ABSTRACT

The dynamics of floating offshore wind turbines (FOWTs) poses a great challenge for their coupled analysis. While the model-based method is efficient, the computational fluid dynamics (CFD) provides a high-order model for FOWTs. In the present paper, a multi-layer mesh technique is developed in the CFD framework to deal with the coupled FOWT motions. Mesh motion decomposition in translation and rotation is the key in the mesh manipulation which helps maintain mesh quality during structural movement. The mesh method is then combined with the finite element mooring model to form a coupled CFD analysis model for FOWTs.

INTRODUCTION

The advancement of floating offshore wind turbines (FOWTs) along with the exploration of offshore wind energy has been ocean engineering trends for decades. FOWTs are designed to be deployed in deep waters where more stable wind resources abound in comparison to onshore and nearshore sites, and have become one of the research focuses in the wind energy community. One of the challenges faced by the FOWT practitioners is the accurate evaluation of dynamics of the complete floating system under wind and wave conditions. The FOWT is a multi-body system consisting of the wind turbine, the control sector, the tower, the floating platform for supporting the upper structure and the mooring system for restricting the drift motion (Liu et al., 2017). The aerodynamics of the wind turbine is affected due to the motions of the supporting platform in six degrees of freedom (DOFs), showing greater uncertainties in the power production and higher fatigue failure probability of the blades (Liu et al., 2019; Tran and Kim, 2016a). The hydrodynamics of the platform, on the contrary, is modified due to the wind-induced constant inclination and variational pitching motion (Antonutti et al., 2016). The addition of the mooring systems further complicates the coupled effects between different components of the FOWTs (Hall et al., 2014).

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