Dynamic modeling of an ostraciiform robotic fish based on angle of attack theory

This paper focuses on the dynamic modeling of a self-propelled, multimodal ostraciiform robotic fish, whose three active joints (two pectoral fins and one caudal fin) are actuated by a Central Pattern Generator (CPG) controller. Compared with other dynamic modes for robotic fish, we introduce angle of attack (AoA) theory on the fish modeling, which can be used to further explore the relationship between swimming efficiency and AoA of robotic fish. First, by using the quasi-steady wing theory, AoA of the oscillatory fins are explicitly derived. Then, with the simplification of the robot as a multi-rigid-body mechanism, AoA-based fluid forces acting on the oscillatory fins of the robot are further approximately calculated in a three-dimensional context. Next, by importing the driving signals (generated by CPG control law) into a Lagrangian function, the differential-algebraic equations are employed to establish a hydrodynamic model for steady swimming of the ostraciiform robotic fish for the first time. Finally, comparative results between simulations and experiments for forward and turning gaits of the robot are systematically conducted to show the effectiveness of the built AoA-based dynamic model.