Gaussian mixture model for extreme wind turbulence estimation

Abstract

Abstract. Uncertainty quantification is necessary in wind turbine design due to the random nature of the environmental inputs, through which the uncertainty of structural loads and response under specific situations can be quantified. Specifically, wind turbulence (described by the standard deviation of the longitudinal wind speed over a 10 min time duration) has a significant impact on the extreme and fatigue design envelope of the wind turbine. The wind parameters (mean and standard deviation of longitudinal wind speed over 10 min time duration) are not independent stochastic variables, and structural reliability analysis or uncertainty quantification therefore requires these wind parameters to be correlated stochastic parameters. An accurate probabilistic model should be established to model the correlation among wind parameters. Compared to univariate distributions, theoretical multivariate distributions are limited and not flexible enough to model the wind parameters from different sites or direction sectors. Copula-based models are often used for correlation description, but existing parametric copulas may not model the correlation among wind parameters well, due to limitations of the copula structures. The Gaussian mixture model is widely applied for density estimation and clustering in many domains, but limited studies have been conducted in wind energy and few have used it for density estimation of wind parameters. In this paper, the Gaussian mixture model is used to model the joint distribution of mean and standard deviation of longitudinal wind speed over 10 min time duration, which is calculated from 15 years of wind measurement time series data. As a comparison, the Nataf transformation (Gaussian copula) and Gumbel copula are compared with the Gaussian mixture model in terms of the estimated marginal distributions and conditional distributions. The Gaussian mixture model is then adopted to estimate the extreme wind turbulence (wind parameters for extreme load), which could be taken as an input to design loads used in the ultimate design limit state of turbine structures. The wind parameter contour associated with a 50-year return period computed from the Gaussian mixture model is compared with what is used in the design of wind turbines as given in IEC 61400-1. The Gaussian mixture model is able to model the joint distribution of wind parameters well, where the estimated tail distributions of both the marginal distributions and conditional distribution have good accuracy, and it is a good candidate for extreme turbulence estimation.