Design and Hydrodynamic Analysis of a Robotic Boxfish Using Lift-based and Drag-based Swimming Modes for Propulsion

This paper presents a new design for a robotic boxfish with a 2-DOF pectoral fin each side and a 1-DOF caudal fin. The pectoral fin designed is able to simulate the fin-base pitching and the fin-foil flapping, suggesting a combination of lift-based and drag-based kinematics. Based on Lattice-Boltzmann Method, the hydrodynamic characteristics of prototype's rigid pectoral fin was numerically calculated, so as to analyze the effects of motion parameters such as the offset angles of oscillation, phase lags, and amplitudes. Experiments in which the prototype relying on its pectoral fins alone for propulsion showed that by combining the motion parameters, the robotic boxfish was able to achieve highly maneuverable movements such as straight or inverted swimming, upward floating, downward diving and in-situ turning.