The aim of this study was to improve the swimming efficiency of a bionic robotic fish propelled by its pectoral fins by investigating its burst-and-coast gait, with the central objective of minimizing the energy consumption during swimming. To this end, we first defined the robotic fish and then established the corresponding three-degree-of-freedom motion laws governing the pectoral fins. Based on this framework, we proposed two measurement parameters for characterizing robotic fish’s burst-and-coast gait: the pectoral fin oscillation period and the duty cycle. The hydrodynamic parameters of the robotic fish under different motion conditions were obtained through computational fluid dynamics (CFD) numerical simulations. Analysis indicates that the velocity and energy consumption of robotic fish during intermittent pectoral fin propulsion exhibit nonlinear variations with oscillation period, revealing an optimal period that significantly reduces energy expenditure. Furthermore, continuous fin flapping does not necessarily yield greater efficiency; instead, a burst-and-coast propulsion strategy achieves an excellent balance between velocity and energy consumption, demonstrating higher propulsion efficiency. Third, a burst-and-coast gait model was established based on multilayer perceptron, using the numerical simulation dataset described above as input. The results show that when the pectoral fin oscillation period is 1.55 s and the duty cycle is 0.72, the cost of transport reaches its minimum while maintaining sufficient swimming velocity. In addition, the flow-field structure and fluid-dynamics parameters around the robotic fish were calculated using CFD. The results show that during the burst phase, two sets of vortex rings are generated around the fish body. These vortex rings detach from the tail, enabling the robotic fish to produce continuous thrust even during the coast phase. • The burst and coast swimming gait of a robotic fish driven by pectoral fins is defined, and key driving parameters are proposed. • The influence of duty cycle and motion period on burst and coast motion was studied using computational fluid dynamics numerical simulation. • Based on the optimal energy consumption and speed, the optimal swimming and sliding gait was obtained through optimization.
Li et al. (Sun,) studied this question.