Hydrodynamic analysis and motion simulation of fin and propeller driven manta ray robot

Current research on the hydrodynamics of manta ray robots is limited to the qualitative study of pectoral fin performance; other aspects such as the hydrodynamics and motion simulation of the overall robot are rarely addressed. A hydrodynamic analysis is therefore used in this study in conjunction with a six degrees of freedom (6DOF) motion equation to conduct motion simulations predicting the hydrodynamic characteristics and motion performance of a proposed manta ray robot. Though the rising and diving motions of manta ray robots are typically realized through a buoyancy adjustment device or a rudder used for attitude adjustment, these methods are slow. This study accordingly proposes a hybrid manta ray robot driven by two pectoral fins and two vertical propellers used as auxiliary power for attitude adjustment. A structural model of the proposed manta ray robot is provided and used to conduct a complete hydrodynamics analysis and establish the 6DOF motion equation. An empirical equation is then established to describe the hydrodynamics of the pectoral fins, and its applicability is proven using a computational fluid dynamics simulation. The motion of the robot is predicted in different situations using motion simulations, demonstrating that the robot provides relatively good motion performance. The relationship between the forward speed of the robot and the flapping speed of the pectoral fins is then discussed based on the simulation results. The motion simulation results also show that the propellers can effectively adjust the posture of the robot and help to improve robot motion stability by countering the effects of the pectoral fin flapping movement. Finally, the applicability of the 6DOF motion equation simplify verified by a computational fluid dynamics motion simulation. The findings of this study are expected to provide theoretical guidance for the optimization of the proposed manta ray robot structure and its control system design.