“身体-尾鳍”游动模式下鱼类多部位协调机理的模型研究

Fish can swim effectively, powerfully and agilely. The understanding of its mechanism is still one of the key factors restricting the development of the design of bionic fish. What is the effect of muscle power of different parts of a fish on their swimming behavior? How can fish improve the behavior of swimming through coordinating the muscle power of different parts? So far, the research on these problems has not been published. In this topic, the muscle power of every part was looked as the concentrated torque. By analyzing the fluid-structure interaction response of rigid-flexible composite beam, the dynamic mechanism of fish swimming in BCF (Body and/or Caudal Fin) mode was studied. By analyzing the dimensionless mathematical model of the self-propelled composite beam, a parameter space in which the self-propulsion behavior changes obviously with parametric variation was given, and the parameter selection in numerical simulation was optimized. The effect of single excitation on the self-propelled behavior of composite beam was studied by numerical simulation, and the relationship between the optimal single excitation form and the structural parameters of the composite beam was analyzed. Based on the response of single excitation, the effect of two excitations synergy on self-propulsion response was studied, and the change law of the self-propulsion behavior with the variation of two excitations cooperation was presented. The expected results of this topic had laid a foundation for revealing the coordination mechanism of an infinite number of parts on the fish body, and provided new ideas for the design and control of bionic fish.

鱼类游动具有高效、强力和灵活的特点，其机理认识是限制仿生鱼设计发展的关键因素之一。鱼类不同部位的肌肉发力对其游动行为有什么作用？鱼类如何通过各部位肌肉协调发力改善游动行为？目前，对于这些问题的研究还未见诸文献。本课题采用集中力矩作为各部位肌肉能量释放的力学表现，通过分析刚-柔性组合梁的流固耦合响应研究了鱼类在“身体-尾鳍”游动模式下的动力学机理。通过自推进组合梁数学模型的特征分析建立了对自推进行为有明显影响的参数空间，优化了数值模拟中的参数选择方式；通过数值模拟研究了不同位置单点激励对组合梁自推进行为的影响，分析了最佳单点激励形式与组合梁结构参数之间的关系；以单点激励下的自推进响应为参照研究了两点激励协同效应对组合梁自推进行为的影响，分析了其自推进行为随两点激励协作方式的变化规律。本课题的预期成果为揭示鱼体上无限多个部位的协作机制奠定了基础，并为仿生鱼的设计和控制提供了新的思路。

鱼类游动具有高效、强力和灵活的特点，其机理认识是限制仿生鱼设计发展的关键因素之一。本课题采用集中力矩作为各部位肌肉能量释放的力学表现，通过分析刚-柔性组合梁的流固耦合响应研究了鱼类在“身体-尾鳍”游动模式下的动力学机理。通过自推进组合梁数学模型的特征分析发现，梁的推进效率和推进力与其所受到的动力学边界条件密切相关。水下组合梁在自推进过程中由于受到流体力的作用可能发生失稳，单一主动控制迎流边的升沉运动可以提高组合梁失稳对应的速度阈值。推进力主要受到柔性梁共振效应的影响，且主动控制组合梁迎流边的运动可以增大其推进力；推进效率受到共振效应和运动相位调谐的共同影响，且运动相位调谐的影响更明显。这一结论对于认识鱼类尾鳍的控制有一定的指导作用。将鱼体简化为刚柔组合梁，只在刚柔性组合梁连接点处施加激励，通过数值模拟研究了不同位置单点激励对组合梁自推进行为的影响。研究发现，当柔性梁刚度较小时，激励位置越接近迎流边其推进效率越大；当柔性梁刚度越大时，激励位置越靠后其推进效率越大。这一发现与自然界中鱼类的游动行为相契合，鱼类的身体越柔软其上的波动部分占比越大。组合梁尾端上的流体力具有阻碍其推进的效果，因此鱼类的尾尖部位都特别柔软以减小这种阻碍效果。根据自然界中鱼类抽象组合梁模型，以刚性梁和柔性梁长度比为1/9分析两点激励协同效应对组合梁自推进行为的影响。给定刚性梁的俯仰运动，并在不同位置施加额外力矩模拟肌腱发力。研究发现，附加力矩并不是一直改善组合梁的推进行为。当额外力矩与俯仰运动反相时，组合梁的推进效率最低；当额外附加力与俯仰运动同相时，组合梁推进效率最高。额外附加力矩能够改变组合梁的振动形状，使得振幅和运动相位发生改变。组合梁的迎流边和尾尖上的流体力阻碍其运动，且推进力主要分布在中段。本课题的预期成果为揭示鱼体上无限多个部位的协作机制奠定了基础，并为仿生鱼的设计和控制提供了新的思路。