Dynamic analysis of lowering operations during floating offshore wind turbine assembly mating

Abstract

An integrated method for tower–nacelle–rotor assemblies has been proposed as an innovative approach to the transportation and installation of floating offshore wind turbines. This efficient approach offers potential value to the industry with increasing turbine sizes. During the mating phase at an offshore site, the installation system becomes a complex multibody system that involves a vessel, a wind turbine assembly, a crane, and a floating foundation. While much existing research focuses on the steady-state dynamic analysis of the lifted turbine assembly in fixed positions, the lowering operation of the assembly is an unsteady process with potential risks. To this end, this paper develops a fully coupled multibody model for the lowering scenario, accounting for the effects of environmental loads on the overall dynamic responses and the couplings between the multibodies. The study reveals the occurrence of re-impact phenomena between the foundation and the lifted structure under environmental loads, and the backward motion of the installation vessel during lowering. The selection of lowering speed and time instant for starting the operation both influence the occurrence of re-impact. Numerical simulation results offer valuable insights for heavy payload lowering operations and contribute to further decision making of assembly transportation and installation processes.