Research On 3D Motion Mechanism And Experiments Of Biomimetic Flexible Fish Fin Based On SMA

Fish which is the oldest vertebrate in the world possesses the excellent swimming performance of high efficiency, high maneuverability and low noise in the water environment, after more than 500 million years evolution in the nature. Inspired by the outstanding propulsive performance of fish, biomimetic underwater propulsive technology is slowly becoming a hot research topic, over the past decade, the function of the flexible, agile and complex motions of fin during the rapid, highly efficient and highly maneuverable propulsion of fish, especially attracts more and more attention from scholars. Generally speaking, investigating new biomimetic flexible fish fin provides new ideas and references for the future underwater vehicle, and possesses very important research value.This thesis takes the pectoral fin of Ornamental Carp as a research object of flexible fin. Surrounding the implementation of three-dimensional motion mechanisms of the flexible pectoral fin, this dissertation carried out the bionic experimental study of pectoral fin, the study of underwater actuating mechanism of SMA (Shape Memory Alloy) flexible actuator and mechanical design of biomimetic flexible pectoral fin, the study of three-dimensional motion mechanism of biomimetic flexible pectoral fin and the hydrodynamic experimental study of biomimetic flexible pectoral fin. The main research contents and contributions of this thesis are listed as follows:(1) The bionic experimental study of the pectoral fin is carried out, obtaining the morphological parameters of pectoral fin and the mechanical properties of fin ray, analyzing the EMG characteristics of the muscle activity of pectoral fin ray, and extracting five basic gesture from the complex motions of pectoral fin through the kinematics studies and discovering the characteristic of asymmetric flap of pectoral fin. We first carry out the morphological study of the pectoral fin to get the shape and structure parameters, and to analyze the bone structure of pectoral fin and the EMG signal features of the muscle activity of pectoral fin ray, accordingly obtaining the flapping law of the pectoral fin, providing a reference and foundation for the developing of the biomimetic flexible pectoral fin. Then we comprehensively analyze the basic features of the movements of pectoral fin when fish is cruising, turning, ascending, descending and retreating respectively, by observation and high speed photography technology. After a mass of image processing, five basic gestures are extracted from the complex 3-D movements of pectoral fin:Relaxation. Expansion, Bending, Cupping and Undulation.(2) Based on the predominant performances of SMA. an underwater implemented mechanism of SMA flexible actuator is proposed, meanwhile the prototype of biomimetic flexible pectoral fin is developed, and analyze the implementation of the five basic gestures of biomimetic flexible pectoral fin in detail. First, the thermo-mechanical coupling characteristics and constitutive models of shape memory alloy (SMA) are explored, and the thermo-mechanical coupling characteristics of SMA wire is emphatically studied. Then a novel implementation mechanism of SMA underwater actuator and two implemented method, which are wire-shape SMA flexible actuator and plate-shape SMA flexible actuator, are proposed, based on the excellent performances of SMA:Large output of force, large deformation, high power weight ratio, low driving voltage and long cycle. The wire-shape SMA flexible actuator is achieved by the "Pull-Pull" deflection method, and has the characteristics of simple structure, low driving current (1A or so), high responding speed (Up to 6-10Hz in the simulation), while the plate-shape SMA flexible actuator is achieved by the "Bend-Bend" deflection method, and has the characteristic of large structure stiffness and large output of force. To integrate the advantages of the two type of actuators, the prototype of biomimetic flexible pectoral fin is designed and developed, and the five basic gestures of the biomimetic flexible pectoral fin are analyzed respectively in detail.(3) A kinematics modeling and analysis of SMA flexible fin ray is carried out, meanwhile, the 3-D motional mechanism of the biomimetic flexible pectoral fin is studied and the control system of the biomimetic flexible pectoral fin is designed and developed. The SMA flexible fin ray, capable of bending in two dimension, can be driven in three manner, based on this kinematics feature of SMA flexible fin ray, a kinematics model is established and the space movement equation of the SMA fin ray is obtained. In view of the characteristics of the SMA flexible actuator, matrix control method is put forward to control the movements of the biomimetic flexible pectoral fin, describing the 3-D motional mechanism of the biomimetic flexible pectoral fin. The control system of the biomimetic flexible pectoral fin, including hardware control system and software control system, is investigated, providing a solid foundation and a research platform for the motion control and the performance testing experimental study of the biomimetic flexible pectoral fin.(4) Experimental study on the motion performance of the SMA flexible actuator and the Hydrodynamics of the biomimetic flexible pectoral fin is carried out, obtaining the law of the influence on the hydrodynamics of the kinematics parameters. First, the influence on the motion performance of wire-shape SMA actuator of different current and oscillation frequency is studied, the results show that, the maximal flapping angle of the SMA flexible actuator increases with the increase of the current linearly, while decreases when the oscillation frequency increases. During the observed SMA flexible actuator with different SMA wire of different diameters, the one with the SMA of the diameter 0.15mm displays outstanding performance:maximal flapping angle up 89.7°, maximal frequency up to 5Hz, which is accord with the results of numerical analysis. Next, the motion performance and the hydrodynamics of biomimetic flexible pectoral fin are investigated. The experimental results reveal that, the expansion ratio of the biomimetic pectoral fin increases with the increase of current in linear, maximal expansion ratio up to 1.45. In the bending motion experiment, the spanwise force and the yaw moment are relatively large, while in the undulation motion experiment, the lift force and roll moment are relatively large, of the both motion experiments, the forces all lies in the interval [0.08,0.012] N, while the moments all lies in the internal [0.01,0.05] Nm. Then, orthogonal experimental design is adopted to optimize the hydrodynamics experiments which are designed to investigate the influence on the hydrodynamics of flapping amplitude, flapping frequency, pitching angle, asymmetric flapping coefficient and speed of "simulating fish". The experimental results show that:The thrust is affected relatively largely by the flapping amplitude, the pitching angle and the speed of "simulating fish". The lift force is mainly influenced by the pitching angle and the asymmetric flapping coefficient. The spanwise force is largely influenced by the asymmetric flapping coefficient, increasing with the increase of the asymmetric flapping coefficient. The yaw moment are largely affected by the pitching angle and the speed of "simulating fish". And the flapping frequency, the asymmetric flapping coefficient and the speed of "simulating fish" affect the roll moment largely. The pitch moment is influenced by the asymmetric flapping coefficient relatively largely. The forces and the moments of all the directions, are lies at about 0.5N and about 0.1 Nm respectively. Meanwhile, range analysis method is employed to analyze the experimental results and obtain the optimum combination of motion parameters for the target hydrodynamics.