Effects of Modeling Parameter Uncertainty on the Structural Response of Offshore Wind Turbines

The design of complex structures like Offshore Wind Turbines (OWTs) is commonly based on the results of deterministic structural analyses, carried out on finite element models of the structural system. However, the assessment of the structural response is affected by significant uncertainties, due to the random variability of both the environmental actions and the geometric and mechanical properties of the structure. An efficient procedure to deal with the uncertainty of modeling and loading parameters requires the characterization of the probability distribution functions of the parameters of the models of the actions and structural response, and the assessment of the probability distributions of the response parameters. Neglecting pertinent sources of uncertainty can lead to an incorrect evaluation of the stochastic structural response, and to an improper risk assessment. This paper focuses on the effects on the structural response of an OWT induced by the uncertainty of the parameters used to describe the environmental actions and the finite element model of the structure (referred to as the modeling parameters). A proper probability characterization of the parameters is assumed, and the relevance and the propagation of the uncertainty to the response are investigated. Reference is made to an OWT with a jacket support structure. Analyses are carried out in frequency domain by adopting a linear elastic finite element model, and the response uncertainty is estimated by using a sampling technique. The results presented in this paper are considered useful for the preliminary design phase, where upper and lower bounds of the stochastic structural response have to be estimated in order to select the design configuration.