286
fi n. This resulted in an engineered fi n that had a similar interaction with the water as
the biological fi n and that created close approximations of the three-dimensional
motions, fl ows, and forces produced by the sunfi sh during low speed, steady
swimming. Experimental trials were conducted during which biorobotic fi ns of
seven different stiffness confi gurations were fl apped at frequencies from 0.5 to
2.0 Hz in fl ows with velocities that ranged from 0 to 270 mm/s. The results of the
trials revealed that slight changes to the fi n’s mechanical properties or to the operating
conditions can have signifi cant impact on the direction, magnitude and time course
of the propulsive forces. In general, the magnitude of the 2-D (thrust and lift)
propulsive force scaled with fi n ray stiffness, and increased as the fi n’s fl apping
speed increased or as the velocity of the fl ow decreased” (Tangorra et al. 2010 ).
Interestingly, searobins ( Triglidae ) and batfi sh ( Ogcocephalidae ) use their pectoral fi ns to walk on substrates (Ward 2002 ).
Anal Fin The anal fi sh fi n is a single structure with location on the underside of the
body just forward of the caudal fi n. The function of anal fi n is to stabilize the animal
while it is swimming. It was reported (Standen and Lauder 2005 ) that “both dorsal
and anal fi ns in bony fi sh L. macrochirus produce balancing torques during steady
swimming. During maneuvers, fi n area is maximized and mean lateral excursion of
both fi ns is greater than during steady swimming, with large variation among maneuvers. Fin surface shape changes dramatically during maneuvers. At any given point
in time the spanwise (base to tip) curvature along fi n rays can differ between adjacent
rays, suggesting that fi sh have a high level of control over fi n surface shape. Also,
during maneuvers the whole surface of both dorsal and anal fi ns can be bent without
individual fi n rays exhibiting signifi cant curvature,” (Standen and Lauder 2005 ).
However, in case of brook trout ( Salvelinus fontinalis ) the relationship between anal
and dorsal fi ns is more complex. As reported by Standen and Lauder ( 2007 ):
1. Anal fi ns produce lateral jets to the same side as dorsal fi ns, confi rming the hypothesis that anal fi ns produce fl uid jets that balance those produced by dorsal fi ns.
2. In contrast to previous work on sunfi sh L. macrochirus , neither dorsal nor anal
fi ns produce signifi cant thrust during steady swimming; fl ow leaves the dorsal
and anal fi ns in the form of a shear layer that rolls up into vortices similar to
those seen in steady swimming of eels.
3. Dorsal and anal fi n lateral jets are more coincident in time than would be
predicted from simple kinematic expectations; shape, heave and pitch differences
between fi ns, and incident fl ow conditions may account for the differences in
timing of jet shedding.
4. Relative force and torque magnitudes of the anal fi n are larger than those of
the dorsal fi n; force differences may be due primarily to a larger span and a more
squarely shaped trailing edge of the anal fi n compared to the dorsal fi n; torque
differences are also strongly infl uenced by the location of each fi n relative to
the fi sh’s centre of mass.
5. Flow is actively modifi ed by dorsal and anal fi ns resulting in complex fl ow
patterns surrounding the caudal fi n. The caudal fi n does not encounter freestream fl ow, but rather moves through incident fl ow greatly altered by the action
of dorsal and anal fi ns.
7 Fish Fins and Rays as Inspiration for Materials Engineering and Robotics
fi n. This resulted in an engineered fi n that had a similar interaction with the water as
the biological fi n and that created close approximations of the three-dimensional
motions, fl ows, and forces produced by the sunfi sh during low speed, steady
swimming. Experimental trials were conducted during which biorobotic fi ns of
seven different stiffness confi gurations were fl apped at frequencies from 0.5 to
2.0 Hz in fl ows with velocities that ranged from 0 to 270 mm/s. The results of the
trials revealed that slight changes to the fi n’s mechanical properties or to the operating
conditions can have signifi cant impact on the direction, magnitude and time course
of the propulsive forces. In general, the magnitude of the 2-D (thrust and lift)
propulsive force scaled with fi n ray stiffness, and increased as the fi n’s fl apping
speed increased or as the velocity of the fl ow decreased” (Tangorra et al. 2010 ).
Interestingly, searobins ( Triglidae ) and batfi sh ( Ogcocephalidae ) use their pectoral fi ns to walk on substrates (Ward 2002 ).
Anal Fin The anal fi sh fi n is a single structure with location on the underside of the
body just forward of the caudal fi n. The function of anal fi n is to stabilize the animal
while it is swimming. It was reported (Standen and Lauder 2005 ) that “both dorsal
and anal fi ns in bony fi sh L. macrochirus produce balancing torques during steady
swimming. During maneuvers, fi n area is maximized and mean lateral excursion of
both fi ns is greater than during steady swimming, with large variation among maneuvers. Fin surface shape changes dramatically during maneuvers. At any given point
in time the spanwise (base to tip) curvature along fi n rays can differ between adjacent
rays, suggesting that fi sh have a high level of control over fi n surface shape. Also,
during maneuvers the whole surface of both dorsal and anal fi ns can be bent without
individual fi n rays exhibiting signifi cant curvature,” (Standen and Lauder 2005 ).
However, in case of brook trout ( Salvelinus fontinalis ) the relationship between anal
and dorsal fi ns is more complex. As reported by Standen and Lauder ( 2007 ):
1. Anal fi ns produce lateral jets to the same side as dorsal fi ns, confi rming the hypothesis that anal fi ns produce fl uid jets that balance those produced by dorsal fi ns.
2. In contrast to previous work on sunfi sh L. macrochirus , neither dorsal nor anal
fi ns produce signifi cant thrust during steady swimming; fl ow leaves the dorsal
and anal fi ns in the form of a shear layer that rolls up into vortices similar to
those seen in steady swimming of eels.
3. Dorsal and anal fi n lateral jets are more coincident in time than would be
predicted from simple kinematic expectations; shape, heave and pitch differences
between fi ns, and incident fl ow conditions may account for the differences in
timing of jet shedding.
4. Relative force and torque magnitudes of the anal fi n are larger than those of
the dorsal fi n; force differences may be due primarily to a larger span and a more
squarely shaped trailing edge of the anal fi n compared to the dorsal fi n; torque
differences are also strongly infl uenced by the location of each fi n relative to
the fi sh’s centre of mass.
5. Flow is actively modifi ed by dorsal and anal fi ns resulting in complex fl ow
patterns surrounding the caudal fi n. The caudal fi n does not encounter freestream fl ow, but rather moves through incident fl ow greatly altered by the action
of dorsal and anal fi ns.
7 Fish Fins and Rays as Inspiration for Materials Engineering and Robotics