Kriging models for aero-elastic simulations and reliability analysis of offshore wind turbine support structures

ABSTRACT

The existence of uncertainties in material properties, environmental loads and soil properties as well as the presence of nonlinearities introduced by the control systems have a remarkable influence on the dynamic response of offshore wind turbine (OWT) support structures. The reliability computations of these structures need to consider implicit expensive-to-evaluate limit state functions, implying large computational costs. This paper addresses these limitations by proposing a computationally-efficient reliability framework for OWT support structures, based on the use of a kriging model to approximate the response of the system, capturing both the dynamic behaviour of the structure and inherent uncertainties. The surrogate model is built with sample points from stochastic fully coupled simulations in the time-domain. A thorough sensitivity study is performed on the influence of number of sample points, the seeds used to obtain each point, the range of the variables and the inherent variability in turbulent wind and stochastic waves. The framework is used to evaluate the reliability of the NREL 5 MW turbine model, mounted on a monopile with a flexible foundation for the severest Design Load Cases (DLCs) from the IEC 61400-3. The results agreed with the general literature showing that the structure is far from failure.

KEYWORDS:

• Offshore wind turbine
• design load case
• support structure
• Kriging
• reliability
• surrogate models

Acknowledgments

This PhD research is funded by Lloyd’s Register Group Services Ltd., Aberdeen. Sriramula’s work within the Lloyd’s Register Foundation Centre for Safety and Reliability Engineering at the University of Aberdeen. The Foundation helps to protect life and property by supporting engineering-related education, public engagement and the application of research.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

A. Morató http://orcid.org/0000-0003-3994-5805

Additional information

Funding

This PhD research is funded by Lloyd’s Register Group Services Ltd., Aberdeen.