Hydrodynamic performance of a biomimetic undulating fin robot under different water conditions

Inspired by the agile swimming behavior of the Black Ghost Knife Fish utilizing undulating propulsion in complex aquatic environments, this study investigates the locomotion principles and hydrodynamic performance of an undulating propulsion system under varying hydrodynamic conditions through numerical simulations and experiments. The influence of the fin aspect ratio on the thrust performance of the robot was explored, revealing a linear correlation between the aspect ratio and thrust generation. Furthermore, based on an aspect ratio of 0.3, the effects of frequency, amplitude, and wavenumber on the robot's swimming performance were examined. The results indicated a quadratic relationship between frequency and thrust, a linear relationship between amplitude and thrust, and a trend where thrust initially increased and then decreased with wavenumber, reaching an optimal level around wavenumber 1. Using numerical simulations and experimental investigations, the thrust performance of the robot under wave conditions demonstrated a noticeable reduction in hydrodynamic performance compared to still water conditions. The effects of frequency, amplitude, and wavelength on thrust remained consistent with still water conditions, but the instantaneous thrust became unstable. The current conclusions provide valuable insights for designing and optimizing undulating propulsion robots, offering systematic guidance for selecting appropriate motion parameters to accomplish different tasks.