Swimming and maneuvering of a bio-robotic sea lion

Abstract

Unmanned Underwater Vehicles (UUVs) are increasingly tasked to operate in complex, cluttered littoral environments where traditional systems lack the necessary maneuverability. To address these limitations, this research adapted the propulsive and maneuvering strategies of the California sea lion (Zalophus californianus) to develop a highly maneuverable, biorobotic platform. The primary objective was realized through the design, fabrication, and analysis of SEAMOUR (Stroke Experimentation and Maneuver Optimizing Underwater Robot), a multi-body system capable of modeling the sea lions use of distributed control surfaces and flexible flippers for propulsion and maneuvering. The investigation utilized a multi-tiered experimental and numerical framework to characterize propulsive and maneuvering dynamics of the system. This approach progressed from quantifying the lift and thrust generation of simplified flipper systems to conducting full-scale free-swimming techniques. The investigation combined multiple analytical methods, including biological kinematic analysis, Computational Fluid Dynamics (CFD), and multi-axis force and torque studies. Furthermore, a high-fidelity numerical model was used to expand the experimental space, while also being paired with Reinforcement Learning (RL) algorithms to explore optimize propulsive gaits beyond biological observation. A series of quantitative experiments explored the system's capabilities, establishing its maneuvering and propulsive performance. These investigations revealed that the system's geometric profile renders pitch-based turns significantly more effective than yaw-based turns. This finding validates the biological strategy of banking to orient the body's maximum surface area into the direction of the turn. Experimental results also demonstrated that passive structural flexibility of the fore flippers enhances thrust by better directing forces while dampening actuator load. Results demonstrated that the integration of flexible fore flippers with an active, articulated head and pelvis enabled the execution of tight, multi-axis turns with a turning radius of approximately 0.5 body lengths (R/BL), a performance metric superior to traditional UUVs systems. The conclusion of this work establishes that high-performance maneuvering is achieved through the synergistic coordination of distributed control surfaces and compliant mechanisms. Ultimately, this research demonstrates that adapting propulsive and maneuvering approaches used by California sea lions for the development of highly maneuverable, biorobotic UUVs offers a viable pathway for future UUV development.