Design And Hydrodynamic Analysis Of Ups And Downs Robotic Fish Propelled By Two-degree Of Freedom Pectoral Fins

The bionic object of the Median Paired Fin(MPF)propulsion mode has become a focus area for research scholars at home and abroad,due to its efficient,stable propulsion,reliable maneuverability and strong anti-jamming capability.The rapid development of robotics will inevitably greatly promote this research to practical steps.The research of bionic thrusters mainly goes through three phases: design of the mechanism,hydrodynamic analysis and experimental research.This paper mainly starts from the following three aspects:(1)A box-fish was used as a bionic object to design a bionic robotic fish with two-degree of freedom pectoral propulsion and its three-dimensional movement.Based on the modular design concept,a variable-length pectoral fin drive shaft and a pectoral fin propulsion mechanism with two-degree of freedom movement are designed,according to the principle of a crank-slider mechanism,a buoyancy control system and a pitch adjustment mechanism are designed by changing the relationship between the center of gravity and the buoyancy center.Considering the effect of shape on the swimming performance of robotic fish,a spindle-shaped fish shell with good streamline performance was designed.The control system consisting of man-machine interaction layer,hardware control layer and information acquisition layer realized the swimming of robotic fish.Dynamic control,and finally complete the prototype design of two-degree-of-freedom pectoral fin propulsion fish.(2)A sinusoidal movement model of unilateral pectoral fins of robotic fish was established.Using computational fluid dynamics,the wavy wing motion,the front and rear raccoon motions and its compound motions of the two were numerically simulated,the hydrodynamics were given,the relationships between propulsion and kinematic parameters,pressure cloud maps and velocity cloud maps of pectoral fin movements.The analysis shows that the generation of thrust is caused by the pressure difference between the downstream and the inflow planes of the pectoral fins.At the same time,it shows greater movement speeds at the positions of the pectoral fins and near the fish body,by changing the kinematic parameters and hydrodynamics.The analysis results showed that the frequency of the fin movement and the front and rear raccoon wings were both 1.0 Hz,the pectoral fins showed a large propulsive force when the amplitude was both at the same time,which in turn increased the swimming speed of the robotic fish.(3)With the designed two-degree-of-freedom pectoral fin propulsion robotic fish as the experimental platform,based on the numerical analysis results,the swimming experiments of the bionic robotic fish,such as swimming,turning and pitching were carried out.In the experiment,the effects of frequency and amplitude on the linear velocity of linear motion and the angular velocity of in situ turning were analyzed.The results show that the maximum linear velocity of robotic fish swimming is 0.32m/s,the maximum value of the angular velocity of in-situ turning motion is 0.28rad/s,and the maximum value of the angular velocity of left-turning swimmer is 0.39rad/s.The change trend is consistent with the theoretical analysis results,which shows the effectiveness of the proposed method.