Unsteady Mechanisms of Force Generation in Aquatic and Aerial Locomotion

Dickinson, Michael H.

doi:10.1093/icb/36.6.537

Cited by 153 publications

(109 citation statements)

References 29 publications

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“…In contrast, measuring forces exerted by biological surfaces acting in water has proven to be challenging (11,12). We used digital particle image velocimetry (DPIV; a technique in which a laser light sheet illuminates a thin section of water to permit visualisation of fluid particle movement) to quantify forces produced as lizards ran across water.…”

Section: Methodsmentioning

confidence: 99%

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Running on water: Three-dimensional force generation by basilisk lizards

Hsieh

Lauder

2004

Proc. Natl. Acad. Sci. U.S.A.

113

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Water provides a unique challenge for legged locomotion because it readily yields to any applied force. Previous studies have shown that static stability during locomotion is possible only when the center of mass remains within a theoretical region of stability. Running across a highly yielding surface could move the center of mass beyond the edges of the region of stability, potentially leading to tripping or falling. Yet basilisk lizards are proficient water runners, regularly dashing across bodies of water to evade predators. We present here direct measurements of time-averaged force produced by juvenile plumed basilisk lizards (Basiliscus plumifrons) while running across water. By using digital particle image velocimetry to visualize fluid flow induced by foot movement, we show that sufficient support force is generated for a lizard to run across water and that novel strategies are also required to run across a highly yielding surface. Juvenile basilisk lizards produce greatest support and propulsive forces during the first half of the step, when the foot moves primarily vertically downwards into the water; they also produce large transverse reaction forces that change from medial (79% body weight) to lateral (37% body weight) throughout the step. These forces may act to dynamically stabilize the lizards during water running. Our results give insight into the mechanics of how basilisk lizards run across water and, on a broader scale, provide a conceptual basis for how locomotor surface properties can challenge established rules for the mechanics of legged locomotion.Basiliscus plumifrons ͉ hydrodynamics ͉ particle image velocimetry ͉ locomotion R unning across water is a dramatic example of a locomotor function once thought to be limited to small-bodied invertebrates (e.g., see refs. 1-4). Although considerable literature is available that examines the biomechanics of movement across solid surfaces, very little is known about how softer, more yielding surfaces, such as water, affect legged locomotion. Water provides an unusual challenge, because it readily yields to any applied force. As a result, it would be expected that any animal attempting to walk across water would sink toward the supporting limb.There are few vertebrates capable of running across water. Waterfowl are known to slap the water with their feet during flapping take-off. However, they obtain a great deal of lift from their wings. Anolis lizards and baby green iguanas have been reported to run short distances across water. This capability, however, seems to be limited primarily to smaller-bodied individuals. Basilisk lizards (Basiliscus sp.) are unique in that they regularly run across water, using only their feet as a source of both lift and thrust. This behavior is prevalent among hatchlings through adults and is made more spectacular by their large size range: Hatchlings weigh Ϸ2 g, whereas adults can weigh Ͼ200 g. Basilisk lizards, therefore, serve as interesting model organisms for examining the mechanics of this remarkable locomotor fe...

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Section: Methodsmentioning

confidence: 99%

“…where is the density of water (998.23 kg͞m 3 at 20°C), ⌫ (m 2 ͞s) is the average circulation around the centers of vorticity, and A (m 2 ) is the projected area of the vortex ring on the light sheet (11,13). Time, t, for stroke forces was the time from the start of stroke to the frame being analyzed.…”

Section: Figmentioning

confidence: 99%

Running on water: Three-dimensional force generation by basilisk lizards

Hsieh

Lauder

2004

Proc. Natl. Acad. Sci. U.S.A.

113

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“…Vortex formation is indeed an inescapable consequence of any unsteady motion in water occurring at high Reynolds numbers (Dickinson 1996), and has consequently been much studied in the context of animal propulsion in fluid media at Re .100…”

Section: Introductionmentioning

confidence: 99%

Danger of zooplankton feeding: the fluid signal generated by ambush-feeding copepods

2010

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Zooplankton feed in any of three ways: they generate a feeding current while hovering, cruise through the water or are ambush feeders. Each mode generates different hydrodynamic disturbances and hence exposes the grazers differently to mechanosensory predators. Ambush feeders sink slowly and therefore perform occasional upward repositioning jumps. We quantified the fluid disturbance generated by repositioning jumps in a millimetre-sized copepod (Re $ 40). The kick of the swimming legs generates a viscous vortex ring in the wake; another ring of similar intensity but opposite rotation is formed around the decelerating copepod. A simple analytical model, that of an impulsive point force, properly describes the observed flow field as a function of the momentum of the copepod, including the translation of the vortex and its spatial extension and temporal decay. We show that the time-averaged fluid signal and the consequent predation risk is much less for an ambush-feeding than a cruising or hovering copepod for small individuals, while the reverse is true for individuals larger than about 1 mm. This makes inefficient ambush feeding feasible in small copepods, and is consistent with the observation that ambush-feeding copepods in the ocean are all small, while larger species invariably use hovering or cruising feeding strategies.

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“…1 A notable example of an unsteady flight mechanism is the "clap and fling" discovered by Weis-Fogh, 3 but there are a variety of behaviors associated with efficient flight. 2,5,6 Certain body movements must be associated with unsteady aerodynamics, and the hovering we consider in this paper is of that kind. Imagine a planar wing executing a vertical flapping movement as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

Hovering of a passive body in an oscillating airflow

2006

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Small flexible bodies are observed to hover in an oscillating air column. The air is driven by a large speaker at frequencies in the range 10-65 Hz at amplitudes 1 -5 cm. The bodies are made of stiffened tissue paper, bent to form an array of four wings, symmetric about a vertical axis. The flapping of the wings, driven by the oscillating flow, leads to stable hovering. The hovering position of the body is unstable under free fall in the absence of the airflow. Measurements of the minimum flow amplitude as a function of flow frequency were performed for a range of self-similar bodies of the same material. The optimal frequency for hovering is found to vary inversely with the size. We suggest, on the basis of flow visualization, that hovering of such bodies in an oscillating flow depends upon a process of vortex shedding closely analogous to that of an active flapper in otherwise still air. A simple inviscid model is developed illustrating some of the observed properties of flexible passive hoverers at high Reynolds number.

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Unsteady Mechanisms of Force Generation in Aquatic and Aerial Locomotion

Cited by 153 publications

References 29 publications

Running on water: Three-dimensional force generation by basilisk lizards

Running on water: Three-dimensional force generation by basilisk lizards

Danger of zooplankton feeding: the fluid signal generated by ambush-feeding copepods

Hovering of a passive body in an oscillating airflow

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