A Soft Robotic Model to Study the Effects of Stiffness on Fish-Like Undulatory Swimming

The tadpole tail fin is a simple double layer of skin overlying loose connective tissue. Collagen fibres in the fin are oriented at approximately +/-45 degrees from the long axis of the tail. Three tests were conducted on samples of the dorsal tail fin from 6-10 Rana catesbeiana tadpoles to establish the fin's viscoelastic properties under (1) large-deformation cyclic loading at 1 and 3 Hz, (2) small-deformation forced vibration at 1 and 3 Hz, and (3) stress relaxation under a 0.1 s loading time. The fin was very fragile, failing easily under tensile loads less than 7 g. It was also strikingly viscoelastic, as demonstrated by 72+/-1 % hysteresis loss (at 3 Hz), 16+/-3 % stress remaining after 100 s of stress relaxation and a phase angle of 18+/-1 degrees in forced vibration. As a consequence of its viscoelastic properties, the fin was three times stiffer in small than in large deformation. This may account for the ability of the fin to stay upright during normal undulatory swimming, despite the absence of any skeletal support. Tadpoles in nature are often found with damaged tails. We suggest that the unusually viscoelastic and fragile nature of the fin helps tadpoles escape the grasp of predators. Because the fin deforms viscoelastically and tears easily, tadpoles can escape predators and survive otherwise lethal attacks with only minor lacerations to the fin. Recent studies have shown that certain tadpoles develop taller fins in the presence of predators. This developmental plasticity is consistent with the tail fin acting as a protective but expendable 'wrap' around the core muscle tissue.

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Undulatory Swimming Performance and Body Stiffness Modulation in a Soft Robotic Fish-Inspired Physical Model

Soft Robotics ◽

10.1089/soro.2016.0053 ◽

2017 ◽

Vol 4 (3) ◽

pp. 202-210 ◽

Cited By ~ 23

Author(s):

Ardian Jusufi ◽

Daniel M. Vogt ◽

Robert J. Wood ◽

George V. Lauder

Keyword(s):

Physical Model ◽

Swimming Performance ◽

Robotic Fish ◽

Undulatory Swimming

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Body movement distribution with respect to swimmer’s glide position in human underwater undulatory swimming

Human Movement Science ◽

10.1016/j.humov.2014.08.017 ◽

2014 ◽

Vol 38 ◽

pp. 305-318 ◽

Cited By ~ 3

Author(s):

Stefan Hochstein ◽

Reinhard Blickhan

Keyword(s):

Body Movement ◽

Undulatory Swimming

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Numerical investigation of hydrodynamic characteristics of fish-like undulation using the adaptive dynamic-grid method

Modern Physics Letters B ◽

10.1142/s0217984921502997 ◽

2021 ◽

pp. 2150299

Author(s):

Zeyu Guo ◽

Gucheng Zhu ◽

Zuogang Chen ◽

Yukun Feng

Keyword(s):

Frictional Force ◽

Control Method ◽

Turbulent Viscosity ◽

Flow Characteristics ◽

Grid Method ◽

Wave Number ◽

Hydrodynamic Characteristics ◽

Substantial Impact ◽

Vortex Patterns ◽

Undulatory Swimming

To investigate the hydrodynamics of undulatory swimming, a key issue in numerical analysis is to determine the correlation between undulatory locomotion and the flow characteristics. In this study, a novel dynamic-grid generation method, the adaptive control method, is implemented to deal with the moving and morphing boundaries in an unsteady flow field at all Reynolds numbers. This method, based on structured grids, can ensure the orthogonality and absolute controllability of the grids and is performed to precisely simulate the wake and the boundary layer. The NACA0010 wing is employed as a two-dimensional (2D) body model of a fish in the simulations. To maintain the calculation stability, the increase stage of the amplitude is defined as a smooth transitional stage. Analysis of hydrodynamic coefficients reveals that undulation results in a significant increase of frictional force in laminar flow [Formula: see text]. However, the undulation also results in a reduction of the frictional force when the fish swims in turbulent flow [Formula: see text]. The vorticity distribution and the [Formula: see text]-criterion are both used to accurately capture the shedding vortexes in the wake. Furthermore, these vortex pairs have a substantial impact on the turbulence and the wake, in which the turbulent kinetic energy and the turbulent viscosity ratio both decrease at [Formula: see text]. The wake of an undulatory fish presents different vortex patterns with various kinematic parameters. When the phase velocity is greater than the incoming velocity and the wave number is sufficiently large, thrust is yielded, accompanying the distinct reverse Karman Street in the wake.

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UNDULATORY SWIMMING: HOW TRAVELING WAVES ARE PRODUCED AND MODULATED IN SUNFISH (LEPOMIS GIBBOSUS)

Journal of Experimental Biology ◽

10.1242/jeb.192.1.129 ◽

1994 ◽

Vol 192 (1) ◽

pp. 129-145 ◽

Cited By ~ 12

Author(s):

J Long ◽

M Mchenry ◽

N Boetticher

Keyword(s):

Muscle Activation ◽

Axial Skeleton ◽

The Body ◽

Lepomis Gibbosus ◽

Axial Muscle ◽

Locomotor Muscles ◽

Undulatory Swimming ◽

Swimming Kinematics ◽

Tail Beat

We have developed an experimental procedure in which the in situ locomotor muscles of dead fishes can be electrically stimulated to generate swimming motions. This procedure gives the experimenter control of muscle activation and the mechanical properties of the body. Using pumpkinseed sunfish, Lepomis gibbosus, we investigated the mechanics of undulatory swimming by comparing the swimming kinematics of live sunfish with the kinematics of dead sunfish made to swim using electrical stimulation. In electrically stimulated sunfish, undulatory waves can be produced by alternating leftright contractions of either all the axial muscle or just the precaudal axial muscle. As judged by changes in swimming speed, most of the locomotor power is generated precaudally and transmitted to the caudal fin by way of the skin and axial skeleton. The form of the traveling undulatory wave  as measured by tail-beat amplitude, propulsive wavelength and maximal caudal curvature  can be modulated by experimental control of the body's passive stiffness, which is a property of the skin, connective tissue and axial skeleton.

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Large-amplitude undulatory fish swimming: fluid mechanics coupled to internal mechanics

Journal of Experimental Biology ◽

10.1242/jeb.202.23.3431 ◽

1999 ◽

Vol 202 (23) ◽

pp. 3431-3438 ◽

Cited By ~ 4

Author(s):

T.J. Pedley ◽

S.J. Hill

Keyword(s):

Vortex Ring ◽

Large Amplitude ◽

Muscle Activation ◽

Bending Moment ◽

Hydrodynamic Pressure ◽

Moment Equation ◽

Panel Method ◽

The Body ◽

Undulatory Swimming ◽

Body Theory

The load against which the swimming muscles contract, during the undulatory swimming of a fish, is composed principally of hydrodynamic pressure forces and body inertia. In the past this has been analysed, through an equation for bending moments, for small-amplitude swimming, using Lighthill's elongated-body theory and a ‘vortex-ring panel method’, respectively, to compute the hydrodynamic forces. Those models are outlined in this review, and a summary is given of recent work on large-amplitude swimming that has (a) extended the bending moment equation to large amplitude, which involves the introduction of a new (though probably usually small) term, and (b) developed a large-amplitude vortex-ring panel method. The latter requires computation of the wake, which rolls up into concentrated vortex rings and filaments, and has a significant effect on the pressure on the body. Application is principally made to the saithe (Pollachius virens). The calculations confirm that the wave of muscle activation travels down the fish much more rapidly than the wave of bending.

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