Inspired by Sharks: A Biomimetic Skeleton

Inspired by Sharks: A Biomimetic Skeleton for the Flapping,
Propulsive Tail of an Aquatic Robot

John H. Long, Jr., Tom Koob, Justin Schaefer, Adam Summers,
Kurt Bantilan, Sindre Grotmol, Marianne Porter.

ABSTRACT:

The vertebral column is the primary stiffening element of the body of fish. This
serially jointed axial support system offers mechanical control of body bending
through kinematic constraint and viscoelastic behavior. Because of the functional
importance of the vertebral column in the body undulations that power swimming,
we targeted the vertebral column of cartilaginous fishes—sharks, skates, and rays—
for biomimetic replication. We examined the anatomy and mechanical properties of
shark vertebral columns. Based on the vertebral anatomy, we built two classes of
biomimetic vertebral column (BVC): (1) one in which the shape of the vertebrae
varied and all else was held constant and (2) one in which the axial length of the
invertebral joint varied and all else was held constant. Viscoelastic properties of
the BVCs were compared to those of sharks at physiological bending frequencies.
The BVCs with variable joint lengths were then used to build a propulsive tail, consisting
of the BVC, a vertical septum, and a rigid caudal fin. The tail, in turn, was
used as the propeller in a surface-swimming robot that was itself modeled after a
biological system. As the BVC becomes stiffer, swimming speed of the robot increases,
all else being equal. In addition, stiffer BVCs give the robot a longer stride
length, the distance traveled in one cycle of the flapping tail.

Marine Technology Society Journal,
July/August 2011 Volume 45 Number 4

SOURCE: PDF Download