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.

1. FLOATING OFFSHORE WIND FARM
ILLAS SISARGAS
ramonbarturen@gmail.com
bernardinocounago@gmail.com
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2. 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 .
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3. • Depth: [250m-400m]
• 1. Emplazamiento del parque
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

4. 2. Sizing process
Parameter
model
Inertia and CoG
Weight estimation estimation
GM > 0
M  A33
Tz  2
gAw
Design Constraints
 F d 
  arctg  
   GM 
Final decisions.
Initial dimensions are fixed
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5. 3. Loads in floating structures.
Cargas en estructuras offshore
Pesos
Estáticas Presión hidrostática
Sustentación
Corriente
Arrastre
Constantes
Viento
Dinámicas
Ecuación de Morison
Difracción
Excitación
Dinámicas Fuerzas Froude-Krylov
1er
orden
Masa añadida
Radiación
Amortiguamiento
Olas Potencial
Deriva
Fuerzas estacionaria
2ºorden Viscosa
Slow drift
motion
Efecto
Slamming
Olas
Otras
Rompientes
Efecto Run-up y
[NREL picture]. sloshing 5

6. 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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7. 4. General Arrengement
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8. 5. Hydrostatic and stability.
• Nowadays, there is not specific rules • General stability criteria for oil and gas
for floating offshore wind turbine platforms is applied.
platforms. • The basics rules that we have to evaluate
• Tanks comparments are the easiest – Area under heeling and righting arms:
A+B>1,3(B+C)
division as posible.
See figure: – Static angle of heel θ1 (first intersection point) shall not
be 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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9. 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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10. 5. Damage stability criteria
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11. 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.
(M total  A)η  Bhyd η  Chyd η  Fwaves
 
 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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12. 6. SEAKEEPING. PHASE I
• 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
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13. 6. SEAKEEPING. PHASE II
• Frecuency domain analysis.
• Wave direction. Fore sea (0º)
• Heave, surge and ptich are the
most important responses.
• Heave resonance period 17,5 s.
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14. 6. SEAKEEPING: NACELLE ACCELERATIONS
FASE I FASE II
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 14

15. 7. MOORING SYSTEM.
P Platform position at sea
Definition of mooring
system
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16. 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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17. 8. MOORING.
Static analysis
Horizontal offset 143 m and ptich angle 6,4 º
Fairlead tension in fore lines: 83 ton
Reduction change length 620 m.
Horizontal design force effect (90 ton)
Horizontal offset 61 m y pitch angle 6,1 º
Fairlead tension in fore lines: : 106 ton
Dynamic analysis in different seastates
Same effect with 620 m lines(90 ton)
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18. 8. MOORING.
Dynamic analysis
SEASTATE 1. NORMAL OPERATION
• Low excurssions and rotations.
• Tension (95 ton) far from breaking loads.
• Mooring system is suitable.
SEASTATE 2. EXTREME OPERATION SEASTATE 3. 50 YEARS STORM
Bigger tensions (140 ton) although far from breaking loads.  Tension 250 ton Chain grade R3.
High motions. ¿is it possible wind turbine running?
Developer has to decide
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19. 8. MOORING. FINAL ARRENGEMENT
Características generales
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
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20. 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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21. 8. MAIN SECTIONS
PONTOONS COLUMNS
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22. 8. STRUCTURE. GENERAL VIEW.
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23. 8. NODE STRUCTURAL DETAIL
COLUMN WITH DECKS
TOWER WITH DECK
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24. 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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25. 9. Ancillary systems
 Lighting, signaling and buoying
 Access and docking
 Comunications: SCADA system
 Paint and cathodic protection.
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26. 10. Electric engineering.
 Uninterrupted power system (UPS)
120 Ah / 60 kVA / max current 115 A
Situated in pump rooms
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27. 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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28. 11. Construction and installation: 3,5 years
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29. 11. Operation and maintenance
 20 years lifecycle operation
 Dismantling vs increasing lifecycle
 Operating a vessel in property
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30. 12. Costs
Shipowner of
Vessel
Decrease other
expenditures
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31. 12. Viability
Rendimiento del
dinero prestado: 8%
Rate 190 €/MWh
TIR 1%
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32. Thanks.
• 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:
ramonbarturen@gmail.com
bernardinocounago@gmail.com
Rights reserved to autors and Politechnic University of Madrid (UPM)
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