Passive cambering and flexible propulsors: cetacean flukes

Fish, Frank E.; Nusbaum, Moira K; Beneski, John T.; Ketten, Darlene R.

doi:10.1088/1748-3182/1/4/s06

Cited by 61 publications

(30 citation statements)

References 26 publications

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“…While previous work has shown that movements of the tailstock passively affect the shape of the flukes (Fish et al, 2006), there is no evidence documenting that movements (or removal) of the fluke influence the shape of the tailstock. The animal was placed on its left side and positioned longitudinally such that its rostrum and the caudal vertebrae of the tailstock were on the center line of the apparatus.…”

Section: Mechanical Testsmentioning

confidence: 88%

Ontogenetic changes in the structural stiffness of the tailstock of bottlenose dolphins (Tursiops truncatus)

Etnier

McLellan

Blum

et al. 2008

Journal of Experimental Biology

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SUMMARYLate-term fetal bottlenose dolphins (Tursiops truncatus) are bent ventrolaterally en utero, requiring extreme flexibility of the axial skeleton and associated soft tissues. At birth, neonatal dolphins must immediately swim to the surface to breath, yet the dorsoventral oscillations used during locomotion may be compromised by the lateral flexibility evident in the fetus. The unique fetal position of dolphins, coupled with their need to swim at birth, places conflicting mechanical demands on the tailstock. Our previous research demonstrated that neonatal dolphins possess laterally placed, axial muscles that are functionally specialized to actively maintain the straightened posture of the tailstock. Here, we investigated the development of passive lateral stability in the tailstock of bottlenose dolphins by performing whole-body bending tests on an ontogenetic series of stranded dolphin specimens (N=15), including fetuses, neonates and juveniles (total length 58-171 cm). Structural stiffness increased, while overall body curvature decreased, with increasing body length. Scaling analyses suggest that increased structural stiffness is due to increases in size and probably changes in the passive material properties of the tailstock through ontogeny. The neutral zone was approximately constant with increasing size, while the relative neutral zone (neutral zone/total length) decreased. The lateral stability of the tailstock appears to be controlled by a combination of active and passive systems and the role of these systems varies through ontogeny. While neonates use active, muscular mechanisms to limit lateral deformations of the tailstock, the stability of the maturing tailstock is due primarily to its passive tissue properties.

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Section: Mechanical Testsmentioning

confidence: 88%

Ontogenetic changes in the structural stiffness of the tailstock of bottlenose dolphins (Tursiops truncatus)

Etnier

McLellan

Blum

et al. 2008

Journal of Experimental Biology

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“…During swimming, the cambering of flukes of a cetacean can increase the production of hydrodynamic forces, particularly during direction reversal in the oscillatory cycle [18]. Ahlborn et al studied the effect of tail stiffness in the fast-start swimming of fish [19], [20].…”

Section: Introductionmentioning

confidence: 99%

Kinematic Condition for Maximizing the Thrust of a Robotic Fish Using a Compliant Caudal Fin

et al. 2012

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The compliance of a fin affects the thrust of underwater vehicles mimicking the undulatory motion of fish. Determining the optimal compliance of a fin to maximize thrust is an important issue in designing robotic fish using a compliant fin. We present a simple method to identify the condition for maximizing the thrust generated by a compliant fin propulsion system. When a fin oscillates in a sinusoidal manner, it also bends in a sinusoidal manner. We focus on a particular kinematic parameter of this motion: the phase difference between the sinusoidal motion of the driving angle and the fin-bending angle. By observing the relationship between the thrust and phase difference, we conclude that while satisfying the zero velocity condition, the maximum thrust is obtained when a compliance creates a phase difference of approximately π/2 at a certain undulation frequency. This half-pi phase delay condition is supported by thrust measurements from different compliant fins (four caudal-shaped fins with different aspect ratios) and a beam bending model of the compliant fin. This condition can be used as a guideline to select the proper compliance of a fin when designing a robotic fish.Index Terms-Compliant fin, flapping, flexible fin, flexible foil, half-pi phase delay, maximum thrust, pseudo-rigid-body model, robotic fish, underwater robot.

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“…The effect of flexibility has been studied mainly in flapping foils with 2-D (heaving and pitching) kinematics (Liu and Bose, 1997;Prempraneerach et al, 2003). It has been demonstrated numerically Zhu and Shoele, 2008) and experimentally (McHenry, 1995;Triantafyllou et al, 2005;Fish et al, 2006;Lauder et al, 2006; that flexibility is instrumental to the production of propulsive forces and to the efficiency of flapping locomotion. When properly set along the chord and the span, passive flexibility improves propulsive efficiency, and under the correct operating conditions can increase peak thrust and lift forces.…”

Section: Introductionmentioning

confidence: 99%

The effect of fin ray flexural rigidity on the propulsive forces generated by a biorobotic fish pectoral fin

Tangorra

Lauder

Hunter

et al. 2010

Journal of Experimental Biology

132

108

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SUMMARYA biorobotic pectoral fin was developed and used to study how the flexural rigidities of fin rays within a highly deformable fish fin affect the fin's propulsive forces. The design of the biorobotic fin was based on a detailed analysis of the pectoral fin of the bluegill sunfish (Lepomis macrochirus). The biorobotic fin was made to execute the kinematics used by the biological fin during steady swimming, and to have structural properties that modeled those of the biological fin. This resulted in an engineered fin that had a similar interaction with the water as the biological fin and that created close approximations of the three-dimensional motions, flows, and forces produced by the sunfish during low speed, steady swimming. Experimental trials were conducted during which biorobotic fins of seven different stiffness configurations were flapped at frequencies from 0.5 to 2.0Hz in flows with velocities that ranged from 0 to 270mms -1 . During these trials, thrust and lift forces were measured, kinematics were recorded in three dimensions, and digital particle image velocimetry was used to evaluate flow hydrodynamics. The results of the trials revealed that slight changes to the fin's mechanical properties or to the operating conditions can have significant 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 fin ray stiffness, and increased as the fin's flapping speed increased or as the velocity of the flow decreased.

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Passive cambering and flexible propulsors: cetacean flukes

Cited by 61 publications

References 26 publications

Ontogenetic changes in the structural stiffness of the tailstock of bottlenose dolphins (Tursiops truncatus)

Ontogenetic changes in the structural stiffness of the tailstock of bottlenose dolphins (Tursiops truncatus)

Kinematic Condition for Maximizing the Thrust of a Robotic Fish Using a Compliant Caudal Fin

The effect of fin ray flexural rigidity on the propulsive forces generated by a biorobotic fish pectoral fin

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