Towards Unusual Rolled Swimming Motion of a Bioinspired Robotic Hammerhead Shark Under Negative Buoyancy

In nature, the hammerhead shark possesses a special rolled swimming motion to combat the effects of inborn negative buoyancy. Inspired by this natural mechanism, we developed a novel biomimetic robotic hammerhead shark to explore the distinctive rolled swimming motion mode. First, a scaled-down robotic prototype is constructed based on the morphological characteristics of the hammerhead shark. Second, the kinematics and dynamics of fish-like swimming are built, thereafter, model identification and validation are performed to improve the accuracy of the robotic model. Furthermore, the physical effects of the long dorsal fin and the rolling state on swimming performance are investigated indepth by numerically simulating the lift and drag forces over different fin surfaces and the dynamic torque of the body. Finally, extensive aquatic experiments demonstrate the remarkable improvements on locomotion performance and propulsive efficiency of the robotic hammerhead shark by the proposed rolled motion. The obtained results provide a new solution for the long voyage of high-load robotic fish system.