Department of Mechanical and Aerospace Engineering, University of Rome "La Sapienza", Rome, Italy.
CNR-INM, Marine Technology Research Institute, Rome, Italy.
Sci Rep. 2022 Mar 23;12(1):4946. doi: 10.1038/s41598-022-08923-5.
Velocity burst and quick turning are performed by fish during fast maneuvers which might be essential to their survival along pray-predator encounters. The parameters to evaluate these truly unsteady motions are totally different from the ones for cruising gaits since a very large acceleration, up to several times the gravity, and an extreme turning capability, in less than one body length, are now the primary requests. Such impressive performances, still poorly understood, are not common to other living beings and are clearly related to the interaction with the aquatic environment. Hence, we focus our attention on the water set in motion by the body, giving rise to the relevant added mass and the associated phenomena in transient conditions, which may unveil the secret of the great maneuverability observed in nature. Many previous studies were almost exclusively concentrated on the vortical wake, whose account, certainly dominant at steady state, is not sufficient to explain the entangled transient phenomena. A simple two-dimensional impulse model with concentrated vorticity is used for the self-propulsion of a deformable body in an unbounded fluid domain, to single out the potential and the vortical impulses and to highlight their interplay induced by recoil motions.
鱼类在快速机动中会进行速度爆发和急转弯，这对于它们在捕食者相遇时的生存可能至关重要。评估这些真正非稳态运动的参数与巡航步态的参数完全不同，因为现在主要要求是非常大的加速度，达到重力的几倍，以及极端的转弯能力，不到一个身体长度。这些令人印象深刻的性能仍然知之甚少，在其他生物中并不常见，并且显然与与水环境的相互作用有关。因此，我们将注意力集中在由身体引起的运动水中，产生相关的附加质量和瞬态条件下的相关现象，这可能揭示自然界中观察到的高机动性的秘密。许多以前的研究几乎完全集中在旋涡尾流上，尽管旋涡尾流在稳态下肯定占主导地位，但它不足以解释纠缠的瞬态现象。对于无界流场中可变形物体的自推进，使用带有集中涡度的简单二维脉冲模型来分离势和涡旋脉冲，并突出它们由反冲运动引起的相互作用。
