Influence of wind shear uncertainty in long term extreme responses of an offshore monopile wind turbine

• Published in: Volume 2A: Structures, Safety, and Reliability
• Main Authors: Barreto, David, Karimirad, Madjid, Ortega, Arturo
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Society of Mechanical Engineers (ASME) 2020
• Subjects: Arctic
• Online Access: https://pure.qub.ac.uk/en/publications/b4cf6829-ec8b-4c0e-9446-860a9c16f74b; https://doi.org/10.1115/OMAE2020-18506

In the field of stochastic dynamics of marine structures, the determination of long-term extreme responses is a crucial aspect to ensure the desired level of structural reliability. The calculation of these responses requires precise knowledge of the environmental conditions and reliable methods to predict the values associated with a reliability target level. While there is a very precise method to determine the value of these extreme values, e. g. the full long-term analysis (FLTA), this approach is computationally expensive. Then, approximated methods are needed. One practical approach for the determination of the most relevant environmental conditions for extreme calculation is the environmental contour method (ECM). However, some limitations have been detected when this method is used for offshore structures that consider survival strategies e. g. offshore wind turbines (OWT). Lastly, a modified ECM procedure (MECM) has been developed with the purpose to bypass the limitations of the traditional ECM. This method is based on short-term simulations and through an iterative process by testing many environmental contours in the operational range allows finding an important wind speed with its corresponding return period and thus, the problem that traditional ECM has, is avoided. The environmental conditions, which are represented by a large number of parameters, are also an important aspect of extreme calculation. Whereas some of them are treated as stochastic values, some are considered deterministic and, therefore the existence of uncertainties in their measured/estimated values is inevitable. These uncertainties are addressed by adopting values recommended by standards and guidelines and, in practice, it is often necessary to be conservative when there is a lack of information about the specific site studied. Therefore, the understanding of the impact that these uncertainties can have on the loads/responses that govern the design of offshore structures, especially wind turbines, is of great relevance. In ...