Seismic Fragility Analysis of Monopile Offshore Wind Turbines under Different Operational Conditions

Renjie Mo,Haigui Kang,Miao Li,Xuanlie Zhao

doi:10.3390/en10071037

Renjie Mo, Haigui Kang + Show 2 more

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https://doi.org/10.3390/en10071037

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Abstract

Offshore wind turbines in seismic active areas suffer from earthquake impacts. In this study, seismic fragility analysis of a monopile offshore wind turbine considering different operational conditions was performed. A finite element model for a 5 MW monopile offshore wind turbine was developed using the OpenSees platform. The interaction between the monopile and the seabed soil was modeled as a beam-on-nonlinear-winkler-foundation (BNWF). A nonlinear time history truncated incremental dynamic analysis (TIDA) was conducted to obtain seismic responses and engineering demand parameters. Potential damage states (DSs) were defined as excessive displacement at the nacelle, rotation at the tower top, and the allowable and yield stresses at the transition piece. Fragility curves were plotted to assess the probability of exceeding different damage states. It was found that seismic responses of the wind turbine are considerably influenced by environmental wind and wave loads. Subject to earthquake motions, wind turbines in normal operation at the rated wind speed experience higher levels of probability of exceeding damage states than those in other operational conditions, i.e., in idling or operating at higher or lower wind speed conditions.

Highlights

The depletion of fossil fuel reserves, deterioration of the global environment, and the ever-increasing demand for energy force people to utilize renewable energy
Rather than proposing a new fragility analysis method, this paper focuses on the vulnerability of the offshore wind turbine
Fragility curves for damage state DS2, as plotted in Figure 10b, showed a similar trend concerning environmental load effects as that of the damage state DS1

Summary

Introduction

The depletion of fossil fuel reserves, deterioration of the global environment, and the ever-increasing demand for energy force people to utilize renewable energy. Offshore wind turbines can be operating under different operation conditions when an earthquake occurs [4,5], resulting in different combinations of seismic load and environmental wind and wave loads acting on the wind turbine supporting structures. These combinations of loads cause different nonlinear dynamic responses for offshore wind turbines, which may exceed limit states of the structure and cause failure in both the power generation system and the supporting foundations. Investigations should be conducted to understand the responses of Energies 2017, 10, 1037; doi:10.3390/en10071037 www.mdpi.com/journal/energies

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