Enhancing Metachronal Swimming Efficiency through Dynamic Substructure Oscillation*

Metachronal paddling is a swimming technique commonly used by various small invertebrates like ctenophores, gossamer worms, shrimp, and krill, especially in environments with low-to-intermediate Reynolds numbers. These creatures synchronize their appendages in a metachronal sequence to enhance propulsive efficiency through interactions between adjacent appendages. This efficiency gain can be enhanced by increasing the number of appendages, although there is a threshold beyond which no further efficiency can be gained. Drawing inspiration from gossamer worms, which combine body oscillations with metachronal appendage movements, we propose that oscillating the body or substructures can overcome these efficiency limits, improving swimming performance as additional appendages are incorporated. To investigate this hypothesis, we utilized a fluid-structure interaction solver that integrates an immersed boundary method-based computational fluid dynamics solver with a finite element method-based structural solver, through two-way coupling. We simulated passively deforming plates stroking in a metachronal order, with the rotation pivot fixed on either a stationary or a deformable substructure following a sinusoidal pattern. Preliminary findings indicate that a dynamic, waving substructure not only increases thrust during the power stroke but also reduces drag during the recovery stroke, compared to a stationary substructure.