This study investigates how dynamically adjusting the bending stiffness of a heaving foil affects its propulsion performance in a flow of Reynolds number 200. The foil is forced to oscillate sinusoidally at the leading edge, and its bending stiffness is tuned in a square-wave manner. Such a fluid-structure interaction (FSI) problem is explored using an immersed boundary lattice Boltzmann method (IBLBM) based numerical framework. The results reveal that when the lower and upper bounds of the foil's time-dependent bending stiffness are moderate, the net thrust can be evidently enhanced compared to those in the corresponding constant-bending-stiffness cases, while the propulsion efficiency is not apparently ameliorated. The most significant enhancement is observed when the bending stiffness has lower and upper bounds of the same duration (i.e. a duty cycle of 1/2) and also it remains at the lower bound during stroke reversals (corresponding to an actuation phase angle of [Formula: see text]). When the two bounds simultaneously increase or decrease, however, dynamically adjusting the bending stiffness fails to improve the net thrust. Through this study, competitions among various forces/moments, including the inertial force, tension force, bending moment and fluid loading, acting on the foil and their influences on the foil's dynamics are also unveiled.

中文翻译：

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通过动态调整其柔韧性来提高柔韧性箔的推进性能。

这项研究调查了动态调节升沉箔片的弯曲刚度如何在雷诺数为200的流动中影响其推进性能。该箔片被迫在前缘处以正弦振动，并以方波方式对其弯曲刚度进行调整。使用基于浸入式边界格子玻尔兹曼法（IBLBM）的数值框架探索了这种流固耦合（FSI）问题。结果表明，当箔片随时间变化的弯曲刚度的上限和下限适中时，与相应的恒定弯曲刚度情况相比，净推力可以明显提高，而推进效率却没有明显改善。当弯曲刚度的下限和上限相同时（例如，占空比为1/2），并且在行程反转期间仍保持在下限（对应于[公式：参见文本]的致动相角）。但是，当两个边界同时增大或减小时，动态调整弯曲刚度将无法提高净推力。通过这项研究，还揭示了作用在金属箔上的各种力/力矩之间的竞争，包括惯性力，拉力，弯矩和流体载荷，以及它们对金属箔动力学的影响。