Accuracy of calculation procedures for offshore wind turbine support structures

1. Accuracy of calculation procedures for offshore wind turbine support structures Pauline de Valk – 27th of August 2013

2. Content • Introduction • Approach • Modeling • Results • Conclusions and recommendations 1

3. Content • Introduction • Approach • Modeling • Results • Conclusions and recommendations 1

4. Offshore wind energy shows potential to become one of the main energy suppliers • Demand for energy continues to increase • Offshore wind energy • More steady wind flow and average wind speed is higher than onshore Energy demand TWh Introduction Approach Modeling Results Conclusions and recommendations 2

5. Offshore wind energy shows potential to become one of the main energy suppliers • Demand for energy continues to increase • Offshore wind energy • More steady wind flow and average wind speed is higher than onshore • Cost of energy (€/kWh) should be decreased • Structural optimization design Energy demand TWh Introduction Approach Modeling Results Conclusions and recommendations 2

6. Optimize structural design of the support structure • Support structure one of the main cost items • In order to optimize one should have confidence in the outcome of calculation procedures Introduction Approach Modeling Results Conclusions and recommendations 3

7. Thesis objective ‘‘Investigate the validity and conservatism Introduction Approach Modeling Results Conclusions and recommendations 4

8. Thesis objective ‘‘Investigate the validity and conservatism of the current calculation procedures Introduction Approach Modeling Results Conclusions and recommendations 4

9. Thesis objective ‘‘Investigate the validity and conservatism of the current calculation procedures for offshore wind turbine support structures Introduction Approach Modeling Results Conclusions and recommendations 4

10. Thesis objective ‘‘Investigate the validity and conservatism of the current calculation procedures for offshore wind turbine support structures and propose improved procedures Introduction Approach Modeling Results Conclusions and recommendations 4

11. Thesis objective ‘‘Investigate the validity and conservatism of the current calculation procedures for offshore wind turbine support structures and propose improved procedures based on these findings.” Introduction Approach Modeling Results Conclusions and recommendations 4

12. Content • Introduction • Approach • Modeling • Results • Conclusions and recommendations 5

13. Offshore wind turbine support structure is custom engineered for every wind farm Foundation designer (FD) Turbine designer (TD) Introduction Approach Modeling Results Conclusions and recommendations 6

14. Offshore wind turbine support structure is custom engineered for every wind farm Foundation designer (FD) Turbine designer (TD) 1 (Adjust) design foundation Introduction Approach Modeling Results Conclusions and recommendations 6

15. Offshore wind turbine support structure is custom engineered for every wind farm Foundation designer (FD) Turbine designer (TD) 1 2 (Adjust) design foundation Integrate foundation model in aero-elastic model Introduction Approach Modeling Results Conclusions and recommendations 6

16. Offshore wind turbine support structure is custom engineered for every wind farm Foundation designer (FD) Turbine designer (TD) 1 2 (Adjust) design foundation Integrate foundation model in aero-elastic model 3 Run aero-elastic simulation (and adjust tower design) Introduction Approach Modeling Results Conclusions and recommendations 6

17. Offshore wind turbine support structure is custom engineered for every wind farm Foundation designer (FD) Turbine designer (TD) 1 2 (Adjust) design foundation Integrate foundation model in aero-elastic model 3 Run aero-elastic simulation (and adjust tower design) 4 Extract interface loads/displacements between tower and foundation Introduction Approach Modeling Results Conclusions and recommendations 6

18. Offshore wind turbine support structure is custom engineered for every wind farm Foundation designer (FD) Turbine designer (TD) 1 2 (Adjust) design foundation Integrate foundation model in aero-elastic model 3 Run aero-elastic simulation (and adjust tower design) 5 4 Apply interface loads/displacements on detailed foundation model Extract interface loads/displacements between tower and foundation Introduction Approach Modeling Results Conclusions and recommendations 6

19. Offshore wind turbine support structure is custom engineered for every wind farm Foundation designer (FD) Turbine designer (TD) 1 2 (Adjust) design foundation Integrate foundation model in aero-elastic model 6 3 Run simulation Run aero-elastic simulation (and adjust tower design) 5 4 Apply interface loads/displacements on detailed foundation model Extract interface loads/displacements between tower and foundation Introduction Approach Modeling Results Conclusions and recommendations 6

20. Offshore wind turbine support structure is custom engineered for every wind farm Foundation designer (FD) Turbine designer (TD) 1 2 (Adjust) design foundation Integrate foundation model in aero-elastic model 6 3 Run simulation Run aero-elastic simulation (and adjust tower design) 5 4 Apply interface loads/displacements on detailed foundation model Extract interface loads/displacements between tower and foundation Introduction Approach Modeling Results Conclusions and recommendations 6

21. Calculation post-processing analyses Dynamic analysis Force controlled fwind fwind g fwave g fwave fwave Introduction Approach Modeling Results Conclusions and recommendations 7

22. Calculation post-processing analyses Dynamic analysis Force controlled Dynamic or Quasi-static fwind fwind g fwave g fwave fwave Introduction Approach Modeling Results Conclusions and recommendations 7

23. Calculation post-processing analyses Dynamic analysis Force controlled fwind Dynamic or Quasi-static fwind fwind fwave g fwave g fwave Displacement controlled ub fwave fwave ub Introduction Approach Modeling Results Conclusions and recommendations 7

24. Calculation post-processing analyses Dynamic analysis Force controlled fwind Dynamic or Quasi-static fwind fwind fwave g fwave g fwave Displacement controlled Dynamic or Quasi-static ub fwave fwave ub Introduction Approach Modeling Results Conclusions and recommendations 7

25. Calculation post-processing analyses Dynamic analysis Force controlled fwind Dynamic or Quasi-static fwind fwind fwave g fwave g fwave Displacement controlled Dynamic or Quasi-static ub fwave fwave ub Introduction Approach Modeling Results Conclusions and recommendations 7

26. Dynamic versus quasi-static analysis • Dynamic analysis • Quasi-static analysis • Only accurate if structure is excited below first eigenfrequency Introduction Approach Modeling Results Conclusions and recommendations 8

27. Dynamic versus quasi-static analysis • Dynamic analysis • Quasi-static analysis • Only accurate if structure is excited below first eigenfrequency Introduction Approach Modeling Results Conclusions and recommendations 8

28. Dynamic versus quasi-static analysis • Dynamic analysis • Quasi-static analysis • Only accurate if structure is excited below first eigenfrequency Amplitude 1 1 __ __ ≈ ≈ K ω2M Frequency Introduction Approach Modeling Results Conclusions and recommendations 8

29. Dynamic versus quasi-static analysis • Dynamic analysis • Quasi-static analysis • Only accurate if structure is excited below first eigenfrequency Amplitude 1 1 __ __ ≈ ≈ K ω2M Frequency Introduction Approach Modeling Results Conclusions and recommendations 8

30. Dynamic versus quasi-static analysis • Dynamic analysis • Quasi-static analysis • Only accurate if structure is excited below first eigenfrequency Amplitude 1 1 __ __ ≈ ≈ K ω2M Frequency Introduction Approach Modeling Results Conclusions and recommendations 8

31. Design cycle for offshore wind turbine support structure Foundation designer (FD) Turbine designer (TD) 1 2 (Adjust) design foundation Integrate foundation model in aero-elastic model 6 3 Run simulation Run aero-elastic simulation (and adjust tower design) 5 4 Apply interface loads/displacements on detailed foundation model Extract interface loads/displacements between tower and foundation Introduction Approach Modeling Results Conclusions and recommendations 9

32. Design cycle for offshore wind turbine support structure Foundation designer (FD) Turbine designer (TD) 1 2 (Adjust) design foundation Integrate foundation model in aero-elastic model 6 3 Run simulation Run aero-elastic simulation (and adjust tower design) 5 4 Apply interface loads/displacements on detailed foundation model Extract interface loads/displacements between tower and foundation Introduction Approach Modeling Results Conclusions and recommendations 9

33. Reduction of foundation to lower computation costs • Reduce large number of DoF into smaller set of generalized DoF • Size(ũ) << size(u) • Lower computation costs • Approximation of exact solution • Reduction basis contains limited number of deformation shapes • Only accurate if • Spectral convergence • Spatial convergence Introduction Approach Modeling Results Conclusions and recommendations 10

34. Reduction of foundation to lower computation costs • Reduce large number of DoF into smaller set of generalized DoF • Size(ũ) << size(u) • Lower computation costs • Approximation of exact solution • Reduction basis contains limited number of deformation shapes • Only accurate if • Spectral convergence • Spatial convergence = + + Introduction Approach Modeling Results Conclusions and recommendations 10

35. Reduction of foundation to lower computation costs • Reduce large number of DoF into smaller set of generalized DoF • Size(ũ) << size(u) • Lower computation costs • Approximation of exact solution • Reduction basis contains limited number of deformation shapes • Only accurate if • Spectral convergence • Spatial convergence = + + Introduction Approach Modeling Results Conclusions and recommendations 10

36. Reduction methods Guyan reduction + …. + Static constraint modes Introduction Approach Modeling Results Conclusions and recommendations 11

37. Reduction methods Craig-Bampton reduction + + + Static constraint modes Fixed interface vibration modes Introduction Approach Modeling Results Conclusions and recommendations 12

38. Reduction methods Augmented Craig-Bampton reduction + + + Fixed interface vibration modes Modal Truncation vectors Static constraint modes Introduction Approach Modeling Results Conclusions and recommendations 13

39. Impact on fatigue damage results • Offshore wind turbine exposed to cyclic loading • Fatigue is one of the main design drivers • Impact of error in the reponse on the accuracy of the fatigue damage results Introduction Approach Modeling Results Conclusions and recommendations 14

40. Content • Introduction • Approach • Modeling • Results • Conclusions and recommendations 15

41. Monopile versus Jacket Introduction Approach Modeling Results Conclusions and recommendations 16

42. Wind, wave and operational loads • Wind loads • Random load, wide frequency spectrum • Excite frequencies up to 7 Hz Energy ω Introduction Approach Modeling Results Conclusions and recommendations 17

43. Wind, wave and operational loads • Wind loads • Random load, wide frequency spectrum • Excite frequencies up to 7 Hz • Wave loads • Wave frequencies are generally lower • Excite frequencies up to 0.5 Hz Energy ω Energy ω Introduction Approach Modeling Results Conclusions and recommendations 17

44. Wind, wave and operational loads • Wind loads • Random load, wide frequency spectrum • Excite frequencies up to 7 Hz • Wave loads • Wave frequencies are generally lower • Excite frequencies up to 0.5 Hz • Operational loads • Rotation frequency of the rotor (1P) • Blade passing frequency (3P) Energy ω Energy ω Energy ω Introduction Approach Modeling Results Conclusions and recommendations 17

45. Content • Introduction • Approach • Modeling • Results • Conclusions and recommendations 18

46. Quasi-static post-processing analyses fwind Dynamic analysis fwave fwave Introduction Approach Modeling Results Conclusions and recommendations 19

47. Quasi-static post-processing analyses Quasi-static fwind Dynamic analysis Force controlled fwind g fwave g fwave fwave fwave Introduction Approach Modeling Results Conclusions and recommendations 19

48. Quasi-static post-processing analyses Quasi-static fwind Dynamic analysis fwind Force controlled fwind fwave g fwave fwave g fwave Quasi-static Displacement controlled ub fwave fwave ub Introduction Approach Modeling Results Conclusions and recommendations 19

49. Accuracy of quasi-static post-processing Elastic energy in the foundation structure Energy [J] Energy [J] ωfree Excitation frequency [Hz] Introduction Approach Modeling Results Conclusions and recommendations 20

50. Accuracy of quasi-static post-processing Elastic energy in the foundation structure Energy [J] ωfree Energy [J] ωfree ωfixed Excitation frequency [Hz] Introduction Approach Modeling Results Conclusions and recommendations 20