The speed-up of robotic fish is hoped to aim at practical use. It is therefore important to develop methods for making such robots swim faster, and computer simulations are invaluable. In this study, a computational simulation model was developed for three-dimensional fluid-structure interaction analysis. The flow around the caudal fin can be analyzed by treating the fin as an elastic body. Experiments were also carried out and good agreement was found between the experimental results and those of the numerical analysis. Moreover, the effects of the flexibility of caudal fin on the robot's propulsive performance were investigated using computational simulations.

A fish robot with image sensors is useful to research for underwater creatures such as fish. However, the propulsion velocity of a fish robot is very slow compared with live fish. It is necessary to swim at a speed several times faster than the speed of the current robots for various usages. Therefore, we are searching for the method of making the robot swim fast. The simulation before making the robot is important. We have made the computational simulation program of three-dimensional fluid-structure analysis. The flow around the caudal fin can be examined by analyzing the fin as an elastic body. We compared the results of numerical analysis with the results of PIV measurement. Both were agreed well. Because the performance of a fish robot with two joints is better than that of a fish robot with one joint, we searched for an excellent fin for the fish robot with two joints by using CFD. We confirmed that the swimming performance of a fish robot becomes very good when the caudal fin is rigid except for the root of the fin which is comparatively flexible.

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