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HYBRID WAVE TANK TESTING OF FLOATING WIND TURBINES
Vincent Arnal, Jean-Christophe Gilloteaux, Félicien Bonnefoy, Sandrine Aubrun
LHEEA, Ecole Centrale de Nantes, France
115th EAWE PhD Seminar - 31/10/2019
215th EAWE PhD Seminar - 31/10/2019
OUTLINE
• Wave tank testing of floating wind turbines
• Presentation of the hybrid testing system
• Ongoing and future wave tank tests
3
Wave tank testing of floating wind turbines
Why including aerodynamics loads ? Mean positions Influence of Controler Aerodynamic damping Additionnal excitation
Objective? Validation of the design (Floater, moorings, …) Validation and calibration of numerical models
𝐹𝑎𝑒𝑟𝑜
15th EAWE PhD Seminar - 31/10/2019
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Wave tank testing of floating wind turbines
15th EAWE PhD Seminar - 31/10/2019
Drag diskGeometry
scaled rotorThrust matched
scaled rotor
100% physical
MeanThrustforce
Unsteadyaerodynamicforce
Test of Control strategies
Actuatorresponsetime
Scalability to large rotor (10-15 MW)
Porous Disk + + - - - - -
Geometry scaled rotor + - - ++ -
Thrust Match rotor ++ - - ++ -
Wind
Reynolds
Wave
Froude
Hybrid with actuators
Wind generation system performance at Ecole Centrale de Nantes
Blade Pitch control
Rotor Nacelle Assembly
5
Real-Time Hybrid model testing - Principle:
Physic → Numeric
Motions of
Platform and tower
Physic ← Numeric
Rotor Force (Aero, Gyro, Inertia...)
Full scale :Simulation of a wind turbine :Wind + Aero + Servo + ElasticAdapted OpenFAST
Model Scale:Waves + Platform + Tower + Moorings+ Actuators
Motions
RNA Force
©SINTEF Ocean (Thys, 2018)
15th EAWE PhD Seminar - 31/10/2019
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Wave tank hybrid testing of FWT : actuators
15th EAWE PhD Seminar - 31/10/2019
SINTEF Ocean 6 cables(Chabaud, 2016);(Sauder et al., 2016);...
SOFTWIND Project
Purpose: Development of an experimental platform based on a hybrid approach for the wave tank testing of floating wind turbines.
Objectives: • Accurate and robust experimental platform• Test of innovative control strategies developed by the SME D-Ice Eng
On-land
IH Cantabria 6 on-board fans(Urbán and Guanche, 2019); (Battistella et al., 2018)
On-board
Bandwidth ??
7
SOFTWIND Hybrid system
Wave tank
2C Force transducer
Actuator (s)
Floater
Mast
ESC
Motion Capture system
Accelerometer
Host PC
Wind turbine Simulation
FAST code
NI CompactRIO controler
Actuator command
Data acquisition
Dry
15th EAWE PhD Seminar - 31/10/2019
6 DoF Hexapod
Dry
8
TEST BENCH Validation of the methodology
Overall validated methodology1. Realistic FWT motions 2. Motions reproduced by Hexapod3. Motions capture4. Force computed in real-time by integrated
numerical code5. Actuator commanded to reproduce this force
Success Indicators :• The real-time computed force corresponds
to the load case we are reproducing.• The actuator reproduces with a sufficient
accuracy the setpoint force.
𝐻𝑠[m]
𝑇𝑝[s]
𝑈𝑤[m/s]
Mean thrust
[kN]
LC1 3 5 11.4 680
LC2 4 5 18 320
LC3 6 10 11.4 680
LC4 7 10 18 320
LC5 7 17 11.4 660
LC6 8 17 18 320
OC3 Hywind Spar – 5MW scale 1:30• Rigid blades and tower• Active controler
Name of FWT OC4_Semi OC3_Spar TripleSpar_10MW
Representative
picture
[14] [17] [15]
Wind Turbine NREL-5MW [18] NREL-5MW [18] DTU-10MW [19]
15th EAWE PhD Seminar - 31/10/2019
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OC3 Hywind Spar – 5MW at scale 1:30Waves conditions : Severe Sea State, 𝐻𝑠 = 8.6𝑚 𝑇𝑝 = 13𝑠;
Wind conditions : Normal Turbulence Model, 𝑈𝑤 = 18𝑚. 𝑠−1; 𝑇𝐼 = 14.6%;
3P
Waves
Improvement with the use of inverse dynamicsBut still 30 ms pure delay
TEST BENCH Validation of the methodology
15th EAWE PhD Seminar - 31/10/2019
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Calibration / characterization : • Modal frequency, • Structural damping• Stiffness
Challenge : Measure relative flexible towermotions (small amplitude and high frequency) Use Inertial Measurement Units and Motion Capture system (Kalman filters)
Structure to limite weight effectsof the cables
Moving to wave tank tests: 1. Flexible tower at scale 1:40
Flexible MAST
15th EAWE PhD Seminar - 31/10/2019
Qualysis markers
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Calibration / characterization : • Wind turbine tower modal frequency• Evaluation of structural damping• Evaluation of mast stiffness
15th EAWE PhD Seminar - 31/10/2019
Moving to wave tank tests: 1. Flexible tower at scale 1:40
12
Floating fish farm with a 10MW turbine : (October 2019)
SPAR with the DTU 10MW RWT (Nov. – Dec. 2019)
Under construction!!
15th EAWE PhD Seminar - 31/10/2019
Moving to wave tank tests: 2. Ongoing experiments
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CONCLUSION
• Development of a hybrid wave tank testingmethodology Implementation and validation of the
communication
• Actuators Selection Identification of performances Command improvements
• Wave tank tests Additionnal complexity with flexible mast Ongoing !
1415th EAWE PhD Seminar - 31/10/2019
SOFTWIND project: Schedule
THANK YOU FOR YOUR ATTENTION
15th EAWE PhD Seminar - 31/10/2019 15
16
Loads acting on a RNA
15th EAWE PhD Seminar - 31/10/2019
𝐹𝑠𝑒𝑡 =
𝐹𝑎𝑒𝑟𝑜 𝑥𝐹𝑎𝑒𝑟𝑜 𝑦𝐹𝑎𝑒𝑟𝑜 𝑧0
𝑀𝑎𝑒𝑟𝑜 𝑦
𝑀𝑎𝑒𝑟𝑜 𝑧
+
000
𝑀𝑥 𝐿𝑆𝑆 𝑟𝑖𝑔𝑖𝑑
00
+
0000
𝑀𝑔𝑦𝑟𝑜 𝑦
𝑀𝑔𝑦𝑟𝑜 𝑧
+
𝐹𝐼𝑛𝑒𝑟𝑡𝑖𝑎 𝑓𝑙𝑒𝑥 𝑥
𝐹𝐼𝑛𝑒𝑟𝑡𝑖𝑎 𝑓𝑙𝑒𝑥 𝑦
𝐹𝐼𝑛𝑒𝑟𝑡𝑖𝑎 𝑓𝑙𝑒𝑥 𝑧
𝑀𝐼𝑛𝑒𝑟𝑡𝑖𝑎 𝑓𝑙𝑒𝑥 𝑥
𝑀𝐼𝑛𝑒𝑟𝑡𝑖𝑎 𝑓𝑙𝑒𝑥 𝑦
𝑀𝐼𝑛𝑒𝑟𝑡𝑖𝑎 𝑓𝑙𝑒𝑥 𝑧
Aerodynamics Aerodynamicsand free rotor
speed
Inertia Rotor –rotating= Gyro
Inertia Rotor - flexible
Rotor Nacelle Assembly
RNA Physical model Numerical modelGravityInertial | 6 DOF platformInertial | flexible towerInertial | flexible bladesInertial | rotating blades (gyroscopic)AerodynamicsFree rotor speed
ElastoDyn outputs fromOpenFAST v2.1
MethodologySpecifications of actuators setpoints :
Preliminary analysis of the characteristics of the aerodynamic tensor based on numericalsimulations of:
For Norm Design Load Cases of type 1.X (power
production)
Severe waves Normal Turbulence Model Wind-wave misalignment
3 different FOWTs: • OC4 semi submersible (5MW)• OC3 Hywind (5MW)• Triple Spar (10MW)
Analysis of the relative contributions of the different frequencies of interest=> Standard deviations of the aerodynamic load components by frequency bandwidth
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