Supplementary material from "Bio-inspired Forward and Backward Swimming Gaits Resulting From Fluid-Structure Interactions"

Biological undulatory swimmers display a wide range of gaits and are adept at swimming in different directions. This study explores the impact of passive dynamics as a result of fluid-structure interaction on the gaits of a model swimmer through computational simulations. Inspired by slender-bodied natural aquatic swimmers, the model consists of a flexible body and a rigid head. Systematically varying body stiffness and head pitching, the research replicates various swimming patterns observed in nature (both forward and backward). Optimal forward gaits, akin to anguilliforms and carangiforms, result from low to high bending rigidity and small pitching amplitudes. Conversely, low bending rigidity with high pitching amplitude produces backward swimming (tail-first), similar to mosquito larvae, exhibiting unique flow-field features and generating backward propulsion forces. The study underscores the significant role of passive dynamics in undulatory swimming and the potential for diverse gait generation through tailored structural and kinematic design in bio-inspired devices.