Performance of Machines with Flexible Bodies Designed for Biomimetic Locomotion in Liquid Environments

The self-propelled swimming performance of two prototypes designed to mimic the kinematics of real fish swimming at high Reynolds numbers is presented. The design methodology uses structural compliance instead of discrete assemblies to achieve desired kinematics. Experiments took place at Reynolds numbers between 15×103 and 90×103. A prototype with a thick peduncle, low aspect ratio caudal fin, and uniform material distribution throughout its flexible tail, reached a maximum forward velocity of 0.11ms− 1 that coincided with a maximum thrust of 0.2N. A second prototype with a thin peduncle, high aspect ratio caudal fin, and nonuniform material distribution throughout its tail, reached a maximum forward velocity of 0.31ms− 1 that coincided with a maximum thrust close to 0.11N. Peak velocities and thrusts occured at driving frequencies between 2.7Hz and 3.5Hz for the type of kinematics used, and corresponded to Strouhal numbers close to 1.75 and 0.8 respectively. Mechanism motions were achieved in open loop, hence improvements can be made by implementing closed loop control to correct errors in desired kinematics. Finally, this study shows that simpler, more robust mechanisms, as the ones accomplished with our new design methodology, can display similar or better performance than the state of the art.