Flammang Brooke E, Alben Silas, Madden Peter G A, Lauder George V
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
J Morphol. 2013 Sep;274(9):1044-59. doi: 10.1002/jmor.20161. Epub 2013 May 30.
Ray-finned fishes are notable for having flexible fins that allow for the control of fluid forces. A number of studies have addressed the muscular control, kinematics, and hydrodynamics of flexible fins, but little work has investigated just how flexible ray-finned fish fin rays are, and how flexibility affects their response to environmental perturbations. Analysis of pectoral fin rays of bluegill sunfish showed that the more proximal portion of the fin ray is unsegmented while the distal 60% of the fin ray is segmented. We examined the range of motion and curvatures of the pectoral fin rays of bluegill sunfish during steady swimming, turning maneuvers, and hovering behaviors and during a vortex perturbation impacting the fin during the fin beat. Under normal swimming conditions, curvatures did not exceed 0.029 mm(-1) in the proximal, unsegmented portion of the fin ray and 0.065 mm(-1) in the distal, segmented portion of the fin ray. When perturbed by a vortex jet traveling at approximately 1 ms(-1) (67 ± 2.3 mN s.e. of force at impact), the fin ray underwent a maximum curvature of 9.38 mm(-1) . Buckling of the fin ray was constrained to the area of impact and did not disrupt the motion of the pectoral fin during swimming. Flexural stiffness of the fin ray was calculated to be 565 × 10(-6) Nm2 . In computational fluid dynamic simulations of the fin-vortex interaction, very flexible fin rays showed a combination of attraction and repulsion to impacting vortex dipoles. Due to their small bending rigidity (or flexural stiffness), impacting vortices transferred little force to the fin ray. Conversely, stiffer fin rays experienced rapid small-amplitude oscillations from vortex impacts, with large impact forces all along the length of the fin ray. Segmentation is a key design feature of ray-finned fish fin rays, and may serve as a means of making a flexible fin ray out of a rigid material (bone). This flexibility may offer intrinsic damping of environmental fluid perturbations encountered by swimming fish.
辐鳍鱼类以其灵活的鳍而闻名，这些鳍能够控制流体动力。许多研究已经探讨了灵活鳍的肌肉控制、运动学和流体动力学，但很少有研究调查辐鳍鱼鳍条究竟有多灵活，以及灵活性如何影响它们对环境扰动的反应。对蓝鳃太阳鱼胸鳍鳍条的分析表明，鳍条较近端的部分是不分节的，而鳍条远端的60%是分节的。我们研究了蓝鳃太阳鱼在稳定游泳、转弯动作、悬停行为期间以及在鳍摆动过程中受到涡旋扰动影响鳍时胸鳍鳍条的运动范围和曲率。在正常游泳条件下，鳍条近端不分节部分的曲率不超过0.029 mm-1，鳍条远端分节部分的曲率不超过0.065 mm-1。当受到以约1 m s-1速度行进的涡旋射流扰动时（冲击时力为67±2.3 mN标准误差），鳍条的最大曲率为9.38 mm-1。鳍条的屈曲被限制在冲击区域，并且在游泳过程中不会干扰胸鳍的运动。计算得出鳍条的弯曲刚度为565×10-6 Nm2。在鳍与涡旋相互作用的计算流体动力学模拟中，非常灵活的鳍条对冲击的涡旋偶极子表现出吸引和排斥的组合。由于其较小的弯曲刚度，冲击涡旋传递给鳍条的力很小。相反，较硬的鳍条会因涡旋冲击而经历快速的小振幅振荡，在鳍条的整个长度上都有很大的冲击力。分节是辐鳍鱼鳍条的一个关键设计特征，并且可能是一种用刚性材料（骨骼）制造灵活鳍条的方式。这种灵活性可能为游泳鱼类遇到的环境流体扰动提供内在阻尼。
