An experimental study on the effects of solid and liquid ballast on dynamic responses of a 15MW tri-column semi-submersible floating wind turbine

• Dynamic behavior of a tri-column floating wind turbine under three ballast configurations • Solid ballast and liquid ballast with and without baffles are compared and analyzed • Liquid ballast alters restoring stiffness and enhances hydrodynamic damping, especially in surge, pitch, and yaw motions • Solid-ballast model tests may misrepresent real FWT dynamics by neglecting liquid–structure interactions Floating wind turbines (FWTs) offer a viable approach to harness offshore wind resources; however, substantial discrepancies exist between conventional model basin experiments and full-scale engineering applications. In conventional model testing, solid ballast is typically employed to replicate the dynamic response of FWTs, whereas in practical systems, liquid ballast is utilized to fine-tune the ballast mass, control the draft, and maintain platform trim. Such fundamental differences in ballast configurations can lead to distinct dynamic behaviors. This study experimentally examines the effects of three ballast configurations (solid ballast, liquid ballast with internal baffle, and liquid ballast without baffle) on the dynamic responses of a 15 MW tri-column FWT through 1:60 scale semi-physical model test in wave basin. The tests were performed under regular wave, irregular wave, and combined wind–wave conditions. Results demonstrate that the use of liquid ballast generally increases surge motion under moderate wave conditions but mitigates yaw motion, particularly under extreme waves. Pitch motion exhibits non-monotonic behavior, decreasing under moderate conditions yet amplifying during extreme wind–wave interactions. Additionally, liquid ballast effectively reduces nacelle accelerations and tower base loads. These results emphasize the influence of ballast configuration on FWT dynamics and point out possible simulation errors when liquid ballast effects are ignored. The study supports more reliable design and greater stability of floating wind turbine systems.