Site-specific ultimate limit state fragility of offshore wind turbines on monopile substructures

Abstract

Assessing the risk posed by severe storms to offshore wind turbines (OWTs) is a challenging task. Stochastic environmental conditions represent the main source of variable loading; consequently, a high level of uncertainty is associated with assessing structural demand on OWT structures. Failure of any of the primary structural components implies both complete loss of the OWT and loss of earnings associated with production stoppage. In this paper, we propose the use of a probabilistic risk modelling framework to assess the structural risk posed by extreme weather conditions to OWTs. To achieve this, fragility functions are developed for OWTs on monopile foundations exposed to extreme metocean conditions using dynamic aeroelastic simulations. Structural fragility represents a key component of any probabilistic risk model and expresses the likelihood of different levels of damage experienced by an OWT over a range of wind and wave hazard intensities. We compare the effect of various modelling and analysis choices on the obtained fragility functions and investigate potential interdependencies between failure modes of OWT structural components. Results from this study highlight how different assumptions affect the estimated structural performance and the resulting structural fragility of a case-study OWT. We apply the proposed framework to two case-study sites, one in the USA East Coast and one in the North Sea, discussing possible outcomes of the proposed framework.

A probabilistic framework for offshore wind turbine loss assessment

“…All the structural components are exposed to this form of failure and should therefore be assessed by an analytical model as empirical failure data is very scarce. This includes the tower, monopile, transition piece and blades; see [27] for a detailed discussion on the topic…”

“…This is achieved by running the simulation repeatedly over a discrete set of IM values, resulting in a set of analysis outputs corresponding to each realization of the IM. Scatter in the fragility function parameters is caused by different wind and wave time-series causing different structural loading, and the effect of other random variables modelling structural demand and capacity [27]. The probability of failure can be estimated as the mean number of structural analyses resulting in the exceedance of the considered limit state (i.e., failures) at each IM value.…”

“…Two OWF locations, which have previously been used by the authors to derive fragility relationships for OWTs on monopile foundations [27], are investigated in this paper. These Towards Resilient OWF: A Probabilistic Framework for OWT Loss Assessment 10/06/2019 9 of 20 sites are located at Ijmuiden K13, off the coast of the Netherlands, and off the coast of Massachusetts (at 40.5°N 69.3°W), USA.…”

Plasticity of Bead-on-Plate Welds Made with the Use of Stored Flux-Cored Wires for Offshore Applications

“…Predicting environmental loading is one of the key challenges in the design and construction of offshore structures [ 1 , 2 , 3 ]. These harmful loads include the influence of wind and water: waves, ocean currents, and even atmospheric precipitation [ 4 , 5 , 6 ].…”

Study on the Influence of Baseline Control System on the Fragility of Large‐Scale Wind Turbine considering Seismic‐Aerodynamic Combination

“…Mardfekri and Gardoni [33] developed a probabilistic framework to assess the structural performance of offshore wind turbines under multiple hazards. Wilkie and Galasso [34] proposed the use of a probabilistic risk modelling framework to assess the structural risk posed by extreme weather conditions to offshore wind turbines. Avossa et al [35] presented the preliminary results of a probabilistic framework for the design and assessment of land-based horizontal axis wind turbines subjected to combined wind and seismic actions.…”