Biomechanical Modeling of Ray Pectoral Fins to Inform the Design of AUV Propulsion Systems

Abstract

The ongoing demand for higher performing unmanned underwater vehicle systems for military and exploratory applications calls for unprecedented approaches to researching and developing new technologies. Autonomous Underwater Vehicles (AUVs), like their aerial counterparts (UAVs), are a type of naval craft that can carry out missions with minimal or no human interaction. The ever-increasing mission complexity of underwater vehicles has driven engineers and scientists to explore new sources of inspiration for the design of AUV propulsion systems. Fortunately, the many examples of successful underwater propulsion systems can be found in nature, such as the flapping fins of fish or undulating bodies of eels. Since there are literally thousands of examples in nature of how underwater propulsion can be achieved, it is important to realize which types of biological propulsion systems might be best for inspiring artificial propulsions systems for use in AUVs. In the present study, the mechanics of the pectoral fins of skates and rays is investigated to elucidate the underlying mechanisms responsible for their impressive propulsive ability. Batoid rays are of significant interest due to their unique body construct and performance characteristics with their pectoral fins used for both propulsion and control. Although the highly functioning fins of batoids have been recognized, the biomechanics behind their function is not well understood. Therefore the goal of this research is to investigate the musculoskeletal system of batoid rays, identify key biomechanical design features, elucidate the role of musculoskeletal design on fin kinematics and hydrodynamics, and to apply the lessons learned to the design of AUV propulsion systems.
Computerized Tomography (CT) scans of the cownose ray (Rhinoptera bonasus) and Atlantic ray (Dasyatis sabina) skeletons reveal a complex system of cartilaginous joints and segments that provide for the support structure of batoid fins. Features of the skeletal design believed to be important for kinematics and propulsion were identified. A biomechanical model of the skeletal structure was developed to simulate ray swimming kinematics and uncover the role of skeletal design on kinematics. The biomechanical model was then interfaced with an advanced panel method Computational Fluid Dynamics (CFD) model to establish a link between the skeletal structure and hydrodynamic performance, and an investigation into the role of skeletal design on hydrodynamics was conducted. Lastly, the applicability of skeletal design features of biology to the design of AUV propulsion systems was explored through the design, fabrication, and testing of bio-inspired artificial pectoral fin skeletons.
The development of the biomechanical model with fluid-structure interaction can be used as a tool for transferring the biological design principles of ray fins to the design of artificial systems for AUV propulsion. Ultimately, the objective of this work was to establish an interface between biology and engineering to aid in the development of next generation AUV technology. The present study introduced an approach of first analyzing the biomechanics of ray pectoral fins, gaining knowledge of how the real biological system works through fluid-structure modeling, then using this new knowledge to drive the design of simplified artificial versions of ray pectoral fins for underwater propulsion. The latter was done to test whether or not the biomechanical design approach of pectoral fin propulsion systems found in nature could be an effective approach for the design of artificial fins, as well as to learn if the form and function relationships revealed through computational modeling can hold for simplified, artificial structures, that could be used for propulsions and control of next generation AUVs.