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Semi-active flapping foil for marine propulsion

机译：船用半主动扑翼箔

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摘要

The present study deals with numerical investigation of a semi-active flapping foil of which the kinematics is characterized by an imposed heave motion and a free pitch motion. A torsion spring is attached to the foil and acts to restore the foil parallel to the advance velocity. The prescribed flapping foil has been simulated using a boundary element method in combination with a Newton-Euler solver in order to study the influence of flapping frequency and spring stiffness on the propulsive performance. The spring stiffness has strong influence on the induced pitch angle and the effective angle of attack which consequently determines the openwater characteristics. The stiff spring resists the foil from pitching resulting in high heave force, while the more elastic hinge leads to drag generation at the end of each stroke. The results demonstrate that the semi-active flapping foil attached to an appropriate torsion spring performs efficiently over a wide range of advance ratio like a controllable-pitch propeller. The best efficiency is found for a Strouhal number and a pitch amplitude as reported in biological researches. The numerical results also imply that the resonance seems to have less influence on the propulsive performance.
机译：本研究涉及半主动式拍打箔的数值研究，其运动学特征在于施加的升沉运动和自由俯仰运动。扭力弹簧连接到箔片上，并起到使箔片平行于前进速度的作用。为了研究拍打频率和弹簧刚度对推进性能的影响，已使用边界元方法结合牛顿-欧拉求解器对规定的拍打箔进行了模拟。弹簧刚度对引起的俯仰角和有效攻角有很大影响，因此决定了开阔水域的特征。坚硬的弹簧可防止金属箔倾斜，从而避免产生较大的升力，而更具弹性的铰链会在每个冲程结束时产生阻力。结果表明，与可控螺距螺旋桨一样，附着在适当扭力弹簧上的半主动式拍打箔片可在较大的前进比范围内有效地发挥作用。如生物学研究中所报道的，对于斯特劳哈尔数和音高振幅，发现最佳效率。数值结果还暗示，共振似乎对推进性能的影响较小。

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