Meeting Abstract
Metachronal paddling of multiple appendages is a swimming strategy used by many ecologically important marine species across a wide range of body sizes and Reynolds numbers. The appendages in metachronal paddling are stroked in an oscillatory pattern, with a phase lag between each neighboring appendage. The ratio of inter-appendage distance (D) to appendage length (L) has been previously reported to fall within the range of 0.2-0.65 for over 30 crustacean species, as well as one ctenophore species known to use metachronal paddling (Murphy et al., Mar. Biol., 158, 2011). Small inter-appendage spacing could allow for thrust augmentation through shear layer interaction in the fluid, while large inter-appendage spacing could effectively isolate appendages from each other. We developed a self-propelled metachronal swimming robot (“krillbot”) in order to determine the effects of varying different physical and kinematic parameters on metachronal swimming performance. In this study, we use krillbot to investigate the effects of varying inter appendage spacing on thrust, swimming speed, and fluid dynamic characteristics of the wake. When kinematic parameters are maintained across varying inter-appendage spacing, decreasing spacing results in increased swimming speed. However, very small inter-appendage spacing restricts the possible kinematics parameter space, requiring either stroke amplitude or phase lag between adjacent appendages to be small to avoid collisions between neighboring appendages for a purely metachronal stroke pattern. Interestingly, animals with low D/L ratios (e.g., mantis shrimp, copepods) typically use their paddling appendages for rapid acceleration rather than routine swimming, performing a hybrid stroke consisting of a metachronal power stroke and nearly synchronous recovery.
