Session: 20-17-01: Rising Stars of Mechanical Engineering

Paper Number: 172487

Three-Dimensional Flow Mechanics and Their Relationship to Fin Stiffness Patterns in Caudal-Fin-Based Propulsion 

Oceans are the largest unexplored and untapped resource on Earth. Their dynamics and effect on the global ecosystem remain poorly understood. UUVs are revolutionizing both our ability to learn about the oceans and the way we operate in them. But state-of-the-art UUVs have limited capabilities, and UUV missions achievable to date have been unable to fully meet our needs. Biological swimmers show agility and efficiency characteristics that largely surpass those of any manmade propeller, and there is a strong drive to create bio-inspired propulsion systems for UUVs that can match their performance characteristics. The ability to approach the locomotor performance of biological swimmers will break capability and cost barriers for a wide range of applications, including environmental monitoring and sensing, maintenance of industrial infrastructure, ocean cleanup efforts, aquaculture, and improved defense systems.

In fish and marine mammals, the use of fins with non-uniform and tunable mechanical properties, in combination with advanced sensorimotor control, is thought to be one of the main drivers of performance. It enables them to leverage complex three-dimensional and unsteady fluid mechanisms to improve efficiency and agility. Such mechanisms may include optimal vortex formation and shedding, resonant mechanics, delayed stall, jet vectoring and wake capture, among others. They have a tight two-way coupling with the structural dynamics and remain poorly understood. This research will carry out investigations into the unsteady 3-D fluid mechanisms and fluid-structural mechanics generated by the passive deformation of caudal (rear) fins of non-uniform stiffness distributions in thunniform swimming – the most efficient swimming mode in nature.

Caudal fin flexibility affects performance through two mechanisms (i) resonant mechanics and Strouhal number matching and (ii) determining the hydrodynamic shape that the fin presents to the flow. The effect and flow mechanisms associated with the latter, which is dependent on stiffness distribution in addition to mean stiffness value, have remained largely unexplored in the literature. Here, we will offer new insights into the hydrodynamics of fins that have stiffness distributions of similar complexity to biological swimmers while undergoing fully passive deformations. Up to date, such an analysis has been limited by the size of the parametric space and computational cost of 3D fluid-structure interaction problems. In this research, a new approach will be established that combines hardware-in-the-loop optimization, automated experiments and pneumatically actuated soft robotics to find optimal 2-D stiffness distributions of the caudal fin both for propulsion and maneuvering. In-depth analysis of the optimum will yield new insights into the flow features that lead to optimality and how these features change with swimming velocity and maneuver.

Presenting Author: Cecilia Huertas-Cerdeira University of Maryland

Presenting Author Biography: Cecilia Huertas-Cerdeira is an Assistant Professor in the Department of Mechanical Engineering at the University of Maryland, College Park. She has broad research interests in the fields of Unsteady Fluid Mechanics and Fluid-Structure Interactions. Her group leverages a combination of experimental, analytical and data-driven tools to tackle problems ranging from bio-inspired robotics to efficient aviation, wind energy harvesting and heat transfer enhancement. She received her PhD at the California Institute of Technology in 2019, for which she was awarded the William F. Ballhaus Prize. She was a recipient of the NSF CAREER Award in 2024.

Authors:

Cecilia Huertas-Cerdeira University of Maryland