Rigid-flexible coupling dynamics for bionic body-caudal-fin propulsion

With growing adoption of body-caudal-fin (BCF)-based bionic propulsion robots, optimizing thrust generation has become a critical focus of research. Despite extensive experimental efforts, theoretical studies in this area remain insufficient. This paper attempts to simplify the swing of the caudal fin as a rotation problem of the hub-beam system. Employing the Euler–Bernoulli beam theory to describe the elastic deformation of the beam and the Morison equation to describe the hydrodynamic load, the governing equation of this system is derived based on the principle of virtual work. We then investigate the effects of material properties, motion parameters, and structural parameters on thrust generation. Our model suggests that the flexibility of the beam can greatly increase instantaneous thrust. In addition, the thrust calculated by our model agrees well with the experiment results. Our work can provide guidance on choosing the proper material and rotation mode to improve propulsion performance in the design of BCF bionic robots.