Dynamic Response of Spar Wind Turbine Moored by Dynamic Catenaries Under Random Wind and Wave Loads

Abstract

Abstract As offshore wind turbine is developed toward larger water depth, the dynamics coming from structural and fluid inertia and damping effects of the mooring-line gets more obvious, that makes the response analysis of the large floating wind turbine under wind&wave load more challenging. In this study, the dynamic response of a spar floating wind turbine under random wind and wave loads is examined by the modified FEM simulations. Here an integrated system including flexible multi-bodies such as blades, tower, spar and mooring-lines is considered while the catenary dynamics is involved. The dynamic restoring performance of the catenary mooring-line is analyzed based on the vector equations of 3D curved flexible beam and its numerical simulations. Then the structural responses, e.g. the top tension, structural displacements and stress of the tower and the blade, undergoing random wind&wave loads, are examined. Morevoer, the influences of the catenary dynamics on its restoring performance and the hysteresis behavior are presented. Our numerical results show: the dynamics of mooring-line may significantly increase the top tension, and, particularly, the snap tension could be more than 3 times larger than the quasi-static one. Moreover, the structural response under random wind&wave load gets smaller mainly because of the hysteresis effect coming from the mooring-line dynamics. The floating body displacement at surge frequency is around 20% smaller, and the tower root stress at bending frequency is about 30% smaller than the quasi-static values respectively.