Bio-inspired intermittent locomotion: A novel energy-saving strategy for manta ray-inspired underwater vehicles

Bio-inspired underwater vehicles, recognized for their high propulsion efficiency and maneuverability, play a crucial role in ocean exploration and underwater surveying. However, their limited energy density restricts their ability to perform prolonged tasks. Intermittent locomotion, commonly employed by marine organisms to minimize energy expenditure, presents a viable solution. However, most studies on the energy-saving mechanisms of intermittent locomotion in bio-inspired vehicles rely on numerical simulations; experimental validation remains limited, especially for undulating fin-based vehicles. This study presents a bio-inspired manta ray prototype featuring a two-degree-of-freedom (2DOF) flexible pectoral fin capable of both flapping and torsional motion. Hydrodynamic experiments were conducted to examine the influence of duty cycle (DC) on energy efficiency. The results demonstrate that intermittent locomotion can save up to 70.4 % of energy relative to continuous locomotion (A=70°; f=0.8Hz; DC=0.9). Furthermore, at low duty cycles (0.1–0.3), intermittent locomotion yields higher propulsion efficiency, with the most notable improvements occurring at low frequencies, resulting in up to 11.9 % higher efficiency. Particle Image Velocimetry (PIV) was used to analyze vortex shedding and uncover the underlying energy-saving mechanisms. These findings lay the groundwork for long-duration underwater missions utilizing bio-inspired manta ray vehicles.