A novel numerical strategy for the simulation of irregular nonlinear waves and their effects on the dynamic response of offshore wind turbines

We present a novel numerical procedure for the prediction of nonlinear hydrodynamic loads exerted on offshore wind turbines exposed to severe weather conditions. The main feature of the proposed procedure is the computational efficiency, which makes the numerical package suitable for design purposes when a large number of simulations are typically necessary. The small computational effort is due to (i) the use of a domain-decomposition strategy, that, according to the local wave steepness, requires the numerical solution of the nonlinear governing equations only on a limited number of reduced regions (sub-domains) of the whole space-time domain, (ii) the choice of the particular numerical method for the spatial discretization of the governing equation for the water-wave problem. Within the potential flow assumption, the Laplace equation is solved by means of a higher-order boundary-element method (HOBEM). For the time evolution of the unsteady free-surface equations the 4th-order Runge-Kutta algorithm is adopted. The compound solver is successfully applied to simulate nonlinear waves up to overturning plunging breakers, that may cause severe impact loads on the wind turbine substructure. Emphasis is finally given to wind turbine exposed to realistic environmental conditions, where the proposed tool is shown to be capable of capturing important nonlinear effects not detected by the linear models routinely adopted in the design practice.