Research On The Motion Of A Floating VAWT With Considering The Effect Of Floating Foundation’s Motions On The Aerodynamic Loads

Ever-increasing demand for energy boosts the application of the wind turbines in the deep water.The application of the VAWTs in the offshore wind industry has some potential due to its economical installation and maintenance.More and more efforts have been invested in developing floating vertical axis wind turbines(FVAWTs),but the research on the FVAWTs is still at an early stage.In this paper,the concept of design the 5MW Darrieus wind turbine blade system,refer to the Technical University of Denmark’s DeepWind project announced the vertical axis vanes and Truss Spar floating foundation,a kind of Spar type floating vertical axis wind turbine suitable for a depth of 200 meters is designed.Using HydroD mudule to calculate hydrodynamic coefficients of surge、heave and pitch of the wind turbine floating foundation,including added mass of the structure、potential damping、transfer function of the first order wave force and RAO curves.And using spectral analysis to do a short notice,certifying well hydrodynamic performance of the floating foundation.Based on DMSV theory considering the variable interference factor and Gormont-Berg model,a computing code of aerodynamic forces of the wind turbine was developed considering the dynamic stall,Reynolds number variation and motions of the floating foundation.The coupling equations of heave and pitch motions of the floating VAWT were established and solved numerically.The model tests with a scale ratio of 1:70,were carried out to verify the validity of the coupling motion equations.The inherent characteristics and damping of the motion of the wind turbine system are calculated by the free decay test.The motion of the wind turbine system and the effect of aerodynamic forces on the wind turbine system were analyzed by means of wind test.It is found that the RAO curves obtained by numerical calculation agree well with those obtained by model tests if the wind forces are not considered.If the wave and wind forces are considered simultaneously,the differences between the results of numerical calculation and those of model test are obvious near the extreme values of the heave and pitch RAO curves.This is because the differences between the numerical calculation model and the model tests,mainly including the degree of freedom of the floating VAWT motions,mooring system,the damping and the wind forces.The wind forces have little influences on the heave motions of the floating VAWT,while it obviously increases the pitch motions of the floating VAWT.The floating VAWT has good motion performance,the heave and pitch frequencies of the floating VAWT are dominated by the wave frequencies,the 2P response of pitch motion of the floating VAWT is not significant.