Natural fish have evolved with an excellent swimming performance after millions of years. Based on the flexible features of the pectoral fin, this paper focuses on the kinematics and hydrodynamics of the fin when fish are swimming stably in still water in labriform mode. The locomotion mechanism based on the morphology of the pectoral fin is applied to establish a kinematic model composed of five rays and membranes, which is adopted to control the pectoral fin to reach deformation in approximately the same way as the labriform mode. A semi-empirical theoretical model based on the kinematics is proposed to calculate the hydrodynamic force. In order to study the flow field, the numerical simulation of fluid-structure interaction is carried out and the results are validated by the present semi-empirical model, which also verifies the feasibility of the semi-empirical theoretical model for describing the dynamics of the pectoral fin under a complex water environment. In addition, the relationship between propulsion performance and locomotion parameters (e.g. frequency of motion, amplitude of flapping and rowing angle, and phase lag between flapping and rowing) of the multi-degree of freedom flexible pectoral fin is also revealed. It is found that the frequency and amplitude of the flapping angle have a significant influence on the hydrodynamic thrust, while the rowing angle and phase lag have little effect. The established models and the results provide effective tools and significant reference for the design of bionic pectoral fins.

中文翻译：

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唇形游泳过程中五线柔韧胸鳍的理论和数值研究。

经过数百万年的发展，天然鱼的泳姿极佳。基于胸鳍的柔韧性特征，本文着重研究了鱼类在呈扇形模式的静止水中稳定游泳时，鳍的运动学和流体动力学。应用基于胸鳍形态的运动机制，建立了由五种射线和膜组成的运动学模型，该模型用于控制胸鳍达到与唇形形态大致相同的变形。提出了基于运动学的半经验理论模型来计算流体动力。为了研究流场，进行了流固耦合的数值模拟，并通过现有的半经验模型对结果进行了验证，这也验证了用半经验理论模型描述复杂水环境下胸鳍动力学的可行性。此外，还揭示了多自由度柔性胸鳍的推进性能和运动参数（例如运动频率，拍打幅度和划船角度以及拍打和划船之间的相位滞后）之间的关系。发现拍打角的频率和幅度对流体动力推力有显着影响，而划船角和相位滞后影响很小。建立的模型和结果为仿生胸鳍的设计提供了有效的工具和重要的参考。此外，还揭示了多自由度柔性胸鳍的推进性能和运动参数（例如运动频率，拍打幅度和划船角度以及拍打和划船之间的相位滞后）之间的关系。发现拍打角的频率和幅度对流体动力推力有显着影响，而划船角和相位滞后影响很小。建立的模型和结果为仿生胸鳍的设计提供了有效的工具和重要的参考。此外，还揭示了多自由度柔性胸鳍的推进性能和运动参数（例如运动频率，拍打幅度和划船角度以及拍打和划船之间的相位滞后）之间的关系。发现拍打角的频率和幅度对流体动力推力有显着影响，而划船角和相位滞后影响很小。建立的模型和结果为仿生胸鳍的设计提供了有效的工具和重要的参考。发现拍打角的频率和幅度对流体动力推力有显着影响，而划船角和相位滞后影响很小。建立的模型和结果为仿生胸鳍的设计提供了有效的工具和重要的参考。发现拍打角的频率和幅度对流体动力推力有显着影响，而划船角和相位滞后影响很小。建立的模型和结果为仿生胸鳍的设计提供了有效的工具和重要的参考。