Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA.
Proc Biol Sci. 2011 Dec 22;278(1725):3670-8. doi: 10.1098/rspb.2011.0489. Epub 2011 May 4.
Understanding how moving organisms generate locomotor forces is fundamental to the analysis of aerodynamic and hydrodynamic flow patterns that are generated during body and appendage oscillation. In the past, this has been accomplished using two-dimensional planar techniques that require reconstruction of three-dimensional flow patterns. We have applied a new, fully three-dimensional, volumetric imaging technique that allows instantaneous capture of wake flow patterns, to a classic problem in functional vertebrate biology: the function of the asymmetrical (heterocercal) tail of swimming sharks to capture the vorticity field within the volume swept by the tail. These data were used to test a previous three-dimensional reconstruction of the shark vortex wake estimated from two-dimensional flow analyses, and show that the volumetric approach reveals a different vortex wake not previously reconstructed from two-dimensional slices. The hydrodynamic wake consists of one set of dual-linked vortex rings produced per half tail beat. In addition, we use a simple passive shark-tail model under robotic control to show that the three-dimensional wake flows of the robotic tail differ from the active tail motion of a live shark, suggesting that active control of kinematics and tail stiffness plays a substantial role in the production of wake vortical patterns.
了解运动生物如何产生运动力对于分析身体和附肢振动过程中产生的空气动力学和水动力流模式至关重要。过去，这是通过需要重建三维流模式的二维平面技术来实现的。我们应用了一种新的、完全三维的体积成像技术，可以即时捕获尾流流模式，这是功能脊椎动物生物学中的一个经典问题：游泳鲨鱼不对称（异尾）尾巴的功能是捕捉尾巴扫过的体积内的涡度场。这些数据用于测试以前从二维流分析估计的鲨鱼涡尾的三维重建，并表明体积方法揭示了以前从未从二维切片重建的不同涡尾。水动力尾流由每半次鱼尾摆动产生的一对双连接涡环组成。此外，我们使用机器人控制下的简单被动鲨鱼尾巴模型来表明机器人尾巴的三维尾流与活鲨鱼的主动尾巴运动不同，这表明运动学和尾巴刚度的主动控制在产生尾流涡旋模式方面起着重要作用。
