J. Meléndez Javier A. Ramos March 16,

2 Contents 1 Introduction Background Existing Vessels Customer Requirements Design Approach Specific Requirements Design Philosophy Hull Subdivision and Tank Layout Guidelines Outer Hull Dimensions General Arrangement Cargo Storage and Slop Tanks Ballast Tanks Mooring System Accomodations Machinery Rooms Intact and Damaged Stability Loading Conditions Lightship Full Load Loading Conditions Intact Stability Requirements Analysis Damaged Stability Requirements Analysis Structural Design Strength Section Design Hull Girder Analysis Appendix 1: Ship Geometry 15 6 Appendix 2: Hull Subdivision and Layout 16 7 Appendix 3: Hull Loading Parameters 17 8 Appendix 4: MATLAB Scripts 17 9 References 20 2

3 List of Figures 1 Rendering of the outer hull Cargo tank layout Slop tank layout Seawater ballast tanks Mooring equipment, machine room, and collision compartments Fuel and lube oil tanks Positive and negative shear forces along the FPSO FPSO section modulus

4 List of Tables 1 Cargo tank data Lightships weight blocks Full load weight blocks Damage stability results for 50% cargo load Hull Girder Thicknesses Ship Geometric Parameters Hull Subdivision and Layout Parameters Hull Loading Parameters

5 Abstract Now is the time for all good men to come to the aid of their country. 1 Introduction 1.1 Background Floating Production Storage and Offloading Vessels (FPSOs) are self-sustaining platforms that produce, store, and offload oil continuously over a long period. This is a departure from the previous offshore drilling philosophy, which employed fixed platforms in relatively shallow water depths (no more than 150 meters). FPSOs also remove the need to transport oil through pipelines from the drilling site to the shore a costly, difficult, and risky procedure. Instead, oil can be separated and stored onboard the vessel until a tanker arrives to transport the oil back to shore facilities. FPSOs are commonly employed in a variety of environments, including the Indian Ocean, the North Sea, and the African coast. FPSOs must be able to withstand extreme environmental conditions, and for this reason, require a reliable mooring system to keep the vessel within the working area. 1.2 Existing Vessels Currently, there are over eighty Floating Production Storage and Offloading Vessels (FPSOs) operating across the globe. The older FPSOs are conversions of oil tanker hulls, while the newer vessels are designed and constructed specifically for this purpose. FPSOs are preferable to traditional systems due to their environmental versatility, durability, independence, and lack of infrastructure construction, such as seabed pipelines. FPSOs permit oil field exploration and development in areas of the globe where the infrastructure is minimal, such as the African Coast and the Indian Ocean. 1.3 Customer Requirements Company Foo has requested an FPSO that will operate in the Gulf of Mexico at a depth of 1000 meters. This project will require a stable, weathervaning hull with a single-point mooring system. The FPSO will be classed through the American Bureau of Shipping (ABS), and will meet the MARPOL double-hull tanker requirements from Annex 1 to minimize marine pollution and environmental impact in the event of damage to the vessel. The FPSO must be able to remain operational for twenty years. Company Foo has designated a set of standard operating conditions for the FPSO. The FPSO must be able to operate continuously under sustained winds of up to 15 m/s, a current speed of up to 1.2 m/s, a wave height of up to 4.0 m, and a peak wave period of 10.0 seconds. Company Foo has also designated a set of extreme operating conditions for the FPSO. The FPSO does not need to continue normal operations under these conditions, but it must be able to resume functionality when conditions abate. The extreme operating conditions consist of a wind speed of up to 40.0 m/s, a current speed of up to 1.5 m/s, a wave height of 12.0 m, and a peak wave period of 14.0 seconds. 5

6 1.4 Design Approach Key design considerations for this FPSO were hull stability, durability, and load-bearing capacity; optimization of cargo production, storage, and offloading; human health and safety; and load-bearing capacity of the mooring system. Several software packages were used to design the vessel. These packages were Rhino s ORCA extension, MaxSurf, the POSSE software suite, and MATLAB. Rhino ORCA and MaxSurf were used to design the outer hull, while POSSE was used to create the internal layout and the section modulus of the FPSO. POSSE was also used to perform intact stability and damage analysis. MATLAB was used to calculate vessel parameters in accordance with requirements laid out by MARPOL and ABS Specific Requirements Company Foo requires an FPSO that can produce 150,000 barrels of oil per day. The FPSO must have a storage capacity of 2 million barrels of oil. The FPSO will undergo its offloading routine every ten days. fooooo Design Philosophy The mission of an FPSO is to be a self-sustaining, safe, secure oil-producing platform that must produce continuously over the life of the vessel. The oil production and storage must occur in a safe, environmentally friendly, and reliable way. fooooo fooooo 2 Hull Subdivision and Tank Layout 2.1 Guidelines All structural design decisions, such as tank placement, double hull thickness, cargo tank capacity, bulkhead placement, and accomodation design and location, were made in consultation with the American Bureau of Shipping s Common Structural Rules for Oil Tankers and MARPOL s Regulations for the Prevention of Pollution by Oil. 2.2 Outer Hull Dimensions Guidelines for the outer dimensions of length (L), beam (B), and depth (D) were given by the customer. These guidelines were 300 m in length, 60 m in beam, and 30 m in depth. These dimensions were adjusted slightly to increase cargo storage, adjust length-to-beam ratio, and provide necessary seawater ballast. A slightly longer length of 360 m was settled on early in the design process to allow for a larger cargo storage area of 240 m. Hull subdivision and tank layout parameters, described in the following sections, were calculated for several different beam values, with length-to-beam ratio varying from five to six. Ultimately, a beam of 64 m was decided on. This beam size optimizes cargo space while restricting the seawater ballast required by the ABS and MARPOL. The depth remained at 30 m, and the design waterline resulted in a draft of 20 m. 6

7 2.3 General Arrangement Figure 1: Rendering of the outer hull The FPSO is arranged into sixteen identical oil tanks, with eight on each side of the longitudinal bulkhead. The total cargo tank volume is 336,000 m 3, or 2.1 million barrels. Even at 95% capacity, or 319,200 m 3, the FPSO will be able to store just over 2 million barrels of oil, meeting the customer specifications. Collision bulkheads are placed according to Section 5 of the ABS Common Structural Rules for Oil Tankers. The foreward collision bulkhead is located 10 meters from the forward perpendicular, and extends upward to the freeboard deck. The aft collision bulkhead is located 10 meters from the forward perpendicular, and similarly extends upward to the freeboard deck. There is a longitudinal bulkhead along the centerline throughout the length of the ship. 2.4 Cargo Storage and Slop Tanks Cargo storage tanks are subject to a number of regulations to minimize spillage in the event of damage. A double hull is used to protect cargo spaces and prevent spillage. The thickness of the double hull was calculated using the guidelines posted in Section 5 of the ABS Common Structural Rules for Oil Tankers. The minimum double bottom depth, d db is the lesser of d db = B 15 m, but not less than 1.0 m (1) The minimum double side width, w ds, is the minimum of d db = 2.0m (2) w ds = DW T m, but not less than 1.0 m (3) w ds = 2.0m (4) 7

8 Using these guidelines, a double hull thickness of 4.0 m was selected. This design was chosen so as to increase the amount of seawater ballast available in the double hull, and to improve ship damage resistance. Cargo tank dimensions were calculated using the ABS and MARPOL guidelines. The maximum oil outflow from a single tank was calculated as the maximum of DW T and 30,000 m 3. Using this guideline, the maximum oil outflow was calculated to be 28,284 m 3. The maximum volume of an individual cargo tank 75% of the maximum oil outflow. For Team FOO, the maximum volume of an individual cargo tank was 22,500 m 3. The maximum length of an individual tank is also regulated by MARPOL. This length can be calculated using the following stipulation, L ind max = ( 1 w ds ) L (5) 4 B The beam and depth of an individual tank are not regulated by MARPOL. An individual tank depth of 25 m and an individual tank beam of 28 m were selected to maximize the cargo volume. Sixteen individual tanks were placed in the cargo area, eight on the port side of the longitudinal bulkhead, and eight on the starboard side. The total cargo volume, therefore, is 336,000 m 3, or 2.1 million barrels of oil. This exceeds the directive of 2 million barrels dictated by the customer. The cargo storage tank layout can be seen in Figure 2. Figure 2: Cargo tank layout The total volume of the slop tanks must be at least two percent of the total cargo volume. The slop tanks on the team FOOBAR FPSO have a total tank volume of 6,720 m 3. The MARPOL guidelines indicate that this total volume must be divded over at least two tanks. The slop tanks were divided into two equal tanks with a total volume of 3,360 m 3. The slop tank layout and location can be seen in Figure 3 on the next page. Table 2.4 on the facing page gives a more complete breakdown of the cargo tank dimensions, capacities, and locations. 8

9 Figure 3: Slop tank layout Compartment Capacity (m 3 ) Aft Bound. (m-fp) Foreward Bound. (m-fp) 100% Full LCG (m- FP) 100% Full VCG (m- BL) 100% Full TCG (m- CL) Starboard 0 14, A A A S Starboard 1 21, A A A S Starboard 2 21, A A A S Starboard 3 21, A A A S Starboard 4 21, A A A S Starboard 5 21, A A A S Starboard 6 21, A A A S Starboard 7 21, A 90.0 A A S Starboard 8 21, A 60.0 A 75.0 A S Starboard 9 12, A 30.0 A 45.0 A S Port 0 14, A A A P Port 1 21, A A A P Port 2 21, A A A P Port 3 21, A A A P Port 4 21, A A A P Port 5 21, A A A P Port 6 21, A A A P Port 7 21, A 90.0 A A P Port 8 21, A 60.0 A 75.0 A P Port 9 12, A 30.0 A 45.0 A P Table 1: Cargo tank data 2.5 Ballast Tanks Seawater ballast tanks are required to help the vessel maintain stability when operating with little cargo weight, such as immediately after offloading. The double bottom and double hull are used for seawater ballast, and are divided into tanks paralleling the divisions of the cargo tanks. Two additional seawater ballast tanks were installed in the forward section of the ship. The total seawater ballast can 9

10 be determined using the following criteria, SW total = V cargo total 2.4 (6) For this vessel, the total amount of seawater ballast needed is 140,000 m 3. The 4 m double bottom and 4 m double hull provide a total of 119,040 m 3 of seawater ballast. The two foreward tanks provide an additional 20,000 m 3 of seawater ballast. The seawater ballast tanks can be seen in Figure 4. Figure 4: Seawater ballast tanks 2.6 Mooring System The mooring system equipment is housed in two compartments in the bow of the ship. These compartments extend from 30 m aft of the forward perpendicular to the forward perpendicular and are located on either side of the longitudinal bulkhead. The mooring system equipment compartments can be seen in Figure 5. Figure 5: Mooring equipment, machine room, and collision compartments 10

11 2.7 Accomodations For safety reasons, the accomodations turret must be located at least 33 meters from the production deck. Therefore, the accomodations turret (containing the crew quarters, the galley, and other worker facilities) is located 153 meters aft of midships, 33 meters to the stern of the aft end of the production deck. There are also two fresh water tanks located in the aft of the ship. These tanks are located aft of the stern collision bulkhead (between the aft perpendicular and 10 meters forward of the aft perpendicular). Each tank contains a total of 1,133 m 3 of fresh water. 2.8 Machinery Rooms According to the ABS Common Structural Rules for Oil Tankers, the machinery spaces must be positioned aft of the cargo and slop tanks. The machinery rooms on the FPSO are located between 320 meters aft of the forward perpendicular and 350 meters aft of the forward perpendicular. The machinery rooms can be seen in Figure 5 on the preceding page. Two Wärtsilä 32 9L32 medium-speed diesel engines power the FPSO. The Wärtsilä 32 is the most commonly used marine engine for offshore and drilling vessels, allowing for easy maintenance, repairs, and spare parts. The 9L32 has a horsepower of 4,320 kw at a 480 kw cycle. The 9L32 has a maximum length of m, a maximum width of m, and a maximum height of m. The 9L32 weighs 84 metric tons. The FPSO fuel tank is located below the machinery rooms in the aft of the ship on the starboard side of the ship. The fuel tank contains 9,240 m 3 of fuel oil. The FPSO also contains a lube oil tank underneath the port machinery room. The lube oil tank contains 9,240 m 3 of lube oil. The fuel tanks can be seen in Figure 6. Figure 6: Fuel and lube oil tanks 11

12 3 Intact and Damaged Stability 3.1 Loading Conditions Lightship The lightship loads include hull weight and outfittings (distributed uniformly along the length of the FPSO), machinery and engine weight, accomodations, and the external mooring system. The total lightship load for the FPSO is 122,320 MT, centered at 10 meters aft of midships. Table gives a breakdown of the lightship weight blocks. Block Weight (MT) LCG (m-fp) Aft Bound. (m-fp) Forward Bound. (m-f Engine Room A A A Mooring Structure 10, A 30.0 A 0.0 Accomodations 17, A A A Production Equipment 32, A A 30.0 A Hull Structure 61, A A 0 Total 122,320 Table 2: Lightships weight blocks Full Load A fully loaded ship includes the lightship loads in addition to a full cargo load, a full fuel tank, full fresh water tanks, full slop tanks, and a full lube oil tank. Table gives a breakdown of the full weight blocks. Block Weight (MT) LCG (m-fp) Aft Bound. (m-fp) Forward Bound. (m-fp) Lightships 122, A A 0.0 Cargo Oil 336, A A 30.0 Fuel Oil A A A Lube Oil A A A Slop Tanks 17, A 60.0 A 30.0 A Fresh Water A A A Total 496,986 Table 3: Full load weight blocks Loading Conditions Intact stability was analyzed at a fully loaded condition (98% of a full cargo load), a half-loaded condition (50% of a full cargo load), and an empty condition (2% of a full cargo load). Damage stability analysis was only performed at the half-loaded condition. 12

13 3.2 Intact Stability Requirements The requirement for intact stability as given by the customer indicates that the FPSO can experience no more than 1 meter of trim at either the bow or the stern Analysis The maximum sagging condition was analyzed at the 98% cargo condition. Trim of less than 1 meter at bow and stern was achieved when all forward seawater ballast tanks were filled to 60%. Two wing seawater ballast tanks at midships on each side (port and starboard) were filled to 40%. The maximum hogging condition was analyzed at the 2% cargo condition. Trim of less than 1 meter at bow and stern was achieved when the large forward seawater ballast tank located foreward of the cargo area was filled to 95%. The large aft seawater ballast tank located aft of the cargo area was filled to 20%, and the wing tanks at midships on both port and starboard side were filled to 95%. 3.3 Damaged Stability Requirements MARPOL requirements dictate damage assumptions used in this model. The longitudinal extent of side damage is given as the lesser of either 1L 2 3 or 14.5 m. In this case, a 14.5 meter horizontal gash was 3 used to simulate side damage. MARPOL also indicates that the angle of heel cannot exceed 25, and the righting lever must be at least 0.1 meters long within 20 of equilibrium position. The area under the curve in this range cannot be less than meter-radians. 100% permeability was assumed in all damage simulations. The damage stability was analyzed at 50% cargo load Analysis Since the FPSO and the tank configuration are symmetrical about the centerline, the damage simulation was only run on the starboard side. It is assumed that the port side will yield identical results, heeling to port side instead of to starboard side. Damage was assumed to have penetrated through the double hull and the double bottom in each case. Damage results can be seen in Table on the next page. 4 Structural Design 4.1 Strength Section Design The hull section was designed using the POSSE Section Modulus Editor and MATLAB. A MATLAB script was used to calculate thicknesses of hull plates and dimensions of hull girders. ABS Guidelines for Classing FPSOs were used to determine critical forces and moments, and then, relevant geometries. 13

14 Tanks Damaged Heel ( ) Draft FP (m) Draft AP (m) Metacentric Height (m) Mooring, Slop Slop, Cargo Tank Cargo Tanks 8 & Cargo Tanks 7 & Cargo Tanks 6 & Cargo Tanks 5 & Cargo Tanks 4 & Cargo Tanks 3 & Cargo Tanks 2 & Cargo Tank 0, Fuel Cargo Tank 0, Fuel Table 4: Damage stability results for 50% cargo load The MATLAB script is provided in full in Appendix 5. The maximum sagging moment was calculated to be kn, while the maximum hogging moment was calculated to be kn. The shear forces distributed along the length of the ship are seen in Figure 7. Figure 7: Positive and negative shear forces along the FPSO The minimum section modulus was calculated to be 1,468,900 cm 3. The hull girder section modulus was calculated to be 1,073,600 cm 3. Since the minimum section modulus is greater than the hull girder section modulus, the design section modulus is m 3. A section view can be seen below in Figure 8 on the next page. 4.2 Hull Girder Analysis The same MATLAB script was also used to calculate plate, girder, and stringer thicknesses according to the ABS Guidelines from Classing FPSOs. The minimum hull girder moment of inertia was calculated to be 1588 cm 2 -m 2. Plate and girder thicknesses are given in Table 4.2 on the facing page. 14

15 Figure 8: FPSO section modulus Plate/Girder Minimum Thickness (mm) Plates Keel plate Breadth of Keel Plating 2600 Bottom/bilge/side shell Tank shell Non-watertight bulkheads 8.10 Girders Main double bottom Double bottom stringer Double bottom floors/side transverses Other Table 5: Hull Girder Thicknesses 5 Appendix 1: Ship Geometry Parameter Value Units Symbol Displacement MT Displaced Volume m 3 V Length 360 m L Beam 64 m B Depth 30 m D Draft 22 m T Block Coefficient C b Prismatic Coefficient C p Section Area Coefficient C m Waterplane Area Coefficient C wp Table 6: Ship Geometric Parameters 15

16 6 Appendix 2: Hull Subdivision and Layout Parameter Value Units Symbol Deadweight MT DWT Oil Outflow m 3 O out Maximum Tank Volume m 3 V tank max Actual Cargo Tank Volume m 3 V tank Maximum Cargo Tank Length m L tank max Actual Cargo Tank Length 30 m L tank Cargo Tank Width 28 m B tank Cargo Tank Depth 25 m D tank Total Cargo Volume m 3 V cargo total Required Seawater Ballast m 3 V SW Required Slop Volume 6720 m 3 V slop tot Individual Slop Tank Volume 3360 m 3 V slop ind Table 7: Hull Subdivision and Layout Parameters 16

17 7 Appendix 3: Hull Loading Parameters Parameter Value Units Symbol Lightships Loads MT W light Hull Structure Weight MT W struc Mooring Weight MT W mooring Engine Weight 100 MT W eng Platform Weight MT W platform Miscellaneous (inc. Accomodations) MT W misc Table 8: Hull Loading Parameters 8 Appendix 4: MATLAB Scripts %%tankdimensions.m %%This script calculates tank parameters and ballast according to MARPOL and ABS regulations. L=360; %length B=64; %beam D=30; %depth T = 22; %draft CB=0.93; %blockcoefficent V=CB*L*B*T; %displacement deadweight=0.75*v; oiloutflow=max(deadweight^(1/3)*400,30000); %[m3] slop=0.02*deadweight; % maxtankvolume=0.75*oiloutflow; wallthick=4; %[m] bottomthick=4; %[m] maxindtankl=(0.25*wallthick/b+0.15)*l; tankw=(b-2*wallthick)/2; tankd=25; tankl=30; tankv=tankw*tankl*tankd; %individual tank volume totaltankv=16*tankv; %total tank volume sloptotal=0.02*totaltankv; slopind=sloptotal/2; SWballast=totaltankV/2.4; wingswtotal=wallthick*tankl*8*d*2; bottomsw=bottomthick*tankl*8*b; totaldoublehullsw=wingswtotal+bottomsw; SWremaining=SWballast-totaldoublehullSW; 17

18 %%Weight Calculations. Added on March 5, 2012 %%Total lightships weight: subtract cargo weight, fuel weight, half of slop %%tank weight. Latter two values gathered from POSSE Ship Project Editor. %%All weights are in metric tons. lightshipstot = V - totaltankv ; perclightships = lightshipstot/v; %percentage of total weight that is lightships hullstructure = 0.13*V; %hull structure weight mooringweight = 10000; %mooring structure weight engineweight = 100; %approx. weight of two Wartsila 32 diesel engines platformweight = 0.07*V; %weight of production platform accomodations = lightshipstot - (engineweight + mooringweight +... platformweight + hullstructure); %weight of accomodations, etc. %%% ABS Guidelines for Classing FPSO s. July 2009 %%% Hull Girder Structural Requirements Calculations %%% All units METRIC %%% David Cope clc clear all close all %% Ship Particulars L = 360; % Length of the waterline in meters B = 64; % length of the midships beam in meters Cb = 0.95; %Block Coefficient %% Wave Bending Moment Amidships k1 = 110; % kn-m k2 = 190; %kn-m Bvbm = 1; %Environemntal Safety Factor. 1.0 means operation in all ocean conditions if L<= 300 %m C1 = ((300-L)/100)^1.5; else if L> 300 && L<=350 C1 = elseif L>350 && L<=500 C1 = ((L-350)/150)^1.5; end end Mws = -k1*bvbm*c1*l^2*b*(cb+0.7)*10^-3; % Sagging Moment 18

19 Mwh = k2*bvbm*c1*l^2*b*cb*10^-3; % Hogging Moment %% Wave Shear Force distribution % Distribution Factors taken at positions starting at Aft Perpendicular and % moving forward in increments listed below. Pos = L*[ ]; % Positions forward of AP Fa = (0.92*190*Cb)/(110*(Cb+0.7)); F1 = [0 Fa Fa ]; Fb = (190*Cb)/(110*(Cb+0.7)); F2 = [ Fb Fb 0]; k = 30; Bvsf = 1.0; Fwp = k*bvsf.*f1*c1*l*b*(cb+0.7)*10^-2; % For positive shear force Fwn = -k*bvsf.*f2*c1*l*b*(cb+0.7)*10^-2; % For negative shear force %% Hull Girder Section Modulus % From Steel Vessel Rules 3-2-1/3.7 if Mws > Mwh %where Mw is the max wave induced bending moment Mw = Mws; else Mw = Mwh; end Msw = *9.81; % m-mtstill water bending moment due to maximum loads and buoyancy conditi Mt = Mw + Msw; fp = 17.5; %nominal allowable bending stress kn/cm^2 C2 = 0.01; SM1 = Mt/fp; % Hull Girder Section Modulus SM2 = C1*C2*L^2*B*(Cb+0.7); % Minimum Section Modulus if SM1>SM2 SMdesign = SM1/100^2 % Design Section Modulus m^3 elseif SM1<SM2 SMdesign = SM2/100^2 end 19

20 %% Minimum Hull Girder Moment of Inertia I = L*SMdesign/33.3 % cm^2-m^2 %% General Scantling calculations based on SVR 5A % Plating (mm) Keelplate = *L; % Kel plate thickness. If L>300, then use no more than 300m bkl = 800+5*L; % Breadth of keel plating to extend over the flat of bottom for the complete length of the ship. Cannot be less than value. BShellplate = *L; % Bottomshell/bilge/side shell plate not including along the keel TankShell = *L; % Hull internal tank boundaries Other = *L; % Non-watertight bulkheads between dry spaces and other plates in general % Primary Support Members (mm) Maingirder = *L;% Double bottom girders Girder = *L; % Other double bottom girders Bottom = *L; % Double bottom floors, web plates of side transverses and stringers in double hull Rest = *L; % Web and flanges of vertical web frames on longitudinal bulkheads, horizontal stringers on transverse bulkhead, deck transverses (above and below upper deck) and cross ties. 9 References Chapter III: Requirements for minimizing oil pollution from oil tankers due to side and bottom damages, Regulations MARPOL Consolidated Edition, Guide for Building and Classing Floating Production Installations. American Bureau of Shipping. April 2010 consolidation. Lecture and course notes for Yuming Liu and David Cope. Unpublished. Massachusetts Institute of Technology, Spring Haveman et al. Design of a Floating, Production, Storage, and Offloading Vessel for Operation in the South China Sea. Texas A&M University. May 15, Allen et al. Design of a Floating Production Storage and Offloading Vessel for Offshore Indonesia. Texas A&M University. May 15,