Numerical Simulation for Installation of Jacket Foundation of Offshore Wind Turbines

Abstract

A large contribution to the overall project costs of an offshore wind farm originates from the transport and installation of the substructures. A better understanding of the operational limits that apply for the installation helps to improve the project execution and thus reduces costs. It is important to analyze in which sea states the installation can be carried out safely. A coupled analysis model consisting of a vessel the jacket and couplings is implemented in SIMO. Time domain simulations of the the lowering and landing process of a jacket substructure are carried out for a jack-up and a floating vessel. Based on operational criteria a workability analysis is performed and the limiting sea states are determined. The jacket substructure needs to be lowered into pre-installed foundation piles and the jacket motions are thus limited to a certain threshold in order for the installation to be successful. The jack-up vessel is fixed and consequently there are no crane tip motions. The jacket is thus only excited by waves and the motions are small enough for the jacket to successfully enter the foundation piles for all investigated sea states. The floating vessel is excited by waves and the vessel motions lead to larger motions in the jacket too. The jacket does therefore not always enter the foundation piles. The success rate depends on the wave period and decreases for larger wave periods, close to the excitation periods of the vessel. While the floating vessel is only suited for operations in small wave periods the jack-up vessel was able to operate in all investigated sea states.