Assessment of the Distribution of the Gaps Between Ring Flange Connections in Offshore Wind Turbines

Abstract

Ring flange connections are commonly used to connect the tower of offshore wind turbines with monopile foundations. Studs in these ring flange connections are sensitive to fatigue damage accumulation, which is aggravated by gaps between the flanges. Such gaps are inevitable because of imperfections (out-of-flatness) of the flanges. Given the sensitivity of the forces in the studs with respect to the gaps, this study investigates the gaps of ring flange connections and proposes a method to assess the gap height and angle. To this end, the joint distributions of the gap heights and angles are determined for different tower diameters and production tolerances using manufacturing data. The type and parameters of the marginal distributions of the gap heights and angles are determined using the Maximum Likelihood Estimation method. Data censoring is applied to ensure that the tails of the gap height and gap angle distributions are accurately captured. Then, using the censored data and corresponding marginal distributions, the copula of the joint distribution is determined. The results show that the data is best represented by Weibull and Beta distributions for the gap height and angle, and the dependence structure is best described with Clayton copulas.