A Numerical Analysis of an Undulatory Mechanical Fin Driven by Shape Memory Alloy

Many fishes use undulatory fin to propel themselves through the underwater environment. These locomotor mechanisms have a popular interest to many researchers. In the present study, we perform a three-dimensional unsteady computation of an undulatory mechanical fin that is driven by shape memory alloy (SMA). The objective of the computation is to investigate the fluid dynamics of force production associated with the undulatory mechanical fin. An unstructured, grid-based, unsteady Navier-Stokes solver with automatic adaptive remeshing was used to compute the unsteady flow around the fin through five complete cycles. The pressure distribution on fin surface was computed and integrated to provide fin forces which were decomposed into lift and thrust. Finally, a comparison was conducted to reveal the dynamics of force generation according to the kinematic parameters of the undulatory fin (amplitude, frequency and wavelength).

I. INTRODUCTION

There are various kinds of fishes living in the underwater environment possessing daedal swimming mode which can be divided into two types based on the propulsive structure used: body and/or caudal fin locomotion (BCF) and median and/or paired fin (MPF) locomotion [1]. Swimming performance shows that fin based propulsors in some fishes are capable of generating thrusts that can power a very high speed [2]. In addition, these fishes are highly maneuverable in a complex three-dimensional underwater environment. For example, Batoids propel themselves through the water with their greatly expanded pectoral fins to achieve agile movement [3].