Showing papers on "Aquatic locomotion published in 2014"

Scaling macroscopic aquatic locomotion

Abstract: Nonlinear inertial flows usually influence the motion of swimming organisms, but most studies focus on the tractable case of swimmers too small to feel such effects. A mechanistic principle now unifies the varied dynamics of macroscopic swimmers. Inertial aquatic swimmers that use undulatory gaits range in length L from a few millimetres to 30 metres, across a wide array of biological taxa. Using elementary hydrodynamic arguments, we uncover a unifying mechanistic principle characterizing their locomotion by deriving a scaling relation that links swimming speed U to body kinematics (tail beat amplitude A and frequency ω) and fluid properties (kinematic viscosity ν). This principle can be simply couched as the power law Re ∼ Swα, where Re = UL/ν ≫ 1 and Sw = ω AL/ν, with α = 4/3 for laminar flows, and α = 1 for turbulent flows. Existing data from over 1,000 measurements on fish, amphibians, larvae, reptiles, mammals and birds, as well as direct numerical simulations are consistent with our scaling. We interpret our results as the consequence of the convergence of aquatic gaits to the performance limits imposed by hydrodynamics.

Scaling macroscopic aquatic locomotion

Abstract: Nonlinear inertial flows usually influence the motion of swimming organisms, but most studies focus on the tractable case of swimmers too small to feel such effects. A mechanistic principle now unifies the varied dynamics of macroscopic swimmers. Inertial aquatic swimmers that use undulatory gaits range in length L from a few millimetres to 30 metres, across a wide array of biological taxa. Using elementary hydrodynamic arguments, we uncover a unifying mechanistic principle characterizing their locomotion by deriving a scaling relation that links swimming speed U to body kinematics (tail beat amplitude A and frequency ω) and fluid properties (kinematic viscosity ν). This principle can be simply couched as the power law Re ∼ Swα, where Re = UL/ν ≫ 1 and Sw = ω AL/ν, with α = 4/3 for laminar flows, and α = 1 for turbulent flows. Existing data from over 1,000 measurements on fish, amphibians, larvae, reptiles, mammals and birds, as well as direct numerical simulations are consistent with our scaling. We interpret our results as the consequence of the convergence of aquatic gaits to the performance limits imposed by hydrodynamics.

Aquatic Locomotor Kinematics of the Eastern Water Dragon (Intellagama lesueurii)

Abstract: Quantitative studies of the axial undulatory swimming techniques used by secondarily aquatic vertebrates have been largely restricted to crocodilians. Numerous members of the suborder Lacertilia (lizards) are also known to swim using axial undulatory techniques, but how they do so has received minimal attention from the scientific community. We investigated the morphology and undulatory locomotor kinematics adopted by the Eastern Water Dragon (Intellagama lesueurii) through observation of natural swimming and filming of animals in a flume tank with a high speed camera. We found that morphological modifications associated with improved swimming ability and correlations between wave characteristics and swimming velocity are limited to the tail. The shape of dorsal spines and the reduction in the width of transverse processes of the caudal vertebrae result in a mediolaterally compressed tail instead of the typically rounded or dorsoventrally compressed tail seen in other Australian agamids. Axial undulatory swimming in I. lesueurii was found to be conceptually similar to that of crocodilians, but the relatively long and thin terminal part of the tail produces a different shaped undulatory wave. Unlike crocodilians and fishes, I. lesueurii does not use frequency moderated velocity control. Instead, changes in velocity are solely controlled by the phase speed of the propagating wave. The combined effect of these traits is comparable efficiency and performance in the water relative to that of crocodilians and an improvement relative to terrestrial lizards. Although no extant members of the suborder Lacertilia (lizards) are known to be fully aquatic, some species are known to have close associations with freshwater, brackish and marine habitats (Bartholomew et al., 1976; Bauer and Jackman, 2008). These associations range from dependence on riparian vegeta- tion to active foraging in the water (Dawson et al., 1977; Shine, 1986; Mayes et al., 2005). Aquatic dependence is found with increased frequency among varanids, iguanids, scincids, and agamids from tropical latitudes, and it is among these species that improved aquatic locomotor capabilities relative to more terrestrial species are likely to occur. When presented with the challenge, most terrestrial lizards have some capacity to swim (Braun and Reif, 1985). The action of walking can often be coopted for swimming (Snyder, 1962; Gray, 1968; Ritter, 1996); however, in the absence of morphol- ogies associated with aquatic locomotion, this technique is highly inefficient (Braun and Reif, 1985). Morphological traits such as streamlining help to reduce drag (Lighthill, 1969, 1970) and webbed limbs can increase propulsive force. Animals may further adapt to the aquatic environment by changing their locomotor technique altogether. Key to this study is the tendency for secondarily aquatic tetrapods to posses flattened tails (Bedford and Christian, 1996) that are used as an aquatic locomotor organ. Braun and Reif's (1985) review of vertebrate swimming grouped aquatic locomotor techniques into two broad catego- ries: axial and paraxial. Axial techniques use the cyclic beating of the trunk to propagate a travelling sinusoidal wave while paraxial techniques use appendages such as arms and legs. Axial undulatory techniques are considered to provide the most efficient method for aquatic propulsion (Braun and Reif, 1985), and animals that use them usually rely on the tail as the main locomotor organ. Typically, axial undulation incorporates a travelling sinusoidal wave, generated rostrally and travelling caudally. Tails or fins are used to amplify the effect of the undulation. The shape of the sinusoidal wave can be used to further define the type of axial undulation (Breder, 1926; Braun and Reif, 1985). The propulsive wave type is categorized by two factors: the relative length of the sinusoidal wave, and to which part of the body the wave is confined. Propulsive techniques that use wavelengths shorter than the animal's body length are defined as undulatory, and wavelengths longer than the animal's body length are said to be oscillatory. Hence, a complete wave is observed within the length of an animal in undulatory swimming where as an incomplete wave is observed in oscillatory swimming. Where pronounced changes in wave amplitude are observed between the animal's trunk and caudal section, they are said to be refined to a subset of the animal's body. Based on these observations Braun and Reif's (1985) proposed the following categories: undulatory, subundu- latory, oscillatory, and suboscillatory.

Experimental study of flapping foil propulsion system for ships and underwater vehicles and PIV study of caudal fin propulsors

Abstract: Deep sea aquatic animal propulsors are classified into four main categories lift-based propulsion, drag-based propulsion, undualtion mode and jet propulsion. In order to develop combined flapping and undulation mode propulsion for ships and underwater vehicles a brief introduction is given to lift-based propulsors and undulation mode. Combined bio-mimetic flapping and undulation mode propulsion systems for underwater vehicles have advantages such as ecologically pure, relatively low operational frequency and higher efficiency. This system can combine the function of propulsor, control device and stabilizer, provides static thrust, high maneuverability, less conspicuous wake and less cavitation problem than conventional propellers. In this paper, we experimentally study the application of a lift-based fore flipper locomotion applied to a 3m ship model, the concept of which resembles to the propulsion of penguins and turtles and present the results and observations. An electro-mechanical drive and transmission system is designed to actuate a pair of oscillating foils fitted at the bottom of the ship model. The model performances, both resistance and propulsion aspects, were studied. Sharks exhibit high-performance aquatic locomotion through oscillation of its homocercal forked caudal fin. This paper also presents the PIV measurements carried out on a live shark fish to understand and analyze the hydrodynamic behavior of its propulsion using the caudal fin. The velocity vector plots shows that the fins and caudal fins produce reverse von Karman vortex street resulting in a aftward jet formation which gives it the propulsive force.