Theoretic And Experimental Resaerch On Propulsion By Bionic Undulatory Fin

Undersea swimming robot by bionic undulatory fin is not only a complicated intelligent robot with new locomotion method, but also an undersea vehicle with new concept. Bionic swimming robots by long undulatory fin would have extensive application in military and civilian. Being a part of "New bionic swimming undersea vehicle by long undulating fin and its key technologies" research, bionics on the locomotion mode of Ariiform fish, modeling and dynamic analysis of bionic undulating fin, and effects of configurational parameters and kinematic parameters of biofin to propulsive performance were studied in this paper.The main contents and contributions of this paper are summarized as follows:(1) The kinematic database on amiiform fish cruising by long-based fin was established. The characteristics of the body shape and configuration and the kinematics of steady forward swimming were distilled from the observation and experimental data, which provide the bionic foundation for modeling the biofin, validating the undulatory propulsion theory, conformating the form and structure for CFD simulation, and designing the mechanical biofin.(2) On the basis of the experimental data on G. niloticus cruising, the hydromechanical performances of the undulatory long dorsal fin propeller of G. niloticus were estimated applying the large amplitude elongated-body theory. The hydromechanical efficiency of the undulatory long dorsal fin system ranged from 81.664% to 86.420% over a speed rang of 0.728～0.985 l/s. It is suggested that the undulatory long dorsal fin propulsion is an efficient swimming mode which fits the underwater environment.(3) The validity of momentum and energy transferred to the surrounding water by long flexible fins was analysed. It is shown that long flexible fins undulating provided an effective means of momentum transfer, by allowing large amounts of water to be moved by small body masses. This paper discussed the fluid mechanical mechanisms of force production in undulatory long-dorsal fin propulsion. Force generation of undulatory long-dorsal fin results from delayed stall. We infered that lift and pressure drag generate by the same fluid phenomena at high angles of attack, which differs from steady-state mechanisms at low angles of attack.(4) A simplified physical model on the long-based undulatory fin of an Amiiform fish G. niloticus was brought forward, which was composed of N equal thin rods and a rectangular elasticmembrane connecting them together. We established a kinematic model of the long-based undulatory fin on the basis of analyzing the long-based dorsal fin locomotion and considering the fluid-structure interaction. Further, the equilibrium equations of the undulatory fin were obtained by applying the membrane theory of thin shells in which the geometrical non-linearity of the structure was taken into account. The thrust and propulsive efficiency of the long-based fin undulating may be analyzed by applying the derived kinematic model and equilibrium equations of the undulatory fin.(5) On the basis of analyzing the measure methods of propulsive performance parameters of bionic undulatory fin, we designed and developed a bionic experimental measure system. The experiment methods on the influence of the bionic fin's configuration parameters and kinematic parameters of the propulsive performance were studied. The experimental scheme was holistically optimized by multi-objiective orthogonal experimental design method. A range analysis and a variance analysis of orthogonal experiment were carried out. It shows that:1) Ray figure, ray swing frequency, wave number and fin membrane rigidity are the key factors to influence bionic fin propulsive performance.2) Augmenting ray swing frequency is a direct and effective approach to improve bionic fin kinematic performance.3) Ray figure is the chief effect factor to propulsive power and propulsive efficiency. Augmenting the aspect ratio of the bionic fin may increase propulsive velocity, but also reduce the propulsive efficiency. Appropriately mending ray obliquity may improve propulsive speed and propulsive efficiency simultaneously.4) Under the same conditions, the propulsive efficiency of the flexible bionic fin is obviously greater than that of the rigid bionic fin.These results are not only of theoretical significance, but also of potential application value for designing new bionic swimming undersea vehicle by long undulating fin.