mooring 37 to 74

Industry Mooring Standards
● API RP 2SK – Design and Analysis of Station keeping Systems for Floating Structures (2005) ● API RP 2SM– Recommended Practice for Design, Manufacture, Installation, and Maintenance of Synthetic Fiber Ropes for Offshore Mooring (2001, 2007) ● API Spec 2F – Mooring Chain (1997) ● API RP 2I – In-service Inspection of Mooring Hardware for Floating Drilling Units (2008)
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API Tension Limits & Safety Factors
Analysis Method Intact Intact Damaged Damaged Quasi-static Dynamic Quasi-static Dynamic
Tension Limit (% of MBS) 50 60 70 80
Equivalent Factor of Safety 2.0 1.67 1.43 1.25
Courtesy of API RP 2SK
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API & ABS Tension Criteria for MODU
● Tension factor of safety – survival condition
Analysis Method Intact Intact Damaged Damaged Quasi-static Dynamic Quasi-static Dynamic
ABS Factor of Safety 1.80 1.50 1.25 1.09
API Factor of Safety 2.00 1.67 1.43 1.25
Courtesy of API RP 2SK
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API & ABS Tension Criteria for MODU
● Tension factor of safety – operating condition
ABS Factor of Safety 2.7 2.25 1.8 1.57 API Factor of Safety NA NA NA NA
Courtesy of API RP 2SK
Analysis Method Intact Intact Damaged Damaged Quasi-static Dynamic Quasi-static Dynamic
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API Anchor Design Criteria
● Drag anchor safety factors
Quasi Static Analysis MODU Intact condition Damaged condition Permanent Mooring Intact condition Damaged condition 1.5 1.0
Courtesy of API RP 2SK
Dynamic Analysis
1.0 Not required
0.8 Not required
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Dynamic & Quasi–Static Analysis
● Two degree motions: surge, sway ● Static vessel and line movement (catenary) ● Ignore inertia and damping
Quasi-static Analysis
6 degree motions: surge, sway, heave, roll, pitch, yaw
Dynamic Analysis
Dynamic vessel and line movements 42

Technologies
● Mooring
■ ■ ■
Geotechnical and soil mechanics Anchors and piles Mooring legs and tendons Statistical analysis Waves Current Wind Performance Structures Flow assurance
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● Metocean
■ ■ ■ ■
● Risers
■ ■ ■
ABS Applied Software
● ANSYS: General FEM, Strength, strain, soils, heat transmission ● NASTRAN: General FEM, Strength, strain ● SACS/STRUCAD: Structural analysis program ● FEMAP: General FEM pre-process and post-process tools ● AQWA: Hydrodynamic analysis, linear frequency domain, motion with mooring analysis ● OSAS: FEM Structural analysis incorporates wave loads generated by AQWA
Drilling companies need software to analyze mooring and station keeping capabilities for most drilling operations
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ABS Software
● CAP: Fully coupled nonlinear time domain analysis with mooring, Riser, tendon tension computed dynamically ● DEEPCAT: Fully coupled nonlinear time domain analysis with mooring, riser, tendon tension computed dynamically ● DMOOR: De-coupled mooring analysis in time domain ● FLEXCOM-3D: General purpose, non-linear, 3D finite element for static and time-domain dynamic analysis for flexible and rigid risers, TLP tethers, jack-up platforms, mooring systems, and steel catenary risers ● Hydros3: Hydrodynamics motion analysis program
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ABS Software
● MULTISIM/TDSIM: Non-linear time domain analysis with mooring/riser/tendon tension computes quasi-statically (partially coupled with vessel motions) ● MORA: Hydrodynamic motion analysis program ● SPLASH: Coupled frequency domain Programs ● SeaSafe: Naval architecture hydrostatics, stability and loading instrument program
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Mooring Components and Hardware
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Mooring Components/Hardware
● Mooring Line Components ● Winching system ● Anchoring system
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Chain Type & Grade
● Type
■ ■
Stud Link (Welded, Unwelded) Studless
● Grade
■
Grade 3, K3, R3, ORQ (Oil Rig Quality) Grade 4, K4, R4 ORQ + 20%, R3S R4S, R5 (new)
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■ ■ ■
Fatigue Due to Loose Stud
● High stress concentration:
■ ■
Bend zone (fixed stud) Stud area (loose or no stud)
● Local stress concentration factor at stud footprint:
■
1.5 – 2.0
Courtesy of UT Short Course on FPS
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Studless Chain
● No stud related problems
■ ■ ■ ■
Loose stud Crack at stud weld Corrosion at stud/link Fatigue
● Easier to make ● Easier to inspect ● Lower fatigue resistance ● More difficult to deploy (not suitable for drilling rig)
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Typical Wire Rope Construction
Sheathed Spiral Strand (Permanent Mooring)
Non-Sheathed Spiral Strand
Non-Sheathed Spiral Strand With Zinc Fillers
Multistrand
6 Strand IWRC (MODU Mooring)
8 Strand IWRC
Courtesy of API RP 2SK
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Life Expectancy of Wire Rope
● Galvanized 6- strand: 6-8 years ● Galvanized unjacketed spiral strand: 10-12 years ● Galvanized unjacketed spiral strand with zinc filler wires: 15-17 years ● Galvanized jacketed spiral strand: 20-25 years ● Galvanized jacketed spiral strand with zinc filler wires: 30-35 years
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Winching Equipment for Chain
Courtesy of API RP 2SK
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Chain Jack & Bending Shoe Fairlead
● Chain Jack
■ ■
Low speed For permanent mooring
● Chain bending shoe
■ ■
D/d can be 70 Damage to nylon pad Seldom used
Courtesy of API RP 2SK
■
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Drum Type Winch & Fairlead for Wire Rope
● Operation is fast and smooth ● Tension capacity depends on number of layers ● Can be problem for very deepwater
Courtesy of API RP 2SK
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Commercial Drag Anchors
● Large number of commercial anchors is used by the offshore industry
Courtesy of API RP 2SK
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Drag Anchor Design Curve
in Soft Clay
● Developed by NCEL (Naval Civil Engr. Lab., 1987) ● One for soft clay, one for sand ● Anchor manufacturers may provide higher design curves
in Soft Clay
Courtesy of API RP 2SK
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Dynamic Positioning
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Benefits of DP
● Unlimited water depth ● Transit with no tugs ● Easy evacuation from site ● Directionality with environmental loads ● Easy for avoidance of obstructions ● Allows positioning with respect a many beacons:
■ ■ ■ ■ ■
Well head Other vessels Geographic points GPS Seabed beacons
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Dynamic Positioning Systems
● For levels of redundancy and automation
■ ■ ■ ■
DPS-0 DPS-1 DPS-2 DPS-3
● DP Notations is optional
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Notations DPS-0 & DPS-1
● DPS-0
■ ■
Centralized manual position control and automatic heading control Maintain position and heading under the specified maximum environmental conditions Independent centralized manual position control with automatic heading control Automatically maintain position and heading under the specified maximum environmental conditions
● DPS-1
■ ■
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Notations DPS-2 & DPS-3
● DPS-2
■
Automatically maintain position and heading within a specified operating envelope under specified maximum environmental conditions during and following any single fault, excluding a loss of compartment or compartments.
● DPS-3
■
Automatically maintaining position and heading within a specified operating envelope under specified maximum environmental conditions during and following any single fault, including complete loss of a compartment due to fire or flood.
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Rules, Regulations & Standards
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ABS Rules & Guides
● Rules for building and Classing Steel Vessels ● Rules for Building and Classing Mobile Offshore Drilling Units (2008): for Circle P Notation ● Guidance Notes on the Application of Synthetic Ropes for Offshore Mooring (1999) ● Guide for Certification of Offshore Mooring Chain (2009, effective 2011)
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ABS Mooring Notations for MODU
● Is based on internationally agreed equations – applies to E all trading vessels. Not required except for drillships (may change in future) M Typically it applies to MODU who voluntarily require inspection of the mooring equipment on the basis of owner specified standards P Highest noted mooring system, it follows ABS Standards for anchors, chain, and equipment. Mooring analysis is required; typically based on API RP-2SK
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IMO MODU Code
● 1989 Code requires that the mooring be to the satisfaction of the administration ● 1991 Amendments to the 1979 and 1989 Codes and the 2009 revision requires mooring analysis
API RP 2SK is applied for design criteria unless otherwise specified by owner
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Verification Regime for Coastal State Regulations
● China State Administration of Work Safety (SAWS) ● Australia National Offshore Petroleum Safety Authority (NOPSA) ● US Minerals Management Service (MMS) ● UK Health and Safety Executive (HSE) ● Norwegian Petroleum Directorate (NPD) ● Canadian Petroleum Board (CNSOPB, CNLOPB) ● Directoria de Portos e Costas (DPC – Brazil)
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Class Exercise
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Class Exercise – Conceptual Design
● Develop a conceptual design for a floating production installation for the following four cases: a) North Sea, 600 ft water depth (Severe winter storm) b) Gulf of Mexico, 5000 ft water depth (Severe hurricane & loop current) c) Brazil, 4000 ft water depth (Median environment w/long swells) d) West Africa, 100 ft water depth (Mild environment w/long swells)
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Class Exercise – Conceptual Design
● For each case, specify the following and give the reasons and assumptions for the selection: 1. Production Vessel 1. Semi submersible 2. Ship-shaped vessel 3. Spar 4. Barge 5. Newbuild or conversion
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Class Exercise – Conceptual Design
2.
Type of Mooring ● Spread ● Turret (Specify location of turret) ● Number of lines/pattern e.g 12-line symmetric, 3x3, 4x3, 3x4, etc. ● Catenary or taut leg? ● Thruster assist? ● Disconnectable ?
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Class Exercise – Conceptual Design
3.
Mooring Line ● All chain ● All wire rope ● Combination chain/wire rope ● Fiber rope ● Buoy / clump weight
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https://www.sodocs.net/doc/865167163.html,
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