Research On Propulsion Performances Of Flexible Undulating Fin Based Biomimetic System

Propellers have been playing an increasingly important role in underwater devices for resources exploration. As traditional propulsions (such as jets and axial propellers) have little advantages of propulsive efficiency at low speed, maneuverability, power consumption and acoustic noise, designing of alternative high-performance underwater propulsion becomes one of most interested research topics. Fish owes their unique morphological characteristics and movement modes for living in deep sea environment after billions of years of evolution and natural selection. In comparison against body/caudal fin (BCF) modes, the flexible undulating fin-based propulsion mode (as one of median/paired fin modes) offers several advantages including good propulsive efficiency, great maneuverability, and low underwater acoustic noise at low speeds; as a result, it is a source of biologically inspiration for future propeller designs.This dissertation presents the design and modeling of a flexible undulating fin-based propulsion system and findings of computational and experimental investigations.Firstly, a new design of a long flexible undulating fin inspired by the knifefish has been developed with the aid of an experimental investigation. Secondly, the hydrodynamics of a flexible undulating fin has been numerically modeled based on the conservation equations of mass and momentum. The three dimensional unsteady fluid controlled equations take into account the effects of fluid-solid interaction and have been numerically solved using computational fluid dynamics (CFD) method for the pressure and velocity distributions and the forces acting on the undulating fin in the neighborhood of the undulating fin. Thirdly, a fin-based robotic fish (driven by a single DC-motor) has been designed and developed for forward propulsion using the undulating fin which propagates the wave in the opposite direction of the swim. The feasibility and reliability of the design have been examined experimentally, which also provides a basis for validating the computed thrust. The theoretical predication, which agrees well with the measured data validating the numerical model, offers guidance for performances improvements of future designs.To improve the propulsion performances, the undulating lateral fin has been numerically solved using a three-dimensional unsteady method based on fluid-solid interaction effect, for optimizing the design of the robotic fish based on flexible lateral fins, which method is experimentally validated previously by comparing the computed thrust against data measured on the prototype long flexible-fin mechanism. Thus a prototype paired lateral-fin mechanism has been developed and experiments have been done validating for feasibility and reliability of the system. The results show that this analysis method is feasible and reasonable for analyzing and optimizing the propulsion performance.In summary, the hydrodynamic model and numerical results of the flexible undulating fin provide a good foundation for research and development of a flexible undulating fin based system.