Structural probabilistic assessment of offshore wind turbine operation fatigue based on Kriging interpolation

Abstract

The probabilistic analysis of Offshore Wind Turbines (OWT) is not a new practice. The standards for designing OWT (IEC 61400 class) emphasizes that assessing uncertainty is of major importance inside the design chain. Still, major challenges related to the uncertainty and the probabilistic assessment pose to the sector and its development. The analysis of operational loads is one them. The problem of analyzing extreme responses or cumulated damage in operation during the design phase is significantly related to its high computational cost. As we progressively add complexity to the system to account for its uncertainties, the computational effort increases and a perceptive design becomes a heavy task. If an optimization process is then sought, the designing effort grows even further. In the particular case of fatigue analysis, it is frequent to not be able to cover a full lifetime of simulations due to computational cost restrictions. The mentioned difficulties fomented the utilization of surrogate models in the reliability analysis of OWT. From these surrogate approximations the ones based on Kriging models gained a special emphasis recently for structural reliability. It was shown that, for several applications, these models can be efficient and accurate to approximate the response of the system or the limit state surfaces. The presented paper tackles some of the issues related to their applicability to OWT, in a case specific scenario of the tower component subjected to operational fatigue loads. A methodology to assess the reliability of the tower component to fatigue damage is presented. This methodology combines a Kriging model with the theory of extreme values. A one-dimensional Kriging case using the state of art NREL's monopile turbine is presented.The reliability of the OWT tower is calculated for 20 years. The results show that the usage of a Kriging model to calculate the long term damage variation shows a high potential to assess the reliability of OWT towers to fatigue failure.

Reliability assessment with density scanned adaptive Kriging

“…The added complexity of time-variant reliability analysis is indicative of the importance of AK, and in particular, of efficient metamodeling approaches. Other examples of the application of the Kriging models for practical structural engineering problems can be found in [19][20][21][22][23][24][25].…”

On the suitability of the generalized Pareto to model extreme waves

“…Examples of relevant works that use Kriging models to assess a system's performance in a probabilistic way are presented in (Hua et al, 2004;Bichon et al, 2008;Echard et al, 2011;Echard et al, 2013, Yan et al 2015. In the specific case of OWT Kriging models were also widely applied not only to infer on probabilistic behaviour, but also to reduce computational time (Maki et al, 2012;Morató et al, 2016;Teixeira et al, 2017a).…”