Theoretic And Experimental Research On Propulsion Flexible Biomimetic Undulatory Robotic Fin

With the development of our society, the resource of the earth is gradually exhausted. The ocean which occupies more than 70% of surface area of our earth contains huge potential and infinite profound. Therefore, the development of high performance Automatic Underwater Vehicle (AUV) to explore the unknown areas and rich resource of the undersea environment has become one of the popular voice recently all over the world. Fishes, the main residents of the ocean with billions of years' evolution and nature selection, have grown special characteristics of shapes and motion modes that are suitable for ocean condition. Among them the undulatory fin propulsion mode has the special advantages on high swimming efficiency, high maneuverability, less disturbance and convenience of being transplanted to underwater vehicles. Generally speaking, such a bio-propulsion mode provides a novel scheme for the development of future aquatic robots, it possesses values of both theoretical research and prospective for wide applications.This thesis takes Bluespotted stingray as a research object. After detailed investigations on its morphology, kinematics character and inner physiology structure, we propose a bionic undulatory fin based on pectoral fin structure, kinematics as well as propulsive function, including bionic design scheme, computational fluid dynamic (CFD) and the corresponding experimental validation. Furthermore, a new actuator driven by smart material is initially investigated, which provides an innovative idea and another choice for the bionic design of underwater vehicles. Through this research work, we may draw the following four points:1. Bionic design and analysis of the undulatory fin propulsion system.According to our qualitative observation combined with research work done by Rosenberger et al on Bluespotted stingray, we present morphology, undulatory kinematics character and inner physiology structure of its widely expanded pectoral fin as well as some quantitive conclusions of the variation of these parameters with propulsion velocity. It provides adequate guidance for bionic design and control of undulatory mechanical fin. Inspired by Bluespotted stingray and modular design motivation, we build a Bluespotted stingray model. According to our knowledge, it's the first Rajiform underwater robot in China. Hereby, the kinematical and dynamic performance of a single fin ray together with the whole fin is in-depth studied, followed by the analysis on thrust and velocity generated by undulatory motion of the mechanical fin. On the integrative design of the propellant system and the control system of our bionic Bluespotted stingray, a novel control method has been proposed for propulsion and gesture control. By actively modulating multi design parameters combined with infrared sensor array, we finally achieve several locomotion behaviors including: cruising, turning, depth control and obstacle avoidance.2. Computational Fluid Dynamic analysis of the undulatory fin propulsion system. Set up both 2D and 3D simplified undulatory kinematical equations. The governing equations are the incompressible, unsteady Navier-Stokes equation that is discretized using the finite volume method (FVM) with an implicit segregated solver approach. The pressure velocity coupling of the continuity equation was achieved using the SIMPLE algorithm. By combining with unstructured mesh and adaptive re-meshing, we implement the numerical analysis on oscillatory motion of fin ray and undulatory motion of bio-fin. The flowing aspects have been investigated to reveal the contribution to the propulsion performance: kinematical parameters, undulatory modes, fin shapes, stiffness and obliquity of fin rays. The field information around swimming fin and the force coefficient are obtained from the calculation. With these results, we analyze the forming mechanism of reverse Karman vortex streets and producing of thrust of fin during its motion by vortex dynamics. To be more important, these computational results of the undulatory fin model have been validated by experimental tests.3. Experimental tests on the undulatory fin propulsion system. The experiment is divided into two main parts: the tests on fin ray with oscillatory motion and the tests on fin with undulatory motion according. The equipment for the fin ray tests consists of motion control system, digital particle image velocimetry (DPIV) system and force measurement system. The motion control system can imitate the oscillatory motion of fin rays, the DPIV can display the vortex structure in the wake, while the force measurement system is used for lift and drag testing during oscillating. The equipment for the fin tests consists of velocity measurement system, propulsion force measurement system and power measurement system. We adopt orthogonal experimental design and use both range analysis and variance analysis to make a detailed study on the influence of kinematics parameters (such as frequency, amplitude, wavelength), undulatory modes, fin shapes as well as their correlations on propulsion velocity, thrust and efficiency. In addition, we test the influence of fin stiffness on propulsion performance. The experimental tests show the feasibility and creditability of the theoretic and computational conclusions.4. Improvement of the undulatory fin propulsion system. There exists great difference between electro-mechanical system and animal muscle on driven principle, form, performance, etc., particularly lacks efficient energy storage element that similar to the muscle tendon of animals. Therefore, we further carry out research on smart material driven bio-fin, the character of which is much close to muscles. After comparing the performance of several recently available smart materials, we finally choose N_iT_i Shape Memory Alloy (SMA). According to the structure of flexible bio-fin along with the characteristic of SMA, a couple of differentially equipped SMA plates with single Shape Memory Effect (SME) act as the function of fin ray. The deformation information is detected and feedback by strain transducer, and then achieve both oscillatory and undulatory motion of the flexible fin through Fuzzy Logic Control (FLC) algorithm. The preliminary experiments present the relationship between the bending force and the thickness of SMA plate, the relationship between the maximal bending angle and the thickness of SMA plate, and the relationship between the maximal bending angle and the heating current. This is meant for an initial optimal design of SMA bio-fin.