Effects of non-uniform stiffness on the swimming performance of a passively-flexing, fish-like foil model
Effects of non-uniform stiffness on the swimming performance of a passively-flexing, fish-like foil model
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DOI：
10.1088/1748-3190/10/5/056019
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发表时间：
2015-10-01
影响因子：
3.4
通讯作者：
Lauder, George V.
中科院分区：
文献类型：
--
作者：
Lucas, Kelsey N.;Thornycroft, Patrick J. M.;Lauder, George V.
简单的机械模型模拟鱼类最近已被用来有针对性地研究个别因素，有助于游泳运动，而没有混淆整个鱼体的复杂性。然而，与这些统一的模型不同，鱼体以其非统一的材料特性而闻名。特别地，弯曲刚度沿鱼的前后轴沿着减小。为了确定非均匀弯曲刚度在鱼类推进过程中的作用，我们研究了四种翼型模型配置，这些翼型模型通过粘附塑料片层来产生高（5.5）的离散区域。X. 10（-5）Nm（2））和低（1.9. X. 10（-5）Nm（2））生物学相关量级的弯曲刚度。这导致了两个均匀的对照箔和两个具有高刚度的前部区域和低刚度的后部区域的箔。使用机械扑翼控制器，我们测量了三个方向上的力和扭矩，并量化了起伏（无俯仰）和恒定0度攻角方案下的游泳性能。在雷诺数21000 - 115000和Strouhal数类似于0.20 - 0.25时，箔自推进，这是鱼类运动的特征值。虽然以前的模型强调均匀分布和起伏运动，非均匀刚度分布和0度迎角俯仰程序的组合能够更好地再现自由游动的鱼的运动学。这种组合在最大化游泳性能方面同样至关重要，并以较低的运输成本获得较高的自推进速度，并以相对较高的效率获得较大的推力系数。因为这些度量不是全部一起最大化，所以"最佳"刚度分布的选择将取决于致动约束和性能目标。这些改进的模型可以更详细，更准确地分析鱼一样的游泳。
Simple mechanical models emulating fish have been used recently to enable targeted study of individual factors contributing to swimming locomotion without the confounding complexity of the whole fish body. Yet, unlike these uniform models, the fish body is notable for its non-uniform material properties. In particular, flexural stiffness decreases along the fish's anterior-posterior axis. To identify the role of non-uniform bending stiffness during fish-like propulsion, we studied four foil model configurations made by adhering layers of plastic sheets to produce discrete regions of high (5.5. x. 10(-5) Nm(2)) and low (1.9. x. 10(-5) Nm(2)) flexural stiffness of biologically-relevant magnitudes. This resulted in two uniform control foils and two foils with anterior regions of high stiffness and posterior regions of low stiffness. With a mechanical flapping foil controller, we measured forces and torques in three directions and quantified swimming performance under both heaving (no pitch) and constant 0 degrees angle of attack programs. Foils self-propelled at Reynolds number 21 000-115 000 and Strouhal number similar to 0.20-0.25, values characteristic of fish locomotion. Although previous models have emphasized uniform distributions and heaving motions, the combination of non-uniform stiffness distributions and 0 degrees angle of attack pitching program was better able to reproduce the kinematics of freely-swimming fish. This combination was likewise crucial in maximizing swimming performance and resulted in high self-propelled speeds at low costs of transport and large thrust coefficients at relatively high efficiency. Because these metrics were not all maximized together, selection of the 'best' stiffness distribution will depend on actuation constraints and performance goals. These improved models enable more detailed, accurate analyses of fish-like swimming.