【作者】 杨少波；

【导师】 邱静； 韩小云；

【作者基本信息】 国防科学技术大学 ， 机械工程， 2010， 博士

【摘要】 随着海洋资源的大量开发和海洋战略的日益凸显,水下推进技术正成为国内外研究的热点。作为一种新型的鱼类仿生推进模式,牛鼻鲼胸鳍升力模式相比于传统的螺旋桨推进模式,具有摆动频率低、升力大、机动性能优良、水扰动噪声低等优点,这对于研究新型的水下机器人具有重要的意义。本文以牛鼻鲼为研究对象,从牛鼻鲼的形态学、解剖学、胸鳍扇动仿生的角度,通过有限元仿真和机器鱼实验两种技术手段对牛鼻鲼泳动时的运动学、水动力变化和涡结构演化进行研究,分析了牛鼻鲼胸鳍升力模式的形态适应性,重点研究和讨论了牛鼻鲼游动的三个特点,即自主游动、展向柔性以及胸鳍的非对称摆动。主要研究内容与创新点如下：1.结合牛鼻鲼外形、运动和受力分析,揭示了牛鼻鲼对生存环境的形态适应性,从生物力学的角度阐述了牛鼻鲼的外形具有减小阻力和增加推力的作用,而这正是牛鼻鲼长期在水中形态适应性的结果。2.通过建立三维有限元仿真模型,利用鳍条的多点激励模仿肌肉的内力作用、多鳍条组合模仿胸鳍扇动的方式,考虑流固耦合进行了模型的自主游动仿真,并结合胸鳍扇动和模型的运动结果、水动力结果和涡结构演化揭示了牛鼻鲼胸鳍升力模式推进的特征：(1)由于胸鳍通过胸鳍上的鳍条按一定相序依次摆动,自主产生由前往后的推进波,从而推动模型前进,这说明牛鼻鲼依靠胸鳍扇动过程形成的推进波实现推进或机动；(2)净推力在一个周期内呈现双峰特征,这种在胸鳍的上挥和下拍冲程中能够连续做正功的特性表明牛鼻鲼胸鳍升力模式的推进效率较高,而这一特性也与Heine的活体观测结果和Clark的模型实验结果相吻合；(3)结合水动力和涡结构的分析,牛鼻鲼通过控制胸鳍摆动,形成有利的反卡门涡街,从而诱导射流获得需要的推力和升力。3.利用观测和仿真结果设计并研制出自主游动的仿牛鼻鲼胸鳍模式机器鱼,分析揭示了胸鳍的摆动参数即鳍条摆动频率、鳍条摆幅和相邻鳍条相位差对机器鱼平均前游速度的影响规律：(1)当机器鱼鳍条摆动频率低于0.8Hz时,机器鱼平均前游速度与鳍条摆动频率、鳍条最大摆幅和相邻鳍条相位差成正比关系；(2)当机器鱼鳍条摆动频率在0.8Hz～1Hz范围时,机器鱼平均前游速度与鳍条摆动频率基本没有关系；(3)当机器鱼鳍条摆动频率在1Hz～2Hz范围时,机器鱼平均前游速度只决定于相邻鳍条相位差。4.通过测量并定量比较刚性鳍条机器鱼和柔性鳍条机器鱼的水动力和涡结构,讨论了胸鳍的展向柔性对机器鱼游动性能的影响；结果表明,鳍条的展向柔性不仅提高了前进时和后退时的推力性能,还大大改善了游动平稳性能。5.牛鼻鲼胸鳍的摆动主要表现为时间非对称摆动,即在实际游动过程中常以上挥急回的方式摆动。通过从模型仿真、运动测试和水动力测量方面定量比较柔性鳍条机器鱼的非对称摆动,发现胸鳍升力模式推进存在着较佳不对称范围和最佳不对称系数：和对称摆动相比,非对称摆动的机器鱼在较佳范围内的推进性能不仅得到增强,且游动更趋于平稳；机器鱼在不对称系数0.56工况下拍动,速度和推力均在较佳范围内表现最大。本文针对牛鼻鲼的泳动完成了从“形似”到“神似”的有益探索,它在自主游动仿真方面的尝试将对粘性流体中的胸鳍升力模式推进及机动的机理研究提供新思路,而在机器鱼的胸鳍摆动参数、胸鳍展向柔性和胸鳍的非定常运动方面的研究,将有助于胸鳍升力模式机器鱼的研制和开发,并具有重要的理论和工程应用价值。更多还原

【Abstract】 With the development of ocean resources exploring and marine sovereignty safeguarding, underwater propulsion has been becoming a hot research field concerned by more and more scientists and engineers all over the world. Under such circumstances, some biologically inspired propulsors are suggested and designed to mimic fish swimming modes. One typical case is pectoral lift-based mode inspired by Cownose Ray. Compared to the traditional propellers, this bionic propulsion mode presents some obvious advantages with lower oscillation frequency, higher lift force, greater maneuverability and lower noise. Thus, it is of great significance to improve performance of underwater autonomous vehicles.In this dissertation, kinematics, hydrodynamics and vortex structure of Cownose Ray in swimming are explored by taking advantages of the finite element simulation and experimental validation with the robotic fish. Furthermore, it is ascertained how morphology of Cownose Ray with pectoral lift-based mode is adapted to the complex environment. In particular, three characteristics, in terms of autonomous swimming, spanwise flexibility and asymmetric oscillation, are respectively studied. The main contributions in this work can be summarized as follows:1. Morphology of Cownose Ray adapting to the living circumstance is at first introduced. By observing the swimming kinematics and analyzing the force of Cownose Ray, morphology of Cownose Ray does reduce drag force and increase propulsive force, which is naturally selected during a long period adapting to water surroundings.2. A three-dimensional finite element model is established. Under this computational model, the autonomous swimming mode is simulated and analyzed with the coupling of fluid-structure, by using fin-ray animations to imitate the muscle internal force and using fin-surface combination to mimic the pectoral fins oscillation. Swimming behaviors of Cownose Ray are illustrated by kinematic results, hydrodynamic results and vortex structures. Moreover, swimming performance of pectoral lift-based mode is discussed at length.(1) As all the pectoral fin rays oscillate in specified orders, an autonomous propulsive wave appears from the leading edge to the trailing edge. In a result, the Cownose Ray computational model is propelled, to validate that the propulsive waves of pectoral oscillation can generate effective propulsion and maneuvering as well;(2) The propulsive net force presents double crests in one period. It shows both the upstroke and the downstroke of pectoral fins can produce positive power. This feature of the continuous power indicates high propulsive efficiency of pectoral lift-based mode;(3) Cownose Ray can skillfully control the oscillation of pectoral fins to form the useful con-Karman gait, and therefore induce shed fluid to attain the required propulsive force and lift force.3. An autonomous robotic fish with pectoral lift-based mode is designed and developed, based on the observation of fish swimming and corresponding simulations. The relative contribution of the fin beat frequency, the largest amplitude of fin rays and the phase difference between the adjacent fin rays to the forward velocity is originally investigated:(1) When the pectoral fins flap in frequencies lower than 0.8Hz, the forward velocity of the robotic fish keeps direct ratio to these three variables;(2) When the pectoral fins flap in frequencies between 0.8Hz and 1Hz, the forward velocity has no remarkable relationship with fin beat frequency;(3) When the pectoral fins flap in frequencies between 1Hz and 2Hz, the forward velocity is only dependent on the phase difference between the adjacent fin rays.4. Affection of spanwise flexibility of the pectoral fins on the swimming of the robotic fish is also explored, by measuring and quantitatively comparing the hydrodynamic force and vortex structure of the robotic fish. This prototype can be equipped with both rigid and flexible fin rays. Experimental results show that spanwise flexibility not only increases the forward and backward propulsive force, but also greatly improves the swimming stability.5. Pectoral flapping of Cownose Ray exhibits asymmetric oscillation, which means a slower downstroke following a quicker upstroke in one flapping circle. Asymmetric oscillation with flexible fin rays is quantitatively investigated through comparisons among mathematical model, kinematics and hydrodynamics of the robotic fish. A better asymmetric range and optimum factor are also studied and discovered. In detail, compared to the symmetric oscillation, asymmetric oscillation with a better asymmetric range can improve propulsive performance, and meanwhile swimming becomes more stable; as for the experimental range,, the velocity and the propulsive force of the robotic fish is optimum in the case of 0.56 of asymmetric factor.All the above achievements make a beneficial exploration for the imitation on Cownose Ray swimming from "imitation in shape" to "resemblance in function". In this work, the simulation of autonomous swimming will give a new alternative to the mechanics of pectoral lift-based swimming mode in the viscous fluid. Discussion on the oscillation variables, spanwise flexibility of the pectoral fins and the pectoral asymmetric oscillation should have potential for the design and exploration of underwater autonomous vehicles, theoretically and applicably.更多还原