Robotic Models for Studying Undulatory Locomotion in Fishes

Abstract

A B S T R A C TMany fish swim using body undulations to generate thrust and maneuver in three dimensions. The pattern of body bending during steady rectilinear locomotion has similar general characteristics in many fishes and involves a wave of increasing amplitude passing from the head region toward the tail. While great progress has been made in understanding the mechanics of undulatory propulsion in fishes, the inability to control and precisely alter individual parameters such as oscillation frequency, body shape, and body stiffness, and the difficulty of measuring forces on freely swimming fishes have greatly hampered our ability to understand the fundamental mechanics of the undulatory mode of locomotion in aquatic systems. In this paper, we present the use of a robotic flapping foil apparatus that allows these parameters to be individually altered and forces measured on self-propelling flapping flexible foils that produce a wave-like motion very similar to that of freely swimming fishes. We use this robotic device to explore the effects of changing swimming speed, foil length, and foil-trailing edge shape on locomotor hydrodynamics, the cost of transport, and the shape of the undulating foil during locomotion. We also examine the passive swimming capabilities of a freshly dead fish body. Finally, we model fin-fin interactions in fishes using dual-flapping foils and show that thrust can be enhanced under correct conditions of foil phasing and spacing as a result of the downstream foil making use of vortical energy released by the upstream foil.

Soft tissue preservation in a fossil marine lizard with a bilobed tail fin

“…It has previously been shown that different modes of undulatory locomotion can generally be correlated with different body shapes 50 , and the relationship between swimming performance and body form has been examined using both empirical and numerical methods 38,39 . However, the morphology of the asymmetric tail fin in mosasaurs falls between the two categories previously examined 38,39 , and no numerical studies of hypocercal (or epicercal) performance in various kinematic regimes are available, although a recent investigation of tail form employing passive robotic swimmers did include epicercal variants in the form of foils with an angled trailing edge 51 . These epicercal foils yielded higher velocities for any given tail beat frequency, but were found to be less efficient in terms of power requirements.…”

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

“…For most of the rayfinned fishes, the caudal fin does not move only in two dimensions: under the control of the intrinsic musculature, the fin rays actively move as the fish swims, forming a complex three-dimensional (3D) propulsive surface [22][23][24][25]. Earlier studies on caudal fin active deformation investigated the hydrodynamic effects of different motion patterns and fin ray stiffness at a constant flow speed and found that this kind of three-dimensional motion may contribute to the fish's manoeuvrability [13,[26][27]. However, although the musculature of the caudal fin is seperate from the posterior axial body musculature, bony fishes are able to control the caudal peduncle and the fin surface simultaneously, so the three-dimensional caudal fin motion should not be considered separately.…”

Theoretical Insights on Contraction-Type Iterative Learning Control for Biorobotic Systems with Preisach Hysteresis

“…Since 2001, bio-inspired undulating fin models [4][5][6][7][8][9][10][11] have been developed to investigate the undulation principles of knifefish. The aforementioned inconsistency does exist and has prevented robotic fish models from replicating the locomotion or behaviours of their biological counterparts.…”