Abstract
ABSTRACTAquatic and terrestrial animals have different swimming performances and mechanical efficiencies based on their different swimming methods. To explore propulsion in swimming frogs, this study calculated mechanical efficiencies based on data describing aquatic and terrestrial webbed-foot shapes and swimming patterns. First, a simplified frog model and dynamic equation were established, and hydrodynamic forces on the foot were computed according to computational fluid dynamic calculations. Then, a two-link mechanism was used to stand in for the diverse and complicated hind legs found in different frog species, in order to simplify the input work calculation. Joint torques were derived based on the virtual work principle to compute the efficiency of foot propulsion. Finally, two feet and swimming patterns were combined to compute propulsive efficiency. The aquatic frog demonstrated a propulsive efficiency (43.11%) between those of drag-based and lift-based propulsions, while the terrestrial frog efficiency (29.58%) fell within the range of drag-based propulsion. The results illustrate the main factor of swimming patterns for swimming performance and efficiency.
Highlights
The bodies of aquatic and terrestrial animals have diverse shapes and moving patterns that result in distinct swimming performances
Frog swimming efficiency slightly exceeded drag-based swimming efficiency In this study we used a model similar to Richards’ research (Richards, 2008), where the frog model was built as planar linkages with webbed feet, but we further established the dynamic equations and computed the joint input work and propulsive efficiency according to the virtual work principle
A large gap remains between the lift-based swimming pattern of the aquatic frog and those utilized by many other aquatic animals
Summary
The bodies of aquatic and terrestrial animals have diverse shapes and moving patterns that result in distinct swimming performances. Fish generally wave their body-caudal fins (BCF) and median or paired fins (MPF) for propulsion through water (Sfak et al, 1999; Chu et al, 2012); these fins create minimal drag and strong liftbased thrusts, leading to swimming efficiency as high as 80% (Fish, 1996). Drag-based propulsions like paddling and flapping are utilized by terrestrial mammals or semi-aquatic animals, which have low swimming efficiencies. Research into frogs’ swimming methods treats the webbed foot as the main propulsive unit, and the foot shape and motion patterns differ by species. Different methods can be used to analyze propulsive forces related to morphological and kinematic patterns
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