Investigating the Impact of Three-Degree-of-Freedom Bionic Pectoral Fins' Spatial Configuration on Robotic Fish Propulsion Efficiency

Based on the fact that the spatial geometry of bionic pectoral fins has a significant effect on the swimming performance of jack mackerel, in this paper, the spatial shape of three-degree-of-freedom bionic rigid pectoral fins was optimized by using a neural network method and numerical simulation of Computational Fluid Dynamics (CFD) to improve the efficiency of pectoral fin propulsion. By observing the different kinematic patterns of pectoral fin propulsion and backswing stroke in fish, an optimization model was developed using a genetic algorithm and back propagation (BP) neural network, in which the concave pectoral fin parameters, such as pectoral fin bending angle, pectoral fin chord length, and pectoral fin area, were taken as design variables and maximum propulsion force was taken as the objective function. Given the three-degree-of-freedom motion law of the pectoral fin, CFD numerical simulation of the bionic robotic fish was used to obtain different concave pectoral fin thrust datasets and combined with the established optimization model to obtain the concave pectoral fins with the largest average value of the thrust during the pectoral fin motion cycle. Numerical simulations of the planar pectoral fins and the optimized concave pectoral fins are performed to analyze the hydrodynamic coefficients and vortex cloud diagrams, and the analysis results show that the optimized pectoral fins produce enhanced lift and reduced drag, which improves the swimming performance of the robotic fish. The results of the physical experiment verified the validity of the results obtained from the numerical simulation analysis.