Leaping fishbot by combustion and propulsion hybrid actuation

Abstract Autonomous underwater vehicles have been extensively developed in the past decades and deployed for various ocean research activities. While the leaping‐out motions of underwater creatures have motivated the development of underwater robots with the motion ability to jump out of water, the dynamics of such jumping robots have not been fully described. In this study, we developed a leaping fishbot, a flying fish‐inspired underwater soft robot that can leap out of the water and further sail on the surface using the combustion and propulsion hybrid actuation. Specifically, the fishbot uses the transient driving method, in which a premixed oxygen–propane gas generates an instant pushing impulse to launch the robot out of the water at a transiently high speed while the attached jetting propellers provide a sustained thrust as it swims on the water surface at a stable velocity. A series of flume experiments and solid–fluid hybrid computational fluid dynamics numerical simulations were conducted to study the kinematic performance of the robot. Experimental results established a quantitative relationship between the kinematic performance, gas amount, and launch angle. The numerical results accurately predicted the water–air multiphase jumping motions, the numerical result of kinematic was significantly agreeing with the experimental results, the error in the horizontal direction is less than 15%, and that in the vertical direction is less than 10%. We further analyzed the flow field generated by the leaping fishbot to gain a better understanding of the velocity and vortex distribution around it. Our research findings provide valuable insights into bionic application of underwater robots in the future.