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基于改进波动方程的MPF推进模式鲼类游动特性研究

RESEARCH ON THE SWIMMING CHARACTERISTICS OF STINGRAYS BASED ON THE MPF PROPULSION MODE OF MODIFIED WAVE EQUATION

  • 摘要: 胸鳍或中间鳍推进模式(medianand or paired fin propulsion, MPF)鲼类以其游动高效且稳定而成为越来越多仿生学者的研究对象. 研究选取胸鳍为类三角形的鲼类进行仿生建模, 针对其游动姿态与推进模式, 改进波动方程建立双鳍对称运动模型, 并运用计算流体力学(computational fluid dynamics, CFD) 的方法结合动网格技术对其进行数值模拟, 研究其推进机理与游动特点, 在此基础上, 通过改变胸鳍波动频率、波动幅值和体波波长等生物学特征探究不同参数对MPF推进模式鲼类游动能力的影响规律. 研究结果表明: 在胸鳍向上波动或向下波动阶段, 胸鳍末端均存在明显的低压中心, 大部分推进力主要由胸鳍末端的涡量差产生; 向上和向下波动双鳍的过程中鱼体会产生周期性的升力, 频率与摆幅更大时升力系数峰值更高. 在相同初速度与相同鱼体初始运动状态下, 鱼体在3 Hz与A= 0.125L时垂向位移分别可达2.32和1.81 m, 可获得最大垂向提升涨幅. 体波波长决定鱼体胸鳍波动主要位置, 当λ= 0.6L即胸鳍波动主要位置靠近中性纵剖面时鱼体推进力系数均值仅有0.02, 而当λ= 1.05L即胸鳍波动主要位置靠近胸鳍末梢时鱼体具有较高的推进力, 推进力系数均值可达0.14. 本研究结果可以为基于MPF推进模式的仿生水下机器鱼提供设计与制作基础.

     

    Abstract: The median and/or paired fin propulsion (MPF) mode has attracted increasing attention from bionics researchers due to the efficient and stable swimming ability of rays. In this study, a ray species with triangle-like pectoral fins was selected for bionic modeling. Focusing on its swimming posture and propulsion mode, a dual-fin symmetric motion model was established by improving the wave equation. The computational fluid dynamics (CFD) method combined with dynamic mesh technology was employed to conduct numerical simulations, exploring the propulsion mechanism and swimming characteristics. Based on these findings, the effects of different parameters, including pectoral fin wave frequency, wave amplitude, and body wave wavelength, on the swimming ability of MPF-mode rays were investigated by varying these biological characteristics. The results revealed that distinct low-pressure centers emerged at the tips of the pectoral fins during both the upward and downward flapping phases, with the majority of propulsion force generated by the vorticity difference at the fin tips. During the upward and downward flapping of both fins, the fish body generated periodic lift, and the peak lift coefficient increased with higher flapping frequency and amplitude. Under the same initial velocity and fish body motion state, the vertical displacements of the fish body reached 2.32 m and 1.81 m, respectively, at 3 Hz andA= 0.125L, achieving the maximum vertical lift increase. The body wave wavelength determined the primary position of pectoral fin fluctuation. Whenλ= 0.6L, indicating a primary oscillation point closer to the neutral longitudinal plane, the mean propulsion force coefficient averages at a mere 0.02. Conversely, whenλ= 1.05L, positioning the primary oscillation near the pectoral fin tips, the fish exhibits a significantly higher mean propulsion force coefficient of 0.14.The findings of this study can serve as a foundation for the design and fabrication of bionic underwater robotic fish based on the MPF propulsion mode.

     

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