This document discusses improving the efficiency and accuracy of reduced models used in load calculations for offshore wind turbine design. It evaluates different foundation modeling and reduction methods, including using refined reduced models like the augmented Craig-Bampton method. It also examines modeling the tower with more modes for improved accuracy and linearizing the soil model while combining it with non-linear pile models. The overall goal is to enhance load calculation methods by developing more accurate reduced models and efficient recovery-run procedures.

2. Introduction
Thesis goal
Refined foundation models
Conclusion
Physical problem
Industrial approach and limitations
Fully coupled approach
M¨u + C ( ˙u) ˙u + K(u)u = fa(u) + ff ( ˙u) (1)
Physical phenomena included
• Inherently coupled structures
• Non-linear aerodynamic
forces fa(u)
• Non-linear wave forces ff ( ˙u)
• Non-linear damping C( ˙u)
• Non-linear soil K(u)
Dawid Augustyn MSc. Presentation 1 / 12

3. Mode 16
f = 2.289 Hz, ζ = 0.03

4. Introduction
Thesis goal
Refined foundation models
Conclusion
Physical problem
Industrial approach and limitations
Sequential integrated approach
Ma 0
0 ˜Mj
¨ua
¨˜uj
+
Ca 0
0 ˜Cj
˙ua
˙˜uj
+
Ka 0
0 ˜Kj
ua
˜uj
=
fa
˜fj
+
ga
gj
,
ga + gj = 0.
Equivalent to (1) if non-reduced, non-linear foundation model MjCjKj is applied
Limitations
• Linearized substructure
• Substructure model reduced
˜Mj = TT
MjT
Dawid Augustyn MSc. Presentation 2 / 12

5. Introduction
Thesis goal
Refined foundation models
Conclusion
Thesis goal
Improved efficiency and accuracy of reduced models used in load calculations for an
offshore wind turbine design.
Dawid Augustyn MSc. Presentation 3 / 12

6. Introduction
Thesis goal
Refined foundation models
Conclusion
Foundation modelling and recovery-run procedures
Tower modelling
Non-linear soil modelling
Foundation modelling and recovery-run procedures
Objectives
• Quality of reduced models (Guyan,
Craig-Bampton, Augmented CB)
• Efficiency of recovery-run (FC, DE)
Methodology
1 (Reduced) Foundation models
2 Aero-elastic FLEX5
3 Recovery-run
Dawid Augustyn MSc. Presentation 4 / 12

7. Introduction
Thesis goal
Refined foundation models
Conclusion
Foundation modelling and recovery-run procedures
Tower modelling
Non-linear soil modelling
200 205 210 215 220
−0.02
−0.01
0
0.01
t [s]
u[m]
0.2 0.4 0.6 0.8 1 1.2 1.4
0
1
2
3
4
x 10
−3
f [Hz]
u[m]
200 205 210 215 220
−0.02
−0.01
0
0.01
t [s]
u[m]
0.2 0.4 0.6 0.8 1 1.2 1.4
0
1
2
3
4
x 10
−3
f [Hz]
u[m]
Guyan
Craig-Bampton
Augmented Craig-Bampton
Full
Figure 1: Force-Controll –
out-of-plane brace displacement
(wind+wave).
Figure 2: Direct-Expansion –
out-of-plane brace displacement
(wind+wave).
Dawid Augustyn MSc. Presentation 5 / 12

8. Introduction
Thesis goal
Refined foundation models
Conclusion
Foundation modelling and recovery-run procedures
Tower modelling
Non-linear soil modelling
Main findings
Table: Reduction methods’ outlook
Reduction method Static Dynamic Internal loading
Guayn
Craig-Bampton
Augmented Craig-Bampton
Table: Recovery-run methods’ outlook
Recovery run Pros Cons
Force-Controlled Robust Time-Consuming
Direct Expansion Efficient Refined reduction method
Augmented Craig-Bampton + Direct Expansion =
Dawid Augustyn MSc. Presentation 6 / 12

9. Introduction
Thesis goal
Refined foundation models
Conclusion
Foundation modelling and recovery-run procedures
Tower modelling
Non-linear soil modelling
Tower modelling
Objectives
• Modal tower representation
• How many modes?
Methodology
1 Nacelle reactions
2 Time integration
3 Reaction, displacement convergence
Dawid Augustyn MSc. Presentation 7 / 12

10. Introduction
Thesis goal
Refined foundation models
Conclusion
Foundation modelling and recovery-run procedures
Tower modelling
Non-linear soil modelling
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0.5
0.6
0.7
0.8
0.9
1
Number of tower bending modes
Convergence[Modal/FEM]
Tower top ux
Tower bottom Fx
Suggested
Current FLEX5
Figure: Convergence including only bending modes (per 1 direction).
Main findings
• Modal tower representation can successfully be applied in an aero-elastic code
Approach Number of bending modes Error
Current modal 2 25%
Suggested modal 10 1%
Dawid Augustyn MSc. Presentation 8 / 12

11. Introduction
Thesis goal
Refined foundation models
Conclusion
Foundation modelling and recovery-run procedures
Tower modelling
Non-linear soil modelling
Non-linear soil modelling
Objectives
• How to linearize soil
• Combination of linear SE and
non-linear piles
Methodology
1 Non-linear non-reduced model
2 Linearized soil included in SE
3 Linear jacket with NL piles
Dawid Augustyn MSc. Presentation 9 / 12

12. Introduction
Thesis goal
Refined foundation models
Conclusion
Foundation modelling and recovery-run procedures
Tower modelling
Non-linear soil modelling
0 5 10 15 20 25
2
2.2
2.4
x 10
−3
uz[m]
F EMNL SELIN SENL
0 5 10 15 20 25
3
3.5
4
x 10
−3
t [s]
uz[m]
0 5 10 15 20 25
3
3.5
4
x 10
−3
t [s]
uz[m]
FEM NL SE INIT SE MAX
Dawid Augustyn MSc. Presentation 10 / 12

13. Introduction
Thesis goal
Refined foundation models
Conclusion
Foundation modelling and recovery-run procedures
Tower modelling
Non-linear soil modelling
Main findings
• Difference between linear and non-linear models– 20%
• Non-linear pile combined with reduced jacket
Approach Efficiency Accuracy Implementation
FEMNL
SELIN
SENL
User linearized /
0
0.2
0.4
0.6
0.8
1
z
t/tmax
k0
kULS k
ULS
= 0.60 k
0
Dawid Augustyn MSc. Presentation 11 / 12

14. Introduction
Thesis goal
Refined foundation models
Conclusion
Conclusions
Thesis goal
Improved efficiency and accuracy of reduced models used in load calculations for an
offshore wind turbine design.
Improvement investigated in the thesis
Aspect
Approach
Improvement
Current Improved
Wave loading 200 modes for CB 50 modes for ACB Efficiency
Recovery-run 500 sec. – Force-Controlled 1 sec. – Direct-Expansion Efficiency
Tower modelling 25% error – two modes 1% error – ten modes Accuracy
Soil 20% – error for linearized soil Exact – non-linear soil Accuracy
where: CB– Craig-Bampton, ACB– Augmented Craig-Bampton
Dawid Augustyn MSc. Presentation 12 / 12