Effect of Stiffness Degradation of Clay in the Dynamic Response of Monopile-Supported Offshore Wind Turbines
Stiffness degradation studies for monopile-supported offshore wind turbines (OWTs) are usually limited to the geotechnical domain, largely ignoring the dynamic loads from the wind and the waves. This paper makes use of a time-domain approach, coupling aerodynamic and hydrodynamic loads, to investigate the influence of stiffness degradation in clay on the response of a monopile-supported OWT in a water depth of 20 m. p-y curves are used to represent the soil–structure interaction (SSI) in the lateral direction and a suitable degradation method is applied to consider the effects of cyclic loading. It is observed that the influence of stiffness degradation wanes with increasing number of load cycles. OWT’s being highly dynamic structures; the debilitating effects of stiffness degradation cannot be entirely discounted.
This work was supported by a grant from the Ministry of Human Resource Development, Govt. of India. The authors would like to acknowledge the help of Tore Holmas, with USFOS and Jason Jonkman, with FAST.
- Carswell, W., Fontana, C., Arwade, S. R. & DeGroot, D. J. (2015). Comparison of cyclic P-Y methods for offshore wind turbine monopiles subjected to extreme storm loading. In Proceedings of 34th International Conference on Ocean, Offshore and Arctic Engineering, Newfoundland, Canada.Google Scholar
- DNV-OS-J101. (2014). Design of offshore wind turbine structures. AS, Norway: Det Norske Veritas.Google Scholar
- Gao, Z., Saha, N., Moan, T., & Amdahl, J. (2010). Dynamic analysis of offshore fixed wind turbines under wind and wave loads using alternative computer codes. In Proceedings of 3rd EAWE Conference, TORQUE 2010: The Science of Making Torque from Wind, Crete.Google Scholar
- IEC. (2009). IEC 61400-3: Wind turbines part 3: Design requirements for offshore wind turbines. International Electrotechnical Commission.Google Scholar
- Johannessen, K., Meling, T. S., & Haver, S. (2002). Joint distribution for wind and waves in the northern North Sea. International Journal of Offshore and Polar Engineering, 12 (1), 1–8.Google Scholar
- Jonkman, B. J. (2009). Turbsim User’s guide: V. 1.50.Google Scholar
- Jonkman, J. M., & Buhl Jr., M. L. (2005). FAST—User’s guide (Technical Report NREL/EL-500-38230). Golden, CO: National Renewable Energy Laboratory.Google Scholar
- Jonkman, J. M., Butterfield, S., Musial, W., & Scott, G. (2009). Definition of a 5-MW reference wind turbine for offshore system development (Technical Report NREL/TP-500-38060). Golden, CO: National Renewable Energy Laboratory.Google Scholar
- Matlock, H. (1970). Correlations for design of laterally loaded piles in soft clay. In Proceedings of Offshore Technology Conference, Dallas, Texas.Google Scholar
- Morison, J. R., O’Brien, M. P., Johnson, J. W., & Schaaf, S. A. (1950). The force exerted by surface waves on piles. Petroleum Transactions, 189, 149–154.Google Scholar
- Søreide, T. H., Amdahl, J., Eberg, E., Holmås, T., Hellan Ø. (1993). USFOS-A computer program for progressive collapse analysis of steel offshore structures. Theory Manual, SINTEF.Google Scholar