Numerical Simulation And Control Of Self-Propelled Swimming Of Bionics Fish School

In this thesis, numerical simulation and control of self-propelled swimming of 2D and 3D bionics fish and fish school in a viscous flow in a tank are investigated. The swimming rule and the profile of 3D fish from previous experimental measurements of living fish are used in the study. The main work and results are as follows:A parallel software package for the 2D and 3D moving boundary problem is obtained, which combines the adaptive multigrid finite volume method and the methods of immersed boundary and VOF (Volume of Fluid). The reliability of the algorithm and code is verified with the numerical results of flow around a 2D circular cylinder and a self-propelled airfoil with heave and pitch motion.A complete control method of fish motion is proposed for the first time, by investigating the parameters of self-propelled swimming of a 2D bionics fish. The locomotion speed is adjusted by the flapping frequency of the tail, and the direction of swimming is controled by the oscillating of the head of a fish. The results show that with this control method, a bionics fish can turn around and swim in a ring-shaped path. The radius of turnning is direct proportional to the maximum angle of attack of the head, and is inverse proportional with the length of body used to control the direction.The results show that the "channeling effect" of swimming of a fish school do exist. A fish in the school can utilize the favorable side vortices to enhance its propulsion effciency, in case of the fish is not fall behind too much. If the distance of falling behind is larger than the length of a fish, the effect of energy saving can be neglected. The optimal distance of falling behind is about half of the body length of a fish. In addition, the smaller the lateral distance between two fish, the stronger of the effect of energy saving. But at the sametime, the fish in the preceding column will consume extra energy, and the smaller the lateral distance, the larger the extra consumption of energy. When a fish takes advantage of oncoming vortices induced by the preceding fish, there will be about 15%～25% of energy saving, which is very close to the estimation of Magnuson, i.e., there will be 10%～20% energy saving from schooling. Therefore, small fish should follow bigger fish...