Biomimetic micro underwater vehicle with ostraciiform locomotion: system design, analysis and experiments
Date
2006
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Publisher
University of Delaware
Abstract
Centimeter scale Micro Underwater Vehicles (MUVs) capable of autonomous navigation can be used in applications such as marine organism sensing, ship wreck exploration, pipeline inspection, environmental monitoring, chemical and pollution detection, etc. Compared to conventional propeller based MUVs, a bio-inspired design which mimic the impressive swimmers existing in nature can result in highly maneuverable and energy efficient MUVs. Fish using Ostraciiform locomotion for cruise and maneuver with multiple oscillating fins and a rigid body such as the boxfish is especially suitable as a model for small size MUVs. Boxfish are usually found in tropical coral reefs, they are known for their abilities to swim smoothly through turbulent waters, and their exceptional maneuverability and stability are characteristics desirable in a micro underwater vehicle. ☐ This thesis presents the design, analysis and development of a bio-inspired boxfish MUV. Recent observations from biologists provide the data on morphology and swimming modes of boxfish. We have investigated the flapping fin hydrodynamics using experimental platform and body hydrodynamic stability analysis using simulation studies to arrive at the final design of a boxfish robot. ☐ First, experimental studies were conducted to characterize and optimize the flapping fin propulsion and maneuvering of the caudal and pectoral fins. To this end, a robotic flapper capable of three rotational degree of freedom - flapping, rotation, and deviation - was designed to mimic the motion of the fins. A fixed beam based force sensor was developed and attached to the flapper to measure the instantaneous forces generated by the fin motion. The flapper is mounted on a linear stage and is submerged in a 60in × 30in × 30in oil tank to study both stationary and forward motions. The hydrodynamic force generation of caudal fin and pectoral fins has been modeled using a combination of quasi-steady state analytical model with empirically matched lift and drag coefficients. Optimal fin parameters such as shape, flexibility, and fin motion kinematics have been investigated. ☐ Second, fluid flow simulations on 3D CAD models of boxfish-like body shapes were investigated to arrive at the body shape of the MUV. Our simulation results shows counter-rotating vortices generated along the keels and edges of the outer shell under water disturbances, a results in agreement with the recent discoveries and fluid flow experiments conducted by biologists. Furthermore, we have developed a potential flow based body-fluid interaction model to simulate the rigid body dynamics and study the vortex induced stability in boxfish-like body shape designs. ☐ Finally, a robotic prototype was developed based on the above analysis. The propulsion and maneuvering of the prototype is achieved by a single DOF caudal fin and two 2-DOF pectoral fins. The fin motion transmission mechanisms are mounted on a parallel plate chassis structure. An onboard microprocessor is programmed to achieve motion control and obstacle avoidance. Rapid prototyping techniques have been used to faithfully reproduce the engineered outer body shape.