Dynamic analysis of a tri-floater with vertical axis wind turbine supported at its centroid

Abstract

The paper deals with the dynamic analysis of a tri-floater with a 1 MW offshore Vertical Axis Wind Turbine (VAWT) placed at its centroid. Six line catenary mooring system was used for controlling the horizontal movement of the floater. The floater was modeled as a rigid body with six degrees of freedom. Mass, damping and hydrostatic stiffness were calculated by using hydrostatic stability condition. The aerodynamic load on Vertical Axis Wind Turbine was calculated via the stream tube theory. Wave profile was calculated using Airy’s wave theory followed by the use of Morison’s equation to determine the inertial and drag forces on the floater. A computer program was developed by using the MatLab package for force calculation including wind and wave excitations as a dynamic analysis. The Newmark beta method was performed for these analyses. The equation of motion for the floater was solved in time domain. Restoring force by mooring lines at each instant of time was calculated based on the cable profile. Responses of the tri-floater with VAWT in different sea conditions were analyzed. It was proven that surge, heave and pitch are the predominant motions for a straight (00) wave. These motions were also analyzed for the waves with different inclinations and their responses were also considered and compared.