Locomotion of animals, whether by running, flying, swimming or crawling, is crucial
to their survival. The natural environments they encounter are complex containing
fluid, solid or yielding substrates. These environments are often uneven and inclined, which
can lead to slipping during footsteps presenting great locomotor challenges. Many animals
have specialized appendages for locomotion allowing them to adapt to their environmental
conditions. Aquatically adapted animals have fins and flippers to swim through the water,
however, some species use their paddle-like appendages to walk on yielding terrestrial substrates
like the beach. Beach sand, a granular medium, behaves like a solid or a fluid when
stress is applied. Principles of legged locomotion on yielding substrates remain poorly understood,
largely due to the lack of fundamental understanding of the complex interactions
of body/limbs with these substrates on the level of the Navier-Stokes Equations for fluids.
Understanding of the limb-ground interactions of aquatic animals that utilize terrestrial
environments can be applied to the ecology and conservation of these species, as well as
enhance construction of man-made devices.
In this dissertation, we studied the locomotion of hatchling loggerhead sea turtles on
granular media integrating biological, robotic, and physics studies to discover principles
that govern fin and flipper locomotion on flowing/yielding media. Hatchlings in the field
modified their limb use depending on substrate compaction. On soft sand they bent their
wrist to utilize the solid features of sand, whereas on hard ground they used a rigid flipper
and claw to clasp asperities during forward motion. A sea turtle inspired physical model in
the laboratory was used to test detailed kinematics of fin and flipper locomotion on granular
media. Coupling of adequate step distance, body lift and thrust generation allowed the robot
to move successfully forward avoiding previously disturbed ground. A flat paddle intruder
was used to imitate the animal's flipper in physics drag experiments to measure the forces
during intrusion and thrust generation.MSCommittee Chair: Goldman, Daniel; Committee Member: Goodisman, Michael; Committee Member: Yen, Jeanett
