A Study on Shallow Water Mooring System of Floating Offshore Wind Turbine with Sinker

Abstract

The purpose of this study is to investigate the feasibility of catenary chain mooring with sinker in the shallow waters of 50 to 100 meters depth facing the open ocean. Although the effect of the sinker can be expected to reduce the hardening nonlinearity of the catenary characteristics statically, it is necessary to consider the dynamic effects of sinkers ascending or sitting off the sea floor. As the procedure, we set the environmental design conditions assuming the coastal area of Japan and the semi-submersible type floating offshore wind turbine model, and perform static analysis to investigate the effect of parameters on the mooring characteristics, and then dynamic analysis to judge the strength feasibility of the mooring chains in storm conditions. Catenary theory is applied to the static analysis, and OrcaFlex is used for dynamic analysis to consider the interaction between the floating body, mooring system and sea floor in time domain. The pros and cons of using sinker in “Catenary chain with intermediate sinker type” and “Catenary with Hinged Arm Sinker Mooring type” are discussed to clarify the design considerations.