Research On The Underwater Bionic Undulatory-Fin Propulsor And Its Control Method

Underwater propulsion technology is an absolutely key component which determines the voyage, velocity and maneuverability of the underwater vehicles. It is full of economic and military significance to develop new-type bionic underwater propulsors for the requirements in better performance, higher efficiency, less disturbance, etc. The underwater bionic undulatory-fin propulsor, inspired by undulations of the median and/or paired fin (MPF) fish, has advantages in simplicity in structure, agility in control and uniformity in fluid load distribution. Such a new-type bionic propulsor has been paid more and more attention to by many related research institutes of the world since 2000s.In this thesis, the bionic inspirations, mechanical structure, control method and experiments of the undulatory-fin propulsor were investigated deepgoingly and systematically. The main research contents are listed as follows:1. Bionic inspirations from the Amiiform fish "Gymnarchus niloticus", which generally swims by undulations of the long dorsal fin, are extracted to answer why and how the mechanical structure and control system are designed for the undulatory-fin propulsor. We established a two-view synchronous imaging apparatus to observe the dorsal fin's outline as well as shape in the different movements, and to analyze its morphological characteristics, the inner structure as well as the central neural control mechanism, aided by the X-ray images. The swimming characteristics were analyzed during the starting, stopping, straight cruise and maneuvering motion. And furthermore, we set up a kinematical model to describe the line swimming motion of the undulatory-fin propulsor and we can construct several fin shapes by regulating kinematical parameters of the propulsive velocity, amplitude as well as frequency.2. An undulatory-fin experimental device was accomplished which is composed of multiple parallel joints and whose undulation parameters can be independently regulative. Hereby, the dynamic performance was in-depth studied. In detail, we presented three design principles of the bionic undulatory-fin propulsor, built a novel dynamic model with considerations of the elastic fin's deformation and the unsteady fluid action, and analyzed the dynamic performance of the single joint as well as the whole bionic undulatory device. Moreover, a simply thrust prediction model was set up based on the actuator-disc theory.3. The bionic neural network control system was established with the basis of a new-style neural oscillator, and the various motions of the undulatory-fin propulsor can be effectively controlled by this neural network. The new-style neural oscillator, which is composed of two neurons and whose oscillation parameters are independently controlled by three special coefficients in the dynamic equations, possesses advantages of simple connections and convenient engineering application. Taking the neural oscillator as the basic component, we designned a single-joint neural network control system, and studied its corresponding control algorithms for motions, such as starting, stopping and uniform-amplitude swimming. Furthermore, a bionic CPGs (central pattern generators) neural network control system is presented to control the movements of the undulatory-fin propulsor, and to design the control algorithms for starting, stopping and steady swimming for the undulatory-fin propulsor. What's more, we accomplished the close-loop control by introducing a neural estimator, and applied this method into controlling the undulatory amplitude. The results verify that the bionic neural network control method can be more effective than the traditional reverse-kinematics method, and can be adaptive to various bionic robots. From the view point of bionics, the work in this thesis may promote the undulatory-fin propulsor from "likeness in shape" to " similarity in spirit".4. We carried out several experiments on hydrodynamics, kinematics and fluid fields, to analyze the thrust, lateral force, swimming velocity and fluid field structure during the undulatory-fin propulsion. To be more meaningful, the parameters in the simply thrust prediction model are identified with the measurement data. And several key factors which have great influence on the undulatory-fin propulsor are proposed and analyzed.