Showing papers on "Aquatic locomotion published in 1996"

Transitions from Drag-based to Lift-based Propulsion in Mammalian Swimming

Abstract: Synopsis. The evolution of fully aquatic mammals from quadrupedal, terrestrial mammals was associated with changes in morphology and swimming mode. Drag is minimized by streamlining body shape and appendages. Improvement in speed, thrust production and efficiency is accomplished by a change of swimming mode. Terrestrial and semiaquatic mammals employ drag-based propulsion with paddling appendages, whereas fully aquatic mammals use lift-based propulsion with oscillating hydrofoils. Aerobic efficiencies are low for drag-based swimming, but reach a maximum of 30% for lift-based propulsion. Propulsive efficiency is over 80% for lift-based swimming while only 33% for paddling. In addition to swimming mode, the transition to high performance propul? sion was associated with a shift from surface to submerged swimming providing a reduction in transport costs. The evolution of aquatic mam? mals from terrestrial ancestors required increased swimming performance with minimal compromise to terrestrial movement. Examination of modern analogs to transitional swimming stages suggests that only slight modification to the neuromotor pattern used for terrestrial locomotion is re? quired to allow for a change to lift-based propulsion.

Mechanics of propulsion by multiple fins: kinematics of aquatic locomotion in the burrfish (Chilomycterus schoepfi)

Abstract: Locomotion in tetraodontiform fishes (puffers and relatives) involves the use of multiple fins for propulsion during swimming. A variety of tertraodontiform swimming modes have been defined, but the contributions of pectoral, dorsal, anal, and caudal fins to the propulsion in these fish remain largely unknown. We used video analysis to study swimming behaviour of the striped burrfish ( Chilomycterus schoepfi ). Burrfish swam in a flow tank at speeds of 0.5–6.3 standard body lengths per second, during which all fins oscillated at all speeds. The oscillation frequency range of all fins was 2.1–9.2 Hz, increasing with velocity. Pectoral fins were always out of phase, usually by 180 degrees (alternate left and right beats). Reduced frequency parameters for all fins were high (0.65–12.1) indicating that acceleration reaction is the dominant mechanism of thrust. Phase lag between anal and caudal fins assumed three distinct states which suggests that burrfishes alter the patterns of fin motion in discrete stages analogous to gaits. Rapid oscillation of five fins in various degrees of asynchrony is a mechanism to produce relatively constant thrust from multiple periodic motions.

Issues for aquatic pedestrian locomotion

Abstract: SYNOPSIS. Aquatic pedestrian locomotion represents an important mode of locomotion for many aquatic and amphibious animals, both extant and extinct. Unlike terrestrial locomotion where weight is the defining force, in aquatic locomotion buoyancy and hydrodynamic forces may be as important as weight. Aquatic pedestrian locomotion differs fundamentally from swimming because pedestrians must maintain contact with the substratum in order to locomote. Ambient water motion may constrain or prevent locomotion of aquatic pedestrians by requiring that they actively grip the substratum. A comprehensive biomechanical analysis of aquatic pedestrian locomotion will require an integration of hydrodynamics with terrestrial locomotor dynamics.