Session: 02-06-01: Structural Dynamics and Control of Aerospace Structures

Paper Number: 137916

137916 - Heterogeneous Stiffness in Stingray Fins for Simplified Undulatory Propulsion 

Stingrays are efficient swimmers that leverage heterogeneous stiffness for low energy propulsion. The heterogeneous stiffness allows them to have a very simple actuation pattern with a complex and efficient propulsive pattern. The majority of stingray-inspired robot developments have been focused on engineering efficient soft actuators. The architecture of the skeletal system (pectoral fins) of stingrays is rarely examined as an essential subsystem of their propulsive action. In this study, the role of the dynamic behaviors of the skeleton in propulsive dynamics are examined computationally and experimentally. The pectoral fin musculature is omitted to determine, in isolation, the mechanistic connections between the skeletal morphology of the pectoral fins and propulsive performance. Simplified, 3D-printed analogues of the fin skeleton were fabricated to emulate differential stiffening owing to the arrangement of mineralized cartilage radials running from pelvic girdle to wing tip. The study identifies two important architectural patterns: 1) offset - the angle between the ends of radials of successive fin rays; and 2) trajectory - the splay of the fin rays as they span out from the pelvic girdle. The models with offset radials generate traveling waves, while those without do not, when actuated vertically in still water. Models with trajectories remain stable at increased frequency while those without the fins go out of sync. Finite element analysis shows the mode shapes dynamics as a function of offset and trajectory patterns. Comparison of mode intervals reveals that skeletal arrangement has a large effect on anisotropic stiffness of the fin.   This correlates with the mode shapes of the computational and physical models. Understanding the relation between complex geometry and mode shapes will allow us to design structures that will be able to move efficiently through a fluid with simple actuation. This work demonstrates how heterogenous stiffening can be used to enable efficient aerial and aquatic propulsion.

Presenting Author: John Michael Racy University of Washington

Presenting Author Biography: John Michael Racy is a member of the Illimited Lab at the University of Washington, Seattle. He is currently an Undergraduate of Mechanical Engineering at the University of Washington, Seattle. His previous research experience was gained at the Friday Harbor Labs using micro-CT scanning and 3d printing to investigate comparative biomechanics in fishes. His research on how generative design offers insight into loading regimes in stingrays led to his current work related to undulated structures.