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Abstract:The objective of this study is to illustrate the unsteady aerodynamic effects of a floating offshore wind turbine experiencing the prescribed pitching motion of a supporting floating platform as a sine function. The three-dimensional, unsteady Reynolds Averaged Navier-Stokes equations with the shear-stress transport (SST) k-ω turbulence model were applied. Moreover, an overset grid approach was used to model the rigid body motion of a wind turbine blade. The current simulation results are compared to various approaches from previous studies. The unsteady aerodynamic loads of the blade were demonstrated to change drastically with respect to the frequency and amplitude of platform motion.

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The prediction of dynamic characteristics for a floating offshore wind turbine (FOWT) is challenging because of the complex load coupling of aerodynamics, hydrodynamics, and structural dynamics. These loads should be accurately calculated to yield reliable analysis results in the design phase of a FOWT. In this study, a high-fidelity fluid-structure interaction simulation that simultaneously considers the influence of aero-hydrodynamic coupling due to the dynamic motion of a FOWT has been conducted using computational fluid dynamics based on an overset The dynamic influence of aero-hydro-structure interaction due to the coupled wind-wave loads on a floating offshore wind turbine (FOWT) is still not well understood. Various experimental floating substructures in both wave basin facilities and ocean coasts have been constructed or are in the planning stages throughout the world. 1-7 The current status of both of them is well described in the previous studies. [2][3][4] From the viewpoint of engineering, compared to a full-scale test on an ocean field, a wave basin test for a scaled-down model can reduce risk, cost, and uncertainties in the design. Dynamic characteristics of floating structure from a wave basin test can be approximately evaluated. However, its results are highly influenced by purpose of tests and quality of experiment equipment (eg, installed sensors and wind and wave generation quality). Moreover, previous experimental works did not adequately consider the same material, construction methods, or deployment method as the full-scale system. 7 In particular, a scaled-down model experiment in a wave basin inherently has limitations on the simultaneous satisfaction of both Froude and Reynolds scaling laws. [8][9][10][11] The scaled-down model is typically scaled by the dimensionless Froude number to ensure the similarity of platform hydrodynamic whereas the tip-speed ratio and wind speed to wave celerity ratio between scales is maintained to entirely consistent with Froude scaling. 8 However, an experiment on a FOWT is usually more expensive than a sophisticated design tool, which is preferred for cost-effective solutions during the design process. Therefore, sophisticated modeling tools must be developed to accurately simulate the complex multiphysical phenomena induced by aero-hydro-multibody dynamic coupling for a FOWT. 1 The dynamic characteristics of FOWTs have been properly analyzed by fully coupled aero-hydro-servo-elastic dynamic approaches. [12][13][14] However, the unsteady aerodynamic calculation in these approaches was performed using the well-known blade element momentum (BEM)