Bionic parallel undulating fins: Influence of unsteady coupling effect on robot propulsion performance

Inspired by the undulatory propulsion methods and parallel swimming behaviors of creatures like stingrays, this study investigates the impact characteristics of unsteady coupling effects on two adjacent undulating fin bodies, under various vertical distances and "gait" patterns. By constructing a numerical model of two-dimensional parallel undulating fins, numerical simulations were conducted to analyze the vertical distances and motion parameters of the parallel dual-undulating fins under both in-phase and anti-phase conditions. The results indicate that the variations in the hydrodynamic performance of parallel dual-undulating fins essentially stem from changes in the fluid pressure field and velocity field caused by changes in their relative spatial positions. Compared to single undulating fin propulsion, the parallel arrangement of undulating fins in in-phase conditions results in a decrease in average thrust and efficiency, but a more stable instantaneous thrust. In contrast, the parallel arrangement in anti-phase conditions leads to an increase in average thrust and efficiency. It is worth noting that the parallel dual-undulating fins in anti-phase with low wave number and close proximity exhibits better hydrodynamic performance potential. The current research may provide a basis for the control optimization of underwater biomimetic undulating fin robots, aiming to meet the mission requirements in various scenarios.