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

Abstract

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.

Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure

“…Fish fins undergo considerable deformation during movement [14] and this deformation is under partial active control and is a key factor in allowing thrust generation throughout the fin or tail beat cycle [45,46]. The approach of comparing the [13,28] with highvorticity regions used to produce hypothetical vortex ring structure circled in white.…”

A robotic fish caudal fin: effects of stiffness and motor program on locomotor performance

“…This design process was similar to that used for the robotic pectoral fin by developed in Tangorra et al Tangorra et al, 2010). The robotic caudal fin model was scaled to have linear dimensions approximately four times larger than an adult bluegill sunfish of 20cm total length.…”

“…This range encompassed both very stiff (2000ϫ) and very compliant (150ϫ) fins. A further discussion of fin ray scaling to match the material properties of manufactured fin rays to those of the bluegill sunfish is given in Tangorra et al (Tangorra et al, 2010). The fin rays were manufactured using fused deposition modeling (Stratasys Inc., Eden Prairie, MN, USA; material: ABS plastic) and stereolithography (3D Systems, Rock Hill, NC, USA; material: Accura 40 UV resin), and were approximately 10cm long, excluding the attachment base (Fig.4).…”

Investigation of Fish Caudal Fin Locomotion Using a Bio-Inspired Robotic Model

“…As many recent studies have reported that fish can actively deform their fins to achieve different types of locomotion, more and more researchers have realized the importance of these flexible propulsion surfaces on enchancing ability of swimming. Such propulsion surfaces include dorsal fins [2][3][4] and pectoral fins [5][6][7] in body and caudal fin (BCF) propulsion and ribbon fins [8][9][10] in median and paired fin (MPF) propulsion. As the most conspicuous appendage of the fish's body, the caudal fin has also been studied extensively [11][12][13][14][15].…”