Wake-based unsteady modeling of the aquatic beetle Dytiscus marginalis

Dytiscus marginalis simultaneously uses its hind legs to propel itself through the water. Previous work has suggested that use of synchronized leg motions, such as that used by D. marginalis, allows it to swim with higher hydrodynamic efficiency than similarly sized insects that alternate their legs during swimming. A model is developed based on the generation of vortices in the wake to calculate the relative efficiency of synchronized-leg-swimming kinematics compared to alternating-leg-swimming kinematics. The model agrees well with measured values of swimming speeds during steady state and predicts an overall hydrodynamic swimming efficiency of 18% for synchronized-leg-swimming. Additionally, synchronized-leg swimming is calculated to be 39% more hydrodynamically efficient than alternating-leg-swimming kinematics, thus verifying previous suggestions of greater hydrodynamic efficiency in D. marginalis based on swimming observation.

► Model based on wake vortices and dimensions/kinematics provides forces and motion.
► Results show good agreement with observed swimming speeds of D. marginalis.
► Model allowed comparison synchronized-leg swimming to alternating-leg swimming.
► Synchronized-leg swimming is shown to be 39% more hydrodynamically efficient.
► Superiority of synchronized-leg swimming is robust to significant perturbations.