Zhu Qiang, Shoele Kourosh
Department of Structural Engineering, University of California, San Diego, La Jolla, CA 92093, USA.
J Exp Biol. 2008 Jul;211(Pt 13):2087-100. doi: 10.1242/jeb.016279.
We examine numerically the performance of a thin foil reinforced by embedded rays resembling the caudal fins of many fishes. In our study, the supporting rays are depicted as nonlinear Euler-Bernoulli beams with three-dimensional deformability. This structural model is then incorporated into a boundary-element hydrodynamic model to achieve coupled fluid-structure interaction simulation. Kinematically, we incorporate both a homocercal mode with dorso-ventral symmetry and a heterocercal mode with dorso-ventral asymmetry. Using the homocercal mode, our results demonstrate that the anisotropic deformability of the ray-reinforced fin significantly increases its capacity of force generation. This performance enhancement manifests as increased propulsion efficiency, reduced transverse force and reduced sensitivity to kinematic parameters. Further reduction in transverse force is observed by using the heterocercal mode. In the heterocercal model, the fin also generates a small lifting force, which may be important in vertical maneuvers. Via three-dimensional flow visualization, a chain of vortex rings is observed in the wake. Detailed features of the wake, e.g. the orientation of the vortex rings in the heterocercal mode, agree with predictions based upon particle image velocimetry (PIV) measurements of flow around live fish.
我们通过数值方法研究了一种由类似许多鱼类尾鳍的嵌入式鳍条增强的薄箔的性能。在我们的研究中，支撑鳍条被描述为具有三维可变形性的非线性欧拉 - 伯努利梁。然后将这种结构模型纳入边界元流体动力学模型，以实现流固耦合相互作用模拟。在运动学方面，我们纳入了具有背腹对称性的正尾模式和具有背腹不对称性的歪尾模式。使用正尾模式，我们的结果表明，鳍条增强鳍的各向异性可变形性显著提高了其产生力的能力。这种性能提升表现为推进效率提高、横向力降低以及对运动学参数的敏感性降低。通过使用歪尾模式，观察到横向力进一步降低。在歪尾模型中，鳍还会产生一个小的升力，这在垂直机动中可能很重要。通过三维流动可视化，在尾流中观察到一串涡环。尾流的详细特征，例如歪尾模式中涡环的方向，与基于对活鱼周围流动的粒子图像测速（PIV）测量的预测结果一致。
