Development of a robotic dolphin capable of underwater horizontal and surface vertical movement

To address the limitations of bionic underwater vehicles (BUVs) in terms of surface operation capabilities, this study developed a robotic dolphin capable of achieving multiple underwater and surface motion modes, inspired by the vertical surface behavior of biological dolphins. By establishing a physical model of the dolphin and a multi-body cooperative kinematic model involving the body, caudal fin, and pectoral fins, numerical simulations were conducted to analyze the hydrodynamic performance of the dolphin's underwater horizontal motion and surface vertical motion. Based on these findings, the robotic dolphin's body module, caudal fin module, pectoral fin module, center-of-mass adjustment module, and corresponding control system were designed. Experimental studies on underwater/surface multi-mode motion were conducted using the constructed prototype platform, with results compared to numerical simulations. The results show that the robotic dolphin can achieve an underwater horizontal propulsion speed of 0.796 m/s and a horizontal turning speed of 19.51°/s, as well as a surface vertical propulsion speed of 0.192 m/s and a vertical turning speed of 55.82°/s. During underwater horizontal motion, the caudal fin provides the primary thrust, while the pectoral fins enable highly maneuverable in-place turning; in surface vertical motion, the caudal fin stabilizes the standing posture while the pectoral fins generate thrust for propulsion and torque for in-place turning. The center-of-mass adjustment module facilitates the transitions between postures. This study significantly enhances the surface operational capabilities of traditional BUVs, laying a scientific foundation for developing novel underwater/surface dual-mode operational robots.