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This presentation is a general overview of a floating offshore wind farm. The main goal is to design a semisubmersible platform for 5MW wind turbine. Most relevant marine topics were studied: sizing,stability,seakeeping,mooring,structure,ancillary systems,costs and viability.
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FLOATING OFFSHORE WIND FARM
ILLAS SISARGAS
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Project aims
Semisubmersible floating platform desing for 5MW wind turbine.
100 MW floating offshore wind farm.
Platform integration in the wind farm: Electric solution.
Mooring and seakeeping grid mooring array synergies .
Wind farm O&M: Full maintenance strategy.
Expenditures analysis and financial viability study .
1. Emplazamiento del parque• Depth: [250m-400m]
• Average distance to shore : 30 km.
• Annual average wind speed : 10,05 m/s Predominant direction: NE-SW
• Typical wave height: 2,5 m Predominant direction: NW-SE
• Significant wave height (50 years) :13,09 m
• Maximun wave height (50 years): 24 m
• Seabed type : Sandy-rocky
• Area: 17,25 km2
2. Sizing process
Final decisions.
Initial dimensions are fixed
Design Constraints
Parameter
model
Weight estimationInertia and CoG
estimation
GM > 0
w
zgA
AMT
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GM
dFarctg
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3. Loads in floating structures.
Dinámicas
Pesos
Viento
Corriente
Presión hidrostática
Olas
Cargas en estructuras offshore
Constantes
Dinámicas
Sustentación
Arrastre
Ecuación de Morison
Radiación
Excitación
Masa añadida
Amortiguamiento
Froude-Krylov
Difracción
Fuerzas
1er
orden
Fuerzas
2ºorden
Deriva
estacionaria
Potencial
ViscosaSlow drift motion
Efecto
Slamming
Olas
Rompientes
Efecto Run-up y
sloshing
Otras
Estáticas
5[NREL picture].
4. Lines optimization.• External hull
Lines optimization of the initial model:
Improve hydrodynamic behavior. Reduction of waves and currents loads.
Remove corners to avoid tensions ocurred during welding process.
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4. General Arrengement
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5. Hydrostatic and stability.
• Nowadays, there is not specific rules for floating offshore wind turbine platforms.
• Tanks comparments are the easiestdivision as posible.
See figure:
• General stability criteria for oil and gas platforms is applied.
• The basics rules that we have to evaluate
– Area under heeling and righting arms: A+B>1,3(B+C)
– Static angle of heel θ1 (first intersection point) shall notbe greater than 15º -17º, (depending of rule).
– Metacentric height GM shall be greater than 1m in transit, operation and survival condition .
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5. Watertight stability criteria
• Static angle of heel is 11º < 15º
• Ratio area Righting/Heeling is more than 1,3
• WATERTIGHT STABILITY CRITERIA IS PASSED.
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5. Damage stability criteria
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6. Seakeeping
DESIGN REQUIREMENTS.• Platform eigenperiods shall not be the same as wave periods in the
wind farm location.
• Nacelle accelerations should be < 3 m/s2.
ANALYSIS • Frecuency domain analysis.
Restoring forces of mooring are disregarded in catenary moored floating structures, in first approximation.
Aerodynamics effects are not included in the numerical model.
Time domain analysis is not necessary in the first steeps of the design.
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waveshydhydtotal FηCηBηA)(M
6. SEAKEEPING. PHASE I
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• Frecuency domain analysis.
• Wave direction. Fore sea (0º)
• Until 11 s period waves, heave motion is very small
• Heave resonance period is 11 s antiheave plates are neccesary
6. SEAKEEPING. PHASE II
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• Frecuency domain analysis.
• Wave direction. Fore sea (0º)
• Heave, surge and ptich are themost important responses.
• Heave resonance period 17,5 s.
6. SEAKEEPING: NACELLE ACCELERATIONS
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FASE I
Periodo propio en largada (s) 13,18 17,5
Periodo propio en deriva (s) 0 0
Periodo propio en arfada (s) 0 0
Periodo propio en balance (s) 20,9 34
Periodo propio en cabeceo (s) 20,9 34
Periodo propio en guiñada (s) 0 0
Seastate 1 Seastate 2 Seastate 3
Velocidades en largada (m/s) 0,26 3,6 4,061
Velocidades en deriva (m/s) 0,34 2,55 1,42
Velocidades en arfada (m/s) 0,039 3,19 0,398
Velocidades en balance (rad/s) 0,0007 0,022 0,012
Velocidades en cabeceo (rad/s) 0,0019 0,028 0,017
Velocidades en guiñada (rad/s) 0,0009 0,0025 0,0024
Aceleraciones en largada (m/s2) 0,148 1,52 1,17
Aceleraciones en deriva (m/s2) 0,037 1,035 0,399
Aceleraciones en arfada (m/s2) 0,197 1,42 0,16
Aceleraciones en balance (rad/s2) 0,00042 0,0089 0,0033
Aceleraciones en cabeceo (rad/s2) 0,0012 0,012 0,0048
Aceleraciones en guiñada (rad/s2) 0,00043 0,0013 0,00063
FASE II
7. MOORING SYSTEM.
P Platform position at sea
Definition of mooring
system
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7. MOORING.
Static analysis.
• Depth: 250 m
• Initial chain length : 680 m
• Chain type: Studless; Diameter 75 mm.
• Breaking loads:
• Grado 2: 2928,3 kN (298,6 ton)
• Grado 3: 4189,5 kN (427,2 ton)
• Grado 4: 5856,7 kN (597,2 ton)
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8. MOORING.
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Static analysis
Horizontal design force effect (90 ton)
Same effect with 620 m lines(90 ton)
Horizontal offset 143 m and ptich angle 6,4 º
Fairlead tension in fore lines: 83 ton
Reduction change length 620 m.
Horizontal offset 61 m y pitch angle 6,1 º
Fairlead tension in fore lines: : 106 ton
Dynamic analysis in different seastates
8. MOORING.
Dynamic analysisSEASTATE 1. NORMAL OPERATION
• Low excurssions and rotations.
• Tension (95 ton) far from breaking loads.
• Mooring system is suitable.
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SEASTATE 2. EXTREME OPERATION
Bigger tensions (140 ton) although far from breaking loads.
High motions. ¿is it possible wind turbine running?
Developer has to decide
SEASTATE 3. 50 YEARS STORM
Tension 250 ton Chain grade R3.
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8. MOORING. FINAL ARRENGEMENT
Profundidad d m 250
Tipo de fondeo catenaria
Longitud de líneas L m 620
Tipo de eslabón sin contrete
Dimensiones eslabón 75 mm
Grado R3
Carga de rotura KN 4189,5
Relación L/d 2,48
Características generales
8. STRUCTURAL DEFINITION.
• Local Design DNV OS-C101 Rules
– Hydrostatic pressures
– Dynamic affects
• Global Design Buckling, fatigue
Column-Pontoon nodes definition
Deck-columns definition.
FEM methods
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8. MAIN SECTIONS
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PONTOONS COLUMNS
8. STRUCTURE. GENERAL VIEW.
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8. NODE STRUCTURAL DETAIL
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COLUMN WITH DECKS
TOWER WITH DECK
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9. Ancillary systems : active ballast
Submerged pumps: 500 m³/h
Automatic ballast system Anti- rotations
Piping of GRE high performance with sea water
Simplification: no remote operated valves
Maintenance from upper zone of columns
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Lighting, signaling and buoying
Access and docking
Comunications: SCADA system
Paint and cathodic protection.
9. Ancillary systems
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10. Electric engineering.
Uninterrupted power system (UPS)
120 Ah / 60 kVA / max current 115 A
Situated in pump rooms
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10. Electric engineering.
Cable in wind farm 33kV.
Cable to shore 132 kV
Platform with subestation
4 trafo 25kVA
One platform with different design
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11. Construction and installation: 3,5 years
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11. Operation and maintenance
20 years lifecycle operation
Dismantling vs increasing lifecycle
Operating a vessel in property
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12. Costs
Shipowner of
Vessel
Decrease other
expenditures
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12. Viability
Rendimiento del
dinero prestado: 8%
Rate 190 €/MWh
TIR 1%
Thanks.
Rights reserved to autors and Politechnic University of Madrid (UPM)
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• Ramón Barturen, MSc. Marine Engineer (UPM) and Master in Marine Bussines and Laws (IME)
• Bernardino Couñago, MSc. Marine Engineer (UPM)
Project supervision
• D. Manuel Moreu Munaiz
• D. Miguel Ángel Herreros Sierra
For any question, please, contact us: