The Numerical Simulation For Free Swimming Of Bionic Fish With Pectoral Fin

In this paper, through solving the 3D incompressible unsteady N-S equation using the finite volume method and combining with overse grid system, the hydrodynamic performance of a rigid pectoral fin is computed, and the free swimming and motion control of bionic fish with pectoral fins is numerically simulated. The main work and results are as follows:The overset grid technique, which deals with the complex shape and moving boundary in numerical simulation and can obtain the flow field of the global domain, is developed based on the work done, and is applied in the numerical simulation of free swimming of bionic fish with pectoral fins.Hooks-Jeeves method is used to optimize the motion parameters of a pectoral fin, and a set of motion parameters is obtained, which can generate the maximum average thrust and zero average lift force. Furthermore, the effect of several parameters on the hydrodynamic performance of a pectoral fin is studied: the average thrust is the monotonic decreasing function and odd function of the phase of flapping angle; the average thrust increases quickly with increasing amplitude of flapping angle and increasing angular velocity; the average thrust firstly increase and then decrease with increasing amplitude of feathering angle; with increasing Reynolds number, the average thrust increases slowly, the pressure part of thrust increases and the friction part decreases; with the increasing velocity of incoming flow, the average thrust decreases quickly, but the average lateral force increases.The model of free swimming of bionic fish with pectoral fins is established. The cruise of bionic fish with pectoral fins is numerically simulated, at the initial phase the average thrust generated by pectoral fins is larger than the average resistance of bionic fish and the bionic fish is accelerating, after some time, the average speed of bionic fish become steady and is 0.28m/s, when the average thrust generated by pectoral fins is equal to the average resistance of bionic fish, and bionic fish is cruising. The ratio of thrust and power at the case of free swimming decreases by 35% compared with the case of one single pectoral fin without bionic fish body. Then the realization of acceleration swimming and deceleration swimming of bionic fish through changing the amplitude of flapping angle and angular velocity respectively is numerically simulated, the results shows that the time spent for acceleration swimming or deceleration swimming through changing angular velocity is less than through changing the amplitude of flapping angle, which demonstrates the maneuvering performance of acceleration swimming or deceleration swimming through changing angular velocity is better. Finally the realization of turning motion of bionic fish in X-Y plane through the asymmetric motion of a pair of pectoral fins is numerically simulated, the results shows the turning diameter is 1.25 times of the body lengh(0.8m) of bionic fish and the time for turning a cycle is about 32s.As a preliminary try in this paper, the fuzzy control algorithm is used for the motion control of bionic fish, through controlling the motion of a pair of pectoral fin, the bionic fish arrive at the target location and stop there with less time cost.