Bioinspired Design and
Engineering
From Hydrodynamic Features of Boxfish to Aerodynamic Performance of a Mercedes-Benz Concept Car
Boxfishes are rigid-bodied marine
fishes that live
predominantly in shallow-water, highly energetic, tropical
reef environments. Despite their ungainly appearance
(2/3 to 3/4 of their bodies is encased in a bony and
often ornamented carapace), boxfishes are remarkably
stable and maneuverable swimmers. They are able to maintain
smooth swimming trajectories with minimal pitching, rolling,
and yawing even in highly turbulent waters. Moreover,
they are capable of swimming rapidly (>6
body lengths s-1), can spin around with a
minimal turning radius, and can hold precise control
of their positions and orientations. The Doctoral research
work of Dr. Ian Bartol at Caltech and UCLA (see references
1 & 2) revealed that keel contours and other physical
characteristics of the rigid carapace produce spiral
vortices that are central to the boxfishes' sophisticated
self-correcting mechanism. For example, when a boxfish
pitches upwards in a turbulent environment, spiral flows
develop and grow above the keels, with maximum vortex
circulation and peak vorticity occurring at the posterior
edge of the carapace. The low pressures that result from
the vortices pull the back-end of the fish upwards, returning
it to a level trajectory. Our research also indicates
that some species of boxfishes, such as the buffalo trunkfish,
have drag coefficients (CD) < 0.1.  The
characteristics of boxfishes, i.e., rigid exteriors,
boxy cross sections with low CD, high stability,
and high maneuverability, lend themselves well to biomimetic
design. In fact, Mercedes-Benz (reference 3) unveiled
a bionic concept car in June 2005 that is based on the
contours of the boxfish carapace and takes advantage
of its drag reduction benefits. The Office of Naval Research,
which funded our research, is applying our findings to
the development of underwater robots. Understanding how
fins interact with the body-induced flows to improve
maneuverability is the focus of current boxfish research
by our group.
Collaborators
Ian K. Bartol, Daniel Weihs, Paul W. Webb, Malcolm S. Gordon, and Jay Hove
References
(1) Hydrodynamic stability of
swimming in ostraciid fishes: role of the carapace
in the smooth trunkfish Lactophrys triqueter (Teleostei:
Ostraciidae), Ian K. Bartol, Morteza Gharib,
Daniel Weihs, Paul W. Webb, Jay Hove, and Malcolm S.
Gordon, The
Journal of Experimental Biology: 206,
725-744 (2003)
(2) Body-induced vertical flows:
a common mechanism for self-corrective trimming control
in boxfishes, Ian K. Bartol, Morteza Gharib,
Paul W. Webb, Daniel Weihs, and Malcolm S. Gordon, Journal
of Experimental Biology: 208, 327-344 (2005)
(3) The
Mercedes-Benz Bionic Car as a Concept Vehicle (link
to web DaimlerChrysler page)
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