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OC 3 : Benchmark Exercise of Aero-elastic Offshore Wind Turbine Codes

OC 3 : Benchmark Exercise of Aero-elastic Offshore Wind Turbine Codes. J A Nichols and T R Camp, Garrad Hassan and Partners Ltd. J Jonkman and S Butterfield, NREL T Larsen and Anders Hansen, Risø J Azcona, A Martinez and X Munduate, CENER F Vorpahl and S Kleinhansl, CWMT

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OC 3 : Benchmark Exercise of Aero-elastic Offshore Wind Turbine Codes

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  1. OC3: Benchmark Exercise of Aero-elastic Offshore Wind Turbine Codes J A Nichols and T R Camp, Garrad Hassan and Partners Ltd. J Jonkman and S Butterfield, NREL T Larsen and Anders Hansen, Risø J Azcona, A Martinez and X Munduate, CENER F Vorpahl and S Kleinhansl, CWMT M Kohlmeier, T Kossel and C Böker, Leibniz University of Hannover D Kaufer, SWE University of Stuttgart

  2. Outline • Background and partners • Objectives • Project phases and approach • Phase III: offshore tripod • Results • Future work

  3. Background and Partners • The Offshore Code Comparison Collaboration (OCCC) has been coordinated within the IEA Wind Annex XXIII by the National Renewable Energy Laboratory (NREL). • Project group consists of research bodies, universities and partners from industry. Phase III includes contributions from: • National Renewable Energy Laboratory (NREL) (USA) • Endowed Chair of Wind Energy of the Universität Stuttgart (D) • Garrad Hassan (UK) • Risø National Laboratory (DK) • National Renewable Energies Center (CENER) (ESP). • Fraunhofer Centre for Wind Energy and Maritime Engineering (D) • Leibniz University of Hannover (D) • Simulation tools: • Bladed, Flex5, FAST, HAWC2, ADCoS, WaveLoads and ANSYS

  4. Objectives • Establishment of a suite of benchmark simulations to test new codes and for training of new analysts • Identification and verification of code capabilities and limitations of implemented theories • Investigation and refinement of applied analysis methodologies • Investigation on the accuracy and reliability of results obtained by simulations to establish confidence in the predictive capabilities of the codes • Identification of further research and development needs

  5. Project Phases PhaseIV PhaseII PhaseI PhaseIII

  6. Basic Structure Full simulation Wind Loads Wave Loads Static Simulation Dynamics Approach • At each stage simulations are selected to highlight different areas of interest • To start with, only basic models are used • Then more features are added • This facilitates identifying the differences between the different codes

  7. Phase III: Offshore Tripod • Significant jump in complexity from monopile substructure. • Statically indeterminate • Loads influenced by relative deflection of members

  8. Modelling – wave loads • Importance of modelling the structure near the sea surface in detail • Without a fine discretisation, sharp jumps are seen in load signals Axial Force (kN)

  9. Modelling – overlapping members • It is important to take account of the overlapping regions when structure members join at nodes • In this case, the volume which could be double-counted would be 8% of the total volume below sea level having a significant effect on buoyancy and wave loads.

  10. Modelling – shear deflection • Bernoulli-Euler theory only considers pure bending of a beam. • One side is compressed while the other is stretched. • In real beams, there is some shear deformation of the material. • This becomes important once relative deflection of joined members becomes important. l x M P

  11. Modelling – shear deflection

  12. Results - Eigenanalysis

  13. Results – Output Locations

  14. Results – bending moments due to wave loads

  15. Results – shear forces due to wave loads

  16. Results – axial forces due to wave loads

  17. Motion of the dynamic support structure

  18. Future Work • Phase IV beginning • Floating spar-buoy structure • Stretching the limits of existing wind turbine codes • Involvement of codes used by oil and gas companies to model offshore structures

  19. Conclusions • Identification of important issues for space-frame offshore support structures. • Encouragement for the development of existing codes to incorporate these features. • Establishment of baseline load calculations and results for new codes to be tested against. • A number of engineers are now equipped with experience of modelling offshore structures with greater knowledge of the factors which influence loading results.

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