Chinese Journal of Theoretical and Applied Mechani ›› 2017, Vol. 49 ›› Issue (4): 920-928.DOI: 10.6052/0459-1879-17-042

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A MODIFIED MODEL FOR THE VIBRATIONS OF A TWO-DEGREE-OF-FREEDOM HYDROFOIL-ROD SYSTEM CONSIDERING 3D EFFECT

Wang Renfeng1,2, You Yunxiang1,2, Chen Ke1,2, Duan Jinlong1,2   

  1. 1. Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai Jiao Tong University, Shanghai 200240, China;
    2. State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
  • Received:2017-02-17 Online:2017-07-15 Published:2017-08-01
  • Contact: U661.1

Abstract:

The classical Theodorsen equation for the motions of two-degree-of-freedom foils is modified with associated mass parameter ε and circulation parameter δ by 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-g curve which varies with the mass ratio μ, two types (Type I and Type Ⅱ) of flutter are defined. The influences of the bracing stiffness kh, the torsional stiffness kα, the locations of the center of gravity xα and the angle of attack AOA on 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 kh, kα, xα and AOA on the flutter speed VF. When the values of the parameters are in certain ranges respectively, flutter Type Ⅱ may occur. Specifically, a larger kh or a smaller AOA leads into a larger VF. While, VF first increases and then decreases with the increase of k α or xα. Moreover, VF only exists in a relatively narrow range of xα, which reflects that the vibration pattern of the hydrofoil-rod system is high sensitive to xα. Therefore, the probability of the occurrence of flutter can be reduced by avoiding the narrow range of xα during design phase. On the other hand, according to the slow reaction of VF to kh and kα, once flutter occurs, flutter can be eliminated by locking the rigid shaft with hydraulic devices.

Key words:

two-degree-of-freedom system|flutter|low mass ratio|experiment

CLC Number: