A high-speed bionic robot actuated by flow-induced flutter of a folded gradient soft pipe

This paper proposes a novel actuation mechanism based on high-frequency flow-induced flutter in a gradient-discontinuous soft pipe. The actuator of the bionic fish is inspired by the tentacles of pipe anemones. The actuator consists of a gradient-discontinuous soft pipe with a thin membrane attached to its outer surface. Fluid flow through the pipe induces high-frequency flutter, which drives the attached membrane and generates propulsive force. First, an absolute nodal coordinate formulation (ANCF)-based dynamic model is established to predict the vibration response of the gradient-discontinuous soft pipe conveying fluid. The optimal configuration of the gradient-discontinuous pipe for enhanced propulsion is determined through theoretical predictions. The effects of internal flow velocity on the pipe response are then investigated theoretically, and the model is experimentally validated at an internal flow velocity of 5 m/s. Subsequently, numerical simulations are performed to investigate the effects of membrane dimensions on the vibration response and hydrodynamic performance and to identify the optimal membrane geometry. Finally, swimming experiments are conducted using membranes of different widths. The results identify a bending angle of 60°, a membrane length of 65 mm, and a membrane width of 45 mm as the optimal design parameters at an internal flow velocity of 5 m/s. The designed bionic fish achieves the highest mean swimming velocity of 20.3 cm/s (3.38 BL/s) with the 45-mm-wide membrane. The present study provides a novel driving approach for achieving high-frequency responses in flexible actuators.