Meeting Abstract
104.4 Wednesday, Jan. 7 X-ray study of subsurface locomotion of a sand swimming lizard: the effect of material preparation MALADEN, R.D.*; GOLDMAN, D.I.; Georgia Institute of Technology; Georgia Institute of Technology rmaladen@gatech.edu
Animals that move within desert sand contend with material that can display solid and fluid-like behavior and can exist in a range of packing fractions whose mechanical response to stress can govern ability to move through the material. We used high-speed x-ray imaging to reveal how a small (10 cm) desert dwelling lizard (the sandfish Scincus scincus ) swims within a granular medium, and how the animal is affected by the preparation (packing fraction – Φ of the media. We used a fluidized bed to prepare a system of glass beads (particle size: 0.3mm, similar in size range of desert sand) into naturally occurring loose and tight packing (represented by the packing fraction Φ 58% and 63% by volume). Once below the surface, x-ray video revealed that the organism no longer used limbs for propulsion. It placed them against its sides and executed a large amplitude undulatory gait using its body to propel itself at speeds up to ~1 body-length/sec. For a given Φ the animal increased swimming speed by increasing temporal frequency, while maintaining a single period traveling wave along its body and tail. Surprisingly, the sandfish was able to move at both a higher frequency and velocity in the more resistive tightly packed media. While the slope of the velocity frequency regression was not statistically different for different packings (P>0.05),the range was extended: maximum frequency and velocity of (2.9Hz,7.9cm/sec) in loosely packed material and (4Hz,10.2cm/sec) in tightly packed material. Since physics equations do not exist for granular media in the regime encountered by the sandfish, we developed a direct simulation of a model sandfish in granular media to reveal the how material preparation and oscillation frequency govern thrust and drag to determine swimming velocity.
