Pitch motion reduction of semisubmersible floating offshore wind turbine substructure using a tuned liquid multicolumn damper

A tuned liquid multicolumn damper (TLMCD) composed of three liquid columns and bottom connecting pipes is proposed to reduce the pitch motion of a semisubmersible substructure for wind turbine. The pitch damping of the semisubmersible floating offshore wind turbine (FOWT) substructure scale model with TLMCD in regular waves is studied experimentally. The TLMCD with the optimized mass ratio and tuning ratio provides effective pitch motion control especially near resonance period. The OpenFOAM is further developed to simulate dynamic response of the FOWT substructure under internal sloshing and external wave excitations, where the wave elevation and the FOWT substructure response have been validated against the experimental data. The design natural frequency of the TLMCD is equal to that of the FOWT substructure, and the analytical solutions and numerical results of liquid column decay are in good agreements. The motion response of the FOWT substructure, velocity distribution and the wall pressure are used to analyze the damping mechanism of the TLMCD. Based on the hydrodynamic moment, the energy dissipation characteristics of the TLMCD are analyzed quantitatively, where the damping and exciting moment are distinguished from each other. The analyses show that the TLMCD has the best damping effect near resonance frequency, where the 2.0% mass ratio of the liquid can reduce the maximum pitch motion by 10.84% to 18.53%.