Abstract:The classical Theodorsen equation for the motions of two-degree-of-freedom foils is modified with associated mass parameter εand circulation parameter δby considering the 3D effect of low aspect ratios, and the comparison between the calculation and classical experimental values demonstrates the modified equation is effective. According to the shape of V-gcurve which varies with the mass ratio μ, two types (Type Ⅰ and Type Ⅱ) of flutter are defined. The influences of the bracing stiffness k _h, the torsional stiffness k _α, the locations of the center of gravity x _αand the angle of attack AOAon the characteristics of the flutter of a hydrofoil-rod system have been analyzed, and the comparison with experimental values shows that the numerical results are reasonable. The calculation shows the significant impacts of k _h, k _α, x _αand AOAon the flutter speed V _F. When the values of the parameters are in certain ranges respectively, flutter Type Ⅱ may occur. Specifically, a larger kh or a smaller AOAleads into a larger V _F. While, V _Ffirst increases and then decreases with the increase of k α or x _α. Moreover, V _Fonly exists in a relatively narrow range of x _α, which reflects that the vibration pattern of the hydrofoil-rod system is high sensitive to x _α. Therefore, the probability of the occurrence of flutter can be reduced by avoiding the narrow range of x _αduring design phase. On the other hand, according to the slow reaction of V _Fto k _hand k _α, once flutter occurs, flutter can be eliminated by locking the rigid shaft with hydraulic devices.