September 28-3, 24 DP Design & Control System A Feasible Concept of Bi-axial Controlled DP for FPSOs in Benign Environment Authors: Onno A.J. Peters IHC Gusto Engineering BV (Netherlands) Jaap-Harm Westhuis IHC Gusto Engineering BV (Netherlands) Jo. A. Pinkster Delft University of Technology (Netherlands)
HOLDING STRUCTURE SBM SBM IMODCO IHC Caland Atlantia Dredging / Shipbuilding IHC Holland Merwede IHC Gusto Engineering MSC GustoMSC- Ocean Design Inc. GustoMSC Dutch holding of international companies working in offshore, dredging and marine industries
Content History Theoretical Background Design Knowledged based design Software use FPSO concepts Environmental conditions Results Conclusions
History Basic idea created in 1971 to investigated stability Bi-axial DP was introduced in the late 198 s: SWOPS II model tests simulations Never actually applied Conventional DP 154, DWT Weathervaning mode Only one FPSO with DP
Theoretical background Modern DP control systems can be divided in two separate functions: PDI-control KALMAN control Thruster system Bi-axial DP concentrate thrusters at one end of the vessel, COT x no heading control F F M x, req y, req ψ, req = P = P = FP x y x + D x x & + I x y + D y y& + I y COT ψ + D ψ& + I y ψ, req xψ ψ xdt y dt ψ dt
Theoretical background Choice of center of thrust Choice of center of rotation Stability of DP-control Naturally stable, COR forward of COG Unstable, COR aft of COG COR COT c g COG
Design Bi-axial DP controlled FPSO s Combining know-how: Drill ships FPSO s Dynamic Positioning DP vessel designs In-house developed software Equipment Thrusters Retrieval systems Contacts: Sister companies Technology institutes
Validity of Software Software validated against model tests DP drill ship (Glomar C.R. Luigs, Glomar Jack Ryan) Moored FPSO s Feedback from clients Drill ships Dredgers 6. 5. Maximum excursion [m] + 3 3 % % 4. 3. -33% 2. 1.. high beam c u rre n t. 1. 2. 3. 4. 5. 6. MARIN
Concept 1 Early Production FPSO
Concept 2 New-built 2mln barrel FPSO
Environmental Conditions Bi-axial DP tested in 9 squall events: Increasing speed and shifting direction Maximum squall wind speed is 28 m/s Feasibility of concept 1: Sea-states related to squall events 1-year return Brazilian condition Feasibility of concept 2: Squall events combined with 1-year West of African swell
m /s in d p ee n d s W i Environment squall events S quall 1 Squall 2 Squall 3 3 315 3 315 3 315 25 27 25 27 25 27 2 225 2 225 2 225 15 18 15 18 15 18 1 135 1 135 1 135 5 9 5 9 5 9-2 -1 1-1 1 2-2 2 4 S quall 4 Squall 5 Squall 6 3 315 3 315 3 315 25 27 25 27 25 27g d e 2 225 2 225 2 225n 15 18 15 18 15 18 n i tio 1 135 1 135 1 135 r 5 9 5 9 5 9-2 2-2 2-1 1 2 n d d i W i S quall 7 Squall 8 Squall 9 3 315 3 315 3 315 25 27 25 27 25 27 2 225 2 225 2 225 15 18 15 18 15 18 1 135 1 135 1 135 5 9 5 9 5 9-1 1 2-4 -2 2-1 1 2 Time in s
Results Concept 1 Added 4x3.6 MW thruster power versus 6x2.7 MW for conventional DP concept No thrusters added in the pump room Lay-out changed to ensure stable bi-axial control Maximum offset in 1-year Brazilian condition appr. 36.2 m Operation in water depth larger than 6 m
Results Concept 1 15 Bi-axial, COT=85.7m COR=7.m, 1-year, wa:14 wi:16 cu:295, single failure Conventional DP, COR=-35m, 1-year, wa:14 wi:16 cu:295, zero required moment, single failure 15 1 1 5 5 y_cor [m] y_cor [m] -5-1 -15 timetrace COR extreme positions COR mean position COR extreme positions COG mean vessel contour extreme vessel contours starting position vessel max radial offset:36.2 [m] -15-1 -5 5 1 x_cor [m] -5-1 timetrace COR extreme positions COR mean position COR extreme positions COG mean vessel contour extreme vessel contours starting position vessel max radial offset:42. [m] -1-5 5 1 15 x_cor [m] Demo Concept 1
Results Concept 2 6x3.6=21.6 MW total thruster power Single thruster failure allowed Maximum simulated offset appr. 2.5 m y_cor [m] 1 5-5 -1 COT=99m COR=152m, 1yr swell+squall 7, wa:24 sq:18 cu:225-15 Demo Concept 2 timetrace COR -2 extreme positions COR mean position COR extreme positions COG mean vessel contour -25 extreme vessel contours starting position vessel max radial offset:2.5 [m] -3-35 -3-25 -2-15 -1-5 5 1 x_cor [m]
Conclusions Concept 1 Early production FPSO Reduction of installed thruster power Reduction of conversion costs Behavior comparable to Conventional DP Single thruster failure allowed Concept 2 2mln barrel FPSO 21.6 MW installed thruster power feasible for West of Africa Single thruster failure allowed Competitive with turret moored system
Summary Bi-axial DP Passively react on large and rapid environmental changes, without use of algorithms determining the best heading