Effects of Mooring Line Loads on the Stability of Floating Offshore Wind Turbine Structures

Abstract

Consideration of catenary, semi-taut or taut mooring systems in the stability assessments of floating offshore wind turbine structures (FOWTs) required by various rules and regulations of government authorities and classification societies is reviewed. This consideration is categorised into four different levels of mooring line load effects on floating stability from Level 0 as no mooring effect to Level 4 as full mooring effects. Since no commercial ship stability software considers performing stability calculations for a floating body attached to a mooring system, two newly developed stability calculation algorithms are presented to deal with intact and damage stability of FOWTs with catenary/semi-taut/taut mooring systems for stationary or transient design load cases respectively. The results of intact and damage stability analyses for a FOWT in a power production, emergency shutdown and parked conditions show that detrimental effects of mooring system occur at Level 2 or Level 3 with some partial effects, while Level 4 with full effects provides a favourable positive impact.