Meeting Abstract

S7-1.1  Saturday, Jan. 5   Size-dependent mode choices in aquatic locomotion VOGEL, Steven; Duke University svogel@duke.edu

All active fliers get about in a similar fashion, with oscillating wings; but aquatic locomotion, less constrained by gravity, offers a complex set of choices. Should swimming be done on the surface or submerged? If on the surface, should it rely on static–surface tension (contact line) or displacement–or dynamic (aquaplaning) support? If submerged, should it use internal (jet) or external (fins, paddles, cilia) propulsors? If propulsors are external, should they cover its surface or be localized? If localized and numerous, should they be in one or another preferred pattern? If localized but few, should they be located laterally or caudally? Should non-jet submerged propulsion be drag-based or lift-based? Complicating matters somewhat, no single criterion establishes biological superiority–usually meaning functional effectiveness. Thus niche-dependent biological factors may favor maximization of speed, acceleration, or energetic efficiency, or perhaps minimization of structural investment or such things as acoustic or hydrodynamic disturbance or visual profile. But we can discern some general rules that arise from physical considerations that should guide the selective process–besides the biological constraints of ancestry and development and ecological biases such as trophic preferences. Of especial interest, given the extreme size-range of nature�s swimmers, most of our rules for who swims how turn out to be strongly size-dependent. In some instances, familiar dimensionless numbers and indices prove satisfactory–Reynolds, Froude, Bond, and Weber number together with Froude propulsion efficiency. For others, we can contrive semi-empirical scaling rules or ad hoc dimensionless numbers of predictive value.