Tuna can change the area and shape of the median fins, including the first dorsal, second dorsal, and anal fins. The morphing median fins have the ability of adjusting the hydrodynamic forces, thereby affecting the yaw mobility of tuna to a certain extent. In this paper, the hydrodynamic analysis of the median fins under different morphing states is carried out by the numerical method, so as to clarify the influence of the erected median fins on the yaw maneuvers. By comparing the two morphing states of erected and depressed, it can be concluded that the erected median fins can increase their own hydrodynamic forces during the yaw movement. However, the second dorsal and anal fins have limited influence on the yaw maneuverability, and they tend to maintain the stability of tuna. The first dorsal fin has more lift increment in the erection state, which can obviously affect the hydrodynamic performance of tuna. Moreover, as the median fins are erected, the hydrodynamic forces of the tuna’s body increase synchronously due to the interaction between the body and the median fins, which is also very beneficial to the yaw motion. This study indicates that tuna can use the morphing median fins to adjust its mobility and stability, which provides a new idea for the design of robotic fish.

中文翻译：

---

偏航运动中金枪鱼中鳍变形的水动力分析

金枪鱼可以改变中鳍的面积和形状，包括第一背鳍，第二背鳍和肛门鳍。变形中鳍具有调节流体动力的能力，从而在一定程度上影响金枪鱼的偏航性。本文通过数值方法对不同变形状态下的中鳍进行了水动力分析，以阐明竖立中鳍对偏航操纵的影响。通过比较竖立和下沉的两种变形状态，可以得出结论，竖立的中鳍可以在偏航运动中增加其自身的流体动力。然而，第二背鳍和肛门鳍对偏航机动性的影响有限，并且它们倾向于保持金枪鱼的稳定性。第一背鳍在勃起状态下具有更大的升力增量，这显然会影响金枪鱼的水动力性能。此外，由于竖立了中鳍，金枪鱼身体的水动力由于身体与中鳍之间的相互作用而同步增加，这也非常有利于偏航运动。这项研究表明，金枪鱼可以利用变态的中鳍来调节其活动性和稳定性，这为机器人鱼的设计提供了新思路。