Influence of wind-waves energy transfer on the impulsive hydrodynamic loads acting on offshore wind turbines

This paper draws some preliminary considerations about the direct wind effects on the kinematics and dynamics of steep extreme waves propagating near offshore wind turbines. Most of the hydrodynamic load models currently employed in designing offshore wind turbines take into account only indirectly the role of the wind. In fact, once the sea severity upon a certain wind speed is established, the sea state is fully determined by means of the significant wave height and the peak spectral period. In contrast, recent experimental results show that the local wind strongly influences the evolution of steep waves. A wind-waves energy transfer model is here implemented in a fully nonlinear potential flow model for wave-propagation. First, the laboratory experimental evidences about the influence of the wind on the propagation of steep waves are confirmed numerically by simulating the 2D propagation of a Gaussian wave packet. Second, real environmental conditions are reproduced in the near field of an offshore wind turbine using linear-nonlinear potential flow models within a novel coupling strategy. Different wind-wave relative speeds are simulated attempting to quantify the influence of the wind on the wave propagation. Although a reliable evaluation of this influence is still an open issue, the importance of some physical parameters, such as the duration of the energy transfer, is highlighted. (C) 2011 Elsevier Ltd. All rights reserved.