# Aerodynamics and Motion Performance of the H-Type Floating Vertical Axis Wind Turbine
## 1 Introduction  
With the increase of unit capacity, size of the offshore wind turbine is getting bigger and bigger. The instability of floating horizontal axis wind turbine (HAWT) may become obvious as the huge drive system is placed on the top of the high tower [1]. The drive system of Vertical Axis Wind Turbine (VAWT) is installed on the bottom, which has little effect on the dynamic behavior of the tower. This makes floating VAWT more advantageous in the development of large-scale offshore wind power [2].  
Darrieus wind turbine is the earliest lift type VAWT, and it has the higher power coefficient comparing with other VAWT [1]. According to the form of the blade, the Darrieus wind turbine includes curved blade and straight blade, withib which the \(\Phi\)-type and the H-type are the most common. With the development of the offshore wind farm, the feasibility of the Darrieus wind turbine is assessed to be used in deep water and supported by the floating foundation.  
The research on the floating VAWT has been carried out, including the aerodynamic load calculations of the floating VAWT, the motion comparison of the VAWT supported by different floating foundations, the influences between aerodynamic and hydrodynamic loads, and so on. Some methods and codes were developed to calculate the floating VAWT, including the FloVAWT code [3], the enhanced Hawc2 code [4], Simo-Riflex-DMS (AC) code [5, 6], and a rigid-flexible coupling code [7]. The motion performances of the floating VAWT were investigated by these codes. [PERSON] studied the feasibility of a 5 MW \(\Phi\)-type wind turbine supported by a rotating spar type foundation by using the enhanced Hawc2 code [4]. [PERSON] and [PERSON] calculated the responses of vertical wind turbinessupported by different floating foundations by using the FloVAWT code [8]. [PERSON] et al. implemented the AC method in the Simo-Reflex to conduct the fully coupled aero-hydro-servo-elastic simulation of the floating VAWT [6; 9]. [PERSON] et al. put forward the concept of a three-blade H-type wind turbine installed on a semi-submersible floating foundation [10].  
In the above research, the form of the floating foundations mainly includes Spar type, Semi-submersible type, and TLP type. [PERSON] et al. studied the motion performance of a 5 MW VAWT supported by the truss Spar platform [11], which had shorter length than the existent spar type foundation [12; 13; 14] and can be used in the moderate water depth with good motion performance, and had lighter weight than the existing semi-submersible type foundation [15]. The above codes cannot be used to calculate the truss Spar type VAWT, as the nonlinear coupling between the heave and pitch of truss Spar foundation is important, similar to the deep see Spar platform [16; 17], and this is not considered in the above methods.  
Compared with \(\Phi\)-type, H-type is easier to manufacture and has higher power output [18]. In this paper, we studied the motion performances of the H-type VAWT supported by a truss Spar type floating foundation. The aerodynamic loads were calculated considering the dynamic stall and motions of the floating foundation. The surge-heave-pitch coupling nonlinear motion equations of the floating VAWT were established, and the motions of the floating VAWT were assessed.