Floating offshore wind turbines (FOWTs) enable access to deep-water sites with strong and consistent wind resources but introduce aero-hydro-servo-elastic complexity through platform motions and mooring dynamics that can affect power production. This thesis investigates how floater type and mooring stiffness influence energy yield using time-domain simulations of the IEA 15 MW reference turbine in OpenFAST. Four floating concepts (WindCrete spar, ActiveFloat and VolturnUS-S semi-submersibles, and a reference tension-leg platform) are evaluated under identical conditions and compared to a fixed reference case.

Free-decay tests are used to determine natural periods and damping, followed by operational simulations to assess platform motions, power variation, and annual energy production (AEP). Results show that floater type strongly affects dynamics, with the TLP exhibiting minimal motion and semi-submersibles the largest surge response. Although power variation increases significantly (4–14×) for floating systems, all concepts achieve AEP within 2% of the fixed turbine. Mooring stiffness mainly influences motion response but has limited impact on mean power.