Department of Structural Engineering, University of California, San Diego, La Jolla, CA 92093, USA.
J Exp Biol. 2010 Jun 15;213(Pt 12):2038-47. doi: 10.1242/jeb.040162.
We numerically examine the fluid-structure interaction and force generation of a skeleton-reinforced fin that geometrically, structurally and kinematically resembles the pectoral fin of a fish during labriform swimming. This fin contains a soft membrane with negligible bending stiffness and 12 embedded rays (modeled as beams). A potential flow-based boundary element model is applied to solve the fluid flow around the fin, in which the vorticity field is modeled as thin vorticity sheets shed from prescribed locations (the sharp trailing edge). The fin motion is actuated by dorsoventral and anteroposterior rotations of the rays (the motion of each ray is controlled individually), as well as pitching motion of the baseline. Consequently, the fin undergoes a combination of flapping (lift-based) and rowing (drag-based) motions typical in labriform swimming. The fin motion contains two strokes: a recovery stroke and a power stroke. The performance of the fin depends upon kinematic parameters such as the Strouhal number, the phase lag between rays, the pitching motion of the baseline and the passive deformations of the rays. The most interesting finding is that the strengthening of the ray at the leading edge plays a pivotal role in performance enhancement by reducing the effective angle of attack and decreasing the power expenditure during the recovery stroke.
我们通过数值方法研究了一种骨骼增强鱼鳍的流固耦合和力的产生，这种鱼鳍在几何形状、结构和运动方面类似于鱼类的水平游动胸鳍。该鱼鳍的柔性膜具有可忽略的弯曲刚度，且有 12 个嵌入式鱼鳍条（建模为梁）。应用基于势流的边界元模型来求解鱼鳍周围的流场，其中涡度场被建模为从指定位置（锋利的后缘）脱落的薄涡旋片。鱼鳍的运动由鱼鳍条的背腹向和前后向旋转（每条鱼鳍条的运动都可以单独控制）以及基线的俯仰运动来驱动。因此，鱼鳍经历了水平游动中典型的拍打（基于升力）和划动（基于阻力）运动的组合。鱼鳍的运动包含两个冲程：一个恢复冲程和一个动力冲程。鱼鳍的性能取决于运动学参数，如斯特劳哈尔数、鱼鳍条之间的相位滞后、基线的俯仰运动和鱼鳍条的被动变形。最有趣的发现是，在前缘增强鱼鳍条起到了至关重要的作用，通过减小有效攻角和减少恢复冲程期间的功率消耗来提高性能。
