Spatial Grid Resolution Effects on Dynamics of Offshore Wind Turbines

Abstract Modelling a proper stochastic inflow wind field for dynamic analysis of an offshore wind turbine (OWT) is affected by turbine specifications and wind characteristics. These considerations and assumptions could potentially have a significant effect on the motions and structural loads and dynamic responses of the system. Previous studies have investigated the impact of various parameters — such as yaw misalignment, aerodynamic properties, blade mass imbalance, turbulence spectra, shear, veer, spatial coherence, component correlation, ant etc. — which could vary at different offshore sites and under different atmospheric conditions. Among different influencing factors in modelling the turbulence field, the importance and potential sensitivity of the system’s dynamics to the spatial grid resolution have not yet been fully explored. The present study, therefore, seeks to assess the influence of this variable on the dynamics of bottom-fixed and floating supported OWTs; and provide a basis for an acceptable grid spacing resolution for inflow turbulence generation to preserve a certain level of accuracy in estimating the response statistics. To this aim, a series of stochastic inflow wind fields with different degrees of coarseness from the typically recommended resolution, i.e., maximum chordlength, up to twelve times of this value have been simulated; and the dynamic behaviour of two bottom-fixed and floating supported OWTs during normal operational conditions were analyzed. Response statistics for different spatial grid resolutions were compared with the “base inflow” case. The results demonstrated that the extent of impact that spatial grid resolution has on the dynamics of an OWT is greatly sensitive to not only the controlling strategy but also can the type of supporting structure and design-deriving response variable. By understanding the extent of spatial grid resolution influence on various response variable for two bottom-fixed and floating supported models, insights into potential modification required in regards to this parameter for establishing efficient and physically consistent stochastic inflow wind fields are provided.