ABSTRACT

In the long-term operation of the floating offshore wind turbines, structural risk assessment is necessary in the same way that the seismic risk assessment performed for onshore structures. Because increment of the occurrence frequency of strong wind and the occurrence of unexpected strong wind which are not assumed in the planning and design phase can be enough considered. this study presents an evaluation method of damage probability of the floating offshore wind turbines subjected to both random wind and wave loads is presented to establish a structural risk assessment method for the wind turbines. The response of the structure for the random loads is analyzed by a stationary random vibration theory. The structural damage probability is evaluated by using a first order reliability method. Numerical example presents to show the damage probability of the structure during operation and shutdown for different wind speed.

INTRODUCTION

In the structural planning and design of the floating offshore wind turbines, evaluations for sectional forces and motion characteristics by wind and wave loads is especially important to assure sustainable driving condition of the structures during operation period. However, from the long-term viewpoint, structural risk assessment is necessary for the structures in the same way that the seismic risk assessment performed for the onshore structures because increment of the occurrence frequency of strong wind and unexpected strong wind can be enough considered.

The dynamic behaviors of the offshore wind turbines for wind and wave have been investigated in many studies (Phuc and Ishihara, 2007; Hu et al., 2011; Karimirad and Moan, 2011; Myhr and Nygaard, 2015; Wehmeyer and Rasmussen, 2015; Suzuki et al., 2019; Mantadakis, Loukogeorgaki and Karimirad, 2021). Moreover, from a view point of the long-term operation, dynamic behaviors with partially damage of the structural element of offshore wind turbines have been studied (Bae and Kim, 2015; Karimirad and Michailides, 2019). The authors (2022) have proposed an evaluation method of damage probability of floating wind turbine by static wind and random wave loads. However, no studies on structural damage risk evaluation of the offshore wind turbine for wind and wave loads have been seen. The structural damage risk evaluation of the offshore wind turbines becomes necessary in long-term operation.

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