Experimental And Numerical Researches On Undulatory Dorsal/Median Fin Propulsion Modes

The undulatory dorsal/median fin propulsion modes as represented by amiiform and balistiform fish are of great significance for bionic propulsion research, particularly for the design and control of underwater vehicles, which are generally employed at slow speeds, offering greater maneuverability and better propulsive efficiency. Based on bionic experiments in Gymnarchus niloticus and Rhinecantbus aculeatus, this paper presents a parameterized description of undulatory dorsal/median fin propulsion modes. By referring to large-amplitude elongated body theory and computational fluid dynamics simulation, this paper also provides an explanation of the external morphological and kinematic phenomena that are closely related to propulsion characteristics.First, an experimental apparatus for undulatory dorsal/median fin propulsion modes is established. Based on morphological and kinematic data of the body and the dorsal/median fins of specimens, the analysis shows that the slender body is well streamlined, symmetrical. The unsymmetrical phenomenon of the wave form of dorsal fin undulation is discussed and a description is given on basis of parameterized formulation. Typical estimation of kinematic parameters (cruising speed, wave speed, wave length and frequency) based on experimental data of the cruising specimens indicates there is significant correlation between cruising speed and other parameters. Finally, the phase relationships between the movements of boxfish fins are estimated to describe coordination between the propulsors.The kinetic characteristic is formulated to describe undulatory dorsal/median fin propulsion modes. The locomotor hypotheses about the kinematics of undulatory swimming are experimentally tested, while the parameters describing wave form are discussed with respect to some constrained conditions that must be satisfied during undulatory swimming. The parameterized formulation is validated qualitatively by comparing it with experimental results. Finally, the values of kinematic parameters in typical swimming are estimated for theoretical calculation and computational simulation.Based on the kinematic formulation, this paper applies large-amplitude elongated body theory to propulsive performance of undulatory dorsal/median fins and establishes a set of equations for estimation of the propulsive force and the propeller efficiency. The calculations based on experimental data coincide with Blake's result in 1980.Since these theoretical analyses are based on inviscid potential flow theory, theoretical calculation and computational simulation may complement each other. The hydrodynamics and undulating propulsion of specimens were studied using three dimensional computational fluid dynamics (CFD) modeling. The CFD analysis using kinematic model of undulatory dorsal/median fin draws a series of conclusions, which include that the body drag increases significantly with the lateral body oscillation; the body drag is minimum while the start point of...