SEQUENTIALLY COUPLED ANALYSIS FOR A SEMI-SUBMERSIBLE FLOATING OFFSHORE WIND TURBINE

Given the UK's target of achieving 5 GW of floating wind power by 2030, it is crucial to have reliable approaches to optimize the floating foundations to support new generation wind turbines that will fulfil this target. This paper presents a sequentially coupled analysis for the 15MW VolturnUS-S reference floating wind turbine using Ansys AQWA, a software that does not possess the capability for a fully coupled analysis like OpenFAST or Bladed software. The main reason for using Ansys AQWA in this study is its ability to transfer hydrodynamic loads and cable forces to Ansys Mechanical smoothly. This capability ensures that these loads and forces are accurately incorporated into the floater's finite element analysis (FEA). This paper uses OpenFAST to estimate the tower-based forces and moments for the 15MW VolturnUS-S reference floating wind turbine, which are subsequently imported into Ansys AQWA. OpenFast simulations are conducted for six wind speeds for each wind speed in the design load case matrix. The simulations are performed in no-wave and wind conditions to prevent double-counting hydrodynamic loads. In addition, the effects of enabling and disabling the platform's degrees of freedom on the aerodynamic loads are examined. Afterwards, these loads are imported into Ansys AQWA, and simulations are conducted for three design load cases. The results are validated against published literature that employs a fully coupled approach, revealing certain discrepancies in the floater response. The results tend to slightly overestimate cable tension, suggesting that this approach yields a conservative estimate of the tension in the mooring cables.