Rigid multibody dynamic modeling for a semi-submersible wind turbine

This paper presents a rigid multibody dynamic model for a Floating Offshore Wind Turbine, and its dynamic responses are simulated. This system consists of four important mechanical rigid parts, referred to as platform, tower, nacelle, and rotor. The platform is constrained by three cables connected to the seabed, known as the mooring system. Buoyancy and hydrodynamic forces are also applied to the platform. The semi-submersible platform is investigated as one of the latest proposed designs for the platform, which plays an important role in the stability and minimization of applied forces to the whole structure. Turbine’s rotor is modeled as a rigid disk rotating about its shaft axis and under the influence of aerodynamic force and torque. Therefore, the platform with six, and rotor with one Degree of Freedom in combination with the tower and nacelle, form a seven Degree of Freedom holonomic system. Euler–Lagrange equations are utilized to formulate the system’s equations of motion. In numerical simulation section, dynamic responses under four load cases are presented and validated against “Fatigue, Aerodynamics, Structures and Turbulence” module outputs under the same conditions. The effects of considering pontoons and cross braces on dynamic responses are also investigated. Moreover, the effect of the rotor’s gyroscopic moment is examined.