Fish Frank E, Nicastro Anthony J, Weihs Daniel
Department of Biology, West Chester University, West Chester, PA 19383, USA.
J Exp Biol. 2006 Feb;209(Pt 4):590-8. doi: 10.1242/jeb.02034.
The spinner dolphin (Stenella longirostris) performs spectacular leaps from the water while rotating around its longitudinal axis up to seven times. Although twisting of the body while airborne has been proposed as the mechanism to effect the spin, the morphology of the dolphin precludes this mechanism for the spinning maneuver. A mathematical model was developed that demonstrates that angular momentum to induce the spin was generated underwater, prior to the leap. Subsurface corkscrewing motion represents a balance between drive torques generated by the flukes and by hydrodynamic forces at the pectoral fins, and resistive torques, induced by the drag forces acting on the rotating control surfaces. As the dolphin leaps clear of the water, this balance is no longer maintained as the density of the air is essentially negligible, and a net drive torque remains, which permits the dolphin's rotation speed to increase by as much as a factor of three for a typical specimen. The model indicates that the high rotation rates and orientation of the dolphin's body during re-entry into the water could produce enough force to hydrodynamically dislodge unwanted remoras.
长吻飞旋海豚（Stenella longirostris）在跃出水面时会围绕其纵轴旋转多达七次，做出惊人的跳跃动作。尽管有人提出在空中时身体扭转是实现旋转的机制，但海豚的形态结构排除了这种旋转动作的机制。研究人员开发了一个数学模型，该模型表明，在跳跃之前，在水下就产生了用于诱导旋转的角动量。水下螺旋式运动代表了尾鳍产生的驱动扭矩与胸鳍处流体动力产生的驱动扭矩以及作用在旋转控制面上的阻力所产生的阻力扭矩之间的平衡。当海豚跃出水面时，由于空气密度基本可忽略不计，这种平衡不再维持，从而留下净驱动扭矩，这使得典型标本的海豚旋转速度能够增加多达三倍。该模型表明，海豚重新入水时身体的高旋转速度和方向能够产生足够的力，以流体动力学方式甩掉不想要的印鱼。
