INTEGRATED HYDRODYNAMIC-STRUCTURAL PERFORMANCE OF A TENSION-LEG PLATFORM FLOATING WIND TURBINE: A THREE-REGIME RESPONSE MODEL FOR DESIGN ENVELOPE DEFINITION WITH APPLICATION TO THE GULF OF GUINEA

This study presents an integrated hydrodynamic-structural analysis of a Tension-Leg Platform (TLP) Floating Offshore Wind Turbine (FOWT) using an ANSYS AQWA–Static Structural workflow. The NREL 5-MW turbine was modeled on a four-column TLP with 2.50 MN pretensioned tendons at 170 m water depth. RAOs revealed heave resonance at 0.0376 Hz (3.03 m/m), pitch resonance at 0.081 Hz (3.14°/m), and surge compliance at 0.016 Hz (2.44 m/m). Time-domain simulations across five sea states (Hs = 2.0–10.0 m) demonstrated three response regimes. Under mild conditions (Hs = 2.0 m), surge was ±7.3 m, heave ±1.8 m, and pitch ±9°, with tendon tensions varying ±8%. Under severe conditions (Hs = 5.0 m), responses remained stable. Under extreme conditions (Hs = 10.0 m), catastrophic instability occurred, with surge reaching ±108 m, heave −55 m, and pitch ±25°, with slack-snap events producing 87.57 MN peak tensions. Fatigue life was 165 years for Case 1, while Cases 2–5 resulted in immediate ULS failure. The tower-nacelle interface was critical (von Mises stress = 3.888 MPa). The primary contribution is a validated three-regime model: Regime I (Hs ≤ 3.5 m), Regime II (3.5–6.0 m), and Regime III (>7.5 m). For the Gulf of Guinea (50-year Hs = 5.5 m), the platform operates in Regime II, requiring tendon diameter increase from 0.15 m to ≥0.25 m or synthetic fiber ropes.