Undulatory vs. gliding locomotion: Effects on underwater object detection

Abstract

Underwater object detection based on flow sensing is crucial for bio-inspired robotics, due to its reliable performance in turbid environment. Nevertheless, how locomotion patterns affect sensing performance remains poorly understood. We employ numerical simulations to systematically compare flow sensing performance between two fundamental patterns, which are undulatory and gliding motions, through pressure signal analysis on a foil interacting with a stationary cylinder. The effects of different tail-beat frequencies and lateral distances are also considered. Key findings demonstrate that undulatory locomotion remarkably amplifies effective pressure signals, particularly at higher tail-beat frequencies, whereas gliding provides superior suppression of self-generated flow noise. Both locomotion patterns exhibit exponential signal attenuation with increasing lateral distance, though undulatory motion significantly extends the detection range. These findings propose a hybrid strategy: undulatory motion for long-range detection and gliding motion for high-precision perception. Flow analyses identify a characteristic counter-clockwise vortex structure induced by the cylinder, which directly correlates with the effective pressure signal. Spatiotemporal analysis of cylinder-induced flow perturbations demonstrates that undulatory motion substantially enhances the positive vorticity perturbations on the foil posterior, generating a more pronounced and spatially extended region of negative pressure perturbation. The study advances understanding of locomotion-modulated sensing and provides reliable guidance for bio-inspired robotic design on adaptive underwater navigation.