The existing amphibious robots cannot usually enjoy a superior adaptability in the underwater environment by replacing the actuators. Based on the bionic prototype of the Portunus trituberculatus, a new leg-paddle coupling crablike robot with a composite propulsion of walking legs and swimming legs is developed, with both the abilities of walking and swimming under water. By simulation and experiment, the effects of the phase difference, the flapping amplitude and the angular bias of the coupling movement, as well as the Strouhal number on the hydrodynamic performance of the swimming legs are studied, and the time dependent tail vortex shedding structure in a cycle is obtained. Both experimental and numerical results indicate that the thrust force with a high propulsion efficiency can be generated by a flapping swimming leg. This work can further be used for analysis of the stability and the maneuverability of the swimming leg actuated underwater vehicles.
